Connective Tissues

Lesson Name : Connective Tissues Lesson Developer : Dr. Zubeda College/Department : Zoology

Institute of Life Long Learning, University of Delhi

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Connective Tissues Table of Contents •

Introduction

•

General Features of Connective Tissue

•

Locations of Connective Tissues

•

Functions of Connective Tissues

•

Components of Connective Tissue (I) Specialized cells in Connective Tissue 1. Fibroblasts 2. Macrophages 3. Plasma cells 4. Mast cells 5. Adipocytes 6. Leukocytes (II) Extracellular Matrix in Connective Tissue i.

Ground Substance

ii.

Connective Tissue Fibers a. Collagen fibers b. Elastic fibers c. Reticular fibers

•

Classification of Connective Tissues A.

EMBRYONIC CONNECTIVE TISSUES i.

Mesenchyme

ii. B.

Mucous connective tissue

MATURE CONNECTIVE TISSUES 1.

CONNECTIVE TISSUE PROPER I.

Loose Connective Tissues i.

Areolar connective tissue

ii.

Adipose connective tissue

iii.

Reticular connective tissue

II. Dense Connective Tissues

2.

i.

Dense regular connective tissue

ii.

Dense irregular connective tissue

iii.

Elastic connective tissue

SUPPORTING CONNECTIVE TISSUE Institute of Life Long Learning, University of Delhi

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Connective Tissues I. Cartilage i.

Hyaline cartilage ii.

Fibrous cartilage

iii. Elastic cartilage II. Bone Tissue i.

Compact bone

ii. Spongy bone 3.

FLUID CONNECTIVE TISSUE I. Blood Tissue II. Lymph

•

Summary

•

Exercises

•

Glossary

•

References

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Connective Tissues Learning objectives •

To discuss the common characteristics features of connective tissues.

•

To describe the functions and location of connective tissues.

•

To describe the different components (cells, fibers, ground substance) of connective tissues.

•

To classify the various types of connective tissues.

•

Describe the structure, location and function of each type of connective tissues.

•

Describe the different cells found in connective tissue.

INTRODUCTION Animal tissue is an assemblage of identical cells derived from the same origin which is for performing specific function. Tissues of animal are classified into four major categories: epithelial, connective, muscle and nervous tissues (Fig 1). All these categories of tissues are organized to form organs and structures of animal body. Although each of the animals usually has these four kinds of tissues, the appearance and expression of all these tissues types may vary. Connective tissue is one of the four major categories of animal tissues that supports, joins and separate different forms of tissues and organs of the body. Connective tissue is present all over the body excluding the central nervous system. Cells of the connective tissue are more broadly apart from each other as compared to those in epithelial tissues. Connective tissues contains larger amount of extra-cellular matrix which is considerably absent in epithelial tissue.

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Connective Tissues

Fig. 1. Four basic types of tissues. Source: http://cnx.org/contents/4e46e67c-5867-4d6b-8583-fa0bba6d65af@1 CC Image Credit: CC BY-SA 4.0

GENERAL FEATURES OF CONNECTIVE TISSUE Followings are the general features of connective tissues which are different from the other types of tissues of animals: • Connective tissues are present in all part of the body excluding central nervous system. • These tissues are never exposed to the outer environment. • In their various forms, connective tissues have a variety of functions. Institute of Life Long Learning, University of Delhi

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Connective Tissues • Most of the connective tissues contain a lot of blood vessels (means they are highly vascular). • They have receptors which can perceive pain, pressure, temperature, and other sensations. • Connective tissue fills spaces between organs and tissues, and provides structural and metabolic support for other tissues and organs. • Connective tissues consist of two chief components: extra-cellular matrix and cells. • Extra-cellular matrix in connective tissues is the substances located in spaces between cells. • The cells of connective tissues secrete extra-cellular fibers and account for the many of the functional properties of the tissue in addition to controlling the surrounding watery environment via specific proteoglycan molecules.

LOCATIONS OF CONNECTIVE TISSUES Connective tissues are the most diverse and widely distributed tissues in the body. Bone, blood, and fat are well-known connective tissues which perform many different functions and constitute different properties.

FUNCTIONS OF CONNECTIVE TISSUES Connective tissues provide a protective structural framework for other tissue types. Functions of connective tissue are followed as: 1. Support and protection: The cells of connective tissue produce minerals and fibers that make up the bony structural framework in the body. As a result, it protects delicate organs, and covers and connects the other types of tissues. 2. Transport: Fluid connective tissues such as blood and lymph efficiently carry substances from one area to another area of the body. 3.

Storage: Adipose cells in the connective tissues store fats a form of energy until it is required.

4. Defense:

It

involves defense against

microbes through

the intercellular

interactions and antibodies production by specialized cells of connective tissues. Institute of Life Long Learning, University of Delhi

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Connective Tissues COMPONENTS OF CONNECTIVE TISSUE Main components of connective tissue are (I) specialized cells and (II) extracellular matrix. The extracellular matrix is made up of fibers in a protein and polysaccharide matrix, secreted and organized by cells in the extracellular matrix. While epithelial tissues are mainly composed of cells, major volume of connective tissues is occupied by the extracellular matrix. Variations in the composition of the extracellular matrix, determines the properties of the connective tissue. For example, if the matrix is calcified, it can form bone or teeth. Specialized forms of extracellular matrix also make up tendons, cartilage, and the cornea of the eye. General connective tissue is either loose, or dense, depending on the arrangment of the fibers. The cells sit in a matrix made up of glycoproteins, fibrous proteins and glycosoaminoglycans, which have been secreted by the fibroblasts, and the major component of the matrix, is in fact, water.

(I) SPECIALIZED CELLS IN CONNECTIVE TISSUE Various

cells

of

connective

tissues

produced

from

embryonic

cells

called

mesenchyme. Mesenchyme arises from mesoderm, an embryonic germ layer, and is composed of stellate or fusiform cells embedded in a gelatinous ground substance. Mesenchyme is the stem tissue of all the connective tissues of the body. Each major type of connective tissue contains an immature class of cell with a name ending in blast, which means to grow. These immature cells are termed fibroblasts in case of loose and dense connective tissues while it is named as chondroblasts in cartilage and osteoblasts in bone. The types of cells in connective tissues vary according to the type of tissue and include the following:

1. Fibroblasts (Fig. 2) Structure:

These are bulky and flat cells containing branching projections. Fibroblasts contain large and oval shaped nuclei with one or two conspicuous nucleoli.

Occurrence: These are distributed generally every connective tissues, and usually are the most abundant. Function and Importance: Institute of Life Long Learning, University of Delhi

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Connective Tissues (i)

Fibroblasts migrate through the connective tissues, secreting the fibers and certain components of the ground substance of the extracellular matrix.

(ii)

In mature tissue, fibroblasts become dormant. When there is injury, they start to produce new fibers.

(iii)

The active fibroblast contains a lot of rough endoplasmic reticulum necessary for production of collagen and elastin fibers.

(iv)

Proteoglycan is a main constituent of the ground substances in connective tissues and is produced through fibroblasts.

Fig. 2. Fibroblasts in cell culture of mouse of embryo. Source: http://en.wikipedia.org/wiki/Fibroblast#mediaviewer/File:NIH_3T3.jpg CC Image credit: CC BY 2.5

2. Macrophages (Fig.3) Structure:

It arises from a type of white blood cell termed as monocytes. Macrophages are not in regular shape and have short branching processes. It is also called histiocyte.

Occurrence: After fibroblasts, macrophages are present in numerous numbers in loose connective tissue. Importance: At first, these cells are not active. After inflammation, they intensively turn

into

amoeboid

and

phagocytic

stage

termed

as

angry

macrophages. They directly engulf blood cells, bacteria, dead cells and Institute of Life Long Learning, University of Delhi 7

Connective Tissues debris digesting this material with powerful enzymes. These cells are an important constituent of the reticuloendothelial system (RES) positioned in the spleen, liver, lymph nodes and other organs. Types of macrophages:

Fixed macrophages exist in in a particular tissue;

example includes alveolar macrophages in the lungs or spleenic macrophages in the spleen. Wandering macrophages have the ability to move throughout the tissue and gather at sites of infection or inflammation to carry on phagocytosis.

Fig.3. Right Image: Connective tissue stained for ED2 surface marker to visualize macrophages in rat, ICC (Immunocytochemistry) stain, at 40x. Left image: Macrophages in Liver of rabbit, ink (carbon) injected. Note: Macrophages are usually difficult to distinguish from other cell types in connective tissues. One way to visualize them is to inject an experimental animal with very fine carbon particles. Macrophages which come into contact with the Institute of Life Long Learning, University of Delhi

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Connective Tissues circulating particles will phagocytose some of them. In sections the particles will be visible as dark, black-brown accumulations in the cytoplasm of the macrophages. Source: http://www.lab.anhb.uwa.edu.au/mb140/

Image Credit: Blue Histology images copyright Lutz Slomianka 1998-2009. The literary and artistic works on the original Blue Histology website may be reproduced, adapted, published and distributed for non-commercial purposes.

3. Plasma cells (Fig. 4) Structure:

These are small cells which arise from B lymphocyte, a type of white blood cell. Their appearance is quite characteristics: (1) Plasma cells have basophil cytoplasm and an eccentric nucleus; (2) Plasma cell have distinct clear perinuclear region of the cytoplasm which contains a large number of Golgi bodies.

Occurrence: Although they are found in many places in the body, most plasma cells reside in connective tissues especially in the gastrointestinal and respiratory tracts. It plays an important role in body’s immune response. Importance: Plasma cells release antibodies and proteins that attack or reduce the effect of foreign materials in the body.

Fig.

4.

Plasma

perinuclear

cell

region

with of

distinct

the

clear

cytoplasm

containing a large number of Golgi bodies. Source: http://en.wikipedia.org/wiki/Plasma_cell#mediaviewer/Fil e:Plasmacell.jpg Image Credit: This image is in the public domain because its copyright has expired. This applies worldwide.

4. Mast cells (Fig. 5) Structure:

These are large cells (20-30µm) packed with intensely basophilic granules that most of the time obscure the nucleus.

Occurrence: These are generally abundant around blood vessels. These are very much similar to the blood basophils. So, these cells also have mediators e. g. histamine, heparin and serotonin for instantaneous hypersensitivity.

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Connective Tissues Importance: Although best known for their role in allergy and anaphylaxis, mast cells play an important protective role as well, being familiarly involved in wound healing and defense against pathogens.

Fig.5. Right Image: Mast Cells, Tongue - toluidine blue stain. Left image: Mast cell in Mesentery of Rat, stained with cresyl violet stain. The cytoplasm of the mast cells is however filled with dark, blue / violet grains which represent their secretory vesicles. Source: http://www.lab.anhb.uwa.edu.au/mb140/

Image Credit: Blue Histology images copyright Lutz Slomianka 1998-2009. The literary and artistic works on the original Blue Histology website may be reproduced, adapted, published and distributed for non-commercial purposes.

5. Adipocytes (Fig.6)

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Connective Tissues Structure:

These are also called fat cells or adipose cells. In the beginning these cells resemble to fibroblasts except they have abundant vacuoles of fat droplets.

Occurrence: They are prevalent underneath to the skin and around organs for example heart and kidneys. These are frequently found arranged near to small blood vessels. Importance: These cells store triglycerides the form of fat.

Fig.6.

White adipose cells-Adipocytes. Source:

http://en.wikipedia.org/wiki/Adipocyte#mediaviewer/File:Blausen_0012_AdiposeTissue.png Image Credit: CC BY-SA 3.0

6. Leukocytes (Fig.7.) Structure:

These are white blood cells that move along with the connective tissues around blood vessels. Leukocytes are composed of basophils, eosinophils, neutrophils, monocytes and lymphocytes.

Occurrence: Eosinophils are most prevalent throughout the respiratory, digestive tracts and in active mammary tissue.

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Connective Tissues Importance: In normal condition, these are less in numbers in connective tissue. But in some conditions they move from blood into connective tissues. For instance, neutrophils get together at region of infection and eosinophils move to region of parasitic invasions and involved in the

allergic reactions.

Fig.7.

Luekocytes.

Source: http://cnx.org/contents/[email protected]:122/Anatomy_&_Physiology Image Credit: CC BY-SA 4.0

(II) EXTRACELLULAR MATRIX IN CONNECTIVE TISSUE The cells of connective tissue are interspersed in a large volume of extra-cellular matrix. This extra-cellular matrix (ECM) is secreted by the cells. It constitutes protein fibers interpose in an amorphous mixture of large protein-polysaccharide molecules termed as ground substance. All molecules found in the ECM share common domains, and the function of the ECM relies largely on the interactions between these molecules. Each connective tissue cell secretes a different ratio of ECM molecules that contribute to the formation of many different architectural arrangements; therefore, the ECM possesses specific mechanical and biochemical properties for the tissue in which it is present. For instance, the properties of the ECM in loose connective tissue are different from those of the ECM in cartilage or bone. The followings are description of two major components of extracellular materials: (i) ground substance and (ii) fibers.

i. Ground Substance

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Connective Tissues Ground substance is the part of the extracellular matrix that occupies the spaces between the cells and fibers. It may be fluid, semi fluid, jellylike or calcified. Functions of ground substance are followed as: •

It supports cells and helps in connecting cell to cell.

•

Helps in water storage.

•

Works as an exchanging medium between the blood and cells.

•

It has an important role in which ways tissues develop, migrate, proliferate, and change shape, and in what ways they perform their metabolic functions.

Ground substance consists predominately of three groups of molecules (Fig.8): (1)Proteoglycans (e.g., aggrecan, syndecan), very large macromolecules composed of a core protein; (2)glycosaminoglycan molecules (GAGs) (e.g., dermatan sulfate, keratan sulfate, hyaluronan), which are covalently bound to the proteoglycans; and (3)multiadhesive glycoproteins (such as fibronectin and laminin). The size and structure of the three groups of molecules vary enormously.

Physical properties of Glycosaminoglycan (GAGs): The GAGs are the most abundant heteropolysaccharide components of ground substance. These molecules represent long-chain unbranched polysaccharides composed of repeating disaccharide units. The disaccharide units contain either of two modified sugars—N-acetylgalactosamine or N-acetylglucosamine— and a uronic acid such as glucuronate or iduronate. GAGs (except hyaluronan) are synthesized by connective tissue cells as a covalent, posttranslational modification of proteins called proteoglycans. For example, heparin is formed by enzymatic cleavage of heparan sulfate; dermatan sulfate is similarly modified from chondroitin sulfate. GAGs are highly negatively charged because of the sulfate and carboxyl groups located on many of the sugars. The high density of the negative charge (polyanions) attracts water, forming a hydrated gel. The gel-like composition of ground substance permits rapid diffusion of water-soluble molecules. At the same time, the rigidity of the GAGs provides a structural framework for the cells. GAGs are located primarily within the ground substance as well as on the surface of cells within the extracellular matrix. On the basis of differences in specific sugar residues, the nature of their Institute of Life Long Learning, University of Delhi 13

Connective Tissues linkages, and the degree of their sulfation, a family of seven distinct GAGs is recognized.

Different molecules of Glycosaminoglycan (GAGs): •

Hyaluronic acid is a gelatinous, jelly-like substance which attaches cells together, responsible for lubrication of various joints of the body, and assists in maintaining the shape of the eye balls. White blood cells, sperm cells, and some

bacteria

produce

hyaluronidase,

an

enzyme

that

breaks

apart

hyaluronic acid, thus causing the ground substance of connective tissue to become more liquid. The ability to produce hyaluronidase helps white blood cells move easily through connective tissues to reach sites of infection and aids penetration of an oocyte by a sperm cell during fertilization. It also accounts for the rapid spread of bacteria through connective tissues. •

Chondroitin sulfate gives support and stickiness in cartilage, bone, skin, and blood vessels.

•

The skin, tendons, blood vessels, and heart valves have dermatan sulfate; bone, cartilage, and the cornea of the eyeball contain keratan sulfate.

Multiadhesive glycoproteins: Multiadhesive glycoproteins accounts for linking parts of the ground substance together and to the surface of cells. The main multiadhesive glycoproteins of connective tissues are the fibronectin, which attaches to collagen fibers and ground substance, joining them to one another. Fibronectin also attaches cells to the ground substance.

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Connective Tissues

Fig.8. Structural arrangement of ground substance. It consists of proteoglycans (core protein), glycosaminoglycan (dermatan sulfate, chondroitin sulfate, hyaluronic acid), multiadhesive glycoproteins (link protein). Source: http://greatcourse.cnu.edu.cn/xbswx/wlkc/kcxx/download/04/xbbm.htm Image credit: written for permission

Value addition: Did you Know Heading text: Nutritional Supplements for Joint Diseases In the recent years, chondroitin sulfate and glucosamine have been used as nutritional supplements either alone or in combination to encourage and retain the structure and function of joint cartilage, to give pain relief from osteoarthritis, and to decrease joint swelling. More research is needed to determine how they act and why they help some people and not others. Source: Principles of Anatomy & Physiology- Tortora, G.J. & Derrickson, B.

ii.

Connective Tissue Fibers

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Connective Tissues Three basic kinds of fibers are embedded in the extracellular matrix between the cells are: (a) collagen fibers; (b) elastic fibers, and (c) reticular fibers. These are formed from protein subunits secreted by fibroblasts. They function to strengthen and support connective tissues.

a. Collagen fibers (Fig. 9) These fibers are very strong and resist pulling forces, but they are not stiff, which allows tissue flexibility. The properties of different types of collagen fibers vary from tissue to tissue. For example, the collagen fibers found in cartilage and bone form different form different association with surrounding molecules. As a result of these associations, the collagen fibers in cartilage are surrounded by more water molecules than those in bone, which gives cartilage a more cushioning effect. It is found in most types of connective tissues like bone cartilage, tendons and ligaments. Chemically, collagen fibers consist of the protein collagen, which is the most abundant protein in our body (approximately 25% of the total). Each collagen fiber consists of aggregates of tropocollagen molecules. Each tropocollagen molecule is composed of 3 polypeptide chains which are helically arranged around each other and cross-linked for structural strength.

b. Elastic fibers (Fig. 9) Elastic

fibers

contain

the

protein

elastin surrounded by a glycoprotein named fibrillin, which adds strength and stability. They are branched and wavy and after stretching will return to their original length. These fibers are lesser in width than collagen fibers, branch

and

unite

together

to

constitute a fibrous network within a connective tissue.

Fig. 9. Collagen and elastic fibers intermingle in the dermis, i.e. the

connective

tissue

beneath

the

epithelium of the skin. Immediately beneath

the

epithelium

both

fibre

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Connective Tissues types are relatively fine - they appear much thicker in the deeper parts of the dermis. Source: http://www.lab.anhb.uwa.edu.au/mb140/

Image Credit: Blue Histology images copyright Lutz Slomianka 1998-2009. The literary and artistic works on the original Blue Histology website may be reproduced, adapted, published and distributed for non-commercial purposes.

c. Reticular fibers (Fig. 10) Reticular fibers (reticulum, a network), the least common of the three, are thinner than collagen fibers and commonly form a branching, interwoven framework in various organs. It consists of collagen arranged in thin bundles having a covering of glycoprotein, give support in the walls of blood vessels and form a network surrounding the cells in some tissues, such as areolar connective tissue, adipose tissue, nerve fibers, and smooth muscle tissue. Reticular fibers

are plentiful in

reticular connective tissue.

Fig.

10.

Reticular

fibers

appear as fine black lines in liver, Reticulin Stain. The fibers surround

the

individual

sheets

of

hepatocytes and are the only fibrous connective

tissue

component

supporting the cells. While providing support, the fine, open meshwork of reticular fibers facilitates the exchange of

substances

hepatocytes

and

between the

blood,

the which

circulates in the irregularly shaped blood

vessels

between

the

hepatocytes. Source: http://www.lab.anhb.uwa.edu.au/mb1

40/

Image Credit: Blue Histology images copyright Lutz Slomianka 1998-2009. The literary and artistic works on the original Blue Histology website may be reproduced, adapted, published and distributed for non-commercial purposes.

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Connective Tissues Value addition: Did you Know Marfan

Syndrome

It is a hereditary disorder arises from the defective fibrillin gene. It results in abnormal production of elastic fibers. Tissues with much more elastic fibers become deformed or weaken. Structures affected most seriously are the outer layer of the bones, the ligament which hold the lens of the eye and the walls of the large arteries. People with marfan syndrome tend to be tall and have abnormally long arms, legs, fingers, and toes. A common symptom is blurred vision; arise due to the dislocation of the eye. Around 90 percent of individuals with Marfan syndrome have structural abnormalities in their cardiovascular systems. The most dangerous potential result is that the weakened connective tissues in the walls of major arteries, such as the aorta, may burst, causing a sudden, fatal loss of blood. See

the

video

on

Marfan

Syndrome

https://www.youtube.com/watch?v=IBVs40B0CKE Source: Principles of Anatomy & Physiology- Tortora, G.J. & Derrickson, B. and Youtube

CLASSIFICATION OF CONNECTIVE TISSUES Connective tissue is one of the four basic tissue types. It fills the spaces between organs and tissues, and provides them with structural and metabolic support. Basically, Connective tissue can be classified on the basis of their maturity i.e. (A) Embryonic and (B) Mature connective tissue. Followings are details about each type of Connective tissue.

1.

EMBRYONIC CONNECTIVE TISSUES

Embryonic connective tissues are present basically in the embryo (human which is being developed during initial two months of pregnancy), and in the fetus (human which is being developed during pregnancy period of third month till birth). These are of two types, mesenchyme and mucous connective tissue. (i) Mesenchyme

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Connective Tissues It is primitive, unspecialized connective tissue found abundantly in the early embryo. Gradually, it is reduced in quantity as it differentiates to form other connective tissues.

Structure:

Its chief components are mesenchymal cells and a ground substance which is initially fluid but becomes more fibrous with development. These cells are not regular in shape and embedded in semifluid ground substance which is composed of delicate reticular fibers. Mesenchymal cells are interconnected by slender cell processes (Fig. 11).

Location:

It is located almost exclusively under skin and along developing bones of embryo; some in adult connective tissue, especially along blood vessels.

Function:

It forms almost all other types of connective tissue.

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Connective Tissues Fig. 11. Sectional view of embryonic mesenchyme which forms all other type of tissue. Source: http://www.lab.anhb.uwa.edu.au/mb140/ Image Credit: Blue Histology images copyright Lutz Slomianka 1998-2009. The literary and artistic works on the original Blue Histology website may be reproduced, adapted, published and distributed for non-commercial purposes.

(ii) Mucous (or mucoid) connective tissue It is a transient tissue, which is intermediate between mesenchyme, and more fully (mature) differentiated connective tissues. As Wharton’s jelly, a chief component of the umbilicus, mucous connective tissue does not differentiate further. Structure:

It is composed of widely scattered fibroblasts with some macrophages and

lymphocytes.

These

are

embedded

in

gelatinous

and

characteristically abundant ground substance consists of fine collagen fibers (Fig. 12). Location:

It is chiefly located in fetus.

Function:

It forms the umbilical cord.

Fig. 12. Umbilical Cord, Human - H&E.

Within the umbilical cord, there are

three large vessels and their walls. Mucoid connective tissue fills the space between the vessels and the simple squamous epithelium lining the surface of the umbilical cord. Source: http://www.lab.anhb.uwa.edu.au/mb140/ Image Credit: Blue Histology images copyright Lutz Slomianka 1998-2009. The literary and artistic works on the original Blue Histology website may be reproduced, adapted, published and distributed for non-commercial purposes.

2. MATURE CONNECTIVE TISSUES

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Connective Tissues These are the second major subclass of connective tissues. These are present in the newborn. Their cells develop chiefly from mesenchyme. Based on the physical properties of their matrix, further mature connective tissues are classified into three major types which are given in Figure 13.

Fig. 13. Classification of Mature Connective tissue. Source: ILLL in house 1.

CONNECTIVE TISSUE PROPER

Connective tissue proper consists of many types of cells and fibers within a matrix containing a syrupy ground substance. Some cells of connective tissue proper are "permanent residents'; others are not always present because they leave to defend and repair areas of injured tissue. Connective tissue proper is categorized as either loose connective tissues or dense connective tissues on the basis of the relative proportions of cells, fibers, and ground substance. Details about these types of mature connective tissues are followed as: Institute of Life Long Learning, University of Delhi

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Connective Tissues I.

Loose Connective Tissues

Loose connective tissues are the packing material in human body. The fibers of loose connective tissues are loosely arranged between cells. Loose connective tissue forms a layer that separates the skin from underlying muscles, providing both padding and a considerable amount of independent movement. Pinching the skin of the arm, for example, does not distort the underlying muscle. The ample blood supply in this tissue carries wandering cells to and from the tissue and provides for the metabolic needs (oxygen and nutrients) of nearby epithelial tissue. They also anchor blood vessels and nerves, store lipids, and provide a route for the diffusion of materials. The different kinds of loose connective tissues are areolar connective tissue, adipose tissue, and reticular connective tissue. (i)

Areolar connective tissue: It is one among the most abundant connective

tissues in the body. Structure:

It consists of fibers (collagen, elastic, reticular) arranged randomly and

several kind of cells such as fibroblasts, macrophages, plasma cells, adipocytes, mast cells, and a few white blood cells, embedded in semi-fluid ground substance viz. hyaluronic acid, chondroitin sulfate, dermatan sulfate, and keratan sulfate. Location:

It is known as packing material of the body as it is found in nearly every body structure. It is present in subcutaneous layer deep to skin, papillary region of dermis, lamina propria of mucous membranes (Fig. 14), near blood vessels, nerves, and body organs.

Function:

It provides strength, elasticity and support to the different body parts.

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Connective Tissues

Fig. 14.

Areolar connective tissue in mesentery of peritoneal

cavity at 10x and 40x magnification, EL staining. Source: http://www.lab.anhb.uwa.edu.au/mb140/ Image Credit: Blue Histology images copyright Lutz Slomianka 1998-2009. The literary and artistic works on the original Blue Histology website may be reproduced, adapted, published and distributed for non-commercial purposes.

(ii)

Adipose connective tissue: Adipose tissue or fat is a loose connective

tissue containing large numbers of fat cells, or adipocytes. Structure:

It contains cells or adipocytes arise from fibroblasts which are modified to store triglycerides as conspicuous and centrally located fat droplets. Cell is packed with a single, large triglyceride droplet, cytoplasm and nucleus are pressed towards boundary of cell. There are two types of adipose tissue (Fig. 15):

(a)

White Adipose tissue: This composes 20 to 25 % of the body weight

in healthy adults. The amount of adipose tissue in an individual is determined the balance between energy intake and expenditure. It is found supporting the kidneys and the eyes, between muscle fibers and under the skin, where it acts as a thermal insulator and energy store. (b)

Brown Adipose tissue: This (BAT) is characteristically found in the

fetus and newborn. It includes most abundant capillary network and several pigmented mitochondria that are responsible for aerobic cellular respiration. When brown tissue is metabolized, it produce less energy and considerably more heat than other fat, contributing to the maintenance of body temperature. In some adults it is present in small amounts. Location:

It is present in subcutaneous layer inner to skin, surrounding heart and kidneys, yellow bone marrow, stuffing around joints. It fills bony socket behind the eyeball. It dominates extensive areas of loose connective tissue in the pericardial

and peritoneal

(abdominal)

cavities. Function:

It provides insulation that slows heat loss through skin. Institute of Life Long Learning, University of Delhi

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Connective Tissues It provides another source of padding and shock absorption for the body. It stores energy in the form of fat; maintains and protects organs. In newborns, BAT produces heat to maintain proper body temperature.

Fig. 15.

Sections of skin showing white adipose tissue, H&E

stain (Left) and

- sections of kidney showing brown adipose

tissue, trichrome stain (Right). Source: http://www.lab.anhb.uwa.edu.au/mb140/

Image Credit: Blue Histology images copyright Lutz Slomianka 1998-2009. The literary and artistic works on the original Blue Histology website may be reproduced, adapted, published and distributed for non-commercial purposes.

Value addition: Did you Know Heading Text: Weight Control and Liposuction Body text: Adipocytes are metabolically active cells; their lipids are continually being broken down and replaced. When nutrients are scarce, adipocytes deflate like collapsing balloons. This deflation occurs during a weight-loss program. In adults, Institute of Life Long Learning, University of Delhi

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Connective Tissues adipocytes cannot divide. Though, an excess of circulating lipids can stimulate the division of connective tissue stem cells, which then differentiate into additional fat cells. As a result, areas of loose connective tissue can become adipose tissue after chronic overeating. In the procedure known as liposuction, unwanted adipose tissue is surgically removed. Because adipose tissue can regenerate through differentiation of stem cells, liposuction provides only a temporary and potentially risky solution to the problem of excess weight. Post surgical complications that may develop include fat that may enter blood vessels broken during the procedure obstruct blood flow, infection, loss of feeling in the area, fluid depletion, injury to internal structures, and severe pain. Watch the video on liposuction:

https://www.youtube.com/watch?v=Xlxja7O_h4Y

Source: Principles of Anatomy & Physiology- Tortora, G.J. & Derrickson, B. and Youtube

(iii) Structure:

Reticular connective tissue It consists of fine interlocking network of reticular fibers (thin form of collagen fiber) and reticular cells (Fig. 16).

Location:

It is present in liver, spleen, lymph nodes; red bone marrow; reticular lamina of basement membrane; around blood vessels and muscles.

Function:

It forms stroma (supporting framework) of organs; binds smooth muscle tissue cells; filters and eliminates damaged blood cells on spleen and microorganisms in lymph nodes.

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Connective Tissues

Fig. 16. Sections of accessory digestive glands in liver showing reticular

connective

tissue,

RET

stain,

at

10x

and

40x

magnification. Source: http://www.lab.anhb.uwa.edu.au/mb140/

Image Credit: Blue Histology images copyright Lutz Slomianka 1998-2009. The literary and artistic works on the original Blue Histology website may be reproduced, adapted, published and distributed for non-commercial purposes.

II.

Dense Connective Tissues

It contain more fibers, which are thicker and more densely packed, but have noticeably less number cells than loose connective tissues. Dense connective tissues consist mostly of collagen fibers; they may also be called fibrous, or collagenous tissues. Dense connective tissues are tough, strong, and durable. They resist tension and distortion and interconnect bones and muscles. Dense connective tissue also forms a thick fibrous layer, called a capsule that surrounds internal organs (e.g. liver, kidneys, and spleen) and encloses joint cavities. There are three kinds: dense regular connective tissue, dense irregular connective tissue, and elastic connective tissue. Institute of Life Long Learning, University of Delhi

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Connective Tissues (i) Structure:

Dense regular connective tissue: In dense regular connective tissue, the collagen fibers are parallel to each other, packed tightly, and aligned with the forces applied to the tissue. Tendons are cords of dense regular connective tissue that attach skeletal muscles to bones. Their collagen fibers run along the length of the tendon and transfer the pull of the contracting muscle to the bone. Ligaments resemble tendons but connect one bone to another. Ligaments often contain elastic fibers as well as collagen fibers

and

thus

can

tolerate

a

modest

amount

of

stretching.

Aponeuroses are layers of tendon like materials which join muscle to muscle and muscle to bone. Location:

It is present as Tendons (Fig. 17), Ligaments and Aponeuroses in the body.

Function:

It provides strong attachment between various structures. Tissue structure withstands pulling (tension) along long axis of fibers.

Fig. 17. Muscle-Tendon Junction of rat showing dense regular connective

tissue,

van

Gieson

stain. Nuclei are often elongated, and their long axis runs parallel to the course of the collagen fibres. Source:http://www.lab.anhb.uwa.edu.au/mb140 / Image Credit: Blue Histology images copyright Lutz Slomianka 1998-2009. The literary and artistic works on the original Blue Histology website may be reproduced, adapted, published and distributed for non-commercial purposes.

(ii)

Dense irregular connective tissue Institute of Life Long Learning, University of Delhi

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Connective Tissues Structure:

Dense irregular connective tissue contains an interwoven meshwork of collagen fibers with a few fibroblasts(Fig.18). This structural pattern provides support to areas subjected to stresses from many directions and gives skin its strength.

Location:

It occurs in sheets, such as fasciae (tissue beneath skin and around muscles and other organs), reticular (deeper) region of dermis of skin, fibrous pericardium of heart, periosteum of bone, perichondrium of cartilage, joint capsules, membrane capsules around various organs (kidneys, liver, testes, lymph nodes, valves of heart.

Function:

It provides pulling (tensile) strength in many directions.

Fig. 18. Non-lactating Breast H&E Dense irregular connective tissue forms the dermis of the skin. Beneath the skin forming the mammae (nipples), dense connective

tissue

areas

are

very

extensive. This tissue surrounds the resting mammary gland. Dark spots scattered between the collagen fibres represent the nuclei of the cells. Source: http://www.lab.anhb.uwa.edu.au/mb14 0/ Image Credit: Blue Histology images copyright Lutz Slomianka 1998-2009. The literary and artistic works on the original Blue Histology website may be reproduced, adapted, published and distributed for noncommercial purposes.

(iii) Structure:

Elastic connective tissue It is predominantly elastic fibers with fibroblasts between fibers and yellowish in colour.

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Connective Tissues Location:

It is found in lung tissue, walls of elastic arteries, trachea, bronchial tubes, vocal cords, suspensory ligaments of penis and some ligaments between vertebrae.

Function:

It allows stretching of various organs. It is sturdy and move back to original shape after being stretched. Elasticity is important for normal functioning of lung tissue and elastic arteries.

Fig.

19.

artery

Sections

showing

of

elastic

connective

tissue,

elastin and eosin stain. Source: http://www.lab.anhb.uwa.edu.a u/mb140/ Image Credit: Blue Histology images copyright

Lutz

Slomianka

1998-

2009. The literary and artistic works on

the

website

original may

Blue be

Histology

reproduced,

adapted, published and distributed for non-commercial purposes.

Value addition: Did you Know Video on tendon and related disease Difference between ligaments and tendons can be seen in following video https://www.youtube.com/watch?v=PdJ5QDkqG2g To see the video on Tendinitis a disease caused due to inflammation of tendon, click the following hyperlink Institute of Life Long Learning, University of Delhi

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Connective Tissues https://www.youtube.com/watch?v=p5vnf0VLvxQ Source: youtube

2.

SUPPORTING CONNECTIVE TISSUE

Supporting connective tissues includes cartilage and bone. These tissues constitute a strong framework which supports the rest parts of the body. These connective tissues are composed of the extra-cellular matrix rich in fibers. In some cases, it contains deposits of insoluble calcium salts. Different characteristic features of cartilage and bone are compared in tabulated form also (see Table 1).

I. Cartilage Cartilage composed of a dense network of collagen and elastic fibers which are embedded in the chondroitin sulfate, a jelly like ground substance. Cartilage can tolerate noticeably more stress than loose and dense connective tissues. The strength of cartilage is owing to its collagen fibers, and its resilience (ability to move back its original shape after being stretched) is owing to chondroitin sulfate. Cells of mature cartilage, termed chondrocytes, prevail singly or in groups within spaces termed as lacunae in the extracellular matrix. A covering of dense irregular connective tissue termed as perichondrium surrounds the surface of most cartilage (Fig. 19). Perichondrium has blood vessel and nervous system and is the source of cartilage cells. Because cartilage contains no blood supply, it repairs slowly subsequent to an injury.

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Connective Tissues

Fig. 19. Structure of Cartilage Source: http://cnx.org/contents/[email protected]:6/Siyavula:_Life_Sciences_Grade_ Image Credit: CC BY-SA 4.0

Value addition: Did you Know Heading Text: Antiangiogenesis factor Body text: Cartilage does not have a blood supply because it secretes an antiangiogenesis factor. It is a substance that prevents blood vessel growth. Because of this property, antiangiogenesis factor is being studied as a possible cancer treatment. If the cancer cells can be stopped from promoting new blood vessel growth, their rapid rate of cell division and expansion can be showed or even halted. Watch

the

video

on

Antiangiogenesis

factor

https://www.youtube.com/watch?v=AiTW2Dsk748 Source: Principles of Anatomy & Physiology- Tortora, G.J. & Derrickson, B. and youtube

Three main kinds of cartilage are hyaline cartilage, elastic cartilage, and fibrous cartilage (Fig. 20). (i) Structure:

Hyaline cartilage It consists of a resilient gel as ground substance and appears in the body as a bluish- white, shiny substance. It constitutes very thin collagen fibers are not easily visible in microscope. Prominent Institute of Life Long Learning, University of Delhi

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Connective Tissues chondrocytes are found in lacunae surrounded by perichondrium. Exceptions are articular cartilage in joints and cartilage of epiphyseal plates, where bones lengthen during growth. Location:

Most abundant cartilage in body. It is prevalent at ends of long bones, anterior end of ribs, nose, parts of larynx, trachea, bronchi, bronchial tubes, embryonic and fetal skeleton.

Function:

It forms smooth surfaces for movement at joints It provides flexibility and support. It is weakest type of cartilage.

(ii) Structure:

Fibrous cartilage: It is also called as fibrocartilage. Cells of fibrous cartilage are chondrocytes that are scattered between visibly thick bundles of collagen fibers within the extracellular matrix. It lacks perichondrium.

Location:

It is prevalent in pubic symphysis, intervertebral discs, menisci (cartilage pads) of knee, portions of tendons that insert into cartilage.

Function:

It support and joins structures together. Strength and rigidity compose it as the strongest type of cartilage.

(iii) Structure:

Elastic cartilage: Chondrocytes are embedded in fine network of elastic fibers within extracellular matrix. It has perichondrium. It is also termed as yellow cartilage.

Location:

It forms lid on top of larynx, parts of external ear (auricle), auditory tubes.

Function:

It gives strength and elasticity and maintains shape of certain structures.

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Connective Tissues

Fig.

20.

Cartilage

is

a

connective

tissue

consisting

of

collagenous fibers embedded in a firm matrix of chondroitin sulfates. (a) Hyaline cartilage provides support with some flexibility. The example Institute of Life Long Learning, University of Delhi

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Connective Tissues is from dog tissue. (b) Fibrocartilage provides some compressibility and can absorb pressure. (c) Elastic cartilage provides firm but elastic support. Source: http://cnx.org/contents/fe382569-de99-4d07-a334757fb577e488@4/Connective_Tissue_Supports_and Image Credit: CC BY-SA 4.0

Value addition: Did you Know Cartilages and Joint Injuries Numerous complex joints in our body (e. g. knee) have both hyaline cartilage and fibrous cartilage. The hyaline cartilage wrap bony surfaces and fibrous cartilage cushion in the joint keep away from bone-to-bone contact when movements are underway. Damage in these joints can produce tears in the fibrous cartilage cushion that does not or poorly repair as the cartilages are avascular. This loss of cushioning places more strain on the cartilages within joints and leads to further joint damage. Eventually, joint mobility is severely reduced. Surgery usually results in only a temporary or incomplete repair. Video

on

Cartilages

related

injuries:

https://www.youtube.com/watch?v=FMXAJhtM1ZA Source: Principles of Anatomy & Physiology- Tortora, G.J. & Derrickson, B. and youtube

Repair and Growth of Cartilage Metabolically, cartilage is a relatively inactive tissue that grows slowly. When injured or inflamed, cartilage repair proceeds slowly, in large part because cartilage is avascular.The growth of cartilage follows two basic patterns: interstitial growth and appositional growth. Interstitial growth: In this pattern of growth, there is growth from inside the tissue. When cartilage grows by interstitial growth involves two events: (i) Cartilage increases rapidly in size due to the cell division of prevailing chondrocytes and Institute of Life Long Learning, University of Delhi

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Connective Tissues (ii) Continuous deposition of increasing amount of extracellular matrix by the chondrocytes. Appositional growth: In this pattern of growth, there is growth at the external layer of the tissue. When cartilage grows by appositional growth, cells in the inner cellular layer of the perichondrium differentiate into chondroblasts.

II.

Bone Tissue

Cartilage, joint, and bones make up the skeletal system. The skeletal system supports soft tissues, protects delicate structures, and works with skeletal muscles to generate movement. Bones store calcium and phosphorus, contain red bone marrow, which generates blood cells and contain yellow bone marrow, a storage site for triglycerides. Bones are organs comprised of many different connective tissues. These include bone or osseous tissue, periosteum, red and yellow bone marrow and endosteum (Fig. 21). Bone tissue is classified as either compact or spongy, depending on how its extracellular matrix and cells are organized.

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Connective Tissues Fig. 21. Sectional view of several osteons (Haversian systems) of bone. Source: http://cdn.intechopen.com/pdfs-wm/44658.pdf Image Credit: CC BY-SA 3.0

(i) Structure:

Compact bone (Fig. 22) Compact bone comprised of tightly packed osteons or haversian systems. The osteon contains a central canal termed as osteonic (haversian) canal that is enclosed by concentric rings (lamellae) of matrix. Mature bone cells (osteocytes) are placed in spaces between the rings of matrix termed as lacunae. Small channels termed as canaliculi radiate from the lacunae to the central osteonic (haversian) canal to give passageways by the hard matrix. The osteonic canals constitute blood vessels and nerves which are parallel to the long axis of the bone. These blood vessels interlinked through the way of perforating canals with vessels on the surface of the bone. In compact bone, the haversian systems are packed closely together to form a solid mass.

(ii) Structure:

Spongy (cancellous) bone (Fig. 22) Spongy bone is lighter and less dense than compact bone. It contains plates (trabeculae) and bars of bone neighbouring to small and irregular cavities which have red bone marrow. The canaliculi attach to the neighbouring cavities, instead of a central haversian canal, to receive their blood supply. The trabeculae are organized to give maximum strength. The trabeculae of spongy bone follow the lines of stress and can realign if the direction of stress changes.

Location:

Compact and spongy bones tissue constitute the various parts of bones of the body.

Function:

It provides support, protection and storage. It contains blood forming tissue. It provides levers that act with muscle tissue to enable movement. Institute of Life Long Learning, University of Delhi

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Connective Tissues

Fig. 22. Compact bone. (a) Compact bone is a dense matrix on the outer surface of bone. Spongy bone, inside the compact bone, is porous with web-like Institute of Life Long Learning, University of Delhi

37

Connective Tissues trabeculae. (b) Compact bone is organized into rings called osteons. Blood vessels, nerves, and lymphatic vessels are found in the central Haversian canal. Rings of lamellae surround the Haversian canal. Between the lamellae are cavities called lacunae. Canaliculi are microchannels connecting the lacunae together. (c) Osteoblasts surround the exterior of the bone. Osteoclasts bore tunnels into the bone and osteocytes are found in the lacunae. Source: http://cnx.org/contents/d418b229-8a72-47e4-b4c5-741556d7a3cc@5 CC Image Credit: CC BY-SA 4.0

Table 1: Comparison between features of Bone and Cartilage FEATURES

BONE

CARTILAGE

STRUCTURAL FEATURES Cells

Osteocytes housed in lacunae within matrix

Chondrocytes located in lacunae within matrix

Ground substance

Chondroitin sulfate (Proteinpolysaccharide gel) and water

Fibers

A small volume of liquid surrounding insoluble crystals of calcium salts (calcium phosphate and calcium carbonate) Collagen fibers predominate

Blood supply

Contains blood vessels

Has no blood vessels

Outer covering of tissue

Periosteum (except at joints), a fibrous membrane containing nerves, lymphatic vessels and capillaries

Strength

Strong: resists distortion until breaking point is reached

Perichondrium (except at joints); composed of outer layer of dense connective tissue and inner layer of cells that differentiate into chondrocytes; fibrocartilage has no perichondrium Limited: bends easily but difficult to break

Collagen, elastic, reticular fibers (proportions vary)

METABOLIC FEATURES Oxygen demands

High

Low

Nutrient delivery

By diffusion through cytoplasm and fluid in canaliculi

By diffusion through selectively permeable intercellular matrix

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Connective Tissues Growth

Appositional growth only

Interstitial and appositional growth

Repair capabilities

Extensive

Limited

3. FLUID CONNECTIVE TISSUE Fluid connective tissues include blood and lymph which are characteristic collections of cells in a fluid extra-cellular matrix. Under normal conditions, the proteins dissolved in this watery matrix do not form large insoluble fibers. In blood, the watery matrix is called plasma.

I.

Blood Tissue

Structure:

Blood tissue is a connective tissue having liquid extra-cellular matrix and formed elements. The extra-cellular matrix is termed as blood plasma and has no fibers. The blood plasma is pale yellow fluid which consists generally of water with a wide variety of dissolved materials (e.g.

nutrients,

wastes,

enzymes,

plasma

proteins,

hormones,

respiratory gases, and ions). Suspended in the blood plasma are formed elements or solid cells—red blood cells, white blood cells and platelets (Fig. 23). Red blood cells (RBC) are shaped like biconcave discs (round discs with a dimple in the top and another in the bottom). White blood cells (WBC) are slightly larger than red ones and are more irregular in shape. Platelets are fragments of cells floating in the plasma. Location:

It is located within blood vessels, within chambers of heart.

Function:

(i) Red blood cells contain red pigment called haemoglobin which carry oxygen from the lungs to the various body tissues and remove some carbon dioxide from them. (ii) White blood cells carry on phagocytosis and mediate allergic reactions and immune system responses. They fight pathogens by various mechanisms.

Some engulf

or swallow up pathogens, some

generate chemicals called antibodies to kill the pathogens while a third type release antitoxins, chemicals which neutralize the poisons Institute of Life Long Learning, University of Delhi

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Connective Tissues produce by the pathogens. When seen at under a microscope white blood cells may appear purple because a dye is used to stain them. (iii) Platelets are essential for blood clotting and stick together where a blood vessel is damaged to close the wound. (iv)

Plasma carries many important chemicals around the body

including the waste carbon dioxide from respiration, hormones, urea, and glucose and also transports heat.

Fig. 23. Blood is a connective tissue that composed of predominantly erythrocytes (red blood cells), various leukocytes (white blood cells) and platelets. Source: http://cnx.org/contents/d418b229-8a72-47e4-b4c5741556d7a3cc@5 CC Image Credit: CC BY-SA 4.0

II.

Lymph

Structure: Lymph is the extra-cellular fluid that moves in lymphatic vessels. This is the connective tissue which comprised of various forms of cells in a transparent liquid extracellular matrix that resembles to blood plasma although contains much Institute of Life Long Learning, University of Delhi

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Connective Tissues less protein. The composition of lymph varies from one part of body to another. For example, lymph leaving lymph nodes includes many lymphocytes, a type of white blood cell, in contrast to lymph from the small intestine, which has a high content of newly absorbed dietary lipids. The three main forms of lymphocyte are thymus cells (T cells), B cells (bursa-derived cells) and natural killer (NK) cells. Lymphocytes have characteristically large nucleus (Fig. 24). Location:

It is located within lymphatic vessels.

Function:

It facilitates the immune system to the body.

Fig. 24. A lymphocyte (stained) surrounded by red blood cells. Source: http://en.wikipedia.org/wiki/Lymphocyte Image Credit: CC BY-SA 3.0

Value addition: Video Heading text: Connective tissue To see the video on different types Connective tissue, click the following hyperlink https://www.youtube.com/watch?v=WXDILPU_aLQ Source: Youtube Institute of Life Long Learning, University of Delhi

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Connective Tissues

Summary •

Connective tissue is one of the four general classes of animal tissues (those are epithelial, muscle, and nervous tissues).

•

It fills the spaces between organs and tissues, and provides structural and metabolic support for other tissues and organs.

•

Connective tissues consist of two basic elements: extracellular matrix and cells.

•

Every kind of connective tissues has distinctive properties, depending on the specific extracellular materials comprises of ground substance and fibres, between the cells.

•

Ground substance consists predominately of three groups of molecules: Proteoglycans (core protein), glycosaminoglycan molecules (GAGs) which are covalently bound to the proteoglycans; and multiadhesive glycoproteins. Basic types of fibres are embedded in the extracellular matrix between the cells are collagen fibres, elastic fibres and reticular fibres.

•

Various types of connective tissues are summarized in following table:

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Connective Tissues

Type of Connective Tissue Major Sub-types types

CONNECTIVE TISSUE PROPER

EMBRYONIC CONNECTIVE TISSUES

Mesenchym e

Mucous connective tissue

Structural characteristics

Location

Function

Cells present

Fibers Present

Extracellular matrix Semifluid ground substance

Under skin, bones of embryo, blood vessels of adult

Forms all other types of connective tissue

Fibroblasts

Collagen

Viscous ground substance

Umbilical cord

support

Loosely arranged fibers in gelatinous ground substance

Skin , dermis, lamina propria, blood vessels, nerves

Gives strength, elasticity, support

Mesenchymal cells

Collagen or reticular

Loose Connective tissue Collagen, Fibroblasts, Areolar Macrophages , adipocytes, mast cells, plasma cells

elastic, reticular

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Diagram

43

Connective Tissues Adipose

Adipocytes

Reticular, collagen

Closely packed cells with a small amount of gelatinous ground substance

Skin, heart, kidneys, yellow bone marrow, padding around joints

Energy storage, maintain body temperature

Reticular

Reticular cells

reticular

Loosely arranged fibers in gelatinous ground substance

Liver, spleen, lymph nodes, red bone marrow

Support, removes worn-out blood cells and microbes

Dense connective tissue Dense regular

Fibroblasts

Collagen

Parallelarranged bundles of fibers with few cells and little ground substance

Tendons, Ligaments and Aponeuroses

Provide great tensile strength

Dense irregular

Fibroblasts

Collagen (some elastic)

Irregularly arranged bundles of fibers with few cells and little ground substance

Dermis, pericardium of heart, peristoeum of bone

Provide high tensile strength

Elastic

Fibroblasts

Elastic

Little ground substance

Wall of arteries, trachea, vocal cords

Allows stretching of various organs

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Connective Tissues

SUPPORTING CONNECTIVE TISSUE

Cartilage Hyaline

Chondrocytes

Collagen (some elastic)

Limited ground substance; dense; gel matrix

Ribs, nose, parts of larynx, trachea, bronchial tubes

Provides flexibility and support for movement at joints

Fibrocartilag e

Chondrocytes

Collagen (some elastic)

Limited ground substance; intermediate between hyaline cartilage and dense connective tissue

Intervertebral discs, mensci of knee

Support and joining structures together

Elastic

Chondrocytes

elastic

Limited ground substance; flexible but firm gel matrix

Top of larynx, pinnae, auditory tubes

Maintain shapes, provides strength and elasticity

Collagen

Rigid, calcified ground substance with osteons

Make up the various parts of bones of the body

Support, protection, stores blood forming tissue

Bone (Osseous tissue) Osteoblasts, Compact osteocytes (dense)

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FLUID CONNECTIVE TISSUE

Connective Tissues Spongy (cancellous )

Osteoblasts, osteocytes

Collagen

Rigid calcified ground substance (no osteons)

Forms various parts of bones

Support, protection, stores blood forming tissue

Blood

Erythrocytes, Leukocytes, platelets

‘Fibers’ are soluble proteins that form during clotting

Matrix is liquid blood plasma

Blood vessels

Erythrocyte s transport oxygen; Luekocytes provide immunity

Lymph

Lymphocytes

‘Fibers’ are soluble proteins

Matrix is liquid lymph

Lymphatic vessels

Provide immunity

Image source: 1. http://www.lab.anhb.uwa.edu.au/mb140/ 2. http://cnx.org/contents/[email protected]:6/Siyavula:_Life_Sciences_Grade_ 3. http://cnx.org/contents/[email protected]:122/Anatomy_&_Physiology

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Connective Tissues

Exercises I. Multiple choice questions: 1. Connective tissue composed of three essential components? A. cells, ground substance, and protein fibers B. cells, ground substance, and carbohydrate fibers C. matrix, ground substance, and fluid D. collagen, ground substance, and protein fibers Answer: A. 2.

A section of tissue showed that cells located in spaces scattered in a transparent background. This is perhaps ________. A. Dense connective tissue B. loose connective tissue C. hyaline cartilage D. bone Answer: C.

3. Which connective tissue specialized for fat storage? A. adipose tissue B. tendon C. reticular tissue D. dense connective tissue Answer: A. 4. Ligaments join bones together and bear up a lot of stress. What kind of connective tissue should you expect ligaments to contain? Institute of Life Long Learning, University of Delhi

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Connective Tissues A. areolar tissue B. adipose tissue C. dense regular connective tissue D. dense irregular connective tissue Answer: C.

5. In bone, the main cells are ________. A. fibroblasts B. chondrocytes C. lymphocytes D. osteocytes Answer: D. 6. Which cell type secretes histamine A.

Macrophage

B.

mesenchymal cell

C.

adipocyte

D.

mast cell

Answer: D. 7. Identify a cell type A.

mesenchymal cell

B.

monocyte

C.

mast cell

D.

fibrocyte

Answer: C.

8. Identify the INCORRECT statement A.

Ground substance is placed among connective tissue fibers and cells.

B.

Adipose tissue may have a structural and cushioning function. Institute of Life Long Learning, University of Delhi

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Connective Tissues C.

Type III tropocollagen is the central form of tropocollagen in collagen fibers.

D.

Production of heat by the oxidation of fatty acids is a particular characteristic of brown adipose tissue.

Answer: C.

9. Identify a tissue type A.

Dense regular connective tissue

B.

Loose irregular connective tissue

C.

white adipose tissue

D.

brown adipose tissue

Answer: D.

10. Identify the CORRECT statement A.

Connective tissue cells are the dominant tissue component in dense connective tissue.

B.

Adipose tissue can have a structural, cushioning function

C.

Ground substance is an effective barrier to the diffusion of gases, ions, and small molecules.

D.

Type I tropocollagen is the dominant form of tropocollagen in reticular fibres.

Answer: B.

11. Identify a tissue type A.

Dense regular connective tissue

B.

Reticular connective tissue

C.

white adipose tissue

D.

mesenchymal connective tissue

Answer: D. Institute of Life Long Learning, University of Delhi

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Connective Tissues

12. Identify a tissue type A.

Mast cell

B.

Adipocyte

C.

mesenchymal cell

D.

Macrophage

Answer: D.

13. Identify a cell type A. Mast cell B. Adipocyte C. mesenchymal cell D. Macrophage Answer: C.

14. Which cell type is involved in the synthesis and maintenance of the extracellular components of connective tissues? A. Mast cell B. Adipocyte C. Fibrocyte Institute of Life Long Learning, University of Delhi

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Connective Tissues D. Macrophage Answer: C. 15. Identify the INCORRECT statement A. Connective tissues can be classified by the density and orientation of connective tissue fibres B. Mucous connective tissue is common in adult individuals. C. Adipose tissue and reticular connective tissue are special variants of loose connective tissue D. The local release of histamine and heparin increases blood flow and the permeability of blood vessels Answer: B. 16. Identify a tissue type A. Dense regular connective tissue B. Reticular connective tissue C. white adipose tissue D. loose irregular connective tissue Answer: D.

17. Identify a tissue type A. Dense regular connective tissue B. Reticular connective tissue C. white adipose tissue D. Brown adipose tissue Answer: C.

18. Identify a tissue type A. Dense irregular connective tissue B. Reticular connective tissue Institute of Life Long Learning, University of Delhi

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Connective Tissues C. white adipose tissue D. loose irregular connective tissue Answer: A

19. Identify a tissue type A.

Dense irregular connective tissue

B.

Reticular connective tissue

C.

Dense regular connective tissue

D.

loose irregular connective tissue

Answer: C

20. Identify a tissue type A.

mesenchymal connective tissue

B.

Reticular connective tissue

C.

Dense regular connective tissue

D.

white adipose tissue

Answer: B

II.

Define the following 1.

Mesenchyme Institute of Life Long Learning, University of Delhi

52

Connective Tissues

III.

IV.

2.

Perichondrium

3.

Osteons

4.

Ground substance

5.

Macrophages

6.

Chondrocytes

Briefly write short notes on 1.

Connective Tissue Fibers

2.

Lymph

3.

Glycosaminoglycan (GAGs)

4.

Specialized cells in connective tissue

5.

Extracellular Matrix

6.

Embryonic connective tissue

Differentiate between 1.

Periosteum and Perichondrium

2.

Interstitial growth and Appositional growth

3.

White Adipose tissue and Brown Adipose tissue

4.

Loose connective tissue and Dense connective tissue

5.

Cartilage and Bone

6.

Compact and spongy bone

7.

Areolar connective tissue and reticular connective tissue

8.

Dense regular connective tissue and Dense irregular connective tissue

V.

Long answer type questions

1.

Explain the general features of connective tissues.

2.

Describe the various functions of connective tissues. Institute of Life Long Learning, University of Delhi

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Connective Tissues 3.

What are the components of connective tissues? Explain their role in making connective tissue with example.

4.

Give the classification of connective tissues with their location and functions.

5.

Cartilage heals very slowly. Explain the reason.

6.

Explain two types of Adipose tissue with their location and function.

7.

Describe the structure and function of the various types of loose and dense connective tissues.

8.

Describe the haversian systems of bone with diagram. Explain difference between compact and spongy bone.

9.

Describe types of the fluid connective tissues with the diagram.

Glossary Tissue: It is an assembly of similar cells arises from the same origins which carries out specific function. Connective tissue: It is a type of animal tissue which supports, connects or separates various forms of tissues and organs of the body. Extracellular matrix: It is made up of fibers in a protein and polysaccharide matrix, secreted and organised by cells of connective tissue. Adipocytes: These are cells of connective tissue which reserves triglycerides and are also called fat cells or adipose cells. Leukocytes: These are white blood cells which move along with the connective tissues adjacent to blood vessels. Histamine: It is a chemical that widens small blood vessels as a component of the inflammatory response.

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Connective Tissues Ground substance: It is the constituent of a connective tissue lie between the cells and fibers which is perhaps fluid, semi fluid, viscous or calcified. Glycosaminoglycan (GAGs): These are heteropolysaccharide components of ground substance with high density of the negative charge (polyanions) to attracts water, forming a hydrated gel in order to permit rapid diffusion of water-soluble molecules. Mesenchyme: It is a type of embryonic connective tissues which are present basically in embryo forms almost all other types of connective tissue. Cartilage: It is supporting connective tissue which contains a dense network of collagen fibers and elastic fibers lie within the chondroitin sulfate. Osteon: It forms compact bone and contains central canal termed the osteonic or haversian canal, which is enclosed by concentric rings (lamellae) of matrix. Blood tissue: It is a fluid connective tissue composed of liquid extracellular matrix and formed elements i.e. red blood cells, white blood cells and platelets. Leukocytes: These are (also called white blood cell) colorless, nucleated blood cells, the chief function of which is to protect the body from disease. Basophils: Granular leucocytes that stain with a basic (alkaline) stain and store histamine and heparin. Eosinophils: Granular leucocytes that stain with eosin; they release antihistamines and are especially active against parasitic worms. Neutrophils: Granular leucocytes that stain with a neutral dye and are the most numerous of the leukocytes; especially active against bacteria. Monocytes: Agranular leukocytes of the myeloid stem cell line that circulate in the bloodstream; tissue monocytes are macrophages. Lymphocytes: Agranular leukocytes of the lymphoid stem cell line, many of which function in specific immunity. Institute of Life Long Learning, University of Delhi

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Connective Tissues

References 1. Michael H. Ross and Wojciech Pawlina Histology: A Text and Atlas. 6th edition. 2. Ross and Wilson. Anatomy and Physiology: In health and illness. Tenth Edition 3. Tortora, G.J. and Grabowski, S. Principles of Anatomy and Physiology. 13th Edition. 4. Hill, R. W., Wyse, G. A. and Anderson, M. (2006). Animal Physiology. p.355. 5. Randall, D., Burggren W. and French, Kathleen (2001). Eckert Animal Physiology. 6. Widmaier, E.P., Raff, H. and Strang, K.T. (2008). Vander’s Human Physiology, XI Edition, McGraw Hill. 7. Prof. A.K. Jain. Textbook of Physiology 8. Guyton, A.C. and Hall, J.E. (2011). Textbook of Medical Physiology, XII Edition, Harcourt Asia Pvt. Ltd. W.B. Saunders Company.

Web Links 1. http://cnx.org/contents/[email protected]:6/Siyavula:_Life_Sciences_Grade_ Institute of Life Long Learning, University of Delhi

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Connective Tissues 2. http://www.lab.anhb.uwa.edu.au/mb140/ 3. http://cnx.org/contents/fe382569-de99-4d07-a334757fb577e488@4/Connective_Tissue_Supports_and 4. http://www.cliffsnotes.com/sciences/anatomy-andphysiology/tissues/connective-tissue 5. http://kentsimmons.uwinnipeg.ca/cm1504/15lab42006/lb4pg6.htm

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