UNIT 3 TISSUES SUBOBJECTIVES 3.1 I can describe the structures and functions of epithelial tissues. 3.2 I can describe the structures and functions of the types of glands. 3.3 I can describe the components of connective tissue and their functions. 3.4 I can describe the structures and functions of the connective tissues. 3.5 I can describe the structures and functions of cartilage tissue. 3.6 I can describe the structure and function of bone tissue. 3.7 I can describe the structure and function of blood tissue. 3.8 I can describe the structures and functions of muscle tissue. 3.9 I can describe the structure and function of nervous tissue. 3.10 I can describe the structure and function of the major types of epithelial membranes.
Evolution Connection 3.11 I can describe the evidence for, and explain how mammary glands evolved from epithelia involved in the innate immune response.
Breast beginnings http://scienceblogs.com/pharyngula/2006/05/19/breast-beginnings/ Four of my favorite things are development, evolution, and breasts, and now I have an article that ties them all together in one pretty package. It’s a speculative story at this point, but the weight of the evidence marshaled in support of the premise is impressive: the mammalian breast first evolved as an immunoprotective gland that produced bacteriocidal secretions to protect the skin and secondarily eggs and infants, and that lactation is a highly derived kind of inflammation response. That mammary glands may have had their origin as inflamed glands suppurating mucus may not be the most romantic image to arise in a scientific study, but really—they got better and better over the years. Vorbach et al. have carried out a descriptive analysis of the elements of breast milk and lactation and come to this conclusion on the basis of three general lines of evidence.
Immunoprotective proteins are a significant component of breast milk. The nutritional components of milk are synthesized by enzymes that are derived from immunoprotective proteins. Many of the molecular regulators of lactation are shared with inflammation pathways.
My previous article on mother’s milk gave a highly abbreviated list of the components found in milk, but there’s more detail in the list below. Milk is much, much more than baby food—it’s an incredible cocktail of interesting proteins, and 1) many of them are shared with mucus secretions produced by other secretory epithelia, and 2) many of them are elements of the innate immune system. Milk is actually a kind of anti-microbial snot mixed in with a lot of fat and sugar.
(click for larger image) Molecules that play a dual role in immunity and nutrition. Proposed origin of milk as an antimicrobial mucus secretion containing many evolutionarily conserved, protective molecules, which today comprise part of the whey proteins of milk (blue). Two of these molecules, xanthine oxidoreductase and lysozyme, evolved due to gene sharing and gene duplication additional functions in the ancient mammary epithelium such as milk fat droplet secretion and the unique synthesis and secretion of alactalbumin as well as the milk sugar lactose. The secretion of these calorie-rich components markedly increased the nutritional value to milk (green). The nutritional and protective importance of milk was further expanded by serum-derived proteins that comprise part of the whey proteins of milk (red). In particular, lactose and its derivatives are osmotically active and draw water into milk. Caseins are the major protein source of milk in higher mammals. While the calcium-sensitive α1 α2, β, γ, δ-caseins presumably originated de novo, the calcium-insensitive κ-casein shows structural and sequence similarities to fibrinogen (purple). Abbreviation: Ab, antibody; Ig, Immunoglobulin; PRM, Pattern Recognition Molecule; PRR, Pattern Recognition Receptor; XOR, Xanthine oxidoreductase. The innate immune system is a primitive defense system that uses peptides that recognize various common microbial surface molecules, and also uses enzymes that produce chemical agents lethal to bacteria. It’s a first line of defense that differs from the more specific immune system in that it doesn’t require specialized immune system cells and also doesn’t acquire the kind of highly refined specificity we see in antibodies (note, too, that antibodies are also secreted in milk—they are the IgG, IgE, and IgM molecules listed above.) One key element in milk is XOR, xanthine oxidoreductase. This enzyme mediates purine catabolism and, for instance, the synthesis of uric acid, but also generates reactive oxygen species and reactive nitrogen species, compounds that can be voraciously reactive and interact destructively with bacteria. You may have heard of one reactive nitrogen species, the nitrites that hot dogs are loaded with as preservatives. Reactive oxygen species are chemicals like hydrogen peroxide, which is often used as a disinfectant, and superoxide anions and hydroxyl radicals. Another is lysozyme, a protein that hydrolyzes the polysaccharides (sugars) that make up bacterial cell walls. This is a very common component of the innate immune system of many animals: you ooze this protein out of your skin, your mucus is loaded with it, and it’s also found in high concentrations in other places, such as egg whites. It’s simply generally useful protection to be able to chemically strip bacteria of their protective coats. Other proteins also have bacteriocidal functions, and are found in other glandular secretions: lactoferrin and transferrin, lactoperoxidase (which as you might guess from the name, synthesizes reactive oxygen species), defensins (which disrupt bacterial membranes), and pattern recognition molecules (PRMs), which bind to certain common molecular motifs on bacterial surfaces. It’s so sweet and tasty, yet so deadly to microbes! Now wait, you may be wondering…how is this evidence that milk’s original function was immunoprotective? If you’re secreting a sweet and fatty nutritious substance for your young, it would definitely be advantageous to load it up with antimicrobials to keep the nasty beasties from growing in it. XOR and lysozyme and all those others could have been added secondarily.
One reason to think otherwise is that those protective molecules are universal to vertebrates—lizards and birds have them, too. These enzymes and other proteins came first. Those of you wise in the ways of evolution are saying to yourselves, “So what? It’s another example of cooption, taking a protein used for one function and adapting it to another.” And you’d be right: that’s only suggestive. Another good reason, though, is to look at the enzymes responsible for generating the nutritive components of milk, the lactose sugars and the fat droplets. Breaking up fat into droplets and enveloping them with some kind of coat to promote suspension in water is an essential function in the production of milk. The protein that is responsible for this structural function, and which if knocked out prevents lactation and actually leads to collapse of the mammary gland, is…XOR! This is a wonderful example of a protein doing double duty, as an enzyme responsible for bacteriocidal action and as a structural protein involved in solubilizing fats. It almost certainly had the enzymatic function first, and if any cooption was going on, it was to recruit an immunoprotective protein to secondarily assist in a nutritive function. The other essential nutritive component of milk is lactose, the milk sugar. Lactose is an odd and unusual sugar—that’s actually it’s advantage, that it is a sugar that many bacteria have difficulty digesting (it’s not just people that can be lactose intolerant!)— and it requires a specific synthetic complex consisting of β-1,4 galactosyltransferase and α-lactalbumin for its production. Where did α-lactalbumin come from? It’s sequence makes the homologies clear: the α-lactalbumin gene is a modified copy of…lysozyme! I think that’s remarkable. The two primary nutritive components of milk, the sugars and fats, are the product of novel activity by proteins that are clearly primitively associated with innate immunity. To further the similarities, the authors give a long list of components of signaling pathways that are typically associated with inflammatory and immune system responses and are also essential in lactation. For instance, the transcription factor NF-kB, which is also a hot candidate molecule in cancer research, is involved in regulating the expression of various cytokines and antimicrobial agents; transgenic mice that knock out this pathway also exhibit developmental failures in the differentiation of the mammary gland. They’ve modified other elements of this pathway (RANKL, C/EBPβ, TNF-α) which act in inflammation responses, and they all also induce developmental problems in mammary gland tissue and reduce or shut down lactation. I’ve just finished teaching a human physiology course in which we learned the basics of endocrinology, and I gave my students the usual story on the pituitary hormone prolactin: it regulates milk production. It’s too bad I hadn’t read this paper earlier, because it makes the story much, much more complicated (my students are probably relieved, though—the class was complicated enough as it was). Prolactin is known as a key lactogenic hormone but, depending on the cellular context, prolactin can also act as an antiinflammatory or proinflammatory cytokine. Interestingly, it has been demonstrated that prolactin is involved in the protective as well as the nutritional role of milk. Prolactin participates in regulating the secretion of immunoglobin A (IgA), the prominent Ig in mucus and milk that inhibits the colonization of pathogenic bacteria on mucosal surfaces. Changes in the secretion of IgA are associated with the anti-inflammatory potential of epithelial tissues. In addition, prolactin stimulates the uptake of some amino acids and glucose, as well as the synthesis of casein, α-lactalbumin, lactose and milk fat droplets in the lactating mammary epithelium. Finally, prolactin and IFN-γ also stimulate the expression of XOR in mammary epithelial cells via the Jak/Stat signaling pathway. Thus, multiple small molecules and ligandreceptor systems that have critical roles in inflammatory responses exert dual and, in many cases, essential functions in immunity and mammary gland biology. Gee, I’m going to have to revise and add some stuff in that class next time I teach it. Very cool. Their model for the evolution of the mammary gland is illustrated below. It’s reasonable, and the molecular evidence is persuasive. Basically, the process began as the secretion of antimicrobials agents from the skin of the early mammal (something we still do) as a protective function. This function was
elaborated by infoldings of epithelia to increase surface area and generate reservoirs of mucus and the antimicrobials. Eggs and infants would have benefitted from more copious secretions from the mother, coating them as well with this immunoprotective substance. The young would have also lapped up the tasty rich goo, and infant survival would have been promoted by changes that caused the secretion of ever-richer substances. Proposed evolution of the mammary gland from a mucus-secreting epithelial gland. Mammary glands presumably evolved as mucus-secreting skin glands that similar to many mucus surface epithelia secreted antimicrobial enzymes such as XOR and lysozyme. The evolution of additional functions of XOR and lysozyme in the ancient mammary epithelium resulted in the secretion of fat droplets, α-lactalbumin and lactose. Consequently, the mammary gland evolved from a protective immune organ into a reproductive organ unique to the class mammalia. One question not addressed by the paper is why only females lactate—you’d think the young would have benefitted if Papa Proto-mammal was also slathering them with immunoprotective slime. I’d guess that this supports the idea that those ancient males weren’t particularly involved in caring for their progeny, so it made little difference in infant survival if the father turned these secretions down to a level sufficient to selfishly protect just himself. These secretions are also expensive—I’ve seen figures that suggest that a third to half of the energy budget of nursing small mammals may be leaking out their lactating teats—so it would have been advantageous for those slacking males to shut down the production so necessary for female reproductive success. Vorbach C, Capecchi MR, Penninger JM (2006) Evolution of the mammary gland from the innate immune system? BioEssays 28:606-616.
READINGS: SUBHEADINGS 1)
All of chapter 5
MORPHEMES TO MEMORIZE http://quizlet.com/_et7ui 1) 2) 3) 4) 5) 6)
Adipfat Chondrcartilage –cyt cell EpiUpon, after, in adition –glia glue Hist-
Web, tissue 7) HyalResemblance to glass 8) Interamong 9) Macrlarge 10) Neurnerve 11) Osbone
12) PhagTo eat 13) Pseudfalse 14) Squamscale 15) Stratlayer 16) Striagroove
STRUCTURES TO MEMORIZE http://quizlet.com/_f77o7
Figure 5.1 page 134 memorize all structures
Figure 5.2 page 134 memorize all structures
Figure 5.3 page 135 memorize all structures
Figure 5.5 page 136 memorize all structures
Figure 5.7 page 137 memorize all structures
Figure 5.6 page 136 memorize all structures
Figure 5.8 page 137 memorize all structures
Figure 5.9 page 138 memorize all structures
Figure 5.11 page 140 memorize all structures
Figure 5.18 page 144 memorize all structures
Figure 5.20 page 145 memorize all structures
Figure 5.19 page 145 memorize all structures
Figure 5.21 page 121 memorize all structures
Figure 5.22 page 146 memorize all structures
Figure 5.24 page 147 memorize all structures
Figure 5.26 page 149 memorize all structures
Figure 5.28 page 150 memorize all structures
Figure 5.30 page 151 memorize all structures
Figure 5.25 page 148 memorize all structures
Figure 5.27 page 149 memorize all structures
Figure 5.29 page 151 memorize all structures
Figure 5.31 page 152 memorize all structures
OTHER VOCABULARY TO MEMORIZE http://quizlet.com/_f77dx 3.1 1) 2)
Tissue similar cells of the same origin that perform a specific function Epithelial tissue lines cavities and covers the surfaces of structures throughout the body
3) Basement membrane a thin sheet of fibers that lines epithelium. It sticks the epithelium to its loose connective tissue. 4) Simple squamous epithelium involved in filtration and diffusion. Found in air sacs of lungs, walls of capillaries, and the linings of blood and lymph vessels 5) Simple cuboidal epithelium involved in secretion and absorption. Found in kidney tubules, surface of ovaries, and the linings of kidneys 6) Simple columnar epithelium involved in protection, secretion, and absorption. Found in linings of uterus, stomach, and intestines 7) Cilia projections of epithelial cells into a lumen that move substances 8) Microvilli hair-like processes of cells that wisp substances in one direction. They are also involved with secretion and absorption 9) Goblet cells single celled glands found in epithelia that secrete mucin, which mixes with water forming mucus 10) Mucus a slippery fluid mostly of glycoproteins. Also contains lysozymes and antibodies 11) Pseudostratified columnar epithelium _____ cells that appear layered because the nuclei are at different levels, but each cell reaches the basement membrane. They line repiratory passages, protect, secrete and move mucus 12) Stratified squamous epithelium involved in protection. Found in the outer layer of skin, linings of oral cavity, throat, vagina, and anal canal 13) Keratin a fibrous protein type that is the main structural unit of hair, nails, and the outer layer of skin 14) Stratified cuboidal epithelium involved in protection. Found in the larger ducts of mammary gland, salivary glands, sweat glands, and the pancreas 15) Stratified columnar epithelium involved in protection and secretion. Located in the Vas deferens, part of the male urethra, and parts of the pharynx 16) Transitional epithelium multiple layers of epithelial cells which can contract and expand 17) Glandular epithelium The type of epithelium that secretes into ducts that open onto surfaces like skin or into body fluids is 3.2 18) Exocrine gland excretes product through a duct into a cavity or out of the body 19) Endocrine gland a gland that secretes its product directly into the blood stream 20) Merocrine gland an exocrine gland that secretes its product into a duct via exocytosis. Found in salivary glands, pancreatic glands, and sweat glands 21) Apocrine gland An exocrine gland that secretes bits of the cell in the form of vesicles. Examples include a few types of sweat glands like those of the arm pits and mammary glands. 22) Holocrine gland an exocrine gland that secretes by the disintigration of hole cells filled with the secretory product. Found in sabaceous glands 3.3 23) Connective tissue tissue that supports, connects, or separates different tissues and organs of the body
24) Matrix The gelatinous extracellular material that includes ground substance and fibrous proteins. It sticks tissue cells and cell layers together 25) Ground substance a gel-like material that surrounds connective tissue cells 26) Fibroblast a cell that synthesizes the extracellular matrix and collagen 27) Macrophage Amoeboid cells that roam connective tissue and engulf foreign particles and debris of dead cells. 28) Mast cell a cell found in various tissues that produces histamine and heparin which cause inflammation. They are involved in allergic responses and defense against pathogens 29) Collagenous fibers fibers made of the most abundant protein found in animals. They have diverse functions including tension resistance. 3.4 30) Connective tissue proper unspecialized connective tissue found throughout the body that has various functions 31) Areolar tissue loose connective tissue that binds different tissue types together while providing cushioning. It has loosely organized fibers and significant vascularization. It is found throughout the body. 32) Adipose tissue loose connective tissue specialized for storage of fat. It protects vital organs, insulates, and stores energy. 33) Reticular connective tissue Loose connective tissue dominated by _____ fibers. Provides structural support for lymphatic organs, the spleen, and liver 34) Dense connective tissue parallel collagen fibers that connect different tissues and resists tension well in one direction. Found in ligaments, and tendons 35) Elastic connective tissue connective tissue that can stretch. It is found in hollow organs such as the bladder and arteries 3.5 36) Cartilage flexible connective tissue with extensive extracellular matrix and no direct blood supply. Found throughout the body. 37) Chondrocyte a cell found in cartilage tissue types that produces and maintains the matrix of cartilage 38) Lacunae a tiny cavity found in bone and cartilage tissue where osteocytes and chondrocytes are located 39) Hyaline cartilage composed mostly of extracellular matrix. Has a glassy appearance and is found on the ends of bone and the supporting rings of respiratory passages 40) Elastic cartilage cartilage composed of collagen and elastic fibers that support and provide shape. Found in the outer ear, Eustachian tubes, and epiglottis 41) Fibrocartilage cartilage with many large cartilage fibers. Supports, protects, and provides framework. Located between vertebral disks, pelvic girdle, and knee 3.6 42) Bone dense connective tissue that supports and protects organs, produces red and white blood cells, and stores minerals 43) Osteocyte bone cells that regulate the cell types that form bone and reabsorb bone. They also regulate phosphate metabolism.
44) Lamellae cylindrical sheets of bone matrix 45) Haversian canals the channel formed by lamellae where blood vessels and nerves travel through bone 46) Osteon the structural unit of bone consisting of concentric layers of lamellae surrounding a channel (Haversian canal) that contains blood vessels and nerves 47) Canaliculi tiny spaces where the processes of an osteocyte extend through and connect to other osteocytes. The membranes of the cells are fastened by gap junctions. 3.7 48) Plasma the noncellular, watery portion of blood that suspends the other components of blood 49) Red blood cell cells without a nucleus packed with hemoglobin, which carries oxygen 50) White blood cell a cell that defends against pathogens and foreign materials 51) Platelets cell fragments that cause clotting and produce growth factors involved in tissue repair 3.8 52) Muscle tissue soft tissue composed of myofibrils that may be smooth or striated. They are involved in both voluntary and involuntary movement 53) Skeletal muscle tissue striated _____ tissue that is under voluntary control. Moves and supports bone 54) Smooth muscle tissue non-striated _____ tissue under involuntary control. Involved in organ movements 55) Cardiac muscle tissue involuntary _____ tissue, single nucleated, and striated with intercalated discs. Self-contracting 56) Intercalated disc structures with specialized gap junctions that connect heart muscle and allow for coordinated muscle contractions 3.9 57) Nervous tissue soft tissue composed of neurons and glial cells that transmit electrical messages that control body function 58) Neuron an electrically excitable cell that transmits electrical messages to and from organs and tissues 3.10 59) Organ two or more tissues grouped together performing the same function 60) Synovial membrane A membrane between a joint capsule and joint cavity that secretes a lubricating fluid 61) Cutaneous membrane protects the organism from pathogens and desiccation. Insulates, regulates body temperature, and produces vitamin D
