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The endocrine system (overview) Primary text: Vander’s physiology, Chapter 11

Result of growth hormone deficiency

Result of growth hormone overproduction

Thyroid hormone overproduction

A pump for insulin delivery

Principle of endocrine signalling Endocrine gland

Target Cell-1

Target Cell-2

Hormone

Target Cell-3

Hormones are used for long range intercellular communication within the body.

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The endocrine system: a system of endocrine (ductless) glands or specialised cells which can secrete hormones directly into local capillaries for distribution around the body.

ENDOCRINE (traditional)

For a molecule to be classifiable as a hormone it must:

a) be synthesised and secreted by specific type of cells (NB: these are not always anatomically distinct cells assembled as a “gland” i.e. vitamin D3 is produced by skin cells)

b) be secreted into the blood stream and travel in the blood c) bind to specific receptors on target cells, where it exerts various actions d) In addition, hormones often affect metabolism, cell division, gene expression.

HORMONES ARE EITHER: 1. Derivatives of the amino acid tyrosine: a) catecholamines

(adrenaline and noradrenaline)

b) thyroid hormones

thyroxine (T4) and triiodothyronine (T3)

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2. Proteins/peptides – long chains of aminoacids (eg insulin)

3. Steroids: eg cortisol, tesosterone

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Secretion of hormones is regulated by: 1. Ca2+ -dependent exocytosis (pituitary hormones, insulin, adrenaline) Ca2+

Synthesis - storage in vesicles - vesicle fusion with the membrane – hormone release.

2. By cleavage of the storage molecules (thyroid hormones – from thyroglobulin). 3. Adrenal steroids: little storage but massive pool of the precursors: synthesised on command (ACTH) and immediately secreted.

Some of the endocrine glands in man ACTH, GH, LH, FSH, TSH, PROLACTIN

hypothalamus

ADH, OXYTOCIN Thyroxine (T4)& triiodothyronine (T3) Calcitonin Cortisol, aldosterone Adrenaline Insulin Glucagon Estrogens Progesteron Androgens

Organisation of the endocrine circuits which operate via anterior pituitary

Hypothalamus Anterior Pituitary Endocrine glands controlled by pituitary

Targets throughout the body

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Hypothalamus

Mammary glands Uterus

Target endocrine glands Tissues of the body

Organisation of the endocrine circuits which operate via anterior pituitary HYPOTHALAMUS RELEASING (INHIBITORY)FACTORS (HORMONES) 

ANTERIOR PITUITARY

“Trophic” Trophic  hormones hormones

TSH

TARGET ENDOCRINE  GLANDS

Thyroid

Adrenal cortex

thyroxine

cortisol

HORMONES 

ACTH

FSH LH FSH, LH

Gonads

sex steroids

TARGET TISSUES AND ORGANS

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HYPERthyroidism (Toxic goiter)

HYPOthyroidism (cretinism)

Hypothalamus Posterior y Pituitary A direct channel

Targets throughout the body

Hypothalamus

Vasopressin Oxytocin

(anti-diuretic hormone)

Tissues of the body

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There are many hormones produced by specialised

cells in various organs which are not controlled by the pituitary.. In some cases these are “true” glands, pituitary sometimes just groups of specialised cells present in various tissues.

“True” glands

“Groups of cells”

Pancreas

cells in kidney Cells in the atria of the heart

Renin-producing i d i

Adrenal medulla

Targets throughout the body

Blood glucose

Insulin

Endocrine gland ANTERIOR PITUITARY

Major hormone Primary targets Trophic hormones Other ~endocrine~ glands and various tissues ACTH (adrenocortico…) TSH (thyroidstimulating...)

Adrenal cortex

LH (luteinizing hormone {corpus luteus – yellow body}

Ovaries

Testes

Female hormones↑ Ovulation Male hormones↑

FSH (folliclestimulating…)

Ovaries Testes

Follicle growth ↑ Sperm formation ↑

GH (growth…)

Liver, cartilages, muscles, many other Breasts

Growth of almost all types of cells.

Prolactin

POSTERIOR PITUITARY

Primary effects Stimulate hormones secretion and proliferation of the organs’ tissue Secretion of cortisol ↑ Secretion of T3 and T4 ↑

ADH (antidiuretic…) also called VASOPRESSIN OXYTOCIN

Thyroid

kidneys, higher concentrations – blood vessels Uterus Mammary glands

Growth of tissue and milk expression H2O retention and vasoconstriction, BP increase Contraction Milk expression

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Endocrine gland

Major hormone

THYROID

Thyroxine (T4) & tri-iodothyronine (T3)

Primary targets

Calcitonin

Bone

PARATHYROIDS

Parathyroid hormone

Bone, intestine, kidneys

ADRENAL cortex

Cortisol

Liver, muscles, immune cells etc…

Most organs

(glucocorticoid) Aldosterone

Kidneys

ADRENAL medulla

Adrenaline& Noradrenaline

Cardio-vascular system, lungs, liver

PANCREAS, islets of Langerhans

Insulin

many cells

Glucagon

Liver and fat

ESTROGENS, mainly estradiol

Female genitals, mammary glands

GESTAGENS, i.e. progesterone

Uterus

Testosterone

Prostate, seminal vesicles, other organs

OVARIES

Mammary glands TESTES

Primary effects Rate of cell respiration↑ overall metabolism ↑ CNS: excitability & emotional reactivity ↑ growth (young children)↑ Ca2+ concentration in blood↓ Ca2+ concentration in blood↑ “Stress” hormone, glucose and fatty acids mobilisation, protein catabolism↑ Na+ retention, K+ excretion Blood pressure↑, blood glucose↑, components of fight-or-flight status Cellular uptake of glucose, formation of glycogen and fat. Blood glucose ↓ Breakdown of glycogen and fat. Blood glucose ↑ Develop female sex charateristics. Increase sex drive (central effect). “Pro-gestational” action – decrease in excitability and contractility Development of the secretory tissue Promotes male secondary sex characteristic, skeletal muscles: “anabolic” effect.

RECEPTORS: Located intracellular

Located at the membrane

Receptors which operate via gene expression (steroid and thyroid hormones)

Receptors which themselves are ion channels (“A”)

Hormones act on

Receptors which act as enzymes y (for ( example, p the insulin receptor) Receptors which are coupled via G-proteins (for example adrenalin receptors)

Intracellular receptors may be located as free-floating proteins in the cytoplasm or nucleus

DNA

GENE expression

CHANGE of cell function

Protein Synthesis

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RECEPTORS: Located intracellulary

Located at cell membrane

Receptors which operate via gene expression (steroid hormones)

Receptors which themselves are ion channels (“A”) Receptors which act as y ( p enzymes (for example, the insulin receptor)

Hormones act on

Receptors which are coupled to their targets via G-proteins (for example adrenalin receptors)

Receptors which act as enzymes -PO4 -PO4

-PO4

Changes in -PO 4 -PO cell’s proteins -PO4

4 -PO 4-PO4 -PO 4 -PO -PO4 4

Cell response

RECEPTORS: Located intracellularly Located at cell membrane Receptors which operate via gene expression (steroids)

Hormones act on

Receptors which themselves are ion channels (“A”) Receptors which act as enzymes (kinases, for example, l the h insulin i li receptor) or directly coupled to enzymes Receptors which are coupled via G-proteins (for example adrenalin receptors)

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Boy-ohboy!!!!!!

Medical importance of endocrine system 1. Numerous diseases result from pathologically low or high concentration of hormones: - diabetes (two forms due to insufficiency of 2 different hormones) - dwarf dwarfism sm and gigantism g gant sm - many forms of infertility and many more... 2. Numerous drugs act like hormones or their antagonists: - bronchial asthma (allergic constriction of bronchi) - prevention of pregnancy (contraception) - treatment of hormonal diseases - to enhance muscle growth (illegal doping!) 3. Numerous unwanted (side-) effects of drugs are due to their interactions with hormones

Questions to consider: - Concentration of which hormones are likely to be elevated during pregnancy? - What would happen to blood glucose levels if a bulk dose of insulin was injected? - Why Wh is i it common practice ti to t check h k blood bl d concentrations of thyroid hormones in newborn children?

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