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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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