animal endocrine systems biology 2: form and function
Post on 26-Dec-2015
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Hormones regulate...
• Together with nervous system, responsible for regulation of body organs
• Secreted by ductless glands into surrounding capillary network
• Long-term, narrow-to-broad impact mediated by contact of hormone with receptor molecules at target site
• Receptor molecules may be internal or external to cell• Endocrine system is distinct to organ self-regulation,
or autocrine/paracrine system
There are four classes of hormone
• Polypeptides - short chains < 100 amino acids in sequence, e.g., ADH
• Glycoproteins - long chains (100+) of amino acids connected to carbohydrate, e.g., FSH
• Amines - derivatives of tyrosine and tryptophan, e.g., epinephrine, thyroxine
• Steroids - lipid derived– sex steroids, e.g., testosterone– corticosteroids, e.g., aldosterone
In mammals, there is a close association between the endocrine and neural systems...• Nervous system-controlled endocrine glands
include:– Adrenal medulla– Posterior and anterior pituitary (via
Hypothalamus)– Pineal gland
• Examples of non-nervous system controlled endocrine secretion include pancreas (insulin), and adrenal cortex (aldosterone)
Hormones that enter cells
• Includes all lipophilic (lipid-soluble) hormones (e.g., steroids, thyroxine)
• Bind to specific receptors in cytoplasm, which then moves to the nucleus, or binds directly to receptor proteins in nucleus
• Receptor molecule, once activated, binds to portions of DNA and stimulates transcription, ultimately effecting protein production and cell metabolism
Hormones that do not enter cells...
• Water soluble hormones that bind to the outside of cell membranes, requiring a secondary messenger inside cell to complete message
• Secondary messengers include– Cyclic AMP
– IP3/Ca2+
Cyclic AMP• e.g., effects of epinephrine on -adrenergic centers• Binding of epinephrine to G-protein receptor causes G-protein
sub-unit to disassociate• G-protein sub-unit binds with membrane enzyme adenlyl
cyclase• Adenlyl cyclase, now activated, catalyzes formation of cAMP
from ATP• cAMP binds to and activates protein kinase-A, responsible for
phosphorylation of certain proteins specific to tissue/cell– in liver, stimulates conversion of glycogen to glucose– In cardiac muscle, increases speed and force of heart beat
Inositol triphosphate/Ca2+
• e.g., effects of epinephrine on -adrenergic centers• Binding of epinephrine to G-protein receptor causes G-protein
sub-unit to disassociate• G-protein sub-unit binds with, and activates membrane
enzyme phospholipase C
• Phospholipase C cleaves certain phospholipids to produce IP3
• IP3 binds with receptors on endoplasmic reticulum, stimulates release of Ca2+
• Ca2+ binds to calmodulin, which activates different types of protein kinases, causing phosphorylation of different cellular proteins
The Posterior Pituitary
• neurally derived: hormones are part of neuroendocrine reflex.
• Secretes Antidiuretic hormone (ADH) and Oxytocin (although both are made in the hypothalamus) – ADH stimulates water retention by the kidneys
(alcohol inhibits ADH, causing dehydration)– Oxytocin stimulates uterine contractions and
milk-ejection reflex
Anterior pituitary• Epithelially-derived tissue, produces
– GH, growth hormone (somatotropin)
– ACTH, adrenocorticotropic hormone (corticotropin)
– TSH, thyroid stimulating hormone (thyrotropin)
– Gonadotropins LH (luteinizing hormone) and FSH (follicle stimulating hormone)
– Prolactin (PRL)
– MSH, Melanocyte-stimulating hormone
Control of the Anterior Pituitary by the Hypothalamus is still hormone-mediated
• Releasing and inhibitory hormones are secreted by the hypothalamus and carried via a c apillary network connected to a second caillary network - the hypothalamo-hypophyseal portal system
• for example, gonadotropin releasing hormone (GnRH) stimulates the release of FSH and LH
• In turn, hypothalamus is controlled by negative feedback inhibition
Other endocrine glands
• Adrenal glands– The adrenal medulla secrets epinephrine
and norepinephrine, triggering alarm responses across the body at various targets, preparing the body for ‘fight or flight’
– The adrenal cortex secretes cortisol and other glucocorticoids, an aid in glucose homeostasis, as well as aldosterone, responsible for salt balance
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