endocrine system
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Today’s class
Endocrine glands and hormones Mechanisms of hormone action Hypothalamus and pituitary gland Adrenal gland Thyroid and parathyroid glands Pancreas
Nervous and endocrine systems
Two systems of internal communication and regulation act individually or together
Nervous system high-speed electrical signals via neurons
Endocrine system endocrine glands secrete hormones
slower, longer-acting responses
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Endocrine glands
Ductless Secrete hormones
into bloodstream hormones affect
target with receptor some prehormones
and prohormones
fig 16.1
Types of chemical signals
pheromones endocrine paracrine
Human Reproductive Biology, 3/e. by S. Mader. McGraw Hill publishers. 2005. fig 5A
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Structural categories of hormones
Polypeptides and proteins Amino acid derivatives (amines) Steroids (Eicosanoids)
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Examples
(Anatomy and Physiology, 8/e, Seeley, Stephens and Tate, 2008, McGraw Hill, fig 17.3)
(autocrine regulator)
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General hormone effects Interactions
Synergistic (effect of 2 combine better than one)
Permissive Antagonistic
Concentration half-life (how long in the blood stream)
Target cell specificity receptor type, number and affinity upregulation, desensitization/downregulation
Importance of receptorse.g. complete androgen insensitivity syndrome (AIS)
XY individual testes present no ovaries or uterus testosterone
synthesized but no functional receptor
10Human Reproductive Biology, 3/e. by S. Mader. McGraw Hill publishers. 2005. fig 3.14
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Mechanisms of hormone action Peptide/protein/amines: receptors in Plasma membrane (cuz the
molecules are too big) different mechanisms, between from getting point A to B e.g.
cAMP – second message. 1st message in hormone DAG/IP3 (phospholipase C) – cut the phosphol
tyrosine kinase Activate “premade” proteins
Lipids: intracellular receptors reach target via carrier proteins in plasma
why the need for carrier? Need a carrier cuz there hydrphobic and direct to the right tissue
nuclear hormone receptors as transcription factors They create protein with transcription, translation, termination.
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Phospholipase C system
PIP2 IP3 + DAGphospholipase C
Human Physiology, 10e, by Fox, McGraw Hill publishers, 2008, fig 11.9
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Insulin and its tyrosine kinase receptor
Human Physiology, 10e, by Fox, McGraw Hill publishers, 2008, fig 11.11
no second messenger required
Control of hormone release
Endocrine gland stimuli Humoral Neural Hormonal
Nervous system modulation
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Hypothalamus and pituitary Control much of endocrine system Integrate nervous and endocrine systems
receives nerve signals from body initiates appropriate responses
Neurosecretory cells Posterior pituitary – not true (keeper and releaser of
hyperthalmus) stores and releases hormones made by hypothalamus
Anterior pituitary Hypthalmus when to make/ nt make the hormones
true endocrine gland makes 6 trophic hormones
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Targets of anterior pituitary hormones
Human Physiology, 10e, by Fox, McGraw Hill publishers, 2008, fig 11.15
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Hypothalamus and anterior pituitary
Hypothalamic-releasing hormones stimulate anterior pituitary gonadotropin-releasing hormone (GnRH) prolactin-releasing hormone (PRH) growth hormone-releasing hormone
(GHRH) corticotropin-releasing hormone (CRH) thyrotropin-releasing hormone (TRH)
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Hypothalamus-pituitary-target axis
Hypothalamus anterior pituitary target GnRH FSH, LH gonads sex hormones PRH prolactin mammary glands GHRH growth hormone various CRH ACTH adrenal cortex
corticosteroids (stress response) TRH TSH thyroid metabolism hormones
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Feedback examples
hypothalmus-pituitary-gonad axis
hypothalmus-pituitary-thyroid axis
Human Physiology, 10e, by Fox, McGraw Hill publishers, 2008, figs 11.17, 11.18
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Thyroid gland
Located just inferior to larynx
Follicles follicular cells
thyroxine colloid fluid
Parafollicular cells calcitonin
fig 16.8
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Thyroid hormones
T3 and T4 (thyroxine) elevate basal metabolic rate
stimulate protein synthesis, increase respiration, etc
Calcitonin lowers blood calcium concentrations
inhibits dissolution of calcium phosphate in bone
stimulates excretion of calcium in urine
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Diseases of thyroid: hypothroidism
Hypothyroidism: thyroid function slower than normal metabolism myxedama (fluid/mucoprotein accumulation
in subcutaneous tissue) Causes
Gland defect (e.g. by Hashimoto’s thyroiditis) Too little TRH and/or TSH for trophic effects Endemic goiter: by iodine deficiency
Hyperthyroidism: thyroid function more rapid than normal metabolism e.g. by Grave’s disease (autoimmune)
autoantibodies are TSH receptor agonists
fig 16.10
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Parathyroid glands
4 glands embedded in lateral lobes of thyroid gland
Secrete parathyroid hormone (PTH) control of blood Ca2+ levels
fig 16.11
Adrenal gland
Outer cortex no neural innervation steroid hormones
corticosteroids (corticoids) aldosterone effects will be covered in more
detail with urinary system Medulla
preganglionic sympathetic neurons catecholamines
epinephrine (mainly) norepinephrine 31
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Pancreas Exocrine and endocrine Islets
alpha cells: glucagon in response to blood glucose
stimulates liver: glycogen glucose, fat hydrolysis
beta cells: insulin in response to blood glucose
promotes entry of glucose into tissue glucose glycogen, fat
feeding versus fasting?
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Pancreas and blood glucose homeostasis
Human Physiology, 10e, by Fox, McGraw Hill publishers, 2008, fig 11.31
fig 16.18
Other hormones
Pineal gland: melatonin Gonads (testes and ovaries): sex
hormones will be covered with reproductive system
Other organs (non-endocrine glands) secrete hormones heart, GI tract, kidneys, skin, adipose
tissue, skeleton, thymus38
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