Chapter 17


◦ Differentiation of reproductive and CNS in fetus
◦ Stimulation of growth and development
◦ Coordination of the male and female reproductive system
◦ Maintenance of internal environment
◦ Adaptation to emergency demands of the body

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◦ Specific rates and rhythms of secretion
 Diurnal, pulsatile and cyclic and patterns depend upon circulating substances
◦ Operate within feedback systems (+/-)
◦ Affect only target cells with appropriate receptors
◦ The liver inactivates hormones, rendering the hormones more water soluble for renal excretion

•
Hormones are released:
– In response to an alteration in the cellular environment
– To maintain a regulated level of certain substances or other hormones
•
Mechanism – release
– Chemical factors (blood sugar , Ca ++ levels)
– Endocrine factors (FSH → ovary → E)
– Neural control (CRF → pituitary → ACTH)
Feedback


Hormone Transport (Table 17-1)
Hormones are released into the circulatory system by endocrine glands
◦
circulate in free unbound forms
 Short-acting responses
 Bind to surface receptors
◦ Lipid-soluble hormones are primarily circulating bound to a carrier (Table 17-2)
 Rapid and long-lasting response
 Bind to cytoplasm or nucleoplasm receptor


Cellular Mechanisms of Hormone Action
Target cell – recognize, bind and initiate

Up – regulation

Down – regulation
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Hormone effects
◦ Direct – stimulation
◦ Permissive – facilitates maximum response/function


Cellular Mechanisms of Hormone Ac t ion
◦ Located in the plasma membrane or in the intracellular compartment of the target cell

◦
◦ High molecular weight
Cannot diffuse across the plasma membrane


Cellular Mechanisms of Hormone Action
◦ Easily diffuse across the plasma membrane and bind to cytoplasm or nuclear receptors


Cellular Mechanisms of Hormone Action
Water-soluble hormones
◦ First messenger
 Signal transduction
◦ Second messenger molecule (Table 17-3)

 Calcium
Cyclic adenosine monophosphate (cAMP)
 Cyclic guanosine monophosphate (cGMP)
 Tyrosine kinase system


Cellular Mechanisms of Hormone Action
Lipid-soluble hormones
◦ Steroid hormones
 Androgens, estrogens, progestins, glucocorticoids, mineralocorticoids, thyroid hormones, vitamin D, retinoid
◦ Diffuse across the plasma membrane
 Bind to cytoplasmic or nuclear receptors
 Activate DNA transcriptn and translation

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

Steroid
Hormone
Mechanism

•
•
Structure and Function of the Endocrine
Glands
Hypothalamus
Pituitary gland
(adenohypophysis)
A) Chromophobes – non-secretory cells
B) Chromophils - secretory cells
7 cell types → specific hormones


Structure and Function of the Endocrine
Glands
◦ Posterior pituitary (neurohypophysis)
 Synthesized with binding proteins in the neurons of the supraoptic and paraventricular nuclei of the hypothalamus → stored
 Anti-diuretic hormone (ADH)
 Oxytocin


Control of Posterior Pituitary Hormones
Release (both)
◦ Stimulation of cholinergic receptors by Ach, angiotensin II , and Bendorphins

Inhibition
◦ B-adrenergic receptors

•
Anti-diuretic hormone
– Controls plasma osmolality
– ↑ permeability of distal renal tubules and collecting ducts
– Pharmacological levels ADH (vasopressin) → vasoconstriction and ↑ BP
– Regulation
• Osmoreceptors of the hypothalamus
• Baroreceptors: L atrium, carotid and aortic arches
(intravascular volume) also: stress, trauma, pain, exercise, nausea, nicotine, heat, morphine → ↑ secretion, ↓ HTN, alcohol and ↑ plasma volume


◦ Uterine contractions and milk ejection with lactation
◦ Role in sperm motility in men
◦ ADH effect-weak

•
•
•
•
“ controls the rate of metabolic processes”
Bilobed either side of trachea – joined by isthmus
Follicles – follicle cells surrounding colloid
Parafollicular cells (C cells)
– Secrete calcitonin (↓ serum Ca ++ by # bone – resorption)
Regulation
– Thyrotropin – releasing hormone and thyroid stimulating hormone


Thyroid hormones
◦ Iodine – required for synthesis
◦ 90% T
4 and 10% T
3
◦ Bound to mostly thyroxine - binding globulin -
◦ Regulation negative feedback
 TRH - ↑ cold exposure, stress and ↓ T
4
◦ Effects
 ↑ metabolism of protein, fat and glucose → rapid ↑ heat production and body temperature
 Normal linear growth requires TH
 CNS and ANS require TH


Parathyroid hormone
◦
◦ ↑ Ca ++ and↓ PO
4
= - bone, kidneys
Antagonist of calcitonin



The pancreas is both an endocrine and an exocrine gland
Islets of Langerhans
◦ Secretion of glucagon and insulin
◦ Cells
 Alpha – glucagon
 Beta – insulin
 Delta – somatostatin and gastrin
 F cells – pancreatic polypeptide

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Endocrine Pancreas
◦ Synthesized from proinsulin
◦ Secretion is promoted by ↑ blood glucose
◦
◦ Facilitates the rate of glucose uptake into the cells
Anabolic hormone


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
◦ Secretion is promoted by decreased blood glucose levels
◦ Stimulates glycogenolysis, gluconeogenesis and lipolysis
Somatostatin (delta cells)
◦ Regulation alpha and beta cell secretions

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Adrenal cortex
◦ 80% of an adrenal gland’s total weight
◦ Zona glomerulosa – aldosterone 15%
◦ Zona fasciculata – glucocorticoids 78%
◦ Zona reticularis – androgens and estrogens (others)
◦ 7%

Adrenal medulla
◦ Innervation by SNS

Adrenal Cortex
“all hormones derived from cholesterol”

Stimulated by adrenocorticotropic hormone
(ACTH)

Glucocorticoid hormones
◦ Direct effect on carbohydrate metabolism
◦ Anti-inflammatory and growth suppression effects
◦ Influences awareness and sleep habits
◦ Inhibits bone matrix-protein matrix
◦ Cortisol – most potent naturally occurring

(+)
Stres s
Hypoxia
(+)
Hypoglycemia
Hyperthermia
Exercise
Cortisol insufficiency
(+)
Hypothalamus
Corticotropin-releasing factor
(CRF)
Anterior pituitary
Adrenocorticotropic hormone
(ACTH)
Diurnal rhythms
( - )
( - )
Somatostatin
Hypothalamic lesions
Adrenal cortex
Glucocorticoids
(especially cortisol)


Adrenal Cortex
Mineralocorticoid hormones – Aldosterone
◦ ↑ Na+ uptake in epithelial cells – distal nephrons
◦ ↑ Na retention with loss of K + and H +
◦ Regulation by the renin-angiotensin system
 Na + and H
2
O depletion
 ↑ K + excreteion
 ↓ blood volume


Adrenal Cortex
Adrenal estrogens and androgens
◦ Estrogen secretion is minimal (vs. ovary)
◦ Androgens – weak
 Converted by peripheral tissues to stronger androgens such as testosterone


Adrenal Medulla
Chromaffin cells (pheochromocytes)
◦ Secrete catecholamines – epinephrine and norepinephrine
◦ “Fight or Flight Response”
 SNS, hypoglycemia, hypoxia, hypercapnia, acidosis, hemorrhage, glucagon, nicotine, pilocarpine, histamine and angiotensin II
◦ Epinephrine is 10x more potent than NE
◦ Promote hyperglycemia