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
◦ 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
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
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
Endocrine Pancreas
◦ Synthesized from proinsulin
◦ Secretion is promoted by ↑ blood glucose
◦
◦ Facilitates the rate of glucose uptake into the cells
Anabolic hormone
◦ Secretion is promoted by decreased blood glucose levels
◦ Stimulates glycogenolysis, gluconeogenesis and lipolysis
Somatostatin (delta cells)
◦ Regulation alpha and beta cell secretions
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