Chapter 17. The Endocrine System Functions ◦ Differentiation of reproductive and CNS in fetus ◦ Stimulation of growth and development ◦ Coordination.
Post on 11-Jan-2016
224 Views
Preview:
Transcript
Chapter 17
The Endocrine SystemFunctions
◦ 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
HormonesGeneral characteristics
◦ 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
Regulation of Hormone Release
• 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
◦Water-soluble hormones 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 Action
Hormone receptors◦ Located in the plasma membrane or in the
intracellular compartment of the target cell
Water-soluble hormones (peptides)◦ High molecular weight
◦Cannot diffuse across the plasma membrane
Cellular Mechanisms of Hormone Action
Lipid-soluble hormones
◦ 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
–Anterior pituitary (adenohypophysis)
A) Chromophobes – non-secretory cellsB) Chromophils - secretory cells
7 cell types → specific hormones
Structure and Function of the Endocrine Glands
Pituitary gland◦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 B-endorphins
Inhibition◦B-adrenergic receptors
Posterior Pituitary• 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
Oxytocin◦ Uterine contractions and milk ejection with
lactation
◦ Role in sperm motility in men
◦ ADH effect-weak
Thyroid Gland“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 Gland Thyroid hormones
◦ Iodine – required for synthesis◦90% T4 and 10% T3
◦Bound to thyroxine - binding globulin - mostly
◦Regulation - negative feedback TRH - ↑ cold exposure, stress and ↓ T4
◦Effects ↑ metabolism of protein, fat and glucose →
rapid ↑ heat production and body temperature Normal linear growth requires TH CNS and ANS require TH
Parathyroid Glands Parathyroid hormone
◦ ↑ Ca++ and↓ PO4= - bone, kidneys
◦ Antagonist of calcitonin
Endocrine Pancreas 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 PancreasInsulin
◦ Synthesized from proinsulin◦ Secretion is promoted by ↑ blood glucose◦ Facilitates the rate of glucose uptake into
the cells◦ Anabolic hormone
Synthesis of proteins, lipids and nucleic acids
Endocrine PancreasGlucagon
◦ Secretion is promoted by decreased blood glucose levels
◦ Stimulates glycogenolysis, gluconeogenesis and lipolysis
Somatostatin (delta cells)◦ Regulation alpha and beta cell secretions
Adrenal Glands 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
Hypothalamus
Anterior pituitary
Adrenal cortex
Corticotropin-releasing factor (CRF)
Adrenocorticotropic hormone (ACTH)
Glucocorticoids(especially cortisol)
HypoxiaHypoglycemiaHyperthermiaExerciseCortisol insufficiency
Stress
Diurnal rhythms
( - )
SomatostatinHypothalamic lesions
( - )
(+)
(+)
(+)
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 H2O 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
top related