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Anterior Pituitary Hormones
- • Growth hormone (GH)
- • Thyroid-stimulating hormone (TSH) or thyrotropin
- • Adrenocorticotropic hormone (ACTH)
- • Follicle-stimulating hormone (FSH)
- • Luteinizing hormone (LH)
- • Prolactin (PRL)
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Growth Hormone (GH)
- • Produced by somatotrophs
- • Stimulates most cells, but targets bone and skeletal muscle
- • Promotes protein synthesis and encourages use of fats for fuel
- • Most effects are mediated indirectly by insulin-like growth factors (IGFs)
- • GH release is regulated by
- • Growth hormone–releasing hormone (GHRH)
- • Growth hormone–inhibiting hormone (GHIH) (somatostatin)
- • Direct action of GH
- • Stimulates liver, skeletal muscle, bone, and cartilage to produce insulin-like growth
- factors
- • Mobilizes fats, elevates blood glucose by decreasing glucose uptake and
- encouraging glycogen breakdown (anti-insulin effect of GH)
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Thyroid-Stimulating Hormone (Thyrotropin)
- • Produced by thyrotrophs of the anterior pituitary
- • Stimulates the normal development and secretory activity of the thyroid
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Adrenocorticotropic Hormone (Corticotropin)
- • Secreted by corticotrophs of the anterior pituitary
- • Stimulates the adrenal cortex to release corticosteroids
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Gonadotropins
- • Follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
- • Secreted by gonadotrophs of the anterior pituitary
- • FSH stimulates gamete (egg or sperm) production
- • LH promotes production of gonadal hormones
- • Absent from the blood in prepubertal boys and girls
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Prolactin (PRL)
- • Secreted by lactotrophs of the anterior pituitary
- • Stimulates milk production
- • Blood levels rise toward the end of pregnancy
- • Suckling stimulates PRH release and promotes continued milk production
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Oxytocin
- • Stimulates uterine contractions during childbirth by mobilizing Ca2+ through a PIP2-
- Ca2+ second-messenger system
- • Also triggers milk ejection (“letdown” reflex) in women producing milk
- • Plays a role in sexual arousal and orgasm in males and females
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Antidiuretic Hormone (ADH)
- • Hypothalamic osmoreceptors respond to changes in the solute concentration of the
- blood
- • If solute concentration is high
- • Osmoreceptors depolarize and transmit impulses to hypothalamic neurons
- • ADH is synthesized and released, inhibiting urine formation
- • If solute concentration is low
- • ADH is not released, allowing water loss
- • Alcohol inhibits ADH release and causes copious urine output
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Thyroid Hormone (TH)
- • Actually two related compounds
- • T4 (thyroxine); has 2 tyrosine molecules + 4 bound iodine atoms
- • T3 (triiodothyronine); has 2 tyrosines + 3 bound iodine atoms
- • Major metabolic hormone
- • Increases metabolic rate and heat production (calorigenic effect)
- • Plays a role in
- • Maintenance of blood pressure
- • Regulation of tissue growth
- • Development of skeletal and nervous systems
- • Reproductive capabilities
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Calcitonin
- • Produced by parafollicular (C) cells
- • Antagonist to parathyroid hormone (PTH)
- • Inhibits osteoclast activity and release of Ca2+ from bone matrix
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Parathyroid Hormone
- • Functions
- • Stimulates osteoclasts to digest bone matrix
- • Enhances reabsorption of Ca2+ and secretion of phosphate by the kidneys
- • Promotes activation of vitamin D (by the kidneys); increases absorption of Ca2+ by
- intestinal mucosa
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Adrenal Cortex
- • Three layers and the corticosteroids produced
- • Zona glomerulosa—mineralocorticoids
- • Zona fasciculata—glucocorticoids
- • Zona reticularis—sex hormones, or gonadocorticoids
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Mineralocorticoids
- • Regulate electrolytes (primarily Na+ and K+) in ECF
- • Importance of Na+: affects ECF volume, blood volume, blood pressure, levels of
- other ions
- • Importance of K+: sets RMP of cells
- • Aldosterone is the most potent mineralocorticoid
- • Stimulates Na+ reabsorption and water retention by the kidneys
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Glucocorticoids (Cortisol)
- • Keep blood sugar levels relatively constant
- • Maintain blood pressure by increasing the action of vasoconstrictors
- • Cortisol is the most significant glucocorticoid
- • Released in response to ACTH, patterns of eating and activity, and stress
- • Prime metabolic effect is gluconeogenesis—formation of glucose from fats and
- proteins
- • Promotes rises in blood glucose, fatty acids, and amino acids
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Gonadocorticoids (Sex Hormones)
- • Most are androgens (male sex hormones) that are converted to testosterone in tissue
- cells or estrogens in females
- • May contribute to
- • The onset of puberty
- • The appearance of secondary sex characteristics
- • Sex drive
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Adrenal Medulla
- • Chromaffin cells secrete epinephrine (80%) and norepinephrine (20%)
- • Epinephrine stimulates metabolic activities, bronchial dilation, and blood flow to
- skeletal muscles and the heart
- • Norepinephrine influences peripheral vasoconstriction and blood pressure
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Pineal Gland
- • Small gland hanging from the roof of the third ventricle
- • Pinealocytes secrete melatonin, derived from serotonin
- • Melatonin may affect
- • Timing of sexual maturation and puberty
- • Day/night cycles
- • Physiological processes that show rhythmic variations (body temperature, sleep,
- appetite)
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Pancreas: Glucagon
- • Major target is the liver, where it promotes
- • Glycogenolysis—breakdown of glycogen to glucose
- • Gluconeogenesis—synthesis of glucose from lactic acid and noncarbohydrates
- • Release of glucose to the blood
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Pancreas: Insulin
- • Effects of insulin
- • Lowers blood glucose levels
- • Enhances membrane transport of glucose into fat and muscle cells
- • Participates in neuronal development and learning and memory
- • Inhibits glycogenolysis and gluconeogenesis
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Ovaries and Placenta
- • Gonads produce steroid sex hormones
- • Ovaries produce estrogens and progesterone responsible for:
- • Maturation of female reproductive organs
- • Appearance of female secondary sexual characteristics
- • Breast development and cyclic changes in the uterine mucosa
- • The placenta secretes estrogens, progesterone, and human chorionic gonadotropin
- (hCG)
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Testes
- • Testes produce testosterone that
- • Initiates maturation of male reproductive organs
- • Causes appearance of male secondary sexual characteristics and sex drive
- • Is necessary for normal sperm production
- • Maintains reproductive organs in their functional state
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Other Hormone-Producing Structures
- • Heart
- • Atrial natriuretic peptide (ANP) reduces blood pressure, blood volume, and blood
- Na+ concentration
- • Gastrointestinal tract enteroendocrine cells
- • Gastrin stimulates release of HCl
- • Secretin stimulates liver and pancreas
- • Cholecystokinin stimulates pancreas, gallbladder, and hepatopancreatic sphincter
- • Kidneys
- • Erythropoietin signals production of red blood cells
- • Renin initiates the renin-angiotensin mechanism
- • Skin
- • Cholecalciferol, the precursor of vitamin D
- • Adipose tissue
- • Leptin is involved in appetite control, and stimulates increased energy expenditure
- • Skeleton (osteoblasts)
- • Osteocalcin prods pancreatic cells to divide and secrete more insulin, improving
- glucose handling and reducing body fat
- • Thymus
- • Thymulin, thymopoietins, and thymosins are involved in normal development of the
- T lymphocytes in the immune response
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