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Transcript
Chapter Outline The Endocrine System: Endocrine Glands and Hormone Actions I. II. III. IV. V. Primary Endocrine Organs Secondary Endocrine Organs Hormone Actions at the Target Cell Abnormal Secretion of Hormones Hormone Interactions Endocrine Glands z z Derived from epithelial tissue Primary endocrine organs z z z The primary function is the secretion of hormones Hormones are chemicals messengers that secreted by specialized cells Secondary endocrine organs z The secretion of hormones is secondary to other functions Endocrine Organs Figure 6.1 I. Primary Endocrine Organs z z Hypothalamus and pituitary gland are connected via infundibulum Hypothalamus z z z Part of brain Synthesize ADH and oxytocin Produce releasing and inhibiting topic hormones that regulate the secretion of anterior pituitary gland hormones z Pituitary gland z Figure 6.2 Anterior lobe is a “typical” endocrine gland that synthesizes and secrets hormones Figure 6.2b 1 z Pituitary gland z z z Posterior lobe contains neural endinds that originated from the hypothalamus. These neural endings stores and releases two hypothalamic neurohormones Neurohormones stored by posterior pituitary z Antidiuretic hormone (ADH or vasopressin) z z z Is made in paraventricular nucleus of hypothalamus Functions in water balance and osmolarity Oxytocin z z Is synthesized by supraoptic nucleus of hypothalamus Functions in milk ejection Figure 6.3 Neural Connection to Posterior Pituitary Hypothalamic-Pituitary Portal System z Tropic Hormones Portal system z z Links two capillary beds Exchange between blood and tissue occurs in capillaries Affect release of another hormone z z Releasing hormones Inhibiting hormones Figure 6.4 Common Tropic Hormone Pathway z Hypothalamus secretes releasing or inhibiting hormone into capillary bed z z z Tropic Hormones of Hypothalamus and Anterior Pituitary Blood with tropic hormones enters portal vein Hypothalamic tropic hormones access anterior pituitary secretory cells through capillary beds alter release of anterior pituitary tropic hormones Anterior pituitary tropic hormones enter bloodstream in same capillary bed and travel to distant endocrine gland to trigger release of hormone Target Figure 6.5 2 Control of Hypothalamic Tropic Hormone Release z z Hypothalamus Tropic hormone 1 secretion Neural input Hormonal z z Negative Feedback Loops Short loop negative feedback Long loop negative feedback Negative feedback Circadian rhythm z Anterior pituitary Tropic hormone 2 secretion Suprachiasmatic nucleus of hypothalamus Endocrine gland Hormone 3 secretion Target cell response Figure 6.6 Pineal Gland Feedback Control: Thyroid z Hypothalamus Thyrotropin releasing hormone (TRH) secretion z Glandular tissue in brain Secretes melatonin Anterior pituitary z Thyroid stimulating hormone (TSH) secretion z Long loop negative feedback Function unknown May be involved in circadian rhythms Thyroid gland Thyroid hormone secretion Target cell response Figure 6.7 Thyroid and Parathyroid Glands Figure 6.2a Hormones of the Thyroid Gland z Two thyroid hormones z z z z z T4, tetraiodothyronine (thyroxin) T3, triiodothyronine Regulate metabolism rate Critical for normal growth and development Calcitonin z Lowers calcium levels in blood Figure 6.8 3 Parathyroid Hormone (PTH) z Thymus z Raises calcium levels in blood z z Promote the release of calcium from bone Stimulate z Calcium absorption by intestine z Calcium reabsorption by kidney z Vitamin D3 synthesis z z z Adrenal Glands z Locates close to the heart Secretes thymosin Regulates T cell function Critical for immune function Adrenal Glands Located above kidney also called suprarenal glands Figure 6.9a Hormones of the Adrenal Gland: Adrenocorticoids z Mineralocorticoids (aldosterone) z z z Adrenal Medulla z Secreted from zonae glomerulosa Regulates sodium and potassium levels z z z z Secreted from zonae fasciculata and reticularis Regulates body’s response to stress Regulates metabolism z Sex hormones (androgens) z z Secreted from zonae fasciculata and reticularis Regulate reproductive function Secretory cells = chromaffin cells z Glucocorticoids (cortisol) z z Figure 6.9b z 80% epinephrine (adrenaline) 20% norepinephrine <1% dopamine (prolactin secretion, a neurotransmitter that involved in pleasure and awards) Epinephrine and norepinephrine are involved in metabolism, cardiac function and fight or flight Under neural control 4 Anatomy of the Pancreas Endocrine Pancreas z Islets of Langerhans z z z z Alpha cells: glucagon Beta cells: insulin Delta cells: somatostatin (inhibit secretion of pancreatic hormones; regulate the function of digestive function) F cells: pancreatic polypeptide Figure 6.10 Exocrine Pancreas z Acinar and duct cells secrete fluid and enzymes into digestive tract Gonads z Male—testes z z z Testosterone Androstenedione Female—ovaries z z z Estradiol Progesterone Placenta of pregnant female z II. Secondary Endocrine Organs z z z Heart: atrial natriuretic peptide (ANP) Kidneys: erythropoietin GI tract: several z z z z z Cholecystokinin Secretin Gastrin Estrogens and progesterone III. Hormone Actions at the Target Cell z z z Control of hormone levels in blood Transport of hormones Hormone interactions Liver: insulin-like growth factors (somatomedins) Skin and kidneys: calcitriol 5 Control of Hormone Levels in Blood z z z Neural Control of Hormone Release Rate of hormone secretion Amount of hormone bound to plasma proteins Rate of hormone metabolism Figure 6.11 Hormonal Control by a Circadian Rhythm Humoral Control of Hormone z Neural control of circadian rhythm z Hormonal control of circadian rhythm z z z z Suprachiasmatic nucleus of the hypothalamus Melatonin Resets daily cycle based on light stimulus All tropic hormones of hypothalamus affected by circadian rhythm from suprachiasmatic nucleus Figure 6.12 Transport of Hormones z Hydrophilic hormones z z z Peptides, catecholamines Dissolved in plasma Rate of Hormone Metabolism z z z Hydrophobic hormones z z z z z Steroids, thyroid hormones Bound to carrier proteins Only free hormone can bind to receptor Only free hormone can be metabolized Longer half-life Sites of hormone metabolism z z Target cell by lysosome Blood by proteolytic enzymes Liver Steroids and thyroid hormones are metabolized more slowly than peptide enzymes z z They are bound to carriers in blood Lipophilic hormones can be stored in adipose tissue 6 IV. Abnormal Secretion of Hormones z z Hormone levels must be kept in balance Pathologies z z z Hyposecretion: too little Hypersecretion: too much Abnormal Tissue Responsiveness z z The effects of combined actions z z z Primary z z Abnormality in endocrine organ secreting hormone Secondary z Normal hormone levels Tissue responds inappropriately V. Hormone Interactions z Primary versus Secondary Secretion Disorders Abnormality in tropic hormone z z Antagonism z Antagonism Synergistic or additive Permissiveness The effects of hormones oppose each other. z Blood calcium level z z z z z z Effects of two hormones favor each other but the net effect exceeds the sum of individual effects Example: Glucagon, cortisol, and epinephrine on blood glucose Parathyroid hormone ↑ calcium level Calcitonin ↓ Blood glucose level z Synergism Hypothalamic tropic hormone Anterior pituitary tropic hormone Glucagon ↑glucose level Insulin↓ Permissiveness z z One hormone needed for another to exert its effects Examples: z z Thyroid hormones cause expression of adrenergic receptors in bronchiolar smooth muscle Estrogen causes expression of progesterone receptors in uterus 7