Organs of the Endocrine System and Their Products The following major glands will be covered one at a time with their products: 1. Pituitary gland / Hypothalamus 2. Thyroid gland 3. Parathyroid gland 4. Adrenal gland 5. Pancreas (also has exocrine function) 6. Gonadal hormones (ovaries and testes) 7. Thymus

1. Pituitary Gland (Hypophysis) located in sella turcica of sphenoid bone (in cranial cavity), inferior to hypothalamus consists of two lobes: A. neurohypophysis (~ posterior pituitary) attached to hypothalamus by infundibulum contains axons and axon terminals of neurosecretory cells whose cell bodies are in hypothalamic nuclei B. adenohypophysis (~ anterior pituitary) consists of glandular epithelium http://www.usc.edu/hsc/dental/ghisto/end/c_1.html

A. Neurohypophysis (Posterior Pituitary) consists of nerve fibers (axons of neurosecretory cells with cell bodies in hypothalamus) and pituicytes (glial cells that support nerve fibers) acts primarily as a storage and releasing area for hormones actually made in hypothalamic nuclei hormones released in response to impulses from hypothalamus (neural control) hormones are short amino acid chains (peptides) oxytocin antidiuretic hormone (ADH or “vasopressin”)

A. Neurohypophysis: Oxytocin (OT) action, in pregnant or nursing women: stimulates contraction of smooth muscle of uterine wall during labor and delivery stimulates ejection of milk in lactating mothers action, in men and non-pregnant women, may be involved in sexual arousal and orgasm

A. Neurohypophysis: Oxytocin (OT) control: during labor/delivery, positive feedback: stretching of uterus/cervix --> sensory impulses to hypothalamus --> increased secretion of OT --> increased contraction suckling: sucking of infant on breast --> sensory to hypothalamus --> oxytocin release --> release of milk

A. Neurohypophysis: Antidiuretic Hormone (ADH) action: antidiuretic hormone (ADH) directly affects blood pressure - acts as powerful vasoconstrictor --> increases blood pressure (hence name “vasopressin”) action: affects water balance (indirect affect on blood pressure) - acts on tubules of kidney to increase reabsorption of water  less water lost in urine

A. Neurohypophysis: ADH disorders: hyposecretion due to damage of hypothalamic nucleus or neurohypophysis--> diabetes insipidus - excessive urine production (polyuria) and thirst hypersecretion --> SIADH (syndrome of inappropriate ADH secretion) - water retention, headache, cerebral edema, weight gain, hypoosmolarity

Antidiuretic Hormone (ADH): Control neural control: increased electrolyte (NaCl) concentration --> affects (supraoptic) nucleus in hypothalamus --> impulse to neurohypophysis --> release of ADH --> increased water reabsorption --> decrease in electrolyte concentration other stimuli: pain, low BP, morphine, barbiturates, nicotine, aldosterone (hormone from adrenal cortex - hormonal control) inhibition: alcohol (results in more urine production and, potentially, dehydration) diuretic drugs - some act to supress ADH secretion; used to treat hypertension and congestive heart failure

B. Adenohypophysis (Anterior Pituitary) linked to hypothalamus via hypophyseal portal system (capillary networks and small veins) carries regulatory hormones from hypothalamus to pituitary releasing hormones stimulate secretion of pituitary hormones inhibitory hormones inhibit secretion consists of epithelial cells all hormones produced are proteins tropic hormones - affect some endocrine glands or provide maintenance oversight for other organs

B. Adenohypophysis: Growth Hormone (GH) highest levels during evening and sleep action: stimulates increased rate of protein synthesis leading to cell growth and division bones and skeletal muscle respond more than other body cells action: stimulates use of fat as energy source and decreases rate of glucose uptake and glucose metabolism (diabetogenic effect – “spares” glucose) control: release stimulated by GHRH (growth hormone releasing hormone) from hypothalamus inhibited by GHIH (from hypothalamus) and somatomedins (produced by liver under GH stimulation)

Growth Hormone (GH): Disorders hypersecretion gigantism (in children) up to 8’ tall, normal body proportions acromegaly (after epiphyseal plates close) enlargement of extremities and face, thickening of soft tissue hyposecretion pituitary dwarfism - in children, up to 4’ tall progeria - premature aging, atrophy of body tissues acromegaly associated with pituitary tumor

Growth Hormone Excess in childhood leads to GIGANTISM

Growth Hormone Excess in adulthood leads to ACROMEGALY

B. Adenohypophysis: Prolactin (PRL) action: stimulates milk production in mammary glands; helps stimulate development of mammary glands (along with other hormones); in males, may help regulate testosterone production control: stimulation: PRH (prolactin-releasing hormone from hypothalamus), high estrogens, breast-feeding inhibition: PIH (hypothalamus), stimulated by rising PRL levels, low estrogen

B. Adenohypophysis: Prolactin (PRL) Disorders hyperprolactinemia = hypersecretion due to adenohypophyseal tumors; results in galactorrhea, lack of menses and infertility in women, impotence in men

B. Adenohypophysis: Thyroid-Stimulating Hormone (TSH) TSH = thyrotropin action: stimulates secretion of hormones from thyroid gland (T4 and T3); also stimulates development of thyroid in youth control: release stimulated by TRH (thyroid releasing hormone from hypothalamus) inhibited by rising levels of thyroid hormones and by GHIH

B. Adenohypophysis: Adrenocorticotropic hormone (ACTH) ACTH=corticotropin action: stimulates release of hormones from adrenal cortex control: release stimulated by CRH (corticotropin-releasing hormone from hypothalamus) release inhibited by rising levels of glucocorticoids from adrenal cortex

B. Adenohypophysis: Gonadotropins regulate activity and secretion by gonads (testes in males; ovaries in females) control: stimulated by GnRH (gonadotropin-releasing hormone from hypothalamus) release of GnRH is inhibited by rising levels of estrogens, progestins and androgens (testosterone) two important hormones FSH LH

Gonadotropins: Follicle-Stimulating Hormone (FSH) action: females (ovaries) - stimulates development of ovarian follicles and estrogen production males (testes) - stimulates sperm production and development inhibited by inhibin and testosterone from testes (feedback to hypothalamus and anterior pituitary) and estrogen, progesterone and inhibin from ovaries (feedback to anterior pituitary)

Gonadotropins: Luteinizing Hormone (LH) LH=lutropin action: females (ovaries) - induces ovulation; stimulates secretion of estrogens and progestins (e.g., progesterone) males (testes) - stimulates production of androgens (e.g., testosterone ) inhibited by estrogen, progesterone and inhibin form ovaries (feedback to anterior pituitary) and by inhibin and testosterone from testes (feedback to hypothalamus and anterior pituitary)