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
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) - PowerPoint PPT Presentation
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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 gland3.Parathyroid gland4.Adrenal gland5.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
• 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
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): DisordersDisorders:
• 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
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)