Chapter 18

location and structure of the pituitary gland
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location and structure of the pituitary gland
· Located in the brain below the hypothalamus
· Posterior pituitary: develops from the floor of the brain and connects to the hypothalamus by the infundibulum
· Anterior pituitary: develops from the roof of the embryonic oral cavity
o Secretes 9 major hormones
o Not a nervous system structure
physical, neural, and vascular connection between the hypothalamus and the pituitary gland
· Hypothalamus: regulates secretion of the anterior pituitary gland through hormones and action potentials
o Site where nervous and endocrine systems interact
· Pituitary gland (hypophysis): secretes at least 9 major hormones that regulate numerous body functions and other endocrine glands
· Infundibulum: connects hypothalamus to posterior pituitary
the structure that serves as the primary point of interaction between the nervous and endocrine systems
hypothalamus
how the hypothalamus regulates hormone secretion from the anterior pituitary
· Hypothalamohypophysial portal system: connects the hypothalamus and the anterior pituitary
o Hormones are produces in hypothalamic neurons
o Through the portal system, the hormones inhibit or stimulate hormone production in the anterior pituitary
how the hypothalamus regulates hormone secretion from the posterior pituitary
· Hypothalamohypophysial tract: connects the hypothalamus and the posterior pituitary
o Neurohormones are produces in hypothalamic neurons
o The hormones move down the axons of the tract and are secreted from the posterior pituitary
o Nervous structure
major hormones of the posterior pituitary
vasopressin (ADH) and oxytocin
antidiuretic hormone (ADH)
· also known as vasopressin; promotes increased water reabsorption by the kidneys
o Feeling thirsty
o Target tissue: kidneys
oxytocin
· promotes uterine contractions during delivery; causes milk ejection in lactating women
o Does not increase milk production
o Target tissue: uterus, mammary glands`
major hormones of the anterior pituitary
1. Follicle-Stimulating Hormone (FSH)
2. Luteinizing Hormone (LH)
3. Thyroid Stimulating Hormone (TSH)
4. Adrenocorticotropic Hormone (ACTH)
5. Growth Hormone (GH)
6. Prolactin
Growth hormone (GH)
· stimulates growth in most tissues and is a regulator of metabolism
o Secretion increases is response to low blood glucose, stress, and an increase in certain amino acids
§ Plays an important role in regulating blood nutrient levels between meals
o Target tissue: most tissues
o Regulated by 2 hypothalamic hormones: GHRH & GHIH
§ Growth hormone-releasing hormone (GHRH): released from the hypothalamus, causes release of GH from the anterior pituitary
§ GHIH: inhibits production of GH by anterior pituitary, secreted in response to high blood glucose levels
Thyriod-stimulating hormone (TSH)· causes secretion and storage of hormones T3 and T4 from and within the thyroid gland; increases activity of phospholipase that opens Ca2+ channels, increasing Ca2+ concentration in cells of the thyroid gland o Target tissue: thyroid glandAdrenocorticotropic hormone (ACTH)· causes cortisol secretion from the adrenal cortex o Causes aldosterone secretion from the adrenal cortex o Target tissue: adrenal cortexmelanocyte-stimulating hormone (MSH)· causes melanocytes to increase production of melanin in the skin o Target tissue: melanocytes in the skinluteinizing hormone (LH)· ovulation and progesterone production in ovaries; testosterone synthesis and support for sperm cell production in testes o Target tissue: ovaries and testesFollicle-stimulating hormone (FSH)· follicle maturation and estrogen secretion in ovaries; sperm cell production in testes o Target tissue: follicles in ovaries; seminiferous tubules in malesprolactin· role in milk production o Target tissue: ovaries and mammary glands in femalesstructure of the thyroid gland· Located in the anterior neck; consists of two lateral lobes connected by a median tissue called the isthmus o Follicles: produce thyroglobulin o Parafollicular cells: produce calcitonincondition that lead to T3 and T4 secretion and the effects on their target tissues· Regulated by thyrotroponin-releasing hormone (TRH) and thyroid-stimulating hormone (TSH) · TRH from the hypothalamus increases TSH secretion o Increases as a result of chronic exposure to cold o Decreases as a result of food deprivation, injury, and infection · TSH from the anterior pituitary increases T3 and T4 secretion · Negative feedback mechanismHyperthyroidism· when the thyroid gland produces too much thyroxin o Causes increase in metabolism, causing weight loss and rapid, irregular heartbeatHypothyroidismA disorder caused by a thyroid gland that is slower and less productive than normalrole of calcitonin in blood calcium level maintenance· Parafollicular cells secrete calcitonin · Blood Ca2+ levels drop = calcitonin levels drop · Blood Ca2+ levels rise= calcitonin levels rise Targets the skeleton to: · Inhibit osteoclast activity (reduce release of calcium from the bone matrix) · Stimulate Ca2+ uptake (incorporation into the bone matrix)role of PTH in maintenance of blood calcium levels· PTH increases the release of Ca2+ from bones into blood by increasing the number of active osteoclasts o Stimulates osteoclast activitylocation and structure of the parathyroid glands· 4 tiny glands embedded in the posterior aspect of the thyroid o Secrete a polypeptide hormone (PTH)conditions that cause release of PTH and the effect· Decreased blood Ca2+ levels stimulate PTH secretion · Promotes Ca2+ reabsorption by the kidneys and the formation of active vitamin D by the kidneys · Active vitamin D increases Ca2+ absorption by the intestinelocation and layers of the adrenal glands· Paired, pyramid-shaped organs that sit on top of the kidneys · Adrenal medulla (inner area): epinephrine and norepinephrine · Adrenal cortex (outer area): composed of three layers o Zona glomerulosa o Zona fasciculata o Zona reticularismajor hormones of the adrenal medulla· Epinephrine (80%) and norepinephrine (20%) o prepare the body for physical activity o Increasing heart rate and force of contraction o Released by the sympathetic division of the ANS in response to emotions, injury, stress, exercise, low blood glucose levelszona glomerulosamineralocorticoids (aldosterone); Regulate electrolytes in extracellular fluidzona fasciculata· glucocorticoids o Helps the body resist stress by keeping blood sugar levels relatively constant; maintaining blood volume and preventing water shift into tissue § Cortisolzona reticularis· gonad corticoids o Most are androgens, most important is testosterone, contribute to onset of pubertylocation and structure of the pancreas· Triangular gland, that has both exocrine and endocrine cells, located behind the stomach o Acinar cells: produce an enzyme-rich juice used for digestion o Pancreatic islets: § Alpha cells produce glucagon § Beta cells product insulintwo major hormones produced by the pancreasinsulin and glucagoninsulino Target tissues: liver, adipose tissue, muscle, satiety center in the hypothalamus o When blood glucose is high, glucose is moved into bodies cellsglucagono Target tissue: liver o Causes the breakdown of glycogen to glucose; stimulates the synthesis of glucose from amino acids o When blood glucose is low, glucose is moved into the bloodstreamtestes· secrete testosterone o Initiates maturation of male reproductive organsovaries· secrete estrogen and progesterone o Maturation of reproductive organshow is the placenta a temporary endocrine gland· Secretes human chorionic gonadotropin (hCG) o Essential for the maintenance of pregnancy -only present during pregnancyhormones secreted by the pineal gland· Melatonin: can inhibit reproductive maturation; may regulate sleep-wake cyclesthymus· thymopoietin and thymosin o Essential for the development of T lymphocytesgastrointestinal tractproduces gastrin, secretin, and cholecystokinin (regulate digestive function)kidneys· produce erythropoietin o Stimulates red blood cell production