Pituitary Lecture Flashcards
Pituitary Gland
Hypophysis
Lies in bony cavity at the base of the brain (sella turcica- protection)
Connected to the hypothalamus by the hypophysial stalk
Consists of anterior pituitary (adenohypophysis) and posterior pituitary (neurohypophysis) separated by the pars intermedia
Anterior Pituitary Hormones
Growth hormone Thyroid stimulating hormone Adrenocorticotropin Prolactin Luteinizing Hormone Follicle-stimulating hormone - Regulated by the "releasing and inhibiting hormones" from the hypothalamus
Growth hormone
Increases both size and number of cells
Secreted by somatotropes
Stimulates lipolysis
Inhibits action of insulin on carbs and lipid metabolism
- Stimulates fat catabolism, glucose conservation and increases protein deposition
TSH
Stimulates the thyroid to produce T3/T4
Secreted by thyrotropis
Maintains size of follicular cells
Adrenocorticotropin
Acts on adrenal cortex to release its hormones
Secreted by corticotropes
- Stimulates production of glucocorticoids and androgens by the adrenal cortex
- Maintains size of zonas in the cortex
Prolactin
Acts on mamary gland to start producing milk
Secreted by lactotropes
Milk production and secretion and mammary gland development
LH and FSH
Gonadotropic hormones
Secreted by gonadotropes
FSH: stimulates development of follicles and regulates spermatogenesis in the testes
LH: Causes ovulation and formation of corpus luteum, production of estrogen, progesterone and testosterone, and controls growth of ovaries and testes
Naming
___ic hormone or ____in
Secretory cells: name of hormone + trope (means cell)
Control of Anterior Pituitary Secretion by Hypothalamus
Neurons synthesize and secrete hypothalamic releasing and inhibiting hormones
Collected by the capillary bed in the median eminence of the hypothalamus
Transported to anterior pituitary via hypothalamic-hypophysial portal vessels
Bind to receptors on cells differentiated to secrete or inhibit secretion of the hormone
Thyrotropin-releasing hormone
Stimulates TSH by thyrotropes
- Hypothalamus-pituitary-thyroid axis
Corticotropin-releasing hormone
Stimulates secretion of ACTH by adrenocorticotropin by corticotropes
Growth hormone-releasing hormone
Stimulates secretion of growth hormone by somatotropes
- GH Inhibiting hormone inhibits release of growth hormone
Gonadotropin-releasing hormone
Stimulates secretion of LH and FSH by gonadotropes
Prolactin inhibiting hormone
Inhibits secretion of prolactin by lactotropes
Function of Growth Hormone
Promotes increased size of cells, increased mitosis, overall growth of the body
- Stimulates cartilage and bone growth –> increase in the growth of the skeletal frame
- Causes liver to form somatomedins
Growth of skeletal frame?
Osteoblast deposit new bone, osteoclast remove old bond
- GH stimulates osteoblast
Bones become thicker throughout life under the influence of GH
Long bones grow in length at the epiphyseal cartilage
Long bone growth?
Increased deposition of protein by the chondrocytic and osteogenic cells that cause bone growth
Increased rate of division/mitosis of these cells
Converts chondrocytes into osteogenic cells, causing deposition of new bond
Somatomedin C
Bone growth
- Prolonged duration of action: GH is weakly bound to plasma proteins (20 min half life) or strongly bound ( 20 hr halflife)
- Direct agent of the indirect GH
Metabolic Effects of Growth Hormones
Promotes protein deposition in tissues (promotes synthesis and reduces degradation)
Enhances fat utilization for energy ( increase lean body mass; ketogenic effect: large amounts of acetoacetic acid formed by liver –> ketosis –> fatty liver)
Decreases carb utilization
— Enhances body protein, uses up fat stores and conserves carbs
Decreased carb utilization?
Decrease glucose uptake in skeletal muscles and fat
Increase production by liver and increased insulin secretion
Diabetogenic effect: GH induced “insulin resistance”
Diabetogenic effect: GH induced “insulin resistance”?
Attenuates insulins action to stimulate uptake and utilization of glucose
Attenuates insulins ability to inhibit gluconeogensis
Leads to increased blood glucose concentration and increase in insulin secretion
Regulation of GH secretion
Pulsatile pattern
Normal: 1.6-3 ng/ml
Increase concentration when starving, hypoglycemia, exercise, excitement and trauma
Hypoglycemia and protein deficiency are potent simulators of GH
Regulation of GH Secretion
Hypothalamus secretes 2 factors to control growth hormone release
- GH- releasing hormone and GH- inhibitory hormone
- Also subject to negative feeback
Dwarfism
Deficiency in growth hormone during childhood
If detected early, can be treated
Gigantism
Excessive GH released due to anterior pituitary tumor in childhood
Associated with hyperglycemia –> 10% develope diabetes mellitus
Treatment: removal of tumor or irradiation of gland
Acromegaly
Caused by anterior pituitary tumor after adulthood
- Bones become thicker and soft tissues continue to grow
- Protrusion of lower jaw, forward slanting forehead, enlarged hands and fee and nose, hunched back
- Enlarged tongue, liver and kidneys
- No increase in height
Posterior Pituitary
Cell bodies (supraoptic and paraventricular nuclei) in the hypothalamus synthesize hormones
- Antidiuretic hormone (vasopressin) - supra
- Oxytocin hormone - para
- transported to nerve endings for release
Function of ADH
Minute amounts cause decreased excretion of water by kidneys –> concentrated urine, increased permeability of collecting ducts, conserve water
- Release stimulated by: osmotic regulation - high concentration of electrolytes
- Dilute body fluids inhibit
- Mediated by osmoreceptors in the brain (swell = ADH off, shrink = ADH on)
High concentration of ADH
Constrict arterioles throughout the body –> increase aterial pressure
- Decreased blood volume : decreased excitation of stretch receptors in atria end of baroreceptors
Oxytocin
Causes contraction of the unterus during labor: stimulates cervix –> secretes oxytocin –> contractions
Aids in milk ejection: releases stimulated by suckling –> secrete oxytocin –> contraction of myoepithelial cells –> milk from alveoli to ducts —> milk let down (milk ejection)
