Week 7: Histology of Endocrine Organs Flashcards
3 classes of hormone
- amino acids -> peptides
- tyrosine -> amines
- cholesterol -> steroids
lipophilic hormones
readily enter target cell -> bind to cytoplasmic receptors -> transported to nucleus -> initiate changes in gene expression
most peptide and catecholamines bind to
membrane receptors -> initiate cascade of second messengers -> activate or induce transcription factors -> regulate cellular function
anterior pituitary is
- adenohypophysis
* glandular portion derived from outpouching of roof of mouth (rathke’s pouch)
posterior pituitary is
- neurohypophysis
- neural portion derived from outpouching on floor of embryonic brain and it continuous with hypothalamus via infundibulum
neurons of supraoptic nuclei in hypothalamus produce
Antiduiretic hormone (ADH), aka vasopressin
neurons of paraventricular nuclei in hypothalamus produce
oxytocin
what is stored in posterior pituitary
ADH and oxytocin
3 types of cells in anterior pituitary
- acidophils - stain pinkish-red
- basophils - stain bluish-purple
- chromophobes - do not stain
posterior pituitary consist of
terminal ends of hypothalamic axons from supraoptic and paraventricular nuclei and pituicytes
oxytocin
- made in hypothalamus, stored and released by posterior pituitary
- acts on smooth muscle of uterus for contractions and myoepithelial cells of breast for lactation
antidiuretic hormone (ADH)
- made in hypothalamus, stored and released by posterior pituitary
- acts on cells in kidney collecting tubules to increase permeability to water to decrease urine production
- also causes constriction of arterioles to increase blood pressure
acidophils of anterior pituitary produce
- Growth hormone (GH) in somatotrophs
* Prolactin in mamotrophs
growth hormone (GH)
stimulates liver to secrete IGF-1 -> bone and soft tissue growth
prolactin
causes initiation and maintenance of post partum lactation
basophils of anterior pituitary produce
- thyroid stimulating hormone (TSH) in thyrotrophs
- follicle stimulating hormone (FSH) in gonadotrophs
- luteinizing hormone (LH) in gonadotrophs
- adrenocorticotrophic hormone (ACTH) in corticotrophs
thyroid stimulating hormone (TSH)
stimulates thyroid to make and secrete T3 and T4 for regulation of cellular metabolism
follicle stimulating hormone (FSH)
- females: stimulates follicle development in ovary which causes production of progesterone and estrogen
- males: causes sertoli cells to secrete ABP
luteinizing hormone (LH)
- females: causes estrogen and progesterone production
* males: causes leydig cells to produce testosterone, which stimulates spermatogenesis
adrenocorticotrophic hormone (ACTH)
causes adrenal cortex to secrete glucocorticoids (95% is cortisol) and androgens which are important for regulation of metabolism and immune responses and secondary sex characteristics
thyroid gland arises
as a midline outpouching of the floor of the pharynx
thyroid follicle
- most of thyroid is several million follicles
* a single follicle is a ball of cells with central lumen filled with colloid composed of iodothyroglobulin
epithelial lining of thyroid follicles
simple cuboidal, called follicular cells
parafollicular cells of thyroid
- cells in the interstitium around follicles also called C cells
- responsible for calcitonin secretion
calcitonin
- released by parafollicular cells in thyroid
- calcium homeostasis - lowers blood calcium
- effects osteoclasts to decrease bone turnover
- also effects kidney and gut to increase calcium excretion
thyroglobulin synthesis (exocrine phase)
- TSH stimulates follicular cell
- iodide uptake via ATP dependent pump
- diffusion of iodide through cell
- synthesis of thyroglobulin and exocytosis into colloid
- oxidation of iodide by thyroid peroxidase
- transfer of iodine to tyrosyl residues of thyroglobulin
- storage of iodothyroglobulin in colloid
thyroid hormone synthesis and release (endocrine phase)
- TSH stimulates follicular cell
- colloid droplet containing iodothyroglobulin endocytosis
- fusion of droplet with lysosome and degradation to T3 and T4
- release of T3 and T4 into bloodstream and interaction with binding proteins
ratio of T3:T4 released into blood
1:20
what do T3 and T4 do
increase basal metabolic rate in adult and influence growth and neurological development in fetus
T3 or T4 more active?
•T3 more active and has T3 in target tissues
parathyroid glands organization
2 pairs of glands surrounded by a thin CT capsule that divides it into course clumps of cells
parathyroid glands secrete
parathyroid hormone (PTH)
parathyroid hormone essential for
physiologic maintenance of circulating [calcium]
2 types of cells in parenchyma of parathyroid
1) chief (principal) cells
2) oxyphil cells
Chief cells of parathyroid parenchyma
form the bulk of parathyroid and synthesize and release PTH
oxyphil cells of parathyroid
stain lighter than chief cells and exact function is uncertain
decreased circulating calcium stimulates
- PTH secretion -> increased number of osteoclasts present in bone -> increased bone turnover
- PTH also causes gut and kidneys to increase absorption and retention of calcium
medulla of adrenal gland composed of
chromaffin cells that synthesize and secrete catecholamines (epinephrine and norepinephrine)
epinephrine
- the major secretory product of medulla of adrenal gland
* increases heart rate and constricts blood vessels (increase BP)
norepinephrine
dilates blood vessels and increases glucose release
3 zones of adrenal cortex
zona glomerulosa, zona, fasciculata, and zona reticularis
zona glomerulosa of adrenal cortex
- foamy appearance
* produces mineralcorticoid aldosterone
aldosterone
involved in reabsorption of sodium and water by salivary glands, sweat glands, and kidney -> increased blood volume (and therefore BP)
what stimulates zona glomerulosa to secrete aldosterone?
- serum potassium (K+)
- increased angiotensin II
- decreased plasma volume
zona fasciculata
- cells arranged in long, straight columns
- lightly staining
- secrete glucocorticoids
glucocorticoids
- 95% is cortisol
- enhance glucose synthesis by liver to elevate blood sugar
- suppress inflammatory and immune response
- cause catabolism (break down) of proteins, which may lead to muscle wasting
what stimulates glucocorticoid release by zona fasciculata of adrenal cortex?
ACTH stimulation
low concentrations of cortisol causes increased ACTH production
zona reticularis
- innermost layer of cells in adrenal cortex
* secrete androgens
androgens
less potent form of testosterone, progesterone, and estrogen
what stimulates androgen secretion by zona reticularis of adrenal cortex??
ACTH stimulation