Endocrine System Flashcards
Where do exocrine glands release their secretions?
onto an epithelial surface through a duct
What do endocrine glands do?
secrete hormones into blood vessels or into the surrounding tissue fluid
What are the 3 hormone types?
- amino acid derivatives e.g. adrenaline, TH, catecholamines derived from phenyl, alanine and tyrosine
- steroid hormones e.g. androgens and oestrogens
- peptide hormones e.g. insulin, prolactin, ACTH, FSH, LH, GnRH
Where is the pituitary gland?
in the Sella turcica connected to the hypothalamus by the infundibulum
What is the anterior pituitary (pars distalis) composed of?
chromophobes and chromophils
What are the 2 types of chromophils?
acidophils and basophils
What do acidophils secrete?
- somatotropes (GH)
- lactotrophs (prolactin)
What do basophils secrete?
- thyrotropes (TSH)
- gonadotropes (LH, FSH)
- corticotropes (ACTH)
What do chromophobes have?
numerous blood vessels, delicate connective tissue framework and the connective tissue capsule
What does the hypophyseal portal circulation do?
carry releasing hormones from the hypothalamus to the adenohypophysis targeting the acidophils and basophils and causing the release of hormones into the bloodstream
What does the posterior pituitary (pars nervosa) consist of?
unmyelinated axons from neurons in the supraoptic and paraventricular nuclei of the hypothalamus
What are Herring bodies?
storage sites of the neurosecretory material of the pars nervosa neurons
What is the pars intermedia?
a structure that lies between the pars distalis and pars nervosa consisting mainly of colloid-filled cysts lined by cuboidal epithelium
What are the 2 secretions of the hypothalamus and what do they do?
- TRH - acts on thyrotropes in the anterior pituitary gland and stimulates release of TSH
- GnRH - released in a pulsatile manner and stimulates gonadotrophs of the anterior pituitary gland
What are the 6 hormones of the anterior pituitary gland and what do they do?
- GH – stimulate the cell growth i.e. skeletal muscle cells and chondrocytes
- prolactin – promotes milk secretion
- TSH – stimulates TH synthesis
- ACTH – stimulates the secretion of steroid hormones by the adrenal cortex of the adrenal gland
- FSH – promotes ovarian follicle development and oestrogen secretion in women and spermatogenesis in men
- LH – induces ovulation in women and androgen secretion in men
What are the 2 hormones of the posterior pituitary gland and what do they do?
- vasopressin/ADH - maintains water balance in the body
- oxytocin - stimulates contraction of uterine smooth muscle during childbirth and mammary glands during breast-feeding
Where is the thyroid gland located?
in the neck, in front of the larynx and trachea, below the thyroid cartilage closely associated with the major blood vessels
What does the thyroid gland consist of?
2 lobes united by the isthmus
What does each thyroid follicle consist of?
a single layer of cuboidal epithelial cells
What are the 2 cell types in the thyroid follicle and what do they secrete?
- follicular cells - TH
- parafollicular cells - secrete calcitonin
What is the bulk of T3 derived from?
deiodination of T4 in peripheral tissues especially in the liver and kidney
What are the 3 main carriers of thyroid hormone in the blood?
- thyroxine-binding globulin
- transthyretin
- albumin
What does calcitonin do in the bone and kidney respectively?
- bone - inhibits osteoclast action
- kidney - inhibits tubular reabsorption of calcium and phosphorus
Where is the parathyroid gland?
embedded in the posterior surface of the thyroid gland separated by a fibrous capsule
What is the parathyroid gland composed of?
chief cells and oxyphilic cells
What are the 3 functions of PTH?
- simulates osteoclasts to reasborb bone mineral, releasing calcium into the blood
- stimulates tubular reabsorption of calcium in the kidney
- enhances absorption of calcium from the small intestine
How does PTH increase calcium absorption?
by stimulating production of the active form of vitamin D from the kidney
What does vitamin D do?
induce synthesis of a calcium-binding protein in intestinal epithelial cells that facilitates efficient absorption of calcium into blood
What is PTH secreted by?
chief cells in the parathyroid gland
Where is the adrenal gland and what does it consist of?
on the superior poles of the kidneys consisting of a central medulla and outer cortex
What are the 3 zones of the adrenal gland and what do they do?
- glomerulus - secretes mineralocorticoids which maintain electrolyte and water balance
- fasiculata - secretes glucocorticoids which accelerate the rate of glucose synthesis and glycogen formation
- reticularis - secretes androgens
What is cortisol?
the most potent glucocorticoid widely used in ointments to treat inflammatory conditions of the skin
What does excessive and long-term use of oral steroid tablets do?
suppress the immune system
What does aldosterone do?
act on cells of the late DCT and medullary collecting duct to increase sodium reabsorption and potassium secretion
What does excess aldosterone lead to?
hypernatremia, hypokalaemia and metabolic alkalosis
What is the adrenal medulla composed of?
chromaffin cells (modified sympathetic ganglion cells) and blood vessels
What do chromaffin cells secrete?
adrenaline and noradrenaline
Where is the pancreas?
between the duodenum, spleen and stomach
What is the endocrine and exocrine pancreas made up of respectively?
- exocrine - acinar and duct tissue
- endocrine - islets of Langerhans
What are the 4 types of secretory cells in pancreatic islets?
- alpha cells - secrete glucagon
- beta cells - secrete insulin
- delta cells - secrete somatostatin
- F cells (rare) - secrete pancreatic polypeptide
