Endocrine System. A. Introduction 1. endocrine organs - hypophysis, thyroid gland, adrenal gland, parathyroid gland, pineal gland. 3. Typical secretions: hormones which affect distant targets and/or many tissues
1. endocrine organs -
hypophysis, thyroid gland, adrenal gland,
parathyroid gland, pineal gland
3. Typical secretions: hormones which affect distant targets and/or many tissues
a. peptide hormones - proteins, glycoproteins, or peptides which bind to receptors on cell surfaces; work via second messengers, water soluble; e.g. insulin, glucagon, follicle stimulating hormone
b. steroid hormones - lipid soluble and bind to intracellular targets, e.g. to DNA or hormone receptors; derived from cholesterol, e.g. progesterone, estradiol, testosterone
c. amino acid derived hormones - water soluble, catecholamines, thyroxin and epinephrine
Canine, dorsal view, calvarium removed.
Ventral view, canine brain
with primary capillary
These factors are transported to the adenohypophysis by small portal veins where they leave the capillaries to act on the secretory cells there.
Releasing or inhibiting factors bind to receptors in or on the secretory cells in the adenohypophysis to affect their secretion rates of a DIFFERENT hormone. E.g. Corticotropin releasing hormone stimulates the release of corticotropin (ACTH)
Divided into 3 visibly different zones, all of which are steroid-secreting and all of which synthesize hormones from cholesterol, but in different regions different types of hormones are produced.
a. zona glomerulosa
outermost layer, cells look clustered
Secretes mineralocorticoids (e.g. aldosterone, which is involved in salt balance via the kidney), and deoxycorticosterone.
Secretion is stimulated by angiotensin II from juxtaglomerular apparatus and ACTH from hypophysis.
Adrenal gland, medulla
cells (virtually every cell)