6/7 hormones are tropic hormones stimulate other endocrine glands or cells to secrete other hormones.
1. Thyrotropic cells in the pars distalis synthesize and secrete thyroid-stimulating hormone (TSH), also called thyrotropin. TSH regulates the
release of thyroid hormone from the thyroid gland. Increased secretion of TSH results from pregnancy, stress, or exposure to low temperatures.
2. Mammotropic cells, also called lactotropic cells, in the pars distalis synthesize and secrete prolactin (PRL). In females, prolactin regulates mammary gland growth and breast milk production. Recent studies suggest that prolactin receptors occur on many
body organs, and in males may influence the sensitivity of interstitial cells in the testes to the effects of luteinizing hormone for testosterone secretion.
3. Corticotropic cells are located in
the pars distalis. These cells synthesize and secrete adrenocorticotropic hormone (ACTH), also called corticotropin. ACTH stimulates the adrenal cortex to produce and secrete its own hormones.
4. Somatotropic cells in the pars distalis synthesize and secrete growth hormone (GH), also called somatotropin. GH stimulates cell growth as well as cell division (mitosis) and affects most body cells, including adipose connective tissue, but specifically those of the skeletal and muscular systems. GH exhibits its tropic effects by stimulating the liver to produce insulin-like growth factor 1 and 2(IGF-1andIGF-2),also called somatomedin, the hormone that stimulates growth at the epiphyseal plates of long bones.
5, 6. Gonadotropic cells in the pars distalis synthesize and secrete both follicle-stimulating hormone (FSH) and luteinizing hormone (LH), collectively called gonadotropins. These hormones act in both females and males to influence reproductive system activities by regulating hormone synthesis by
the gonads, as well as the production and maturation of gametes in both sexes.
supraoptic nucleus is located superior to the optic chiasm, and the paraventricular nucleus is in the anterior-medial region of the hypothalamus adjacent to the third ventricle. The neuron cell bodies in both nuclei produce two closely related peptide hormones, antidiuretic hormone (ADH) and oxytocin. ADH and oxytocin are transported from the hypothalamus to the posterior pituitary via the hypothalamo-hypophyseal tract.
-ADH is released from the posterior pituitary in response to various stimuli, including a decrease in blood volume, a decrease in blood pressure, or an increase in the concentration of specific electrolytes (salts) in the blood, all of which indicate that the body is dehydrated. ADH primarily increases water retention from kidney tubules during urine production, resulting in more concentrated urine and conservation of the body's water supply. Another consequence of its release is the vasoconstriction of blood vessels, resulting in increased blood pressure; thus, ADH is also referred to as vasopressin (v̄-s̄-press ́in; vas = vessel, pressium = to press down).
-oxytocin stimulates contraction of the uterine wall to facilitate labor and childbirth
-yellow in color from stored lipids in cells that synthesize more than 25 different steroid hormones called corticosteroids which is stimulated by ACTH
3 Different Regions
-zona glomerulosa (ball of yarn) is the thin, outer cortical layer composed of dense, spherical clusters of cells. These cells synthesize mineralocorticoids, a group of hormones that help regulate the composition and concentration of electrolytes (ions) in body fluids. The principal mineralocorticoid is aldosterone, which regulates the ratio of sodium (Na+) and potassium (K+) ions in our blood by stimulating Na+ retention and K+ secretion. If the ratio of these electrolytes becomes unbalanced, body functions are dramatically affected; severe imbalances can result in death.
-zona fasciculata (bundle of parallel sticks) is the middle layer and the largest region of the adrenal cortex. It is composed of parallel cords of lipid-rich cells that have a bubbly, almost pale appearance. Glucocorticoids are synthesized by these cells. Glucocorticoids stimulate metabolism of lipids and proteins, and help regulate glucose levels in the blood, especially as the body attempts to resist stress and repair injured or damaged tissues. The most common glucocorticoids are cortisol (hydrocortisone) and corticosterone
-zona reticularis (network), is a narrow band of small, branching cells. These cells are capable of secreting minor amounts of sex hormones called gonadocorticoids. The primary gonadocorticoids secreted are androgens, which are male sex hormones. In females, the androgens are converted to estrogen. The amount of androgen secreted by the adrenal cortex is small compared to that secreted by the gonads.