Endocrine System and Hormones

Hormones

• Chemical messengers that function mostly endocrine, but some are mixed.
• Released directly into extracellular fluid.
• Exocrine glands secrete into ducts.

Glands

• Pituitary (anterior and posterior)
• Thyroid
• Parathyroid
• Thymus
• Pineal
• Adrenal
• Pancreas
• Gonads

Pituitary Gland

• Located in the Sella Turcica of the sphenoid bone.
• Contains 2 lobes: Anterior and Posterior.
• The anterior secretes more.

Anterior Pituitary

• Manufactures four tropic hormones that target glands to release other hormones
• TSH (thyroid stimulating hormone) = targets the thyroid and stimulates secretion of thyroid hormones.
• FSH = stimulated by GnRH (Gonadotropin releasing hormone) and targets the gonads.
• FSH stimulates sperm production in males, and ovarian follicle maturation/estrogen production in females.
• LH = stimulated by GnRH and leads to testosterone production in males.
• LH = ovulation/estrogen + progesterone production in females.
• ACTH = CRH stimulates release (Corticotropin Releasing Hormone) and targets the adrenal cortex.
• CRH and GnRH are released by the hypothalamus and target the anterior pituitary.

Anterior Pituitary Non-Tropic hormones

• GH (Growth Hormone) and GHRH (growth hormone releasing hormone stimulates release).
• GH and GHRH target the liver, muscle, bone, and cartilage.
• They also stimulate body growth, protein synthesis, and conserve glucose.
• Prolactin = Decrease in Prolactin inhibition hormone stimulates release, which then leads to milk production.

Posterior Pituitary

• Oxytocin stimulates powerful uterine contractions during birth and also stimulates milk ejection.
• ADH targets kidneys and leads to water conservation (Anti-Diuretic Hormone).
• Both oxytocin and ADH are stimulated by impulses from the hypothalamus.

Pineal Gland

• Secretes melatonin, exhibiting a daily cycle.

Thyroid

• Produces Thyroglobulin which is known as T3 and TH Precursor.
• T3 and T4 are stimulated by TSH.
• T3 and T4 increase basal metabolic rate and regulates tissue growth and development.
• Calcitonin = causes deposit of calcium in bones.
• C-cells produce calcitonin.
• Thyroid globulin makes T3 and T4.
• T3 and T4 are released into extracellular fluid.

Parathyroid Gland

• PTH (Parathyroid hormone) = low levels of calcium in the blood stimulates release.
• PTH targets bones and kidneys, increasing blood calcium by stimulating osteoclasts and kidneys to reabsorb calcium.

Thymus

• Produces peptide hormones, which may play a role in T lymphocyte development.
• It helps in the immune system (white blood cells).

Adrenal Gland (medulla)

• Epinephrine and Norepinephrine are produced by chromaffin cells.

Adrenal Gland (cortex)

• Zona glomerulosa produces Mineral corticoids in the superficial layer.
• Zona fasciculata produces Glucocorticoids in the middle layer.
• Zona reticularis produces Gonadocorticoids in the deep layer.
• Aldosterone (mineralcorticoid) increases sodium absorption and H20 absorption (in the glomerusa layer of cortex).
• Aldosterone also increases K secretion.
• Cortisol (glucocorticoids) breaks down fat and protein, inhibits the immune response, and is secreted from the fasciculata of cortex.
• Gonadocorticoids are mostly converted to testosterone and estrogen in the reticularis layer of cortex.
• Epinephrine and Norepinephrine is essentially the "fight or flight" or response, they increase the heart rate in response to some stimuli.

Pancreas

• Insulin: an increase of glucose blood levels increases insulin release and transport of glucose.
• Glucose is then converted into glycogen, fat and protein.
• Glucagon: a decrease of glucose blood levels increases glucagon release and leads to the break down of glycogen and lactic acid into glucose.

Gonads

• Estrogen is stimulated by LH and FSH release, leading to female reproductive organ maturation.
• Estrogens and Progestrone regulate the menstrual cycle and breast development.
• Testosterone promotes male reproductive organ development, sperm production, and sex drive.