Endocrine Glands + Hormones

Hypothalamus

• “master control center” → assisting the pituitary gland

• produces antidiuretic hormone (ADH)

• oxytocin (OT)

• regulatory hormones

→ Releasing hormones (RH): stimulate the production and secretion of specific anterior pituitary hormones

→ Inhibiting hormones (IH): deter the production and secretion of specific anterior pituitary hormones

Pituitary: Anterior Pituitary (adenohypohysis)

• most of the pituitary gland is composed of the anterior pituitary (adenohypophysis)

→ regulatory hormones reach the anterior pituitary gland by traveling through a blood vessel network called the hypothalamo-hypophyseal

Pituitary gland: Posterior pituitary (neurohypohysis)

→ the neural connection between the hypothalamus and the posterior pituitary gland is called the hypothalamo-hypophyseal tract

→ hypothalamic neurons: neurosecretory cells bc they secrete hormones

→ releases Antidiuretic hormone (ADH): water reabsorption, concentrating urine, can increase blood pressures

→ releases Oxytocin: stimulates uterine contractions during childbirth, milk ejection, social bonding + pleasure

Thyroid gland

• the thyroid gland is butterfly shaped, composed of left and right lobes

• avg weight in adults: 25-30 grams (largest gland)!

• highly vascular = red color

Calcitonin (CT): secreted by parafollicular cells reduces calcium levels in the body fluids, decreases bone reabsorption by osteoclasts and increases calcium loss through kidneys

Thyroid Hormone (TH): increases metabolism, oxygen use, growth, and energy use, supports and increases rate of development

Parathyroid glands

• small, brownish-red are located on the posterior surface of the thyroid gland

• chief cells are source of Parathyroid Hormone (PTH) 

→ increases calcium lvls in blood through bone reabsorption 

→ increases calcium absorption by small intestine by calcitriol 

→ decreases calcium loss through the kidneys

Adrenal Glands (suprarenal): Adrenal Cortex

are paired, pyramid shaped endocrine glands anchored on the superior surface of each kidney

• has an outer adrenal cortex and inner adrenal medulla

Adrenal Cortex

• synthesize more than 25 diff steroid hormones called corticosteroids

→ vital to our survival; trauma to or removal of the adrenal glands requires corticosteroid supplementation throughout life

Zona glomerulosa (outer cortical layer): synthesize mineralocorticoids

→ grp of hormones that help regulate the composition and concentration of electrolytes(ions) in body fluids; aldosterone (regulating Na+ and K+ ions in blood

Zona fasculata (middle layer): Glucocorticoids elevate blood gluclose lvls and stimulate use of lipids and proteins as energy resources

→ esp when the body attempts to resist stress + repair injured/damaged tissues

→ most common glucocorticoids are cortisol and corticosterone

Zona reticularis: secrete gonadocorticoids

→ androgens, which are sex hormones

Adrenal Glands (suprarenal): Adrenal Medulla

• inner core of each adrenal gland

• has a red-brown color bc its highly vascularized

• secretes epinephrine (also called adrenaline)

• secretes norepinephrine (also called noradrenaline)

→ these hormones work together w/ the sympathetic division of the autonomic nerv sys to prepare body for fight or flight responses

Pancreas

performs both exocrine and endocrine activities → considered a heterocrine or mixed gland

• mostly composed of cells called pancreatic acini → producing alkaline pancreatic juice that helps w/ digestion

• has endocrine cells called pancreatic islets (islets of Langerhans) which produce their own hormone

Alpha Cells

• secrete glucagon when blood glucose lvls drop

• live breaks down glycogen into glucose and release glucose into the blood to increase blood sugar lvls

• stimulates adipose cells to break down lipid and secrete it into the blood

Beta Cells

• secrete insulin when blood glucose lvls are too high

• liver + body cells respond to insulin by taking up the glucose, thus lowering blood sugar lvls

• also promotes glycogen synthesis + lipid storage

Delta Cells

• stimulated by high lvls of nutrients in the blood

• synthesize somatostatin (growth hormone-inhibiting hormone)

• slows the release of insulin and glucagon + activity of digestive organs, slowing the rate of nutrient entry into the blood

F cells

• stimulated by protein digestion in the digestive tract

• secrete pancreatic polypeptide (PP) to suppress and regulate somatostatin secretion from delta cells

Pineal Gland

composed primarily of pinealocytes which secrete melatonin

→ a hormone that makes us drowsy

→ its production tends to be cyclic; it increases at night and decreases during the day

• helps regulate circadian rhythm (24 hr body clock)!

Thymus

• the size of thymus varies among individuals; relatively large in infants, continues to grow until puberty then diminishes in size and activity.

• functions in association w/ the lymphatic system to regulate and maintain body immunity

→ produces thymopoietin and thymosin (grp of complimentary hormones)

→ hormones act by stimulating and promoting the differentiation, growth, and maturation of T-lymphocytes

Gonads

primary sex organs

Ovaries

• Estrogen: stimulates development of reproductive organs, follicle maturation, regulates menstrual cycle, stimulates growth of mammary glands

• Progesterone: regulates menstrual cycle, stimulates growth of uterine lining, stimulates growth of mammary glands

Testes

• Androgens (primarily testosterone): stimulates reproductive organ development, production of sperm

gonads also produce inhibin

• inhibits follicle-stimulating hormone secretion