The Endocrine System Pt. 2

Calcitriol

The active form of vitamin D.

• Increases calcium absorption from the small intestine.

• Helps maintain calcium and phosphate balance.

• Works with PTH in regulating blood calcium.

Overall effect: Increases intestinal calcium absorption and supports calcium homeostasis.

Bone

Stores calcium and can release in into the blood

Kidneys

Filter calcium, reabsorb some, and excrete the rest in urine

Small Intestine

Absorbs calcium from food

Parathyroid Glands

Release PTH in response to low blood calcium

Thyroid C Cells

Release calcitonin

Hydroxyapatite

Calcium and phosphate homeostasis are linked because both are components of … the mineral that gives bones much of their strength.

Osteoporosis

Involves loss of bone mass and deterioration of bone structure, increasing the risk of fractures

Thymus

• It supports T-lymphocyte development.

• It decreases in size with age.

• It secretes thymosin, thymulin, and thymopoietin, which help support T-cell development and immune function.

Adrenal Cortex

Out region of adrenal glands, produces steroid hormones, helps regulate blood pressure, metabolism, and other function

Adrenal Medulla

Inner region of adrenal glands, produces catecholamines, releases epinephrine and norepinephrine, supports rapid sympathetic responses.

Zona Glomerulosa

Layer of adrenal cortex, Produces aldosterone, which promotes sodium retention and potassium secretion by the kidneys, helps maintain blood volume and pressure.

Zona Fasciculata

Layer of adrenal cortex, Produces cortisol, which helps regulate metabolism and the body’s response to stress.

Zona Reticularis

Produces adrenal androgens and other sex steroids.

Synergism

Hormone interaction where two or more hormones act together to produce an effect greater than the sum of their individual effects.

Permissiveness

Hormone interaction where one hormone allows another hormone to exert its full effect.

Antagonism

Hormone interaction where two hormones have apposing effects, Ex: Insulin lowers blood glucose, while glucagon raises blood glucose.