Endocrine System Overview

Study Notes

Endocrine glands release hormones directly into the bloodstream
Hormones regulate various bodily functions
The pituitary gland is often called the master gland because it controls other glands

Located near the kidneys
Composed of cortex and medulla
Cortex produces steroid hormones (e.g., mineralocorticoids, glucocorticoids, androgens)
Medulla produces catecholamines (e.g., epinephrine, norepinephrine)
Pituitary ACTH stimulates adrenal gland growth and hormone synthesis
Stress (hypoglycemia, hypothermia, shock) stimulates ACTH release
Adrenal cortex is controlled by ACTH from the pituitary gland
Adrenal medulla is a part of the sympathetic nervous system

Mineralocorticoids (Zona glomerulosa): Primarily aldosterone, regulates fluid and electrolyte balance (e.g. sodium, potassium)
- Released in response to hyponatremia, hyperkalemia, and angiotensin II
- Maintains salt balance
- Increases sodium absorption and potassium excretion
Glucocorticoids (Zona fasciculata): Primarily cortisol, regulates metabolism, immune response, and stress response. Vital for life.
Affects many organs.
Androgens (Zona reticularis): Regulates sexual function
Catecholamines (Adrenal Medulla): Epinephrine and norepinephrine, are involved in the fight-or-flight response.
- Increase blood pressure, heart rate, and cardiac output
- Bronchodilation
- Glycogenolysis (breakdown of glycogen to glucose)

Aldosterone is a key mineralocorticoid
Secretion is stimulated by low blood sodium, high potassium, and angiotensin II
Increases sodium retention and potassium excretion in the kidneys
Imbalances in aldosterone secretion cause specific medical conditions (hyperaldosteronism, hypoaldosteronism)

Cortisol secretion is tightly regulated by feedback loops
The hypothalamus releases corticotropin-releasing hormone (CRH)
CRH stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH)
ACTH stimulates the adrenal cortex to release cortisol
Cortisol inhibits the release of CRH and ACTH (negative feedback)

Metabolic effects: Raises blood sugar levels (increases glucose production via gluconeogenesis), reduces glucose use by tissues, and increases protein breakdown. Influences metabolism of carbs, fats, and proteins.
Maintenance of circulatory functions
Hematological effects: Decreases other blood cells (except RBCs and platelets), has anti-inflammatory effects, stabilizes lysosomes of certain white blood cells.

Gastric effects: Increases hydrochloric acid and decreases mucosal cell proliferation, making the stomach more acidic
Psychological effects: Can cause various psychological effects (euphoria, psychosis, depression, etc.)
Lung surfactant: Can increase lung surfactant levels in late pregnancy
Aldosterone-like effects: Plays a role in fluid balance akin to aldosterone

Excessive cortisol production
Characterized by specific symptoms (e.g. moon face, buffalo hump, muscle wasting, thin skin, poor wound healing)

Insufficient cortisol production
Characterized by specific symptoms (e.g., fatigue, weakness, low blood pressure, weight loss, skin darkening, altered electrolyte levels)

Releases catecholamines (epinephrine and norepinephrine)
Responds to sympathetic nervous system stimulation
Actions: vasoconstriction, increased heart rate, cardiac output, bronchodilation, glycogenolysis, and increased BMR

Synthesized in the hypothalamus and stored in the posterior pituitary
Released in response to nerve signals from the cervix during childbirth, nipple stimulation during breastfeeding
Functions include initiating labor contractions, and stimulating milk ejection
Regulation of uterine muscle contractions during childbirth
Promotes milk ejection (let-down reflex) in nursing