Adrenal & Pituitary Glands Notes

Adrenal Glands

• Located on top of each kidney.
• Composed of two distinct glands: adrenal medulla (inner portion) and adrenal cortex (outer portion).

Adrenal Medulla

• Consists of modified neurons called chromaffin cells.
• Functions as part of the sympathetic nervous system.
• Secretes catecholamines (epinephrine and norepinephrine) in response to stimulation.

Catecholamines:

• Prepare the body for physical activity.
• Increase heart rate and blood pressure.
• Stimulate circulation to muscles.
• Dilate bronchioles.
• Inhibit digestion and urinary production.
• Boost glucose levels by:
  • Breaking down glycogen into glucose (glycogenolysis).
  • Converting fatty acids and amino acids into glucose (gluconeogenesis).

Adrenal Cortex

• Consists of three layers of glandular tissue.
• Each layer secretes a different corticosteroid.

Layers:

• Zona glomerulosa (outermost): secretes mineralocorticoids.
• Zona fasciculata (middle): secretes glucocorticoids.
• Zona reticularis (innermost): secretes sex steroids.

Classes of Hormones Secreted by Adrenal Cortex

• Mineralocorticoids

  • Principal hormone: aldosterone.
  • Acts on kidneys to promote $Na$ retention and $K^+$ excretion.
  • Causes water retention.

• Glucocorticoids

  • Principal hormone: cortisol.
  • Help the body adapt to stress and repair damaged tissue.
  • Stimulate the breakdown of fat and protein.
  • Convert fat and protein to glucose.
  • Release fatty acids and glucose into the blood.
  • Have an anti-inflammatory effect.
  • Suppress the immune system if secreted over a long term.
  • Essential for maintaining normal blood pressure.

• Sex Steroids

  • Include a weak form of androgen converted to testosterone.
  • Stimulate development of pubic and axillary hair and sustain sex drive (libido) in both sexes.
  • Include small amounts of estrogen (only source after menopause).

  *The testes produce much more testosterone, making adrenal cortex an unimportant source of testosterone in men.

Hormones of the Adrenal Glands

Adrenal Disorders

• Cushing Syndrome:
  • Hypersecretion of cortisol.
  • Symptoms: "moon face," "buffalo hump," hyperglycemia, muscle weakness, edema, muscle wasting, loss of bone mass, hypertension.
  • Hypersecretion of adrenal androgens: premature puberty in children, development of masculine characteristics in women.
• Addison's Disease (Adrenal Cortical Insufficiency):
  • Hyposecretion of mineralocorticoids and glucocorticoids.
  • Symptoms: loss of fluid and electrolytes, weakness, muscle wasting, dehydration, weight loss.
  • Life-threatening if untreated.

Hypothalamic-Pituitary-Adrenal (HPA) Axis

• Amygdala signals the hypothalamus during stressful events to activate the sympathetic nervous system and fight-or-flight response.
• The HPA axis is stimulated to help the body cope.

Process:

1. Hypothalamus releases corticotropin-releasing hormone (CRH).
2. CRH prompts the pituitary to release adrenocorticotropic hormone (ACTH).
3. ACTH travels to the adrenal cortex, causing the adrenal glands to secrete cortisol.
4. Cortisol causes physiological changes: increased heart rate, increased blood pressure, elevated blood glucose levels.

• Chronic, low-level stress keeps the HPA axis activated, leading to health issues (e.g., increased susceptibility to infection, type 2 diabetes, obesity, cardiovascular disease, and depression).

Pituitary Gland

Posterior Pituitary

• Composed of neural tissue.
• Stores hormones synthesized by the hypothalamus (antidiuretic hormone (ADH) and oxytocin (OT)).
• Hypothalamic neurons synthesize hormones sent to the posterior pituitary for storage.
• Releases hormones when stimulated by the nervous system.

Control of Pituitary Secretions

• Hormones are released in phases or pulses (e.g., growth hormone mainly secreted at night).
• Controlled by the central nervous system and target organs (negative feedback).

Control by the Central Nervous System

• The brain monitors conditions and triggers hormone release as needed (e.g., TSH release when cold).

Control by Negative Feedback

• The hormone released by a target endocrine gland feeds back to the pituitary, inhibiting further release of the tropic hormone.

Hormones of the Pituitary Gland