Endocrine System III: Adrenal Glands and Gonads

Overview

This section covers the structure and function of the adrenal glands and gonads (ovaries and testes), focusing on their roles in hormone production and regulation within the endocrine system.

Adrenal (Suprarenal) Glands

Structure and Location

• Paired, pyramid-shaped organs located on top of each kidney.

• Each adrenal gland consists of two distinct regions:

  • Adrenal cortex: Outer region composed of glandular tissue; responsible for synthesizing and secreting corticosteroid hormones.

  • Adrenal medulla: Inner region composed of nervous tissue; part of the sympathetic nervous system.

Adrenal Cortex

The adrenal cortex is divided into three layers, each producing different types of corticosteroids:

• Zona glomerulosa: Produces mineralocorticoids (e.g., aldosterone).

• Zona fasciculata: Produces glucocorticoids (e.g., cortisol).

• Zona reticularis: Produces gonadocorticoids (e.g., androgens).

Table: Adrenal Cortex Layers and Hormones

Mineralocorticoids (Aldosterone)

• Aldosterone is the most potent mineralocorticoid.

• Regulates electrolyte balance, primarily sodium (Na+) and potassium (K+).

• Promotes Na+ reabsorption (leading to water retention) and K+ elimination in the kidneys.

• Influences extracellular fluid volume, blood volume, and blood pressure.

• Helps maintain extracellular osmotic balance and resting electrical potential of cells.

Glucocorticoids (Cortisol)

• Cortisol is the primary glucocorticoid in humans.

• Functions include:

  • Reducing inflammation and suppressing the immune system.

  • Promoting the breakdown of fat, protein, and carbohydrates to increase blood glucose (gluconeogenesis).

  • Secreted in response to stress.

• Disorders:

  • Hypersecretion: Cushing's syndrome/disease (characterized by high blood glucose, muscle and fat breakdown, fat redistribution, weight gain, and increased risk of infection).

  • Hyposecretion: Addison's disease (characterized by low blood glucose, weight loss, fatigue, and muscle weakness).

Gonadocorticoids (Sex Hormones)

• Primarily androgens (male sex hormones), which are less potent than testosterone in males.

• Functions in females include:

  • Onset of puberty

  • Development of secondary sex characteristics

  • Sex drive

  • Estrogen synthesis after menopause

• Hypersecretion: Adrenogenital syndrome (masculinization), especially noticeable in females and pre-pubescent males (e.g., development of male secondary sex characteristics, enlarged genitalia).

Adrenal Medulla

• Composed of chromaffin cells that secrete catecholamines:

  • Epinephrine (adrenaline): ~80%

  • Norepinephrine (noradrenaline): ~20%

• Effects are brief and include:

  • Increased heart rate and blood pressure

  • Bronchial dilation (enhanced gas exchange)

  • Increased blood glucose (for ATP production)

  • Blood flow redirected to essential organs (brain, heart, skeletal muscle, liver)

  • Vasoconstriction in most other organs

• Not essential for life, but important for acute stress response (fight-or-flight).

Gonads

Ovaries

• Produce estrogens and progesterone.

• Functions of estrogens:

  • Development of secondary sexual characteristics (breast enlargement, hip widening, increased fat deposits in buttocks, thighs, and hips).

  • Growth of body hair.

  • Maturation of reproductive organs.

• Functions of progesterone:

  • Regulates cyclic changes in the uterine mucosa (menstrual cycle).

  • Essential for egg maturation (ovarian cycle).

Testes

• Produce testosterone.

• Functions:

  • Maturation of male reproductive organs.

  • Development of secondary sex characteristics (increased muscle mass, bone density, body and facial hair, deeper voice).

  • Maintenance of reproductive organs in a functional state.

  • Regulation of sex drive and necessary for normal sperm production.

  • Influences certain behaviors (e.g., aggression).

Clinical and Therapeutic Uses of Sex Hormones

• Anabolic steroids: Used to enhance male characteristics and increase muscle strength.

• Estrogen therapy: Used to replace hormones after menopause or ovariectomy.

• Sex change therapy: Used to induce physical characteristics of the opposite sex.

Summary Table: Major Endocrine Glands and Their Hormones

Key Terms

• Corticosteroids: Steroid hormones produced by the adrenal cortex.

• Mineralocorticoids: Regulate mineral balance (e.g., aldosterone).

• Glucocorticoids: Regulate metabolism and stress response (e.g., cortisol).

• Gonadocorticoids: Sex hormones produced by the adrenal cortex (e.g., androgens).

• Catecholamines: Hormones produced by the adrenal medulla (e.g., epinephrine, norepinephrine).

Example: Hormonal Response to Stress

• During stress, the hypothalamus signals the pituitary to release ACTH, which stimulates the adrenal cortex to secrete cortisol.

• The adrenal medulla releases epinephrine and norepinephrine, preparing the body for a 'fight-or-flight' response.