Hormonal Regulation Notes

Hormonal Regulation of Stress and Blood Sugar

Regulation of Stress

Adrenal Gland

• Located on top of the kidneys.
• Composed of two layers:
  • Inner layer: Adrenal medulla.
  • Outer layer: Adrenal cortex.

Adrenal Medulla: Short-Term Stress Response ("Fight or Flight")

• Produces hormones: epinephrine and norepinephrine.
• Neural signal from the hypothalamus directly stimulates the adrenal medulla to secrete these hormones.

Short term stress response

• Heartbeat and blood pressure increase.
• Blood glucose level rises.
• Muscles become energized.

Mechanism:

1. Stress triggers a signal from the hypothalamus.
2. The signal travels via neurons to the adrenal medulla.
3. The adrenal medulla secretes epinephrine and norepinephrine.

Effects of Epinephrine and Norepinephrine:

• Increase in breathing rate, heart rate, blood pressure, and blood flow to the heart and muscles.
• Conversion of glycogen to glucose in the liver, increasing blood sugar levels.
• Dilation of pupils.
• Decrease in blood flow to the extremities.

Adrenal Cortex: Long-Term Stress Response

• Produces hormones: glucocorticoids (cortisol) and mineralocorticoids (aldosterone).
• The hypothalamus releases corticotropin-releasing hormone (CRH).
• CRH stimulates the anterior pituitary to release adrenocorticotropic hormone (ACTH).
• ACTH stimulates the adrenal cortex to produce cortisol and aldosterone.
• Negative feedback mechanism regulates this process.

Effects of Cortisol and Aldosterone:

• Cortisol: Raises blood glucose levels and suppresses the immune system.
• Aldosterone: Increases reabsorption of sodium at the kidneys, leading to increased blood pressure.

Comparison of Short-Term and Long-Term Stress Responses

Short-Term

• Heart rate and blood pressure increase.
• Blood flow to the heart and muscles increases.
• Breathing rate increases.
• Blood glucose rises.
• Rate of cellular metabolism increases.

Long-Term

• Kidney absorbs sodium ions and water, increasing blood volume and pressure.
• Protein and fat metabolism stimulated, releasing glucose.
• Inflammation is reduced, and immune cells are suppressed.

Chronic Stress

• Sustained levels of cortisol and aldosterone in the blood.
• Long-Term Health Effects:
  • Impaired thinking/memory recall.
  • Hypertension (high blood pressure).
  • High blood sugar, leading to diabetes.
  • Increased susceptibility to infection.
  • Anxiety and depression.
  • Weight gain/loss.

Addison’s Disease

• Damage to the adrenal gland results in inadequate amounts of mineralocorticoids and glucocorticoids.
• Symptoms:
  • Hypoglycemia (low blood sugar).
  • Rapid weight loss.
  • Loss of sodium and water from the blood, decreasing blood pressure.
  • Severe electrolyte imbalance.

Regulation of Blood Sugar

Pancreas

• Contains clusters of endocrine cells (alpha and beta) called the Islets of Langerhans.
• Secretes two antagonistic hormones:
  • Insulin (from beta cells).
  • Glucagon (from alpha cells).

Insulin

• Secreted after eating in response to high blood glucose levels.
• Actions:
  • The liver stores glucose as glycogen.
  • Muscle cells store glycogen and build protein.
  • Adipose tissue uses glucose to form fat.
  • Lowers blood glucose levels.

Glucagon

• Secreted in between eating in response to low blood glucose levels.
• Actions:
  • The liver breaks down glycogen to glucose.
  • Adipose tissue breaks down fat to glucose.
  • Raises blood glucose levels.

Homeostasis

• Normal blood glucose range: $75 \text{ mg} - 110 \text{ mg/100 mL}$

Diabetes Mellitus

• Chronic condition characterized by hyperglycemia.
• Blood glucose levels rise sharply after meals and remain significantly elevated.

Types of Diabetes

Type I

• Age of Onset: Childhood.
• Progression: Abrupt.
• Cause: Beta-cells degenerate, leading to no insulin production.
• Treatment: Insulin injections.

Type II

• Age of Onset: Adulthood.
• Progression: Gradual.
• Cause: Insulin resistance at receptors.
• Treatment: Weight loss, diet, exercise, and medications.