Hormonal Control During Exercise

Chapter 4: Hormonal Control During Exercise

Overview of Hormonal Control

• The endocrine system employs chemical communication, which is slower to respond but offers longer-lasting effects compared to the nervous system's electrical communication.

• Its primary role during rest and exercise is to maintain homeostasis by constantly monitoring the internal environment.

• Functions include controlling and regulating cell and organ activity, coordinating the integration of physiological systems, controlling substrate metabolism, and regulating fluid and electrolyte balance.

The Endocrine System: Glands and Hormones

• The endocrine system comprises various glands located throughout the body, each secreting specific hormones. Key glands include:

  • Hypothalamus

  • Pituitary gland

  • Thyroid gland

  • Parathyroid glands

  • Thymus gland

  • Adrenal glands

  • Pancreas

  • Kidneys

  • Adipose tissue

  • Ovaries (in females)

  • Testes (in males)

• (Refer to Figure 4.1 for a visual representation of these glands).

Types of Hormones

Steroid Hormones

• Origin: Derived from cholesterol.

• Solubility and Membrane Permeability: They are lipid-soluble, allowing them to diffuse easily through cell membranes.

• Secretion: Secreted by four major glands:

  • Adrenal cortex (e.g., cortisol, aldosterone)

  • Ovaries (e.g., estrogen, progesterone)

  • Testes (e.g., testosterone)

  • Placenta (e.g., estrogen, progesterone)

• Mechanism of Action:

  1. The steroid hormone enters a cell (due to its lipid solubility).

  2. It binds to a specific receptor located inside the cell, either in the cytoplasm or the nucleus, forming a hormone-receptor complex.

  3. This complex enters the nucleus and activates the cell's $ext{DNA}$, directing gene activation.

  4. This process regulates the synthesis of messenger $ext{RNA}$ ($ext{mRNA}$) and, subsequently, protein synthesis within the cell.

  5. $ext{mRNA}$ leaves the nucleus and enters the cytoplasm to direct protein synthesis. (Refer to Figure 4.2 for a visual pathway).

Nonsteroid Hormones

• Solubility and Membrane Permeability: Not lipid-soluble; therefore, they are unable to cross cell membranes.

• Groups:

  • Protein or Peptide Hormones: Constitute most nonsteroid hormones. They are secreted by the pancreas, hypothalamus, and pituitary gland.

  • Amino Acid–Derived Hormones: Include thyroid hormones ($ext{T}<em>3$ and $ext{T}</em>4$) and adrenal medulla hormones (epinephrine and norepinephrine).

• Mechanism of Action:

  1. Nonsteroid hormones cannot pass directly through the cell membrane.

  2. They bind to specific receptors located on the outer surface of the cell membrane, forming a hormone-receptor complex.

  3. This complex activates an enzyme (e.g., adenylate cyclase) within the cell membrane.

  4. The activated enzyme catalyzes the formation of