Hormonal Control During Exercise -- Basics

Hormonal Control During Exercise

Basics

• The endocrine system plays a crucial role in the communication of hormones during exercise.

Endocrine System

Overview

• Communication System:

  • Nervous System: Utilizes electrical communication.

  • Endocrine System: Employs chemical communication.

• Response Time:

  • Endocrine system is slower to respond than the nervous system but has longer-lasting effects.

• Functions:

  • Maintains homeostasis through hormones.

  • Controls and regulates cellular and organ activity.

  • Acts on specific target cells.

Functions During Exercise

• Constantly monitors the internal environment.

• Coordinates integration of physiological systems during rest and exercise.

• Maintains homeostasis when performing physical activities.

• Controls substrate metabolism, ensuring energy availability.

• Regulates fluid and electrolyte balance to support bodily functions.

Key Glands in the Endocrine System

• Hormone-Producing Glands:

  • Hypothalamus

  • Pituitary gland

  • Thyroid gland

  • Parathyroid glands

  • Thymus gland

  • Adrenal glands

  • Pancreas

  • Kidneys

  • Adipose tissue

  • Ovaries (in females)

  • Testes (in males)

Types of Hormones

Steroid Hormones

• Characteristics:

  • Derived from cholesterol.

  • Lipid-soluble, enabling them to diffuse through cell membranes.

• Major Glands Producing Steroid Hormones:

  • Adrenal cortex: Secretes cortisol and aldosterone.

  • Ovaries: Produce estrogen and progesterone.

  • Testes: Produce testosterone.

  • Placenta: Also secretes estrogen and progesterone.

Nonsteroid Hormones

• Characteristics:

  • Not lipid-soluble; cannot cross cell membranes.

• Groups:

  • Protein or peptide hormones (produced by pancreas, hypothalamus, pituitary gland).

  • Amino acid-derived hormones (e.g., Thyroid hormones T3 and T4, adrenal medulla hormones like epinephrine and norepinephrine).

Hormone Secretion

• Hormonal Release Patterns:

  • Secreted in bursts (pulsatile).

  • Plasma concentrations of hormones fluctuate over short and long periods.

• Regulation Mechanism:

  • Negative feedback regulation.

  • Hormone release induces changes in the body; significant changes inhibit further secretion, while minor changes can promote more secretion.

  • Analogy: Similar to a home thermostat controlling temperature.

Hormone Actions

• Understanding Hormone Activity:

  • Plasma concentration alone may not accurately indicate hormone activity.

  • Cells can alter sensitivity and the number of receptors present on their surfaces:

    • Downregulation: Reduces receptor number during high plasma concentrations (desensitization).

    • Upregulation: Increases receptor number during high plasma concentrations (sensitization).

Hormone Receptors

• Specificity of Hormones:

  • Hormones use specific receptors to limit their scope of effects.

  • No receptor present means no hormonal effect can occur on the target cell.

  • Hormone effects are mediated when the hormone binds to its specific receptor to form a hormone-receptor complex.

  • A typical cell may have between 2,000 to 10,000 hormone receptors.

Steroid Hormone Actions

• Mechanism:

  • As lipid-soluble molecules, steroid hormones can cross cell membranes.

  • Receptors located inside cells (in the cytoplasm or nucleus).

  • Hormone-receptor complex can enter the nucleus and bind to DNA, directing gene activation.

  • Regulates mRNA and protein synthesis, impacting cellular activity.

Nonsteroid Hormone Actions

• Mechanism:

  • Nonsteroid hormones, being not lipid-soluble, cannot cross cell membranes.

  • Act via receptors on cell membranes leading to the activation of second messengers, which amplify the hormone's effects.

• Common Second Messengers:

  • Cyclic adenosine monophosphate (cAMP)

  • Cyclic guanine monophosphate (cGMP)

  • Inositol triphosphate (IP3)

  • Diacylglycerol (DAG)

Hormones: Prostaglandins

• Characteristics:

  • Classified as pseudo-hormones derived from arachidonic acid.

  • Act as local hormones affecting the immediate area.

  • Key Functions:

    • Mediate inflammatory responses (e.g., swelling, vasodilation).

    • Sensitize free nerve endings, contributing to the sensation of pain.