Hormonal Regulation of Metabolism During Exercise

The Hormonal Regulation of Metabolism During Exercise

Overview

  • Hormones play a crucial role in regulating physiological variables during exercise.

  • Various endocrine glands in the body secrete hormones that influence metabolism of carbohydrates and fats.

Endocrine Glands and Their Hormones

  • Each endocrine gland can produce multiple hormones.

  • These hormones are responsible for regulating bodily functions during physical activity.

Key Endocrine Glands Involved in Metabolism Regulation

Major Endocrine Glands

  • Anterior pituitary gland

  • Thyroid gland

  • Adrenal gland

  • Pancreas

Functions of Hormones

  • Released hormones from these glands affect carbohydrate and fat metabolism during exercise.

Anterior Pituitary Gland

Anatomy and Function

  • Attached to the inferior part of the hypothalamus.

  • Composed of three lobes: anterior, intermediate, and posterior.

  • Secretes hormones in response to hypothalamic factors (releasing and inhibiting).

Hormones Released

  • Growth Hormone (GH)

    • An anabolic hormone producing tissue and organ growth.

    • Promotes muscle hypertrophy and stimulates fat metabolism.

    • Release is proportional to exercise intensity.

Thyroid Gland

Key Hormones

  • Secretes triiodothyronine (T3) and thyroxine (T4).

Effects of T3 and T4

  • Increases metabolic rates across all tissues.

  • Enhances protein synthesis and increases the number and size of mitochondria.

  • Promotes glucose uptake by cells and accelerates glycolysis/gluconeogenesis.

  • Mobilizes free fatty acids (FFA).

Regulation of T3 and T4

  • Anterior pituitary releases thyrotropin (TSH), which stimulates the release of T3 and T4.

  • Exercise increases TSH release:

    • Short term: Increased T4.

    • Prolonged exercise: Constant T4, decreased T3.

Adrenal Gland

Adrenal Medulla

  • Secretes catecholamines (80% epinephrine, 20% norepinephrine).

  • In response to exercise, sympathetic nervous system activation leads to increased catecholamine release.

  • Effects include:

    • Elevated heart rate and contractile force.

    • Increased blood pressure and glycogenolysis.

    • Enhanced FFA mobilization and blood flow to skeletal muscles.

Adrenal Cortex

  • Releases corticosteroids, primarily cortisol (a glucocorticoid).

  • Functions of cortisol:

    • Stimulates gluconeogenesis.

    • Increases FFA mobilization and protein catabolism.

    • Acts as an anti-inflammatory and suppresses immune reactions.

Pancreas

Major Hormones

  • Insulin: Decreases blood glucose levels, countering hyperglycemia, and promotes glucose transport into cells and glycogen storage.

  • Glucagon: Increases blood glucose levels, countering hypoglycemia by promoting glycogenolysis and gluconeogenesis.

Regulation of Carbohydrate Metabolism During Exercise

Importance of Glucose

  • Vital for energy supply during exercise.

Key Processes

  • Glycogenolysis: Conversion of glycogen to glucose.

  • Gluconeogenesis: Conversion from fatty acids and proteins to glucose.

Requirements for Adequate Glucose

  • Glucose must be released by the liver and taken up by muscles.

  • Hormones that increase circulating glucose:

    • Glucagon

    • Epinephrine

    • Norepinephrine

    • Cortisol

Factors Affecting Circulating Glucose During Exercise

  • Growth Hormone (GH): Increases FFA mobilization and reduces cellular glucose uptake.

  • T3 and T4: Enhance glucose catabolism and fat metabolism.

  • Liver glucose release depends on exercise intensity and duration.

Exercise Intensity and Duration Effects

  • Increased exercise intensity leads to:

    • Higher catecholamine release.

    • Increased glycogenolysis (liver and muscles).

    • Muscle glycogen usage precedes liver glycogen usage.

  • Prolonged exercise results in:

    • Increased usage of liver glycogen.

    • Glucagon levels rise as glycogen stores deplete.

Role of Insulin During Exercise

  • Insulin facilitates glucose uptake in muscle cells.

  • During exercise:

    • Insulin concentrations decrease.

    • Cellular insulin sensitivity increases.

    • More glucose is absorbed by cells despite lower insulin levels.

Hormonal Changes Over Time During Exercise

Percent Change in Hormones

  • Epinephrine and norepinephrine levels rise significantly, counteracted by fluctuating levels of cortisol, glucose, and glucagon as exercise duration increases.

Changes in Glucose and Insulin Levels Over Time

  • As exercise progresses, levels of glucose and insulin shift, highlighting the dynamic response of metabolic hormones during physical activity.

Regulation of Fat Metabolism During Exercise

Importance of FFA Mobilization

  • Essential for endurance exercise, especially when glycogen stores are low.

Lipolysis

  • The process of breaking down triglycerides to FFAs and glycerol is accelerated through:

    • Decreased insulin.

    • Increased levels of epinephrine, norepinephrine, cortisol, and GH.

Summary of Lipolysis

  • Lipolysis is stimulated by key hormones that act via lipase, facilitating the utilization of fat as an energy substrate during exercise.