Endocrine (cont’d pt. 2)

Overview of Hormones and Endocrine Function

Hormonal Classifications

  • Mineralocorticoids:
    • Example: Aldosterone
    • Function: Balances sodium and potassium levels in the blood
      • Mechanism: Instructs kidneys to retain sodium
      • Relation to Blood Pressure: Retaining sodium also retains water, affecting blood pressure
      • High sodium can worsen blood pressure issues for certain individuals.

Cortisol

  • Classification: Glucocorticoids
  • Function: Glucose sparing effect
    • Definition: Reserves available glucose for the brain during stress or insufficient calorie intake
    • When glucose is limited, the body begins to break down fats and proteins for energy, sparing glucose for the brain (which primarily uses glucose).
  • Connection to Stress: Cortisol acts during stress to manage energy distribution in the body.

Androgens and Sex Hormones

  • Source: Adrenal cortex
  • Production in Females: Primary source of androgens
  • Implications of Excess Androgens in females: Can lead to masculinization (e.g., facial hair) due to overproduction from adrenal tumors.

The Pancreas

  • Description: A mixed gland with both exocrine (producing digestive enzymes) and endocrine functions
  • Endocrine Part: Comprised of pancreatic islets (1% of the gland).
  • Key Hormones:
    • Glucagon:
    • Function: Raises blood glucose levels by promoting the breakdown of glycogen in the liver to increase glucose in the bloodstream
    • Trigger: Released when blood sugar is low.
    • Insulin:
    • Function: Lowers blood glucose levels by facilitating the uptake of glucose into cells
    • Common Issue in Diabetes: Insulin production issues or resistance may lead to high blood glucose.

Gonads as Endocrine Organs

  • Classification: Mixed glands (endocrine and exocrine functions)
  • Hormones Produced:
    • Ovarian Hormones: Estrogens, progesterone, inhibin
    • Testicular Hormones: Testosterone, androgens

Other Hormones From Various Organs

  • Kidneys:
    • Hormones:
    • Vitamin D (activation)
    • Erythropoietin: Stimulates red blood cell production
    • Renin: Part of blood pressure regulation
  • Heart:
    • Hormone: ANP (Atrial Natriuretic Peptide)
    • Function: Lowers blood pressure
  • Digestive Tract: Over 10 enteric hormones affecting local signals.
  • Adipose Tissue:
    • Hormone: Leptin
  • Bone:
    • Hormone: Osteocalcin

Hormone Regulation Mechanisms

  1. Humoral Regulation:

    • Definition: Changes in blood levels of certain nutrients or ions directly stimulates hormone secretion.
    • Example: Parathyroid hormone secretion in response to low calcium levels.

  2. Neural Regulation:

    • Control via the nervous system
    • Example: Sympathetic nervous stimulation triggers the adrenal medulla to release epinephrine and norepinephrine.

  3. Hormonal Regulation:

    • Regulation by other hormones.
    • Example: Hypothalamus produces hormones that control the anterior pituitary, which release other hormones to adrenal glands or gonads.

Hormone Chemistry

Types of Hormones:
  • Steroid Hormones: Derivatives of cholesterol (e.g., testosterone, estradiol)
  • Protein and Glycoprotein Hormones: Made from amino acids, include insulin, angiotensin II.
  • Monoamines: Modified amino acids (e.g., thyroxine, epinephrine)
Hormone Interaction with Cells
  • Receptors:
    • Hormones act only on target cells with specific receptors (may be on the plasma membrane or within the cell).
  • Hydrophobic Hormones: Can pass through cell membranes to bind with nuclear receptors (e.g., steroids).
  • Hydrophilic Hormones: Typically bind to surface receptors, triggering second messenger systems without entering the cell.

Hormone Clearance

  • Most hormones are deactivated by the liver and kidneys and excreted in urine or bile.
  • Metabolic Clearance Rate (MCR): Time taken for half of a hormone to be cleared from the bloodstream.

Regulation of Hormone Sensitivity

  • Upregulation: Increase in number of receptors enhances response
  • Downregulation: Decrease in receptor numbers reduces responses

Hormonal Interactions

  • Synergistic Effects: Multiple hormones work together for a greater effect (e.g., growth hormone and IGF).
  • Permissive Effects: One hormone enhances the effect of another (difficult to clarify without examples).
  • Antagonistic Effects: One hormone opposes the action of another (e.g., insulin vs glucagon).

Stress and Cortisol

  • Definition of Stress: Any situation upsetting homeostasis—can be physical or emotional.
  • General Adaptation Syndrome: Describes the body’s response to chronic stress, consisting of three stages:
    1. Alarm Reaction: Immediate response to stress (e.g., fight-or-flight).
    2. Stage of Resistance: Body copes by prioritizing glucose for the brain at the expense of other systems.
    3. Stage of Exhaustion: Body can no longer maintain physiological stress responses, leading to severe health consequences (e.g., immune response failure).

Paracrine Secretions

  • Definition: Local signals affecting neighboring cells without entering the bloodstream (not hormones).
  • Examples:
    • Histamine: Causes local inflammation by dilating blood vessels.
    • Nitric Oxide: Increases blood flow locally (related to erectile function).
    • Icosanoids: Local hormones involved in inflammation.