Endocrine Hormones and Musculoskeletal System Function

Posted on Nov 15, 2025 in Human Biology

The Endocrine System: Chemical Messengers

Endocrine glands respond to stimuli by producing hormones transported in the blood throughout the body. Each hormone affects its target cell, which contains specific receptors. Hormones are chemical messengers that activate or stop, accelerate or delay processes within organs. Hormone receptors cause chemical reactions inside the cell, producing a response.

Hypothalamus Function

The Hypothalamus produces nerve signals and hormones, specifically releasing factors and inhibiting factors. These factors act on the pituitary gland and control the release of its hormones.

Major Endocrine Glands and Hormones

Pituitary Gland (Two Lobes)

  • Anterior Lobe Hormones:
    • Growth Hormone: Promotes growth.
    • TSH (Thyroid-Stimulating Hormone): Stimulates production of thyroid hormones.
    • Gonadotropins (FSH & LH): Act on ovaries and testes.
    • ACTH (Adrenocorticotropic Hormone): Stimulates secretion from the adrenal glands.
    • Prolactin: Promotes breast growth and milk production.
  • Posterior Lobe Hormones:
    • Antidiuretic Hormone (ADH): Prevents water loss in kidneys.
    • Oxytocin: Causes uterine contractions and milk expulsion after birth.

Other Key Glands

  • Thyroid Gland (Neck):
    • T3 & T4: Increase cellular metabolic consumption, protein synthesis, glucose utilization, and growth.
    • Calcitonin: Regulates calcium levels in the blood and aids bone development.
  • Parathyroid Glands: (Four small dots at the back of the thyroid)
    • Parathyroid Hormone (PTH): Increases the amount of calcium in the blood by stimulating its release from bones.
  • Adrenal Glands (Above Kidneys):
    • Cortex: Produces Cortisol (synthesis of glucose and breakdown of fats and proteins).
    • Medulla: Produces Adrenaline (Epinephrine).
  • Pancreas (Behind Stomach):
    • Insulin: Reduces glucose in the blood; used as energy in tissues.
    • Glucagon: Increases glucose in the blood.
  • Gonads:
    • Testes: Produce Testosterone (stimulates sperm production and secondary sex characteristics).
    • Ovaries: Produce Estrogens (secondary sex characteristics) and Progesterone (prepares the uterus for pregnancy).

Endocrine System Disorders

  • Hypofunction: Insufficient hormone production.
  • Hyperfunction: Excessive production of a hormone.
  • Dysfunction: Alteration in hormone receptors.

Specific Endocrine Conditions

  • Diabetes Mellitus: Increased glucose in the blood, potentially affecting the cardiovascular system, liver, and retina.
    • Type 1: Deficiency in insulin production by the pancreas (often diagnosed in youth).
    • Type 2: Pancreas produces insulin, but cells do not respond effectively (often diagnosed in older adults).
  • Hyperthyroidism: Excess thyroid hormone production, leading to an increase in metabolism.
  • Hypothyroidism: Deficit in thyroid hormone production, causing a slowdown in metabolism.
  • Dwarfism and Gigantism: Result from deficient or excessive production of growth hormone by the pituitary gland.

Musculoskeletal System Mechanics

How Muscles Contract and Move the Body

When a muscle contracts, it thickens and reduces the distance between the tendons at both ends. The contracted muscle pulls on the connected bone, moving it if it is part of a joint. When the muscle relaxes, it lengthens and stops pulling on the bone, allowing the bone to return to its initial position.

Components of the Musculoskeletal System

  • Skeletal System (Bones, Joints, and Ligaments):
    • Supports the weight of the body.
    • Produces blood cells in the bone marrow.
    • Stores calcium and phosphorus.
    • Protects internal organs.
  • Muscular System (Skeletal Muscles):
    • Attached to bones via tendons.
    • The Musculoskeletal System acts as a system of levers where the active component (muscles) exerts force on the passive component (bones) to cause body movement.
    • Muscle Tone: Continued involuntary contractions of muscles that keep the muscle firm.

Musculoskeletal Disorders

  • Osteoporosis: Loss of bone mass, resulting in weakened bones.
  • Arthritis: Inflammation of a joint.
  • Osteoarthritis: Degeneration of joint cartilage.
  • Muscle Cramp: Involuntary, sustained contraction of a muscle.
  • Sprain: Twisting of a joint, which can cause breakage of fibers in ligaments.
  • Dislocation: Two bones move from their normal position within a joint.
  • Fracture: A break in a bone.
  • Slipped Disc: Displacement of an intervertebral disc, which may compress a nerve, causing pain.
  • Torn Cartilage: Tearing of the meniscus in the knee.