Endocrine Glands Overview

ENDOCRINE GLANDS

  • Pineal gland

  • Pituitary gland

    • Master gland, location: base of the brain, attached to hypothalamus by a short stalk, fits into a small bony cavity in the cranium.

    • Structure: pea-shaped, about 1-1.5 cm, comprised of two lobes (anterior and posterior).

  • Thyroid gland

  • Thymus

  • Adrenal gland

  • Pancreas

  • Testis

  • Ovary

PITUITARY GLAND

Structure and Location

  • The pituitary gland, known as the "master gland", is located at the base of the brain, just attached to the hypothalamus.

  • It fits snugly into a bony cavity within the cranium.

  • Its size is approximately 1-1.5 cm and has two primary lobes: anterior and posterior.

Anterior Lobe Functions

  1. Thyroid Stimulating Hormone (TSH):

    • Function: Stimulates the thyroid to secrete thyroxin.

  2. Growth Hormone (GH):

    • Function: Promotes growth of the skeleton and muscles, maintains muscle mass and bone mass, affects fat distribution in the body.

    • Disorders:

      • Hypersecretion leads to gigantism in children, often caused by a tumor.

      • Hyposecretion results in pituitary dwarfism, characterized by heights of 91-122 cm, leading to sexual immaturity, which can be treated with synthetic growth hormone.

  3. Follicle Stimulating Hormone (FSH):

    • Function:

      • Stimulates maturation and releasing of eggs during oogenesis in females.

      • In males, stimulates spermatogenesis.

    • Disorders:

      • Hyposecretion leads to infertility; hypersecretion can result in multiple births.

  4. Luteinizing Hormone (LH):

    • Function:

      • Works together with FSH in normal functioning of ovaries and testes.

  5. Prolactin:

    • Function: Stimulates mammary glands to secrete milk.

Posterior Lobe Functions

  1. Antidiuretic Hormone (ADH):

    • Function: Controls osmoregulation in the kidney.

  2. Oxytocin:

    • Function: Causes milk letdown in nursing mothers and stimulates contraction of uterine muscles, facilitating labor.

Hormonal Interactions

  • FSH and LH target reproductive organs in both males and females and are essential for the normal functions of these organs.

GROWTH HORMONE DISORDERS

  • Hypersecretion leads to gigantism in children;

  • Hyposecretion leads to growth disorders and can result in pituitary dwarfism.

  • In adults, excess growth hormone results in acromegaly, characterized by enlarged bones of the face, hands, and feet, along with thickening of soft tissues (including an enlarged tongue).

THYROID GLAND

Structure and Location

  • The thyroid gland consists of two lobes, located on either side of the trachea, just below the larynx.

Function

  • The thyroid produces and secretes thyroxine, essential for metabolism; this regulates the body's ability to break down food, store energy, and release energy.

Thyroxin Functions

  • Increases basal metabolic rate in all body cells.

  • Increases the rate at which cells release energy from carbohydrates.

  • Promotes normal functioning of both the heart and nervous system.

Iodine Importance

  • Iodine, primarily found in seafood, is essential for thyroxine formation.

  • Goiter: Swelling of the thyroid due to lack of iodine.

  • Goiter can lead to Grave’s disease: an autoimmune condition targeting the thyroid leading to swelling.

Disorders of Thyroid Hormone Levels

  1. Hypothyroidism:

    • Under-secretion of thyroxin, results in low metabolism.

    • In children: leads to cretinism.

    • In adults: leads to myxoedema.

  2. Hyperthyroidism:

    • Over-secretion of thyroxin, associated symptoms and effects not provided.

PARATHYROID GLANDS

  • Location: Located behind the thyroid, comprised of four tiny glands.

  • Function: Secretion of Parathyroid Hormone (PTH) which mobilizes calcium from bones into the bloodstream.

PANCREAS

Location and Dual Function

  • The pancreas is located in the abdomen, behind the stomach.

  • Functions both as an endocrine and exocrine gland.

    • Endocrine Function: Secretes insulin and glucagon through the islets of Langerhans into the bloodstream.

    • Exocrine Function: Secretes pancreatic juice into pancreatic ducts leading to the duodenum.

Islets of Langerhans Hormones

  1. Alpha Cells

    • Secrete glucagon:

      • Function: Increases blood glucose levels when they fall below normal.

  2. Beta Cells

    • Secrete insulin:

      • Function: Decreases blood glucose levels when they rise above normal.

Regulation of Blood Glucose Levels

  • Glucagon and insulin have antagonistic effects on blood glucose levels:

    • When blood glucose levels drop, alpha cells detect and release glucagon, promoting conversion of glycogen to glucose and increasing blood glucose levels.

    • When blood glucose levels rise, beta cells detect the change and release insulin, promoting glucose absorption and conversion to glycogen, thus decreasing blood glucose.

HORMONES AND THEIR FUNCTIONS

Hormone

Target Organ(s)

Function

STH (Growth Hormone)

Bones and muscles

Promotes growth

TSH

Thyroid gland

Stimulates the secretion of thyroxin

ADH

Nephrons of the kidneys

Controls osmoregulation

LH

Ovaries/Testes

Stimulates oogenesis/spermatogenesis

Prolactin

Mammary glands

Stimulates milk production

DIABETES MELLITUS

  • Type 1 Diabetes (Insulin-dependent):

    • Typically starts in childhood, autoimmune in nature where insulin-producing beta cells in the pancreas are destroyed.

    • Result: Glucose remains in blood (hyperglycemia).

    • Treatment: Daily insulin injections, exercise, blood sugar monitoring.

  • Type 2 Diabetes (Non-insulin dependent):

    • Characterized by insulin resistance, usually starts in adulthood, associated with obesity, and lack of exercise.

    • Result: Body produces less insulin or is unable to use insulin.

    • Treatment: Exercise, healthy diet, oral drugs, insulin for severe cases.

ADRENAL GLANDS

Structure and Location

  • Adrenal glands are pyramid-shaped, located on top of each kidney and comprised of an inner medulla and outer cortex.

Adrenal Cortex Functions

  • Secrets steroid hormones:

    1. Aldosterone:

    • Function: Causes sodium reabsorption from nephron filtrate and potassium movement into filtrate.

    1. Cortisol:

    • Function: Increases resistance to stress, maintains blood pressure and glucose levels; serves as an anti-inflammatory and anti-allergic hormone.

  • Adrenocorticotropin (ACTH):

    • Stimulates cortisol production in the adrenal glands.

Adrenal Medulla Functions

  • Secretes adrenaline (epinephrine), the 'fight or flight' hormone, active during moments of sudden danger or excitement, leading to bodily preparations for action.

GONADS

Structure and Function

  • Gonads: reproductive organs (testes in males, ovaries in females).

  • Function: Produce gametes and secrete a variety of sex hormones.

Ovaries Functions

  • Oestrogen:

    • Stimulates physical growth and development of secondary sexual characteristics during puberty.

    • Maturation and functionality of reproductive organs.

  • Progesterone:

    • Works with oestrogen to promote changes in the endometrial lining for pregnancy and maintains the lining during pregnancy; keeps smooth muscle in the uterus relaxed.

Causes of Female Infertility

  • Infrequent/absent ovulation due to changes in FSH and LH secretion (caused by under- or overweight, extreme stress, diabetes, or thyroid malfunction).

  • Blocked oviducts preventing sperm-egg meeting, uterine issues like fibroids preventing embryo implantation.

  • Treatment options: Fertility drugs containing FSH/LH, surgical options (unblocking tubes), assisted conception techniques like IVF.

Testes Functions

  • Secrete Testosterone:

    • Causes rapid physical growth increase, secondary sexual characteristics during puberty, maturation of reproductive organs, maintenance of organ function, and sex drive.

Male Infertility

  • Causes: Issues affecting sperm production or transport in the testes.

  • Treatment options: Hormone injections of male hormones (LH, FSH), surgical interventions to clear blocked ducts.

ADDITIONAL QUESTIONS TO CONSIDER

  • Diagram of homeostatic control of glucose levels provided in accompanying materials.

  • Exercise on identifying and explaining functions of various hormones and homeostatic mechanisms.

  • Discussion of hyperglycemia: definitions, causes, instant fixes, and long-term complications of diabetes.

  • Treatment and management differences between type 1 and type 2 diabetes.