The Endocrine System

Thyroxine

Deficiency Symptoms: Slow metabolism and retarded mental and physical development.

Excess Symptoms: Increased heart rate and blood pressure, weight loss, nervousness and trouble sleeping.

Negative Feedback Mechanism:

  1. The pituitary gland releases a hormone called TSH (Thyroid Stimulating Hormone)
  2. This causes the thyroid to release thyroxine.
  3. The build-up of thyroxine in the blood inhibits the production of further TSH by the pituitary.
  4. This stops the production of more thyroxine.

Hormone supplements

Insulin

The failure of the Islets of Langerhans in the pancreas to produce insulin leads to diabetes.

  • Diabetics must take regular insulin supplements in the form of injections.

Hormone Replacement Therapy (HRT)

At menopause, a woman's ovaries stops making oestrogen and progesterone. This causes hot flushes, night sweating and mood changes.

  • HRT involves taking a daily supplement of oestrogen and progesterone by tablet to relieve the menopausal symptoms.

The endocrine system: A group of glands that produce chemicals called hormones, many of which are proteins.

Hormones: Chemical messengers produced in endocrine glands and transported in the blood to a particular area where they have their effect.

Endocrine glands: Ductless

  • their secretions diffuse directly into the blood.

Exocrine glands: Have ducts to carry their secretions, e.g. Salivary glands.

The main endocrine glands

  1. Pituitary
    Location: Below the brain
    Hormone: TSH
    Function: Stimulates the thyroid to produce thyroxine.
  1. Thyroid
    Location: Around the larynx
    Hormone: Thyroxine
    Function: Controls metabolic rate of body cells.

3.Adrenals
Location: Over each kidney
Hormone: Adrenaline
Function: Prepares the body for fight or flight.

  1. Islets of Langerhans
    Location: In the pancreas
    Hormone: Insulin
    Function: Regulates blood sugar levels.

Comparison of Nerve Action and Hormone Action

Nerve action

  1. Message is electrical
  2. Transmission is rapid

Hormone action

  1. Message is chemical
  2. Transmission is slow