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:
- The pituitary gland releases a hormone called TSH (Thyroid Stimulating Hormone)
- This causes the thyroid to release thyroxine.
- The build-up of thyroxine in the blood inhibits the production of further TSH by the pituitary.
- 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
- Pituitary
Location: Below the brain
Hormone: TSH
Function: Stimulates the thyroid to produce thyroxine.
- 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.
- Islets of Langerhans
Location: In the pancreas
Hormone: Insulin
Function: Regulates blood sugar levels.
Comparison of Nerve Action and Hormone Action
Nerve action
- Message is electrical
- Transmission is rapid
Hormone action
- Message is chemical
- Transmission is slow