Endocrine system

ENDOCRINE SYSTEM.

LESSSON OBJECTIVES. Define the term: hormone.

Outline the Endocrine System.

Compare action, distinguishing between exocrine & endocrine glands.

State the location of the principal glands in the human.

Outline for each gland, one hormone & its function.

Explain 1 Hormone giving a description of its deficiency symptoms, excess symptoms & corrective measures

Name 2 examples of hormone supplements & their use

The endocrine system is a group of specialised tissues (glands) that produce chemicals called hormones, manyof which are proteins.

Thyroid

Pancreas

Adrenal

Pituitary

O

The ability to detect change and to respond is called sensitivity. Response is a form of defence that allows organisms to survive.

Response in the Human

----- The Endocrine System

The endocrine glands are often called ductless glands.

Exocrine glands have ducts to carry their secretions,e.g. salivary glands.

The endocrine glands interact with the nervous system to provide the communication, co-ordination and control within the body.

Hormones are chemical ‘messengers’, produced inspecialised glands, and transported in the blood to aparticular area (the target organ), where they have theireffect.

The action of hormones is slower and more general thannerve action and they control mainly long-term changes suchas growth, metabolism and sexual maturity.

On passing through the liver, the hormones are broken down and excreted by the kidneys.

The nervous system relies on electrical signals, carried by specialised cells, and is involved in fast responses.

COMPARISON OF THE ENDOCRINE AND NERVOUS SYSTEMS.

Endocrine Nervous

Cells involved Gland Sense receptor

Message Chemical (Hormone)

Electrical(Impulse)

Carried by Blood Nerve cell

Message sent to Cells throughout the body

A specific cell or tissue

Received by Target organ Effector (muscle or gland)

Endocrine Nervous

Speed of transmission

Usually slow Rapid

Effects Can be widespread Localised usually

Duration long-lasting (hours)

Usually brief (seconds)

COMPARISON OF THE ENDOCRINE AND NERVOUS SYSTEMS

ENDOCRINE GLANDS

Most hormone activity is controlled directly or indirectly by the hypothalamus and pituitary gland.

The brain region keeps a check on internal organs and activities, such as the level of carbon dioxide or water in the blood.

The pituitary is often called the ‘master gland’, as many of its hormones trigger other glands to release theirs.

It produces ADH to stimulate water reabsorption in the kidneys, TSH which stimulates the thyroid gland to release thyroxine, and FSH which controls the functions of the reproductive organs.

•The pituitary gland produces the ‘growth hormone’ This causes the body to absorb amino acids and form proteins therefore allowing growth and elongation of the bones of the skeleton.

Overproduction of this hormone produces gigantism and underproduction causes dwarfism.

•The hypothalamus gland produces hormones that control the pituitary gland in response to messages from the brain and other hormones. An example of a hormone produced by the hypothalmus is growth hormone releasing factor (GHRF) which causes the production of growth hormone in the pituitary.

THE PILEAL GLAND.

• The pileal gland is a small gland within the brain which produces melatonin, the hormone produced in the dark.

• It is involved in biological rhythms such as ovulation, sleep and activity patterns and sexual maturity.

The thyroid gland, in the neck, produces thyroxine, which stimulates metabolism.

The parathyroid produces parathyroid hormone, which increases blood calcium levels.

In oral contraceptives, oestrogen and progesterone are taken to prevent pregnancy – hormone supplement

PANCREAS gland:

In some people, the pancreas cannot produce insulin, which results in diabetes mellitus.

Glucose cannot get into cells, which disrupts metabolism.

Regular daily injections of insulin are required – hormone supplement.

OVARIES gland:

The pancreas is both an endocrine and exocrine gland.

Insulin stimulates cells to absorb glucose from the blood, and store it as glycogen.

The Islets of Langerhans produce insulin, while the rest produces enzymes for digestion.

The adrenal gland produces adrenaline, which helps the body cope with emergencies —the ‘flight or fight’ hormone.

The ovary produces oestrogen and progesterone to prepare the female for pregnancy.

The testes produce testosterone which triggers sperm production and growth in the male.

Endocrine glands can sometimes malfunction

Low levels of thyroxine reduce the rate of metabolism and can result in retarded mental and physical development (cretinism)

Symptoms include tiredness, lack of energy, slow mental and physical activity and weight gain.

Taking the hormone in tablet form once a day can solve the problem – hormone supplement

THYROID gland:

Excess thyroxine can greatly increase metabolic rate. Treatment is often by removal of part of the gland.

DISORDERS of the Endocrine System

THYMUS GLAND.

• Located behind the breastbone in the upper chest.

• Produces the hormone thymosin which causes the lymphocytes to mature and become active.

• Involved in the immune system.

ADRENAL GLANDS.

• Located at the top of the kidneys.• Used in the body to cope with stress.• Outer adrenal cortex produces the hormone

corticosteroids which help to control long term stress.

• The inner medulla produces adrenaline which is the fright or flight hormone.

ADRENALINE EFFECTS.

• Increase blood flow to the heart, muscles and brain.

• Reduced blood flow to the skin and kidneys helping to reduce blood loss.

• Opens the bronchioles to open allowing increased air flow.

• Increases glucose levels in the body.• Increases mental alertness.

CONTROL OF THYROXINE.

NORMAL CONC. OF THYROXINE:

• If it is normal, it inhibits the pituitary from releasing thyroid stimulating hormone (TSH) therefore no further thyroxine is made.

LOW CONC. OF THYROXINE:

• When they fall below the required level, the pituitary gland produces thyroid stimulating hormone (TSH) causing more thyroxine to be made until it resumes to normal levels.

CONTROL OF THYROXINE LEVELS.

GOITRE.

• This is an enlargement of the thyroid gland which indicates a underproduction of thyroxine caused by a lack of iodine in the diet.

• A low conc causes the pituitary to produce TSH which is carried by the blood to the thyroid.

• TSH combines with iodine in the thyroid to produce thyroxine, if this cannot happen TSH is stored in the thyroid causing it to swell (goitre).

• This can be treated by the intake of iodine in the diet

EXAM QUESTIONS.

• 2008 Q13 C (II)

• 2007 Q4, Q15 B

• 2005 Q14C