Chemical Co-ordination in Humans

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Human metabolism - regulated by series of hormones produced by different endocrine glands.

These endocrine glands form an integrated system (keeps body functioning at optimum level)

Levels of these hormones must be kept within narrow limits (homeostasis)

Endocrine and Exocrine Glands

EXOCRINE GLANDS

secrete their products (often enzymes) through a duct usually into a cavity in the body

eg: salivary gland secretes saliva into the mouth cavity

ENDOCRINE GLANDS

secrete products (hormones) directly into the blood which carries them to their target organs

eg. adrenal gland secretes adredalin into the blood

HOW THE ENDOCRINE SYSTEM WORK

Made up of 3 main components:

Endocrine glands - secrete chemical messengers (hormones), found in all parts of the body.

Hormones - large organic compounds (mainly protein/sometimes lipids), secreted into blood where the reach target organs to cause a specific response.

Receptors - complex molecules found on the cell membrane of the target organ once they have been activated by specific hormones.

Main Endocrine Glands

1. HYPOPHYSIS OR PITUITARY GLAND

The master gland, which regulates the functioning of the other endocrine glands.

Found in the small cavity in the skull under the brain.

Its connected to the hypothalamus of the brain.

Growth hormone = regulates growth of the body (especially bones + muscles)

Undersecretion - leads to dwarfism

Oversecretion in youth - leads to gigantism (as all bones in limbs grown)

Oversecretion in adulthood - leads to acromegaly (which all bones in hands, feet + face grow)

Thyroid-stimulating hormone (TSH) = stimulates the thyroid gland to produce thyroxin

Reproductive regulating hormones = FSH/ LH are produced to control functioning of the ovaries & testes

Prolactin = stimulates the mammary glands to produce milk

2. HYPOTHALAMUS

Found on the underside of brain.

Produces 2 hormones which are released from the pituitary gland.

ADH = controls reabsorption of water in the kidneys & thus regulates blood pressure

Oxytocin = stimulates the uterus to contract to start the birth process

3. THYROID GLAND

Found at the base of the neck (just below the larynx).

Consists of 2 lobes (one on each side of the trachea).

Functions

Secretes thyroxin (contains an element of ioidine)

Thyroxin regulates the basal metabolic rates (the rate at which respiration occurs in all body cells)

Necessary for proper growth & development of all body organs

Increases activity of nervous system

Increases cardio output & heat beat

Effects of thyroid malfunction

in childhood, insufficient thyroxin leads to cretinism (mental development & physical growth are retarded)

In adulthood, insufficient thyroxin causes myxoedema & low metabolic rate (leads to weight increase & slow down of mental alertness & reactions)

Too much thyroxin increases metabolic rate causing weight loss, restlessness & nervous tension (eyeballs may protrude causing exopthalmic goitre)

Goitre = insufficient iodine prevents thyroxin production, leading to an enlargement of the thyroid gland.

4. ADRENAL GLANDS

2 adrenal glands (one on top of each kidney).

Adrenalin = the emergency hormone (prepares the body to cope with dangerous & stressful situations) - flight or flight.

Increases heart beat and circulation.

Raises blood pressure.

Speeds up conversion of glycogen to glucose in the liver (thus raising glucose levels).

Dilates bronchioles & speeds up breathing rate.

Increases skeletal muscle tone.

Constricts blood vessels leading to the skin & digestive system while dilating those supplying the heart, brain & muscles.

Dilates the pupils of the eye for clearer vision.

Makes body hair stand on end (goose bumps).

Cortisone = reduces swelling & inflammation and helps control water balance in body.

Aldosterone = regulates the salt balance in body by controlling reabsorption of Na,K & Cl ions in kidney.

5. ISLETS OF LANGERHANS

Specialised groups of endocrine cells scattered throughout the pancreas.

Composed of 2 different types of cells (alpha & beta cells).

They control the blood glucose level by producing insulin & glucagon.

Glucagon

produced by the alpha cells when blood glucose level drops too low.

stimulates the liver to break down stored glycogen into glucose & releases it into the blood.

raises the blood glucose level.

Insulin

produced by beta cells when blood glucose levels rises above ideal.

lowers the amount of glucose in the body by stimulating the liver to convert glucose to glycogen & storing it or stimulating the absorption & break down of glucose by cells (especially muscles).

if pancreas odes not produce insulin, a person will suffer from diabetes.

6. REPRODUCTIVE ORGANS OR GONADS

Testes = secrete the male hormone (testosterone) which controls sperm production & development of male body characteristics.

Ovaries = secrete 2 female hormones (oestrogen & progesterone) which control ovulation & development of female body characteristics.

Control of Hormone production: negative feedback

The level of different hormones must be kept withing a narrow range for optimum body functioning.

Pituitary gland controls output of the other glands by a negative feedback mechanism.

This involves a complex interaction between 2 hormones (with an increase of 1 hormone causing a decrease in the level of another).

TSH and thyroxin levels

if thyroxin level in body dis too low - pituitary produces TSH which stimulates the thyroid to produce more thyroxin.

when thyroxin levels are correct - pituitary reduces the amount of TSH produced, so less thyroxin is produced preventing the thyroxin levels from rising too high.

Insulin, glucagon & the blood glucose level

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Insulin, glucagon and the blood glucose level

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