The human endocrine system

Hormone

A hormone is a chemical substance, produced by a gland and carried in the bloodstream, which alters the activity of specific target organs

What happens to a hormone once it has been used

It is destroyed by the liver

Describe the effects of hormones in comparison to the nervous system

Hormones can control the body, and the effects are much slower than the nervous system, but they last for longer.

differences between nervous and hormonal control

	Nervous	Hormonal
Type of signal	Electrical (chemical at synapses)	Chemical
Transmission of signal	By nerve cells (neurones)	By the bloodstream
Effectors	Muscles or glands	Target cells in particular tissues
Type of response	Muscle contraction or secretion	Chemical change
Speed of response	Very rapid	Slower
Duration of response	Short (until nerve impulses stop)	Long (until hormone is broken down)

What is known as the master gland

The Pituitary Gland in the brain

What does the pituitary gland do?

• It secretes several hormones into the blood in response to the body's condition

• These hormones can also act on other glands to stimulate the release of different types of hormones and bring about effects

Give the source, organ, role and effect of ADH

• Pituitary gland,

• kidneys

• Controlling the water content of the blood

• Increases reabsorption of water by the collecting ducts

Give the source, organ, role and effect of Adrenaline

• Adrenal Glands

• respiratory and circulatory systems

• Preparation for ‘fight or flight’

• Increases breathing rate, heart rate, flow of blood to muscles, conversion of glycogen to glucose

Give the source, organ, role and effect of Insulin

• Pancreas

• Liver

• Controlling blood glucose levels

• Increases conversion of glucose into glycogen for storage

Negative Feedback

A negative feedback control system responds when conditions change from the ideal or set point and returns conditions to this set point. There is a continuous cycle of events in negative feedback.

Stages in Negative Feedback

• if the level of something rises, control systems reduce it again

• if the level of something falls, control systems raise it again

Give an example of negative feedback

• The control of body temperature

• If the body is too hot, it will sweat to release heat

• If the body is too cold, it will shiver to increase the temperature

Thyroxine

• produced from the thyroid gland, which stimulates the basal metabolic rate.

• It controls the speed at which oxygen and food products react to release energy for the body to use.

• Thyroxine plays an important role in growth and development.

TSH

Thyroid Stimulating Hormone

What does low thyroxine levels in the bloodstream do?

Low thyroxine levels in the bloodstream stimulate the hypothalamus to release TRH and this causes the pituitary to release TSH so the thyroid releases more thyroxine. So blood levels return to normal.

What does normal thyroxine levels in the bloodstream do?

Normal thyroxine levels in the bloodstream inhibit TRH release from the hypothalamus and this inhibits the release of TSH from the pituitary, so normal blood levels are maintained.

Why is glucose needed in cells

for respiration

What happens when blood glucose concentration is too high

the pancreas releases insulin which then moves the glucose from the blood into cells

in liver and muscle cells, glucose is converted into glycogen for storage

What happens when blood glucose concentration is too low

the pancreas doesn’t release insulin and so glucose does not get converted into glycogen for storage

What is Type 1 diabetes

Type 1 diabetes is a disorder in which the pancreas fails to produce enough insulin.

It can be detected from an early age

How can you treat type 1 diabetes

By injecting insulin

What is type 2 diabetes

In type 2 diabetes the person's body cells no longer respond to insulin produced by the pancreas.

It is more common in older people.

How can you treat type 2 diabetes

Exercise, diets (specifically diets that cut out carbohydrates as they are digested into glucose)

What does glucagon do?

Glucagon stimulates the release of stored glucose (glycogen) into the blood to raise the blood glucose concentration

Testosterone

made in the testes

controls the development of male secondary sexual characteristics

oestrogen

produced by the ovaries

controls the development of female secondary sexual characteristics

Give some changes during puberty

Boys only	Boys & girls	Girls only
Voice breaks	Pubic hair grows	Voice deepens gradually
Hair grows on face and body	Underarm hair grows	Hips get wider
Body becomes more muscular	Sexual organs grow and develop	Breasts develop
Testes start to produce sperm cells		Ovaries start to release egg cells - menstruation starts