B11: Hormonal coordination

Endocrine system

a coordination and control system consisting of glands that secrete hormones

How does the endocrine system work?

glands secrete hormones into bloodstream; blood carries hormone to target organ(s); target organ has receptors on cell membranes that pick up hormone molecules; response triggered in cell

Examples of fast-acting hormones

insulin, adrenaline

Examples of slow-acting hormones

growth and sex hormones

Location of pituitary gland

brain

Hormones secreted by pituitary gland (two examples)

FSH (in women), ADH

Role of pituitary gland

(aka. master gland) secretes variety of hormones that act on other glands and stimulate them to release hormones

Location of thyroid gland

neck

Hormone secreted by thyroid gland

thyroxine

Role of thyroid gland

controls basal metabolic rate of body, important part in growth and development

Location of pancreas

behind stomach

Hormone secreted by pancreas

insulin, glucagon

Role of pancreas

controls blood glucose levels

Location of adrenal gland

above kidneys

Hormone secreted by adrenal gland

adrenaline

Role of adrenal gland

prepares body for stressful situations (triggers 'flight or flight' response)

Location of ovaries

lower abdomen

Hormone secreted by ovaries

oestrogen

Role of ovaries

controls development of female secondary sexual characteristics, involved in menstrual cycle

Location of testes

scrotum

Hormone secreted by testes

testosterone

Role of testes

controls development of male secondary sexual characteristics, involved in sperm production

Features of hormonal system

• chemical signalling

• transmission by bloodstream

• targeting cells in target organs

• slow, long-lasting response

• irreversible (possibly permanent) effect

Features of nervous system

• electrical signalling

• transmission by neurones

• targeting specific muscles/glands

• rapid, short-lived responses

• reversible, temporary effects

When blood glucose levels are high…

• pancreas releases insulin

• insulin allows glucose to move into cells

• soluble glucose converted to glycogen (insoluble carbohydrate)

• insulin controls storage of glycogen in liver and muscles

• excess glucose converted into lipids and stored

• blood glucose falls

When blood glucose levels are low…

• pancreas releases glucagon

• glucagon makes liver break down glycogen back into glucose

• stored glucose released into bloodstream

• blood glucose rises

Glucose

sugar used in respiration

Glycogen

storage carbohydrate found in liver and muscles

Glucagon

hormone that stimulates liver to break down glycogen to glucose

Type 1 diabetes

disorder in which the pancreas does not produce enough (or any) insulin, usually developed in young children/teenagers

Type 2 diabetes

disorder in which body cells stop responding properly to insulin released, linked to obesity and lack of exercise, risks increase with age

How is type 1 diabetes treated?

insulin injections, controlling carbohydrate intake, exercise

How is type 2 diabetes treated?

controlled carbohydrate intake, exercise/losing weight, drugs which make insulin more effective, insulin injections

Two cures for type 1 diabetes

transplanting pancreas/pancreatic cells, producing insulin-secreting cells from embryonic stem cells

Risks of pancreas transplant

operations are difficult and risky, not enough donors (very few transplants take place), insulin exchanged for immunosuppressants

Risks of producing insulin-secreting cells from embryonic stem cells

ethical issues, insufficient research, not yet tested on humans

Negative feedback system

works to maintain a steady state by triggering responses that counteract a change in environment

In a negative feedback loop…

values (eg levels of thyroxine/insulin) will vary around a normal level within a limited range

When is TSH (thyroid stimulating hormone) produced?

when detected levels of thyroxine in blood below/above normal; amount of TSH released from pituitary gland increases (if levels of thyroxine falls)/decreases (if levels of thyroxine rises); IS controlled by negative feedback

Effect of adrenaline

• increased heart rate and breathing rate

• stored glycogen converted to glucose (for respiration)

• dilated pupils (to allow more light)

• increased mental awareness

• blood to be diverted away from digestive system to muscles of limbs

When is adrenaline produced?

in times of fear/stress to prepare body for 'flight or flight'; once danger is over, adrenal glands stop releasing adrenaline and systems return to resting levels; is NOT controlled by negative feedback

Primary sexual characteristics

ones you are born with; ovaries (in girls) and testes (in boys)

Secondary sexual characteristics

developed during puberty, controlled by reproduction hormones

Oestrogen

main female reproductive hormone, produced by ovaries

Changes taken place in puberty in females

• growth spurt

• hair growth under arms and pubic hair

• breasts develop

• external genitals grow and skin darkens

• fat deposited on hips, buttocks and thighs

• brain matures

• mature eggs start to form every month in ovaries

• uterus grows and becomes active

• menstruation begins

Changes taken place in puberty in males

• growth spurt

• underarm hair

• pubic hair

• facial hair

• skin darkens

• larynx enlarges and voice breaks

• testes grow

• produce sperm throughout lifetime

• shoulder and chest broaden as muscles develop

• brain matures

Hormones involved in menstrual cycle

FSH (follicle stimulating hormone), LH (luteinising hormone), oestrogen, progesterone

Production and role of FSH

• Produced in pituitary gland

• Causes a follicle (containing egg) to mature

• Stimulates oestrogen secretion

Production and role LH

• Produced by the pituitary gland

• Causes ovulation (which then results in formation of corpus luteum, aka. remains of follicle after ovulation)

Production and role of oestrogen

• Produced in ovaries

• Causes uterus lining to grow

• Stimulates LH secretion

• Inhibits FSH secretion

Production and role of progesterone

• Produced in ovaries by corpus luteum

• Maintains uterus lining

• Inhibits LH and FSH secretion

Stages of the menstrual cycle

Stage 1 (day 1-4): menstruation- uterus lining breaks down

'' 2 (day 4-14): uterus lining thickens

'' 3 (day 14-28): ovulation- release of egg

'' 4 (day 28-): uterus lining maintained until cycle repeats