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GCSE Biology Summary Notes Hormonal Control
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Summary Notes on the GCSE Biology topic Hormonal Control, specifically curated for the AQA Biology Exam Board.
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Hormonal ControlThe Endocrine System
The endocrine system is made up of glands that secrete hormones. A hormone is a protein
chemical that produces an effect, secreted by a gland into the bloodstream to target an
organ. Hormones act on glands and stimulate them to release hormones, to bring about
specific effects. They trigger a response from one organ. The target organ has receptors on
the cell membrane that pick up the hormone molecules triggering a response in the cell, can
only bind to specific receptors due to a specific shape.
The pituitary gland releases LH (luteinising hormone), TSH (thyroxine
stimulating hormone) and FSH (follicle stimulating hormone) they
control the growth in children and stimulates thyroid gland to produce
thyroxine to control rate of metabolism.
The thyroid produces ADH (antidiuretic hormone) and thyroxine which control the
metabolic rate of the body.
The pancreas secretes insulin and glucagon which controls the levels of glucose in the blood.
The adrenal gland releases adrenaline which prepares the body for stressful situations, the
fight or flight response.
The ovaries produce oestrogen and progesterone which controls the development of the
female secondary sexual characteristics and menstrual
cycle.
The testes secrete testosterone which control the
development of the male secondary sexual
characteristics, sperm cycle.
In men it stimulates the testes to make sperm and the
male sex hormone testosterone. In women it stimulates
ovaries to produce and release eggs and make female sex
hormone oestrogen.
Some hormones released by the pituitary gland affect other specific endocrine glands. FSH
stimulates the ovaries to make the female sex hormone oestrogen. TSH stimulates the
thyroid gland to make thyroxine which controls your metabolic rate.
Female Reproductive System
The ovaries are a gland and secrete
progesterone and oestrogen.
Nervous System vs Endocrine System
, Endocrine System Nervous System
long lasting effect short effect
slower travel faster travel
travels in blood travels in nerves
chemical messenger electrical impulse
received by organs received by effectors
hormones electrical impulse
secreted by glands receptors detecting a stimulus
Puberty
During puberty big physical changes take place. Reproductive organs become more active
and the body takes on its adult form. Hormone play an important role in human
reproduction at every stage. During puberty, the reproductive hormones control the
development of secondary sexual characteristics.
A primary sexual characteristic is one you are born with, such as ovaries and testes.
A secondary sexual characteristic are ones that develop due to puberty, in males due to
testosterone, facial hair, voice breaks, grow (taller, broader shoulders, longer penis, bigger
testes), pubic and underarm hair. In females due to oestrogen breasts develop, underarm
and pubic hair, grow (broader hips) and menstrual cycle begins.
The Menstrual Cycle
Day 1 – 4: The uterus lining breaks down and the follicle is tiny, menstruation occurs here.
FSH levels are rising, produced in the pituitary gland it is secreted and travels in the
bloodstream to the uterus causing a follicle to mature. It also stimulates oestrogen
production – positive feedback.
Day 5 – 11: Oestrogen levels are rising, produced in the ovaries it stimulates the uterus
lining to thicken. It stimulates LH which inhibits FSH which is negative feedback – else
multiple follicles would mature.
Day 12 – 14: LH levels surge, produced in the pituitary gland. LH causes ovulation and
stimulates progesterone.
Day 15 – 23: Progesterone levels gradually rise, produced in the ovaries. It maintains the
uterus lining and inhibits FSH and LH which stops the cycle repeating too early. The uterus
lining continues to thicken, ready for implantation.
Day 24 – 28: Progesterone levels are falling, therefore FSH can now be secreted and the very
thick uterus lining breaks down.
Hormone Roles
FSH:
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