Homeostasis and Response
Map Your Gaps
Card 1 of 10
Swipe right if you know it, left if you don't
✔ Know
✖ Don't know
Homeostasis
Homeostasis is the regulation of internal conditions to maintain optimum conditions for cell function, in response to internal and external changes.
Every control system in the body follows the same receptor-coordinator-effector pattern.
Homeostasis — Key Knowledge
- Conditions controlled body temperature, blood glucose concentration, water levels, ion levels
- Control systems have three components receptors detect stimuli, coordination centres process information, effectors bring about responses
- Effectors muscles or glands
- Automatic control may involve nervous responses or chemical/hormonal responses
The nervous system
The nervous system enables rapid reactions to surroundings and coordinates behaviour.
The nervous system produces fast, short-lived responses — contrast this with the slower, longer-lasting hormonal system.
The nervous system — Key Knowledge
- Pathway stimulus, receptor, sensory neurone, relay neurone in CNS, motor neurone, effector
- Central nervous system brain + spinal cord
- Effectors muscles contract or glands secrete
- Synapses junctions between neurones where neurotransmitters diffuse across the gap to trigger the next impulse
Reflex arcs
Reflexes are rapid, automatic responses that protect the body — they bypass the conscious brain.
Reflexes are fast because the signal goes through the spinal cord, not the brain.
Reflex arcs — Key Knowledge
- Reflex arc pathway receptor, sensory neurone, relay neurone in spinal cord, motor neurone, effector
- Automatic not learned, not under conscious control
- Protective function e.g. pulling hand from a hot object
The brain
The brain is made of billions of interconnected neurones and controls complex behaviour.
Our understanding of the brain is still limited, making treatment of brain disorders difficult.
The brain — Key Knowledge
- Cerebral cortex consciousness, intelligence, memory, language
- Cerebellum balance, coordination of movement
- Medulla oblongata unconscious activities — heartbeat, breathing
- Studying the brain CT scans, MRI scans, studying patients with brain damage, electrical stimulation
The eye
The eye is a sense organ containing receptors that detect light.
Accommodation questions often come up — remember ciliary muscles and suspensory ligaments work as a pair.
The eye — Key Knowledge
- Cornea refracts light
- Iris controls pupil size to regulate light entry
- Lens focuses light — changes shape for near and distant objects
- Retina contains light receptors
- Optic nerve carries impulses to the brain
- Accommodation ciliary muscles contract and suspensory ligaments slacken for near objects — lens goes fat; ciliary muscles relax and ligaments pull tight for distant objects — lens goes thin
- Myopia short-sightedness — corrected by concave lens or laser surgery
- Hyperopia long-sightedness — corrected by convex lens or laser surgery
The endocrine system
The endocrine system is made up of glands that secrete hormones directly into the blood to act on target organs.
The pituitary gland is called the master gland because it controls the release of hormones from other glands.
The endocrine system — Key Knowledge
- Pituitary gland master gland — secretes hormones that act on other glands
- Thyroid gland, Adrenal glands, Pancreas, Ovaries female
- Testes male
- Hormones vs nerves hormones are chemical messengers, slower acting, longer lasting, carried in blood
Blood glucose regulation
The pancreas monitors blood glucose and releases hormones to keep it within a normal range.
Insulin and glucagon have opposite effects — a common exam comparison.
Blood glucose regulation — Key Knowledge
- Blood glucose too high pancreas releases insulin, cells take up glucose, liver converts glucose to glycogen
- Blood glucose too low pancreas releases glucagon, liver converts glycogen back to glucose
- Type 1 diabetes pancreas produces little or no insulin — autoimmune, treated with insulin injections
- Type 2 diabetes body cells no longer respond to insulin — linked to lifestyle, managed by diet and exercise
Reproductive hormones and the menstrual cycle
Four hormones interact to control the menstrual cycle in a feedback loop.
The interaction between these four hormones is a negative feedback loop — each one influences the others.
Reproductive hormones and the menstrual cycle — Key Knowledge
- FSH from pituitary — stimulates egg maturation and oestrogen production
- Oestrogen from ovaries — thickens uterus lining, inhibits FSH, stimulates LH release
- LH from pituitary — triggers ovulation
- Progesterone maintains uterus lining
- Cycle sequence FSH rises, egg matures, oestrogen rises, LH surges, ovulation occurs, progesterone maintains lining
Contraception and fertility treatment
Hormones can be used to prevent or assist pregnancy.
Hormonal contraceptives work by mimicking pregnancy hormones to suppress the normal cycle.
Contraception and fertility treatment — Key Knowledge
- Hormonal contraception pill, implant, injection — prevent ovulation or thicken cervical mucus
- Barrier methods condoms, diaphragm — physically block sperm
- Other methods intrauterine devices, surgical sterilisation
- Fertility treatment FSH and LH given to stimulate ovulation
- IVF eggs collected, fertilised externally, embryos implanted
Plant hormones
Auxin is a plant hormone that controls how shoots and roots respond to light and gravity.
Auxin has opposite effects in shoots and roots — it promotes elongation in shoots but inhibits it in roots.
Plant hormones — Key Knowledge
- Phototropism growth response to light — shoot bends towards light
- Gravitropism growth response to gravity — roots grow downwards
- Auxin mechanism in shoots moves to shaded side, causes cells to elongate more, shoot bends towards light
- Auxin mechanism in roots accumulates on lower side, high concentration inhibits root cell growth, root grows downwards
- Uses of plant hormones auxins as weedkillers and rooting powder, gibberellins for seed germination and flowering, ethene for ripening fruit
Map your gaps
Homeostasis and Response
0%confident
✔
0
0
❓
0
0
✖
0
0