IMAT Biology · Human Anatomy and Physiology
The Brain, the Eye, Hormones and Reproduction
Each brain region has its own jobs, the eye turns light into nerve impulses, and hormones carried in the blood control glucose, growth and the reproductive cycle.
Why this matters
The ministry papers asked which structure sets the circadian rhythm (2023), which hormones of the adrenal gland and pancreas work together (2023), what insulin does (2025) and which hormone drives labour (2026). Earlier papers asked about brain regions (2016, 2017), the eye and rod cells (2020, 2021), hormones in general (2012, 2017), glucose control (2011, 2014) and the menstrual cycle (2015).
Concept 1 of 5: Regions of the brain and their functions
The brain is divided into regions with different jobs. The big folded cerebrum does conscious work; the small cerebellum at the back fine-tunes movement; the brainstem keeps you alive without thinking; and the hypothalamus, deep in the middle, runs homeostasis and links the nervous system to the hormones.
Definition
- The cerebrum has two hemispheres joined by the corpus callosum; its outer layer, the cortex, handles thought, memory, language, voluntary movement and the senses.
- The hippocampus and amygdala lie deep inside the cerebrum: the hippocampus forms new memories, the amygdala handles emotions such as fear.
- The hypothalamus controls the pituitary gland, which hangs just below it.
- The medulla oblongata connects the brain to the spinal cord and controls heart rate, breathing and blood pressure without conscious thought.
- The daily (circadian) rhythm: a small master clock in the hypothalamus drives the pineal gland, which releases melatonin in the dark. Melatonin carries the clock's signal to the rest of the body, so the pineal gland is the gland usually named as regulating the circadian rhythm.
| Region | Main functions |
|---|---|
| Cerebrum (cerebral cortex) | Conscious thought, memory, language, voluntary movement, interpreting senses |
| Corpus callosum | Links the left and right hemispheres |
| Hippocampus | Forming new long-term memories |
| Amygdala | Emotions, especially fear |
| Thalamus | Relays sensory signals to the cortex |
| Hypothalamus | Body temperature, water balance, hunger and thirst; controls the pituitary |
| Pineal gland | Secretes melatonin at night; regulates the circadian rhythm of sleep |
| Cerebellum | Balance, posture and coordination of movement |
| Medulla oblongata | Heart rate, breathing rate, blood pressure; reflexes such as swallowing and coughing |
Practice this conceptself-check · 3 quick reps
Cerebrum and cerebellum are easy to swap
The cerebrum (the large upper brain) holds memory and conscious thought. The cerebellum (the small region at the back, below it) coordinates movement. Loss of memory points to the cerebrum, loss of balance to the cerebellum.
Concept 2 of 5: The eye: its parts, rods and cones, and how light is detected
The front of the eye focuses light, like a camera lens, onto the retina at the back. There, two kinds of light-sensitive cell turn light into nerve impulses: rods work in dim light but see no colour, cones need bright light but see colour and fine detail.
Definition
- Rods: very sensitive, work in dim light, black and white only. Many rods share one nerve pathway, so detail is poor. Their pigment is rhodopsin: light splits it into opsin and retinal (bleaching), which starts the signal. Retinal is made from vitamin A (retinol), so a lack of vitamin A causes night blindness.
- Cones: need bright light, give colour vision (three types, for red, green and blue light) and sharp detail. They are packed in the fovea.
- Accommodation: for a near object the ciliary muscle contracts, the suspensory ligaments slacken and the lens becomes fatter.
- Pupil reflex: in bright light the circular muscles of the iris contract and the pupil gets smaller.
- Impulses travel along the optic nerve to the visual cortex at the back of the cerebrum.
| Part | Function |
|---|---|
| Cornea | Transparent front; does most of the bending of light; has no blood vessels |
| Iris | Coloured muscular ring that controls the size of the pupil |
| Lens | Fine focusing; changes shape for near and far objects |
| Ciliary muscle and suspensory ligaments | Change the shape of the lens |
| Retina | Contains the rods and cones |
| Fovea | Only cones; the sharpest vision |
| Blind spot | Where the optic nerve leaves; no rods or cones |
| Choroid | Blood vessels and dark pigment that stops light reflecting inside the eye |
| Sclera | Tough white outer coat |
Practice this conceptself-check · 4 quick reps
Retinal, retinol, opsin and opsonin
Light splits rhodopsin into opsin and retinal (the aldehyde). Retinol is vitamin A, the raw material. Opsonin is something different: a molecule that marks pathogens for phagocytes.
Concept 3 of 5: Endocrine glands, their hormones and how hormones act
Hormones are chemical messages sent by post rather than by wire. A gland releases them into the blood, they reach every cell, but only cells with the right receptor respond. That makes hormones slower than nerves, but their effects can be widespread and long-lasting.
Definition
- Endocrine glands have no ducts: they release hormones directly into the blood. Exocrine glands (salivary glands, sweat glands, the digestive part of the pancreas) release secretions through ducts.
- Every hormone is a chemical. It travels at the speed of blood flow and can affect one or several target organs.
- Peptide and protein hormones (insulin, glucagon, ADH) and amine hormones such as adrenaline bind receptors on the cell surface and act through a second messenger such as cyclic AMP.
- Steroid hormones (cortisol, aldosterone, oestrogen, progesterone, testosterone) are lipid-soluble: they cross the membrane, bind a receptor inside the cell and change which genes are expressed.
- The anterior pituitary controls several other glands, so pituitary failure has many effects at once: no ADH means large volumes of urine, and no FSH and LH means infertility in both sexes.
| Gland | Hormone | Chemical type | Main effect |
|---|---|---|---|
| Anterior pituitary | FSH, LH, TSH, ACTH, growth hormone, prolactin | Peptide and protein | Controls the gonads, thyroid and adrenal cortex; growth; milk production |
| Posterior pituitary | ADH and oxytocin (made in the hypothalamus) | Peptide | Water reabsorption in the kidney; uterine contraction and milk release |
| Thyroid | Thyroxine; calcitonin | Amine (contains iodine); peptide | Raises metabolic rate; lowers blood |
| Parathyroids | Parathyroid hormone | Peptide | Raises blood |
| Adrenal medulla | Adrenaline | Amine | Fight or flight: raises heart rate, breathing rate and blood glucose |
| Adrenal cortex | Cortisol; aldosterone | Steroid | Raises blood glucose in stress; increases reabsorption |
| Pancreas (islets) | Insulin (beta cells); glucagon (alpha cells) | Peptide | Lowers and raises blood glucose |
| Ovaries | Oestrogen, progesterone | Steroid | Female characteristics; build and keep the uterine lining |
| Testes | Testosterone | Steroid | Male characteristics; sperm production |
| Pineal gland | Melatonin | Amine | Daily sleep rhythm |
Practice this conceptself-check · 4 quick reps
Hormones do not flow down ducts
Endocrine glands are ductless and release hormones straight into the blood. Secretions that flow down ducts, such as bile or pancreatic juice, are exocrine. Steroids such as testosterone and oestrogen are hormones too.
Concept 4 of 5: Blood glucose control: insulin, glucagon and adrenaline
Cells need a steady supply of glucose, but meals arrive in bursts. After a meal insulin stores the extra; between meals glucagon releases the store. In an emergency adrenaline releases it too, so on raising glucose the adrenal gland and the pancreas work together.
Definition
- The islet cells of the pancreas detect blood glucose directly and respond by secreting hormones; the loop needs no brain.
- Glycogenesis: making glycogen from glucose. Glycogenolysis: breaking glycogen down to glucose. Gluconeogenesis: making new glucose from amino acids, lactate or glycerol.
- Insulin is a peptide hormone. It makes muscle and fat cells take up glucose (by adding glucose carriers to their membranes), drives glycogen and fat synthesis, and lowers blood glucose.
- Type 1 diabetes: the immune system destroys the beta cells, so no insulin is made. Type 2 diabetes: insulin is made but cells respond poorly to it.
| Hormone | Made by | Released when | Effects |
|---|---|---|---|
| Insulin | Beta cells of the islets | Blood glucose is high | Glucose uptake into muscle and fat; glycogen and fat made; blood glucose falls |
| Glucagon | Alpha cells of the islets | Blood glucose is low | Liver breaks down glycogen and makes new glucose; blood glucose rises |
| Adrenaline | Adrenal medulla | Stress, fear or exercise | Glycogen breakdown in liver and muscle; blood glucose rises fast |
| Cortisol | Adrenal cortex | Long-term stress | Gluconeogenesis; blood glucose rises |
Practice this conceptself-check · 3 quick reps
Glucagon is a hormone; glycogen is the store
Glucagon (the hormone) causes glycogen (the stored polysaccharide) to be broken down. Insulin does the opposite: it promotes glycogen and fat synthesis and is a peptide, not a steroid, made by the pancreas, not the adrenal gland.
Concept 5 of 5: Reproductive organs, the menstrual cycle, pregnancy and birth
The menstrual cycle is a monthly hand-over between the pituitary and the ovary. Pituitary hormones grow an egg; the ovary's hormones build the uterine lining; a surge releases the egg; and if no embryo arrives, the hormone support collapses and the lining is shed.
Definition
- Male: testes (sperm made in the seminiferous tubules; testosterone from cells between them), epididymis (sperm mature and are stored), sperm duct (vas deferens), seminal vesicles and prostate (add fluid), urethra.
- Female: ovaries (eggs and hormones), oviducts (fertilisation happens here; ciliated epithelium moves the egg), uterus (lining called the endometrium), cervix, vagina.
- Cycle (about 28 days): menstruation (days 1 to 5); follicle phase (FSH grows a follicle, whose oestrogen rebuilds the lining); ovulation (about day 14); luteal phase (the empty follicle becomes the corpus luteum, which makes progesterone).
- Around ovulation LH and FSH reach their peak; oestrogen peaks just before and then falls; progesterone starts to rise.
- If no embryo implants, the corpus luteum breaks down, progesterone falls and menstruation begins. If one implants, its hCG keeps the corpus luteum going until the placenta takes over.
- Birth: oxytocin causes uterine contractions, which cause more oxytocin release (positive feedback).
| Hormone | Made by | Role |
|---|---|---|
| FSH | Anterior pituitary | Growth of a follicle; sperm production in males |
| LH | Anterior pituitary | A surge triggers ovulation and forms the corpus luteum; testosterone production in males |
| Oestrogen | Growing follicle | Rebuilds the uterine lining; a high level triggers the LH surge |
| Progesterone | Corpus luteum, later the placenta | Keeps the lining thick; inhibits FSH and LH |
| hCG | The early embryo | Keeps the corpus luteum alive; detected by pregnancy tests |
| Oxytocin | Made in the hypothalamus, released by the posterior pituitary | Uterine contractions in labour; milk release |
| Prolactin | Anterior pituitary | Milk production |
Practice this conceptself-check · 4 quick reps
Progesterone comes from the corpus luteum, not the pituitary
The pituitary makes FSH and LH. The ovary makes oestrogen (follicle) and progesterone (corpus luteum). Oxytocin, not LH or FSH, drives the contractions of labour.
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (5)
Regions of the brain and their functions9 rows
| Region | Main functions |
|---|---|
| Cerebrum (cerebral cortex) | Conscious thought, memory, language, voluntary movement, interpreting senses |
| Corpus callosum | Links the left and right hemispheres |
| Hippocampus | Forming new long-term memories |
| Amygdala | Emotions, especially fear |
| Thalamus | Relays sensory signals to the cortex |
| Hypothalamus | Body temperature, water balance, hunger and thirst; controls the pituitary |
| Pineal gland | Secretes melatonin at night; regulates the circadian rhythm of sleep |
| Cerebellum | Balance, posture and coordination of movement |
| Medulla oblongata | Heart rate, breathing rate, blood pressure; reflexes such as swallowing and coughing |
The eye: its parts, rods and cones, and how light is detected9 rows
| Part | Function |
|---|---|
| Cornea | Transparent front; does most of the bending of light; has no blood vessels |
| Iris | Coloured muscular ring that controls the size of the pupil |
| Lens | Fine focusing; changes shape for near and far objects |
| Ciliary muscle and suspensory ligaments | Change the shape of the lens |
| Retina | Contains the rods and cones |
| Fovea | Only cones; the sharpest vision |
| Blind spot | Where the optic nerve leaves; no rods or cones |
| Choroid | Blood vessels and dark pigment that stops light reflecting inside the eye |
| Sclera | Tough white outer coat |
Endocrine glands, their hormones and how hormones act10 rows
| Gland | Hormone | Chemical type | Main effect |
|---|---|---|---|
| Anterior pituitary | FSH, LH, TSH, ACTH, growth hormone, prolactin | Peptide and protein | Controls the gonads, thyroid and adrenal cortex; growth; milk production |
| Posterior pituitary | ADH and oxytocin (made in the hypothalamus) | Peptide | Water reabsorption in the kidney; uterine contraction and milk release |
| Thyroid | Thyroxine; calcitonin | Amine (contains iodine); peptide | Raises metabolic rate; lowers blood |
| Parathyroids | Parathyroid hormone | Peptide | Raises blood |
| Adrenal medulla | Adrenaline | Amine | Fight or flight: raises heart rate, breathing rate and blood glucose |
| Adrenal cortex | Cortisol; aldosterone | Steroid | Raises blood glucose in stress; increases reabsorption |
| Pancreas (islets) | Insulin (beta cells); glucagon (alpha cells) | Peptide | Lowers and raises blood glucose |
| Ovaries | Oestrogen, progesterone | Steroid | Female characteristics; build and keep the uterine lining |
| Testes | Testosterone | Steroid | Male characteristics; sperm production |
| Pineal gland | Melatonin | Amine | Daily sleep rhythm |
Blood glucose control: insulin, glucagon and adrenaline4 rows
| Hormone | Made by | Released when | Effects |
|---|---|---|---|
| Insulin | Beta cells of the islets | Blood glucose is high | Glucose uptake into muscle and fat; glycogen and fat made; blood glucose falls |
| Glucagon | Alpha cells of the islets | Blood glucose is low | Liver breaks down glycogen and makes new glucose; blood glucose rises |
| Adrenaline | Adrenal medulla | Stress, fear or exercise | Glycogen breakdown in liver and muscle; blood glucose rises fast |
| Cortisol | Adrenal cortex | Long-term stress | Gluconeogenesis; blood glucose rises |
Reproductive organs, the menstrual cycle, pregnancy and birth7 rows
| Hormone | Made by | Role |
|---|---|---|
| FSH | Anterior pituitary | Growth of a follicle; sperm production in males |
| LH | Anterior pituitary | A surge triggers ovulation and forms the corpus luteum; testosterone production in males |
| Oestrogen | Growing follicle | Rebuilds the uterine lining; a high level triggers the LH surge |
| Progesterone | Corpus luteum, later the placenta | Keeps the lining thick; inhibits FSH and LH |
| hCG | The early embryo | Keeps the corpus luteum alive; detected by pregnancy tests |
| Oxytocin | Made in the hypothalamus, released by the posterior pituitary | Uterine contractions in labour; milk release |
| Prolactin | Anterior pituitary | Milk production |
Watch out for (5)
- Cerebrum and cerebellum are easy to swap→ Regions of the brain and their functions
- Retinal, retinol, opsin and opsonin→ The eye: its parts, rods and cones, and how light is detected
- Hormones do not flow down ducts→ Endocrine glands, their hormones and how hormones act
- Glucagon is a hormone; glycogen is the store→ Blood glucose control: insulin, glucagon and adrenaline
- Progesterone comes from the corpus luteum, not the pituitary→ Reproductive organs, the menstrual cycle, pregnancy and birth
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