IMAT Biology · Formula sheet

Human Anatomy and Physiology formulas

3 formulas, 31 reference tables and 36 common traps for IMAT Biology Human Anatomy and Physiology, grouped by subtopic.

Tissues, Bone and Homeostasis

The four basic tissue types and how they build organs

Tissue	Kind	Where found	Job
Epithelial	Squamous: flat cells, one layer thick	Alveoli, capillary walls (endothelium), Bowman's capsule	Short path for diffusion and filtration
Epithelial	Ciliated columnar, with mucus-making goblet cells	Trachea, bronchi, oviducts	Moves mucus, or an egg, along the tube
Epithelial	Cuboidal	Kidney tubules, glands	Secretion and absorption
Epithelial	Stratified squamous: many layers	Epidermis of the skin, mouth, oesophagus	Resists wear and drying
Connective	Cartilage, bone, blood, fat, tendons, ligaments	Throughout the body	Support, joining, transport, storage
Muscle	Skeletal, cardiac, smooth	Attached to bones; heart wall; walls of gut and blood vessels	Contraction
Nervous	Neurones and supporting glial cells	Brain, spinal cord, nerves	Carries electrical signals

Blood is a connective tissue: its cells sit in a liquid matrix, the plasma.

Bone cells, cartilage and the structures of a joint

Structure	What it is	Job
Osteoblast	Bone-building cell	Secretes collagen and lays down calcium phosphate to make new matrix
Osteocyte	Former osteoblast trapped in the hard matrix	Maintains the bone around it and senses mechanical load
Osteoclast	Large cell with many nuclei	Dissolves (resorbs) bone matrix, releasing calcium into the blood
Cartilage	Chondrocytes in a collagen matrix, no blood supply	Smooth, shock-absorbing joint surfaces; flexible support
Tendon	Tough, hardly stretchy bundle of collagen	Joins a muscle to a bone, so the muscle can pull it
Ligament	Collagen with some elastic fibres	Joins bone to bone and holds a joint together
Synovial membrane and fluid	Lining of a movable joint capsule	Fluid lubricates the joint and feeds the cartilage

Memory aid: osteoblasts build, osteoclasts cut away.

Homeostasis and negative feedback loops

Controlled value	Receptor	Control centre	Effectors
Core temperature	Thermoreceptors in the skin and hypothalamus	Hypothalamus	Sweat glands, skin arterioles, skeletal muscle
Blood glucose	Alpha and beta cells of the pancreatic islets	The pancreas itself	Liver, muscle and fat cells
Blood water content	Osmoreceptors in the hypothalamus	Hypothalamus, via ADH from the posterior pituitary	Collecting ducts of the kidney
Blood carbon dioxide and pH	Chemoreceptors in the medulla, aorta and carotid arteries	Medulla oblongata	Diaphragm and intercostal muscles
Blood pressure	Baroreceptors in the aorta and carotid arteries	Medulla oblongata	Heart and arterioles

Temperature control: responses to heat and to cold

Effector	Response when too hot	Response when too cold
Skin arterioles	Vasodilation: more blood flows near the surface and loses heat	Vasoconstriction: less blood flows near the surface
Sweat glands	Secrete sweat, which evaporates and removes heat	Little or no sweat
Skeletal muscle	No shivering	Shivering: rapid contractions release heat from respiration
Hair erector muscles	Relax, hairs lie flat	Contract, hairs stand up and trap air (a small effect in humans)
Metabolic rate	Not raised	Raised by thyroxine and adrenaline

Common traps

Skin is an organ, endothelium is a tissue

Options often mix the two levels. Skin contains several tissues, so it is an organ. Endothelium, cartilage and blood are each a single tissue, even though blood flows.

Tendons join muscle to bone, ligaments join bone to bone

The two are often swapped in the options. A tendon transmits the pull of a muscle to a bone. A ligament holds two bones together at a joint. Neither carries nerve impulses or stores energy for the muscle.

Positive feedback does not mean good feedback

Positive and negative describe the direction of the response, not whether it helps. Negative feedback opposes the change and keeps things stable; positive feedback amplifies it and is used only when a process must be driven to completion.

Capillaries do not move towards the skin

Flushed skin is caused by arterioles widening so more blood flows through the capillaries already there. Options saying the capillaries move closer to the surface are wrong.

The Heart, the Cardiac Cycle and Blood Vessels

Learn this subtopic in the notes

Cardiac output, stroke volume and heart rate

Cardiac output

CO = SV \times HR \qquad SV = EDV - ESV

$CO$ cardiac output, in mL/min or L/min
$SV$ stroke volume, in mL per beat
$HR$ heart rate, in beats per minute
$EDV, ESV$ volume in the ventricle at the end of diastole and at the end of systole, in mL

Double circulation and the main blood vessels

Vessel	From and to	Oxygen content	Notable feature
Aorta	Left ventricle to the body	High	Highest blood pressure
Pulmonary artery	Right ventricle to the lungs	Low	The only artery with deoxygenated blood; high $\mathrm{CO_2}$
Pulmonary vein	Lungs to the left atrium	High	The only vein with oxygenated blood; lowest $\mathrm{CO_2}$
Venae cavae	Body to the right atrium	Low	Lowest blood pressure
Hepatic portal vein	Gut to the liver	Low	Highest glucose and amino acids after a meal
Hepatic vein	Liver to the vena cava	Low	Carries the urea the liver has just made
Renal artery	Aorta to the kidney	High	Still carries urea to be removed
Renal vein	Kidney to the vena cava	Low	Lowest urea concentration in the body

Heart structure, the pacemaker and the control of heart rate

Structure	Where	Job
Sinoatrial node (SAN)	Wall of the right atrium	Pacemaker: starts each wave of excitation, which spreads over both atria
Atrioventricular node (AVN)	Between the atria and the ventricles	Delays the wave by about 0.1 s so the atria empty first
Bundle of His and Purkinje fibres	In the septum and the ventricle walls	Carry the wave to the apex, so the ventricles contract from the bottom up
AV valves	Between each atrium and ventricle	Stop backflow into the atria when the ventricles contract
Semilunar valves	At the base of the aorta and the pulmonary artery	Stop backflow into the ventricles when they relax
Cardiovascular centre	Medulla oblongata	Adjusts heart rate through sympathetic and parasympathetic nerves

The cardiac cycle: pressure changes and valve positions

Phase	Atria	Ventricles	AV valves	Semilunar valves
Atrial systole	Contract: volume falls, pressure rises	Relaxed, receiving the last blood	Open	Closed
Start of ventricular systole	Relaxed, begin to fill	Contract; pressure rises above the atria but not yet above the arteries	Closed (first sound)	Closed
Ventricular ejection	Relaxed, filling	Pressure above the aorta and pulmonary artery: blood leaves	Closed	Open
Start of ventricular diastole	Relaxed, filling	Relax; pressure falls below the arteries	Closed	Close (second sound)
Passive filling	Relaxed; blood flows through	Relaxed; pressure below the atria	Open	Closed

Common traps

Artery does not mean oxygenated

An artery is any vessel carrying blood away from the heart. The pulmonary artery carries blood low in

\mathrm{O_2}

to the lungs, and the pulmonary vein carries blood rich in

\mathrm{O_2}

back to the heart.

The brain changes the heart rate but does not start the beat

Each beat starts at the sinoatrial node. The medulla only adjusts the rate through autonomic nerves. Pick the medulla oblongata, not the cerebrum or cerebellum, for the nervous control of heart rate.

Valves follow pressure, not timing words

Do not learn the cycle as a list of times. Compare the pressure on each side of a valve: higher upstream means open, higher downstream means closed. An option saying an AV valve is open while its ventricle contracts is always wrong.

Left and right contract together

Both atria contract together, then both ventricles. The right atrium does not contract at the same moment as the left ventricle, and one AV valve does not open as the other closes.

Convert litres to millilitres before dividing

Cardiac output is usually given in L/min and stroke volume in mL. Dividing litres by beats per minute gives litres per beat, so 20 L/min at 160 per minute is 0.125 L, which is 125 mL, not 0.125 mL.

Blood Cells, Immune Defences and Blood Groups

Learn this subtopic in the notes

Blood: plasma, red cells, white cells and platelets

Component	Structure	Main job
Plasma	Water with glucose, amino acids, ions, urea, hormones and plasma proteins (albumin, fibrinogen, antibodies)	Transport; carries most $\mathrm{CO_2}$ as hydrogencarbonate ions
Red blood cell (erythrocyte)	Biconcave disc, no nucleus, full of haemoglobin	Carries $\mathrm{O_2}$ from the lungs to the tissues
Neutrophil	Lobed nucleus, granular cytoplasm; the commonest white cell	Phagocytosis; first to arrive at an infection
Monocyte and macrophage	Large cell with a kidney-shaped nucleus; becomes a macrophage in tissues	Phagocytosis and presenting antigens to lymphocytes
Lymphocyte	Large round nucleus, little cytoplasm	Specific immunity: B cells make antibodies, T cells kill or coordinate
Platelet	Cell fragment without a nucleus	Starts blood clotting

Non-specific defences: barriers, phagocytes and inflammation

Defence	How it works	Where
Skin	Tough outer layer of dead keratinised cells; slightly acidic surface	Body surface
Mucus and cilia	Mucus traps microbes and dust; cilia sweep it up to the throat	Airways
Stomach acid	pH about 2 kills most swallowed microbes	Stomach
Lysozyme	Enzyme that breaks bacterial cell walls	Tears, saliva, nasal mucus
Phagocytes	Engulf and digest pathogens	Blood and tissues
Inflammation	Histamine causes vasodilation and leaky capillaries	Site of injury or infection

B and T lymphocytes, antibodies and immune memory

Cell	Made in	Matures in	Job
B lymphocyte	Bone marrow	Bone marrow	Binds antigen, divides, becomes plasma cells and memory cells
Plasma cell	Lymph nodes and spleen, from a B cell	Already mature	Secretes large amounts of one antibody
Helper T cell	Bone marrow	Thymus	Releases cytokines that activate B cells, killer T cells and macrophages; the cell HIV destroys
Cytotoxic (killer) T cell	Bone marrow	Thymus	Kills body cells infected by viruses, and cancer cells
Memory B and T cells	Bone marrow	As their parent cell	Survive for years and start a fast secondary response

Active and passive immunity, and how vaccines work

Type	How it is gained	Memory cells	Example
Natural active	Catching the disease	Yes, long-lasting	Immunity after recovering from measles
Artificial active	Vaccination	Yes, long-lasting	The measles, mumps and rubella vaccine
Natural passive	Antibodies cross the placenta, or come in breast milk	No, lasts weeks to months	Protection of a newborn baby
Artificial passive	Injection of ready-made antibodies	No, lasts weeks	Antivenom after a snake bite; tetanus antitoxin

ABO and Rhesus blood groups, transfusions and transplants

Blood group	Antigens on red cells	Antibodies in plasma	Can safely receive red cells from
A	A	Anti-B	A and O
B	B	Anti-A	B and O
AB	A and B	Neither	A, B, AB and O
O	Neither	Anti-A and anti-B	O only
Rh negative	No D antigen	Anti-D only after exposure	Rh negative only

Common traps

Red cells do not fight infection or clot blood

Their one main job is carrying

\mathrm{O_2}

. White cells defend, platelets and fibrin clot, and

\mathrm{CO_2}

goes to the lungs (mostly in the plasma as hydrogencarbonate), never to the liver.

Beta cells are not immune cells

Beta cells are in the pancreas and make insulin. The cells that defend against infection are phagocytes and lymphocytes (B cells and T cells), plus the antibodies that plasma cells make.

B for bone marrow, T for thymus

Both kinds of lymphocyte are formed from bone marrow stem cells. B cells also mature there; only T cells are processed in the thymus. An option saying B cells mature in the thymus is wrong.

Passive immunity has no memory

Received antibodies are proteins that are slowly broken down. Because the person's own B cells were never activated, no memory cells form and the protection does not last.

Universal donor means no antigens, not no antibodies

Group O plasma does contain anti-A and anti-B. Group O is the universal donor of red cells because those cells carry neither A nor B antigen, so the recipient's antibodies have nothing to attack.

Airways, Breathing and Gas Transport

Learn this subtopic in the notes

Minute ventilation and dead space

Ventilation

V_E = V_T \times f \qquad V_A = (V_T - V_D) \times f

$V_E$ minute ventilation, in mL/min
$V_T$ tidal volume, in mL
$f$ breathing rate, in breaths per minute
$V_D$ dead space volume, in mL
$V_A$ alveolar ventilation, in mL/min

The airway from the nose to the alveoli

Structure	Tissues	Job
Nasal cavity	Ciliated epithelium, mucus, many blood vessels	Filters, warms and moistens air
Epiglottis	Elastic cartilage	Closes the larynx when swallowing
Trachea	C-shaped cartilage rings, ciliated epithelium with goblet cells, smooth muscle	Kept open by cartilage; mucus and cilia remove dirt
Bronchi	Cartilage plates, ciliated epithelium	Carry air into each lung
Bronchioles	Smooth muscle and elastic fibres, no cartilage	Branch through the lung; adjust airflow
Alveoli	Squamous epithelium, elastic fibres, surfactant	Gas exchange with the capillaries

Inhaling and exhaling: volume and pressure changes

Feature	Inhalation	Quiet exhalation
Diaphragm	Contracts, flattens and moves down	Relaxes and domes upward
External intercostal muscles	Contract: ribs move up and out	Relax: ribs move down and in
Volume of the thorax	Increases	Decreases
Pressure in the lungs	Falls below atmospheric pressure	Rises above atmospheric pressure
Air flow	Into the lungs	Out of the lungs

Carrying oxygen and carbon dioxide: haemoglobin and the Bohr effect

Situation	Effect on affinity for oxygen	Result
Lungs: high partial pressure of oxygen	Haemoglobin loads oxygen	Blood leaves about 97% saturated
Active muscle: high carbon dioxide, low pH, warm	Affinity falls; curve shifts right (Bohr effect)	More oxygen unloaded to the muscle
Fetal haemoglobin	Higher affinity; curve lies to the left	Takes oxygen from the mother's blood in the placenta
Myoglobin in muscle	Much higher affinity; far to the left	Stores oxygen and releases it only when oxygen is very low
Carbon monoxide	Binds haem about 200 times more strongly than oxygen	Less oxygen carried; can be fatal

Common traps

Gas exchange happens only in the alveoli

The trachea, bronchi and bronchioles only conduct air. The diaphragm is a muscle that moves air. Neither the trachea nor the diaphragm exchanges gases.

The diaphragm moves down when you breathe in

Contraction flattens the dome and pulls it down, which increases the volume of the thorax and lowers the pressure inside. Options pairing inhalation with a rising diaphragm, a falling thorax volume or a rising lung pressure are wrong.

Fast shallow breathing wastes air

The dead space is filled on every breath whatever its size. Halving the breath and doubling the rate keeps the minute ventilation the same but sends much less fresh air to the alveoli.

High carbon dioxide lowers affinity, it does not raise it

In the Bohr effect carbon dioxide and acid make haemoglobin release oxygen. More oxygen (a higher partial pressure) makes haemoglobin load, not release. Most carbon dioxide travels as hydrogencarbonate, not as carbaminohaemoglobin.

The Digestive System, Enzymes and Absorption

Learn this subtopic in the notes

Organs of the digestive system and what each one does

Organ	Main job	Secretes
Mouth	Chewing; starts starch digestion	Saliva: salivary amylase and mucus
Oesophagus	Moves food to the stomach by peristalsis	Mucus
Stomach	Stores and churns food, starts protein digestion, kills microbes	$\mathrm{HCl}$ , pepsinogen, mucus; the hormone gastrin
Duodenum	Receives bile and pancreatic juice; most chemical digestion	Mucus, brush-border enzymes; hormones secretin and CCK
Ileum	Absorbs the products of digestion	Brush-border enzymes
Large intestine	Absorbs water and ions; gut bacteria make vitamin K	Mucus
Liver	Makes bile; stores glycogen; makes urea	Bile (into the bile duct)
Gall bladder	Stores and concentrates bile	Releases bile after a fatty meal
Pancreas	Exocrine: digestive juice. Endocrine: insulin and glucagon	Pancreatic juice with enzymes and $\mathrm{HCO_3^-}$

Digestive enzymes: source, substrate, product and best pH

Enzyme	Made by	Substrate and product	Best pH
Salivary amylase	Salivary glands	Starch to maltose	About 7
Pepsin	Stomach wall, as pepsinogen	Proteins to shorter polypeptides	About 2
Pancreatic amylase	Pancreas	Starch to maltose	Slightly alkaline
Trypsin	Pancreas, as trypsinogen	Proteins to peptides	Slightly alkaline
Lipase	Pancreas	Triglycerides to fatty acids and monoglycerides (and glycerol)	Slightly alkaline
Maltase	Brush border of the small intestine	Maltose to glucose	Slightly alkaline
Lactase and sucrase	Brush border	Lactose to glucose and galactose; sucrose to glucose and fructose	Slightly alkaline
Peptidases	Brush border and pancreas	Peptides to amino acids	Slightly alkaline

Bile, pancreatic juice and the control of pH in the gut

Secretion	Made by	Contains	Effect
Gastric juice	Stomach wall	$\mathrm{HCl}$ , pepsinogen, mucus	Lowers pH to about 2; starts protein digestion
Bile	Liver (stored in the gall bladder)	Bile salts, hydrogencarbonate, bilirubin; no enzymes	Emulsifies fats; helps neutralise acid
Pancreatic juice	Exocrine cells of the pancreas	Hydrogencarbonate, amylase, trypsinogen, lipase	Neutralises acid; digests all three food types
Intestinal secretions	Lining of the small intestine	Mucus and brush-border enzymes	Finish digestion

Absorption in the small intestine and the main nutrients

Product	How it enters the cells	Where it goes next
Glucose and galactose	Co-transport with sodium ions	Blood capillaries, then the hepatic portal vein to the liver
Fructose	Facilitated diffusion	Blood capillaries, then the hepatic portal vein
Amino acids	Co-transport with sodium ions	Blood capillaries, then the hepatic portal vein
Fatty acids and monoglycerides	Diffusion through the membrane	Rebuilt into fats, then into the lacteals (lymph)
Water	Osmosis	Blood (small and large intestine)

Common traps

The stomach digests; the small intestine absorbs

The stomach's main digestive job is breaking food down with acid and pepsin, plus churning. It does not absorb nutrients to any real extent, filter toxins (the liver does that) or make bile.

Amylase makes maltose; it does not digest it

Amylase breaks starch into maltose. Digesting maltose is maltase's job. Options saying amylase digests maltose, or that it produces glucose directly, are wrong.

Emulsifying is not digesting

Bile salts split fat into smaller droplets but break no chemical bonds and do not lower lipase's activation energy. Bile makes digestion faster only by giving lipase more surface to work on.

Fats bypass the hepatic portal vein

Sugars and amino acids go straight into the capillaries and to the liver. Fats leave the villus in the lacteals as chylomicrons and reach the blood later through the lymph system.

The Kidney, the Nephron and Water Balance

Learn this subtopic in the notes

Net filtration pressure in the glomerulus

Net filtration pressure

P_{\text{net}} = P_G - (P_C + \pi_G)

$P_G$ blood pressure in the glomerular capillaries, in mmHg
$P_C$ fluid pressure in Bowman's capsule, in mmHg
$\pi_G$ oncotic pressure of the plasma proteins, in mmHg

The nephron: filtration, reabsorption and secretion

Region	What happens	Water reabsorbed here?
Glomerulus and Bowman's capsule	Ultrafiltration: water, glucose, amino acids, ions and urea leave the blood	No: this is filtration, not reabsorption
Proximal convoluted tubule	Reabsorbs all glucose and amino acids and most $\mathrm{Na^+}$ ; cells have microvilli and many mitochondria	Yes, about two thirds of it
Descending limb of the loop of Henle	Permeable to water, which leaves into the salty medulla	Yes
Ascending limb of the loop of Henle	Pumps out $\mathrm{Na^+}$ and $\mathrm{Cl^-}$ , making the medulla salty; impermeable to water	No
Distal convoluted tubule	Adjusts $\mathrm{Na^+}$ , $\mathrm{K^+}$ and $\mathrm{H^+}$ (blood pH)	Some
Collecting duct	Water leaves by osmosis into the salty medulla, controlled by ADH	Yes, a variable amount

Osmoregulation: ADH, aldosterone and the concentration of urine

Situation	ADH release	Collecting duct	Urine
Dehydration, sweating or a salty meal	Increases	More aquaporins, more water reabsorbed	Small volume, concentrated
Drinking a lot of water	Decreases	Fewer aquaporins, less water reabsorbed	Large volume, dilute
Alcohol, or a drug that blocks ADH release	Decreases	Less water reabsorbed	Large volume; lower urea concentration
Damage to the posterior pituitary	Little or none	Almost no water reabsorbed there	Very large volumes of dilute urine

Common traps

Urea is in every part of the nephron

Urea is filtered in the glomerulus and is never fully reabsorbed, so the fluid in every region, from the capsule to the collecting duct, contains it. An option naming a region with no urea is wrong.

The glomerulus filters; it does not reabsorb

Water leaves the blood in the glomerulus. Reabsorption of water happens in the tubules and the collecting duct, so the glomerulus is the one structure not involved in water reabsorption.

Blood proteins oppose filtration

Plasma proteins stay in the blood and hold water there by osmosis. They pull water back into the capillaries, so they never help water move into the tubule. The only force pushing water out is the blood pressure from the heart.

Less ADH means more urine but lower urea concentration

If urea production is unchanged, less ADH leaves more water in the urine, so the same urea is more diluted and its concentration falls. The volume rises; the concentration does not.

Nerve Impulses, Synapses, Reflexes and Muscle Contraction

Learn this subtopic in the notes

Resting potential, action potential and conduction speed

Stage	Membrane potential	What the ions do
Resting	About $-70\ \text{mV}$	Pump moves $\mathrm{Na^+}$ out and $\mathrm{K^+}$ in; $\mathrm{K^+}$ leaks out
Depolarisation	Rises past threshold (about $-55\ \text{mV}$ ) to about $+30\ \text{mV}$	Voltage-gated $\mathrm{Na^+}$ channels open; $\mathrm{Na^+}$ floods in
Repolarisation	Falls back towards $-70\ \text{mV}$	$\mathrm{Na^+}$ channels close; voltage-gated $\mathrm{K^+}$ channels open; $\mathrm{K^+}$ flows out
Hyperpolarisation	Briefly below resting, about $-80\ \text{mV}$	$\mathrm{K^+}$ channels are slow to close
Refractory period	Returning to rest	$\mathrm{Na^+}$ channels cannot reopen yet

The cholinergic synapse and the neuromuscular junction

Step	Event
1	An action potential arrives at the presynaptic knob
2	Voltage-gated $\mathrm{Ca^{2+}}$ channels open and $\mathrm{Ca^{2+}}$ diffuses into the knob
3	Vesicles fuse with the membrane and release ACh into the cleft by exocytosis
4	ACh diffuses across the cleft and binds receptors on the postsynaptic membrane
5	$\mathrm{Na^+}$ channels linked to the receptors open; $\mathrm{Na^+}$ enters and the membrane depolarises; at threshold a new action potential starts
6	Acetylcholinesterase hydrolyses ACh; the choline is taken back and ACh is remade using ATP

Reflex arcs and the sympathetic and parasympathetic systems

Target	Sympathetic effect	Parasympathetic effect
Heart rate	Increases	Decreases (vagus nerve)
Bronchioles	Widen	Narrow
Pupil	Dilates	Constricts
Gut movement and secretion	Decrease	Increase
Saliva	Small amount, thick	Large amount, watery
Adrenal medulla	Stimulated to release adrenaline	No effect

Muscle types, skeletal muscle structure and the sarcomere bands

Band or line	What it contains	During contraction
A band	The whole length of the thick (myosin) filaments, with overlapping actin	Stays the same length
I band	Thin (actin) filaments only	Gets shorter
H zone	Thick filaments only, in the centre	Gets shorter and may disappear
Z line	Anchors the thin filaments at each end of a sarcomere	Z lines move closer together
M line	Holds the thick filaments at the centre	Stays at the centre

A sarcomere runs from one Z line to the next.

From nerve impulse to cross-bridge cycle: calcium, troponin and ATP

Step	Event
1	Acetylcholine at the neuromuscular junction depolarises the muscle fibre membrane (sarcolemma)
2	The depolarisation spreads down the T-tubules into the fibre
3	The sarcoplasmic reticulum releases $\mathrm{Ca^{2+}}$ , which diffuses into the sarcoplasm
4	$\mathrm{Ca^{2+}}$ binds troponin; troponin changes shape and moves tropomyosin off the myosin-binding sites on actin
5	A myosin head, already carrying ADP and phosphate, binds actin: a cross-bridge forms
6	ADP and phosphate are released and the head tilts: the power stroke pulls actin towards the centre
7	A new ATP binds the head, which detaches from actin
8	The head hydrolyses ATP and re-cocks, ready for the next cycle

Common traps

Synapses and long axons do not speed up transmission

Myelin, nodes of Ranvier and a wider axon all increase speed. A longer axon only means a longer journey, and each synapse adds a delay because a chemical must diffuse across the gap.

Breaking down the transmitter is not what makes a synapse one-way

Acetylcholinesterase ends each signal so the next one can be told apart. Direction comes from where things are: transmitter release on one side, receptors and their ion channels on the other.

Count only the synapses inside the CNS

The junction between the motor neurone and the muscle is a synapse too, but it lies outside the CNS. In a three-neurone reflex arc the two synapses in the spinal cord are the ones inside the CNS.

The filaments slide; they do not shorten

Actin and myosin filaments keep the same length during contraction. Only the overlap changes, so the A band, which is the length of a myosin filament, stays constant while the I band and H zone shrink.

Calcium binds troponin, and ATP makes myosin let go

Options swap troponin and tropomyosin, or claim ATP makes actin and myosin bind. The truth: calcium binds troponin, which moves tropomyosin; ATP binding releases the myosin head from actin, and its hydrolysis re-cocks the head.

The Brain, the Eye, Hormones and Reproduction

Learn this subtopic in the notes

Regions of the brain and their functions

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 detected

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 act

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 $\mathrm{Ca^{2+}}$
Parathyroids	Parathyroid hormone	Peptide	Raises blood $\mathrm{Ca^{2+}}$
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 $\mathrm{Na^+}$ 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 adrenaline

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 birth

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

Common traps

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.

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.

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.

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.

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.

Human Anatomy and Physiology formulas

Tissues, Bone and Homeostasis

The four basic tissue types and how they build organs

Bone cells, cartilage and the structures of a joint

Homeostasis and negative feedback loops

Temperature control: responses to heat and to cold

Common traps

The Heart, the Cardiac Cycle and Blood Vessels

Cardiac output, stroke volume and heart rate

Double circulation and the main blood vessels

Heart structure, the pacemaker and the control of heart rate

The cardiac cycle: pressure changes and valve positions

Common traps

Blood Cells, Immune Defences and Blood Groups

Blood: plasma, red cells, white cells and platelets

Non-specific defences: barriers, phagocytes and inflammation

B and T lymphocytes, antibodies and immune memory

Active and passive immunity, and how vaccines work

ABO and Rhesus blood groups, transfusions and transplants

Common traps

Airways, Breathing and Gas Transport

Minute ventilation and dead space

The airway from the nose to the alveoli

Inhaling and exhaling: volume and pressure changes

Carrying oxygen and carbon dioxide: haemoglobin and the Bohr effect

Common traps

The Digestive System, Enzymes and Absorption

Organs of the digestive system and what each one does

Digestive enzymes: source, substrate, product and best pH

Bile, pancreatic juice and the control of pH in the gut

Absorption in the small intestine and the main nutrients

Common traps

The Kidney, the Nephron and Water Balance

Net filtration pressure in the glomerulus

The nephron: filtration, reabsorption and secretion

Osmoregulation: ADH, aldosterone and the concentration of urine

Common traps

Nerve Impulses, Synapses, Reflexes and Muscle Contraction

Resting potential, action potential and conduction speed

The cholinergic synapse and the neuromuscular junction

Reflex arcs and the sympathetic and parasympathetic systems

Muscle types, skeletal muscle structure and the sarcomere bands

From nerve impulse to cross-bridge cycle: calcium, troponin and ATP

Common traps

The Brain, the Eye, Hormones and Reproduction

Regions of the brain and their functions

The eye: its parts, rods and cones, and how light is detected

Endocrine glands, their hormones and how hormones act

Blood glucose control: insulin, glucagon and adrenaline

Reproductive organs, the menstrual cycle, pregnancy and birth

Common traps

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