Fundamentals
The core facts every aspirant should own — each a titled nugget with a real-world story, the concept in plain words, and a memory trick. Works even when the internet doesn't.
300 fundamentals
“Your kidneys filter your entire blood volume about 60 times every day.”
Humans mainly excrete urea, so we are ureotelic.
Memory trick: ammonia is toxic, so mammals convert it to safer urea.
“Your kidneys filter your entire blood volume about 60 times every day.”
A frequent error is thinking humans excrete ammonia directly. In reality, humans mainly excrete urea, so we are ureotelic.
Memory trick: ammonia is toxic, so mammals convert it to safer urea.
“Your kidneys filter your entire blood volume about 60 times every day.”
Antidiuretic hormone controls how much water is reabsorbed, concentrating the urine.
Memory trick: more ADH → more water saved → concentrated urine.
“Your kidneys filter your entire blood volume about 60 times every day.”
A frequent error is thinking urine concentration is fixed. In reality, antidiuretic hormone controls how much water is reabsorbed, concentrating the urine.
Memory trick: more ADH → more water saved → concentrated urine.
“Your kidneys filter your entire blood volume about 60 times every day.”
Ultrafiltration pushes water and small solutes out of the blood in the glomerulus; reabsorption takes back the useful ones in the tubule.
“Your kidneys filter your entire blood volume about 60 times every day.”
Ureotelic animals (mammals) excrete urea; uricotelic animals (birds, reptiles) excrete uric acid to save water.
“Your kidneys filter your entire blood volume about 60 times every day.”
The cortex is the outer kidney region with glomeruli; the medulla is the inner region with the loops that concentrate urine.
“Your kidneys filter your entire blood volume about 60 times every day.”
Roughly 99% of the glomerular filtrate is reabsorbed; only about 1% is excreted as urine.
“A reflex yanks your hand off a hot pan before your brain even hears about it.”
A frequent error is thinking the axon receives signals. In reality, the nerve cell that carries impulses, with dendrites (receive), an axon (transmit) and synapses (connect).
Memory trick: dendrites receive, axon sends — remember 'axon = away'.
“A reflex yanks your hand off a hot pan before your brain even hears about it.”
A frequent error is thinking the impulse jumps the synapse as electricity. In reality, an electrical signal (action potential) travels within a neuron; a chemical signal crosses the synapse.
Memory trick: within a neuron = electrical; across a synapse = chemical (neurotransmitter).
“A reflex yanks your hand off a hot pan before your brain even hears about it.”
A frequent error is thinking every response goes through the brain first. In reality, a fast, involuntary response routed through the spinal cord without waiting for the brain.
Memory trick: reflexes bypass the brain for speed — hand off a hot pan instantly.
“A reflex yanks your hand off a hot pan before your brain even hears about it.”
The central nervous system is the brain and spinal cord (processing); the peripheral nervous system is the nerves connecting them to the body.
“A reflex yanks your hand off a hot pan before your brain even hears about it.”
A sensory neuron carries signals from receptors to the CNS; a motor neuron carries commands from the CNS to muscles/glands.
“A reflex yanks your hand off a hot pan before your brain even hears about it.”
Resting potential is the neuron's charged 'ready' state (about −70 mV); an action potential is the brief reversal that carries the impulse.
“A reflex yanks your hand off a hot pan before your brain even hears about it.”
The signal crosses a synapse chemically, using neurotransmitters, not as an electric spark.
“A pinch of adrenaline can turn an ordinary person briefly superhuman in an emergency.”
A frequent error is confusing endocrine glands with exocrine glands that use ducts. In reality, chemical messengers released by ductless (endocrine) glands into the blood to act on target organs.
Memory trick: endocrine = ductless, hormones into blood; exocrine = ducts (sweat, saliva).
“A pinch of adrenaline can turn an ordinary person briefly superhuman in an emergency.”
Pancreatic hormones — insulin lowers blood glucose, glucagon raises it.
Memory trick: Insulin puts glucose IN (storage) → lowers blood sugar.
“A pinch of adrenaline can turn an ordinary person briefly superhuman in an emergency.”
A frequent error is swapping their roles. In reality, pancreatic hormones — insulin lowers blood glucose, glucagon raises it.
Memory trick: Insulin puts glucose IN (storage) → lowers blood sugar.
“A pinch of adrenaline can turn an ordinary person briefly superhuman in an emergency.”
A frequent error is thinking thyroid problems don't relate to diet. In reality, the thyroid hormone that controls the body's metabolic rate; it needs iodine.
Memory trick: iodine deficiency → low thyroxine → goitre.
“A pinch of adrenaline can turn an ordinary person briefly superhuman in an emergency.”
The 'master gland' that controls several other endocrine glands.
Memory trick: the pituitary signals the thyroid, adrenals and gonads.
“A pinch of adrenaline can turn an ordinary person briefly superhuman in an emergency.”
A frequent error is thinking each gland works fully independently. In reality, the 'master gland' that controls several other endocrine glands.
Memory trick: the pituitary signals the thyroid, adrenals and gonads.
“A pinch of adrenaline can turn an ordinary person briefly superhuman in an emergency.”
Endocrine glands are ductless and release hormones into the blood; exocrine glands (sweat, salivary) release secretions through ducts.
“A pinch of adrenaline can turn an ordinary person briefly superhuman in an emergency.”
A hormone is a chemical messenger carried by blood to a target; an enzyme is a catalyst that speeds a specific reaction where it is made.
“A pinch of adrenaline can turn an ordinary person briefly superhuman in an emergency.”
Insulin LOWERS blood glucose; it is glucagon that raises it.