Physiology
What the body does: cardiac, respiratory, nervous, digestive, renal and endocrine function explained through the anatomy.
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Blood pressure
The pressure blood exerts on artery walls: systolic at the peak of ejection, diastolic between beats.
Brain functions
Different regions specialise: the cortex for perception, movement, language and thought; deep nuclei for movement and emotion; the brainstem for life support;…
Breathing (ventilation)
Air moves in and out because muscles change the volume of the chest: the diaphragm and external intercostals enlarge it for inspiration; relaxation and elastic…
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Carbon dioxide removal and acid-base balance
Carbon dioxide, the waste of metabolism, is carried mostly as bicarbonate and breathed out; the balance between the two sets blood acidity.
Cardiac output
The volume of blood the heart pumps per minute: heart rate multiplied by stroke volume, about five litres at rest.
Circulation
Two circuits in series: the pulmonary circulation loads blood with oxygen in the lungs, the systemic circulation delivers it to every organ.
The cardiac cycle
One heartbeat is a sequence of filling and ejection: diastole, when the ventricles relax and fill, and systole, when they contract and pump.
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Electrical conduction of the heart
A wiring system of specialised muscle cells spreads each heartbeat from the sinoatrial node through the atria, the atrioventricular node and the bundle…
Electrolytes
Sodium, potassium, calcium, magnesium, chloride and bicarbonate carry charge, set the water distribution between compartments and make nerves and muscles…
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Feedback mechanisms and homeostasis
Negative feedback, where a rise in the output switches off its own production, holds temperature, glucose, blood pressure and hormones near their set points.
Fluid balance
Water in equals water out: thirst, antidiuretic hormone and the kidneys keep the body's 40 litres of fluid within a litre of its set point.
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Gas exchange
Oxygen and carbon dioxide cross the thin wall between alveoli and capillaries by diffusion, driven by differences in partial pressure.
Gender-affirming hormone therapy: what changes in the body
Feminising therapy (oestradiol with testosterone suppression) and masculinising therapy (testosterone) shift the body's sex-hormone environment towards that of…
Glomerular filtration
Blood pressure forces water and small solutes out of the glomerular capillaries into the nephron, about 180 litres a day, while cells and proteins stay behind.
Gut motility
Coordinated waves of smooth muscle contraction (peristalsis) move contents along the tract, run by the gut's own nervous system and tuned by the vagus nerve…
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Heart rate
How often the heart beats, set by the sinoatrial node and adjusted second by second by the autonomic nervous system and hormones.
Hormone regulation: the hypothalamic-pituitary axis
The hypothalamus tells the pituitary, the pituitary tells the glands, and the glands' hormones report back: a chain of command that links the brain to the…
Hormones
Chemical messengers released into the blood that act on distant cells carrying the right receptor, coordinating growth, metabolism, stress and reproduction…
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Liver functions
The liver processes everything absorbed from the gut, stores and releases fuel, makes most blood proteins, detoxifies drugs and produces bile.
Lung volumes and capacities
The amounts of air the lungs move and hold, measured by spirometry and used to separate obstructive from restrictive disease.
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Menopause
The permanent end of periods when the ovaries run out of responsive follicles and stop making oestrogen; it happens at an average age of 51 in the UK, is…
The major endocrine glands
Pituitary, thyroid, parathyroids, adrenals, pancreatic islets, gonads and pineal each make a signature set of hormones; several other organs, including the…
The menstrual cycle
A roughly monthly cycle in which one ovary matures and releases an egg while the uterus builds a lining and then sheds it as a period if no pregnancy follows,…
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Nerve signals
Information travels as brief electrical pulses, action potentials, whose rate carries the message; at synapses it becomes chemical.
Neurons
The nerve cell: a body with branching dendrites that receive signals and a single axon that carries them onward, sometimes for a metre.
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Pancreatic functions
One organ, two jobs: exocrine cells pour digestive enzymes and bicarbonate into the duodenum; the islets of Langerhans release insulin and glucagon into the…
Pregnancy and birth: how the body changes
From fertilisation in the fallopian tube to birth about 40 weeks later, pregnancy remodels almost every maternal system, from blood volume and kidney…
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Sensory systems
Receptors convert light, sound, chemicals, pressure and temperature into nerve signals that the thalamus and cortex turn into perception.
Sex hormones and puberty
Oestradiol, progesterone and testosterone are steroid hormones made mainly by the ovaries and testes under the control of the hypothalamus and pituitary; they…