Cells and the cycle

Membrane: controls exchange.
Nucleus: holds DNA.
Mitochondria: supply energy.
Ribosomes: make proteins.
Lysosomes: break down unwanted material.
Endoplasmic reticulum: moves material internally.

Interphase includes G1, S and G2; S copies DNA. M separates the copied DNA (prophase, metaphase, anaphase, telophase). G0 is a resting state outside the cycle, not cell death. With low-LET (linear energy transfer) radiation, M and G2 are generally sensitive and late S relatively resistant; this is not universal.

Systems and homeostasis

Cells form tissues, organs and systems; systems help keep internal conditions stable (homeostasis).

System	Main functions
Urinary	Waste removal; water, electrolyte and acid–base balance.
Respiratory	Oxygen entry, carbon dioxide removal, acid–base regulation.
Circulatory	Transport, immune defence, clotting, temperature control.
Digestive	Food breakdown, absorption, solid-waste elimination.
Nervous	Electrical coordination of conscious and automatic activity.
Skeletal	Support, protection, movement, calcium storage, blood-cell production.
Muscular	Voluntary skeletal movement; involuntary smooth and cardiac contraction.
Endocrine	Hormones enter blood to regulate activity.
Skin	Protection, temperature control, sensation, vitamin D production.
Reproductive	Reproductive-cell production and transport.

Renal assessment

In nephrons, glomeruli filter blood; tubules return most filtered water. Creatinine comes from muscle metabolism; the kidneys clear it. Muscle mass and age change it, so an in-range result can hide reduced filtration.

eGFR (estimated glomerular filtration rate) is calculated from serum creatinine; it estimates how much fluid the glomeruli filter out of the blood each minute (mL/min/1.73 m²). In AKI (acute kidney injury), eGFR may misrepresent current function.

ESUR 2026 risk factors for iodinated contrast (need clinical review):

IV (intravenous) or arterial second-pass exposure: eGFR below 30 mL/min/1.73 m².
Arterial first-pass exposure, or ICU (intensive care unit) patient: eGFR below 45 mL/min/1.73 m².
Known or suspected AKI.

First-pass (little dilution before the kidneys): left heart, suprarenal aorta, renal arteries. Second-pass (after dilution): right heart, carotid or infrarenal arteries. ACR 2026 recommends IV fluid (volume expansion) prophylaxis for AKI or eGFR below 30 mL/min/1.73 m² outside maintenance dialysis.

Adult observations

Typical resting values:

Pulse: 60–100 beats/min; breathing: 12–20 breaths/min.
Temperature: 36.5–37.3 °C; BP (blood pressure): 90/60–120/80 mmHg (cuff at heart level).
SpO₂ (pulse-oximeter oxygen saturation): 95–100%, not a universal oxygen target; poor circulation or probe displacement can mislead.

Systolic pressure is higher (ventricular contraction); diastolic is lower (between contractions). Compare observations with baseline. New cyanosis, breathing difficulty or altered consciousness needs prompt clinical escalation.

Physiology in imaging

Ventilation moves air; perfusion supplies blood; gas exchange occurs between alveoli and capillaries.

Preserved ventilation with reduced perfusion may suggest embolism, but is not specific. A barium swallow can show peristaltic waves pushing the bolus on; with liquid barium, gravity does much of the work. Kidneys excrete contrast into urine. Rapid tracer excretion suits drainage assessment; cortical retention suits tissue/scarring assessment.