Anatomy and Physiology: free practice, theory and problems

1. Cells, tissues and homeostasis

What is it about?

The body is built from cells that work together in tissues and organs. For the cells to function, the conditions around them must be kept stable: temperature, pH, blood glucose and fluid. This is called homeostasis, and much of nursing is about noticing when homeostasis fails.

Concepts

• The nucleus contains DNA and controls the cell.
• The mitochondria produce energy (ATP) through cellular respiration.
• The ribosomes make proteins.
• The cell membrane lets some substances in and out (selectively permeable).
• The four tissue types: epithelial tissue (covers and lines surfaces), connective tissue (supports and binds, e.g. bone, cartilage and blood), muscle tissue and nervous tissue.
• Homeostasis is usually controlled by negative feedback: a deviation triggers a response that counteracts it. Example: a high temperature causes sweating and dilated blood vessels in the skin.
• Positive feedback amplifies a process, for example contractions during childbirth.

Common mistakes

• Thinking blood is not a tissue. Blood counts as connective tissue.
• Mixing up negative and positive feedback.

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2. Heart and circulation

What is it about?

The heart is two pumps in one. The right side pumps oxygen-poor blood to the lungs (pulmonary circulation). The left side pumps oxygen-rich blood out to the body (systemic circulation). The left ventricle has the thickest wall because it must pump against the highest pressure.

The path of the blood

Venae cavae → right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary artery → lungs → pulmonary veins → left atrium → mitral valve → left ventricle → aortic valve → aorta → the body.

Concepts and formulas

• The sinus node in the right atrium is the heart's natural pacemaker.
• Arteries carry blood away from the heart, veins carry blood towards it. (The pulmonary artery carries oxygen-poor blood.)
• Cardiac output: $CO = SV \cdot HR$, stroke volume times heart rate. Normally about 5 L/min at rest.
• Mean arterial pressure: $MAP \approx DBP + (SBP - DBP)/3$. A MAP above about 65 mmHg is needed to perfuse the organs.
• The coronary arteries supply the heart muscle itself with blood.

Common mistakes

• Thinking all arteries carry oxygen-rich blood.
• Swapping the mitral and tricuspid valves: tri(cuspid) is on the right, mitral on the left.

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3. Respiration

What is it about?

Respiration brings oxygen into the blood and carbon dioxide out. The air passes through the nose, pharynx, larynx, trachea and bronchi to the alveoli, where gas exchange happens by diffusion through a very thin wall.

Concepts and formulas

• The diaphragm is the most important muscle of inspiration. When it contracts, the volume of the chest increases and air flows in.
• Expiration at rest is passive.
• Surfactant lowers the surface tension in the alveoli so that they do not collapse.
• In healthy people the main stimulus to breathe is the CO₂ level in the blood (via pH), detected in the brainstem.
• Tidal volume: air per normal breath, about 500 mL in adults.
• Minute ventilation: $V_E = V_T \cdot RR$ (tidal volume times respiratory rate).
• Normal respiratory rate in adults at rest: 12–20 per minute.
• Oxygen saturation (SpO₂) is normally 96–100% in people with healthy lungs.

Common mistakes

• Thinking that breathing out at rest requires muscle work.
• Thinking low oxygen is the main breathing stimulus in healthy people. It is CO₂.

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4. The nervous system

What is it about?

The nervous system receives signals, processes them and controls muscles and glands. It is divided into the central nervous system (the brain and spinal cord) and the peripheral nervous system (the nerves out in the body).

Concepts

• The neuron (nerve cell) has dendrites that receive signals, a cell body and an axon that passes the signal on.
• Myelin around the axon makes the signal travel much faster.
• In the synapse the signal is transferred chemically by neurotransmitters, for example acetylcholine and noradrenaline.
• The autonomic nervous system controls what we do not control voluntarily:
• Sympathetic ("fight or flight"): higher heart rate and blood pressure, dilated pupils, dilated bronchi, less gut activity.
• Parasympathetic ("rest and digest"): lower heart rate, more gut activity and saliva production.
• The cerebellum controls balance and coordination. The brainstem controls breathing, circulation and consciousness. The cerebrum handles thinking, language and voluntary movement.

Common mistakes

• Thinking the sympathetic system always "increases" everything. It inhibits digestion, for example.

Practise the nervous system in the app →

5. Kidneys, fluids and electrolytes

What is it about?

The kidneys clean the blood, regulate fluid volume, electrolytes and acid–base balance, and produce hormones. The functional unit is the nephron.

Concepts

• In the glomerulus the blood is filtered into primary urine (about 180 litres a day). Almost everything is reabsorbed in the tubules, leaving 1–2 litres of urine.
• ADH (antidiuretic hormone) from the pituitary increases water reabsorption: less and more concentrated urine.
• Aldosterone from the adrenal cortex increases reabsorption of sodium (and water) and increases excretion of potassium.
• The adult body is about 60% water. About two thirds is inside the cells.
• Important normal values: sodium about 137–145 mmol/L, potassium 3.5–5.0 mmol/L.
• Too little urine: below about 0.5 mL/kg/h in adults over several hours should be reported.

Common mistakes

• Mixing up ADH and aldosterone: ADH is about water, aldosterone about sodium (and potassium).
• Underestimating potassium: both high and low potassium can cause dangerous heart rhythm disturbances.

Practise kidneys, fluids and electrolytes in the app →

6. Digestion and nutrition

What is it about?

Digestion breaks food down into small molecules that can be absorbed into the blood. It starts in the mouth and ends in the large intestine.

Concepts

• The mouth: chewing and amylase in saliva start the breakdown of carbohydrates.
• The stomach: hydrochloric acid and pepsin start the breakdown of proteins, and the acid kills many microbes.
• The small intestine: almost all absorption of nutrients happens here. The villi give an enormous surface area.
• The liver makes bile, which emulsifies fat so it can be broken down. Bile is stored in the gallbladder.
• The pancreas makes digestive enzymes and the hormones insulin (lowers blood glucose) and glucagon (raises blood glucose).
• The large intestine absorbs water and salts.
• Fat-soluble vitamins: A, D, E and K.

Common mistakes

• Thinking the stomach is responsible for most absorption. It is the small intestine.
• Thinking bile is an enzyme. It emulsifies fat but does not break it down itself.

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