Essentials of Clinical Medicine Introduction to physiology

Introduction to Physiology Anatomy – how things are constructed Physiology – how things work

Physiology The movement of water, ions and molecules throughout the body, and particularly across membranes. The movement of fluids and gases through the body, usually through tubes The movement of parts of the body relative to other parts The movement of the body relative to the surroundings   3

Introduction to physiology

ICF 28 10 4 Total body water 42 Extra-cellular fluid 14 Plasma and Tran Interstitia Cell membrane ICF Capillary membrane 28 10 4 Total body water 42

Water compartments in health TBW = 60% BODY WEIGHT = 42 litres   Divided into ICF – 2/3 [66%] = 28 ECF – 1/3 [33%] = 14 Interstitial = 10 Intravascular/plasma = 3 Transcellular [Cell wall, CSF etc] = 1

Introduction to physiology liquid

Does this matter? Yes!

Diffusion

Flow of fluids through a tube Dependent on Force – pressure difference Tube – diameter [fourth power] and length Fluid – viscosity and density Flow – laminar or turbulent

Quiet Noisy

Length Pressure difference Diameter [ 4th power!] Viscosity Normal in blood vessel

Abnormal in blood vessel, usual in respiratory Length Pressure difference Diameter Density Abnormal in blood vessel, usual in respiratory

Laminar flow is silent - so if you hear a noise [murmur or bruit] Does this matter? Yes! Laminar flow is silent - so if you hear a noise [murmur or bruit] in the cardiovascular system it must mean there is turbulent flow and something is wrong! E.g. arteries in the neck or kidneys. In the heart, you will hear the NORMAL heart sounds, which are caused by the valves closing; if you hear any other noise, something is wrong!

Does this matter? Yes! Turbulent flow is noisy and in the respiratory system, flow is usually at least partially turbulent. So you can normally hear breath sounds. You can also hear abnormal sounds, such as a wheeze caused by asthma.

Atherosclerosis 18

Does this matter? Yes! Atheroma can occur in any artery and is a major cause of death and disability Brain – stroke Heart - heart attack Kidneys – renal failure Peripheral – lose limb

Length Pressure difference Diameter [d 4th] Viscosity

Length Pressure difference Diameter [d 4th] Viscosity

Equilibrium between plasma and interstitial fluid is established Governed by ‘Starling forces’ where loss of fluid from the plasma, owing to hydrostatic pressure is opposed by reabsorption of fluid into plasma, owing to colloid osmotic pressure or oncotic pressure EH Starling

Hydrostatic pressure forces fluid out of the plasma across capillary walls Arteriolar Venular Hydrostatic pressure hydrostatic pressure 35mm Hg hydrostatic pressure 15mm Hg filtration of plasma

Colloid osmotic pressure 25mm Hg Impermeance of plasma proteins generates a colloid osmotic pressure Colloid osmotic pressure draws fluid back into capillaries from interstitial space Arteriolar Venular Colloid osmotic pressure 25mm Hg

equilibrium between plasma and interstitial fluid Filtration pressure = hydrostatic pressure – colloid osmotic pressure Arteriolar Venular hydrostatic pressure 35mm Hg hydrostatic pressure 15mm Hg Colloid osmotic pressure 25mm Hg reabsorption at venular end

Does this matter? Yes! Things can go wrong! Fall in plasma protein Defect in capillary membrane Rise in venous pressure

Does this matter? Yes! Oedema Starvation [low input of nutrients] Liver failure [not enough made] Anaphylaxis Heart failure