Plasma Pale yellow liquid of blood Plasma leaks out of capillaries Water with substances dissolved Glucose (nutrient), urea (waste) Plasma Proteins Plasma leaks out of capillaries Forms tissue fluid Plasma proteins too big to leak

Tissue Fluid Similar to plasma, but Few plasma proteins & RBCs WBCs can squeeze through capillaries into tissue fluid

Formation of Tissue Fluid Depends on pressure in blood vessel (from artery) Balanced by tendency for water to move: from high water potential in tissue fluid (few plasma proteins) to low water potential in blood (lots of plasma proteins; concentrated solution) Fluid flows out of capillary at arterial end of capillary bed Into capillary at venous end of capillary bed

Homeostasis Tissue fluid is the external environment of most cells Exchange of material happens through tissue fluid Constancy of tissue fluid required Glucose, water, pH, waste, temperature Oedema is build up of tissue fluid

Lymph 90% tissue fluid seeps back into capillaries 10% collected in lymph vessels Dead-end vessels Valves allow flow into lymph vessels Valves allow large protein molecules through (cannot get back into capillaries) Lymph similar composition to tissue fluid

Unusual Tissue Fluid Liver: Small Intestine: High protein concentrations in tissue fluid & lymph Small Intestine: High lipid concentration in lymph after a meal ‘Lacteal’ is a lymph vessel in each villus Absorb lipids

Fate of Lymph Form larger vessels Empty into subclavian veins (beneath collar bone) Movement by muscles and valves Some smooth muscle in walls Slow: 100cm3h-1 (blood 80cm3 s-1)

Lymph Nodes Protection against disease in nodes: Phagocytes remove pathogens etc Lymphocytes secrete antibodies

Blood ~5dm3 25 million million RBCs 0.5 million million WBCs 6 million million platelets

Red Blood Cells Erythrocytes (‘red cells’) Red due to haemoglobin (globular protein) Transports oxygen First formed in liver as a foetus Before birth, bone marrow takes over First in long bones eg femur, humerus Later more in skull, ribs, pelvis Short life, cell membrane becomes fragile often rupture in spleen

RBCs are Unusual Small; 7µm (cf liver cell 40µm average) All haemoglobin is close to surface Capillaries can also be small Efficient diffusion Biconcave disc shape Increases surface area:volume Faster diffusion No nucleus, mitochondria, ER More room for haemoglobin More capacity to transport oxygen

White Blood Cells Leucocytes (‘white cells’) Fight disease Made in bone marrow Have a nucleus Larger than RBCs (except lymphoyctes) Usually spherical Fight disease Phagocytes (phagocytosis) Lobed nuclei, granular cytoplasm Lymphocytes (antibodies) Large round nucleus, little cytoplasm, smaller