Plasma

• Pale yellow liquid of blood– 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 seepsback 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:– 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

1. Small; 7µm (cf liver cell 40µm average)– All haemoglobin is close to surface– Capillaries can also be small– Efficient diffusion

2. Biconcave disc shape– Increases surface area:volume– Faster diffusion

3. No nucleus, mitochondria, ER– More room for haemoglobin– More capacity to transport oxygen

White Blood Cells

• Leucocytes (‘white cells’)– 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