3. Blood, tissue fluid, lymph

• BLOOD

  • Main transport medium of human circulatory system
  • Consists of yellow liquid = plasma --> carries components like:
  • Dissolved glucose + aminos
  • Mineral ions
  • Hormones
  • Large plasma proteins
• Plasma also transports:

  • Red blood cells
  • Many different types of white blood cells
  • Carries platelets = fragments of large cells called megakaryocytes found in red bone marrow + involved in clotting mechanism of blood
  • Plasma makes up 55% of blood by volume = much of that vol is water
  • Only plasma + RBC's = involved in transport functions of blood
• Functions of blood

  • Transport of:
  • O2 to + co2 from = respiring cells
  • Digested food from small intestine
  • Nitrogenous waste products from cells --> excretory organs
  • Chemical messages [hormones]
  • Food molecules from storage compounds --> cells that need them
  • Platelets to damaged areas
  • Cells + antibodies involved in immune response
  • Blood also contributes to maintenance of steady body temp + acts as a buffer = minimising pH changes
• TISSUE FLUID

  • Substances dissolved in plasma can pass through fenestrations [pores] in capillary walls = except large plasma proteins
  • Plasma proteins = have an osmotic effect

  --> give blood in capillaries high solute potential [low WP] compared to surrounding fluid

  --> due to this water has a tendency to move into blood in capillaries from fluid = by osmosis

  • Oncotic pressure: tendency of water to move into blood by osmosis = -3.3KPa
• TISSUE FLUID

  • As blood flows through arterioles --> capillaries still under pressure from surge of blood that occurs whenever heart contracts = hydrostatic pressure
  • At arterial end of capillary = hydrostatic pressure forcing fluid out of capillaries is high = 4.6KPa 
  • Its higher than oncotic pressure attracting water in by osmosis = so fluid squeezed out of capillaries
• TISSUE FLUID: fluid that fills spaces between cells

  --> has same composition as plasma without RBC'S + plasma proteins

  --> diffusions between blood + cells through tissue fluid

  • As blood moves through capillaries towards --> venous system = balance of force changes

  --> hydrostatic pressure falls to = 2.3KPa in vessels as fluid has moves out + pulse lost

  --> oncotic pressure still = -3.3KPa so its now stronger than hydrostatic pressure, so water moves back into capillaries by osmosis as it approaches venous end of capillaries
• TISSUE FLUID

  • At arterial end = hydrostatic pressure is greater than oncotic pressure so tissue fluid is forced out of capillaries
  • At venous end = hydrostatic pressure is lower than oncotic pressure so fluid is drawn back into capillary
  • By the time blood returns to veins = 90% of tissue fluid is back in blood vessels
• LYMPH

  • Some tissue fluid doesn't return to capillaries
  • 10% of liquid that leaves blood vessels drains into a system of tubes called = lymph capillaries --> where its lymph
  • Lymph: similar in to plasma + tissue fluid = has less o2 & fewer nutrients

  --> have fatty acids that have been absorbed into lymph from villi of small intestine

  • Lymph capillaries join up to form larger vessels --> fluid is transported through them by squeezing muscles
  • One way valves = prevent back-flow of lymph
  • Eventually lymph returns to blood flowing into right + left subclavian veins [under clavicle/collar bone]
• LYMPH 2

  • Along lymph vessels are = lymph nodes
  • Lymphocytes build up in lymph nodes + produce antibodies = passed in blood
  • Lymph nodes also intercept bacteria + other debris from lymph = ingested by phagocytes found in nodes

  --> lymphatic system = plays major role in defense mechanism of body

  • Enlarged lymph nodes = sign that bodies fighting of pathogens

  --> neck, armpits, stomach, groin = sites of major lymph nodes [lymph glands]