Body Fluids and Blood - Tagged 2.pdf

Body Fluids and Blood Dr Stephan Menzel Red Cell Research Unit ([email protected]) Based on an original lecture by Professor Jeremy PT Ward 1/11/23 MBBS1 PPP Menzel  = key points / slides 1...

Body Fluids and Blood Dr Stephan Menzel Red Cell Research Unit ([email protected]) Based on an original lecture by Professor Jeremy PT Ward 1/11/23 MBBS1 PPP Menzel  = key points / slides 1 Part I: Body Fluids Describe volumes and composition of the body fluid compartments. Explain the principles underlying the measurement of spaces. Describe how osmolarity and equilibria act across membranes and capillaries. Give examples of plasma proteins and their roles. Part II: Introduction to blood cells Categorise the main types of cells found in the blood, including their appearance and function. 1/11/23 MBBS1 PPP Menzel 2  Part I Body fluids 1/11/23 MBBS1 PPP Menzel 3  Body fluids Typical ~60% water 70kg young man How is it distributed, and in what? 1/11/23 MBBS1 PPP Menzel 4  3 main Body fluid fluid compartments compartments O2/CO2 Nutrients Intracellular Kidney Plasma Gut Metabolites Interstitial Diffusion 1/11/23 MBBS1 PPP Menzel Transport 5  Body fluid compartments Blood cells Blood volume 8% b.w., 5.5 L Plasma space 5% (volume) ~3.5 L Extracellular 15% space (ECS) Total Body Water (TBW) Interstitial Body space ~10.5 L wt. ~14 L Total H 2O 60% TBW ~ 42 L body 40% Water content weight Intracellular of lean tissue body space (ICS) ~28 L ~0.71L / Kg wt. (depend - fat content) ↑fat ↓ water 1/11/23 MBBS1 PPP Menzel  6  Other fluid compartments “Transcellular fluids” Cerebrospinal fluid (CSF) 150ml Aqueous and vitreous humors of the eye Synovial fluid Amniotic fluid GI tract secretions lymph Note that these spaces are part of the ECS, but may have slow diffusion to and from plasma 1/11/23 MBBS1 PPP Menzel 7  How can we measure fluid compartments? Dilution method Add known amount of substance (S) to unknown volume (V) – i.e. S grams in V litres Measure concentration (C; grams per litre) C = S/V so: V= S/C 1/11/23 MBBS1 PPP Menzel 8  Unknown volume (V) ? Add 20 red molecules (S) Mix, take 1 ml sample Sample concentration: 2 red per ml (C) added 20 red, So total vol = 10 ml S (amount added) Volume = Concentration 1/11/23 10 = 20 / 2 per ml MBBS1 PPP Menzel 9  What substances can we use? Distributes in space of interest, non-toxic, not metabolised quickly Plasma volume: – something that does not cross capillaries – large size- Evans Blue, labeled Inulin, Albumin ECS: – Something that does not enter cells easily – 24Na, Sucrose TBW: – something that distributes with all water – 3H2O 1/11/23 MBBS1 PPP Menzel 10  How do we derive other spaces? 5% Plasma volume Interstitial space ECS = 15% Interstitial Total Body Water (TBW) b.w. space ECS - plasma volume Intracellular space 40% Intracellular = b.w. space TBW - ECS 1/11/23 MBBS1 PPP Menzel 11  Constituents of body fluids Major constituents: Ions (electrolytes) in solution – E.g. cations: Na+, K+, Ca2+, Mg2+ – E.g. anions: Cl-, HCO3-, PO42- Proteins Dissolved gases, nutrients, metabolites Cells in blood 1/11/23 MBBS1 PPP Menzel 12  Ionic composition of Extra- and Intracellular fluids Na+, Cl- & K+ are the major ions in body fluids They therefore determine osmolarity The concentrations of Na+, K+ & Ca2+ differ considerably between ECF & ICF These differences are fundamental for cell function (e.g. membrane potential, signalling) But osmolarity of ICF and ECF must be equal Why? 1/11/23 MBBS1 PPP Menzel 13  Osmotic Pressure & Osmolarity  Determined by total number of freely diffusible entities in solution (e.g. ions) Unit: Osmole ( 6.022  1023 entities = 1 mole) – Osmolarity means 1 osmole per litre – Osmolality means 1 osmole per kg E.G. 140 mmol/litre NaCl  280 mosm/litre (1 mol/l NaCl = 1 mol/l Na+ + 1 mol/l Cl-) So: 10mmol/litre CaCl2  30 mosm/litre Relationship to pressure: 1 osmole in 22.4 litres exerts 760mmHg  1 osmole / litre exerts 1/11/23 >17,000mmHg! MBBS1 PPP Menzel 14  Osmotic Pressure & Osmolarity Osmolarity of plasma controls plasma volume Osmolarity of intracellular fluid cell volume osmolarity of plasma ~290 mosmol / litre Very important this is strongly controlled – why? Equiv to > 5000 mmHg – so 1% difference between extra- and intracellular osmolarity would exert >50mmHg pressure across cell membrane Sometimes called “tonicity” – only applies when solutions are separated by semi-permeable membrane Isotonic solution has same tonicity as plasma isotonic or “normal” saline = 0.9% w/v NaCl 1/11/23 MBBS1 PPP Menzel  15 Crystalloid vs. oncotic osmotic pressure  Crystalloid osmotic pressure is due to small diffusible ions (e.g. Na+, Cl- and K+ in body fluids) Cell membranes largely impermeant to ions, so intra- and extracellular osmolarity must be equal Ions (e.g. Na+, Cl-) cross capillary walls easily, so no crystalloid osmotic pressure difference. Proteins do not - as there is little protein in interstitial fluid, they exert an oncotic (or colloidal osmotic) pressure of about 25 mmHg NB: [Protein] ~70 g/L ( 2mM) Oncotic pressures vital for fluid transport across capillaries 1/11/23 MBBS1 PPP Menzel 16  Cell Interstitial fluid Cell membrane Osmotic pressure Osmotic pressure 1/11/23 MBBS1 PPP Menzel 17 Membrane impermeable to ions, permeable to water  Plasma Interstitial fluid Oncotic pressure Capillary wall  In practice, the oncotic pressure in capillaries is more 1/11/23 Wall or less balanced permeable by crystalloid to ions: the outward MBBS1 PPP Menzel hydrostatic pressure 18 osmotic pressures equal  Ionic composition Plasma Intracellular [Na+] 140 [Na+] 10 mmol/l mmol/l [K + ] 4 mmol/l [K+] 120 mmol/l [Ca2+] 2 mmol/l [Ca2+]~100 nmol/l Anions include: Cl- 110 Anions include: amino acids, Cl-, proteins etc Bicarbonate Na + 24mmol/l major ion, K+ major ion,  controls  controls blood volume cell volume 1/11/23 MBBS1 PPP Menzel 20  Ionic composition Important: Relative concentrations of K+, Na+ and Ca2+ between intracellular and extracellular spaces are critical for cell function, in particular the membrane potential, action potential, and nerve and muscle function. KNOW these values!! (especially for plasma) 1/11/23 MBBS1 PPP Menzel 21  Plasma proteins Total quantity: ~70g per litre Albumin, 48 g/litre – Plasma oncotic (colloidal osmotic) pressure (25mmHg; capillary fluid transport) – transport, buffering of pH , , and  globulins, 0.7-13 g/litre each – Haemostasis, transport, immune system Fibrinogen, 3 g/litre – Haemostasis NB- protein content 1/11/23 MBBS1 of interstitial fluid is low  PPP Menzel 22  Part II Introduction to blood cells 1/11/23 MBBS1 PPP Menzel 23  Body Fluids and Blood Learning Outcomes After this lecture, students should be able to: 1. Name the body fluid compartments and give values for their volumes in the adult human 2. Outline dilution method for measuring them 3. List & give concentrations for main constituents of plasma, ECF and ICF 4. State osmolarity of plasma and how it influences fluid movement 5. Classify plasma proteins and outline function 6. State normal RBC & WBC counts and Hb. Explain what is meant by “anaemia”. 1/11/23 MBBS1 PPP Menzel 32 Official Textbook: Vander? Optional further reading: Cardiovascular system at a Glance Physiology textbooks eg Vander, Ganong, Silverthorn Haematopoiesis – Lecture (possibly online) by Dr Simon Pitchford 1/11/23 MBBS1 PPP Menzel 33  Take Home Questions You make up an isotonic solution by adding KCl to 1 litre of H2O - how many grams of KCl do you add? - is it safe to infuse this into a patient? You inject 0.5 ml of saline containing 1 g/L Evans Blue into a patient – you take a sample after 30 min, which you find contains 125 g/L - What is the plasma volume of the patient? If their PCV is 0.45, what is their blood volume? Their red cell count is 4 x 1012/litre: What is the MCV (mean cell volume)? 1/11/23 MBBS1 PPP Menzel 34