PowerPoint Presentation

[Audio] Overview of fluid and solute balance in the body What is meant by fluid and solute balance? Describe water balance in the body How much of the body is made up of water? How is total body water distributed? How does water move between extracellular and intracellular compartments?.

[Audio] What is meant by fluid and solute balance? To maintain homeostasis, what comes in the body must eventually be used or excreted Input + production = utilization + output.

[Audio] Describe water balance in the body In the processs of metabolism, some water is actually produced Water inputs = Ingestion 2.2 L/day Cellular metabolism 0.3 L/day 2.2 L/day + 0.3 L/day = 2.5 L/day Total body water Digestive tract Renal tubules 42 L/day We will see shortly that during filtration, lots of that water is actually reabsorbed from the renal tubules Water outputs = Other losses Excretion 0.1 L/day Excretion 1.5 L/day 0.9 L/day When we expire (like breath out air), we also excrete some water 0.1 L/day Little portion of water gets excreted via the digestive tract + 0.9 L/day + 1.5 L/day Urine Feces Insensible loss, sweating = 2.5 L/day Water loss from the surfaces of our body that we don't detect Ex. breathing Water balance: input = output This helps us maintain homeostasis —> The key place where we can regulate this is at the kidneys Approximate values for a 70kg individual.

[Audio] How much of the body is made up of water? ~60% of body weight is water Range: 50% obese to 70% child Fat cells are less likely to hold water than muscle cells 70kg adult: total body water = 42 L.

[Audio] Here for physiology, we consider the lumen of the GI tract and respiratory tract as the external surface, thus not part of our body How is total body water distributed? Air External environment Nutrients, water, inorganic ions Internal environment Gastrointestinal tract O2 CO2 Lungs GI tract Blood vessels Cell membrane Secretion Heart Absorption Blood cells Filtration Reabsorption Secretion Cells (nerve, muscle, etc.) Kidneys Epithelial cell layer Excretion Unabsorbed material Urine.

[Audio] Gastrointestinal tract Lungs Kidneys All the water that is inside our body (regardless of it being inside cells or outside of cells) Total body water (TBW) Blue = water.

[Audio] Text Gastrointestinal tract Lungs Blood vessels Kidneys One compartment of the total body water - ICF is the water inside all cells + water inside blood cells Intracellular fluid (ICF) Blue = water.

[Audio] We can devide extracellular fluid into 2 parts: (1) Plasma: which is water in blood (2) Interstitial Fluid: water that baths the cells the water that baths the tissue cells as well as the water that is found in the blood - plasma Extracellular fluid (ECF) Blue = water.

[Audio] Extracellular fluid (ECF) Water inside blood vessels Plasma Blue = water.

[Audio] Extracellular fluid (ECF) Water that baths the cells Interstitial fluid (ISF) Blue = water.

[Audio] How is total body water distributed? = 60% of body weight Blue = water Turns out, the volume of intracellular fluid is actually greater than that of extracellular fluid 11 ICF 2/3 TBW ECF 1/3 TBW.

[Audio] Body water contains ions, proteins and other molecules Regardless of being intra or extra cellular ICF ECF We learned that there is more K+ inside cells Na+ K+ Na+ Ca2+ K+ PO4 HPO4 HCO3 ClThese ions and proteins etc are gonna influence that water movement between these compartments proteinHCO3 (protein-) amino acidsThese ions are gonna contribute to the osmolarity of the fluids —> Osmolarity is the total concentration of solute particles (osmoles) per liter of solution (𝑂𝑠𝑚/L) 12.

[Audio] How is water moving in and out! External–internal exchange cells epithelial cells external plasma interstitial fluid blood cells In: → Nutrients, electrolytes, water, oxygen, etc Out:  Wastes and unneeded material (including excess water).

[Audio] How does water move between extracellular and intracellular compartments? 1) Osmosis Governs primarily between inside vs outside cells 2) Starling forces (out of and into capillaries) Governs fluid into and out of capillaries 14.

[Audio] Recall: Plasma membrane Summary: we get little amounts of water moving throguh the hydrophobic region of the membrane, but a lot of water moves through the aquaporin channels (if they are present in the cell/plasma membrane) —> Water moves through both pathways via diffusion —> This water movement is always passive and NOT influenced by the membrane potentials of the cells —> Water moves from an area of low osmolarity to an area of high osmolarity Hydrophobic (and water) – cross phospholipid bilayer The phosphlipid portion of the membrane is hydrophobic: —> water can cross but not very easily, anything that is lipid soluble can cross easily Hydrophilic (e.g. ions, glucose, amino acids, water) – use membrane proteins for transport Fig. 2.16 Transport protein for water = aquaporin (water channel) Specifically allows water to move through it 15.

[Audio] Movement of water: Osmosis = Diffusion of water through a semipermable membrane -Always passive -Unaffected by membrane potentials -Water moves from area of low osmolarity to and area of higher osmolarity.

[Audio] Molarity Molarity = concentration of a substance in 1 L solution number of moles of that subatance in that 1L of fluid 1 mole of a substance = 6 X1023 molecules e.g. glucose (C6H12O6) 1 mole = 180 g Make up to 1 L with water = 1 M solution of glucose e.g. NaCl 1 mole = 58.5 g Make up to 1 L with water = 1 M solution of NaCl 17.

[Audio] Osmolarity Osmolarity = concentration of particles in 1 L solution ions When you put glucose into a solution, it stays as glucose and does not dissociate e.g. glucose 1 Molar solution of glucose = 1 Osmolar solution of glucose Salts dissociate e.g. NaCl 1 Molar solution of NaCl = 2 Osmolar solution of NaCl Bc one salt dissociates into 2 ions Note: 1 Osmolar (Osm) = 1000 milliOsmolar (mOsm) 18.

[Audio] 1) Osmosis Pure water 0 mOsM 300 mOsM Osmosis is example of flow down gradients: Water moves from high water to lower water i.e. Lower osmolarity to higher osmolarity 19 if too much water moves in, the cell is gonna burst.

[Audio] Osmosis: Example 2 1000 mOsM 300 mOsM Cell is gonna shrink 20.

[Audio] Review question If a cell with an osmolarity of 300 mOsM were placed in a solution of 150 mM NaCl what would happen? A. It would swell B. It would shrink C. No change C.

[Audio] External–internal exchange cells epithelial cells external plasma interstitial fluid blood cells In: → Nutrients, electrolytes, water, oxygen, etc Out:  Wastes and unneeded material (including excess water).

[Audio] The movement of water is determined by all of these forces combined, tending to create the "Net Filtration Pressure", the net of forces for some filtration of the fluid to move out of the plasma and into the tisssues 2) Starling forces What governs water going into and out of blood stream P Tissue oncotic Capillary hydrostatic pressure pressure P The fluid/water pressure that tends to favor movement of water out of the capillary Tendency to draw water out if there was lots of protein in the interstitial fluid RBC rotein P P P P P P P P WBC P One of the key protein in cells is albumin P P P P P P The proteins in or out of the blood stream will also influence how water moves in and out P As water moves out, there is also gonna be a build-up of fluid in the tissues if that is not drained by lymphatics for example Tissue hydrostatic pressure Capillary oncotic pressure 23 The idea is that fluids are drawn in when there is more protein present A fluid pressure that is gonna favor the water/fluid to move back into the capillary.

[Audio] Pathways for movement of substances into/out of the body Respiration O2 Cells Ingestion Extracellular connective tissue (including bone) Filtration Absorption Secretion Plasma and interstitial fluid (extracellular fluid) Lumen of digestive tract Lumen of renal tubules Secretion Reabsorption (Minimal) Excretion Other losses Excretion Feces Urine Sweating, hemorrhage, Respiration CO2.

[Audio] Summary Fluid and solute entry into and production in the body is balanced by use and output On average 2.5 L of water enters the body/is produced each day and the same amount is removed About 60-65% of body weight is water 2/3 is intracellular and 1/3 is extracellular Water moves between compartments via osmosis and due to Starling forces?.