chapter 27 lecture one is an introduction to fluid balance body fluid is all the water and dissolved solutes in all of your body fluid compartments and we have a number of different mechanisms that are going to regulate the total volume how it's distributed and the concentration of the different solutes and the ph it's really important that we maintain homeostasis the body fluids or it could be fatal so here's an example excessive blood loss sweating vomiting or diarrhea coupled with the intake of plain water so that decreases your sodium concentration but the interstitial fluid and plasma causing something called hyponatremia remember natrium is sodium so hypo is below sodium you have decreased osmolarity of the interstitial fluid and plasma followed by osmosis of water into the intracellular fluid remember osmosis is movement of water across the semi-permeable membrane in order to dilute solutes so if you're hyponatremic it means that you're you know very low levels of sodium in your extracellular fluid you have more sodium in your intracellular fluid so water is going to move in that direction the cells are then you suffer from water intoxication your cells swell up and you can have convulsions coma and die so there's only two places for exchange between the compartments the cell membranes separate the intracellular from interstitial and then the capillaries separate the plasma from the interstitial fluids as i said it's important that we keep these volumes constant and the electrolytes have to be constant as well because water follows solute where salt goes water follows now women have a total body mass that consists of about 45 solids and 55 fluids guys have more fluids uh because women store fat so we tend to have more fat guys have more fluids of the fluids that we have in our body two-thirds of it is found inside of cells one-third is extracellular and of that 80 is going to be interstitial and the remaining 20 is going to be plasma so again the exchange is between the cell membrane and the interstitium and the interstitium and the capillary water is the main component of all body fluids interstitial fluid can be characterized as different things like lymph csf gastrointestinal fluids synovial fluid fluid in the eye ears and the peritoneal fluids as well as the glomerular filtrate selectively permeable membranes allow certain things to pass others not and this is what we have in the individual cells as well as the cells of the blood vessel walls but this is not to say that fluid remains constant because it doesn't move it's constantly moving from one compartment to another and making it just adjustments however the volume is going to stay fairly stable so fluid balance not only indicates water balance but also electrolyte balance electrolytes are are molecules that have charges and so the two are inseparable osmosis is the main way water moves in and out and most of the solutes in body fluids are electrolytes electrolytes are remember charged molecules they're compounds that dissociate into ions like hydrochloric acid dissociates into hydrogen ions and chloride ions excuse me sodium chloride into sodium ions and chloride ions and so forth now of the water we have in our body it makes 45 to 75 body weight as you get older you tended to have more fat less muscle and so your body your proportion of body that is water decreases the gains of water come from drinking ingested liquids the fluid portion of foods you eat that makes the bulk of it then we have metabolic water now remember when we uh looked at the different types of monomers that form polymers and that are broken back down into monomers when you make a bond you lose water when you break a bond you gain water you add water back to it that's dehydration synthesis and hydrolysis well dehydration synthesis you're losing a water molecule from the compound every time you make it which means you're gaining that water and that's metabolic water gain it comes from reactions dehydration synthesis reactions mainly during aerobic respiration but also during other types of dehydration synthesis any type of anabolic reaction where you're building something you're going to lose water so we may we bring in about two and a half liters a day of fluid through these different mechanisms we lose water the gi tract as part of the feces through our lungs through respiration remember when you exhale you exhale water vapor and carbon dioxide the skin we lose water through there through both sensible perspiration the perspiration you can feel as well as insensible perspiration the perspiration you can't feel and then through the kidneys about a liter in half so our water loss and water gain have to be equal the main regulation of fluid gain is thirst so you're dehydrated decreased flow of saliva and increased osmolarity of the blood remember osmolarity is the concentration of solutes so as the relative amount of water in the blood decreases the solute concentration gets higher we're also going to have a decreased blood volume the dry mouth decreased saliva gives you dry mouth and pharynx the increased blood osmolarity stimulates the osmo receptors in the hypothalamus and that's going to um cause the release of adh from the posterior pituitary decreased blood volume gives us decreased blood pressure and we're going to start releasing renin from the juxtaglomerular cells of the kidneys in order to increase angiotensin to formation which causes the vasoconstriction as well as release of aldosterone so now we're having adh being released aldosterone being released um all of these stimulate the thirst center and the hypothalamus it increases thirst and it's going to make you want to to have a drink have something to drink to alleviate that thirst as well as can try to decrease fluid loss so that's going to help to increase body water to normal level and relieve dehydration so thirst is the main regulator of fluid gain the metabolic water volume like i said is mostly coming from aerobic cellular respiration but any type of anabolic reaction is going to produce water as a byproduct when water loss is greater than water gain dehydration occurs and that causes the process that i just spoke of when you drink water or drink liquids it returns your body water to normal the loss of body water excess solutes pains meant depends mainly on regulating how much is lost in urine and under normal conditions that's that's regulated by these three hormones antidiuretic hormone which is released from the posterior pituitary atrial naturatic peptide which is released from the atria of the heart and aldosterone which is released as part of the renin angiotensin aldosterone system it's produced in the adrenal cortex and it's a steroid hormone all of these help to regulate the production of urine remember adh and aldosterone are going to de decrease urine formation and increase fluid reabsorption amp does the opposite okay because that's being released because the atria and the heart are stretching because the fluid volume is too high and so the negative feedback loop would suggest that the answer to that is to decrease the fluid and you decrease it through an increase in filtration and as well as an increase in urine