BIO 251 1st Edition Lecture 22 Outline of Last Lecture I. Tubular reabsorption a. Processb. Reabsorption of Ba+ in proximal tubule c. Reabsorption of Na+ in distal tubule d. Reabsorption of substances via Na+ dependent secondary active transporte. Reabsorption of substances via Na+ dependent passive processesf. Reabsorption of phosphateII. Tubular secretion a. H+b. K+c. Waste ions III. Urine concentration a. Countercurrent multiplication b. Controlling urine concentrationOutline of Current Lecture I. Input & output of fluids & ionsa. Balance conceptb. Types of input & outputThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.II. Fluid & ion distribution in body a. Fluid compartment within bodyb. Ion distribution c. Mvmt of water ions w/I ECFd. Regulation of fluid/ion distrbIII. Regulation of ECF volume a. Na+ balanceb. Mechanisms regulating Na+ in kidney c. Control of Na+ reabsorptionIV. Regulation of ECF osmolarity a. Purpose b. How ECF effects ICFc. Mechanisms of water regCurrent LectureI. Input and Output of Fluids and IonsA. Balance concept (Fig 19.2)1. If the amount of fluids & ions are to remain stable in body, input must equal output.2. Not all input and output pathways are regulateda) most input pathways are poorly regulated(1) people will eat & drink what they want even if they don’t need it(2) H+ ions are uncontrollably produced internallyb) some output poorly regulated(1) Salt, water and H+ are lost uncontrollably through vomiting and sweatingc) Humans regulate water, salt and H+ balances primarily through kidney functionB. Types of input and output (Fig 19.1 & 19.3)1. Inputa) From Environment(1) ingestion, inhalation, absorptionb) Metabolically produced(1) products (e.g., amino acids) and by-products (e.g., H+ and water) of metabolic processes2. Outputa) Excretion to environment(1) through kidneys, digestive tract, lungs, body surface (e.g., urine, feces, sweat,water vapor in breath, sloughed off skin)b) Metabolically consumedII. Fluid and Ion Distribution in Body (review from Topic 1)A. Fluid Compartments within Body (Fig 1.5)1. Intracellular Fluid (ICF)a) within cells2. Extracellular Fluid (ECF)a) outside cellsb) further compartmentalized into(1) Plasma(2) Interstitial fluid(3) Boundry is capillary walls3. Boundry between ECF and ICF are cell membranesB. Ion Distribution among compartments1. Table 4.1C. Movement of water and ions within the ECF1. Water moves freely by osmosis between plasma and interstitial fluid2. Most solutes (EXCEPT plasma proteins) move freely by passive means between plasma and interstitial fluidD. Movement of water and ions between ECF and ICF1. Water moves freely between ECF and ICFa) This movement is determined by osmotic effects alone2. Ions do not move easily between ECF and ICFa) Solute movement restricted across cellular membranesb) Cellular proteins in the ICF usually can’t leave cells and generally are not found in the ECF.c) Na+ and K+ and their associated anions are unequally distributed between ECF and ICF; this is maintained in large part by the Na+-K+-ATPase pump.E. Regulation of fluid and ion distribution1. The ECF is intermediate between the ICF and the external environment.a) All exchanges of water and solutes between the ICF and the external environment must go through the ECF.2. Plasma is the only fluid that has its volume and composition regulated. However, if plasmavolume or composition changes:a) the interstital fluid also changesb) the ICF changes to the extent allowed by cell membrane permeability3. Why you must regulate fluid and ion levels:a) ECF volume must be regulated to maintain blood pressure. Maintenance ofsalt balance is the primary way that ECF volume is regulated over the long termb) ECF osmolarity (mg solutes/ml fluid) must be regulated to prevent shrinking or swelling of cells because ECF osmolarity affects ICF osmolarity. Maintenance of water balance is the primary way this is accomplished.c) ECF volume and ECF osmolarity are intimately related to each other!III. Regulation of ECF Volume: Controlling the Amount of Na+.A. Purpose: Long term regulation of blood pressure by regulating plasma volume, which isaccomplished by regulating the total quantity of Na+.1. Baroreceptor reflex and fluid shifts between the plasma and interstitial fluid are importantshort term mechanisms of regulating blood pressure.2. If plasma volume is too far from normal, short term mechanisms are ineffective, so amount of Na+ must be regulated3. Increases in Na+ lead to increases in ECF volume (because of osmotic forces: if you hold on to Na+, you automatically hold onto water too) and hence increase blood pressure; decreases in Na+ lead to decreases in ECF volume and hence decreases in blood pressure.B. Na+ Balance1. Input: eating salt; not well controlled (most Americans eat way more salt than is needed)2. Output: Loss of salt in sweat, feces, and urine; only excretion in urine is regulated.C. Mechanisms regulating Na+ excretion in kidney1. Control of filtration rate in kidneya) increasing filtration rate causes an increase in Na+ filtration and hence Na+excretion; water is excreted along with the Na+, so ECF volume decreasesb) decrease in filtration rate leads to decrease in Na+ filtration and excretion; Na+ and associated water conserved, which leads to an increase in ECF volume.2. Control of Na+ reabsorbed in kidneys (Fig 18.3, 19.15, 19.16, 19.17, 19.18)a) In proximal tubule and loop of Henle, a constant percentage of filtered Na+ is reabsorbed, regardless of the absolute amount present.b) In the distal tubule, Na+ reabsorption is regulated.c) Primary positive regulation system is the renin-angiotensin-aldosterone system; you can upregulate or downregulate this system to alter Na+ and hence bp.(1) If Na+ levels fall (which causes a decline in ECF volume and bloodpressure), the juxtaglomerular apparatus secretes the hormone renin into the blood.(2) Renin activates angiotensinogen by converting it to angiotensin I, which is then converted to(3) angiotensin II by angiotensin converting enzyme found mostly in lungs.(4) Angiotensin II then stimulates the adrenal cortex to secrete(5) aldosterone, which increases Na+ reabsorption in the distal and collecting tubules by adding more Na+-K+-ATPase pumps to the basolateral membranes.(6) This promotes Na+ retention, and so increases ECF volume and arterial bloodpressure(7)