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UNC-Chapel Hill BIOL 252 - Urinary System Part 2

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BIOL 252 1st Edition Lecture 22 Outline of Last Lecture I. How significant is pulmonary elasticity?II. VentilationIII. Resistance to AirflowIV. Respiratory VolumesV. Restrictive Pulmonary DisordersVI. Obstructive Pulmonary DisordersVII. Gas exchangeVIII. Gas transportIX. Urinary SystemX. Kidney FunctionXI. Nitrogenous WastesXII. NephronOutline of Current LectureI. Steps in Urine FormationII. Renal CorpuscleIII. Regulation of Glomerular FiltrationIV. Proximal Convoluted Tubule: Tubular reabsorptionCurrent LectureI. Steps in Urine Formationa. Glomerular filtration: creates plasmalike filtrate of bloodb. Tubular reabsorption: removes useful solutes from filtrate, returns them to bloodi. Tubular secretion: removes additional wastes from blood, adds them to filtratec. Water conservation: removes water from urine and returns it to blood; concentrates wastes II. Renal Corpusclea. Glomerulus and Bowman’s capsule comprise renal corpuscleb. Podocytes – because they have feet; interdigitate with neighbors i. Make narrow slit called a filtration slitii. If something goes from capsular space to blood, will have to go through filtration slits c. Capsular space – where filtrate goes These 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.d. Physiologyi. Filtration w/out reabsorptionii. Blood hydrostatic pressure: 60 out, pressure w/in capillaryiii. Colloid osmotic pressure: 32 in, pressure due to high osmolarity of blood (due to proteins) – proteins in blood, osmosis (water) tends to go into capsular space iv. Capsular pressure: 18 in, pressure within the glomerular capsule1. Due to confined space v. NET filtration pressure: 10 mm Hg pushing in outward direction – pushes fluid through tubule system e. Importance of NFPi. Determines flowii. Glomerular filtration rate = volume of filtrate over time1. Typical male: 180 L/dayiii. How is NFP related to GFR1. If one goes up, the other goes up 2. Proportionaliv. How can we lower filtration rate?1. Efferent arteriole constrictiona.2. Constricting systemic arteriolesa. Constricting arterioles increases peripheral resistanceb. Resistance increasing = higher BP (the same as elevating aortic BP)3. Elevating aortic blood pressurea. BHP increases (>60)b. Increases NFP  increases GFP 4. Afferent arteriole constrictiona. Making it smaller decreases pressure in glomerulus f. Importance of GFRi. Affects reabsorption and secretionii. If GFR too high, reabsorption insufficientiii. If GFR too low, wastes are reabsorbed III. Regulation of Glomerular Filtrationa. Renal Autoregulationi. Tubuloglomerular feedback: tells filtration apparatus how it should change – controls vasoconstriction of afferent arteriole 1. Macula densa controls afferent arteriole diameter2. If salty filtrate b/c left too many things behind, slow down filtration rate3. Salty filtrate slows GFR; dilute filtrate increases GFRii. Myogenic mechanism1. Afferent arteriole responds to pressure and controls its own diameter2. High arterial BP (running, etc. elevates BP) a. If arterial pressure goes up by 10 to 70 mm Hg, afferent arterioles constrict b. Sympathetic controli. Under fight or flight, afferent arterioles constrict b/c of higher arterial blood pressure AND must divert blood to parts of body that need it1. Divert away from digestive organs and kidneys 2. At the consequence of renal function, dramatically decreases NFPc. Renin-angiotensin-aldosterone mechanism i. Hormone systemii. When BP drops below ability to autoregulate, renin released from JG cellsiii. Angiotensinogen converted to angiotensin I by reniniv. Angiotensin I converted to angiotensin II by ACE1. Angiotensin II a. Affects hypothalamus; makes brain think we’re thirstyi. Adding water to blood elevates BP b. Vasoconstriction = elevated BPi. Arterioles constrict increases peripheral resistance increases BP – restores filtrationc. To adrenal cortex i. Aldosterone stimulates even more reabsorption (pull sodium into blood) – water in tubules will follow itii. Reabsorb sodium and water (retaining as much water as possible)iii. Increases BP and restores filtration iv. Urine is very concentrated – more wastes/volume of water d. Which would NOT result in afferent arteriole vasoconstriction?i. Severe hemorrhage1. Hypovolemia (low BHP) – causes us to have afferent arteriole dilation and possibly renin release ii. High glomerular hydrostatic pressure1. High BHP = high NFP; want to lower it2. Lower NFP by arteriole constrictioniii. Elevated angiotensin II1. Increases BP, causes constriction of afferent arteriole iv. High osmolarity in DCT 1. GFR is high – pushing fluid too quickly2. Must lower GFR => must lower NFP3. Lower NFP by afferent arteriole constriction IV. Proximal Convoluted Tubule: Tubular reabsorptiona. Movement of substances from filtrate to blood occurs via “paracellular route”b. And via “transcellular route”c. Transport maximumi. Limit to amount of solute that renal tubules can reabsorb ii. If you have diabetes, hyperglycemia (too much glucose)1. Filter huge amounts of it – reach transport maximum2. All transporters


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