phys renal lec 2

Health kidneys produce large volume of filtrate per day. Blood is filtered, filtrate has to be processed by tubule. How much fluid is filtered a day, and how much urine is made a day

(180 liters filtered a day - that moves to bowman's capsule?). Majority of the fluid is going right back to the body. Seems counterproductive. Only make around 2 litres of urine a day

List and describe the four pressures that affect glomerular filtration

1. Hydrostatic pressure of glomerular capillaries (Pgc) - pressure coming from movement of fluid, caused by blood flowing into the glomerulus (through heart pushing blood through organs). a. Promotes filtration (from capillary to b. Value of ~55 mm Hg (biggest factor) 2. Colloid Osmotic Presure of Glomerular Capillaries. Protiens in capillaries, they draw water towards themsevles. a. Inhibit filtration, slow it down.(πGC) b. Value of ~30 mm Hg 3. Hydroystatic pressure of Bowman's Capsule ( PBC) a. Pressure caused by filtrate remaining in bowman's space, that fluid sits inside that space, its going to cause a blockakge, its in the way b. Inhibits filtration c. ~15 mm Hg 4. Colloid osmotic pressure of Bowman's capsule ( πBC) a. Favors filtration if there are proteins in BC (proteins would draw water toward them, this IF should never happen, if glomerulus is working properly, protiens shouldn't get in, something is wrong. Net filtration pressure = • Net filtration pressure = (PGC + πBC)- (PBC + πGC) • Since πBC ~ 0, then ( if healthy person, then simplify[below]) • Net filtration pressure = (PGC) - (PBC + πGC) • Net filtration pressure = (55 mm Hg) - (15 mm Hg + 30 mm Hg) • Net filtration pressure = 10 mm Hg = healthy • @ 15 mm Hg = More filtration

smooth muscle of the afferent arteriole contracts (constricts afferent arteriole) - diameter decreases. What happens to renal blood flow, to renal BP? To filtration? How does it act as a safety mechanism

BF decreases, less blood able to be filtered out, BP decrease - which means hydrostatic pressure of glomeruls in corpuscle decreases, less pressure less filtration. Glomerulus protected. Should still fitler same amount of blood as calm and relaxed.

GFR

Glomerular filtration rate, amount of fluid filtered in a day by the kidneys (180 L/day)

• What happens when you filter too much or too little

If you filter more fluid, burst nephrons, not enough filtration you don't get rid of all those things you need to get rid of

Forces work together, in the renal corpuscle to produce the

NET FILTRATION PRESSURE

Complete the chart that applies the information after calculating the filtered load

Substance Filtered load (day) Amount Excreted % Reabsorbed Water 180 L 1.8 L (180 - 1.8)/180 * 100 = 99% Sodium 630 g 3.2 g (630g - 3.2g)/630 g * 100 = 99.5% Glucose 180 g 0 g 100% Urea 56 g 28 g (56 g - 28 g)/ 56 g * 100 = 50%

Describe the auto regulatory mechanisms of the kidney

We have autoregulation of GFR, our body takes care of it. Despite everything that happens, we need to still filter. Make sure pressures inside the kidney stay the same. Two autoregulatory mechanisms that function to keep GFR fairly constant throughout the day: 1. Myogenic Response 2. Tubuloglomerular Feedback If blood pressure increases in the body, that will be detected by these two mechanisms - does this by more stretching by arterioles (myogenic response)+ more ions being filtered than normal (tubuloglomerular feedback.. Body detects more ions than normal, BP must be going up.

Renal handling

What does the tubule do to that particular thing in your blood. • Filtered load calculates how much of a substance filters into Bowman's space in a day. ( how much are you filtering in a day) • Determined by the concentration of that substance in the blood and the individuals GFR • Filtered load X (e.g., urea, amino acids, glucose) = [concentration of X]plasma x GFR (how much of that thing should have been filtered into bowmans space). • Renal handling is then determining how much of that substance gets into the urine (excreted) and hypothesizing how that substance was handled - was that substance fully reabsorbed, some or none of it?.

What happens if afferent arteriole dilated, and efferent arteriole dilated

answer later

What if proteins got in bowman's capsule*

colloid osmotic pressure, promotes filtration. 1. Colloid osmotic pressure of Bowman's capsule ( πBC) a. Favors filtration if there are proteins in BC (proteins would draw water toward them, this IF should never happen, if glomerulus is working properly, protiens shouldn't get in, something is wrong.

Filtration only happens in the

corpuscle

• What would be the correct substance to measure?

creatinine - always there, filters in bowman's space, body doesn't want to keep it - fully secreted. Slight problem with creatinine, because some is secreted. Invasive tests, injected with protein - inulin, know concentration 100%

• Would do you think would be a bad substance to evaluate to determine GFR?

glucose (100% reabsorbed)

• What would happen to GFR if the afferent arteriole constricted?

less blood, less pressure inside corpuscle, decrease GFR

If net filtration pressure is less than 10 mm Hg, what happens to filtration?

less filtration

• What would happen to the GFR if the efferent arteriole constricted?

more blood (increased volume), increase pressure inside corpuscle, filter more fluid, increase GFR

If net filtration pressure is 10 mm Hg, then

proper filtration can occur

Tubuloglomerular feedback

when BP goes up initially, you start making more filtrate intially, more fluid getting into bowmans space, more fluid = more ions. That filtrate travels through tube, ions are higher than they are, BP might be up. Increase ION in filtrate can affect GFR through this mechanism. • Content of the filtrate can affect the GFR locally • If Na+ and Cl- levels higher than "normal" due to an increase ○ Macula densa cells detect level of Na and Cl- and release a chemical messenger ○ Chemical messenger to juxtamedullary? cells causes the afferent arteriole to constrict ○ Decreasing diameter, Blood flow decreases in the glomerulus, protecting it from bursting and slowing down how much fluid is being filtered. • Think of this scenario only when BP increases, she wont test if BP goes down in this particular topic

Complete the sample calculations for filtered load, use 1 mg/ml of glucose

• Example Glucose • Filtered load X = [X]plasma x GFR • [glucose]plasma = 1 mg/ml (not talking about liters anymore) • GFR = 180 L/day or 125 ml/min ○ Conversion - 180 L/day x 1000ml/L x day/1440 min. ○ Cross out = 125 ml/min • Filtered load glucose = 1 mg/ml x 125 ml/min (GFR) • Filtered load glucose = 125 mg glucose excreted per minute. Whole lot of glucose that could possibly make it into urine. • Evaluate glucose in urine and observe no glucose. What happened to all of the glucose that filtered? All got reabsorbed

Regulation of GFR by blood flow

• GFR can be increased or decreased quickly by constricting or dilating the arterioles surrounding the corpuscle. Plus hormones

List the factors affecting GFR

• Net filtration pressure (sums of forces that exist in corpuscle) ○ Had 4 faces, but the forces that was the largest was the glomeral hydrostatic. You get that from your heart (normal BP and good heart).mostly affected by the renal blood flow (right amount of blood - 20% from heart) and blood pressure (PGC) • Filtration coefficient ○ Are we capable of filtering the right amount, we are because we have the barriers, those spaces. mostly affected by the spaces in between podocytes and integrity (permeability, spaces can change) of the basal lamina (sticky tissue is a certain diameter, certain composition, can change composition if kidney gets infected, or genetic disease •

How to measure GFR? (pic)

• Recall: • Urine (what is excreted) is the result of the processes of the kidney • Excretion = Filtration - Reabsorption + Secretion • We can determine an individuals GFR by selecting the correct substance to evaluate in their urine/ (audio?). • Select a substance that is excreted and NOT reabsorbed. Rate of creatinine excretion from the body is equivalent to the GFR MEASUREMENTS- [Creatinine]plasma = 1 mg/L [Creatinine]urine = 90 mg/L (collect for 24 hours, extrapolate how much fluid they must of filtered.) Urine/day = 2 L CALCULATION ([Creatinine]urine * Urine/day) / [Creatinine]plasma = 180 L/day = GFR. (90 mg/l * 2 L/day)/ 1 mg/L = 180 L/day = GFR

Myogenic response

○ Afferent (goes into glomerulus, brings blood into corpuslce) arteriole stretches ○ -> stretch sensitive ion channels in arteriole, open ○ -> smooth muscle cells depolarize ○ -> voltage-gated calcium channels in smooth muscle open ○ smooth muscle of the afferent arteriole contracts (constricts afferent arteriole) - diameter decreases. ○ blood flow decreases in the glomerulus