What are the major activities of the kidney?
How do you determine the amount of material excreted by the kidney?
Amount filtered - Amount reabsorbed + Amount Secreted = Total amount secreted.
Gross drawings of the kidney are shown below. What is indicated by each number?
1= Renal artery. 2 = Interlobar artery. 3 = Interlobular artery. 4 = Arcuate artery. 5 = Glomerular Arterioles
What is an easy way to differentiate the cortex from the medulla of the kidney on a histology slide?
Acuate arteries separate the two.
How do capillaries divide in the kidney downstream from the glomerulus?
Into peritubular networks and vasa recta
What structures are indicated in the image seen below?
That is a glomerulus. #1 = glomerular capillaries. #2 = an arteriole (can't tell whether is afferent or efferent).
How is renal blood flow auto regulated?
Myogenic and Tubuloglomerular feedback.
How is the structure indicated below involved in auto regulation?
This is a glomerular arteriole. The reaction to stretch in smooth muscle is constriction. Thus, when blood pressure goes up, the afferent arterioles constrict to maintain a steady perfusion rate to the glomerulus. When BP drops, the efferent arteriole constricts to maintain glomerular perfusion pressure.
Identify the structures labeled in the image below.
1: Renal corpuscle (glomerulus & Bowman's capsule). 2: Tubule system. 3: Proximal Convoluted Tubule. 4: Loop of Henle. 5: Distal Convoluted Tubule. 6: Collecting Duct.
What layers make up the renal corpuscle?
Visceral layer covered in podocytes and the parietal layer on the inside of Bowman's capsule.
Label all of the different structures seen below.
1: Urinary Space. 2: Renal Corpuscle. 3: Capillary & Endothelial cell. 4: Parietal layer of Bowman's capsule. 5: Podocyte
What are the structures indicated in the image below?
1: Afferent arteriole. 2: Efferent arteriole. 3: Parietal Layer. 4: Urinary Space. 6: Proximal Tubule
What type of capillaries make up the glomerular capillaries?
Fenestrated endothelium. This is what allows for filtration.
What structures are indicated in the image below?
1: Podocyte. 2: Primary Process 3: Secondary process (Pedicel)
What structures are seen in this image?
Note the fenestrated capillaries do not have a diaphragm. The modified basement membrane acts as a barrier to many molecules that could normally escape through the pores of the fenestrated endothelia because it has highly charged particles.
What cell is the macrophage of the urinary system? What flavors are there?
Mesangial cell. Intraglomerular mesangial cells are phagocytes in the basement membrane that keep the glomerular basement membrane free of debris. Extraglomerular mesangial cells are a part of the juxtaglomerular apparatus.
What cells are indicated in the image below?
Note that podocytes look similar, but will be located more on the periphery while mesangial cells will be located in clusters.
What capillary pressures favor glomerular filtration? Oppose it?
60 mmHg capillary pressure favors it. 15 mmHg interstitial Bowman's pressure and 27 mmHg osmotic force oppose it. This makes for a net glomerular filtration pressure of 18.
What is the basic clearance formula for any substance X? How do you apply this formula clinically?
Why is inulin a good tool for measuring glomerular filtration rate?
There is no reabsorption or secretion that happens with inulin, taking the convoluted tubules out of the GFR equation. It is only filtered and excreted and is thus a direct measure of GFR.
Since inulin is very difficult to use in a clinical setting, what do we use?
Creatinine. It is created at a fairly constant level. In the blood, creatinine levels will rise if GFR falls and vice versa.
How do demographics affect serum creatinine levels?
Males and african-americans have the highest levels of creatinine. People with higher muscle mass will also have higher creatinine levels.
How do we estimate renal blood flow?
PAH is a molecule that is almost entirely cleared from the blood from filtration and secretion. Since clearance is near 100% from the plasma, we can estimate renal plasma flow.
What correction must you make if you want to estimate renal blood flow with PAH levels?
PAH is in the plasma and = Renal plasma flow, and plasma is only about 1/2 of blood volume.
What cells are in the proximal convoluted tubule?
Cuboidal cells with a brush border of microvilli. Lots of mitochondria are found at the base to fuel the Na-ATPase.
What cells are in the thin descending loop of Henle?
Simple squamous cells
Where does the nephron end?
Connecting tubule. It connects the distal convoluted tubule to the collecting duct.
What is a typical glomerular filtration rate?
How much of the GFR do proximal tubules typically capture? How does this affect the rest of the nephron?
65%. Glomerular flow decreases with each portion distal to it.
What portion of the kidney is responsible for water retention or water reabsorption?
What is the fate of materials reabsorbed by the proximal convoluted tubule?
They traverse the cell and exist the basement membrane into the interstitial space. Here it can enter the peritubular capillaries through aquaporin channels.
What is responsible for the nephron's ability to reabsorb many different materials?
The Na-ATPase pump. It keeps the gradient in the PCT cells so particles can be co-transported in with Na.
What materials are secreted by the PCT?
Creatinine, choline, urate and hydrogen.
Why do diabetics pee out glucose?
The high levels of glucose in the plasma exceed the T.m. (transport maximum) and it can no longer be reabsorbed.
Why is thirst and/or frequent urination an early sign of diabetes?
Glucose levels are so high that the nephron cannot reabsorb it all. The increased concentration of glucose in the lumen of the nephron creates an osmotic force that pulls water into the lumen.
Is reabsorption or secretion happening at the thin descending limb of the loop of Henle?
Water is leaving w/ no active ion transport
What is the tonicity of the urine at the thin ascending limb of the loop of Henle?
Na & Cl are passively leaving the lumen, but is impermeable to water, making it hypotonic.
At what point in the loop of Henle does active ion transport begin?
Thick ascending portion. Na, Cl and K are transported across the tubular cells. The gradient created by transport of these ions also aids in recovery of Ca and Mg. Additionally, no water is leaving at this point.
What materials are recovered at the distal tubules? What are secreted?
Recovered: most ions (Ca, Mg, HCO3, Na, K, Cl). Secreted: ammonium, potassium and hydrogen
How do you distinguish between the proximal and distal tubules of the nephron histologically?
The nuclei are more apical and there is not a brush border in the distal tubules.
What is the function of the cells indicated in the image below?
This is the macula densa portion of the distal tubule. They monitor the sodium chloride concentration and water volume in the tubular fluid. When they sense decreased NaCl levels from decreased GFR, they release ATP onto the mesangial cells. Mesangial cells' Ca2+ channels open and acton on renin secreting cells. Renin is secreted, angiotensin II is made, efferent arteriolar resistance is increased and glomerular hydrostatic pressure is increased.
What are the different components of the collecting system?
Connecting piece, collecting tubule (cortical), collecting tubule (medullary) and a collecting duct.
What type of regulation occurs at the cell indicated below?
This is a principal cell of the cortical collecting tubule. Principal cells (light cells) are involved in water regulation. It's functional channels are the aquaporins.
What type of regulation occurs at the cell indicated below?
This is an intercalated cell of the cortical collecting tubule. Intercalated cells (dark cells) are involved in acid/base regulation. It's functional channels are different ion pumps.
What key histological feature helps you differentiate collecting tubules from nephron tubules?
The boundaries between cells are more definite in the light microscope view of collecting cells.
Identify the different structures seen in the image below.
This is a section from the medullary collecting ducts. You know you're in the ducts and not the collecting tubules because you mostly see principle cells with definite boundaries. Also note proximity of vasa recta that recapture water released from the collecting ducts and tubules.
Where are you transitioning from in the EM of the kidney seen below?
Note the transition from cuboidal to columnar epithelial cells. This indicates movement from collecting ducts to ducts of Bellini (papillary ducts) and on to minor calyces.
What structures are labeled below?
This is a ureter. Note the stratified transitional epithelium that will carry on into the bladder.
What histological characteristic of the bladder shows its ability to expand as urine enters and contract to expel it?
It has multiple layers of smooth muscle in varying orientations. The transitional epithelium (dome/umbrella cells) is also able to expand and compact.
How does the epithelium vary in the structure whose images are shown below?
This is the urethra, note the smooth muscle is not as well defined as it is in the ureters. It begins with transitional epithelium. It then begins to change into pseudo stratified epithelium and finally becomes a stratified squamous epithelium.
How does micturition occur?
Parasympathetic reflex slightly contracts wall of bladder as it fills and expands. Once it fills to about 150cc, you become conscious of a full bladder. At this point you consciously control the bladder with the external sphincter up to about 300-400cc. Relaxation of the external sphincter and contraction of the abdominal muscles empties the bladder.