Urinary System

Question 1

The kidneys maintain the body’s internal environment by doing what?

Answer 1

Keeping the fluids of the body (blood plasma and interstitial fluid) isotonic to the fluid inside the cells. More specifically, the kidey’s function are: regulating the total amount of water in the body (so regulating blood pressure), regulating the concentrati of solutes in the body, regulating the concentration of ions in the fluids, long-term acid/base balance, excreting metabolic wastes like urea and other toxins like alcohol, producing the hormone erythropoietin, and converting vitamin D to the active form of vitamin D.

Question 2

Be able to label a diagram with these structures: kidney, renal artery and vein, hilum, ureter, bladder, urethra, adrenal gland.

Answer 2

Done

Question 3

What is the name of the membrane that anchors the kidney to the adrenal gland and surrounding structures?

Answer 3

The renal facia.

Question 4

What is the name of the fat that cushions the kidney on the outside?

Answer 4

Perirenal fat capsule.

Question 5

Where would you find the fibrous capsule?

Answer 5

Adheres to the outside of the kidney and protects the kidney from infection.

Question 6

If you were to take a frontal section of the kidney, you would see three regions inside. What are they called? Label, in addition, renal pelvis, major calyces and minor calyces.

Answer 6

The renal cortex, which is outside and looks lighter, the renal medulla, which includes renal pyramids and renal columns and the renal pelvis. The renal pelvis is funnel shaped tube that is continuous with the ureter.

Question 7

What is a nephron? What’s its main function?

Answer 7

The nephron is the functional unit of the kidney. In other words, if you take one nephron and study its parts, you know all the parts of the kidney. The kidney is made up of many millions of nephrons. The main function of the nephron is to make urine out of filtrate.

Question 8

What is filtrate?

Answer 8

Filtrate is the fluid of the blood that passes through a filter (the glomerulus capillary bed) and enters the nephron.

Question 9

Be able to draw or look at a picture and label: glomerulus, bowman’s capsule, proximal convoluted tubule, nephron loop (descending and ascending limbs), distal convoluted tubule and collecting tubule.

Answer 9

Done

Question 10

What structures make up the renal corpuscle? What part of the kidney do they exist in?

Answer 10

The renal corpuscle is the glomerular capsule, and the glomerulus.

Question 11

What part of the kidney do the renal tubules exist in?

Answer 11

The renal tubules begin in the cortex and some of them extend into the medulla.

Question 12

What type of epithelial cell makes the glomerular capillaries? What does it mean to say that they are fenestrated?

Answer 12

Simple squamous epithelial cells. Fenstrations are pores, spaces between the cells where fluid from the blood can pass through into the renal corpuscle.

Question 13

Describe the glomerular capsule parietal layer and visceral layer.

Answer 13

The parietal layer is continous with the tubule, the outside layer. The visceral layer lines the capillary bed (glomerulus).

Question 14

What type of epithelial cells form the proximal convoluted tubule? What advantage does the brush border (microvilli) of these cells have?

Answer 14

SImple cuboidal epithelial cells. The brush border increases the surface area to make more room for reabsorption of solutes from the filtrate back into the body.

Question 15

What type of epithelial cells form the descending nephron loop? Ascending loop?

Answer 15

Simple squamous epithelial cells in the descending loop. Simple cuboidal to small columnar cells in the ascending limb.

Question 16

What type of epithelial cells form the distal convoluted tubule? Do they have microvilli?

Answer 16

Simple cuboidal epithelium, but they are shorter then the cells in the proximal tubule and don’t have a brush border.

Question 17

What types of cells are found lining the collecting tubule? What’s the function of each cell type?

Answer 17

There are two types of simple cuboidal epithelial cells lining the collecting duct. Principal cells maintain the body’s water and Na+ balance, maintaining homeostasis of blood pressure. The intercalated cells help maintain the blood pH.

Question 18

What part of the kidney is the collecting tubule in?

Answer 18

The pyramids found in the medullar.

Question 19

Urine goes from the papilla of the pyramids of the medulla into this structure:

Answer 19

Minor calyx.

Question 20

Give the similarities and differences between the cortical and juxtamedullary nephrons.

Answer 20

The loop of henle in a cortical nephron is shorter and remains in the cortex. The loop of henle in a juxtamedullary loop dips into the medulla. The fuction of this longer loop is to help concentrate urine when you are dehydrated.

Question 21

Give the similarities and differences between the peritubular capillaries and vasa recta.

Answer 21

They are both capillary beds. The peritubular capillaries wrap around the proximal and distal convoluted tubules and the vasa recta wrap around loop of henle.

Question 22

What is the juxtaglomerular complex?

Answer 22

This is the most distal part of the ascending loop of the nephron (loop of henle), where it touches the afferent arteriole. There are three kinds of specialized cells here. Macula densa cells are in the ascending loop of henle. They have chemoreceptors in them monitoring the level of Na+ in the filtrate. If the filtrate leaving the body is to salty, then blood pressure might fall. If it isn’t salty enough, blood pressure might be too high. Granular cells are in the arteriole wall. THese are smooth muscle cells with granules that are full of renin. They also have mechanoreceptors that monitor stretch. If the arteriole is too full, they can tighten, slowing the flow down. If there isn’t enough stretch, meaning that there is less blood entering, they relax, allowing more blood to flow into the glomerulus. In this way, we get a consistent amount of fluid entering the kidney. Last, there are extraglomerular mesangial cells. THese are between the arteriole and the tubule cells. They help pass signals between the macula densa and granular cells through their gap junctions.

Question 23

What is the role of macula densa cells? Where would you find them?

Answer 23

See above.

Question 24

What is the role of the granular cells? Where would you find them?

Answer 24

See above.

Question 25

What is the role of the extraglomerular mesangial cells? Where would you find them?

Answer 25

See above.

Question 26

What are the three processes of urine formation and adjustment of blood composition?

Answer 26

Glomerular filtration, tubular reabsorption and tubular secretion.

Question 27

Why is pressure inside the glomerular capillaries so high? How does this high pressure help to form filtrate?

Answer 27

Pressure inside the glomerulus is high because the diameter of the afferent arteriole is bigger than the diameter of the efferent arteriole. More blood enters than can leave.

Question 28

How does the structure of the glomerulus increase filtrate volume?

Answer 28

FIrst, there is high pressure because of the smaller efferent arteriole. Second, there are pores (fenstrations) between the simple squamous epithelial cells in the glomerulus. Third, the mesangial cells can contract. This adjusts the surface area of the glomerulus. When contracted, there is less surface area, less filtrate is made.

Question 29

How many glomeruli are in each kidney?

Answer 29

About 1 million per kidney.

Question 30

Explain how glomerular filtration rate affects blood pressure.

Answer 30

If blood pressure is high, there is more fluid coming to the glomerulus, more pressure builds up in the glomerulus and more fluid enters the filtrate. If blood pressure is low, then less fluid is delivered and there is less filtrate made.

Question 31

What is renal autoregulation? What two methods are used?

Answer 31

Renal autoregulation refers to the way/s that the kidney controls the rate of filtration in the glomeruli. There are two ways this happers: myogenic control and tubuloglomerular feedback mechanisms.

Question 32

Describe myogenic mechanism of renal autoregulation.

Answer 32

Smooth muscle contracts when it’s stretched and relaxes when it isn’t stretched. If blood pressure is high there is an increased blood volume. This stretches the walls of the arteriole. The smooth muscle in those walls tenses or contracts, not allowing the diameter of the arteriole to increase. In this way, the amount of blood entering the glomerulus doesn’t necessarily increase when blood volume is high. The opposite is also true, when blood volume is low and there is less pressure on the wall of the arteriole, the smooth muscle isn’t stretched and it then relaxes. This increases the diamter, allowing more fluid through. In this way the kidney is getting a consistent amount of fluid entering the glomerulus each minute instead of highs and lows.

Question 33

Describe the tubuloglomerular feedback mechanism.

Answer 33

The macula densa cells in the JGC respond to high levels of NaCl in the filtrate. When there is a lot of filtrate it is pushed through the nephron more quickly, allowing less time for Na+ to be reabsorbed, so there is a higher concentration of it at the top of the loop of henle as compared to ‘normal’. The macula densa cells stimulate the smooth muscle to contract, decreasing flow to the glomerulus, giving the nephron more time to reabsorb Na+ and Cl-. This keeps blood pressure down.

Question 34

During the renin-angiotensin-aldosterone mechanism, what stimulates the granular cells to release renin?

Answer 34

Low blood pressure (lack of stretch).

Question 35

What is tubular reabsorption and why is it important?

Answer 35

Our total blood volume of plasma enters the kidney and becomes filtrate every 22 minutes. So, if all of that then were to pass as urine, we wouldn’t have enough fluid in the body to maintain life. Reabsorbption of many things in the filtrate back into the body maintains fluid levels, ion levels and more.

Question 36

Describe the transcellular route of water and solutes during reabsorption.

Answer 36

The transcellular route means that molecules from the filtrate diffuse into the cells lining the tubules. From there they diffuse out of the basolateral membrane (the bottom of the cell) into the intersticial fluid. From there, they move into the blood.

Question 37

Describe the paracellular route of water and solutes during reabsorption.

Answer 37

The paracellular route of reabsorption describes how molecules move from the filtrate between cells that line the tubules and into the blood. This is much less common, as there are generally tight junctions between these cells.

Question 38

Describe how sodium is transported across the basolateral membrane.

Answer 38

The reabsorption of Na+ provides the means for almost everything else to be reabsorbed, including water. Na+ moves from the filtrate into the cells lining the tubules. Co-transport is used. Na+ moves into teh cell with glucose, amino acids, an ion or a vitamin. Na+ moves into the extracellular space across teh basolateral membrane by primary active transport. This keeps the concentration of Na+ inside the cell low, so more Na+ is attracted to the cell from the filtrate. Na+ then moves into capillaries by a pressure gradient and an osmotic gradient.

Question 39

Describe how sodium is transported across the apical membrane of the cells lining the tubule.

Answer 39

See above.

Question 40

What does it mean to say that transporters are ‘saturated’? What happens to excess solutes if they can’t be transported back into the blood?

Answer 40

Transporters are saturated when they are all moving a molecule across a membrane. When this happens, the rate of movement is at its highest. If there are more molecules, they will pass in the urine.

Question 41

What is absorbed in the proximal convoluted tubule?

Answer 41

65% of Na+ and water, most ions, uric acid and about 50% of the urea.

Question 42

What part of the nephron tubule allows water to be reabsorbed?

Answer 42

The descending loop. Water can’t move across the ascending loop.

Question 43

What’s the action of antidiuretic hormone? Where is it secreted? What stimulates its secretion?

Answer 43

Antidiuretic hormone acts on the principal cells of the collecting duct. It causes them to make aquaporins. Aquaporins are transport proteins for water. The more a cell has, the more water can be reabsorbed from the filtrate back into the body. ADH is made when we are dehydrated and is used to conserve water and create a concentrated urine. ADH is made by the hypothalamus and stored in the posterior lobe of the pituitary gland.

Question 44

What’s the action of aldosterone? Where is it secreted? What stimulates its secretion?

Answer 44

Aldosterone is made by the adrenal glands. It fine tunes the level of Na+ in the body. Decreased blood volume/blood pressure causes aldosterone to be secreted. It also acts on the principal cells of the collecting duct. It causes them to make transport proteins specific for Na+. More Na+ is retained, moves into the blood, causes water to follow it and blood pressure is restored.

Question 45

What’s the action of atrial natriuretic peptide (ANP)? Where is it secreted? What stimulates its secretion?

Answer 45

ANP is made by cells in the atria of the heart when blood pressure is high. Cells in this area respond to stretch. If they stretch too much, they respond by making ANP. ANP causes less Na+ transport proteins to be made, less Na+ is retained and more is excreted. Therefore, less water is attracted to the blood and blood volume/pressure falls.

Question 46

What is tubular secretion? Where does it occur?

Answer 46

Tubular secretion is the opposite of reabsorption. During secretion wastes can be moved into the filtrate from the cells lining the tubes of the kidney. Drugs and other toxins can be expelled this way. If blood pH is too low, H+ ions can be expelled this way.

Question 47

If you’re dehydrated how do the kidneys respond? Overhydrated?

Answer 47

If you are dehydrated aldosterone and ADH are secreted. They act on principal cells in the collecting duct causing them to retain more water and Na+. If you are overhydrated, ANP is secreted and causes less Na+ to be retained.

Question 48

Describe the countercurrent multiplier.

Answer 48

This describes how teh fluids in the lower parts of the medulla of the kidney have highly concentrated solutes and fluids higher in the kidney (towards the cortex) have lower concentrations of solutes. Water diffuses out of the loop of henle in the descending limb. The filtrate is becoming more and more concentrated. It is the most concentrated as it will get at the bottom of the loop. As it enters the ascending loop, the tube is no longer permeable to water, but it is permeable to Na+. The concentrated filtrate loses Na+ to the fluid surrounding the tube. It loses more at the lower levels, because this is where the filtrate is the most concentrated. As it ascends, the filtrate becomes less concentrated, so Na+ still moves out, but at a slower rate.

Question 49

Be able to label a diagram with these structures: renal pelvis, ureters, bladder, urethra.

Answer 49

Done

Question 50

Describe how the anatomy of the bladder allows it to collapse when empty, then fill without a big rise in pressure.

Answer 50

This is due to two things. First, the rugae which are infoldings of the mucosa stretch out at the bladder fills. Second, the mucosa is made up of transitional epithelium in this location. As the bladder fills, the transitional epithelium stretch, absorbing the increased volume without putting pressure on the walls of the bladder itself.