Urinary System Chapter 24

Question 1

net filtration pressure

Answer 1

-is much higher in the glomerulus vs. other capillary beds because the blood pressure is much higher there 55mmHg vs. < 18mmHg elsewhere

Question 2

glomerular hydrostatic pressure

Answer 2

• HPg

- glomerular blood pressure; forcing particles out of the capillary

Question 3

glomerular filtration rate

Answer 3

• GFR

- volume of filtrate formed each minute by combined activity of all 2 million glomeruli

Question 4

anuria

Answer 4

-abnormally low urine output-less than 50 mL per day

Question 5

organs that make up the urinary system

Answer 5

• kidney( form urine)
• urinary bladder( stores urine)
• ureters
• urethra (transport urine outside)

Question 6

what are 5 functions of the kidneys?

Answer 6

1. filter 200mL of fluid from the blood stream every day which allows toxins, metabolic wastes, excess ions to leave the body and returns needed substances to
   the blood
2. Regulate the volume and chemical makeup of the blood, maintaining proper balance between salts & water and between acids & bases
3. Aid in glucose production
4. Produce the hormones renin and erythropoietin
5. Metabolize Vitamin D to its active form

Question 7

What substances can pass from blood to the kidney during glomerular filtration and what can’t?

Answer 7

1. pass freely- water, glucose, amino acids and nitrogenous wastes (ammonia)- 5nm, blood cells, plasma proteins

Question 8

2 mechanisms by which the kidney can autoregulate GFR?

Answer 8

1. myogenic mechanism-increased systemic BP causes afferent arterioles to constrict, decrease amount of blood entering
   - decreased systemic BP cause afferent art. to dilate , will allow more blood into glomerulus
2. Tubuloglomerular feedback mechanism- directed by the macula densa of the JGA.
   - these cells respond to filtrate NaCl concentration
   - if GFR is too fast, there is not enough time for NaCl to be reabsorbed, so the high level of NaCl triggers the macula densa cells to signal the afferent arteriole to constrict and slow blood flow and therefore decrease NFP and GFR
   - if GFR is too slow, there is less NaCl and this tells the macula densa cells send signals to the afferent arteriole to dilate and increase blood flow and thus NFP and GFR

Question 9

What are 5 ways in which Angiotensin II restores blood volume/pressure?

Answer 9

1) Vasoconstriction of arterioles to raise BP
2) Stimulates reabsorption of Na+, and water follows, increasing BP and blood volume
3) Stimulates hypothalamus to release antidiuretic hormone (ADH) and activates the thirst center, to increase blood volume
4) Decreases peritubular capillary hydrostatic pressure, which increases fluid reabsorption
5) Causes the glomerular mesangial cells to contract and reduce GFR by decreasing surface area of glomerular capillary available for filtration

Question 10

What 3 factors trigger the release of renin?

Answer 10

1) reduced stretch of granular cells (when BP drops below 80mmHg)
2) Stimulation of granular cells by input from macula densa cells which were activated by low NaCl (low blood flow)
3) Direct stimulation of granular cells by the renal sympathetic nerves.

Question 11

aquaporin

Answer 11

water moves by osmosis through these membrane channels

Question 12

osmolality

Answer 12

-in solution, the number of solute particles dissolved in one kilogram of water; this reflects the solution’s ability to cause osmosis

Question 13

osmotic activity

Answer 13

• water movement across semi-permeable membrane (hi to lo)
• this ability know as osmotic activity and is determined by number of solute particles that can’t pass through the membrane

Question 14

countercurrent multiplier

Answer 14

-flow of filtrate through ascending and descending limbs of loop of Henle

Question 15

countercurrent exchanger

Answer 15

-flow of the blood through the ascending and descending portions of the vasa recta blood vessels

Question 16

chronic renal disease

Answer 16

• GFR (Glomerular Filtration Rate) of <60mL per min for at least 3 months
• caused by: diabetes mellitus, hypertension

Question 17

renal failure

Answer 17

-GFR < 15 mL per min, filtrate formations decreases or stops completely, allowing ionic and pH imbalances and waste accumulation in the blood

Question 18

how is Na+ reabsorbed (what are the mechanisms) during tubular absorption?

Answer 18

Always active and via transcellular route, Na+ enters the luminal surface of the tube cell via facilitated diffusion through channels or as a part of a co-transport mechanism

Question 19

which substances are reabsorbed via secondary active transport?

Answer 19

• glucose
• amino acids
• vitamins

Question 20

How are water and other lipid-soluble substances such as ions and urea reabsorbed

Answer 20

• passive tubular reabsorption -includes: osmosis, diffusion and facilitated diffusion and is driven by electrochemical gradients that are set up by active reabsorption of Na+
• water > aquaporins
• solutes> ions & urea

Question 21

What substances are reabsorbed into the proximal convoluted tube (PCT)?

Answer 21

-most nutrients, 65% of water & sodium, most actively transported ions
The descending & ascending loops of Henle:
-water leaves descending, not ascending-no aquaporins
- solutes leave(active or passive)
ascending, not descending
The distal convoluted tubule DCT and collecting duct?
- reabsorption of: additional Na+ & H2O

Question 22

What does ADH (antidiuretic hormone) do and how does it work?

Answer 22

-enhances water absorption by inserting aquaporins into the collecting ducts

Question 23

What does aldosterone do and how does it work?

Answer 23

• Increases sodium reabsorption by causing cells in the collecting ducts and distal portion of DCT to build and retain more luminal Na+/K+ channels and more basolateral Na+-K+ ATPases
• this serves to increase blood volume and BP (because water follows Na+)

Question 24

What does Atrial natriuretic peptide ANP do?

Answer 24

-ANP reduces blood sodium, decreasing blood volume and pressure

Question 25

What are 4 functions of tubular secretions?

Answer 25

1) Disposing of drugs and metabolites that are tightly bound to plasma proteins (these aren’t filtered)
2) Eliminating undesirable end products that have been reabsorbed by passive processes
ex. urea and uric acid
3) Ridding the body of excess K+
4) Controlling blood pH

Question 26

Where does urea leave and enter the filtrate in the kidneys?

Answer 26

As filtrate flows through the collecting ducts in the inner medulla, highly concentrated urea diffuses into the interstitial space.
From here, urea re-enters the ascending limb of the limb of the loop of Henle and is recycled
-ADH enhances urea transport in the collecting duct, allowing urea recycling to be enhanced and creating more concentrated urine
-

Question 27

How does concentration of blood in the vasa recta change as it flows through the kidney?

Answer 27

As blood descends from cortex to medulla, it becomes more concentrated, and as it comes back up toward the cortex it is less concentrated.

Question 28

Dilute urine

Answer 28

• urine is already dilute while traveling through the ascending loop of Henle, so kidneys just have to allow the hypo-osmotic urine to continue to the renal pelvis
• No ADH is being released by the posterior pituitary, so no aquaporins are formed in the membranes of the collecting ducts and no further water absorption occurs, the most dilute urine has an osmolality of about 50 mOsm

Question 29

Concentrated urine

Answer 29

• when the body is dehydrated, high levels of ADH are released, causing many aquaporins to be formed in the collecting duct and up to 99% of water left in the filtrate can be reabsorbed
• water reabsorption depending on the presence of ADH is called facultative water reabsorption

Question 30

How does alcohol and caffiene work as diuretics?

Answer 30

1. Alcohol- increase urinary output, by inhibiting ADH release -no aquaporins
2. Caffeine- inhibits Na+ reabsorption

Question 31

What is renal clearance?

Answer 31

Volume of plasma that’s completely cleared of a substance every minute
- renal clearance rates can provide information about renal function or the cause of renal disease