Urinary System Chapter 24 Flashcards
net filtration pressure
-is much higher in the glomerulus vs. other capillary beds because the blood pressure is much higher there 55mmHg vs. < 18mmHg elsewhere
glomerular hydrostatic pressure
- HPg
- glomerular blood pressure; forcing particles out of the capillary
glomerular filtration rate
- GFR
- volume of filtrate formed each minute by combined activity of all 2 million glomeruli
anuria
-abnormally low urine output-less than 50 mL per day
organs that make up the urinary system
- kidney( form urine)
- urinary bladder( stores urine)
- ureters
- urethra (transport urine outside)
what are 5 functions of the kidneys?
- 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 - Regulate the volume and chemical makeup of the blood, maintaining proper balance between salts & water and between acids & bases
- Aid in glucose production
- Produce the hormones renin and erythropoietin
- Metabolize Vitamin D to its active form
What substances can pass from blood to the kidney during glomerular filtration and what can’t?
- pass freely- water, glucose, amino acids and nitrogenous wastes (ammonia)- 5nm, blood cells, plasma proteins
2 mechanisms by which the kidney can autoregulate GFR?
- 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 - 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
What are 5 ways in which Angiotensin II restores blood volume/pressure?
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
What 3 factors trigger the release of renin?
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.
aquaporin
water moves by osmosis through these membrane channels
osmolality
-in solution, the number of solute particles dissolved in one kilogram of water; this reflects the solution’s ability to cause osmosis
osmotic activity
- 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
countercurrent multiplier
-flow of filtrate through ascending and descending limbs of loop of Henle
countercurrent exchanger
-flow of the blood through the ascending and descending portions of the vasa recta blood vessels
chronic renal disease
- GFR (Glomerular Filtration Rate) of <60mL per min for at least 3 months
- caused by: diabetes mellitus, hypertension
renal failure
-GFR < 15 mL per min, filtrate formations decreases or stops completely, allowing ionic and pH imbalances and waste accumulation in the blood
how is Na+ reabsorbed (what are the mechanisms) during tubular absorption?
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
which substances are reabsorbed via secondary active transport?
- glucose
- amino acids
- vitamins
How are water and other lipid-soluble substances such as ions and urea reabsorbed
- 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
What substances are reabsorbed into the proximal convoluted tube (PCT)?
-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
What does ADH (antidiuretic hormone) do and how does it work?
-enhances water absorption by inserting aquaporins into the collecting ducts
What does aldosterone do and how does it work?
- 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+)
What does Atrial natriuretic peptide ANP do?
-ANP reduces blood sodium, decreasing blood volume and pressure
What are 4 functions of tubular secretions?
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
Where does urea leave and enter the filtrate in the kidneys?
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
-
How does concentration of blood in the vasa recta change as it flows through the kidney?
As blood descends from cortex to medulla, it becomes more concentrated, and as it comes back up toward the cortex it is less concentrated.
Dilute urine
- 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
Concentrated urine
- 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
How does alcohol and caffiene work as diuretics?
- Alcohol- increase urinary output, by inhibiting ADH release -no aquaporins
- Caffeine- inhibits Na+ reabsorption
What is renal clearance?
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
