Renal Lectures (8) Flashcards
Urine characteristics used in history as health indicators
L1
→ color (black - blackwater fever, too much Hb in pee)
→ clarity (froth: high protein)
→ odor (infection)
→ taste (diabetes - honey urine disease)
Primary Kidney Function
L1
→ homeostatic regulation of water and ion content in blood (fluid electrolyte balance)
Fluid-electrolyte balance is kept in kidneys how?
(secondary kidney functions)
L1
→ regulation of ECF volume (indirectly blood pressure) → osmolarity regulation → ion balance maintenance → pH homeostatic regulation → waste excretion → hormone production (like renin)
Can lose ___ kidney function before it affects homeostasis
L1
3/4
→ can have only 1/2 a kidney
Main structures in the urinary system
L1
→ ureter, urinary bladder, ureter, kidneys (2 concave structures, located retroperitoneally lying against peritoneal tissue layer)
→ adrenal glands on top kidney
→ Kidneys receive 20-25% of CO to ensure homeostasis maintained (issues fixed quickly)
Kidney structures
L1
→ outer region: cortex
→ inner portion: medulla (renal pyramids)
→ nephrons: make up bulk of kidneys, found in inner medulla
→ renal pelvis and ureter connects with nephrons so urine flows into them and into bladder
→ nephrons are functional unit of kidneys, ~1 million/kidney
→ 80% are cortical nephrons, 20% are juxtamedullary nephrons
Blood enters the kidneys via the _____, and then goes through ______.
L1
Blood enters the kidneys via renal artery → afferent arterioles → glomerulus (ball of capillaries) → efferent arterioles → peritubular capillaries → the renal vein
at glomerulus: where nephrons make contact with blood/solutes
*in juxtamedullary nephrons, peritubular capillaries is VASA RECTA
The glomerulus is the site of?
L1
filtration
→ blood enters the glomerulus and will filter into the bowman’s capsule, and if the fluid not reabsorbed, will be excreted
One nephron has 2 ____.
L1
2 arterioles and 2 sets of capillaries that form a portal system
Bowman’s Capsule
Parts of Nephron? Start at Bowman’s Capsule
L1
→ single layer of epithelial cells
→ where the glomerulus capillaries make contact with nephrons
*solutes and blood flows from capsule → proximal tubule → descending loop of Henle → ascending loop of Henle → distal tubule → collecting duct (ureter)
4 processes of kidneys?
L1
→ filtration (blood→lumen)
→ reabsorption (lumen→blood)
→ secretion (blood→lumen)
→ excretion (lumen→outside)
When/where do each of the kidney’s processes occur?
L1
→ Filtration: bulk flow of fluid/solutes in blood from glomerulus into bowman’s capsule lumen
→ Secretion: substances move from blood into lumen of any part of nephron via transporters
→ Reabsorption: In proximal tubule, some solutes/fluid moves from lumen back into blood (amnt depends on homeostasis needs)
→ Excretion: whatever is left in the nephron gets excreted out
Approximately ___ of plasma is filtered at the glomeruli/day
→ process of reabsorption in each structure of nephron
L1
180L
→ 99% reabsorbed, only ~1.5L is excreted
→ ~70% of reabsorption occurs at the proximal tubule via transporters. By end of proximal tubule, only ~55L is left that will go to loop of henle (30% of original vol)
→ loop of henle makes dilute urine: descending has water reabsorption so hyperosmotic. ascending has solutes reabsorbed, more than the amount of water reabsorbed (so dilute now) i.e. hypoosmotic. By end of loop, only 18L left (10%)
→ distal tubule and collecting duct finely regulate salt and water balance under hormone control (what does body need?)
→ 1.5L (0.8%) urine exits body, can be hyper or hypoosmotic, depends on body
Amount excreted =
L1
Amount filtered - amount reabsorbed + amount secreted
ex, 720mmol - 684mmol + 43mmol = 79mmol
→ these types of questions on exam can be 1 solute (like K+)
Filtration fraction
of all the plasma vol entering afferent arterioles, only 20% of that vol filters into bowman’s capsule. 80% continues on to the peritubular capillaries. In the proximal tubule of nephron, 19% is reabsorbed, so ,1% of vol is actually excreted. >99% enters kidneys and returns to systemic circulation
If someone’s cardiac output is 5L/minute, and the kidneys get ~20% of that, and ~60% of the blood is plasma, how much is entering the glomerulus everyday, if only 20% of the plasma filters into the bowman’s capsule?
THe number we find here is called?
L1
CO = 5L/min
Kidneys getting 1L/min
60% of 1L is 0.6L/min of plasma
20% of that plasma is filtered. thats 0.12L/min
0.12L/min x 60min/hour x 24 hours/day
= ~173L plasma filtered/day
round up to 180
this # is someone’s GLOMERULAR FILTRATION RATE (GFR) which can help to understand how well kidneys are functioning
Renal corpuscle: fluids and solutes passing into bowman’s from the glomerulus
L1
→ pass triple filtration barrier
- Capillary endothelial cells of glomerular capillaries → fenestrations (pores)
- Basal lamina surrounding glomerular capillary: mesangial cells can contract, and pull walls of capillaries together so there is less exposure to bowman’s and less filtration (reduces SA)
- Podocyte end-feet within renal corpuscle (surrounds glomerulus) act as barriers where substances have to fit in between the podocytes to enter lumen of bowman’s
Pressures governing filtration from glomerulus capillaries into renal tubules (bowman’s, etc)
L2
→ hydrostatic of glomerular capillaries, 55mm Hg: favours filtration! So over all bp drives filtration through 3 barriers and into capsule
→ colloid (oncotic) of blood, 30 mmHg: pressure gradient bc of plasma proteins in capillaries, draws fluid back into capillaries, opposes filtration (favours reabsorption)!
→ hydrostatic of bowman’s, 15 mmHg: fluid already in the nephron opposes filtration
Net filtration pressure 10 mmHg
→ not a lot, but pores let fluid go through and theres ~2 million nephrons so tons occuring
GFR basics
Factors affecting GFR?
L2
→ vol of fluid filtered from glomerulus into bowman’s per unit time
→ normally 125ml/min or 180L/day
→ plasma vol is ~3L so kidneys filter all plasma vol ~60x /day
→ If not reabsorbed, we’d run out of plasma in ~24 minutes
FACTORS
→ filtration pressure
→ filtration coefficient (slit surface area and permeability)
Why is GFR relatively constant throughout range of bp?
What if afferent arteriole resistance increases?
L2
→ many structures controlling amnt of blood flowing into glomerulus and nephron to prevent damage: renal arterioles, afferent and efferent alter their constriction
→ afferent arteriole: can constrict (inc resistance) to reduce blood flowing into the glomerulus, as well as capillary bp and thus GFR
Renal blood flow depends on ____.
What if resistance in efferent arteriole is inc?
Afferent resistance dec (dilates)?
L2
Overall resistance: resistance in afferent + efferent arterioles
→ inc resistance in efferent arterioles to reduce overall flow in response to high bp: filtration will increase since afferent letting in same amount, but less leaving. Pooling will occur in glomerulus. inc hydrostatic pressure, inc GFR
→ dec resistance in afferent: blood flow increases since afferent letting more in, but since same amount leaving, blood will pool in glomerulus. Hydrostatic pressure inc, GFR inc.
What type of regulation of renal blood flow is most common?
Common themes: when does GFR and RBF dec/inc?
L2
Constricting afferent arteriole in response to inc bp
→ RBF and GFR not always proportional: GFR can inc when RBF dec, or they can both inc/dec etc
→ any dilation will increase RBF, any constriction will dec it
→ pooling will inc hydrostatic pressure and GFR (i.e. dilating afferent or constricting efferent)
→ dilating efferent or constricting afferent dec GFR bc less blood in there so less hydrostatic pressure
How does GFR autoregulate?
L2
*protects filtration barriers from high bp (and high GFR) that would damage them (hypertension)
→ myogenic response of afferent arterioles: as bp goes up, blood flow inc coming into afferent arterioles, blood stretches smooth muscle in walls, will reflectively constrict
→ tubuloglomerular feedback: juxtaglomerular apparatus (nephron loops back on itself so ascending Henle passes b/n arterioles) has macula densa cells that sense inc in distal tubule blood flow and release paracrines to affect arteriolar diameter
How does stretch activate myogenic activity of afferent arterioles?
L2
→ stretch membranes open → let Na or Ca in → vascular smooth muscle depolarizes → L type Ca channels open → inc in intracellular Ca turns on myosin light chain kinase → leads to constriction