The Kidney Flashcards
What jobs does the kidney do?
- Water balance (ECF volume, blood pressure, osmolarity)
- Ion homeostasis (remove excess Na+)
- PH balance
- Excretion of water soluble wastes (nitrogenous waste such as urea)
- Production of hormones (epinephrine)
Main purpose of kidneys
Filter blood every 5-6 min which allows us to intake different food/drinks while maintaining homeostasis.
Outer part of the kidney
Cortex
Inner part of the kidney
Medulla
Functional Unit of the kidney
Nephron
These nephrons make up only 20% of the kidney but are primarily responsible for secretion / reabsorption
Juxtamedullary Nephron
The capillary beds around juxtamedullary nephrons
Vasa recta
The Renal Corpuscle
Glomerulus + Bowman’s Capsule
The parts of the nephron (in order)
- Bowman’s capsule 2. Proximal Convoluted Tubule 3. Loop of Henle (descending, ascending) 4. Distal Convoluted Tubule 5. Collecting Duct
Renal Pelvis
Where all the collecting ducts meet to funnel into the ureter, which leads to the bladder
Three Main Forms of Nitrous Waste
Ammonia, Urea, Uric acid
This determines what kind of nitrous waste you produce
Storage requirements! Ammonia is very caustic, so needs to be diluted; uric acid is very expensive to make, but requires very little water, which is why birds produce.
Where does the water in our body come from
Diet (about 30%), derived from metabolism (10%), ingested via liquid (60%)
In what ways is liquid from our bodies excreted
Feces (5%), evaporation (35%), urine (60%)
Where does a kangaroo rat get most of its water??
Metabolism!!
What surrounds any average old nephron
Peritubular Capillaries
Three key processes of nephron
Glomerular filtration, Tubular secretion, Tubular reabsorption
How much of what is filtered is reabsorbed?
99% or MORE!
% Water reabsorbed
99%
% glucose reabsorbed
100% or you’re in trouble
% sodium reabsorbed
99.5%
% urea reabsorbed
44%
What does glomerulus do
Creates the filtrate, and it is the ONLY place in nephron that filters; pushed out everything EXCEPT large molecules and blood cells. Water and small molecules pass through fenestrations.
How does glomerulus filter
Blood pressure! Anatomy increases blood pressure here, and it is greater than the combined force of osmotic pressure (which would pull liquid back into bloodstream) and fluid pressure in Bowman’s capsule. Net pressure about 10 mm Hg.
Journey of molecules from glomerulus to Bowman’s Capsule
First push through fenestrations in capillary epithelium, then move through basal lamina, then through slit pores in Bowman’s capsule epithelium created by weird Dr. Seuss like cells called ‘podocytes’. THREE LAYERS OF FILTRATION!
Glomerular Filtration Rate
The volume filtered through the kidneys per unit time, many kinds of hormonal regulations will regulate GFR
Autoregulation of GFR
Controlled by constriction / dilation of afferent & efferent arterioles: constrict afferent arteriole and reduce flow to glomerulus, ergo reduce GFR; constrict efferent arteriole and pressure builds up in glomerulus, ergo increase GFR.
Myogenic Feedback
Control of GFR via myogenic response, aka smooth muscle in arterioles.
If blood flow too high, arterioles constrict, reducing flow. If blood flow too low, arterioles relax, allowing more flow through.
Tubuloglomerular Feedback
- GFR increases.
- Flow through Loop of Henle increases.
- Macula densa cells sense this.
- Paracrine signal (unclear what this is) from macula densa to afferent arterioles.
- Constriction of afferent arterioles
- Reduction of GFR
What is the difference between filtrate and plasma?
Filtrate is destined to be excreted unless reabsorbed; plasma contains large molecules, blood cells, proteins, etc.
What is the difference between filtrate and urine?
Urine WILL be excreted. Filtrate is still undergoing process of secretion and reabsorption. Only becomes urine once leaves collecting duct (point of no return).
What the PCT Reclaims
Glucose, amino acids, most ions - and water follows
How is everything reclaimed in the PCT?
Symports - and these are usually symports powered by sodium gradient! (Water follows solute, so doesn’t need any help)
How Sodium is Reclaimed in PCT
ENaC (Epithelial Sodium Channel) on apical membrane takes sodium down gradient into low concentration of cell. Sodium potassium pump then returns to interstitial fluid (where sodium is high).
Apical Membrane
The side of the cell that faces the lumen (usually has villi)
Basolateral membrane
The side of the cell that does NOT face the lumen but instead faces the bloodstream
How Glucose is Reclaimed in PCT
SGLT carrier protein symport takes sodium down gradient and glucose up gradient across apical membrane. The glucose goes into blood down gradient via GLUT. Sodium leaves via pump, as always.
Any restrictions on the GLUT transporter?
Yes, transport maximum. If this gets maxed out, reach renal threshold and excrete glucose in urine. Diabetes!
Renal Threshold
Point at which saturation of GLUT carrier protein occurs and kidneys begin to excrete glucose
Filtration of Glucose
NEVER AFFECTED because no transport proteins. No matter how much glucose, will ALL get filtered. The trouble is with reabsorption in the PCT and transport max of GLUT.
Pressure gradient beyond Bowman’s capsule
Changes to filter reabsorption: so hydrostatic pressure decreases and colloidal osmotic pressure increases. Net 20 mm Hg pressure to reabsorb.
Clearance
A way of determining GFR. If you know that something should be totally excreted, the rate at which it is excreted also tells you the rate at which it is filtered
Inulin clearance
Plant-derived molecule that will neither be secreted nor absorbed. So its clearance rate can tell us GFR by proxy
Glucose clearance
NO glucose should be cleared (none should be excreted). ALL should be reabsorbed.
Urea clearance
Where filtration > excretion, there is net reabsorption. This happens with urea.
Penicillin Clearance
When filtration < excretion, there is net secretion (movement from bloodstream into filtrate). This happens with penicillin.
Micturition
aka peeing
- Stretch receptors in bladder fire
- Parasympathetic neurons fire. This causes the TONIC internal sphincter of bladder to release.
- Motor neurons STOP firing. This causes the ‘voluntary’ external sphincter at bottom of urethra to open, as well.
- Smooth muscle contracts.
- TALLY HO!
The Bladder at Rest
Bladder surrounded by smooth muscle is not stretched. Internal sphincter, controlled by smooth muscle (not voluntary control) is contracted. External sphincter controlled by SKELETAL MUSCLE (ergo voluntary) is also contracted.
