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What are the functions of the kidneys?

- Regulate extracelluar fluid and blood pressure
- Regulation ofosmolality
- Maintains ion balance
○ Sodium/potassium is excreted here (main route)
- Regulating pH (h+ and Hco3)
○ Daily (diet state, more meat more acid)
○ pH disturb (kidneys help alleviate that)
- Excretion of waste
○ Creatinine (creatine in muscles byproduct)
○ Urea (product of protein breakdown)
○ Hormone metabolites
○ Urobilinogen (biliruben from erythrocytes)

= Production of hormones
1) Erythropoietin: RBC making
- When kidney is low in oxygen
2) Renin: regulate blood pressure.
3) VIT D activated
Angitension 2: has the enzyme to convert 1 to 2: regulate blood pressure as well as renin.


How are the functions of the kidneys accomplished?

3 processes within the nephron
1. Filtration
2. Reabsorption
3. Secretion

Axial Specialization: when we receive fluid, along the nephron it goes through different regions (assembly line)

Coordinated function:
multiple segments (one region interacts with other regions WITHIN one nephron) - can talk to itself
Multiple organs: blood pressure, pH regulation (lungs, liver)


Describe the gross anatomy of the kidneys

Kidneys (2)
Ureter (take pee to bladder)
Urethra (connection to genitals)

- Cortex (everything outer pink)
- Medulla (everything in inner pink)
- Renal pyramids
- Nephron (functional unit of kidney)
- Renal pelvis: where urine drains into
- Ureters: drains from renal pelvis


Describe the anatomical and functional units of the kidney.

Functional unit of the kidney
Nephrons sit across cortex and medulla
1million nephrons per kidney

Anatomical Units
- Proximal Tubule: closest to renal corpuscle (PCT)
- Loop of Henle (PST, IDLH IALH) TAL: dips into medulla
- Depending on location of renal corpuscle, the amount in the medulla is different.
- Distal tubule
- Collecting duct: drain into renal pelvis
Functional Units
- Filtration: movement of blood molecules into the nephron.
- Renal corpuscle: 1 closer to medulla or 2 closer to cortex
- Reabsorption/secretion: Renal tubule: 3 tubules. Anywhere you can modify the composition along the tubule. Movement back into blood and blood into nephron. Modifies what's in the tube as you go along towards collecting duct.
- Regulation: Juxtaglomerular apparatus: interface where distal tubule connects with glomerulus (blood supply to corpuscle)
- Do we need more/less blood
- Excretion: Collecting duct. No longer to modify the fluid, now you have what's excreted.

Fewer loops of Henley that reaches down: that’s why pyramids are triangular.


Describe the renal corpuscle

Renal Corpuscle: initial delivery for processing
- Site of filtration!

1. Bowman's capsule: yellow bulb with fluid space
- Basement membrane (outer portion)
- Parietal epithelium (inside of the cavity- continues into the nephron)
2. Glomerular capillary tufts/glomerulus: capillaries WITHIN bowman's capsule.
- Endothelial cells: little cells, line vessels, have LARGE openings (fenestrated, large window holes)
§ Good for movement of blood into bowman's capsule.
- Glomerular basement membrane: what passes through the filter is determined here
- Epithelium: visceral. Line the outside. Podocytes. Determine what types of molecules get through.

Together: these make renal corpuscle.

Blood comes from afferent arterial.
Then glomerular capillary bed
Exit through efferent arteriole.


Describe the epithelial cells of the nephron

Collecting duct.

Structurally different.
1. Thickness is varied
- As you move towards loop of henle they THINNER
- Thin descending limb
- Thin ascending limb (1)
- Thick ascending limb (2)
Thin because of epithelial cells. Opening size is the same.
Thicker because of more "machinery" in them.
Do they rely on NaK ATPase? Needs lots of mitochondria. Need to generate gradient for movement
2. Changes in surface area: larger surface area more proximally.
- More able to do transport.
- Proximal does a bunch of transport.
3. Permeability differences.
Tight junctions get tighter.
Ability to pass between cells is reduced (more selective)


Describe filtration in vascular and tubular nephrons.

Filtration needs to be adjusted, but don't wanna lose liquid.
Lots is reabsorbed.

Blood delivered to afferent
Filtration at glomerulus (blood into bowman's capsule)
Blood goes out through efferent arteriole

Nephron and vasculature are CLOSE TOGETHER. Movement of substances between them.

Reabsorption: from tubular lumen into the blood.
- From proximal tubule to end of duct

Secretion: from blood to lumen, happens along tubule NOT at glomerulus. (before proximal tubule is filtration, but after proximal tubule is SECRETION)



What is the blood flow in the nephrons>

Any blood coming into the kidney comes through the renal artery.
All blood to kidney goes through glomerolus

Efferent arterioles supply either peritubular capillaries (coritcal region) or vasa recta medullary region)

Blood exits kidney via renal vein no matter where it comes from


How much fluid is delivered to the kidneys?

How much fluid is delivered to kidneys?

20% of the plasma that enters glom, goes into nephron.
Larget amount reabsorbed (other 80%)

99% returned
1% is the urine. 1.5 L/Day

Filtration fraction: % plasma volume that goes into the tubule.
- Need to know amount that's filtered
- Need to know amount delivered.
- Tels you how healthy your kidneys are
- Filration fraction dicreases with kidney disease (impaired filtration)
Filtered is reduced but delivered is the same.


How do we measure renal blood flow?

Ways into/out of the kidney.
- TO kidney: comes through renal artery.
- FROM kidney: exits through renal vein, or exits through urine.

Measure through a urine sample or renal artery. Hard to get a renal sample (vein output)

Measure artery and urine.Blood delivery to the kidneys
All blood goes through renal artery
All fluid leaving kidney goes through
1) Blood in renal vein
2) Urine in ureter

To assess it: only collect urine.
Easy to collect arterial blood and urine. Diffult to collect venous blood


Describe the measurement of renal PLASMA flow

Measurement of renal plasma flow (RPF) not blood
- No hematocrit in the nephron
- Only fluid, not blood.

Substance we use for renal plasma flow
- PAH: Para amino-hippuric acid
- Partially filtered at glomerulus (20%)
- Super secreted.
- Anything in vasculature (not in glomerulus (80%) goes back into the nephron.
- Venous PAH will be close to zero.

Take what's found in urine, compare it to arterial supply. Determine renal plasma flow!
- 600 mL per minute delivered to the kidneys.

Hematocrit of blood is 45% of actual blood volume (55% plasma)
- Use that with RPF, then adjust to renal blood flow
- 1L/min