Anatomy Lecture Exam 3

What do kidneys monitor?

Waste levels, fluid levels, electrolytes and their gradients

When does formation of urine stop?

Never

What does the nephron do?

Filtration, reabsorption, and secretion

Filtration

Hydrostatic pressure pushes small molecules (glucose, amino acids, and water) through the filtration membrane, large molecules (proteins) are left behind, GFR ,not enough surface area to filtered all of blood at once

What is reabsorption

Nutrients and water, and solutes (100% of amino acids and glucose) are moved from blood to ISF to capillary, driven by concentrations, into plasma

Secretion

Electrolytes out of plasma, solutes added to filtrate, needs a transporter

Excretion=

Filtration-reabsoprtion+secretion

Renal pelvis

Hollow space

Ureter

Goes to bladder

Papilla

Tip/end of renal pyramid, where urine drips into renal pelvis

Column

Area between renal pyramids

Cortex

Area between the renal pyramid and outside of kidney

Medulla

Region pyramids are in

Nephron

Smallest functional part of the renal system, produce urine, cortical and juxtamedullary

Cortical nephron

85%, only go into renal pyramid a little

Juxtamedullary nephron

15%, helps conserve water, goes deep into the renal pyramid

Afferent atriole

Goes into glomerular capsule

Medulla densa cells

Monitor osmolarity of fluid in distal convoluted tube, face the rest of the nephron

Juxtaglomerular cells

Secrete renin

Efferent arteriole

Moves away from the nephron

Where is the filtration membrane?

Between the glomerular capsule and glomerular capillaries  

What are the glomerular capillaries?

Afferent and efferent

Glomerular capsule

Cup to capture filtrate

Renal corpuscle

Capillaries and glomerular capsule

Peritubular capillaries

Run along nephron into the renal vein and body

Proximal convoluted tube

Secretion and absorption

Nephron loop

A lot of water absorption

Renal tube

Descending limb, nephron loop, and ascending limb

Collecting duct

Leads to papilla, shared by many nephrons

What does filtration rely on?

Blood flow/ hydrostatic pressure

What are the steps of urine production?

1) Blood coming in

2) Filtration (20%)

2a) Unfiltered blood leaves (80%)

3) Reabsorption

4) Secretion

5)Urine final product is excreted

What is the renal plasma flow in the afferent capillary?

625 mL/min

What parts of blood are filtered?

Plasma

Urine

The final product of the renal system

When does filtrate become urine?

Once in the collecting duct

What is the anatomy of the filtration membrane?

1) Fenestrated capillary

2) basement membrane

3) Filtration slits formed by podocytes

Filtration slits

Space between podocytes

What molecules can pass through the filtration membrane?

Water, glucose, amino acids, electrolytes, urea, small molecules

What molecules can’t pass through the filtration membrane?

RBC, white blood cells, large proteins, some drugs, platelets, and large molecules

Pc

Capillary hydrostatic pressure, pushes blood through, shouldn’t drop below Pbc+ pic, includes glomerular capillary

Pi

0, interstitial hydrostatic pressure

Pi C

Capillary oncotic pressure, stable value, from proteins

Pi i

Should be 0, interstitial oncotic pressure, from proteins

Capillary hydrostatic pressure is greater than oncotic pressure

Filtration

Capillary oncotic pressure is greater than hydrostatic 

Reabsorption

Jbulk=

Kf(Pc-6pic)

What is 6

Reflection constant, 1 normally, 0 if proteins get into interstitial fluid

What is Kf

Permeability constant

Pbc

Hydrostatic pressure due to fluid in glomerular capsule

Pi bc

Oncotic pressure of glomerular capsule, from proteins, usually 0

GFR

Glomerular filtration rate, rate at which blood is filtered at kidneys, between 90-125 mL/min

What affects GFR?

Kidney health, male vs female, body size, and age

GFR=

Kf(Pc- Pbc)- piC

Pc is greater than Pbc and pic

Filtration

Pc is less than Pbc and pi c

Reabsorption

How does the sympathetic NS affect GFR?

It can override GFR, doesnt regulate it but can change it

How is GFR regulated?

Myogenic mechanism and tubuloglomerular mechanism, adjustments to the glomerular capillary hydrostatic pressure

Myogenic mechanism

Autoregulation, smooth muscle, allow stretch and contraction to match blood flow/ BV and GFR

Why is there more smooth muscle around the afferent vessel than the efferent vessel?

This results in faster regulation

What happens when BP gets too high?

The filtration membrane can be damaged

How are BP and GFR related?

Proportionally

Tubuloglomerular mechamism

Works with myogenic mechanism, auto and paracrine regulation, uses macula densa, bring DCT back to glomerular capsule to help regulate blood flow, fixes blood pressure

What % of blood is filtered?

20%

What % of renal blood goes to the peritubular capillary?

80%, 500 mL/ min

Transporter maximum

Maximum concentration of substance in filtrate, when transporters become saturated

What is the transporter maximum of glucose?

225 units

Less than 225 units of glucose

No glucose in urine

More than 225 units of glucose

Glucose excreted in urine

Clearance

Volume of plasma from which a substrate is removed per unit of time, good indicator of kidney function and renal plasma flow

How do you calculate clearance

Excretion (mg/min)/ plasma concentration (mg/mL)

How is excretion sampled?

From urine

How is plasma concentration smapled?

Blood

Inulin

Plant polysaccharide, filtered but not secreted, indicator of GFR

Creatinine

Product of protein breakdown, filtered and then a little bit is secreted

PAH

Para amino hippuric acid, not produced naturally in the body, indicator of renal plasma flow, filtered and completely secreted

Apical surface

Facing the lumen

Basolateral surface

Facing the basement membrane

Transcellular

Going through the cell

Paracellular

Going between the cells

What kind of capillary is the peritubular capillary?

Fenestrated

What transporters/ channels are in the tubule?

Aquaporins, SGLT, GLUT1, K+ leak channels, K+/Na+ ATP pumps

SGLT

Na+ glucose co-transporter

GLUT1

glucose transporter

What are the barriers to solutes?

Tubular cells, basement membrane, ISF, fenestrated capillary

How do solutes move?

Using channels, pumps, and carriers

What are the forms of transport?

Diffusion, osmosis, cotransport, and pumps

What kinds of transport can be saturated?

Cotransport and pumps

Draw and label a nephron

Microvilli

Maximize surface area

How does Na+/K+ ATPase pump work?

Removes Na+ from cell, generates a gradient between filtrate and ICF

What allows Na+ and CO- counter transport?

Gradient

Where does Na+ and CO- counter transport occur?

On apical surface

How does the removal of Na+ affect filtrate?

It makes it more negative, repels anions (Cl- and HCO3-) and they leave filtrate paracellularly or transcellularly

How is H2O pulled out of filtrate?

When electrolytes are reabsorbed it is pulled out osmotically, hydrostatic pressure pushes it out, starling forces

How do solutes leave filtrate?

When H2O leave the filtrate becomes more concentrated, solutes diffuse out paracellularly (K+, Na+, Cl-, Mg2+, Ca2+, urea), pulled along with water when it is reabsorbed

What molecules have a lot of reabsorption?

H2O, glucose, amino acids, electrolytes

What molecules have some secretion?

Penicillin, other drugs, and H+ ions

Does K+ travel transcellulary?

No, it will leak out

Where does glucose transport stop?

After the PCT

How are amino acids transported?

Co transport with Na+