9.5 Renal phys

Question 1

What are the 3 main processes that occur at the glomerulus?

Answer 1

Glomerular Filtration:
Separation of cells and large proteins from plasma, fluid and small molecules
Tubular Reabsorption
Valuable substances selectively returned back into the blood from the nephron
Tubular Secretion
Unneeded substances selectively removed from the blood and transported into the nephron

Question 2

What structures filter in the glomerulus?

Answer 2

fenestrated capillaries; blocks red and white blood cells, everything else can get out
basement membrane; blocks proteins, other solutes can pass
podocyte filtration slits; blocks macromolecules
mesangial cells will clean up any macromolecules that build up here

Question 3

What is the net filtration pressure in a normal glomerulus?

Answer 3

NFP= Outward pressures- Inward pressures
Hydrostatic pressure of glomerulus - (Hydrostatic pressure of capillary + osmotic pressure of glomerulus)
= 55 - (15+30)
= +10 mmHg

Question 4

What 3 mechanism control the GFR?

Answer 4

Myogenic Mechanism
Tubuloglomerular Feedback Mechanism
SNS control

Question 5

What is the myogenic mechanism of GFR control?

Answer 5

local, intrinsic control
afferent arteriole senses stretch when systemic blood pressure is too HIGH, responds by contracting
result: decrease GFR to prevent damage to glomerulus
(the reverse is also true, will dilate if BP is too low)

Question 6

What is the tubuloglomerular feedback method of GFR control?

Answer 6

local, intrinsic control
GFR too FAST means NaCl will be HIGH
macula densa in JGA sense HIGH NaCl levels in the filtrate and release vasocontriction signals (ATP, vasoactive chemicals)
result: decrease GFR to reduce flow and allow more time to process
(the reverse is also true, vasoactive chemicals will be inhibited if NaCl is too low)

Question 7

How does the SNS control GFR?

Answer 7

extrinsic control
during shock, severe hemorrhage conditions, arterial BP <80mmHg
epinephrine and norepinephrine released systemically to shunt blood to brain, vital organs
afferent arteriole vasoconstriction
result: decrease GFR to increase blood volume and blood pressure in the body

Question 8

What is BUN?

Answer 8

Blood Urea Nitrogen
blood is tested for nitrogenous waste
Normal = 5-20mg/dL
requires liver processing of amino acids  ammonia -> urea
requires kidney excretion of urea

Question 9

What is azotemia?

Answer 9

High blood urea nitrogen levels

Question 10

What can increase BUN?

Answer 10

high protein diet
muscle protein breakdown
dehydration – BUN : water ratio is high if water is low
renal dysfunction – accumulation of urea due to low GFR

Question 11

What is acute glomerulonephritis?

Answer 11

inflammation of the glomerulus
leads to hyperpermeability at glomerular membrane, loss of albumin protein from blood
loss of colloid oncotic pressure, edema, puffy eyes, decreased GFR, oligouria (low urine output), hematuria, proteinuria, hypertension
leads to 25-50% of all end-stage renal disease (EDRD)
renal failure can occur within weeks

=Lose proteins in blood, lose osmotic pressure (colloid pressure of albumin) -> edema, swelling (puffy eyes) decreased GFR/more

Question 12

What are causes of acute glomerulonephritis?

Answer 12

bacterial, viral, fungal infections that lead to autoantibodies, or antigen/antibody complexes that damage glomerulus
group A beta-hemolytic streptococcus (GABHS)
autoimmune disease: ex: systemic lupus erythematosus

Question 13

What is nephrotic syndrome?

Answer 13

Signs:
hypoalbuminemia
edema
proteinuria

Causes:
glomerulonephritis
diabetes mellitus
autoimmune disease

Question 14

What hormone stimulates Na+ reabsorption?

Answer 14

Aldosterone

Question 15

Why does nutrient reabsorption require Na+?

Answer 15

Nutrients need secondary active transport-

Need to go down concentration gradient, water follows salt

Question 16

What is nutrient Tmax? What can overwhelm it?

Answer 16

Limit to how much the transporters can move

Nor all conditions: all glucose returns to blood; BUT diabetes overwhelms transporters, excrete in urine

Question 17

What is the renal threshold?

Answer 17

When plasma concentration of substance exceeds ability of carries then it will be “excess” that stays in filtrate, lost in urine
= SETS amount of substance in blood/urine

Question 18

Describe the renal threshold of glucose and PO4-

Answer 18

Glucose: renal threshold is very high compared to normal glucose intake
glucose is entirely reabsorbed
exception: uncontrolled diabetes mellitus, excessive blood sugar levels
Phosphate: renal threshold is equal to normal PO4 intake
excess PO4 is quickly eliminated
PTH adjusts the renal threshold for phosphate (adjusted by PTH)

Question 19

Where does most reabsorption the place?

What is reabsorbed in each area of the nephron?

Answer 19

The PCT performs most of the reabsorption, fine-tuning and dilution/concentration of the urine occurs in the remaining tubules via water and ion regulation
PCT Reabsorption:
Na+, nutrients, ions, water, lipid-soluble substances, urea
65% of total water and Na+, 99% nutrients, majority of ions
Loop Of Henle Reabsorption:
water, Na+, ions
DCT Reabsorption:
Na+, Ca2+ (parathyroid hormone dependent)
Collecting Duct Reabsorption:
Na+ (aldosterone dependent), ions, water (ADH dependent, secondary to aldosterone), urea