L25 : Glomerulus and Filtration pt. 1

what within the kidneys produce erythropoeitin?

fibroblasts

MCQ: what component of the glomerular filtration barrier repels negatively charged molecules from the glomerular lumen?

glomerular basement membrane

MCQ: why are large plasma proteins like albumin normally excluded from filtrate?

filtration barrier has size and charge selectivity

how is the glomerular filtrate different than plasma?

1. has no proteins

2. has no blood cells

MCQ: why do blood cells not normally appear in the urine of healthy animals?

they are too large to pass through the filtration barrier

glomerular filtration rate (GFR)

total volume of filtrate produced in each nephron per minute by both kidneys

why is there variation in GFR?

change in net filtration pressure

what does the net filtration pressure in the kidneys depend on?

hydration of the animal

urine

blood-filtered fluid submitted to the reabsorption of valuable substances in the tubular system and excretion of waste products

MCQ: a 6-year-old cat undergoes a long surgical procedure. Post-op, hypotension is noted, and the cat produces minimal urine. What physiological factor is primarily responsible for the decreased GFR?

decreased glomerular hydrostatic pressure

how will a lower urinary tract obstruction or kidney stone affect GFR?

will decrease blood flow leading to a decreased GFR

how will NSAID toxicity affect GFR?

will increase vasoconstriction of afferent arterioles due to no prostaglandins being produced and GFR will decrease

how does tying-up cases (rabdomyosis) in horses affect GFR?

muscle breakdown = release of myoglobins = myoglobinuria = obstruction of tubules = blocking capsular hydrostatic pressure = decereased GFR

what will lead to an increase in glomerular hydrostatic pressure?

1. increase arterial blood pressure

2. afferent arteriole vasodilation

3. moderate efferent arteriole vasoconstriction

GHP

glomerular hydrostatic pressure

what will lead to a decrease in glomerular hydrostatic pressure?

1. afferent arteriole vasoconstriction

2. efferent arteriole vasodilation

GCOP

glomerular colloid osmotic pressure

what will lead to a relative increase in GCOP?

1. dehydration

2. decreased renal blood flow

3. severe efferent vasoconstriction

what happens to GFR if GHP increases?

increased GFR

what happens to GFR if GHP decreases?

decreased GFR

what happens to GFR if GCOP increases?

decreases GFR

what happens to GFR if GCOP decreases?

increases GFR

what will lead to a decrease in GCOP?

1. hypoproteinemia

2. increased renal blood flow

CHP

capsular hydrostatic pressure

capsular hydrostatic pressure

hydrostatic pressure in the bowman’s capsule

what happens to GFR if we increase CHP?

decreases GFR

what will cause an increase in CHP?

1. urinary obstruction

2. kidney edema

efferent arteriole vasodilation

lowers resistance downstream of the filtration area to reduce the pressure of capillaries of glomerulus

afferent arteriole vasodilation

lowers resistance upstream of the filtration area to create an increase in pressure in the capillary

MCQ; an animal is given a vasoconstrictor that selectively affects the afferent arteriole. What is the expected physiological response in the glomerular capillaries?

reduced glomerular hydrostatic pressure and decreased GFR

severe efferent arteriole vasoconstriction

• increases GHP but decreases blood flow to decrease GFR

• low blood flow increases GCOP

effects of severe arteriole vasconstriction

1. increase GHP

2. decrease plasma flow

3. increase GCOP

4. decrease GFR

when does severe arteriole vasconstriction occur>

from overactvation of RAAS (ex: congestive heart failure)

MCQ: what endogenous molecule can cause efferent arteriole vasoconstriction?

angiotensin 2

moderate arteriole vasoconstriction

higher resistance downstream of the filtration area to increase GHP and GFR

MCQ: nitric oxide is an afferent vasodilator produced by endothelial cells. What is the expected renal effect of blocking nitric oxide synthesis?

afferent arteriole vasoconstriction and decreased GFR

afferent arteriole vasoconstriction

higher resistance upstream of the filtration area decreases GHP and GFR

GHP is related to

blood pressure

GCOP is related with

plasma proteins

when does filtration increase?

when the glomerular hydrostatic pressure increases

when does filtration decrease?

when GCOP or CHP increase

MCQ: what is the main starling force that causes filtration in any capillary?

hydrostatic pressure

how is glomerular filtration controlled?

increasing or decreasing the resistance of afferent and efferent arteriole to blood flow through vasoconstriction or vasodilation

what is resistance of arterioles dependent on?

diameter of arterioles

increased blood flow= _____ GFR

increased

decreased blood flow= _____ GFR

decreased

what happens when flow speed increases?

reabsorption time decreases and valuable substances lost in urine

what happens when flow speed decreases?

excretion of waste products decreases

why is there a decrease in the amount of waste produces excreted when we have decreased flow speed?

water gets reabsorbed easier and faster than solutes leading to an increased solute concentrate = no concentration gradient = no elimination of waste products