Lesson 25: Glomerulus and Filtration

What are the large plasma proteins like albumin normally excluded form the filtrate?

The filtration barrier has size and charge selectivity

What is the most likely result of damage to be basement membrane of the glomerular filtration barrier?

Proteinuria

Why do blood cells normally not appear in the urine of healthy animals?

They are too large to pass through the filtration barrier

What component of the glomerular filtration barrier repels negatively charged molecules from the glomerular lumen?

Glomerular basement membrane

What is the difference between plasma and the glomerular filtrate?

Glomerular filtrate has no significant amount of proteins

What is the definition of the glomerular filtration rate?

Volume of filtrate produced into Bowman;s capsules by both the kidneys each minute

What can cause variation in GFR?

Change in net filtration pressure

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

Urine

What is highly critical in the tubular system due to the transport processes involved are saturable, which means they have a limited transport capacity?

Flow speed

How does increased flow speed effect the reabsorption time and valuable substances?

Decrease in reabsorption

Valuble substances are lost

How does the decrease in flow speed effect the reabsorption and the excretion of waste?

Increase reabsorption of water causing a concentrated solutes

Solutes follow the gradient causing to get reabsorbed making it have a difficult time excreting waste.

What is directly effected by the glomerular filtration rate?

Flow speed

How does the glomerular filtration regulated?

By increasing or decreasing the resistance of the afferent and efferent arterioles via vasoconstriction/vasodilation

What is the main Starling Forces that cause filtration in any capillary?

Hydrostatic pressure

Which type of Glomerular pressure is related to blood pressure?

Glomerular hydrostatic pressure

Which type of glomerular pressure is related to plasma proteins?

Glomerular colloid osmotic pressure

Which glomerular pressure is the pressure in the Bowman’s capsule?

Capsular hydrostatic pressure

Filtration increases when the glomerular hydrostatic pressure does what?

Increase

Filtration decreases when which two glomerular pressures increase?

Glomerular colloid osmotic pressure

Capsular hydrostatic pressure

How does afferent arteriole vasoconstriction effect the GHP and GFR?

Decreases GHP and GFR

How does Afferent Arteriole Vasoconstriction reduce pressure in the glomerulus?

Causing higher resistance upstream of the filtration area

Nitric oxide is an afferent arteriole vasodilator produced by endothelial cells, what is the expected renal effect of blocking nitric oxide synthesis?

Afferent arteriole vasoconstriction and decreased GFR

How does efferent arteriole vasoconstriction effect the GHP and GFR?

Increase both GHP and GFR

How does efferent arteriole vasoconstriction cause an increase in pressure in the glomerulus?

By causing higher resistance downstream of the filtration area

What endogenous molecule can cause efferent arteriole vasoconstriction?

Angiotensin II

How does SEVERE efferent arteriole vasoconstriction effect the glomerular pressures?

Increase GHP but decrease blood flow but then starts to decrease

Increase in GCOP

Decrease in GFR

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

How does afferent arteriole vasodilation effect the GHP and GFR?

Increase both GHP and GFR

How does Afferent Arteriole vasodilation create an increase in the pressure in the glomerulus?

Lower resistance upstream of the filtration area

How does efferent arteriole vasodilation effect the GHP and GFR?

Decreases both GHP and GFR

How does efferent arteriole vasodilation reduce the pressure in the glomerulus?

Lowers resistance downstream of the filtration area

What are three causes that lead to an increase in GHP which leads to a increase in GFR?

Increase Arterial BP

Afferent Arteriole Vasodilation

Moderate Efferent Arteriole Vasoconstriction

What are two causes that lead to an decrease in GHP which leads to a decrease in GFR?

Afferent Arteriole Vasoconstriction

Efferent Arteriole Vasodilution

What are three causes that lead to an increase in GCOP which leads to a decrease in GFR?

Dehydration

Decrease renal BF

Severe efferent vasoconstriction

What are two causes that lead to an decrease in GCOP which leads to a increase in GFR?

Hypoproteinemia

Increase renal BF

What are two causes that lead to an increase in CHP which leads to a decrease in GFR?

urinary obstructions

kidney edema

A 6 year old cat undergoes a long surgical procedure. Postoperatively, hypotension is noted, and the cat produces minimal urine. What physiological factor is primarily responsible for the decreased glomerular filtration rate?

Decreased glomerular hydrostatic pressure

What is the main purpose of autoregulation in renal blood flow?

Maintain constant GFR despite blood pressure changes

How does the tubuloglomerular feedback contribute to the autoregulation of the glomerular filtration rate?

by detecting sodium chloride concentration at the mascula densa and signaling afferent arteriole changes

GFR is not perfectly constant. Therefore, an increase in blood pressure is accompanied by a slight increase in the GFR, resulting in higher urine output. What is this process called?

Pressure Diuresis

What is the intrinsic mechanism maintain the GFR almost constant between ~75-160 mmHg?

Autoregulation

What are the consequences of a marked decrease in the GFR?

Low tubular flow speed

prolongs the time for reabsorption

Both valuable and waste products reabsorbed

What are the consequences of a marked increase in the GFR?

hight tubular flow speed

shortens the time for reabsorption

valuable substances are excreted excepted reabsorbed

If there is an increase in arterial pressure stretches the wall of the arteriole. What reflex responds by constricting, and the initially increased blood flow returns to normal?

Myogenic reflex

Why is the myogenic reflex not full proof?

The system is efficient in a specific blood pressure range. Above or below this range, the activity is limited.

How does the afferent arteriolar vasodilator feedback increase the GFR if its too low?

Flow speed decrease → more Na and Cl are reabsorbed → Macula Densa sense the reduced concentration of Na Cl → Macula Densa release nitric oxide which dilate the afferent arterioles → increasing the GFR

What is the primary response of the afferent arteriole during the myogenic reflec when arterial pressure increases?

Vasoconstriction to normalize blood flow

How does the afferent arteriolar vasodilator feedback increase the GFR if its too low?

Flow speed decreases → Decrease Na Cl due to increase reabsorption → Increase production of Renin from the juxtaglomerular cells → Renin forms Angiotensin II → Angiotensin II selectively constricts the efferent arterioles → increases GFR

How does the Tubuloglomerular feedback lower the GFR if its to high?

Increase GFR → Increases filtrate volume causing it to flow more rapidly → increase in Na Cl because it doesn’t have the time to reabsorb → Macula densa release adenosine in response → Adenosine cause afferent vasoconstriction → Mecula densa signal for the reduced production of renin from JC → decrease in angiotensin II→ vasodilatation of efferent arterioles→ GFR decreases back to normal.

What happens to renin release when the tubular flow speed decreases?

Renin release increases

What effect does the RAAS system have in the short term?

Increases blood pressure

What effect does the RAAS have in the long term?

Aldosterone increases blood volume

What are the stimuli for the RAAS system?

Hypotension

Hyponatremia

Increase Sympatheitc activation

Hyperkalemia

What are the four effects that Angiotensin II have on the body?

1. Promotes vasoconstriction of efferent arterioles

2. Promotes vasoconstriction of systemic BV

3. Promotes aldosterone release, increasing Na and H2O resorption

4. Stimulates the thirst center in the hypothalamus, which increases fluid intake

How does an inhibitor of an ACE affect blood pressure?

Decrease preload because without angiotensin the BV wont vasoconstrict causing less blood traveling to the heart

Decrease Afterload due to less H2O reabsorption causing a decrease in blood volume → Blood pressure