The Glomerulus

Question 1

In health, during the glomerular filtration barrier, what happens to Albumin molecules?

Answer 1

They are restricted from the filtrate and remain in the blood due to their size and negative charge.

Question 2

What is the function of the “Slit Diaphragm” in a healthy kidney?

Answer 2

It acts as the final physical barrier between the Podocytes to prevent protein leakage.

Question 3

In Disease during the glomerular filtration barrier, what happens to the Podocytes?

Answer 3

They undergo effacement (flatten out and lose their foot processes), which widens the gaps for protein to pass through.

Question 4

What is the primary visual difference in Albumin location in the diseased glomerular filtration barrier?

Answer 4

Albumin molecules are seen leaking through all three layers and entering the “primary urine” (filtrate)

Question 5

What clinical finding results from the breakdown shown in the diseased glomerular filtration barrier?

Answer 5

Proteinuria (mainly Albuminuria), which can lead to a loss of osmotic pressure in the blood

Question 6

How does the GBM change in the diseased state?

Answer 6

It becomes more permeable/disorganized, allowing more solutes and proteins to pass.

Question 7

What are the three layers of the Glomerular Filtration Barrier from the blood side to the urine side?

Answer 7

1. Fenestrated Endothelium (with Glycocalyx)
2. Glomerular Basement Membrane (GBM)
3. Podocytes (with Slit Diaphragms)

Question 8

What is the primary function of the Glycocalyx in the first layer of the barrier?

Answer 8

It provides a negative charge that repels negatively charged proteins like Albumin.

Question 9

What is Capillary Hydrostatic Pressure (P_c)?

Answer 9

The “Pushing” force of blood pressure. It pushes fluid out of the capillary and into the interstitium/tubule

Question 10

What is Capillary Colloid Osmotic Pressure (pi_c)?

Answer 10

The “Pulling” force of plasma proteins (mainly Albumin). It holds or pulls fluid into the capillary.

inside the blood vessel, pulls fluid INTO the blood

Question 11

What is Interstitial Hydrostatic Pressure (P_i)?

Answer 11

The pressure of the fluid in the tissue space. It typically opposes filtration by pushing back against the capillary.

Question 12

What is Interstitial Colloid Osmotic Pressure (pi_i)?

Answer 12

The “Pulling” force of proteins in the tissue. It pulls fluid out of the capillary into the tissue.

In the tissue space, pulls fluid OUT of the blood.

Question 13

In a healthy dog or cat, which of these two pressures is significantly higher?

Answer 13

Capillary Colloid Osmotic Pressure (because most Albumin is trapped in the blood).

Question 14

Is the “draw” of water toward Albumin an active or passive process?

Answer 14

Passive. It is driven by the laws of osmosis (no ATP required).

Water follows solutes

Question 15

What are the four Starling Forces specifically at the Glomerulus?

Answer 15

1. Hydrostatic pressure (capillary)
2. Colloid osmotic pressure (capillary)
3. Hydrostatic pressure (Bowman’s space)
4. Colloid osmotic pressure (Bowman’s space)

Question 16

Which force is the primary driver of Net Filtration Pressure and GFR?

Answer 16

Glomerular Capillary Hydrostatic Pressure (The “Push” from the heart/blood pressure).

Question 17

In a healthy animal, what is the relative strength of Colloid Osmotic Pressure in Bowman’s space?

Answer 17

Negligible / Near Zero (Because the filter excludes proteins, there is no “pull” from the urine side).

Question 18

Which two forces oppose filtration (try to stop fluid from leaving the blood)?

Answer 18

1. Capillary Colloid Osmotic Pressure (Albumin “pull”)
2. Bowman’s Space Hydrostatic Pressure (Fluid “pushing back” from the tubule).

Question 19

Besides the Starling Forces, what other component factors into the GFR calculation?

Answer 19

Kf (Filtration Coefficient), which accounts for the surface area and permeability of the filter.

Question 20

What is the single “Inflow” vessel that brings blood into the glomerulus?

Answer 20

The Afferent Arteriole.

Question 21

What are the two “Outflow” possibilities for fluid entering the glomerulus?

Answer 21

1. Filtration into Bowman’s Space.
2. Exit through the Efferent Arteriole.

Question 22

What determines if fluid goes into Bowman’s Space vs. the Efferent Arteriole?

Answer 22

The Net Filtration Pressure (the balance of Starling forces across the filter).

Question 23

If the Efferent Arteriole “constricts” (narrows), what happens to filtration?

Answer 23

It increases filtration because blood is “backed up,” increasing the hydrostatic pressure in the glomerulus.

Question 24

What happens to the blood that does NOT get filtered into Bowman’s Space?

Answer 24

It continues into the Efferent Arteriole and eventually becomes the peritubular capillaries.

Question 25

According to the diagram (slide 6), what is the single main driver that pushes fluid into Bowman’s Space?

Answer 25

Glomerular Capillary Hydrostatic Pressure (H_gC).

Question 26

Why does the arrow for Bowman’s Hydrostatic Pressure point UP in slide 6?

Answer 26

Because it is a "back pressure" from the tubule that opposes filtration by pushing against the capillary.

Question 27

In a "Diseased" state, how does Bowman’s Osmotic Pressure change?

Answer 27

It increases because leaking protein starts "pulling" water into the tubule, increasing total filtration.

Question 28

What is the primary role of the Afferent Arteriole (AA)?

Answer 28

It serves as the inflow vessel, bringing blood from the renal artery into the glomerular capillaries.

Question 29

What is the primary role of the Efferent Arteriole (EA)?

Answer 29

It serves as the outflow vessel, carrying blood that was not filtered out of the glomerulus.

Question 30

If the Afferent Arteriole (AA) constricts, what happens to GFR and Renal blood flow?

Answer 30

GFR decreases because less blood and less hydrostatic pressure are entering the "filter." RBF decreases

Question 31

If the Efferent Arteriole (EA) constricts, what happens to GFR and Renal blood flow?

Answer 31

GFR increases because it creates "back pressure" (a backup of blood) inside the glomerulus. RBF decreases.

Question 32

What is the primary effect of dilating the Afferent Arteriole (AA) on GFR and Renal blood flow?

Answer 32

GFR Increases (because more blood volume and higher hydrostatic pressure enter the glomerulus). RBF increases as well

Question 33

What is the primary effect of dilating the Efferent Arteriole (EA) on GFR and Renal blood flow?

Answer 33

GFR Decreases (because the "exit door" is wide open, reducing the back-pressure inside the glomerulus). RBF increases.

Question 34

How does a tubular/urinary obstruction affect Starling forces?

Answer 34

It increases Bowman’s Hydrostatic Pressure (P_BS), which pushes back against the capillary.

Question 35

What is the result of a urinary obstruction on GFR?

Answer 35

Net Filtration Pressure decreases, leading to a decrease in GFR (can lead to post-renal azotemia).

Question 36

Initially, how does systemic hypertension affect the glomerulus?

Answer 36

It increases Capillary Hydrostatic Pressure (P_GC), leading to increased net filtration pressure and GFR.

Question 37

How does chronic hypertension lead to a decrease in GFR?

Answer 37

Chronic high pressure causes thickening/scarring of the filter, which decreases K_f (surface area and permeability).

Question 38

What is the initial mechanical effect of immune-antibody complexes sticking in the glomerulus?

Answer 38

They physically block the filter, reducing the effective surface area (K_f) and making filtration less effective

Question 39

What is the secondary "biological" effect of immune complex deposition in the glomerulus?

Answer 39

They trigger inflammation, which damages the basement membrane and causes podocyte (foot process) detachment.

Question 40

If an immune response ruptures the filtration wall, what "not normal" items appear in the urine?

Answer 40

Large, charged molecules (like Albumin) and potentially cells (RBCs/WBCs).

Question 41

What is the full formula for the glomerular filtration rate (GFR)?

Answer 41

GFR = Kf x NFP

Question 42

Where does the "Ultrafiltrate" go immediately after leaving Bowman's space?

Answer 42

Into the PCT (Proximal Convoluted Tubule).

Question 43

Azotemia: how can you relate an increase in serum creatinine to GFR?

Answer 43

An increase in creatinine (azotemia) would indicate that GFR is decreased.

Question 44

Why does proteinuria lead to edema?

Answer 44

Loss of albumin decreases oncotic pressure, allowing fluid to leak out of capillaries into tissues.

Question 45

What is the medical term for fluid accumulation in the abdomen due to low protein?

Answer 45

Ascites.

Question 46

How does the body respond to the "low volume" state caused by protein loss?

Answer 46

It activates the RAAS (Renin-Angiotensin-Aldosterone System) to retain sodium and water.

Question 47

What is the primary purpose of the "tug-of-war" between Starling's forces?

Answer 47

To facilitate the continuous exchange of nutrients and waste between blood and tissues.