S3) GFR and Glomerulus Flashcards
Label the following blood vessels showing the blood supply and drainage of the kidney:
Label the following structures in the lobe of the kidney:
Describe the anatomical course of blood supply from the aorta to the peritubular capillaries / vasa recta
Abdominal aorta → renal artery → segmental artery → interlobar artery → arcuate artery → interlobular artery → afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries / vasa recta
Describe the anatomical course of blood drainage from the interlobular vein to the inferior vena cava
Interlobular vein → arcuate vein → interlobar vein → segmental vein → renal vein → inferior vena cava
Where do the peritubular capillaries drain?
Peritubular capillaries drain into the interlobular veins
Where do the vasa recta drain into?
Vasa recta drain into interlobular veins and arcuate veins
Compare and contrast the cortical and juxtamedullary nephrons in terms of:
- Location
- Glomerulus size
- Loop of Henle
- Cortical nephron:
I. Found in outer part of cortex
II. Small glomerulus
III. Short LoH slightly in medulla
- Juxtamedullary nephron:
I. Found in inner part of cortex next to medulla
II. Big glomerulus
III. Long LoH in medulla
Compare and contrast the cortical and juxtamedullary nephrons in terms of:
- Diameter of afferent arteriole
- Course of efferent arteriole
- Cortical nephron:
I. AA diameter > EA diameter
II. EA forms peritubular capillaries
- Juxtamedullary nephron:
I. AA diameter = EA diameter
II. EA forms vasa recta
Compare and contrast the cortical and juxtamedullary nephrons in terms of:
- Sympathetic nerve stimulation
- Concentration of renin
- Ratio
- Cortical nephron:
I. Rich stimulation
II. High [renin]
III. 90% in kidney
- Juxtamedullary nephron:
I. Poor stimulation
II. Low [renin]
III. 10% in kidney
What is the value for renal blood flow?
Renal Blood Flow (RBF) is ~1.1L/min
How is renal plasma flow calculated?
- Haematocrit is normally ~0.45
- Hence, plasma ~ 0.55
Plasma x RBF = RPF
0.55 x 1.1L /min = 605 mL/min of plasma
Where is the glomerulus found?
In the cortex
What happens to the blood in the glomerulus?
- 20% of blood from renal artery is filtered at any one time
- 80% blood arriving exits via efferent arteriole (unfiltered)
What is the normal total glomerular filtrate per day?
140 – 180 L /day (~125 ml/min)
Which two structures compose the renal corpuscle?
- Glomerulus
- Bowman’s capsule
State the structure and function of the renal corpuscle
- Structure: filtration barrier produced by capillary endothelium and visceral layer of Bowman’s capsule
- Function: produces ultra filtrate of plasma
What sort of epithelium is found in the parietal layer of Bowman’s capsule?
Simple squamous epithelium
Filtration is a selective process.
Which substances are filtered and which aren’t?
- Filtered: water, salts and small molecules
- Not filtered: cells and large proteins
What is the end product of filtration?
The end product of filtration (ultrafiltrate) is identical to plasma without the large proteins and cells
Identify the 3 layers of the filtration barrier
- Capillary endothelium
- Basement membrane
- Podocyte layer (visceral layer)
Describe the structure and function of the capillary endothelium
- Structure: permeable
- Function: filtrate (H2O, salts, glucose) moves between cells
Describe the structure and function of the basement membrane
- Structure: acellular gelatinous layer of collagen/glycoproteins
- Function:
I. Permeable to small proteins
II. Glycoproteins (- charge) repel protein movement
Describe the structure of the podocyte layer
Contain pseudopodia which interdigitate and form filtration slits
Explain the role of permeable selectivity of the filtration barrier to ensure the overall selectivity of filtration
Only particles with the following pass through:
- Small molecular weight
- Effective radius less < 1.48 nm
Explain the effect of the filtration barrier’s charge on ensuring the overall selectivity of filtration
- Negative charge of barrier repels proteins (only a few small proteins pass through)
- Removing this negative charge increases the filtration of anions e.g. proteinuria
Identify the three physical forces involved in the filtering of plasma to form ultra filtrate
- P<strong>GC</strong> – Hydrostatic pressure in the capillary
- P<strong>BC</strong> – Hydrostatic pressure in the Bowman’s capsule
- π<strong>GC</strong> – Oncotic pressure difference between the capillary and tubular lumen
What conditions are necessary for the net filtration pressure to decrease?
- PGC decreases
- PBC increases
- πGC increases
What conditions are necessary for the net filtration pressure to increase?
- PGC increases
- PBC decreases
- πGC decreases
Which pressure gradient favours filtration?
PGC – hydrostatic pressure in plasma
Which pressure gradient opposes filtration?
- PBC – hydrostatic pressure in tubule
- πGC – oncotic pressure in glomerulus
Identify three processes that drive the autoregulation of the glomerulus
- Myogenic mechanism
- Tubuloglomerular feedback
- Glomerulotubular balance
Why do we need the autoregulation of GFR?
- Keeps RBF and GFR constant
- Within the range 80-180 mmHg
What would happen if we didn’t have autoregulation?
Slight change in BP would cause significant change in GFR:
E.g. 25% increase in BP → 125 mmHg → 225 L/day GFR → 4.6L day urine
What does the myogenic mechanism entail?
- Arterial smooth muscle responds to increases and decreases in vascular wall tension
- Occurs rapidly
The myogenic mechanism is a property predominantly of the preglomerular resistance vessels.
Identify them
- Arcuate arteries
- Interlobular arteries
- Afferent arteriole
Illustrate how the myogenic response is PGC regulated
- Increase GFR (Increase PGC)
I. Dilate AA
II. Constrict EA
- Decrease GFR (Decrease PGC):
I. Dilate EA
II. Constrict AA
Describe the myogenic autoregulation of the BP
- ↑ BP → afferent arteriole constriction
- ↓ BP → afferent arteriole dilatation
GFR is unchanged in both
What does the tubuloglomerular feedback do?
TG feedback links control of distal solute delivery to the JGA with renal arteriolar resistance and hence, tubular reabsorption
What are the two components of TG feedback?
- Afferent arteriole resistance
- Efferent arteriolar feedback (hormonal)
Explain how changes in tubular flow rate change the amount of NaCl that reaches the distal tubule
Increased aBP
= Increased PGC
= Increased RPF
= Increased GFR
= Increased [Na+] and [Cl+] in distal tubule
What role do macula densa cells have in autoregulation?
Macula densa cells are sensors of DCT luminal [NaCl]
The macula densa stimulates the juxtaglomerular apparatus to releases chemicals which regulate arterial tone.
Identify them and their effects
- Adenosine: reduces GFR (A1 receptors constrict AA and A2 receptors dilate EA)
- Prostaglandin: increases GFR (vasodilates AA)
Sympathetic nerve fibres innervate AA and EA.
What effect does this have?
- Sympathetic innervation is low (no effect on GFR)
- Vasoconstriction can be stimulated by fight/flight, haemorrhage or ischaemia (reduces GFR)
What effect does the parasympathetic nervous system have on the kidney?
PNS releases nitrous oxide for endothelial cells and vasodilation
Autoregulation by glomerulotubular balance is a second line of defence.
What does it do?
Glomerulotubular balance blunts Na+ excretion response to any GFR changes
What type of epithelia is found in the proximal convoluted tubule?
Simple cuboidal epithelia
What adaptation do cells in the PCT have to help reabsorption?
- Microvilli
- Numerous mitochondria
What type of epithelia is found in the descending limb of the Loop of Henle?
Simple squamous epithelia
Why are there few mitchondria in the cells of the descending limb of the Loop of Henle?
- Only passive transport occurs
- ATP is not needed
What type of epithelia is found in the ascending limb of the Loop of Henle?
Simple squamous epithelia
Which organelle is abundant in the cells of the ascending limb of the Loop of Henle and why?
- Mitochondria
- Active absorption of Na+, K+, Cl-
What type of epithelia is found in the collecting duct?
- Simple columnar epithelium (no microvilli)
- Simple cuboidal epithelium (no microvilli)
What structure is formed from the merging of the collecting ducts and what does it do?
Papillary duct – acts as a gateway to the minor calyx
