9: Physiology 3 Flashcards by Ross Wilson

What are the three barriers which make up the glomerular membrane?

Endothelium of glomerular capillaries

Basement membrane

Podocytes of Bowman’s capsule and their slit processes

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Glomerular capillaries are more ___ than other capillaries.

permeable

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What is the glomerular basement membrane made up of?

Type IV collagen

(Goodpasture’s syndrome is a Type II hypersensitivity reaction where antibodies attack the Type IV collagen of the basement membrane)

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What charge does the glomerular basement membrane have?

Negative charge

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What’s good about the negativity of the glomerular basement membrane?

Large negatively charged proteins can’t pass through it

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Is filtration an active or passive process?

Active process

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What is hydrostatic pressure?

Fluid pressure

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What is oncotic pressure?

Pressure exerted by negatively charged plasma proteins

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The glomerular capillaries have a high, constant ___.

pressure

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What is the fluid pressure within Bowman’s capsule called?

Does it push fluid in or out of the glomerular capillaries?

Bowman’s capsule HYDROSTATIC pressure

Pushes fluid INTO capillary

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What type of pressure keeps plasma proteins within the capillary?

What causes this?

Capillary oncotic pressure

Negatively charged basement membrane

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What is the value of the oncotic pressure of Bowman’s capsule?

Zero

No plasma protein in the capsule

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Which forces

a) aid filtration
b) block filtration?

a) Capillary blood pressure

b) Bowman’s capsule hydrostatic pressure, capillary oncotic pressure

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What is the name for the total force which aids glomerular filtration?

What value does it have?

Net filtration pressure

10 mmHg

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What is GFR?

Glomerular filtration rate

Rate of filtration of protein-free plasma into Bowman’s capulse per unit time

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What is the equation for GFR?

GFR = K_f x net filtration pressure

K_f= filtration coefficient, or how permeable the glomerular membrane is

Net filtration pressure was 10 mmHg according to last slide

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What is the main determinant of GFR?

Capillary hydrostatic pressure

which is the strongest force pushing plasma out of the capillaries

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What is the normal GFR?

120 ml/min

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What extrinsically regulates GFR?

Sympathetic nervous system

via Baroreceptor reflex

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Increasing glomerular capillary blood pressure also increases ___.

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GFR

What increases and decreases capillary blood flow and therefore blood pressure, GFR?

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Vasodilation of afferent arteriole increases GFR

Vasoconstriction of afferent arteriole decreases GFR

How do you calculate MABP?

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((2 x diastolic) + (systolic)) / 3

How does renal blood flow and therefore GFR react to short term changes in blood pressure?

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Not very much

autoregulation to prevent water and electrolyte imbalance

When is autoregulation of renal blood flow and GFR useful?

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Exercise - BP increases but you don’t want to lose too much water and electrolytes

Low BP - you still want to filter adequately

What is **myogenic regulation** of GFR?

**Increased blood flow / BP causes walls of arteriole to stretch** **Automatic constriction of smooth muscle to reduce blood flow \> reduce GFR** Keeps GFR the same during short term hypertension/hypervolaemia

Which part of the distal tubule regulates GFR?

**Juxtaglomerular apparatus**

If solute concentration in the distal tubules increases, which cells cause **smooth muscle constriction** in the afferent arteriole to reduce blood flow and therefore GFR?

**Macula densa cells** detect inc salt **Granular/juxtaglomerular cells** cause smooth muscle constriction This is the short term regulation, juxtaglomerular apparatus also involved in RAAS which is the long term regulation

How do kidney stones affect GFR?

**Blockage in collecting system, buildup of filtrate** so Bowman's hydrostatic pressure increases, stronger force AGAINST plasma movement into capsule from capillary, GFR decreases

How does **diarrhoea** affect GFR?

**Dehydrated** **Same amount of plasma protein** Capillary oncotic pressure increases (against movement OUT of capillary into bowman's) GFR decreases

What is Kf a measure of?

**Filtration coefficient** i.e surface area available for filtration

What is **plasma clearance**?

**How effectively kidneys can clear blood of a substance**

What is the unit of plasma clearance?

**Volume per MINUTE**

What is the equation for **plasma clearance**?

**Plasma clearance** = rate of excretion / [X]_plasma Where rate of excretion = [X]_urine x urine flow rate

What substance is used to determine the GFR of patients? Why?

**Inulin** (not insulin) It passes straight through glomerular membrane with no trouble, and isn't reabsorbed, so **Plasma clearance** = **GFR**

Inulin needs to be infused into the patient before determining their GFR. What is naturally produced, freely filtered like inulin and can be used instead?

**Creatinine**

Under normal circumstances, how much **glucose** is reabsorbed by the nephrons?

**All of it**

What is the clearance of glucose in normal patients?

**Zero**

What does glycosuria mean?

**Glucose in the urine, i.e clearance isn't zero, i.e kidney problem** diabetes, cushing's, acromegaly...

When may **clearance** be **higher** or **lower** than **GFR**?

**When substance is reabsorbed into capillaries or secreted into tubules**

If **clearance is less than GFR**, the substance is being \_\_\_.

**reabsorbed**

If **clearance =** **GFR,** the substance is being \_\_\_.

**neither reabsorbed nor secreted**

If **clearance \> GFR** then the substance is being \_\_\_.

**secreted** into the tubules

What is the clearance of a) glucose b) creatinine c) inulin d) PAH?

**a) 0** **b) GFR** **c) GFR** **d)** Equal to **renal plasma flow** (some reabsorbed and ALL secreted)

What chemicals are used as **a) renal blood flow** **b) GFR** markers?

**a) PAH** **b) Creatinine, inulin**

What is **filtration fraction**?

**The proportion of plasma flowing through the glomeruli which is actually filtered**

How do you calculate **filtration fraction**?

**Filtration fracture** = GFR / Renal blood flow

What percentage of blood is filtered in the a) **glomerulus** b) **peritubular capillaries**?

**a) 20%** **b) 80%**

How do you know that renal blood flow is 25% of cardiac output?

cuz you can use all of the above to calculate renal blood flow

9: Physiology 3 Flashcards

(48 cards)