Glomerular Filtration

Question 1

What happens during filtration?

Answer 1

Proteins are filtered out of the plasma at the glomerular capillaries

Question 2

What is the glomerular filtration rate (GFR)?

Answer 2

180/l

Question 3

What is the advantage of the GFR being high?

Answer 3

It means that the kidney has ample opportunity to regulate the ECF volume/composition and eliminate any ‘nasty’ substances

Question 4

What happens during reabsorption?

Answer 4

Substances that the boy wants are reabsorbed (e.g. glucose) and those it doesn’t want stay in the tubule and are excreted

Question 5

What happens during excretion?

Answer 5

Substances may be specifically removed from the body this way

Question 6

What is the rate of blood flow to the kidneys?

Answer 6

1200ml/min (20-25% of total cardiac output)

Question 7

Why are the kidneys so vulnerable to vascular disease?

Answer 7

The high blood flow (they have the highest BF/g of any tissue in the body)

Question 8

What happens to the RBCs and plasma when it reaches the Bowman’s capsule?

Answer 8

None of the RBCs and only a fraction of the plasma is filtered through the capsule. The remainder passes through the efferent arterioles into the peritubular capillaries and then into the renal vein

Question 9

How much plasma flows through the kidneys per minute?

Answer 9

660ml/min (55% of BV/min)

Question 10

What is the normal glomerular filtration rate?

Answer 10

125 ml/min

Question 11

What percentage of the renal plasma becomes glomerular filtrate?

Answer 11

19% (GFR/Renal plasma flow)

Question 12

What does the glomerular filtration depend on?

Answer 12

Hydrostatic forces favouring filtration and the oncotic pressure forces favouring reabsorption

Question 13

What factors effect the filterability of solutes across the glomerular filtration barrier?

Answer 13

Molecular size, electrical charge and shape

Question 14

What structures prevent filtration of specific molecules?

Answer 14

Fenestrations: stops blood cells passing through
Basal lamina: prevents filtration of larger proteins
Slit membrane between pedicels: prevents filtration of medium proteins

Question 15

Why is the glomerular capillary pressure higher than most capillaries?

Answer 15

The arterioles are short and wide and offer little resistance to flow so the blood arriving at the glomerulus still has a high hydrostatic pressure

Question 16

Why is there a high post-capillary resistance?

Answer 16

The efferent arteriole is long and narrow

Question 17

What is the golden rule of circulation?

Answer 17

If you have a high resistance, hydrostatic pressure upstream increases while the pressure downstream is decreased

Question 18

What factors affect the GFR?

Answer 18

Primary factor: glomerular capillary pressure
sympathetic VC nerves: afferent and efferent constriction and greater sensitivity of afferent arterioles
Circulating catecholamines: constriction primarily afferent
Angiotensin II: constriction of efferent at low conc. and both afferent and efferent at high conc.

Question 19

At what range of MBP does the renal vasculature autoregulate the BF and GFR?

Answer 19

60-130 mmHg

Question 20

What happens when the MBP falls below 60mmHg?

Answer 20

Filtration falls and ceases altogether when MBP = 50mmHg

Question 21

What happens if the mean arterial pressure increases?

Answer 21

There is an autonomic increase in afferent arteriolar constriction, preventing a rise in glomerular capillary pressure

Question 22

What happens to the autoregulation where the blood volume/BP face serious compromise?

Answer 22

Activation of VC nerves and A II can override the autoregulation, liberating blood for immediately more important organs

Question 23

How much blood can be liberated from the kidneys during haemorrhage etc.

Answer 23

800ml/min

Question 24

What happens if there is a prolonged reduction in blood flow to the kidneys?

Answer 24

Irreparable damage which may then lead to death due to the disruption of the homeostasis in the kidneys

Question 25

What effect does endurance training have on blood flow to the kidneys?

Answer 25

Adaption of skeletal muscle so its requirement for blood flow is more efficient and there is less need to take it from the kidneys

Question 26

Which part of the kidneys is responsible for reabsorption?

Answer 26

Peritubular capillaries

Question 27

Is the pressure in the peritubular capillaries high or low?

Answer 27

Low: hydrostatic pressure has to overcome the frictional resistance in the efferent arterioles

Question 28

What happens to the blood in the efferent arterioles after 20% of the plasma has filtered into the Bowman’s capsule?

Answer 28

It has a higher concentration of plasma proteins

Question 29

How much of the water, glucose, sodium and urea filtered out at the glomerulus are reabsorbed within the tubule?

Answer 29

99% of Water
100% of Glucose
99.5% of Sodium
50% of Urea