Lecture 5 - GFR and filtration

Question 1

What is reabsorbed in the kidney?

Answer 1

Water
Na+
Cl- 
HCO3- 
Glucose
Amino acids

Question 2

What substance is actively secreted

Answer 2

H+ - lose more than filtered

Question 3

Ultrafiltrate

Answer 3

water, ions and all small molecules - plasma without plasma proteins

Not:
RBCs
WBCs
Albumin

Question 4

Filtration rate

Answer 4

180 L/ day filtered 10 x

Question 5

Average urination a day

Answer 5

1.5 L

Question 6

Total body water

Answer 6

42 L

Question 7

ECF water

Answer 7

1/3rd - 14 L

Question 8

Intracellular water

Answer 8

2/3rds - 28 L

Question 9

Interstitial water

Answer 9

3/4 of ECF - 10.5 L

Question 10

Plasma water

Answer 10

1/4 of ECF - 3.5 L

Question 11

Haematocrit

Answer 11

2 L RBC
3.5 L plasma

5.5 L circulating volume

Question 12

Predominant ion in intracellular fluid

Answer 12

K+

Less Na+
Many large organic anions

Question 13

Predominant ion in extracellular fluid

Answer 13

Na+

Less K+
Main anion = Cl- and HCO3-

Question 14

Osmolarity

Answer 14

number of osmoles in 1 L of fluid

Question 15

Osmolality

Answer 15

Solute per kg of solvent

Question 16

Water in regards to cell membranes

Answer 16

Can cross cell membranes freely

Question 17

Glomerulus

Answer 17

Tuft of capillaries between the afferent and efferent arteriole in the renal cortex

Question 18

Renal plasma flow (RPF)

Answer 18

800ml/ min

Question 19

GFR

Answer 19

125ml/min

Question 20

Filtration fraction

Answer 20

Proportion of fluid from the renal artery that passes into the renal tubules
GFR/RPF
Normally 20%

80% of the blood from the renal artery exits through the efferent arteriole and is unfiltered

Question 21

Basement membrane

Answer 21

Acellular gelatinous layer of glycoproteins

Negatively charged

Question 22

Podocytes

Answer 22

Wrap around the outside of the capillary loop

Gaps in podocytes = filtration slits - increases filtering capacity

Question 23

What is the basement membrane selective against?

Answer 23

Large negatively charged substances such as proteins

Question 24

What makes the basement membrane selective?

Answer 24

Podocytes
Negatively charged
Fenestrations in the capillary endothelium

Question 25

What is the largest substance that can pass through the basement membrane?

Answer 25

Insulin

Question 26

Proteinuria

Answer 26

In some disease processes, the negative charge of the basement membrane is lost so proteins are more readily filtered. Therefore protein in the urine.

Question 27

Pressures in the glomerulus

Answer 27

P(GC) - Hydrostatic pressure in the glomerulus capillary P(BC) - Hydrostatic pressure in the Bowman's capsule π(GC) - Oncotic pressure in the glomerulus capillary

Question 28

Net filtration pressure

Answer 28

Net filtration pressure = PGC - (PBC + πGC)

Question 29

Oncotic pressure in Bowman's capsule

Answer 29

Proteins do not get filtered into the Bowman's capsule so there is no oncotic pressure exerted here

Question 30

Where is oncotic pressure highest?

Answer 30

Efferent arteriole as less water

Question 31

Autoregulation of GFR

Answer 31

Maintains GFR when blood pressure is within the physiological limits (80-180) By constricting or dilating the afferent and efferent arteriole

Question 32

Tubular secretions

Answer 32

``` H+ K+ NH4+ - ammonium ions Creatinine urea drugs e.g. penicillin hormones - insulin ```

Question 33

Arteriole response to high BP

Answer 33

Afferent arteriole constricts

Question 34

Intrinsic autoregulation responses of the kidney

Answer 34

Myogenic response | Tubuloglomerular feedback

Question 35

Myogenic renal autoregulation

Answer 35

1. High BP 2. Opens stretch sensitive, non-selective cation channels in the afferent arteriole smooth muscle. 3. Influx of Na+ causes depolarisation 4. Ca2+ influx causes contraction Rapid In pre-glomerular blood vessels i.e. arcuate - afferent arteriole

Question 36

Tubuloglomerular feedback

Answer 36

1. High BP 2. Increased NaCl and H2O delivery to the distal convoluted tubule and cortical collecting duct 3. The macula densa cells sense an increase in GFR (salinity sensing) 4. Move more Na+ and Cl- and K+ ions intracellularly visa NKCC2 into macular densa which causes ATP release 5. ATP converted to adenosine once it leaves the macula densa cells. 6. Adenosine binds to A1 receptors located on the mesangial cells in the afferent arteriole causing activation of G proteins. 7. Gi inhibits adenylate cyclase and Go leads to an increase in intracellular calcium which spreads to mesangial cells SM via gap junctions 5. Contraction of afferent arterioles which decreases PGC and GFR (NaCl also inhibits renin release in granular cells)

Question 37

Why does GFR decrease in response to high BP

Answer 37

To protect the distal tubule and collecting duct from overloading

Question 38

Autoregulation when GFR decreases

Answer 38

1. Less NaCl is delivered to the macula densa cells of the distal convoluted tubule 2. Prostaglandins are released from the macula densa cells 3. Causes vasodilation of the afferent arteriole 4. PGC and GFR increases

Question 39

RAAS

Answer 39

1. Prolonged decrease in BP 2. Renin released from granular cells 3. Renin converts angiotensinogen to Angiotensin I 4. Ang I to Ang III 5. Ang II causes vasoconstriction of the efferent arteriole 6. Increases PGC and GFR

Question 40

Sympathetic regulation

Answer 40

Normally sympathetic innervation is low 1. Low BP due to e.g. severe haemorrhage 2. Increase in sympathetic nerve activity 3. Stimulates constriction of the afferent arteriole via noreadrenaline. 4. PGC and GFR decreases (preserves blood volume as blood is diverted to the muscles and heart)

Question 41

Parasympathetic regulation

Answer 41

1. High BP 2. Ach release 3. Release of NO from endothelial cells 4. Efferent arteriole dilation 5. Decrease PGC and GFR

Question 42

Glomerulotubular balance

Answer 42

The PCT absorbs 67% of filtered load therefore depends on GFR. Blunts sodium excretion