Filtering Blood

Question 1

ULTRAfiltration

Answer 1

• Filtration of small molecules from blood under high pressure
• Happens at the glomerulus and Bowman’s capsule
• High hydrostatic/ blood pressure at glomerulus
  - Left ventricle contracts/ ventricular systole
  - Afferent arteriole has wider diameter than efferent so efferent arteriole has a narrower lumen
  - Bottleneck effect = increase in pressure of glomerulus

Question 2

3 layers

Answer 2

• Glomerulus capillaries have endothelium cells with fenestrations/ small pores between them
• Basement membrane- has pores and acts as a molecular sieve or dialysing membrane through which large molecules can’t pass
  - Made of collagen and glycoproteins
• Podocytes (squamous epithelial cells)- podocyte feet wrap around capillary and have filtration slits

Question 3

Process of ultrafiltration

Answer 3

• Systole and arterioles increase the blood pressure
• Forces small solutes/ components of plasma through fenestrae, basement membrane and slits between pedicels into the Bowman’s capsule
• Molecules <30000 RMM can pass through basement easily
• Molecules with RMM>68000 too large (proteins, blood cells, platelets)

Question 4

What small molecules are present in glomerular filtrate

Answer 4

Forced from glomerulus into capsule and pass through the gaps:

• Glucose
• Water
• Amino acids
• Urea
• Fatty acids
• SMALL proteins

Question 5

High arterial pressure effect

Answer 5

• Increased glomerular filtration
• Dehydration
• Increased volume urine
• Damaged kidney

Question 6

Cause of protein in urine

Answer 6

• Greater glomerular pressure
• Damage to basement membrane
• Proteins forced through

Question 7

Low protein diet effect on filtration rate

Answer 7

• Less protein in the plasma
• Osmotic pressure decreases / water potential higher
• Overall pressure forming filtrate increases = more filtrate produced
• Rate of filtration faster

Question 8

Effect of blood loss

Answer 8

• Blood pressure decreased
• Less filtrate formed
• Lower filtration rate

Question 9

How to increase glomerular pressure (arterioles)

Answer 9

1) Constrict efferent arteriole so that it gets narrower

2) Dilate the afferent arteriole so that it gets wider

Question 10

Arterioles adjusting to pressure

Answer 10

Too high

• Circular muscles contract making the lumen smaller
• Less difference between diameter of afferent and efferent arteriole
• Pressure drops

Question 11

Selective reabsorption

Answer 11

Uptake of specific useful molecules from filtrate back into bloodstream

Question 12

Adaptations of PCT cells

Answer 12

• Microvilli to provide larger and increased SA for reabsorption
• Large no of mitochondria = ATP for active transport of Na+ ions and glucose
• Folded basement membrane
• Tight junctions between cells = molecules do not diffuse between adjacent cells
• Close association with capillaries = short diffusion pathway

Question 13

Glucose selective reabsorption

Answer 13

ALL GLUCOSE REABSORBED

• Facilitated diffusion through protein channels or carriers
• Glucose + amino acids diffuse with Na+ ions via co-transport proteins
• Glucose and amino acids diffuse out of PCT into blood
• Glucose also actively transported from PCT cells into blood

Question 14

Water selective reabsorption

Answer 14

90% OF WATER REABSORBED

• Absorbed by osmosis
• From an area of high w.p to an area of low w.p
• Across partially permeable membrane into PCT wall and into blood
• No energy required = no ATP

Question 15

Na+ ions selective reabsorption

Answer 15

• Facilitated diffusion into cell from glomerular filtrate
• Active transport from cell into blood via the Na/K pump in basal membrane
• ATP used
• Higher [Na+] in filtrate so more moves into cell via f.d

Question 16

Cl- ions selective reabsorption

Answer 16

• Facilitated diffusion through protein channels or carriers into PCT wall and into blood
• Down the concentration gradient
• No energy required

Question 17

Why are proteins not reabsorbed into bloodstream?

Answer 17

• Too large to pass through and diffuse back into the blood

- No specific carrier or channel proteins for them to diffuse back in

Question 18

Why does [urea] increases along PCT?

Answer 18

Water has been reabsorbed into the capillaries as it leaves the tubule by osmosis. Urea not reabsorbed (very little)

Question 19

Respiratory inhibitor (PCT)

Answer 19

• Inhibits active transport
• Glucose reabsorption prevented
• Water reabsorption still occurs
• Ratio/ concentration of glucose increases

Question 20

Glucose and NaCl to prevent dehydration

Answer 20

• More glucose and sodium absorbed from gut into blood
• More glucose and Na+ in glomerular filtrate
• More Na+ ions diffuse into PCT cells (higher conc grad)
• More glucose co-transported
• Lowers water potential so more water reabsorbed by osmosis

Question 21

Function of loop of Henle

Answer 21

Creates osmotic (conc) gradient/ low water potential in the medulla so water can be reabsorbed

Question 22

Loop of Henle

Answer 22

• Descending limb permeable to water
• Ascending limb impermeable to water
• Water leaves descending limb by osmosis
• Na+ ions are retained = going down conc increases
• At apex, Na+ very concentrated as filtrate rich in Na+
• Na+ and Cl- ions actively transported out of ascending limb
• Lower w.p in tissue fluid of medulla
• Countercurrent system

Question 23

Longer loop

Answer 23

• Lower water potential in medulla
• As more ions actively transported
• More water leaves collecting duct by osmosis