Renal System

Question 1

process of evolution in kidneys

Answer 1

1. auqatic organisms used cellular transport to miaintain differences between ECF and seawater
2. development of out epithelial layer to restrict water flow into body
3. terrestrial environment = diversifying limits to water loss

Question 2

vertebrate renal evolution

Answer 2

1. pronephros = single giant nephron does filtration for body, simple blood vessels and cilia on tubules for filtration, k=kidney directly connected to veins, single nephron
2. mesonephros = bowmans capsules formed at end of tubules (c shaped cups capsules), 24-100 nephrons, glomeruli present
3. Metanephric = ureter emergence, clusers of many smaller nephrons (millions)

Question 3

loop of henle

Answer 3

• used to concentrate urne
• ascending loop not formed a birth
• ascending and descending limbs

Question 4

features and functions of kidneys

Answer 4

• villi = increase SA for transport
• mitochondria abundance = energy for active transport
• tight junctions = block passage of solutes between cells -> barrier = control
• transporters = allow movement/transport
• renal tubules are lined with epithelial cells -> used paracellular and transcellular transport

Question 5

What is transcellular transport

Answer 5

• need proteins on both sides of membrane/cell to move solutes through

Question 6

what is paracellular transport

Answer 6

• solute moves through junctions between cells

Question 7

process occuring in kidneys

Answer 7

1. filtrattion -> movement of solutes/solvent from blood into kidney (bulk movement from glomerullar capillaries to neohron)
2. reabsorption -> movement from filtrate to peritubular capillaries (back into renal vein and blood)
3. secretion -> movement of specific solutes from peritubular capillaries back into filtrate
4. Excretion -> loss of filtrate as urine intto bladder via ureters

Question 8

explain the structure of glomerulus

Answer 8

• coarse seive
• capillaries are very leaky between cells (only protein and blood filtered)
• epithelial cells = podocytes

Question 9

what is GFR

Answer 9

• glomerular filtration rate
• volume of fluid filtered by both kidneys per unit of time

Question 10

What factors determine GFR

Answer 10

1. permeability of filtration barrier
2. SA for filtration
3. glomerular filtration pressure (only one to change short term)

Question 11

What two pressure gradients determine filtration across the glomerulus

Answer 11

1. hyrdostatic pressure (exerted by fluid inside pressure on walls)
2. oncotic pressure (exerted by water moving down conc gradient)

Question 12

what are the pressure gradient differences across the glomerular capillary and bowman’s capsule?

Answer 12

1. hydrostatic pressure higher in glomerulus than bowman’s
2. osmotic pressure higher in glomerular capillary due to proteins (no protein in bowman’s capsule)

Question 13

how does capillary hydrostatic pressure influence GFR

Answer 13

• mean arterial pressure (increased = increased glomerular pressure = increased filtration)
• afferent resistance -> increased resistance = decreased glomerular pressure = lower filtration)
• efferent resistance = high glomerular pressure = higher filtration

Question 14

what occurs in the proximal tubule?

Answer 14

• bulk reabsorption of nutrients
• unregulated absorption

Question 15

features of proximal tubule for absorption

Answer 15

• surrounded by dense capillary network
• winding structure (convoluted)
• extensive microvilli,
• high numbers of mito,
• “leaky” tight junctions (lots of stuff leaving tubule between cells),
• many and diverse transporters

Question 16

What occurs in the descending limb of henle

Answer 16

• passive water reabsorption
• permeable to water, not salt/ solutes
• water moves down electrochemical gradient through aquaporins in descending Limb all the time (always there)

Question 17

How does ECF concentration determine conc of urine in descending loop

Answer 17

• fluid can only have osmolarity same as ECF because will only flow when there is a concenntration gradient
• must be a difference for water to flow, so once it reaches isotonic level will stop
• further down loop, more concentrated

Question 18

What occurs in ascending loop of henle?

Answer 18

• active solute reabsorption
• impermeable to water and salt is actively transported
• decreasing concentration on ascension -> removing salt
• transporters moving Na+ and Cl- across into blood, dependent on K+ cycling on both apical and basolateral membranes because sets up conc gradients

Question 19

What occurs in the Collecting duct?

Answer 19

• regulated water reabsorption
• use of hormones to control transport
• fine tuning of composition of urine in distal tubule

Question 20

Effects of ADH (antidiuretic hormone

Answer 20

• opposes production of urine (decrease vol), will increase reabsorption of water into blood to reduce filtrate
  -passive movement of water turned on and off by hormones moving aquaporins

Question 21

steps of ADH movement of aquaporins

Answer 21

1. ADH acts on basolateral membrane receptors
2. triggers exocytosis of aquaporin storage vesicles inside membrane cells of collecting duct
3. increases aquaporins in luminal membrane
4. increases water reabsorption

Question 22

How is concentration of urine changing dwn collecting duct if no ADH present?

Answer 22

• it cannot change because water can’t move across the apical/lumen membrane