Lecture 35

Question 1

what are the three parts of a nephron?

Answer 1

• proximal tubule
• distal tubule
• renal corpuscle

Question 2

how does the kidney filter blood? what is filtered? and much does it filter a day?

Answer 2

1. blood flows in
   - some will be filtered trough the “ sieve “
   - some will stay in the blood vessels

1b. once they have been filtered into the nephron substances have 2 options:

2a reabsorped: move out of the nephron back into the blood (stay in the body)

2b stay in the nephron and end up in the urine (leave the body)

Question 3

define reabsorption.

Answer 3

moves out of the nephron back into the blood (stays in the body)

1. Lumen-> apical side-> trough/between cells-> basolateral side-> interstitial space-> bloodstream

Question 4

describe the two pathways that substances use to cross an epithelium.

Answer 4

Para cellular pathway

• ” between “ cells
• transports proteins not required
• permeability depends on “tightness” of junction (leaky or tight)

Trans Cellular pathway

• “trough cells”
• apical (lumen) and Basolateral (bottom) membrane transport

requires:

• permeability (membrane transport proteins etc)
• driving force (gradient or energy)
• can be:
• automatic
• controlled by hormones

Question 5

what are the two factors that determine whether a substance will be able to cross a cell membrane ?

Answer 5

the type of transport
- Active or passive transport

Passive
- no energy required and is driven by a gradient (diffusion or osmosis)

Active

• needs a driving force
• ATP - primary
• secondary- uses movement of one substance down its gradient to drive another substance against its gradient

Question 6

describe the difference between a leaky and tight epithelium

Answer 6

Leaky epithelium

• leaky ‘tight junctions’
• water can move via both the trans and the paracellular pathway

Tight epithelium

• tight ‘tight junctions’
• water has to go via the transcellular pathway (using channels)

Question 7

what are the main functions of the proximal tubule?

Answer 7

need to reabsorb 90-99% of the water and ions and all of the nutrients that are filtered back into the blood stream (keep them in the body)
it

Question 8

how are the nutrients reabsorbed in the nephron?

Answer 8

the proximal tubule cells have leaky epithelium

the proximal tubule cells

• low sodium concentration inside
• high potassium concentration inside
• negative RMP

blood:
- high sodium concentration inside

Glucose and amino acids reabsorbed using:

Apical membrane:
- sodium- coupled secondary active transport

driven by the:

• sodium electrochemical gradient
• electrochemical gradient for sodium is created by Na+/K+ ATPase pumps

Basolateral membrane:
- facilitated diffusion
reabsorption of glucose and AA’s causes sodium reabsorption as well.

where sodium goes, water will follow by osmosis
this is helped by: Leaky junctions (paracellular) and aquaporins (transcellular

chloride follows via the para- cellular pathway down its electrochemical gradient

Question 9

what are the main functions of the distal tubule?

Answer 9

Fine tuning reabsorption (hormonal control)

1-10% of water
1-10% Na+ and Cl- ions
- tight epithelia- trans- cellular transport only