7,8-mamallian kidney

Question 1

/The renal system

Answer 1

providea linl betwen the blood stream and urinary system
acting as a filter system regulating content of blood and removing waste products

Question 2

What are the kidneys functions a brief overview ?

Answer 2

main is to maintain the constancy of the internal environment :Homeostasis
via regulation of the body balnacing water,various inorganic ions,
Determines the propeties of ECF relating to osmolarity

Question 3

Composition of plasma vs urine ?

Answer 3

urine volume and osmolarity vary with fluid intake
contains trace amount of most plasma substituents bt normally protein,glucose and amino acid are absent
others are in excess =more conc in urine

Question 4

What is the blood and nerve supply to the kidney ?

Answer 4

kidneys continously filter the blood
Renal arteries : deliver~25% of total cardiac ouput to kidneys
Efferent arteriioles of outer cortex or those close to medul;la give rise to pertibular capillaries or vasa recta

Kidneys are innervated by sympathetic
and parasympathetic nerve fibres (latter:
efferent fibres from vagus nerve).

Question 5

What is the nephron ?

Answer 5

functional unit of kidney
1. renal corpuscle:initial filtering componant
2. Tubule:fluid filled cylinder

Question 6

What are the 3 major processes in the nephron ?

Answer 6

1. Filtration:occurs in the glomerulas filtration of blood plasma forms the filtrate which then enters the tubule
2. Reabsorption:selective movement of substances fro the tubular fluid
3. Secretion :selective movement of substances from the blood into the tubular fluid

Both reabsorption and secretion take place along the length of the
renal tubule (remember has many divisions!); are aided by the existence
of peritubular capillaries and vasa recta

Question 6

What is in the renal corpucle ?

Answer 6

Glomerulus –>Bowmans capsule

Question 6

The structure of renal corpuscle ?

Answer 6

contains glomerulas inside BC
Glomerulas:contain parallel running capillaries
-Is the 1st capillary bed:high pressure in glomerulas
-Specialised 4 filtration
Fenstrated epithelium
Bowmans capsule :an external parietal layer and inner visceral layer ;latter clings to glomerulas capillaries -consist of podocytes

Question 7

What are the main stages of urine ?

Answer 7

Nephron regulates=internal environment ultrafiltration followed by selective modification of filtrate
1. ~20 % plasma filtered into Bowmans capusle to proximal tubule
2. obligatory reabsorption of all filtered glucose ,AA,
3. Loop of henle ,osmotic gradient created by NaCl reapsorption into interstitial fluid -noH2O uptake
4. distil tubule-regulated absorption/secretion

5: collecting duct, anti-diuretic hormone (ADH) released if
osmolarity is high (>290 mOsm/l): so to regulate water loss

Question 7

What is renal tubule ?

Answer 7

Proximal tube
Loop of henle
distil convuluted tube
collecting duct system

Question 7

What are the 2 types of nephrons ?

Answer 7

1. Majority :Cortical (leftside)
2. 15-20% juxtamedullary the loop of henle plunges deep into medulla responsible for generating an osmotic gradient

Question 8

What is the filtration membrane of renal corpuscle ?

Answer 8

lies bewteen the blood in glomerulas & filtrate
-forms solute-rich but virtually cell & protein free filtrate from the blood
3 layers :
1. Capillary enodothelium :contains pores which icnreases the membrane permeability
2. Basement membrane :consists of fibrils of -vely charged glycoproteins;main site of filtration of proteins
3. Bowmans capsule epithelium:contains pododcytes that extend pedicals to form filtration slits
4. Filtrate enters through into the Bowmans space

Question 9

Define Ultrafiltration ?

Answer 9

Process by which small molecules and ions pass through capillary well ;plasma proteins do not

Question 10

What is glomerulas filtration rate ?

Answer 10

rate at which kidneys form the ultrafiltrate is measured
Also net filtration pressure is the sum of the opposing pressures

Question 11

What are filtration ,reabsorptio and secretion important for ?

Answer 11

conserving electrolytes and regulating osmolality :transcellular /paracellular routes

Question 12

Transcellular/Paracellular routes of reabsorption and secretion in renal tubule ?

Answer 12

1. Transport across the apical membrane
2. diffusion through cytosol
3. transport across the basolateral membrane
4. movement through the interstitial fluid and into the capilary
   Also includes movement through leaky tight junctions particularly in proximal cinvulted tubule
   movement through interstitial fluid and into capillary

Question 13

What does reabsorption and secretion depend on ?

Answer 13

1. The leakiness of junctions between tubulsr epithelial cells
2. Expression of diff carriers ,channels and pumps on both the apical and basolateral membranes

Question 14

What is the Proximal convulted tubule ?

Answer 14

Reabsorption of e.g. amino acids and glucose are linked to the Na+
gradient across the apical membrane; driving force is provided by
the sodium pump (Na+,K+-ATPase) at the basolateral membrane.

Secretion (from blood into proximal tubule) also occurs for e.g. organic
anions (e.g. p-aminohippurate, PAH) and drugs (e.g. penicillin).

Question 15

PCT:Reabsorption ?

Answer 15

1.A the basolateral membrane, Na’ is pumped into the interstitial space by the Na’-K’ ATPase. Active Na’ transport creates concentration gradients that drive:
2. “Downhill” Na’ entry at the apical membrane.
3 Reabsorption of organic nutrients and certain ions by cotransport at the apical membrane.
4.Reabsorption of water by osmosis through aquaporins. Water reabsorption increases the
concentration of the solutes that are left behind. These solutes can then be reabsorbed as they move down their gradients:
5.Lipid-soluble substances diffuse by the transcellular route.
6.Various ions (e.g., CI}, Ca21, K’) and urea diffuse by the paracellular

Question 16

PCT and 2 generalisations ?

Answer 16

1. Na+ reabsorption is an active process occurring along the renal
   tubule (except at the descending limb of the loop of Henle).
2. H20 reabsorption is by osmosis (passive) and is dependent
   upon Na+ reabsorption

Question 17

pH Balance in PCT ?

Answer 17

The kidneys have 2 main functions with regards to pH balance:
1. To reabsorb/eliminate the filtered HCO3-:
o 99 % is reabsorbed to ensure buffer is not excreted in urine:
~85% proximal tubule; ~15% distal tubule/collecting duct.
2. To excrete (or retain) H+:
o <0.05%: as free H+ (limited by minimum attainable pH = 4.5).
o ~60%: as ammonia (NH3) or the ammonium ion (NH4+).
o ~40%: combines with urinary buffers (mainly phosphate,
HPO42-/H2PO4-) as titratable phosphoric acid (H3PO4).

Many diseases are associated with changes in acid-base balance (</> pH 7.4):
low pH (too much [H+]) = acidosis; pH too high (drop in [H+]) = alkalosis.

Question 18

What does the Juxtamedullary loop of henle actually do ?

Answer 18

plunges deep into medulla; is
responsible for generating an
osmotic gradient (important
for reabsorption of water).

Here, water reabsorption
is not coupled to solute
reabsorptio

Question 19

NaCl reabsorption in loop of henle ?

Answer 19

Epithelial cells of the thick
(not the thin) part of the
ascending limb of loop of
Henle possess a symporter
called NKCC2 or BSC1 →
transports Na+, K+ and Cl-
into the tubule cell across
its apical membrane.
Note: this transport is used
to generate the osmotic
gradient in renal medulla.

Question 20

Counter current multiplier in loop of henle ?

Answer 20

• Kidneys use countercurrent mechanisms: fluid in descending and ascending limbs of the loop flow in opposite directions.
• Multiplier: creates an osmotic gradient in renal medulla; concentrates descending loop fluid but decreases osmolality in ascending loop fluid… Water/solute movement creates a
  hyperosmotic medullary interstitial fluid, ISF.
• Kidneys create and use a medullary osmotic gradient to regulate
  urine concentration and volume.
  maintain a constant
  osmolality of extracellular fluid, ECF
  (so to prevent cells shrinking / swelling)

Question 21

Estabalishing osmotic gradient of renal medulla ?

Answer 21

initial state :renal medulla ISF
he thick asending limb pumps NaCl into the interstitium generating a small osmotic gradient

Fluid in the descending limb equilibrates with the interstitium and flows towards the hairpin bend. As it does so, it extends the zone of high osmolality deeper into the medulla
This process is continued until the tubular fluid at the hairpin bend reaches an osmolality of c. 1200 mOsmol kg-1
Eventually this hyperosmotic fluid enters the ascending limb which pumps NaCl against a gradient 200 mOsmol kg-
* As a result, the osmolality
of the interstitium increases further

Question 22

Distal convuluted tubule ?

Answer 22

Distal segments of renal tubule are more concerned with fine-tuning
→ determine final amounts excreted in urine by adjusting rates of
reabsorption, and in few cases, of secretion:
o Homeostatic controls, i.e. hormones act on these segments.

Question 23

Reabsorption in DCT ?

Answer 23

n distal tubule (and collecting ducts) reabsorption of Na+ (~12%),
water and secretion of K+ is closely regulated:
o First part of the distal tubule (attached to loop of Henle):
Similar to loop of Henle in that: active transport of NaCl; but
water impermeable → tubular fluid becomes even more dilute.
o Second part of the distal tubule (near collecting duct):
No active transport of NaCl; water permeable → reabsorption of
water into ISF by osmosis (aquaporins).
o Principal (P) cells: Na+ reabsorption is linked to K+ secretion.
o Water reabsorption follows passively.

Remember the intercalated (I) cells? They regulate acid-base balance by actively
secreting hydrogen ions (H+; type A cells do this); also, they reabsorb HCO3

Question 24

Collecting duct and reabsorption of urea ?

Answer 24

Water is reabsorbed from urine/tubular fluid into the interstitial fluid by osmosis (under the influence of anti- diuretic hormone (ADH /vasopressin).
Urine/tubular fluid more concentrated…
major solute-urea preserve osmotic gradient
inner medulla=ADH increases permeability of urea->pasively reabsorped