7,8-mamallian kidney Flashcards
/The renal system
providea linl betwen the blood stream and urinary system
acting as a filter system regulating content of blood and removing waste products
What are the kidneys functions a brief overview ?
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
Composition of plasma vs urine ?
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
What is the blood and nerve supply to the kidney ?
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).
What is the nephron ?
functional unit of kidney
1. renal corpuscle:initial filtering componant
2. Tubule:fluid filled cylinder
What are the 3 major processes in the nephron ?
- Filtration:occurs in the glomerulas filtration of blood plasma forms the filtrate which then enters the tubule
- Reabsorption:selective movement of substances fro the tubular fluid
- 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
What is in the renal corpucle ?
Glomerulus –>Bowmans capsule
The structure of renal corpuscle ?
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
What are the main stages of urine ?
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
What is renal tubule ?
Proximal tube
Loop of henle
distil convuluted tube
collecting duct system
What are the 2 types of nephrons ?
- Majority :Cortical (leftside)
- 15-20% juxtamedullary the loop of henle plunges deep into medulla responsible for generating an osmotic gradient
What is the filtration membrane of renal corpuscle ?
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
Define Ultrafiltration ?
Process by which small molecules and ions pass through capillary well ;plasma proteins do not
What is glomerulas filtration rate ?
rate at which kidneys form the ultrafiltrate is measured
Also net filtration pressure is the sum of the opposing pressures
What are filtration ,reabsorptio and secretion important for ?
conserving electrolytes and regulating osmolality :transcellular /paracellular routes
Transcellular/Paracellular routes of reabsorption and secretion in renal tubule ?
- Transport across the apical membrane
- diffusion through cytosol
- transport across the basolateral membrane
- 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
What does reabsorption and secretion depend on ?
- The leakiness of junctions between tubulsr epithelial cells
- Expression of diff carriers ,channels and pumps on both the apical and basolateral membranes
What is the Proximal convulted tubule ?
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).
PCT:Reabsorption ?
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
PCT and 2 generalisations ?
- Na+ reabsorption is an active process occurring along the renal
tubule (except at the descending limb of the loop of Henle). - H20 reabsorption is by osmosis (passive) and is dependent
upon Na+ reabsorption
pH Balance in PCT ?
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.
What does the Juxtamedullary loop of henle actually do ?
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
NaCl reabsorption in loop of henle ?
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.
Counter current multiplier in loop of henle ?
- 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)
