gus1 k6_tubular reabsorption and secretion gus-k6

7/29/2019 GUS1 K6_Tubular Reabsorption and Secretion GUS-K6

1/34

Early Filtrate Processing


2/34

In the early tubular segment of the

nephron reabsorb solutes and water of the

filtrate back into the blood to restore its

volume and composition. They also

remove some solutes from the blood and

secrete them into the filtrate to fine tune

the bloods composition


3/34

Gambaran seluler dari tubulusrenalis

Tubulus proximal: simple cuboidal cells(brush border cells ok terdapat microvilli)

Thin loop of henle: simple squamous cell,highly permeable to water not to solute

Thick ascending loop of henle & earlydistal tubule: cuboidal cells, highlypermeable to solutes, particularly NaCl butnot to water


4/34

Late distal tubule and cortical collectingduct: cuboidal cells has two distinctfunction:

1. principal cells; permeability to water

and solutes are regulated by hormonesand,

2. intercalated cells; secretion of hydrogen

ion for acid/base balancing

Medullary collecting duct; principal cells;hormonally regulated permeability to

water and urea


5/34


6/34

Tubular Reabsorption

By passive diffusion

By primary active transport: Sodium

By secondary active transport: Sugars andAmino Acids

Endositosis ; small proteins and peptide

hormones


7/34

Reabsorption Pathways

There are two reabsorption pathways:

1. the transcellular pathway (>>)

2. the paracellular pathway

To be reabsorbed into the blood, substances

in the filtrate must cross the barrier

formed by the tubular cells.


8/34

Reabsorpsi Filtrat


9/34

Trancellular pathway : Through luminal

and basolateral membranes of the tubularcells into the interstitial space and theninto the peritubular capillaries.

Paracellular pathway : through the tightjunctions into the lateral intercellularspace.

Water and certain ions use bothpathways, especially in the proximalconvoluted tubule.


10/34

Diffusion of WaterWater diffuses from the lumen through the

tight junctions into the interstitial space:

1. Water will move from its higherconcentration in the tubule through thetight junctions to its lower concentration in

the interstitium. 2. Water will also move through the

plasma membranes of the cells that are

permeable to waterAir dapat berdifusi di seluruh bagian

tubulus kecuali di thick segment of theascending limb loop of Henle


11/34

Sodium ReabsorptionDapat mengalami reabsorpsi di seluruh tubulus kecuali

thin segmeny of the limb Loop of Henle

Keluar dari sel ke

interstiital

Lumen

Plasma

Cells

PUMP: Na/K ATPase

Sodium

Potassium

Chloride

Water


12/34

Tubular Secretion

Protons (acid/base balance)

Potassium

Organic ions Zat-zat lain yg tidak normal ada dalam

darah spt obat-obatan dan bahan-bahan

toksik


13/34

Transport Maximum (Tm)

For most actively reabsorbed solutes, theamount reabsorbed in the PCT is limited only bythe number of available transport carriers forthat specific substance.

This limit is called the transport maximum, or Tm.

If the volume of a specific solute in the filtrateexceeds the transport maximum, the excess

solute continues to pass unreabsorbed throughthe tubules and is excreted in the urine.


14/34

Reabsorption: Receptors can Limit

Figure 19-15: Glucose handling by the nephron


15/34

Renal threshold of the plasma- past this

point the kidney cannot reabsorb any

longer and substance will be secreted (ie:

too much glucose). Minimal 225 mg/minglucose Tm pada beberapa nefron

Renal treshold; ambang maks konsentrasi

zat dalam darah yg tidak dijumpai dalamurin


16/34

The final processing of filtrate in thelate distal convoluted tubule andcollecting ducts comes under directphysiological control in response tochanging physiological conditions and

hormone levels. Membrane permeabilities and cellular

activities are altered in response to the

body's need to retain or excrete specificsubstances.


17/34

Distal Tubule & Collecting Duct

The Late Distal Tubule & CCT arecomposed of principal cells & intercalatedcells

Intercalated cells secrete hydrogen ionsinto filtrate

Principals cells perform hormonally

regulated water & sodium reabsorption &potassium secretion


18/34

Role of Aldosteron

Principal cells are more permeable tosodium ions and water in the presence of

Aldosterone & ADH

Low level of Aldosterone result in littlebasolateral sodium/potassium ATPase ionpump activity & few luminal sodium &

potassium channel


19/34

Aldosteron increases the number of

basolateral Na/K pump and luminal Na& K channels

Since there are no basolateral K

channel, K ion are secreted into theinstead of returning to the interstitium

Without an increase in waterpermeability, the interstitial osmolarity

increases


20/34

Role of ADH

Principals cells are more permeable to

water on the presence of ADH


21/34


22/34

80% of the blood goes back, only 20% of

the volume is filtered. Of this 20%, only

19% will be reabsorbed.

-total volume that is filtered is only about

180L/day, and 1% of this will excreted.


23/34

Reabsorption in Proximal Tubule

Glucose and Amino Acids

67% of Filtered Sodium

Other Electrolytes 65% of Filtered Water

50% of Filtered Urea

All Filtered Potassium


24/34

Juxtaglomerular apparatus

As the thick ascending loop of henletransition into early distal tubule, the

tubule runs adjacent to the afferent andefferent arteriole.

Where these structure are contact they

form the monitoring structure called thejuxtaglomerular apparatus (JGA), which iscomposed macula densa and JG cells


25/34

Figure 19-9: The juxtaglomerular apparatus


26/34

TUBULOGLOMERULAR FEEDBACK &GLOMERULOTUBULAR BALANCE

Signals from the renal tubule in each nephronfeedback to affect filtration in its glomerulus. As therate of flow through the ascending limb of the loopof Henle and first part of the distal tubule increases,glomerular filtration in the same nephron decreases,and, conversely, a decrease in flow increases theGFR

This process, which is called tubuloglomerularfeedback, tends to maintain the constancy ofthe load delivered to the distal tubule.

The sensor for this response is the macula densa.


27/34

The amount of fluid entering the distaltubule at the end of the thick ascending

limb of the loop of Henle depends on theamount of Na+ and Cl in it.

The Na+ and Cl enter the macula densa

cells via the Na

K

2Cl cotransporter intheir apical membranes.

The increased Na+ causes increased Na, K

ATPase activity and the resultantincreased ATP hydrolysis causes moreadenosine to be formed.


28/34

Presumably, adenosine is secreted from thebasal membrane of the cells. It acts via

adenosine A1 receptors on the macula densacells to increase their release of Ca2+ to thevascular smooth muscle in the afferent

arterioles. This causes afferent vasoconstriction and a

resultant decrease in GFR.

Presumably, a similar mechanism generates asignal that decreases renin secretion by theadjacent juxtaglomerular cells in the afferent

arteriole but this remains unsettled


29/34


30/34

Conversely, an increase in GFR causes anincrease in the reabsorption of solutes,and consequently of water, primarily inthe proximal tubule, so that in general thepercentage of the solute reabsorbed is

held constant.

This process is called glomerulotubularbalance, and it is particularly

prominent for Na+.


31/34

The change in Na+ reabsorption occurs withinseconds after a change in filtration, so it seemsunlikely that an extrarenal humoral factor isinvolved.

One factor is the oncotic pressure in theperitubular capillaries.

When the GFR is high, there is a relatively largeincrease in the oncotic pressure of the plasmaleaving the glomeruli via the efferent arterioles andhence in their capillary branches.

This increases the reabsorption of Na+ from thetubule. However, other as yet unidentifiedintrarenal mechanisms are also involved.


32/34

Sympathetic control

In extreme stress or blood loss,sympathetic stimulation overrides the

autoregulation

Increased sympathetic discharge causeintense constriction of renal blood vessel

Blood is shunted to other vital organs GFR reduction causes minimal fluid loss

from blood


33/34

Reduction filtration can not go indefinitely,a waste product build up & metabolicimbalances increase in blood

IV fluid increases blood volume restoresblood pressure to resting levels reduced

sympathetic stimulation allows for normal

arteriole diameter GFR & filtrate flow isnormalized


34/34

Sympathetic Regulation of GFR

Insert fig. 17.11

gus1 k6_tubular reabsorption and secretion gus-k6

Documents