kidney 44 student bio 2 may 2011 1

8/3/2019 Kidney 44 Student Bio 2 May 2011 1

1/66

Chapter 44

Osmoregulation and

ExcretionRec. Dur.: 4h (8-9)


2/66

Gross structure of the kidney

Detailed structure of the nephron and associatedblood vessels

Osmoregulation

Excretion


3/66

At the end of the lesson, u should be able to:

A. Anatomy of Mammalian kidney

Describe how the processes of osmoregulation and excretioncontribute to fluid and electrolyte homeostasis.

Outline the gross structure of the kidney and the detailedstructure of the nephron and associated blood vessels

with emphasis on transport processes and their relevant

proteins (e.g., transport of glucose, Na+, Cl-, water, K+).

Ultrafiltration


4/66


A. Anatomy of Mammalian kidney

Trace a drop of filtrate from Bowmans capsule to its releasefrom the body as urine

Interpret the histology of the kidney, as seen in sections underthe light microscope.

Explain the functioning of the kidney in the control of water andmetabolic waste levels of the body fluids.


5/66


B. Renal processes of regulation of water and solutes

Describe the hormonal regulation of fluid and electrolytebalance by antidiuretic hormone (ADH) and atrial natriureticpeptide (ANP).

KIV 2011?: Outline the mechanism of dialysis in the case of

kidney failure.


6/66

Overview: A Balancing Act

Osmoregulation regulates soluteconcentrations and balances the gain and lossof water

Excretion gets rid of nitrogenous metabolitesand other waste products


7/66

Fig. 44-2

Selectively permeablemembrane

Net water flow

Hyperosmotic side Hypoosmotic side

Water

Solutes


8/66

Osmosis and Osmolarity

Cells require a balance between osmotic gainand loss of water

Osmolarity, the solute concentration of a

solution, determines the movement of wateracross a selectively permeable membrane

If two solutions are isoosmotic, the movement

of water is equal in both directions If two solutions differ in osmolarity, the net flow

of water is from the hypoosmotic to the

hyperosmotic solution Adequate self-study material


9/66

Urea

The liver of mammals and most adultamphibians converts ammonia to less toxicurea

The circulatory system carries urea to thekidneys, where it is excreted


10/66

Concept 44.3: Diverse excretory systems arevariations on a tubular theme

Excretory systems regulate solute movementbetween internal fluids and the externalenvironment


11/66

Fig. 44-14a

A:

B: (Red) & (blue)

E:

D:

C:

F:

(a) Excretory organs and major

associated blood vessels

G:

Can u name these?


12/66

Fig. 44-14b

(b) Kidney structureSection of kidneyfrom a rat 4 mm

C:

B:

D:

A:

Can u name these?

Fi 44 14


13/66

Fig. 44-14cB:A:

E:

(c) Nephron types

Torenalpelvis

D:

C:Can u name these?

Fi 44 14d


14/66

Fig. 44-14d

A:

B:

SEM

C:

E:

F:D:

(d) Filtrate and blood flow

G:

H:

i:

J:

K:

L:M:

10 m

Can u namethese?

Fi 44 10


15/66

Fig. 44-10

Capillary

Excretion

Secretion

Reabsorption

Excretorytubule

Filtration

Urine


16/66

Excretory Processes

Most excretory systems produce urine byrefining a filtrate derived from body fluids

Key functions of most excretory systems:

Filtration: pressure-filtering of body fluids

Reabsorption: reclaiming valuable solutes

Secretion: adding toxins and other solutesfrom the body fluids to the filtrate

Excretion: removing the filtrate from the

system Adequate self-study material


17/66

Kidneys

Kidneys, the excretory organs of vertebrates,function in both excretion and osmoregulation

Adequate self-study material


18/66

Structure of the Mammalian Excretory System

The mammalian excretory system centers onpaired kidneys, which are also the principal siteof water balance and salt regulation

Each kidney is supplied with blood by a renalartery and drained by a renal vein

Urine exits each kidney through a duct calledthe ureter

Both ureters drain into a common urinarybladder, and urine is expelled through aurethra



19/66

The mammalian kidney has two distinctregions: an outer renal cortex and an innerrenal medulla



20/66

The nephron, the functional unit of thevertebrate kidney, consists of a single longtubule and a ball of capillaries called theglomerulus

Bowmans capsule surrounds and receivesfiltrate from the glomerulus



21/66

Filtration of the Blood

Filtration occurs as blood pressure forces fluidfrom the blood in the glomerulus into the lumenof Bowmans capsule

Filtration of small molecules is nonselective

The filtrate contains salts, glucose, aminoacids, vitamins, nitrogenous wastes, and other

small molecules


P h f h Fil


22/66

Pathway of the Filtrate

From Bowmans capsule, the filtrate passesthrough three regions of the nephron: theproximal tubule, the loop of Henle, and thedistal tubule

Fluid from several nephrons flows into acollecting duct, all of which lead to the renalpelvis,which is drained by the ureter

Cortical nephrons are confined to the renalcortex, while juxtamedullary nephrons haveloops of Henle that descend into the renalmedulla


Bl d V l A i d i h h N h


23/66

Blood Vessels Associated with the Nephrons

Each nephron is supplied with blood by anafferent arteriole, a branch of the renal arterythat divides into the capillaries

The capillaries converge as they leave theglomerulus, forming an efferent arteriole

The vessels divide again, forming the

peritubular capillaries, which surround theproximal and distal tubules



24/66

Vasa recta are capillaries that serve the loopof Henle


C t 44 4 Th h i i d f


25/66

Concept 44.4: The nephron is organized forstepwise processing of blood filtrate

The mammalian kidney conserves water byproducing urine that is much moreconcentrated than body fluids


LE 26-12


26/66

Nephron loop

Urine storage

and elimination

Reabsorption

Secretion

Glomerular capsule

KEY

Glomerulus

Proximal convoluted tubule Distal convolutedtubule

Collecting duct

Leak channel

Countertransport

Exchange pump

Cotransport

Diffusion

Tubular fluid

Cells ofproximal

convolutedtubule

Glucose andother organic

solutes

H+ HCO3 CO2 H2OH2CO3

H+

H+

Na+ Na+Na+

HCO3

CO2

H2CO3

H+

H2O

HCO3

Na+

H+

Facilitateddiffusion

HCO3

Na+

2 K+

3 Na+

2 K+

3 Na+

Peritubularcapillary

FYI only

LE 26-12-3


27/66

Reabsorption

Secretion

KEYLeak channel

Countertransport

Exchange pump

Cotransport

Diffusion

Tubular fluid

Cells ofproximal

convoluted

tubule

Glucose andother organic

solutes

H+ HCO3 CO2 H2OH2CO3

H+

H+

Na+ Na+Na+

HCO3

CO2

H2CO3

H+

H2O

HCO3

Na+

H+

Facilitateddiffusion

Na+

2 K+

3 Na+


HCO3

3 Na+

2 K+

FYI only

F Bl d Filt t t U i A Cl L k


28/66

From Blood Filtrate to Urine: A Closer Look

Proximal Tubule

Reabsorption of ions, water, and nutrientstakes place in the proximal tubule

Molecules are transported actively andpassively from the filtrate into the interstitialfluid and then capillaries

Some toxic materials are secreted into thefiltrate

The filtrate volume decreases



29/66

The function of the loop of

Henle is to concentrate sodiumions and chloride ions in the

interstitial fluid in the medulla.

Play animation


30/66

Descending Limb of the Loop of Henle Reabsorption of water continues through

channels formed by aquaporin proteins

Movement is driven by the high osmolarity ofthe interstitial fluid, which is hyperosmotic tothe filtrate

The filtrate becomes increasingly concentrated



31/66

The epithelium of the ascending limb is permeable to sodiumions and chloride ions but not to water.

As filtrate ascends in the thin segment of the ascending limb,

sodium ions and chloride ions diffuse into the interstitial fluid.

Play animation

LE 26-13P i l l t d t b l KEYT b l fl id


32/66

Nephron loop

Urine storageand elimination

Glomerular capsule

Glomerulus

Proximal convoluted tubuleDistal convoluted

tubule

Collecting duct

Reabsorption

Secretion

KEY

Leak channel

Exchange pump

Cotransport

Diffusion

Na+CI

H2O

2 CI

Na+K+

Tubular fluid

PeritubularfluidNa+

K+K+

K+

CI

K+

CORTEX

DCT andcollecting duct(variablepermeabilityto water;impermeable

to urea)

Papillary duct(permeabilityto urea)

Thin descendinglimb (permeable

to water,impermeable

to urea)

MEDULLA Urea120012001200

900900

600300

300

300

100

H2O

H2O

H2O

H2O

H2O

1200

900

600

300 100

H2O

300

H2O

600

900

Na+CI

Na+CI Na+CI

Na+CI

Na+CI

300mOsm/L

1200

Thindescendinglimb(permeableto water;impermeableto solutes)

Thickascending

limb(impermeable

to water;active solute

transport)

The mechanism of sodium and chloride ion transportinvolves the Na+K+/2CIcarrier at the apical surfaceand two carriers at the basal surface of the tubularcell: a potassiumchloride cotransport pump anda sodiumpotassium exchange pump. The net resultis the transport of sodium and chloride ions into theperitubular fluid.

The permeability characteristics of both the loop and the collectingduct tend to concentrate urea in the tubular fluid and in the medulla.The nephron loop, DCT, and collecting duct are impermeable to urea.As water reabsorption occurs, the urea concentration rises. Thepapillary ducts permeability to urea accounts for roughly one -third

of the solutes in the deepest portions of the medulla.

Active transport of NaCI along the ascendingthick limb results in the movement of water fromthe descending limb.

FYI only

LE 26-13a


33/66

Reabsorption

Secretion

KEY

Leak channel

Exchange pump

Cotransport

Diffusion

2 CI

Na+

Tubular fluid

Peritubularfluid

K+

K

+

CI

Na+

K+

K+K+

FYI only


34/66

Ascending Limb of the Loop of Henle In the ascending limb of the loop of Henle, salt

but not water is able to diffuse from the tubule

into the interstitial fluid The filtrate becomes increasingly dilute



35/66

Water is able to move out by osmosis because ofthe high osmotic concentration of the interstitial fluid

in the medulla.

Play anima

Play animation

LE 26-14


36/66

Nephron loop

Urine storageand elimination

Glomerularcapsule

Glomerulus

Proximalconvoluted tubule

Distal convoluted tubule

Collecting duct

Reabsorption

Secretion

KEY

Leak channel

Exchange pump

Cotransport

Diffusion

Countertransport

CINa+

Tubular fluid

K+

Entire DCT

Na+

Na+K+

Na+K+

Na+K+

Na+

K+

Na+

K+

Na+

CI

Na+CI


Sodium and chloride

reabsorption

Aldosterone-sensitiveportion of DCT and

collecting duct

Sodiumpotassium exchange

FYI only

LE 26-14aTubular fluid


37/66

Reabsorption

Secretion

KEY

Leak channel

Exchange pump

Cotransport

Diffusion

Countertransport

CINa+

Tubular fluid

K+

Entire DCT

Na+

Na+

K+

K+

CI

Na+CI


Sodium and chloride

reabsorption

FYI only

LE 26-14b


38/66

Reabsorption

Secretion

KEY

Leak channel

Exchange pump

Cotransport

Diffusion

Countertransport

Na+

Na+K+

Na+K+

Na+K+

Na+

Aldosterone-sensitiveportion of DCT and

collecting duct

Sodiumpotassium exchange

FYI only

LE 26-14cTubular Hydrochloric Ammonium


39/66

Reabsorption

Secretion

KEY

Leak channel

Exchange pump

Cotransport

Diffusion

Countertransport

H+

Entire DCTand

collectingduct

H+

secretion and HCO3

reabsorption

HCO3 Sodium bicarbonate


CO2

Na+ HCO3

H+HCO3

CO2

Na+

HCO3

CI

H+HCO3

H+

HCO3

H+

H+

CO2

CO2

CI

CI

CI

Na+

Na+

Na+

HCO3

HCO3

CI

CI

CI

H2CO3

H2O

NH4

NH4

NH4

Aminoacid

deamination

fluidy

acid chloride

FYI only


40/66

Distal Tubule

The distal tubule regulates the K+ and NaClconcentrations of body fluids

The controlled movement of ions contributes topH regulation



41/66

Collecting Duct

The collecting duct carries filtrate through themedulla to the renal pelvis

Water is lost as well as some salt and urea,and the filtrate becomes more concentrated

Urine is hyperosmotic to body fluids


Fig. 44-15


42/66

Key

Activetransport

Passivetransport

INNERMEDULLA

OUTERMEDULLA

H2O

CORTEX

Filtrate

Loop ofHenle

H2O K+HCO3

H+ NH3

Proximal tubule

NaCl Nutrients

Distal tubule

K+ H+

HCO3

H2O

H2O

NaCl

NaCl

NaCl

NaCl

Urea

Collectingduct

NaCl

By what process are

substances moving?

Fig. 44-16-1


43/66

Key

Activetransport

Passivetransport

INNERMEDULLA

OUTERMEDULLA

CORTEXH2O

300300

300

H2O

H2O

H2O

400

600

900

H2O

H2O

1,200

H2O

300

Osmolarity ofinterstitial

fluid(mOsm/L)

400

600

900

1,200

In which direction ismedullary/ interstitialfluid concentration

gradient?By what process isH2O moving?What causes it tomove?

Effects oninterstitial fluid?Is this consideredreabsorption or

excretion?

Fig. 44-16-2


44/66

Key

Activetransport

Passivetransport

INNERMEDULLA

OUTERMEDULLA

CORTEXH2O

300300

300

H2O

H2O

H2O

400

600

900

H2O

H2O

1,200

H2O

300


fluid(mOsm/L)

400

600

900

1,200

100

NaCl

100

NaCl

NaCl

NaCl

NaCl

NaCl

NaCl

200

400

700

By what process areNa+, Cl- moving?What causes them to

move?Effects on interstitialfluid?Is this consideredreabsorption or

excretion?

Fig. 44-16-3


45/66

Key

Activetransport

Passivetransport

INNERMEDULLA

OUTERMEDULLA

CORTEXH2O

300300

300

H2O

H2O

H2O

400

600

900

H2O

H2O

1,200

H2O

300


fluid(mOsm/L)

400

600

900

1,200

100

NaCl

100

NaCl

NaCl

NaCl

NaCl

NaCl

NaCl

200

400

700

1,200

300

400

600

H2O

H2O

H2O

H2O

H2O

H2O

H2O

NaCl

NaCl

Urea

Urea

Urea

H2ONa+, Cl-UreaBy what process

are these moving?What causes it tomove?Effects on interstitialfluid?Is this consideredreabsorption orexcretion?

Solute Gradients and Water Conservation


46/66

Solute Gradients and Water Conservation

Urine is much more concentrated than blood

The cooperative action and precisearrangement of the loops of Henle and

collecting ducts are largely responsible for theosmotic gradient that concentrates the urine

NaCl and urea contribute to the osmolarity of

the interstitial fluid, which causes reabsorptionof water in the kidney and concentrates theurine



47/66

In the proximal tubule, filtrate volumedecreases, but its osmolarity remains the same



48/66

The collecting duct conducts filtrate through theosmolarity gradient, and more water exits thefiltrate by osmosis

Urea diffuses out of the collecting duct as ittraverses the inner medulla

Urea and NaCl form the osmotic gradient that

enables the kidney to produce urine that ishyperosmotic to the blood



49/66

Animals that musttightly regulate body

water stores (desertanimals) have verylong loops of Henleand large osmoticgradients

Brooker1e

Mammals


50/66

Mammals

The juxtamedullary nephron contributes towater conservation in terrestrial animals

Mammals that inhabit dry environments have

long loops of Henle, while those in fresh waterhave relatively short loops


Dehydration


51/66

Playanimation

Can u.c.d. aquaporin?

Perspiration causes loss of water and sodium ions.

Blood levels of ADH and aldosterone increase

Aldosterone increases no. of Na+/K+ pumps (yellow) & Na+,

K+ channels Body fluid is conserved and urine volume decreases.


52/66

Playanimation

Dehydration

In severe dehydration condition,

low volume of urine excreted

may be concentrated to about 1400 mOsm/L

Adequate self-study material after viewing anime:Overhydration


53/66

Play

animation

Slurrrrpp

Thirsting for

exam tips?

Can u.c. any

aquaporin?

Overhydration triggers a decrease in ADH and aldosterone

No. of Na+/K+ pumps & Na+, K+ channels decreases

Reabsorption of water and sodium ions decreasesUrine volume increases

Adequate self-study material after viewing anime:Overhydration


54/66

Playanimation

ADH levels are very low or absent

Duct cells remain impermeable to water and urea

Urine is very dilute and high in volume Final urine may have an osmolarity as low as 100 mOsm/L


55/66

Playanimation

Adequate self-study material after viewing anime:With normal

hydration, normal ADH results in a few water channels ADH facilitates the diffusion of urea out of the medullary

collecting duct

Urea is responsible for up to 40% of the interstitial fluid

osmolarity Urea circulates back into the loop of Henle and returns to

collecting ducts

Urine is concentrated to about twice normal body osmolarity

(600 mOsm/L)

Fox 11e: Table 17.2


56/66

Summary of transport processes in renal tubule &collecting duct


Antidiuretic Hormone


57/66

The osmolarity of the urine is regulated bynervous and hormonal control of water and saltreabsorption in the kidneys

Antidiuretic hormone (ADH) increases waterreabsorption in the distal tubules and collectingducts of the kidney

An increase in osmolarity triggers the releaseof ADH, which helps to conserve water


Fig. 44-19

Osmoreceptors inINTERSTITIALFLUID

COLLECTINGDUCT


58/66

Thirst

Drinking reducesblood osmolarity

to set point.

phypothalamus trigger

release of ADH.

Increasedpermeability

Pituitarygland

ADH

Hypothalamus

Distaltubule

H2O reab-sorption helpsprevent further

osmolarityincrease.

STIMULUS:Increase in blood

osmolarity

Collecting duct

Homeostasis:Blood osmolarity

(300 mOsm/L)

(a)

Exocytosis

(b)

Aquaporinwaterchannels

H2O

H2O

Storagevesicle

Second messengersignaling molecule

cAMP

FLUID

ADH

receptor

ADH

DUCTLUMEN

COLLECTINGDUCT CELL

*nervous and hormonalcontrols involved in theregulation of kidney

function


59/66

Mutation in ADH production causes severedehydration and results in diabetes insipidus

Alcohol is a diuretic as it inhibits the release of

ADH


Fig. 44-21-3 Liver*Why does


60/66

Renin

Distaltubule

Juxtaglomerularapparatus (JGA)

STIMULUS:Low blood volumeor blood pressure

Homeostasis:Blood pressure,

volume

Angiotensinogen

Angiotensin I

ACE

Angiotensin II

Adrenal gland

Aldosterone

Arterioleconstriction

Increased Na+and H2O reab-

sorption indistal tubules

aldosterone,increase

blood volumeandpressure?

Na+ causes:


61/66

heart to make more ANP Atrial natriuretic peptide

(ANP) secreted from atriaof heart to decrease sodiumreabsorption in kidney

*What does this to bloodconcentration of Na+?

Brooker1e (text & pix)

The Renin-Angiotensin-Aldosterone System


62/66

The renin-angiotensin-aldosterone system(RAAS) is part of a complex feedback circuitthat functions in homeostasis

A drop in blood pressure near the glomeruluscauses the juxtaglomerular apparatus (JGA)to release the enzyme renin

Renin triggers the formation of the peptideangiotensin II



63/66

Angiotensin II

Raises blood pressure and decreases bloodflow to the kidneys

Stimulates the release of the hormonealdosterone, which increases blood volumeand pressure


Homeostatic Regulation of the Kidney


64/66

ADH and RAAS both increase waterreabsorption, but only RAAS will respond to adecrease in blood volume

Another hormone, atrial natriuretic peptide(ANP), opposes the RAAS

ANP is released in response to an increase in

blood volume and pressure and inhibits therelease of renin


You should now be able to:


65/66

1. Define osmoregulation, excretion

2. Using a diagram, identify and describe thefunction of each region of the nephron

3. Explain how the loop of Henle enhanceswater conservation

4. Describe the nervous and hormonal controls

involved in the regulation of kidney function


66/66

THE END

kidney 44 student bio 2 may 2011 1

Documents