Chapter 26

Chapter 26

The Urinary System

Three major functions:

excretion:

elimination:

regulate blood plasma:

removal of organic wastes from body fluids

discharge of waste products into the environment

volume and solute concentration

Major organs

kidneys (2)

urinary tract:ureters (2)

urinary bladder (1)

urethra (1)

produce urinewater, soluble compounds

kidney to urinary bladder

temporary storage of urine

urinary bladder to exterior

regulate blood volume and pressure

regulate [ions] in bloodNa+, K+, Cl-, etc.,

stabilize blood pH

conserve nutrientswhile getting rid of wastes

detoxify compounds

Other important functions:

kidney location

fig. 26-2a

fig. 26-2

The Kidneys

location

on either side of vertebral columnaround T12 to L3capped by adrenal glandretroperitonealsupported by CTsurrounded by adipose (cushioning)

to here 4/4/07lec# 35

The Kidneys

anatomy:

hilum indentationentry/exit

uretersrenal artery, vein, nerves

fig. 26-4a

The Kidneys

anatomy:

renal cortexrenal medullarenal pyramidsminor calyxmajor calyxrenal pelvis

nephronstubularfunctionalnumerousvascular

The Kidneys

blood supply

20-25% of cardiac output

renal artery

segmental artery

interlobar artery

arcuate artery

kidney vasculature

fig. 26-5a

fig. 26-5a

The Kidneys

blood supply

coming off of arcuate arteries interlobular arteries afferent arteriole glomerulus efferent arteriole peritubular capillary interlobular veins arcuate veins

fig. 26-5a

The nephron overview

renaltubule renal

corpuscle

renalcorpuscle

renaltubule

fig 26-6

fig. 26-6a

The nephron:partsBowman’s

capsule

Bowman’scapsule

proximalconvoluted

tubulepct

loop ofHenle

loop o

f H

enle

distalconvoluted

tubule

dct

fig. 26-9

fig. 26-6a

The nephron:blood supply

afferentarteriole

efferentarteriole

glomerulus(capillary bed)

?

afferentarteriole

efferentarteriole

glomerulus(capillary bed)

fig. 26-6a

The nephron:blood supply

peritubularcapillaries

The nephron: Bowman’s capsule

fig 26-6a

hollow structuretwo layers

visceral (inner)parietal (outer)

surrounds glomerulus

fig. 26-8


What is between blood and space?

podocytes and filtration slits

lamina densa (connective tissue)

fenestrated endothelium (capillary)

filtration slits

podocyte 1

podocyte 2

pedicel

pedicel

fig. 26-8


fig. 26-10

endotheliumlamina densafiltration slits

= filtration membrane

blood

capsular space

fig. 26-10

blood pressure forces water and small solutes across “membrane” into Bowman’s capsule

wastes

but also

waterglucose

amino acidsvitamins

fatty acidsetc.

= glomular filtrate

fig. 26-10

fig. 26-10

but not:

cellslarge plasma proteins

fig. 26-6a

proximalconvoluted

tubulepct

The nephron: proximal convoluted tubule

The nephron: proximal convoluted tubule

cuboidal cellsmicrovillireabsorption

remove water, nutrients etc., from the glomerular filtrate and release them into the peritubular fluid

fig. 26-6a

loop ofHenle

loop o

f H

enle

The nephron: loop of Henle

The nephron: loop of Henle

descending limbthick pumps Na+ Cl- out of

fluidthin permeable to H2O

ascending limbthinthick

fig. 26-6a

The nephron: distal convoluted tubule

distalconvoluted

tubule

dct


active secretion (ions, acids, drugs)

selective reabsorption of Na+ and Ca2+

selective reabsorption of H2O


also part of the jg apparatus (JGA)

(juxtaglomerular)

macula densa (DCT)juxtaglomerular cells (afferent arteriole)

secrete EPO, renin

juxtaglomerular apparatus

The collecting system

DCT

collecting duct

papillary duct

minor calyx

…

100 keys (pg. 959)

“The kidneys remove waste products from the blood; they also assist in the regulation of blood volume and blood pressure, ion levels, and blood pH. Nephrons are the primary functional units of the kidneys.”

Renal Physiology

what is the kidney doinghow does it accomplish these tasks

Goal regulate volume and composition of the blood

involves excretion of wastes

Renal Physiology

three major organic wastes

urea

creatinine

uric acid

21g / dayfrom amino acid breakdown

1.8 g / dayfrom CP breakdown

480 mg / dayrecycling RNA N-bases

Renal Physiology

three major organic wastes

can be eliminated only when dissolved in urine (H2O loss)

production of hyperosmotic urinerestrict excessive H2O lossreabsorb useful molecules

Renal Physiology: steps

1. filtration

blood pressure forcing water and small solutes (good and bad) from capillaries into capsular space


2. reabsorption

remove water and many solutes from filtrate by:

diffusion, osmosischannel-mediated diffusioncarrier-mediated transport


2. reabsorption

many different proteins involveda cell may have many functionsdifferential distribution of proteinstransport can be saturated


3. secretion

transport of solutes from body fluids into the tubular fluid (or filtrate)

table 26-2

to here 4/11/07lec# 36

Filtration

filtration membrane

lets water and small solutes through

cells and plasma proteins stay in capillaries

100 keys (pg. 969)

“Roughly 180 L of filtrate is produced at the glomeruli each day, and that represents 70 times the total plasma volume. Almost all of that fluid volume must be reabsorbed to avoid fatal dehydration.”

Filtration: hydrostatic pressure

glomerular hydrostatic pressure (GHP)push fluid out of vessels (bp)

capsular hydrostatic pressure (CsHP)push fluid back into vessels

net hydrostatic pressure (NHP)

NHP = GHP - CsHP

50 - 1535 = mm Hg

Filtration: colloid pressure

blood colloid osmotic pressure (BCOP)

proteins in blood (hyperosmotic)

draw water back into blood

~ 25 mm Hg

Filtration: filtration pressure (FP)

FP = NHP - BCOP

35 - 2510 = mm Hg

importance of blood pressure

20% drop in blood pressure50mm Hg to 40mm Hg

filtration would stop

Filtration: filtration rate (GFR)

glomerular filtration rate (GFR)

amount of fluid pushed into the capsular space each minute

GFR ~ 125 ml / min

180 liters (~50 gallons)/ day


affected by filtration pressure (FP)

change FP

change GFR

significant factor in FP is…… blood pressure


control of GFR

adequate blood flow to glomerulusadequate filtration pressure

autoregulationhormonal regulationautonomic regulation


autoregulation

lower bp

afferent arteriole dilateglomerulus dilateefferent arteriole constrict


autoregulation

higher bp

afferent arteriole contractless blood in

lower GHP


hormonal regulation

renin-angiotensin system

renin is released when:

drop in bpJG cells stimulated by sym.lower osmolarity of tubular fluid


hormonal regulation

renin

angiotensin II

constrict afferent art.secretion of aldosteronethirstsecretion of ADHgeneral vasoconstriction

bp

bp


hormonal regulation

fluid loss

bp

bp

GFR

ANPBNP

GFRNa+ reabsorptionurine production

fig. 26-11


autonomic (ANS) regulation

sympathetic stimulation

powerful vasoconstrictionof afferent arteriole

GFR

bp

bp


maximal physical exertion(ie., marathon, etc.,)

blood to muscleless blood to kidney

proteinuriahematuria

damage to glomerulus

Renal Physiology: reabsorption/secretion

PCT reabsorbs 60-70% of filtrate

peritubularfluid

peritubularcapillaries


PCT reabsorb organic nutrientsactive reabsorption of ionsreabsorption of H2Opassive reabsorption of ionssecretion


PCT reabsorb organic nutrients

99% absorbed before reaching the loop of Henle

facilitated transportcotransport

(carrier proteins)


PCT active reabsorption of ions

Na+

K+

HCO3-

active transport

(carrier proteins and ATP)


PCT reabsorption of H2O

solutesH2O

filtrate

osmosis

fig. 26-12

Renal Physiology: loop of Henle

countercurrent exchange (multiplication)

fluids moving in opposite directions

descendinglimb

ascendinglimb


thin descending limb

thick ascending limb

permeable to H2Oimpermeable to solutes

impermeable to bothcontains Na+ + Cl- pumps



contains Na+ + Cl- pumps

pumps ions out of the tubular filtrateinto the peritubular fluid

makes peritubular fluid hyperosmotic

fig 26-13

ascending limb is not permeable, but has pumps

Na+-K+/2Cl-

transporter

fig 26-13a

Na+-K+/2Cl-

transporter



contains Na+ + Cl- pumps

makes peritubular fluid hyperosmoticas thin, descending limb passes down, H2O diffuses out making fluid more concentrated

fig 26-13

permeable to H20,not solutes

that makes tubular fluid more concentrated

which means there are more ions to pump out

positive feedback maintains a hyperosmotic peritubular fluid

sets up a concentration gradient within the medulla of the kidney

papillary duct is only place permeable to urea

to here 4/13lec # 37

Renal Physiology: distal convoluted tubule

only 15-20% of original volume of filtrate makes it to the DCT

final adjustments are made here:

reabsorption

secretion


reabsorption

remove Na+ and Cl- from filtrate

aldosterone stimulates the Na+ pumps in some parts of the DCT

fig. 26-14


secretion

K+ sodium-potassium exchange

H+ secreted to raise blood pHHCO3

- is produced (buffer blood)

fig. 26-14c

Renal Physiology: the collecting system

reabsorption and secretion

collecting ducts gather tubular fluid from many nephrons and transport it toward the ureter through the concentration gradient set up in the medulla


regulation

aldosterone

ADH

activate Na+ pumps of DCT and collecting duct

controls permeability of collecting duct to H2O


reabsorption

Na+

Bicarbonate

Urea

aldosterone controlledexchange for K+

exchange for Cl-

usually diffuses out of lower portion of collecting duct


secretion

can secrete H+ to raise pHor

bicarbonate to lower pH

100 keys (pg. 976)

“Reabsorption involves a combination of diffusion, osmosis, channel-mediated diffusion, and active transport. Many of these processes are independently regulated by local or hormonal mechanisms. the primary mechanism governing water reabsorption can be described as “water follows salt.” Secretion is a selective, carrier-mediated process.”

What happens to all that stuff that has been reabsorbed and put into the peritubular space?

taken up by the peritubular capillariesand returned to circulation.

Control of water reabsorption

will determine:

volume of urineosmotic concentration of urine


85% will occur no matter what

PCTdescending limb of loop of Henle

osmosis


remaining 15% is reabsorbed (or not) by the DCT

and the collecting duct

(27 L / day)


DCT and the collecting duct are usually impermeable to H2O

except in the presence of ADH

fig. 26-15

no ADH with ADH

more, dilute urine less, concentrated urine


diabetes insipdus

underproduction of ADH

not enough water reabsorbed(too much water lost)


diabetes insipdusflow through tasteless

>10 liters of urine / dayvery thirsty


ANPBNP

natriuretic peptidesoppose action of ADH

Diuretics: drugs that promote H2O loss

reduce blood volumeblood pressureECF

Normal Urine

clearsterileyellowodorous

urinalysis

no bacteriaurobilin pigmentevaporation of small molecules

ammonia etc.,ketones ?

color, appearance, taste, chemical

fig. 26-16

sum

mary

Urine transport, storage and eliminationfig. 26-4afig. 26-7a

Urine transport, storage and elimination

collecting ductminor calyx

major calyxrenal pelvis

ureter

fig. 26-17


ureterurinary bladder

fig. 26-18c


ureterurinary bladder

sphincters (2)urethra

urethral opening

Urine transport, storage and eliminationfig. 26-18

Urine transport, storage and eliminationfig. 26-18


micturation reflex

1. stretch bladder2. sense3. stimulate muscle4. relax sphincter(s)


micturation reflex

incontinence

inabililty to voluntarily control urination

Aging and the urinary system

1. decline in # of functional nephrons2. reduction in GFR

(#1, reduced blood flow)3. less responsive to ADH4. voiding problems

loss of muscle tonecerebral damagebph

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Chapter 26