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Urinary SystemUrinary SystemUrinary SystemUrinary System OverviewOverviewOverviewOverview of the Urinary SystemUrinary SystemUrinary SystemUrinary System

• Principal organs = Kidneys

• Accessory organs = Ureters,

Bladder, and Urethra

• The Urinary System regulates the content

of blood plasma to maintain homeostasis

of the internal fluid environment within

normal limits.

http://www.nottingham.ac.uk/nursing/sonet/rlos/bioproc/kidneyanatomy/4.html

KidneysKidneysKidneysKidneys• Bean-shaped.

• Left kidney is often

larger than the right.

• Right kidney is a

little lower than the

left.

• Located against the posterior wall of the

abdomen.Refer to page 830

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KidneyKidneyKidneyKidney ---- Anatomy

Refer to page 831

Kidneys are highly vascular!

KidneyKidneyKidneyKidney –––– Blood Flow

• About 1/5 of all the blood

pumped by the heart per

minute goes to the kidneys.

• Renal artery – large branch

of abdominal aorta; brings blood into each kidney.

Refer to page 831

1.

4.

3.

2.

5.

6.

brings bloodinto the kidney.

KidneyKidneyKidneyKidney –––– Blood FlowBlood FlowBlood FlowBlood FlowBranching off the interlobular arteries are the

afferent arterioles supplying the glomerular

capillaries, which drain into efferent arterioles.

Efferent arterioles divide into peritubular

capillaries that provide an extensive blood

supply to the cortex. Blood from these

capillaries collects in renal venules and leaves

the kidney via the renal vein.

http://www.nottingham.ac.uk/nursing/sonet/rlos/bioproc/kidneyanatomy/4.html

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6.

7.

8.

9.

Do you see an exception

to ““““the rule”””” here?

Ball of capillaries

Continued …

Peritubularcapillaries

ball of capillaries

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Kidney Kidney Kidney Kidney –––– Blood FlowLet’’’’s recap!

Abdominal aorta Renal artery

Segmental arteries Lobar arteries

Interlobar arteries Arcuate arteries

Interlobular arteries Afferent arteriole

Glomerulus Efferent arteriole

Peritubular capillaries (vasa recta)

Interlobular veins Arcuate veins

Interlobar veins Lobar veins

Segmental veins Renal vein Inferior vena

cava …

;ephron!

• Cortical nephrons - located in the renal cortex;

• Juxtamedullary nephrons – lie near the

junction of the cortical and medullary layers and

have loops of Henle that dip deep into the medulla.

They play an important role in concentrating urine.

Microscopic functional unit of the kidney!

constitute about 85% of total nephron numbers.

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;ephron

1. Renal corpuscle = Glomerulus + Bowman’’’’s capsule

2. Proximal convoluted tubule

3. Loop of Henle

4. Distal convoluted tubule

5. Collecting duct

Parts of the nephron in the direction of blood flow …

Renal corpuscle?

Proximal convoluted tubule?

Loop of Henle?

Distal convoluted tubule?

Collecting duct?

D

A

B

C

E

Now you try!

Renal Corpuscle

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Bowman’s capsuleContains the primary

filtering device of the

nephron, the glomerulus,a network of fine capillaries.

Podocytes

Afferent arteriole

Bowman’s

Space

(contains

glomerular

filtrate!)

2 layers of

epitheliumEfferent arteriole

Podocytes - cells of the inner wall of Bowman’’’’s

capsule. They are a crucial part of glomerular filtration.

Adjacent podocytes interlock to cover the glomerular

capillaries; but the podocytes leave gaps or thin

filtration slits.

Podocytes form

the final filtration

barrier that

restricts the

passage of

albumin, while

allowing water and

small solutes to

enter the nephron.

Over the past few

years, the renal

research

community has

come to realize

that these

podocytes are

primary targets of

the majority of

glomerular

diseases!

Glomerulus• Main filter of the nephron

• Located within Bowman's

capsule.

• Resembles a twisted mass

of tiny tubes through which

the blood passes.

• Semipermeable, allowing water and soluble wastes to

pass through and be excreted out of the Bowman's

capsule as filtrate. The filtered blood passes out of the

glomerulus into the efferent arteriole.

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Blast from the Past! Proximal Convoluted Tubule

• Wall made up of one layer of epithelial

cells with a brush border of microvilli

facing the lumen of the tubule.

• Restores much of the filtrate to the

blood in the peritubular capillaries.

• The length of a proximal convoluted tubule tends

to be several times greater than that of a distal

convoluted tubule.

Initial segment of the nephron’s tubule

;ephron Tubule

Can you

find the

proximal

convoluted

tubule?

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Loop of Henle• Leads from the proximal

convoluted tubule to the

distal convoluted tubule

in the kidney.

• Its primary function is to

reabsorb water and ions

from the filtrate.

Can you

find the

Loop of

Henle?

Descending Limb:• Much thinner wall than the

thick part of the ascending limb.

• Allows water and urea to

diffuse freely into or out of the

tubule, depending on their

concentration gradients.

Ascending Limb:

• Much thicker wall than the

descending limb.

• LIMITS the diffusion of

most molecules including

water and urea!

Distal Convoluted Tubule

• Portion of the nephron

between the loop of

Henle and the

collecting duct system.

• It is partly responsible

for the regulation of

potassium, sodium,

calcium, and pH.

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Can you

find the

distal

convoluted

tubule?

Collecting Duct

• Connects nephrons

to ureter.

• Like the distal convoluted tubule, it

participates in electrolyte and fluid

balance through reabsorption and

excretion, processes regulated by the

hormones aldosterone and antidiuretic

hormone.

Can you

find the

collecting

duct?

Let’s Review!

http://www.nottingham.ac.uk/nursing/sonet/rlos/bioproc/kidneyanatomy/4.html

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Let’s Review!

(again)• Tube which

carries the urine

from the kidneys

to the bladder.

• Composed of 3

layers: a mucous

lining, a muscular

middle layer, and a

fibrous outer layer.

UretersUretersUretersUreters

Urinary Bladder

In woman, it rests on the anterior vagina and

in front of the uterus. In men, it sits on the

prostate.

• Muscular bag which

stores and expels urine.

• Located behind the

pubic symphysis and

in front of the

rectum.

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• Wall is mostly

smooth muscle tissue

= detrusor musclewith criss-crossing

bundles of oblique,

circular, and

longitudinal.

Urinary Bladder

• Lined with mucous transitional epithelium

which forms folds called rugae – can distend

considerably!

Involuntary

Voluntary

Urethracanal through which urine is

discharged from the bladder

In females, the urethra lies

posterior to the symphysis

pubis and anterior to the

vagina. It is about 3 cm long.

In males, the urethra is part

of the urinary system, as

well as part of the

reproductive system … In the male, after leaving the bladder, the urethra passes

through the prostate gland where it is joined by 2

ejaculatory ducts. From the prostate, it extends through the

penis, and ends as a urinary meatus. A male’’’’s urethra is

about 20 cm long.

Urethra

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Chief functions of the kidney are to:

• Process blood plasma

• Excrete urine

Basic functional unit of the kidney is the nephronwhich forms urine via 3 processes:

1. Filtration 2. Reabsorption 3. SecretionRefer to

page 839

What Do Our

Kidney’s Keep In Check?

• Sodium

• Potassium

• Chloride

• ;itrogenous wastes (especially urea)

;OTE: Our kidneys do not only filter out harmful or

excess material. At first, they filter out most of the blood

plasma; then they reabsorb what should be kept before

the filtrate becomes urine!

190 L

189 L

Refer to

page 839

g

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Filtration• Passive process based on hydrostatic

pressure of the blood in the glomerulus.

•Movement of water

and protein - free

solutes from the

plasma in the

glomerulus into

Bowman’s capsule.

Filtration occurs faster out of glomerular capillaries

than all other capillaries because of the many pores

(fenestrations) and the higher hydrostatic pressure!

Regulation of Glomerular Filtration

Intrinsic - Renin

Extrinsic - Sympathetic Nervous System

Renin is an enzyme released by the

Juxtaglomerular Apparatus to help

control the body's sodium-potassium

balance, fluid volume, and blood pressure.

Plasma renin activity (PRA), also called plasma

renin assay, may be used to screen for high blood

pressure (hypertension) of kidney origin.

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• Located where the afferent arteriole

brushes past the distal tubule

• Important to

maintenance of

blood flow

homeostasis by

secreting renin

when blood

pressure in the

afferent arteriole drops.

Juxtaglomerular Apparatus Reabsorption• 2nd step in urine formation.

• Passive & Active transport mechanisms

from all parts of the

renal tubules.

• MOST reabsorption into

the peritubular blood

is from the

Proximal Tubule!

Reabsorption in the Proximal Tubule

1. Sodium is actively transported out of the tubule fluid

and into the blood.

2. Glucose and amino acids ““““hitch a ride”””” with sodium

and passively move out of the tubule fluid (Sodium

cotransport).

3. Chloride ions passively move into blood plasma b/c

of imbalance of electrical charge.

4. Blood is now hypertonic to filtrate, so water passively

moves into the blood (Osmosis!)

5. About ½ of the urea moves out of the tubule. http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/kidney.html

Refer to page 841

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Reabsorption in the Loop of Henle

Countercurrent flow refers to flow in opposite directions.

Tubule filtrate in the loop of Henle flows in a countercurrent

manner, as does blood flowing within the vasa recta of the

peritubular capillary network.

is due to : COU;TERCURRE;T FLOWCOU;TERCURRE;T FLOW !

Refer to page 842

• ;a+ and Cl- are actively

pumped from the ascending limb into the interstitial fluid.

Water is ;OT allowed to

follow! ���� Interstitial fluid

develops a high solute

concentration.

• H2O leaves the descendinglimb and enters the interstitial

fluid.

• Urea diffuses into the

descending limb

Refer to page 843

This makes the tubule

fluid dilute

(HYPOTO;IC) and

creates a high osmotic

pressure, or high

solute concentration,

of the medulla’s

interstitial fluid.

Reabsorption in the Loop of HenleThe filtrate entering is

ISOtonic to interstitial fluid.

Both are 300 mOsm.

The filtrate leaving

is now HYPOtonic!

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Reabsorption in the Loop of Henle

Reabsorption in the

Distal Tubules and Collecting Ducts

• Distal tubule reabsorbs some sodium

by active transport. H2O cannot follow!

Therefore, the solute concentration of

the tubule fluid continues to decrease.

• The collecting duct also prevents H2O

from leaving the filtrate.

Hypotonic

urine is

produced by

the nephron.

However, ADH (antidiuretic hormone)

prevents

excessive H2O

loss

Refer to page 844

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Hypertonic urine can be formed

when ADH is present. ADH, a posterior pituitary hormone,

increases the water permeability of the

distal tubule and collecting duct.

Refer to page 845

Effect of ADH on ;ephron

SecretionMovement of molecules out of the blood and into the tubule for excretion

• Descending limb of Loop of Henle –

removes urea by diffusion.

• Distal Tubule and Collecting Tubules –

Secretes K+, H+, and ;H4+…… K+ or H+ ions are actively

transported out of the blood into the tubule fluid in exchange for

,a+ that diffuse back into the blood.

• K+ secretion increases when blood aldosterone increases.

Aldosterone is a hormone secreted by the adrenal cortexthat targets distal and collecting tubule cells and causes them to

move ;a+ out of the tubule and K+ in!

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Urine Formation

http://www.sumanasinc.com/webcontent/animations/content/kidney.html

and ���� http://www.youtube.com/watch?v=aQZa;X;roVY&;R=1

Refer to page 847

Urine

Volume

REVIEW of Regulation of Urine Volume

Renin is secreted by Juxtaglomerular Apparatus. Renin triggers

the release of Angiotensin II, which triggers the release of

aldosterone from the adrenal cortex and ADH from the pituitary!

ADH, secreted by the pituitary gland, increases water

reabsorption by the kidneys by increasing water permeability of

the distal tubules and collecting ducts. ADH reduces water loss!

Aldosterone, secreted by adrenal cortex, increases distal

tubule absorption of sodium, raising the sodium concentration of

blood and thus promoting reabsorption of water

Begins with a in blood pressure …

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Approximately 95% water with several substances

dissolved in it. The most important are…

;itrogenous wastes – result of protein metabolism;

Ex: Urea (most abundant solute in urine), uric acid,

ammonia, and creatinine

Electrolytes – mainly the following

ions: sodium, potassium, ammonium,

chloride, bicarbonate, phosphate, and

sulfate; amounts and kinds of minerals

vary with diet and other factors

Urine Composition

Urea

Toxins – during disease, bacterial poisons leave

the body in the urine.

Pigments – especially urochromes (yellowish

pigments from the break down of old rbc’s.

Hormones – high hormone levels may spill

into the filtrate.

Abnormal constituents – such as blood,

glucose, albumin, casts (chunks of material like

mucus that harden inside the urinary passages

and are then washed out in the urine), or

calculi (small stones).

Urine Composition

Eating asparagus can cause

a strong odor caused by the

body's breakdown of

asparagusic acid.

Very spicy foods can have a

similar effect because their

compounds sometimes pass

through the kidneys without

being fully broken down

before exiting the body.

Micturition (Urination)• Urinary control depends

upon communication

between the cerebrum,

pons, and peripheral nerves.

• We feel the need to void

when the bladder is about

250 ml full. Ascending

fibers send this message to

the cerebrum.

• The cerebrum now switches the pons to emptying

mode. The internal sphincter relaxes and detrusor

contraction begins!

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Most kidney stones are carried out of the kidney

and through the urinary tract when they are still

small enough to pass

easily out of the body.

Larger stones,

however, may become

stuck in the tubes that

carry urine from the

kidney to the bladder

(ureters).

Kidney StonesKidney StonesKidney StonesKidney Stones

The Artificial Kidney:

Here is a picture of the

dialysis machine.

It is “slow dialysis” used

over a 24 hour period on

critically ill patients who

cannot tolerate the large

fluid shifts of hemodialysis.

This is an active filtration

system.

-----------------------------------

Peritoneal Dialysis uses

membranes in the abdomen

to create dialysis .

,ot commonly used in the

ICU.Thanks Mrs. Cusack!

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Urinary Tract InfectionUrinary Tract InfectionUrinary Tract InfectionUrinary Tract InfectionUTI - infection anywhere in the

urinary tract. Usually, a UTI is

caused by bacteria that can also

live in the digestive tract, in the

vagina, or around the urethra.

Most often these bacteria enter the

urethra and travel to the bladder

and kidneys. Usually, your body

removes the bacteria, and you have

no symptoms. However, some

people seem to be prone to

infection, including women and

older people.

You should see your doctor if you

have any of these symptoms:

• Burning feeling when you urinate

• Frequent or intense urges to

urinate, even when you have little

urine to pass

• Pain in your back or lower

abdomen

• Cloudy, dark, bloody, or unusual-

smelling urine

• Fever or chills

Urinary Tract InfectionUrinary Tract InfectionUrinary Tract InfectionUrinary Tract Infection