dr. k urinary system

Copyright © 2010 Pearson Education, Inc.

Urinary System


What are the organs that comprise the urinary system?


Urinary System Organs

• Kidneys

• Urinary bladder

• Ureters

• Urethra

Copyright © 2010 Pearson Education, Inc. Figure 25.1

Esophagus (cut)Inferior vena cava

Adrenal gland

Hepatic veins (cut)

Renal artery

Renal hilum

Renal vein

Iliac crest

Kidney

Ureter

Urinary

bladder

Urethra

Aorta

Rectum (cut)

Uterus (part of female reproductive system)

Copyright © 2010 Pearson Education, Inc. Figure 25.21b

Ureter

Trigone

Peritoneum

Rugae

Detrusor muscle

Bladder neck

Internal urethralsphincter

External urethralsphincter

Urogenital diaphragm

Urethra

External urethralorifice

Ureteric orifices

(b) Female.

Copyright © 2010 Pearson Education, Inc. Figure 25.21a

Ureter

Trigone of bladder

Prostate

Membranous urethra

Prostatic urethra

Peritoneum

RugaeDetrusor muscle

Bladder neckInternal urethral sphincter

External urethral sphincterUrogenital diaphragm

Spongy urethra

Erectile tissue of penis

Ureteric orificesAdventitia

(a) Male. The long male urethra has three

regions: prostatic, membranous and spongy.

External urethral orifice


Urethra

• Sphincters

• Internal urethral sphincter

• Involuntary (smooth muscle) at bladder-

urethra junction

• Contracts to open

• External urethral sphincter

• Voluntary (skeletal) muscle surrounding the

urethra as it passes through the pelvic floor


Urinary System

In general, what are the functions of the urinary system?


Urinary System General Functions

• Kidneys are major excretory organs

• Removal of toxins, metabolic wastes, and excess ions from the blood

• Regulation of blood volume, chemical composition, and pH

• Endocrine functions of kidney

• Renin: regulation of blood pressure and kidney function

• Erythropoietin: regulation of RBC production

• Activation of vitamin D

• Urinary bladder is the temporary storage reservoir for urine

• Ureters transport urine from the kidneys to the bladder

• Urethra transports urine out of the body


What is the composition of urine?


Physical Characteristics of Urine

• Color and transparency

• Clear, pale to deep yellow (due to urochrome)

• Drugs, vitamin supplements, and diet can alter

the color

• Cloudy urine may indicate a urinary tract

infection



• Odor

• Slightly aromatic when fresh

• Develops ammonia odor upon standing

• May be altered by some drugs and vegetables



• pH

• Slightly acidic (~pH 6, with a range of 4.5 to

8.0)

• Diet, prolonged vomiting, or urinary tract

infections may alter pH


Chemical Composition of Urine

• 95% water and 5% solutes

• Nitrogenous wastes: urea, uric acid, and creatinine

• Other normal solutes

• Na+, K+, PO43–, and SO4

2–,

• Ca2+, Mg2+ and HCO3–

• Abnormally high concentrations of any constituent may indicate pathology


Renal Calculi

• Kidney stones form in renal pelvis

• Crystallized calcium, magnesium, or uric acid

salts

• Larger stones block ureter, cause pressure and pain in kidneys

• May be due to chronic bacterial infection,

urine retention, ↑Ca2+ in blood, ↑pH of urine


Location of The Kidneys


Kidney Anatomy

• Retroperitoneal, in the superior lumbar region

• Right kidney is lower than the left


Body wall

• Perirenalfat capsule

Renalartery

Renalvein

Inferior vena cava

Aorta

• Fibrouscapsule

• Renal fasciaanteriorposterior

Supportivetissue layers

Body of

vertebra L2

PeritoneumPeritoneal cavity(organs removed)

Anterior

Posterior(a)


anatomy of the kidneys


Kidney Anatomy

• Convex lateral surface, concave medial surface

• Renal hilum leads to the renal sinus

• Ureters, renal blood vessels, lymphatics, and nerves enter and exit at the hilum

• Layers of supportive tissue surround the kidney

1. Renal fascia

• The anchoring outer layer of dense fibrous connective tissue

2. Perirenal fat capsule

• A fatty cushion

3. Fibrous capsule

• Prevents spread of infection to kidney


Internal Kidney Anatomy

• Renal cortex

• A granular superficial region

• Renal medulla

• The cone-shaped medullary (renal) pyramids separated by renal columns

• Lobe

• A medullary pyramid and its surrounding cortical tissue

• Papilla

• Tip of pyramid; releases urine into minor calyx

• Renal pelvis

• The funnel-shaped tube within the renal sinus

• Major calyces

• The branching channels of the renal pelvis that

• Collect urine from minor calyces

• Empty urine into the pelvis

• Urine flows from the pelvis to ureter


Renal cortex

Renal medulla

Major calyx

Papilla ofpyramid

Renal pelvis

Ureter

Minor calyx

Renal column

Renal pyramid in renal medulla

Fibrous capsule

Renalhilum

(a) Photograph of right kidney, frontal section (b) Diagrammatic view


Blood and Nerve Supply

• Arterial flow into and venous flow out of the kidneys follow similar paths

• Nerve supply is via sympathetic fibers from the renal plexus


Cortical radiate vein

Cortical radiate artery

Arcuate vein

Arcuate artery

Interlobar vein

Interlobar artery

Segmental arteries

Renal artery

Renal vein

Renal pelvis

Ureter

Renal medulla

Renal cortex

(a) Frontal section illustrating major blood vessels


The Nephron: The Repeated Functional Unit of the Kidney


Functions in

reabsorption

and

secretion

freely permeable to water

function more in secretion than reabsorption

function in maintaining the acid-base balance of the body and help maintain the body’s

water and salt balance


Nephrons

• Cortical nephrons—85% of nephrons; almost entirely in the cortex

• Juxtamedullary nephrons

• Long loops of Henle deeply invade the medulla

• Extensive thin segments

• Important in the production of concentrated

urine


Nephrons

• Structural and functional units that form urine

• ~1 million per kidney

• Parts of the nephron

• glomerulus: a tuft of capillaries

• renal tubule: begins as cup-shaped glomerular (Bowman’s) capsule surrounding the glomerulus

• renal corpuscle

• Glomerulus + its glomerular capsule

• Fenestrated glomerular endothelium

• Allows filtrate to pass from plasma into the glomerular capsule


Renal Tubule

Glomerular capsule

• Parietal layer: simple squamous epithelium

• Visceral layer: branching epithelial podocytes

• Extensions terminate in foot processes that cling to basement membrane

• Filtration slits allow filtrate to pass into the capsular space


Cortical nephron• Has short loop of Henle and glomerulusfurther from the corticomedullary junction

• Efferent arteriole supplies peritubular capillaries

Juxtamedullary nephron• Has long loop of Henle and glomeruluscloser to the corticomedullary junction

• Efferent arteriole supplies vasa recta

Corticomedullaryjunction

UreterRenal pelvis

Kidney

Cortex

Medulla

(a)

Cortical radiate veinCortical radiate arteryAfferent arteriole

Afferent arteriole

Collecting ductDistal convoluted tubule

Efferent arteriole

Vasa rectaLoop of HenleArcuate arteryArcuate vein

Peritubular capillaries

Glomerular capillaries (glomerulus)Glomerular(Bowman’s) capsule

Renalcorpuscle

Ascending or thick limb of the loop of Henle

Descendingor thin limb of loop of Henle

Efferent arteriole

Proximalconvoluted tubule


Vascular Resistance in Microcirculation

• High resistance in afferent and efferent arterioles

• Causes blood pressure to decline from

~95 mm Hg to ~8 mm Hg in kidneys


A Portion of the Nephron Called the Juxtaglomerular Apparatus


Glomerulus

Glomerular capsule

Afferent arteriole

Efferent arteriole

Red blood cell

Podocyte cell body (visceral layer)

Foot processesof podocytesParietal layer

of glomerularcapsule

Proximaltubule cell

Lumens of glomerularcapillaries

Endothelial cellof glomerularcapillary

Efferent arteriole

• Macula densa cellsof the ascending limbof loop of Henle

• Granular cells

• Extraglomerularmesangial cells

Afferent arteriole

Capsularspace

Renal corpuscleJuxtaglomerularapparatus

Mesangial cellsbetween capillaries

Juxtaglomerularapparatus


Juxtaglomerular Apparatus (JGA)

• One per nephron

• Important in regulation of filtrate formation and blood pressure

• contains renin

• act as mechanoreceptors that sense blood pressure

• act as chemoreceptors that sense NaCl content of filtrate


The Portion of the Nephron Called the Glomerulus: The glomerular capillaries

and filtration membrane


Glomerular capillarycovered by podocyte-containing visceral layer of glomerular capsule

Glomerular capillaryendothelium (podocyte covering and basement membrane removed)

Proximal convolutedtubule

Parietal layerof glomerular capsule

Afferentarteriole

Glomerular capsular space

Fenestrations(pores)

Efferentarteriole

Podocytecell body

Foot processesof podocyte

Filtration slits

Cytoplasmic extensionsof podocytes

(a) Glomerular capillaries

and the visceral layer of

the glomerular capsule

Copyright © 2010 Pearson Education, Inc. Figure 25.9c

(c) Three parts of the filtration membrane

Fenestration(pore)

Filtrate in

capsular

space

Foot processesof podocyte

Filtration slit

Slit diaphragm

Capillary

Filtration membrane

• Capillary endothelium• Basement membrane• Foot processes of podocyte

of glomerular capsule

Plasma


Filtration Membrane

• Porous membrane between the blood and the capsular space

• Consists of

1. Fenestrated endothelium of the glomerular capillaries

2. podocytes with foot processes and filtration slits

3. Gel-like basement membrane

4. glomerular mesangial cells that engulf and degrade macromolecules

• Allows passage of water and solutes smaller than most plasma proteins

• Fenestrations prevent filtration of blood cells

• Negatively charged basement membrane repels large anions such as plasma proteins

• Slit diaphragms also help to repel macromolecules


Kidney Physiology: Mechanisms of Urine Formation


General Facts about Urine Formation

• The kidneys filter the body’s entire plasma volume 60 times each day

• Filtrate

• Blood plasma minus proteins

• Urine

• <1% of total filtrate

• Contains metabolic wastes and unneeded substances


Corticalradiateartery

Afferent arteriole

Glomerular capillaries

Efferent arteriole

Glomerular capsule

Rest of renal tubulecontaining filtrate

Peritubularcapillary

To cortical radiate vein

Urine

Glomerular filtration

Tubular reabsorption

Tubular secretion

Three major

renal processes:


Mechanisms of Urine Formation: A three step process

1. Glomerular filtration - passive mechanical process driven by hydrostatic pressure, GFR or glomerular filtration rate is the volume of filtrate formed per minute by the kidneys (120–125 ml/min)

2. Tubular reabsorption

• Returns all glucose and amino acids, 99% of water, salt, and other components to the blood

3. Tubular secretion

• Reverse of reabsoprtion: selective addition to urine


If hydrostatic pressure drives glomerular filtration (#1 on previous slide), then what is

the driving force for reabsorption and secretion (#2 and #3 on previous slide)?


If hydrostatic pressure drives glomerular filtration (#1 on previous slide), then what is

the driving force for reabsorption and secretion (#2 and #3 on previous slide)?

Passive transport (osmosis)

and

Active transport (pumps requiring energy such as ATP)

as shown in the next slide


Loop of Henle

Osmolalityof interstitialfluid(mOsm)

Inner

medulla

Outer

medulla

CortexActive transport

Passive transport

Water impermeable

(a) Countercurrent multiplier.

The long loops of Henle of the juxtamedullary nephrons create the medullary osmotic gradient.

The ascending limb:

• Impermeable to H2O• Permeable to NaClFiltrate becomes increasingly dilute as NaCl leaves, eventually becoming hypo-osmotic to blood at 100 mOsm in the cortex. NaCl leaving the ascending limb increases the osmolality of the medullary interstitial fluid.

Filtrate entering the loop of Henle is isosmotic to both blood plasma and cortical interstitial fluid.

The descending limb:

• Permeable to H2O• Impermeable to NaClAs filtrate flows, it becomes increasingly concentrated as H2Oleaves the tubule by osmosis. The filtrate osmolality increases from 300 to 1200 mOsm.

H2O

H2O

H2O

H2O

H2O

H2O

H2O

NaCI

NaCI

NaCI

NaCI

NaCI


What regulates the rate of glomerular fitration (urine production) ?


Regulation of Glomerular Filtration

• GFR is tightly controlled by two types of mechanisms

• Intrinsic controls (renal autoregulation)

• Act locally within the kidney

• Extrinsic controls

• Nervous and endocrine mechanisms that

maintain blood pressure, but affect kidney

function


Intrinsic control for the rate of glomerular fitration (urine production)


Intrinsic Control

• ↑ BP → constriction of afferent arterioles to drive BP back

down and protect glomeruli from damage due to high BP

• ↓ BP → dilation of afferent arterioles to drive BP back up


Extrinsic control for the rate of glomerular fitration (urine production)


Extrinsic Controls: Sympathetic Nervous System

Under normal conditions at rest

• Renal blood vessels are dilated

• Renal autoregulation mechanisms prevail

Under extreme stress

• Norepinephrine is released by the sympathetic nervous system

• Epinephrine is released by the adrenal medulla

• Both cause constriction of afferent arterioles, inhibiting filtration and triggering the release of renin


So what happens when renin is released?


So what happens when renin is released?

What happens is several steps which are called the “renin-angiotensin mechanism?


Renin-Angiotensin Mechanism

• Triggered when renin is released (by the granular cells of the JGA)

angiotensinogen (a plasma globulin)

renin →

angiotensin I

angiotensin converting enzyme (ACE) →

angiotensin II


So now what? What is the job of angiotensin II ?


Effects of Angiotensin II

1. Stimulates the reabsorption of Na+

2. Triggers adrenal cortex to release aldosterone

3. Stimulates the hypothalamus to release ADH and activates the thirst center

4. increases fluid reabsorption

5. decreasing the surface area available for filtration, i.e., decreases filtration


Stretch of smoothmuscle in walls of afferent arterioles

Blood pressure inafferent arterioles; GFR

Vasodilation ofafferent arterioles

GFR

Myogenic mechanismof autoregulation

Release of vasoactivechemical inhibited

Intrinsic mechanisms directly regulate GFR despite

moderate changes in blood pressure (between 80 and 180 mm Hg mean arterial pressure).

Extrinsic mechanisms indirectly regulate GFR

by maintaining systemic blood pressure, whichdrives filtration in the kidneys.

Tubuloglomerularmechanism ofautoregulation

Hormonal (renin-angiotensin)mechanism Neural controls

SYSTEMIC BLOOD PRESSURE

GFR

Macula densa cellsof JG apparatus

of kidney

Filtrate flow andNaCl in ascending

limb of Henle’s loop

Targets

Granular cells ofjuxtaglomerular

apparatus of kidney

Angiotensinogen Angiotensin II

Adrenal cortex Systemic arterioles

(+) Renin

Release

Catalyzes cascaderesulting in conversion

(+)

(+)

(+)

Kidney tubules

Aldosterone

Releases

Targets

Vasoconstriction;peripheral resistance

Blood volume

Na+ reabsorption;water follows

Systemic

blood pressure

(+)

(+)

(–)

Increase

Decrease

Stimulates

Inhibits

Baroreceptors inblood vessels of

systemic circulation

Sympatheticnervous system

(+)

(–)

Vasodilation ofafferent arterioles

dr. k urinary system

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