Chapter 25Chapter 25

The Urinary SystemThe Urinary System

Consists of two kidneys, two ureters, one urinary Consists of two kidneys, two ureters, one urinary bladder and a urethra.bladder and a urethra.Functions:Functions:1. Regulates plasma concentrations of Na+, K+ , Cl-, 1. Regulates plasma concentrations of Na+, K+ , Cl-, Ca++ & Mg++, as well as glucose, AA & creatinine. Ca++ & Mg++, as well as glucose, AA & creatinine.2. Endocrine function: regulates blood volume and 2. Endocrine function: regulates blood volume and blood pressure; produces erythropoietin and blood pressure; produces erythropoietin and releases renin. Renin is produced by the Juxta- releases renin. Renin is produced by the Juxta- glomerular cells (JG) near afferent/efferent arterioles glomerular cells (JG) near afferent/efferent arterioles and regulates synthesis of Angiotensin-II. and regulates synthesis of Angiotensin-II. 3. Stabilizes blood pH in concert with respiratory 3. Stabilizes blood pH in concert with respiratory system and breathing (CO2).system and breathing (CO2).4. Eliminates organic waste products (e.g. ammonia 4. Eliminates organic waste products (e.g. ammonia as urea and uric acid, toxic substances and drugs).as urea and uric acid, toxic substances and drugs).5. Synthesizes calcitrol from5. Synthesizes calcitrol from Vitamin D and helps Vitamin D and helps regulate Ca++ levels.regulate Ca++ levels.

The Urinary SystemThe Urinary System

The KidneysThe KidneysLocation:Location: retroperitoneal in superior lateral abdominal cavity retroperitoneal in superior lateral abdominal cavity

one on each side of body behind liver and stomach.one on each side of body behind liver and stomach.

StructureStructure: : TwoTwo bean shaped organs ~ 12cm x 6cm x 3cm: bean shaped organs ~ 12cm x 6cm x 3cm: GW ~ 150 gms.GW ~ 150 gms.

Surrounding Tissue Layers:Surrounding Tissue Layers:– renal capsule – strong fibrous outer covering of renal capsule – strong fibrous outer covering of

kidney provides a barrier to infection from kidney provides a barrier to infection from surrounding organs.surrounding organs.

– adipose capsule – middle layer of fat protects kidney adipose capsule – middle layer of fat protects kidney from concussive blows and attaches kidney to from concussive blows and attaches kidney to posterior wall of abdomen.posterior wall of abdomen.

renal fascia – outermost layer of fibrous CT; surrounds renal fascia – outermost layer of fibrous CT; surrounds kidney and adrenal glands; anchors them to kidney and adrenal glands; anchors them to surrounding structures.surrounding structures.

Retroperitonel positionRetroperitonel position

The kidneysThe kidneys

Kidneys makeup ~ 0.4% Body Weight but receive Kidneys makeup ~ 0.4% Body Weight but receive ~21% of Cardiac Output (5 l/min).~21% of Cardiac Output (5 l/min).

Gross internal appearance of kidneys:Gross internal appearance of kidneys: CortexCortex (light pinkish in natural state) granular (light pinkish in natural state) granular outer layer.outer layer.

MedullaMedulla (darker reddish brown) inner layer with (darker reddish brown) inner layer with cone shaped tissue masses (renal pyramids).cone shaped tissue masses (renal pyramids).

PelvisPelvis (inner core), conical shaped funnels that (inner core), conical shaped funnels that lead to the hilus and ureter.lead to the hilus and ureter. Often filled with adipose. Often filled with adipose.

Blood flow to kidneyBlood flow to kidney

Approximately 125 ml of blood is cleared by Approximately 125 ml of blood is cleared by kidneys each minute =~ 140-180 l/day.kidneys each minute =~ 140-180 l/day.

Vascular supply is via renal artery from aorta Vascular supply is via renal artery from aorta and return is via renal vein to inferior vena and return is via renal vein to inferior vena cava.cava.Path is from aorta Path is from aorta → renal artery → segmental → renal artery → segmental arteries → interlobar arteries → arcuate arteries → arteries → interlobar arteries → arcuate arteries → inter-lobular arteries → afferent arteriole → glomerulus inter-lobular arteries → afferent arteriole → glomerulus → efferent arterioles → peritubular capillaries or vasa → efferent arterioles → peritubular capillaries or vasa recta → interlobular veins → arcuate veins → recta → interlobular veins → arcuate veins → interlobar veins → renal veins → inferior vena cava.interlobar veins → renal veins → inferior vena cava.

Blood flowBlood flow

to kidneyto kidney

Renal innervationRenal innervation

The nerve supply to the kidneys is almost The nerve supply to the kidneys is almost entirely sympathetically mediated.entirely sympathetically mediated.Nerves from the superior mesenteric ganglion Nerves from the superior mesenteric ganglion enter at the renal hilus and regulate blood flow enter at the renal hilus and regulate blood flow to the kidneys.to the kidneys.If arterial blood flow drops the sympathetic If arterial blood flow drops the sympathetic nerves stimulate the release of renin which lead nerves stimulate the release of renin which lead to synthesis of Angiotensin II (Ag-II), a very to synthesis of Angiotensin II (Ag-II), a very potent vasoconstrictor that will increase the potent vasoconstrictor that will increase the blood pressure and consequently increase the blood pressure and consequently increase the blood flow.blood flow.

The NephronThe Nephron

Consists of: Renal corpulse + renal tubuleConsists of: Renal corpulse + renal tubule

Afferent and Afferent and efferentefferent arterioles arterioles → glomerular → glomerular capillaries which filter the blood plasma.capillaries which filter the blood plasma.

Renal corpuscleRenal corpuscle = Glomerulus + Bowman’s = Glomerulus + Bowman’s capsule (glomerular capsule) - filters blood capsule (glomerular capsule) - filters blood

Renal tubuleRenal tubule = Proximal and distal convoluted = Proximal and distal convoluted tubules plus loop of Henle.tubules plus loop of Henle.

- Descending and ascending limbs of loop of - Descending and ascending limbs of loop of HenleHenle exhibit thick and thin segments. exhibit thick and thin segments.

The NephronThe Nephron

Renal corpuscleRenal corpuscle + + Renal tubuleRenal tubule

How urine is formedHow urine is formed1.1. Glomerular formationGlomerular formation: blood plasma is filtered into : blood plasma is filtered into

glomerular space = glomerular filtrate. Lacks cells glomerular space = glomerular filtrate. Lacks cells and proteins. Contains water + solutes and proteins. Contains water + solutes ((glucose, AA, glucose, AA, FA, vitamins, nitrogenous watses, and electrolytesFA, vitamins, nitrogenous watses, and electrolytes).).

2.2. Tubular reabsorption Tubular reabsorption of useful solutes of useful solutes (e.g. glucose, AA, (e.g. glucose, AA,

electrolytes, etc.)electrolytes, etc.) from filtrate from filtrate → → back into the blood.back into the blood.

3.3. Tubular SecretionTubular Secretion of waste products of waste products (e.g. H+, drugs, (e.g. H+, drugs,

toxic agents)toxic agents) from blood into filtrate for elimination from from blood into filtrate for elimination from the body as urine.the body as urine.

Water conservationWater conservation: water is reabsorbed all along the : water is reabsorbed all along the nephron especially in collecting duct. (nephron especially in collecting duct. (Helps maintain Helps maintain vascular volume and pressure).vascular volume and pressure).

Steps in urine formationSteps in urine formation

Kidney (Renal) nephronsKidney (Renal) nephronsThe Nephron is structural and functional unit of kidneyThe Nephron is structural and functional unit of kidneyCortical nephronsCortical nephrons – ~ 2.1 million/ kidney; – ~ 2.1 million/ kidney; The glomerulus is higher in the cortex with short loop The glomerulus is higher in the cortex with short loop of Henle dipping into the medulla.of Henle dipping into the medulla.– Account for 85% of kidney nephronsAccount for 85% of kidney nephrons– Dilute the urine but do not concentrate itDilute the urine but do not concentrate it

Juxtamedullary nephronsJuxtamedullary nephrons – ~ 0.4 million/ kidney. – ~ 0.4 million/ kidney. The glomerulus is near cortical/medullary border in The glomerulus is near cortical/medullary border in cortex and loop of Henle is very long descending deep cortex and loop of Henle is very long descending deep into the medulla.into the medulla.– Account for 15% of kidney nephronsAccount for 15% of kidney nephrons– Functions in concentrating of urineFunctions in concentrating of urine

Renal nephronsRenal nephrons

Cortical nephronCortical nephron

JuxtamedullaryJuxtamedullary

Medullary borderMedullary border

Cortical and juxta-Cortical and juxta-medullary nephronsmedullary nephrons

Renal corpuscles for bothRenal corpuscles for bothnephrons are all in thenephrons are all in thecortex.cortex.

Loop of Henle dips intoLoop of Henle dips intothe medulla for boththe medulla for bothnephrons.nephrons.

Cortical nephrons loopsCortical nephrons loopsare shorter and dip slightlyare shorter and dip slightlyinto the medulla.into the medulla.

Juxtamedullary nephronJuxtamedullary nephronloops dip deeper into theloops dip deeper into themedulla.medulla.

SEM of GlomeruliSEM of Glomeruli

TEM of a glomerular capillary shows podocyte TEM of a glomerular capillary shows podocyte with pedicels and filtration slits and pores. with pedicels and filtration slits and pores.

Nephron histologyNephron histologyBowman’s capsule-Bowman’s capsule- inner (visceral) layer of podocytes wrapped inner (visceral) layer of podocytes wrapped

around capillaries and outer (parietal) layer of simple squamous around capillaries and outer (parietal) layer of simple squamous epitheliumepithelium

Proximal convoluted tubules (PCT)-Proximal convoluted tubules (PCT)- consists of simple cuboidal consists of simple cuboidal epithelium with microvilli (brushed border).epithelium with microvilli (brushed border).

Distal convoulted tubule (DCT)-Distal convoulted tubule (DCT)- consists of simple cuboidal consists of simple cuboidal epithelium and no microvilli; (Affected by aldosterone and PTH).epithelium and no microvilli; (Affected by aldosterone and PTH).

Loop of Henle –Loop of Henle – “U” shaped with the thick segment of cuboidal “U” shaped with the thick segment of cuboidal epithelium and thin segment of simple squamous epithelium.epithelium and thin segment of simple squamous epithelium.

Collecting ducts are not part of nephron but empty into papillary Collecting ducts are not part of nephron but empty into papillary duct and then minor calyx. They are lined with simple cuboidal duct and then minor calyx. They are lined with simple cuboidal epithelium and 2 types of cells (intercalated and principal cells). epithelium and 2 types of cells (intercalated and principal cells). Effected by 2 hormones ANP & ADHEffected by 2 hormones ANP & ADH

Glomerular capsule with parietal and visceral Glomerular capsule with parietal and visceral layers; afferent and efferent arterioles, JGA etc.layers; afferent and efferent arterioles, JGA etc.

Cortical nephronCortical nephron-short loop of Henle-short loop of Henle

with peritubular with peritubular

capillariescapillaries Functions to formFunctions to form

urineurine..

JuxtamedullaryJuxtamedullary

nephronnephron -Glomerulus is-Glomerulus is

In cortical layer.In cortical layer.

Vasa recta goesVasa recta goes

deep into med-deep into med-

ulla.ulla.

--Function is toFunction is to

concentrate urineconcentrate urine

and conserve water.and conserve water.

Juxtaglomerular apparatusJuxtaglomerular apparatusOccurs at vascular pole of renal capsule.Occurs at vascular pole of renal capsule.

Consists of three cell types:Consists of three cell types:1.1. Macula densaMacula densa group of sensory epithelial cells in the group of sensory epithelial cells in the

distal convoluted tubule, next to afferent arteriole MD distal convoluted tubule, next to afferent arteriole MD monitors flow and urine composition. monitors flow and urine composition. Communicates Communicates with the JG cells.with the JG cells.

2.2. Juxtaglomerular (JG) cellsJuxtaglomerular (JG) cells = enlarged sm.m. cells on = enlarged sm.m. cells on afferent and efferent arterioles. When stimulated afferent and efferent arterioles. When stimulated they constrict to reduce flow through the glomerulus. they constrict to reduce flow through the glomerulus. JG cells also secrete renin into blood JG cells also secrete renin into blood →→ AG-II. AG-II.

3.3. Mesangial cellsMesangial cells located between afferent and located between afferent and efferent arterioles and may modulate communication efferent arterioles and may modulate communication between the two arterioles.between the two arterioles.

See next slide for clarification.See next slide for clarification.

Glomerulus with Juxtaglomerular apparatus Glomerulus with Juxtaglomerular apparatus (Saladin 25.9)(Saladin 25.9)

DCT

DCT

Macula densa

JG cells

Symp. Nerve

Afferent arteriole

Histologic slide of a Glomerular capsule with Histologic slide of a Glomerular capsule with parietal and visceral layers; afferent and parietal and visceral layers; afferent and efferent arterioles, Macula densa, JG cells, etc.efferent arterioles, Macula densa, JG cells, etc.

Nephron fctns.Nephron fctns.

1. Filtration1. Filtration

2. Reabsorption2. Reabsorption

3. Secretion3. Secretion

Summary of urine flowSummary of urine flow

Afferent arteriole enters Glomerulus Afferent arteriole enters Glomerulus → → glomerular filtrate → Proximal convoluted glomerular filtrate → Proximal convoluted tubule → Descending loop of Henle → tubule → Descending loop of Henle → Ascending loop of Henle → Distal Ascending loop of Henle → Distal convoluted tubule → Collecting duct → → convoluted tubule → Collecting duct → → → Papillary duct → → Papillary duct → Minor calyxMinor calyx → → Major Major calyxcalyx → Renal pelvis → Ureter → Urinary → Renal pelvis → Ureter → Urinary bladder → → Urethra → Outside.bladder → → Urethra → Outside.

Summary of urine flowSummary of urine flow

UretersUretersMuscular tube lined with transitional epithelium. Wall consists ofMuscular tube lined with transitional epithelium. Wall consists of

two layers of smooth muscle (inner longitudinal and outer circulartwo layers of smooth muscle (inner longitudinal and outer circular

layer). Urine moves by peristalsis “milking action” from renallayer). Urine moves by peristalsis “milking action” from renal

pelvis to bladder.pelvis to bladder.

Enter bladder fromEnter bladder from posteriorposterior

and below. Small flap of and below. Small flap of

mucosa acts as a valve.mucosa acts as a valve.

~ 25 cm long; 1.7 cm diam.~ 25 cm long; 1.7 cm diam.

Urinary BladderUrinary BladderMuscular storage bag lined with transitional epithelium, withMuscular storage bag lined with transitional epithelium, with

lamina propria underneath and detrusor muscle in wall. Detrusorlamina propria underneath and detrusor muscle in wall. Detrusor

muscle is 3 separate layers of smooth muscle. muscle is 3 separate layers of smooth muscle.

Rugae present when emptyRugae present when empty

Vol.Vol. can hold up to 800 ml.can hold up to 800 ml.

when fullwhen full..Two ureters and urethra formTwo ureters and urethra form

““trigone” at base of bladder.trigone” at base of bladder.

UrethraUrethraHistology: First part of tractHistology: First part of tract

is transitional, is transitional, →→ pseudo- pseudo-

stratified columnar stratified columnar →→

stratified squamous epithel.stratified squamous epithel.

at external orifice.at external orifice.

Males 3 areas:Males 3 areas:

1. Prostatic urethra1. Prostatic urethra

2. Membranous urethra2. Membranous urethra

3. Spongy urethra in penis. 3. Spongy urethra in penis.

♂ ♂ uurethra serves for urine rethra serves for urine excretion and sperm excretion and sperm ejaculation. ejaculation.

♀ ♀ urethra for urethra for urine excretion urine excretion

onlyonly..

Bladder and urethra of femaleBladder and urethra of female

UrethraUrethra

Urine release is controlled by an internal and Urine release is controlled by an internal and external urethral sphincter.external urethral sphincter.Internal sphincter is a thickened extension of Internal sphincter is a thickened extension of the detrusor muscle and is involuntarily the detrusor muscle and is involuntarily controlled.controlled.External sphincter is composed of skeletal External sphincter is composed of skeletal muscle and is under voluntary control. It is muscle and is under voluntary control. It is located where the urethra penetrates the pelvic located where the urethra penetrates the pelvic floor.floor.