Ch 23: Urinary SystemCh 23: Urinary System

Objectives

Identify and describe the components of the urinary system and their function

Describe the (histological) organization of the nephron

Identify the blood vessels that supply blood to the nephrons

Describe the blood flow through and around the nephron

Trace a drop of filtrate as it becomes urine

Functions of Urinary System Functions of Urinary System (Kidneys):(Kidneys):

● Regulate fluid balance (fluid volume) of the body

● Excrete organic waste products and conserve nutrients, etc

Stabilize pH

Regulate electrolyte concentrations in the blood

Endocrine functions

Kidney LocationKidney Location

•Lateral to vertebral column high Lateral to vertebral column high on body wall, under floating ribs, on body wall, under floating ribs, in in retro-peritonealretro-peritoneal position position (posterior to the parietal (posterior to the parietal peritoneum)peritoneum)•The right kidney is slightly inferior The right kidney is slightly inferior to the left kidney in order to to the left kidney in order to accommodate the liveraccommodate the liver•Surrounded by the renal capsule Surrounded by the renal capsule with a fat padwith a fat pad•12 x 6 x 3 cm12 x 6 x 3 cm

•Bean shapedBean shaped•Hilus Hilus – indentation– indentation

Internal AnatomyInternal Anatomy

Cortex:Cortex: outer layer, light reddish brown, outer layer, light reddish brown, granular appearance (due to many granular appearance (due to many corpuscles)corpuscles)

Medulla:Medulla: darker striped appearance (due darker striped appearance (due to tubules) Subdivided into to tubules) Subdivided into distinct distinct renal pyramids, renal pyramids, terminating with a terminating with a papilla. Separated by papilla. Separated by renal columnsrenal columns from the cortexfrom the cortex..

Pelvis:Pelvis: Expanded proximal ureterExpanded proximal ureter

Compare to Fig 23.3

Renal CirculationRenal Circulation20-25% of cardiac output!!20-25% of cardiac output!!

R L

Nephron = functional unitNephron = functional unit

Nephron =Nephron =

» Renal CorpuscleRenal Corpuscle

– GlomerulusGlomerulus

– Bowman’s (Renal) CapsuleBowman’s (Renal) Capsule

» PCT (proximal convoluted PCT (proximal convoluted tubule)tubule)

» LOH (loop of Henle)LOH (loop of Henle)» DCT (distal convoluted tubule)DCT (distal convoluted tubule)

(>106/kidney)

Fig 23.6

Renal Corpuscle

Uriniferous Tubule p 691

Nephron + Collecting Duct (tubule)» Renal Corpuscle» PCT» LOH» DCT» CD

This diagram has an important inaccuracy!

See Fig 23.4

Two Types of Nephrons

Cortical nephrons Cortical nephrons (85%) (85%) shorter, mostly in cortex of shorter, mostly in cortex of kidney, produce kidney, produce "standard" urine"standard" urine

Juxtamedullary nephrons Juxtamedullary nephrons (15%), "juxta = next to" the (15%), "juxta = next to" the medulla - responsive to medulla - responsive to ADH, can produce ADH, can produce concentrated urineconcentrated urine due to due to longer Loops of Henlelonger Loops of Henle

Fig 23.9

The Renal CorpuscleThe Renal Corpuscle

1. Capillary endothelium1. Capillary endotheliumFenestratedFenestrated

What gets through?What gets through?

2. Basement membrane2. Basement membrane

3. Glomerular epithelium3. Glomerular epithelium (= visceral (= visceral layer of Bowman’s capsule)layer of Bowman’s capsule)slit pores between pedicles of slit pores between pedicles of podocytespodocytes

Note: Note: Capsular Epithelium Capsular Epithelium is simple is simple squamous epitheliumsquamous epithelium

Filtration: Passage across three Filtration: Passage across three barriersbarriers

Juxtaglomerular (JG) ApparatusJuxtaglomerular (JG) Apparatus

Juxtaglomerular Apparatus = Macula densa + Juxtaglomerular cells (smooth muscle fibers from afferent arteriole)

Macula densa monitors BP

JG cells produce renin and EPO

Blood Pressure

Urine collection:

Collecting ducts within Collecting ducts within each renal papilla each renal papilla release urine into release urine into minor minor calyx calyx → major calyx → → major calyx → renal pelvis → ureterrenal pelvis → ureter

Ureters

From kidney to bladder Enter the bladder at an

angle» Trigone

Retroperitoneal Transitional Epithelium Nephroliths

This is another inaccuracy!!

Nephrolithiasis

Occurs when urine becomes too concentrated and substances crystallize. Symptoms arise when stones begin to move down ureter causing intense pain. Kidney stones may form in the pelvis or

calyces of the kidney or in the ureter.

Urinary Bladder

Retroperitoneal, behind pubisRetroperitoneal, behind pubis Internal folds - rugae - permit Internal folds - rugae - permit

expansion (max. holding capacity expansion (max. holding capacity ~ 1L)~ 1L)

Trigone - area at base delineated Trigone - area at base delineated by openings of ureters and urethra by openings of ureters and urethra - without muscle - without muscle

Internal urethral sphincter - Internal urethral sphincter - involuntary sphincterinvoluntary sphincter

Urinary Bladder

Urinary Bladder Histology

1. transitional epithelium from renal pelvis to neck of urethra.

2. detrusor muscle – smooth muscle2. detrusor muscle – smooth muscle

empty bladderempty bladder

full bladderfull bladder

Urethra, Female

External urethral sphincterExternal urethral sphincter– – voluntary at pelvic floorvoluntary at pelvic floor

3-5 cm – from base of 3-5 cm – from base of bladder to vestibulebladder to vestibule

UTIs (esp. UTIs (esp. E.coliE.coli))

Urethra, Male

Male – 18-20 cmMale – 18-20 cm1. 1. prostatic urethraprostatic urethra – from – from

base of bladder through base of bladder through prostate glandprostate gland

2. 2. membranous urethramembranous urethra – – between prostate gland & between prostate gland & base of penisbase of penis

3. 3. penile (spongy) urethrapenile (spongy) urethra – – traverses penis to orificetraverses penis to orifice

Male vs. Female

Fig 23.17

A drop of filtrate

• Glomerular capillaries to

• Podocytes• Bowman’s Space• PCT• LOH• DCT

•Collecting Duct•Minor calyx•Major calyx•Renal Pelvis•Ureter•Urethra

•Prostatic, membranous and penile in male

Kidneys may sustain 90% loss of nephrons and still not show apparent symptoms!!!

2-4 % of population only have 1 kidney!

Manneken PisFountain

Brussels, 1619