Ch 26: Urinary SystemCh 26: Urinary SystemObjectives

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

Functions of Urinary System (Kidneys):

● Regulate fluid balance (fluid volume) of the body

● Excrete organic waste products and conserve nutrients, etc

Stabilize pH

Regulate ion concentrations in the blood

Kidney Kidney LocationLocation

Lateral to vertebral column high on body wall, under floating ribs in retro-peritoneal position

Surface Anatomy

Size of bar of soap Bean shapedHilus – indentation

Three layers Renal fascia – fibrous tunic Adipose capsule – protects kidney Renal capsule – anchors kidney to body wall,

continuous with peritoneum

Sectional Anatomy

Cortex: outer layer, light reddish brow, granular appearance (due to many capillaries)

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

Fig 26-3

Urine collection: Ducts within each renal

papilla release urine

into minor calyx

major calyx

renal pelvis

ureter

Renal CirculationRenal Circulation

Segmental arteries

Interlobar arteries

Arcuate arteries

Interlobular arteries

Afferent arterioles

Glomerulus

Efferent arterioles

Peritubular capillaries

Segmental veins

Interlobar veins

Arcuate veins

Interlobular veins

Venules

Renal Artery Renal Vein

Fig 26-4

Functional unit: Nephron

Renal corpuscle:» Glomerulus

» Bowman’s capsule

Tubular passageways with associated blood vessels:» PCT

» LOH

» DCT

» CD

(>mio/kidney)

Fig 26-8

Fig 26-6

Filtration: Passage across Three Barriers

Capillary endotheliumFenestrated

What gets through?

Basement membrane

Glomerular epithelium (= visceral layer of Bowman’s capsule)slit pores between pedicels of podocyte

Fig 26-8

Two Types of Nephrons

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

Juxtamedullary nephrons (15%), "juxta-next-to" the medulla - responsive to ADH, can concentrate urine

Juxtaglomerular Apparatus

Macula densa

+Juxtaglomerular cells

(smooth muscle fibers from afferent arteriole)

= Juxtaglomerular Apparatus

= Endocrine system structure (renin and EPO)

Urine Transport, Storage, and Urine Transport, Storage, and EliminationElimination

Trace drop of urine from kidneys to outside world

Lining of these parts?

Nephroptosis (= floating kidneys)

Nephrolithiasis

Nephrolithiasis

Occurs when urine becomes too concentrated and substances crystalize. 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.

Anatomy of Urinary Bladder

Retroperitoneal, behind pubis Internal folds - rugae - permit expansion (max. holding

capacity ~ 1L) Trigone - area at base delineated by openings of ureters

and urethra - without muscle Internal urethral sphincter - involuntary sphincter

Histology1. transitional epithelium2. detrusor muscle – smooth muscle

Fig 26.10

Urethra

External urethral sphincters – voluntary at pelvic floor

Female - short – from base of bladder to vestibule

Male1. prostatic urethra – from base of bladder through

prostate gland2. membranous urethra – between prostate gland &

base of penis3. penile (spongy) urethra – traverses penis to orifice

UTIs (esp. E.coli)

Male versus Female

The End

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