filtration barrier

Filtration Barrier

• Lamina rara externa

• Lamina densa• Lamina rara

interna

Glomerular Filtration

• Filtering of blood in the renal corpuscle

• Glomerular filtrate – fluid that seeps from the glomerular capillaries into the Bowman’s space

Renal Tubule

• Proximal convoluted tubule• Loop of Henle– Thick descending limb– Thin descending and ascending limbs– Thick ascending limb

• Distal convoluted tubule• Collecting tubules and ducts

Renal Tubule

Proximal Convoluted Tubule

Loop of Henle Distal Convoluted Tubule

Epithelium Simple cuboidal Thick descending limb: simple cuboidalThin limb: simple squamousThick ascending: simple cuboidal

Simple cuboidal

Function Reabsorb 70-80% of H2O and sodiumReabsorb glucose, AA, chloride

H2O reabsorption except: Thick ascending: impermeable to water, NaCl reabsorption

Secretes potassium and hydrogenSmall H2O and Na reabsorption

Types of Nephrons

• Short-looped (cortical) - majority– Renal corpuscles located in outer portions of

cortex– Short Henle’s loop (no thin ascending limb)

• Long-looped (juxtamedullary)– Renal corpuscles are near the corticomedullary

junction– Long Henle’s loop (go deep into medulla, have

thin ascending limb)

Juxtaglomerular Apparatus

• Microscopic structure in the kidney which regulates the function of each nephron

• Found between the vascular pole of the renal corpuscle and the returning DCT of the same nephron

• Function: regulates filtrate formation and systemic BP

Juxtaglomerular Apparatus

• 3 cells:– Juxtaglomerular cells– Mesangial cells– Macula densa cells - area of closely packed

specialized columnar cells lining the wall of the distal tubule• Sense changes in solute concentration and flow rate of

filtrate

BLADDER AND URINARY PASSAGES

• Renal calyces• Renal pelvis• Ureter• Urinary bladder

• Same histologic structure• Walls of ureter becoming gradually thicker as

proximity to the bladder increases

BLADDER AND URINARY PASSAGES

• Function:– Store the urine

formed in the kidneys and conduct it to the exterior

BLADDER AND URINARY PASSAGES

• Mucosa:– Transitional epithelium– Lamina propria: loose to dense CT

• Muscular layer – OCIL • Adventitia or serosa– Only upper part of bladder covered by peritoneum

URETHRA

• Terminal portion of the urinary system• Function:– Passageway for urine– Males: passageway for urine and sperms

Male Urethra

• 20 cm in length• 3 segments:– Prostatic urethra– Membranous urethra– Spongy urethra (penile, cavernous)

• Terminates in the external urethral orifice (meatus)

Male Urethra

Prostatic Membranous Penile

Length and location

3-4 cmTraverses the prostate gland

1 cm Traverses the sphincter urethrae muscle

15 cm Traverses the penis

Lining epithelium

Transitional Pseudostratified columnar

Pseudostratified columnarEUM: Stratified squamous non-keratinized

Glands Urethral glands of Littre (lamina propria)

Bulbourethral glands of Cowper (embedded in the sphincter urethrae muscle)

Bulbourethral glands of Cowper

Female Urethra

• Shorter (4 cm)• Closely attached to

anterior wall of vagina

• Opens directly in front of the vaginal opening on the vestibule of the external genitalia

Female Urethra

Female Urethra

• Mucosa– Transitional → stratified squamous non-

keratinized– Lamina propria: loose CT, mucus-secreting

urethral glands

• Muscular layer: circularly arranged smooth muscle cells

Female Urethra

• Distal segment is surrounded by circularly-arranged striated (voluntary) muscle fibers (sphincter urethrae muscle – external sphincter)