chapter 16 - urinary/renal system

kidneys

• retroperitoneal — located behind the peritoneum between the dorsal body and parietal peritoneum

• each contains: artery, vein, ureter

• due to the position of the liver, the right is slightly lower

hilus

medial indentation of the kidney

real capsule

connective (adipose) tissue that functions to protect and support the kidney

internal gross anatomy of the kidneys

1. renal cortex — perimeter; lots of surface area

2. renal medulla — contains renal pyramids

   • each pyramid is separated by “renal columns” — downward extensions of cortical tissue

   • renal columns contain blood vessels

   • 6 columns/kidney

   • apex (renal papilla) = narrow end of the pyramid

   • collecting ducts exit at the renal papilla, material (newly formed urine) drains into 4-5 minor calyces

     • minor calyces drain into 2-3 major calyces

     • then into renal pelvis

     • then into ureter

apex (renal papilla)

the narrow end of a renal pyramid; which collecting ducts exit at

nephron

the functional unit of the kidney

• composed of a renal corpuscle and renal tubule

renal corpuscle

• located within the renal cortex

• site of blood filtration — first step in urine formation

• composed of: glomerulus, Bowman’s capsul

glomerulus

a (knot of) capillary bed within the Bowman’s capsule

Bowman’s capsule

encases glomerulus and drains filtrate received into the proximal convoluted tubule

1. outer layer → simple squamous epithelium

2. inner layer → consists of podocytes wrapped around glomerular capillaries

filtration membrane

a membrane in which blood is filtered from glomerulus into Bowman’s capsule; consisting of…

1. glomerular endothelium — porous epithelial layer, composed of simple squamous cells

2. basement membrane — attach glomerular endothelium to podocytes of Bowman’s capsule

3. podocytes of Bowman’s capsule

   • composed of simple epithelium — allowing filtrate to easily cross thru into the proximal convoluted tubule

   • made of podocytes with foot processes containing filtration sites

renal tubules in which filtrate that passes through Bowman’s capsule moves into

1. proximal convoluted tubule (PCT) — located within the cortex

2. loop of henle — begins as descending loop, transitions into ascending loop located in medulla

3. distal convoluted tubule (DCT) — located within the cortex

cortical nephrons

• 85% of all nephrons

• renal corpuscle → near surface of the kidney in the cortex

• loop of henle → shorter, located in outer medulla

• composed of peritubular capillaries

juxtamedullary nephrons

• 15% of all nephrons

• renal corpuscle → in cortex, very close to medulla

• loops of henle → very long, penetrate deep into medulla

• contain peritubular capillaries and vasa recta

• allow for the concentration and dilution of urine

juxtamedullary apparatus

located at the point of contact between distal convoluted tubule and afferent arteriole

• functions to regulate blood pressure, ion concentration of blood, and formation of filtrate by nephron

• consists of:

  1. tubular portion — macula densa

     • composed of modified cells of distal convoluted tubule — cells are taller and narrower

  2. arteriolar portion

     • composed of both afferent and efferent arteriole

     • juxtaglomerular cells = modified smooth muscle cells which contain granules; produce hormonal enzyme called renin

ureters

function to transport newly formed urine from the kidneys to urinary bladder

• retroperitoneal

• consist of 3 layers:

  1. mucosa — made of transitional epithelium; permits stretching; in contact with urine

  2. muscularis externa — layer of smooth muscle

  3. serosa/adventitia

urinary bladder

• mainly retroperitoneal

• composed of 3 layers:

  1. mucosa — transitional epithelium with rugae

  2. muscularis externa — smooth muscle, called “detrusor muscle”

  3. adventitia — posterior and inferior surfaces; serosa on superior surface

• internal structure:

  • trigone = triangle formed by openings of the 2 ureters and uretra

    • smooth (lacks rugae)

  • openings remain fixed in position — do not move if the bladder is full or empty

urethra

connects the urinary bladder to the outside of the body

• male → long; transports urine and semen

• female → short; transports only urine

  • easy for bacteria to enter and travel thru → more prone to infection

• internal and external sphincters surround its proximal opening

• wall is smooth muscle

  • lined with mucosa — touching the lumen (open to the outside)

  • transitional proximal to the bladder

  • becomes stratified squamous near the end

internal urethral sphincter

urethral sphincter that is formed from the the thickening of detrusor muscle at the base of the bladder

• composed of smooth muscle — not much control; opens the second the bladder signals it’s full

external urethral sphincter

urethral sphincter that surrounds the urethra as it passes through the urogenital diaphragm

• composed of skeletal muscle