Urinary System Flashcards
Excretion
removal of organic waste products from
body fluids
Regulation
maintenance of homeostasis in volume and solute concentration of plasma
Elimination
discharge of waste products into environment
The Kidneys
• Paired, retroperitoneal organs (behind abdominal wall)
• Surrounded by:
- Fibrous capsule
- Fat capsule
- Renal fascia
The Nephron
• Functional unit of the kidney
• ~1.25 million per kidney
Juxtamedullary nephron
• Consists of a renal corpuscle and a renal tubule
• Surrounded by capillary network
Renal corpuscle
•Site where filtration of
plasma occurs
•Blood pressure pushes fluid
out of capillaries into
capsular space
- Continuous with renal tubule
Glomerulus
- Capillary network
- Blood arrives via afferent arteriole (in)
- Blood leaves via efferent arteriole (out)
Glomerular capsule has 2
layers
- Outer capsular epithelium
- Inner visceral epithelium
- Capsular space between
- Podocytes: large cells in visceral epithelium
• Wrap around capillaries
. “Feet” called pedicels
Renal tubule
•Proximal convoluted tubule (PCT)
- Simple cuboidal epithelium w/microvilli
• Nephron loop
- Thin segment: simple squamous; thick:
simple cuboidal
• Distal convoluted tubule (DCT)
- Simple cuboidal epithelium
•Empties into collecting duct
Nephron structure
• 85% are cortical nephrons
- Almost entirely within cortex
- Nephron loops surrounded by peritubular capillaries
• 15% are juxtamedullary nephrons
- Nephron loops extend into medulla
- Surrounded by vasa recta
Filtration
- BP forces H2O and small solutes from plasma into
nephron
Reabsorption
- Removal of water & solutes from filtrate into blood
Secretion
Addition of solutes to filtrate from blood
Nitrogenous wastes
• Urea: breakdown of amino acids
• Creatinine: breakdown of creatine phosphate
• Uric acid: breakdown of RNA nitrogenous bases
• Others: ammonia, urobilin, bilirubin…
Glomerular Filtration
• Filtration membrane
- Capillary membrane
• fenestrated (has holes)
• Prevents movement of blood cells
- Dense layer
• Only allows small proteins, nutrients and ions through
- Filtration slits
• Prevent passage of most proteins
Filtration Pressures
• Glomerular Hydrostatic Pressure (GHP)
- Blood pressure in capillaries
- 50 mmHg
• Capsular Hydrostatic Pressure (CsHP)
- Resistance in nephron
- 15 mmHg
• Net Hydrostatic Pressure (NHP)
- Difference between GHP and CsHP
- 50 mm Hg - 15 mm Hg = 35 mm Hg
Colloid osmotic pressure (COP)
-Osmotic pressure resulting from suspended proteins
- Tends to draw water back into plasma
- 25 mm Hg
Filtration pressure
- Difference between NHP and COP
- 35 mm Hg - 25 mm Hg = 10 mm Hg
If blood pressure goes up then filtration pressure increase which
Results in more filtrate produce
Glomerular Filtration Rate (GFR)
• Amount of filtrate produced by the kidneys each minute
• Averages 125 mL/min
• Glomeruli generate 180 L filtrate per day
- 99% reabsorbed in renal tubules
Autoregulation
• Decline in glomerular blood pressure triggers:
- Dilation of afferent arteriole and glomerular capillaries
- Constriction of efferent arteriole (increases pressure)
Hormonal Regulation
• Renin-angiotensin system
• Renin produced in nephrons at the juxtaglomerular complex (JGC)
Juxtaglomerular complex (JGG)
- Epithelial cells of DCT near renal corpuscle (macula densa)
- Smooth muscle fibers in afferent arteriole
Renin released due to:
- Decline in BP at glomerulus
- Decline in osmotic concentration (ie. solute concentration) of tubular fluid at macula densa
•no enough solutes, not enough filtration so increases solutes for more filtration