Chapter 35
Structure and Function of the Renal
and Urologic Systems
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Structures of the Kidney
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Kidneys
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Retroperitoneal
Renal capsule
Renal fascia
Hilum
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Structures of the Kidney
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Structures of the Kidney
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Renal cortex
Renal medulla
Renal pyramids
Renal columns
Minor calyx
Major calyx
Renal pelvis
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Structures of the Kidney
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Nephron
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1.2 million nephrons per kidney
Functional unit of the kidney
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Superficial cortical nephrons
Midcortical nephrons
Juxtamedullary nephrons
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Nephron
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Renal corpuscle
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Glomerulus
Bowman capsule
Mesangial cells
Bowman space
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Glomerulus
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Filtration
Formation of primary urine
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Glomerulus
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Glomerular filtration membrane
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Glomerular endothelium
Basement membrane
Capillary epithelium
• Also referred to as podocytes or visceral epithelium
• Filtration slits
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Nephron
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Juxtaglomerular apparatus
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Juxtaglomerular cells
Macula densa
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Juxtaglomerular Apparatus
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Nephron
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Renal tubules
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Proximal tubule
 Loop of Henle
 Distal tubule
 Collecting duct
 Principal cells
 Intercalated cells
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Structures of the Kidney
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Structures of the Kidney
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Blood Vessels
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Renal arteries
Interlobar arteries
Arcuate arteries
Interlobular arteries
Afferent arterioles
Glomerular capillaries
Efferent arterioles
Peritubular capillaries and vasa recta
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Structures of the Kidney
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Structures of the Kidney
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Ureters
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30 cm long
Long, intertwining muscle bundles
Pass obliquely though posterior aspect of bladder
Peristaltic activity
Micturition compresses the lower end of the ureter
to avoid urine reflux
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Structures of the Urologic System
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Bladder
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Detrusor muscle
Transitional epithelium
Trigone
Micturition reflex
Urethra
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Internal and external sphincters
3 to 4 cm in females
18 to 20 cm in males
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Bladder and Urethra
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Renal Blood Flow (RBF)
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Receive 1000 to 1200 ml of blood per minute
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600-700 ml as plasma (renal plasma flow [RPF])
Glomerular filtration rate (GFR)
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Filtration of plasma into the Bowman space
20% of the RPF (120-140 ml/min)
Directly related to the perfusion pressure in the
glomerular capillaries (RBF)
• Strict maintenance of 80-180 mmHg provides constant
GFR
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Regulation of RBF/GFR
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Autoregulation
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Myogenic mechanism (stretch)
Tubuloglomerular feedback (NaCl content)
Neural regulation
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Sympathetic nervous system
• Vasoconstriction (diminishes GFR)
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Renal Functions
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Regulation of blood volume and serum
osmolarity (water/sodium balance)
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ADH
Renin-angiotensin-aldosterone system
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Renal Functions
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Excrete metabolic wastes
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Regulate acid-base balance
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Creatinine, urea (end product of protein
metabolism), certain drugs
Balance of H+ and HCO3
Secrete hormones
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Renin-angiotensin-aldosterone system
Erythropoietin
Conversion of vitamin D to usable form
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Renal Processes
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Filtration
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Tubular reabsorption
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Movement of fluid/solutes from tubular lumen to
the peritubular capillaries
Tubular secretion
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Movement of protein free plasma across the
glomerular membrane (hydrostatic pressure)
Transfer of substances from the peritubular
capillaries to the tubular lumen
Excretion
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Elimination of fluids/substances in the final urine
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Nephron Function
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Glomerular filtration
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Net filtration pressure
• Glomerular hydrostatic pressure
• Capsular hydrostatic pressure
• Blood oncotic pressure
Filtration rate
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Tubular Transport
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Active transport of fluids and substances
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Reabsorption: normally 99% of the glomerular
filtrate is reabsorbed!
Urea: major constituent of urine, along with
water
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50% of urea is reabsorbed, 50% excreted in the
urine
Provides osmotic gradient
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Renal “Clearance”
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The ability of the kidneys to filter a substance
and excrete it in the urine is a reflection of the
GFR, tubular secretion, and tubular reabsorption
(thus also RBF and functioning of nephrons)
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Glomerular Filtration
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Nephron Function
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Nephron Function
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Concentration and Dilution of
Urine
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Countercurrent exchange system
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Contributes to production of concentrated urine
Fluid flows in opposite direction through parallel
tubes
Fluid moves up and down the parallel limbs of the
loop of Henle
The longer the loop, the greater the concentration
gradient
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Countercurrent Exchange System
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Concentration and Dilution of
Urine
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Urea
Catecholamines
Antidiuretic hormone (ADH)
Urodilantin
Natriuretic peptide
Diuretics
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Renal Hormones
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Vitamin D
Erythropoietin
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Tests of Renal Function
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Clearance and glomerular filtration rate
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Inulin
Creatinine
Clearance and renal blood flow
Blood tests
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Plasma creatinine concentration
Plasma cystatin C concentration
Blood urea nitrogen (BUN)
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Tests of Renal Function
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Urinalysis
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Urine color
Urine pH
Specific gravity
Urine sediment
• RBCs
• Casts
• Crystals
• WBCs
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Tests of Renal Function
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Urinalysis
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Reagent strips (dipsticks)
• Glucose
• Bilirubin
• Urobilinogen
• Leukocyte esterase
• Nitrates
• Ketones
• Proteins
• RBCs, hemoglobin, and myoglobin
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Aging and Renal Function
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Decrease in kidney size
Decrease in renal blood flow and GFR
Number of nephrons decrease due to renal
vascular and perfusion changes
Glomerular capillaries atrophy
Tubular transport response decreases
Increased bladder symptoms
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Urgency, frequency, and nocturia
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