Chapter 15, Urinary System, Part A

Chapter 15: Urinary System
Part A: Kidneys & Urine
1. Functions of the urinary system
a. Elimination of waste products:
i. Nitrogenous wastes: urea, uric acid, ammonia
ii. Toxins—harmful or fatal in small doses
iii. Drugs—have specific and significant effects on the cells
b. Regulate aspects of homeostasis
i. Water balance—osmosis
ii. Electrolytes: ions such as Na, Ca, Mg, Cl
iii. Acid-base balance in the blood
iv. BP = blood pressure
v. RBC = red blood cell production
vi. Activation of vitamin D
2. Organs of the system
a. Kidneys—where blood is actively processed
i. Renal=kidney
b. Ureters—tubes draining kidneys
c. Urinary bladder—urine storage
d. Urethra—from bladder to exterior of body
3. Kidneys
a. Location
i. Retroperitoneal = against the dorsal body wall
ii. Level of the T12 to L3 vertebrae
iii. Right kidney is slightly lower than the left (due to the position of the liver)
b. Features
i. Shape
ii. Renal hilum—a medical indentation where several structures enter or exit the kidney (ureters, renal blood vessels, and nerves)
iii. Adrenal gland sits atop each kidney
c. Coverings
i. Fibrous capsule
• Surrounds each kidney—connective tissue
ii. Perirenal fat capsule
• Surrounds the kidney and cushions against blows
iii. Renal fascia
• Outermost capsule that helps hold the kidney in place against the muscles of the trunk wall
d. Anatomical regions – renal:
i. Cortex—outer region
ii. Medulla—inside the cortex
iii. Pelvis—inner collecting tube, like a funnel
e. Internal structures
i. Renal or medullary pyramids—triangular regions of tissue in the medulla
ii. Renal columns—extensions of cortex-like material inward that separates the pyramids
iii. Renal calyces (calyx)—cup-shaped structures that funnel urine towards the renal pelvis
f. Blood supply
i. 25% of the total blood supply of the body passes through the kidneys each minute
ii. Renal artery provides each kidney with arterial blood supply
iii. Arterioles and capillary beds – details below
• Renal artery divides
4. Nephrons
a. Structural and functional units of the kidneys
b. Over a million in each kidney
c. Responsible for forming urine
d. Main structures of the nephrons:
i. Glomerulus—ball of capillaries
ii. Renal tubule—kidney filtering tubes
e. Anatomy (Glomerulus)
i. Knot of capillaries
ii. Capillaries are covered with Podocytes from the renal tube
iii. Glomerulus sits within a glomerular (Bowman’s) capsule (the first part of the renal tubule)
iv. Renal tubule extends from glomerular capsule and ends at the collecting duct:
• Glomerular (Bowman’s) capsule
• Proximal convoluted tubule (PCT)
• Loop of Henle—deep into medulla
• Distal convoluted tubule (DCT)
f. Types
i. Cortical nephrons
• Located entirely in the cortext
• Includes most nephrons
ii. Juxtamedullary nephrons
• Found at the boundary of the cortex and medulla
• Extend deeper into kidney
g. Collecting ducts
i. Receives urine from many nephrons
ii. Runs through the medullary pyramids
iii. Delivers urine into the calyces and renal pelvis
h. Capillary beds (2 sets)
i. Glomerulus
• Arterioles leading in and out
a. Afferent arteriole—comes in
b. Efferent arteriole—goes out
• Specialized for filtration
• High pressure forces fluid and solutes out of blood and into the glomerular capsule
ii. Peritubular
• Arise from efferent arteriole of the glomerulus
• Normal, low Pressure capillaries
• Adapted for absorption instead of filtration
• Cling close to the renal tubule
5. Urine formation
a. Glomerular filtration
i. Nonselective passive process
ii. Water and solutes smaller than proteins are forced through capillary walls
iii. Proteins and blood cells are normally too large to pass through the filtration membrane
iv. Filtrate is collected in the glomerular capsule and leaves via the renal tubule
b. Tubular reabsorption
i. Peritubular capillaries reabsorb useful substances:
• Water
• Glucose
• Amino Acids
• Ions
ii. Some reabsorption is passive, most is active
iii. Most reabsorption occurs in the proximal convoluted tubule
iv. Materials not reabsorbed
• Nitrogenous waste products:
a. Urea—protein breakdown
b. Uric acid—nucleic acid breakdown
c. Creatinine—associated with creatine metabolism in muscles
c. Tubular secretion = reabsorption in reverse
i. Movement from the peritubular capillaries into the renal tubules
ii. Examples
• Hydrogen and potassium ions
• Creatinine
• H+, K+, creatinine, drugs, pH control
iii. Materials left in the renal tubule move toward the ureter
d. Urine
i. Characteristics
• Yellow color due to the pigment urochrom (from the destruction of hemoglobin) and solutes
a. Concentration
• Odor—slightly aromatic
• Sterile—kills many bacteria becase
• Normal pH of around 6
• Specific gravity = density
a. 1.001 to 1.035
• Normal production in 24 hours, about 1.0 to 1.8 liters of urine are produced
• Urine vs. filtrate
a. Filtrate = contains everything that blood plasma does (except proteins)
b. Urine = is what remains after the filotrate has lost most of its water, nutrients, and necessary ions.
ii. Contains substances less valuable or harmful to the body:
• Nitrogenous wastes
iii. Does not contain things that are valuable or are too large to diffuse through membranes: