Urinary System Flashcards
What type of organ are kidneys considered?
A major excretory organ, maintaining the body’s internal environment
What are the functions of the kidneys?
- Regulate total water volume and total solute concentration in water
- Ensure long term acid-base balance
- Excrete metabolic wastes, toxins, and drugs
- Produce erythropoietin to regulate RBC production and renin to regulate blood pressure
- Activate vitamin D
What is the function of ureters?
Transport urine from kidneys to urinary bladder
What is the function or urinary bladder?
Temporary storage reservoir for urine
What is the function of urethra?
Transports urine out of body
What is the order of urine flow?
Renal pyramid -> minor calyx -> major calyx -> renal pelvis -> ureter
What are nephrons?
The structural and functional units that form urine
What are the main two parts of nephrons?
- Renal corpuscle
- Renal tubule
What are the two main parts of renal corpuscle?
- Glomerulus:
- Tufts of capillaries composed of fenestrated endothelium; highly porous
- Filtrate: plasma derived fluid that renal tubules process to form urine - Glomerular capsule
- Aka Bowman’s capsule; cup shaped, hollow structure surrounding glomerulus
- Consists of two layers
What are the two layers of glomerular capsule?
- Parietal layer: simple squamous epithelium
- Visceral layer: clings to glomerular capillaries; branching epithelial podocyes; filtration slits b/w foot processes allow filtrate to passes into capsular space
What are the three major parts of the renal tubule?
- Proximal convoluted tubule
- Nephron loop
- Distal convoluted tubule
What does distal convoluted tubule drains into?
Collecting duct
What are the characteristic of the proximal convoluted tubule?
- Cuboidal cells with dense microvilli that form brush border
- Reabsorption and secretion
- Confined to cortex
What are the characteristics of the nephron loop?
- Aka loop of Henle
- U shaped structure consisting of two limbs; descending and ascending limb
What are the characteristics of the distal convoluted tubule?
- Cuboidal cells with very few microvilli
- More secretion than reabsorption
- Confined to cortex
What are the characteristics of the collecting duct?
Contains two cell types:
- Principal cells; maintain water and calcium balance
- Intercalated cells; maintain acid-base balance of blood
What are the two major groups of nephrons?
- Cortical nephrons: Make up 85% of nephrons; almost entirely in cortex
- Juxtamedullary nephrons: important in production of concentrated urine; long nephron loops deeply in medulla; peritubular capillaries “vasa recta”
What is the role of juxtaglomerular complex?
- Regulate the rate of filtrate formation (GFR) and blood pressure
- Production of concentrated urine
What is a macula densa and what does it do?
Tall, closely packed cells of ascending limb which contains chemoreceptors that sense NaCl content of filtrate
What are granular cells and what does it do?
Enlarged, smooth muscle cells of arteriole; act as mechanoreceptors to sense blood pressure in afferent arteriole; contain renin
What are extraglomerular mesangial cells?
Located between arteriole and distal tubule cells
How many times do kidneys filter body’s entire plasma volume?
60
Urine is produced from _____?
Less than 1% of original filtrate; contains metabolic wastes and unneeded substances
What does porous membrane b/w blood and interior of glomerular capsule do?
Allows water and solutes smaller than plasma proteins to pass
What are the three layers of the filtration membrane?
- Fenestrated endothelium of glomerular capillaries
- Basement membrane: focused basal laminae of two other layers
- Foot processes of podocytes with filtration slits; slit diaphragms repel macromolecules
What types of molecules do filtration membranes allow to pass through?
Molecules smaller than 3nm; water, glucose, amino acids, nitrogenous wastes
What happens to the plasma proteins in the filtration membrane?
Remain in blood to maintain colloid osmotic pressure to prevent loss of all water to capsular space
What are the three steps of the urine formation?
- Glomerular filtration; produces cell and protein free filtrate
- Tubular reabsorption; selectively returns 99% of substances from filtrate to blood in renal tubules and collecting ducts
- Tubular secretion: selectively moves substances from blood to filtrate in renal tubules and collecting ducts
Glomerular filtration is a ______ process
Passive (no metabolic energy required)
_______ pressure forces fluids and solutes through filtration membrane into glomerular capsule
Hydrostatic
Why are hydrostatic pressure in glomerular capillaries higher than the ones in capillary beds?
The efferent arteriole is a high-resistance vessel with a diameter smaller than afferent arteriole
How to calculate NFP (Net filtration pressure)?
Outward pressures – inward pressures
What happens during tubular reabsorption?
- It quickly reclaims most of tubular contents and returns them to blood
- Takes place in the renal tubules and collecting ducts
- Almost all organic nutrients are reabsorbed
- Includes active and passive tubular reabsorption
Reabsorption is hormonally regulated in which areas?
ADH
- Released by the posterior pituitary gland
- Causes principal cells of collecting ducts to insert aquaporins in apical membranes, increasing water reabsorption
- Increase in ADH = increase in water reabsorption
Aldosterone
- Targets collecting ducts and distal convoluted tubule
- Promotes synthesis of apical Na and K channels, and basolateral Na KPhase for Na reabsorption
- Increase blood pressure and decrease K levels
What are the functional characteristics of PCT (proximal convoluted tubule)?
- Site of most reabsorption
- All nutrients, e.g. glucose and amino acids
- 65% of sodium and water reabsorbed
- Many ions
- Almost all uric acid
- About half of urea (later secreted back into filtrate)
What happens in the descending limb of the nephron loop?
H2O can leave, solutes cannot
What happens in the ascending limb of the nephron loop?
H2O cannot leave, solutes can
What are the functional characteristics of DTC (distal convoluted tubule) and collecting duct?
- Reabsorption is hormonally regulated
ADH released by posterior pituitary gland
- Causes principal cells of collecting ducts to insert aquaporins in apical membranes, increasing water reabsorption (increase in ADH = increase in water reabsorption)
Aldosterone
- Promotes synthesis of apical sodium and potassium channels, and basolateral sodium potassium ATPases for sodium reabsorption
- Increase blood pressure and decrease potassium levels
What is tubular secretion?
Reabsorption in reverse
- Occurs in PCT
- Selected substances are moved from peritublar capillaries through tubule cells out into filtrate e.g. K, H, NH4, creatinine, organic acids and bases
What are tubular secretion important for?
- Disposing of substances e.g. drug or metabolites that are bound to plasma proteins
- Eliminating undesirable substances that were passively reabsorbed e.g. urea and uric acid
- Ridding body of excess potassium
- Controlling blood ph by altering amounts of H or HCO3 in urine
What is GFR (glomerular filtration rate) ?
The amount of filtrate formed by both kidneys in one minute
- Normal GFR = 125ml/min
- Depends on the NFP (net filtration pressure)
What does NFP (net filtration pressure) rely on?
The difference of forces b/w hydrostatic pressure and colloid osmotic pressure
What is chronic renal disease defined as?
GFR < 60 ml/min for 3 months
- Decrease of filtrate formation
- Accumulation of nitrogenous wastes in blood
- Acidic ph
What is renal failure defined as?
GFR < 15 ml/min
- Causes uremia; ionic and hormonal imbalances, metabolic abnormalities, toxic molecule accumulation
- Fatigue, anorexia, nausea, mental changes, cramps
- Treated with hemodialysis
