Anatomy Exam 3 - Urinary System

Kidneys

production of urine and other functions

Ureters

transport urine from kidneys to urinary bladder

Urinary Bladder

temporary storage reservoir for urine

Urethra

transports urine out of body

Gross Anatomy of Kidneys

right kidney lower than left due to liver; ureters, renal blood vessels, lymphatics, and nerves enter and exit at renal hilum

Renal Cortex

granular-appearing superficial region

Renal Medulla

deep to cortex, composed of cone-shaped medullary (renal) pyramids

Function of Kidneys

regulating total water volume and total solute concentration; excreting metabolic wastes, toxins, and drugs; carrying out gluconeogenesis, if needed; producing erythropoietin and renin, activating vitamin D

Physiology of Kidney

180L of fluid processed daily; only 1.5L of urine; kidney filters body’s plasma volume 60x each day; consume 20-25% of oxygen used by body at rest; filtrate is basically blood plasma minus protein

Nephrons

structural and functional units that form urine (>1million per kidney)

Renal Corpuscle

made up of glomerulus and glomerular capsule;

Glomerulus

highly porous capillaries; blood pressure is high because afferent arterioles are larger in diameter than efferent arterioles

Glomerular Capsule

structure surrounding glomerulus; filtrate passes into capsular space

Renal Tube

proximal convoluted tubule; nephron loop; distal convoluted tubule

Proximal Convoluted Tubule

cuboidal with brush border

Nephron Loop

thin (squamous) and thick (cuboidal or columnar)

Distal Convoluted Tubule

cuboidal with few microvilli

Collecting Duct

receives filtrate from multiple nephrons; two cell types - principal cells that are short microvilli with water and sodium balance, and intercalated cells that are abundant microvilli and acid-base balance

Juxtaglomerular Complex

involves modified portions of the distal portion of ascending limb of nephron loop and afferent (sometimes efferent) arteriole

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; quickly reclaims most of tubular contents and returns them to blood; selective epithelial process where almost all organic nutrients are reabsorbed and water and ion reabsorption is hormonally regulated and adjusted

Tubular Secretions

selectively moves substances from blood to filtrate in renal tubules and collecting ducts; occurs almost completely in PCT; selected substances are moved from peritubular capillaries through tubule cells out into filtrate; important for secretion of drugs or metabolites bound to plasma proteins, eliminating undesirable substances that were passively reabsorbed, riddling body of excess potassium, controlling blood pH; substances synthesized in tubule cells are also secreted

Filtration Membrane

porous membrane between blood and interior of glomerular capsule; allows water and solutes smaller than plasma proteins to pass (normally no cells can pass)

Glomerular Filtration Rate (GFR)

volume of filtrate formed per minute by both kidneys; directly proportional to net filtration pressure, total surface area available for filtration, and filtration membrane permeability; constant GFR is important as it allows kidneys to make filtrate and maintain extracellular homeostasis

Anuria

abnormally low urinary output (less than 50ml/day); may indicate that glomerular blood pressure it too low to cause filtration; renal failure and this can also result from situations in which nephrons stop functioning

Nephron Capillary Beds

efferent arteriole leaving glomerulus feeds into either peritubular capillaries or vasa recta; peritubular capillaries are adapted for absorption of water and solutes; vasa recta function in formation of concentrated urine

Transport Maximum

renal capacity for tubular reabsorption of any specific substance is called transport maximum (Tm); reflects number of carriers in renal tubules that are available; transcellular transport systems are specific and limited

Renal Threshold

plasma concentration of a solute (normally filtered but completely reabsorbed) at which some of the solute is excreted; results from saturation of reabsorption transported

Regulation of Urine Concentration and Volume

kidneys make adjustments as needed to maintain body fluid osmotic concentration around 300mOsm; only small amounts of urine if the body is dehydrated, or dilute urine if overhydrated; accomplished by using countercurrent mechanisms

Countercurrent Mechanisms

establish and maintain medullary osmotic gradient; countercurrent multiplier and countercurrent exchanger

Countercurrent Multiplier

interaction of filtrate flow in ascending/descending limbs of nephron loops in juxtamedullary nephrons; creates medullary osmotic gradient

Countercurrent Exchanger

blood flow in ascending/descending limbs of vasa recta; preserves medullar osmotic gradient

Medullary Osmotic Gradient

used by collecting used to vary urine concentration; extends from renal cortex through medulla

Urea Recycling and Medullary Gradient

urea helps form osmotic gradient; urea enters filtrate in ascending thin limb of nephron loop by facilitate diffusion; in deep medullary region, highly concentrated urea leaves collecting duct and enters interstitial fluid of medulla; urea than moved back into ascending thin limb

Urine

95% water and 5% solutes; nitrogenous wastes (urea, uric acid, creatinine)

Diuretic

chemical that enhance urinary output; ADH inhibitors such as alcohol, sodium reabsorption inhibitors such as caffeine or hypertension drugs; osmotic diuretics which are substances no reabsorbed

Renal Clearance

volume of plasma kidneys can clear of a particular substance in a given time; tests are used to determine GFR to help determine glomerular damage and follow progress of renal disease

Chronic Renal Disease

defined as GFR <60ml/min for 3 months; filtrate formation decreases, nitrogenous wastes accumulate in blood, pH becomes acidic; seen in diabetes mellitus and hypertension

Renal Failure

defined as GFR <15 ml/min; causes uremia which is ionic and hormonal imbalances, metabolic abnormalities, and toxic molecules; fatigue, anorexia, nausea, mental changes, and cramps; treatment includes hemodialysis or transplant

Ureters

tubes that convey urine from kidneys to the bladder; begin as continuation of renal pelvis; enter base of bladder through posterior wall; as bladder pressure increases, distal ends of ureters close, preventing backflow of urine

Renal Calcui

kidney stones in renal pelvis; crystallized calcium, magnesium, or uric acid salts; large stones can block ureter, obstructing urine flow, causing excruciating pain from flank to abdomen

Urinary Bladder

muscular sac for temporary urine storage of urine

Internal Urethral Sphicter

bladder-urethra junction; smooth muscle

External Urethral Sphincter

as it passes through pelvic floor; skeletal muscle

Micturition

process of urine leaving the body

Reflexive Urination (Urination in Infants)

distension of bladder activates stretch receptors; leads to contraction of detrusor and opening of internal and external sphincters; inhibition of somatic pathways to external sphincter allow its relaxation and opening; pontine control centers mature between ages 2 and 3

Urinary Incontinence

in adults, usually caused by weakened pelvis muscles; stress incontinence via increased abdominal pressure; overflow incontinence when bladder overfills

Urinary Retention

unable to expel urine; common after general anesthesia, hypertrophy of prostate; treatment is catheterization

Urinary Tract Infection

caused by improper toilet habits, bacteria introduction; more common in women due to shortness of urethra