Urinary System 1

• Excrete waste products from the body's fluids
• Eliminate waste products from the body into the environment
• Regulate the volume and pH of blood plasma
• Regulate erythrocyte production
• Regulates body's nutrient and electrolyte levels
• Help the liver detoxify poisons

• Filters blood plasma by returning useful chemicals to blood and eliminating waste
• Regulates blood volume/pressure by eliminating or conserving water
• Regulates osmolarity of blood by controlling amount of solutes eliminated
• Secretes renin (hormone), which also controls blood pressure and electrolytes
• Secretes erythropoietin to stimulate red blood cell production
• Regulates CO2 concentration and pH of blood
• Synthesize calcitriol to regulate calcium concentrations
• Can synthesize glucose from amino acids in extreme starvation

Any substance that is useless to the body or present in excess of the body's needs

Waste produced by the body

Removes CO2 and other gases

Removes water, inorganic salts, lactic acid, urea in sweat

Removes water, salts, CO2, lipids, bile pigments, cholesterol, food residue

Removes many metabolic wastes, toxins, drugs, hormones, salts, H+, water

One of the vital roles of kidneys is to excrete nitrogenous waste

Formed from ammonia when proteins are broken down

Produced when creatine phosphate is broken down

Produced when RNA is recycled

Measure of nitrogenous waste levels in blood

Elevated BUN

Syndrome of diarrhea, vomiting, dyspnea, and cardiac arrhythmia from toxicity of nitrogenous waste

Layer of collagen covering outer surface of kidneys; provides protection from trauma and infection

Thick layer of adipose tissue surrounding the fibrous capsule; cushions kidneys

Fibrous outer layer that anchors kidney to abdominal wall

• Lateral surface receives renal nerves, blood vessels, and ureter (at hilum)
• Renal Sinus: Area around hilum that contains blood and urine-collecting structures

• Renal Columns: extensions of cortex between the pyramids
• Renal Pyramids: 6-10 per kidney

Pyramid plus overlying cortex

Cup at the papilla (point) of the pyramid that collects urine

Convergence of several minor calyces

Convergence of several major calyces

Continuation of renal pelvis down to urinary bladder

Kidneys receive 20-25% of cardiac output

• Afferent arterioles branch off of interlobular arteries, and each one supplies one nephron
• Nephrons carry out all of the filtering/regulation functions of the kidney
• 1.2 million in each kidney

• Afferent arterioles become ball of capillaries (glomerulus)
• Blood drained from glomerulus by efferent arterioles
• Efferent arterioles lead to peritubular capillaries (cortex) or vasa recta (medulla)

Nerves wrapped around renal artery that go to blood vessels and tubules of nephron

• Reduces glomerular blood flow and rate of urine production
• Stimulates kidneys to secrete renin, which stimulates water and salt reabsorption at nephron

• From vagus nerve
• Increases rate of urine production

• Renal Corpuscle: consists of glomerulus and glomerular (Bowman's) capsule; filters blood plasma
• Renal Tubule: long coiled tube that converts filtrate into urine

• Perietal (outer) layer is epithelium
• Visceral (inner) layer consists of podocytes that wrap around capillaries of glomerulus
• Capsular space separates the two layers, site of glomerular filtrate collection

• Connected to corpuscle
• Longest, most coiled region
• Microvilli for absorption

• U-Shaped portion with descending and ascending limb
• Thick segments: active transport of salts
• Thin segments: permeable to water

• The end of the nephron
• Shorter and less coiled than PCT

• Receives fluid from several nephrons and takes it to medulla
• Many converge at tip of medullary pyramid in papillary duct

• Most nephrons
• Short loops, almost entirely within cortex
• Peritubular capillaries around PCT and DCT

• Long nephron loops into medulla
• Vasa recta around loop of Henle

Glomerular Filtration, Tubular Reabsorption and Tubular Secretion, and Water Conservation

• Fluid in capsular space
• Blood plasma without protein

• Fluid in renal tubule
• Similar to glomerular filtrate, but some substances added/removed

• Fluid after it enters collecting duct
• Tubular fluid with water content changes

• Glomerular capillaries are fenestrated (filtration pores)
• Substances leaving the blood in glomeruli must pass through filtration slits between podocyte "feet"

• Filtration pores allow everything but blood cells through
• Basement membrane is negatively charged gel that repels anions and large molecules
• Filtration slits also negatively charged to repel anions

• All small molecules (<3 nm) can pass through: water, electrolytes, glucose, amino acids, fatty acids, nitrogenous wastes, vitamins
• Some small substances prevented from crossing membrane because they are bound to protein: calcium, iron, thyroid hormone
• Kidney infection, trauma, strenuous exercise can damage filtration membrane
• Proteinuria: protein in urine
• Hematuria: blood cells in the urine

• GFR: the amount of filtrate formed per minute by the 2 kidneys combined
• 105-125 ml/min (150-180 L/day)
• Eliminating 1-2 L of urine per day, so 99% of filtrate is reabsorbed
• If GFR is too high, fluid flows through renal tubules too quickly for proper reabsorption
• Urine output rises, dehydration, electrolyte depletion
• If GFR is too low, wastes are reabsorbed
• GFR regulated by adjusting glomerular blood pressure

Nephrons control blood flow themselves (local control)

Smoot muscles in afferent arterioles passively stretch and contract to maintain stable flow of blood to glomerulus

• Glomerulus gets feedback about tubular fluid composition and adjusts filtration
• Uses juxtaglomerular apparatus

Structure at the end of the nephron loop that contacts afferent and efferent arterioles

• Patch of epithelial cells at the end of the loop of Henle
• Senses variations in flow of fluid composition and secretes chemical that stimulates juxtaglomerular cells

• Smooth muscle cells in the arteriole across from macula densa
• Dilate or constrict arterioles based on signal from macula densa

• Between afferent and efferent arterioles and among capillaries
• Propagate signal from macula densa to glomerulus