Chapter 25) Urinary System

Question 1

Kidney Functions

Answer 1

• Regulates total water volume and solute concentration
• Regulates ECF ion concentrations
• Ensured long-term acid base balance
• Removal of metabolic Wastes, toxins and drugs

Question 2

Endocrine Functions of the Kidney

Answer 2

• Rennin) Regulation of blood pressure
• Erythopoitein) Regulation of RBC production

Question 3

Kidney Anatomy

Answer 3

• Bean shaped organs that lie in a retroperiotneal position (between body wall and dorsal peritonium) in superior lumbar region
  
  • T12-L3
  • about 150g (5oz)
  • Right kidney lower than left because of liver
• Adrenal (suprarenal) gland atop each kidney
• Convex Lateral Surface and Concave Medial Surface
  
  • Renal Hilum) cleft on mediald surface that leads to internal space called renal sinus.
• Renal Fascia (supporting tissue)
  
  • anchoring layer of dense fibrous connective tissue
• Perirenal Fat Capsule (Supporting tissue)
  
  • Fatty cushion
• Fibrous Capsle (supporting tissue)
  
  • prevents spread of infection of kidneys

Question 4

Internal Kidney Anatomy

Answer 4

• Renal Cortex) superficial region
• Renal medulla) cone shaped medullary pyrmaids
  
  • seperated by renal colums
• Papilla) top of renal pyramid
  
  • releases urine into minor calyx
• Lobe) medullary pyrmaid and surrounding cortical tissue
  
  • about 8 per kidney
• Renal Pelvis) Tube continuius with urteter
• Minor calyces) drain pyrmaids at papillae
• Major Clyces)
  
  • collect urine from minor calyces
  • empty urine into renal pelvis
• Urine Flow
  
  • Renal Pyrmaid > Minor Calyx > Major Calyx > Renal Pelvis > Ureter
• Pyelonephritis) inflmation/ infection of entire kidney

Question 5

Blood and Nerve Supply of the Kidneys

Answer 5

• Kidneys cleasne blood and adjust its composition
• Renal Arteries deliver 1/4 of total cardiac output to kidneys each min
• Arterial and Venous flow use similar paths
• Renal Plexus) networ of autonomic nerve fibers that provide nerve supply to kidneys and ureter
• No segmental veins
  *

Question 6

Nephrons

Answer 6

• Nephrons) Sturctural and Functional units that form the urine
  
  • about 1 million per kidney
• Two main parts
  
  • Renal Corpscule
  • Renal Tubule

Question 7

Renal Coruscle (Nephron)

Answer 7

• Two Parts

1. Glomerulus)
   
   • Tuft of capillaries;
   • fenestrated endothelium > Higly porus > allows large ammout or solute rich but protien free fluid to flow into glomular capsule
   • Fluid is Filitrat; or the raw material the renal tubes process
2. Glomular Capsule (Bowman’s Capsule)
   
   • Cup-shaped, hollow structure surrounding glomerulus
   • External Parietal Layer) simple squamous epithelium
   • Internal Visceral Layer) conists of podocytes (foot cells) that cling to glomular capillaries
   • Fenestrations allow filtrate to pass into capsular space

Question 8

Renal Tubule (nephron)

Answer 8

• Proximal Convoluted Tubule
  
  • Proximal > Closest to the renal corpuscle
  • Cubodial cells with dense micro villi and large mitochondria
  • Functions in reabsorption and secretion
• Nephron Loop)
  
  • descedning and ascending limbs
  • Proximal part of descending limb continuious with proximal tububule (same cells)
  • Distal descending limb) simple squamous epithlium
  • Thick ascening limb) cuboidal cells to columnar cells)
• Distal Convoluted Tubule (DCT)
  
  • Cubodial Cells wit very few microvili
  • Function more in secretion than reabsorption

Question 9

Collecting Ducts

Answer 9

• Two cell types found in collecting ducts
• Principal Cells
  
  • more numerous
  • sparse, short microvilli
  • Mantain water and Na+ balance
• Intercalated cells
  
  • Cuboidal cells with abundent microvilli
  • two types; A and B
  • Help mantian acid-base balance
• Collcting ducts
  
  • recive filtrate from many nephrons
  • Run through medullary pyrmids (striped appearence)
  • Fuse together to deliver urine through parillae into minor calyces

Question 10

Classes of Nephrons

Answer 10

• Cortical Nephrons) 85; almost entirely in cortex
• Juxtamedullary Nephrons)
  
  • long nephron roots indvade medulla
  • Ascending limbs have both thick and hting segments
  • concentrtates urine

Question 11

Nephron Capillary beds

Answer 11

• Glomerulus) Specilized for filtration
  
  • fed and drined by arteriole (affrent arteriole> glomerulus > efferent arteriole)
  • Higher blood pressure because affrent arterioles larger than efferent ones (high-resistance vessels)
• Peritubular capillaries
  
  • low pressure, porous capillaries adapted for absorption of water and solutes
  • arise from effrent arteioles; empty into venules
  • cling to ajacent renal tubules
• Vasa Recta
  
  • Long, thin-walled vessels parallel to long nephron loops of juxtamedullary nephrons
  • Form concentrated urine

Question 12

Juxtaglomerular Complex (JGC)

Answer 12

• One per nephron
• Distal portion of ascending limb of the nephron loop lies against the afferent arteriole; feeds the glomerulus
• Modified portions of
  
  • distal protion of ascending limb of nephron loop
  • Afferent (sometimes efferent) arteriole
• Important in regulation of rate of filtrate formation and blood pressure
• Macula Densa) Dense spot
  
  • tall, closley pact cells of ascending limb
  • Chemoreceptors; sense NaCl content of the filtrate
• Granular Cells (juxtaglomerular/ JG cells)
  
  • enlarges smooth muscle cells of arteriole
  • release enzyme renin
  • mechnoreceptors; sense blood pressure
• Extraglomerular mesangial cells
  
  • Between arteriole and tubule cells
  • Interconnected with gap junctions
  • May pass signals between macule densa anc granular cells

Question 13

Mechanisms of Urine Formation

Answer 13

• Glomerular filtration) dumping into waste container
  
  • takes place in renal capsule
  • produces cell and protein free filtrate
  • passive proccess
• Tubular resabsoprtion ( reclaiming what the body needs)
  
  • selectivly returns all glucose and amino acids and 99% of water
  • moves stuff from filtrate to renal tubules and collecting ducts
  • anything not reabsorbed becomes urine
• Tubular Secretion) Selectively adding to the waste container
  
  • selivtively moves substances from blood to filtrate in renal tubes and collectind ducts
• Kidneys filter entire plasma volume 60 times a

Question 14

Filtration Membrane

Answer 14

• Membrane between blood and interior of glomerular capsule
  
  • no cells can pass
  • three layers

1. Fenestrated Endothelium) of glomerular capillaries
2. Basement Membrane) lies between the other two layers composed of fused basal laminae
3. Foot Processes of Podocytes) filtration slits between foot processes.
   
   • prevent any macromolecules that exit from the basment membrane from traveling farther (slit diaphragms)
   • moleciles smaller than 3 nm (water, glucose, amino acids, nitrogonuses wastes) pass from blood into glomelural capsule. `
   • Glomular Mesangeal cells) specilized pericytes called glomuerular mesingial cells.

Question 15

Pressures that Affect Filtration

Answer 15

• Hydrostatic pressure in glomerular capillaries (Glomerular blood pressure)(outward pressure)
  
  • Chief force pushing water and solutes out of blood
  • Quite high compared to other capilalries because of high resistance afferent arteriole
• Colloid Osmotic Pressure in Capsular Space of Glomular Capsule (Outward).
  
  • would pull filtrate into the tubule but is zero because no protein enters
• Hydrostatic pressure in capsular space (HP_cs)(Inward)
  
  • Pressure of the filtrate in the capsule
  • about 15 mm Hg
• Colloid Osmotic Pressure in capillaries (OP_gc)
  
  • Pull of proteins in the blood
  • 30 mm Hg
    *

Question 16

Net Filtration Pressure (NFP)

Answer 16

• NFP) Net filtration pressure
  
  • 55 mm Hg forcing out
  • 45 mm Hg opposing
  • Net force = 10 mm Hg outwatd
• NFP is the main controllable factor that determines glomerular filtration rate (GFR)
  
  • Volume of filtrate formed per minute by both kidneys
• GFR is directly proportional too
  
  • NFP) hydrostatic pressure in glomerous
  • Total surface area avaible for filtration
  • Filtration membrane permiablility) fenestrated.

Question 17

Regulation of Glomerular Filtration

Answer 17

• GFR is tightly regulated to serve two crucial, somtimes apposing needs
  
  • Constant GFR allows kidneys to make filtratre and mantain GFR in kidney (intrensic controls)
  • GFR affects systemic blood pressure (extrensic controls)
• Intrensic Controls) act locally to mantaon GFR
  
  • MAP = 80-180 mmHg
  • Autoregulation ceases if out of that range
• Extrinsic Controls
  
  • Nervous and endocrine mechanisms
  • take predominance if blood pressure is out of MAP
• NFP rises = GFR rises

Question 18

Intrensic Control Mechanisms (GFR)

Answer 18

• Myogenic Mechanism) vascular smooth muscle contracts when strethced
  
  • High BP > Muscle Stretch> Constriction of Affrent Aterioles
  • Low BP > dilation of affrent arteries
• Tubloglomerular Feedback Mechanism) Respond to NaCl concentration
  
  • Macula sensa cells respond to NaCl concentration
  • High NaCl > Afferent arteiole constriction > NaCl reabsorption
  • GFR low> Afferent dilation

Question 19

Extrensic Controls

Answer 19

• Sympathetic Nervous System
  
  • Normal conditions at rest (renal blood vessels dialated and autoregulation mechanisms prevail)
  • Low BP/ extracellular fluid volume = Norepinephrine release = vasoconstriction / increased BP of Afferent arterioles.
• Renin-Angiotension-Aldesterone Mechanism
  
  • Low BP > Rennin by granular cells of kidnies > Angiotensin II
  • stimulated by sympatetic nervous system, low NaCl in filtrate, and mechanoreceptors (granular cells)

Question 20

Tubular Reabsorption

Answer 20

• Most tubular contents reabsorbed to the blood.
• Selective, transepithelial process
  
  • all organic nutrients reabsorbed
  • inculed active and passive tubular reabsorption
• Transcellular Route
  
  • Apical membrane > Cytosol of tubule cells > Basolateral Membrane > Endotlelium of peritubular capillaries
• Paracellular Route) Between tubile cells
  
  • limited by tight juntions
  • allows Ca2+, Mg2+, K+, and Na+ to pass thrrough.

Question 21

Tubular Reabsorption of Sodium

Answer 21

• Most abundant cation in the filtrate
• Transport across the basolateral membrane
  
  • primarually Na+-K+ ATPase pump
  • pumps to peritubular capillaries
• Transport across apical membrane
  
  • Na+ passes through apical membrane by secondary active transport (cotransport)
  • or via facillated difffusion
  • Does not use any energy

Question 22

Reabsoprtion of Nutrients and Ions

Answer 22

• Organic Nutrients) reabsorbed by secondary active transport with Na+
  
  • glucose, amino acids, some ions and vitiamins
  • gradient created by Na+-K+ pumping across basolateral membrane
• Cotransported solutes move across the basolateral membrane via facilitated diffusion via other transport protiens.

Question 23

Passive Tubular Reabsorption of Water

Answer 23

• Movment of Na+ and other solutes creates osmotic graidient for water
  
  • moved across channel via aquaporians

Question 24

Passive Tubular Reabsorption of Solutes

Answer 24

• Solute concentration in filtrate increases as water is reabsorbed > creates concentration gradient for solutes
  
  • Fat soluable substances, some ions and urea follow water down concentration gradient.

Question 25

Transport Maximum

Answer 25

• Transcellular transport systems for various solutes are specific and limited
• Tramsport maximim (Tm)
  
  • reflects number of carriers in renal tubules avaible to carry a specific substance
  • Pleanty of trasnporters for susbtances that need to be retained (ex glucose) and few or none for substances of no use
  • When carriesrs saturated excess is secreted in the urine

Question 26

Reabsorptive Capibilities of Renal Tubules and Collecting Ducts

Answer 26

• Entire renal tubule is involed but PCT cells are most active
• PCT
  
  • Site of reabsorption
  • All nutrients, 65% of Na+ and Water and many ions.
  • Uric acid and 1/2 of urea are reabsorbed but later secreted back into filtrate
• Nephron loop
  
  • descending loop) H2O can leave, solutes cannot
  • Ascending Limb) H2O cannot leace; Solutes can
  • vital to ability to concentrate or dilate urine.
• DCT and collecting duct
  
  • Most water and solute have been reabsorbed by the time DCT is reached
  • small ammout of filtrared load is removed.

Question 27

Reabsorptive Capabilites of Renal Tubules and Collecting Ducts

Answer 27

• Reabsorption Hormonally Regulated
• Antidiuretic hormone (ADH)
  
  • released by posterior petuitary
  • Causes Principal cells (water and Na+) to insert aquaporians into collecting ducts.
  • ADH levels increase > Increased water reabsorption
• Aldesterone
  
  • Increases Na+ and therefore water via osmosis
  • Targets collecting ducts and Distal DCT.
  • Increases blood pressure. Decreases K+ levels.
• Atrial Natriuetic Peptide (ANP)
  
  • reduces blood Na+to reduce blood volume/ pressure
• Parathyroid hormone (PTH) acts on DCT to increase Ca2+ reabspprtion

Question 28

Tubular Secretion

Answer 28

• Reabsoprtion in reverse; one major exception is PCT is main site of secretion.
  
  • collecting ducts partially active
  • Selected substances (K+, H+, NH4+, creatine, organic acids/bases) move from Peritubular Capilaries throigh tubule cells to the filtrate
  • Substances created in tubule cells also secreted.
• Important for

1. Disposal of Substances (like Drugs) that are tightly bound to plasma proteins
2. Eliminates Undesireable substances (urea and uric acid)
3. Rids body of excess K+ (aldesterone)
4. Controls blood pH (altering ammounts of H+ and HCO3- in urine)
   
   • ph drops > more H+ in urine
   • pH rises > more Cl- is absorbed than HCO3-; HCO3- leaves the body

Question 29

Regulation of Urine Concentration and Volume

Answer 29

• Osmolaity
  
  • number of sulute per kg of H2O
  • reflects ability to cause osmosis
• Osmolality of Body Fluids
  
  • expresssed in milliosmole (mOsm)
  • kidneys mantain osmality of blood plasma at ~300 mOsm by regulating urine concentration and volume
• Countercurrent mechanism
  
  • how kidneys regulate urine concentration and volume
  • term countercurrent means fluid flows in opposite directions through the same adjacent sements
  • makes it possible to echange material between segments.
• Countercurrent multiplier) interacttion of filtrate flow in ascedning and descending limbs of long nephron loops
• Countercurrent exhanger) Blood flow through the ascending and descending portions of the vasa recta.

Question 30

Coutercurrent Multiplier: Loop of Henle

Answer 30

• Depends on activly transporting solutes out of the ascending limb
  
  • start of positve feeback
• Two limbs of nephron loop are close enough to influence exhancges with the interstital fluid they share.
• More NaCl in ascending limb = More water diffuses out of descending limb = Saltier filtrate in descending limb
• Salty Filtrate in descending limb icreases osmolity of medullary interstitial fluid further.
• Descending Limb)
  
  • Freely permiable to H2O
  • H2O passes out of filtrate to hyperosmotic medullary interstitial fluid.
  • Filtrate osmolality increases to 1200~ mOsm
• Ascending Limb
  
  • Impermiable to H2O
  • Selectively permeable to solutes (Na+ and Cl- actively reabsorbed in thick segment)
  • Filtrate osmoality decreased to 100 mOsm
  • 200 mOsm difference between the indide and outside of ascening limb

Question 31

Countercurrent Exchanger

Answer 31

• Vasa Recta acts as countercurrent exchangers
• Perserves gradeient by
  
  • Preventing rapid removel of salt from medullary interstitial space
  • Removing Reabsorbed water
• Blood entering and leaving Vasa Recta have nearly same solute concentration
  
  • Water is picked up in ascending vesa recta from descending vasa recta and any lost from nephron loop and collecting duct.
  • Volume of blood at end of vasa recta grater than the begining

Question 32

Formation of Dilute or Concentrated Urine

Answer 32

• Medullary Osmotic Gradient) created by the kidneyes to conserve water
  
  • Overhydration > large volume dilutue urine (low ADH production)(~100 mOsm concentration)
  • Dehydration > small volume concentrated urine (ADH releases) (~1200 mosm)
• Urea helps form medullary gradient
  
  • urea enters filtrate in ascending limb
  • gets left behind during cortical reabsorption of water
    *

Question 33

Diueretics

Answer 33

• Chemicals that enhance urinary output.
• ADH Inhibitors (alchocol)
• Na+ reabsorption inhibitors
  
  • Inhibits water reabsorption
  • Caffeine, Drugs for hypertension or edema
• Osmotic Diuretics) substance not reabsorbed so water stays in urine
  
  • ex) glucose in diabetice

Question 34

Renal Clearance

Answer 34

• Volume of Plasma from which the kidneys clear (completely remove) a particular substance in a given time
  
  • usually 1 minute
• Used to determine Glomular filtration rate (GFR)
  
  • to detect dlomerular damage
  • to follow progress of renal disease.
• C=UV/P
  
  • C) Renal clearence rate
  • U) concentration of substance in urine
  • V) flow rate of urine formation
  • P) concentration of the same substance in the plasma.
• Inulin (plant polysacharide)
  
  • used to determine GFR because it is freely filtered (not absorbed)
  • Concentration of U=125 used to test (C=125)
  • C < 125 ml/min = Substance reabsorbed
  • C= 0, Substance completely reabsorbed/not filtered
  • C=125, No Net reabsorption
  • C > 125 no net reabsorption.

Question 35

Physical Characteristice of Urine

Answer 35

• Color and Transparency
  
  • pale to deep yellow
  • Urocrome; a pigment from hemoglobin gives yellow color
  • Abnormal color may indicate UTI
• Odor
  
  • develops an ammonia odor
  • may be altered by some drugs and vegtables
• pH
  
  • slightly acidic; about pH of 6 with a range of 4.5-8
  • Acidic diet (protien, whole wheat) > lower pH
  • Alkaline diet (vegitarien), vomiting, UTI > higher pH
• Specific Gravity
  
  • ratio of mass of substance to an equal volume of distilled water
  • 1.001 to 1.035

Question 36

Chemical Composition of Urine

Answer 36

• 95% water and 5% solutes
• Nitrogenous Wastes
  
  • Urea (from amino acid breakdown) largest component
  • Uric acid) from nucleic acid metabolism
  • Creatnine (metabolite of creatine phosphate)
• Other normal solutes
  
  • Na+, K+, PO4^3-, SO₄^3-, Ca²⁺, Mg²⁺, HCO3₃-
    *

Question 37

Ureters

Answer 37

• Convey urine from the kidneys to the bladder
  
  • begin at level of L2, runs obliquley to bladder wall
  • Prevents backflow of urine
• Three Layers of Ureter Wall
• Mucosa) Transitional epitelium
• Muscularis) smooth muscle sheets
  
  • contracts in response to streatch
  • propels urine into bladder
• Adventitia) outer fibrous connective tissue.

Question 38

Renal Calculi

Answer 38

• Kidney stones
• Crytlized calcium, magnesium or uric acid salt
  
  • most are small and pass easy

Question 39

Urinary Bladder

Answer 39

• Muscular sac for temportary storage of urine
  
  • Males) prostate gland inferior to bladder
  • Females) bladder is anterior to vagina
• Trigone (triangle)
  
  • Smooth triangular are outlined by opening for ureters and urethrea
  • Infections tend to presist in this region
• Layers of the bladder wall
  
  • Mucosa) transitional epithelial mucosa
  • Thick detrusor muscle) three layers of smooth mucle
  • Fibrous adentitia (exept on its superior surface)
• Rugae folds appear when

Question 40

Urethra

Answer 40

• Muscular tube draining urinary bladder
• Mostly psuedostratified columnar epithelium
  
  • Transitional epithelium near bladder
  • Stratified squamous epithelium near external urethral orifice
• Sphincters
  
  • Internal urethral sphincter) Involuntary
  • External uretheral sphincter) voluntery
• Female Urethra
  
  • 3-4 cm
  • tightly bound to vaginal wall
  • External uretheral opening) anterior to vagina, posterior to the clit
• Male Urethra carries semen and urine
  
  • Prostatic urethra) within prostate gland
  • Intermidite part of urehtra) urogenital diaphragm to begining of penis
  • Spongy urethra) passes throigh penis; opens via external urethral orifice

Question 41

Micturition

Answer 41

• Urination or voiding) act of emptuign the urinary bladder
• Three simuletanous events
  
  • contraction of detrusor muscle by ANS
  • opening of internal uretheral sphincer by ANS
  • Opening of external sphincter by somatic nervous system
• Refelxive urination (occurs in infants)
• Micturition (when pontine control center matures between ages of 2 and 3)
• Pontine storage center
  
  • inhibits urination
  • excited sympatiehtic and somatic pathways
• Pontine micturition center promotes micturition
  
  • Excited parasympathetic pathways
  • Inhibits sympathetic and somatic efferent pathways.

Question 42

Incontience

Answer 42

• Weakened pelvic muscles are normal cause
• Stress Incontience (laughing and coughung)
  
  • Increased intradominal pressure forces urine through the sphincter
• Overflow incontinence
  
  • urine dribbles when bladder overfills.

Question 43

Urinary retention

Answer 43

• Bladder unable to expel urine
• common after general anstesia
• Hytrophy of the prostate
• Treament) catheter