Chapter 25) Urinary System Flashcards
Kidney Functions
- Regulates total water volume and solute concentration
- Regulates ECF ion concentrations
- Ensured long-term acid base balance
- Removal of metabolic Wastes, toxins and drugs
Endocrine Functions of the Kidney
- Rennin) Regulation of blood pressure
- Erythopoitein) Regulation of RBC production
Kidney Anatomy
- 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
Internal Kidney Anatomy
- 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
Blood and Nerve Supply of the Kidneys
- 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
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Nephrons
- Nephrons) Sturctural and Functional units that form the urine
- about 1 million per kidney
- Two main parts
- Renal Corpscule
- Renal Tubule
Renal Coruscle (Nephron)
- Two Parts
- 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
- 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
Renal Tubule (nephron)
- 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
Collecting Ducts
- 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
Classes of Nephrons
- Cortical Nephrons) 85; almost entirely in cortex
- Juxtamedullary Nephrons)
- long nephron roots indvade medulla
- Ascending limbs have both thick and hting segments
- concentrtates urine
Nephron Capillary beds
- 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
Juxtaglomerular Complex (JGC)
- 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
Mechanisms of Urine Formation
- 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
Filtration Membrane
- Membrane between blood and interior of glomerular capsule
- no cells can pass
- three layers
- Fenestrated Endothelium) of glomerular capillaries
- Basement Membrane) lies between the other two layers composed of fused basal laminae
- 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.
Pressures that Affect Filtration
- 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 (HPcs)(Inward)
- Pressure of the filtrate in the capsule
- about 15 mm Hg
- Colloid Osmotic Pressure in capillaries (OPgc)
- Pull of proteins in the blood
- 30 mm Hg
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Net Filtration Pressure (NFP)
- 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.
Regulation of Glomerular Filtration
- 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
Intrensic Control Mechanisms (GFR)
- 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
Extrensic Controls
- 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)
Tubular Reabsorption
- 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.
Tubular Reabsorption of Sodium
- 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
Reabsoprtion of Nutrients and Ions
- 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.
Passive Tubular Reabsorption of Water
- Movment of Na+ and other solutes creates osmotic graidient for water
- moved across channel via aquaporians
Passive Tubular Reabsorption of Solutes
- 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.
Transport Maximum
- 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
Reabsorptive Capibilities of Renal Tubules and Collecting Ducts
- 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.
Reabsorptive Capabilites of Renal Tubules and Collecting Ducts
- 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
Tubular Secretion
- 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
- Disposal of Substances (like Drugs) that are tightly bound to plasma proteins
- Eliminates Undesireable substances (urea and uric acid)
- Rids body of excess K+ (aldesterone)
- 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
Regulation of Urine Concentration and Volume
- 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.
Coutercurrent Multiplier: Loop of Henle
- 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
Countercurrent Exchanger
- 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
Formation of Dilute or Concentrated Urine
- 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
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Diueretics
- 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
Renal Clearance
- 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.
Physical Characteristice of Urine
- 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
Chemical Composition of Urine
- 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+, PO43-, SO43-, Ca2+, Mg2+, HCO33-
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- Na+, K+, PO43-, SO43-, Ca2+, Mg2+, HCO33-
Ureters
- 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.
Renal Calculi
- Kidney stones
- Crytlized calcium, magnesium or uric acid salt
- most are small and pass easy
Urinary Bladder
- 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
Urethra
- 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
Micturition
- 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.
Incontience
- 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.
Urinary retention
- Bladder unable to expel urine
- common after general anstesia
- Hytrophy of the prostate
- Treament) catheter