Chapter 26 - Urinary System Flashcards
2 Main Functions of the Urinary System
- Osmotic Regulation = Regulating osmotic pressure of H20 & other body fluids
- Elimination of nitrogenous & other wastes
4 Different Types of Nitrogenous Wastes
- Amino Acids
- Ammonia
- Urea
- Uric Acid
Amino Acids
- 4 Uses:
1. Protein synthesis
2. ATP synthesis
3. Gluconeogenesis
4. Fat synthesis - Amine (NH2) groups must be removed before 2, 3, or 4
Ammonia
- NH2 groups + hydrogen = Ammonia (NH3)
- Very toxic
- Excreted by fish & amphibians
- NH3 + H20 -> NH4+ + OH- = ammonium hydroxide
Urea
-Main nitrogenous waste excreted by mammals
-Less toxic than ammonia
-Synthesis requires significant amounts of energy
-Is an amino acid
*Liver urea cycle:
CO2 + 2NH3 + ATP -> Urea + H2O
Uric Acid
- Excreted by birds, reptiles & insects
- Relatively non-toxic
- Low water-solubility
- Synthesis is energy-demanding
- Nucleic acid metabolism: purines (G & A) -> xanthine hypoxanthine -> uric acid
4 Components of the Human Urinary System
- Kidneys (pair)
- Ureters (pair)
- Urinary Bladder
- Urethra
Kidneys
- Shaped like kidney-beans
- Location: paravertebral & retroperitoneal; below diaphragm
3 Layers Surrounding Kidneys
- Renal Capsule: Around outside of kidney
- Adipose Capsule: Surrounds renal capsule
- Renal Fascia: CT outside of adipose capsule
Hilum
Concave depression at center of kidney
Nephroptosis
- AKA “Floating Kidney”
- Occurs due to weakening of renal fascia & adipose tissue
- Can lead to hydronephrosis
Hydronephrosis
Atrophy of the kidneys, leading to renal failure
3 Areas of the Kidney
- Cortex
- Medulla
- Pelvis
* All 3 are composed of parenchyma & supporting stroma
Renal Cortex
- Granular outer & juxtamedullary areas
- Composed of renal columns
Renal Medulla
- Striated, located in the middle area
- Composed of renal pyramids
Renal Pelvis
- Hollow, inner area for urine collection (via minor calyces)
- Renal sinus = fat-filled cavity
8 Functions of the Kidneys
- Regulates blood & ECF electrolytes
- Regulates blood volume
- Regulates blood pH
- Removes toxic wastes & foreign substances from blood
- Regulates blood pressure
- Maintains blood osmolarity
- Produce hormones (calcitriol, EPO)
- Helps regulate blood glucose via glycogenolysis, glycogenesis & gluconeogenesis
Nephrons
- Functional units of the kidneys
- 2 main components
2 Main Components of the Nephrons
- Renal Corpuscle
2. Renal Tubule
Renal Corpuscle (2 Parts)
- Bowman’s Capsule
2. Glomerulus
Bowman’s Capsule
- AKA “Glomerular Capsule”
- Cuplike structure, which receives glomerular filtrate
- 2 Layers: visceral layer & parietal layer
- Capsular Space/ “Bowman’s Space” = Space between visceral & parietal layers; receives glomerular filtrate
Glomerulus
Capillary tuft surrounded by visceral layer of Bowman’s capsule
Filtration Membrane of the Glomerulus (3 Parts)
- Fenestrated Glomerular Endothelium
- Glomerular Basement Membrane
- Slit Membrane
Fenestrated Glomerular Endothelium
- Permeable to plasma components
- Contains mesangial cells; regulate the surface area available for filtration
Glomerular Basement Membrane
- Impermeable to larger proteins
- Heparan sulfate prevents passage of albumin into urinary filtrate
Slit Membrane
- Supported by filtration slits, formed by pedicels of podocytes
- Impermeable to medium-sized proteins
- Albumin may penetrate, if not already excluded by heparan sulfate
Renal Tubule (4 Parts)
- Proximal Convoluted Tubule
- Nephron Loop
- Distal Convoluted Tubule
- Connecting Tubule
Proximal Convoluted Tubule
- Part of renal tubule close to renal corpuscle
- Made of simple cuboidal cells w/ long apical microvilli (For increased surface area)
Nephron Loop
- Consists of descending & ascending limbs
- Descending limb & proximal thin portion of ascending limb = simple squamous epith.
- Thick portion of ascending limb (TAL) = cuboidal & columnar epith.
Macula Densa
Area where TAL contacts afferent arteriole
Juxtaglomerular (JG) Cells
Cells that secrete renin
Juxtaglomerular Apparatus (JGA)
- Composed of macula densa + JG cells
- Helps regulate blood pressure
Distal Convoluted Tubule
- Part of renal tubule distant from renal corpuscle
- Composed of cuboidal epithelium
Connecting Tubule
Links nephron to collecting duct
2 Cell Types in Connecting Tubule & Collecting Duct
- Principal Cells: Aldosterone-sensitive & ADH-sensitive cells
- Intercalated Cells w/ H+ ATP=ase pumps
2 Types of Nephrons
- Cortical Nephrons
2. Juxtamedullary Nephrons
Cortical Nephrons
- 80-85% of all nephrons
- Glomeruli + PCT + DCT + CT in outer 1/3 of cortex
- Short nephron loops
- Peritubular capillary network (arises from efferent arteriole); surrounds loops
Juxtamedullary Nephrons
- Enable concentration of urine
- Glomeruli + PCT + DCT + CT near cortical-medullary boundary
- Long nephron loops -> almost to renal papillae
- Loops surrounded by long vasa recta
Collecting Ducts
- Have cortical & medullary segments
- Consist of principal & intercalated cells
- Several CTs link to a single CD in the cortex
- CD conducts urine to papillary duct -> renal pelvis
Renal Pyramids
- Cone-shaped, striated kidney areas
- Inverted pyramid shape
- Striations = nephron loops, CDs & papillary ducts; converge on a minor renal calyx
- Several Minor Calyces -> a Major Calyx -> Renal Pelvis -> Ureter -> Urinary Bladder
Renal Columns
Cortex between renal pyramids
Renal Papilla
Apex of renal pyramid
Renal Lobe
Renal pyramid + overlying cortex + 1/2 of two adjacent renal columns
Overview of Renal “Plumbing”
- 1 mil. nephrons/kidney
- 10 nephrons/collecting duct
- 100k collecting ducts/kidney
- 250 collecting ducts/papillary duct
- 30 papillary ducts/renal papilla
Nephrons’ Blood Supply
Aorta -> R & L Renal Artery -> Segmental arteries -> Interlobar arteries -> Arcuate arteries -> Cortical Radiate arteries -> Afferent Arteriole -> Glomerulus -> Efferent Arteriole -> Peritubular Capillary network (including vasa recta) -> Cortical Radiate veins -> Arculate veins -> Interlobar veins -> Segmental veins -> R & L Renal Vein -> Inferior Vena Cava
3 Processes of Urine Formation
- Glomerular Filtration (F)
- Tubular Reabsorption (R)
- Tubular Secretion (S)
Rate of Urinary Excretion of a Solute
Filtration Rate + Secretion Rate - Reabsorption Rate
Glomerular Filtration
- Hydrostatic pressure causes small water-soluble molecules move into Bowman’s space -> glomerular filtrate
- Blood cells & most plasma proteins usually excluded from glomerular filtrate by the 3 part filtration membrane
- Daily volume of glomerular filtrate = 150 - 180 L
- Urine volume/day = 1-2 L
Filtration Fraction
- Percentage of plasma volume entering afferent arteriole that becomes glomerular filtrate
- Normal: 16 -20%
- FF Increased in glomerulonephritis
Determinants of Net Filtration Pressure (NFP)
- Glomerular Blood Hydrostatic Pressure (GBHP)
- Capsular Hydrostatic Pressure (CHP)
- Blood Colloidal Osmotic PRessure (BCOP)
Equation of NFP
NFP = GBHP - CHP - BCOP
*Normally, GBHP = 55mmHg, CHP = 15mmHg, BCOP = 30 mmHg; NFP = 10 mmHg
Glomerular Filtration Rate
- Total volume of filtrate produced by renal corpuscles of the two kidneys in one minute
- Approx. 125 mL/min (males)
- Approx. 105 mL/min (females)
- To maintain homeostasis, GFR should remain fairly constant over a wide range of arterial pressures
- If too fast, essential solutes lost in urine
- If too slow, excess solutes & wastes reabsorbed into blood
NFP Changes
- Lead to changes in glomerular filtration rate (GFR)
- Glomerulonephritis -> Decreased BCOP -> Increased NFP -> Increased GFR
- Hemorrhage/shock -> Decreased BP -> Decreased GBHP -> Decreased NFP -> Decreased GFR
- Nephrolithiasis -> Increased CHP -> Decreased NFP -> Decreased GFR
3 Methods of GFR Regulation
- Renal Autoregulation
- Hormonal Regulation
- Neural Regulation
Renal Autoregulation
-Ability of kidneys to maintain a constant BP & GFR despite changes in systemic blood pressure
2 Mechanisms of Renal Autoregulation
- Myogenic Mechanism
2. Tubulo-glomerular Feedback Mechanism
Myogenic Mechanism
Increased BP -> Increased renal blood flow & glomerular blood flow -> Increased GFR & Afferent arteriole stretch -> VC -> Decreased GBF & RBF -> Decreased GFR
Tubulo-glomerular Feedback Mechanism
Decreased BP -> Decreased NFP & GFR -> Decreased tubular flow rate -> PCT & Loop of Henle reabsorb more salt & H2O -> Decreased [Na+] in fluid seen by macula densa of JGA -> Increased NO release -> Vasodilation -> Increased glomerular blood flow -> Increased NFP & GFR -> Increased [Na+]
2 Hormones for Hormonal GFR Regulation
- Angiotensin 2
2. Atrial Natriuretic Peptide
Angiotensin 2
Goes to afferent arteriole VC -> Decreased renal blood flow & glomerular blood flow -> Decreased GFR -> Decreased tubular flow rate -> Increased salt & H2O reabsorption in PCT & nephron loop -> Increased blood pressure
Atrial Natriuretic Peptide (GFR Regulation)
Cause increased blood volume -> Increased atrial wall stretch -> ANP release -> Relaxation of mesangial cells -> Increased glomerular surface area -> Increased GFR (salt & H2O excretion -> Decreased blood volume)
Neural Regulation of GFR
- In fight/flight, sympathetic VC fibers -> decreased glomerular blood flow & decreased GFR
- Leads to decreased urine output & increased blood to muscles, heart & brain
- Also, decreased GFR -> Decreased tubular flow rate -> PCT & nephron loop reabsorb more salt & H2O -> Increased salt & H2O in blood -> Increased BP
Tubular Reabsorption
- To maintain homeostasis, H2O, nutrients, ions, etc must be selectively reabsorbed from urinary filtrate to blood
- Occurs mostly in PCT
- Active or passive transport
- 2 reabsorption routes: transcellular & paracellular
- PCT cells: lumenal microvilli & many mitochondria
Transport Maximum
Maximum amount of substance reabsorbed per unit time
*Example: Glycosuria in diabetes mellitus -> Osmotic diuresis -> Polyuria
Obligatory H2O Reabsorption
When H2O follows reabsorbed solutes, primarily glucose & Na+ due to osmotic gradients that are created between the filtrate and the ICF of the renal tubular cells
Facultative H2O Reabsorption
When the permeability of the DCT and CD cells to H2O is directly controlled by ADH
Tubular Secretion
Process that adds non-filtered wastes to tubular fluid (e.g. ions, toxins drugs, nitrogenous wastes)
PCT (Reabsorption & Secretion)
- “Early” PCT sites use Na+ symporters
- Na+/H+ antiporters are also used
- HCO3- ions are reabsorbed
- H2O reabsorption in “early” PCT -> reabsorption of ions & urea in “late” PCT
- Urea & NH3 are nitrogenous wastes that are reabsorbed
Aquaporin-1
- Water pores
- Found in the PCT
Nephron Loop (Reabsorption & Secretion)
- Fluid is still isotonic
- Thin descending limb of nephron loop is permeable to H2O but impermeable to solute
- Thin & thick ascending limbs are impermeable to H2O but permeable to solute
- Different sites for electrolyte & H2O reabsorption -> independent regulation of urinary volume & urinary osmolarity
- TAL has a Na+/K+/2Cl- symporter
- K+ leaks back into tubular lumen -> interstitial fluid becomes negatively charged, attracting Na+, K+, Ca+2, Mg+2 from the lumen into the interstitial fluid
- Since TAL is H2O impermeable, electrolyte reabsorption -> fluid osmolarity drops
“Early DCT” (Reabsorption & Secretion)
- Na+/Cl- symporters found in early DCT
- Also site of PTH-stimulated Ca+2 reabsorption
“Late DCT” (Reabsorption & Secretion)
2 Cell Types for Reabsorption & Secretion:
- Aldosterone-sensitive Principal Cells
- Intercalated Cells
Aldosterone-sensitive Principal Cells (Reabsorption & Secretion)
- Unequally “exchange” Na+ for K+
- This mechanism = apical membrane Na+ & K+ leak channels
- Main mechanism for eliminating excess K+ ions
- ADH-sensitivity -> Increased H2O reabsorption
Intercalated Cells (Reabsorption & Secretion)
Reabsorb K+ & HCO3- and secrete H+
2 Tests for Evaluating Kidney Function
- Urinalysis
2. Blood Tests
Urinalysis
Tests used to analyze urine composition
3 Factors Analyzed in Blood Tests
- Blood Urea Nitrogen (BUN)
- Plasma Creatinine
- Renal Plasma Clearance
Blood Urea Nitrogen (BUN)
Increased levels of BUN is a diagnosis for certain kidney diseases
Plasma Creatinine
- Breakdown of skeletal muscle creatine phosphate
- If creatine rises . 1.5 mg/dL -> Poor renal function
Renal Plasma Clearance
- Reflects ability of kidneys to remove a specific substance from blood
- Renal plasma clearance affected by filtration, reabsorption & secretion
- Normal renal plasma clearance of glucose = 0mL/min
- Renal plasma clearance of urea = 70mL/min
- Renal plasma clearance of a filtered substance (which is not reabsorbed/secreted) approximates the GFR
- Renal plasma clearance of creatinine = 120-140mL/min
- Renal plasma clearance of insulin = 125 mL/min
Equation for Renal Plasma Clearance
- U = Urinary concentration of a substance (mg/mL)
- P = Plasma concentration of a substance (mg/mL)
- V = Urine flow rate (mL/min)
- U x V / P (in mL/min)
Mechanisms for Control of Rena H2O Excretion
- 90% obligatory H2O reabsorption (linked to solute reabsorption)
- 10% facultative H2O reabsorption (ADH-regulated in CT & CD)
Counter-current Mechanism
- Required to excrete very hypertonic urine
- Fluid flows in parallel tubes in opposite directions
- Exchange of H2O & solutes between tubes & slow flow rate (both have similar compositions)
- Seen in vasa recta
- Occurs due to juxtamedullary nephrons & vasa recta
- This mechanism -> kidneys able to excrete iso-osmolar, hypo-osmolar, hyper-osmolar urine
2 Components of Counter-current Mechanism
- Counter-current Multiplier
2. Counter-current Exchanger
Counter-current Multiplier (CCM)
=Ascending & descending limbs of nephron loops of J-M nephrons
- Thich Ascending Limb = impermeable to H2O, actively transports NaCl via lumenal Na+/K+/2Cl- co-porter
- Descending Limb = H2O permeable & solute impermeable
Physiology of CCM (7 Steps)
- Na+ & Cl- pumped out of TAL into peritubular fluid
- Osmolarity of peritubular fluid increases near descending limb
- H2O flows from descending limb to peritubular fluid
- Increased [solute] in descending limb
- Very concentrated solution accumulates in ascending limb -> Increased NaCL transport into peritubular fluid (medullary concentration gradient: 300-1,200 mOsmol/L)
- Urea recycling in deep medulla reinforces salt gradient
- Hypotonic fluid arrives at DCT
Counter-current Exchanger
- Vasa recta = capillaries running parallel w/ nephron loops of J-M nephrons
- Vasa recta maintain medullary concentration gradient while delivering nutrient blood supply
- Vasa recta has very slow blood flow + freely permeable to H2O & salt; leads to complete equilibrium between blood & interstitial fluid
- As blood flows into inner medulla, H2O lost & salt gained
- As blood flows back toward the cortex, H2O gained & salt lost
- Removal of solutes & H2O by vasa recta balances rates of solute & H2O reabsorption by tubule; leads to medullary concentration gradient protected & reabsorbed H2O/solutes returned to general circulation
2 Benefits of the CCM
- Method for reabsorbing solutes/H2O before the fluid reaches CT & CD
- Concentration gradient in medulla allow ADH-dependent H2O reabsorption from CT & CD
ADH & H2O Reabsorption
- ADH -> Increased CT & CD permeability to H2O (due to insertion of aquaporin-2)
- H2O uptake is osmotically-driven through these H2O channels, and would not occur w/o the presence of salt gradient set up in the medullary intestitium by the CCM
- If blood osmotic pressure increases -> ADH release by posterior pituitary
- If blood osmotic pressure decreases -> No ADH released -> diuresis (increased urine output)
Diabetes Insipidus
Diabetes caused by lack of ADH, causing polyuria, leading to excessive H2O loss
5 Drugs Affecting H2O Balance
- Ethanol: Inhibits ADH secretion -> diuresis
- Caffeine: Inhibits Na+ reabsorption by renal tubule
- Furosemide: Blocks Na+/K+/2Cl- co-porter of TAL
- Thiazides: Block Na+/Cl- symporter in DCT
- IV mannitol: Blocks PCT Na+ uptake
* Diuretic drugs = hypertensive; lead to increased urine, decreased blood volume & pressure
4 Hormonal Regulators of Reabsorption & Secretion
- ADH (Covered in ADH & Reabsorption)
- Renin-Angiotensin-Aldosterone System
- Atrial Natriuretic Peptide
- Parathyroid Hormone
Renin-Angiotensin-Aldosterone (RAA) System (4 Steps)
- Release of renin by JGA
- Renin converts Angiotensinogen -> Angiotensin I
- Angiotensin Converting Enzyme (ACE) converts Angiontensin I -> Angiotensin II
- Vasoconstriction, increased Na+ reabsorption + increased aldosterone release by adrenal cortex
* Activated by hemorrhaging, Na+ deficiency, or dehydration
* System works to increase BP back to normal levels
* Hypertension may result if mechanism defective -> continual stimulation of RAA system
Aldosterone & Kidneys
- Aldosterone = adrenal cortex hormone (mineralocorticoid)
- Function Na+ & K+ homeostasis
- Mechanism: Principal cells of the CT & CD reabsorb Na+ & secrete K+ due to aldosterone-inducible insertion of channels & pumps)
- Since [Na+] > [K+] -> lumenal negative potential -> H+ pumping by intercalated cells of CT & CD to re-establish charge balance
- Mechanism produces what looks like Na+ for K+ or H+ exchange
- Leads to increased blood Na+, increased Cl- & H2O reabsorption & increased blood volume & pressure
Atrial Natriuretic Peptide (Reabsorption & Secretion)
- Increased blood volume -> atrial release of ANP -> decreased blood volume via:
1. ANP -> mesangial cell relaxation -> increased glomerular capillary surface available for pressure filtration -> increased GFR
2. Inhibition of PCT & CD Na+ H2O reabsorption
3. Inhibition of aldosterone & ADH Secretion
Parathyroid Hormone (PTH)
- Decreased blood Ca+2 levels -> PTH release -> increased reabsorption of Ca+2 in DCT
- PTH inhibits phosphate reabsorption in PCT
3 Processes of Blood pH Regulation
- H+ secretion
- HCO3- reabsorption
- HCO3- secretion
- Acidic blood -> 1 & 2 increases + 3 decreases
- Basic blood -> 1 & 2 decreases + 3 increases
Kidney Dialysis
Treatment of temporary or permanent renal failure
2 Types of Kidney Dialysis
- Hemodialysis
2. Peritoneal Dialysis
Hemodialysis
- Patient’s heparinized blood is passed through a semipermeable membranous tube in contact w/ dialysate
- Substances in high concentration in blood move into the dialysate
- 50-250 g urea can be removed by 4-6 hour dialysis treatment
- Done 2-3 times/week
6 Drawbacks of Hemodialysis
- Anticoagulant use
- Hemolysis
- Infection risk & possible septicemia
- Restriction of dietary fluid & protein
- Time consuming
- Loss of nutrients, hormones, etc.
Peritoneal Dialysis
- Dialysis fluid is run into peritoneal cavity
- Peritoneal membranes = dialysis membrane
- 4-5 exchanges/day (each exchange = 4=6 hours)
- Drawback: peritonitis
Ureters
- Retroperitoneal tubes from kidneys -> urinary bladder
- Function: Transport urine from kidney to bladder via peristaltic contractions
3 Layers of the Ureters
- Mucosa: Transitional epithelium + goblet cells + lamina propria
- Muscularis: Smooth muscle (inner longitudinal + outer circular); causes peristalsis
- Adventitia: Fibrous outer coat
Vesico-uretal Sphincters
- Long intra-mural segment = a good valve; as bladder fills, ureter compressed closed
- Short intra-mural segment = a poor valve
- If sphincter defective, ascending infection -> Pyelonephritis (inflammation of kidney tissue, calyces and renal pelvis)
Urinary Bladder
- Distensible muscular sac behind pubis symphysis
- Function: store urine until micturition
- 2 inlets (ureters) & 1 outlet (internal urethral orifice) -> trigone
3 Tunics/Coats of Bladder Wall
- Mucosa: Made of transitional epithelium (changes as stored urine volume increases); has rugae (folds)
- Muscularis: Detrusor muscle contractions expel urine
- Adventitia: Has serosa = visceral peritoneum, covering top of bladder
Cystoscopy
=Endoscopic exam of urethra & bladder
- Assesses cancer & infection (biopsy of abnormal tissue)
- Removes calculi in urolithiasis
- Evaluates obstruction due to benign prostatic hyperplasia
Urinary Retention
Failure to void completely -> stasis -> possible cystitis & possible pyelonephritis
Bladder Atony
A large, dilated & non-emptying urinary bladder
Urinary Incontinence
Lack of voluntary control over micturition
Micturition
=Urination
- Result of relaxation of internal urethral sphincter (involuntary) & external urethral sphincter (voluntary)
- Also involves detrusor muscle contraction
5 Types of Urinary Incontinence
- Stress: Represents weak control of external urethral sphincter
- Overflow: Continuous dribble of urine released from overly full bladder
- Urgency: Failure to restrain urine discharge
- Functional: Person recognizes the need to urinate but is unable to get to the toilet
- Total: Return to pre-potty training state
Urethra
Tube from urinary bladder to external urethral orifice
Gender Differences Between Male & Female Urethra
- Female: External urethral orifice between clitoris & vagina
- Male: External urethral orifice opens at tip of glans penis
3 Segments of Male Urethra
- Prostatic Urethra
- Intermediate Urethra
- Spongy Urethra; passes through penis within the corpus spongiosum
Histology of the Urethra
- Mucosa; consists of:
- transitional epithelium
- stratified/pseudostratified columnar epith.
- non-keratinized stratified squamous epith. - Muscularis
- Inner layer = circular
- Outer layer = longitudinal - Adventitia
- Made of areolar CT
