Urinary System Flashcards
components of the Urinary System
– Kidneys
– Urinary Tract
* Ureters
* Urinary Bladder
* Urethra
Functions of the Urinary System
- Excretion by the Kidneys:
– removal of organic wastes from body fluids - Elimination by the Urinary Tract:
– discharge of waste products - Homeostatic regulation of plasma volume and solute
concentrations by the kidneys:
– Blood volume, BP
– Concentration of ions
– Stabilize blood pH
– Conserve nutrients
– Assist liver: deamination, detoxification - Other kidney functions:
– Gluconeogenesis during starvation
– Produce renin to regulate BP
– Produce erythropoietin for RBC production
– Convert Vitamin D to calcitriol for calcium absorption in the GI tract
Kidneys
- 1% body weight
- Retroperitoneal, posterior abdominal wall
- Adrenal gland anchored superior
3 layers CT anchor kidneys
- Renal capsule:
- collagen fibers covering organ - Adipose capsule:
- adipose cushion around the renal capsule - Renal fascia:
- collagen fibers fused to renal capsule and deep
fascia of body wall and peritoneum
Renal ptosis
floating kidney
– Cause → Starvation or injury
– Result → Kidney becomes loose from body wall
* Kidney could twist blood vessels or ureters
Hilum
– Point of entry for renal artery and renal nerves
– Ureters enter and exit
* Hilum opens to renal sinus
* Renal sinus lined with renal capsule that is contiguous with outside
Kidney has two layers
cortex and medulla
cortex
superficial
* Contact renal capsule
* Houses filtration structures = nephrons
medulla
6-18 renal pyramids
* Parallel bundles of collection tubules
* Apex = papilla, points toward renal sinus
kidney divided into sections
renal lobes
– renal pyramid + surrounding cortex called renal columns
– Lobe is site for urine production
renal sinus
- Internal cavity within kidney
- Lined by fibrous renal capsule
– Bound to outer surfaces of structures in renal sinus
– Stabilizes positions of ureter, renal blood vessels, and nerves
renal papilla
Ducts discharge urine into minor calyx, a cup-shaped drain
major calyx
Formed by four or five minor calyces
renal pelvis
– Fills majority of renal sinus
– Funnels urine into ureters
Nephron
– Microscopic, tubular structures in cortex of each
renal lobe
– Where urine production begins
Pyelonephritis
– Inflammation of kidney
– Infection usually enters from ureter and spreads up
through ducts to nephron
Two important capillary beds associated with each
nephron
- Glomerulus capillary:
- filtration - Peritubular capillaries:
- reclaim filtrate, concentrate urine
* Both connected to arterioles only (not for oxygen
exchange)
* Afferent arteriole → capillary → efferent arteriole
Blood Supply and Innervation to Kidney
- Receives 20-25% cardiac output
- Highly vascularized, many capillaries involved in
filtration (nephrons) - Innervation from Renal Plexus controlled by ANS
- Most is sympathetic to
1. Adjust rate of urine formation - Change blood pressure (BP) and flow at nephron
2. Stimulate release of renin - Restricts water and sodium loss at nephron
The Nephron
Consists of renal corpuscle and renal tubule
Renal corpuscle
- Spherical structure consisting of:
– Glomerular capsule (Bowman’s capsule)
– Cup-shaped chamber
– Capillary network (glomerulus)
Renal tubule
- Long tubular passageway
- Begins at renal corpuscle
collecting system
- A series of tubes that carries tubular fluid away
from nephron
Each nephron empties into it
collecting ducts
- Receive fluid from many nephrons
- Each collecting duct:
– Begins in cortex
– Descends into medulla
– Carries fluid to papillary duct that drains into a
minor calyx
Two types of nephrons
Cortical nephron
Juxtamedullary nephrons
Cortical nephron
Majority
* In cortex, short loop of Henle
Juxtamedullary nephrons
15%
* At cortex/medulla interface
* Long loops of Henle
* Important for water conservation and urine
concentration
Renal Corpuscle
- Site of filtration
- 2 parts- glomerular capsule, glomerulus
glomerular capsule
Thin parietal epithelium, forms capsule around
glomerulus
Glomerulus structure
- Fenestrated capillaries covered by podocytes
- Podocytes are on the visceral epithelium
– Wrapped around the capillaries, to create filtration
slits on surface of capillaries
– Slits smaller than fenestrations in glomerular
capillaries to restrict filtration of large molecules
Glomerulus
- Consists of about 50 intertwining capillaries
- Blood delivered via afferent arteriole
- Blood leaves in efferent arteriole:
– flows into peritubular capillaries
– which drain into small venules
– and return blood to venous system
Golmerulonephritis
– Inflammation of glomeruli
– Prevents filtration
– Can be result of antigen/Ab complexes
trapped in filtration slits following allergy or
blood infection
renal tubule
- Reabsorption to process raw filtrate into urine
- 3 parts- PCT, loop of Henle, DCT
PCT (proximal convoluted tubules)
- Simple cuboidal epithelium with microvilli
- Reabsorbs organic nutrients, ions, water, small plasma
proteins from filtrate exiting glomerular capsule
Loop of Henle
- Simple squamous epithelium
- Reabsorbs Na+, Cl-, H2O form filtrate
- Important to regulate volume and solute concentration
of urine - Descending and ascending limbs
DCT (distal convoluted tubules)
- Simple cuboidal epithelium
- Flat surface
- Four important functions
1. Secretion
2. Reabsorb Na+ and Ca++ from filtrate
3. Optional H2O reabsorption from filtrate under
hormonal control
4. Contribute to formation of Juxtaglomerular
Apparatus
Juxtaglomerular Apparatus (JGA) consists of two cell types
- Endocrine cells of DCT = macula densa
- Granular cells of afferent arteriole =
Juxtaglomerular cells
Together cells in JGA monitor blood and produce
- Renin: Enzyme, restricts Na+ and H2O at nephron
- Erythropoietin: hormone, stimulates RBC
production
The Collecting System
The distal convoluted tubule opens into the collecting
system
– Individual nephrons drain into a nearby collecting duct
– Several collecting ducts:
* Converge into a larger papillary duct
* Which empties into a minor calyx; major calyx
– Transports tubular fluid from nephron to renal pelvis
– Adjusts fluid composition
– Determines final osmotic concentration and volume of urine
Polycystic Kidney Disease
Genetic, cysts form that cause swelling of kidney tubules, compression reduces function
Urine Transport, Storage, and Elimination
Take place in the urinary tract
* Ureters
* Urinary bladder
* Urethra
Structures involved in Urine Transport, Storage, and Elimination
Minor and major calyces, renal pelvis, ureters,
urinary bladder, and proximal portion of
urethra
* Are lined by transitional epithelium
* That undergoes cycles of distention and contraction
Ureters
– Connect renal pelvis to urinary bladder
– Wall layers
1. Inner mucosa
– Transitional epithelium and lamina propria
2. Middle muscular layer
– Longitudinal and circular bands of smooth muscle
3. Outer connective tissue layer
– Continuous with fibrous renal capsule and peritoneum
– Contractions occur every 30 sec to force urine toward
bladder
Urinary Bladder
– Wall folded into rugae when empty – allows expantion
– Wall layers
* Mucosa with transitional epithelium
* Muscularis layer with 3 layers of smooth muscle =
detrusor muscle
1. Contraction causes expulsion of urine from bladder
2. Detrusor muscle thickened around urethral opening to
create the internal urethral sphincter
» Provides involuntary control over release of urine
* Adventitia = Fibrous, Anchors bladder to pelvic
floor
Urethra
– Single tube, connects bladder to environment
– Lined with pseudostratified columnar epithelium
– Passes through band of skeletal muscle that forms
external urethral sphincter
* under voluntary control
* relaxation results in urination (micturition)
Kidneys help regulate:
– blood volume and pressure
– ion levels
– blood pH
Nephrons are
primary functional units of
kidneys
Urinary System Function
Is to produce urine
The Goal of urine production
Is to maintain homeostasis
* By regulating volume and composition of blood
* Including excretion of metabolic waste product
The Phases of urine production
Filtrate production - everything in blood plasma except large proteins and cells
Urine production - metabolic waste, 1% filtrate
Common Wastes
- Urea: from catabolism of amino acids
- Creatinine: from catabolism or damage of skeletal muscle
tissue
– Creatine phosphate is energy storage of muscle - Uric acid: from recycling of nucleic acids
- Urobilin: from breakdown of hemoglobin (yellow color)
Waste excretion
- All wastes excreted as solution in water
- Loss of filtering → toxic waste buildup
– death in a few days - Dialysis → blood filtering machine used for patients with
kidney failure
Waste Excretion carried out by four body systems
– Respiratory system—CO2, small amounts of other
gases, and water
– Integumentary system—water, inorganic salts,
lactate, and urea in sweat
– Digestive system—water, salts, CO2, lipids, bile
pigments, cholesterol, and other metabolic waste
– Urinary system—many metabolic wastes, toxins,
drugs, hormones, salts,+
H , and water
Urine Formation
- Glomerular Filtrations
– Blood hydrostatic pressure forces water and
solutes through glomerular wall - Tubular Reabsorption
– Selective uptake of water and solutes from filtrate - Tubular Secretion
– Transport of wastes from capillaries to tubules - Water conservation
– Urine concentration
Glomerular Filtration
Occurs through filtration
membrane
1. Fenestrated endothelium of
glomerular capillaries
- Restricts cells
2. Podocytes (visceral
epithelium of capsule)
- Filtration slits restrict solutes
protein sized and larger
3. Fused basal lamina for both
Filtration is passive but
all small solutes escape
e.g. glucose, amino
acids, etc.
Filtrations depends on:
- Large surface area
- High glomerular blood pressure
- Good permeability
Glomerular Filtration Rate (GFR)
– Amount of filtrate kidneys produce/minute
– ~125 ml/min → ~50gallons (180L)/day
– 99% reabsorbed, 1% lost as urine
Filtration Pressure
– Glomerular filtration rate depends on filtration
pressure
– Any factor that alters filtration pressure alters
GFR
–Drop in blood pressure = decrease GFR
* Decrease 15% BP = 0 GFR
Net Filtration Pressure (NFP)
– Is the average pressure forcing water and
dissolved materials:
* Out of glomerular capillaries
* Into capsular spaces
At the glomerulus, NFP is the difference between
- Hydrostatic pressure and blood colloid osmotic
pressure across glomerular capillaries
Regulation of Filtrations
3 Levels of GFR Control
- Autoregulation (local level)
- Neural regulation (by sympathetic division of
ANS) - Hormonal regulation (initiated by kidneys)
Autoregulation of GFR
Functions to maintain constant GFR with normal blood
pressure fluctuations in systemic arteriole pressure
- Reduced blood flow/BP triggers
- High blood flow/BP triggers
Reduced blood flow/BP triggers
- Dilation of afferent arteriole and glomerular capillaries
- Constriction of efferent arteriole
- All functions to INCREASE PRESSURE at the glomerulus to
INCREASE GFR
High blood flow/BP triggers
- Constriction of afferent arteriole and glomerular capillaries
- Dilation of efferent arteriole
- All functions to DECREASE PRESSURE at the glomerulus to
DECREASE GFR
Autonomic Nervous System
Regulation
Sympathetic nervous system causes
* Vasoconstriction of afferent arterioles
– Decrease GFR
– Decrease Urine Production
– Prolonged sympathetic stimulation can cause hypoxia
of kidneys and waste accumulation in blood
* Hormonal release
Hormonal Regulation
Extrinsic regulation aimed at maintaining systemic blood
pressure
A. Renin = Enzyme released by juxtaglomerular
apparatus in response to:
1. Decline in BP in kidney
2. Decline in osmotic concentration of filtrate
3. Direct sympathetic stimulation
B. Naturietic Peptide
Renin
- Renin act upon angiotensinogen in blood to form
Angiotensin II which triggers:
1. Arteriole constriction to elevate BP
2. Secretion of aldosterone from adrenal glands
» Aldosterone promotes sodium reabsorption in
kidney tubules
3. Stimulates thirst
4. Release of ADH from pituitary (ADH promotes water
uptake in tubules) - Effect =
– Increase blood volume
– Decrease urine production
Natriuretic Peptide
- Hormone released in response to stretching in heart or
aorta (increase blood volume) - Triggers
1. Dilation of afferent arteriole
2. Constriction of efferent arteriole - Effect =
– Increase GFR
– Increase Urine Production
– Decrease blood volume
Reabsorption and Secretion
Occur in every segment of nephron except
renal corpuscle
Reabsorption
recovers useful materials from filtrate
Secretion
ejects waste products, toxins, and other
undesirable solutes
At the kidneys, reabsorption and secretion involves:
- Diffusion
- Osmosis
- Channel-mediated diffusion
- Carrier-mediated transport
» Facilitated diffusion
» Active transport
» Cotransport
» Countertransport
PCT reabsorption
– PCT reabsorbs 60-70% of filtrate
1. Reabsorption of 99% of organic nutrients by
facilitated diffusion and cotransport
2. Passive reabsorption of ions by diffusion
3. Selective reabsorption of ions by active transport
- Ion pumps controlled by hormones
4. Reabsorption of water by osmosis
- Water follows ions
Tubular reabsorption of nitrogenous wastes
–Urea passes through epithelium with water
–Uric acid is reabsorbed, but later portions of the nephron secrete it
–Creatinine is not reabsorbed—it is passed in urine
Transport maximum (Tm)
maximum rate of reabsorption
for a solute, which is reached when all transport proteins
are saturated
Concentration higher than transport maximum
- Exceeds reabsorptive abilities of nephron
- Some material will remain in the tubular fluid and appear in the urine
Renal threshold
Is the plasma concentration at which a specific compound or ion begins to appear in urine
Glycosuria
glucose in urine
* Glucose levels in blood/filtrate exceed renal threshold
Aminoaciduria
amino acids in urine
* an abnormal amount of amino acids in the urine
Loop of Henle reabsorption
– Functions to concentrate filtrate
– Reabsorbs 1/2 remaining water and 2/3 Na+ and Cl- by
countercurrent multiplications
* Ascending limb pumps ions from filtrate to medulla
* High ion concentration then causes water to move by
osmosis out of descending limb
Countercurrent Multiplier
- Is mechanism by which the nephron loop continually
recaptures salt and returns it to medulla - Is exchange that occurs between 2 parallel segments of loop
of Henle:
– the thin, descending limb
– the thick, ascending limb
Countercurrent
Refers to exchange between tubular fluids
moving in opposite directions:
– fluid in descending limb flows toward renal pelvis
– fluid in ascending limb flows toward cortex
Multiplier
Refers to effect of exchange:
– increases as movement of fluid continues
Benefits of Countercurrent Multiplication
- Efficiently reabsorbs solutes and water:
– before tubular fluid reaches DCT and collecting
system - Establishes concentration gradient:
– that permits passive reabsorption of water from
tubular fluid in collecting system
DCT reabsorption
DCT and collecting duct reabsorb variable amounts of water and
salt and are regulated by several hormones
– Aldosterone promotes Na+ uptake back and K+ loss in the
urine via sodium potassium pump
– Parathyroid hormone and calcitriol promote Ca++ uptake
– ADH stimulates water uptake
– Natriuretic peptides are secreted by heart in response to high blood pressure - result in the excretion of more salt
and water in the urine
Tubular Secretion
Selectively removes solutes from blood → delivers them to
filtrate
1. Dispose of drugs and wastes that were not filtered
2. Eliminate wastes that were reabsorbed
3. Rid body of excess K+
4. Control blood pH: Remove H+
* CO2 + H2O <–> H2CO3 <–> H+ + HCO3-
**Bicarbonate ions used to buffer blood pH but H+ must
be secreted into filtrate
The collecting duct (CD) can produce a hypertonic urine
- CD runs through medulla, and reabsorbs water,
making urine up to 4 times more concentrated - Medullary portion of CD is more permeable to
water than to NaCl - As urine passes through the increasingly salty
medulla, water leaves by osmosis, concentrating
urine
Reabsorption involves
diffusion, osmosis, channel-
mediated diffusion, and active transport
Many processes are independently regulated by
local or
hormonal mechanisms
The primary mechanism governing water reabsorption is
“water follows salt”
Secretion is
a selective, carrier mediated process
water conservation
– Obligatory water reabsorption occurs by osmosis in PCT
and descending loop of Henle
* Cannot be prevented
– Facultative water reabsorption can occur in DCT and
collecting ducts
* ADH causes formation of water channels by triggering
insertion of aquaporin proteins in cell membrane of
DCT and collecting ducts
* Aquaporins allow more osmosis to concentrate urine
and conserve water
control of water volume
- Diuretics = Substance that cause water loss
- Diabetes insipidus = not enough ADH
* Produce large quantities of dilute urine
* Up to 24 L/day, normal = 1.2 L/day - Anuria = low urinary output
* Less than 150 ml/day
* Usually due to events that block filtration
– Nephritis
– Immune reactions
– Severe injuries
Electrolyte Balance
amount of electrolytes absorbed by small intestine balances the amount lost from the
body (urine)
Physiological importance of electrolytes
- Chemically reactive and participate in metabolism
- Determine electrical potential (charge difference)
across cell membranes - Strongly affect osmolarity of body fluids
- Affect body’s water content and distribution
- Major cations: Na+, K+, Ca++, Mg++, and H+
- Major anions: Cl-, HCO3- (bicarbonate), and PO3-4
differences between electrolyte
concentrations of blood plasma or extracellular fluid
(ECF) and intracellular fluid (ICF)
- But overall, have the same osmolarity (300 mOsm/L)
- Plasma is representative of ECF, as concentrations
between plasma and tissue fluid differ only slightly
Major cations
sodium, potassium, calcium, magnesium
Both - Sodium-potassium pump
major anions
chloride and phosphates
Sodium
– Principal cation in ECF
– Most significant solute in determining total body water and
distribution of water among fluid compartments
– Important for electrical signaling in nerve and muscle cells
– Regulation by aldosterone, ADH, Natriuretic peptides
Potassium
– Most abundant cation of ICF
– Electrical signaling in nerve and muscle cells
– Essential cofactor for protein synthesis and other processes
– Aldosterone stimulates renal secretion of K+
Calcium
– Lends strength to skeleton
– Muscle contraction
– Second messenger for some hormones and
neurotransmitters
– Activates exocytosis
– Essential factor in blood clotting
– Reabsorption regulated by PTH, calcitriol (vitamin D)
Magnesium
– About 54% in bone and about 45% in intracellular fluid
– Intracellular Mg2+ is complexed with ATP
– Serves as a cofactor for enzymes, transporters
– PTH governs the rate of reabsorption
Chloride
– Most abundant anion in ECF
– Major contribution to ECF osmolarity
– Required for the formation of stomach acid (HCl)
– Major role in regulating body pH
– Chloride shift that accompanies CO2 loading and unloading
in RBCs
– Regulation - chloride passively follows Na+, K+ and CA++
Phosphates
– Relatively concentrated in ICF due to hydrolysis
– Every process that depends on ATP depends on phosphate
ions
– Part of some buffers that stabilize the pH of body fluids
Acid-base balance
state in which the pH of the body fluids is
maintained within normal homeostatic limits (7.35 to 7.45)
The pH of a solution is determined by its hydrogen ions (H+)
An acid is any chemical that releases H+
Buffer systems
are mixtures composed of weak acids and weak
bases
Physiological buffer
system that stabilizes pH by controlling
the body’s output of acids, bases, or CO2
- bicarbonate
- phosphate
- protein systems
CO2 + H2) <-> H2CO3- <-> HCO3- + H+
H2PO4- <-> HPO42- + H+
Urinalysis
examination of physical and
chemical properties of urine
– an important diagnostic tool
Renal clearance
the volume of blood plasma
from which a particular waste is completely
removed in one minute
Measuring glomerular filtration rate (GFR)
to assess kidney disease
Urine composition and properties:
- Appearance
– Varies from clear to deep amber depending on state of hydration - Odor
– Bacteria degrade urea to ammonia, some foods and diseases
impart particular aromas - Specific gravity—ratio of density of a substance to that of distilled
water - Osmolarity ranges from 50 mOsm/L in a hydrated person to 1,200
mOsm/L in dehydrated person - pH ranges from 4.5 to 8.2, usually 6.0 (mildly acidic)
- Chemical composition: 95% water, 5% solutes
- Normal volume for average adult—1 to 2 L/day
When bladder contains ~ 200ml urine
- Stretch receptors triggered
- Signal sent to the spinal cord
- Stimulates contraction of detrusor muscle and relaxation
of the internal urethral sphincter
Voluntary control of bladder
Voluntary maintenance of contracted external urethral
sphincter prevents urination until is time to urinate
1. The micturition center in the pons receives signals from
stretch receptors
2. signals from the pons cease, and external urethral
sphincter relaxes; urine is voided
If volume exceeds ~500 ml
Forced relaxation of internal and external urethral
sphincters will result in non-voluntary
urination/micturition
Incontinence
– Inability to voluntarily control urine excretion
– Due to:
* loss of muscle tone
* Damage to sphincters
* Damage to nerves or control centers in brain
Age Related Changes
- Decline in functional nephrons
- Reduction in GFR
– Damage or decrease blood flow - Reduced sensitivity to ADH = dilute urine
- Problems with micturition
– Incontinence
– Urinary retention, enlarged prostate
