Urinary System Functions€¦ · •Three processes are involved in urine formation and adjustment...
Transcript of Urinary System Functions€¦ · •Three processes are involved in urine formation and adjustment...
Urinary System Functions
• Major excretory pathway for wastes transported by blood
– Filtration, secretion, and reabsorption by the kidney’s microscopic tubules
– Includes wastes from metabolism, excess water and excess solutes, absorbed substances
• Collection, transport, exit of urine – product of kidney’s function
– Responsive to condition
– Role in maintenance of blood volume and pressure
• Urine release controlled by reflex actions
• Regulation of hemopoesis
Organs and Vessels of the Urinary System
Esophagus (cut)
Inferior vena cava
Adrenal gland
Hepatic veins (cut)
Renal artery
Renal hilum
Renal vein
Iliac crest
Kidney
Ureter
- peristalsis
Urinarybladder
Urethra
Aorta
Rectum (cut)
Uterus (part of femalereproductive system)
Figure 25.2 Dissection of urinary system organs (male).
Renal artery
Renal hilum
Renal vein
Kidney
Ureter
Urinarybladder
Figure 25.3a Position of the kidneys against the posterior body wall.
Inferior
vena cava
Aorta
Supportive
tissue layers
• Renal fascia
• Perirenal
fat capsule
• Fibrous
capsule
anterior
posteriorRenal
artery
Renal
vein
Peritoneum Peritoneal cavity
(organs removed)
Anterior
Posterior
Body of
vertebra L2
Body wall
Three layers of supportive tissue surround kidney
Renal fascia
outer layer of dense fibrous connective tissue
Perirenal fat capsule
Fatty cushion
Fibrous capsule
Transparent capsule
Kidney Function
Maintain the body’s internal environment by:
– Regulating total water volume and total solute concentration in water
– Regulating ion concentrations in ECF
– Ensuring long-term acid-base balance
– Excreting metabolic wastes, toxins, drugs
– Producing erythropoietin (EPO) and renin
– Activating vitamin D
– Carrying out gluconeogenesis, if needed
Figure 25.4 Internal anatomy of the kidney.
Renal cortex
Renal medulla
Major calyx
Papilla of pyramid
Renal pelvis
Ureter
Minor calyx
Renal column
Renal pyramid inrenal medulla
Fibrous capsule
Renalhilum
Photograph of right kidney, frontal section Diagrammatic view
Blood flow critical – 25% of each ejection enters kidney vessels. Kidneys monitor and facilitate • Favorable BP• Oxygen carrying ability
Figure 25.5a Blood vessels of the kidney.
Arcuate vein
Arcuate artery
Interlobar vein
Interlobar artery
Segmental arteries
Renal artery
Renal vein
Renal pelvis
Ureter
Renal medulla
Renal cortex
Cortical radiate
artery
Cortical radiate
vein
Frontal section illustrating major blood vessels
Cortical radiate arteries supply the glomerulus –location of blood filtration
Glomeruli and portions of nephrons are located in the renal cortex
About 8 lobes (pyramid & surrounding cortex) per kidney
11 cm x 6 cm x 3 cm150 g / 5 oz
Physiology of Kidney
• Values for Average Human
• 180 L of fluid processed daily, but only 1.5 L of urine is formed– Kidneys filter body’s entire plasma volume 60 times
each day
– “Filtrate” is basically blood plasma minus proteins
• Urine is produced from filtrate– Urine
• <1% of original filtrate
• Contains metabolic wastes and unneeded substances
• Kidneys consume 20–25% of oxygen used by body at rest
Nephrons and Nephron Structure
• Structural and functional units that form urine
• > 1 million per kidney
• Two main parts
– Renal corpuscle
• Glomerulus – “tuft” of capillaries and visceral layer
• Glomerular (or Bowman’s) capsule, parietal layer
– Renal tubules
• Including tubules, loop, and ducts
• Collecting ducts in the thousands, drain nephrons
Figure 25.6 Location and structure of nephrons.
Fenestratedendotheliumof the glomerulus
Apical microvilli
Cortex
Medulla
Podocyte
Basement membrane
Mitochondria
Apical side
Basolateral side
Highlyinfolded
basolateralmembrane
Proximal convolutedtubule
Distal convolutedtubule
Thick segment
Collectingduct
Intercalatedcell
Principal cell
Thin segment
Proximal convoluted tubule cells
Glomerular capsule: parietal layer
Glomerular capsule: visceral layer
Distal convoluted tubule cells
Nephron loop (thin-segment) cells
Collecting duct cells
Renal cortex
Renal medulla
Renal pelvis
Ureter
Kidney
Renal corpuscle
• Glomerular capsule
• Glomerulus
Nephron loop
• Descending limb
• Ascending limb
Terminates at renal papilla
His
tolo
gy o
f co
rpu
scle
an
d n
earb
y t
ub
ule
s Renal corpuscle
Distal convoluted
tubule (clear lumen)
Proximal convolutedtubule (fuzzy lumen due to long microvilli)
• Squamous epitheliumof parietal layer ofglomerular capsule
• Glomerular capsularspace
• Glomerulus
Figure 25.12a The filtration membrane.
Glomerular capillarycovered by podocytesthat form the visceral layerof glomerular capsule
Proximal convolutedtubule
Parietal layerof glomerular capsule
Afferentarteriole
Glomerular capsular space
Efferentarteriole
Filtration Membrane:• Fenestrated capillaries • Visceral layer glomerular capsule
with filtration slits• Produce solute rich, virtually
protein free filtrate
Figure 25.12b The filtration membrane.
Glomerular capillary endothelium (podocyte coveringand basementmembrane removed)
Fenestrations (pores)
Podocyte cell body
Foot processesof podocyte
Filtration slits
Cytoplasmic extensionsof podocytes
Glomerular capillary surrounded by podocytes
Figure 25.12d The filtration membrane.
Fenestration (pore)
Filtrate incapsular
space
Foot processes of podocyte
Filtration slit
Slit diaphragm
• Basement membrane
• Capillary endotheliumCapillary
• Foot processes of podocyte of glomerular capsule
Plasma
Filtration membrane
Three layers of the filtration membrane
Allows molecules smaller than 3 nm to pass: Water, glucose, amino acids, nitrogenous wastes, most solutes*Normally no cells can pass*
Plasma proteins remain in plasma to maintain colloid osmotic pressurePrevents loss of all water to capsular space*Proteins in filtrate indicate membrane problem*
Figure 25.10 Juxtaglomerular complex (JGC) of a nephron.
Glomerulus
Glomerular
capsule
Afferent
arteriole
Efferent
arteriole
Red blood cell
Podocyte cell body
(visceral layer)
Foot processes
of podocytes
Parietal layer
of glomerular
capsule
Proximal
tubule cell
Lumens of
glomerular
capillaries
Endothelial cell
of glomerular
capillary
Efferent arteriole
Afferent arteriole
Capsular
space
Renal corpuscleJuxtaglomerular complex
Glomerular mesangial
cells
Juxtaglomerular
complex
• Macula densa cells
of the ascending limb
of nephron loop
• Extraglomerular
mesangial cells
• Granular cells
Blood pressure in glomerulus high because:• Afferent arterioles are larger in
diameter than efferent arterioles• Arterioles are high-resistance vessels
Figure 25.9 Blood vessels of the renal cortex.
Afferentarteriole
Peritubularcapillary bed
Efferentarteriole
Glomerulus
Renal Tubules and Collecting Duct
Renal tubule is about 3 cm (1.2 in.) long
• Single layer of epithelial cells in 3 major parts1. Proximal convoluted tubule (closest to renal corpuscle)
• Cuboidal cells with dense “brush border” microvilli, confined to cortex
– high surface area to interact with filtrate
– large mitochondria to support active transport functions
• Functions in (significant) reabsorption and secretion
2. Nephron loop – formerly ‘loop of Henle’ –thick and thin limbs
3. Distal convoluted tubule• Farthest from renal corpuscle, confined to cortex
• Cuboidal cells with very few microvilli
• Function more in secretion than reabsorption
• drains into collecting duct
Cortex-medulla junction
Kidney
Cortical radiate vein
Cortical radiate artery
Afferent arteriole
Afferent arteriole
Collecting duct
Distal convoluted tubule
Nephron loop
Arcuate artery
Arcuate vein
Descendinglimb ofnephron loop
Ascending limbof nephron loop
Peritubularcapillaries
Glomerulus(capillaries)
Glomerularcapsule
Proximalconvolutedtubule
Renalcorpuscle
Efferentarteriole
• 85% of all nephrons
• Almost entirely in cortex
• Short nephron loop
• Glomerulus further from the cortex-medulla junction
• Efferent arteriole supplies peritubular capillaries
Cortical nephron
• Long nephron loop
• Glomerulus closer to the cortex-medulla junction
• Efferent arteriole supplies vasa recta
• Long nephron loops deeply
invade medulla
• Important in production of
concentrated urine
Juxtamedullary nephron
Efferent
arteriole
Vasa recta
‘Thin’ sections -Simple squamous
Cuboidal or columnar
Renal Tubule and Collecting Duct (cont.)
• Collecting ducts
– Cells lining ducts participate in fine-tuning of water, sodium ion, and acid-base balance between blood and urine
– Receive filtrate from many nephrons
– Run through medullary pyramids
• Give pyramids their striped appearance
– Ducts fuse together to deliver urine through papillae into minor calyces
Nephron Capillary Beds
• Renal tubules are associated with two capillary beds– Glomerulus
– Peritubular capillaries
• Low-pressure, porous capillaries adapted for absorption of water and solutes
• Arise from efferent arterioles
• Cling to adjacent renal tubules in cortex
• Empty into venules
• Juxtamedullary nephrons are associated with Vasa recta– Long, thin-walled vessels parallel to long nephron loops of juxtamedullary
nephrons
– Arise from efferent arterioles serving juxtamedullary nephrons
• Instead of peritubular capillaries
– Function in formation of concentrated urine
Juxtaglomerular Complex (JGC)
• Each nephron has one
• Modified portions of distal portion of distal tubule and Afferent arteriole
• Regulates rate of filtrate formation and blood pressure
• Three cell populations are seen in JGC:
1. Ascending limb macula densa contains chemoreceptors that sense NaCl content of filtrate
2. Granular cells (or JG cells) act as mechanoreceptors to sense blood pressure in afferent arteriole
Enlarged, smooth muscle cells of arteriole
Contain secretory granules that contain enzyme renin
3. Extraglomerular mesangial cells may be autoregulatorysmooth muscle cells, may also contribute to renin secretion and perhaps EPO
Steps in Urine Production
• Three processes are involved in urine formation and adjustment of blood composition:
1. Glomerular filtration: produces cell- and(mostly) protein-free filtrate
2. Tubular reabsorption: selectively returns 99%of substances from filtrate to blood in renaltubules and collecting ducts
3. Tubular secretion: selectively movessubstances from blood to filtrate in renal tubulesand collecting ducts
Figure 25.11 The three major renal processes.
1
2
3
3
2
1
Corticalradiateartery
Afferent arterioleGlomerularcapillaries
Efferent arteriole
Glomerular capsule
Renal tubule and
collecting duct
containing filtrate
Peritubular
capillary
To cortical radiate vein
Urine
Glomerular filtration
Tubular reabsorption
Tubular secretion
Three majorrenal processes:
Urine ProductionStep 1: Glomerular Filtration• Glomerular filtration is a passive process
• No metabolic energy required
• Hydrostatic pressure forces fluids and solutes through filtration membrane into glomerular capsule
• Control over systemic blood pressure very important to this process - necessitates kidney’s role in BP control
Pressures That Affect Filtration• Outward pressures promote filtrate formation
• Hydrostatic pressure in glomerular capillaries (HPgc) • Essentially glomerular blood pressure • 55 mm Hg compared to ~ 26 mm Hg seen in most capillary beds• Efferent arteriole
• high-resistance vessel• diameter smaller than afferent arteriole
• Inward Pressures inhibit filtrate formation:• Hydrostatic pressure in capsular space (HPcs)
• 15 mm Hg capsule filtrate “back” pressure• Colloid osmotic pressure in capillaries (OPgc)
• “pull” of proteins in blood; 30 mm Hg
• Filtrate formation the result of net filtration pressure (NFP): sum of forces
• 55 mm Hg forcing out minus 45 mm Hg opposing = net outward force of 10 mm Hg
• Main controllable factor determining glomerular filtration rate (GFR)
Figure 25.13 Forces determining net filtration pressure (NFP).
HPgc = 55 mm Hg
NFP = Net filtration pressure
= outward pressures – inward pressures
= (HPgc) – (HPcs + OPgc)
= (55) – (15 + 30)
= 10 mm Hg
Afferentarteriole
Glomerularcapsule
Efferentarteriole
OPgc = 30 mm Hg
HPcs = 15 mm Hg
Normal Glomerular Filtration Rate (GFR) = 120–125 ml/min
Dependent on glomerular hydrostatic pressure and surface area for filtration
Step 2: Tubular Reabsorption
• Quickly most of tubular contents and to blood• Whole volume of plasma enters proximal convoluted tubule
every 22 minutes
• Selective transepithelial process• Almost all organic nutrients like glucose and amino acids are
reabsorbed
• Water and ion reabsorption are hormonally regulated and adjusted
• Peritubular capillaries nearby contain blood that just left the glomerulus
• Includes active and passive tubular reabsorption• Primary and secondary active transport
• Diffusion, facilitated diffusion, osmosis
Transcellular and paracellular routes of tubular reabsorption.
Filtrate
in tubule
lumen
Transcellular route
Paracellular route
Tight
junction
Apical
membrane Capillary
endothelial
cell
Tubule cell
Basolateral
membranes
Interstitial
fluid Peri-
tubular
capillary
H2O and
solutes
H2O and
solutes
Lateral
intercellular
space
Transport across the apical
membrane.
The transcellular route
involves:
Diffusion through the cytosol.
Transport across the
basolateral membrane.
Movement through the
interstitial fluid and into the
capillary.
• Movement through leaky
tight junctions, particularly in
the proximal convoluted
tubule.
• Movement through the
interstitial fluid and into the
capillary.
The paracellular route involves:
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3 4
421
4
3
2
1
Reabsorption by PCT cells
Filtratein tubulelumen
GlucoseAmino acidsSome ionsVitamins
Lipid-solublesubstances
Various ionsand urea
3Na+
2K+
3Na+
2K+
K+
H2O
Na+
Nucleus
Tubule cell
Paracellularroute
Tight junction
Interstitialfluid Peri-
tubularcapillary
Primary active transport
Passive transport (diffusion)
Secondary active transport
Transport protein
Ion channel
Aquaporin
At the basolateral membrane,Na+ is pumped into the interstitialspace by the Na+-K+ ATPase. ActiveNa+ transport creates concentrationgradients that drive:
“Downhill” Na+ entry at theapical membrane.
Reabsorption of organicnutrients and certain ions bycotransport at the apicalmembrane.
Reabsorption of water byosmosis through aquaporins.Water reabsorption increases theconcentration of the solutes thatare left behind. These solutes canthen be reabsorbed as they movedown their gradients:
Lipid-soluble substancesdiffuse by the transcellular route.
Various ions (e.g., Cl−, Ca2+,K+) and urea diffuse by theparacellular route.
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6
4
3
2
1
1
2
3
4
5
6
Tubular Reabsorption of Nutrients, Water, and Ions
• Passive tubular reabsorption of water• Movement of Na+ and other solutes creates osmotic
gradient for water
• Water is reabsorbed by osmosis, aided by membrane pores called aquaporins
• Obligatory water reabsorption:
• Aquaporins are always present in PCT
• Facultative water reabsorption:
• Aquaporins are inserted in collecting ducts onlyif ADH is present
• Passive tubular reabsorption of solutes• Solute concentration in filtrate increases as water is
reabsorbed
Transport Maximum
• Transcellular transport systems are specific and limited
• Transport maximum (Tm) exists for almost every reabsorbed substance
• Reflects number of carriers in renal tubules that are available
• When carriers for a solute are saturated, excess is excreted in urine
• Example: hyperglycemia leads to high blood glucose levels that exceed Tm, and glucose spills over into urine
Hormonal Control Over Reabsorption
• Antidiuretic hormone (ADH)• Released by posterior pituitary
• Causes principal cells of collecting ducts to insert aquaporins in apical membranes, increasing water reabsorption
• Aldosterone• Mineralocorticoid from the adrenal cortex
• Targets collecting ducts and distal DCT
• Promotes synthesis of apical Na+ and K+ channels,and basolateral Na+-K+ pumps for Na+ reabsorption
• As a result, most Na+ reabsorbed (and water follows)
• Atrial natriuretic peptide
Step 3: Tubular Secretion
• Occurs mostly in PCT with ‘fine-tuning’ in DCT and collecting duct
• Selected substances are moved from peritubular capillaries through tubule cells out into filtrate
• K+, H+, NH4+, creatinine, organic acids and bases
• Substances synthesized in tubule cells also are secreted (example: HCO3
–)
• Important for:• Disposing of substances, such as drugs or metabolites• Eliminating undesirable substances that were passively
reabsorbed (example: urea and uric acid)• Ridding body of excess K+
• Controlling blood pH by altering amounts of H+ or HCO3– in
urine
Sum
mar
y o
f tu
bu
lar
reab
sorp
tio
n a
nd
sec
reti
on
.Cortex
Outer
medulla
Inner
medulla
Reabsorption
Secretion
65% of filtrate volumereabsorbed• H2O• Na+, HCO3
−, and many other ions• all glucose, amino acids, and other nutrients
Regulated reabsorption
• H+ and NH4+
• Some drugs
Regulatedsecretion• K+ (by
aldosterone)
Regulatedsecretion• K+ (by
aldosterone)
• Reabsorption or secretionto maintain blood pHdescribed in Chapter 26;involves H+, HCO3
−,and NH4
+
Regulatedreabsorption• H2O (by ADH)• Na+ (by
aldosterone; Cl−
follows)• Urea (increased
by ADH)
• Na+, K+, Cl−
• Urea
• H2O
• Na+(by aldosterone;Cl− follows)
• Ca2+ (by parathyroidhormone)
No stimulus needed -
automatic
No solutes can leave the descending
limbNo water can leave the ascending
limb
Regulation of Urine Concentration and Volume
• Kidneys make adjustments needed to maintain body fluid osmotic concentration at around 300 mOsm
• Same as plasma• Limits osmosis between cells and fluids = balance, no cells swell or
shrink
• osmolality is a measure of the osmoles (Osm) of solute per kilogram of solvent (osmol/kg or Osm/kg)
• osmolarity is defined as the number of osmoles of solute per liter (L) of solution (osmol/L or Osm/L)
• Body fluids expressed in milliosmoles (mOsm) = 0.001 osmol• 1 mole NaCl/l = 2 osmoles NaCl/l
• Urine volume and concentration vary based on • Your hydration status: drinking, sweating
• Small amount of concentrated urine if the body is dehydrated• Large amount of dilute urine if overhydrated
Regulation of Urine Concentration and Volume
• Accomplish this by using countercurrent mechanism• Fluid flows in opposite directions in two adjacent segments of
same tube
• Countercurrent mechanisms work together to:• Establish and maintain medullary osmotic gradient from renal
cortex through medulla• Gradient runs from 300 mOsm in cortex to 1200 mOsm at bottom of
medulla
• Countercurrent multiplier creates gradient
• Countercurrent exchanger preserves gradient
• Collecting ducts can then use gradient to vary urine concentration
Juxtamedullary nephrons create an osmotic gradient within the renal medulla that allows the kidney to produce urine of varying concentration.
400
300
300
600
900
1200
400
300
300
600
900
1200
400
300
300
600
900
1200
The long nephron loops of
juxtamedullary nephrons create
the gradient. They act as countercurrent multipliers.
The vasa recta preserve the
gradient. They act ascountercurrent exchangers
(see Figure 25.18).
The collecting ducts of
all nephrons use the gradient
to adjust urine osmolality
(see Figure 25.19).
The big picture:
Three key players
interact with the
medullary osmotic
gradient.Lower
concentration
of solutes
Higher
concentration
of solutes
The osmotic
gradient:
The osmolality (solute
concentration) of the
medullary interstitial
fluid progressively
increases from the 300
mOsm of normal body
fluid to 1200 mOsm at
the deepest part of the
medulla.
Long nephron loops of juxtamedullary nephrons create the gradient.
As water and solutes are reabsorbed, the loop first concentrates the filtrate, then dilutes it.
The countercurrent multiplier depends on three propertiesof the nephron loop to establish the osmotic gradient.
These properties establish a positive feedback cyclethat uses the flow of fluid to multiply the power ofthe salt pumps.
Filtrate flows in the opposite direction
(countercurrent)through twoadjacent parallel
sections of anephron loop.
The descending limb is permeable
to water, but notto salt.
The ascendinglimb is
impermeable towater, and pumpsout salt.
Water leaves thedescending limb
Osmolality of filtratein descending limb
Salt is pumped outof the ascending limb
Interstitial fluidosmolality
Osmolality offiltrate entering the
ascending limb
NaCIH2O
Active transport
Passive transport
Water impermeable
NaCIH2OStart
here
Filtrate entering thenephron loop is isosmoticto both blood plasma andcortical interstitial fluid.
Water moves out of thefiltrate in the descending limbdown its osmotic gradient.This concentrates the filtrate.
Filtrate is at its most diluteas it leaves the nephron loop.At 100 mOsm, it is hypo-osmotic to the interstitial fluid.
Na+ and Cl– are pumped outof the filtrate. This increases theinterstitial fluid osmolality.
Filtrate reaches its highestconcentration at the bend of theloop.
300
300
1200
100
Nephron loop
400
600
900
1200
300
300
H2O
Cortex
Outer
medulla600
NaCI
400
700
Inner
medulla
NaCI
NaCI
NaCI
NaCI
H2O
H2O
H2O
H2O
H2O
400
900
200
100
Os
mo
lali
ty o
f in
ters
titi
al fl
uid
(m
Os
m)
1
2
3
4
5
H2O
The counter-current flowof fluid movesthrough twoadjacent parallelsections of vasarecta.
NaCI
NaCI
NaCI
NaCI
NaCI
NaCI
NaCI
NaCI
1200
300
300
400
400
600
600
900
900
325
Vasa recta
To veinBlood fromefferentarteriole
H2O
H2O
H2OH2O
H2O
H2O
H2O
400
600
900
1200
300
H2O
• The vasa recta are highly permeable to water and solutes.• Countercurrent exchanges occur between each section of
the vasa recta and its surrounding fluid. As a result:• The blood within the vasa recta remains nearly isosmotic
to the surrounding fluid.• The vasa recta are able to reabsorb water and solutes into the
general circulation without undoing the osmotic gradientcreated by the countercurrent multiplier.
Vasa recta preserve the gradient.
Formation of Dilute or Concentrated Urine
• Established medullary osmotic gradient can now be used to form dilute or concentrated urine
• Without gradient, would not be able to raise urine concentration > 300 mOsm to conserve water
• Overhydration produces large volume of dilute urine• ADH production decreases; urine ~100 mOsm
• If aldosterone present, additional ions can be removed, causing water to dilute to ~50 mOsm
• Dehydration produces small volume of concentrated urine
• Maximal ADH is released; urine ~1200 mOsm
If we were so overhydrated we had no ADH...
Osmolality of extracellular fluids
ADH release from posterior pituitary
Number of aquaporins (H2O channels) in collecting duct
H2O reabsorption from collecting duct
Large volume of dilute urine
Cortex
NaCI
300
400600
900 700
1200
100
100
300
300
600
900
1200
100
100
Urea
Outermedulla
Innermedulla
Collectingduct
DCT
NaCI
Descending limbof nephron loop
NaCI
H2O
H2O
100
Large volumeof dilute urineActive transport
Passive transport
Osm
ola
lity
of
inte
rsti
tial fl
uid
(m
Osm
)
If we were so dehydrated we had maximal ADH...
Osmolality of extracellular fluids
ADH release from posterior pituitary
Number of aquaporins (H2O channels) in collecting duct
H2O reabsorption from collecting duct
Small volume of concentrated urine
300
300
400
600
900
1200
100
Urea
H2O
H2O
Outer
medulla
Inner
medulla
DCT
300
300
600
900
1200
Descending limb
of nephron loop
Cortex
NaCI
NaCI
NaCI Urea
300
400600
700
1200
Collecting duct
H2O
H2O
H2O
H2O
H2O
150
H2O
H2O
Small volume of
concentrated urine
900
Osm
ola
lity
of
inte
rsti
tial fl
uid
(m
Osm
)
Urea contributes to the
osmotic gradient. ADH
increases its recycling.
100
Urine
• Chemical composition • 95% water and 5% solutes
• Nitrogenous wastes • Urea (from amino acid breakdown): largest solute component
• Uric acid (from nucleic acid metabolism)
• Creatinine (metabolite of creatine phosphate)
• Other normal solutes found in urine• Na+, K+, PO4
3–, and SO42–, Ca2+, Mg2+ and HCO3
–
• Abnormally high concentrations of any constituent, or abnormal components may indicate pathology
• pH• Urine is slightly acidic (~pH 6, with range of 4.5 to 8.0)
Substances Filtered and Reabsorbed by the Kidney per 24 Hours
Substance Amount filtered (g) Amount reabsorbed (g) Amount in urine (g) % Reclaimed
Water 180 L 178- 179 L 1-2 L 99
Small Proteins 2 1.9 0 95-100
Chlorine 630 625 5 99
Sodium 540 537 3 99
Potassium 28 24 4 86
Bicarbonate 300 299.7 0.3 99.9
Glucose 180 180 0 100
Urea 53 28 25 50
Uric acid 8.5 7.7 0.8 91
Creatinine 1.4 0 1.4 0
Source: Open Stax. Anatomy and Physiology (open source text book) https://opentextbc.ca/anatomyandphysiology/chapter/25-6-tubular-reabsorption/ . Accessed 10/8/18
Jon Barron of the Baseline of Health Foundation. 03/26/2012. What Is the Urinary System, Functions | Kidneys & Urinalysis Newsletter. https://jonbarron.org/article/physiology-urinary-system . Accessed 10/8/18
Structure of the urinary bladder and urethra
Ureter
Trigone of bladder
Prostate
Intermediate part of the urethra
Prostatic urethra
Peritoneum
Rugae
Detrusor
Bladder neck
Internal urethral
sphincter
External urethral sphincter
Urogenital diaphragm
Spongy urethra
Erectile tissue
of penis
Ureteric orifices
Adventitia
External urethral
orifice
Male. The long male urethra has three regions: prostatic,
intermediate, and spongy.
Structure of the urinary bladder and urethra.
Female.
Ureter
Trigone
Peritoneum
Rugae
Detrusor
Bladder neck
Internal urethral
sphincter
External urethral sphincter
Urogenital diaphragmUrethra
External
urethral orifice
Ureteric orifices
Urinary Bladder (cont.)
• Urine storage capacity• Collapses when empty
• Rugae appear
• Expands and rises superiorly during filling without significant rise in internal pressure
• Moderately full bladder is ~12 cm long (5 in.) and can hold ~ 500 ml (1 pint)
Micturition, also called urination or voiding
Three simultaneous events must occur1. Contraction of detrusor by ANS
2. Opening of internal urethral sphincter by ANS
3. Opening of external urethral sphincter by somatic nervous system