10/31/2018

1

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

10/31/2018

2

Figure 25.3a Position of the kidneys against the posterior body wall.

Inferiorvena cava

Aorta

Supportive

tissue layers

• Renal fascia

• Perirenalfat capsule

• Fibrouscapsule

anteriorposteriorRenal

artery

Renalvein

Peritoneum Peritoneal cavity(organs removed)

Anterior

Posterior

Body ofvertebra 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

10/31/2018

3

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

10/31/2018

4

Figure 25.6 Location and structure of nephrons.

Fenestratedendotheliumof the glomerulus

Apical microvilli

Cortex

M edulla

Podocyte

Basement membrane

Mitochondria

Apical side

Basolateral side

Highlyinfolded

basolateralmembrane

Proximal

convolutedtubule

Distal

convolutedtubule

Thick segment

Collecting

duct

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 of

glomerular 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

10/31/2018

5

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

10/31/2018

6

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

Peritubular

capillaries

Glomerulus

(capillaries)

Glomerularcapsule

Proximalconvolutedtubule

Renalcorpuscle

Efferent

arteriole

• 85% of all nephrons

• Almost entirely in cortex

• Short nephron loop

• Glomerulus further from the cortex-medulla junction

• Efferent arteriole supplies peritubularcapillaries

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

10/31/2018

7

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

10/31/2018

8

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 major

renal 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

10/31/2018

9

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

10/31/2018

10

Transcellular and paracellular routes of tubular reabsorption.

Filtrate

in tubulelumen

Transcellular route

Paracellular route

Tight

junction

Apical

membrane Capillary

endothelialcell

Tubule cell

Basolateral

membranes

Interstitial

fluid Peri-

tubularcapillary

H2O and

solutes

H2O and

solutes

Lateral

intercellularspace

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 thecapillary.

• Movement through leaky

tight junctions, particularly inthe proximal convoluted

tubule.

• Movement through theinterstitial fluid and into the

capillary.

The paracellular route involves:

3

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.

5

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

10/31/2018

11

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

10/31/2018

12

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 drugsRegulatedsecretion• K+ (byaldosterone)

Regulatedsecretion• K+ (byaldosterone)

• Reabsorption or secretionto maintain blood pHdescribed in Chapter 26;involves H+ , HCO3

−,

and NH4+

Regulatedreabsorption• H2O (by ADH)• Na+ (by

aldosterone; Cl−

follows)• Urea (increasedby 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

10/31/2018

13

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 as

countercurrent 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 twoadj acent parallel

sections of anephron loop.

The descending limb is permeable

to water, but not

to salt.

The ascendinglimb is

impermeable to

water, and pumpsout salt.

Water leav es thedescending limb

Osmolality of filtratein descending limb

Salt is pumped outof the ascending limb

Interstitial fluidosmolality

Osmolality offiltrate entering the

ascending limb

NaCIH2O

Activ e transport

Passiv e transport

Water impermeable

NaCIH2OStarthere

Filtrate entering thenephron loop is isosmoticto both blood plasma andcortical interstitial fluid.

Water mov es out of thefiltrate in the descending limbdown its osmotic gradient.This concentrates the filtrate.

Filtrate is at its most diluteas it leav es 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

medulla

600

NaCI

400

700

Inner

medulla

NaCI

NaCI

NaCI

NaCI

H2O

H2O

H2O

H2O

H2O

400

900

200

100

Os

mo

lali

ty

of

inte

rsti

tia

l 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.

10/31/2018

14

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

Os

mo

lali

ty o

f in

ters

titi

al fl

uid

(m

Os

m)

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

Os

mo

lali

ty o

f in

ters

titi

al fl

uid

(m

Os

m)

Urea contributes to the

osmotic gradient. ADH

increases its recycling.

100

10/31/2018

15

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 fi ltered (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.

10/31/2018

16

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