Transcript BIO 169 THE URINARY SYSTEM CHAPTER 26 created by Dr. C. Morgan TOPICS Introduction and Organization Kidney Structure and Blood Supply Renal Physiology Urine Transport, Storage, and Elimination Aging and.

BIO 169
THE URINARY
SYSTEM
CHAPTER 26
created by Dr. C. Morgan
1
TOPICS
Introduction and Organization
Kidney Structure and Blood Supply
Renal Physiology
Urine Transport, Storage, and Elimination
Aging and the Urinary System
Resource: IPCD
Urinary System
2
Introduction and Organization Objectives
Discuss the role of the urinary system.
List the functions of the urinary system
List the organs of the urinary system.
Briefly characterize the nature of urine.
3
Introduction and Organization
After your blood has completed tissue exchange, it
contains quantities of waste products, increased CO2,
and perhaps imbalances of electrolytes.
Your lungs eliminate the excess CO2.
Since the blood is reused, somehow it must be cleansed of
the other wastes and its fluid volume and electrolytes
adjusted on a continual basis.
The role of the kidneys is to perform these tasks.
These activities are closely regulated and cellular life of all
tissues is closely integrated with the urinary system via
the blood.
4
Introduction and Organization (cont)
The functions of the urinary system are:
*to regulate fluid volume and blood pressure
*to regulate plasma ion concentrations
*assist in the homeostasis of blood pH
*to conserve nutrient molecules, especially glucose and
amino acids
*to rid the body of organic waste products
*help the liver to detoxify poisons
The organs are the kidneys, ureters, urinary bladder and
urethra.
Urine is a filtrate of the blood made by the kidneys, stored in
the bladder, and eliminated from the body via the urethra.
5
Introduction and Organization (cont)
Urinary System
Organs
Fig. 1
6
TOPICS
Introduction and Organization
Kidney Structure and Blood Supply
Renal Physiology
Urine Transport, Storage, and Elimination
Aging and the Urinary System
7
Kidney Structure and Blood Supply Objectives
Examine the gross anatomy of the kidneys.
Study the sectional anatomy of the kidneys.
Describe the blood supply to the kidneys.
Discuss the innervation of the kidneys.
Describe the structure of the nephron and
collecting system.
8
Kidney Structure and Blood Supply (cont)
retroperitoneal



Fig. 2 a
9
Kidney Structure and Blood Supply
T12 – L3 level
Fig. 2 b
10
Kidney Structure and Blood Supply (cont)

Sectional Anatomy


Fig. 4 a
11
Kidney Structure and Blood Supply (cont)
Renal Blood Flow
Fig. 5 b
Fig. 5 a
12
Kidney Structure and Blood Supply (cont)
Renal Blood Flow
20 – 25% of the cardiac output
flows through the kidneys
(1200 ml / minute)
Fig. 5 c,d
13
Kidney Structure and Blood Supply (cont)
Innervation:
Renal nerves, mostly postganglionic sympathetic fibers
from the mesenteric ganglion, branch to follow the
tributaries of the renal arteries.
Sympathetic fibers reach each nephron.
Sympathetic output
*changes the blood flow and pressure at the nephron
*and stimulates the release of renin (RAA response)
14
Kidney Structure and Blood Supply (cont)
The nephron is the functional unit of the kidney.
There are about 1.25 million nephrons / kidney residing in
the outer medulla and cortex.
About 85% of all nephrons are situated in the kidney
cortex so are called cortical nephrons.
15% of the nephrons are called juxtamedullary
nephrons because they have long loops of Henle that
project into the medulla.
The peritubular capillaries that surround these nephrons
are continuous with the vasa recta, a parallel capillary
loop that is adjacent to the loop of Henle.
The juxtamedullary nephrons give the kidneys the ability
to produce a very concentrated urine.
15
Kidney Structure and Blood Supply (cont)
Two types of
nephrons
Fig. 7 a
16
Kidney Structure and Blood Supply (cont)
Materials are
exchanged between the
peritubular capillaries
and the surrounding
interstitium.
Fig. 7 b
Peritubular
capillaries
surrounding a
cortical nephron
17
Kidney Structure and Blood Supply (cont)
Peritubular capillaries
and vasa recta
surrounding a
juxtamedullary
nephron
Fig. 7 c
18
Kidney Structure and Blood Supply (cont)
The Nephron
Fig. 6
TABLE 1
19
Kidney Structure and Blood Supply (cont)
A filtrate of the blood is formed in the renal corpuscle.
The renal corpuscle consists of Bowman’s capsule
containing a knot of capillaries called the glomerulus.
Extending from the capsule is a long renal tubule which
is divided into regions, each characterized by cells with
unique structural features.
The renal tubule empties into a collecting duct which is
continuous with a collecting system.
Once the filtrate reaches the papillary duct of the
collecting system it will undergo no more changes so
may be called urine.
20
Kidney Structure and Blood Supply (cont)
The nephron and collecting ducts engage in three
activities: filtration, reabsorption, and secretion.
Filtration of the blood occurs across the walls of the
glomerular capillaries to form a filtrate that passes
through the tubules of the nephron and collecting duct.
As the filtrate passes through the tubules, it is modified.
Reabsorption is the process of moving the materials to
be kept back to the blood vascular system.
Secretion is moving some substances from the interstitial
space into the filtrate so it is eliminated in urine.
Special characteristics of the cells along the length of the
nephron accomplish these tasks using the transport
mechanisms familiar to you (diffusion, facilitated
diffusion, co and active transport).
21
Kidney Structure and Blood Supply (cont)
Renal corpuscle
Filtration membrane
Fig. 8 b
22
22
Kidney Structure and Blood Supply (cont)
Podocytes are specialized
epithelial cells that cover the
surface of the glomerular
capillaries with adjacent
processes called pedicles.
The podocytes are continuous
with the epithelial cells that
form the capsular wall.
The capillaries are very
permeable because they
have pores (fenestrations).
Filtrate flow: fenestrations 
capillary lamina densa 
slits between pedicles
capsular space.
filtration membrane
Fig. 8 d
23
23
Kidney Structure and Blood Supply (cont)
The filtration membrane will not let red blood cells and
large proteins through so they are retained in the blood
as important osmotic pressure components.
Crossing the membrane to become filtrate components
are water, electrolytes, glucose, amino acids, vitamins,
metabolic waste products, fatty acids, and additional
miscellaneous solutes.
The solutes and water that are needed by the body must
be recovered by reabsorption as the filtrate passes
along the tubules and collecting system.
Glomerulonephritis is an inflammatory condition caused
by an abundance of Ag/Ab complexes that clog the
filtration membrane thereby slowing filtration.
24
Kidney Structure and Blood Supply (cont)
The proximal convoluted tubule is the first segment of
the nephron.
Glucose, amino acids, some proteins, and ions are
transported from the filtrate into the interstitial space
outside the PCT with water following by osmosis.
Some secretion of H+ (ammonium, creatinine, drugs, and
toxins) also occurs in the PCT.
Microvilli increase the surface area of cuboidal cells
making up the PCT.
60–70% of the filtrate volume is reabsorbed in the PCT.
25
Kidney Structure and Blood Supply (cont)
The PCT descends toward the medulla to become the first
“leg” of the loop of Henle.
There are thick and thin segments in the loop of Henle.
The thick segments consist of cuboidal cells.
The thin segments consist of squamous cells.
The ascending limb thick segment cells pump Na+ and
Cl¯ out into the interstitium.
The interstitium of the medullary region contains a
progressively greater concentration of solutes toward
the renal pelvis.
Water moves out of the permeable thin segments due to
the osmotically concentrated medullary interstitium.
26
Kidney Structure and Blood Supply (cont)
The cells of the thick segment of the ascending limb of the
loop of Henle are impermeable to water and solutes but
as Na+ and Cl¯ are actively transported into the
interstitium the filtrate becomes progressively less
concentrated than the blood.
The thick segment of the loop of Henle makes a sharp
bend near the renal corpuscle to become the distal
convoluted tubule (DCT).
DCT cells do not have microvilli.
The DCT is the site of active secretion of H+ ions, acids,
or other molecules along with additional selective
reabsorption of Na+ and Ca2+ from the remaining filtrate.
Water may also be selectively reabsorbed in the DCT.
27
Kidney Structure and Blood Supply (cont)
At the junction with the ascending limb of the loop of
Henle, a group of the DCT cells, the macula densa cells,
are special because they contact some modified smooth
muscle cells in the wall of the afferent arteriole that
delivers blood to the renal corpuscle.
The smooth muscle cells are the juxtaglomerular cells
which secrete the enzyme renin (RAA cascade of
events for blood pressure control) and erythropoietin.
Together these cells form the juxtaglomerular
apparatus (JGA).
28
Kidney Structure and Blood Supply (cont)
Fig. 8 b
the JGA
29
Kidney Structure and Blood Supply (cont)
As the filtrate again passes toward the renal pelvis through
the collecting ducts and papillary duct, its concentration is
adjusted by hormonally regulating water, Na+, and
bicarbonate ion reabsorption as well as some final
secretion.
The collecting system path:
Collecting ducts papillary ducts minor calyx major
calyx renal pelvis.
Cells of the collecting system are columnar epithelium.
30
Kidney Structure and Blood Supply (cont)
Review
Reabsorbed materials
pass from tubular
filtrate into the
interstitial space then
into the capillaries.
TABLE 1
Secreted materials pass from capillaries into
the interstitial space and then into the filtrate.
31
TOPICS
Introduction and Organization
Kidney Structure and Blood Supply
Renal Physiology
Urine Transport, Storage, and Elimination
Aging and the Urinary System
32
Renal Physiology Objectives
Discuss the role of the kidneys in excretion of
wastes.
Describe the fluid dynamics affecting filtration.
Discuss the regulation of renal function by
autoregulation and neural mechanisms.
Describe the events of reabsorption.
Describe the events of secretion.
Discuss countercurrent exchange.
Discuss hormonal control of kidney function.
Describe the composition of normal urine.
33
Renal Physiology
The kidneys function to regulate the volume and
composition of the blood.
Cellular metabolism generates a number of organic waste
products that end up as dissolved solutes in the blood
which must be removed from the body.
Urea, generated from the breakdown of amino acids,
represents most of the organic waste (21 g / day).
Creatinine is generated in muscle tissue as creatine
phosphate is broken down (1.8 g / day).
Uric acid is generated by the breakdown of nucleic
acids and recycling of RNA (480 mg / day).
The kidneys can spare water loss by excreting a urine
that is 4 to 5 times more concentrated than normal body
fluids.
34
Renal Physiology (cont)
Although urine is a filtrate of the blood, its composition is
very different from other body fluids (see TABLE 2).
Kidney function embraces the three processes, filtration,
reabsorption, and secretion (see TABLE 3).
Filtration:
The blood pressure is the driving force for filtration at the
glomerulus, the only place filtration occurs.
Because there are forces that oppose filtration, the
critical factor is the net filtration pressure (NFP).
The diameter of the afferent and efferent arterioles may
be controlled in order to help maintain an optimal NFP.
If the NFP drops too low (<10 mm Hg), kidney function
stops.
35
Renal Physiology (cont)
Blood pressure is the driving force for filtration
but there are opposing forces at work.
Filtration occurs through the filtration membrane.
Fig. 10 a
36
Renal Physiology (cont)
The glomerular filtration rate (GFR) is the amount of
filtrate produced per minute (about 125 ml for 2 kidneys).
About 10% of the fluid passing through the kidneys
appears as filtrate (180 l / day) with 99% reabsorbed
back into the blood.
Regulating GFR is critically important.
NFP = GHP – CsHP = 50 mmHg – 15 mmHg = 35 mm Hg
FP = NHP – BCOP = 35 mmHg – 25 mm Hg = 10 mm Hg
A decrease in glomerular blood pressure by only 20% will
stop filtration.
GFR is controlled by kidney autoregulation, neural
mechanisms, and the RAA (renin-angiotensinaldosterone) response to falling blood pressure.
37
Renal Physiology (cont)
H2O and small solutes
pass through the
filtration membrane
Fig. 10 b
38
Renal Physiology (cont)
A number of tests are used to evaluate kidney filtration.
The creatinine clearance test is used to estimate GFR.
Creatinine is not reabsorbed from the filtrate so a
comparison between blood and urine levels is calculated.
If 84 mg of creatinine appears in the urine each hour and
the plasma concentration is 1.4 mg / dl, the GFR =
84 mg/hr = 60dl / hr = 100 ml / min
1.4 mg/dl
About 15% of the creatinine does enter by secretion so if
more accuracy is required, inulin, a protein that is
neither reabsorbed nor secreted, is administered to more
accurately determine GFR.
39
Renal Physiology (cont)
Autoregulation of GFR is achieved by adjusting the
diameter of the afferent and efferent arterioles,
glomerular capillaries and their supporting cells.
If the systemic blood pressure declines, the following
responses to maintain GFR occur.
*the afferent arteriole dilates
*supporting cells relax and capillaries dilate
*the efferent arteriole constricts.
If the systemic blood pressure rises, stretch of the afferent
arteriole results in a reflex constriction of its smooth
muscle cells which decreases blood flow to the
glomerulus in order to regulate GFR.
40
Renal Physiology (cont)
Hormonal regulation of GFR is due to the reninangiotensin system and atrial natriuretic peptide.
Renin is released from the JGA when renal blood flow
declines or the osmotic concentration of the fluid in the
DCT decreases (because flow slowed, more solutes
were pumped out along the ascending loop of Henle).
Angiotensin II
*vasoconstricts peripheral systemic arterioles and
precapillary sphincters
*constricts the efferent arteriole and stimulates
reabsorption of Na+ and H2O along the PCT
*stimulates aldosterone release, thirst, ADH release, and
peripheral sympathetic vasoconstriction
41
Renal Physiology (cont)
Hormonal regulation of GFR (cont)
In response to rising blood pressure, cells of the right
atrium release ANP which causes
*dilation of the afferent arteriole and constriction of the
efferent arteriole to increase GFR and urine production
Increased urine production lowers blood volume resulting
in a decrease in blood pressure.
Autonomic regulation of GFR is due to the sympathetic
activation triggered by a sudden fall in blood pressure
which vasoconstricts the afferent arteriole to decrease
GFR temporarily (protecting vital organs).
A similar response occurs during strenuous exercise.
42
Renal Physiology (cont)
Regulation
of GFR
Fig. 11 b
43
Renal Physiology (cont)
Reabsorption and Secretion along the renal tubule:
Solutes that need to be retained in the body are
reabsorbed from the filtrate and others that need to be
removed from the body are secreted into the filtrate
along the renal tubule.
The transport mechanisms utilized by tubule cells include
simple diffusion, facilitated diffusion, active
transport, and two additional transport mechanisms that
secondarily depend on the solute gradients set up by
active transport—cotransport and countertransport.
The rate of transport of a substance through a tubule cell
depends on the number of carrier proteins present in
its cell membrane on the apical and basolateral
surfaces.
44
Renal Physiology (cont)
The solute concentration at carrier saturation is the
transport maximum (Tm).
When the filtrate concentration of a substance exceeds
the Tm, the remaining molecules of that substance will
appear in the urine.
The renal threshold is the plasma concentration of a
substance when it begins to appear in the urine.
The renal threshold for glucose is about 180 mg / dl and
for amino acids it is about 65 mg / dl.
Some substance are not transported by tubule cells so
they always appear in the urine.
TABLE 3 lists various substances in relation to renal
transport.
45
Renal Physiology (cont)
Osmolarity refers to the number of solute particles in a
fluid.
Osmolarity is expressed in osmoles per liter (Osm/l) or
milliosmoles per liter (mOsm/l).
A one Osm/l solution has one mole (grams = to molecular
weight) of a dissolved solute in a liter of solvent.
Most body fluids, including blood, have an osmotic
concentration of about 300 mOsm/l.
Each 1 mOsm/l = 19.3 mm Hg osmotic pressure
Ion concentrations reported in millequivalents per liter are
based on the number of cations and anions in solution.
For substances with a single charge, a one mOsm/l
solution is also a 1 mEq/l solution.
46
Renal Physiology (cont)
osmotic
concentrations
of the blood
and filtrate
Fig. 16
47
47
Renal Physiology (cont)
Cells of the initial portion of the renal tubule, the PCT, are
responsible for reabsorbing
*around 70% of the filtrate volume,
*all of the glucose, amino acids, and other nutrients,
*many solutes including Na+, K+, Ca2+, bicarbonate ions,
and others.
PTH stimulates Ca2+ reabsorption.
PCT cells also actively secrete H+.
Active transport of Na+ at the basolateral surface sets up
the gradient for reabsorption of Na+ coupled to the
secretion of H+ using a countertransport protein and with
the reabsorption of glucose using a cotransport protein
on the apical surface of PCT cells.
48
Renal Physiology (cont)
Transport
along the PCT
absorption of CO2
from tubular fluid
provides for
reabsorption of
bicarbonate ions
and secretion of H+
Fig. 12
microvilli
present
note how
Na+ is
reabsorbed
by several
types of
transport
proteins
pump
49
Renal Physiology (cont)
Loop of Henle and Countercurrent Exchange
Of the remaining filtrate entering the loop of Henle, ½ of
the water and ⅔ of the Na+ and Cl– ions will be
reabsorbed through its specialized cells.
Water is reabsorbed from the filtrate as it passes down the
descending limb of the loop of Henle and Na+ and Cl–
are reabsorbed by active transport across the cells of the
ascending limb of the loop of Henle to produce a filtrate
with a solute concentration ⅓ that of the plasma.
The descending limb is permeable to water and
impermeable to solutes.
The thick ascending limb is impermeable to water and
solutes but has ion transporters powered by many
Na+/ K+ exchange pumps on the basolateral surface.
50
Renal Physiology (cont)
Ascending Limb
Fig. 13 a
51
51
Renal Physiology (cont)
Loop of Henle -countercurrent
multiplier
Fig. 13 b
medulla
52
Renal Physiology (cont)
The highly concentrated filtrate at the tip of the loop of
Henle (1200 mOsm/l) is isotonic with the peritubular fluid.
The peritubular fluid is composed of 750 mOsm/l of Na+
and Cl¯ pumped from the ascending limbs and the
balance is mostly urea.
Much of the urea diffused into the peritubular fluid from the
distal papillary ducts which are permeable to urea.
The countercurrent mechanism
• facilitates the reabsorption of water and solutes before
the fluid reaches the DCT and
• establishes a concentration gradient for the hormonedependent reabsorption of water in the collecting system.
53
Renal Physiology (cont)
The loop of Henle, DCT, and most of the collecting duct length are
impermeable to urea so filtrate concentration rises as H2O is reabsorbed.
Fig. 13 c
54
54
Renal Physiology (cont)
The DCT receives a filtrate volume that has been reduced
by 80% and 85% of the solutes have been reabsorbed.
There is a high concentration of urea and organic wastes in
the filtrate of the DCT where secretion by active transport
adds additional solutes.
Final adjustments to water volume and ions occur in the
DCT and collecting ducts.
Reabsorption of Na+ and Cl– ions is powered by the
basolateral Na+/ K+ exchange pumps.
As Na+ is reabsorbed, K+ is secreted—especially along the
aldosterone-sensitive distal portion of the DCT and the
collecting duct.
Ca2+ is reabsorbed along the DCT in response to PTH and
calcitriol hormones (calcitriol secreted by kidneys).
55
55
Renal Physiology (cont)
entire DCT
cotransport of
Na+ and Cl–
secretion of K+
exchange pump
Fig. 14 a
56
Renal Physiology (cont)
distal DCT
aldosterone regulated
Na+ channels are
present in the distal
DCT and collecting
ducts
Na+ is
exchanged
for K+
Na+ is reabsorbed
K+ is secreted
Fig. 14 b
57
57
Renal Physiology (cont)
The DCT and collecting ducts are important sites of
solute secretion, especially H+ and K+ (already
discussed).
Despite the tubular processing, blood entering the
peritubular capillaries may still contain undesirable
solutes.
If these materials pass into the peritubular fluid, they may
be secreted into the lumen of the DCT or collecting
system to be eliminated in the urine.
H+ and K+ are both coupled to Na+ reabsorption but by
different transport proteins.
58
Renal Physiology (cont)
DCT and
collecting
ducts
Two exchange
pumps result in
the secretion of
H+ and
reabsorption of
HCO3¯
* important in
maintaining
blood pH
a.a. deamination
also generates
bicarbonate as
ammonium ions
are secreted
Fig. 14 c
59
Renal Physiology (cont)
Collecting System
The final concentration of urine is established as it passes
through the collecting system where reabsorption of
water and Na+ is controlled by hormones.
Antidiuretic hormone (ADH) and aldosterone control
these final adjustments by regulating the number of
transport channels present in the tubule cells.
Aldosterone, a hormone from the adrenal cortex,
enhances reabsorption of Na+ by stimulating the insertion
of Na+ pumps in principal cells of the late DCT and
proximal collecting ducts.
Elevated K+ in the blood and adrenocorticotropic
hormone (ACTH) from the anterior pituitary stimulates
the secretion of aldosterone.
60
Renal Physiology (cont)
When Na+ is reabsorbed via aldosterone regulated active
transport channels, it is in exchange for K+ which is
secreted into the filtrate (see Fig. 14 b, slide 57).
Along the collecting ducts, bicarbonate ions are
reabsorbed in exchange for Cl– .
There is a relatively high concentration of urea in the
filtrate that enters the collecting system.
Urea diffuses into the interstitium as it passes into the
medullary region.
H+ and HCO3– pumps present in intercalated cells of the
collecting system adjust these ions which aids in
maintenance of body fluid pH (slide 59).
Recall that the volume of urine excreted is related to
maintenance of fluid balance and blood pressure.
61
Renal Physiology (cont)
Most water reabsorption occurs by osmosis along the PCT
and descending limb of the loop of Henle.
A small amount of osmosis occurs along the DCT and
collecting system as solutes are reabsorbed.
This osmotic reabsorption of water is termed obligatory
water reabsorption (85%) since there are no control
mechanisms operating to limit this osmosis.
The remaining reabsorption of water occurs as facultative
water reabsorption which is subject to hormonal control.
ADH stimulates the insertion of water channels in principal
cells along the late DCT and collecting ducts.
62
Renal Physiology (cont)
In the absence
of ADH there
will be a large
volume of dilute
urine excreted.
1200 mOsm / l
Fig. 15 a
63
63
Renal Physiology (cont)
In the presence of
ADH there may be
only a small volume
of concentrated
urine excreted.
Urine
concentration
cannot exceed
the osmolarity of
the medullary
interstitial fluid
1200 mOsm / l
Fig. 15 b
64
64
Renal Physiology (cont)
There is always some ADH present which results in about
1200 ml / day of normal urine output at a
concentration of 800 – 1000 mOsm / l.
In diabetes insipidus, there is inadequate ADH and urine
output climbs to as much as 24 liters / day.
Recall that atrial natriuretic peptide (ANP), a hormone
secreted from cells of the right atrium when stretch
receptors are activated, opposes the effects of ADH.
The loss of additional fluid helps to lower blood pressure.
Recall that the RAA response to falling blood pressure
stimulates ADH secretion to enhance blood volume and
hence raise blood pressure.
65
Renal Physiology (cont)
Fig. 16 b
66
Renal Physiology (cont)
The Vasa Recta
The solutes and water that are reabsorbed into the kidney
interstitium must be returned to the systemic circulation.
These reabsorbed materials enter the peritubular
capillaries that surround the kidney tubules.
The blood that leaves the efferent arteriole of the
juxtamedullary nephrons also passes deep into the
medulla within capillaries known as the vasa recta.
The vasa recta capillaries parallel the long loops of
Henle and collecting ducts.
Blood flowing in the vasa recta capillaries picks up
solutes as it courses toward the medulla and water as it
returns toward the cortical region.
67
Renal Physiology (cont)
vasa recta
urea
Fig. 16 a
68
68
Renal Physiology (cont)
When blood leaves the glomerulus, it has a concentration
of 300 mOsm / l.
As blood flows toward the medulla, it gains solutes,
especially Na+Cl– transported out of the ascending limb of
the long loops of Henle.
As blood flows from the medulla, it gains water reabsorbed
from the descending limb of the loops of Henle and from
water channels along the collecting ducts.
This countercurrent vasa recta flow facilitates the return of
reabsorbed materials while maintaining the osmotic
gradient in the medulla.
The vasa recta capillaries are permeable to urea which
moves according to its medullary concentration gradient.
69
Renal Physiology (cont)
Composition of Normal Urine
99% of the 180 liters of filtrate is reabsorbed with the
filtrate that becomes urine chemically quite variable.
TABLES 5 and 6 list some typical urine values.
The pH ranges from 4.5 – 8 with pH 6 mid-range.
The specific gravity is 1.003 – 1.030 (water is 1.0).
Osmolarity is 855 – 1335 mOsm / l; 93 – 97% H2O.
Color is clear yellow and it is sterile.
Hemoglobinbilirubinurobilinogensurobilins
Urinalysis is the analysis of urine.
Impaired kidney function: dialysis or transplantation.
70
TOPICS
Introduction and Organization
Kidney Structure and Blood Supply
Renal Physiology
Urine Transport, Storage, and Elimination
Aging and the Urinary System
71
Urine Transport, Storage, and Elimination Objectives
Describe the structure of the ureters.
Describe the structure of the urinary bladder.
Describe the structure of the urethra.
Discuss the micturition reflex and urination.
Describe several disorders involving the above
structures.
72
Urine Transport, Storage, and Elimination
Urine produced in the renal tubules passes from the
collecting ducts to the renal pelvis.
A ureter leads from each kidney to the urinary bladder.
The ureter is a muscular, retroperiotoneal tube that
joins the posterior surface of the bladder.
Peristaltic smooth muscle contractions move the urine
along the ureters.
The detrusor muscle of the urinary bladder is composed
of circular and longitudinal smooth muscle layers with a
transitional epithelial lining.
Contraction of the detrusor muscle forces urine out of
the body via the urethra which is guarded by internal
(involuntary) and external (voluntary) sphincters.
73
Urine Transport, Storage, and Elimination (cont)

stabilizes
position
Bladder
position
Fig. 19 a
74
Urine Transport, Storage, and Elimination (cont)

Fig. 19 b
Bladder
position
Bladder is
anchored by
ligaments to
the pelvis.
75
Urine Transport, Storage, and Elimination (cont)
Urinary
Bladder
3 smooth
muscle layers
(middle one is
circular)
Fig. 19 c
76
Urine Transport, Storage, and Elimination (cont)
The micturition reflex controls the elimination of urine
from the bladder.
The reflex involves activation of stretch receptors in the
detrusor muscle wall which send afferent impulses to
the CNS via the pelvic nerve.
There is a spinal reflex arc and an afferent pathway to
the brain.
Parasympathetic motor neurons stimulate muscle
contraction and relaxation of the internal urethral
sphincter (external sphincter is voluntary).
When the fluid volume is about 500 ml, the reflex results
in urination which empties the bladder almost
completely.
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Urine Transport, Storage, and Elimination (cont)
Micturition
Reflex
Fig. 21
78
78
Urine Transport, Storage, and Elimination (cont)
Urinary Tract Disorders
Blockages of the collecting ducts or ureters may result
from a buildup of casts which are collections of
cells, blood clots, lipids or other materials.
Kidney “stones” or calculi are mineral deposits or uric acid
crystals that result in urinary obstructions.
Sound wave energy or lasers are used to shatter calculi.
Bladder cancer kills 9500 people per year and is related
to environmental factors including smoking.
Incontinence is the inability to control urination voluntarily.
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Urine Transport, Storage, and Elimination (cont)
Urinary Tract Disorders (cont)
Urinary tract infections are usually caused by invading
bacteria from the intestinal tract.
An upper urinary tract infection (pyelonephritis)
involves the ureters and / or kidneys.
A lower urinary tract infection (cystitis) involves the
bladder and / or urethra.
UTIs are the most common type of infection acquired
during a hospital stay.
Infections acquired as a result of a hospital stay are
called nosocomial infections.
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TOPICS
Introduction and Organization
Kidney Structure and Blood Supply
Renal Physiology
Urine Transport, Storage, and Elimination
Aging and the Urinary System
81
Aging and the Urinary System Objectives
Discuss some age related changes in the urinary system.
Aging and the Urinary System
Renal function declines due to
*a decrease in the number of functional nephrons
(30 – 40% decrease by age 85)
*a reduced GFR in remaining functional renal corpuscles
*a reduced sensitivity to hormones, especially ADH
*urination problems and loss of sphincter muscle tone
causes incontinence compounded by shrinking bladder
size
*decreased total body water content and net mineral loss
82
TOPICS
Introduction and Organization
Kidney Structure and Blood Supply
Renal Physiology
Urine Transport, Storage, and Elimination
Aging and the Urinary System
83