A&P 2
URINARY SYSTEM
Instructor Terry Wiseth
Kidney Function
Daily the kidneys filter about 200 quarts of blood
Produces 2 quarts of waste product and extra water
Major Functions of Urinary System
1)
Clears blood of waste products of metabolism
Uremia
accumulation of toxic levels of wastes in blood
2) Maintain normal:
H2O and electrolyte balance
fluid
volumes
blood
pressure
body pH
Detailed Functions of
Urinary System
1) Removal of organic wastes
2) Regulate ion concentrations
3) Regulation of the acid-base balance
4) Regulation of RBC production
5) Regulation of blood pressure
6) Control glucose and amino acid concentration
7) Elimination of toxic substances
Functions of Urinary
System
1) Removal of organic wastes
Urea
Uric acid
Creatinine
Breakdown products of hemoglobin and hormones
2) Regulation of the concentrations of important
ions
Excretion of:
Sodium (Na+)
Potassium (K+)
Calcium (Ca++)
Magnesium (Mg++)
Sulfate (SO4-)
Phosphate (PO4-)
3) Regulation of the acid-base balance of the body
control the elimination of:
Hydrogen (H+)
Bicarbonate (HCO3-)
Ammonium (NH4+)
4) Regulation of RBC production
Release erythropoietin
regulates the production of RBC in
the bone marrow
5) Regulation of blood pressure
Regulate the fluid volume of the body and thus blood
pressure
Produces the enzyme Renin
regulates blood pressure and water
retention
6) Limited control of blood glucose and blood amino
acid concentration
Excrete excess amounts of:
Glucose
Amino acids
7) Elimination of toxic substances
Pollutants
Food additives
Drugs
Other chemicals foreign to the body
Kidney Failure
Blood
constituents cannot be held in normal concentrations
Urinary Anatomy
Kidney
Ureter
Bladder
Urethra
Kidneys
Excretory Organs
Intestine
Skin
Lungs
Kidney
Excretes
N2
wastes
Toxins
H20
Electrolytes
Kidney Location
Paired bean shaped organs below the diaphragm and
liver
About the size of a fist
Microscopic Structure
Nephron
unit of
function
1.25
million / kidney
Highly
vascular
20%
of blood pumped / min
Nephron
Organ of function in the kidney
Glomerulus
Tubule
Nephron Anatomy
1) Glomerulus
Arterioles
Bowman’s Capsule
2) Tubule
Proximal
Loop of Henle
Ascending
Descending
Distal
Collecting
Urine Formation
Actions
in forming urine
1)
Filtration
2)
Reabsorption
3)
Secretion
Glomerulus
Glomerular
Filtration
blood
flows through glomerular capillaries
H2O
and solutes filter out into Bowman’s Capsule
Glomerular Filtration
Blood
flows through glomerular capillaries
H2O
and solutes filter out into Bowman’s Capsule
Renal Blood Vessels
Arterial blood enters the kidney through the Renal artery
Renal artery branches into numerous Afferent arterioles which supply each
glomerulus
Afferent arterioles feed capillary networks, Glomerular
tuft in the glomerular capsule
Blood remaining leaves the capillary network by way
of the Efferent
arteriole
Peritubular capillaries surround the renal tubules
where reabsorption and secretion occurs
Venous blood leaves the kidney by way of the renal
vein
Glomerular Filtration
Pressure gradient causes filtration
some kidney diseases the
permeability of glomerulus increases
allows blood proteins to filter
out into the capsule
Glomerulus
The glomerular capsule is made up of two layers of
cells
The outer layer is made up of regular epithelial
cells
The inner layer is made up of cells called Podocytes
Podocytes
Podocytes are tightly attached to
the glomerular capillaries and highly branched with extensions called Pedicels
Glomerulus
Gaps in contacts between cells are called Slit
pores
These pores prevent medium size protein molecules
from leaving the capillary
Endothelial cells that line the glomerular
capillaries have large pores called Fenestrae
Do not allow passage of RBC, WBC and platelets
Glomerular capillaries are 400 times more permeable
to plasma water and dissolved solutes than other capillaries
Filtrate passes:
through the capillary fenestrae
through the slit pores
What passes through as filtrate?
Electrolytes, nutrients,
nitrogen wastes, small hormones, water
What does not pass through as filtrate?
Cells, large proteins
Glomerular Filtration
High blood pressure in the glomerulus forces small
molecules from blood into the Bowman’s capsule
Glomerular
Filtration
TEM of filtration slits from capillaries in Bowman’s Capsule
Glomerular Filtration
Stress can lead to constriction of afferent and
efferent arterioles
Causes filtration rate to
lower and renal suppression “kidney shutdown”
The speed of filtration is called the Glomerular
Filtration Rate (GFR)
Kidneys able to filter:
125 mL
per minute
Forms 1 mL
of urine
180 L per day (45 gallons)
5 L blood filtered 56 times
per day
Glomerular Filtration
Rate
Directly related to systemic blood pressure
↓ BP = ↓
glomerular filtration
↑ BP = ↑
glomerular filtration (slight)
Glomerular Filtration
During exercise blood pressure rises
Incoming blood pressure is regulated by
vasoconstriction of the afferent arterioles
Accomplished by increased sympathetic nerve activity
Action of exercise induced vasoconstriction
Preserves blood volume
Diverts blood to muscles and heart
The same sympathetic response and vasoconstriction
occurs during cardiovascular shock
Vasoconstriction decreases the blood pressure
entering the glomerular capillaries enough to compensate the increased BP from
exercising
This limits the formation of overwhelming amounts of
urine during exercise
Convoluted Tubule
Fluid from glomerulus is called filtrate
Filtrate flows through a long convoluted tubule
Proximal Convoluted
Tubule
The first portion of the tubule is called the
Proximal Convoluted Tubule (PCT)
Loop of Henle
The middle portion is called the Loop of Henle (LH)
Distal Convoluted Tubule
The terminal end is called the Distal Convoluted
Tubule (DCT)
Collecting Duct
Numerous tubule empty into
a common Collecting Duct (CD)
Tubular Reabsorption
Tubular reabsorption involves the movement of
solutes from tubular fluid back to the blood
Water follows passively by osmosis
Movement of solutes and water from the tubule back
to blood occurs by a number of different mechanisms:
1) simple diffusion (Na+,
Cl-)
2) facilitated diffusion (glucose, urea)
3) active co-transport
(glucose)
4) active transport pumps
(Na+, K+)
5) osmosis (water)
Simple Diffusion
Diffusion is the movement of molecules from areas of
higher concentration to areas of lower concentration
Movement of solutes occurs as long as there is a
concentration difference and the molecule can pass by the membrane
Active Transport
Glucose, Ions, Proteins are able to be moved against
their concentration gradients
These processes require input of large amounts of
energy from the cell (ATP)
Glucose, amino acids, ions and other useful
substances are actively transported from the tubule into blood
Protein pumps embedded in cell membranes are able to
selectively transport materials in and out of the cell
Sodium – Potassium Pump
Osmosis
Osmosis is the diffusion of water from areas of
higher concentration to areas of lower concentration
Consider a 6 % NaCl solution
6 % NaCl
94 % H20
Given a 6% solution on one side of a semipermeable membrane and a 7% solution on the other side
H20 will move from the 6% solution
(94% H20) to the
7% solution (93% H20)
Movement of water between the tubular fluid,
interstitial fluid and the vascular system can be controlled by altering the
concentrations of solutes in each of the compartments
The trick is to move solutes by active and passive
transport mechanisms, changing the relative solute concentrations
Water then moves by osmosis with the changing solute
concentrations
Tubular Reabsorption
Most tubular reabsorption occurs in the proximal
tubule
Fine tuning and regulation of reabsorption occurs in
the more distal regions
Tubular Reabsorption
The proximal tubules and Loop of Henle
reabsorb about 95 % of the water completely unregulated
The distal and collecting tubule reabsorb less than
10 % of the water but it is here that water reabsorption is effectively regulated
Proximal Tubular
Reabsorption
Na+ concentrations are equal in proximal
tubule fluid and peritubular capillaries
Proximal tubule cells have numerous microvilli which border the lumen of the proximal tubule
Microvilli increase the total surface
area for reabsorption
Na+ leaves proximal tubule by simple
diffusion into proximal tubule cells
Glucose follows by a co-transport mechanism against
their concentration gradient
Na+ is transported by sodium-potassium
pump from proximal tubule cells into the peritubular capillaries
Proximal tubule cells maintain low Na+
concentrations due to sodium-potassium pump action
Glucose is transported by facilitated diffusion from
the proximal tubule cell into the peritubular
capillaries
Diffusion of Na+ into peritubular
capillaries does not occur as fast as sodium-potassium pumps pump Na+
out of the proximal tubule cells
Thus Na+ accumulates in the surrounding
interstitial fluid
This accumulation creates a potential difference
across the wall of the tubule
The electrical gradient favors the passive movement
of Cl- ions into the interstitial fluid
The resulting accumulation of NaCl
increases osmotic pressures in the interstitial fluid in comparison with the
proximal tubule
The osmotic gradient causes H2O to move
by osmosis from the proximal tubule to the interstitial fluid and into the
proximal tubular cells
NaCl and H2O then
move passively into the peritubular capillaries and
returned to the blood
Tubular Reabsorption
99% of the filtrate is returned to the vascular
system
A concentration gradient must be maintained between
tubular fluid and blood that favors osmotic return of water to the vascular
system
Only 65 % of the salt and water in the original
glomerular filtrate is reabsorbed across the proximal tubule
Proximal tubule cells are freely permeable to water,
so salt and water are removed in proportionate amounts
20 % of the salt and water in the original
glomerular filtrate is reabsorbed in the descending loop of Henle
Neither the Proximal tubule
or the
Loop of Henle is subject to hormonal regulation
90 % of filtered salt and water is reabsorbed in a
constant fashion in the initial sections of the tubule
Reabsorption is costly in terms of energy
expenditures
Accounting for 6 % of the calories consumed by the
body at rest
% remaining is reabsorbed by distal tubules under
the influence of hormone action
Glucose Reabsorption
if blood glucose levels
exceed threshold amount (150mg/100ml) not all glucose is reabsorbed
Renal Diabetes
sometimes maximum transfer capacity
is reduced and excess glucose appears in urine even though blood glucose level
is normal
Loop of Henle
In order for water to be reabsorbed by osmosis the
surrounding interstitial fluid must be hypertonic
The osmotic pressure of the interstitial fluid in
the renal medulla is raised to over four times that of plasma
Descending
Water diffuses out of the tubule by osmosis
The descending loop does not actively transport NaCl but is permeable to water
Water is drawn out by osmosis and enters blood
capillaries of the vasa recta
Reabsorption from Loop of
Henle
Tubular fluid
NaCl concentration is thus increased
and volume is decreased
Ascending
Salts are actively transported out of the tubule,
but water cannot follow because the walls of this portion of the tubule are
impermeable to water
NaCl is actively transported
from the Ascending Loop into the surrounding interstitial fluid
Na+ diffuses from the filtrate into the
cells of the Ascending Loop
Accompanied by the active transport of K+
and Cl-
Ascending
Na+ is then transported to the
interstitial fluid by active transport
(Na+/K+
pumps)
Cl- follows the Na+
by electrical attraction
The effect of NaCl
movement to the interstitial fluid is the same as in the Proximal Tubule
The Ascending Loop however, is not permeable to
water
Tubular fluid becomes dilute as it approaches the
Distal Tubule
Loop of Henle
Reabsorption from Loop of Henle
NaCl is trapped in interstitial
fluid of kidney medulla
Reabsorption from Distal Tubules
Proximal tubules reabsorb
66% of Na+
Distal tubules reabsorb 10%
of Na+
Distal tubules reabsorb H2O if antidiuretic hormone (ADH) is present (also called
Vasopressin)
ADH (Antidiuretic Hormone)
acts on the last part of the Distal Tubule to increase the permeability of the
tubule
Permits water reabsorption
to concentrate the urine
ADH also acts on the
collecting duct to reabsorb water into the blood
Distal Tubule
Na+ and HCO3- ions
are resorbed from the urine in exchange for K+ and H+
excretion
regulating the pH and ionic
concentration of the blood
Functions which are dependent on the hormone aldosterone secreted by the adrenal gland
Distal Tubule
Aldosterone increases Na+
permeability and water reabsorption
Lack of aldosterone causes
Na+ impermeability
Na+ remains in the filtrate and larger amounts
of water are excreted as dilute urine
Tubular Reabsorption
Collecting Duct
As the urine passes down the duct, water moves by
osmosis from the duct into the blood
The collecting tubules aid in concentrating the
urine by water removal
Water transport is possible by the varying
permeability of the collecting duct
Permeability of the collecting duct is under the
influence of ADH
High ADH results in more reabsorption of water (more
concentrated urine)
Low ADH results in the loss of water and diluted
urine
As the urine passes down the duct, water moves by
osmosis from the duct into the blood
Collecting Duct
Tubular Secretion
Filtration is main route by which substances enter
the urine pathway
Secretion is a second way for substances to enter
the urine
Secretion is the opposite of reabsorption
Substances move out of the capillaries into the
interstitial fluid and then into the tubular filtrate
Some antibiotic drugs and plasma protein molecules
are eliminated from the blood by secretion
Secretion of K+
and H+ occur across the distal tubule
Allows the kidney to finely
regulate blood concentrations of K+ and pH
Kidney Physiology
Regulation of Urine Volume
1) ADH
2) Aldosterone
3) Extracellular fluid volume
4) Urine solute concentration
Regulation of Urine
Volume
1)
ADH
Produced by the hypothalamus
Released from the posterior pituitary
Secretion of ADH is
stimulated by increasing solute concentrations in the blood
ADH increases causes a retention
of water and thus decrease in solute concentration
Control of ADH
A)
ADH Presence
More water is reabsorbed
Decrease in urine volume
B)
ADH Absence
Less water is reabsorbed
Increase urine volume
Diabetes
Insipidus
Disease associated with inadequate secretion or
action of ADH
Causes collecting ducts to not be very permeable to
water
Large amounts of dilute urine is produced
Dehydration that results causes intense thirst
2) Aldosterone
Increases Na+
reabsorption in distal tubule with H2O following
3)
Extracellular Fluid Volume
Urine volume relates directly to extracellular fluid
volume (ECF)
ECF ↓ urine
volume ↓
ECF ↑ urine
volume ↑
Rapid ingestion of large amount of fluid and
resulting increased ECF leads to increased urinary output
4)
Urine Solute Concentration
High solute concentration in urine increases urine
volume by osmotic pressure
Untreated diabetes void large amounts of urine because
excess glucose in blood “spilling over”
Influence of Kidney on Blood Pressure
Renal
Hypertension
Decreased
blood flow to kidney
Constriction
of arterioles
Increased
BP
Diuretics
Varying types of diuretics
act on different areas of the nephron
Increases the volume of
urine excreted
Effectively lowers blood
volume
Treats:
Hypertension
Congestive heart failure
Edema
Examples of diuretics
Furosemide
Mannitol
Spironolactone
Complications may arise from the use of diuretics
that cause an excessive loss of K+ in the urine
Hypokalemia (low blood K+)
may result
Can lead to neuromuscular disorders and electrocardiographic abnormalities
Ureters
Tubes
leading from kidney to bladder
Urine
moves by peristaltic movement
Renal
Calculi (kidney stones)
Stones develop in kidney, washed out by urine into ureter
Distend ureter walls
Pain
Kidney Stones
Renal calculi are composed of crystals and proteins
that grow until they break loose and pass into the urine collection systems
Calcium oxalate, calcium phosphate, uric acid, cystine are
normally present in urine in a supersaturated state from which they crystalize
Large stones may obstruct the flow of urine
Can be removed surgically or by a noninvasive
procedure called shock wave lithotripsy
Bladder
collapsible, elastic bag
Ureters
2
Urethra
1
Bladder
Bladder
epithelium is surrounded by thick muscular layer
The urinary bladder is lined by epithelial tissue
which is constantly shed
Rapid proliferation of epithelial cells lining the bladder
gives rise to a high incidence of cancer
Bladder Endoscopy
Endoscopy is often used to help in
diagnosing bladder cancer
Functions of Bladder
1) Reservoir
for urine
2) Expels
urine
distended
causes sensation and desire to void
Micturition Reflex
Involuntary and voluntary muscular sphincters
surround the urethra
Micturition is controlled by reflex
centers in the spinal cord
Stretch receptors in urinary bladder activate this
center
Rhythmic contractions of bladder and relaxation of
involuntary urethral sphincter muscles cause a sense of urgency which is perceived by
the brain
When
urination is consciously allowed to occur the brain
sends impulses to inhibit contraction of the voluntary urethral sphincter
muscles and urine is expelled
Ability to voluntarily inhibit micturition
develops at age 2 or 3
Corticospinal tract needs to grow and connect the
motor cortex of the brain to the spinal motor neurons
Urethra
Passageway
for eliminating urine
Urine
H2O
95%
N2 wastes
Electrolytes
Toxins
Pigments
Hormones
Urine
Blood
in the urine is abnormal and requires a Doctor’s visit
RBC
in the Urine
Oxalate
Kidney Disease
Small declines in renal function do not cause a
problem
Health is maintained with only 50% of renal function
Dialysis or transplant is required if renal function
drops below 10%
Diabetic Nephropathy
High Blood Pressure
Polycystic Kidney Disease
Drug Usage
Acute Renal Failure
Chronic Renal Failure
Glomerulonephritis
Diabetic Nephropathy
If sugar stays in the blood instead of breaking
down, it can act like a poison
High blood sugar levels can cause nephron damage
High Blood Pressure
Can cause damage to the small blood vessels in the
kidneys
Damaged vessels cannot filter poisons from the blood
Renal Blood Vessel Cast
Polycystic Kidney Disease
A genetic disorder in which many cysts grow in the
kidneys
Cysts slowly replace much of the mass of the kidney
leading to kidney failure
Drug Usage
Some over the counter medicines can damage the nephrons
Aspirin, acetaminophen, ibuprofen
Recreational drugs also damage the nephrons
Alcohol, cocaine etc
Acute Renal Failure
Losing a large amount of blood can cause sudden
kidney failure
Some drugs or poisons can cause the kidneys to stop
working
May be reversed if kidneys are not seriously damaged
Chronic Renal Failure
Gradual loss of kidney function
Sometimes called “silent” kidney disease
Glomerulonephritis
Inflammation of the glomeruli
Suspected to be an autoimmune disease
Causative antibodies may be produced as a result of
streptococcus infections (strep throat)
Destruction of glomeruli
can lead to leakage of proteins into the urine
Can lead to edema
Lab Tests for Kidney
Function
Laboratory tests on urine and blood samples can be
performed to test for various kidney malfunctions
Creatine
Urea (Nitrogen)
Protein
Electrolytes (K+, Na+)
Cholesterol
RBC Count (Anemia)
Creatine
Waste product of the blood
Created by the normal breakdown of muscle during
activity
Normally filtered from the blood to the urine
Urea
Waste product of protein metabolism is urea a nitrogen
containing compound
Normally filtered from the blood to the urine
Dehydration or heart failure can also result in high
blood urea
Protein
Normally protein is left in the blood and not
filtered out to the urine
Proteinuria means protein in the urine
Foamy urine in the toilet can be indicative of high
protein in the blood
Electrolytes
Na+
Insufficient removal of Na+
can raise blood pressure
K+
Failure to remove excess K+
can slow the heart rate
Cholesterol
High blood cholesterol levels can accelerate kidney
failure
Research has shown that individuals with high
cholesterol levels are more likely to have kidney problems
RBC Count
Anemia is a condition in which the blood has a low
RBC count
Erythropoietin (EPO) is produced by the kidney which
stimulates bone marrow to produce RBC
Diseased kidneys may not make enough EPO
Dialysis
Dialysis refers to the separation of molecules by
diffusing through a semi-permeable membrane
Two types of Dialysis
1) Hemodialysis (Artificial Kidney)
2) Peritoneal dialysis (CAPD)
Hemodialysis
Blood is sent through a machine that filters away
waste products
Clean blood is returned to the body
Performed three times per week for 3 to 4 hours
Peritoneal Dialysis
A dialysate fluid is
inserted into the abdomen
The fluid captures waste products from the blood
After a few hours the fluid containing the wastes is
drained
Continuous ambulatory peritoneal dialysis (CAPD) is
performed 4 times a day
Can be performed without going to a
Kidney Transplant
A donated kidney may come from a donor who has
recently died or from a living person
The donor kidney has a higher percentage chance of
being successful if the recipient and the donor are a “good match”
A “good match” will have a lower chance of being
rejected by the recipient’s immune system
Immunosuppressant drugs are used to suppress the
immune system to prevent rejection