LEARNING OBJECTIVES
Listed in the Class Notes below=
bold, and blue background
- Read the Class Notes, using the Textbook
illustrations to help understand the concepts. Read the chapter using the
Class Notes as your guide. There are many questions included
to help tie the systems and concepts together into an integrated,
holistic understanding of anatomy and physiology.
- Take the
Ch.
18 self test in the online textbook.
DO NOT EMAIL THIS TEST TO YOUR INSTRUCTOR. It is a learning tool
only.
These tests will also include
questions that are NOT covered in this course.
- Use any resources on the
Online Textbook,
to integrate your learning.
|
Class Notes
Use the diagrams in the book to enhance
comprehension of these concepts.
Chapter 18: The
Urinary
System
The #1 function of the urinary system is to retain water
in the body.
The functional unit of the urinary system is the Nephron.
Urine is produced by the kidney... Specifically, urine
starts out as filtrate, in the renal corpuscle. The nephron
reabsorbs water and nutrients while excreting wastes and other molecules.
There are over 1 million nephrons which collectively reabsorb 99% of the
water from the filtrate - which CONCENTRATES the liquid. Note that
although 99% of the water has been reabsorbed from the urine - urine is
still at least 93% water when expelled from the body.
The urinary system:
1. filters the liquid from the blood, then
2. selectively reabsorbs ions and nutrients and then
3. concentrates the filtrate by reabsorbing water by
osmosis.
|
The filtrate is passed through an increasing osmotic
concentration gradient two (2) times.
|
Each time, more water is reabsorbed
and the filtrate is more concentrated. In this manner, the nephron
reabsorbs 99% of the water in the filtrate.
The renal cortex has an interstitial fluid concentration
of 300 mOsm, the same as blood and normal body tissues. The concentration
in the renal medulla increases toward the renal pelvis and reaches
1200-1400 mOsm. These high concentrations remove water from the filtrate
via osmosis. The filtrate is passed through this gradient two times.
Use the diagrams in the book to enhance
comprehension of these concepts.
Renal cortex:
300 mOsm outer layer of the kidney.
------------------------
Renal medulla:
600 mOsm inner layer
900 mOsm
1200 mOsm middle of kidney
NOTE: Osmolarity is a measure of the concentration of
solutes in a solution. The concentration of the body fluids is
measured in mOsm, or milli Osmoles. The concentration (300 mOsm) of
the interstitial fluid in the renal cortex is the NORM for the entire
body. Concentration is the number of solutes per unit volume.
At 300 mOsm - There are 300 'units' in a volume of
solution.
At 600 mOsm - there are 600 'units' in a volume of solution. i.e. 2 times
as concentrated
as that at 300 mOsm.
At 900 mOsm - there are 900 'units' in a volume of solution. i.e. the
solution is 3 times as
concentrated as that at 300 mOsm.
At 1200 mOsm, that area of the renal medulla is 4 times as
concentrated as the renal cortex.
i.e. there are 4 times as many solutes per unit volume.
The fluids in the renal cortex are in equilibrium with
each other - osmosis causes movement of water until the solutions reach
equilibrium. The interstitial fluids of the renal medulla are
increasingly concentrated - a concentration gradient with about 1350 mOsm
at the point that is deepest in the renal medulla. As a liquid (the
urinary filtrate in the tubules of the nephron) passes through this
increasingly concentrated interstitial fluid, the water osmoses until it
reaches equilibrium between the concentrations inside the tubules and the
interstitial fluids.
The filtrate starts in the renal cortex and passes down through
the increasingly concentrated interstitial fluids in the renal medulla and loses 80% of the water in the filtrate
during this 1st pass through the concentration gradient. Since the
filtrate is almost 100% water, it therefore loses about 80% of the volume
of the original filtrate volume.
Remember: the primary function of the urinary
system is to reabsorb water.
The remaining volume of filtrate (20% of the original
volume) then
goes back up to the renal cortex and passes back down through the renal medulla a
second time, losing more water. About 99% of the water in the original
filtrate volume is reabsorbed by passing the filtrate through this Osmotic
concentration gradient two times.
What is the process by which water
is reabsorbed?
What are the cellular transport processes described in Chapter 3?
Which cellular transport process describes the movement
of water?
What drives osmosis?
Define concentrate and
concentration.
Concentrate - to increase the number of particles
(solutes, ions, electrolytes, etc) in a solution.
You can concentrate a solution by
removing some solvent (but leaving solutes) - osmosis.
Or you can increase the number of
solutes - Active transport; diffusion, and
excretion.
Concentration - a measure of the actual number of particles in a
solution.
You can change the concentration of a
solution by adding or removing some solvent (but leaving
solutes) - osmosis.
Or you can increase or decrease the
number of solutes -
Active transport;
Diffusion, and
Excretion.
The Urinary system uses each of these.
List the location of each process.
The nephron makes the filtrate more concentrated --
producing urine.
The primary method to increase the concentration is
osmosis.
Describe the
functions of the Urinary System
Regulate blood volume and blood pressure
The number one function is to keep water in the body, so that the
blood volume is sufficient
to maintain blood pressure.
Remember Frank Starling's Law of the Heart?
Review Chapter 11, 12, 13.
The heart must have
something to pump. As blood volume decreases, there is less
blood to pump.
Therefore, blood pressure decreases, and less oxygen and nutrients
are delivered to the
peripheral tissues.
Regulate plasma ion concentration
Reabsorb electrolytes, ions, etc.
Regulate pH of the blood - excrete or reabsorb H+
and other 'acids'.
Conserve valuable nutrients - sugar, proteins,
amino acids, etc
Excrete metabolic wastes, toxins, and excess water
soluble nutrients
Describe the location and general function of each organ
in the urinary system
4 organs
Kidneys (two) - where the filtrate is produced and
concentrated into urine.
Retroperitoneal - outside the peritoneum.
Two regions
cortex - the outer region - where filtrate
is produced
The solute
concentration of the interstitial fluid is the same as that of the blood
(and all other
bodily fluids)
medulla - the inner region - where water
is filtrate is concentrated to produce urine.
The
solute concentration of the interstitial fluid steadily increases with
depth into the center
of the medulla (kidney).
UREA - the primary solute that creates the concentration gradient.
Na+ - sodium - adjusts the concentration of the interstitial
fluids.
Ureters (two) - peristalsis transports urine from the kidneys to the urinary
bladder.
Retroperitoneal.
Urinary bladder - Temporary storage of urine.
Urethra - transports urine and dumps it outside the body
Gravity is the primary force.
Males: About 7 inches long. Transports both urine and
semen.
Females: About 1 inch long. Only transport urine.
What organ produces urine?
What are the two main regions?
What is the general activity in each region?
What is the function of urea in the
interstitial fluid of the renal medulla?
What is the function of Na+ in the
interstitial fluid of the renal medulla?
Name the parts of a nephron
The Nephron is the functional unit of the kidney.
There are about 1 million nephrons which produce the filtrate - the ions and water
are reabsorbed,
and
wastes excreted.
There are 2 basic parts of the nephron: (use
the illustration in your text)
1.
Renal corpuscle – where filtrate is produced. Filtrate is 300
mOsm.
Bowman's capsule- the Capsule that surrounds the Glomerulus.
Glomerulus – the capillary bed inside the bowman's
capsule where the filtrate
is ‘squeezed’
from blood.
2. a Tube system - where the filtrate is
concentrated (water reabsorbed) and wastes
excreted. (aka 'tubules')
Proximal convoluted tubule
(PCT) – reabsorption of
nutrients: ions, organic molecules, vitamins, and water.
This is the first section of the tubule system and
receives filtrate directly from
the renal corpuscle.
In the renal cortex - active transport of
ions and diffusion pull nutrients into
interstitial spaces - water follows
due to osmosis.
Descending limb of loop of Henle – reabsorption of
nutrients and water.
Transports the filtrate from the cortex
down into the medulla.
This is the FIRST time the filtrate passes down into the renal
medulla through
the concentration gradient. Reabsorbs 80% of the
volume (water) from the
original filtrate, as it goes deeper into
the medulla where the interstitial fluid
becomes steadily more concentrated
(600 to 900 to 1335 mOsm) .
Osmosis.
Active transport and diffusion of nutrients.
Loop of Henle – in the medulla, the point for a
nephron with the highest
concentrated interstitial
fluid.
Only 20% of original filtrate volume is left – filtrate is
CONCENTRATED.
This is the 'turnaround point' - where filtrate heads
back toward the cortex
(remember - the
filtrate must pass through the concentration gradient in the
medulla 2 times).
Ascending limb of loop of Henle – transports the
remaining 20% of filtrate from
the medulla back to the cortex.
The Na/K pump in the
walls of the tube reabsorb Na+ into the interstitial fluids
of the medulla and
secretes K+ into the filtrate. The walls of the tube are
waterproof. No water reabsorption or loss. Removal of Na+
returns the
concentration of the filtrate to 300 mOsm.
Describe the Na/K pump.
Review Chapter 3, 4, and 7, 8, and 9 Muscular
and Nervous systems - Resting
Membrane Potential, Action Potential, etc.
| Physical
exercise results in sweating
(loss of water). The nephron reabsorbs water - partly by
increasing the Na/K pump in the ascending limb of the loop of
Henle. Water is reabsorbed - BUT K+ are lost.
Loss of K+ can result in 'cramps'.
Review Chapter 7, 8, and 9 - RMP, AP and the neuro-muscular
junction and the sliding filament theory of muscle contraction.
If too little K+ can cause problems with
skeletal muscle contractions - what is the effect on cardiac
muscle? |
What is the
function of Na+ in the interstitial fluid of the renal medulla?
The remaining volume of filtrate
passes from the region of the renal medulla back to the renal cortex via
the ascending limb of the loop of Henle.
Distal Convoluted Tubule (DCT) – the part of the
tubule farthest from the renal
corpuscle.
Back in the renal cortex, the remaining 20% of the filtrate
now has a solute
concentration of 300 mOsm again
(remember,
Na+ were reabsorbed in the Ascending limb) –
but the volume is 20% of original volume
(80% of the water has been
reabsorbed).
Waste
products: H+, drugs, urea and uric acid, etc are excreted here.
One of the functions of the
urinary system is to regulate pH - therefore, H+
are excreted
here.
Collecting Duct – receives filtrate from many DCTs,
i.e. LOTS of nephrons.
Filtrate that enters is 300 mOsm.
It passes the filtrate through the increasingly
concentrated osmotic gradient of the renal
medulla a second time, and more water is
removed. By the time the filtrate drips into
the renal pelvis (as urine) only about 1% of the original volume remains
- about 99% of
the original volume was reabsorbed by passing the filtrate through the
osmotic gradient
2 times!!
What is the
primary function of the urinary system?
Filtrate - the liquid in the nephron and collecting
duct from which water and nutrients are
reabsorbed and into which wastes are excreted.
When the concentrated liquid passes
through the renal papilla into the minor calyx it
is called
Urine - the liquid entering the minor calyx. From this point
on... the components are no
longer changed - no more reabsorption, no more
excretion.
How much water, as a percentage, is reabsorbed from the
filtrate?
What ‘force’ causes this reabsorption of water?
Reveiw Chapter 3, Cellular Transport Mechanisms.
How is the nephron able to reabsorb so much water?
Be sure you know the sequence of the nephron structures.
Know their relation to each other and the function of
each part.
What is the renal corpuscle?
Name the parts.
What is the bowman's capsule?
What is the glomerulus?
Describe it.
List the parts of the nephron and the function of each part.
What do 'proximal' and
'distal' mean in the context of the renal corpuscle and the PCT and DCT?
Which parts are located in the renal cortex and which are in the renal
medulla?
Define 'cortex' and 'medulla'.
List all the places in the body where a cortex and a medulla are
found.
In the nephron:
Where are nutrients reabsorbed?
Where does filtration occur?
Where are wastes and toxins excreted?
Where is water reabsorbed?
Where is excess K+ lost?
Define glomerular filtration rate
GFR (Glomerular Filtration Rate) is the amount of filtrate produced in the kidneys
each minute. With 1 million nephrons there is about 6 m2 of filtration surface,
which produces about 125 ml/min! or 180 l (50 gal)/day of
filtrate! 99% is reabsorbed (60-70% between the glomerulus and the Loop of
Henle). 1.2 l/day of urine produced.
NOTE: the nephrons produce 180 l/day of filtrate
but only 1.2 l/day of urine!
They reabsorb 99% of the volume of the filtrate (water).
The walls of the glomerulus (like other capillaries)
have fenestrate (tiny holes). Capillary blood pressure forces water
and small solutes OUT of the capillary into the space around the
glomerulus and within the bowman's capsule. This solution (water and
solutes) is the filtrate.
Capillary blood pressure must exceed blood osmotic
pressure so that water can be forced out of the capillary. Filtration pressure
is the net pressure difference between
capillary blood pressure and blood osmotic pressure. Efferent arteriole
diameter is smaller than afferent diameter. Ca. 10 mm Hg. Slight decreases
in BP will stop glomerular filtration – hemorrhaging, shock, dehydration
can cause dangerous or even fatal reduction in kidney function.
What does GFR stand for?
How much filtrate is produced per minute?
How much filtrate is produced per day?
What is the 'force' that causes the
solution to 'filter' out of the capillary through the finestrae.
Why are the nephrons so effective at
reabsorbing water?
They pass the filtrate
through the osmotic gradient of the renal medulla two times!
| When blood pressure drops,
the flow of blood to the kidneys is reduced (to maintain blood flow
to the vital organs). Prolonged reduction of blood flow can
result in permanent damage to the kidney tissues.
Long distance running, marathon and
triatheletes, often lose so much water that kidney function stops
completely - due to low capillary blood pressure - due to the
Sympathetic Nervous System shunting blood flow to the brain, heart,
lungs and skeletal muscles. |
Explain the interaction between capillary blood pressure
and blood proteins
How is the filtrate produced?
Blood proteins, RBCs, platelets, etc are too large to pass through the
finestrae of the glomerulus and therefore are retained inside the
capillary while water and smaller molecules are forced out of the
capillary (due to capillary blood pressure) through the finestrae.
Water continues to be forced out of the blood until the
capillary blood pressure is equal to the osmotic blood pressure - the two
opposing pressures reach equilibrium.
In the capillary beds of the normal peripheral tissues:
As water is forced out via hydrostatic pressure, the
amount of water inside the capillary decreases and the blood protein
concentration therefore increases. This sets up an osmotic pressure
gradient that ‘pulls’ water back into the capillary.
At the arteriolar end of the capillary bed, capillary
blood pressure is greater than osmotic pressure resulting in a net
movement of water out of the capillary. At the venule end, osmotic
pressure within the capillary is similar to that in the interstitial
spaces and higher than the hydrostatic pressure, resulting in a net
movement of water into the capillary.
In the nephron:
The blood passes out of the glomerulus - but the filtrate passes from the
renal corpuscle into the proximal convoluted tubules.
Compare and contrast filtrate
production vs normal capillary functioning.
Describe how the kidneys function in maintaining normal
blood volume and pressure
1. The reabsorption of water from the filtrate puts water
back into the vascular system.
(the filtrate was forced from the vascular
system)
2. Putting the water into the vascular system maintains
Blood Volume
3. Maintaining blood volume maintains Blood Pressure.
How is water returned to the vascular
system?
Water is reabsorbed via osmosis into the interstitial
spaces. Capillaries, that have lost filtrate in the glomerulus, pass
down into the renal medulla. As it passes down the concentration
gradient, the fluid inside the capillary goes to equilibrium with the
interstitial fluids. By the time the capillary reaches the innermost
area of the renal medulla, the concentration of the blood is about 1300 mOsm.
As the capillary heads back to the Renal Cortex, the now highly concentrated
blood osmotically pulls water from the increasingly less concentrated
interstitial fluids.
Water osmoses back into the venous capillaries.
Define osmosis, active transport,
diffusion.
Review Chapter 3, Cellular
Transport Mechanisms
State the hormones that affect kidney function
These three hormones CONCENTRATE urine - they cause the
nephron to reabsorb MORE water.
ADH
Aldosterone
Renin
When the levels of these hormones increase, then MORE
water is reabsorbed.
I.e. LESS urine is produced.
The urine is CONCENTRATED.
What happens to urine when you
exercise, work, or play, without drinking lots of water?
Why?
This 1 (one!) hormone DILUTES urine - it shuts down the
other hormones -and causes the nephron to excrete more water.
ANP
When the levels of ANP increase, LESS water is reabsorbed.
I.e. MORE urine is produced.
The urine is DILUTE.
What happens to urine when you drink
lots of water.... or....beer?
Why?
Where are ADH, Aldosteron, Renin and ANP produced?
Review Chapter 10, Endocrine System.
What is the function of each?
Compare and contrast Concentrated with Dilute.
Define dehydration and hydration.
Compare and contrast the effects of hydration and dehydration on:
ECF and ICF
production of ADH, Aldosterone, Renin,
and ANP
Blood volume and Blood Pressure.
Concentration of bodily fluids
(blood, lymph, cerebrospinal fluid, etc), filtrate, urine, etc.
Define diuretic, antidiuretic.
Caffeine is a diuretic
- what does this mean?
Describe how the kidneys help to maintain normal blood pH
and electrolyte balance
Wastes such as uric acid, toxins and drugs are secreted
into the Distal Convoluted Tubule and then out of the body in urine.
When the body is too acidic - too many H ions - excess H+
are secreted into the DCT and out of the body in urine.
Excess H+ (acid), K, other ions, drugs and Nitrogenous
wastes are excreted in what part of the nephron?
|
Regulation of pH
There are three methods by which pH is
regulated:
Respiratory system - controlling the
breathing rate (hyperventilate vs.
hypoventilate) rapidly controls the level of carbonic acid,
and
therefore the level of H+.
Blood proteins - plasma
proteins such as albumins, are polar
molecules and can H-'bond' to H+ or release bonded H+ as
needed.
Kidneys - excrete excess acids and H+. |
Describe the three methods by which
the body regulates pH.
How does hyperventilating and hypoventilating affect carbonic acid and
pH?
Review
Chapter 15, Respiratory System.
How does H-bonding to plasma proteins affect pH.
Review Chapter 2, and 11.
How does the kidney regulate pH?
Define:
acidosis,
acidotic,
alkalosis,
alkalotic,
pulmonary acidosis,
pulmonary alkalosis,
metabolic acidosis,
metabolic alkalosis.
Review Chapter 15, pH regulation
What is the set point for pH in the
body?
How does the set point affect whether a person is considered
acidotic or alkalotic?
What is the range of pH in the body?
Why is it important to maintain the
pH within the 'range'?
Define denature. Review Chapter
2, Organic Molecules.
Describe the characteristics of normal urine
normal pH
average 6; range 4 to 8
(depends on diet)
water content
93% to 97%
concentration (osmolarity)
1300 mOsm to 855 mOsm
specific gravity
1.03 gm/cm3 to 1.003 gm/cm3
daily volume
about 1.2 liters
color
clear yellow
odor
varies with diet (asparagus can cause an 'odor', etc)
bacterial content
Sterile
What is the connection between water content,
concentration and specific gravity?
The lower the water content (93%) the higher the concentration, and
heavier (specific gravity)
Solutes increase the 'mass (weight)' - therefore, urine
is heavier than pure water.
Solutes decrease the percentage of water,
therefore, increased
solute concentration = lower percent water.
What affects urine color and odor?
What affects daily volume?
Total fluid (water) intake.
Compare and contrast Filtrate (in the
bowman's capsule) and Urine.
Nephrons are exposed to many adverse conditions over time
and become damaged. Eventually, many stop functioning, resulting in
kidney failure.
2 compartments: ICF and ECF.
The Components of the fluids differ but osmolarities are identical
- because the water
osmoses until it reaches equilibrium.
The two fluids are in equilibrium with each other.
How does water move back and forth between the two
compartments?
What is the force that drives the movement of water?
(see Chapter 3, cellular transport mechanisms)
The Osmolarities of the ICF and ECF are identical because water moves back and forth between ICF and ECF
due to osmosis until equilibrium is established. Anytime there is
the least concentration difference, water osmoses until equilibrium is
re-established.
Osmolarity is a measure of the solute concentration
of a solution.
Explain how water is taken in by the body and exits the
body.
Review the Characteristics of Water.
The two water compartments of the body.
How water moves between the two water compartments.
