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Chapter: 17 Excretory System
and Liver
• All animals excrete nitrogenous
waste products and some animals
also balance water and solute concentrations.
• The chemical composition
of the blood is regulated by
the liver.
I.
Nitrogenous waste products and excretion
A. Excretion: process of removing metabolic
wastes and helps to maintain homeostasis by
regulating the content of water and other
substances in the blood
1. Blood plasma of an animal is a constantly
changing solution
2. Blood supplies the substances needed for
an animal’s metabolism and removes
molecular waste products from tissues
3. Blood needs to be continuously filtered
and cleaned
B. Waste products from the metabolism of amino
acids
1. Body has no way to store excess amino
acids (not needed for protein synthesis)
2. Deamination: chemical changes in which
the amine group (NH2) is removed
3. Amine group is incorporated into 3 types of
waste molecules
a) Ammonia
b) Urea
c) Uric acid
4. Kidney: all mammals and some other
animals use it to filter and clean the blood of urea
and other wastes
5. Malpighian tubules: structures in insects to
filter the blood
C. Evolutionary history, habitat, and the type of
nitrogenous waste
1. Nitrogenous waste: contains one or more
atoms of nitrogen from deamination of amino
acids
a) Animals form of nitrogenous waste is
based on ancestral origins and the
emerging species is most likely to use
the same nitrogenous waste type
b) Animals can’t evolve an entirely new
physiology even when they undergo enough
change to qualify as a new species
Nitrogenous waste slides
2. Fish: use ammonia
a) Aquatic habitat means that they have an
unlimited watery supply that they can use to
dilute and flush out the highly toxic ammonia
b) Ammonia is very energy inexpensive
Paramecium
3. Mammals: produce and excrete urea
a) Urea is only toxic at relatively high
concentration levels and mammals can cope
with certain levels of urea
b) Level of urea needs to be kept under control
by the constant filtering of the kidneys
c) Urea is a component of urine and can be
stored in the bladder
d) Water is not as accessible to mammals like it
is to fish, so their system needs less water for
dilution and elimination compared with ammonia
4. Birds and reptiles: egg that is self-contained for
nutrients and water for development and hatching
a) Ammonia can’t be stored within egg, so
evolutionary solution was uric acid
b) Uric acid is not water soluble and can be
stored within the egg, but it is energy expensive
to produce
c) Adult bird continue to produce uric acid and
allows them to require less water
5. Insects: uric acid using Malpighian tubules
a) Insects have an open circulatory system, so their
internal organs are bathed in blood
b) Malpighian tubules: small tubes that lie within
the pools of blood
i) Closed at distal end and open into the
insect’s gut at the proximal end
ii) Nitrogenous waste (uric acid), water and
many salt ions (Na+, K+, Cl-) remain in the
tubules are eliminated
iii) Useful substances, non-excess water, and
unused nutrients from the blood are
transported back into the pool of blood of the
body cavity
Note: Humans and other vertebrates have a closed
circulatory system: Blood is contained in vessels
Slides
D. Anatomy and function of the kidney
1. Function: Filter waste products from the blood
2. Two bean-shaped organs located in the back
behind the stomach and liver
3. Urine: fluid produced by the kidneys that
consists of water and dissolved waste products
that have been removed from the blood
4. Structure
a) Cortex: outermost portion
b) Medulla: inner portion
c) Renal pelvis: funnel-shaped structure in the
center in which urine is collected
d) Renal artery: transports nutrients and wastes
into the kidneys
e) Renal vein: carries filtered blood out of kidneys
Draw a kidney
Structure of the Kidneys
Section 38-3
Kidney
Nephron
Bowman’s
capsule
Cortex
Capillaries
Glomerulus
Medulla
Renal
artery
Renal vein
Ureter
Collecting
duct
Vein
To the bladder
Artery
Loop of Henle
To the ureter
E. Nephrons: filtering units of kidneys
1. Each kidney has 1.25 million nephrons
2. Nephron structure includes
a) Glomerulus: capillary bed which
filters various substances from the blood
b) Bowman’s capsule: surrounds the
glomerulus
c) Small tubule that extends from Bowman’s
capsule
i) Proximal convoluted tubule
ii) Loop of Henle
iii) Distal convoluted tubule
d) Peritubular capillary bed: second capillary
bed that surrounds the three part tubule
Nephrons
3. Materials are exchanged between tubule and blood
by three major processes
a) Ultrafiltration: process by which various
substance are filtered through the glomerulus from
the blood into Bowman’s capsule
b) Reabsorption: process that recovers needed
substances are returned to the blood
c) Secretion: process in which substances (waste)
pass from blood into filtrate in the distal
convoluted tubule
Kidney processes
Section 38-3
The Nephron
Reabsorption
Filtration
Most filtration occurs in the
glomerulus. Blood pressure forces
water, salt, glucose, amino acids,
and urea into Bowman’s capsule.
Proteins and blood cells are too
large to cross the membrane; they
remain in the blood. The fluid that
enters the renal tubules is called
the filtrate.
As the filtrate flows through the
renal tubule, most of the water
and nutrients are reabsorbed into
the blood. The concentrated fluid
that remains is called urine.
Secretion
Substances such as hydrogen
ions are transferred from the
blood to the filtrate.
F. Blood is ultrafiltered within Bowman’s capsule
1. Afferent arteriole: small branch of the renal
artery that brings unfiltered blood to the nephron
2. Inside Bowman’s capsule, afferent arteriole
branches into the glomerulus
a) Glomerulus walls have fenestrations (small
slits) that open when blood pressure is
increased
b) Efferent arteriole: drains blood from the
glomerulus and has a smaller diameter than
afferent
c) Connecting a larger diameter blood vessel
to a smaller diameter creates a higher pressure
where they join in the glomerulus
3. Ultrafiltration: process by which various
substances are filtered through the glomerulus
under unusually high blood pressure in the
capillary bed
4. Filtrate: fluid that is ultrafiltered from the
glomerulus passes through the basement membrane
(prevents large molecules like proteins from
becoming a part of the filtrate)
5. Filtrate then enters the proximal convoluted
tubule
6. Blood that did not get filtered, including all of
the cells, proteins, and other molecules, exit the
Bowman’s capsule by the efferent arteriole
G. Reabsorption recovers substances that are needed
1. Filtrate: contains needed substances that body
can’t lose as a part of the urine
a) Most of water
b) Many salt ions
c) All of the glucose
2. These substances are reabsorbed back into the
blood
Note: Total volume of blood is filtered about 25 times
each day. Reabsorption is very important.
3. Much of reabsorption occurs in proximal convoluted
tubule
a) Substances leave the tubule and are put back into
the blood via the peritubular capillary bed
(surrounds (peri-) the tubule)
b) Proximal convoluted tubule wall is a single cell
thick made up of a single ring of cells
i) Lumen: interior of the tube that filtrate
flows through
ii) Microvilli: located on the interior side of
the cells to increase surface area for
reabsorption
4. Types of transport mechanisms for reabsorption
a) Salt ions (Na+, Cl-, and K+): leave the filtrate
and are returned to the blood
i) Actively transported into the tubule cells
ii) Move into the intercellular fluid outside
the tubule
iii) Salt ions are taken into the peritubular
capillary bed
b) Water: moves by osmosis following the movement
of the salt ions
i) Water moves from a hypotonic region to a
hypertonic region following the pathway of
the solutes
ii) Water remains in the filtrate awaiting a
control mechanism that will determine how
much water the body can eliminate in the urine
c) Glucose: active transport moves all of the
glucose in the filtrate back into the blood
H. Secretion: substances pass from blood into
filtrate in the distal convoluted tubule
1. Wastes and toxic materials
2. Hydrogen ions to adjust pH of blood
I. Formation of urine: remaining fluid and wastes
in the distal convoluted tubule form urine
1. Flows into a collecting duct where more
water moves out
2. 99% of water is returned to the blood by the
end of the process
Process
J. Kidney nephrons and osmoregulation
1. Water is the solvent of life and is in almost
all body fluids
a) Cytoplasm, blood plasma, lymph,
and intercellular fluid
b) Some water needs to be eliminated
in the urine each day
2. Amount eliminated depends on many
physiological factors
a) Total volume of water ingested as liquid
and food
b) Perspiration rate: exercise level and
environmental temperature
c) Ventilation (breathing) rate: water is
exhaled when we breathe out: dependent on
activity/exercise level
3. Osmoregulation: body’s response mechanisms
that attempt to maintain homeostatic levels of
water
4. Loop of Henle creates a hypertonic environment in
the medulla of the kidney
a) Remaining water and dissolved solutes
enters the descending portion of the loop of
Henle
b) Segment of the loop is permeable to water
but impermeable to salt ions loop of Henle
c) Filtrate then enters the ascending portion of the loop of
Henle: impermeable to water, but permeable to salt ions
d) Filtrate moves up the ascending portion of the loop, salt
ions are pumped out and enter the intercellular fluid
e) Loop of Henle extends down into the medulla of the
kidney: medulla is an area with many ions (hypertonic) in
comparison with the fluids within the tubules
f) Some water moves out of the descending portion by
osmosis, the filtrate that moves up the ascending loop and
into the distal convoluted tubule is still hypotonic (high water
content)
Nephrons Kidney
5. ADH controls reabsorption of water in the
collecting duct
a) Filtrate that enters collecting duct is a
dilute form of urine with a high amount of water
b) Some of the water is reabsorbed through the
wall of the collecting duct
c) Collecting duct is differentially permeable to
water and depends on the presence or absence of
antidiuretic hormone (ADH)
d) ADH is secreted from the posterior lobe of the
pituitary gland and targets the tissue of the
kidney collecting ducts
e) ADH present: collecting duct becomes
permeable to water and water moves by osmosis
out of the collecting duct and into the medulla
interstitial fluid to the peritubular capillary bed and
into the blood
f) ADH absent: collecting duct becomes
impermeable to water and water stays in the
collecting duct and urine is more dilute ADH
6.Longer loop of Henle is an adaptation for water
conservation
a) Kidneys are highly diverse organs when
you compare different species
i) Frogs and toads have virtually no loops
of Henle and are unable to conserve water
by mechanism involving a hypertonic
medulla and reabsorption of water from the
collecting duct so their urine is dilute
ii) Vertebrate animals that live in the desert
means that they have adaptions for water
conservation
iii) Kangaroo rat: recycle almost all of their
water and lose very little water to urine due to
a very long loop of Henle that produces a
large hypertonic area for water reabsorption
using ADH mechanism
K. What changes do the kidneys make to the blood?
1. Comparison of the composition of blood entering
a kidney and blood leaving the kidney
a)
b)
c)
d)
e)
f)
Lowered amount of urea
Lowered amount of salt ions
Lowered amount of water
Nearly identical amount of glucose
Nearly identical amount of protein
No change in blood cells
2. Osmoregulators: animals with internal tissues that
have a different solute concentration compared with
environment
a) Need mechanisms that
regulate water balance and
expend energy to achieve it
b) Most animals are
osmoregulators
3. Osmoconformers: animals that have internal
tissues that have the same solute concentration
as their environment (iso-osmotic)
a) Do not need mechanisms to take in or to
eliminate water as water moves in and out
freely because of the osmotic balance
b) Animals are restricted to living in only
those environments to which they are isoosmotically matched
L. Kidney failure: 2 options for patient
1. Kidney dialysis/hemodialysis: patient’s
blood is pumped into a device that contains a
large surface area of a membrane (dialysis
membrane)
a) One side of membrane is patient’s blood
and the other is dialysate (solution similar in
the makeup of blood but without the urea at
the start of process)
b) Urea from blood diffuses through the
membrane and enters the dialysate
c) Balance of water and some ions can be
regulated by adjusting which fluid on either
side of the dialysis membrane has a greater
concentration of each substance
d) Dialysis takes several hours each session
and must be repeated every 1-3 days
Dialysis
Video
Kidney Dialysis
Section 38-3
Blood in tubing flows
through dialysis fluid
Blood pump
Vein
Artery
Used dialysis fluid
Shunt
Air detector
Dialysis
machine
Fresh
dialysis
fluid
Compressed
air
2. Kidney transplant: receive a new kidney from a
donor
a) Patient’s and donor’s tissues must match to
minimize rejection of the organ by the patient’s
immune system: still need to take immunesuppressing drugs
b) Can live normally with one kidney, so a
family member with a tissue match can donate
c) Long waiting list for a kidney from a deceased
donor
M. Other medical issues related to the kidneys
1. Kidney stones: crystalline structures that
form within the kidneys and can cause
blockages and severe pain (especially if they
pass through ureter)
a) Can be broken up into
smaller pieces by ultrasound so
they can pass through the normal
urinary tract
2. Testing urine for chemical composition: can provide
doctor with information concerning you physiology
a) Glucose: healthy person should have no
glucose in urine: should be reabsorbed in
proximal convoluted tubule: can indicate
diabetes if glucose is present in urine
b) Blood cells: Glomerular filtrate should have
no blood cells since they are too large to fit
through the fenestrations of the glomerulus
i) Sign of kidney malfunction
ii) Infection
iii) Bleeding in renal tubes
c) Proteins: too large to fit through the
glomerulus and shouldn’t be found in urine could
indicate many different diseases or conditions
including kidney disease, low blood sugar in
diabetics, high blood pressure, and problems
during pregnancy
d) Drugs: most drugs are filtered in the kidneys
and it has become common for employers and
sports teams to test individuals for prescribed or
unauthorized chemicals
3. Dehydration: too little water intake video
4. Overhydration: too much water intake
Symptoms for both can be serious because water
tis the solvent component of our blood and
cytoplasm
Urine analysis lab
N. Elimination of urine
1. Urine from collecting ducts enters the renal pelvis
2. Ureter: narrow tube that leads from each kidney to
bladder
3. Urinary bladder: muscular sac that stores urine
4. Urethra: tube from bladder that leads out of the
body
Section 38-3
The Urinary System
Vein
Kidney (Cross Section)
Kidney
Cortex
Medulla
Ureter
Urinary bladder
Urethra
Artery
5. Body must remove 500 ml of urine each day to
remove toxic materials from body
6. Adult removes 1.5 L to 2.3 L a day
II. Excretory system
A. Kidneys: primary organs of the excretory system
1. Life –threatening situation if kidneys fail
2. Can survive using one kidney
B. Lungs
1. Eliminate carbon dioxide
2. Carry out detoxification: altering
harmful substances so that they are not
poisonous
C. Skin: secretes sweat to remove excess water and salt
1. Person working in extreme heat can excrete 1L of
water per hour by sweating
2. 10-30 g of salt per day
Types of excretion
Calculation
How much blood does the glomerulus (kidneys)
filter per day?
125 mL of blood is filtered per min
Answer
125 ml/min x 60 min x 24 hr = 180,000 mL /day
1 hr
1 day
180,000 mL x 1 L
= 180 L / day
1000 mL
180L is 47.5 gallons
III. Functions of the liver: remove some substances from
the blood and add others
A. Circulation of blood to and from the liver
1. Liver receives blood from two major blood
vessels and is drained by one
a) Hepatic artery: branch of aorta and
carries oxygenated blood to the liver
tissues
b) Hepatic portal vein: supplies blood to
liver
c) Sinusoids: capillaries of the liver that
blood is carried into
d) Hepatic vein: drains the sinusoids and
blood vessel that takes blood away from liver
2. Hepatic portal vein receives blood from the
capillaries within the villi of the small intestine
and blood within portal vein varies in two ways
from blood that normal enters an organ
a) Low pressure and deoxygenated since it
has already been through a capillary bed
b) Varies in the quantity of nutrients (glucose)
depending on the types of food and timing of
ingestion, digestion, and absorption of food
3. Hepatic vein blood is also low-pressure and
deoxygenated blood, but it doesn’t vary in
nutrients
4. Stabilization of nutrients within the hepatic vein
represents one of the major functions of the
liver
a) Storage of nutrients
b) Release of those nutrients when needed
5. Portal system of circulation: blood travels
through two capillary beds before returning to the
heart to be re-pumped
B. Sinusoids are the capillaries of the liver
1. Hepatocytes (liver cells): job is to
remove or add substances
2. Sinusoids: where exchanges occur
between the blood and the hepatocytes
a) Oxygen-rich blood from hepatic
artery and sometime nutrient-rich blood
from hepatic portal vein both flow into
sinusoids
3. Sinusoids differ from typical capillary beds
a) Wider than capillaries
b) Lined by endothelia cells with gaps
between them
c) Gaps allow large molecules like proteins
to be exchanged
d) Hepatocytes are in direct contact with
blood components making all exchanges
with blood more efficient
e) Sinusoids contain Kupffer cells that help break
down hemoglobin released form older erythrocytes
for recycling cell components
f) Sinusoids receive a mixture of oxygenated
blood (hepatic artery) and nutrient-rich blood
(hepatic portal vein) which eventually drains
into small branches of the hepatic vein
C. Liver removes toxins from the blood
1. Humans ingest a lag number of toxic
substance each day that our bodies eliminate
a) Pesticides and herbicides added to
food produce
b) Food preservatives and food flavor
enhancers
c) Medications and alcohol
2. Kupffer cells: line the inside of sinusoids and
use phagocytosis to remove old erythrocytes
and bacteria from the blood
a) Contain many lysosomes
b) Specialized leucocytes (white blood cells)
3. Hepatocytes: most numerous and most active in
removing and processing chemical toxins from
the blood
a) They are bathed with the plasma
components of the blood
b) Extract toxins from the plasma and do a two
step process to eliminate the toxins
i) Chemically modify the toxin to make it
less destructive
ii) Add chemical components that make it
water soluble
c) Water soluble substance is added back to blood
so it can be eliminated by the kidneys in urine
D. Alcohol consumption damages liver cell over
time
1. Hepatic portal vein brings absorbed
alcohol to the liver first and any alcohol not
removed the first time will be brought back
through the liver sinusoids by the hepatic
artery
2. Each time the blood passes through the
liver the hepatocytes attempt to remove the
alcohol from the blood, so it has a magnified
effect on liver tissue
3. Long-term alcohol abuse has three primary effects
on the liver
a) Cirrhosis: scar tissue left when areas of
hepatocytes, blood vessels, and ducts have been
destroyed by exposure to alcohol (areas no
longer function)
b) Fat accumulation: damaged areas of liver
will build up fat in place of normal liver tissue
c) Inflammation: swelling of damaged liver
tissue as a result of alcohol exposure (alcoholic
hepatitis)
E. Regulation of nutrients in the blood
1. Solutes that are dissolved in blood plasma
must stay within a normal homeostatic range
or there will be problems in the body
2. Maintaining glucose levels in the blood
a) Lowest in morning and highest after
a meal
b) Hepatic portal vein will contain blood with a
very high concentration of glucose after a meal
high in carbohydrates
c) Blood enters sinusoids and some of the excess
glucose is taken in by hepatocytes and
converted to glycogen (helps to keep glucose
level in the blood in normal range)
d) Stored glycogen can be seen
as large vesicles or granules
e) Not eaten: blood glucose levels decrease so stored
glycogen in granules is reconverted to glucose and
added into blood in the sinusoids
f) Homeostatic mechanisms are regulated by
hormones from pancreas
i) Insulin: stimulates hepatocytes to take in
and convert glucose to glycogen when
glucose level is high
ii) Glucagon: stimulates hepatocytes to convert
glycogen back to glucose when glucose level is
low
3. Other nutrients that can be stored in liver
F. Liver recycles components of erythrocytes and
hemoglobin
1. Erythrocytes: life span of 4 months and
need to be replaced by the blood cell forming
tissue of the bone marrow
a) Erythrocytes are anucleate (no
nucleus) so they can’t undergo mitosis
or code for new proteins within the cell
2. At the end of its cellular cycle the erythrocyte’s
membrane becomes weak and ruptures (occurs in
spleen, bone marrow or in bloodstream)
a) Millions of hemoglobin molecules are
released and circulate the bloodstream
b) Circulating hemoglobin are ingested by
Kupffer cells within the sinusoids by
phagocytosis since hemoglobin is a very
large protein
c) Inside the Kupffer cells the hemoglobin is
disassembled into its component parts
i) Four globin proteins are hydrolyzed into
amino acids
ii) Amino acids are released back into blood and
become available to any body cell for protein
synthesis
iii) Iron atom is removed from each heme group:
some is stored in liver and some sent to bone
marrow to make new erythrocytes
iv) Bilirubin/bile pigment: Remaining heme group
without iron is absorbed by hepatocytes and
becomes a part of bile
G. Hepatocytes produce and secret bile and plasma
proteins
1. Bile: added to duodenum during digestion
of fatty acid in order to emulsify fats
a) Lipids tend to coalesce (clump) together
which makes it difficult for lipase to digest the
lipids
b) When bile is added, the resulting
emulsification does not chemically change the
lipids but it breaks up the clumps and increases
the surface area for lipase to catalyze the
digestion
2. Hepatocytes produce bile by converting extra
cholesterol into bile salt which are added to
bilirubin making the bile
a) Bile salts are the emulsifying portion of bile
3. Hepatocytes produce many types of plasma
proteins (proteins that are added into the blood)
a) Albumin: regulates blood osmotic
pressure and acts as a carrier for bile salts and
other fat-soluble substances
b) Fibrinogen: gets converted to fibrin to
form the mesh component of a blood clot
4. Plasma proteins secreted by hepatocytes by the
following process
a) DNA within nucleus of hepatocyte
synthesizes a mRNA for a particular protein
(transcription)
b) mRNA exits the nucleus through pore
c) mRNA finds ribosome on rough ER
d) Plasma protein is synthesized (translation)
e) Plasma protein is transported by a vesicle
to the Golgi apparatus
f) Golgi modifies the proteins and surround it
in another vesicle
g) Vesicle goes to the plasma membrane for
exocytosis (secretion)
h) Plasma protein enters the blood plasma
H. Causes and consequences of jaundice
1. Jaundice: condition characterized by having too
much bilirubin circulating in the bloodstream and
within the body tissues
2. Bilirubin is a yellow pigment so people with
jaundice have a yellow tinge to their skin and
yellowing of the withes of their eyes
3. Bilirubin is formed when hemoglobin molecules
are processed from dying erythrocytes
d) Baby’s liver can then mature for full processing
of bilirubin into bile
e) Severe consequence of untreated jaundice is
acute bilirubin encephalopathy (brain condition) in
which excessive bilirubin is toxic to brain cells
4. Infant jaundice: typically in premature newborns
because their livers are not yet capable of fully processing
bilirubin into bile
a) Bilirubin was processed by the mother’s placenta
b) Soon after birth they may show signs of
yellowing
c) Common treatment: exposure to blue and
green portion of the light spectrum which
changes the shape and structure of bilirubin and then they
can be eliminated in the baby’s urine and stool
5. Adult jaundice: symptom of an underlying
cause of the liver not functioning properly
a) Same symptoms and consequences as
infant jaundice
b) Many other symptoms if liver is not
functioning