Download File - Ms. Richards IB Biology HL

11.3 The Kidney and
Osmoregulation
11.3 The kidney and Osmoregulation
Nature of science: Curiosity about particular phenomena—investigations were carried out to
determine how desert animals prevent water loss in their wastes. (1.5)
Understandings
• Animals are either osmoregulators or osmoconformers
• The Malpighian tubule system in insects and the kidney carry out osmoregulation and removal
of nitrogenous wastes
• The composition of blood in the renal artery is different from that in the renal vein
• The ultrastructure of the glomerulus and Bowman’s capsule facilitate ultrafiltration
• The proximal convoluted tubule selectively reabsorbs useful substances by active transport
• The loop of Henle maintain hypertonic conditions in the medulla
• ADH controls reabsorption of water in the collecting duct
• The length of the loop of Henle is positively correlated with the need for water conservation in
animals
• The type of nitrogenous waste in animals in correlated with evolutionary history and habitat
11.3 The kidney and osmoregulation
Applications and Skills
• Application: Consequences of dehydration and overhydration
• Application: Treatment of kidney failure by hemodialysis or kidney
transplant
• Application: Blood cells, glucose, proteins, and drugs are detected in
urinary tests
• Skill: Drawing and labeling a diagram of the human kidney
• Skill: Annotation of diagrams of the nephron
Retro
1.3 Membrane Structure
Understandings
• Phospholipids form bilayers in water due to the amphipathic properties of phospholipid
molecules
• Membrane proteins are diverse in terms of structure, position in the membrane, and function
• Cholesterol is a component of animal cell membranes
Application and Skills
• Application: Cholesterol in mammalian membranes reduces membrane fluidity and permeability
to some solutes
• Skill: Drawing of the fluid mosaic model
• Skill: Analysis of evidence from electron microscopy that led to the proposal of the DavsonDanielli model
• Skill: Analysis of the falsification of the Davson-Danielli model that led to the Singer-Nicolson
model
For flash cards…
• You need to do
• 11.3 Understandings
• 11.3 Applications and Skills
• 1.3 Understandings (you can reuse from SL if you still have them!)
• 1.3 Applications and Skills (you can reuse from SL if you still have
them!)
• They need to be hand written! They can be on flash cards or
on notebook paper
What is excretion?
• All body cells produce waste products that have to be removed
because they can damage the body
• These waste products are the results of metabolic activities
• Waste products are different for different organisms
• Excretion is the removal from the body of the waste products of
metabolic pathways
• Oxygen is a waste product associated with photosynthesis in
green plants
• Animals excrete carbon dioxide as a consequence of cellular
respiration and nitrogen containing compounds that result from
the breakdown of proteins and nucleic acids.
• When these macromolecules are broken apart for energy or
converted to carbohydrates or fats, enzymes remove nitrogen in
the form of ammonia, a small and very toxic molecule
• How animals excrete or get rid of ammonia correlates with their
evolutionary history and habitat, especially the availability of
water
• Since most metabolic wastes must be dissolved in water when
they are removed from the body (exception is the loss of carbon
dioxide in air breathing animals) the type and quantity of waste
products may have a large impact on water balance
Osmoregulation
• Osmoregulation is the control of the water balance of the blood, tissue,
or cytoplasm of a living organism.
• It is based largely on controlled movement of solutes between internal
fluids and the external environment.
• Osmolarity- total solute concentration expressed as molarity, or moles of
solute per liter of solution, measured in milliOsmoles per liter (mOsm/L)
• Osmolarity of human blood is about 300 mOsm/L, while seawater is about 1,000
mOsm/L
• Osmosis: movement of water across a selectively permeable membrane.
Moves from high osmolarity to low osmolarity
Osmosis
• Remember water moves from high to low concentration
• Isoosmotic (isotonic): 2 solutions separated by a selectively
permeable membrane have the same osmolarity. No net movement
of H2O.
• Hyperosmotic (hypertonic): solution with the greater concentration
of solutes, water moves out of cell
• Hypoosmotic (hypotonic): solution that is more dilute, water moves
into cell
• Water flows by osmosis from a hypoosmotic solution to a
hyperosmotic one.
Osmoconformers
• Osmoconformer- tissues and cells are isosmotic with its
surroundings. All marine animals. No tendency to gain or lose
water. Live in water with stable composition. Squid.
• Disadvantage- cells inside body may not contain the ideal solute
concentration for body processes.
Osmoregulators
• Osmoregulator- controls its internal osmolarity independent of that
of its environment. Freshwater and terrestrial animals like humans.
• Disadvantage- energy has to be used to keep solute concentrations in
the body constant.
Nitrogenous Waste Products- Ammonia
• The habitat an organism live in determines the type of nitrogenous
waste product it will produce
• In aquatic freshwater environment:
• Freshwater fish and amphibian larvae: get rid of nitrogenous waste
as ammonia (toxic because of its basicity= pH 11.6) because they
have access to a lot of water
• Ammonia is lost as ammonium ions (NH4+) across the epithelium of
the gills, with kidneys excreting only minor amounts of nitrogenous
wastes. The gill epithelium takes up Na+ from the water in exchange.
• Advantage: ammonia takes little energy to make
• Disadvantage: highly toxic
Nitrogenous Waste Products- Urea
• Mammals (including marine and terrestrial), marine fish, adult amphibians
cannot excrete ammonia because it is so toxic (basic), and can only be
transported and excreted in large volumes of very dilute solutions, and
most mammals do not have access to enough water
• Instead, mammals (like adult amphibians and many marine fishes) excrete
mainly urea a substance produced in the vertebrate liver by a metabolic
cycle that combines ammonia with CO2.
• The circulatory system carries urea to the excretory organ= the kidney.
• Urea has low toxicity, about 100,000 times less than that of ammonia.
Urea can be safely carried and greatly reduces the amount of water
required for nitrogen excretion.
Nitrogenous Waste Products- Urea
• Some desert mammals have an adaptation that allows them to
produce a very concentrated urine (a very) long Loop of Henle
• The Loop of Henle and the size of the medulla have a role in the
nephron of the kidney in water absorption
• The disadvantage of urea is that animals must expend energy to
produce it from ammonia.
Nitrogenous Waste Products- Uric Acid
• Birds, as well as land snails, insects, and many reptiles, excrete uric
acid as the major nitrogen containing waste.
• It is relatively nontoxic like urea, but unlike urea or ammonia, it is
largely insoluble in watery solutions such as blood and cytoplasm and
can be excreted as a semisolid paste with very little loss of water.
Good for animals with little access to water.
• Cost: uric acid is even more energetically expensive to produce than
urea, requiring lots of ATP to synthesize from ammonia.
• Developmental history of these organisms gives us a clue as to why
uric acid excretion of nitrogenous waste is advantageous, think of
how they develop…
• Embryonically, each has very little access to water.
Nitrogenous Waste Excretion- Insects
• Insects and terrestrial arthropods have Malpighian tubules that remove
nitrogenous wastes and also function in osmoregulation
• Works with their open circulatory system
• Not all of the circulatory fluid, called hemolymph, (not blood) is contained in
blood vessel. As a result, hemolymph is the same as interstitial fluid.
• The heart pumps hemolymph through vessels into sinuses which are fluidfilled spaces where materials are exchanged between the hemolymph and
cells.
• Hemolymph returns to the heart through pores, which are equipped with
valves that close when the heart contracts.
• Branches of this blood vessel carry the hemolymph to different parts of the
body and it is then released and is free to flow gradually through tissues until
it is drawn back into the vessel for re-pumping.
• Body cells are bathed in this fluid and release waste products into it
Malpighian Tubules
Malpighian Tubules
• Located between midgut and hindgut
• Structure: a ring of narrow blind-ended ducts which extend through the body
cavity
• Physiology: Cells in tubule walls extract waste products from the hemolymph
and pass them into the lumen of the tubule. Ammonia is extracted and
converted by the Malpighian tubule cells into uric acid
• Cells in tubule wall transfer mineral ions (Na+, K+, Cl-) by active transport from
the hemolymph to the lumen of the tubule and water follows passively by
osmosis
• This solution drains into the lumen of the hindgut where it mixes with semidigested food and this mixture is carried to the rectum, last section of the gut
• Mineral ions (Na+, K+, Cl-) are pumped by cells in the wall of the rectum from
the feces to the hemolymph and again water follows passively by osmosis
• This process prevents dehydration and achieves osmoregulation
Malpighian Tubules
• Nitrogenous wastes, mainly insoluble
uric acid, eliminated as nearly dry
matter along with feces
• Capable of conserving water very
effectively and is a key adaptation
contributing to these animals’
tremendous success on land
Kidney
• The kidney is central to homeostasis because it disposes of metabolic
wastes and controls body fluid composition by adjusting the rates of
loss of particular solutes
• Like the excretory organs of most animal phyla, kidneys consist of
tubules. These numerous tubules are arranged in a highly organized
manner and closely associated with a network of capillaries.
Skill: Drawing and labeling a diagram of the
human kidney (6 labels)
Renal
Medulla
When you label
remember
everything is
RENAL!!!
Blood flow through the kidney
• Blood enters the kidney through the renal
artery (a branch of the aorta) and exits the
kidney via the renal vein. In fact 20% of
resting cardiac output goes to the kidney
• Urine exits the kidney through a duct called
the ureter and both ureters drain into a
common urinary bladder
• During urination, urine is expelled from the
urinary bladder through a tube called the
urethra
Renal
Medulla
Kidney
• Mammalian kidney has two distinct
regions:
1. an outer renal cortex
2. an inner renal medulla
• A third area is a collecting region for
all of the urine produced by the
kidney’s unit of function, the
nephron. This area is called the renal
pelvis
Renal
Medulla
Nephron
• The functional unit of the vertebrate kidney
is a microscopic excretory tubule called the
nephron
• It consists of a single long tubule and a ball
of capillaries called the glomerulus
• The blind end of the tubule forms a cupshaped swelling called Bowman’s capsule
(also called the glomerular capsule), which
surrounds the glomerulus
• Each human kidney packs a million
nephrons, with a total tubule length of 80
km
Glomerulus
Glomerulus
• The glomerulus acts as a filter for the
blood being carried by the afferent
arteriole
• The lining (endothelium) of the
glomerulus is a single layer of cells
which has pores called fenestrations
(which comes from the word
windows)
• It restricts the passage of red blood
cells and other formed elements
Glomerulus
• The basement membrane of the glomerulus lies between the
endothelium and a layer of Bowman’s capsule
• It consists of fibrils in a glycoprotein matrix and restricts the passage
of larger proteins such as the plasma proteins
• Podocyte specialized epithelial cells that form a layer of the
glomerular (Bowman’s) capsule has filtration slits which restrict the
passage of medium sized proteins
• Extending from each podocyte are 1000’s of foot-like structures
called pedicels that cover the basement membrane
• Podocytes also provide support
Basement membrane in general
Ultrafiltration
• The function of the glomerulus is the
ultrafiltration of blood
• Filtration occurs as blood pressure forces
fluid from the blood in the glomerulus
into the lumen of Bowman’s capsule
• Pressure is high because the vessel taking
blood away from the glomerulus (efferent
arteriole) is narrower than the vessel
bringing blood
• The porous capillaries (fenestrations),
along with podocytes are permeable to
water and small solutes but not to blood
cells or large molecules such as plasma
proteins. Those exit through the efferent
arteriole
Ultrafiltration
• Filtration of small molecules is
non-selective and the filtrate in
Bowman’s capsule contains
salts, glucose, and vitamins,
nitrogenous wastes such as urea
and other small molecules.
• The filtrate moves on into the
next part of the nephron the
proximal convoluted tubule.
Proximal Convoluted Tubule
• Note: Location of the various parts of the nephron
is very important to what can happen in the
different parts of the tubule
• Proximal Convoluted Tubule, like the glomerulus,
is located in the cortex of the kidney
• Secretion and absorption in the proximal
convoluted tubule change the volume and
composition of the filtrate
• The initial filtrate is about 1 liter every 10 minutes
in the two kidneys
• Substances are taken out of the plasma that are
needed by the body
• Process is called selective reabsorption
Nephron
• The nephron has to be able to reabsorb the necessary materials and
put them back into the circulatory system
• The nephron is composed of a single layer of cells
• Cells of the proximal convoluted tubule have microvilli projecting into
the lumen, giving a large surface area for absorption
• Pumps in the membrane re-absorb useful substances by active
transport using ATP produced by mitochondria in the cells
• A constant pH is maintained in the nephron by the controlled
secretion of hydrogen ions by active transport into the lumen
• The epithelium synthesizes and secretes ammonia which
neutralizes the acid and keeps the filtrate from becoming too
acidic
• It reabsorbs 90% of the important buffer, bicarbonate (HCO3-)
• Drugs and other poisons that were processed by the liver pass
from another capillary bed into interstitial fluid and then are
secreted across the epithelium of the proximal tubule into the
nephron’s lumen and get added to the filtrate
• Valuable nutrients, including glucose, amino acids, and potassium
are actively or passively transported from the filtrate to the
interstitial fluid and then move into capillaries and are returned
to the circulatory system.
• Most of the NaCl and water are reabsorbed from the huge initial
volume
• Na+ is actively transported, Cl- follows by passive transport
• As salt moves from the filtrate, water follows by osmosis
• These also diffuse from the interstitial fluid back into the capillary bed to
be returned to the body
• In the end ALL of the glucose, 80% of the water, and 80% of the
mineral ions are reabsorbed
• The rest of the pathway for urine formation includes the Loop of
Henle, which is located in the medulla, the distal convoluted
tubule and the collecting duct
Role of the Medulla
• The interstitial fluid increases in osmolarity from about 300 to 1,200
mosm/L from the cortex to the inner medulla
• Two solutes contribute to this gradient:
1. Urea
2. NaCl
• So the medulla has a concentration gradient of salts. This will cause
water to leave the nephron and go back into the interstitial fluid
• Something has to create and something has to maintain this very
important concentration gradient of salt in order for water to be
reabsorbed…
Role of the Loop of Henle
• The Loop of Henle maintains the interstitial gradient of NaCl
• Descending and ascending parts of the Loop of Henle have different
permeability characteristics which will be discussed soon
Role of ADH
• Antidiuretic hormone (ADH) is also called vasopressin and is a
hormone
• This hormone originates from the posterior pituitary in response to
detection of increased osmolarity by receptors in the hypothalamus
and it increases the permeability of the collecting duct to water
• It allows water to be conserved
• ADH makes the cells of the conducting duct produce membrane
channels called aquaporins that allows for the movement of water
Overview of the role of the Loop of Henle
• Overall it is to create an area of high solute
concentration in the cells and tissue fluid of
the medulla
• Descending limb of the loop of Henle
• Reabsorption of water continues. The
epithelium is freely permeable to water
but not very permeable to NaCl and other
small solutes
• Water moves out by osmosis because the
interstitial fluid bathing the tubule is
hyperosmotic to the filtrate. Osmolarity
of the interstitial fluid becomes greater
from the outer cortex to the inner
medulla of the kidney. So filtrate
continues to lose water.
Overview of the role of the Loop of Henle
• Ascending limb of the loop of Henle
• The epithelium in the region is permeable
to salt but not to water
• In the thin segment of the ascending
loop, NaCl leaves nephron through
diffusion
• In the thick segment NaCl is actively
transported into the interstitial fluid.
• By losing salt without giving up water, the
filtrate becomes progressively more
dilute as it moves up to the cortex in the
ascending limb, but it has added to the
high osmolarity of the interstitial fluid in
the medulla.
Summary
• Descending limb
• Water out passively
• Ascending limb
• Thin segment NaCl out passively
• Thick segment NaCl out actively
So what is the point…
• A longer loop of Henle is an adaptation for water conservation
• Amphibians have almost no Loop of Henle and are unable to
conserve water. Thus their urine is always dilute.
• Vertebrates in desert habitats such as the Kangaroo rate of desert
Southwest US have long loop of Henle and nocturnal behavior
• Also, a positive correlation between the thickness of the medulla
compared to the overall size of the kidney and the need for water
conservation.
• A thicker medulla allows the loops of Henle and collecting ducts to be
longer so that more water can be reabsorbed.
Relationship between maximum solute concentration
(MSC) and concentration factor of urine (CF) and habitat
Species
MSC (mOsm dm-3)
CF
Habitat
Beaver
520
x2
Aquatic
Human
1200
x4
Intermediate
Brown rat
2900
x9
Intermediate
Kangaroo rat
5500
x18
Desert
Hopping mouse
9400
x25
Desert
Distal Convoluted tubule
• Distal convoluted tubule plays a key role in regulating potassium ion
(K+) and NaCl concentrations of body fluid
• It does so by varying the amounts of K+ that is secreted into the
filtrate and the amount of NaCl reabsorbed from the filtrate
• Like the proximal tubule, the distal tubule also contributes to pH
regulation by the controlled secretion of H+ and reabsorption of
bicarbonate
Collecting Duct
• Collecting Duct carries the filtrate through the medulla to the renal
pelvis. It reabsorbs NaCl by active transport
• Collecting duct plays a large role in determining how much salt is
actually excreted in the urine
• Epithelium is permeable to water but not to salt or (in the cortex) to
urea
• As filtrate goes down the collecting duct, it becomes more
concentrated as it loses more and more water by osmosis
• In the inner medulla, the duct becomes permeable to urea because
of the high urea concentration in the filtrate at this point
• Some urea diffuses out of the duct and into the interstitial fluid.
• Along with NaCl, the interstitial urea is a major solute contributing to
the high osmolarity of the interstitial fluid in the medulla.
Skill: Annotation of diagrams of the nephron
1. Glomerulus and Bowman’s
capsule- perform ultrafiltration
2. Proximal convoluted tubuletransfer substances from filtrate
back to blood (selective
reabsorption)
3. Loop of Henle- establishes a salt
gradient, establishes high solute
concentrations in medulla
4. Distal convoluted tubule- adjust
individual solute concentrations
and pH of blood
5. Collecting duct- osmoregulation
Negative Feedback and ADH
• When osmolarity in plasma rises above
the set point of 300 mosm/L, more ADH
is released and reaches the kidney
• Main targets are distal tubule and mainly
collecting duct
• Alcohol inhibits the release of ADH,
causing excessive urinary water loss and
dehydration
Comparing blood in glomerulus, filtrate and
different parts of nephron and urine
Concentration
(mg per 100mL)
Glucose
Urea
Blood in glomerulus 740
90
30
Glomerular filtrate
0
90
30
Filtrate at start of
loop of Henle
0
0
90
Filtrate at end of
loop of Henle
0
0
200
Urine with ADH
0
0
1800
Urine without ADH
0
0
180
Plasma Proteins
• Glucose is not present in the urine but is present in the renal artery,
glomerular filtrate and renal vein (less because of aerobic cell
respiration)
• Urea is increased from 30 mg to 1800 mg in urine and reduced to 24
mg in renal vein.
• Proteins are not present in either the glomerular filtrate or the urine,
but are present at the same level in the renal artery and vein (740
mg)- makes sense it goes in and comes out
• Sodium ions and chloride ions are adjusted to normal levels in the
renal vein by the kidney.
• Oxygen levels are decreased in renal vein in comparison to renal
artery and carbon dioxide levels are increased due to aerobic cell
respiration.
• Urine with ADH contains much more concentrated urea than urine
without ADH.
Comparison of substances in the Renal Artery vs Renal Vein
Renal Artery
Renal Vein
Reason for
difference a /v
Oxygen
Higher
Lower
Aerobic resp. to
Carbon dioxide
Lower
Higher
provide ATP for
kidney function
Glucose
Slightly higher
Slightly lower
Use in cell aerobic
respiration
Urea
Higher
About 20% lower
Excretion in urine
Plasma proteins
Equal
Equal
Not added or
removed
Na+/Cl- ions
Variable
Always at normal
levels
Kidney raises or
lowers
concentrations to
normalize them
Renal
Medulla
Application: Consequences of dehydration
and overhydration
• Dehydration- due to loss of water from the body but not an
equivalent quantity of solutes, so body fluids become hypertonic
• Consequences- thirst, small quantities of dark colored urine, lethargy,
raised heart rate, low blood pressure, constipation, dry mouth and
skin, dizziness, and headache. In severe cases, seizures, brain damage
and DEATH!
• Hypernatremia
Application: Consequences of dehydration
and overhydration
• Overhydration is due to excessive intake of water
• Bodily fluids become hypotonic
• Consequences: behavior changes, confusion, drowsiness, delirium,
blurred vision, muscle cramps, nausea, and vomiting, and in acute
cases seizures, coma, and DEATH!
• Hyponatremia
Application: Blood cells, glucose, proteins,
and drugs are detected in urinary tests
1. Glucose: indicator of diabetes – 100% should be reabsorbed in
proximal convoluted tubules, but if high blood glucose levels, glucose
levels in filtrate with overwhelm the pumps resulting in glucose in the
urine
2. Blood cells: indicator of infections (white blood cells), kidney
damage (red blood cells), and some cancers
3. Proteins: normally, only a small amount. Indication of kidney disease
or damage
4. Drugs: metabolites of legal (antibiotics, anti-inflammatory drugs) and
illegal drugs. Illegal drugs could have been used recreationally or for
athletic advantage.
Kidney Failure
• Symptoms: build up of waste products in the body, weakness, shortness of
breath, lethargy, and confusion
• The inability to remove potassium from the bloodstream may lead to abnormal
heart rhythms and sudden death
• Causes: Diabetes, high blood pressure, autoimmune disease (Lupus, HIV),
genetic disorders (polycystic kidney), injury, some medications, and drugs
• Treatment: Kidney dialysis or hemodialysis or kidney transplant
• Statistics (2011): Prevalence of chronic kidney disease is growing most rapidly in
people ages 60 and older (24.5%). End-stage renal disease (ESRD) incident rates
are more than 3X higher for African Americans than for Caucasians. At end of
2009, more than 871,000 people treated for ESRD. In 2009, 18,000 kidney
transplants in US
• Wolfgang Amadeus Mozart (1791) died of kidney failure
Application: Treatment of kidney failure by
hemodialysis or kidney transplant- History
• 100 A.D. Dialysis began in the bathwaters of the Roman Empire
surrounded by marble, heat, and steam,
• Romans poisoned by the build up of urea in their bodies would
surround themselves with marble, heat, and steam and attempted to
sweat and soak as the toxins in their blood diffused through their skin
into the swirling spa
• Cleansed but totally exhausted
Application: History
• Patients usually died quietly at home of urea poisoning, sometimes called
“dropsy”
• 1850s: search for semipermeable membrane. They first used ox bladder and
later used collodion- syrup made by dissolving cellulose nitrate in ether and
alcohol.
• Until present the material used to wrap cigarettes and the cellulose used as
sausage skin were used
• Choice of membrane critical: if it tore, patient could bleed to death
• Clotting was a problem solved using heparin as an anticoagulant
• Father of modern kidney dialyzer is Willem Kolff, a young physician who worked
in the Netherlands during the Nazi occupation
• Kolff brought his artificial kidney to Mt. Sinai Hospital in New York City and
successfully dialyzed the first patient in 1948
Application: Early Hemodialysis Machine
Application: Modern Hemodialysis Machine
Application: Treatment of kidney failure by
hemodialysis
•
Hemodialysis involves the diffusion of solutes from a higher to a
lower concentration through a semi-permeable membrane
1. Dialysis membrane used in kidney machines is cellulose acetate or
nitrate. It has large pores that let small solute particles pass
through, but not large particles such as plasma proteins or blood
cells
2. Blood flows on one side of the dialysis membrane and dialysis
fluid on the other side.
Application: Dialysis Fluid
a) No urea or other excretory products, so these waste products diffuse into it
from the blood.
b) The same concentration of glucose, mineral ions, and other desirable
substances as normal blood plasma so these substances do not diffuse
unless the level in blood plasma is above or below normal.
c) Dextran, a solute that cannot pass through the dialysis membrane and so
causes excess water to move by osmosis from the blood to the dialysis fluid.
d) High calcium and low potassium concentrations to extract potassium and
add calcium to the blood
e) Hydrogencarbonate (bicarbonate) ions (HCO3- ) to reduce the acidity of the
blood
f) A high solute concentration that will cause excess water to be removed from
the blood by osmosis across the dialysis membrane
Application: Process of Hemodialysis
• Blood flows through tubes or between sheets of
dialysis membrane.
• The blood is taken from the patient (via vein) in and
returned via needles inserted into a blood vessel in
the arm
• Blood passes through a kidney machine for 3-4
hours, 3 times per week.
• Dialysis fluid has to be gradually replaced throughout
a session to maintain the concentration gradient
• A large volume of fluid is used, in contrast to the
human kidney, which can excrete waste products
with a very small loss of water
Application: Treatment of kidney failure by
kidney transplant
• A new kidney from either a living donor or a person who has recently
died is grafted in to the lower abdomen with the renal artery, renal vein,
and ureter connected to the recipient’s blood vessels and bladder
• It is essential that donor and recipient are in the same blood group and
their tissues match as closely as possible to minimize the chance of
rejection of the kidney by recipient’s immune system
• Even with tissue matching, recipient will need immune-suppressing
drugs for the rest of their life, because even well-matched kidneys are
not a perfect tissue match
• The immune system of the body does not recognize the new kidney and
will try to attack it (we will discuss immunology later  )
Retro 1.3 Cell Membrane
1.3.1 Phospholipids form bilayers in water due to the
amphipathic properties of phospholipid molecules
• Phospholipid structure
• Phosphate head- hydrophilic (water loving)
• Two fatty acid tails- hydrophobic (water hating)
• They are amphipathic
• Due to their amphipathic nature when phospholipids are placed in
water they form a bilayer with the hydrophobic tails facing away from
the water and hydrophilic head facing toward the water- micelle
Skill: Drawing of the fluid mosaic model
• Integral proteins are
embedded in the
bilayer
• Peripheral proteins
are attached to one
of the outer surfaces
• Glycoproteins are
proteins with a sugar
unit attached
1.3.2 Membrane proteins are diverse in terms of structure, position in
the membrane and function
• Hormone binding sites
• Has a specific shape that binds a hormone, causes a change in shape, allows for a message to be sent to the
interior of cell
• Ex: Insulin receptor
• Enzymatic activity
• Can be exterior or interior and catalyze reactions, sometimes working in metabolic pathways
• Ex: Cytochrome oxidase
• Cell adhesion
• Can provide permeant or temporary connections between cells (junctions- tight junctions or gap junctions)
• Ex: Cadherin
• Cell-to-cell communication
• Proteins can have carbohydrates attached that allow for cellular recognition
• Ex: Glycoproteins
• Passive transport channels
• Proteins that span the membrane and allow for movement from high to low concentrations
• Ex: Nicotinic acetylcholine receptor (receptor for a neurotransmitter)
• Active transport pumps
• Proteins that move molecules across the membrane with the use of ATP
• Ex: Calcium pump
1.3.3 Cholesterol is a component of animal cell
membrane
• Cholesterol is a steroid
• It is hydrophobic but had one hydrophilic end thus it can fit in the
membrane
• Cholesterol limit the movement of the phospholipids
• Allows membranes to function at a wider temperature range
Application: Cholesterol in mammalian membranes reduces
membrane fluidity and permeability to some solutions
• Since they limit the movement of phospholipids cholesterol reduces
the fluidity of membranes
• It also reduces permeability of the membrane to some hydrophilic
particles like sodium and hydrogen ions
• This allows animals to maintain concentration differences of these ions
• Plant cells do not have cholesterol in their cell membranes
• They depend on saturated and unsaturated fatty acids to maintain
fluidity in their membranes