Download 29.6 Red Blood Cells and Blood Gases

Outline
29.1
Body Water and Its Solutes
29.2
Fluid Balance
29.3
Blood
29.4
Plasma Proteins, White Blood Cells, and Immunity
29.5
Blood Clotting
29.6
Red Blood Cells and Blood Gases
29.7
The Kidney and Urine Formation
29.8
Urine Composition and Function
Goals
1. How are body fluids classified?
Be able to describe the major categories of body fluids, their general
composition, and the exchange of solutes between them.
2. What are the roles of blood in maintaining homeostasis?
Be able to explain the composition and functions of blood.
3. How do blood components participate in the body’s defense
mechanisms?
Be able to identify and describe the roles of blood components that
participate in inflammation, the immune response, and blood
clotting.
4. How do red blood cells participate in the transport of blood
gases?
Be able to explain the relationships among O2 and CO2 transport,
and acid–base balance.
5. How is the composition of urine controlled?
Be able to describe the transfer of water and solutes during urine
formation, and give an overview of the composition of urine.
29.1 Body Water and Its Solutes
• Extracellular fluid
includes blood plasma
(the fluid portion of
blood), interstitial
fluid (the fluid that fills
the spaces between
cells), lymph,
cerebrospinal fluid, and
the fluid that lubricates
joints (synovial fluid).
29.1 Body Water and Its Solutes
• To be soluble in water, a substance must be
an ion, a gas, a small polar molecule, or a
large molecule having many polar,
hydrophilic (water-loving) or ionic groups on
its surface.
• All four types of solutes are present in body
fluids.
• Although these fluids have different
compositions, their osmolarities are the
same.
29.1 Body Water and Its Solutes
• Electrolytes are major contributors to the
osmolarity of body fluids, and move about
as necessary to maintain charge balance.
• Water-soluble proteins make up a large
proportion of the solutes in blood plasma
and intracellular fluid.
• Blood gases (oxygen and carbon dioxide),
along with glucose, amino acids, and the byproducts of protein catabolism, are the
major small molecules in body fluids.
29.1 Body Water and Its Solutes
• Capillaries are where
nutrients and end
products of metabolism
are exchanged
between blood and
interstitial fluid.
• The result of water and
solute exchange at
capillaries is that blood
plasma and interstitial
fluid are similar in
composition.
29.1 Body Water and Its Solutes
• Peripheral tissue is networked with lymph capillaries.
• The lymphatic system collects excess interstitial fluid,
debris from cellular breakdown, and proteins and lipid
droplets too large to pass through capillary walls.
• Lymph enters the bloodstream at the thoracic duct.
• Exchange of solutes between the interstitial fluid and
the intracellular fluid occurs by active transport
(transport requiring energy).
• Sodium ion concentration is high in extracellular fluids
and low in intracellular fluids; potassium ion
concentrations are high inside cells and low outside
cells.
29.2 Fluid Balance
• Preserving fluid balance is crucial in
maintaining physiological homeostasis.
• During the course of an endurance event,
fluid loss occurs with minimal fluid intake.
• Physiologists consider 4% body mass loss
to be the “danger zone.”
• Both intake and output of water are
controlled by hormones.
29.2 Fluid Balance
• A 2% change in osmolarity causes
adjustment in hormone secretion.
• When blood osmolarity rises, secretion of
antidiuretic hormone (vasopressin)
increases.
• The kidneys keep water and electrolytes in
balance by increasing or decreasing the
amounts eliminated. In the kidney,
antidiuretic hormone causes a decrease in
the water content of the urine.
29.2 Fluid Balance
• Osmoreceptors in the hypothalamus and
baroreceptors in the heart and blood vessels
activate the thirst mechanism.
• Both oversecretion and undersecretion of
antidiuretic hormone (ADH) can lead to serious
disease states.
– When ADH secretion is too high, the kidney excretes
too little water, the water content of body
compartments increases, and serum concentrations
of electrolytes drop.
– In diabetes insipidus, too little ADH is secreted and up
to 15 L of dilute urine are excreted each day.
29.3 Blood
• About 55% of blood is plasma; the
remaining 45% is a mixture of red blood
cells, platelets, and white blood cells
(leukocytes).
• Plasma and cells together make up whole
blood.
• Blood serum is the fluid remaining after
blood has completely clotted.
• Blood serum composition is not the same
as that of blood plasma.
29.3 Blood
Major Functions of Blood
• Transport—Oxygen and carbon dioxide are
carried to and from by red blood cells. Nutrients
are carried from the intestine to the sites of their
catabolism. Waste products of metabolism are
carried to the kidneys. Hormones from
endocrine glands are delivered to their target
tissues.
29.3 Blood
Major Functions of Blood
• Regulation—Blood distributes body heat,
participating in regulation of body temperature. It
also picks up or delivers water and electrolytes
as needed. Blood buffers are essential to
maintenance of acid–base balance.
• Defense—Blood carries the molecules and cells
needed for two major defense mechanisms: (1)
the immune response, which destroys foreign
invaders; and (2) blood clotting, which prevents
blood loss and begins healing of wounds.
29.3 Blood
29.3 Blood
29.4 Plasma Proteins, White Blood Cells, and Immunity
• An antigen is any molecule or portion of a
molecule recognized by the body as a
foreign invader.
• Antigens can also be haptens: recognized
as antigens after they have bonded to
carrier proteins.
• Recognition of an antigen can initiate three
responses: inflammation, cell-mediated
response, and antibody-mediated immune
response.
29.4 Plasma Proteins, White Blood Cells, and Immunity
29.4 Plasma Proteins, White Blood Cells, and Immunity
Inflammatory Response
• Inflammation is a nonspecific defense mechanism in
which chemical messengers (histidine) direct
inflammatory response. It includes swelling, redness,
warmth, and pain.
• Histamine causes dilation of capillaries and increases
permeability of capillary walls, increasing blood flow.
• Plasma carrying blood-clotting factors, defensive
proteins, and white blood cells enter the intercellular
space.
• Antigens are destroyed by phagocytes.
• Inflammation caused by a wound will heal completely
only after all infectious agents, dead cells and other
debris have been absorbed into the lymph system.
29.4 Plasma Proteins, White Blood Cells, and Immunity
The Blood–Brain Barrier
• The brain is rigorously isolated from variations in blood
composition.
• The endothelial cells that form the walls of brain capillaries
form a series of continuous tight junctions so that nothing can
pass between them.
• The blood–brain barrier (BBB) serves as internal protection
for the brain.
• Glucose and certain amino acids are brought across the cell
membranes by transport mechanisms specific to each
nutrient.
• Substances soluble in membrane lipids readily breach the
blood–brain barrier. Among such substances are nicotine,
caffeine, codeine, diazepam (Valium, an antidepressant), and
heroin.
29.4 Plasma Proteins, White Blood Cells, and Immunity
Cell-mediated Immune Response
• Cell-mediated immune response is under the control
of T lymphocytes, or T cells.
• It principally guards against abnormal cells and
bacteria or viruses that have entered normal cells. It
also guards against the invasion of some cancer cells
and causes the rejection of transplanted organs.
• The result of T cell recognition of an antigen is
production of cytotoxic, or killer, T cells that can
destroy the invader, helper T cells that enhance the
body’s defenses, and memory T cells that will
immediately generate killer T cells if the same
pathogen reappears.
29.4 Plasma Proteins, White Blood Cells, and Immunity
Antibody-Mediated Immune Response
• B cells identify antigens adrift in body fluids.
• A B cell is activated when it first bonds to an
antigen and then encounters a helper T cell that
recognizes the same antigen.
• This activation often occurs in lymph nodes,
tonsils, or the spleen, which have large
concentrations of lymphocytes.
• Once activated, B cells divide to form plasma
cells that secrete antibodies specific to the
antigen.
29.4 Plasma Proteins, White Blood Cells, and Immunity
Antibody-Mediated Immune Response
• Antibodies are immunoglobulins.
• The body contains up to 10,000 different
immunoglobulins at any given time.
• They are glycoproteins composed of two “heavy”
polypeptide chains and two “light” polypeptide
chains joined by disulfide bonds.
• The variable regions are sequences of amino
acids that will bind a specific antigen.
• Once synthesized, antibodies spread out to find
their antigens.
29.4 Plasma Proteins, White Blood Cells, and Immunity
29.4 Plasma Proteins, White Blood Cells, and Immunity
Antibody-Mediated Immune Response
• Formation of an antigen–antibody complex
inactivates the antigen.
• Activated B-cell division also yields memory cells.
• Immunoglobulin G antibodies (gamma globulins),
protect against viruses and bacteria.
• Allergies and asthma are caused by an oversupply
of immunoglobulin E.
• Autoimmune diseases include attack on
connective tissue in rheumatoid arthritis, attack on
pancreatic islet cells in diabetes mellitus, and a
generalized attack on nucleic acids and blood
components in systemic lupus erythematosus.
29.5 Blood Clotting
• A blood clot consists of blood cells trapped
in a mesh of the insoluble fibrous protein
known as fibrin.
• Clot formation is a multiple-step process
requiring participation of 12 clotting
factors.
– Calcium ion is one of the clotting factors.
– Others, most of which are glycoproteins,
are synthesized in the liver by pathways
that require vitamin K as a coenzyme.
29.5 Blood Clotting
• A deficiency of vitamin K, a competitive
inhibitor of vitamin K, or deficiency of a
clotting factor can cause excessive
bleeding from even minor tissue damage.
• Hemophilia is caused by an inherited
genetic defect that results in the absence
of one or more of the clotting factors.
• Hemophilia occurs in 1 in 10,000
individuals, with 80–90% of hemophiliacs
being male.
29.5 Blood Clotting
• Hemostasis is the body’s mechanism for
halting blood loss.
– Step one is constriction of surrounding blood
vessels.
– Step two is formation of a plug composed of
platelets at the site of tissue damage.
29.5 Blood Clotting
• A blood clot is formed in a process that is
triggered by two pathways.
– The intrinsic pathway begins when blood
makes contact with the negatively charged
surface of the fibrous protein collagen,
which is exposed at the site of tissue
damage.
– The extrinsic pathway begins when
damaged tissue releases an integral
membrane glycoprotein known as tissue
factor.
29.5 Blood Clotting
• A cascade of reactions is initiated when an
inactive clotting factor (a zymogen) is
converted to its active form.
• The newly activated enzyme then
catalyzes the activation of the next factor
in the cascade.
• In the final step of the common pathway,
thrombin catalyzes cleavage of small
polypeptides from the soluble plasma
protein fibrinogen.
29.5 Blood Clotting
• Negatively charged groups make
fibrinogen soluble and keep the molecules
apart.
• Once these polypeptides are removed,
fibrin molecules associate with each other
by noncovalent interactions.
• They are bound into fibers by formation of
amide cross-links between lysine and
glutamine side chains in a reaction
catalyzed by another clotting factor.
29.5 Blood Clotting
• Once the clot has done its job, the clot is
broken down by hydrolysis of peptide
bonds.
29.6 Red Blood Cells and Blood Gases
• Erythrocytes transport blood gases.
• Erythrocytes in mammals have no nuclei or
ribosomes and cannot replicate.
• They must obtain glucose from plasma.
• 95% of the protein in an erythrocyte is
hemoglobin.
• Hemoglobin (Hb) is composed of four
polypeptide chains with central heme groups.
• Each heme can combine with one O2
molecule.
29.6 Red Blood Cells and Blood Gases
Oxygen Transport
• The iron(II) ion, Fe2+ sits in the center of each heme and
binds O2.
• Hemoglobin (Hb) carrying four oxygens (oxyhemoglobin)
is bright red. Hemoglobin that has lost one or more
oxygens (deoxyhemoglobin) is dark redpurple.
• The color of arterial blood carrying oxygen is used in
pulse oximetry.
• Percent saturation, is dependent on the partial pressure
of oxygen in surrounding tissues.
• Oxygen is more readily released to tissues where the
partial pressure of oxygen is low.
29.6 Red Blood Cells and Blood Gases
Carbon Dioxide Transport, Acidosis and Alkylosis
• The relationships among H+ and HCO3–
concentrations and O2 and CO2 partial pressures
are essential to maintaining electrolyte and acid–
base balance.
• Carbon dioxide diffuses into interstitial fluid and then
into capillaries, where it is transported in blood three
ways: (1) as dissolved CO2 (2) bonded to Hb, or (3)
as HCO3— in solution.
• Most of the CO2 is converted to bicarbonate ion
within erythrocytes, which contain a large
concentration of carbonic anhydrase.
29.6 Red Blood Cells and Blood Gases
Carbon Dioxide Transport, Acidosis and Alkylosis
• To maintain electrolyte balance, a Cl– ion enters
the erythrocyte for every HCO3– ion that leaves.
• A cell-membrane protein controls this passive
ion exchange.
29.6 Red Blood Cells and Blood Gases
Carbon Dioxide Transport, Acidosis and Alkylosis
• To counteract the acidity increases caused by
carbonic anhydrase, hemoglobin reversibly
binds hydrogen ions.
• Oxygen is held more firmly when the hydrogen
ion concentration decreases.
• Homeostasis requires a blood pH between 7.35
and 7.45. A pH outside this range creates either
acidosis or alkalosis.
• The wide variety of conditions that cause
acidosis or alkalosis are divided between
respiratory and metabolic malfunctions.
29.6 Red Blood Cells and Blood Gases
29.7 The Kidney and Urine Formation
• The kidneys bear the major responsibility
for maintaining a constant internal
environment in the body.
• About 25% of the blood pumped from the
heart goes directly to the kidneys, where
the functional units are the nephrons.
• Blood enters a nephron at a glomerulus, a
tangle of capillaries surrounded by a fluidfilled space.
• Filtration occurs here.
29.7 The Kidney and Urine Formation
• The pressure of blood
pumped directly from the
heart is high enough to
push plasma and all its
solutes except large
proteins into the the
glomerular filtrate.
• The filtrate flows from the
capsule into the tubule that
makes up the rest of the
nephron, and the blood
enters the network of
capillaries intertwined with
the tubule.
29.7 The Kidney and Urine Formation
• About 125 mL of filtrate per minute enters
the kidneys.
• They produce 180 L of filtrate per day, but
excrete only about 1.4 L of urine.
• Another important function of the kidneys is
reabsorption.
• More of certain solutes must be excreted
than are present in the filtrate. This
situation is dealt with by secretion—the
transfer of solutes into the kidney tubule.
29.8 Urine Composition and Function
• Urine contains the products of glomerular
filtration minus the substances reabsorbed in the
tubules, plus the substances secreted in the
tubules.
• About 50 g of solids (in solution) are excreted
every day—about 20 g of electrolytes and 30 g
of nitrogen-containing wastes.
• Normal urine composition is usually reported as
the quantity of solute excreted per day.
• Laboratory urinalysis often requires collection of
all urine excreted during a 24-hour period.
29.8 Urine Composition and Function
29.8 Urine Composition and Function
Acid–Base Balance
• Respiration, buffers, and excretion of hydrogen
ions in urine combine to maintain acid–base
balance.
• The H+ to be eliminated is produced by the
reaction of CO2 with water in the cells lining the
tubules of the nephrons.
29.8 Urine Composition and Function
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Automated Clinical Laboratory Analysis
When a physician orders chemical tests of blood, urine, or spinal fluid, the
sample goes to a clinical chemistry laboratory where most tests are done by
automated clinical chemistry analyzers.
There are two types of chemical analysis, one for the quantity of a chemical
and the other for the quantity of an enzyme.
Many chemical components are measured directly by mixing a reagent with
the sample—the analyte—and noting the quantity of a colored product
formed by using a photometer.
Many analytes are also substrates for enzyme-catalyzed reactions. Analysis
of the substrate concentration is therefore often made possible by treating
the analyte with appropriate enzymes.
Determination of the quantity of a specific enzyme or the ratio of two or
more enzymes, is invaluable in detecting organ damage that allows
enzymes to leak into body fluids.
Automated analyzers rely on premixed reagents and automatic division of a
fluid sample into small portions for each test.
29.8 Urine Composition and Function
Fluid And Na+ Balance
• The amount of water reabsorbed is dependent
on the osmolarity of the fluid passing through the
kidneys, the antidiuretic hormone–controlled
permeability of the collecting duct membrane,
and the amount of Na+ actively reabsorbed.
• Increased sodium reabsorption means higher
interstitial osmolarity, greater water
reabsorption, and decreased urine volume.
• Decreased sodium reabsorption means less
water is reabsorbed and urine volume increases.
29.8 Urine Composition and Function
Fluid And Na+ Balance
• Reabsorption of Na+ is normally under the
control of the steroid hormone aldosterone.
• The arrival of chemical messengers signaling a
decrease in total blood plasma volume
accelerates the secretion of aldosterone.
• The result is increased Na+ reabsorption in the
kidney tubules accompanied by increased water
reabsorption.
Chapter Summary
1. How are body fluids classified?
• Body fluids are either intracellular or extracellular.
• Extracellular fluid includes blood plasma (the fluid part
of blood) and interstitial fluid.
• Blood serum is the fluid remaining after blood has
clotted.
• Solutes in body fluids include blood gases,
electrolytes, metabolites, and proteins. Solutes are
carried throughout the body in blood and lymph.
• Exchange of solutes between blood and interstitial fluid
occurs at the network of capillaries in peripheral
tissues. Exchange of solutes between interstitial fluid
and intracellular fluid occurs by passage across cell
membranes.
Chapter Summary, Continued
2. What are the roles of blood in maintaining
homeostasis?
• The principal functions of blood are (1) transport
of solutes and blood gases, (2) regulation,
including regulation of heat and acid–base
balance, and (3) defense, which includes the
immune response and blood clotting.
• In addition to plasma and proteins, blood is
composed of red blood cells (erythrocytes),
which transport oxygen; white blood cells
(leukocytes), for defense functions; and platelets,
which participate in blood clotting.
Chapter Summary, Continued
3.
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•
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•
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How do blood components participate in the body’s defense
mechanisms?
The presence of an antigen (a substance foreign to the body)
initiates (1) the inflammatory response, (2) the cell-mediated
immune response, and (3) the antibody-mediated immune
response.
The inflammatory response is initiated by histamine and
accompanied by the destruction of invaders by phagocytes.
The cell-mediated response is effected by T cells that can, for
example, release a toxic protein that kills invaders.
The antibody-mediated response is effected by B cells, which
generates antibodies (immunoglobulins), proteins that complex
with antigens and destroy them.
Blood clotting occurs in a cascade of reactions in which a series of
zymogens are activated, ultimately resulting in the formation of a
clot composed of fibrin and platelets.
Chapter Summary, Continued
4.
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How do red blood cells participate in the transport of
blood gases?
Oxygen is transported bonded to Fe2+ ions in hemoglobin. The
percent saturation of hemoglobin with oxygen is governed by
the partial pressure of oxygen in surrounding tissues and
allosteric variations in hemoglobin structure.
Carbon dioxide is transported in blood as a solute, bonded to
hemoglobin, or in solution as bicarbonate ion. In peripheral
tissues, carbon dioxide diffuses into red blood cells, where it is
converted to bicarbonate ion.
Acid–base balance is controlled as hydrogen ions generated
by bicarbonate formation are bound by hemoglobin. At the
lungs, oxygen enters the cells, and bicarbonate and hydrogen
ions leave. A blood pH outside the normal range of 7.35–7.45
can be caused by respiratory or metabolic imbalance, resulting
in the potentially serious conditions of acidosis or alkalosis.
Chapter Summary, Continued
5. How is the composition of urine controlled?
• The first essential kidney function is filtration, in which
plasma and most of its solute cross capillary membranes
and enter the glomerular filtrate. Water and essential
solutes are then reabsorbed, whereas additional solutes
for elimination are secreted into the filtrate.
• Urine is thus composed of the products of filtration, minus
the substances reabsorbed, plus the secreted
substances. It is composed of water, nitrogen-containing
wastes, and electrolytes that are excreted to help to
maintain acid–base balance. The balance between water
and Na+ excreted or absorbed is governed by the
osmolarity of fluid in the kidney, the hormone
aldosterone, and various chemical messengers.