Transcript The Functions of Blood

Blood
(rev 11/11)
• The circulatory system consists of the heart,
blood vessels and the blood itself.
• The circulatory system is essential to supply all
cells with what they need and removing
substances they no longer need.
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The Functions of Blood
Blood is actually a liquid body tissue and is classified as a
connective tissue
Blood carries out three essential tasks:
• Transportation: oxygen, nutrients, waste,
hormones
• Regulation: body temperature, volume of water
in the body, pH of body fluids
• Defense: contains specialized defense cells to
protect against illness and excessive bleeding
through clotting mechanisms
These are necessary for homeostasis.
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Blood Components
All blood cells and platelets develop from stem cells in the
red bone marrow.
Blood is made up of the following:
• Formed elements (cellular components--45%):
– RBCs or erythrocytes; most abundant cell type; primarily is a
carrier of oxygen and carbon dioxide
– WBCs
– Platelets
• Plasma (liquid components--55%):
–
–
–
–
–
–
Water
Electrolytes (ions of elements)
Proteins (albumins, globulins, clotting proteins)
Hormones
Gases (oxygen and carbon dioxide)
Nutrients and wastes
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RBC (erythrocytes) Production=Erythropoiesis
• Stem cells develop into immature cells called
erythroblasts.
– Erythroblasts become erythrocytes in about 1 week
– They lose their nucleus and organelles as they
mature so they can’t reproduce
– New RBC must develop (from stem cells) because
with no nucleus, RBC can’t accomplish any cellular
activities and wear out quickly
– Old or damaged RBC are removed from blood and
destroyed in the liver and spleen by macrophages in
a process called phagocytosis.
• Many cell components are recycled: hemoglobin is
broken up into its amino acids, iron atoms returned to
bone marrow, heme group is converted to bilirubin
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Red Blood Cells
– contain hemoglobin, a protein which
carries oxygen and carbon dioxide
– RBC live for approximately 4 months.
– As they mature, they expel their nucleus so
they can carry more hemoglobin.
– They also assume a biconcave shape.
This shape makes them more flexible and
allows more of them to fit into blood
vessels to increase the surface area
available for gas (O2 and CO2) exchange.
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Hemoglobin Molecule
• Hemoglobin is an oxygen binding protein
which consists of 4 polypeptide chains
coiled around a “heme group”
• The “heme group” has an iron atom in its
center. This combines easily with oxygen at
the lungs AND lets go of the oxygen when
reaching body tissues.
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Hematocrit
• is a measure of the oxygen carrying capacity
of blood
• is obtained by spinning down blood and
measuring the amount of formed elements
• RBCs make up nearly 99% of formed
elements
• Normal hematocrit
– men: 43-49%
women: 37-43%
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• Regulation of RBC production is a negative
feedback control loop which maintains
homeostasis.
• Cells in the kidneys check the availability of
oxygen. If levels are low, these cells are
signaled to secrete the hormone erythropoietin.
This is carried to red bone marrow where more
RBC are produced.
• When the oxygen levels are appropriate, the
kidney cells stop production of erythropoietin.
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White Blood Cells-WBC or leukocytes
Functions: protection from infection, regulation of the
inflammatory reaction
• Types:
– Granular:
• neutrophils, eosinophils, basophils
• Mature in the red bone marrow
• Granules are actually vesicles filled with proteins
and enzymes
– Agranular:
• lymphocytes, monocytes
• monocytes mature in red bond marrow;
lymphocytes mature in the thymus gland
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Circulating levels of WBC rise whenever the body
is threatened by viruses, bacteria, or other
health challenges
• Each type of WBC can produce chemicals which
travel, via the blood, to the bone marrow where
they stimulate the production of more WBC
Most WBC remain in the blood vessels, but some
circulate in the intercellular fluid and the
lymphatic system.
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Types of WBC
• Neutrophils-most common WBC- approximately
60% of WBC are neutrophils
• see in acute infections; are the first WBC to
combat infection
• main function is phagocytosis (bacteria and
fungi)
– Eosinophils- approximately 2-4% of WBCs
• see in parasitic infections (such as worms) and
in allergic reactions (they release chemicals
that diminish the severity of these reactions)
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– Basophils-are rare, 0.5% of WBCs
• initiate the inflammatory response—
granules in the cell cytoplasm contain histamine
which starts the inflammatory response
– Lymphocytes-second most common WBC, about
30%; found in tonsils, blood, spleen, lymph nodes,
thymus
• manufactures antibodies and eliminates
anything foreign to the body
• play crucial role in immune response
– Monocytes-about 5%
• active in phagocytosis
• elevated in chronic infections
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Platelets
• are small cell fragments (not complete cells) which
play an essential role in the process of blood clotting
• platelet production is regulated by hormone
thrombopoietin
• platelets are stable as they circulate, but when they
encounter a “rough surface” they form a temporary
plug and initiate the clotting mechanism
• the body also requires vitamin K for normal blood
clotting
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• Clotting process or hemostasis (stopping blood)
– damage to a blood vessel triggers a vasospasm or
constriction of the damaged blood vessel
– platelets in the area swell, become sticky, adhere to
the damaged area and produce a plug which will
become the clot
– platelets also release chemicals to help in clot
formation
• prothrombin activator converts prothrombin (a
plasma protein) into thrombin
• thrombin converts the fibrinogen molecules, to
fibrin which traps blood cells, forms a clot and
seals the hole
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• Blood Typing
– Each of us has one of 4 types of blood--A, B, AB, O-along with some specific glycoproteins or antigens
• Our cells have surface proteins that the immune
system can recognize as “self” or “non-self”. The
immune system will recognize foreign cells as nonself .
• An antigen is a non-self cell protein that causes
the immune system to defend itself.
• The immune system builds antibodies-an
opposing protein which can kill the non-self cells.
– and causes them to stick together so it can be
destroyed. So, the transfused blood clumps or clots
within our blood vessels.
– This can be fatal
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• Another antigen found in blood is the Rh
antigen--if you have it, your blood is
classified as Rh positive. If you do not have
this, your blood is classified as Rh negative.
Blood Typing Tests
– Based on the interaction between antigens
and antibodies
– performed with anti-sera which contain
high concentrations of anti-A and anti-B
antibodies
– blood samples are mixed with each anti-sera
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– if agglutination or clumping (similar to
clotting) occurs with
anti-A sera, you have type A blood
anti-B sera, you have type B blood
– if clumping occurs with both anti-A and
anti-B, you have type AB blood
– if no clumping occurs with either anti-A and
anti-B sera, you have type O blood
• so, the antibodies you have in your body are
the opposite of your blood type
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Blood Types Determine Blood Compatibility
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Figure 7.12
Blood Typing
Blood
Type
Reaction
Anti-A Serum Anti-B Serum
Antibody
Type
Type A
Agglutination
Anti-B
antibody
Type B
No
Agglutination
Agglutination
Type AB
Agglutination Agglutination
Type O
No
Agglutination
No
Agglutination
Anti-A
antibody
No antibodies
against major
blood groups
Anti-A & Anti-B
No
antibodies
Agglutination
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Blood Disorders
• Carbon monoxide poisoning: competes with
oxygen
Anemia: reduction in oxygen-carrying capacity
Types of Anemia
• Iron deficiency anemia occurs when there is insufficient
iron ingested so fewer hemoglobin molecules are
available.
• Aplastic anemia where the bone marrow doesn’t
produce enough stem cells
• Hemorrhagic anemia is caused by extreme blood loss
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• Pernicious Anemia where the body is unable
to absorb vitamin B12 from the digestive tract.
The body uses B12 to produce normal RBC.
• Sickle cell Anemia is an inherited disorder in
which the RBC become sickle or crescent
shaped when the oxygen concentration of the
blood is low. This shape doesn’t travel easily
through blood vessels because the cells
clump, get stuck in the vessels and cause a
great deal of pain.
– Sickle shaped cells can’t carry a normal
amount of oxygen.
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• Leukemia is a form of cancer where you see an
uncontrolled production of abnormal or immature WBC in
the bone marrow. This crowds out the production of
normal WBC, RBC, and platelets.
• Multiple myeloma: a form of cancer where abnormal
plasma cells in the bone marrow increase production.
These cells are important for the manufacture of
antibodies.
• Mononucleosis is a contagious infection of lymphocytes
caused by the Epstein-Barr virus.
• Septicemia can also be called “blood poisoning”. It
occurs when organisms invade the blood, overpower our
body’s defenses and multiply rapidly in the blood.
• Thrombocytopenia is a reduction in the number of
platelets.
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Polycythemia is a term used to describe an
abnormally high RBC count
– this increases the thickness of blood and
slows down the flow of blood.
Hemophilia is an inherited condition caused by a
deficiency of one or more clotting factors (known
as clotting factor VIII)
– When a blood vessel is damaged, blood either clots
very slowly or not at all
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The Cardiovascular System
Blood Vessels: Arteries, Veins
Arterial system
Structure:
• Endothelium: thin inner layer of squamous epithelial cells
• Middle: thick layer of smooth muscle woven with elastic
connective tissue
• Outer layer: tough supportive layer of connective tissue,
primarily collagen
– anchors vessels to surrounding tissues and helps protect them
from injury
• Aneurysm: ballooning of the arterial wall
– Endothelium of blood vessel becomes damaged and blood
seeps through and accumulates between the middle and outer
layers of the blood vessel
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The Cardiovascular System
• Functions:
– Arteries: carry blood away from heart
– Need thicker muscular wall due to pressure of blood
being pumped by aorta
– Because blood pressure is less by the time blood has
reached the arterioles, they do not have the
outermost layer of connective tissue and the muscular
layer is thinner.
• precapillary sphincter, a band of smooth muscle, is
located where the arteriole meets the capillary and
controls the blood flow to each capillary
• Capillaries: thin walled blood vessels; branching
design allows exchange of gases, nutrients, waste,
and defensive cells between vessel and tissue
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The Cardiovascular System
– vasoconstriction
– vasodilation
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Venous system
• Functions: carry blood to the heart
• Structure: veins: three layers, thin-walled
– like the walls of arteries, the walls of veins consist of 3
layers of tissue.
• Outer 2 layers are much thinner than those of
arteries
• veins have larger diameters (lumen) than arteries
– the pressure in veins is much lower than that in
arteries which is why their walls are not as strong as
arteries
• Blood pressure lower in veins than in capillaries
– veins can act as a blood volume reservoir
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– the larger diameter of veins allows them to stretch
to accommodate large volumes of blood at low
pressures
– because veins can stretch, it is more difficult for
them to return blood to the heart against the force
of gravity
– people who spend a lot of time on their feet may
get varicose veins because of this
• Factors which help veins to return blood to heart
• Contraction of skeletal muscles-skeletal
muscle pump
• as we move and muscles contract and relax,
they press against veins and help push blood to
the heart
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– One-way valves—blood can only flow in
one direction
• Open passively to allow blood to move toward
the heart and cloose whenever blood begins to
flow backward
– the work of the skeletal muscles helps the valves
pump blood. This is called a skeletal muscle
pump
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Pressure changes associated with breathing
– movements associated with breathing also help
pump blood. This is called a respiratory pump
and helps to push blood from the abdomen to the
chest and to the heart.
• when we breathe, there are pressure changes
in the thoracic and abdominal cavities
• during inhalation, abdominal pressure
increases and squeezes abdominal veins
• simultaneously, pressure within the thoracic
cavity decreases which dilates the thoracic
veins and thus propels the blood.
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Lymphatic System
Function: maintains proper volume of blood and interstitial
fluid; also functions in immune system
– Picks up objects in interstitial fluid that are too large to
diffuse into capillaries
• Lipid droplets absorbed during digestion
• Invading organisms
– Transports these to larger lymphatic vessels which
return the fluid to veins near the heart
• Structure:
– Lymphatic vessels
– Lymph
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The Heart
Structure: composed of cardiac muscle
enclosed by pericardium, a fibrous sac
– Pericardium protects the heart, anchors it to
surrounding structures, prevents it from
overfilling with blood
– Pericardial cavity separates it from heart
muscle itself and contains a tiny amount of
fluid to allow heart and pericardium to glide
smoothly every time the heart contracts
– Heart beat rate determined by the SA Node
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The Heart
• Layers: Epicardium: thin, outermost layer
made up of epithelial and connective
tissue
– Myocardium: thick layer primarily of cardiac
muscle
– Endocardium: innermost layer of endothelial
tissue resting on a layer of connective tissue;
is continuous with the endothelium that lines
blood vessels
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The Heart
• Pericarditis:
– A layer of the heart wall becomes inflamed
• Endocarditis: inflammation of the endocardium
• 4 Chambers: two atrias, two ventricles
– Atrias are on the top
– Ventricles are the 2, more muscular chambers
on the bottom
• Septum, a muscular partition, separates the right
and left sides of the heart
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The Heart
• Valves: prevent blood from flowing backward
– Two atrioventricular valves: tricuspid (right)
and bicuspid (mitral--left)
• Chordae tendinae: strands of connective
tissue which connect to muscular
extensions of the ventricle wall, called
papillary tendons
• These prevent the valves from being
pushed backward
– Two semilunar valves: pulmonary and aortic
• Have 3 flaps
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Flow of blood through the heart:
• Deoxygenated blood through the vena cava
to the right atrium
• Deoxygenated blood through the right
atrioventricular valve to the right ventricle
• Deoxygenated blood through the pulmonary
semilunar valve to the pulmonary trunk and
the lungs
• Oxygenated blood through the pulmonary
veins to the left atrium
• Oxygenated blood through the left
atrioventricular valve to the left ventricle
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• Oxygenated blood through the aortic
semilunar valve to the aorta
Blood flow through the tissues:
• Oxygenated blood through branching
arteries and arterioles to the tissues
• Oxygenated blood through the arterioles to
capillaries
• Deoxygenated blood from capillaries into
venules and veins
• Ultimately to the vena cava and into the
right atrium
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• Coronary arteries supply the heart muscle with
blood (myocardium is too thick to be able to be supplied
with oxygen and nutrients by diffusion from the blood
passing through it)
• Coronary arteries branch from the aorta as it
leaves the heart and encircle the heart’s surface
• Cardiac veins bring the blood back to the right
atrium
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Cardiac cycle is a measure of the blood pumped
with each beat multiplied by the number of
heart beats per minute
• Steps summarized:
1. Heart relaxes and all four chambers fill; blood is
sucked in as the heart muscle expands
2. Atrial contraction: more blood into the already filled
ventricles
3. Ventricular contraction: blood is ejected into the
aorta and pulmonary trunk
•
•
Systole refers to the contraction pressure
Relaxation of the
entire heart = diastole
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Heart Sounds and Heart Valves
• Lub-dub
– Lub signals the closure of the 2 AV valves
– Dub signals the aortic and pulmonary
semilunar valves closing
• Heart murmurs are created by obstructions
the blood encounters as it flows through the
heart
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Cardiac conduction system is a group of
specialized cardiac muscle cells that
initiate and distribute electrical impulses
throughout the heart
– is responsible for the coordinated sequence of
the cardiac cycle which spreads from atria to
ventricles
– Consists of: sinoatrial node, atrioventricular
bundle and its 2 branches and Purkinje
fibers
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• Sinoatrial (SA) node
– Provides the stimulus that starts the heartbeat
• Is a small mass of cardiac muscle cells close to
where the right atrium and the superior vena cava
meet
• Emits an electrical impulse that travels across both
atria stimulating waves of contraction
• Is called the cardiac pacemaker because it
initiates the heartbeat
• Atrioventricular (AV) node
– Located between the atria and ventricles
– Muscle fibers are smaller in diameter which causes a
slight delay of the electrical impulse. This allows the
atria time to contract and empty their blood into the
ventricles before the ventricles contract
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– Atrioventricular bundle:
• Located in the septum between the 2 ventricles
• These fibers branch and extend into Purkinje
fibers, smaller fibers that carry the impulse to all
cells in the ventricular myocardium
• The impulse travels down the septum (to the lower
part of the ventricles) and then spreads rapidly
upward through the purkinje fibers, the lower part
of the ventricles contract first and squeeze blood
into the pulmonary trunk and the aorta.
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Cardiac Conduction System Coordinates Contraction
• SA node: cardiac
pacemaker
• AV node: relay
impulse
• AV bundle and
Purkinje fibers:
carry impulse to
ventricles
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Figure 8.14
Electrocardiograms (EKG/ECG)
We can track the electrical activity of the heart as
weak electrical differences in voltage with an
EKG
– Place “leads” or electrodes at the chest, wrists
and ankles
• Three formations:
– P wave: impulse across atria
– QRS complex: spread of impulse down
septum, around ventricles in Purkinje fibers
(this occurs just as the ventricles start to
contract)
– T wave: end of electrical activity in ventricles
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• Arrhythmias are an abnormal rhythm or rate of
heartbeat
– Some arrhythmias are common and not
potentially dangerous
– ventricular fibrillation is the leading cause of
cardiac death
• Can treat with medication or “cardioversion” with
an electric shock or artificial pacemakers
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Electrocardiograms (EKG/ECG)
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Figure 8.15b,c
Blood Pressure
• Force that blood exerts on the wall of a blood vessel as a
result of the pumping action of the heart
• Definitions: “normal”:
– Systolic pressure: highest pressure, pressure reached
during ventricular contraction to eject blood from
theheart
– Diastolic pressure: lowest pressure, pressure when
the ventricles relax
• Arteries store energy generated during systole
and during diastole they use that stored energy
to supply blood to the tissues
• Measurement: sphygmomanometer
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• Hypertension: high blood pressure:
– Definition
– The silent killer
– Risk factors
• Hypotension: blood pressure too low so blood
can’t be pushed throughout the body and back
to the heart; generally thought of as reducing
blood flow to the brain
– Clinical signs: dizziness, fainting
– Causes: orthostatic, severe burns, blood loss
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Regulation of the Cardiovascular System:
Baroreceptors
Baroreceptors: pressure receptors in aorta and carotid
arteries which help maintain arterial blood pressure
• Steps in mechanism:
– Blood pressure rises, arterial vessels stretched
– Signals sent to cardiovascular center in the brain
– Heart signaled to lower heart rate and force of
contraction
– Cardiac output (amount of blood and rate that the
heart pumps into the aorta) lowered
– Arterioles vasodilate (increasing arteriole diameter)
and thus increasing blood flow to tissues
– Combined effect lowers blood pressure
The opposite happens when blood pressure is too low
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Regulation of the Cardiovascular System: Nervous and
Endocrine Factors
• Medulla oblongata regulates cardiac output (obtained by
multiplying heart rate by stroke volume (volume of blood
pumped out with each heartbeat)
– Sends nerve signals to the heart via:
• Sympathetic nerves: increase heart rate; constrict blood
vessels, raising blood pressure
• Parasympathetic system, a decrease in nerve activity will
dilate blood vessels, lowering blood pressure; decrease heart
rate; dilate blood vessels
• Hormones: epinephrine (adrenaline) and norepinephrine
• Local requirements dictate local blood flow based upon a
need for more or less oxygen and nutrients and waste
products to be removed
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Cardiovascular Disorders
• Angina pectoris: a chest pain warning
• Myocardial infarction/heart attack: permanent
cardiac damage
• Congestive heart failure: decrease in pumping
efficiency
• Embolism: blockage of blood vessels
• Stroke or Cerebrovascular Accident or brain
attack: impaired blood flow with subsequent
damage to the brain
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• Pericarditis:
– Inflammation of the pericardium (sac which
surrounds the heart)
• Endocarditis: inflammation of the endocardium
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Reducing the Risk of Cardiovascular Disease
•
•
•
•
•
Smoking: don’t
Blood lipids: monitor cholesterol levels
Exercise: regular and moderate
Blood pressure: treat hypertension
Weight: being overweight increases risk of heart
attack and stroke
• Control of diabetes mellitus: early diagnosis and
treatment delays onset of related problems
• Stress: avoid chronic stress
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Cardiac Anatomy Quiz
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