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CHAPTERS 11 & 12
BLOOD AND THE
HEART
FUNCTIONS OF THE BLOOD
1. Transport of dissolved gasses, nutrients,
hormones, and metabolic wastes
2. Regulation of pH and electrolyte (ions)
composition of fluids in the body
3. Restriction of fluid losses through
damaged vessels or other sites of injury
4. Defense against toxins and pathogens
5. Stabilization of body temperature
COMPOSITION OF BLOOD
Blood consists of a matrix called PLASMA
and formed elements
PLASMA- contains dissolved proteins; is
slightly denser than water
FORMED ELEMENTS- blood cells and
cell fragments that are suspended in
the plasma
- Erythrocytes (red blood cells, RBCs),
Leukocytes (white blood cells, WBCs),
platelets
Together plasma and formed elements form
WHOLE BLOOD
- an adult man has about 5-6 liters of blood
- an adult woman has about 4-5 liters
Whole blood has the same physical
characteristics:
- temperature of 38º C (100.4º F)
- viscosity 5X greater than water
- pH averaging 7.4
CLOSER LOOK AT PLASMA
Plasma makes up about 55% of the volume
of whole blood
PLASMA PROTEINS
- the large size of most blood proteins
prevents them from crossing capillary
walls
3 Primary Classes of Proteins:
1. Albumins- most abundant; major
contributors to osmotic pressure of the
plasma
2. Globulins- include
antibodies and transport
proteins
- Antibodies attack foreign
proteins and pathogens
- Transport proteins bind
small ions, hormones, or
compounds that might
otherwise be filtered out
of the blood at the
kidneys
3. Fibrinogens- function in blood clotting
- under certain conditions, these molecules
interact and combine to form large strands
of FIBRIN, which provide the basic
framework for a blood clot
The liver synthesizes most of the plasma
proteins
- liver disorders can alter the composition
and functional properties of the blood
CLOSER LOOK AT FORMED
ELEMENTS
HEMOPOIESIS- production of formed
elements
- embryonic blood cells appear in
bloodstream during the 3rd week of
development
- these cells divide rapidly
- the vessels of the yolk sac, an embryonic
membrane, are the primary site of blood
formation for the first 8 weeks of
development
- as other organs appear, some of these cells
move out of the bloodstream into the liver,
spleen, thymus, and bone marrow
- these embryonic cells differentiate into STEM
CELLS that produce blood cells by their
divisions
- liver and spleen are the primary sites of
hemopoiesis from the 2nd to 5th months of
development
- as the skeleton enlarges, bone marrow
becomes increasingly important, and is the
primary site after the 5th month of
development
- in adults, marrow is the only site of RBC
production, and the primary site of WBC
production
RED BLOOD CELLS (RBCs)
- contain the pigment HEMOGLOBIN,
which binds, and transports O2 and CO2
- most abundant blood cells, making up 99%
of the formed elements
HEMATOCRIT- the percentage of whole
blood occupied by cellular elements
RBCs containing
hemoglobin with
bound oxygen give
blood a bright red
color
RBCs containing
hemoglobin NOT
bound to oxygen give
blood a dark red,
almost burgundy color
Carbon Monoxide Poisoning
RBCs AND BLOOD TYPES
ANTIGENS- substances that can trigger
an immune response
- cell membranes contain surface antigens,
substances that the body’s immune
defenses recognize as “normal”
A person’s blood type is a classification
determined by the presence or absence of
specific surface antigens
- the characteristics of RBC surface antigen
molecules are genetically determined
All of the RBCs of any individual have the same
pattern of surface antigens
- Type A blood has antigen A only
- Type B blood has antigen B only
- Type AB blood has both A and B
- Type O blood has neither A nor B
* type O is the most common, followed by A,
B, then AB
ANTIBODIES AND CROSSREACTIONS
Plasma contains antibodies or
AGGLUTININS that will attack surface
antigens on foreign cells
- the plasma of an individual with type A
blood contains circulating anti-B antibodies
which will attack Type B surface antigens
- Type O blood lacks surface antigens A or
B, so plasma contains BOTH anti-A and
anti-B antibodies
- Type AB have no A or B antibodies
If an antibody meets an antigen, a CROSSREACTION occurs
- the RBCs will clump together, called
AGGLUTINATION
- then they may break up or hemolyze
- these clumps can clog blood vessels
The plasma of an Rh-negative individual
does not contain anti-Rh antibodies
- Rh is another surface antigen
- these antibodies are present only if the
individual has been sensitized by previous
exposure to Rh-positive RBCs
* can happen if an Rh-negative mother
gives birth to an Rh-positive baby
WHITE BLOOD CELLS (WBCs)
White blood cells are easily distinguishable
from red blood cells because each has a
nucleus and lacks hemoglobin
- WBCs help defend the body against
invasion by pathogens and remove toxins,
wastes, and abnormal or damaged cells
WBCs are divided into 2 groups, based on
their appearance after staining:
1. Granulocytes- have many stained
granules
2. Agranulocytes- have few if any stained
granules
- the “granules” are secretory vesicles and
lysosomes; agranulocytes also contain
lysosomes, they are just more difficult to
see
Granulocytes: neutrophils, eosinophils,
basophils
Agranulocytes: monocytes, lymphocytes
- most of the WBCs in the body are found in
connective tissue proper and in organs of
the lymphatic system; very few are
circulating
General Functions of WBCs
Basophils, neutrophils, eosinophils, and
monocytes contribute to the body’s
nonspecific defenses of the immune
system
- they do not discriminate between one type
of threat and another
Lymphocytes are responsible for specific
immunity
- this is the body’s ability to attack
pathogens on a specific, individual basis
PLATELETS
Platelets in nonmammalian vertebrates are
nucleated cells called THROMBOCYTES
- because in humans they are cell fragments
rather than individual cells, the term
platelet is used when referring to our blood
Bone marrow contains very large cells with
large nuclei called MEGAKARYOCYTES
- these continuously shed cytoplasm in
small membrane-enclosed packets
- these are platelets
- platelets initiate the clotting process
and help close injured blood vessels
- they are continuously replaced
HEMOSTASIS
HEMOSTASIS- the process that stops
bleeding
- prevents the loss of blood through the
walls of damaged vessels
STEP 1: The vascular phase
- smooth muscle fibers lining a blood
vessel contract, decreasing the
diameter of the vessel
- lasts about 30 minutes
- membranes of cells at the injury site
become sticky, and may stick together to
block the opening
STEP 2: The platelet phase
- platelets begin to attach to the sticky cell
membranes and exposed collagen fibers
within 15 seconds of the injury
- as more platelets arrive, they form a
PLATELET PLUG, which may also close
the opening
STEP 3: Coagulation phase
- does not start until 30 seconds or more
after injury
- this is blood clotting
- circulating fibrinogen is converted into the
insoluble protein fibrin
- blood cells and additional platelets
become trapped in the protein forming
a BLOOD CLOT
CLOTTING PROCESS
Normal coagulation cannot occur unless
plasma contains the necessary
CLOTTING FACTORS
- these include calcium ions, and 11
different plasma proteins
- these proteins are converted to active
enzymes that direct essential reactions in
the clotting response
- most of these are produced by the liver
THE HEART AND
CIRCULATORY SYSTEM
Blood vessels are subdivided into a:
PULMONARY CIRCUIT- carries blood to
and from exchange surfaces of the
lungs
SYSTEMIC CIRCUIT- transports blood to
and from the rest of the body
- each circuit begins at the heart, and blood
travels though these circuits in sequence
ARTERIES- carry blood away from the
heart
VEINS- carry blood to the heart
CAPILLARIES- small, thin-walled vessels
between the smallest arteries and veins
- the thin walls of the capillaries permit
exchange of nutrients, gases, and waste
products between the blood and
surrounding tissue
STRUCTURE OF THE HEART
The heart is a hollow, muscular organ
located in the thoracic cavity between the
lungs and above the diaphragm
- 2/3 of its mass lies to the left of the
middle line of the body
- size usually corresponds to the size of the
person’s clenched fist
- the weight of the heart depends on the
individual’s size, sex, and age
- in embryonic development, the heart has a
fixed number of cardiac muscle cells that
are present at birth and remain through
life- growth of the heart is due to an
increase in the size of the cells
Pericardial Sac
The heart and the base of the heart’s major
blood vessels are enclosed in a slippery,
loose-fitting sac called the PERICARDIUM
2 Layers:
PARIETAL PERICARDIUM- external layer
that is attached to the diaphragm,
sternum, and blood vessels
VISCERAL PERICARDIUM- inner layer that
adheres to the heart wall; also called
EPICARDIUM
Between the 2 layers is a narrow space
called the PERICARDIAL CAVITY
- this is filled with PERICARDIAL FLUID, a
slippery fluid that prevents friction between
the membranes
A = Visceral pericardium
B = Parietal pericardium
Heart Wall
3 distinct layers make up the heart wall:
EPICARDIUM (visceral pericardium)external layer of wall
- usually contains fat
MYOCARDIUM- comprises the bulk of the
heart
- consists of cardiac muscle fibers that are
involuntary
- this layer is responsible for the
contracting action of the heart
ENDOCARDIUM- inner layer; thin
membrane of endothelial and connectivetissue cells
- covers all of inner surface, even the
valves
Chambers and Valves
The heart is divided into right and left
halves, and then each side into upper and
lower chambers
ATRIA- upper chambers
- separated by the INTERATRIAL SEPTUM
VENTRICLES- lower chambers
- separated by INTERVENTRICULAR
SEPTUM
On the outer surface of each atrium is an
external flap called an AURICLE
- can be seen when atrium is not filled
with blood
On the surface of the interatrial septum is an
oval depression called the FOSSA
OVALIS
- this is a remnant of an oval hole called
the FORAMEN OVALE through which
blood passes in the fetal heart
- in the fetus the blood passes directly from
the right side to the left side without
passing through the lungs to become
oxygenated
- Lungs only begin to function as an
oxygen source after birth- the hole
closes
- RIGHT- only gets DEOXYGENATED
blood
- LEFT- only gets OXYGENATED blood
from lungs
APEX- inferior tip of heart
2 types of valves
1. ATRIOVENTRICULAR VALVES
- Tricuspid
- Bicuspid (Mitral)
2. SEMILUNAR VALVES
- Pulmonary Semilunar Valve
- Aortic Semilunar Valve
TRICUSPID- located between the right
atrium and right ventricle
- consists of 3 irregularly shaped flaps or
cusps formed by fibrous tissue
- pointed ends point in toward ventricle
- attached by cords called CHORDAE
TENDINEAE to small muscular projections
called the PAPILLARY MUSCLES
The PAPILLARY MUSCLES are found along
the inner surface of the ventricles
The left atrioventricular opening is guarded by
the BICUSPID or MITRAL VALVE
- consists of 2 flaps or cusps
- heavier and stronger than the tricuspid valve
because the left ventricle exerts greater
force in its contraction
- its cusps are also attached to chordae
tendineae and papillary muscles
The second type of valve is found where the
2 major arteries (pulmonary and aorta)
leave the ventricles
- they are crescent moon shaped and
have 3 flaps
PULMONARY SEMILUNAR VALVEprevents blood in the pulmonary artery
from reentering the right ventricle
AORTIC SEMILUNAR VALVE- prevents
blood from reentering the left ventricle
as it enters the aorta
DIFFERENCES BETWEEN
LEFT AND RIGHT VENTRICLES
The demands on the right and left atria are
very similar, so they look almost identical
Demands on the right and left ventricles are
very different
- the lungs are close to the heart, and the
pulmonary arteries and veins are short
and wide
- the right ventricle does not need to push
very hard to pump blood through the
pulmonary circuit
- the wall of the right ventricle is thin
Pushing blood through the systemic circuit
takes 6-7 times more force than around
the pulmonary circuit
- the left ventricle has a very thick
muscular wall
- as the left ventricle contracts, it bulges into
the right ventricular cavity and helps force
blood out of the right ventricle
BLOOD SUPPLY TO THE
HEART
The heart has its own extensive blood
supply
- the CORONARY ARTERIES supply the
myocardium with blood
- the left coronary artery and the right
coronary artery are the first branches of
the aorta
- from the arteries, blood empties into the
coronary veins, then the coronary sinus
which empties into the right atrium
HEARTBEAT
How can the heart contract without direct
control by the brain or spinal cord?
- a specialized conducting system is found
within the heart- a network of specialized
cardiac muscle cells that initiate and
distribute electrical impulses
The network is made up of 2 types of
cardiac muscle cells that do not contract:
1. Nodal cells
2. Conducting cells
Nodal Cells
- responsible for establishing the rate of
cardiac contraction
Nodal cells are electrically coupled to one
another, to conducting cells, and to normal
cardiac muscle cells
- when action potential appears in a nodal
cell, it sweeps though the conducting
system, reaching all of the cardiac muscle
tissue and causing a contraction
- so nodal cells determine heart rate
Normal rate of contraction is established by
PACEMAKER CELLS, nodal cells that reach
threshold first
- these are located in the SINOATRIAL NODE
(SA node) or cardiac pacemaker, a tissue
mass embedded in the posterior wall of the
right atrium near the entrance of the superior
vena cava
- pacemaker cells depolarize rapidly, resulting in
a heart rate of 70-80 beats per minute
Conducting Cells
The cells of the SA node are electrically
connected to those of a larger
ATRIOVENTRICULAR NODE (AV node)
by conducting cells in the atrial walls
The Conducting System
Consists of 3 structures:
1. Sinoatrial Node (SA Node)- mass of
specialized myocardial cells embedded in
the wall of the right atrium, near where the
superior vena cava enters the heart
- this structure initiates each heart beat and
sets the pace for the heart- called
PACEMAKER
Electrical activity of the SA node occurs on
average of 70 to 72 times per minute and
excites both atria at about the same time
2. ATRIOVENTRICULAR NODE (AV
NODE)- after each atrial contraction, an
impulse reaches the AV node
- located at the base of the right atrium near
the interatrial septum
- a delay occurs for about 0.1 second which
allows the atria to contract and empty their
contents into the ventricles
- the impulse then travels over the
connecting link, the AV bundle
3. ATRIOVENTRICULAR BUNDLE (AV
BUNDLE)- consists of a group of
specialized cardiac muscle fibers adapted
for conduction
- the bundle divides and passes down each
side of the interventricular septum to form
the PERKINJE NETWORK- the
conducting system within the walls of the
ventricles
- contraction proceeds from the inferior
portions of the ventricles upward, ensuring
that the blood leaves the ventricles
through the arteries
The Cardiac Cycle
CARDIAC CYCLE- sequence of heart action
3 stages:
1. Blood enters the atria through the
pulmonary veins and the superior and
inferior venae cavae
2. The pulmonary circuit brings blood from
the lungs while the systemic circuit returns
blood from the head, neck, arms, thorax,
trunk, and legs
3. The right atrium receives blood from the
heart wall itself through the coronary sinus
Diastolic and Systolic Phases
DIASTOLE- the process of filling the atria
and ventricles
- this is a period of relaxation in which the
chambers become distended
- followed by a period of active contraction
called SYSTOLE, which is marked by a
shortening of the muscle bundles
- the total time for a complete cycle is about
0.8 seconds
CONTROL OF THE HEART
Heart is affected by a number of influences:
- Heart rate is affected by the secretions of
endocrine
- Hormones secreted by the thyroid and
adrenal glands increase heart rate- fright
or stress
CHEMICAL INFLUENCE
Many chemical compounds affect the heart
- ATROPINE- active substance that comes
from the deadly plant nightshade
 Greatly accelerates heartbeat
- MUSCARINE- poisonous substance found
in some mushrooms
 Inhibits heart action to the point where
the heart stops beating completely
- NICOTINE
 Blood pressure is raised
 Pulse rate is increased and there is a
constriction of the coronary arteries
 Body temperature in extremities is
decreased due to the constriction of blood
vessels
RATE OF HEART BEAT
Heart rate is affected by several factors:
- age
- sex
- position of body
- amount of physical activity
- temperature of surroundings
- thought processes
- heart rate is faster before birth and steadily
declines after birth until a constant
average is reached
- females usually have a faster heartbeat
than males
EKG
As with all muscles, the heart develops an
electric current when it contracts
- this is a result of the movement of ions
across cell membranes > ACTION
CURRENT
ELECTROCARDIOGRAPH- instrument that
measures and records the electric current
ELECTROCARDIOGRAM (EKG)- resulting
record
Heart Sounds
STETHOSCOPE- instrument to measure the
sound of the heart
WHY DO DOCTORS LISTEN TO THE
HEART?
- by noting the beginning and ending of the
ventricular systole (contraction), one can
time other events in the cardiac cycle
- indicate the condition of the atrioventricular
and semilunar valves
2 heart sounds:
1. Result of the closing of the atrioventricular
valves and the contraction of the muscles
in the walls of the ventricles
- the instant at which the atrioventricular
valves close
- sounds like a lub
- best heard right over the heart, between
the 5th and 6th ribs
2. Represents the sudden closing of the
semilunar valves
- sounds like dub and is shorter in duration
than the first sound
- best heard between the 2nd and 3rd ribs,
near the sternum
HEART DISORDERS
Every heart has the ability to perform work
- if a heart is abnormal at birth, or if an
individual develops certain risk factors, the
life span of the heart may be shortened
Risk Factors:
High cholesterol, high blood pressure,
cigarette smoking, obesity, lack of
exercise, sugar diabetes
ISCHEMIA- lack of blood supply to a
restricted area
INFARCTION- if this restriction results in
destroying tissues of the heart
- one of the many causes of heart attack
FIBRILATION- most common of all serious
heart irregularities
- atria are never completely emptied of blood
and their walls quiver instead of contracting
- beat may be very rapid, irregular, and
disorganized
- AV node is activated at irregular intervals,
resulting in a ventricular irregularity
TACHYCARDIA- rapid heartbeat
- if fibrillation occurs in the ventricles, little or
no blood is pumped out of the heart
through the pulmonary artery or aorta, and
circulation of blood stops> FATAL
HEART MURMURS AND
VALVE DEFECTS
Defective or diseased valves cause most
murmurs
STENOSIS- valve becomes narrow and
blood that forces through becomes
turbulent
- produces a sound
If a valve does not close properly, blood
leaks through it in the wrong direction,
again producing a sound
ATRIAL SEPTAL DEFECT- occurs when the
fetal foramen ovale fails to close
completely after birth
- pressure is lower in right atrium than in left
and blood moves from the left to the right
atrium
- this causes added strain to pulmonary
circulation, resulting in fatigue
VENTRICULAR SEPTAL DEFECT- if the
interventricular septum is defective,
deoxygenated blood may mix with
oxygenated blood in the left ventricle
- affected individual’s blood is not bright red,
and skin, fingernails, and lips appear blue>
CYANOTIC
- can usually be repaired through open heart
surgery