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

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 CROSS-REACTIONS

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 CROSS-REACTION 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 connective-tissue 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 VALVE- prevents 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 VENTRICLESThe 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