BLOOD

Blood

• The only fluid tissue in the human body

• Classified as a connective tissue–Living cells = formed elements–Non-living matrix = plasma

Blood

Physical Characteristics of Blood

• Color range–Oxygen-rich blood is scarlet red–Oxygen-poor blood is dull red

• pH must remain between 7.35–7.45• Blood temperature is slightly higher

than body temperature

Blood Plasma

• Composed of approximately 90 percent water

• Includes many dissolved substances–Nutrients–Salts (metal ions)–Respiratory gases–Hormones–Proteins–Waste products

Plasma Proteins

• Albumin – regulates osmotic pressure

• Clotting proteins – help to stop blood loss when a blood vessel is injured

• Antibodies – help protect the body from antigens

Formed Elements

• Erythrocytes = red blood cells• Leukocytes = white blood cells• Platelets = cell fragments

Photomicrograph of a Blood Smear

Erythrocytes (Red Blood Cells)

• The main function is to carry oxygen• Contains hemoglobin• Anatomy of circulating erythrocytes–Biconcave disks–Essentially bags of hemoglobin–Anucleate (no nucleus)–Contain very few organelles

• 4 - 6 million per mm3 of blood

Hemoglobin

• Iron-containing protein• Binds strongly, but reversibly, to

oxygen• Each hemoglobin molecule has four

oxygen binding sites• Each erythrocyte has 250 million

hemoglobin molecules

Homeostatic Imbalance

• Anemia – decrease in oxygen-carrying ability of blood• May be caused by:

– Low red blood cell count (RBC)– Abnormal or deficient hemoglobin– Lack of B12 or intrinsic factor– Lack of iron– Cancer

• Sickle cell anemia – genetically defective hemoglobin

• Polycythemia – abnormal increase in RBC– May be from bone marrow cancer or living at high

altitudes– Causes increased viscosity of blood

Sickle Cell Anemia

Leukocytes (White Blood Cells)

• Crucial in the body’s defense against disease

• These are complete cells, with a nucleus and organelles

• Able to move into and out of blood vessels (diapedesis)

• Can move by ameboid motion• Can respond to chemicals released

by damaged tissues

Leukocyte Levels in the Blood

• Normal levels are between 4,000 and 11,000 cells per mm3

• Abnormal leukocyte levels– Leukocytosis• Above 11,000 leukocytes/ml• Generally indicates an infection• Could indicate leukemia (WBC cancer)

– Leukopenia• Abnormally low leukocyte level• Commonly caused by certain drugs

Platelets

• Derived from ruptured cells• Needed for the clotting process• Normal platelet count is 250,000 -

500,000/mm3

Hematopoiesis

• Blood cell formation• Occurs in red bone marrow• All blood cells are derived from a

common stem cell (hemocytoblast)• Hemocytoblast differentiation–Lymphoid stem cell produces

lymphocytes–Myeloid stem cell produces other

formed elements

Fate of Erythrocytes

• Unable to divide, grow, or synthesize proteins

• Wear out in 100 to 120 days• When worn out, are eliminated by

phagocytes in the spleen or liver• Lost cells are replaced by division of

hemocytoblasts

Control of Erythrocyte Production

• Rate is controlled by a hormone (erythropoietin)

• Kidneys produce most erythropoietin as a response to reduced oxygen levels in the blood

• Homeostasis is maintained by negative feedback from blood oxygen levels

Control of Erythrocyte Production

Hemostasis

• Stoppage of blood flow• Result of a break in a blood vessel• Hemostasis involves three phases–Platelet plug formation–Vascular spasms–Coagulation

Hemostasis – blooding clotting

Platelet Plug Formation

• Collagen fibers are exposed by a break in a blood vessel

• Platelets become “sticky” and cling to fibers

• Anchored platelets release chemicals to attract more platelets

• Platelets pile up to form a platelet plug

Vascular Spasms

• Anchored platelets release serotonin• Serotonin causes blood vessel

muscles to spasm• Spasms narrow the blood vessel,

decreasing blood loss

Coagulation

• Injured tissues release thromboplastin

• PF3 (a phospholipid) interacts with thromboplastin, blood protein clotting factors, and calcium ions to trigger a clotting cascade

• Prothrombin activator converts prothrombin to thrombin (an enzyme)

• Thrombin joins fibrinogen proteins into hair-like fibrin

• Fibrin forms a meshwork (the basis for a clot)

Blood Clotting

• Blood usually clots within 3 to 6 minutes

• The clot remains as endothelium regenerates

• The clot is broken down after tissue repair

Fibrin Clot

Undesirable Clotting

• Thrombus–A clot in an unbroken blood vessel–Can be deadly in areas like the

heart• Embolus–A thrombus that breaks away and

floats freely in the bloodstream–Can later clog vessels in critical

areas such as the brain

Bleeding Disorders

• Thrombocytopenia–Platelet deficiency–Even normal movements can

cause bleeding from small blood vessels that require platelets for clotting

• Hemophilia–Hereditary bleeding disorder–Normal clotting factors are

missing

Blood Groups and Transfusions

• Large losses of blood have serious consequences–Loss of 15 to 30 percent causes

weakness–Loss of over 30 percent causes

shock, which can be fatal• Transfusions are the only way to

replace blood quickly• Transfused blood must be of the

same blood group

Human Blood Groups

• Blood contains genetically determined proteins

• A foreign protein (antigen) may be attacked by the immune system

• Blood is “typed” by using antibodies that will cause blood with certain proteins to clump (agglutination)

Human Blood Groups

• There are over 30 common red blood cell antigens

• The most vigorous transfusion reactions are caused by ABO and Rh blood group antigens

ABO Blood Groups

• Based on the presence or absence of two antigens–Type A (only A antigen)–Type B (only B antigen)–Type AB (both A and B antigen)–Type O (neither A or B)

Rh Blood Groups

• Named because of the presence or absence of one of eight Rh antigens (agglutinogen D)

• Most Americans are Rh+

• Problems can occur in mixing Rh+ blood into a body with Rh– blood

Rh Dangers During Pregnancy

• Danger is only when the mother is Rh– and the father is Rh+, and the child inherits the Rh+ factor

• The mismatch of an Rh– mother carrying an Rh+ baby can cause problems for the unborn child– The first pregnancy usually proceeds

without problems– The immune system is sensitized after

the first pregnancy– In a second pregnancy, the mother’s

immune system produces antibodies to attack the Rh+ blood (hemolytic disease of the newborn)

Developmental Aspects of Blood

• Sites of blood cell formation–The fetal liver and spleen are early

sites of blood cell formation–Bone marrow takes over

hematopoiesis by the seventh month

• Fetal hemoglobin differs from hemoglobin produced after birth

CARDIOVASCULAR SYSTEM

The Cardiovascular System

• A closed system of the heart and blood vessels–The heart pumps blood–Blood vessels allow blood to

circulate to all parts of the body• The function of the cardiovascular

system is to deliver oxygen and nutrients and to remove carbon dioxide and other waste products

The Heart

• Location–Thorax between the lungs–Pointed apex directed toward left

hip• About the size of your fist

The Heart

The Heart: Coverings

• Pericardium – a double serous membrane–Visceral pericardium• Next to heart

–Parietal pericardium• Outside layer

• Serous fluid fills the space between the layers of pericardium

• Pericarditis – inflammation of pericardium, which causes a decrease in serous fluid

The Heart: Heart Wall

• Three layers– Epicardium• Outside layer• This layer is the parietal pericardium• Connective tissue layer

– Myocardium• Middle layer• Mostly cardiac muscle

– Endocardium• Inner layer• Endothelium

External Heart Anatomy

The Heart: Chambers

• Right and left side act as separate pumps

• Four chambers–Atria• Receiving chambers–Right atrium–Left atrium

–Ventricles• Discharging chambers–Right ventricle–Left ventricle

Blood Circulation

The Heart: Valves

• Allow blood to flow in only one direction• Four valves–Atrioventricular valves – between

atria and ventricles• Bicuspid valve or mitral (left)• Tricuspid valve (right)

–Semilunar valves between ventricle and artery• Pulmonary semilunar valve• Aortic semilunar valve

The Heart: Valves

• Valves open as blood is pumped through

• Held in place by chordae tendineae (“heart strings”)

• Close to prevent backflow

Operation of Heart Valves

The Heart: Associated Great Vessels

• Aorta–Leaves left ventricle

• Pulmonary arteries–Leave right ventricle

• Vena cava–Enters right atrium

• Pulmonary veins (four)–Enter left atrium

Coronary Circulation

• Blood in the heart chambers does not nourish the myocardium

• The heart has its own nourishing circulatory system–Coronary arteries–Cardiac veins–Blood empties into the right

atrium via the coronary sinus

Homeostatic Imbalance

• Valvular stenosis – valve flaps become stiff, often from endocarditis (bacterial infection of endocardium)

• Faulty valves may be replaced by synthetic or pig valves

• Angina pectoris – chest pain as a result of the myocardium being deprived of oxygen

• Myocardial infarction (heart attack) – prolonged angina that kills heart cells

The Heart: Conduction System

• Intrinsic conduction system (nodal system)–Heart muscle cells contract,

without nerve impulses, in a regular and continuous way

The Heart: Conduction System

• Special tissue sets the pace• Sinoatrial node or pacemaker– In right atrium–Starts impulse

• Atrioventricular node–At junction of right atrium and

ventricle• Atrioventricular bundle – In interventricular septum

• Bundle branches• Purkinje fibers– In wall of ventricles

Heart Contractions

Filling of Heart Chambers – the Cardiac Cycle

Homeostatic Imbalance

• Heart block – damage to AV node causing ventricular contraction to beat at own rate (much slower)

• Ischemia – lack of adequate blood supply to heart muscle

• Fibrillation – rapid uncoordinated shuddering of heart muscle (caused by ischemia)

• Tachycardia – rapid heart rate (over 100 bpm)

• Brachycardia – much slower rate (under 60 bpm)

The Heart: Cardiac Cycle

• Atria contract simultaneously• Atria relax, then ventricles contract• Systole = contraction• Diastole = relaxation

The Heart: Cardiac Cycle

• Cardiac cycle – events of one complete heart beat–Mid-to-late diastole – blood flows into

ventricles–Ventricular systole – blood pressure

builds before ventricle contracts, pushing out blood

– Early diastole – atria finish re-filling, ventricular pressure is low

• Heart sounds – lub (closing AV valves) dub (semilunar valves close)

• Heart murmur – abnormal or unusual heart sounds–From blood hitting thin walls–Valves not closing tightly–Narrowed valves

The Heart: Cardiac Output

• Cardiac output (CO)–Amount of blood pumped by each

side of the heart in one minute–CO = (heart rate [HR]) x (stroke

volume [SV])• Stroke volume–Volume of blood pumped by each

ventricle in one contraction

Cardiac Output Regulation

The Heart: Regulation of Heart Rate

• Stroke volume usually remains relatively constant–Starling’s law of the heart – the

more that the cardiac muscle is stretched, the stronger the contraction

• Changing heart rate is the most common way to change cardiac output

The Heart: Regulation of Heart Rate

• Increased heart rate– Sympathetic nervous system• Crisis• Low blood pressure

–Hormones• Epinephrine• Thyroxine

– Exercise–Decreased blood volume

The Heart: Regulation of Heart Rate

• Decreased heart rate–Parasympathetic nervous system–High blood pressure or blood

volume–Dereased venous return

Homeostatic Imbalance

• Congestive heart failure – pumping efficiency of heart is diminished–Often from clogging of coronary

arteries (atherosclerosis), persistent high blood pressure, and MI

• Pulmonary edema – left side of heart fails so blood not pumped out to body, but blood continues to move into lungs causing fluid to leak into lungs–Can lead to suffocation

Blood Vessels: The Vascular System

• Taking blood to the tissues and back–Arteries (away from heart)–Arterioles–Capillaries–Venules–Veins (toward heart)

The Vascular System

Differences Between Blood Vessel Types

• Walls of arteries are the thickest• Lumens of veins are larger• Skeletal muscle “milks” blood in

veins toward the heart• Walls of capillaries are only one cell

layer thick to allow for exchanges between blood and tissue

Movement of Blood Through Vessels

• Most arterial blood is pumped by the heart

• Veins use the milking action of muscles to help move blood

Capillary Beds

• Capillary beds consist of two types of vessels–Vascular shunt

– directly connects an arteriole to a venule

Capillary Beds

• True capillaries – exchange vessels•Oxygen and nutrients cross to cells• Carbon dioxide and metabolic waste products cross into blood

Diffusion at Capillary Beds

Homeostatic Imbalance

• Varicose veins – pooling of blood in feet and legs and inefficient venous return resulting from inactivity or pressure on the veins; veins become twisted and dilated

• Thrombophlebitis – inflammation of vein that results when clot forms in a vessel with poor circulation; if the clot moves to the lungs it causes a pulmonary embolism

Major Arteries of Systemic Circulation

Major Veins of Systemic Circulation

Arterial Supply of the Brain

Hepatic Portal Circulation

Circulation to the Fetus

Pulse

• Pulse – pressure wave of blood

• Monitored at “pressure points” where pulse is easily palpated

Blood Pressure

• Measurements by health professionals are made on the pressure in large arteries–Systolic – pressure at the peak of

ventricular contraction–Diastolic – pressure when ventricles

relax• Pressure in blood vessels decreases as

the distance away from the heart increases

Measuring Arterial Blood Pressure

Comparison of Blood Pressures in Different Vessels

Blood Pressure: Effects of Factors

• Neural factors–Autonomic nervous system

adjustments (sympathetic division)• Renal factors–Regulation by altering blood

volume–Renin – hormonal control

Blood Pressure: Effects of Factors

• Temperature–Heat has a vasodilation effect–Cold has a vasoconstricting effect

• Chemicals–Various substances can cause

increases or decreases• Diet

Factors Determining Blood Pressure

Variations in Blood Pressure

• Human normal range is variable–Normal• 140–110 mm Hg systolic• 80–75 mm Hg diastolic

–Hypotension• Low systolic (below 110 mm HG)• Often associated with illness

–Hypertension• High systolic (above 140 mm HG)• Can be dangerous if it is chronic; weakens myocardium and causes atherosclerosis

Capillary Exchange

• Substances exchanged due to concentration gradients–Oxygen and nutrients leave the

blood–Carbon dioxide and other wastes

leave the cells

Capillary Exchange: Mechanisms

• Direct diffusion across plasma membranes

• Endocytosis or exocytosis• Some capillaries have gaps

(intercellular clefts)–Plasma membrane not joined by

tight junctions• Fenestrations of some capillaries–Fenestrations = pores

Developmental Aspects of the Cardiovascular System

• A simple “tube heart” develops in the embryo and pumps by the fourth week

• The heart becomes a four-chambered organ by the end of seven weeks

• Few structural changes occur after the seventh week