Biology 110
Blood Characteristics:
- pH of blood is maintained between 7.35 and 7.45 by carbonic acid-bicarbonate ion buffer system
- blood accounts for ~ 8% body weight
- blood volume in adults is normally 5-6 L in males and 4-5 L in females
Blood Components:
- plasma & formed elements (erythrocytes, leukocytes & platelets)
- plasma: fluid component of blood; ~ 55% volume of whole blood
- hematocrit: % of total blood volume occupied by erythrocytes (normally between 42% and 47% ± 5%)
Erythrocytes: red blood cells (RBCs)
- small cells; biconcave discs (flattened disc shape with thin, depressed centers - look like mini doughnuts)
- anucleate - RBCs have no nucleus
- function in gas transport
- most of contents of RBC (other than water) is the protein hemoglobin
o hemoglobin is composed of 4 globin polypeptide chains each bound to a heme group
o heme is a ringlike compound with an iron atom at its center
o the iron atom in heme binds to oxygen
o hemoglobin can also bind carbon dioxide; carbon dioxide binds to globin chain amino acids rather than heme
o oxyhemoglobin: hemoglobin with bound oxygen (appears red in color)
o deoxyhemoglobin: hemoglobin without bound oxygen (appears dark purple in color)
- red blood cell count: # of red blood cells in a cubic millimeter (mm3)
o males: 4.6 - 6.2 million cells/ mm3
o females: 4.2 - 5.4 million cells/ mm3
- RBCs last ~ 100-120 days in circulation
o aged & damaged RBCs are broken down in small channels of the spleen, liver & marrow by macrophages
o heme is broken from hemoglobin; iron is salvaged & stored and the remainder of the group is degraded to bilirubin (yellow pigment), which is picked up by the liver, converted into bile & excreted
o globin chains are metabolized are broken down into amino acids for protein synthesis
- Erythrocyte disorders:
o anemias: conditions that involve blood with a very low oxygen-carrying capacity
• caused by an insufficient number of RBCs (hemorrhagic, hemolytic & aplastic anemias), decreased hemoglobin content (iron-deficiency & athlete's anemia) or abnormal hemoglobin (thalassemias & sickle cell anemia)
o polycythemia: abnormal excess of RBCs; increases blood viscosity & can impair circulation
• can be treated by diluting blood with saline
• artificial polycythemia can be induced by infusing RBCs (blood doping used by some athletes to increase available oxygen... considered unfair by many games committees)
- only formed elements with nucleus & normal organelles
- involved in immune responses; protect the body from damage by bacteria, viruses, parasites, toxins & tumor cells
- white blood cell count: 5,000 - 10,000 cells/ mm3 (much fewer than RBCs)
- white blood cells can move out of capillaries & into tissues (RBCs are usually confined to blood)
- Granulocytes: WBCs with membrane-bound cytoplasmic granules
o Neutrophils: most numerous WBCs (~ 60-70% of WBC volume)
• ~ 2x size of RBCs
• very fine, lightly staining granules containing enzymes or antibiotic-like proteins (defensins)
• nucleus has from 3-6 lobes (also known as PMNs (polymorphonuclear leukocytes))
• phagocytic cells (kill bacteria & fungi by oxidation), chemically attracted to sites of inflammation
o Eosinophils: ~ 1-4% of WBCs; about size of neutrophils
• nucleus with 2 lobes (like telephone receiver)
• large, red-staining granules with enzymes
• digest invading parasitic flatworms & roundworms with digestive enzymes
• phagocytic; ingest immune complexes during allergic reactions
o Basophils: ~ 0.5% of WBCs (rare); about size of neutrophils
• large purplish-black-staining granules containing histamine
• histamine: inflammatory chemical - vasodilator & chemoattractant - released by basophils
- Agranulocytes: WBCs without visible granules
o Monocytes: largest WBCs (2-3x size of RBCs); 3-8% of WBCs
• Large U or kidney-shaped nucleus
• differentiate into macrophages in tissues
• macrophages are phagocytic cells that destroy bacteria & help in immune response against viruses
o Lymphocytes: small, medium & large sizes; 20-25% or WBCs
• large spherical nucleus occupies most of cell volume
• most lymphocytes are in lymphatic organs
• T lymphocytes: fight virus-infected cells & tumor cells
• B lymphocytes: give rise to plasma cells that produce antibodies (immunoglobulins)
- Leukocyte disorders:
o Leukemias: cancer of myeloid or lymphoid cell lines
• Leukemias can be acute (rapidly advancing) or chronic (slowly advancing)
• Treated with radiation & chemotherapy & bone marrow transplant to replace cancerous cells
o Infectious mononucleosis: highly contagious viral infection
• caused by Epstein-Barr virus (EBV)
• symptoms (fatigue, aches, fever) last a few weeks until virus is dealt with by immune system
Platelets: cytoplasmic fragments of megakaryocytes with granules containing blood-clotting enzymes
- sometimes referred to as thrombocytes
- platelet count: 150,000-300,000/mm3
- stick together to form a plug to prevent blood loss in torn vessels
- platelet formation regulated by hormone thrombopoietin
- thrombocytopenia: platelet deficiency (less than 50,000/mm3)
Hematopoiesis (hemopoiesis): blood cell formation; occurs in red bone marrow (in adults, in bones of girdles & proximal epiphyses of humerus & femur)
- starts with stem cell called hemocytoblast (hematopoietic stem cell that is used to form all formed elements of blood)
- erythropoiesis (erythrocyte production): hemocytoblast -> myeloid stem cell -> proerythroblast -> early erythroblast -> late erythroblast -> normoblast -> reticulocyte -> erythrocyte
o ~ 2.5 million RBCs produced every second
o controlled hormonally by erythropoietin (EPO) produced by the kidneys (responding to hypoxia (low oxygen levels))
o cell loses its nucleus in transition from normoblast to reticulocyte
- leukopoiesis: WBC production
o stimulated by hormones (cytokines such as interleukins & colony-stimulating factors (CSFs) from macrophages & lymphocytes
Blood Plasma: fluid component of blood
- mostly (~ 90%) water
- serum: plasma without clotting factors (fibrinogen & prothrombin)
- contains over 100 different dissolved solutes, including:
o proteins: albumin, globulins, clotting proteins, etc.
• albumin is majority of plasma protein; albumin is carrier molecule & contributes to plasma osmotic pressure
• globulins include transport proteins & antibodies
• fibrinogen: clotting protein; converted to fibrin to form clot
o nutrients: sugars, amino acids, fatty acids, cholesterol, vitamins, etc.
o electrolytes: cations (positive ions) such as sodium, potassium, calcium & magnesium; anions (negative ions) such as chloride, phosphate & bicarbonate
o respiratory gases: oxygen & carbon dioxide
Blood Functions:
- transport & distribution of oxygen & nutrients, carbon dioxide & metabolic waste, and hormones
- regulation of body temperature, normal pH and fluid volume in cells & tissues
- protection against blood loss (clotting) and infection (white blood cells)
Hemostasis: stoppage of bleeding from a torn blood vessel
- vasoconstriction: blood vessels constrict to reduce blood flow
o caused by damage to smooth muscle, chemicals & reflexes
- platelet plug formation: in response to blood vessel injury, platelets swell & form spiked processes
- coagulation (blood clotting): blood transformed from a liquid to a gel
o prothrombin activator converts the plasma protein prothrombin to thrombin; requires calcium
o thrombin catalyzes joining of fibrinogen molecules in plasma to form a fibrin mesh that seals vessel
o clotting factors enhance clot formation (several require vitamin K for formation)
• anticoagulants inhibit clotting
- clotting disorders:
o hemophilia A: inherited deficiency of clotting factor VIII:C
• hemarthroses: bleeding into joints
• also bleeding into muscles, GI tract & urine
• death may result from intracranial bleeding & neurological damage
- thromboembolytic disorders: a thrombus (clot) forms in an unbroken blood vessel; if it detaches from the vessel wall, the resulting embolus can travel through the blood & block blood vessels
o free blood clots can be treated by anticoagulants aspirin, heparin & warfarin
Human Blood Groups: red blood cells have many (perhaps > 100) cell surface antigens - glycoproteins known as agglutinogens
- antigens determining ABO and Rh blood groups cause transfusion reactions
- ABO blood groups:
o type A blood individuals have A surface antigen; type B blood individuals have B surface antigen; type AB blood individuals have both A & B surface antigens; type O blood individuals have neither A nor B surface antigens
o individuals make antibodies (agglutinins) against the antigen(s) not present on their red blood cells (e.g.: type A blood individuals will make anti-B agglutinins); this does not require previous exposure to the antigen(s)
- Rh blood groups:
o humans may also have one of several Rh factors present on the surface of their red blood cells
o an individual without Rh factor will make antibodies against Rh factor, but only after exposure to the antigen
- Blood Typing & Transfusion reactions: agglutination & hemolysis
o important to determine a person's blood type to match for transfusion (can use antibodies in blood plasma)
o following infusion of mismatched blood, agglutination occurs as antibodies complex with the foreign blood group antigens
o this blocks blood vessels & hinders blood flow; reduces oxygen availability to tissues, as the RBCs are lysed, hemoglobin escapes & may precipitate in kidney tubules leading to renal failure
o treatment involves diluting agents & diuretics
o type O blood is the universal donor
o type AB blood is the universal recipient
Location: extends 12-14 cm within mediastinum, from 2nd rib to 5th intercostal space
Orientation: anterior to vertebral column; posterior to sternum; intermediate to lungs
- base: posterior aspect; mainly left atrium
- apex: inferiolateral aspect; tilted toward left
Pericardium: double-walled sac enclosing heart
- Fibrous pericardium: outer dense connective tissue layer
o anchors heart to surrounding structures (diaphragm, vessels)
o prevents overfilling with blood
- Serous pericardium: deep to fibrous pericardium
o parietal layer: lines internal surface of fibrous pericardium
o visceral layer (epicardium) - deep to parietal layer; outer layer of heart wall
Layers of heart wall:
- epicardium: thin visceral layer of serous pericardium; often accumulates fat
- myocardium: cardiac muscle deep to epicardium; bulk of heart tissue
- endocardium: thin inner myocardial surface; sheet of endothelium (squamous epithelium) resting on connective tissue
o lines chambers & valves; continuous with endothelial linings of major vessels
- 2 superior atria separated by interatrial septum
- 2 inferior ventricles separated by interventricular septum
- left side of heart: walls are thicker & chambers are smaller
- Atria: receiving chambers for blood
o auricles: small protruding appendages that slightly increase atrial volume
o right atrium receives deoxygenated blood from superior vena cava (from areas above diaphragm), inferior vena cava (from areas below diaphragm), & coronary sinus (from myocardium)
o left atrium receives oxygenated blood from pulmonary veins (4, from lungs)
- Ventricles: discharging (pumping) chambers for blood
o papillary muscles: conelike muscle bundles in ventricular cavity; attached to tendon (chordae tendinae) that play a role in valve function
o right ventricle pumps blood into pulmonary trunk (to lungs)
o left ventricle pumps blood into aorta (to systemic circulation/body tissues)
- atrioventricular (AV) valves: prevent backflow of blood from ventricles to atria
o chordae tendinae: collagen cords attached to AV valve flaps; anchor cusps to papillary muscles
o tricuspid valve: right AV valve; has 3 cusps (flaps of endocardium reinforced with CT)
o bicuspid (mitral) valve: left AV valve
- semilunar (SL) valves: prevent backflow of blood from great vessels to ventricles
o aortic semilunar valve: prevents blood from flowing back into left ventricle following ventricular contraction
o pulmonary semilunar valve: prevents blood from flowing back into right ventricle following ventricular contraction
Pathway of blood through heart:
- the heart is a double pump: right side of heart sends oxygen-poor blood to lungs; left side of heart sends oxygen-rich blood throughout the body
- pulmonary circuit: blood vessels that carry blood to & from the lungs
- systemic circuit: blood vessels that carry oxygenated blood to & from all body tissues
- pathway of blood: superior & inferior vena cava->right atrium->tricuspid valve->right ventricle->pulmonary semilunar valve->pulmonary trunk->pulmonary arteries->lungs->pulmonary veins->left atrium->bicuspid valve->left ventricle->aortic semilunar valve->aorta->body tissues
Cardiac output (CO): CO = Stroke Volume (SV) x Heart Rate (HR)
- SV = ml blood pumped per beat
- HR = heartbeats per minute
- normal resting values: SV = 70 ml/beat; HR = 75 beats/min; CO = 5250 ml/min
Cardiac cycle: all events associated with blood flow through heart
- Systole: contraction
- Diastole: relaxation (dilation or expansion)
- Sequence:
o ventricular diastole/atrial systole (0.15 sec.)
o ventricular systole/atrial diastole (0.30 sec.)
o early ventricular diastole (0.40 sec.)
Heart sounds: lub-dub sound
- AV valves close
- SL valves close
- murmurs: irregular sounds often indicative of valve problems
- mitral stenosis: narrowing of opening of bicuspid valve; can be caused by streptococcal bacterial infection (Rheumatic fever); treated with surgery to open valve or artificial valve replacement
- Intrinsic conduction system: noncontractile cardiac cells specialized to initiate & distribute impulses throughout the heart
- Autorhythmic cells: cardiac cells that spontaneously depolarize due to pacemaker potentials caused by gradual influx of sodium ions
o the impulse is transferred from atria to ventricles in a defined sequence through gap junctions between cells
- sequence of excitation:
o sinoatrial (SA) node: autorhythmic cells here are the fastest to generate impulses (~75/min, called sinus rhythm); hence, this is the heart's pacemaker
o atrioventricular (AV) node: receives impulses from SA node; also autorhythmic cells here, but slower impulses (~50-60/min, called junctional rhythm), so these cells do not set the pace unless there is damage to SA node cells
o atrioventricular (AV) bundle (bundle of His): electrical connection between atria & ventricles; transmits impulse to ventricles
o right & left bundle branches: sends impulse along cells of interventricular septum toward apex
o Purkinje fibers: extend from inferior aspect of interventricular septum to apex & into outer walls of ventricles
- electrocardiograph: measures electrical currents generated during heart contraction with a series of electrodes placed on 12 body regions
- electrocardiogram (ECG or EKG): recording from electrocardiograph
Regulation of Heartbeat
- cardiac control center in medulla oblongata of brain controls heart rate through autonomic nervous system (ANS)
o sympathetic division of ANS (cervical & upper thoracic chain ganglia): increases heart rate
o parasympathetic division of ANS (vagus nerve): decreases heart rate
o baroreceptors (pressure receptors) in aorta & carotid arteries send information about blood pressure to cardiac control center
o cerebrum & hypothalamus can activate cardiac control center
o cold temperature lowers heart rate
o ions: calcium, sodium & potassium
- coronary circulation: blood supply to myocardium (cardiac muscle tissue) of heart
- atherosclerosis: accumulation of lipids (cholesterol) in blood vessel walls, forming deposits called plaques
- proper circulation to myocardium is critical; blockage of coronary arterial circulation can be serious/fatal
o angina pectoris: chest pain due to short deficiency of blood supply to myocardium
o myocardial infarct (MI, heart attack or coronary): can result from prolonged blockage
- thromboembolism: blood clot (thrombus) breaks away & flows through blood (embolus); can also block coronary artery
- occluded coronary artery treated with: balloon angioplasty (breaks apart clot); streptokinase (dissolves clot); coronary bypass (portion of vessel taken from another body region & sutured between aorta & coronary artery)
Structure of Blood Vessel Walls:
- tunica interna (tunica intima): innermost tunic (layer)
o endothelium (simple squamous epithelium) lining lumen of all vessels
- tunica media: middle tunic
o mostly smooth muscle cells & sheets of elastin fibers
- tunica externa (tunica adventitia): outermost tunic
o mostly loose collagen fibers; protect & reinforce vessel wall & anchor it to surrounding structures
- elastic (conducting) arteries: thick-walled arteries near heart (aorta & major branches)
- muscular (distributing) arteries: branch from elastic arteries to distribute blood to body organs
o includes most named arteries
- arterioles: vary in size; lead from muscular arteries to capillary beds
o blood flow into capillary beds determined by arteriole diameter
o if arterioles constrict, resistance & blood pressure increase, & vice-versa
- arteriosclerosis: hardening of the arteries due to deposition of calcium salts & scar tissue formation
o can be caused by atherosclerotic plaques restricting nutrition to smooth muscle & elastic tissue in wall of artery
o increases blood pressure & risk of heart attack or stroke
o stroke (cerebrovascular accident (CVA)): a portion of the brain is deprived of oxygen due to hypertension (& cerebral artery burst) or blood clot
Capillaries: smallest blood vessels; exchange materials (gases, nutrients, hormones, etc.) in blood with tissues
- only tunica interna (endothelium)
- precapillary sphincter: smooth muscle encircling entrance to capillary; acts as valve to regulate blood flow into capillary (constricts to send blood through bed (using vascular shunt))
Veins: transport blood toward heart
- venules: smallest veins; carry blood from capillaries to larger veins
- veins: large vessels with all 3 tunics; vessel walls smaller & larger lumens than corresponding arteries
o at any given time, most blood in the body is within veins
o venous valves: formed from folds of tunica externa; flaps that prevent backflow of blood, especially in limbs
o varicose veins: abnormal dilations in superficial veins (hemorrhoids: varicose veins in rectum) due to weakened valves
Systemic Circulation:
- major systemic arteries:
o aorta, aortic arch, descending aorta (thoracic & abdominal aorta)
o 3 branches from aortic arch: brachiocephalic artery, left common acrotid artery & left subclavian artery
o common carotid arteries: serve head
• vertebral & internal carotid arteries give off branches to form Circle of Willis in brain (several paths for blood to brain tissue)
o subclavian arteries: serve arms
o common iliac arteries: branch to internal iliac arteries (serve pelvic organs) & external iliac arteries (serve legs)
- major systemic veins:
o external & internal jugular veins: drain blood from brain, head & neck
o subclavian arteries: drain blood from arms
o brachiocephalic arteries: receive blood from jugular & subclavian veins & enter superior vena cava
o hepatic portal vein: receives blood from abdominal (digestive) organs & enters liver (metabolism & detoxification)
o common iliac veins: receive blood from internal iliac veins (from pelvic organs) & external iliac veins (from legs)
• common iliac veins merge to form inferior vena cava
Coronary Circulation: blood supply to myocardium (cardiac muscle tissue of heart)
- coronary artery & its branches serve myocardium with oxygenated blood
- cardiac veins & branches drain myocardium & send deoxygenated blood through coronary sinus to right atrium
- pulmonary circuit bypasses due to incomplete lung development in fetus
o foramen ovale: sends blood from right atrium to left atrium
• closes to become fossa ovalis after birth
o ductus arteriosus: sends blood from pulmonary trunk to aorta
• closes to become ligamentum arteriosum after birth
- umbilical arteries & veins: travel to & from placenta
- ductus venosus: liver bypass from umbilical vein to inferior vena cava
Pulse: indirect measure of heartbeat/heart rate (measures arterial pressure during cardiac cycle)
- often for convenience radial artery is monitored (radial pulse)
Blood Pressure: pressure (force per unit area) exerted on the walls of a vessel by blood
- measured from brachial artery with sphygmomanometer
- uses auscultatory method (listening for filling of artery as pressure in cuff drops below arterial pressure)
- normal resting ranges: systolic BP: 110-140 mm Hg; diastolic BP: 75-80 mm Hg
- arterial blood pressure: pressure generated in aorta following (left) ventricular systole (~ 40-120 mm Hg)
- capillary blood pressure: ~ 20-40 mm Hg; good intermediate pressure range (facilitates exchange without rupturing thin walls)
- venous blood pressure: decreases to ~ 0-20 mm Hg due to peripheral resistance
- Hypertension: high blood pressure (sustained arterial pressure > 140/90)
o acutely due to exercise, illness
o chronic hypertension may be indicative of increased peripheral resistance (often due to vessel blockage)
• primary hypertension: most cases; no known cause... factors include diet, obesity, age, race heredity, stress & smoking
• secondary hypertension: ~ 10% of cases; due to disorders such as arteriosclerosis & hyperthyroidism
Functions of Lymphatic & Immune System:
- Draining excess interstitial fluid: lymphatic vessels drain excess fluid from tissue spaces & return it to the blood
- Transporting dietary lipids: lymphatic vessels transport lipids & lipid-soluble vitamins (A,D,E & K) absorbed by GI tract to the blood
- Carrying out immune responses: lymphatic tissue initiates specific immune responses to microbes or abnormal cells
Lymphatic Vessels (Lymphatics): system of drainage vessels that collects excess protein-containing interstitial fluid (fluid between cells) & returns it to blood
- lymph is interstitial fluid that has entered lymphatic vessels
- form one-way system; blood flows toward heart
- Lymph capillaries: occur almost everywhere blood capillaries occur (except bones & teeth, bone marrow, & central nervous system (uses CSF to collect fluid))
o the edges of endothelial cells in walls of lymph capillaries loosely overlap forming valves to prevent backflow
o lymphatic capillaries (unlike blood capillaries) can easily take up proteins, foreign cells & debris... fortunately lymph is circulated through lymphoid organs with immune cells to examine the fluid for undesirables
o lymph flows from lymphatic capillaries to collecting vessels, trunks, and ducts
o lymphatic ducts: right lymphatic duct drains lymph from right upper arm, right side of head & thorax; thoracic duct arising from the sac-like cisterna chili drains the rest of the body
o lympathic ducts flow lymph into subclavian veins (return to blood)
- Lymph transport: slow transport; lymph is not pumped, but flows by smooth muscle contraction in the walls of the vessels, pressure changes in the thorax during breathing & valves to prevent backflow
Lymphoid Tissue:
- reticular connective tissue: forms a network around macrophages & lymphocytes in lymphoid organs
- diffuse lymphatic tissue: scattered reticular tissue elements
- lymphatic nodules: tightly packed reticular elements & cells
o germinal centers: actively dividing B cells & T cells
Lymphoid Organs: lymph nodes, spleen & thymus
Spleen: largest lymphoid organ; located in left side of abdominal cavity just below diaphragm
- blood flows through sinuses; spleen removes aged & defective blood cells from circulation & contains macrophages to cleanse blood of foreign matter
- stores breakdown products of red blood cells for later use
- in fetus, produces erythrocytes
- stores blood platelets
- red pulp: most of spleen mass; cleanses blood (macrophages) & removes old RBCs
- white pulp: contains lymphocytes (B cells)
- direct spleen injury can cause it to rupture; treatment = removal (splenectomy)
Lymph Nodes: hundreds of small organs that cluster along lymphatic vessels
- filter lymph: macrophages in sinuses (large capillaries) in lymph nodes remove debris & destroy microorganisms
- activate immune system: lymphocytes within follicles monitor lymph for foreign antigens & mount responses against them
- capsule: dense connective tissue surrounding lymph node with trabeculae that extend inward to divide the node into nodules
o germinal centers: actively dividing B cells & T cells within nodules
- lymph nodes can become inflamed when overwhelmed with foreign substances & can become secondary cancer sites
Tonsils: small organs around the entrance to the pharynx
- contain follicles with germinal centers with dividing B cells
- palatine tonsils: paired at posterior end or oral cavity; most likely to be infected
- lingual tonsils: at base of tongue
- tubal tonsils: at openings of auditory tubes into pharynx
Lymphoid Follicle Aggregates:
- Mucosa-associated Lymphatic tissue (MALT)
o Peyer's Patches in intestine (ileum)
o Appendix
Thymus: bilobed organ in inferior neck extending into mediastinum
- functions in maturation of T cells; mostly in childhood
- size decreases with age as most tissue replaced by connective tissue
- thymic lobules: outer cortex and inner medulla with mature lymphocytes (T cells);
- thymocytes (epithelial cells in stroma) secrete hormones called thymosins for development of T cells