Biology 110

Study Notes Exam 4

 

Chapter 11: Blood

 

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)

 

Leukocytes: white blood cells (WBCs)

-       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

 

Effects of Aging: incidense of anemias, leukemias & clotting disorders increase with age

-       thromboenbolism may be associated with atherosclerosis in elderly

 

 


Chapter 12: The Circulatory System

 

Heart Anatomy

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

 

Chambers of the Heart

-       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)

 

Heart valves

-       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

 

Cardiac Conduction System

-       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

 

Cardiac Disorders

-       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

 

Arteries: transport blood away from the heart

-       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

 

Fetal Circulation

-       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

-       blood pressure increased by:

o      increased cardiac output: heart rate or blood volume increase

o      increased peripheral resistance: increased blood vessel diameter

o      activation of baroreceptors (& medulla oblongata)

o      epinephrine & norepinephrine (vasoconstrictors)

o      aldosterone & ADH (increase blood volume)

-       blood pressure lowered by:

o      activation of baroreceptors (& medulla oblongata)

o      atrial natriuretic peptide (ANP) (inhibits aldosterone & ADH)

 

Blood Flow & Blood Pressure

-       blood flow: volume of blood flowing through a vessel, organ, or circulation in a given period (ml/min)

-       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

o      pressure built up during breathing & skeletal muscle contraction aid in venous blood return

 

-       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

 

 


Chapter 13: The Lymphatic System & Immunity

 

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