BSC2086 Exam 2 Review - Chapter 19 Circulatory System PDF

BSC2086 Exam 2 Review **[Chapter 19 Circulatory System]** **Arteries: carry blood away from heart, receiving blood from heart, carry to capillaries, high pressures, small lumen and large muscle area** [Elastic arteries]: conducting arteries, receive all pressure from heart - Made up of aorta a...

BSC2086 Exam 2 Review **[Chapter 19 Circulatory System]** **Arteries: carry blood away from heart, receiving blood from heart, carry to capillaries, high pressures, small lumen and large muscle area** [Elastic arteries]: conducting arteries, receive all pressure from heart - Made up of aorta and its major branches, closest to heart - Large lumen offers low resistance - Inactive in vasoconstriction - When vessels are entering systole and blood is flowing into arteries high pressure caught by arteries stretch/expanding as flood fills and when Semilunar valves close and heart relaxes, they slowly release the, they slowly recoil and allowing blood to flow through cardiovascular system - Large thick-walled arteries with elastin in all three tunics, more than any other blood vessel type - Act as pressure reservoirs---expand and recoil as blood ejected from heart - Smooth pressure downstream - [Elastin] - [Pressure reservoirs]: catch pressure and distribute even will diastole and heart relax [Muscular arteries]: distributing arteries - Distal to elastic arteries, muscular arteries distribute blood to specific body parts - Constrict and dilate and moves blood at different time and different places - Thick tunica medica with more smooth muscle, less elastic thicker tunica media - Active in vasoconstriction [Arterioles]: mini arteries that branch into capillaries, resistance vessels - Smallest arteries, feed into smaller capillary beds - Control flow into capillary beds via vasodilation and vasoconstriction - Low pressure - Thick as one endothelial tissue - High resistance reduce pressure and flow into capillary beds allows time to exchange fluid with tissues **Capillaries: contact tissue cells, exchanging fluids with tissues, simple smaller vessels with basement membranes and endothelial cells, thin wall the encourages fluid exchange between interstitial space** - **Microscopic blood vessels with extremely thin walls composed of tunica intima (sometimes one cells forms entire circumference)** - **Diffusion** - **Capillaries are where exchange of materials happens** - **Diameter allows only single RBC to pass at a time** - **Exchange vessels: exchange fluid with surrounds tissue** - **Depends on permeability** - **Providing direct access to almost every cell, capillaries from divergent pathways called capillary beds** - **Function:** - **Exchange of gases, nutrients, wastes, hormones, etc., between blood and interstitial fluid** - **Regulate blood pressure** - **thermoregulation** **Less permeable most** [Continuous]: abundant in skin and muscles, most common type - tight junctions connect endothelial cells - Intercellular clefts: allows passage of fluids and small solutes - Blood-brain barrier: formed by tight junctions complete, prevent anything from getting into CNS, nothing leaking, making them move through cells allowing more control [Fenestrated]: filled with fenestra, some endothelial cells contain pores (fenestrations) - more permeable than continuous capillaries - function in absorption or filtrate formation (small intestines, endocrine glands, and kidneys) less common - Fenestrations: pores, holes in endothelial cells that makes them more permeable [Sinusoidal]: fewer tight junctions; usually fenestrated; larger intercellular clefts; large lumens - blood flow sluggish---allows modification - large molecules and blood cells pass between blood and surrounding tissues - found only in liver, bone marrow, spleen, and adrenal medulla - macrophages in lining to destroy bacteria **Capillary Beds** [Microcirculation]: interwoven networks of capillaries between arterioles and venules (shunting across) and have sphincter which allow blood to enter and exit thorough channel into true capillaries - terminal arteriole metarteriole - metarteriole continuous with thoroughfare channel (intermediate between capillary and venule) straight across - thoroughfare channel postcapillary venule that drains bed Vascular Shunt: metarteriole \-\-- thoroughfare channel - directly connects terminal arteriole and post capillary venule True Capillaries: 10-100 exchange vessels per capillary bed - branch off metarteriole or terminal arteriole Precapillary sphincters **Veins: carry blood toward heart, low pressure, large lumen, small muscle area and have valves** [Veins]: large and small are capacitance vessels - Capacitance vessels: blood reservoirs; contain up to 65% of blood supply - Formed when venules converge - Have thinner walls, larger lumens compared to corresponding arteries - Blood pressure lower than in arteries - Thin tunica media, thick tunica externa of collagen fibers and elastic networks. allows to expand to hold blood - Low pressure hard time getting blood back towards the heart - No vasoconstriction or vasodilation - Adaptations ensure return of blood to heart despite low pressure - Large diameter lumens offer little resistance - Venous valves prevent backflow of blood - Most abundant in veins of limbs (esp. lower limbs) [Venules]: smallest components of veins drawing blood out of capillaries - Formed with capillary beds unit - Smallest postcapillary venules - Very porous, allows fluids and WBCs into tissues - Consist of endothelium - Larger venules have one or two layers of smooth muscle cells - Mainly endothelia and tunica media **Structure of Blood Vessel Walls** **Three layers of tissue surrounds lumen, the open space that holds the blood form follows function** - **Thickness of these layers varies between different types of blood vessels** [Tunica Intima]: innermost tunic, directly interfaces with blood - endothelial lining: smooth slippery wall for blood to flow through, less friction so less flow resistance - simple squamous epithelium tissue that is continuous with endocardium - slick surface that reduces friction interfaces with blood needs to be smooth to reduce resistance - Subendothelial layer: support by connective tissue to bring oxygen and nutrients to endothelial layer - Elastic Membrane: stretch and recoil when receiving blood [Tunica Media]: middle most tunic of smooth muscle and sheets of elastin for dilation and constriction, thicker than veins - Regulated in part by the nerve fibers of the autonomic nervous system - Sympathetic vasomotor nerve fibers control vasoconstriction and vasodilation of vessels - Key role in blood flow and blood pressure Vasoconstriction: decrease lumen and increase resistance) Vasodilation: increase lumen and decrease resistance [Tunica Externa]: outer-most tunic, supportive and protective walls, tougher connective tissue with blood vessels. - Collagen fibers protect and reinforce; anchor to surrounding structures - Contains nerve fibers, lymphatic vessels, vasa vasorum - Reinforce the organ Vasa vasorum: vessels of the vessels, bring blood and oxygen to tunic media of vessels themselves **Vascular Anastomoses** [Anastomoses] = interconnections of blood vessels and help distribute bp more evenly [Arterial]: provide alternate pathways (collateral changes) to given body region - Common at joints, I abdominal organs, brain, and heart [Arteriovenous]: vascular shunts of capillaries [Venous]: are common **Physiology of Circulation** [Blood Flow]: volume of blood flowing through vessel, organ, or entire circulation in a given period - Measure in mL/min - Relatively constant when at rest - Varies widely through individual organs, based on needs - Equivalent to cardiac output for entire vascular system - Blood flow (F) directly proportional to BP gradient - If BP gradient increases, blood flow speeds up - Blood flow inversely proportional to peripheral resistance - If peripheral resistance (R) increases, blood flow decreases - F: BP/R - R is more important on influencing local blood flow because easily changed by altering blood vessel diameter [Blood Pressure]: force per unit area exerted on wall of blood vessel by blood - Expressed in mmHg - Measured by systemic arterial BP in larger arteries near heart - Pressure gradient provides driving force that keeps blood moving from higher to lower pressure areas - Influence flow - Heart generates lots of pressure - Systemic Blood Pressure - Pumping action of heart generates blood flow - Pressures results when flow is opposed by resistance - Highest in aorta - Declines throughout pathway - 0 mmHg in right atrium, encourage flow back to right side of heart - Steepest drop occurs in arterioles [Systolic Pressure]: pressure exerted in aorta during ventricular contraction - Average 120 mmHg in normal adult [Diastolic Pressure]: lowest level of aortic pressure, ventricular relaxation [Pulse Pressure]: wave of blood going from 120 to 80 felt as pulse, difference between systolic and diastolic pressure [Mean Arterial Pressure] (MAP): 93.3 is average; pressure that propels blood to tissue - spend more time in diastole than systole so closer to diastole - MAP = diastolic pressure + 1/3 pulse pressure - Pulse pressure and MAP both decline with increasing distance from heart Capillary Blood Pressure: - Ranges from 17 to 35 mmHg - Arterial side: higher pressure - Ventricle side: lower pressure - Low pressure is desirable - High BP would rupture fragile, thin-walled capillaries - Most very permeable so low pressure forces filtrate into interstitial spaces determines exchanges of fluids [Venous Blood Pressure]: changes little during cardiac cycle - Small pressure gradient: about 15 mmHg - Low pressure due to cumulative effects of peripheral resistance - Energy of BP lost as heat during each circuit [Factors aiding Venous Return:] - [Muscular pump]: contraction of skeletal muscles "milk" blood toward heart; valves prevent backflow - Important for lower limbs - Increase amount of blood returning to heart by increasing venous return increase diastolic volume - [Respiratory pump]: pressure changes during breathing move blood toward heart by squeezing abdominal veins as thoracic veins expand - [Venoconstriction]: under sympathetic control pushes blood toward heart - Valves ensure unidirectional flow toward the heart [Maintaining/Control of Blood Pressure] - Require: - Cooperation of heart, blood vessels and kidneys - Supervision by brain - Main factors influencing BP - CO: cardiac output sympathetic NS - CO = SV x HR - Normal: 5-5.5 L/min - Determined by venous return and neural and hormonal controls - Resting HR maintain by cardioinhibitory center via parasympathetic vagus nerves - SV control by venous return (EDV) - During stress, cardioacceleratory center increases HR and SV via sympathetic stimulation increase CO - ESV decreases and MAP increases - PR: peripheral resistance sympathetic NS - Blood volume: urinary system - F = BP gradient/R - CO = BP gradient/R - BP gradient = CO x R - BP = CO x PR (and CO depends on blood volume) - BP varies directly with CO, PR, and blood volume - Changes in one variable quickly compensated for by changes in other variables [Short-term neural and hormonal controls:] counteract fluctuations in BP by altering PR and CO - Changing HR, contractility and radius of blood vessels - Quick fix, minute to minute changes during the day - Neural control of PR - Maintain MAP by altering blood vessel diameter - If low blood volume, all vessels constricted except those to brain and heart - Alter blood distribution to organs in response to specific demands - Included by Baroreceptors in the arteries and aortic arch - Control operate via reflex arcs that involve - [Baroreceptors]: pressure sensors - Arch b/c beginning of circuit - Located in carotid sinuses and aortic arch - Increased BP stimulated baroreceptors to increase input of vasomotor center - Inhibits vasomotor and cardioacceleratory centers causing arteriole dilation and venodilation - Larger radius = less resistance = decreased BP - Stimulate cardioinhibitory center - Decreased BP - Cardiovascular center of medulla: baroreceptors relay information here - Clusters of sympathetic neurons in medulla oversee changes in CO and vessel diameter - Has cardio center - Control changes in HR and CO - Vasomotor center - Control changes if radius - Vasomotor center sends steady impulses via sympathetic efferents to blood vessels moderate constriction called vasomotor tone - Receives input from baroreceptors, chemoreceptors, and higher brain centers - Vasomotor fibers to heart and vascular smooth muscle - Sometime input from chemoreceptors and higher brain centers - [Chemoreceptors] - In aortic arch and large arteries of neck detect increased CO2 or drop in pH or O2 - Cause increased BP by - Signaling cardioacceleratory center increase CO - Signaling vasomotor center increase vasocontriction - Hormonal control: - Short term regulation: via changes in PR - Cause increased BP: - Epinephrine and NE from adrenal gland increased Co and vasoconstriction - Angiotensin II stimulates vasoconstriction - High ADH level causes vasoconstriction - Caused lower BP: - Atrial natriuretic peptide cases decreased blood volume by antagonizing aldosterone - Get rid of water by decreasing Na holding [Long-term renal regulation] counteracts fluctuation in BP by altering blood volume - Renal regulation: - Baroreceptors quickly adapt to chronic high or low BP so are ineffective in short term regulation - Control BP by altering blood volume via kidneys - Kidneys regulate arterial BP - Creating more or less urine - Done by kidneys - Regulate amount of water in cardiovascular system - Affecting preload and CO - Direct renal mechanism - Alters blood volume independently of hormones - Increase BP or blood volume causes elimination of more urine reducing BP - Decreased BP or blood volume causes kidneys to conserve water BP rises - Indirect renal mechanism: renin-angiotensin-aldosterone - Decreased arterial BP release of renin - Renin catalyzes conversion of angiotensinogen from liver to angiotensin I - Angiotensin converting enzyme especially from lungs converts I to II - II causes vasoconstriction - Increase thirst via hypothalamus - Increase water intake - Release ADH to increase water retention - Aldosterone to increase Na - Water follows Na to increase blood volume - Less filtration less urine more blood volume increase BP [Resistance]: peripheral resistance - Opposition to flow - Measure amount of friction blood encounters with vessel walls, generally in peripheral (systemic) circulation - Three important sources: - Blood viscosity: thickness, measure of RBCs and formed elements, and plasma proteins, stickiness - Total blood vessel length: longer the vessel= greater resistance (greater in systemic system) - Blood vessel diameter: greater influence on resistance - Frequent changes alter peripheral resistance - Varies inversely with fourth power of vessel radius - If radius doubles, the resistance is 1/16 as much - Small diameter arterioles major determinants of peripheral resistance - Abrupt changes in diameter or fatty plaques from atherosclerosis increase resistance - Disrupt laminar flow and cause turbulent flow - Irregular fluid motion increase resistance [Circulatory Efficiency] - Vital signs: pulse, BP, RR, and temperature - Pulse: pressure wave caused by expansion and recoil of arteries - Radial pulse at wrist used most routinely - Pressure points: where arteries are close to body surface - Can be compressed to stop blood flow - Blood Pressure: - Systemic BP - Sphygmomanometer: measured indirectly by auscultatory method with \^\^ - Pressure increased in cuff until it exceeds systolic pressure in brachial artery - Pressure released slowly and examiner listen for sounds of Korotkoff with stethoscope - Sounds of Korotkoff: when vessels and partially constricted and blood is flowing turbulently slam against wall of blood vessel - Systolic pressure: less than 120 mmHg, is pressure when sounds first occur as blood starts to spurt through artery - Diastolic pressure: less than 80 mmHg, is pressure when sounds disappear because artery no longer constricted, blood flowing freely - Hypertension: high BP - Sustained elevated arterial pressure of 140/90 or higher - Prehypertension: if values elevate but not yet in hypertension range - Mah be transient adaptations during fever, physical exertion, or emotional upset - Often persistent in obese people - Prolonged HTN major cause of heart failure, vascular disease, renal failure, and stroke - Heart must work harder myocardium enlarges, weakens becomes flabby - Also accelerates atherosclerosis - Primary HTN: caused because of lifestyle or genetics very common - Secondary HTN: caused by another disease less common - Obstructed renal arteries, kidney disease, endocrine disorders - Treatment focuses on correctly underlying cause - Hypotension: low BP - 90/60 - Usually not a concern - Only if it leads to inadequate flow to tissues - Often associated with long life and lack of cardiovascular illness - Orthostatic hypotension: temporary low BP and dizziness when suddenly rising from sitting or reclining position - Chronic hypotension: hint of poor nutrition and warning sign for Addison's disease or hypothyroidism - Acute hypotension: important sign of circulatory shock; threat for surgical patients and those in ICU [Tissue perfusion]: position of sphincter more or less depending on position to capillary bed or directly across from arteries to veins - involved in - Delivery of O2 and nutrients to and removal of wastes from tissue cells - Gas exchange - Absorption of nutrients - Linked to metabolic activities - Larger after a meal - Urine formation - Rate of flow is precisely amount to provide proper function - Brain does not change during activity - But muscles, skin, and heart changes to increase blood flow during activities - Kidneys and abdomen decrease [Velocity of blood flow:] - Changes as travels through systemic circulation - Inversely related to total cross-sectional area - As CSA increases the velocity decreases - Slowest in capillaries allows time for exchange with the tissues - Fastest in aorta; slowest in capillaries; increases in vein - Slow capillary flow allows adipate time for exchange between blood and tissues [Autoregulation]: automatic adjustment of blood flow to each tissue relative to its varying requirements - Controlled intrinsically by modifying diameter of local arterioles feeding capillaries - Independent of MAP which is controlled as needed to maintain constant pressure. \_ drives pressure through cardiovascular system - autoregulation - Organs regulate own blood flow by varying resistance of own arterioles [Metabolic] [controls:] vasodilation of arterioles and relaxation of precapillary sphincters occur in response to declining tissue oxygen, substances from metabolically active tissue (H, K, adenosine, and prostaglandins) and inflammatory chemicals - Effects: - Relaxation of vascular smooth muscle - Release of NO (powerful [vasodilator]) by endothelial cells - Endothelins released from endothelium are potent [vasoconstrictors] - NO and endothelins balanced unless blood flow inadequate, hen NO wins - Inflammatory chemicals also cause vasodilation - [Myogenic] [controls:] keep tissue perfusion constant despite most fluctuations in systemic pressure - Vascular smooth muscle responds to stretch - Passive stretch increased intravascular pressure - Promotes increased tone and vasoconstriction - Reduced stretch promotes vasodilation and increases blood flow to the tissue [Both determine final autoregulatory response ] Long term autoregulation occurs when short-term autoregulation cannot meet tissue nutrient requirements - [Angiogenesis:] number of vessels to region increases and existing vessels enlarge - Generation of blood vessels [Blood Flow] - [Skeletal] [Muscles]: varies with fiber type and activity - At rest, myogenic and general neural mechanisms predominate - During muscle activity: - [Active or exercise hyperemia] -- blood flow increases in direct proportion to metabolic activity - Local controls override sympathetic vasoconstriction - Muscle blood flow can increase 10x - [Brain]: flood flow is constant as neurons intolerant of ischemia; averages 750 mL/min - Metabolic controls: - Decreased pH of increased carbon dioxide cause marked vasodilation - Myogenic controls: - Decreased MAP causes cerebral vessels to dilate - Increased MAP causes cerebral vessels to constrict - [Skin]: blood flow through skin - Supplies nutrients to cells (autoregulation in response to oxygen needs) - Helps regulate body temperature (neurally controlled) -- primary function by hypothalamus - Provides a blood reservoir (neurally controlled) - Temperature regulation: - As temperature rises - Hypothalamic signals reduce vasomotor stimulation of skin vessels - Warm blood flushes into capillary beds - Heat radiates from skin - Sweat causes vasodilation via bradykinin in perspiration - Bradykinin stimulates NO release - As temperature decreases, blood is shunted to deeper, more vital organs - [Lungs]: blood flow is unusual - Pathway short - Arteries/arterioles more like veins/venules (thin walled with large lumens) - Arterial resistance and pressure are low (24/10 mmHg) - Autoregulatory mechanism oppose of most tissues - Low oxygen causes vasoconstrictions; high levels promote vasodilation - Allows blood flow to oxygen rich areas of lungs - [Heart]: blood flow only during ventricular systole - Coronary vessels are compressed - Myocardial blood flow ceases blood flow stops - Stored myoglobin supplies sufficient oxygen - During diastole high aortic pressure forces blood through coronary circulation - At rest \~250 mL/min; control probably myogenic - During strenuous exercise: - Coronary vessels dilate in response to local accumulation of vasodilators - Blood flow may increase three to four times - Important -- cardiac cells use 65% of oxygen delivered so increased blood flow provides more oxygen - [Capillaries]: - Vasomotion - Slow, intermittent flow - Reflects on/off opening and closing of precapillary sphincters [Capillary Exchange of Respiratory Gases and Nutrients] - Diffusion down concentration gradients - Oxygen and nutrients from blood to tissues - CO2 and metabolic wastes from tissues to blood - Lipid soluble molecules diffuse directly through endothelial membranes - Water soluble solutes pass through clefts and fenestrations - Larger molecules such as proteins are actively transported in pinocytotic vesicles or caveolae [Fluid Movements: Bulk Flow] - Fluid leaves capillaries at arterial end; most returns to blood at venous ends - Extremely important in determining relative fluid volumes in blood and interstitial space - Direction and amount of fluid flow depend on two opposing forces: hydrostatic and colloid osmotic pressures Capillary hydrostatic pressure: capillary blood pressure - Tends to force fluids through capillary walls - Greater at arterial end (35 mmHg) of bed than at venule end (17 mmHg) - Directly related to BP mean arterial pressure declines through cardiovascular system Interstitial fluid hydrostatic pressure - Pressure that would push fluid into vessel - Usually assumed to be zero because of lymphatic vessels - Draining fluid from areas Capillary colloid osmotic pressure - Created by nondiffusible plasma protein, which draw water toward themselves - \~25 mmHg Interstitial fluid osmotic pressure - Low (\~1 mmHg) due to low protein content Hydrostatic-osmotic Pressure Interaction:Net Filtration Pressure - NFP -- comprises all forces acting on capillary bed - NFP = (HP­~c~ -- HP~if~ ) -- (OP~c~ -- OP~if~) - Net fluid flow out at arterial end +NFP - Net fluid flow in at venous end -NFP - More leaves than is returned - Excess fluid returned to blood via lymphatic system [Circulatory Shock] - Any condition in which blood vessels inadequately filled and blood cannot circulate normally - Results in inadequate blood flow to meet tissue needs - [Hypovolemic shock]: results from large scale blood loss - [Vascular shock]: results from extreme vasodilation and decreased peripheral resistance - [Cardiogenic shock]: results when an inefficient heart cannot sustain adequate circulation **[Chapter 20 Lymphatics and Lymphoid Organs]** [Lymphatic System]: drain excess fluid from interstitial space, dealing with invaders and waste - Returns fluids that leaked from blood vessels back to blood - Consists of 3 parts: - Lymphatic vessels: similar to capillaries, very permeable, have flap like mini valves, accept interstitial fluid and becomes lymph - Lymph: - As it goes back to heart, it is cleansed at lymph notes - Lymph nodes: macrophages sift through excess lymph fluid and attack and eat any foreign invaders - [Lymphatic organs and Tissues] - Provide structural basis of immune system - House phagocytic cells and lymphocytes - Structures include spleen, thymus, tonsils, other lymphoid tissues - [Lymphatic vessels:] - Lymphatics - Return interstitial fluid and leaked plasma proteins back to blood - \~3 L/day : absorbed by lymphatic sells - Once interstitial fluid enters lymphatics called lymph - Lymph: - One-way system; lymph flows toward heart - [Lymph vessels include:] - [Lymphatic capillaries:] - Similar to blood capillaries except: - Very permeable (take up proteins, cell debris, pathogens, and cancer cells) - Endothelial cells overlap loosely to form one-way **[minivalves]** - **[Flaplike Leak fluid in]** - **[Overlapping endothelial cells anchored to connective tissue that bend inwards to let fluid in and not out ]** - Anchored by collagen, filaments, preventing collapse of capillaries; increased ECF volume opens minivalves - Pathogens travel throughout body via lymphatics - [Collecting lymphatic vessels] - Similar to veins except - Have thinner walls with more internal valves - Collecting vessels in skin travel with superficial veins - Deep vessels travel with arteries - Pulsation of arteries help drive lymph back to the heart - Nutrients supplies from branching vasa vasorum - [Lymphatic trunks and ducts] - Formed by union of largest collecting ducts = trunk - Lymphatic Ducts - Lymph delivered into one of 2 large ducts - Right drains right upper arm and right side of head and thorax - Thoracic ducts drains rest of body - Each empties lymph into venous circulation on its own side of body [Lymph transport] - Lymph propelled by (similar to veins) - Milking action of skeletal muscle - Pressure changes in thorax during breathing - Valves to prevent backflow - Pulsations by nearby arteries - Contractions of smooth muscle in walls of lymphatics [Lymphoid cells] - Lymphocytes: main warrior of immune system arise in red bone marrow - Adaptive immune system - Specific and targeted attacks - Mature into on of the two main varieties - [T cells] - Manage immune response - Attack and destroy infected cells directly - Major response for cancer and viral infection - Looks inside cells and tell them to be apoptotic - [B cells] - Produce plasma cells, which secrete antibodies - Antibodies mark antigens for destruction by phagocytosis or other means - T cells and b cells protect against antigens = anything body perceives as foreign - Bacteria and bacterial toxins, viruses, mismatched RBCs, cancer cells - [Macrophages] phagocytize foreign substances; help activate T cell - Wear on their plasma membrane to show and activate lymphocytes - [Dendritic] cells capture antigens and deliver them to lymph nodes - [Reticular] cells produce reticular fibers that supports other cells in lymphoid organs [Lymphoid Tissue] - Houses and provides proliferation site for lymphocytes - Specific type of response - Surveillance vantage point for lymphocytes and macrophages - Largely reticular connective tissue -- type of loose connective tissue - Organs: - [Lymph nodes:] - Principle lymphoid organs of body - Embedded in connective tissue in clusters along lymphatic vessels - Near body surface in inguinal, axillary, and cervical regions of the body - Function: - Filter lymph -- macrophages destroy microorganisms and debris - Immune system activation -- lymphocytes activated and mount attack against antigens - Germinal centers are sites for proliferation of lymphocytes - Cortex contains macrophages capture and filter foreign invaders and send them to germinal centers to B and T cells - [Spleen ] - Largest lymphoid organ - Served by splenic artery and vein, which enter and exit at the hilum - Cleanses dead RBCs - Stores breakdown products of RBC (e.g., iron) for later use - Store blood platelets and monocytes - May be a site of fetal erythrocyte production (normally ceases before birth) - Contains lymphocytes, macrophages, and huge numbers of erythrocytes - Functions: - Site of lymphocyte proliferation and immune surveillance and response - Cleanses blood of aged cells and platelets, macrophages remove debris - Two distinct areas: - White pup around central arteries - Mostly lymphocytes on reticular fibers; involved in immune function like lymph nodes - Red pulp in venous sinuses and splenic cords - Rich in RBCs and macrophages for disposal of worn-out RBCs and bloodborne pathogens - Composed of splenic cords and sinusoids - Breakdown old RBCs Thymus; - Important functions early in life - Increases in size and most active during childhood - Stops growing during adolescence, then gradually atrophies - Still produces immunocompetent cells, though slowly - Thymic corpuscles involved in regulatory T cell development (prevent autoimmunity) - Stops the development of T cells that would attack antibodies of own cells - T cells mature in thymus - B cells mature in bone marrow [Mucosa-associated Lymphoid Tissue] - lymphoid tissue in mucous membranes throughout body - protection from pathogens trying to enter body - largest collection of MALT in tonsils [Tonsils] - simplest lymphoid organ - gather and remove pathogens in food or air - overlying epithelium invaginates forming deep Tonsillar crypts - trap and destroy bacteria and particulate matter - allow immune cells to build memory for pathogens - bacteria can get trap and swell causing tonsilitis [Peyer's patches] - clusters of lymphoid follicles - in wall of distal portion of small intestine sample gut flora [Peyer's patches and Appendix] - destroy bacteria, preventing them from breaching intestinal wall - generate memory lymphocytes - appendix: store bacteria if stomach Is bleached of good bacteria