Biology - An Illustrated Guide to Science (794127), страница 28
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Aortic and pulmonaryvalves prevent the backflow of bloodfrom the arteries into the ventricles.© Diagram Visual Information Ltd.●161Transport: regulation ofheartbeatHUMAN BIOLOGYKey wordsmedullaoblongataparasympatheticnervous systemsinoatrial nodeHeartbeat regulationcarotid arteryPacemaker regioncarotid sinusThe muscles of the heart are unique inthe body in that they can contractwithout direct nervous stimulation.This means that transplanted hearts,which have no connection to thepatient’s central nervous system, canstill beat.● The organization of the heartbeatdepends on the sin oatrial n ode,called the pacemaker, located near thetop of the heart in the right atrium.●medulla oblongataleft atriumsuperior vena cavasympatheticnervous systemventricleaorticarchsinoatrial node(pacemaker)right atriumCreating a beatatrioventricularnodeSignals from the sinoatrial node causethe atria to contract.
This pushesblood into the ven tricles. By the timethe ventricles have filled with blood,the impulse has reached theventricular walls. The impulse passesalong a bundle of specialized musclefibers, known as the bundle of His,located between the two ventricles.Specialized nerve cells called Purkinjefibers distribute these signals.● The ventricle walls now contract topush blood along the arteries. At thispoint the atrial walls are beginning torelax as the signal has passed on.●bundle of Hisleft ventricleright ventricleinterventricularseptumPurkinje fibersRegulating the heartbeatsensory receptorsensory nervecardio-inhibitor centerparasympathetic (inhibitor) nervecardio-accelerator centersympathetic (accelerator) nervespinalcordThe sinoatrial node produces regularimpulses.● The number of these impulses (andtherefore heartbeats) per minute canbe changed by impulses deliveredfrom the m edu lla oblon gata bynerves of the parasym pathetic(slowing down) and sym pathetic(speeding up) n ervou s system s.●© Diagram Visual Information Ltd.sympathetic ganglion162HUMAN BIOLOGYKey wordsaortaarterycapillarydiastolered bloodcorpusclesmooth musclesystoleveinwhite blood cellTransport: blood vesselsBlood vesselsCut open longitudinallyArteryVeinfibrous (collagen)layer (tunica externa)fibrous (collagen)layer (tunica externa)smooth muscle andelastic fiber layer(tunica media)ArteriesArteries carry blood at high pressureaway from the heart.
They have thethickest walls of all blood vessels, witha layer of sm ooth m u scle in them. Thismuscle can contract to constrict theblood vessels, raising the bloodpressure even further.● The arteries also contain elastic tissuethat facilitates the flow of blood bystretching during diastole andcontracting during systole.
The aortais particularly well supplied with elastictissue.●Capillarysmooth muscle andelastic fiber layer(tunica media)endothelialcellendothelial layer(tunica intima)endothelial layer(tunica intima)CapillariesCapillaries are microscopic bloodvessels that penetrate all active tissues.Their walls are one cell thick and allowthe rapid exchange of materials.● White blood cells can leave capillariesby squeezing between cells of theendothelium. Red blood corpu sclescannot leave capillaries unless thewalls have been damaged. This leadsto a bruise as the blood leaks into thetissues.●VeinsTransverse sectionsVein s are large blood vessels carryingblood at low pressure back toward theheart. They have thinner walls thanarteries, with less muscle.● Valves prevent the backflow of bloodin the veins.Artery●© Diagram Visual Information Ltd.valve flapsVeinlumen (inner spacethrough which blood flows)Capillarylumenendothelial layer(tunica intima)smooth muscle andelastic fiber layer(tunica media)fibrous (collagen) layer(tunica externa)endothelial layer(tunica intima)smooth muscle andelastic fiber layer(tunica media)fibrous (collagen) layer(tunica externa)lumenendothelialcell163Transport: capillariesand tissuesHUMAN BIOLOGYKey wordscapillarylymph vesselred bloodcorpusclewhite blood cellRelationship between capillaries, Iymphatic vessels,and tissue cellsarterioleSize of capillariesCapillaries are microscopic bloodvessels with an internal diametertypically large enough to let red bloodcorpu scles pass in single file.● The total internal volume of thecapillaries in the body is very largebecause of the very large numbers ofcapillaries in each organ.
The totalvolume is up to ten times larger thanthe volume of blood in the system.●tissue fluidlymphatic vesselred bloodcorpuscleExchangetissue cellCapillary walls are one cell thick andallow rapid exchange of materials.Oxygen and food materials pass to thetissues, and wastes pass back into theblood.● White blood cells can leave capillariesby squeezing between cells of theendothelium. Red blood corpusclescannot leave capillaries unless thewalls have been damaged.●Tissue fluid and lymphBlood entering a capillary bed is at ahigher hydrostatic pressure than thefluid surrounding the cells of thetissue.
This causes fluid to leak out ofthe capillaries and surround the cells.This is called tissue fluid.● At the venous (venule) end of thecapillary bed, fluid passes the otherway, but some is always left in thetissues. This fluid is drained away bylym ph vessels and is returned to thebloodstream as lymph fluid in otherparts of the system.venuleblood flowflow of tissue fluid rich in wasteflow of tissue fluid rich in oxygen and foodThe capillary networkThe networks of capillaries linking arteries and veins are known as capillary beds.Each capillary bed provides a link between many arterioles (tiny arteries) and venules(tiny veins).arteriolescapillary bedvenules© Diagram Visual Information Ltd.●endothelium164HUMAN BIOLOGYKey wordslymph vesselpathogenwhite blood cellTransport: lymphaticsystemLymphatic systemjugular veinLymphatic fluidLymphatic fluid is derived from tissuefluid that has been drained away fromtissues by lym ph vessels.● Lymphatic fluid contains a range ofchemicals and white blood cells.
Iteffectively washes the cells and cancarry pathogen s, microorganisms thatcause disease, from tissues toward thelymph nodes.●lymph nodeleft lymphatic ductright lymphatic ductright subclavian veinleft subclavian veinlymph nodeheartVessels, nodes, and ductsLymph vessels are vessels that carrylymphatic tissue toward lymph nodesand then to the bloodstream. In thetissues these vessels are microscopic,typically the size of capillaries, but asthey join up they become larger, andthe largest of them are visible to thenaked eye.● A lymph node is a knot of lymphatictissue that is particularly well-suppliedwith phagocytic lymphocytes.
Theseare able to filter pathogens from thelymph. Swollen lymph nodes are acharacteristic sign of certain infections,as the lymphocytes multiply to combatthe invading microorganisms.● The thoracic duct, the largestlymphatic vessel, collects most of thelymph in the body (except that fromthe right arm and the right side of thechest, neck, and head, which iscollected by the right lymphatic duct)and drains it into the blood stream atthe junction of the left subclavicianvein and left jugular vein.● The lymphatic system also transportsfats from the ileum (small intestine) tothe blood.© Diagram Visual Information Ltd.●thoracic ductileumlymph nodelymph vesselsdirection of Iymph flow165Transport: bloodcomposition●●●●●Key wordsBlood cellsTransports nutrients and waste products.Transports hormones and other signalsubstances.Contains plasma proteins, which are importantin blood clotting and immunity.Regulates water and ionic content of cells anddampens (buffers) changes in pH to maintaina constant environment for tissue function.Regulates body temperature.Leukocytes:granulesThe vast majority of the cells are erythrocytes(red blood corpuscles, which are responsiblefor transporting oxygen and carbon dioxide.There are several types of leukocytes (whiteblood cells), which help to defend the bodyagainst disease:● granulocytes have a granular cytoplasm andengulf bacteria or attack parasites;● lymphocytes produce antibodies and regulatethe immune responses;● monocytes can leave the blood to becometissue macrophages: cells capable of ingestingbacteria, cell debris, and cancer cells.Platelets are bodies formed by the fragmentationof larger cells.
They are vital for blood clottingat sites of injury.Blood components separatedby centrifugationcell membraneCellular componentscytoplasm●Roughly 45 percent of the volume ofwhole blood is made of cells, red andwhite.● Red blood corpu scles are biconcavedisks, packed with hem oglobin , thattransport oxygen from the lungs to thetissues of the body. They have nonucleus when mature and last about120 days. They are made in the redbone marrow of large bones and aredestroyed at the end of their lives bycells in the spleen and liver.● White blood cells include a number ofdifferent types, but all are involved indefense against disease.
They aremade in yellow bone marrow andlymph nodes. White blood cells aremuch less common than red bloodcorpuscles (typically 1 percent),though their numbers increase duringinfection.● Platelets are subcellular componentsthat circulate in the blood and areinvolved in clotting. They aremanufactured in the bone marrow.nucleusLymphocytecell membranecytoplasmnucleusMonocytecell membranecytoplasmnucleusplasma (55%)waterorganicacidsPlasmaerythrocytes(red bloodcorpuscles)cell membranecytoplasmRed blood corpuscle(erythrocyte)blood cells (45%)The liquid component of blood iscalled plasm a. It contains a widevariety of chemicals in solution orsuspension.● Much of the carbon dioxidetransported around the body is carriedin solution in the plasma, although redblood corpuscles are involved inhelping the gas to dissolve.●Plateletssaltsleukocytes(whiteblood cells)andplateletsspleenwhite blood cellGranulocyteFunctions of blood cellsproteinshemoglobinliverplasmaplateletred bloodcorpuscleSurface viewSectioncytoplasmcellmembranecellmembrane© Diagram Visual Information Ltd.Functions of plasmaHUMAN BIOLOGY166HUMAN BIOLOGYKey wordsantibodyantigenplasmared bloodcorpuscleTransport: blood typesAntibody/ antigen composition of different blood typesAabbBlood typesbThere are many ways to classify blood,and a complete typology involvesmore than 20 different criteria.● The first and most commonly citedblood group depends on the ABOsystem, which can place everyone intoone of four groups: A, B, AB, and O.●AabBbAbWhen antigen A reacts with anti-A, redblood cells clump together to form aclot.
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