Biology - An Illustrated Guide to Science (794127), страница 27
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This is calledmechanical digestion and is done bythe teeth. The next stage is chemicaldigestion of large molecules byen zym es.●Nutrition: digestion andabsorptionSequence of digestion1234567StarchMaltoseProteinLarge peptidesFatsFatty acids and glycerolAmino acids891011121314digestionGlucoseLactoseGlucose and galactoseSucroseGlucose + fructoseWaterSaltsabsorptionamylase1pepsinmouth3EnzymesEnzymes, such as amylase and pepsin,are complex proteins that speed upreactions in living organisms.
They areused in digestive processes to breakdown large molecules.● Enzymes are generally specific—theycan only speed up a single reaction,and each step in a chain of reactionsmay need its own particular enzyme.● Digestive enzymes are unusual in thatthey are often able to speed up anumber of reactions among relatedchemicals.
However, the range ofchemicals a digestive enzyme canhandle is still limited, so the gutproduces a range of enzymes to coverall of the chemicals found in food.3© Diagram Visual Information Ltd.4lipase56amylase12peptidasestomach4duodenum7maltase2ileum8lactase910sucrasecolon11AbsorptionAbsorption is the passage of foodchemicals into the body.● This occurs mainly in the lower partsof the gut and is increased by the largesurface area of the ileum (smallintestine).4trypsin●●2678131412157Transport: circulatorysystem mapHUMAN BIOLOGYKey wordsarterycapillarydouble circulationveinArteriesA closed circulationcarotidpulmonarymesenteric(heart)subclavianhepaticVeins(liver)(gut)jugularrenalBlood passes around the body in aclosed circulatory system.
This isdifferent from circulation in manylower animals, where the cells arebathed in blood directly.● The advantage of a closed system isthat it can transport materials muchmore rapidly.● The human circulatory system consistsof a central pump (the heart) andthree types of tubes (arteries,capillaries, and vein s).●subclavianThe heartThe heart consists of two pumps. Theright side pumps blood from the bodyto the lungs. The left side takes bloodfrom the lungs and pumps it aroundthe body. The left side is slightly largerand more muscular because it has agreater distance to push the blood.● This system, known as dou blecircu lation , separates oxygenated anddeoxygenated blood. This means thatthe blood must go through the lungsfor every single circuit of the body.●(heart)cephalichepaticportalhepatic(kidney)aorta(liver)iliac(gut)renalBlood vesselsArteries carry blood away from theheart under high pressure.● Blood from the arteries flows intocapillaries, microscopic blood vesselsthat penetrate every organ in the body.● Blood flows out of the capillaries andinto veins to be carried back to theheart under low pressure.vena cavailiac(kidney)© Diagram Visual Information Ltd.●158HUMAN BIOLOGYKey wordsaortaarteryguthepatic portalveinliverveinTwo circulationsThe pulmonary circulation forms acomplete circuit, taking deoxygenatedblood from the heart to the lungsalong the pulmonary artery and thenreturning oxygenated blood to theheart along the pulmonary vein .● The main circulation in the body takesoxygenated blood from the heart,travelling through the aorta, andreturns deoxygenated blood to theheart through the vena cava.●Transport: circulatorysystem schemeSchematic representation of circulatory system1HEAD AND NECK102ARMS113aHEART13RALARVLV124LUNGSystem planTall arteries arise ultimately from theaorta.
The system is a series of parallelcircuits so each organ has its ownartery supplying oxygenated blood.Each organ also has a vein leading outthat carries blood back to the heart.● The one exception is the liver, whichhas two inputs: the hepatic artery,which provides oxygenated blood, andthe hepatic portal vein , which carriesblood to the liver from the gu t. Thismeans that the chemicals absorbedinto the blood by the gut can besorted and, possibly, changed beforethey pass on to the rest of the body. Asubstance absorbed in the gut thus hasto go through the liver before it canreach any other cell in the body.● The hepatic vein drains blood fromthe liver back to the heart.● Arteries and veins are named after theorgans they serve.●LUNG514LIVER615GUT3b16177KIDNEYS188GONADS199LEGS20© Diagram Visual Information Ltd.Direction of blood flowoxygen-rich blood1–9 Veins1 Jugular2 Subclavian3 Vena cava3a Superior vena cava3b Inferior vena cava4 Pulmonaryoxygen-poor blood56789HepaticHepatic portalRenalGenitalIliacRA Right atrium RV Right ventricleLA Left atriumLV Left ventricle10 –2 0 Arteries10 Carotid11 Subclavian12 Aorta13 Pulmonary14 Hepatic15 Gastric1617181920Anterior mesentericPosterior mesentericRenalGenitallliac159Transport: heart structureHUMAN BIOLOGYKey wordsHeartthoraxventricleExternal view (ventral)left common carotid arteryinnominate arteryleft subclavian arteryaortic archright pulmonary arteryleft pulmonary arterysuperior vena cavaTwo pumpsThe heart consists of two completeand functionally separate pumps heldwithin a single muscle mass in thethorax.● The right side receives blood from thebody and pumps it to the lungs.● The left side, which is slightly moremuscular, collects blood from thelungs and pumps this around thewhole body.●right atriumleft atriumright pulmonaryveinsleft pulmonary veinsright coronaryarteryleft coronary arteryleft ventricleright ventricleinferior vena cavaRight sideaortaSectionleft common carotid arteryinnominate arteryleft subclavian arteryright pulmonary arteryleft pulmonary arteryaortic archleft atriumsuperior vena cavamitral (bicuspid) valveright atriumleft pulmonary veinstricuspid valveaortic valvepulmonary valvevalve tendonright ventricleleft ventricleinferior vena cavaBlood enters the right atrium from thevena cava at low pressure.
The walls ofthe right atrium are fairly thin—if itwere too muscular, the blood wouldnot be able to push into the chamber.● The atrium walls contract, and bloodpasses into the right ven tricle.● The walls of the ventricle are muchmore muscular and give the blood apush out along the pulmonary arteryto the lungs. The tricuspid valveseparating the atrium and ventricleprevents backflow into the atriumduring the power stroke. Thepulmonary valve at the entrance of thepulmonary artery prevents backflowinto the ventricle when it is refillingwith blood again from the atrium.●Left sideThe left side undergoes exactly thesame sequence and has basically thesame structural adaptations.● The muscles of the heart are suppliedwith blood, and so oxygen, throughthe coronary artery, reaches bothsides.aortaSimplified section showing direction of blood flowoxygen-rich bloodoxygen-poor blood© Diagram Visual Information Ltd.●interventricular septum160HUMAN BIOLOGYKey wordsdiastolesystoleventricleTransport: heartbeatPumping action of the heartDiastole (relaxation of heart muscle)Systole (contraction of heart muscle)Atria fill; atrioventricular(mitral and tricuspid) valvesare closed.Ventricles continue to contract;rising pressure pushesopen the aortic andpulmonary valves.Atrioventricular valves arepushed open by risingatrial pressure;ventricles startto fill.Ventricles contract andpressure increases; aorticand pulmonaryvalves remainclosed.Ventricles continue to fillby suction from relaxedventricular wallsand atrialcontraction.Ventricles become full andstretched; atrioventricularvalves close.Diastole and systole●The heartbeat is a complex series ofevents that splits into two maingroups: diastole, where the heartmuscle is relaxed, and systole, wherethe muscle actively contracts.Filling of atriaBlood from the body enters the heartat low pressure through the vena cava.The pressure is sufficient to inflate theatria, which have relatively thin walls.● As the atria fill, the blood pushes itsway through the atrioventricular valvesin the ven tricles.● To complete the process the musclesin the atria contract, the passages tothe veins are constricted, and blood isactively pumped into the ventricles.
Bythe end of diastole, the blood ispresent in the ventricles.●Emptying of the ventriclesWhen the ventricles are full of blood,the atrioventricular valves close. Themuscles in the wall of the ventriclenow contract, and blood is pushedthrough the aortic and pulmonaryvalves along the arteries. Tendonsattached to the atrioventricular valveskeep the atrioventricular valves closedduring this process.● The process begins again as theventricles empty of blood and themuscles relax.
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