Chapter 10: Transport in Humans and Animals

10.1 Types of Circulatory System

• Large multicellular organisms have small TSA/V, so diffusion alone cannot supply cells. (p.168)
• Open system: haemolymph flows into the haemocoel and bathes cells (insects). (p.169)
• Closed system: blood stays in continuous vessels; exchange occurs at capillaries. (p.169)
• Insect heart: when it contracts haemolymph flows out; when it relaxes it returns through ostia. (p.170)
• Fish: two-chambered heart (atrium, ventricle), single circulation. (p.170)
• Amphibians: three-chambered heart, double but incomplete circulation because blood mixes in the ventricle. (p.171)
• Humans: four-chambered heart, complete double circulation. (p.171)

Circulatory systems compared

(p.172)

Feature	Insects	Fish	Amphibians	Humans
Type	Open	Closed	Closed	Closed
Circulations	None	Single	Double	Double
Heart chambers	Many segments	Two	Three	Four
Blood mixing	None	None	Incomplete separation	Complete separation

10.2 Circulatory System of Humans

• Components: blood, heart and blood vessels. (p.173)
• Left ventricle wall is thicker than the right because it pumps blood to the whole body. (p.173)
• Tricuspid valve (right atrium to ventricle, three leaflets) and bicuspid valve (left, two leaflets) prevent backflow. (p.174)
• Semilunar valves at the bases of the aorta and pulmonary artery prevent backflow into ventricles. (p.174)
• Aorta carries oxygenated blood to the body; vena cava returns deoxygenated blood; septum separates left and right sides. (p.174)
• Blood is 55% plasma and 45% cells; plasma is about 90% water. (p.175)
• Plasma proteins: fibrinogen (clotting), albumin (osmotic pressure), globulin (antibodies). (p.175)
• Erythrocytes: biconcave disc, no nucleus at maturity, contain haemoglobin; live up to 120 days. (p.176)
• Haemoglobin combines with O₂ at high partial pressure and releases it at low partial pressure. (p.176)
• Platelets are cell fragments from bone marrow involved in blood clotting; life span less than one week. (p.176)
• Leucocytes: neutrophils and monocytes ingest by phagocytosis; lymphocytes make antibodies; eosinophils fight inflammation and allergy; basophils contain heparin. (p.177)
• Artery: thick, muscular, elastic wall, high pressure, no valves (except semilunar). (p.179)
• Capillary: one cell thick wall, very low pressure, no valves. (p.179)
• Vein: thin wall, large lumen, valves, very low pressure. (p.179)

10.3 Mechanism of Heartbeat

• Cardiac muscle is myogenic: it contracts without nerve impulses. (p.180)
• The sinoatrial (SA) node is the pacemaker in the right atrium wall; impulses spread across both atria, then reach the AV node. (p.181)
• From the AV node impulses pass through the bundle of His and Purkinje fibres to the apex, then the ventricles contract. (p.181)
• "Lub" is closing of tricuspid and bicuspid valves; "dub" is closing of semilunar valves. (p.182)
• Venous blood return is helped by skeletal muscle contraction and valves. (p.182)

10.4 Mechanism of Blood Clotting

• Clotting minimises blood loss and prevents pathogen entry. (p.183)
• Platelets and damaged cells form thrombokinase, which with Ca²⁺ and vitamin K converts prothrombin to thrombin. (p.183)
• Thrombin converts soluble fibrinogen to insoluble fibrin, forming a network that traps erythrocytes. (p.183)
• Thrombosis is formation of a blood clot (thrombus); an embolus is a clot carried by blood; haemophilia is hereditary lack of clotting factors. (p.184)

10.5 Blood Groups of Humans

• Blood group A: antigen A, anti-B; B: antigen B, anti-A; AB: both antigens, no antibody; O: no antigens, anti-A and anti-B. (p.185)
• O can donate to all; AB can receive from all. (p.185)
• Rhesus factor (antigen D): Rh-positive have it, Rh-negative do not. (p.185)
• An Rh-negative mother carrying an Rh-positive foetus may produce anti-D antibodies that endanger a later Rh-positive foetus (erythroblastosis fetalis). (p.186)

10.6 Health Issues Related to the Human Circulatory System

• Keep the circulatory system healthy through a low-fat balanced diet, regular exercise and not smoking or drinking alcohol. (p.187)
• Atherosclerosis is plaque deposition on artery walls; arteriosclerosis is calcium deposition making arteries hard. (p.187)
• Narrowed coronary artery causes angina; complete blockage causes myocardial infarction. (p.187)

10.7 Lymphatic System of Humans

• Tissue fluid forms when high blood pressure at the arteriole end forces plasma out of capillaries; it lacks erythrocytes, platelets and plasma proteins. (p.189)
• At the venule end, about 85% of fluid is reabsorbed; the remaining fluid drains as lymph. (p.189)
• Lymphatic capillaries have one closed end; they merge into lymphatic vessels with lymph nodes. (p.190)
• Lymph is pale yellow; it has more fat and lymphocytes than tissue fluid and lacks plasma protein, erythrocytes and platelets compared with blood. (p.190)
• Lymphatic organs: lymph nodes, spleen, thymus, bone marrow, tonsils, appendix. (p.191)
• Lymph flow is aided by heartbeat, muscle contraction, peristalsis and breathing; valves ensure one-way flow. (p.191)
• Thoracic duct empties into the left subclavian vein; right lymphatic duct into the right subclavian vein. (p.192)
• Necessity: returns excess tissue fluid, transports fat-soluble substances via lacteals, body defence via lymphocytes. (p.192)

10.8 Health Issues Related to the Human Lymphatic System

• Oedema is swelling from tissue fluid not returning to the blood. (p.193)
• Causes: parasitic infection (Brugia sp., lymphatic filariasis), plasma protein deficiency, pregnancy, prolonged bed rest. (p.193)