Circulation and Gas Exchange

1. Circulation and Gas Exchange

2. Open and Closed Circulatory Systems • Both systems have three basic components: • A circulatory fluid (blood or hemolymph) • A set of tubes (blood vessels) • A muscular pump (the heart) • open circulatory system • In insects, other arthropods, and most molluscs • blood bathes the organs directly • no distinction between blood and interstitial fluid (hemolymph)

3. LE 42-3 Heart Heart Hemolymph in sinuses surrounding organs Interstitial fluid Small branch vessels in each organ Lateral vessel Anterior vessel Ostia Dorsal vessel (main heart) Tubular heart Auxiliary hearts Ventral vessels An open circulatory system. A closed circulatory system.

4. closed circulatory system • blood is confined to vessels and is distinct from the interstitial fluid

5. Arteries carry blood to capillaries • where chemical exchange between the blood and interstitial fluid • Veins return blood from capillaries to the heart

6. Fishes • 2 chambered heart • one ventricle and one atrium • Gills for gas exchange

7. Amphibians • 3 chambered heart • two atria and one ventricle

8. Reptiles (Except Birds) • double circulation • pulmonary circuit (lungs) • systemic circuit • 3 chambered heart

9. Mammals and Birds • 4 chambered heart • 2 atria and 2 ventricle • left side receives oxygen-rich blood • right side receives oxygen-poor blood

10. A powerful four-chambered heart was an essential adaptation of the endothermic way of life characteristic of mammals and birds

11. LE 42-4 FISHES AMPHIBIANS REPTILES (EXCEPT BIRDS) MAMMALS AND BIRDS Gill capillaries Lung and skin capillaries Lung capillaries Lung capillaries Pulmocutaneous circuit Pulmonary circuit Gill circulation Pulmonary circuit Right systemic aorta Artery Heart: Ventricle (V) Left systemic aorta A A A A A A Atrium (A) V V V V V Right Left Left Right Right Left Systemic circulation Systemic circuit Systemic circuit Vein Systemic capillaries Systemic capillaries Systemic capillaries Systemic capillaries Systemic circuits include all body tissues except lungs. Note that circulatory systems are depicted as if the animal is facing you: with the right side of the heart shown at the left and vice-versa.

12. Capillaries of head and forelimbs LE 42-5 Anterior vena cava Pulmonary artery Pulmonary artery Aorta Capillaries of right lung Capillaries of left lung Pulmonary vein Pulmonary vein Right atrium Left atrium Left ventricle Right ventricle Posterior vena cava Aorta Capillaries of abdominal organs and hind limbs

13. Pulmonary artery Aorta LE 42-6 Anterior vena cava Pulmonary artery Right atrium Left atrium Pulmonary veins Pulmonary veins Semilunar valve Semilunar valve Atrioventricular valve Atrioventricular valve Posterior vena cava Left ventricle Right ventricle

14. The heart contracts and relaxes in a rhythmic cycle called the cardiac cycle • The contraction, or pumping, phase is called systole • The relaxation, or filling, phase is called diastole

15. LE 42-7 Atrial systole; ventricular diastole Semilunar valves closed 0.1 sec Semilunar valves open AV valves open 0.3 sec 0.4 sec Atrial and ventricular diastole AV valves closed Ventricular systole; atrial diastole

16. The heart rate, also called the pulse, is the number of beats per minute • The cardiac output is the volume of blood pumped into the systemic circulation per minute

17. Maintaining the Heart’s Rhythmic Beat • Some cardiac muscle cells are self-excitable, meaning they contract without any signal from the nervous system

18. The sinoatrial (SA) node, or pacemaker, sets the rate and timing at which cardiac muscle cells contract Impulses from the SA node travel to the atrioventricular (AV) node At the AV node, the impulses are delayed and then travel to the Purkinje fibers that make the ventricles contract

19. Impulses that travel during the cardiac cycle can be recorded as an electrocardiogram (ECG or EKG)

20. LE 42-8 Signals pass to heart apex. Signals are delayed at AV node. Pacemaker generates wave of signals to contract. Signals spread throughout ventricles. SA node (pacemaker) AV node Bundle branches Purkinje fibers Heart apex ECG

21. The pacemaker is influenced by nerves, hormones, body temperature, and exercise

22. Concept 42.3: Physical principles govern blood circulation • The physical principles that govern movement of water in plumbing systems also influence the functioning of animal circulatory systems

23. Blood Vessel Structure and Function The “infrastructure” of the circulatory system is its network of blood vessels All blood vessels are built of similar tissues and have three similar layers

24. Vein Artery LE 42-9 100 µm Endothelium Valve Basement membrane Endothelium Endothelium Smooth muscle Smooth muscle Capillary Connective tissue Connective tissue Vein Artery Venule Arteriole

25. Structural differences in arteries, veins, and capillaries correlate with functions • Arteries have thicker walls that accommodate the high pressure of blood pumped from the heart

26. In the thinner-walled veins, blood flows back to the heart mainly as a result of muscle action

27. LE 42-10 Direction of blood flow in vein (toward heart) Valve (open) Skeletal muscle Valve (closed)

28. Blood Flow Velocity • Physical laws governing movement of fluids through pipes affect blood flow and blood pressure • Velocity of blood flow is slowest in the capillary beds, as a result of the high resistance and large total cross-sectional area

29. 5,000 LE 42-11 4,000 3,000 Area (cm2) 2,000 1,000 0 50 40 Velocity (cm/sec) 30 20 10 0 120 Systolic pressure 100 80 Pressure (mm Hg) 60 Diastolic pressure 40 20 0 Venae cavae Aorta Capillaries Venules Veins Arterioles Arteries

30. Blood Pressure • Blood pressure is the hydrostatic pressure that blood exerts against the wall of a vessel • Systolic pressure is the pressure in the arteries during ventricular systole; it is the highest pressure in the arteries • Diastolic pressure is the pressure in the arteries during diastole; it is lower than systolic pressure • Blood pressure is determined by cardiac output and peripheral resistance due to constriction of arterioles

31. LE 42-12_4 Blood pressure reading: 120/70 Pressure in cuff below 120 Pressure in cuff below 70 Pressure in cuff above 120 Rubber cuff inflated with air 120 120 70 Sounds audible in stethoscope Sounds stop Artery closed Artery

32. Capillary Function Capillaries in major organs are usually filled to capacity Blood supply varies in many other sites

33. Two mechanisms regulate distribution of blood in capillary beds: • Contraction of the smooth muscle layer in the wall of an arteriole constricts the vessel • Precapillary sphincters control flow of blood between arterioles and venules

34. Thoroughfare channel LE 42-13ab Precapillary sphincters Venule Arteriole Capillaries Sphincters relaxed Venule Arteriole Sphincters contracted

35. LE 42-13c Capillaries and larger vessels (SEM) 20 µm

36. The critical exchange of substances between the blood and interstitial fluid takes place across the thin endothelial walls of the capillaries • The difference between blood pressure and osmotic pressure drives fluids out of capillaries at the arteriole end and into capillaries at the venule end

37. LE 42-14 Tissue cell INTERSTITIAL FLUID Net fluid movement out Net fluid movement in Capillary Capillary Red blood cell 15 µm Direction of blood flow Blood pressure Osmotic pressure Inward flow Pressure Outward flow Arterial end of capillary Venous end

38. Fluid Return by the Lymphatic System The lymphatic system returns fluid to the body from the capillary beds This system aids in body defense Fluid reenters the circulation directly at the venous end of the capillary bed and indirectly through the lymphatic system

39. Concept 42.4: Blood is a connective tissue with cells suspended in plasma • In invertebrates with open circulation, blood (hemolymph) is not different from interstitial fluid • Blood in the circulatory systems of vertebrates is a specialized connective tissue

40. Blood Composition and Function • Plasma • Fluid • 55% of blood composition • Cellular Components • 45% of blood composition

41. Plasma • Blood plasma is about 90% water • Solutes • inorganic salts • dissolved ions • sometimes called electrolytes • plasma proteins • influence blood pH, osmotic pressure, and viscosity • lipid transport • Immunity • blood clotting • Ex. albumins, globulins, fibrinogen

42. LE 42-15 Plasma 55% Cellular elements 45% Constituent Major functions Cell type Number Functions Water Solvent for carrying other substances per µL (mm3) of blood Erythrocytes (red blood cells) Ions (blood electrolytes) 5–6 million Transport oxygen and help transport carbon dioxide Sodium Potassium Calcium Magnesium Chloride Bicarbonate Osmotic balance, pH buffering, and regulation of membrane permeability Separated blood elements Leukocytes (white blood cells) Defense and immunity 5,000–10,000 Plasma proteins Osmotic balance, pH buffering Albumin Lymphocyte Basophil Fibrinogen Clotting Defense Immunoglobulins (antibodies) Eosinophil Substances transported by blood Monocyte Neutrophil Nutrients (such as glucose, fatty acids, vitamins) Waste products of metabolism Respiratory gases (O2 and CO2) Hormones Platelets 250,000– 400,000 Blood clotting

43. Cellular Elements • Suspended in blood plasma are two types of cells: • Red blood cells (erythrocytes) transport oxygen • Most abundant • White blood cells (leukocytes) function in defense • Include monocytes, neutrophils, basophils, eosinophils, and lymphocytes • defense • phagocytizing bacteria and debris • producing antibodies • Platelets involved in clotting

44. Erythrocytes, leukocytes, and platelets all develop from a common source, pluripotent stem cells in the red marrow of bones

45. Pluripotent stem cells (in bone marrow) LE 42-16 Myeloid stem cells Lymphoid stem cells Basophils B cells T cells Lymphocytes Eosinophils Neutrophils Erythrocytes Platelets Monocytes

46. Blood Clotting When the endothelium of a blood vessel is damaged, the clotting mechanism begins A cascade of complex reactions converts fibrinogen to fibrin, forming a clot

47. LE 42-17 Endothelium of vessel is damaged, exposing connective tissue; platelets adhere Platelets form a plug Seal is reinforced by a clot of fibrin Collagen fibers Fibrin clot Red blood cell Platelet plug Platelet releases chemicals that make nearby platelets sticky Clotting factors from: Platelets Damaged cells Plasma (factors include calcium, vitamin K) Prothrombin Thrombin Fibrinogen Fibrin 5 µm

48. One type of cardiovascular disease, atherosclerosis, is caused by the buildup of cholesterol within arteries

49. LE 42-18 Connective tissue Smooth muscle Endothelium Plaque 50 µm Normal artery Partly clogged artery 250 µm

50. Hypertension, or high blood pressure, promotes atherosclerosis and increases the risk of heart attack and stroke A heart attack is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries A stroke is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head