BIOL 1030 Introduction to Biology: Organismal Biology. Spring 2011 Section A

Transcription

1 BIOL 1030 Introduction to Biology: Organismal Biology. Spring 2011 Section A Steve Thompson: stthompson@valdosta.edu 1

2 Oxygen in, CO2 out circulation and respiration How animals get the oxygen in and around their body and the carbon dioxide out. 2

3 First, the circulatory system. There are two basic types in animals. Either... Open the heart pumps fluid through short, open-ended vessels that lead to spaces where the fluid bathes all the body's cells. Or... Closed the blood remains inside vessels; arteries take blood away from the heart, and branch into arterioles, then into capillaries; venules unite to form veins, which carry blood back to the heart. Diffusion between the blood s plasma and the body s interstitial fluid occurs in the capillaries for gas and nutrient exchange. 3

4 Here s an example of an open system. The hemolymph bathes all the body tissues. Locomotion helps with pumping too. All Arthropods and many Mollusks do it this way. 4

5 And of a closed system. Either way, it s also known as a cardiovascular system. This is what all vertebrates, as well as Annelids and Cephalopods use. 5

6 Vertebrate circulatory systems vary. Fish have a two chambered heart, with... One atrium (blood enters), and one ventricle (blood exits). Amphibians and most reptiles have three chambers, with... Two atria, and one ventricle. Amphibians also obtain oxygen through moist skin surfaces. Most reptiles furthermore have a partially divided ventricle (more separation = more efficiency). Crocodilians, birds, and mammals have four chambers, (but this is the product of convergent evolution) with... Two atria, and two ventricles. Therefore,... The systemic (to body) and pulmonary (to lungs) circuits are completely separate, with a four chambered heart. This maximizes the amount of oxygen reaching the tissues. 6

7 The situation in fish the least efficient of all the vert s. 7

8 A bit more efficient in amphibians and reptiles. 8

9 And maximally efficient in birds and mammals (and crocodilians). 9

10 The same thing going on in us the two circuits remain separate. 10

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12 The human heart... Is enclosed in the pericardium this gives protection, yet allows free movement. It is... Three layers thick the myocardium (muscle layer) is the thickest. There are two upper atria; and... Two lower ventricles. The... Atrioventricular valves (AV valves) only allow one-way flow from the atrium to the ventricle. And the semilunar valves block blood from reentering the ventricles from the arteries. 12

13 From the outside... the aorta takes oxygenated blood to the rest of the body and the coronary arteries deliver O2 and nutrients to the myocardium. 13

14 A vertical crosssection shows all the parts. The left ventricle pumps blood to the entire body. 14

15 And a horizontal cross-section shows how the valves keep the two circuits separate and unidirectional. 15

16 The circuit routes... The superior and inferior vena cava deliver blood from the entire body (except from the lungs) to the right atrium. This unoxygenated blood then goes through the right AV valve to the right ventricle. And then through... The pulmonary semilunar valve to the pulmonary arteries; Where it goes off to the lungs to pick up oxygen and drop off carbon dioxide. This newly oxygenated blood goes... Back to the heart through the pulmonary veins, and... Into the left atrium through the left AV valve. Where it... Enters the left ventricle and is pumped out the aortic semilunar valve into the aorta; where the... Oxygen rich blood circulates throughout the body before returning back to the heart. And the... Coronary arteries supply blood to the heart muscle itself. 16

17 What about the heartbeat? The cardiac cycle consists of a single contraction and relaxation of the heart muscle. The heartbeat begins in the sinoatrial (SA) node. The SA node is know as a pacemaker because it sets the tempo of the beat. Once begun, the... Impulses race across the atrial wall and the atria contract together to fill the ventricles. The impulse is momentarily delayed at the atrioventricular (AV) node, and then the... Signal is rapidly conducted down and through the ventricle walls such that both ventricles contract together in unison. 17

18 An ECG shows the cycle. 18

19 How about an animation of this? Chapter32/conducting_system_of_the_heart.swf 19

20 And the rest of the blood vessels... Blood flows from the heart (in order) through arteries, arterioles, capillaries, venules, then veins, and back to the heart. There are... Three layers in arteries and veins: An outermost sheath of connective tissue; A middle layer of smooth muscle; and an... Inner layer of endothelium. Arteries are more muscular than veins. 20

21 The layers in cutaway... Notice the much thicker muscle wall in the artery. 21

22 Major blood vessels in humans include... You do need to know some of these pretty much all the major vessels in and out of the heart but not all of them on this chart. 22

23 Capillary beds are a... Network of capillaries connecting arterioles to venules. Capillaries are... Tiny, numerous, and thin; with... Extensive surface area for diffusional exchange of gases, nutrients, and waste. They are a single layer of endothelium thick. Nutrients and oxygen diffuse out to the cells. And in turn... Waste products and carbon dioxide diffuse back into the blood. 23

24 Here s a diagram. 24

25 Capillaries are so small (how small are they?) that blood cells travel through them in single file! 25

26 Veins are a bit different. Their smooth muscle layer is much thinner than arteries (or even absent). Such that... The vessels collapse when empty. Valves help to maintain a one-way flow back to heart in the bigger veins of the lower leg. Skeletal muscles in the legs squeeze veins and help move blood back toward the heart. Portal systems are unusual they are a second set of capillaries before returning to the heart (venule to capillary to venule), e.g. in the hepatic portal system of the liver. 26

27 Here s a diagram of a normal leg vein showing how the calve muscles help deoxygenated blood return to the heart. And a varicose vein. See en.wikipedia. org/wiki/ Varicose 27

28 Blood pressure is the... Force that blood exerts on artery walls. It is... Measured with a sphygmomanometer. Systolic pressure ventricles contracting; Diastolic pressure ventricles relaxing. Units are millimeters of mercury (mm Hg). Normal for a young adult is around 120/80. Pressure falls with distance from the heart. It is under constant negative feedback regulation so that homeostasis can be maintained. 28

29 Blood pressure measurements. 29

30 It is proportional to the distance from the heart. 30

31 Here s the feedback loop for blood pressure (when things are working correctly). 31

32 What about the blood itself? Remember, it is connective tissue. It consists of... Mesoderm derived cells in a liquid matrix. And is made up of red blood cells, white blood cells, and platelets, in plasma. Blood cells originate from stem cells in red bone marrow. Plasma is about 90% water, along with many types of proteins, and other dissolved substances, including glucose. 32

33 know these! 33

34 And be sure to understand all its functions. 34

35 The percentages of the components.... Don t bother memorizing the exact numbers just have a rough feel for them. 35

36 What the parts look like... 36

37 Let s start with red blood cells (RBCs) the erythrocytes. They are packed with hemoglobin for oxygen transport. See: Each hemoglobin quatramer has four iron atoms (the heme group) that each carry one oxygen molecule (O2). RBCs are by far the most numerous cells in blood. They are formed in red marrow, and lack nuclei, ribosomes, and mitochondria at maturity. They... Last about 120 days, before they are... Eventually destroyed and then recycled by the liver and spleen. Your ABO and Rh blood type is determined by antigen proteins on the RBCs surface (see agglutination). 37

38 White blood cells (WBCs) the leukocytes are... Immune system cells, and are... Larger than red blood cells. They... Retain their nuclei, and lack hemoglobin. There are five types (more detail in the immune system lecture later). The proportion of different types can provide doctors clues to what infection or disease a person may have. Leukemias cancers in which bone marrow overproduces white blood cells at the expense of red blood cells. Anemia and a failing immune system result. HIV destroys white blood cells (especially helper T cellss) resulting in AIDS. 38

39 Platelets are thrombocytes. They are small, colorless cell fragments. Platelets travel freely within the vessels... Until the smooth endothelial lining is disrupted by a tear or obstruction, then... They release biochemicals that combine with clotting factors to create a blood clot. 39 Protein threads (fibrin) tying RBCs together into a blood clot.

40 Here s a diagram of how platelets work. 40

41 The lymphatic system... Works with the circulatory system. It... Collects fluids that leaks from capillaries; And removes bacteria, debris, and cancer cells from the fluids, then... Returns it back to the blood. Lymph is the colorless fluid of the system, and is pretty much the same as blood plasma, minus the larger proteins. It originates in lymph capillaries, which have loosely joined cellular linings, and can admit foreign particles from the body tissues and interstitial fluids. 41

42 Then what? The lymph capillaries merge into larger and larger vessels, and eventually... Pass the lymph through the lymph nodes. These contain infection-fighting white blood cells that destroy invaders. There s no pump skeletal muscle contractions and valves in the system help move the lymph throughout the body. The spleen and thymus are also part of this system. Lymph returns to the blood near the heart. 42

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44 Here are the main parts of the lymphatic system. 44

45 The lymphatic system collects fluids that leak from capillaries and passes it on to... 45

46 The lymph nodes, where it is filtered and eventually passed back into the cardiovascular system. 46

47 A major job of the cardiovascular system is to get oxygen around the body and carbon dioxide away, but where s it come from? Remember, cells require oxygen as part of aerobic respiration in order to generate ATP. And... Carbon dioxide is created as the waste product. Animal respiratory systems work with circulatory systems to acquire and deliver oxygen, and to pick up and eliminate carbon dioxide. Animals use different parts of their bodies for these respiratory surfaces. But all... Must be moist to allow gas diffusion. And all... Must have sufficient surface area for the job! 47

48 Simple diffusion is enough for small animals with enough surface area, like flatworms and jellyfish. 48

49 system. 49 Larger animals need larger gas exchange areas and circulatory systems. Earthworms use diffusion across the body surface but do have a circulatory

50 Terrestrial arthropods use tracheae extensively branched internal tubules connecting the atmosphere to tiny tubules around the body s cells. 50

51 Gills many aquatic organisms use these to exchange gases with water. Found in, invertebrates (e.g. mollusks), and vertebrates (fish and amphibians). They are either internal or external to the body. Fish have internal gills. With an extensive surface area, and a... Continuous flow of water from the mouth through the gills. This is another case of... Countercurrent exchange the blood flows through capillaries in a direction opposite to the water flow. 51

52 Fish gills in more detail... It s all about surface area and countercurrent exchange here to maximize the absorbance of oxygen from the water. 52

53 Land vertebrates have lungs... Located inside the body to keep surfaces moist. The mammal lung maximizes available surface area. 53

54 How did it evolve? The transition onto land drove the lung s evolution. It evolved as simple sacs from air bladders; And has an increased surface area in frogs and toads. The reptile lung has even more subdivisions. And the mammalian lungs have alveoli. 54

55 Moving air in and out... Frogs force air into their lungs using the floor of their mouth, and expel it by contracting body wall muscles. 55

56 Birds have multipart air sacs, plus lungs. With unidirectional, cyclic air flow, for efficiency. 56

57 Mammals pull air into their lungs using their diaphragm. 57

58 The human respiratory system The upper respiratory tract consists of: The nose functions in both breathing and olfaction. And it has hairs that block large particles. It also raises the temperature and humidity of the incoming air. The pharynx routes food to the digestive system, versus air toward the lungs (usually). The larynx these support your vocal cords. The glottis the slit-like opening of the larynx. The epiglottis closes off the glottis during swallowing (when all goes well). 58

59 The lower respiratory tract... The trachea has c- shaped cartilage to hold it open. It branches into two bronchi one per lung. And these... Branch repeatedly, decreasing in diameter and wall thickness as they go. Bronchioles are the finest branches. 59

60 And then what? The bronchioles narrow even further into several alveolar ducts. The... Ducts open into grape-like clusters of alveoli. Which are... Tiny sacs only one cell layer thick,... With a vast network of capillaries. This is the respiratory surface, and where gases exchange by diffusion. 60

61 Here s what they look like. 61

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63 The respiratory cycle is... Inhalation air is sucked into the lungs. This happens as the... Muscles of the rib cage and diaphragm contract, which... Expands and elongates the chest cavity, thereby expanding the lungs. The increase in lung volume decreases internal pressure. It requires energy to contract these muscles. Exhalation air flows out of lungs. This happens as the... Muscles of the rib cage and diaphragm relax, which causes... The chest cavity to return to its smaller size, so the lungs also become smaller. The decreased volume increases pressure. No energy is required for this part of the cycle. 63

64 Here s a drawing. 64

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66 Back to the blood gas transport. Pulmonary circulation: Blood from the body travels to the lungs to pick up oxygen and get rid of carbon dioxide. Systemic circulation: Blood from the lungs travels to the body to drop off oxygen and pick up carbon dioxide. Oxygen is carried two ways: There s a small amount dissolved in plasma. But... Most is carried inside red blood cells - the hemoglobin molecule can carry up to four oxygen molecules per hemoglobin quatramer. 66

67 CO2 + H2O H2CO3 H + + HCO3 - Carbon dioxide is carried three ways. There s a small amount dissolved in plasma. And... Some is bound to a different area of hemoglobin; But most of it is transported as bicarbonate ion (HCO3 - ) dissolved in plasma. The reaction works in both directions. This is part of the blood s ability to buffer ph changes. The transfer of gases is by simple diffusion... Based on concentration gradients. 67

68 Here s an overview diagram. 68

69 And an animation... animations/chapter33/gasexchange.swf 69

70 Regulation of breathing... Helps to maintain homeostasis of blood gas concentrations. The most important signal is blood CO2 level; More precisely H + formed from H2CO3. Chemoreceptors in the brain s medulla monitor this. A decline in ph triggers an increase in the breathing rate. Oxygen is less important in regulating your breathing rate than carbon dioxide. The large amount of oxygen bound to hemoglobin provides a large safety margin (except CO). 70

71 Here s where it happens. 71

72 And another feedback loop. That s more than enough for now! Next time the digestive system. 72