Circulation and Gas Exchange 34 Circulation and Gas Exchange

Do now: What is the purpose of a circulatory system? What are the different organs of the human circulatory system? List some organisms that might have circulatory systems different from humans List some organisms that might not have circulatory systems

Main Ideas to know: Different types of circulatory systems Role of carbon dioxide/pH and homeostasis Positive feedback of blood clotting Respiratory pigments

Gastrovascular Cavities Some animals lack a circulatory system Some cnidarians, such as jellies, have elaborate gastrovascular cavities A gastrovascular cavity functions in both digestion and distribution of substances throughout the body 4

Figure 34.2 Flatworms have a gastrovascular cavity and a flat body shape to optimize diffusional exchange with the environment Mouth Gastrovascular cavity 1 mm Figure 34.2 Internal transport in the planarian Dugesia (LM) 5

Open and Closed Circulatory Systems A circulatory system has a circulatory fluid, a set of interconnecting vessels, and a muscular pump, the heart Several basic types of circulatory systems have arisen during evolution, each representing adaptations to constraints of anatomy and environment 6

(a) An open circulatory system (b) A closed circulatory system Figure 34.3 (a) An open circulatory system (b) A closed circulatory system Heart Blood Heart Interstitial fluid Hemolymph in sinuses Branch vessels in each organ Pores Dorsal vessel (main heart) Figure 34.3 Open and closed circulatory systems Tubular heart Ventral vessels Auxiliary hearts 7

All circulatory systems are either open or closed circulatory fluid bathes the organs directly in an open circulatory system Ex: insects, arthropods and molluscs In an open circulatory system, there is no distinction between circulatory fluid and interstitial fluid, and this general body fluid is called hemolymph 8

One or more hearts pump blood through the vessels In closed circulatory systems the circulatory fluid called blood is confined to vessels and is distinct from interstitial fluid Ex: annelids (earthworms), vertebrates One or more hearts pump blood through the vessels Chemical exchange occurs between blood and interstitial fluid and between interstitial fluid and body cells 9

Organization of Vertebrate Circulatory Systems Humans and other vertebrates have a closed circulatory system called the cardiovascular system The three main types of blood vessels are arteries, veins, and capillaries Blood flow is one-way in these vessels 10

Artery Vein Red blood cells Valve Basal lamina Endothelium Endothelium Figure 34.9 Artery Vein LM Red blood cells 100 m Valve Basal lamina Endothelium Endothelium Smooth muscle Connective tissue Smooth muscle Connective tissue Capillary Artery Vein Figure 34.9 The structure of blood vessels Venule Arteriole 15 m Red blood cell Capillary LM 11

Arteries branch into arterioles and carry blood away from the heart to capillaries Networks of capillaries called capillary beds are the sites of chemical exchange between the blood and interstitial fluid Venules converge into veins and return blood from capillaries to the heart Arteries and veins are distinguished by the direction of blood flow, not by O2 content 12

Pulmocutaneous circuit Pulmonary circuit Figure 34.4 (a) Single circulation: fish (b) Double circulation: amphibian (c) Double circulation: mammal Pulmocutaneous circuit Pulmonary circuit Gill capillaries Lung and skin capillaries Lung capillaries Artery Heart: Atrium (A) A A A A Ventricle (V) V V Left Right Left Right Vein V Systemic capillaries Systemic capillaries Figure 34.4 Generalized circulatory schemes of vertebrates Body capillaries Systemic circuit Systemic circuit Key Oxygen-rich blood Oxygen-poor blood 13

Interstitial fluid Blood capillary Adenoid Tonsils Lymphatic vessels Figure 34.12 Interstitial fluid Blood capillary Adenoid Tonsils Lymphatic vessels Thymus (immune system) Lymphatic vessel Tissue cells Lymphatic vessel Spleen Lymph nodes Appendix (cecum) Figure 34.12 The human lymphatic system Masses of defensive cells Peyer’s patches (small intestine) Lymph node 14

Cellular elements 45% Number Cell type Functions per L (mm3) of blood Figure 34.13b Cellular elements 45% Number per L (mm3) of blood Cell type Functions Leukocytes (white blood cells) 5,000–10,000 Defense and immunity Lymphocytes Basophils Eosinophils Monocytes Neutrophils Figure 34.13b The composition of mammalian blood (part 2: cellular) Platelets 250,000–400,000 Blood clotting Erythrocytes (red blood cells) 5,000,000–6,000,000 Transport of O2 and some CO2 15

Stem cells (in bone marrow) Lymphoid Myeloid stem cells stem cells Figure 34.14 Stem cells (in bone marrow) Lymphoid stem cells Myeloid stem cells B cells T cells Figure 34.14 Differentiation of blood cells Erythrocytes Basophils Neutrophils Lymphocytes Monocytes Eosinophils Platelets 16

Blood Clotting Coagulation is the formation of a solid clot from liquid blood A cascade of complex reactions converts inactive fibrinogen to fibrin, which forms the framework of a clot A blood clot formed within a blood vessel is called a thrombus and can block blood flow 17

Fibrin clot formation 1 2 3 Collagen fibers Platelet plug Platelet Figure 34.15 1 2 3 Collagen fibers Platelet plug Platelet Fibrin clot Red blood cell 5 m Clotting factors from: Fibrin clot formation Platelets Damaged cells Plasma (factors include calcium, vitamin K) Figure 34.15 Blood clotting Enzymatic cascade Prothrombin Thrombin Fibrinogen Fibrin 18

Angina pectoris is caused by partial blockage of the coronary arteries A heart attack, or myocardial infarction, 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 Angina pectoris is caused by partial blockage of the coronary arteries and may cause chest pain 19

Concept 34.5: Gas exchange occurs across specialized respiratory surfaces Gas exchange is the uptake of molecular O2 from the environment and the discharge of CO2 to the environment 20

Branch of pulmonary artery (oxygen-poor blood) Branch of Figure 34.20 Branch of pulmonary artery (oxygen-poor blood) Branch of pulmonary vein (oxygen-rich blood) Terminal bronchiole Nasal cavity Pharynx Left lung Larynx (Esophagus) Alveoli Trachea Right lung 50 m Capillaries Bronchus Figure 34.20 The mammalian respiratory system Bronchiole Diaphragm (Heart) Dense capillary bed enveloping alveoli (SEM) 21

Control of Breathing in Humans In humans, the main breathing control center consists of neural circuits in the medulla oblongata, near the base of the brain The medulla regulates the rate and depth of breathing in response to pH changes in the cerebrospinal fluid The medulla adjusts breathing rate and depth to match metabolic demands 22

Homeostasis: Blood pH of about 7.4 Stimulus: Rising level of CO2 Figure 34.23-1 Homeostasis: Blood pH of about 7.4 Stimulus: Rising level of CO2 in tissues lowers blood pH. Figure 34.23-1 Homeostatic control of breathing (step 1) 23

Homeostasis: Blood pH of about 7.4 Stimulus: Rising level of CO2 Figure 34.23-2 Homeostasis: Blood pH of about 7.4 Stimulus: Rising level of CO2 in tissues lowers blood pH. Carotid arteries Figure 34.23-2 Homeostatic control of breathing (step 2) Sensor/control center: Aorta Cerebro- spinal fluid Medulla oblongata 24

Homeostasis: Blood pH of about 7.4 Stimulus: Rising level of CO2 Figure 34.23-3 Homeostasis: Blood pH of about 7.4 Stimulus: Rising level of CO2 in tissues lowers blood pH. Response: Signals from medulla to rib muscles and diaphragm increase rate and depth of ventilation. Carotid arteries Figure 34.23-3 Homeostatic control of breathing (step 3) Sensor/control center: Aorta Cerebro- spinal fluid Medulla oblongata 25

Homeostasis: Blood pH of about 7.4 CO2 level decreases. Stimulus: Figure 34.23-4 Homeostasis: Blood pH of about 7.4 CO2 level decreases. Stimulus: Rising level of CO2 in tissues lowers blood pH. Response: Signals from medulla to rib muscles and diaphragm increase rate and depth of ventilation. Carotid arteries Figure 34.23-4 Homeostatic control of breathing (step 4) Sensor/control center: Aorta Cerebro- spinal fluid Medulla oblongata 26

Concept 34.7: Adaptations for gas exchange include pigments that bind and transport gases The metabolic demands of many organisms require that the blood transport large quantities of O2 and CO2 27

Iron Heme Hemoglobin Figure 34.UN01 Figure 34.UN01 In-text figure, hemoglobin, p. 707 Iron Heme Hemoglobin 28

Respiratory Pigments Respiratory pigments circulate in blood or hemolymph and greatly increase the amount of oxygen that is transported A variety of respiratory pigments have evolved among animals These mainly consist of a metal bound to a protein Ex: hemoglobin A single hemoglobin molecule can carry four molecules of O2, one molecule for each iron- containing heme group 29

CO2 produced during cellular respiration lowers blood pH and decreases the affinity of hemoglobin for O2; this is called the Bohr shift Hemoglobin also assists in preventing harmful changes in blood pH and plays a minor role in CO2 transport 30

Carbon Dioxide Transport Most of the CO2 from respiring cells diffuses into the blood and is transported in blood plasma, bound to hemoglobin or as bicarbonate ions (HCO3–) 31

Respiratory Adaptations of Diving Mammals Diving mammals have evolutionary adaptations that allow them to perform extraordinary feats For example, Weddell seals in Antarctica can remain underwater for 20 minutes to an hour For example, elephant seals can dive to 1,500 m and remain underwater for 2 hours These animals have a high blood to body volume ratio 32

Deep-diving air breathers can store large amounts of O2 Oxygen can be stored in their muscles in myoglobin proteins Diving mammals also conserve oxygen by Changing their buoyancy to glide passively Decreasing blood supply to muscles Deriving ATP in muscles from fermentation once oxygen is depleted 33

Exhaled air Inhaled air Alveolar spaces Alveolar epithelial cells CO2 Figure 34.UN03 Exhaled air Inhaled air Alveolar spaces Alveolar epithelial cells CO2 O2 Alveolar capillaries Pulmonary arteries Pulmonary veins Systemic veins Systemic arteries Heart Figure 34.UN03 Summary of key concepts: double circulation Systemic capillaries CO2 O2 Body tissue 34