1. Chapter 42 – Circulation and Gas Exchange

2. Circulatory system evolution
Gastrovascular cavity: cnidarians and flatworms
Open circulatory: arthropods and most mollusks, organs are bathed in hemolymph (blood & interstitial fluid) in a central cavity, one or more hearts pump blood into sinuses (spaces surrounding organs) where chemical exchange occurs
Closed circulatory: blood confined to vessels
Cardiovascular system: in vertebrates contains heart (atria/ventricles), blood vessels (arteries, arterioles, capillary beds, venules, veins), and blood (circulatory fluid)

3. Circulatory system evolution (cont.)
Fish: 2-chambered heart; single circuit of blood flow
Amphibians: 3-chambered heart; 2 circuits of blood flow- pulmocutaneous (lungs and skin); systemic (everything else)
Reptiles: 3-chambered heart, but septum partially divides the single ventricle
Mammals and Birds: 4-chambered heart; double circulation with 2 circuits – pulmonary (lungs) and systemic; complete separation between oxygen-rich and oxygen poor blood

4. Mammals: double circulation
The right ventricle (1) pumps blood to the lungs via the pulmonary arteries (2)
Blood flows through the capillary beds (3) in the lungs, loading O2 and unloading CO2
Oxygen rich blood returns to the heart via the pulmonary veins to the left atrium (4); then to the left ventricle (5) which pumps blood to the body via the aorta (6)
Oxygen rich blood reaches the capillary beds in the head and forelimbs (7), then the abdominal organs and hind limbs (8) where gas exchange occurs
Blood from the head and forelimbs returns to the heart via the superior vena cava (9) while blood from the abdomen and hind limbs returns via the inferior vena cava (10)
The 2 vena cava dump their blood into the right atrium (11)

5. Double Circulation

6. Mammalian Heart – a closer look
2 atria, 2 ventricles
4 different valves – prevent the backflow of blood and keep it moving in the right direction
2 semilunar valves between ventricles and aorta/pulmonary arteries
2 atrioventricular valves between atria and ventricles

7. The Cardiac Cycle
Cardiac cycle: sequence of filling and pumping (in average human at rest takes 0.8 seconds)
Systole- contraction
Diastole- relaxation
Cardiac output: volume of blood per minute
Heart rate- number of beats per minute
Stroke volume- amount of blood pumped with each contraction
Pulse: rhythmic stretching of arteries by heart contraction

8. The Heartbeat
Sinoatrial (SA) node (“pacemaker”): sets rate and timing of cardiac contraction by generating electrical signals, located in the wall of the right atrium
Atrioventricular (AV) node: relay point (0.1 second delay) spreading impulse to walls of ventricles, located in the wall between the right atrium and ventricle
Electrocardiogram (ECG or EKG)

9. Blood vessel structural differences
Capillaries: endothelium; basement membrane
Arteries: thick connective tissue; thick smooth muscle; endothelium; basement membrane
Veins: thin connective tissue; thin smooth muscle; endothelium; basement membrane

10. The lymphatic system
Lymphatic system: system of vessels and lymph nodes, separate from the circulatory system, that returns fluid and protein to blood
Lymph: colorless fluid, derived from interstitial fluid
Lymph nodes: filter lymph and help attack viruses and bacteria
Helps body defend against infection, regulates protein volume/concentration in blood, and transports fats from digestive tract to circulatory system

11. Blood
Plasma: liquid matrix of blood in which cells are suspended (90%water)
Erythrocytes (RBCs): transport O2 via hemoglobin
Leukocytes (WBCs): defense and immunity, characterized by nuclei
Platelets (thrombocytes): clotting

12. Differentiation of blood cells
Stem cells: pluripotent cells in the red marrow of bones (particularly in the ribs, vertebrae, sternum, and pelvis)
Pluripotent means these cells have the ability to differentiate into any type of blood cell
Erythropoietin – hormone produced in kidneys when tissues not getting enough O2, stimulates production of more erythrocytes

13. Blood Clotting
Blood clotting: fibrinogen (inactive)/ fibrin (active) aggregates into threads to form a clot
Hemophilia – disease characterized by excessive bleeding
Thrombus (clot) – clotting occurs within a blood vessel restricting blood flow, associated with cardiovascular disease

14. Cardiovascular disease
Cardiovascular disease (>50% of all deaths in US), diseases of the heart and blood vessels
Heart attack- death of cardiac tissue due to coronary blockage
Stroke- death of nervous tissue in brain due to arterial blockage
Atherosclerosis: arterial plaque deposits, narrows arteries
Plaque: consist mostly of fibrous connective tissue and muscle cells infiltrated with lipids (cholesterol)
Hypertension: high blood pressure, can promote atherosclerosis
Low-density lipoproteins or LDLs: “bad cholesterol”
High-density lipoproteins or HDLs: “good cholesterol”

15. Gas exchange The uptake of O2 and the discharge of CO2
Aquatic: gills, ventilation (increasing the flow of respiratory medium over the respiratory surface), countercurrent exchange
Terrestrial: tracheal systems (air tubes) and lungs

16. Mammalian respiratory systems
Larynx (upper part of respiratory tract)
Vocal cords (sound production)
Trachea (windpipe)
Bronchi (two tubes to lungs)
Bronchioles
Alveoli (air sacs)
Diaphragm (breathing muscle)

17. Breathing Positive pressure breathing: pushes air into lungs (frog)
Negative pressure breathing: pulls air into lungs (mammals)
Inhalation: diaphragm contraction; Exhalation: diaphragm relaxation
Tidal volume: amount of air inhaled and exhaled with each breath (500ml)
Vital capacity: maximum tidal volume during forced breathing (4L)
Regulation: CO2 concentration in blood (medulla oblongata)

18. Respiratory pigments: gas transport
Oxygen transport-
Hemocyanin: found in hemolymph of arthropods and mollusks (Cu)
Hemoglobin: vertebrates (Fe)
Carbon dioxide transport-
Blood plasma (7%)
Hemoglobin (23%)
Bicarbonate ions (70%)
Deep-diving air-breathers-
Myoglobin: oxygen storing protein