1. Chapters 22-23 Gas Exchange and Circulation

2. Gas exchange Three phases of gas exchange; 1. breathing
2. transport of gases by circulatory system - O2 in, CO2 out
3. cells take up O2 and get rid of CO2
What is the destination of the oxygen?
The mitochondria. All cells need oxygen for cellular respiration

3. Respiratory system – form and function
Since gas exchange occurs by diffusion, the surface area of the respiratory system must be extensive.
Examples-
1. skin breathers – earthworms
2. branched respiratory surfaces – tracheal systems, gills, and lungs

5. Adaptations and environments
Aquatic – water has low O2 content.
How is gas exchange accomplished?
Countercurrent exchange-blood flows in the opposite direction of the water flow.
Why don’t you see terrestrial animals with gills?
They would dry out.
Solution?
Internal respiratory system.

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

8. Structure and function
How does the structure of the alveoli match their function?
Clusters of these air sacs have an enormous surface area – 50 times that of the skin.
Lined with thin epithelial cells lined with capillaries allowing for diffusion of both O2 and CO2 for efficient transport.

9. Transport of gases in the human body
Oxygen and carbon dioxide diffuse down their partial pressure gradients.
What is the transporting vehicle?
Most animals use hemoglobin to transport both O2 and CO2.
How does a human fetus breath?
Capillaries in the umbilical cord exchange gases with the mother’s bloodstream.

10. Circulation system evolution, I
Gastrovascular cavity (cnidarians, flatworms)
Open circulatory - Hemolymph (blood & interstitial fluid). Sinuses (spaces surrounding organs)
Closed circulatory - Blood confined to vessels
Cardiovascular system - heart (atria/ventricles), blood vessels (arteries, arterioles, capillary beds, venules, veins), blood (circulatory fluid)

11. Open vs closed systems

12. Circulation system evolution, II
Fish: 2-chambered heart; single circuit of blood flow
Amphibians: 3-chambered heart; 2 circuits of blood flow- pulmocutaneous (lungs and skin); systemic (some mixing)
Mammals: 4-chambered heart; double circulation; complete separation between oxygen-rich and oxygen poor blood

13. Circulatory system examples

14. Single vs double circulation
What is the difference between single and double circulation?
In fish, the blood travels to the gill capillaries to systemic capillaries before returning to the heart. In land vertebrates, blood is returned to the heart and then pumped a second time between the pulmonary and systemic circuits.
Single vs double circulation

15. Double circulation
From right ventricle to lungs via pulmonary arteries
Capillary beds in lungs to left atrium via pulmonary veins
Left atrium to left ventricle to aorta
Aorta to coronary arteries; then systemic circulation
Back to heart via two venae cavae (superior and inferior); right atrium

16. Blood flow through the human heart

17. The mammalian heart Cardiac cycle: sequence of filling and pumping
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

18. The heartbeat
Sinoatrial (SA) node (“pacemaker”): sets rate and timing of cardiac contraction by generating electrical signals
Atrioventricular (AV) node: relay point (0.1 second delay) spreading impulse to walls of ventricles
Electrocardiogram (ECG or EKG)

19. Cardiovascular disease
Cardiovascular disease (>50% of all deaths)
Heart attack- death of cardiac tissue due to coronary blockage
Stroke- death of nervous tissue in brain due to arterial blockage
Atherosclerosis: arterial plaques deposits
Arteriosclerosis: plaque hardening by calcium deposits
Hypertension: high blood pressure
Hypercholesterolemia: LDL, HDL

20. Structure and function of blood vessels
How does the structure of a capillary relate to its function?
The small diameter and thin walls of the capillary facilitate the exchange of substances between the blood and interstitial fluid.
Structure and function of blood vessels

21. 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

22. BLOOD
Plasma: liquid matrix of blood in which cells are suspended (90% water)
Erythrocytes (RBCs): transport O2 via hemoglobin
Leukocytes (WBCs): defense and immunity
Platelets: clotting
Stem cells: pluripotent cells in the red marrow of bones
Blood clotting: fibrinogen (inactive)/ fibrin (active); hemophilia; thrombus (clot)

24. http://www.hhmi.org/biointeractive/stemc ells/human_emb_dev.html
Stem cells