Circulation

1. Circulation Chapter 23

2. Facilitating Exchanges • Circulatory systems ensure O2, CO2, nutrients, and wastes get to their specific sites in the body • Important for animals to large to survive by diffusion alone • Cnidarians and flatworms have gastrovascular cavities that serve in digestion and distribution • Cells can exchange directly with water surrounding them • Animals with multiple layers of cells need a true circulatory system • Muscular pump (heart) and circulatory fluid (blood)

3. Molecular Exchange • O2 and nutrients must enter cells • CO2 and wastes must exit • Larger organisms have smaller outer surfaces than inner • All cells must be in an aqueous environment • Folds and alternate structures within to facilitate

4. Circulatory Systems • Direct exchange not between blood and body cells • Cells bathed in interstitial fluid that diffusion must pass • Open circulatory system • Many invertebrates including molluscs and all arthropods • Closed circulatory system • Often called a cardiovascular system • Earthworms, squids, octopuses, and vertebrates

5. Open Circulatory System • Fluid pumped through open-ended vessels out to cells • No distinction between blood and interstitial fluid • Body movements circulate fluid to allow exchange • Heart with pores that allows fluid return and prevents backflow • Respiratory exchange through tracheal system

6. Cardiovascular System • Blood confined to vessels • Separate from interstitial fluid • 3 kinds of vessels • Arteries (red) blood Away from heart • Veins (blue) blood to heart • Capillaries transport blood between the 2 • Heart with atrium and ventricle pumps blood to body cells • Arteries to arterioles to capillaries in capillary beds to venules to veins back to heart

7. Cardiovascular System Evolution • Single Circuit pumps blood to capillaries which diffuses to body tissues • Double circulation pumps blood a second time after losing pressure in the capillaries • Pulmonary circuit carries blood between the heart and lungs • Systemic circuit carries blood between the heart and rest of the body

8. Single Circuit • 2 chambered heart • Blood to gill capillaries where pressure is reduced considerably • Flow maintained by organism’s movements • Pressure to low for complex circulation

9. Double Circulation • Amphibians have 3 chambered heart • Pulmocutaneous circuit because gas exchange in lungs and across skin • Mixing occurs, but most blood to proper location • Birds and mammals have 4 chambered hearts • Supports higher metabolic rates • Different ancestral evolution so demonstrates convergent evolution

10. Human Cardiovascular System • R. ventricle to lungs via pulmonary arteries • CO2 and O2 exchange • Pulmonary veins back to L. atria to L. ventricle • Through aorta to systemic circuit • Branches to upper body and lower body separately • O2 poor blood back to R. ventricle via S. and I. vena cava (heart to lungs to heart to body tissue to heart)

11. Cardiac Cycle • Sequence of pumping and filling of the heart • Heart pumps O2 poor blood to lungs and O2 rich blood to body • Diastole=entire heart relaxed, ventricles fill with blood • Systole=atria then ventricle contraction • Left stronger because blood to body, but volume is same in both sides=cardiac output

12. The Beating Heart • Heart rate and cardiac rhythm can vary • Age and fitness can effect • Both increase with increasing activity levels • Blood flow controlled by internal valves • Open when pushed from behind and close when pushed from in front • Heart beat sounds = lub-dub • AV and semilunar valves’ closing respectively • Heart murmur sound when blood squirts backwards

13. Beating to its Own Rhythm • Cardiac muscle tissue cycle without neural input • Pacemaker sets the contraction rate • AV node coordinates, delay to ventricle • Electric shock can be used to reset pacemaker during a heart attack • Artificial pacemaker when self system fails

14. Cardiovascular disease • Disorders of heart and blood vessels • Heart attack is the damage or death of cardiac tissue from blockage of coronary arteries • Stroke is death of brain tissue from vessel blockage to the head • Most caused by arterosclerosis, or plaque build up, which narrows vessel openings • Clots trapped or blood flow is slowed • Anti-inflammatories, angioplasty, and clot-dissolving • Tendency to be inherited, but smoking can increase while exercise and low cholesterol diets can decrease

15. Blood Vessel Functions • Must connect with all body tissues • Remarkable length, close enough for diffusion to occur • Into interstitial fluid first • Transport blood, nutrients, and wastes to disposal organs • Role in homeostasis and the environment of cells

16. Blood Vessel Structure • Capillaries • Thin walls of single layer epithelial tissue • Wrapped in a basal lamina • Larger structures • Same epithelial structure, but reinforced • Supported by elastic fiber layer and smooth muscle • Arteries and arterioles • Thicker and sturdier to accommodate high pressure from heart • Veins and venules • Blood to heart at lower pressure • One way valves to prevent backflow

17. Blood Flow • Blood pressure is the force blood exerts against vessel walls • Pumped to arteries faster than it can flow = stretching of vessels, detected as pulse • Pressure reduces from arteries to capillaries as resistance from vessel walls decreases • Smaller, but more numerous vessels • Relaxing muscles allows vessel dilation = drop pressure • Pressure almost zero at veins • 1 way valves and muscle to propel back to heart

18. Digestive System Muscle Control • Every part of body has blood supply at all times • Certain areas always full, others are rationed by need • Smooth muscle controls arteriole flow • Precapillary sphincters control • Thoroughfare channel is always open • Relaxed vs. contracted While eating While exercising

19. Capillaries • Only vessels that can allow diffusion between blood and interstitial fluid • Exchange of substances by diffusion (O2 and CO2), carried by endocytosis and released by exocytosis, or leaks in wall (water, sugars, and salts) • Direction of movement depends on osmotic and blood pressure differences • Arteriole end blood pressure drives fluid out of capillary • Venous end blood pressure drops so osmotic drives into • Fluid that leaves one end generally reenters at other • Rest returned via lymphatic system

20. Blood Composition

21. RBC Count • Set number needed for healthy organisms • Broken down and recycled every 3-4 months • Fe returned to bone marrow to form new RBCs • Low RBC count = anemia • Excessive tiredness due to lack of O2 • Most commonly due to low Fe (women more likely); also blood loss, vitamin and mineral deficiency, or cancers • Negative feedback sensitive to O2 • Low O2, kidneys produce erthropoietin (EPO) to stimulate bone marrow production of RBCs • Increased RBC production in individuals at high altitudes • Connections to athletic training, blood doping, and artificial EPO injections

22. Blood Clots • Blood platelets and plasma protein fibrinogen prevent death from minor cuts, enable clotting • Upon damage vessel constricts to reduce blood loss • Platelets adhere to epithelium and form a sticky plug to halt blood loss • Clotting factors released from plug to form reinforced patch • Fibrinogen converted to fibrin which traps other blood cells

23. Stem Cells • Unspecialized cells in red marrow of bones that can differentiate into different blood cells • Lymphoid stem cells produce lymphocytes for immune system • Myeloid stem cells produce RBCs, WBCs, and plaelets • Formed in early embryo and make all blood cells for life

24. Leukemia • Cancer of white blood cells or leukocytes • Protect against infections and cancers • Cells become cancerous, grow uncontrollably, and crowd RBCs and platelets • Severe anemia and impaired clotting results • Usually fatal unless treated • Not all responsive to radiation and chemo • Bone marrow transplant, often from a sibling • Lifelong treatment with drugs to avoid rejection of cells • Can treat infected marrow to remove most cancer cells and re-inject • Umbilical cord blood has potential, but unsuccessful so far