Chapter 42- Circulation and Gas Exchange

Background The lowest inverts (jellyfish, etc…) have only a gastrovascular cavity where circulation AND digestion take place simultaneously.

Open vs. Closed Open vs. Closed Circulatory System- All have: - Circulatory fluid (blood) - Tubes (blood vessels) - Muscular pump (heart)

Open vs. Closed Open circulation- Insects/Arthropods/Mollusks - Metabolically cheap - Sinuses- Area surrounding the organs - Blood bathes the organs

Open vs. Closed Closed circulation- Blood is contained within vessels (all mammals) - Metabolically expensive - Called cardiovascular system in mammals - Heart  Arteries Arterioles  Capillaries (site of gas exchange)  Venules  Veins  Heart

Open vs. Closed - Fishes- Heart is 2 chambers - Amphibians and Reptiles- 3 chambers - Mammals and Birds- 4 chambers

The Heart - Pathway of blood through heart (and body)

The Heart - Cardiac cycle- The complete sequence of pumping and filling - Contraction- systole - Relaxation- diastole - Valves in the heart prevent backflow - SA Node- Pacemaker of the heart. Receives original signal then passes signal to the AV node, which delays the pulse and then sends it out

Blood Vessels Blood Vessels - Veins have valves to prevent backflow, arteries do not - Arteries are thicker than veins

Blood Vessels - Layers of blood vessels (from the outside to the inside) - Elastic connective tissue - Smooth muscle - Endothelium- Smooth surface for blood to flow over - Capillaries only have a “basement membrane” and an endothelium

Blood Vessels - Normal blood pressure 120 (systole)/70 (diastole) - Fluid is lost through the capillaries, but returns to the circulatory system by entering into the lymphatic system (direct connection to circulatory system)

Blood Blood- Called hemolymph and is a connective tissue - 90% of it is water - pH of 7.4 - Plasma is the fluid that all of the cells are suspended in

Blood - Cells found in blood - Erythrocytes (red blood cells) - Carry oxygen by having hemoglobin proteins - Each hemoglobin has 4 subunits each with a heme group and an associated iron atom. Iron binds to the O2

Blood - Cooperative binding- when one O2 binds, it makes it easier for more O2 to attach and when one O2 leaves, it makes it easier for more O2 to leave - Each erythrocyte can contain up to 250 million hemoglobin molecules and each can carry four O2 molecules = 1 billion O2 molecules per erythrocyte.

- The lower the pH, the lower the affinity to O2 = Bohr Shift - The lower the pH, the lower the affinity to O2 = Bohr Shift. pH lowers when CO2 levels are high (ie: rigorous exercise) and hemoglobin will be more likely to release O2 to the tissue that needs it.

Blood Leukocytes (white blood cells)- Fight infection Platelets- Blood clotting factor

Gas Exchange - Gas exchange (O2 uptake and CO2 release- flow of molecules is because of diffusion) - The “respiratory medium” is the source of O2 - The “respiratory surface” is the location of gas exchange - Water must be present for the gas exchange to occur

Gas Exchange Groups of Animals and Gas Exchange - Worms- Diffusion through skin (reason they are often flat and long) - Aquatic animals- Gills. Countercurrent exchange

- Insects- Tracheal system (air tubes within body)

- Large animals and birds- Lungs - Tidal flow- The volume of air inhaled and then exhaled