Chapter 42 - Circulatory System

- Gastrovascular cavity - Open and closed circulatory systems

- Cnidarians, flat worms - central cavity for digestion and circulation - single opening - thin layer of cells, nutrients / gas diffuse between cell layers

- Heart: contract to sinuses; relax - out of sinuses - hemolymph - circulatory fluid - vessels pump to sinuses - lower hydrostatic pressure - requires less energy to maintain - invertebrates

- heart (may be more than 1) - circulatory fluid - blood - vessels keep blood separate from organs - higher hydrostatic pressure - requires more energy - more effective delivery of oxygen and nutrients - regulate blood better to organs - annelids, cephalopods, vertebrates

- heart: atria - receive blood entering heart; ventricles - pump blood out of heart - Vessels: veins: portal veins (serve capillary beds in organs); arteries; capillaries - higher metablic rate = more complex circulatory system

- bony fishes, rays, sharks - 2 chambered heart - blood passes through heart once, into atria, transferred to ventricle, out to gills, out to body - through 2 sets of capillary beds, lowers blood pressure - slow rate of circulation

- amphibians, reptiles, mammals - more than 2 chambers, separate left / right - 2 circuits - pulmonary / pulmoncutaneous circuit: out from heart to gas exchange surface; No O₂ initially - systemic circuit: out from heart to rest of body; has O₂

- heart: 3 chambers - 1 atria, 2 ventricles w/ ridge to divide blood - in water shunts blood from lungs to skin to gas exchange

- heart 3 chambers - septum dividing ventricle

- heart 4 chambers - 2 atria, 2 ventricles - left side: oxygen; right side: no oxygen - key adaptation to endothermic life

- Cardiac cycle - 1 complete sequence of pumping and filling - systole - contraction phase - diastole - relaxation phase - cardiac output - volume of blood each ventricle pumps in minute (average 5 L/min) - heart rate - rate of contraction - stroke volume - amount of blood in a single contraction ( avg 70mL)

- Sinoatrial Node (SA) - pacemaker: autorhythmic cells in right atria - Atrioventricular Node (AV): autorhythmic cells in wall between left/right atria; relay point of ventricles - usually controlled by sympathetic (speed up) and parasympathetic (slows down) nerves - can be controlled by hormones when necessary: epinephrine - can be controlled by temperature: 1^oC increases heart rate 10 beats

- heart contraction makes blood pressure - normal = systole/diastole = 120/70 - fluctuates: oscillation (during each cardiac cycle); long term (response to signals that change state of smooth muscle)

- nervous and hormonal response - vascoconstriction - arteriole walls contract, increase pressure - vasodilation - arteriole walls relax, lower pressure - nitric oxide - vasodilation / endothelin - vasoconstriction

- tiny vessel among the capillaries - carry lymph (fluid after it leaves circulatory system) - lymph nodes - help filter lymph before it is returned to circulatory system - ~85% fluid returned to circulatory system through large vessels at base of neck