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Circulation 1 (Animals without a Circulatory System (gastrovascular cavity…
Circulation 1
Animals without a Circulatory System
gastrovascular cavity controls distribution of nutrients across body
need a very simple body plan
get by without circulation
Open vs Closed Circulatory System
Closed
Exchange of nutrients between blood and interstitial fluid, then interstitial fluid and organs (and vice versa)
Efficient delivery of O2 and nutrients
Heart(s) pumps blood through vessels that branch and infiltrate organs
no longer direct contact between blood and organs
pumped at a much higher pressure
Annelids, cephalopods, and vertebrates
Blood contained to vessels (never leaves arteries, veins, or capillaries)
Open
Heart relaxes--> hemolymph is pushed through pores that pores that close when the heart contracts. Relaxes pushes through pores, contraction pulls back to heart
Less energetically costly
Hemolymph has direct exchange of nutrients with body cells
Gas exchange completely separate from circulatory system in insects (through trachea)
Heart pumps hemolymph through circulatory vessels into spaces around organs (body cavity)
Arthropods and some molluscs have open systems
Single vs Double Circulation
Double
Pulmonary
Net diffusion of O2 into blood and CO2 out occurs
Blood returns to left side of heart to complete systemic circuit
Right side of heart pumps oxygen poor blood to capillary beds of gas exchange organ (lungs)
Two circuits of blood flow (pulmonary and systemic)
Systemic
O2 exchange into organs and CO2 into blood
Oxygen poor blood returns to right side of heart, completing the circuit
Left side of heart pumps oxygen-rich blood to body for gas and nutrient exchange for the rest of the body
Amphibians, reptiles, and mammals
Single
Blood entering the heart collects in atrium before entering ventricle for recirculation
Heart consists of 2 chambers: one ventricle(leaves) and one atrium(enters)
Contraction of ventricle pumps blood to capillary beds in the gills, net diffusion of O2 into blood and CO2 out of blood
Blood travels through body and back to heart in single circuit loop
Capillaries converge into vessels that carry blood around body and complete gas exchange with organs
In sharks, rays, and some bony fishes
Cardiac Circuit
Cycle
Atrial systole and ventricular diastole
forces all remaining blood into relaxed ventricle
atrial contracts
Atrial diastole and ventricular systole
eg pulmonary artery and aortas
Ventricles contract to push blood into large arteries
Atrial and ventricular diastole
naturally flows through heart for about .4 seconds
blood returns from large veins to atria, then to ventricles
Contraction = systole, relaxation = diastole