Circulatory Systems Flashcards
Key Concepts
Circulatory systems transport heat, hormones, respiratory gases, blood cells, platelets, immune system components, nutrients, and waste products.
Open circulatory system: fluid leaves the circulatory system and moves between the cells (arthropods and mollusks).
In this system, the fluid is not contained within vessels, and it directly bathes the tissues and organs.
This direct contact facilitates the exchange of gases and nutrients but is less efficient for transporting substances over long distances.
Closed circulatory systems: fluid is contained in a continuous system of vessels (vertebrates, annelids).
Blood is enclosed in vessels, allowing for more efficient transport and higher blood pressure.
This system supports higher metabolic rates and more complex physiological processes.
Vertebrate Circulatory Systems
Vertebrate circulatory systems evolved from a single circuit (fish) to a double circuit (birds and mammals).
Fish: single circuit; heart pumps blood to gills, then to the rest of the body.
The heart pumps blood to the gills where it picks up oxygen and then circulates to the rest of the body before returning to the heart.
Birds and Mammals: double circuit; pulmonary circuit (heart to lungs and back) and systemic circuit (heart to the rest of the body).
In the pulmonary circuit, blood is pumped from the heart to the lungs, where it picks up oxygen and releases carbon dioxide; it then returns to the heart.
The systemic circuit involves pumping oxygenated blood from the heart to the rest of the body, delivering oxygen and nutrients before returning to the heart.
Amphibians: three-chambered heart; partial separation of pulmonary and systemic circulation.
This allows them to shunt blood away from the lungs when they are not breathing air, such as when they are underwater.
Reptiles: three-chambered hearts (except crocodiles); can bypass the pulmonary circuit when not breathing.
Reptiles have a more efficient circulatory system compared to amphibians, with the ability to bypass the pulmonary circuit when necessary.
Birds and Mammals: four-chamber hearts; completely separate pulmonary and systemic circuits.
The complete separation of oxygenated and deoxygenated blood allows for more efficient oxygen delivery to tissues, supporting higher metabolic rates and activity levels.
SUPER IMPORTANT: Birds and mammals are endothermic, meaning they can regulate their own body temperature. Having completely separate pulmonary and systemic circuits are super important in being endothermic.
Pulmonary and Systemic Circuits
Right atrium: receives blood from the systemic circuit.
Left atrium: receives blood from the pulmonary circuit.
Right ventricle: pumps blood through the pulmonary circuit.
Left ventricle: pumps blood through the systemic circuit.
Heart Valves
Atrioventricular (AV) valves: prevent backflow when ventricles contract.
Right: tricuspid valve
Left: bicuspid or mitral valve
Pulmonary and aortic valves: prevent backflow when ventricles relax.
Heart Function and Cardiac Muscle
Cardiac muscle contracts with a wringing motion; left ventricle walls are thicker.
This specialized contraction helps to efficiently eject blood from the ventricles.
The left ventricle has thicker walls because it needs to generate more force to pump blood throughout the systemic circuit.
Pacemaker cells (SA node) generate rhythmic action potentials.
These cells initiate the electrical signals that trigger each heartbeat, ensuring regular and coordinated contractions.
The location of the SA node is in the right atrium.
Autonomic nervous system controls heart rate.
The sympathetic nervous system increases heart rate, while the parasympathetic nervous system decreases it.
Action potential spreads through gap junctions in the atria, then to the ventricles via the AV node and bundle of His.
This coordinated spread ensures that the atria contract before the ventricles, optimizing blood flow.
Ventricle muscle fibers contract for a longer time due to longer opening of voltage-gated Ca^{2+} channels.
Cardiac Cycle
Systole: ventricles contract.
Diastole: ventricles relax.
Heart sounds are created by heart valves slamming shut.
ECG records events in the cardiac cycle.
Blood Components
Blood: connective tissue (cells in blood plasma).
Hematocrit: percent of blood that is red blood cells (RBCs).
Erythrocytes (RBCs): transport respiratory gases; lack nuclei.
Platelets: initiate blood clotting.
Blood Clotting
Cell damage and platelet activation.
Prothrombin converts to thrombin.
Thrombin cleaves fibrinogen to form fibrin.
Fibrin threads form a mesh.
Blood Vessels
Arteries: collagen and elastin fibers to withstand high blood pressures.
Arterioles: resistance vessels; control blood flow to specific tissues.
Capillaries: thin walls for exchange of materials.
Veins: capacitance vessels; store blood.
Starling’s forces: blood pressure (forces water and solutes out) and osmotic pressure (pulls water back in).
Blood-brain barrier: brain capillaries are not very permeable and are wrapped by glia.
Blood Pressure
Blood pressure is highest in the arteries and decreases continuously.
Systole: ventricular contraction (highest pressure).
Diastole: ventricular relaxation (lowest pressure).
Measured with a sphygmomanometer.
Cardiovascular Diseases
Atherosclerosis: hardening of the arteries; plaque formation.
Coronary thrombosis: thrombus in a coronary artery can lead to a heart attack (myocardial infarction).
Embolus: piece of a thrombus that breaks loose; can cause an embolism (blockage).
Control of Circulation
Autoregulation: local control of blood flow in capillary beds.
Hyperemia: low O2 and high CO2 levels cause smooth muscle to relax.
Cardiovascular control center in the medulla controls heart rate and vessel constriction.
Barore