Circulatory System

• The heart is divided into four chambers: two atria and two ventricles.
• There is one atrium and one ventricle on the right side and one atrium and one ventricle on the left side.
• The mammalian heart consists of the endocardium, myocardium, and epicardium.
• The endocardium is the inner layer that lines walls of the heart.
• The myocardium is the middle layer of the heart, consisting of heart muscle cells that make up the middle layer and the bulk of the heart wall, which initiates contractions driving the cardiac cycle.
• The epicardium is the outer layer of the heart which prevents excess expansion or movement of the heart.
• The heart is primarily made of a thick muscle layer, called the myocardium, surrounded by membranes.
• One-way valves separate the four chambers of the heart.
• Blood vessels of the coronary system, including the coronary arteries and veins, keep the heart musculature oxygenated.
• For an adult human at rest with a heart rate of about 72 beats per minute, one complete cardiac cycle takes about 0.8 second.
• During all but 0.1 second of the cardiac cycle, the atria are relaxed and are filling with blood returning via the veins.
• The heart contracts and relaxes in a rhythmic cycle.
• When the heart contracts, it pumps blood; when it relaxes, its chambers fill with blood.
• One complete sequence of pumping and filling is referred to as the cardiac cycle.
• The contraction phase of the cardiac cycle is called systole, and the relaxation phase is called diastole.
• Arteries take blood away from the heart.
• If the blockage is in an artery that supplies the heart or brain, the result could be a heart attack or stroke, respectively.
• The only vessels that provide direct access to nearly every cell in the body are the capillaries.
• Veins carry blood away from the heart.
• The tunics of both arteries and veins consist of three layers.
• Mitral valve is present between right atrium and left ventricle.
• It is the valve's job to not let blood go backwards once it has gone through a valve.
• Lymphatic System and Body Immunity involves filtration of fluids from all capillary beds, immune cells standing ready to respond to foreign cells or chemicals, lipid absorption, fluid recovery, and interference with lymphatic drainage can lead to severe edema.
• Lymph is a clear, colorless fluid, similar to plasma but much less protein.
• Lymphoid Tissues and Organs include lymphatic capillaries, lymphatic collecting vessels, lymphatic trunks, and collecting ducts.
• Lymphatic capillaries are closed at one end, tethered to surrounding tissue by protein filaments, and endothelial cells are loosely overlapped, allowing bacteria and cells entrance to lymphatic capillary.
• Lymphatic vessels form a one-way system in which lymph flows only toward the heart.
• Lymphatic capillaries, lymphatic collecting vessels, lymphatic trunks, and collecting ducts course through many lymph nodes.
• Lymphatic trunks drain major portions of body.
• Collecting ducts include right lymphatic duct, which receives lymph from right arm, right side of head and thorax, and empties into right subclavian vein, and thoracic duct, which is larger and longer, begins as a prominent sac in abdomen called the cisterna chyli, receives lymph from below diaphragm, left arm, left side of head, neck and thorax, and empties into left subclavian vein.
• Lymphatic System and Body Immunity involves immunity, lipid absorption, fluid recovery, and interference with lymphatic drainage can lead to severe edema.
• Lymphocytes include T lymphocytes, which mature in thymus and their activation causes immune response and some directly attack and destroy foreign cells, and B lymphocytes, whose activation causes proliferation and differentiation into plasma cells that produce antibodies.
• Macrophages, dendritic cells, and reticular cells are examples of Antigen Presenting Cells.
• In amphibians, reptiles, birds, and mammals, blood flow is directed in two circuits: one through the lungs and back to the heart, which is called pulmonary circulation, and the other throughout the rest of the body and its organs including the brain, which is called systemic circulation.
• In amphibians, gas exchange also occurs through the skin during pulmonary circulation and is referred to as pulmocutaneous circulation.
• This arrangement is called double circulation.
• Fish have a single circuit for blood flow and a two-chambered heart that has only a single atrium and a single ventricle.
• The atrium collects blood that has returned from the body and the ventricle pumps the blood to the gills where gas exchange occurs and the blood is re-oxygenated; this is called gill circulation.
• The blood then continues through the rest of the body before arriving back at the atrium; this is called systemic circulation.
• The unidirectional flow of blood produces a gradient of oxygenated to deoxygenated blood around the fish’s systemic circuit.