Lewis/Life - Review of Key Concepts

Review of Key Concepts - Chapter 35

A circulatory system consists of fluid, a network of vessels, and a pump. The fluid delivers nutrients and oxygen to tissues and removes metabolic wastes.
In simple animals, open body cavities give interior structures direct contact with fluids from the environment so that nutrients and oxygen can diffuse into cells and wastes can diffuse out. In more complex animals, a heart pumps the fluid to the body cells. In an open circulatory system, the fluid bathes tissues directly in open spaces before returning to the heart. In a closed circulatory system, the heart pumps the fluid (blood or hemolymph) through a system of vessels to cells and back.
Pigments such as hemoglobin and hemocyanin increase the oxygen-carrying capacity of blood or hemolymph.
Vertebrates have closed circulatory systems that increase in complexity in fishes, amphibians, reptiles, birds, and mammals. A double heart and double circulation that separates oxygenated from deoxygenated blood enables land animals to be active.
Human blood is a mixture of cells and cell fragments (collectively called formed elements), proteins, and molecules that are dissolved or suspended in plasma. The formed elements include red blood cells, white blood cells, and platelets. Red blood cells carry oxygen. White blood cells protect against infection. Platelets break and collect near a wound, releasing chemicals that trigger blood clotting. Blood cells originate in bone marrow.
The heart is the muscular pump that drives the human circulatory system. The heart has two atria that receive blood and two ventricles that propel blood in the body. Heart valves separate the right atrium and right ventricle, the left atrium and left ventricle, and the site where the pulmonary and systemic blood pathways leave the heart. Heart valves ensure one-way blood flow.
The pacemaker or sinoatrial (SA) node, a collection of specialized cardiac muscle cells in the right atrium, sets the heart rate. From there, heartbeat spreads to the atrioventricular (AV) node and then along Purkinje fibers through the ventricles.
The circulatory system leads to and from the lungs and to and from the rest of the body. Blood leaves the heart through the aorta and travels in increasingly narrower arteries and arterioles to the capillaries, where nutrient and waste exchange occur. Blood flows from the capillaries to venules and then to veins, and it reenters the heart through the venae cavae. Arteries have thicker, more elastic walls than veins.
The pumping of the heart and constriction of blood vessels produces blood pressure. Systolic pressure is the pressure exerted on blood vessel walls when the ventricles contract. The low point, diastolic pressure, occurs when the ventricles relax.
The circulatory system is controlled to help maintain homeostasis. When the volume of blood entering the heart changes, ventricular contraction changes in response to adjust cardiac output. The autonomic nervous system, under the influence of the brain's vasomotor center, speeds or slows heart rate and dilates or constricts blood vessels in a way that adjusts blood pressure.
The lymphatic system is a network of vessels that collect fluid from the body's tissues, purify it, and return it to the blood. Lymph nodes filter lymph, and the spleen, thymus, and possibly the tonsils manufacture lymphocytes. The blood and lymphatic systems continually supply tissues with nutrients and oxygen and remove or destroy wastes.