BIO - 42.1.2.3

Circulation and Gas Exchange

• Every organism must exchange substances with its environment.
• Exchanges ultimately occur at the cellular level by crossing the plasma membrane.
• Small molecules can move between cells and their surroundings by diffusion.
• Diffusion, random thermal motion, is only efficient over small distances because the time it takes to diffuse is proportional to the square of the distance.
• Specialized structures mediate gas exchange with the environment, such as lungs or gills.
• Vessels enable circulation throughout the body, specifically wide, and thick-walled ones.
• Networks of highly branched, thin-walled vessels maximize exchange surface area.
• A pump such as the heart drives the flow of fluid.
• The heart and all blood vessels make up the cardiovascular system.

Body Plans

• A simple body plan means many or all cells are in direct contact with the environment and are small or thin.
• The Circulatory system is functionally linked to the exchange of gases with the environment and with body cells.
• Some animals lack a circulatory system.
• Cnidarians have elaborate gastrovascular cavities.
• Gastrovascular cavities function in both digestion and distribution of substances throughout the body.
• The body wall that encloses the gastrovascular cavity is only two cells thick.
• Flatworms have a gastrovascular cavity and a flat body minimizing diffusion distances.

Open and Closed Circulatory Systems

• A circulatory system has:
• Circulatory fluid.
• A set of interconnecting vessels.
• A muscular pump, the heart.
• The circulatory system connects the fluid surrounding cells with the organs that exchange gases, absorb nutrients, and dispose of wastes.
• Circulatory systems can be open or closed.
• Open circulatory systems have circulatory fluid called hemolymph that bathes the organs directly, such as insects, arthropods, and some mollusks.
• Closed circulatory systems have blood confined to vessels and district from the interstitial fluid, such as annelids, cephalopods, and vertebrates.
• Both open and closed circulatory systems offer evolutionary advantages.
• Open systems allow use of less energy required than what is needed for closed systems.
• Closed systems allow organisms to grow larger and be more active due to effective delivery of oxygen and nutrients and regulate blood distribution to different organs.

Organization of Vertebrate Circulatory Systems

• Humans and other vertebrates have a closed circulatory system called the cardiovascular system that includes the heart and blood vessels.
• Arteries branch into arterioles and carry blood away from the heart to capillaries.
• Networks of capillaries called capillary beds are the sites of chemical exchange between the blood and interstitial fluid.
• Venules converge into veins and return blood from capillaries to the heart.
• Arteries and veins are distinguished by the direction of blood flow, not which contains oxygen.
• Vertebrate hearts contain two or more chambers.
• Blood enters atria and pumped out through ventricles.
• The number of chambers and extent to which they are separated from one another varies greatly among vertebrates.

Circulation

• Sharks, rays, and bony fishes have single circulation with a two-chambered heart.
• In single circulation, blood leaving the heart passes through two capillary beds before returning.
• Amphibians, reptiles, and mammals have double circulation.
• In double circulation oxygen-poor blood is pumped from the right side of the heart in one circuit, and oxygen-rich blood is pumped from the left side of the heart in a separate circuit. – Oxygen-poor blood flows through the pulmonary circuit to pick up oxygen through the lungs.
• Oxygen-rich blood delivers oxygen through the systemic circuit.
• Double circulation maintains higher blood pressure in the organs than single circulation.
• Some vertebrates with double circulation are intermittent breathers, may pass long periods without gas exchange, or use gas exchange from another tissue.
• Amphibians have a 3 chambered heart with two artria and one ventricle.
• A ridge in the ventricle diverts most of the oxygen-rich blood into the systemic circuit, and most oxygen-poor blood into the pulmocutaneous circuit.
• When underwater, blood flow to the lungs is nearly shut off.
• Turtles, snakes, and lizards have a three-chambered heart: two atria and one ventricle, partially divided by an incomplete septum.
• In alligators, caimans, and other crocodilians, a septum divides the ventricles, but pulmonary and systemic circuits connect where arteries exit.
• Mammals and birds have a four-chambered heart with two atria and two ventricles.
• The left side of the heart pumps and receives only oxygen-rich blood, while the right side receives and pumps only oxygen-poor blood.
• Mammals and birds are endotherms, requiring more O₂ than ectotherms.
• The mammalian cardiovascular system meets the body's continuous demand for O₂.

Mammalian Circulation

• Contraction of the right ventricle pumps blood to the lungs via the pulmonary arteries. The blood flows through capillary beds in the left and right lungs and loads O2 and unloads CO₂.
• Oxygen-rich blood returns from the lungs via the pulmonary veins to the left atrium of the heart.
• Oxygen-rich blood flows into the left ventricle.
• Blood leaves the left ventricle via the aorta, which conveys blood to arteries throughout the body.
• First branches are the coronary arteries, supplying the heart muscle.
• O₂ diffuses from blood to tissues and CO₂ diffuses from tissues to blood.
• Blood returns to the heart through the superior vena cava (blood from head, neck, and forelimbs) and inferior vena cava (blood from trunk and hind limbs)

Heart Anatomy

• The human heart is about the size of a clenched fist.
• It consists mainly of cardiac muscle.
• The two atria have relatively thin walls and serve as collection chambers for blood returning to the heart.
• The ventricles have thicker walls and contract much more forcefully.
• The mammalian heart wall consists of three layers: epicardium, myocardium, and endocardium.
• The heart contracts and relaxes in a rhythmic cycle called the cardiac cycle.
• The contraction or putting phase is called systole.
• The relaxation filling phase is called diastole.
• Heart rate (pulse) is the number of beats per minute.
• Stroke volume is the amount of blood pumped in a single contraction.
• Cardiac output is the volume of blood pumped into the systemic circulation per minute and depends on both rates and stroke volume.
• Four valves prevent the backflow of blood in the heart.
• Atrioventricular (AV) valves tricuspid and mitral separate each atrium and ventricle
• semilunar valves aortic and pulmonic control blood flow to the aorta and the pulmonary artery.
• Defective valves can cause heart murmurs from backflow of the blood.

Rhythmic Heart Beat

• Some cardiac muscle cells are autorhythmic, meaning they contract without any signal from the nervous system.
• Impulses that travel during the cardiac cycle can be recorded as an electrocardiogram (ECG or EKG).
• The sinoatrial (SA) node, or pacemaker, sets the rate and timing at which cardiac muscle cells contract.
• Impulses from the S A node travel to the atrioventricular (AV).
• Here, the impulses are delayed and then travel to the Purkinje fibers, causing the ventricles to contract.
• The pacemaker is regulated by two portions of the system, the sympathetic fight or flight and the parasympathetic rest and digest divisions.
• The sympathetic speeds up the pacemaker.
• The parasympathetic slows down the pacemaker.
• The pacemaker by regulated by hormones and temperature.

Blood Vessel Structure

• All blood vessels contain a central lumen lined with an epithelial layer that lines blood vessels
• This endothelium is smooth and minimizes resistance.
• Arteries and veins both have an endothelium, smooth muscle and collective nerve tissue.
• Arteries have thick elastic walls to accommodate the high pressure of blood pumped from the heart.
• Veins convey blood back to heart at lower pressure so they do not thick walls.
• Unlike Arteries, veins contains valves to maintain unidirectional blood flow.
• Capillaries are slightly wider than a red blood cell.
• Capillaries have walls, the endothelium plus its basal lamina to facilitate the exchange of materials.

Blood Flow

• Physical laws governing movement of fluids affect blood flow and blood pressure.
• Blood slows down as it moves from the arteries to arterioles to the narrow caplilaries.
• This is a result of high resistence.
• Velocity of blood flow is slowest in capillary beds as a result of high resitence.
• Blood flow capillaries is slow for materials to exchange.
• As blood enters venules and veins, the flow speeds up as total cross-srectional area decreases.
• Blood flows from areas of higher pressure to lower pressure.
• Blood pressure is force exerted in all directions, including against the walls of blood pressure.
• The recoil of elastic plays a role in maintain blood pressure.
• Resistance blood flow in the diameters of tiny capalliare dissipate pressure.
• Systolic pressure is the pressure arteries arteries during ventricular systole.
• Dystolic pressure is pressure arteries during dyastole.
• Pulse is the rythmic bulging with each heartbeat.
• Homeostatic mechanisms regulate blood pressure.

Blood Pressure Regulation

• Homeostatic mechanisms regulate arterial blood pressire by altering the diammeter or arterioles.
• Vasoconstriction is the narrow of arterioles walls and increase blood pressure.
• Vasodilation is the increase in pressure and causes blood pressure to fall.
• Nitric Oxide(NO) is inducer of vasodilation.
• The peptide endothelin is an inducer vasoconstriction.
• Vasoconstriction and vasodilation are coupled with blood pressure.

Misc.

• Blood pressure is measured in arteries.
• Humans have a blood pressure of about 120mm Hg at systemole ,70mm Hg.
• Gravity has a significant effect.
• Fainting is a lack of flow to the head.
• Animals with long necks a high systemolic blood pressure.
• Back flow is prevented by the 1 way values.
• Smooth muscles causes venule contractions.
• Capialary functions is 5-10 percent given time.
• The 5-10 percent in filled.
• Blood flow is controled by neves like horomones.
• Two mechanisms regulation ,constriction or dilation for blood flow .
• pre capacity for the blood vessel the fluids draw.
• net movement of the blood inter fluid does fluid return in is done be lymphatic system system.
• lymphatic returns capalories called and drains the neck.
• there is a prevent in vessels that prevant back flow.
• edem a is to the lymph.
• lmyph are for lyhmphs body.
• while is fighting infections .