Chapter 42 Circulation and Gas Exchange PDF

 Chapter 42 Circulation and Gas Exchange Instructor: Erin Heine, PhD Lecture Presentations...

 Chapter 42 Circulation and Gas Exchange Instructor: Erin Heine, PhD Lecture Presentations by Nicole Tunbridge and © 2021 Pearson Education, Inc. Kathleen Fitzpatrick Figure 42.1b CONCEPT 42.1: Circulatory systems link exchange surfaces with cells throughout the body 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  Two options for body plan: Simple body plan, many or all cells are in direct contact with the environment (small or thin) The circulatory system is functionally linked to the exchange of gases with the environment and with body cells (most animals) Gastrovascular Cavities Some animals lack a circulatory system Cnidarians have elaborate gastrovascular cavities These 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 that minimizes diffusion distances Open and Closed Circulatory Systems A circulatory system has A circulatory fluid A set of interconnecting vessels A muscular pump, the heart The circulatory system connects the fluid that surrounds cells with the organs that exchange gases, absorb nutrients, and dispose of wastes Circulatory systems can be open or closed  Open circulatory system In insects, arthropods, and some molluscs Circulatory fluid called hemolymph bathes the organs directly Closed circulatory system Blood is confined to vessels and is distinct from the interstitial fluid Annelids, cephalopods, and vertebrates  Both open and closed circulatory systems offer evolutionary advantages Open systems allow organisms to use less energy than needed in closed systems Closed systems allow organisms to grow larger and be more active due to effective delivery of oxygen and nutrients Closed systems also regulate the distribution of blood to different organs Organization of Vertebrate Circulatory Systems Humans and other vertebrates have a closed circulatory system called the cardiovascular system It includes the heart and blood vessels The three main types of blood vessels: 1. arteries 2. veins 3. capillaries Blood flows only one way in these 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 by O2 content Vertebrate hearts contain two or more chambers Blood enters through atria and is pumped out through ventricles The number of chambers and extent to which they are separated from one another varies greatly among vertebrates Single 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 Double Circulation Amphibians, reptiles, and mammals have double circulation Oxygen-poor blood is pumped from the right side of the heart in one circuit 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 In amphibians, oxygen- poor blood flows through a pulmocutaneous circuit to pick up oxygen through the lungs and skin Oxygen-rich blood delivers oxygen through the systemic circuit Double circulation maintains higher blood pressure in the organs than does single circulation Evolutionary Variation in Double Circulation Some vertebrates with double circulation are intermittent breathers may pass long periods without gas exchange or relying on gas exchange from another tissue (skin) Amphibians have a three-chambered heart: two atria 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 the heart CONCEPT 42.2: Coordinated cycles of heart contraction drive double circulation in mammals 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 and require more O2 than ectotherms The mammalian cardiovascular system meets the body’s continuous demand for O2 Mammalian Circulation Contraction of the right ventricle (1) pumps blood to the lungs (3) via the pulmonary arteries (2) 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 (4) of the heart  Oxygen-rich blood flows into the left ventricle (5) Blood leaves the left ventricle via the aorta (6), which conveys blood to arteries leading throughout the body (7,8) The first branches are the coronary arteries, supplying the heart muscle  O2 diffuses from blood to tissues, and C O2 diffuses from tissues to blood  Blood returns to the heart through the superior vena cava(9) (blood from head, neck, and forelimbs) and inferior vena cava(10) (blood from trunk and hind limbs)  The two venae cavae empty their blood into the right atrium (11) from which the oxygen-poor blood flows into the right ventricle (1) The Mammalian Heart: A Closer Look The human heart is about the size of a clenched fist and 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 Animation: Structure of the Human Heart Figure 42.6  The heart contracts and relaxes in a rhythmic cycle called the cardiac cycle The contraction, or pumping, phase is called systole The relaxation, or filling, phase is called diastole Figure 42.7  Heart rate (pulse) = the number of beats per minute Stroke volume = the amount of blood pumped in a single contraction Cardiac output = the volume of blood pumped into the systemic circulation per minute and depends on both the heart rate and stroke volume  Four valves prevent backflow of blood in the heart The atrioventricular (A V) valves (tricuspid and mitral) separate each atrium and ventricle The semilunar valves (aortic and pulmonic) control blood flow to the aorta and the pulmonary artery  The “lub-dup” sound of a heart beat is caused by the recoil of blood against the A V valves (lub) then against the semilunar (dup) valves Backflow of blood through a defective valve causes a heart murmur Maintaining the Heart’s Rhythmic 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 (E C G or E K G) The sinoatrial (S A) 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) node Here, the impulses are delayed and then travel to the Purkinje fibers that make the ventricles contract  The pacemaker is regulated by two portions of the nervous system: the sympathetic (“fight or flight”) and parasympathetic (“rest and digest”) divisions The sympathetic division speeds up the pacemaker The parasympathetic division slows down the pacemaker The pacemaker is also regulated by hormones and temperature Histology of the Heart  The wall of the heart consists of three layers: 1. Epicardium (external layer) 2. Myocardium (middle layer) 3. Endocardium (inner layer)  Lumen of heart Endocardium Purkinje Fibers myocardium CONCEPT 42.3: Patterns of blood pressure and flow reflect the structure and arrangement of blood vessels The vertebrate circulatory system relies on blood vessels that exhibit a close match of structure and function Blood Vessel Structure and Function All blood vessels contain a central lumen lined with an epithelial layer that lines blood vessels This endothelium is smooth and minimizes resistance Blood Vessel Structure and Function Arteries and veins have an endothelium, smooth muscle, and connective vein tissue Arteries have thick, elastic walls to artery accommodate the high pressure of blood pumped from the heart Because veins convey blood back to the heart at a lower pressure, they do not require thick walls Unlike arteries, veins contain valves to maintain unidirectional blood flow Blood Vessel Structure and Function Capillaries are only slightly wider than a red blood cell Capillaries have thin walls, the endothelium plus its basal lamina, to facilitate the exchange of materials Figure 42.9 Blood Flow Velocity Physical laws governing movement of fluids through pipes affect blood flow and blood pressure Blood slows as it moves from arteries to arterioles to the narrow capillaries This is a result of the high resistance and large total cross-sectional area Velocity of blood flow is slowest in the capillary beds as a result of the high resistance and large total cross-sectional area Blood flow in capillaries is necessarily slow for exchange of materials As the blood enters venules and veins, the flow speeds up as the total cross- sectional area decreases Blood Pressure Blood flows from areas of higher pressure to areas of lower pressure Blood pressure is a force exerted in all directions, including against the walls of blood vessels The recoil of elastic arterial walls plays a role in maintaining blood pressure The resistance to blood flow in the narrow diameters of tiny capillaries and arterioles dissipates much of the pressure Changes in Blood Pressure During the Cardiac Cycle Systolic pressure is the pressure in the arteries during ventricular systole; it is the highest pressure in the arteries Diastolic pressure is the pressure in the arteries during diastole (when the ventricles are relaxed); it is lower than systolic pressure A pulse is the rhythmic bulging of artery walls with each heartbeat Regulation of Blood Pressure Homeostatic mechanisms regulate arterial blood pressure by altering the diameter of arterioles Vasoconstriction is the narrowing of arteriole walls; it increases blood pressure Vasodilation is the increase in diameter of the arterioles; it causes blood pressure to fall Regulation of Blood Pressure: Signaling moledules Nitric oxide (N O) is a major inducer of vasodilation The peptide endothelin is a potent inducer of vasoconstriction Vasoconstriction and vasodilation are often coupled to changes in cardiac output that affect blood pressure Blood Pressure and Gravity Blood pressure is generally measured for an artery in the arm at the same height as the heart Blood pressure for a healthy 20-year-old human at rest is about 120 mm Hg at systole and 70 mm Hg at diastole Gravity has a significant effect on blood pressure  Fainting is caused by inadequate blood flow to the head Animals with long necks require a very high systolic pressure to pump blood a great distance against gravity Because blood pressure is low in veins, one-way valves in veins prevent backflow of blood Return of blood is also enhanced by contraction of smooth muscle in venule walls and skeletal muscle contraction Capillary Function Blood flows through only 5–10% of the body’s capillaries at any given time Capillaries in major organs are usually filled to capacity Blood supply varies in many other sites Blood flow is regulated by nerve impulses, hormones, and other chemicals Capillary Function Two mechanisms regulate distribution of blood in capillary beds 1. Constriction or dilation of arterioles that supply capillary beds 2. Precapillary sphincters that control flow of blood between arterioles and venules The site of all of the action - capillaries The exchange of substances between the blood and interstitial fluid takes place across the thin endothelial walls of the capillaries The difference between blood pressure and osmotic pressure drives movement of fluid: The higher osmolarity of blood is always drawing water into the blood from the surrounding tissue Big proteins in blood Blood pressure is pushing fluids out of the capillaries: Higher pressure at arteriole end Lower pressure are venule end Net movement of fluid out of blood into interstitial fluid – where does it go? Fluid Return by the Lymphatic System The lymphatic system returns fluid that leaks out from the capillary beds Fluid lost by capillaries is called lymph The lymphatic system drains into veins in the neck Valves in lymph vessels prevent the backflow of fluid  Edema is swelling caused by disruptions in the flow of lymph Lymph nodes are organs that filter lymph and play an important role in the body’s defense When the body is fighting an infection, lymph nodes become swollen and tender