Circulation and Gas Exchange

Trading Places Occurs across a moist cell membrane Must be dissolved in water to enter the cell membrane (osmosis) May need internal transport if cells are isolated Animals gain oxygen and nutrients while shedding carbon dioxide and wastes

Trading Places Diffusion too slow time of diffusion is proportional to the square distance the chemical must travel Two Solutions  Body size and shape keep many or all cells in direct contact with the environment Circulation reduces the distance a substance must diffuse to enter or leave a cell Fluid is moved between each cell’s immediate surroundings andthe tissues where exchange with the environment occurs

Gastrovascular Cavities Cnidarians and Platyhelminthes No specific internal transport (circulatory) system Functions in digestion and distribution of nutrients Gastrodermal cells have direct access to nutrients nutrients only have short distance to diffuse

General Properties of Circulatory Systems 3 basic components Heart A muscular pump Circulatory fluid Set of interconnecting vessels

Open Circulatory System Hemolymph bathes the internal organs directly while moving through sinuses Circulation results from contraction of the dorsal vessel (heart) and body movements Relaxation of the “heart” draws the blood back into the ostia (pores) Not energy expensive Arthropods and most mollusks

Closed Circulatory System Blood is confined to vessels and is distinct from the interstitial fluid Heart pumps blood into larger vessels Major vessels branch In organs, nutrients are exchanged through capillaries b/w blood and interstitial fluid Effective delivery of O2 Annelids, squids, octopus, vertebrates

Organization of Vertebrate Circulatory Systems Cardiovascular system Arteries  Arterioles  Capillaries  Venules  Veins Capillary beds Networks of capillaries that infiltrate every tissue

Organization of Vertebrate Circulatory Systems Heart has at least 2 chambers Atria Receives the blood Ventricle Pumping out blood

Organization of Vertebrate Circulatory Systems Single Circulation Blood only passes through the heart once per circuit Double Circulation Blood passes through two circuits Pulmonary circuit Systemic circuit Pulmocutaneous circuit Capillaries in both skin & lungs

Double Circulation in Vertebrates

Mammalian Circulation RV contracts  blood to lungs via pulmonary arteries Blood exchanges O2 and CO2 in the capillary beds of the lungs Pulmonary veins  LA  bicuspid  LV pumps blood into the systemic circuit via the aorta First 2 branches of the aorta are coronary arteries to supply heart muscle Diffusion between capillaries from blood to tissues and tissues to blood Capillaries join venules  veins  superior/inferior vena cava  RA  tricuspid valve  RV

Mammalian Heart and Circulation

Mammalian Heart…a closer look Cardiac cycle Complete sequence of contraction and relaxation Systole heart contracts and pumps the blood Diastole heart relaxes and heart fills with blood

Mammalian Heart…a closer look Cardiac output Volume of blood each ventricle pumps per minute Average is 5 L/min Determined by two factors Heart rate The number of heartbeats per minute Stroke volume Amount of blood pumped by a ventricle in a single contraction Average in a human is 70 mL

Mammalian Heart…a closer look Valves prevent backflow of blood Atrioventricular valves (between atria and ventricles) Bicuspid and tricuspid Semilunar valves (between ventricles and arteries) Aortic and pulmonary Heart Murmur defect in one or more of the valves that allows backflow to occur

Maintaining the Heart’s Rhythmic Beat Myogenic (autorhythmic) cells self-excitable Sinoatrial node (SA node) pacemaker Cluster of cells that controls the rhythm contracts and stimulates the AV node can be influenced by outside forces Atrioventricular node Delay of 0.1 second before stimulating specialized muscle fibers called bundle branches and Purkinje fibers

Blood Vessel Structure and Function Lumen lined with endothelium Smooth to minimize friction

Blood Flow Velocity Blood slows as it moves from arteries to arterioles to capillaries Total cross sectional area is much greater in capillary beds

Blood Pressure

Blood Pressure Hydrostatic force that blood exerts against a vessel wall Pressure greater in arteries and during systole Systolic top # Arterial blood pressure is highest when the heart contracts during ventricular systole Diastolic bottom #

A sphygmomanometer, an inflatable cuff attached to a pressure gauge, measures blood pressure fluctuations in the brachial artery of the arm over the cardiac cycle. The arterial blood pressure of a healthy human oscillates between about 120 mm Hg at systole and 70 mm Hg at diastole.

Blood Pressure Regulation Physical/emotional stress triggers nervous and hormonal responses Nitric Oxide Major inducer of vasodilation Endothelin Major inducer of vasoconstriction

Blood Pressure and Gravity Gravity is a major influence Return of venous blood to heart – Rhythmic contractions of smooth muscle Contraction of skeletal muscles Change in pressure in thoracic cavity

Capillary Function Only 5-10% of capillaries have blood in them at any one given time Each tissue has so many capillaries that tissues have a blood supply all of the time

Capillary Function Fluid exchange b/w capillaries and interstitial fluid Endocytosis and exocytosis Simple diffusion Blood pressure drives fluids out of capillaries Presence of blood proteins pulls fluid back in

Fluid Return by Lymphatic System Lose 4-8 L of fluid from capillaries to tissues daily Return to the blood via the lymphatic system Fluid lost by capillaries  lymph Lymph nodes surround lymph vessels Filter the lymph and house cells that attack viruses and bacteria

Blood

Cellular Elements Erythrocytes (red blood cells) Oxygen transport Biconcave disks Lack nuclei Contain hemoglobin Iron containing protein that transports the O2 Sickle cell anemia

Cellular Elements Leukocytes (white blood cells) 5 major types Fight infection Phagocytic Develop specialized B cells and T cells to mount immune responses against foreign substances Thrombocytes (platelets) cellular fragments Structural and molecular functions in blood clotting

Blood Clotting

Stem Cells and Replacement of Cellular Elements Multipotent; dedicated to replenishing body’s blood cell population Erythropoietin (EPO) Hormone from kidney Stimulates RBC production Negative feedback

Cardiovascular Disease Cholesterol metabolism Low Density Lipoprotein (LDL) Delivers cholesterol to cells for membrane production High Density Lipoprotein (HDL) Scavenges extra cholesterol for return to the liver Inflammation

Cardiovascular Diseases Atherosclerosis chronic cardiovascular disease characterized by plaques that develop on the inner walls of arteries and narrow the width of the vessel Thrombus a blood clot that blocks a major vessel embolus – moving clot

Cardiovascular Diseases Ateriosclerosis degenerative condition of the arteries where plaque hardens Hypertension high blood pressure may promote atherosclerosis

Cardiovascular Diseases Heart attack death of cardiac muscle resulting from prolonged blockage of one or more coronary arteries

Cardiovascular Diseases Stroke death of nervous tissue in the brain often resulting from blockage of arteries in the brain