Chapter 42 Circulation and Gas Exchange

Overview: Trading with the Environment Every organism must exchange materials with its environment Exchanges ultimately occur at the cellular level

In unicellular organisms, these exchanges occur directly with the environment For most cells making up multicellular organisms, direct exchange with the environment is not possible A salmon’s feathery gills are an example of a specialized exchange system in animals

Concept 42.1: Circulatory systems reflect phylogeny Transport systems connect the organs of exchange with the body cells Most complex animals have internal transport systems that circulate fluid

Invertebrate Circulation The wide range of invertebrate body size and form is paralleled by diversity in circulatory systems

Gastrovascular Cavities Simple animals, such as cnidarians, have a body wall only two cells thick that encloses a gastrovascular cavity This cavity functions in both digestion and distribution of substances throughout the body Some cnidarians, such as jellyfish, have elaborate gastrovascular cavities

LE 42-2 Mouth Radial canal Circular canal 5 cm

Open and Closed Circulatory Systems More complex animals have either open or closed circulatory systems Both systems have three basic components: –A circulatory fluid (blood or hemolymph) –A set of tubes (blood vessels) –A muscular pump (the heart)

LE 42-3 Hemolymph in sinuses surrounding organs Heart Anterior vessel Ostia Tubular heart An open circulatory system. Lateral vessel A closed circulatory system. Auxiliary hearts Ventral vessels Dorsal vessel (main heart) Small branch vessels in each organ Interstitial fluid Heart

Hemolymph in sinuses surrounding organs Heart Anterior vessel Lateral vessel Ostia Tubular heart

In insects, other arthropods, and most molluscs blood bathes the organs directly in an open circulatory system There is no distinction between blood and interstitial fluid, and this general body fluid is more correctly called hemolymph

In a closed circulatory system, blood is confined to vessels and is distinct from the interstitial fluid Closed systems are more efficient at transporting circulatory fluids to tissues and cells –Oxygen travels via hemoglobin on blood cells

Survey of Vertebrate Circulation Humans and other vertebrates have a closed circulatory system, often called the cardiovascular system Blood flows in a closed cardiovascular system, consisting of blood vessels and a two- to four-chambered heart

Arteries carry blood AWAY from the heart and to capillaries, the sites of chemical exchange between the blood and interstitial fluid Veins return blood from capillaries INTO the heart Capillaries are very thin to allow gas exchange to occur

Coronary blood vessels: provides the constant supply of oxygen and nutrients needed by the heart

Fishes A fish heart has two main chambers: one ventricle and one atrium Blood pumped from the ventricle travels to the gills, where it picks up O 2 and disposes of CO 2

Amphibians Frogs and other amphibians have a three- chambered heart: two atria and one ventricle The ventricle pumps blood into a forked artery that splits the ventricle’s output into the pulmocutaneous circuit and the systemic circuit

Reptiles (Except Birds) Reptiles have double circulation, with a pulmonary circuit (lungs) and a systemic circuit Turtles, snakes, and lizards have a three- chambered heart

Mammals and Birds In all mammals and birds, the ventricle is divided into separate right and left chambers The left side of the heart pumps and receives only oxygen-rich blood, while the right side receives and pumps only oxygen- poor blood

A powerful four-chambered heart was an essential adaptation of the endothermic way of life characteristic of mammals and birds

LE 42-4 FISHES Gill capillaries AMPHIBIANS Lung and skin capillaries REPTILES (EXCEPT BIRDS) Lung capillaries MAMMALS AND BIRDS Lung capillaries Gill circulation Heart: Ventricle (V) Atrium (A) Artery Vein Systemic circulation Systemic capillaries Systemic circuit Pulmocutaneous circuit Right Left A A V A V A V Systemic capillaries Right Left Pulmonary circuit Right systemic aorta V A V Systemic capillaries RightLeft Pulmonary circuit A Systemic circuit Left systemic aorta Systemic circuits include all body tissues except lungs. Note that circulatory systems are depicted as if the animal is facing you: with the right side of the heart shown at the left and vice-versa.

Concept 42.2: Double circulation in mammals depends on the anatomy and pumping cycle of the heart The human circulatory system serves as a model for exploring mammalian circulation

Mammalian Circulation: The Pathway Heart valves dictate a one-way flow of blood through the heart Blood begins its flow with the right ventricle pumping blood to the lungs In the lungs, the blood loads O 2 and unloads CO 2 Oxygen-rich blood from the lungs enters the heart at the left atrium and is pumped to the body tissues by the left ventricle Blood returns to the heart through the right atrium

LE 42-5 Anterior vena cava Aorta Right atrium Right ventricle Posterior vena cava Aorta Capillaries of abdominal organs and hind limbs Pulmonary vein Pulmonary vein Left atrium Left ventricle Capillaries of head and forelimbs Pulmonary artery Pulmonary artery Capillaries of right lung Capillaries of left lung

Animation: Path of Blood Flow in Mammals Animation: Path of Blood Flow in Mammals

i c a b b’ ee ee L h L L L L a o mq g d f h TO LUNGS FROM LUNGS FROM LOWER BODY FROM UPPER BODY TO LOWER BODY Right Atrium Left VentricleRight Ventricle Left Atrium Pulmonary Arteries TO UPPER BODY Aorta Superior Vena Cava Inferior Vena Cava Pulmonary Veins