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Albia Dugger • Miami Dade College

Eldra SolomonLinda BergDiana W. Martin

Chapter 44(Sections 44.1-44.4)

Internal Transport

Moving Materials

• Cells require a continuous supply of nutrients and oxygen and removal of waste products

• In very small animals, materials are exchanged by diffusion, the net movement of particles from a region of higher concentration to a region of lower concentration

• Fluid between the cells (interstitial fluid) provides a medium for diffusion of oxygen, nutrients, and wastes

Circulatory Systems

• Evolution of specialized circulatory systems allowed animals to increase in size – it transports oxygen, nutrients, hormones, and other materials to the interstitial fluid surrounding all the cells and removes metabolic wastes

• The human circulatory system (cardiovascular system) includes the heart, blood vessels, and blood

• Cardiovascular disease is the leading cause of death in the United States and throughout the world

44.1 TYPES OF CIRCULATORY SYSTEMS

LEARNING OBJECTIVE:

• Compare and contrast internal transport in animals with no circulatory system, those with an open circulatory system, and those with a closed circulatory system

Animals With No Circulatory System

• No specialized circulatory structures are present in sponges, cnidarians (hydras, jellyfish), ctenophores (comb jellies), flatworms, or nematodes (roundworms)

• In cnidarians, the central gastrovascular cavity serves as a circulatory organ as well as a digestive organ

• The flattened body of the flatworm permits effective gas exchange by diffusion

• Fluid in the body cavity of nematodes circulates materials

Circulatory Systems

• Larger animals require a circulatory system to efficiently distribute materials

• A circulatory system typically consist of three parts:• Blood, a connective tissue consisting of cells and cell

fragments dispersed in fluid, usually called plasma• A pumping organ, generally a heart• Blood vessels through which blood circulates

• Two main types of circulatory systems are open and closed systems

Open Circulatory Systems

• Arthropods and most mollusks have an open circulatory system, in which the heart pumps blood into vessels that have open ends

• Blood and interstitial fluid make up hemolymph, which fills large sinuses (the hemocoel or blood cavity)

• Hemolymph bathes the body cells, then re-enters the circulatory system through openings in the heart (arthropods) or through open-ended vessels that lead to gills (mollusks)

Open Circulatory Systems (cont.)

• Most mollusks have a heart with three chambers: two atria receive hemolymph from gills; a single ventricle pumps oxygen-rich hemolymph into blood vessels

• In arthropods, a tubular heart pumps hemolymph into arteries that deliver it to the sinuses of the hemocoel

• Some mollusks and arthropods have a copper-containing hemolymph pigment (hemocyanin) that transports oxygen

Invertebrates With Closed Circulatory Systems

• Annelids, cephalopod mollusks, and echinoderms have a closed circulatory system in which blood flows through a continuous circuit of blood vessels

• Gases, nutrients, and wastes diffuse between blood in the vessels and interstitial fluid that bathes the cells through the thin walls of capillaries

Invertebrates With Closed Circulatory Systems (cont.)

• Proboscis worms (phylum Nemertea) have a complete network of blood vessels but no heart

• Annelids (earthworms) have two main blood vessels, five pairs of contractile blood vessels that act as hearts, and a red pigment (hemoglobin) that transports oxygen

• Cephalopod mollusks (squids and octopods) have accessory “hearts” at the base of the gills, which speed passage of blood through the gills

The Vertebrate Circulatory System

• Vertebrates have a ventral, muscular heart that pumps blood into a closed system of blood vessels

• Capillaries, the smallest blood vessels, have very thin walls that permit exchange of materials between blood and interstitial fluid

• The vertebrate circulatory system consists of heart, blood vessels, blood, lymph, lymph vessels, and associated organs such as the thymus, spleen, and liver

Functions of the Vertebrate Circulatory System

1. Transports nutrients from digestive system or storage to cells

2. Transports oxygen from respiratory structures to cells

3. Transports metabolic wastes from cells to excretory organs

4. Transports hormones from endocrine glands to target tissues

5. Helps maintain fluid balance

6. Helps distribute metabolic heat and maintain body temperature

7. Helps maintain appropriate pH

8. Defends the body against invading microorganisms

KEY CONCEPTS 44.1

• Arthropods and most mollusks have an open circulatory system in which blood bathes the tissues directly

• Some invertebrates and all vertebrates have a closed circulatory system in which a heart pumps blood that flows through a continuous circuit of blood vessels

44.2 VERTEBRATE BLOOD

LEARNING OBJECTIVES:

• Compare the structure and function of plasma, red blood cells, white blood cells, and platelets

• Summarize the sequence of events involved in blood clotting

Blood

• In vertebrates, blood consists of a fluid plasma in which red blood cells, white blood cells, and platelets are suspended

• In humans, blood volume is approximately 5 L (5.3 qt) in an adult female and about 5.5 L (5.8 qt) in an adult male

• About 55% of the blood volume is plasma and 45% is blood cells and platelets

Plasma

• Plasma consists of water (about 92%), proteins (about 7%), salts, and transported materials such as dissolved gases, nutrients, wastes, and hormones

• Plasma contains several kinds of plasma proteins:• Fibrinogen is involved in clotting• Globulins: Alpha globulins (hormones and proteins that

transport hormones); beta globulins (transport fats, cholesterol, vitamins and minerals); gamma globulin (contains many types of antibodies)

• Albumins help control blood’s osmotic pressure

Red Blood Cells

• Erythrocytes or red blood cells (RBCs), are highly specialized for transporting oxygen

• In mammals, the RBC nucleus is ejected – each RBC is a flexible, biconcave disc with an elastic internal framework

• Erythrocytes are produced in red bone marrow of vertebrae, ribs, breastbone, skull bones, and long bones

• As an RBC develops, it produces large quantities of the oxygen-transporting pigment hemoglobin

Red Blood Cells (cont.)

• A human RBC lives about 120 days; old RBCs are removed from circulation by phagocytic cells in the liver and spleen

• New RBCs are produced in bone marrow, regulated by a hormone released by the kidneys (erythropoietin)

• Anemia, a deficiency in hemoglobin, may be caused by: • Loss of blood from hemorrhage or internal bleeding• Decreased production of hemoglobin or red blood cells

(iron-deficiency anemia or pernicious anemia)• Increased rate of RBC destruction (hemolytic anemias)

White Blood Cells

• Leukocytes or white blood cells (WBCs) defend the body against harmful bacteria and other microorganisms

• Leukocytes are amoeba-like cells capable of independent movement – some slip through the walls of blood vessels and enter the tissues

• Human blood contains three kinds of granular leukocytes and two types of agranular leukocytes – all manufactured in the red bone marrow

Granular Leukocytes

• Granular leukocytes have large, lobed nuclei and distinctive granules in their cytoplasm

• Neutrophils are phagocytic cells that ingest bacteria and dead cells – granules contain digestive enzymes

• Eosinophils contain lysosomes with enzymes that degrade cell membranes of parasitic worms and protozoa

• Basophils release histamine in injured tissues and in allergic responses; and heparin, an anticoagulant

Agranular Leukocytes

• Agranular leukocytes lack granules; their nuclei are rounded or kidney-shaped

• Lymphocytes fight infections; some produce antibodies, others directly attack invaders such as bacteria or viruses

• Monocytes are phagocytes that migrate from blood into tissues during an infection; they differentiate into:• Macrophages that engulf bacteria, dead cells, and debris• Dendritic cells, important in the immune system

Leukemia

• Leukemia is a form of cancer in which WBCs multiply rapidly within the bone marrow, crowding out developing RBCs and platelets, leading to anemia and impaired clotting

• Death is often caused by internal hemorrhaging, especially in the brain; or infection

• Leukemia is treated with chemotherapy, and sometimes with radiation therapy or bone marrow transplant

Platelets

• Most vertebrates other than mammals have small, oval, nucleated cells (thrombocytes) that function in blood clotting

• Mammals have platelets, tiny spherical or disc-shaped fragments of cytoplasm pinched off from large cells in the bone marrow (lacking nuclei)

• When a blood vessel is cut, platelets stick to the rough, cut edges and release substances that attract other platelets

Blood Clotting

• Platelets become sticky and adhere to collagen fibers in the blood vessel wall, forming a platelet plug or temporary clot

• Using clotting factors, calcium ions, and compounds released from platelets, prothrombin is converted to thrombin

• Thrombin catalyzes conversion of the soluble plasma protein fibrinogen to an insoluble protein, fibrin

• Fibrin polymerizes, producing long threads that form the webbing of the clot, trapping more blood cells and platelets

KEY CONCEPTS 44.2

• Vertebrate blood consists of plasma, which transports nutrients, wastes, gases, and hormones; red blood cells, which are specialized to transport oxygen; white blood cells, which defend the body against disease; and platelets, which function in blood clotting

44.3 VERTEBRATE BLOOD VESSELS

LEARNING OBJECTIVE:

• Compare the structure and function of different types of blood vessels, including arteries, arterioles, capillaries,

and veins

Blood Vessels

• Vertebrates have three main types of blood vessels

• Arteries carry blood away from the heart; they divide into many smaller branches (arterioles) which lead to capillaries

• Capillaries are microscopic vessels that form networks which exchange materials between blood and tissues

• Veins carry blood back toward the heart

Blood Vessels (cont.)

• Walls of arteries or veins have three layers:• Inner lining: endothelium• Middle layer: connective tissue and smooth muscle cells• Outer layer: connective tissue rich in elastic and collagen

fibers

• Materials are exchanged between blood and interstitial fluid through capillary walls, which are only one cell thick

Blood Vessels (cont.)

• Smooth muscle in arteriole walls can constrict (vasoconstriction) or relax (vasodilation), changing the radius of the arteriole

• Regulated by the nervous system, arterioles help maintain appropriate blood pressure and control the volume of blood passing to a particular tissue

• Small vessels (metarterioles) directly link arterioles with venules (small veins)

Blood Vessels (cont.)

• Capillaries branch off from metarterioles and rejoin them, and also interconnect with one another

• Where a capillary branches from a metarteriole, a smooth muscle cell serves as a precapillary sphincter that directs blood first to one and then to another section of tissue

• Precapillary sphincters (along with the smooth muscle in the walls of arteries and arterioles) regulate the blood supply to each organ and its subdivisions

KEY CONCEPTS 44.3

• Three main types of vertebrate blood vessels are arteries, which carry blood away from the heart; capillaries, which are exchange vessels; and veins, which carry blood back toward the heart

44.4 EVOLUTION OF THE CARDIOVASCULAR SYSTEM

LEARNING OBJECTIVE:

• Trace the evolution of the vertebrate cardiovascular system from fish to mammal

Evolution of the Vertebrate Cardiovascular System

• The vertebrate cardiovascular system became modified as the site of gas exchange shifted from gills to lungs, and as metabolic rates increased

• The vertebrate heart has one or two chambers (atria) that receive blood returning from the tissues and one or two ventricles that pump blood into arteries

• The fish heart has one atrium and one ventricle; there is a single circuit of blood vessels; blood is oxygenated at capillaries in the gills

Evolution of the Vertebrate Cardiovascular System (cont.)

• Amphibians have a double circuit of blood vessels: pulmonary circulation and systemic circulation

• The heart has two atria and one ventricle – a sinus venosus collects oxygen-poor blood returning from the veins and pumps it into the right atrium; blood is oxygenated in lungs and passes directly into the left atrium

• Oxygen-poor blood is pumped out of the ventricle before oxygen-rich blood enters; the conus arteriosus helps separate the two

Evolution of the Vertebrate Cardiovascular System (cont.)

• Most nonavian reptiles have a double circuit of blood flow – a wall partly divides the ventricles

• In crocodilians, the wall between the ventricles is complete –the heart consists of two atria and two separate ventricles

• Nonavian reptiles (and amphibians) do not ventilate their lungs constantly – shunts between the two sides of the heart allow blood to be distributed to the lungs as needed

Evolution of the Vertebrate Cardiovascular System (cont.)

• In birds, mammals, and crocodilians, the septum (wall) between the ventricles is complete

• Biologists hypothesize that the completely divided heart evolved twice during the course of vertebrate evolution; first in the crocodilian-bird clade, then independently in mammals

• The conus arteriosus split and became the base of the aorta and the pulmonary artery; a vestige of the sinus venosus remains as the sinoatrial node (pacemaker)

Evolution of the Vertebrate Cardiovascular System (cont.)

• A complete double circuit allows birds and mammals to maintain relatively high blood pressures in the systemic circulation and lower pressures in the pulmonary circulation

• The pattern of blood circulation in birds and mammals can be summarized as follows:

veins (from organs) → right atrium → right ventricle → pulmonary arteries → capillaries in the lungs →

pulmonary veins → left atrium → left ventricle → aorta → arteries (to organs) → arterioles → capillaries → veins

KEY CONCEPTS 44.4

• During the evolution of terrestrial vertebrates, adaptations in circulatory system structures separated oxygen-rich from oxygen-poor blood

• The four-chambered hearts and double circuits of endothermic birds and mammals completely separate oxygen-rich blood from oxygen-poor blood