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Circulatory Systems

47.1

Types of Circulatory Systems

The two basic types of animal circulatory systems are open systems and closed systems

Water enters the Gastrovascular Cavity: a body cavity with a single opening to the outside that functions as both mouth and anus.

Nutrients are digested within the cavity and distributed throughout the animal;s body and wastes are excreted into the cavity.

Nutrients obtained from digested food reach all the body cells because water circulates throughout the entire cavity

Open Circulatory System: with one or more hearts that pump fluid through vessels that open into the animal’s body cavity, called the hemocoel

Therefore, the fluid in the vessels and the interstitial fluid that surrounds cells mingle in one large mixed compartment, rather than being located in separate body compartments

Hemolymph: mixed fluid, nutrients and wastes are exchanged by diffusion between the hemolymph and body cells, and the hemolymph eventually returns to the heart.

Closed Circulatory System: blood and interstitial fluid are physically separated and differ in their components and chemical composition

Blood: a watery solution containing solutes to be transported throughout the body— is pumped under pressure by one or more contractile muscular hearts.

blood remains within tubelike vessels that distribute it throughout the body

the solutes in blood can be exchanged with environment and the body’s cells

in most cases, blood contains disease fighting cells and molecules

the activity of the closed circulatory system can be adjusted to match an animals metabolic demands.

closed systems generally can heal themselves when wounded by forming clots at the site of injury

these systems grow in size as an animal grows

Some mixing of the two streams of blood, however, does occur in the ventricle and the slightly blood traveling to the tissues is not fully oxygenated

Double Circulation: Crocodiles, Birds, and Mammals

oxygenated and deoxygenated blood are completely separated into two distinct circuits, the systemic circulation and the Pulmonary Circulation

This is made possibly by a heart that has two ventricles that are completely separated by a septum or wall.

when resting or under water, crocs can divert blood btwn the two circuits in water that birds and a mammals cannot.

all animals with double circulations have a left and right atrium and left and right ventricle

in a double circulation the pulmonary circulation delivers oxygenated blood from the lungs to the left atrium, which then passes it on to the left ventricle.

The left ventricle pumps blood to all the body’s tissues via the systemic circulation

Plasma: the top layer of the centrifuged blood sample is a yellowish solution

it contains water and the dissolved organic and inorganic nutrients that were absorbed from the digestive tract or secreted from cells.

Plasma also transport as well as proteins that serve several important functions such as forming blood clots, which seal off wounds to blood vessels.

contains buffers that help keep the body’s pH within its normal range.

maintaining the fluid balance of cells

Leukocytes

Beneath the plasma in our sample is a narrow white layer of leukocytes

all leukocytes perform vital functions that defend the body against infection and disease

Erythrocytes

the bottom visible layer of our blood sample consists of erythrocytes, also called red blood cells.

the term Hematocrit: refers to the volume of blood that is composed of red blood cells, usually between 40 and 65% among vertebrates.

Red blood cells serve the critical function of transporting oxygen throughout the body

Hemoglobin: within the cytosol of red blood cells, however are large amounts of the protein.

Each molecule of hemoglobin contains four proteins subunits, each surrounding an atom of iron in a hemegroup.

Each iron atom reversibly binds to a single molecule of oxygen

Anemia: refers to lower than normal amounts of hemoglobin, which reduces the amount of oxygen that can be stored in the blood.

Platelets

Platelets: are cell fragments that lack a nucleus

Thrombocytes: are intact cells; both play a crucial role in the formation of blood clots, which limit blood loss after injury.

Formed in the bone marrow

Blood Clotting is a Multistep ProcessThe formation of a blood clot in mammals requires several steps, two of which include plateletsUpon injury to a blood vessel, platelets first secrete substances that cause platelets to clamp together and bind to collagen fibers in the surrounding connective tissue at the wound site; this forms a plug that prevents continued blood loss.