Animal Circulatory Systems

• For animals with many cell layers, diffusion distances mean a gastrovascular cavity does not suffice for nutrient and waste exchange.
• A circulatory system reduces the distance substances travel to enter or leave cells.

Basic Components of a Circulatory System

• A circulatory system has three basic components.
• These include a circulatory fluid, a set of interconnecting vessels, and a muscular pump (the heart).
• Oxygen from inhaled air diffuses across two layers of cells in the lungs to reach the blood.
• The circulatory system carries the oxygen-rich blood to all parts of the body.
• Basic circulatory systems arose to adapt to anatomical and environmental constraints.
• Circulatory systems are either open or closed and vary in the number of circuits.
• They also rely on pumps with differing structures and organization.

Open Circulatory Systems in Animals (Arthropods/Molluscs)

• Arthropods and molluscs have open circulatory systems.
• The circulatory fluid directly bathes the organs.
• The circulatory fluid, called hemolymph, is also the interstitial fluid bathing body cells.
• Heart contractions pump the hemolymph through vessels into interconnected sinuses, spaces surrounding the organs.

Closed Circulatory Systems in Animals (Mammals, Reptiles):

• Mammals, reptiles, earthworms, cephalopods, etc. utilize closed circulatory systems.
• Blood, which is the circulatory fluid, is confined to vessels and is distinct from the interstitial fluid.
• One or more hearts pump blood into large vessels, which branch into smaller vessels infiltrating the organs.

The Cardiovascular System

• The closed circulatory system of humans and other vertebrates is called the cardiovascular system.
• Blood circulates to and from the heart through extensive vessels.
• The total length of blood vessels in an average adult human is twice Earth's circumference at the equator.
• Arteries carry blood away from the heart to organs.
• Within organs, arteries branch into arterioles, which carry blood to the capillaries.
• Capillaries are microscopic vessels with thin, porous walls.
• Capillary beds infiltrate tissues, passing within a few cell diameters of every cell.
• At their "downstream" end, capillaries converge into venules, and venules converge into veins, which return blood to the heart.
• Arteries and veins are distinguished by the direction of blood flow, not by oxygen content.

Circulation in Fish

• In bony fishes, rays, and sharks, the heart has two chambers: an atrium and a ventricle.
• Blood passes through the heart once in each complete circuit, called single circulation.

Double Circulation

• Amphibians, reptiles, and mammals have two circuits, called double circulation.
• The pumps for the two circuits are combined into the heart.
• Having both pumps within a single heart simplifies coordination of pumping cycles.

Mammalian Circulation

• The mammalian circulatory system includes the systemic, pulmonary, and coronary circuits.
• Blood is pumped from veins of the systemic circuit into the right atrium, then into the right ventricle.
• Blood enters the pulmonary circuit and gets oxygenated by the lungs.
• The pulmonary circuit returns blood to the heart through the left atrium.
• Blood re-enters the systemic circuit through the left ventricle and is distributed through the aorta.
• The coronary circuit provides blood to the heart.
• Vena cava leads to the right atrium, which leads to the right ventricle.
• Lungs take blood from the right ventricle and return it to the left atrium.
• The left ventricle then sends blood to the aorta for systemic circulation.

Circulation in Plants (Vascular Plants):

• Vascular plants have transport systems.
• Vascular networks allow intercellular communication in land plants.
• The systems consist of tube-like connective tissues called xylem and phloem.
• Xylem transports and stores water and nutrients.
• Phloem transports sugars, proteins, and organic molecules.

Vascular Bundles in Monocots vs Dicots

• In monocots, vascular bundles are scattered throughout the parenchyma tissue with no particular pattern.
• In dicots, vascular bundles occur in a circle around a central region of pith.

Explore animal circulatory systems, their basic components, and how they facilitate nutrient and waste exchange in multicellular organisms. Learn about open and closed systems, the roles of circulatory fluids, vessels, and the heart. Discover how these systems adapt to anatomical and environmental constraints.