What the Heart and Circulatory System Do

  • The circulatory system works closely with other systems in our bodies.
  • It supplies oxygen and nutrients to our bodies by working with the respiratory system.
  • At the same time, the circulatory system helps carry waste and carbon dioxide out of the body.

Functions of the Circulatory System

  • Respiration - delivers oxygen to the cells and removing carbon dioxide from them
  • Nutrition - carries digested food substances to the cells of the body
  • Waste Removal - disposes of waste products and poisons that would harm the body if they accumulated
  • Immunity - helps protect the body from disease
  • Cellular Communication - the circulatory system provides a mode of transport for hormones
  • Thermoregulation - the circulatory system transports heat (can both warm and cool body)

The Heart

  • The heart has four chambers that are enclosed by thick, muscular walls.
  • It lies between the lungs and just to the left of the middle of the chest cavity.
  • The bottom part of the heart is divided into two chambers called the right and left ventricles, which pump blood out of the heart.
  • A wall called the interventricular septum divides the ventricles

Right-Hand Side of the Heart

  • The right-hand side of the heart receives de-oxygenated blood from the body tissues (from the upper- and lower-body via the superior vena cava and the inferior vena cava, respectively) into the right atrium.
  • This de-oxygenated blood passes through the tricuspid valve into the right ventricle.
  • This blood is then pumped under higher pressure from the right ventricle to the lungs via the pulmonary artery.

Left-Hand Side of the Heart

  • The left-hand side of the heart receives oxygenated blood from the lungs (via the pulmonary veins) into the left atrium.
  • This oxygenated blood then passes through the bicuspid valve into the left ventricle.
  • It is then pumped to the aorta under greater pressure (as explained below).
  • This higher pressure ensures that the oxygenated blood leaving the heart via the aorta is effectively delivered to other parts of the body via the vascular system of blood vessels (incl. arteries, arterioles, and capillaries

Arteries

  • are blood vessels that carry blood away from heart.
  • Arterial walls are able to expand and contract.
  • Arteries have three layers of thick walls.

Arterioles

  • are small arteries that connect larger arteries with capillaries.
  • Small arterioles branch into collections of capillaries known as capillary beds.

Capillaries

  • are thin-walled blood vessels in which gas exchange occurs.
  • In the capillary, the wall is only one cell layer thick. .
  • Capillaries are concentrated into capillary beds.
  • Some capillaries have small pores between the cells of the capillary wall, allowing materials to flow in and out of capillaries as well as the passage of white blood cells.
  • Nutrients, wastes, and hormones are exchanged across the thin walls of capillaries.
  • Capillaries are microscopic in size, although blushing is one manifestation of blood flow into capillaries.
  • Control of blood flow into capillary beds is done by nerve-controlled sphincters.

Venules

  • are smaller veins that gather blood from capillary beds into veins.
  • Pressure in veins is low, so veins depend on nearby muscular contractions to move blood along.

Veins

  • carry blood from capillaries to the heart.
  • Veins have valves that prevent back flow of blood.