The Circulatory System - Part 1

The circulatory system is divided into 3 parts:

Circulatory System

Blood

Blood vessels

Heart

Blood

Blood vessels

This exchange occurs primarily through diffusionBlood never makes direct contact with body cellsSubstances are exchanged through interstitial fluid

Function of blood vessels and heart is to move blood to and from cells of body

Circulatory System

When it reaches cells, blood can exchange respiratory gases, nutrients and waste

capillary

blood

cells

interstitial fluid

nutrientsO2

wasteCO2

Average adult has about 5L of blood

Blood

Nutrients

Urea and other wastes

Respiratory gases

Hormones

Special proteins to fight infection and clot wounds

It serves many functions including transport of:

Blood consists of 3 components:

Blood

cells (red and white)

platelets (cell fragments)

plasma and blood proteins

Blood

Platelets, also called thrombocytes, are cell fragments that are involved in forming blood clots

White blood cells (WBC), also called leucocytes and lymphocytes, are slightly larger than RBC and have a nucleus

Plasma is about 90% water and 10% dissolved substances (nutrients, vitamins, minerals, antibodies, hormones, clotting proteins, CO2, urea)Red blood cells (RBC), also called erythrocytes, and are enucleated and biconcave in shapeThey are filled with hemoglobin, which transports oxygen

RBC

platelet

WBC

Relative size and number of RBCs, WBC’s and platelets

Blood

An artery branches into smaller vessels called arteriolesArterioles continue to branch and narrow until they become capillaries

Capillaries are networks of tiny blood vessels (5-10μm in diameter) that extend throughout body

There are 3 types of blood vessels:

Blood Vessels

Arteries take blood (under high pressure) away from heartArteries

Capillaries

Veins return blood to heartVeinsThere are 3 types of blood vessels:

Blood Vessels

They begin as narrow vessels called venules and widen as they near heartBlood is under low pressure in most veins, so they contain one-way valves to prevent back flow of blood