Human Respiratory and Circulatory System Functions

Adaptation of the Alveoli

There are millions of alveoli (300-500 million in two lungs), providing a large surface area. There is a lot of blood around them. The wall is only one cell thick, so it is not difficult for gas to cross it.

Oxygen Transport and Destination

Oxygen travels through capillaries attached to the red blood cells to be transported to the respiring tissues. They form oxyhemoglobin by attaching to hemoglobin. It reaches all the body tissues.

Carbon Dioxide Production and Removal

It is produced in the respiring cells (in the mitochondria). It has to be removed. The carbon dioxide travels dissolved in the plasma.

Effects of Nicotine on the Body

Nicotine is a poisonous and addictive drug. It damages the heart, blood vessels, and nerves (neurons). It makes people addicted to it, so they have more difficulties while giving up smoking.

Components of the Blood

Plasma

Its main job is transporting red blood cells, platelets, heat, fibrinogen (a protein), waste substances (carbon dioxide, urea), food (glucose and amino acids), white blood cells, hormones, and some antibodies.

Red Blood Cells

They are made in the marrow of the long bones thanks to a hormone called EPO. They are destroyed in the spleen.

White Blood Cells

They participate in the immunity and allergic processes.

Platelets

Platelets clump together at wounds to create a clot that protects the body from bacteria. They emit a chemical that makes fibrinogen become fibrin, which does not dissolve in blood. These fibrin strands create a web which traps the blood to avoid it going out.

Elements of the Circulatory System

• Blood
• Vessels (arteries, veins, capillaries)
• Heart

Differences Between Veins and Arteries

Arteries carry blood out from the heart; they are elastic because they have to hold a high pressure. Veins carry blood to the heart. The walls are more rigid because when the blood is reaching the heart, it flows with very low pressure.

The Function of the Heart

Blood is pumped into the tissues rich in oxygen. After giving the tissue its supply, it returns to the heart and is pumped to the lungs so gas exchange occurs, and the cycle starts again.