Page 140 - 84 human physiolofy part-1

Chapter 8

This takes the blood to the lungs where the blood releases carbon dioxide and receives a new supply of
oxygen. The new blood is carried in the pulmonary veins that take it to the left atrium. The left atrium
then contracts and forces blood through the left atrioventricular, bicuspid, or mitral, valve into the left
ventricle. The left ventricle contracts forcing blood through the aortic semilunar valve into the
ascending aorta. It then branches to arteries carrying oxygen rich blood to all parts of the body.

Blood Flow After The Heart

Aorta-Arteries-Arterioles-Capillaries-Venules-Veins-Vena Cava

Blood Flow Through Capillaries

From the arterioles, the blood then enters one or more capillaries. The walls of capillaries are so
thin and fragile that blood cells can only pass in single file. Inside the capillaries, exchange of oxygen
and carbon dioxide takes place. Red blood cells inside the capillary releases their oxygen which passes
through the wall and into the surrounding tissue. The tissue then releases waste, such as carbon dioxide,
which then passes through the wall and into the red blood cells.

The Circulatory System

The circulatory system is extremely important in sustaining life. It’s proper functioning is
responsible for the delivery of oxygen and nutrients to all cells, as well as the removal of carbon
dioxide, waste products, maintenance of optimum pH, and the mobility of the elements, proteins and
cells, of the immune system. In developed countries, the two leading causes of death, myocardial
infarction and stroke are each direct results of an arterial system that has been slowly and progressively
compromised by years of deterioration.

Arteries

Arteries are muscular blood vessels that carry oxygenated blood away from the heart to the body.
The only exception being the pulmonary artery that carries deoxygenated blood to the lungs. Arteries
have a thick wall that consists of three layers. The inside layer is called the endothelium, the middle
layer is mostly smooth muscle and the outside layer is connective tissue. The artery walls are thick so
that when blood enters under pressure the walls can expand.

Arterioles

An arteriole is a small artery that extends and leads to capillaries. Arterioles have thick smooth
muscular walls. These smooth muscles are able to contract (causing vessel constriction) and relax
(causing vessel dilation). This contracting and relaxing affects blood pressure; the higher number of
vessels dilated, the lower blood pressure will be. Arterioles are just visible to the naked eye.

140 | Human Physiology