Human Circulatory and Respiratory Systems Anatomy

Blood Vessels

The set of all blood vessels is called the vascular tree.

Arteries

• Blood vessels that supply blood from the heart to the periphery.
• They branch into smaller vessels (arterioles) as they move away from the heart.
• Most carry oxygen-rich blood and are poor in carbon dioxide (arterial blood).
• The color of the blood is bright red.
• They are typically located in deep zones.
• The wall is thick, rich in smooth muscle and elastic tissue.
• They do not have valves inside.

Veins

• Blood vessels that carry blood from the periphery to the heart.
• They merge into larger vessels (venules) as they approach the heart.
• Most carry oxygen-poor blood, rich in carbon dioxide (venous blood).
• The color of the blood is dark red.
• They are often visible through the skin on the surface.
• Their wall is thinner, rich in elastic fibers, and poor in smooth muscle.
• Valves are present at regular intervals to prevent the backflow of blood.

Capillaries

• These are the smallest vessels and are the most abundant in the body.
• They serve as the place of communication between arterioles and venules.
• Their wall is very thin, allowing for the exchange of substances.

Operation of the Respiratory System

This is similar to respiration, involving the exchange of air between the lungs and the environment, known as pulmonary ventilation. This occurs through a cyclic process involving inspiration and expiration, where gas exchange takes place.

Inspiration

Passage of atmospheric air through the airway to the lungs, which expands the rib cage.

• The intercostal muscles and diaphragm contract.
• The expansion of the rib cage creates a suction effect, causing outside air to enter the respiratory tract until it reaches the alveoli.

Gas Exchange

• Each alveolus is surrounded by a network of capillaries.
• The walls of the alveoli and the capillaries are very thin, allowing the passage of oxygen molecules from the alveoli into the capillaries.
• Simultaneously, carbon dioxide molecules move from the capillaries into the alveoli.

Exhalation

Outflow of air through the airways from the lungs.

• The external intercostal muscles and diaphragm relax.
• The relaxation of these muscles reduces the volume of the rib cage.

Control of Breathing

Respiratory Cycle

The set of inspiration and expiration, including gas exchange.

• Under normal conditions, this cycle repeats 12 to 14 times per minute (normal respiratory rate).
• The rate may increase (tachypnea), decrease (bradypnea), or be suspended (apnea) for extended periods.
• The amount of air moving into and out of the lungs with normal breathing is 0.5 liters.
• The respiratory rate and depth adjust to meet the oxygen needs of the cells.
• Central nervous regulation of breathing is located in the brainstem respiratory center.
• For the respiratory airway to function properly, it must be clean and healthy.
• Proper respiratory hygiene could prevent most pulmonary diseases.