The respiratory system branches like the circulatory. Oxygen and carbon dioxide diffuse between the end of these branches and the bloodstream. What are the ends of those branches called?

What is the purpose of the sphincters where the arterioles branch into the capillary beds?

A. To slow down blood flow so the capillaries don't burst under pressure

B. To block blood from coming back out of the capillary bed too quickly to allow for more complete diffusion of oxygen

C. To control blood flow to different areas of the body depending on activities

D. To speed up blood flow into the capillary bed for faster oxygen exchange

E. They remove carbon dioxide from blood passing through.

1. Ends of the respiratory branches are called alveoli.

2. C. To control blood flow to different areas of the body depending on activities

Explanation:

1. The trachea divides into left and right primary bronchi which in turn divide multiple times upon entering the lungs and make the bronchial tree.

The final branches of the bronchial tree are the terminal bronchioles that lead to alveoli. The alveoli are the balloon-shaped structures and serve as the site of gas exchange between the blood and inhaled air.

2. The opening and closing of sphincters of capillary beds regulate the direction of blood flow. The opening of sphincters allows the blood to flow into associated branches of capillary beds while closed sphincters direct the blood from arterioles to venules via thoroughfare channel.

This local change in blood flow is responsible for the autoregulation of blood flow to different tissues to match their respective metabolic demands. For example, during physical activity, more blood is directed to skeletal and cardiac muscles.