Describe the structure and function of the cardiovascular system and the factors affecting blood flow through it (NGSSS SC.912.L.14.36; Reporting Category 3, Organisms, Populations, and Ecosystems).

What this topic is asking

The NGSSS benchmark SC.912.L.14.36 asks you to describe the cardiovascular system and the factors affecting blood flow through it. For the Florida Biology 1 EOC you need to know the parts (heart, the three vessel types, blood), the path of blood, what blood does, and how factors like heart rate, exercise, vessel diameter, and disease change blood flow. Items often ask you to identify a vessel type or explain how an activity changes blood flow.

The parts of the cardiovascular system

The path of blood and the vessel types

Blood travels in two loops driven by the heart: one to the lungs (to load oxygen and unload carbon dioxide) and one to the rest of the body (to deliver oxygen and nutrients and collect wastes). The three vessel types each have a structure suited to a function:

• Arteries carry blood away from the heart, usually oxygen-rich blood, under high pressure. Their walls are thick and muscular to withstand the pressure. (Memory aid: Arteries carry blood Away.)
• Veins carry blood back to the heart, under lower pressure; many have valves to keep blood moving in one direction.
• Capillaries are the tiny, thin-walled vessels that connect arteries and veins. Their thin walls allow the exchange of oxygen, carbon dioxide, nutrients, and wastes between blood and body cells.

The function of blood

Blood is the body's transport fluid. It carries:

• Oxygen (bound to hemoglobin in red blood cells) to the cells for respiration, and carbon dioxide away.
• Nutrients (such as glucose) from the digestive system to the cells.
• Wastes to organs that remove them.
• Hormones from glands to their targets, and immune cells that defend against pathogens.

This links the cardiovascular system to respiration (delivering glucose and oxygen), the immune system, and homeostasis.

Factors affecting blood flow

So during exercise, blood flow rises because the heart beats faster and vessels to the muscles widen, meeting the higher demand.

Try this

Q1. State the function of arteries, veins, and capillaries. [3]

• Cue. Arteries carry blood away from the heart; veins carry blood back to the heart; capillaries are where exchange of gases, nutrients, and wastes occurs.

Q2. Explain why blood flow increases during exercise and why this is useful. [2]

• Cue. Heart rate increases (and vessels to muscles widen), so blood flow rises, delivering more oxygen and glucose to active muscles and removing carbon dioxide and heat.