The Heart and Circulatory System Structure and Function

This video introduces the heart and circulatory system. It covers the structure and function of the circulatory system, compares and contrasts the types of blood vessels (arteries, veins and capillaries), and explains the internal structure of the heart. The video also reviews the path of blood through the heart, the cardiac cycle, the process of oxygenation, and the role of the coronary vessels and nodes.
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00:00-0:24 Introduction
0:25-1:25 The Circulatory System
1:25-2:12 Types of Blood Vessels: Arteries
2:12-2:54 Types of Blood Vessels: Veins
2:54-3:27 Types of Blood Vessels: Capillaries
3:27-3:54 The Cardiac Cycle
3:55-6:49 Path of Blood Through the Heart
6:50-7:14 The Coronary Vessels
7:15-8:47 The Nodes and Cardiac Conduction
The Circulatory System Loops:
The circulatory system delivers blood to every part of the body. It has three loops; the pulmonary loop which oxygenates the blood in the lungs, the systemic loop which circulates blood throughout the body, and the coronary circuit which supplies blood to the heart muscles.
The Cardiac Cycle:
The heart pumps blood through the body in a repeating process called the Cardiac Cycle. During the Cardiac Cycle, the chambers of the heart rhythmically contract (systole) and relax (diastole). During systole, the heart pushes blood out through its major vessels, and the relaxation of diastole allows the chambers to refill; much like an ordinary pump that you might use to inflate a bicycle tire.
Types of Blood Vessels:
Arteries: Arteries carry blood away from the heart. Usually this means they carry oxygenated blood, but not always. Artery walls consist of three layers of tissue, and arteries also have the thickest, most muscular walls of all the blood vessels because the pressure in them is quite high. Some arteries you might have heard of are the aorta, and also the carotid arteries which run up each side of your neck to supply blood to your brain. The major arteries split into minor arteries, and then into even smaller ones known as arterioles.
Veins: Veins carry blood back to the heart, meaning they USUALLY carry de-oxygenated blood. Veins have 3 layers of wall tissue, but do no not need to be as muscular because the pressure in them is much lower. They also have valves to prevent back-flow because the pressure in them is much lower. A vein you’ve probably heard of is the jugular vein, which runs down the right side of your neck to return blood from the head back to the heart. The major veins split into minor veins, and then into even smaller ones known as venules.
Capillaries: Capillary “beds” are groups of 10-100 tiny blood vessels that branch out from arterioles. Red blood cells can fit through them single file. Because they are so small and have such thin walls, oxygen, carbon dioxide and nutrients can easily diffuse in and out of them through their walls.
Path of Blood Through the Heart:
De-oxygenated blood is funneled back to the heart through a blood vessel called the vena cava. The de-oxygenated blood enters the heart’s right atrium. When the right atrium contracts, it pushes blood into the next chamber, the right ventricle, through a one-way valve called the tricuspid valve (sometimes also called the atrioventricular valve). The valve has flaps that seal tightly to make sure the blood can’t flow backwards. Once the right ventricle is full, it pumps the de-oxygenated blood out towards the lungs so it can be oxygenated. This blood passes through a second valve called the pulmonary valve and into a blood vessel called the pulmonary artery. Even though this pair of blood vessels is carrying de-oxygenated blood, the flow travels away from the heart, so it’s an artery, not a vein.
Once the blood reaches the lungs, gas exchange occurs. The oxygenated blood returns from the lungs via the pulmonary veins. Again, these are flowing back towards the heart, so these blood vessels are veins, even though the blood in them is oxygenated. The blood re-enters the heart in the left atrium. When the atria next contract, the blood is pushed through the mitral valve into the left ventricle. This valve has two flaps, so it’s sometimes also called the “bicuspid valve”. Finally, the left ventricle contracts and forces blood out into the aorta through the aortic valve.
This video covers content that appears on the AP Biology exam, IB exam, NREMT exam and Biology SAT.
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#heart #circulatorysystem #anatomy

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