Heart Anatomy

Each day, the average human heart beats about 100,000 times, pumping 2,000 gallons of blood through the body.

That's a lot of work for an organ no bigger than a large fist and weighing 8 to 12 ounces

The heart is a muscular organ (cardiac muscle) about the size of a fist, located just behind and slightly left of the breastbone. 

The heart pumps blood through the network of arteries and veins of the circulatory system, supplying oxygen and nutrients to the tissues and removing carbon dioxide and other wastes.

The heart's walls consist of three layers of tissue:

  • Myocardium: This is the muscular tissue of the heart.
  • Endocardium: This tissue lines the inside of the heart and protects the valves and chambers.
  • Pericardium: This is a thin protective coating that surrounds the other parts.
  • Epicardium: This protective layer consists mostly of connective tissue and forms the innermost layer of the pericardium.

The physiology of the heart basically comes down to "structure, electricity and plumbing," Phillips told Live Science. 

The average adult has about 1.2 to 1.5 gallons (4.5 to 5.5 litres) of blood circulating inside their body. 

A healthy pulse is usually 60-100 bpm 

A very active person may have a pulse as low as 40 bpm. Larger people tend to have a faster pulse, but it is not usually over 100 bpm.


Vessels for Circulation

  • Arteries: these are vessels which are relatively large in diameter. They have thick muscular walls as there is considerable pressure exerted from the oxygen-rich blood in these vessels. They are responsible for transport away from the heart to tissues. (Tip: remember that arteries take blood away from the heart.)
  • Arterioles: smaller than arteries and provide the link between the arteries and the capillaries 
  • Capillaries: these are very narrow vessels with very thin walls (one cell thick). They form an extensive branching network through tissues and are the sites of exchange between blood and tissues.
  • Venules:  take blood from the capillaries to the veins.
  • Veins: which are the vessels that deliver mostly deoxygenated blood back towards the heart. They are less muscular and fibrous than arteries as pressure is lower, so they are flexible and contain valves to prevent back-flow

Systemic & Pulmonary Loop

Pulmonary circulation moves blood between the heart and the lungs. It transports deoxygenated blood to the lungs to absorb oxygen and release carbon dioxide. 

The oxygenated blood then flows back to the heart. 


Systemic circulation moves blood between the heart and the rest of the body. 

It sends oxygenated blood out to cells and returns deoxygenated blood to the heart 


BLOOD FLOW

How does blood flow through the heart?

Blood flows through your heart and lungs in four steps:

  1. The right atrium receives oxygen-poor blood from the body and pumps it to the right ventricle through the tricuspid valve.
  2. The right ventricle pumps the oxygen-poor blood to the lungs through the pulmonary valve.
  3. The left atrium receives oxygen-rich blood from the lungs and pumps it to the left ventricle through the mitral valve.
  4. The left ventricle pumps the oxygen-rich blood through the aortic valve out to the rest of the body.

Question: 

How many times does a single red blood cell pass through the heart in one complete cycle of circulation? 

RND Intro to Kinesiology
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