How the Heart Functions
The heart is one of the most amazing organs in the body!
Understanding & remembering the anatomy of the heart and how blood flows through it can be a daunting task, but hopefully this video will simplify the process,
so you can do well on your exam questions about the heart.
ANATOMY
The heart is a four-chambered muscle weighing between 7-15 ounces and is a little larger than the size of your fist. The average heart beats 100,000 times per day, pumping about 2,000 gallons of blood.
The heart is surrounded by a double-layered membrane called the pericardium. The inner layer, or visceral pericardium, and the outer layer, the parietal pericardium, contain a clear pericardial fluid between them that reduces the friction produced by the pumping action of the heart.
The heart is divided in half by a muscular wall, the septum. Each half has an upper collecting chamber – the atrium – and a lower pumping chamber – the ventricle.
The left ventricle has the thickest muscular wall, having enough force to push blood through the aortic valve & into the body. You can remember their location, because A comes before V – the atrium is above the ventricle.
THE HEART
Four-chambered muscle
Weighs 7-15 ounces
A little larger than the size of your fist
Average heart beats 100,000 times per day
Pumps about 2,000 gallons of blood daily
Pericardium: double-layered membrane surrounding the heart
Visceral pericardium: inner layer
Parietal pericardium: outer layer
Pericardial fluid: between the layers that reduces friction produced
by the pumping action of the heart.
The heart has 4 valves that control the flow of blood from the atria to the ventricles & from the ventricles into the 2 large arteries connected to the heart.
On the right side of the Heart, we have:
- Tricuspid valve - between the right atrium & right ventricle & has 3 ‘cusps’
- Pulmonary valve - between the right ventricle & entrance to pulmonary artery
- On the left side of the heart, we have
- Bicuspid (mitral) valve - between the left atrium & left ventricle & has 2 ‘cusps’
- Aortic valve - between left ventricle & the entrance to the aorta
The valves are like doors that open & close, preventing blood from flowing backwards – it is the “lub-dub” sound heard with a stethoscope.
The heart takes in oxygen-poor blood from the body (shown in blue) & delivers it to the lungs, where it gets oxygenated. The red portion shows oxygen-rich blood traveling from the lungs through the heart, to the rest of the body.
Remember: Veins bring blood towards the heart, arteries carry blood away from the heart (remember “a” for arteries & away).
Now we will follow the CIRCULATION OF BLOOD THROUGH THE HEART, step by step:
First we’ll look at the flow of blood through the right side of the heart…
Blood enters the heart from the upper & lower body by way of the superior & inferior vena cava. Blood flows from the right atrium (mainly by gravity), through the tricuspid valve, and into the right ventricle. Blood is pumped from the right ventricle, through the pulmonary valve, into the pulmonary artery and on to the lungs to be oxygenated.
On the left side of the heart…
Oxygenated blood returns to the heart by way of the pulmonary vein. Blood enters the left atrium, flows through the bicuspid/mitral valve, and into the left ventricle. When the left ventricle contracts, blood goes through the aortic valve, into the aorta, and on to the rest of the body.
The flow of blood through the atria & ventricles is actually happening simultaneously. Each heartbeat is a two-part pumping action that takes about one second.
You can see as the blood flows from the atria to the ventricles, it goes through the tricuspid & bicuspid valves (also known as the atrioventricular valves). These valves then snap shut, making the first heart sound (S1) or “lub” in “lub dub.” As these 2 valves snap shut, the pulmonary & aortic valves just opened.
The ventricles contract, pumping blood through the pulmonary valve (leading to the lungs) and the aortic valve (leading to the aorta & rest of the body). These valves then snap shut, making the 2nd heart sound (S2) or “dub” in “lub dub.” At the same time, the tricuspid & bicuspid valves just opened. And the process repeats.
To remember the order that blood flows through the heart valves – Tricuspid, Pulmonary, Bicuspid, Aortic – remember “Try Performing Better Always”.
The four chambers of the heart are continually contracting & relaxing in a pattern known as the cardiac cycle.
As blood collects in the atria, the atria contract, pushing the blood through the tricuspid & bicuspid valves, into the ventricles. The ventricles are filling & this phase is called diastole.
When the ventricles are full of blood, they contract to pump blood throughout the body – known as the contraction or pumping phase, which is called systole.
The heart normally beats about 60-80 times per minute when at rest, but this can vary. The heart is a muscle designed to remain strong & reliable for many years.
I covered a lot of information here – be sure to go back and review the diagrams & pictures.