The heart is the muscle that pumps blood through the circulatory system. The circulatory system is made up of blood and blood vessels.
Blood is what carries nutrients and oxygen to cells and tissues, making it a very important substance. The heart rhythmically pumps blood through the circulatory system, which then carries this vital substance to all parts of the body.
There are four stages of pumping blood that the heart performs. These are relaxation, contraction, pressure increase, and relaxation. During the contraction stage, the heart receives nerve signals to contract or squeeze.
These nerve signals are sent from the central nervous system in response to other stimuli such as exercise or stress.
The strength of these nerve signals determines how much blood gets pumped out during each heartbeat. This is why your heart rate can vary depending on what you are doing—your body is responding to your activity level with these nerve signals.
Heart rate and blood pressure are closely linked
The heart automatically adjusts the flow of blood to match activity levels by regulating both heart rate and blood pressure.
Blood pressure is how hard the blood pushes as it moves through the body’s vessels. Heart rate is how often the heart beats per minute.
As you become more active, the heart starts to beat faster to send more blood through the body to match the need for oxygen and nutrients. This is a natural response that helps keep you healthy.
If the heart did not do this, then there would be too much blood in the body at times and not enough at others. This could potentially lead to health problems like blood clots or fatigue.
The heart changes its rate of beating
As we’ve seen, the heart has two jobs. The first is to pump blood out to the body to nourish and oxygenate it.
The second is to regulate the pressure of blood in the body. The heart does this by changing its rate of beating.
The sinoatrial (SA) node is a small group of specialized cells in the wall of the right atrium that functions like a natural clock. It generates an electrical impulse every heartbeat that triggers contraction of the atria and then contraction of the ventricles.
This happens because of a sudden increase in calcium in the cell, which makes the muscle in the walls of these chambers contract. How cool is that? It’s like getting your own little personal heart cell massage every beat!
The SA node also regulates how fast your heart beats, which is why your doctor asks you what your normal resting heart rate is.
The heart changes its rate of beating
In addition to changing the size of the openings in the wall of the heart, the heart can also change how quickly it beats.
This process is called cardiac rhythm and it’s regulated by special cells called pacemaker cells. These cells are located in a part of the heart called the sinus node.
There are various types of pacemaker cells, each responsible for controlling a different stage of the cardiac rhythm. For example, some pacemaker cells control the rate at which blood is pumped out of the heart while others control how quickly the heart changes from beat to beat.
Parasympathetic nerves are nerve fibers that carry signals originating in the brain that reduce activity in certain organs and functions. One such organ is the stomach, where parasympathetic nerves decrease secretion of acid and other substances that aid digestion.(6) Cardiac parasympathetic nerves have an effect on cardiac rhythm similar to those on digestion-related functions.(6) hese nerves have an effect on cardiac rhythm similar to those on digestion-related functions.(6) Cardiac parasympiatric nerve activity increases sinus node cell firing and speeds up conduction throughthe Bundle of His, both of which increase heartbeat frequency.(7) However, they do not seem to affect sinus node cell excitability or Bundle of His conduction.(7) hese factors appear to be independent and only influence heartbeat frequency.(7) Parasympathetes are neurotransmitters in your body that reduce activity in certain organs or systems – namely, your digestive system. hrough this action, they promote relaxation. The same seems true for parasympathetic nerves innervationofcardiacparasympatheticsinneurotransmitteractivityinheartrhythm.
Blood vessels also adjust their diameter
The heart also receives feedback about the body’s needs and automatically makes adjustments to meet those needs.
Blood vessels, or vasculature, contain walls of a special kind of muscle called endothelial tissue. Like every other form of tissue in the body, it requires energy to maintain its structure and function.
Endothelial cells require energy in the form of oxygen, which they extract from blood passing through them. The more blood that passes through them, the more oxygen they receive and the more energy they need to maintain their structure and function.
The heart pumps blood at a consistent rate, so the endothelial cells in blood vessels must have a way to automatically adjust how much oxygen they receive. The answer lies in two small proteins called endothelin-1 and nitric oxide (NO).
It matches the body’s activity level
The heart has two functions: to pump blood to the body and to regulate the flow of blood through the body. The heart does both of these functions simultaneously, and it does them very well.
Blood flow is regulated in two main ways: vasoconstriction and vasodilation.
Vasoconstriction is the narrowing of blood vessels, which lowers the flow of blood. Vasodilation is the widening of blood vessels, which increases the flow of blood.
The sympathetic nervous system controls these processes, acting very quickly to respond to changes in activity levels. The parasympathetic nervous system also plays a role in regulating blood flow, but does it more slowly than the sympathetic nervous system does.
Heart rate and blood pressure are closely linked
Your heart automatically adjusts blood pressure based on activity level. This is why you will never see a picture of a person with high blood pressure sitting still– they would be fainting every few minutes!
Blood pressure is the force of blood pushing against the walls of the arteries. When you’re inactive, the heart beats slower, so it pumps less blood per beat.
Because there’s less demand for oxygen and nutrients, there’s less need for blood volume. The smaller volume of blood flowing through the arteries at any given time keeps pressure low.
When you start to move, the heart has to start pumping more rapidly to supply oxygen and nutrients to your muscles. The body doesn’t want you to overfill with blood, so it increases heart rate to keep Blood Pressure within a normal range.
The heart responds to nervous signals from the brain
Along with signals from the brain, the heart also responds to signals from the rest of the body. These signals tell the heart how much blood to pump and where to pump it.
Proportionally, more blood is needed in response to greater activity in muscles. This is because when we exercise, we need more oxygen and nutrients to our muscles to help us move.
The heart has two pathways that control the flow of blood: one that increases the flow of blood, and one that decreases it.
The first pathway increases the heart rate by releasing a chemical called noradrenaline. The second pathway decreases the diameter of blood vessels, which reduces blood flow. Both of these responses are automatic, or innate.
These signals tell the heart when to speed up or slow down
Another important function of the SA node is to coordinate when the heart beats. The heart doesn’t beat on its own – it needs a signal from another part of the nervous system to tell it when to beat and how hard to beat.
This signal comes from a group of nerves called the autonomic nervous system. Part of this system is a group of nerves called the sympathetic nerves.
The sympathetic nerves come out of the spinal cord and connect to various parts of the heart and blood vessels, as well as other organs, like the lungs and stomach.
When we are physically active, cells in these parts of the body produce a chemical called adrenaline. The sympathetic nerves pick up on this and send a signal back down to the SA node, telling it to speed up how often it sends out the electrical impulse that triggers the heart to beat.
The SA node responds by doing just that – speeding up how often it sends out these impulses.
