Cardiovascular and Hematologic Systems

Lesson 2 Overview

In this lesson, you’ll learn about cardiovascular and hematologic systems. The cardiovascular system is composed of the heart, blood vessels, and blood. You’ll learn the vital role of the heart in blood circulation to deliver oxygen to various body tissues and collect waste throughout the body. The hematologic system further explains the composition, formation, and distribution of blood within your body. You’ll learn the functions of various blood components.

You’ll also gain knowledge of various diseases of the cardiovascular and hematologic systems along with available treatment options. While discussing treatment of these disorders, you’ll learn about the medications used to treat each disorder. Medications listed throughout this lesson are listed as the generic name, with the brand name provided in parentheses.

 

Lesson Objectives

• Describe the anatomy and physiology of the cardiovascular system
• Explain cardiovascular system disorders and treatments
• Identify the composition of blood and hematologic system in general
• Recognize various blood disorders and treatment options

 

The Cardiovascular System

Introduction.

Cardiovascular is made up of two words, cardiac (heart) and vasculature (vessels). The cardiovascular system plays a vital role in supplying oxygen and nutrients to the cells while removing waste. Also called the circulatory system, it consists of the heart, blood vessels, and blood.

Throughout your course, there will be links to the website InnerBody.com. These links provide an interactive look at the organs discussed in your reading. Inner-Body also provides 3-D models of most organs, split-views of each anatomical structure, details about these structures' functions, and much more information that will help you in your studies.

 

The Heart

The heart is the main organ responsible for keeping blood circulating throughout the body. The heart is made up of muscular tissue that contracts and relaxes to receive and distribute blood.

In the most simplistic terms, it's the central pump that drives the circulation. While the heart collects and pumps blood, blood vessels carry blood around the body.

 

The heart is made up of four chambers; the top chambers are called the right atrium and left atrium, and the bottom chambers are called the right ventricle and left ventricle.

Blood is distributed to all body parts and regions via arteries, and veins carry blood back to the heart. The roles of atria (plural for atrium), ventricles, arteries, and veins will be discussed later in this lesson.

 

Think of arteries and veins as one-way streets to transport blood, oriented in opposite directions.

Blood vessels collect impure or deoxygenated blood from all parts of the body to the heart. The heart sends the deoxygenated blood to lungs to oxygenation. The heart collects pure or oxygenated blood from the lungs and then distributes it to the body.

Heart rate controls the contraction and relaxation to allow inflow and outflow of the blood. Contraction of the heart pumps blood out of the heart and into the vessels, while relaxation of the heart allows blood to fill in the heart and passively move from the atria to the ventricles.

 

Cardiovascular Anatomy

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Cardiovascular Physiology

The atria receive blood into the heart, and the ventricles pump blood out of the heart. The left ventricle is much larger and thicker than the right ventricle because it must send blood to the entire body instead of only to the lungs. Blood circulation consists of the following main steps:

1. Body tissues receive oxygen from oxygen-rich blood flowing in the arteries.
2. Veins collect waste gas, carbon dioxide, from the tissue and bring blood mixed with waste gas to the right atrium of the heart.
3. Blood flows into the right ventricle.
4. Blood is pumped to the lungs for oxygenation via the pulmonary artery.
5. Oxygenation of blood takes place in the lung capillaries via exchange of oxygen into the blood and carbon dioxide into lung capillaries. (This carbon dioxide waste is exhaled out and oxygen is inhaled in during breathing.)
6. Oxygenated blood returns back to the heart via the pulmonary vein into the left atrium.
7. Blood flows to the left ventricle.
8. Oxygenated blood is pumped to all body parts from the left ventricle through the aorta.

 

The four chambers of the heart are divided by walls called septa (singular, septum). The interatrial septum partitions the two atria, and the interventricular septum separates the ventricles.

In a normal heart, there's no direct transfer of blood between the two sides of the heart—that's why you should consider the heart to be two separate pumps instead of one.

 

Many people get confused about arteries and veins because we've often heard that arteries carry oxygenated blood and veins carry oxygen-depleted blood. A better way to remember which vessels carry what is to remember that these are one-way vessels, and there are two major kinds of circulation.

All veins carry blood toward the heart.

All arteries carry blood away from the heart. 

You can easily remember this by thinking "a" for away and "a" for artery.

During systemic circulation, veins are carrying oxygen-depleted blood toward the heart. When the heart sends that stale blood out into pulmonary circulation, it sends it by the artery since the blood is going away from the heart to the lungs to pick up more oxygen. Once blood picks up oxygen in the lungs, it has to go back into the heart, so it goes via the veins as shown in the blood circulation image. When the oxygenated blood is back in the heart, it's returned to systemic circulation, going back out of the heart by the arteries.

 

The atrium and ventricle of each side are connected by an atrioventricular valve (AV). The right AV valve, which goes from the right atrium to the right ventricle , is called the tricuspid valve, named for it's three "cusps," or rounded projections. On the left side, the AV valve going from the left atrium to the left ventricle is called the bicuspid valve, but it's perhaps better known as the mitral valve. The cusps "flap" to allow blood to pass through the heart in one direction and prevent backflow into the chamber.

There are also two valves guarding the exits of the ventricles. The pulmonary semilunar valve opens from the right ventricle into the pulmonary artery, which takes blood to the lungs. The aortic semilunar valve opens from the left ventricle into the aorta, which is the main artery that takes blood to the rest of the body.

 

The valves open in only one direction, so if blood tries to enter in a way it's not intended to, the valves will close against it. The closing of valves after cardiac contractions makes the "lub dub" heartbeat sound you hear under a stethoscope 

 

Coronary Circulation

Although the heart is filled with blood all the time, the cells of the heart must receive their own blood supply to maintain function. This blood supply comes from capillary networks. Blood gets pumped through thick arteries at anywhere from 5 to 35 liters per minute, but all tissues—even the heart—need capillary networks so that substances in the blood can diffuse across cell membranes.

The process by which the heart receives its own blood supply is known as coronary circulation. The aorta is the big "pipe" that receives all the oxygenated blood that comes out of the heart, but from there it branches off into smaller vessels that go to different areas of the body.

 

The blood vessels that branch off the aorta to take oxygen-rich blood to feel the tissues of the heart are the coronary arteries. The veins that bring stale blood back to the right atrium to be oxygenated are the coronary veins, which join and form the coronary sinus, a trough-like structure that opens into the right atrium. The superior and inferior vena cava carry blood from the rest of the body to the right atrium.

 

Electrical Conduction

Cardiac muscle isn't like other muscles of the body. It doesn't depend on the nervous system to send impulses to contract and relax. We typically think of a heartbeat as a single contraction of the heart muscle, but that conception isn't technically accurate. It would be more correct to think in terms of a cardiac cycle. 

A single cardiac cycle consists of simultaneous contractions of both atria followed by the simultaneous contractions of both ventricles. Contraction of the ventricles (and relaxation of the atria) is called systole, whereas relaxation of the ventricles is called diastole. One way to remember this is to realize that during diastole, the ventricles dilate (relax) to receive blood.

-What we call blood pressure is actually a measurement of pressure placed on arterial walls during systole and diastole. When a blood pressure reading is taken, the top number is called the systolic pressure, and the bottom number is the diastolic pressure.

 

The timing of each cardiac cycle must be tightly controlled to keep blood flowing smoothly through the lungs and the rest of the body. This occurs automatically, without your conscious thought. The heart itself contains its own control mechanism, such that an isolated heart (removed from the body) can continue to beat.

 

The main control center of the heart is a tiny bundle of nervous tissue called the sinoatrial (SA) node. This remarkable structure lies at the junction between the superior vena cava and the right atrium. The sinoatrial node is also known as the "pacemaker" of the heart because it sets the pace of the heart rate (also known as pulse rate). 

Clinically, a heart rate slower than 60 bpm indicates bradycardia, and a heart rate faster than 100 bpm indicates tachycardia.

 

These contractions are controlled by a web of electricity-conducting fibers. The SA node is the beginning of this conducting system. The following outline explains the conduction process in simple terms:

1. The SA node emits a signal to initiate a single cardiac cycle. This electrical signal spreads out over both of the atria, causing them to contract at the same time; this process is systole.
2. The right atrium sends blood from the superior and inferior vena cava into the right ventricle. The left atrium sends blood from the pulmonary veins into the left ventricles.
3. The electrical impulse from the SA node, now spread out over the atria, converges on the atrioventricular node (AV node). This node is another bundle of nervous tissue located between the atria and ventricles.
4. The ventricles dilate to receive the blood from the atria; this process is diastole. But the ventricles can't contract until they receive the command from the conducting system. This occurs as the AV node allows the electrical impulse to proceed forward.                                                                                                                                                                                                                                                                                                            The impulse travels from the AV node to the bundle of His, which lies in the septum between the two ventricles. The bundle of His divides into two large branches, one going to the right ventricle and the other going to the left ventricle. These divide into smaller and smaller branches until they become the Purkinje fibers.
5. The electrical impulses along these Purkinje fibers stimulate both ventricles to contract simultaneously (systole).                                                                                                                                                                                                                                                                                                                         This series of events completes a single cardiac cycle.

 

Key Points

• The heart has four chambers: the right atrium, left atrium, right ventricle, and left ventricle.
• Heart valves ensure that blood flows in only one direction while traveling through heart chambers.
• Cardiac muscle isn't like the other muscles of the body. It doesn't depend on the nervous system to send impulses to contract and relax.
• Pulmonary arteries deliver deoxygenated blood from the heart to the lungs, and pulmonary veins deliver oxygenated blood from the lungs back to the heart.
• The main function of our heart is to keep blood circulating throughout the body and supply oxygen and nutrients to the cells while removing waste.