Explain the anatomical concepts associated with hematology.
Summarize this module’s key points in 5-6 sentences.
2. Explain the physiological concepts associated with hematology.
Summarize this module’s key points in 5-6 sentences
How does oxygen get to muscles? The answer is the heart and its blood vessels, which together comprise the cardiovascular system. The heart connects everything in the human body. It beats over 100,000 times each day, pumping approximately 2,000 gallons of blood daily. Like other muscles in the body, it is controlled by the nervous system, then influenced by factors such as hormones and the body’s oxygen demands.
The heart is located between the lungs, slightly to the left. Its superior side is called the base. Its inferior tip, the apex, points down and out toward the left axilla.
For purposes of study, the heart is divided into right and left halves. They are physically separated by a septum. While they look anatomically separate, the two sides function at the same time and manage one blood flow. The left half is referred to as systemic, as it takes oxygenated blood out to the rest of the body. The right half is referred to as pulmonary, as it receives de-oxygenated blood back from the body.
Basic Heart Structure and Function.jpg
Basic heart structure and function (Betts et al., 2013)
Heart Layers
The heart is comprised of layers. From outer-most to inner-most, the layers are: fibrous pericardium, serous pericardium (with parietal and visceral layers), epicardium, myocardium, and endocardium. The pericardial layers are more fascial and protective in nature. The Epicardium, myocardium, and endocardium are muscular in nature, with the myocardium providing the actual heart muscle contraction. The myocardium is made of cardiac tissue, which is a type of muscle tissue. Like skeletal muscles, it has striations. Unlike skeletal muscle, cardiac muscle is involuntary, meaning it will contract on its own without conscious thought. Cardiac tissue also has unique structures called intercalated discs that connect the cardiac muscle cells to each other.
Heart Layers.jpg
Heart layers (Betts et al., 2013)
Heart Chambers
The heart is divided into four chambers, each of which is controlled by valves. There are two upper chambers (atria) and two lower chambers (ventricles). The atria are receivers, as the right atrium receives de-oxygenated blood from the systemic circulation. The left atrium receives oxygenated blood from the pulmonary circulation. The ventricles are responsible for pumping blood out of the heart. The right ventricle pumps blood into pulmonary arteries. The left ventricle pumps blood into the aorta.
Heart Anatomy.jpg
Heart anatomy (Betts et al., 2013)
Heart Valves
There are two valves, semilunar valves, which control the interface between the heart and blood vessels. The right heart’s semilunar valve is the pulmonary valve. The left heart’s semilunar valve is the aortic valve. There are two valves, atrioventricular valves (AV valves), that control the interface between the atria and ventricles. The right heart’s AV valve is the tricuspid. The left heart’s AV valve is the bicuspid (also called the mitral valve). All of the valves function to prevent blood back flow. Structurally, all valves have cusps. AV valves additionally have chordae tendineae that attach to papillary muscles within the ventricles.
Two mnemonics to help remember the valves are: “Try Pulling My Aorta” and “LAB RAT.” Try Pulling My Aorta helps remember the order of blood flow through the valves in the heart: Tricuspid, Pulmonary, Mitral, Aortic.
Tricuspid (AV valve)
Pulmonary (Semilunar valve)
Mitral (AV valve, also known as the bicuspid valve)
Aortic (Semilunar valve)
LAB RAT helps remember which side of the heart the AV valves are on.
Left atrium: bicuspid
Right atrium: tricuspid
Coronary Arteries
The heart has its own blood supply via four major coronary arteries: right and left coronary arteries, left anterior descending artery, and left circumflex artery.
Nervous System Components
The entire cardiovascular system is coordinated by the nervous system. The 5 key nervous system components within the heart are the sinoatrial (SA) node, atrioventricular (AV) node, atrioventricular bundle (Bundle of His), right and left bundle branches, and Purkinje fibers. The SA node serves as the heart’s pacemaker, with the AV node available to serve as a backup (but slower) pacemaker. While the nodes signal for contraction, they do not contain contractile tissue themselves. We will re-visit the inner workings of how this system works to create our medical assessment, the electrocardiogram, in our physiology section.
After examining the structures that make up the heart, we can look at how they work. In this section, we will cover blood flow and the neurological flow that creates what we can visualize as an electrocardiogram (EKG).
Blood Flow
The blood flows through the heart in a very specific order.
Hearts Blood Flow.jpg
Heart’s blood flow (Betts et al., 2013)
This can be visualized and memorized as 6 steps for each side of the heart:
Right side:
Vena cava: Deoxygenated blood flows from the body to the heart.
Right atrium: The blood then enters this superior chamber on the right side of the heart.
Tricuspid valve: The blood flows from the right atrium into the right ventricle via this valve
Right ventricle: The blood enters the ventricle, which will contract to send the blood toward the lungs for oxygenation.
Pulmonic valve: The blood leaves the right side of the heart, passing through this valve.
Pulmonary artery: This artery carries the deoxygenated blood to the lungs
Left side:
Pulmonary veins: The pulmonary veins bring oxygenated blood from the lungs to the left side of the heart.
Left atrium: After passing through the pulmonary veins, the oxygenated blood enters this first chamber on the superior left side of the heart.
Bicuspid valve: The blood flows from the left atrium to left ventricle, passing through this AV valve.
Left ventricle: The blood enters this contractile chamber, which will send the oxygenated blood to the body.
Aortic valve: The blood passes through the aortic valve to leave the heart as it heads towards the body.
Aorta: This vessel carries the blood to the systemic circulation.
Neurological Perspective
From the neurological perspective, the flow of nervous system signals within the heart begins at the SA node. The SA node, often referred to as the pacemaker, naturally signals the heart to beat approximately 75 times per minute in adults. This is called the sinus rhythm. The electrical impulse then travels to the AV node, in a process known as depolarization. This depolarization passes thru both atria, causing them to contract. From here, the nervous system signal continues to the atrioventricular bundles (Bundle of His) within the ventricles, and then to the Purkinje fibers, which signal the ventricles to contract.
EKG Components
In healthcare, we visualize this process via the electrocardiogram (EKG). The normal heart rhythm has three key EKG components: P wave, QRS complex, and T wave, each of which signal a specific heart process.
The P wave represents atrial depolarization, where atria contract.
The QRS complex represents ventricular depolarization, where ventricles contract.
The T wave represents ventricular repolarization, where ventricles relax.
The heart rhythm and EKG can be influenced by hormones, stress, neurotransmitters, arousal, and other factors within the body.
QRS complex.jpg
QRS complex.jpg
Electrical Activity of the Heart.jpg
Electrical activity of the heart (Betts et al., 2013)
In abnormal conditions, such as a myocardial infarction (heart attack), the EKG is instrumental in diagnosis and prognosis. Acutely the ST segment will show alterations, and the Q wave will show persistent alteration for several hours. In cases where rapid care is not initiated, the Q wave may remain indefinitely elevated, typically indicating areas of heart tissue death.
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please make sure citaions are in APA