Download Lecture 20: Heart

Lecture 20: Heart
M/O Chapter 22
The Heart
93.
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96.
Describe the position of the heart in the thoracic cavity.
Describe the layers of the pericardium and the location of the pericardial cavity.
Discuss the structure and significance of the endocardium.
Identify the major blood vessels entering and leaving the heart and classify them as either artery or vein,
and determine whether they carry oxygenated or deoxygenated blood.
97. Describe the blood flow through the heart, naming all chambers and valves passed.
98. Compare and contrast the structure and function of the pulmonary and systemic circuits.
99. Trace blood flow through the coronary circulation from the aorta to the right atrium.
The heart is located slightly left of the midline of the body, deep to the sternum, within the pericardial cavity. Remember that the
pericardial cavity is contained within the mediastinum, which is the space between the left and right pleural cavities. The part of the
heart containing the right atrium and ventricle is slightly more anterior, while the left atrium and ventricle is slightly posterior.
The Pericardial Cavity
The heart is contained within the pericardium, which has many layers.
1. The fibrous pericardium is the outermost layer. It is attached to the diaphragm and the vessels that directly leave and enter the
heart.
2. The next layer is the serous pericardium. The serous pericardium has two layers that are separated by a space called the
pericardial cavity.
A. The parietal layer of the serous pericardium lines the deep aspect of the fibrous pericardium.
B. The visceral layer of the serous pericardium lines the superficial surface of the heart itself. This layer is also called the
epicardium.
3. The pericardial cavity contains serous fluid and prevents friction between the beating heart muscle and the rest of the thoracic
cavity.
A. Pericarditis is when the pericardium becomes inflamed. It can be extremely painful and can lead to fluid in the pericardial
cavity, which can potentially cause cardiac tamponade (when the heart cannot beat adequately because it is squeezed by the
fluid found in the pericardial cavity).
4. The heart muscle itself is called myocardium.
5. The inner layer of myocardium is
covered with endocardium, which
is a layer of simple squamous ET
(endothelium) covering a thin layer
of adipose tissue. The endothelium is
continuous with the inner layer of the
blood vessels (tunica intima).
Label this picture of the pericardial cavity,
including all of the following structures:
•
•
•
•
•
•
•
•
•
Fibrous pericardium
Myocardium
Endocardium
Pericardial cavity
Pericardial sac
Serous pericardium
Visceral layer of the serous pericardium
Parietal layer of the serous pericardium
Epicardium
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Summary of the Circulatory System
The heart is actually two pumps, stuck together, carrying out two separate tasks. One pump circulates fresh, oxygenated blood to the
cells in the body. The same pump returns the blood, after it is dirty and used up, to the heart. This is considered the systemic system.
The other pump circulates dirty, used up blood to the lungs, where carbon dioxide is removed and oxygen is absorbed. This freshly
oxygenated blood is then returned to the heart. This is considered the pulmonary system.
Heart Anatomy
The heart has four chambers distributed over two sides. The left side of the heart receives oxygenated blood from the lungs and
pumps it to the body. The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs. Both sides of
the heart receive blood in the atria and pump blood with the ventricles.
1. Used up blood from the body enters the right atrium of the heart via the superior vena cava and the inferior vena cava. Used
up blood from the heart also enters the right atrium via the coronary sinus.
2. The blood passes into the right ventricle, through the right AV valve (aka tricuspid valve).
A. The valve is held into place by chordae tendineae, which are collagen fiber ropes that are connected to the ventricle wall
via papillary muscles.
3. Blood is then sent through the pulmonary semilunar valve into the lungs, via the pulmonary trunk which ultimately branches
into the right and left pulmonary arteries.
4. Blood is oygenated in the lungs, then comes back to the heart via the left and right pulmonary veins.
5. Blood enters the left atrium and is shunted into the left ventricle, through the left AV valve (aka bicuspid or mitral valve).
6. From the left ventricle, fresh oxygenated blood is pumped to the body, through the aortic semilunar valve, via the ascending
aorta.
Coronary Circulation
Before any other body structures receive the oxygenated blood, some of it is siphoned off by the coronary arteries, which branch
off the ascending aorta immediately superior to the aortic semilunar valve. This ensures that the heart always has a fresh supply of
oxygen first, to supply the energy needs required by the cardiac muscle tissue to continue beating until you die.
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Lab 20: The Heart and Great Vessels
Reading: M&O Ch. 22, and portions of Ch. 23
Part 1: Isolated Hearts
Each pair of you will dissect a sheep heart first. Use M&O pp. 671-676 and Figs. 22-6 and 22.8 to find the listed structures. Then,
pick one of the human hearts and review. Take care to note any pathologies you might encounter in the human hearts. If time permits,
look at more than one human heart.
1. Orient the heart as if you were looking at the anterior surface of a patient or cadaver. These instructions might be helpful:
A. Identify the apex, base and diaphragmatic surface of the heart.
B. Hold the heart in your RIGHT hand.
C. Direct the apex toward your thumb and wrist.
D. The base should be held in the space between your thumb and index finger.
E. In this position, you should be viewing the anterior surface of the heart.
2. Keeping this position in mind, identify the following structures on the external surface of the heart.
A. right atrium
B. right ventricle
C. left atrium
D. left ventricle
E. coronary sulcus
F. coronary sinus
G. anterior interventricular sulcus
H. posterior interventricular sulcus
3. Now focus on the great vessels (the ones that enter and exit the heart). See how many of these you can find on your heart.
A. superior vena cava
B. inferior vena cava
C. pulmonary trunk
D. right and left pulmonary arteries
E. pulmonary veins
F. ascending aorta
4. Go ahead and open up the right atrium. Identify the following structures:
A. superior and inferior vena cavae
B. opening of coronary sinus
C. interatrial septum
5. Find the path between the right atrium and the right ventricle. Identify the following structures:
A. right atrioventricular (tricuspid) valve
B. chordae tendinae
C. papillary muscles
D. interventricular septum
E. pulmonary semilunar valve
6. Carefully use a probe to identify the pulmonary trunk as it leaves the right ventricle.
7. Find the left atrium and identify the left and right pulmonary veins which enter it from the lungs.
8. Find the path between the left atrium and the left ventricle. Identify the following structures:
A. left atrioventricular (mitral) valve
B. aortic semilunar valve
9. Examine the aorta and identify the left and right coronary arteries.
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Part 2: Position of the heart
The great vessels are the vessels that enter and exit the heart, and their immediate branches in the thorax. You’ve already seen at least
stumps of the vessels entering and exiting the heart. Turn to the cadavers to see more.
Appreciate the slightly asymmetric placement of the heart within the thorax, slightly to the left side. Also note the approximate rib
levels between which the heart lies. These landmarks will be important to you in clinical practice.
The diaphragm, a skeletal muscle innervated by the phrenic nerve, separates the thoracic cavity from the abdominal cavity. First
examine the contents of the thoracic cavity. The left and right lungs lie in left and right pleural cavities, respectively. These cavities
lie on either side of the mediastinum, a space between the pleural cavities that contains the heart, great vessels, esophagus, and
thymus, a gland of the immune system that atrophies in adults.
What follows is confusing, so read carefully! The heart sits in a compartment in the mediastinum defined by the pericardial sac
and called the pericardial cavity. The pericardial sac consists of an outer fibrous pericardium layer, which is fused to the diaphragm
and great vessels, and a two layered inner serous pericardium. The outer layer of the serous pericardium is the inner surface of the
pericardial sac. The inner layer of the serous pericardium is actually the outer layer of the heart, also called the epicardium. In other
words, between the two layers of the serous pericardium is a space, and it is this space that you put your hand into when you touch the
heart. Because both layers lining this space are serous membranes they ooze serous fluid into the space, and this fluid serves to reduce
friction as the heart expands and contracts.
Part 3: Great Vessels
You are responsible for all the following vessels. Use M&O Figs. 22.6, 22.8 and 23.9 to assist you.
1. Arteries
A. Pulmonary Circulation
i. pulmonary trunk
ii. right pulmonary artery
iii. left pulmonary artery
B. Systemic Circulation
i. aorta (ascending)
ii. aortic arch
iii. thoracic aorta
iv. brachiocephalic artery
v. right subclavian artery
vi. right common carotid artery
vii. left common carotid artery
viii.left subclavian artery
2. Veins
A. Pulmonary Circulation
i. pulmonary veins
B. Systemic Circulation
i. superior vena cava
ii. inferior vena cava
iii. brachiocephalic veins
iv. subclavian veins
Bio 6: Human Anatomy
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Spring 2014: Riggs
External Brain 20: The Heart
93.
94.
95.
96.
Describe the position of the heart in the thoracic cavity.
Describe the layers of the pericardium and the location of the pericardial cavity.
Discuss the structure and significance of the endocardium.
Identify the major blood vessels entering and leaving the heart and classify them as either artery or vein,
and determine whether they carry oxygenated or deoxygenated blood.
97. Describe the blood flow through the heart, naming all chambers and valves passed.
98. Compare and contrast the structure and function of the pulmonary and systemic circuits.
99. Trace blood flow through the coronary circulation from the aorta to the right atrium.
Your Task
1. Label images or DRAW pictures that include ALL required lab structures.
2. Draw a picture that summarizes the systemic vs pulmonary circulations.
3. Draw a picture that summarizes the coronary circulation.
4. Why is the wall of the left ventricle thicker than that of the right?
5. What is the path of blood flow through the heart?
6. Which chambers contain oxygenated, which deoxygenated blood?
7. Did you notice anything unusual in the human heart you examined? Can you explain it?
Bio 6: Human Anatomy
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Spring 2014: Riggs