Anatomy (解剖学) & physiology（生理学）
Lecture one.
Cardiovascular（心脏血管的）system. Anatomy of the heart
The heart:
- Pumps 1.3 gallons of blood per minute. 700000 gallons per year.
- Weighs less than a pound and is the size of a closed fist.
Types of circulation
- Systemic circulation（体循环）：Arteries carry oxygenated blood from the heart to the rest of the body. Veins then return oxygen-depleted blood to the heart.
- Pulmonary circulation (肺循环): pulmonary arteries carry oxygen-depleted blood to the lungs, where it is oxygenated and returned to the heart through pulmonary veins.
- Arteries have thick walls and carry blood away from the heart
- Veins have thin walls and return blood to the heart.
Planes of the body:
- Frontal plane
- Transverse plane
- Sagittal plane
Location of the heart
- The center of the chest in thoracic cavity (胸腔).
- Thoracic cavity contains 3 enclosures
- The mediastinum (中隔膜) is the heart’s enclosure.
- The heart’s right-to-left axis is between the lungs
- Its front-to-back axis is between the sternum(胸板) and backbone
- Its up-and-down axis is between the diaphragm (横隔膜) and neck.
- It sits on the diaphragm
- CPR (stands for: cardiopulmonary resuscitation. 心肺复苏) uses the flexible ribs （肋骨）to compress the heart between the sternum and backbone and pump blood in cases of cardiac arrest (心搏停止). Before the advent of CPR, open cardiac massage(心脏按摩) was used
- Vocabulary: Mortality (死亡率。) posterior (背部。) morbidity (发病率。)
The Heart’s covering is the pericardium (心包膜) meaning”around the heart”
- The pericardium is a saccular (囊状的) structure of tough fibrous (含纤维的) tissue that holds the heart in place and protects it from overexpansion.
- The parietal pericardium (心壁层) lines the walls of the heart’s enclosure
- The visceral pericardium (心包脏层) is a thin layer that covers the adheres（黏附） to the heart.
- The space between the parietal and visceral pericardia is filled with lubricating fluid (润滑液).
- Infections and inflammations (炎症) of the pericardium can cause friction between the heart and the pericardial surfaces, causing severe pain. Trauma（外伤） can cause blood to fill the pericardium, resulting in Constrictive pericarditis (缩窄性心包炎。), blood filling the gap, heart can’t pump itself, causing pericardial tamponade（心包填赛）(blood pressing on the heart). Emergency surgery is necessary to relieve pressure on the heart.
- Vocabulary: Embryology (胚胎学。) Pleura (胸膜。) Pericarditis (心包炎。)
The heart wall has three layers
- The outer layer is the epicardium ( 外心膜。epi means “outer”), which is actually the visceral pericardium. It’s a shiny, transparent, lubricating layer that is an integral part of the heart wall.
- The thin inner layer is the endocardium ( 心内膜。endo means “inner”). It covers the muscle and valves（瓣膜）, and it continues out into the vessels, where it becomes the endothelium（内皮）.
- The middle layer, the myocardium (心肌层。 myo means “muscle”) is powerful, thick, and tireless. It is a specialized form of skeletal muscle that constantly pumps rhythmically without “instruction” from the nerves or blood.
a. It consists of swirled layers of muscle that envelop the heart so that contraction squeezes the chamber to empty them.
b. There are two sets of muscles: one for the ventricles (心室) and one for the atria （心房）. The two sets contract independently.
c. The myocardium is an autonomic （自律的。involuntary）muscle.
- The heart is small, powerful, and untiring organ that pumps blood through more than 50000 miles of vessels.
The nomenclature (命名) of “right and left hearts” indicates an artificial separation of heart function.
- The right (venous) heart receives deoxygenated blood from the body and delivers it to the lungs.
- The left heart receives oxygenated blood from the lungs and delivers it to the body.
- In the embryo, the right and left hearts start out as two separate tubes that eventually fuse.
- The right and left hearts are anatomically different and operate at different pressures. The muscles of the left side are four times thicker and powerful than those on the right side, with pumps blood through a much shorter distance and at lower pressures.
Both sides of the heart have upper and lower chambers.
- The atria (upper chambers) receive blood from the veins and pump it into the ventricles (atrium= waiting rooms).
- The ventricles (lower chambers) receive blood from the atria and pump it to the body and lungs (ventricle= little belly).
- Because the two circulatory systems are connected, both sides of the heart must pump the same amount of blood. Even the smallest mismatch in circulation causes blood to accumulate in one side of the system, such as in heart failure.
- Interventricular septum (室间隔。)
Our four-chambered heart is at the top of the evolutionary line.
- The right atrium (plural is atria) receives deoxygenated blood returning from the body to the heart.
a. Blood returns via the superior and inferior vanae cavae.
b. The right atrium pumps blood into the right ventricle
c. The right atrium is a thin-walled, low-pressure system.
- The right ventricle receives deoxygenated blood from the right atrium.
a. It pumps this deoxygenated blood to the lungs via the pulmonary artery.
b. The right ventricle is a thin-walled, low-pressured system.
- The left atrium receives oxygenated blood from the lungs via the pulmonary veins.
a. It pumps blood into the left ventricle.
b. It’s a thin-walled, high-pressured system.
- The left ventricle receives oxygenated blood from the left atrium.
a. It pumps blood out to the whole body, via the aorta (主动脉。).
b. It’s a thick-walled, high-pressure system.
- The intra-atrial septum separates the atria. It contains a closed embryologic opening. (the foramen ovale 卵圆孔。)
- The intraventricular septum separates the ventricles. It contains part of the conduction system.
- Tricuspid valve (三尖瓣。) mitral valve (二尖瓣。)
The valves of the heart prevent backflow
- The mitral or bicuspid (“two leaves”) valve is located between the left atrium and left ventricle. It prevents backflow into the atrium during systole (心脏收缩).
- The tricuspid valve is located between the right atrium and the right ventricle. It prevents backflow into the atrium during systole.
- The chordae tendineae (腱索) and papillary muscles (乳头肌) hold these valves tightly closed during backflow.
- The aortic (“semilunar,” i.e., shaped like a half moon 大动脉瓣) valve is located between the left ventricle and the aorta. It prevents backflow into the ventricle during diastole (心脏舒张).
- The pulmonic (semilunar) valve (肺动脉瓣) is located between the right ventricle and the pulmonary artery. It prevents backflow into the ventricle during diastole.
- Clinical applications: Damage to the valves can cause stenosis (狭窄。Difficulty in opening), insufficiency (不充分。inadequate closure), or both. Mitral valve prolapse (下垂。脱垂。a slight insufficiency) is common in young women. It is often asymptomatic （无症状的）. These conditions can be treated with valve replacements.
The coronary arteries supply blood to the heart itself.
- The left coronary (冠状动脉) artery comes off the left side of the aorta immediately after leaving the heart. It supplies blood to the right ventricle, lift ventricle, right atrium, and septum.
- The right coronary artery comes off the aorta on the right side, level with the left coronary artery. It supplies blood to the right ventricle, left ventricle, right atrium, and septum.
- Both arteries supply both sides of the heart with plentiful anastomoses (汇合 place where blood vessels join), which provide redundant blood pathways.
- Clinical application: Cessation (休止) of coronary artery flow for more than a few minutes can causes death of the heart muscle, called myocardial infarction (心肌梗塞。“heart attack” or “coronary”). However, more than 70% of the blood flow must be stopped before tissue damage becomes a problem or any symptoms appear.
- The coronary veins drain both sides of the myocardium. They empty progressively into the great cardiac vein, the middle cardiac vein, and from there, into the coronary sinus in the right atrium.
- Anterior interventricular branch （前室间支。）Posterior interventricular branch (后室间支。)
Conduction system
- Muscle is inherently conductive, but during embryologic development, about 1% of the heart muscle differentiates to become able to conduct electrical signals almost as well as nerves. Carries ions.
- Chemical processes in the body produce electrical signals that cause the heart to contact.
- The sinoatrial node (窦房结) is the heart’s primary pacemaker（心脏起搏器）. It is located high in the right atrium.
- The atrioventricular node （房室结） is located just above the atrioventricular septum in the base of the right atrium.
a. The conduction system continues into the ventricles via the atrioventricular bundle (房室束 the bundle of His).
b. The atrioventricular bundle then spreads throughout the ventricles and the septum via the conduction myofibers （肌纤维）of Purkinje.
- This system of conduction is necessary because the myocardium has different inherent contractility (伸缩性) in atria and ventricles and uncoordinated contraction would occur without the conduction system.