Chapter 11
Heart and Vessels
The Heart (the pump of the station)
· Structure and location of the heart
o Apex of the heart is pointed toward left hip and located at the 5th intercostals space. The ventricles are the two lower muscular chambers of the heart.
o Base of the heart is located at the 2nd rib and is the area where the large vessels enter and leave the heart and the location of the two sac like atria chambers.
o The heart is made up of 3 layers of cardiac muscle:
§ Epicardium – also called the visceral pericardium. Helps to protect and anchor the heart to sternum and diaphragm.
§ Myocardium – cardiac muscle arranged like rings around the heart. Layer that contracts. There is a dense fibrous layer deep to the cardiac muscle.
§ Endocardium – Thin sheet of endothelium that is continuous with the vessels that enter and leave the heart.
§ The parietal pericardium is outside/superficial to the epicardium and secrets the serous fluid that lubricates the cardiac sac so the heart can beat in an almost frictionless environment.
o Heart external anatomy
o Heart internal anatomy
o Importance of valves
§ Valves prevent backflow of blood through the heart.
§ Two atrioventricular valves (bicuspid and tricuspid) are anchored to the ventricles by the chordae tendineae (heart strings). The system is a pressurized system.
1. Blood passively fills the chamber, flaps hang down into the ventricles
2. When the ventricles begin to contract, the pressure increases which forces the flaps of the valves closed. The chordae tenineae prevent the flaps from opening back up into the atria.
§ The two semilunar valves (pulmonary and aortic) have 3 cups that fit tightly together. When the ventricles contract the force of the contractions open the valves into the pulmonary vein or aorta as the blood rushes into the vessel. As the ventricle relaxes the cusps come back together.
§ The AV valves and semilunar valves open and close at different time so it is possible to detect problems with individual valves by placing the stethoscope at different points on the chest.
§ When valves do not work properly, the heart is forced to work harder to pump blood, which can weaken the heart over time. Valves can be replaced by pig or synthetic valves.
· Functioning of the heart
o Pathway of blood through the heart and body
o The heart is supplied with nutrients and gases by the cardiac vessels (the presence of the blood in the heart does not accomplish this). These are called coronary arteries and coronary veins.
§ The blood from the veins empties into the coronary sinus in the right atrium.
§ When these vessels become clogged or blocked this can cause chest pain, angina, and if ignored can lead to a cardiac infarction (tissue death from heart attack) when the cells are deprived of oxygen and nutrients.
o Cardiac Cycle
§ Electrical system of the heart determines how often the heart beats and controls the contraction of the heart.
Ø Contractions occur spontaneously but must be regulated so that the chambers of the heart beat in a coordinated way.
It is regulated by two systems:
a. Autonomic nervous system controls the increase or decrease of heart rate.
b. Intrinsic system within the heart tissue which begins at the SA (sinoatrial node) in the right atria, the signal is then carried to the other atria and the AV (atrioventricular node) which carries the impulse to the bottom of the ventricles via the bundle of His.
o This electrical system can be measured by an electrocardiogram (ECG). A normal ECG is shown below.
**Diastole means relaxation and Systole means contraction**
· Cardiac Output and the health of the heart
o Cardiac Output (CO) is a function of stroke volume (volume of blood pumped out with each contraction and heart rate (number of beats per minute)
o Factors affecting cardiac output and effects:
§ Venous return – amount of blood returning to the heart and enlarging the ventricles. The larger the venous return, the more stretched the cells the stronger the contraction. Exercise can increase venous return with the enhanced squeezing action of the skeletal muscles returning blood to the heart. Rapid heart rate or severe blood loss will decrease venous return.
§ Heart rate changes – HR can increase with the loss of blood or can be altered by other factors such as nervous stimulation (sympathetic nerves to speed up), hormones (epinephrine and thyroxine can increase), and changes in ions (lower potassium causes irregular heartbeat).
§ Age, gender, body fitness and body temperature.
Ø Gender – females (72-80 avg. HR), males (64-72 avg. HR)
Ø As you age your heart rate decreases, it is the fastest when you are a fetus (140 to 160)
Ø The colder you are the slower your heart rate.
§ Cardiac congestion – congestive heart failure
Ø Caused by weakening of the heart muscle (clogging of cardiac vessels), heart attack, or high blood pressure.
Ø Failure of left side of the heart causes pulmonary congestion – build up of fluid in the lungs, person can “drown” if not treated.
Ø Failure of the right side of the heart causes peripheral congestion – build up of fluid in the extremities causing edema.
The Vessels – Highway system
· Types of vessels
o Arteries – vessels carrying blood away from the heart. Not always oxygenated blood. Largest and most muscular of the vessels, contain all three tunic layers.
o Arterioles – smaller arteries that feed the capillaries.
o Capillaries – smallest of the vessels and the site of exchange between blood vessels and body tissues. Are only one cell layer thick.
o Venules – drain the capillary bed and lead to veins.
o Veins – Carry blood back toward the heart. Vessel has a reduced smooth muscle layer (smaller and less muscular).
§ Adaptations to help return blood to the heart are valves within the vein to prevent back flow, skeletal muscle contractions pushing blood back up legs and arms, and respiratory pump to push blood through the trunk.
§ Varicose veins occur when the vein becomes distended and the valves stop functioning. Blood can pool and clot in these areas, which if the clot moves can be very dangerous.
· Location of specific vessels:
o Arteries
o Location of Vessels: Veins
· Physiology of Circulation
o Arterial pulse is felt in several places in the body. The pressure you feel when you palpate these areas is the expansion and recoil of the arteries following each heart contraction. These are also the locations of pressure points, areas to apply pressure if person is hemorrhaging.
o Blood pressure measures the pressure the blood exerts on the wall of the artery following each heart contraction. The closer you are to the heart, the higher the pressure will be.
§ Pressure is needed to propel the blood through the vessel system of the body and the elasticity of the arteries is very important to maintaining blood pressure.
§ Pressure is taken by measuring:
Ø Systolic pressure – ventricular contraction, top number, recorded when sounds are first heard in the stethoscope.
Ø Diastolic pressure – ventricular relaxation, bottom number, recorded when the sounds can not be heard in the stethoscope.
§ Factors that affect blood pressure/peripheral resistance
Ø If arteries are narrowed this will increase blood pressure
a. Disease: atherosclerosis
b. Chemicals: nicotine (vasoconstrictor)
c. Diet: high salt, fat and cholesterol
Ø Kidney’s play a major role in regulating blood pressure by stimulating the excretion of more water in the urine or less water.
Ø Hypotension (lower than avg. blood pressure) can be age related as blood pools in the extremities and when going from sitting to standing the BP drops suddenly. Can also be caused by major blood loss.