The heart is situated in the chest cavity and surrounded by a fluid filled sac called pericardium.
The heart is the organ that helps supply blood and oxygen to all parts of the body. It is separated by a septum into 2 halves, which are in turn divided into atria and ventricles. Therefore, the heart is mainly formed of 4 chambers: 2 atria (upper 2 chambers) and 2 ventricles (lower 2 chambers).
The heart wall is formed of:
- epicardium - the outer layer
- myocardium - the middle layer
- endocardium - the inner layer
One way flow through the heart is ensured by 2 sets of valves (4 valves):
- aortic valve: impedes blood flowing back into the ventricle, as it is pumped from the left ventricle into the aorta
- pulmonary semilunar valve: prevents back flow of blood, as it is pumped from the right ventricle to the pulmonary artery
- tricuspid valve(3 cusps): prevents back flow of blood into the right atrium, as it flows from the right atrium to the right ventricle.
- mitral valve (bicuspid valve): prevents back flow of blood into the left atrium, as it is pumped from the left atrium to the left ventricle.
Cardiac output (CO) is the amount of blood pumped by the heart per unit time, measured in liters per minute. In a normal adult heart, the cardiac output is 4.9 L/min. The cardiac output is a function of heart rate and stroke volume.
Stroke volume (SV) is the amount of blood pumped by the left ventricle of the heart in one contraction. Stroke volume is about 70 mls in a normal adult.
Heart rate (HR) is the number of heartbeats per unit of time and is 70 bpm in a normal adult.
CO = HR x SV
Reflex control of heart rate: control center in medulla oblongata.
- sympathetic neurons (like norepinephrine) and parasympathetic neurons (like acetylcholine)
Sympathetic neurons increase the heart rate (sympathetic system - "fight or flight").
Parasympathetic neurons decrease the heart rate (parasympathetic system - "rest and digest").
Blood pressure (BP) is the pressure exerted by circulating blood upon the walls of blood vessels. During each heart beat, BP varies between a maximum (systolic) and a minimum (diastolic) pressure.
BP = CO x Total Peripheral Resistance.
Total Peripheral Resistance is the sum of the resistance of all peripheral vasculature in the systemic circulation.
http://biology.about.com/od/humananatomybiology/ss/heart_anatomy.htm
http://www.medicinenet.com/stroke/article.htm
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