Introduction
- Heart disease is the #1 killer in the United States. It runs in families. Avoid animal fats, exercise are preventive, but not always. Don't skip this reading!
Overview of the Cardiovascular System
- The cardiovascular system refers to the heart, blood vessels and blood
- Its purpose is to transport gases and nutrients
- Blood is inside blood vessels, pumped by the heart.
- Blood vessels surround the lungs and pick up oxygen and release carbon dioxide waste.
- Oxygenated blood immediately returns to the heart
- The heart pumps out oxygenated blood to the whole body
- Here is a good little video of mine on the cardiovascular system (again, do not laugh at the drawings!!!)
The Types of Blood Vessels
- Remember "arteries away, veins toward"
- Arteries take blood away from the heart towards body tissues
- Arteries get smaller and smaller (arterioles are tiny arteries). They lead into capillaries (the smallest blood vessels).
- Capillaries are where oxygen is released and carbon dioxide waste is picked up by the blood. This is called "exchange".
- Venules lead out of capillaries towards veins.
- Veins take blood back to the heart.
The Heart is a Double Pump
- The heart is made of cardiac muscle, but also other tissues, and that is why it is called an organ
- coronary circulation - the blood vessels and blood that feed the heart
- pulmonary circulation - the circulation of blood to the lungs and back to the heart
- systemic circulation - the circulation of blood from the heart, out to the body, back to the heart
- Flow of blood through the heart - blood enters the right atrium (coming from either the superior (top of body) or inferior (lower part of body) vena cava.
- From the right atrium, blood goes through the Right atrioventricular valve (AV) into the right ventricle.
- From the right ventricle, blood travels up the pulmonary trunk, which bifurcates into two pulmonary arteries, taking blood to the lungs.
- From the lungs (picking up oxygen and dropping off carbon dioxide), blood enters the left atrium of the heart through the pulmonary veins.
- From the left atrium, blood flows through the left AV valve (also called mitral valve or bicuspid valve) into the left ventricle.
- From the left ventricle, blood flows up the aorta and out to the body.
- Here's a good video on blood flow through the heart:
- Cardiac cycle - the heart pumps 70 beats per minute (on average)
- the atria contract
- the ventricles contract
- the heart rests
- the cycle repeats itself
- Lubb-dubb = Lubb is when the AV valves shut. They shut when the ventricles start to contract, but haven't yet pushed the blood out (isovolumetric contraction. Dubb is when the ventricles relax again and the semilunar valves shut.
- The heart beats on its own. Why? Because cardiac myocytes (heart muscle cells) generate spontaneous electrical signals
- SA node (sinoatrial node) - primary pacemaker, pacing the heart at 70 bpm
- AV node - secondary pacemaker - would take over if something happened to the SA node - paces the heart at 55 bpm
- Purkinje fibers - also a secondary pacemaker - electrifies the ventricles - paces them at 35 bpm
- EKG (or ECG) - electrocardiography - a tool to study the heart's electrical activity; used to diagnose problems; the graph changes with different types of heart problems
- The heart can also be controlled externally by the parasympathetic (rest and digest) and sympathetic (fight or flight) nervous systems via the cardiac control center in the medulla oblongata
Blood Pressure
- Pulse = heart rate; pulse is the pressure of the blood on the artery wall
- Sphygmomanometer - this is the blood pressure devide.
- They wrap a cuff around the arm and apply pressure to cut off blood flow in the brachial (arm) artery
- The cuff inflates with a bulb to increase the pressure to about 180 mmHg (about 120 mmHg above the systolic (ventricular pressure) - blood flow is cut off.
- Then they gradually release the pressure on the cuff, watching a little gauge as the pressure comes down.
- Meanwhile, they listen to your heart using a stethoscope applied to the inside of the elbow (antecubital). They listen and hear no sound when the cuff is inflated = no blood flow.
- When pressure is gradually released, blood begins to flow. Turbulent flow of the blood is heard as a tapping sound.
- When this begins, the pressure on the gauge is the systolic pressure (high number; denominator)
- When this stops, the pressure on the gauge is the diastolic pressure (low number; numerator)
Two Cardiovascular Pathways
- pulmonary circulation - the circulation of blood to the lungs and back to the heart
- systemic circulation - the circulation of blood from the heart, out to the body, back to the heart
Exchange at the Capillaries
- Gases and nutrients are released to the tissues or released from the tissues into the blood in the capillaries
- Capillary walls are only one single cell thick, so molecules easily diffuse across
- Blood pressure forces fluid out between the capillary cells also (little spaces called clefts) and this fluid goes into the extracellular space
- Osmotic pressure (the ability of blood to draw water into it) is dependent on colloids (particles and salts) in the blood
- At the arteriolar end of a capillary, blood pressure is higher than osmotic pressure, so fluid is forced out
- At the venular end of a capillary, blood pressure is lower than osmotic pressure, so fluid moves into the blood
- see videos in the textbook on this
- also, this one is good:
- see videos in the textbook on this
Cardiovascular Disorders
- Cardiovascular disease (CVD) is the leading cause of death in the United States; please read the do's and don'ts
- CVD includes heart attack, hypertension, aneurysm, atherosclerosis and stroke.
- Bypass surgeries are frequently performed where stents are inserted into coronary arteries to ensure blood flow to the heart when blood vessels are blocked.
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