Cardiovascular++System

The Circulation** **The Circulation is Constructed from Pumps, Tubing and Valves** **The Human Heart is Really 2 Hearts in Series** **The Entire Blood Supply Passes Through the Heart About Once Every Minute** **Valves Keep the Blood Moving in One Direction** **The Major Pump is a Heart with 4 Chambers** > >> > >> **Blood Flow Through Different Parts of the Circulation Must be Balanced** > > **The Muscle Pump Helps Return Blood to the Heart** **Different Blood Vessels have Different Functions** **Blood Flow to the Organs Matches Body Requirements** **Blood Flow through Organs is Regulated by Nerves and Chemical Agents**
 * Cardiovascular System (Heart as a Pump) (Heart Electrical Activity)
 * Pumps:
 * Circulatory pumps (hearts) are vessels filled with the circulatory fluid or blood
 * When muscles around the container contract they exert pressure on the blood, causing it to flow
 * Heart type: pump produces a high pressure which causes blood to flow out through arteries
 * Muscle pump: muscle contraction squeezes veins, causing blood to flow toward heart
 * Tubing or pipes = arteries, capillaries, veins
 * Carry blood toward delivery site
 * Sometimes deliver within a few microns of site (capillaries in tissue)
 * Blood vessels may be elastic (which helps keep the pressure high between heartbeats)
 * Vessels may constrict and dilate (which gives control over the flow)
 * Valves give direction to the flow
 * Blood vessels (including hearts & veins) have flap valves that open in only one direction
 * Example: when pressure increases in veins this opens valves toward the heart and closes those in the other direction -> blood flows toward heart
 * The purposes of circulation:
 * To deliver food materials and oxygen to the tissues
 * To remove waste products and heat
 * These things can be done by diffusion in a small animal, but **in a large animal a circulation is necessary.**
 * Right heart:
 * Pumps to lungs: nearly 100% of the flow goes through the lungs
 * Low pressure side: 25 mm Hg systolic pressure in humans
 * Right ventricle has thin walls
 * Left heart:
 * Pumps to rest of body
 * High pressure side: 120 mm Hg systolic pressure in humans
 * Left ventricle has thick walls
 * Right & and left atria:
 * Help fill the ventricles
 * Very low pressure
 * Thin walls
 * Pumping of the right & lift sides occurs together
 * Must be accurately balanced, otherwise fluid may accumulate in the lungs **(pulmonary edema)**
 * The muscle pump helps return blood to the heart
 * When muscles contract the veins passing through them are squeezed
 * This causes blood to flow toward the heart
 * Valves prevent flow away from the heart
 * This diagram is designed to show the principles of the circulation instead of exact anatomy
 * It does not show the 2 lungs, for example
 * The blood leaves the lungs saturated with oxygen (shown in red).
 * In the capillaries oxygen is given up to the tissues and the blood is partially depleted of oxygen (shown in blue)
 * Note the positions of valves in the heart and veins
 * Your body has approximately 5 liters of blood (large people have a little more, small people a little less)
 * The heart's pumping rate is called the cardiac output: at rest its value is about 5 liters/min
 * Comparing the volume with the cardiac output you can see that the entire blood volume passes through the heart on the average once every minute
 * All of the output from the right heart goes through the lungs (5 liters/min)
 * The output from the left heart splits and goes through different organs
 * General outline of the circulation:
 * [[image:http://members.aol.com/Bio50/LecNotes/LNPics/ln15b.gif width="528" height="118" align="bottom"]]
 * Raising the pressure of blood in a tube will cause it to move in both directions
 * In the body blood flows in only one direction because flow in the other direction is prevented by valves
 * Valves are flaps of flexible material designed to open when pushed in one direction and close when pushed in the other
 * Valves are found in the heart and veins, but not in the arteries
 * The heart has a **__set of 4 valves__**
 * The valves in the veins were first discovered by **Harvey**
 * Our group of animals (the mammals) and the birds have hearts with 4 chambers (amphibians have 3 and fishes 2)
 * The heart is really 2 hearts in series: a right heart and a left heart
 * Each heart has 2 chambers, an atrium and a ventricle
 * The heart acts by contracting and squeezing the blood- this raises its pressure and causes it to move
 * The right heart is the low pressure side- it pumps blood to the lungs
 * The entire blood supply goes through the lungs:
 * Lung blood picks up O2 and eliminates CO2
 * The left heart is the high pressure side- it pumps blood to all the other body organs
 * Different organs get different amounts of blood, according to needs
 * Since blood circulates the flows through each major branch (R heart, lungs, L heart, body organs) must be identical
 * Balance of L and R hearts:
 * Normally balance is maintained by **Starling's mechanism:** more filling of heart causes more vigorous contraction and a higher cardiac output
 * In failure of the left or right heart the balance is upset and fluid will accumulate.
 * If the outputs of the left and right side of the heart are temporarily unbalanced fluid will accumulate in the lungs or in the systemic circulation producing edema:
 * Venous return:
 * Flow into the right heart is called the venous return
 * In exercise venous return must be maintained at adequate levels
 * Requires the [|muscle pump:]see below
 * Valsalva manouver greatly reduces venous return
 * Valsalva manouver is trying to exhale while holding the glottis closed
 * We do the Valsalva manouver during many types of straining, such as lifting a heavy weight, defecating, delivering a baby, etc..
 * Valsalva manouver during heavy exercise can trigger a heart attack in a person with heart disease
 * When muscles contract they squeeze the veins running through them and raise the venous blood pressure- because there are valves the blood flows in one direction, towards the heart
 * This squeezing action is sometimes called the "muscle pump"
 * Example: in walking, when you swing your leg backward, muscles compress the femoral vein, forcing blood towards the heart. Valves prevent flow towards the feet. When you swing the leg forward the femoral vein fills with blood again.
 * The muscle pump is extremely important in returning blood to the heart in exercise
 * After vigorous exercise it is important to "warm down" by walking around- this keeps the muscle pumps going, returning adequate blood to the heart during this important recovery period
 * Joggers sometimes suffer heart attacks if they sit down too soon after a vigorous run. Why is this so? [|Discuss your answer.]
 * Arteries:
 * Designed for high pressure
 * Elastic: must swell to take up blood expelled by the heart
 * Swelling stretches elastic tissue and keeps the blood pressure fairly high between heart beats
 * Small arteries (arterioles) have muscles that contol their diameters (precapillary sphincters): used to control blood flow through an organ
 * Veins:
 * Low pressure
 * Expand to take up blood when animal is not active
 * Capillaries:
 * This is where materials are delivered from blood to cells, and vice versa
 * Thin: one layer of flattened (squamous) cells
 * Not elastic
 * Active organs such as the liver, brain and kidney have high blood flows at rest
 * About 25% of the cardiac output goes to the kidney
 * Composition of the blood is continuously regulated by the kidney
 * Gastrointestinal tract & liver get another 25%
 * Muscle circulation at rest is about 20% of cardiac output
 * Brain needs about 15% of the cardiac output
 * Circulatory system adapts to meet body's needs:
 * In [|exercise blood flow] to active muscles is greatly increased
 * Total cardiac output increases up to ~25 liters/min
 * Percentage to muscles increases to as much as 80%
 * Blood flow to skin is increased or decreased to [|regulate body temperature]
 * What do you think happens to blood flow to the viscera (stomach & intestines) during exercise? What do you think happens to the blood flow to the heart muscle? [|Check your answers.]
 * Blood flow can be increased by increasing the blood pressure (higher cardiac output, constriction of many arterioles)
 * It can also be increased by opening up (dilating) arterioles in the tissue which needs more blood
 * Both cardiac output and blood vessel diameter are controlled by hormones and nerves
 * The regulation is automatic, mostly controlled by the [|autonomic nervous system]