Circulation
1. Importance of a Circ. System
a. Multi-cellular organisms need transport system for nutrients and O2
b. 96 000 km of blood vessels which supply 60 trillion cells
c. Heart pumps 5 L of blood from heart – lungs then back / minute
d. Purpose
1. To dump O2 and pick up wastes (carried to liver/kidneys)
q Then glucose is broken down into C O2 and water
q This releases energy (ATP)
2. Chemical Messenger
q Carrying hormones that are produced in the endocrine gland
3. Distributes Heat
q Regulate heat by adjusting flow to extremities
4. Maintains fluid levels
2. Blood Vessels
a. Arteries
q Carry blood away from the heart
b. Arterioles
q Smaller arteries
c. Capillaries
q Tiniest blood vessels that connect arteries to veins
d. Veins
q Carry blood back to heart
3. Arteries
a. Outer and inner layers of connective tissue
b. Middle muscle fibers and elastic tissue
c. Stretch to accommodate rush of blood
d. Elastic fibers recoil during relaxation phase
e. Aneurysm
4. Arterioles
a. Composed of connective tissue, elastic and muscle
b. Muscle controls diameter
1. Vasoconstriction
q paleness
2. Vasodilation
q Blushing
5. Capillaries
a. Single layer of cells (less than 1 mm long, diameter of 0.005 mm)
b. Ideal for diffusion, easily destroyed though
c. Bruising
q Blood rushes into interstitial spaces
d. O2 diffuses from blood into surrounding tissues
e. Also exchange of minerals, vitamins, nutrients etc.
f. Blood changes to purple/blue colour
6. Veins
a. Capillaries merge and become venules, were deoxygenated blood enters.
b. Venules merge and become veins (increased diameter)
c. Carries blood that is on its way back to the heart
d. Pressure problems
1. Pressure has dropped and the blood must make its way back to the heart
q Valves to prevent backwards flow
q Skeletal muscles also contract and push against veins
1. In Mammals the heart is a double pump, 4 chambered muscle
2. Surrounded by a fluid filled membrane called the pericardium
3. Size of fist, beats 70 times/minute, 300g
4. Double Pump
a. Separated by a wall of muscle (septum)
b. Left side mirrors right side
c. Right side receives deoxygenated blood from tissues, pumps it to lungs (pulmonary circulatory system)
d. Left side received oxygenated blood from the lungs, pumps it to body (systemic circulatory system)
5. Oxygenated Blood from Lungs
a. Oxygenated blood from the lungs is carried through pulmonary veins to the left atrium.
b. Blood flows from the atrium into the left ventricle as it relaxes.
c. The ventricle then contracts, to force blood out to the aorta.
1. AV valve between the atrium and ventricle
2. Semilunar valve between the ventricle and the aorta
d. Oxygenated blood is carried to all parts of the body.
e. The heart itself receives blood from the coronary arteries. They have a very small diameter and may become blocked, producing a heart attack.
6. Deoxygenated blood
a. Blood from the upper body enters the heart through the superior vena cava
b. Blood from lower body enters through the inferior vena cava.
c. Blood moves from the right atrium through an AV valve to the right ventricle.
d. When the right ventricle contracts, blood moves through a semilunar valve into the pulmonary arteries to the lungs.
e. Blood returns from the lungs through the pulmonary veins to the left side of the heart to complete the cycle.
7. Control of the heartbeat
a. Myogenic muscle (contract without external nerve stimulation)
b. Beat is set by sinoatrial (SA) node
1. Located where venae vacae eneters the R atrium
2. Acts as pacemaker
3. Contractions travel to the AV (atrioventricular node)
4. The AV node conducts the nerve impulses towards the ventricles
c. Trachycardia
d. Bradycardia
8. Heart sounds
a. The sounds of the heartbeat are caused by the closing of the heart valves.
b. The first sound (lub) is caused by blood hitting the AV valves as they close.
c. The second sound (dub) is caused by blood hitting the semilunar valves as they close.
d. If the valves do not close properly, some blood can pass through the valves and cause a heart murmur. This can be corrected by replacing the valve.
9. Blood pressure
a. Diastolic pressure
1. When the heart relaxes between beats (diastole) the arterial pressure drops to about 80 mm Hg.
2. The pressure does not drop to 0 because the arterial walls are elastic and apply force on the blood.
3. The 80 mm Hg diastolic pressure keeps the blood flowing between beats.
b. Systolic pressure
1. When the ventricles contract (systole) the pressure in the arteries leaving the heart rises to about 120 millimeters of mercury (mm Hg).
2. Normal values: systolic/diastolic = 120/80 mm Hg.
c. Blood pressure is monitored by the medulla oblongata