Bio 20IB- Circulation

• arteries carry blood away from the heart
• the outer and inner layers of arteries are made of connective tissues

  the middle layer is made of muscle fibers and elastic connective tissue
• when the heart contracts, blood pressure increases in arteries, and when it relaxes blood pressure decreases
• blood from arteries passes into smaller arteries called arterioles
• the middle layer of arterioles are made of elastic fibers and smooth muscle
• the automatic nervous system regulates the diameter of arterioles
• vasoconstriction is the contraction of the heart, relaxation is called vasodilation
• precapillary sphincter muscles regulate the movement of blood from arteries into capillaries. they only open when that area needs blood
• automatic nervous system: the part of the nervous system that controls the motor nerves that regulate equilibrium, and that is not under conscious control
• atherosclerosis is the most common group of disorders called arteriosclerosis
• • atherosclerosis is when fatty material builds up on the walls of the arteries
  • blood can clot which blocks flow which can cause a heart attack
• • and aneurysm is a bulge that forms in the walls of a weakened blood vessel, usually an artery
  • the wall can rupture
  • an aneurysm in the brain can cause a stroke
• • capillaries are the smallest blood vessels in the body and are one cell thick
  • they are the site of fluid and gas exchange between blood and body cells
• • capillaries merge be form venules and then veins
• in veins, blood pressure is reduced, but there are one way valves in veins that help push blood to the heart
• • if pooling of blood occurs over a long time, the valves are damaged leading to bulging of the veins.
  • this is known as varicose veins
• • the heart is a muscular organ, surrounded by a fluid filled membrane called the pericardium.
• • the heart is made of 2 pumps separated by the septum
  • the right side takes deoxygenated blood and pumps it to the lungs
  • the left side takes oxygenated blood from the lungs and pumps it to body cells
• • vessels that carry blood to and from the lungs form the pulmonary circulatory system
• • vessels that carry blood to and from the body form the systemic circulatory system
• ventricle: a muscular, thick-walled chamber of the heart that delivers blood to the arteries
• • vena cava carries deoxygenated blood from the body and brings it to the right atrium
• • oxygenated blood from lungs enter left atrium through the pulmonary veins
• • atrioventricular valves separate the atria from ventricles
  • they allow one way blood flow
  • the are supported by bands of connective tissue called cordae tendinae
• • semilunar valves separate the ventricles from the arteries
  • they allow for one way blood flow
• • the aorta is the largest artery and carries oxygenated blood away from the heart
• • the heart is made of cardiac muscle
  • the muscle can contract without being stimulated by external nerves (myogenic muscle)
• • the hearts tempo is set by the sinoatrial node which is a bundle of specialized nerves in the upper right atrium
• • contractions from SA node passes to the atrioventricular node which passes nerve impulses through the septum and to the ventricles
  • then nerve contractions go up along the outer walls of the ventricles and to the atria
• • heart rate is influenced by the sympathetic and parasympathetic nervous system which conduct impulses from the brain to the SA node
• sympathetic nervous system: a division of the automatic nervous system that prepares the body for stress
• parasympathetic nervous system: a division of the automatic nervous system that returns the body to normal resting levels following adjustments to stress
• • heart sounds are caused by the closing of valves
  • diastole: relaxation of the heart, during which the atria is full with blood
  • systole: contraction of the heart, during which blood is pushed out of the heart
• • cardiac output is defined as the amount of blood that flows from the heart per minute
  • 2 factors affect cardiac output: stroke volume and heart rate
• stroke volume: the quantity of blood pumped with each beat of the heart
• • blood pressure is the force of blood on the walls of the artery.
  • measured with a sphygmomanometer and measures systole and diastole
  • blood pressure depends on cardiac output and arteriolar resistance
• higher cardiac output= higher blood pressure
• • when blood pressure is high, receptors located in the aorta and the carotid arteries respond and send a nerve impulse to the medulla oblongata
  • sympathetic nerve impulses decrease and parasympathetic increase
  • arterioles dilate, heart rate and stroke volume decrease
• thermoregulation: maintenance of body temperature within a range that enables cells to function efficiently
• when the brain sensors a rise in temp, nerve impulses are coordinated with the hypothalamus. 2 things happen:

  • hypothalamus sends signal to sweat glands to begin sweating
  • nerve message sent to blood vessels, which dilate, allowing the blood to lose heat against the cooled skin. The blood returns to the internal organs cooling them down