Download Circulation and the Heart

Miranda Foster, Alexandria Hurley, Aakash Mehta, Mason Lowndes, Jacob Pearl, Will Smith
Circulation and the Heart
How the heart functions
The heart is made of cardiac muscle cells connected by intercalated discs. These discs help facilitate and synchronize
contractions. Contractions begin with the pacemaker, also known as the sinoatrial node, located within the heart for a
myogenic heart and outside the heart for a neurogenic heart. The signal is passed through atria rapidly, making them
contract in unison, to the atrioventricular node in the wall between the right
atrium and ventricle. The atrioventricular node delays the signal for .1
second allowing all the blood to enter the atria completely before contracting
the ventricles. The electrical signals can be seen on an EKG,
electrocardiogram.
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Systole: The phase of contraction of the heart muscle.
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Diastole: The heart’s phase of resting between contractions. During
this phase, the atriums and ventricles fill with blood.
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Animals more complex than hydras, jellyfish, and flatworms have a
heart. These include animals with many layers like vertebrates and
arthropods.
Video/Animation of circulation:
http://www.youtube.com/watch?v=gn6QmETEm8s
The heart depends on other features to function.
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Blood vessels are essential for the heart because they transport the blood utilized by the body from the heart to
the various tissues of the body.
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Without the nutrients and oxygen given to cells, including the heart,
the cells and organs they compose cannot function. The oxygen and
nutrients provided by the circulatory system sustain the heart,
allowing it to function. Also valves force the blood to move in only
one direction. This increases efficiency of the heart, but it also keeps
blood with very low pressure in the veins from flowing backwards.
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Arteries: Blood vessels that carry oxygen rich blood away from the
heart to body tissue. The aorta is the largest artery and is connected
directly to the heart.
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Capillaries: Connect arteries to veins, and allow for oxygen, nutrients,
carbon dioxide, etc. to pass to and from our organ's cells. Capillaries have thin walls and are very narrow/small
in size allowing for diffusion. These capillaries are organized in beds surrounding body tissue. Only 5-10% can be
full because of limited blood volume.
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Veins: Blood vessels that carry oxygen-poor blood back to the heart. This blood is rich in waste products that
must be excreted by the body. The vena cava is the largest vein in the body.
Not all organisms have a heart.
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Unicellular organisms: Unicellular organisms do not have a circulatory system. They use their cell surface as a
point of exchange with the outside environment. Transportation within the cell is facilitated by vesicles. Ex:
Amoeba
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Plants: Plants use two separate systems, the xylem and phloem, to transport water and sugar. The xylem in
plants uses adhesion of water to vascular tissue and transpiration to draw water up from the roots through the
stems to the leaves. The phloem in plants Xylem carries water from the roots through the adhesion of water to
vascular tissue while phloem carries sugars and other products synthesized by the plant.
Miranda Foster, Alexandria Hurley, Aakash Mehta, Mason Lowndes, Jacob Pearl, Will Smith
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Animals: Not all animals have circulatory systems. Jellies and sponges exchange gases, nutrients, and waste by
diffusion. These animals use a gastrovascular cavity. This cavity extends to all internal cells allowing for vast
distribution of nutrients.
How the circulatory system depends upon other body system
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Muscles are vital to the circulatory system. This control of circulation is reliant on precapillary sphincters, rings
of smooth muscle that when contracted prevent blood flow. Muscle also works to move blood in veins as
pressure drops, skeletal muscles contract pushing on veins forcing blood towards the heart.
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The lymphatic system defends against pathogens or toxins in blood, fights infections of cardiovascular organs,
and returns tissue fluid to circulation.
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The cardiovascular system also relies on the digestive system by distributing digestive tract hormones, carries
nutrients to water and ions away from sites of absorptions, and delivers nutrients and toxins to the liver.
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The urinary system is important to the circulatory system, because it delivers blood to the capillaries where
filtration occurs, and accepts fluids and solutes reabsorbed by reproduction.
Various evolutionary trends have resulted in a variety of heart structures.
There are two different circulatory systems: open and closed systems. In open systems, a fluid known as hemolymph
directly coats organs and tissues directly. Closed systems separate blood from the interstitial fluid coating organs.
There are different kinds of hearts found in each system.
Open Systems
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A tubular heart is used to pump hemolymph into sinuses surrounding organs, allowing exchange to occur. This
type of heart can be found in arthropods.
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A dorsal heart pumps blood forward while auxiliary hearts pump blood ventrally. This type of heart can be found
in annelids.
Closed Systems
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Fish have evolved to have a single circuit of blood flow propelled by their two chambered hearts.
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Amphibians have a 3 chamber heart with two circuits. A pulmocutaneous circuit goes to the lung and hearts,
while the systemic circuit goes to the other body tissues. Two atriums receive the blood, but oxygen rich and
poor blood mix due to the lack of separation that exists.
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Reptiles, excluding birds, have evolved to have a septum partially dividing their heart which reduces the mixing
of oxygen rich and poor blood. They also have double circulation with a pulmonary and systemic circuit. An
exception is crocodiles, who have a septum completely dividing the ventricle.
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Mammals and birds are mostly endotherms which require high energy expenditures. To make their circulatory
system more efficient, they have a four chambered heart allowing for complete segregation of both types of
blood. They have the same double circuit that reptiles have, but only have one systemic artery.
Diseases:
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Hemophilia is a collection of diseases in which blood does not clot normally. Symptoms include excessive
bruising, pain and tenderness of the muscles and joints, and severe bleeding after injuries or operations. The
excessive bleeding caused by hemophilia can be lethal. Treatments for hemophilia include receiving clotting
factors through intravenous injection of donated plasma, and various types of medications. Monitoring physical
activity and tending to bleeding joints properly is also vital for those suffering from hemophilia.
Cardiovascular disease is often caused by genetics and lifestyle. Some lifestyle factors include smoking,
unhealthy diet, and lack of exercise. These result in buildup of plaque that clogs arteries, called atherosclerosis.
This increases the chances of a heart attack. Chest pain, or angina pectoris, is a common symptom. A change to
a more healthy lifestyle is necessary to treat the conditions, or they can result in cardiac arrest or a stroke, which
results from lack of oxygen to the heart or brain.