TRANSPORT IN ANIMALS

BY ASHLY MOYHABEER

Transport in animals With aid of diagrams , describe the structure of the human

heart . Include annotated diagrams of the internal structure and

external structure of the heart and associated blood vessels and valves.

Compare the human heart to that of a fish and amphibian (diagrams required)

Describe the structure and function of the cardiac muscle.

THE HUMAN HEART

The human heart is a fist-sized, muscular organ that is hollow. Its job is to pump blood through the body's network of blood vessels. The heart, blood, and blood vessels are part of the circulatory system, which supplies all the body's cells with the oxygen and nutrients they need, and removes waste products. The heart has chambers, valves, arteries, and veins -- and a complex electrical system keeps everything working smoothly and makes the heart beat.

Internal structures of the heart

Right Atrium: The upper right chamber of the heart. During the normal cardiac cycle, the right atrium receives deoxygenated blood from the body (blood from the head and upper body arrives through the superior vena cava, while blood from the legs and lower torso arrives through the inferior vena cava). Once both atria are full, they contract, and the deoxygenated blood from the right atrium flows into the right ventricle through the open tricuspid valve

Left Atrium: The upper left chamber of the heart. During the normal cardiac cycle, the left atrium receives oxygenated blood from the lungs through the pulmonary veins. Once both atria are full, they contract, and the oxygenated blood from the left atrium flows into the left ventricle through the open mitral valve.

Superior Vena Cava: One of the two main veins bringing deoxygenated blood from the body to the heart. Veins from the head and upper body feed into the superior vena cava,which empties into the right atrium of the heart.

Inferior Vena Cava: One of the two main veins bringing deoxygenated blood from the body to the heart. Veins from the legs and lower torso feed into the inferior vena cava, which empties into the right atrium of the heart.

Atrial septum: The wall between the two upper chambers (the right and left atrium) of the heart.

Aorta: The central conduit from the heart to the body, the aorta carries oxygenated blood from the left ventricle to the various parts of the body as the left ventricle contracts. Because of the large pressure produced by the left ventricle, the aorta is the largest single blood vessel in the body and is approximately the diameter of the thumb. The aorta proceeds from the left ventricle of the heart through the chest and through the abdomen and ends by dividing into the two common iliac arteries, which continue to the legs.

Pulmonary veins: The vessels that transport oxygenated blood from the lungs to the left atrium. The pulmonary veins are the only veins to carry oxygenated blood.

Pulmonary Valve: One of the four one-way valves that keep blood moving properly through the various chambers of the heart. The pulmonary valve separates the right ventricle from the pulmonary artery. As the ventricles contract, it opens to allow the deoxygenated blood collected in the right ventricle to flow to the lungs. It closes as the ventricles relax, preventing blood from returning to the heart.

Aortic Valve: One of the four one-way valves that keep blood moving properly through the various chambers of the heart. The aortic valve, also called a semi-lunar valve, separates the left ventricle from the aorta. As the ventricles contract, it opens to allow the oxygenated blood collected in the left ventricle to flow throughout the body. It closes as the ventricles relax, preventing blood from returning to the heart. Valves on the heart’s left side need to withstand much higher pressures than those on the right side. Sometimes they can wear out and leak or become thick and stiff.

Mitral Value: One of the four one-way valves that keep blood moving properly through the various chambers of the heart. The mitral valve separates the left atrium from the left ventricle. It opens to allow the oxygenated blood collected in the left atrium to flow into the left ventricle. It closes as the left ventricle contracts, preventing blood from flowing backwards to the left atrium and thereby forcing it to exit through the aortic valve into the aorta. The mitral valve has tiny cords attached to the walls of the ventricles. This helps support the valve’s small flaps or leaflets.

Tricuspid Valve: One of the four one-way valves that keep blood moving properly through the various chambers of the heart. Located between the right atrium and the right ventricle, the tricuspid valve is the first valve that blood encounters as it enters the heart. When open, it allows the deoxygenated blood collected in the right atrium to flow into the right ventricle. It closes as the right ventricle contracts, preventing blood from flowing backwards to the right atrium, thereby forcing it to exit through the pulmonary valve into the pulmonary artery.

Atria: The two upper cardiac chambers that collect blood entering the heart and send it to the ventricles. The right atrium receives blood from the superior vena cava and inferior vena cava. The left atrium receives blood from the pulmonary veins. Unlike the ventricles, the atria serve as collection chambers rather than as primary pumps, so they are thinner and do not have valves at their inlets.

Ventricles: The two lower cardiac chambers that collect blood from the upper chambers (atria) and pump it out of the heart. Because the ventricles pump blood away from the heart, they have thicker walls than the atria so that they can withstand the associated higher blood pressures. The right ventricle pumps oxygen-poor blood through the pulmonary artery and to the lungs. The left ventricle pumps oxygen-rich blood through the aorta and to the rest of the body.

External structures of the heart

A comparison of a human , fish and amphibian heart

The fish heart (figure 1a) is much different than the amphibian/reptile/bird/mammal heart (figures 1b and c). Hearts are very complex--they're not just a bunch of random arteries and veins connecting tissue. Fish hearts simply draw in deoxygenated blood in a single atrium, and pump it out through a ventricle. This system is termed "single circulation", as blood enters the heart, gets pumped through the gills and out to the body, Blood pressure is low for oxygenated blood leaving the gills.

3 and 4 chambered hearts have a pulmonary circuit (pathways taking blood from heart to lung and back to heart) that is very complex and must be set up such that blood can travel from the heart to become oxygenated in the lungs and then be properly pumped back the heart and out to the body. The 3 (and 4) chambered heart has "double circulation" (figure 1b and c) and is quite different from "single circulation" (figure 1a) of fishes.

"Double circulation" has an interior circuit within the heart--blood enters the heart, leaves the heart and gets oxygenated, enters the heart again, and then gets pumped out to the body. Because "Double circulation" allows oxygenated blood to be pumped back into the heart before going out to the body, it pumps blood with much more pressure and much more vigorously than "single circulation”

Though the 4 chambered heart has 2 atrium-ventricle pairs, both pairs do not do the same thing. There are 4 steps involved with blood entering the heart: 1) oxygen poor blood enters the first atrium. 2) oxygen poor blood is fed to the first ventricle, which pumps it out to the pulmonary circuit (lungs) where it is enriched in oxygen. 3) Oxygen rich blood just leaving the lungs is pumped back into the second atria. 4) Oxygen rich blood is then fed to the second ventricle, which pumps the oxygen rich blood out of the heart and back into the body for usage.

The 4 chambered heart differs from the 3 chambered heart in that it keeps oxygenated blood completely separate from de-oxygnated blood, because there is one ventricle for deoxgynated blood and one for oxygenated blood. In the 3 chambered heart, a single ventricle pumps both out of the heart, and there is some mixing between fresh and old blood.

The 2 ventricle-4 chamber heart prevents mixing allows the blood leaving the heart to have far more oxygen than it would otherwise. This is good for enhancing the more fast paced lifestyle that birds and mammals tend to have, giving an advantage to having a 4 chambered heart.

Structure of the Cardiac Muscle

Functions of the Cardiac Muscle

Function of the Cardiac Muscle: The cardiac muscle functions with the help of its cardiac cells. These cells are responsible for the contraction of this muscle and sending blood to the atria and ventricles. That in turn, reaches the blood vessels of the circulatory system.

Cardiac Muscle Fibers: The cardiac muscle is not linear, unlike the striated or smooth muscles. It forms instead, a complicated and crisscross network of muscle fibers, in any direction possible. The reason is that it performs the action of squeezing, what is called a bulb.

Take an example of a water balloon being applied pressure on by a belt in a single direction. What will happen? Well, some amount of water will still be retained by the balloon. On the contrary, if you squeeze the balloon in all directions, there will be no water left in the balloon. Similarly, the muscle fibers of the cardiac muscle comprise a mesh, squeezing the chambers of the heart, forcing the blood either in lungs or through the entire body.

Metabolism: Believe it or not, our cardiac muscle does not ever get tired! Imagine the amount of pressure we put on it, it still goes on working, unfettered. The secret to it not being tired lies in the mitochondria. The mitochondria act as fuel plants for the cardiac cells. They generate adenosine triphosphate or ATP, a major source of chemical energy for the muscle. Furthermore, lactate is converted into fuel by the cardiac muscles. This implies that even if the rest of the body is starved, the heart will always have fuel! This is one of the most striking aspects of the cardiac muscle function.

Electro Chemical System of the Muscle: If the heart has to function properly, the cardiac muscle needs a special electrical system for sending the correct signals to the corresponding muscle at the appropriate time. This then means that without a delay between the atrium and the ventricles for ensuring that all the blood is pumped out of the heart, it cannot happen.

To facilitate this, the heart has sinoatrial node (SA node) for directing the electrical impulses to the right area of the heart at the right time. In addition to this, the SA node also maintains a tension on the muscles all the time. This helps in maintaining of blood pressure and keeps it ready for the next contraction

T-Tubules: Interestingly , there are pathways for electrical stimulation to reach and activate the muscle. These are called transverse tubules and even though there are fewer of these in the cardiac muscle, they are broader and larger. This facilitates better signal and activation of the muscle.

Questions