Essay # 4 - AP Bio Free Response 2006:

The evolution of circulatory systems allowed larger and more-complex animals to arise.

(a) Describe the respiratory and digestive systems' specialized structures that facilitate the movement of glucose into the circulatory system of mammals. (immense surface area: alveoli & villi, extensive amounts of capillaries, digestive system relies on diffusion, facillitated diffucsion, and active transport, respiratory system uses diffusion and hemoglobin to raise the difference in oxygen pressure potential)

(b) Explain how oxygen and glucose are transported within the circulatory system of mammals. (veins deliver oxygen and glucose to the heart from lungs and intestines, heart sends glucose and oxygen to the tissues via arteries and capillaries)

(c) Explain the transfer of oxygen and glucose from the blood and into active cells of mammals.(blood pressure insures movemnt of plasma out of capillaries and into interstitial, concentration gradients promotes exchange)

Circulatory System

Using your text book, online video, and the Internet for help, answer the questions below.
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Circulatory System (Heart):

The role of the circulatory system is to insure the transport of nutrients to the tissues and wastes away from the tissues of a multi cellular organism. Organisms that are composed of only a few layers of cells will not have a circulatory system because diffusion from and to their environment is sufficient. The majority of multi cellular creatures do have either an open or closed circulatory system.

An open circulatory system(mollusks, arthropods) involves the blood moving from a heart or hearts into artery(ies). The blood leaves the artery(ies) and moves into sinuses (body cavities). Muscular movements of the animals body and the pressure exerted by the movement of blood out of the artery(ies) pushes the blood eventually to a sinus that surrounds the heart(s). Blood enters the heart through tiny holes (ostia) to be pumped back into circulation once more.

A closed circulatory system (vertebrates, many annelids) sends blood from the heart into arteries. From the arteries the blood travels through smaller and smaller arteries until it reaches tiny vessels whose walls are only one cell thick. These vessels are called capillaries. This is where where nutrient for waste exchange occurs. No cell in the body is more than three or four cells away from a capillary. It has been estimated that if all the capillaries could be removed from one adult human and connected end to end rather than highly branched, the vessels length would equal three times the distance traveled around the earth.

Blood eventually leaves the capillaries and moves into tiny veinules which in turn carry the blood to larger veins which return the blood to the heart.The fact that red blood cells and certain macromolecules never leave the blood vessels is what makes this method of circulating materials throughout the body a closed system. In summary, arteries carry blood from the heart to beds of capillaries and veins bring blood from the capillaries back to the heart.

We will focus this activity on the human (closed) circulatory system and begin with the heart.

The heart provides the needed pumping energy to drive blood throughout the body. It is composed of four chambers that efficiently separates the blood transport into two separate circulatory pathways. Pulmonary Circulation carries blood to and from the lungs. Blood brought into the Right Atrium from all parts of the body is pumped into the Right Ventricle. The right ventricle pumps the blood into the Pulmonary Artery that carries the blood to the lungs. Blood returning from the lungs comes back to the heart in the Pulmonary Veins and enters the Left Atrium.

Systemic Circulation transport blood to and from the rest of the body. Blood coming into the Left Atrium from the lungs is pumped into the Left Ventricle. The Left Ventricle then pumps the blood into the Aorta which has numerous branches carrying blood to all parts of the body. Blood returns from all parts of the body back to the Right Atrium via the Superior Vena Cava (upper body) and the Inferior Vena Cava (lower body).

1- What is the value of separating circulation into two separate pathways? (Mammalian Fetus - ductus arteriosus & foramen ovale)

2- Some babies are born with a hole in the septum separating the left and right ventricle. What symptom might be evident at birth to indicate this disorder?

3- What is the function of the heart valves?

Defects in the valves can compromise the efficient circulation of blood. This disorder can be identified using a stethoscope and listening for strange heart sounds or by using a sonogram.

4- What is the name given to the disorder associated with defective heart valves?

Fish have two chambered hearts, amphibians three, and many reptiles have a partially divided ventricle. Only birds and mammals have four chambered hearts. Dividing circulation into two separate pathways has enabled birds and mammals to be warm blooded (endothermic - internal body temperature not directly regulated by environmental temperature)

5- Why would two separate circulatory pathways be needed for an animal to be warm blooded?

The heart must be able to maintain the ideal rate of beating to insure adequate blood flow with limited energy expense to the body. Therefore the heart beats slower when at rest and faster rate when demand for oxygen and nutrients increases (exercise, stress, trauma). To facilitate this need for regulating heart rate and insuring synchronization of atrial and ventricular contractions, the heart is equipped with its own electrical system.

A small node of cardiac cells (SA Node; sometimes referred to as the pacemaker) initiates the electrical current. The current spreads in such a way as to cause both Atria to contract. The current reaches a second node (AV node)which carries the current in a way to cause the ventricles to contract and force the blood up into the arteries.The SA node has two nerves associated with it. One that increases the rate of depolarization and current formation and another that decreases it. As CO2 levels increase and pH decreases (CO2 mixes with water and becomes carbonic acid) the brain detects this and stimulates the SA node to depolarize more rapidly. Scarlet fever and other diseases have been known to create conditions in the body that can impair or even destroy the SA node.

6- What would a person need to do in the event that their SA node has lost normal function?

Monitoring the passage of the electric current through the heart can provide valuable information needed for the diagnosis of heart and circulatory disorders. The device used to monitor the electrical output of the heart is called an EKG machine (Electro "Kardia" Gram). Sensors are placed on the chest, wrists, and ankles that can detect the flow of the current through the heart. If the current is flowing toward the positive pole sensor the line on the EKG moves up. If the current is moving away from the positive pole the line goes down. Different views of this system can be seen by comparing the EKG output between two or more of the sensors placed on the body. A common EKG output produced between two sensors placed on the body is shown below.

Changes in direction of the output is a consequence of the current flowing toward or away from the sensors. Changing the sensors will lead to variations in shape of the EKG. All EKGs will have a P wave (SA node depolarization), a QRS wave (AV node depolarization & conduction through the fibers in the septa) and a T wave (re-polarization of the AV node). Distances between the waves and sizes of the waves can indicate anomalies of the heart.

7- Why isn't a wave showing re-polarization of the SA node revealed?

[Blood Vessels][Blood]