The Cardiovascular System Explained – Part 2

Oct 20, 2014 |

Physiology of the Cardiovascular System

Functions of the Circulatory System
There are three primary responsibilities relegated to the cardiovascular system: conveyance of substances, defense against foreign bodies, and homeostatic regulation.

  • Conveyance: The cardiovascular system carries blood to virtually all of the tissues throughout the body. The blood transports oxygen and vital nutrients as well as removing waste products and carbon dioxide to be either processed or expelled from the body. The distribution of hormones within the body is accomplished by the liquid plasma of the blood.
  • Defense: The body is protected by white blood cells within the cardiovascular system. The leukocytes remove cellular debris and combat any pathogens that may have invaded the body. Further protection is also achieved by the formation of scabs (created by platelets and red blood cells) which close off injuries, stop liquids from escaping and prevent infectious agents from entering the body. Blood also carries antibodies that provide specific immunity to pathogens that the body has previously been exposed to or has been vaccinated against.
  • Regulation: The body’s circulatory system is integral to the body’s capability to maintain internal stability and homeostatic control. The body’s temperature is stabalized by the blood vessels which help to monitor the flow of blood to the skin’s surface. These surface vessels dilate during periods of excessive heating to enable overly-hot blood to dissipate heat into the body’s surroundings. When the body’s temprature is excessively low, such as with hypothermia, these same blood vessels constrict in order to only allow blood to flow to the vital organs of the body’s core. The balance of the the body’s pH is also accomplished by the blood, thanks to the presence of bicarbonate ions, which behave as a buffer solution. Lastly, since the albumins contained in the blood plasma maintain an isotonic environment, they assist in stabalizing the osmotic concentration of the body’s cells.

The Cardiovascular Pump
The human heart contains four chambers and acts as a sort of double-pump, the left and right sides each operating as a seperate pump. Each of these sides are divided by a thick wall of tissue called the septum.

De-oxygenated blood from the veins enters the right side of the heart where it is then pumped into the lungs for oxygenation. The blood from the lungs that has been oxygenated enters the left side of the heart where it is then pumped into the arteries to be transported throughout the tissues of the body. Every single beat of the heart is in actuality the simultaneous contracting of both sides of the heart, demonstrating the extreme efficiency of this vital organ.

Blood Pressure Regulation
There are quite a few way in which the circulatory system can regulate blood pressure. Autonomic nerve impulses from the brain together with specific hormones influence how fast and strong the heart contracts. An increase of force during contraction and higher heart rate results in a rise in blood pressure.

Changes in the blood vessels can also cause blood pressure variations. Vasoconstriction happens when an artery’s diameter decreases due to contraction of the smooth muscle of it’s wall. One example of when this happens is during the sympathetic “fight or flight” response of the autonomic nervous system, resulting in an increase of blood pressure and a decrease in the flow of blood in the constricted area.

Vasodilation is an artery expands as the smooth muscle it’s wall relaxes after the sympathetic response subsides or as result of specific hormones or chemicals in the blood.

Blood pressure can also be affected by the volume of blood in the body. A greater amount of blood increases blood pressure by boosting the volume of blood pumped during each heart beat.

Hemostasis
The platelets are responsible for hemostasis, which is the clotting of blood and development of scabs. Platelets usually remain inactive in the blood unless they come into contact with injured tissue or bleed out of the blood vessels as the result of a wound. When platelets become active, they morph into a spiny ball-like shape which enables them to attach to injured tissues.

At that point, the platelets will begin emitting chemical clotting factors, then initialize the production of protein fibrin to serve as a foundation for the blood clot. They will also start clumping together in order to create a platelet plug. A platelet plug acts as a provisional seal to maintain blood in the vessel, at the same time stopping foreign substances from entering until the damage to the wall of the blood vessel can be repaired by it’s cells.

Posted in: Cardiology Health Basics, EJCPR

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