2.3.1 blood circulatory system  (Page 4/8)

Figure : Details arteries and veins connecting the heart to the lungs Red blood has been oxygenated, blue blood is deoxygenated. . (Wikipedia -http://en.wikipedia.org/wiki/File:Illu_pulmonary_circuit.jpg)

Figure : Very detailed image of the lungs, it is not necessary or required to know all this detail but this is a fantastic image of the lungs –wikipedia (http://en.wikipedia.org/wiki/File:Respiratory_system_complete_en.svg).

Major organs and systemic system: associated major blood vessels the brain, small intestines, liver, kidney.

Figure : Detailed illustration of the systemic circulation. http://en.wikipedia.org/wiki/File:Circulatory_System_en.svg

• All the organs of the body are supplied by blood.
• Each has an artery supplying the organ with blood from the heart, and veins returning blood to the heart.
• Arteries and veins have been named according to the organ which they supply blood to.

The circulatory system forms a closed system.

• Nutrients enter the circulatory system from the digestive system.
• These nutrients first move to the liver via the hepatic portal vein, the liver then controls the nutrient composition of the blood.
• Blood passes from the liver to the heart through the hepatic vein.
• Nutrients are then circulated throughout the body.
• Cells consume the nutrients in the blood and produce metabolic waste. T
• his metabolic waste is circulated in the blood, if it remains in the blood the blood would eventually become toxic.
• The kidneys are supplied with blood via the renal arteries and they remove metabolic waste from the blood, passing it to urine.
• The Brain is supplied with blood via the carotid arteries and the vertebral arteries. The blood is drained via the jugular veins. The brain is suppliedwith 15% of the total amount of blood pumped by the heart.

Mechanisms for controlling cardiac cycle and heart rate (pulse)

• The cardiac cycle is controlled by nerve fibers extending from nodes of nerve bundles through the heart muscle.
• An electrical signal is triggered in the node.
• The electrical signal then spreads through the fibers and causes the heart muscle to contract.

There are two nodes:

1. The sinoatrial node (SA), which initiates the heart cycle. Electrical signals spread from the SA across the atria causing it to contact.
2. The electrical signal also reaches the Atrioventricular node (AV) . Here the signal pauses, before spreading through the ventricles causing them to contract.

• The SA is able to initiate the electrical signal without any stimulation for the nervous system, but it can be controlled by the nervous system.

• The brain does not need to tell the heart to beat; it is able to beat on its own.

• The brain can make the heart rate increase, when for instance you are scared or are running.
• Hormones are also able to increase the heart rate.

Simple simulation of how electrical activity spreads over the heart.

Link : http://en.wikipedia.org/wiki/File:ECG_Principle_fast.gif

Measuring pulse rate: http://www.nlm.nih.gov/medlineplus/ency/article/003399.htm

How the nodes cause contraction

• Human heartbeats originate from the sinoatrial node (SA node) near the right atrium.
• Modified muscle cells contract, sending a signal to other muscle cells in the heart to contract.
• The signal spreads to the atrioventricular node (AV node).
• Signals carried from the AV node, slightly delayed, through bundle of His fibers and Purkinjie fibers cause the ventricles to contract simultaneously. Figure 13illustrates several aspects of this.