The Circulatory System By Akrum Hamdy

The Importance of the Circulatory System Provides a controlled and efficient means of internal transport. Moves blood throughout the body. Carries nutrients to cells Wastes away from cells Chemical messages from cells to distant target tissues. Distributes heat throughout the body and helps to maintain levels of body fluids.

William Harvey It was in 1628, when the English physician William Harvey showed that blood circulated throughout the body in one-way vessels. According to Harvey, blood was pumped out of the heart and into the tissue through one type of vessel and back to the heart through another type of vessel.  The blood, in other words, moved in a closed cycle through the body.

Open vs. Closed Circulatory Systems The more complex the organism, the more complex this system must be. Arthropods, like insects and spiders, have an open circulatory system, in which the blood is pumped forward by the heart, but then flows through the body cavity, directly bathing the internal organs. Vertebrates, like humans, have a closed circulatory system in which the blood stays in the circulatory system as it circulates. Page 313 in the Textbook Animation comparing Open and Closed Circulatory Systems

“Blood Is Bodies Means Of Transportation” Pumped by the heart, blood travels through a network of vessels, carrying materials such as oxygen, nutrients, and hormones to cells in the body and removing these cells waste products. The blood, heart, and blood vessels make up the cardiovascular system. The central organ of this system is the heart.

“The Network of Vessels” We are considered to have a closed circulatory system because blood is contained within either the heart or blood vessels at all times. There are 3 types blood vessels in our circulatory systems: 1. Arteries carry blood away from the heart; under higher pressure 2. Capillaries Tiny connector vessels, that allow for the exchange of fluids, gases, nutrients and waste. 3. Veins carry blood to the heart; under lower pressure Major human blood vessels

Arteries and Arterioles Arteries are blood vessels that carry blood away from the heart. Vessel Walls have 3 layers of tissue: 1. Outer Layer: Connective Tissue 2. Middle Layer: Smooth Muscle Tissue 3. Inner Layer: Epithelial Tissue This enables arteries to withstand the high pressure of blood as it is pumped from the heart. The force that blood exerts on the walls of blood vessels is known as blood pressure. Vessel anatomy

Pulse Every time the heart pumps, a surge of blood enters these arteries and they must stretch to accommodate this inrush of blood (Pulse). The initial inrush of blood due to the heart contraction, is followed by a relaxation phase. In this phase, the pressure in the arteries drops and the elastic fibers in the walls recoil. ***Pulse ONLY occurs in the arteries. The walls of the veins are too weak to withstand the pressure of the blood pumped by the heart.

Arterioles The smallest arteries. Branch from arteries to capillaries.

Regulating Diameter of Arterioles The autonomic nervous system control the diameter of the arterioles. Vasoconstriction: smooth muscles signaled to contact, reducing diameter and blood flow to the tissues. Vasodilatation: smooth muscles relax, increasing diameter and blood flow to the tissues. Pre-capillary sphincter muscles regulate the movement of blood from arterioles to capillaries. “How do you think this processes is connected to blushing?”

Capillaries Composed of single layer of cells, ideal for diffusion. Are the site of fluid and gas exchange between blood and body cells. Their diameter is so small that red blood cells must travel through in single file. Because have a single layer, capillaries are easily destroyed by high blood pressure or any impact (punch) which causes rupturing.

Capillary Diffusion Diffuses from the blood in the capillaries to the surrounding body cells. Oxygenated (oxygen rich) blood appears red. Deoxygenated (oxygen-poor) blood appears purple-blue as it leaves the capillary. Deoxygenated blood collects in small veins called venules and carries it back to the heart. Some proteins are also exchanged via endocyotsis and exocytosis. Water-soluble and ions and vitamins pass through spaces in the walls. Analogy: Huge Crowd

Veins and Venules Capillaries merge and form larger vessels, called venules. Venules merge into veins, which gradually increase in diameter as they approach the heart. Blood flow reduces as it flows from arteries arterioles  capillaries; thus, blood pressure is also reduced which protects the single layered walls of some vessels. The pressure is so low when blood reaches the venules that there is not enough pressure to pump blood back to the heart, especially if at lower limb. How does blood get back to the heart?

Harvey’s Experiment He tied a band around the arm of a subject, restricting venous blood flow. Veins became engorged with blood and swelled He placed a finger on the vein and pushed the blood toward the heart. The vein closed up and collapsed. Repeated the procedure but this time pushed the blood towards the subjects wrist, and bulges appeared in the vein in regular intervals. Dissection of the vein confirmed the presence of valves.

Valves Valves open in one direction steering the blood toward the heart, and do not allow blood to flow down the other direction. When Harvey tried to push the blood toward the wrist, the valves prevented the movement and lead to bulges at the valves. The vein collapsed b/c the band around the subjects arm prevented the passage of blood.

Skeletal Muscles Vein blood flow Venous pressures increase as muscles contract and push against the vein. Muscle bulges  vein contracts (decrease diameter)  vein pressure increases  valves open. Explains why blood pools in the absence of movement. Vein function

Therefore, blood is returned to the heart by the veins due to: 1. One-way Valves 2. Skeletal Muscles (Example: hang one arm motionless and the other above your head) ***There is NO pressure pushing the blood back to the heart; the vein walls cannot withstand this force.

Veins Reservoirs 65% of your total blood volume found in your veins (30% arteries; 5% capillaries). During times of stress, venous blood flow increases to meet the demands.

Veins  Problems: Pooling of blood over time can lead to valve damage. Surface veins gradually become larger and bulge a.k.a. varicose veins Genetic link Lifestyle: prolonged standing or compression, career, pregnancy, tight clothes.

Atherosclerosis Excess lipid in you blood is deposited on the walls of your arteries, slowly narrowing the inside diameter of the blood vessel. When calcium and other minerals deposit on top of this lipid it forms plaque. Atherosclerosis degradation of the blood vessel due to plaque Arteriosclerosis group of disorders that are characterized by the thickening, hardening, and loss of elasticity. Extensions Atherosclerosis.pdf

Atherosclerosis Narrowing arteries increases blood pressure. Blood clots form in blood vessel when plaque gets so big that it bursts through the artery wall. This can totally block the artery and cut of blood flow. This results in inadequate blood and oxygen being delivered to the heart muscles, resulting in chest pains and possibly a heart attack.

Aneurysm A bulge that forms in the wall of a weakened blood vessel, usually and artery. The thinner wall offers less support and eventually ruptures (less oxygen and blood = cell death). Can occur in the heart and the brain. Often due to atherosclerosis. If occurs in the brain, can cause a stroke.