Blood Vessels and Circulation

Tissue is active

Precapillary sphincters are open and blood flows through the capillaries to reach the active tissue cells.

Tissue is less active

Precapillary sphincters close and blood bypasses the capillaries and flows through the thoroughfare channel directly to the venule.

Mostly eliminated in the muscular arteries, no pulse by the time blood leaves the arterioles.

Pulse strength in reference to location?

Vasomotor control

Regulation of the diameter of arterioles.

Increased activity of the vasomotor center causes increased stimulation of arterioles (more norepinephrine release). Vasoconstriction occurs and blood pressure rises. Decreased activity of the vasomotor center causes decreased stimulation of arterioles (less norepinephrine release). Vasodilation occurs and blood pressure drops.

Relationship of arteriole diameter (vasomotor center) and blood pressure.

Vasoconstriction of arterioles will increase peripheral resistance. Increase in peripheral resistance will increase blood pressure. Vasodilation of arterioles will decrease peripheral resistance. Decrease in peripheral resistance will decrease blood pressure.

Relationship of blood vessel diameter and peripheral resistance

Increase in blood volume will increase blood pressure. Decrease in blood volume will decrease blood pressure.

Relationship of blood volume and blood pressure.

Venous Reserve

20% of total blood volume forms this. Located in veins of skin and abdomen (especially the liver). These veins can constrict (venoconstriction) and move their blood into general circulation when needed to: increase circulating blood volume in active tissues, and maintain circulating blood volume in the body after blood loss.

Cross-sectional area

Area of the circle.

Smooth (not pulsatile)

Blood flow in the capillaries, venules and veins (including the vena cavaee)?

Venules

Blood from capillaries moves to here. Thinner-walled than corresponding arterioles. Less smooth muscle and little or no elastic tissue.

Veins

Blood from venules moves into this. Thinner-walled than corresponding arteries. Less smooth muscle and little or no elastic tissue. They function as capacitance vessels-meaning they collapse or distend depending on the total blood volume in the body.

Closed system

Blood is always confined to either heart chambers or blood vessels.

Metarterioles

Branch off at almost right angles to form a terminal arteriole, proximal portion has a incomplete layer of smooth muscle, distal portion is called Thoroughfare channel, with no smooth muscle.

Capillaries

Branch off terminal arterioles or metarterioles. The smallest in diameter of all the blood vessels. Have only thin walled, endothelium present. They function to exchange water, nutrients and wastes between blood and tissues. Form networks called capillary beds.

Nervous control (Short term regulation of blood pressure)

Cardiac output and peripheral resistance can be modified very quickly by?

Precapillary Sphincter

Entrance to the capillaries is guarded by this. Its a thicker ring of smooth muscle. Can be opened or closed to control entrance of blood into capillary beds from the arteriole or metarteriole. Opening is usually under chemical control.

1.Blood vessel diameter-( the smaller the diameter of a blood vessel the greater the resistance in the vessel. Diameter is changed by contraction or relaxation of smooth muscle, causing vasoconstriction and vasodilation. Regulated by the nervous system and substances in blood. 2. Blood vessel length-longer the blood vessel, the greater the surface area of wall in contact and the greater the resistance. Relatively constant over time. 3. Blood viscosity-Due to number of blood cells, under normal conditions it remains relatively constant.

Factors that affect peripheral resistance:

Blood Pressure

Force exerted by the blood against the inner walls of the blood vessels. Most commonly used to refer to Systemic Arterial Pressure.

Arteriovenous Anastomosis

Found in fingers, toes, and ears, play a role in temperature regulation. Highly muscular wall with many adrenergic receptors. One type-short channel that connects an arteriole to a venule so that blood can bypass a capillary bed. "Joining together of blood vessels." *Nervous control.

Velocity

How fast something is moving.

Valves that are present within veins, massaging action of skeletal muscle contractions, and pressure changes in chest cavity during respiration.

How is backflow prevented since veins are under low pressure?

Reciprocal vasomotor control helps to maintain blood pressure.

If blood vessels are dilated in one active area of the body, they must constrict somewhere else in the body in order to maintain systemic blood pressure. Controlled by the vasomotor center.

Vasomotor center

Neural control center for peripheral resistance. Located in the medulla oblongata of the brain. Nerves are entirely sympathetic. Neurotransmitter is norepinephrine.

Tonic Stimulation

Important for maintenance of normal blood pressure. Stimulation by sympathetic nerves from vasomotor center. If all arterioles dilated at the same time, blood pressure would drop to zero. It is necessary for some arterioles to be constricted all the time, even when the body is at rest.

Hepatic Portal Circulation

Involves the stomach, intestines and spleen. After passing through a capillary bed in these organs, the deoxygenated blood is carried to the liver via the hepatic portal vein. The blood passes through a second capillary bed in the liver before being carried to the vena cava to return to the heart.

Large Arteries

More elastic, function to prevent large drops in blood pressure while the ventricles are in diastole. The recoil of these vessels keeps pressure on the blood. Also known as conducting vessels, carrying blood away from the heart towards medium-sized arteries.

Small Arteries

More muscular, function to distribute and send blood to various parts of the body, branch off larger arteries.

Collateral Circulation

More than one artery may supply blood capillaries in a particular organ or region of the body. Provide an alternate way to bring blood to a body organ in case one artery is compressed or obstructed.

Perfusion

Specific volume of blood entering the capillaries per unit of time per gram of tissue. A sense of how well specific tissues are being nourished by the blood flow. (mL/min/g)

Double circuit

The Pulmonary circuit goes from the right ventricle to the lungs to the left atrium. The Systemic circuit goes from the left ventricle to the body tissues to the right atrium.

Systolic pressure

The blood pressure when the ventricles are contracting.

Diastolic pressure

The blood pressure when the ventricles are relaxing.

Pulse pressure

The difference between systolic and diastolic pressures.

Peripheral Resistance (If small, there is more resistance)This will increase blood pressure.

The friction between blood and the walls of blood vessels in the peripheral or systemic circuit of the body.

Arteries

Thick-walled and strong, under high pressure.

Mean Arterial Pressure (MAP)

Used to report a single pressure in the arteries. It is calculated as the diastolic pressure plus one-third of the pulse pressure.

Cardiac Output

Volume of blood discharged from a ventricle per minute, determined by stroke volume and heart rate.

Blood Flow (F)

Volume of blood per unit of time (mL/min) passing through a vessel or a group of vessels.

Arterioles

Walls made of Endothelium and smooth muscle. Function as resistance vessels to regulate blood pressure (dilate to decrease blood pressure/constrict to increase blood pressure) and to regulate blood supply to capillaries (can shunt blood from one area to another in the body).

1. Stomach/Intestines-Too many nutrients after a meal, want to store it in the liver for later when you need it, don't want it in general circulation. 2. Spleen-Breaks down RBC's, don't want Bilirubin/Biliverden in circulation. Dropped off in liver to be excreted as bile.

What are the reasons from having Hepatic Portal Circulation?

1. Cardiac output and peripheral resistance are short term regulations. 2. Blood volume, takes longer to have an effect. (Control by controlling urine volume)

What can control blood pressure?

Pressure pushing the blood, and resistance that opposes blood flow.

What factors affect blood flow?

Blood slows, many arteries as a group have a total cross-sectional area larger than the single aorta.

What happens as blood enters the arteries?

Velocity increases. The total cross sectional area is smaller.

What happens to the velocity of blood flow when it goes from the capillaries to the venules, veins, and the venae cavaee?

Blood flow in the aorta and other arteries (pulses up and down).

What is pulsatile?

Anything that increases cardiac output will increase blood flow; anything that decreases cardiac output will decrease blood flow. Perfusion is directly related to both.

What is the relation of Cardiac Output to Blood Flow and Perfusion?

Increase in cardiac output will increase blood pressure; decrease in cardiac output will decrease blood pressure.

What is the relationship between Cardiac output and blood pressure?

Velocity is inversely related to the total cross-sectional area of the blood vessels that it is flowing through.

What is the relationship of velocity and cross-sectional area?

Aorta

Where is blood the fastest?

Capillaries. Individual capillaries are small in diameter, but the total number of capillaries in the body is large. Because of this great total cross-sectional area, velocity of blood flow is slow in the capillaries. This enhances exchange of materials.

Where is the cross sectional area the greatest?