Functions of the Blood Vessels/Chapter 19

Joe Pistack MS/ED

Blood Vessels

Functions: Act as a delivery system Regulate blood pressure Engage in the exchange of nutrients and

waste between the capillaries and cells Redistribute blood in response to

changing body needs Help regulate body temperature

Blood Vessels•All cells require oxygen

•Without oxygen the cells will die

•Adequate blood flow to all organs is vital

• Ischemia-impaired blood flow to the tissues

▫Ex. of ischemia is a blockage or occlusion of an artery

“5 Cool P’s” of occlusive arterial disease

1. Pain. Diminished oxygen supply stimulates pain receptors.

2. Pulselessness. The blocked artery decreases the flow of blood to the extremity; the pulse distal to the occlusion is diminished or absent.

3. Pallor. Due to lack of blood the extremity is pale, especially when elevated.

“5 P’s”

4. Paresthesia. Diminished blood flow decreases the supply of oxygen to the nerves of the leg, causing numbness and tingling.

5. Paralysis. Persistent oxygen deficit causes permanent nerve damage and paralysis (late sign).

6. Coolness. Blood flow carries heat, decreased blood flow results in a decrease in temperature of the affected extremity.

Blood Pressure

• The force blood exerts against the walls of the blood vessels.

•Blood pressure is determined by the pumping action of the heart and the size (lumen diameter) of the blood vessels.

Measuring Blood Pressure

•Blood pressure in the arteries is caused by the heart’s pumping activity,

•When the ventricles contract, a volume of blood (stroke volume) is pumped out of the ventricle into the artery, thereby increasing pressure.

Measurement of Blood Pressure Systolic pressure - pressure in the arteries at

the peak of the ventricular contraction. ( Top number)

Diastolic pressure - pressure in the large arteries when the ventricles of the heart are relaxing. (Bottom number)

Pulse pressure - difference between the systolic and diastolic pressure. Ex. BP 120/80, 120 -80 =40

Blood Pressure

Blood pressure readings vary according to: Age Gender Size

Blood pressure that is too low: Decrease in blood flow to vital organs Shock may occur Immediate treatment necessary

Blood PressureBlood pressure too high: Blood vessels may burst or rupture Major cause of stroke

Hypertension-long-term or chronic elevation in blood pressure.

Chronic hypertension is a major cause of heart disease.

Blood Pressure

Complications of hypertension: Added strain on the heart Damage to the blood vessels of the kidney Damage to the retina

Measurement of blood pressure provides valuable information regarding a person’s general health.

Blood Pressure

Sphygmomanometer-device with a dial and an inflatable cuff.

Cuff is placed around patient’s upper arm and inflated with air until the brachial artery is compressed, and flow of blood through the artery is stopped.

Stethescope is placed over brachial artery,

distal to or below the cuff, examiner listens for Korotkoff sounds.

Blood Pressure Blood pressure is highest in the aorta

because it is closest to the left ventricle.

Left ventricle pumps blood with great force.

Blood pressure declines as blood flows from the large arteries down to the smaller ones.

Venous Blood Blood pressure is high in the arterial

circulation.

Blood pressure decreases in the veins, it cannot return blood back to the heart without help.

Three mechanisms assist in the return of venous blood: 1. skeletal muscle action

2. respiratory movements 3. constriction of the veins

Skeletal Muscle Action Large veins in the

legs are surrounded by skeletal muscles.

As skeletal muscles contract, they squeeze the large veins, squirting blood back to the heart.

This mechanism is called the skeletal muscle pump.

Explains how exercise is beneficial to improve blood flow.

Respiratory Movements Breathing is performed by the contraction

and relaxation of the skeletal muscles of the chest.

Respiratory movements cause the pressures in the chest cavity to change.

Respiratory Movements During inhalation-diameter of the chest

increases.

Increase in the thoracic size decreases pressure within the thorax and increases pressure within the abdominal cavity.

Increase in abdominal pressure squeezes the vena cava and pushes more blood toward the heart. This effect is called the respiratory pump.

Constriction of the Veins

Most of the blood is located in the venous side of the circulation.

Constriction of the veins pushes additional blood out of the veins toward the heart.

Vasoconstriction occurs by sympathetic nervous system stimulation and hormones that cause vasoconstriction and increasing venous return.

The Heart and Blood Vessels Water flows from an area

of high pressure to an area of low pressure.

Blood pressure is caused by the contraction of the heart muscle.

The stronger the force of contraction, the higher the blood pressure.

No myocardial contraction, no blood pressure—death!

Blood Vessels Arterioles are composed largely of smooth

muscle.

Contraction and relaxation of the smooth muscle allow the arterioles to change the size of their diameter.

Vasodilation Vasodilation occurs when

the muscle relaxes and the opening of the arteriole increases.

Vasodilation decreases the resistance in the blood vessels.

Vasoconstriction occurs when the smooth muscle contracts and the opening of the arteriole becomes smaller.

Vasoconstriction increases the resistance in the blood vessels.

Blood Pressure

When vascular resistance decreases, blood pressure decreases.

When vascular resistance increases, blood pressure increases.

Blood pressure is affected by the ability of the arterioles to dilate and constrict.

Cardiac Output

Cardiac output- is the amount of blood pumped by the heart each minute.

Increase in heart rate or stroke volume can increase cardiac output and increase blood pressure.

Decrease in heart rate or stroke volume can decrease cardiac output and decrease blood pressure.

Blood Pressure

Vascular resistance-caused by the relaxation and contraction of the arterioles.

Factors affecting vascular resistance:

sympathetic nerve activity various hormones pharmacologic agents

Sympathetic Nerve Activity Arterioles are supplied by fibers from the

sympathetic nervous system.

When sympathetic nerves fire, vascular smooth muscle contracts.

Vasoconstriction results.

Vasoconstriction increases vascular resistance and elevates blood pressure.

Hormones

Epinephrine and angiotensin II cause vasoconstriction and elevate blood pressure.

Called vasopressors because they elevate blood pressure.

Some hormones may induce vasodilation , decreasing vascular resistance.

Pharmacologic Agents Many pharmacologic agents affect vascular

resistance.

Drugs that cause vasoconstriction elevate blood pressure, often used to treat shock. Ex. vasopressin, epinephrine, nor-epinephrine.

Antihypertensive agents induce vasodilation, lower vascular resistance, lower blood pressure.

Ex. Amlodipine (Norvasc), enalapril (vasotec).

Blood Pressure

Under normal conditions, blood pressure remains relatively constant.

Regulation of blood pressure involves both rapidly acting and slowly acting mechanisms.

Blood Pressure Baroreceptor reflex: most important rapidly active mechanism. consists of receptors, sensory nerves,

medulla oblongata, and motor nerves. baroreceptors are special receptors or

pressure receptors located in the walls of the aortic arch and carotid sinus.

Baroreceptors sense changes in blood pressure and activate the sensory nerves, then medulla oblongata, then motor nerves which will carry information to the heart and blood vessels.

Baroreceptors Stimuli to the carotid sinus may cause

syncope. Syncope means fainting

Some causes: tight collarsShaving over the neckShowering with spurts of waterShoulder-strap seat belts

Slower-Acting Mechanisms Several mechanisms act slowly to control

blood pressure.

More concerned with long-term relationship of blood pressure.

Renin-angiotensin-aldostrone mechanism is the most important.

Slower-Acting Mechanisms

Activation of the renin-angiotensin-aldosterone mechanism increases blood volume and causes vasoconstriction.

Both of these effects increase blood pressure.

Other hormones that affect blood pressure include: antidiuretic hormone (ADH), atrial natriuretic peptide (ANP), and brain natriuretic peptide (BNP).

Exchange Vessels Exchange vessels, exchange or

swap substances.

As blood flows through the capillaries, substances move out of the capillary into surrounding tissue spaces.

Substances include: oxygen, water, electrolytes, and nutrients needed to live.

The oxygen and nutrients are taken in by the cells and the waste is taken from the capillaries to the kidneys and lungs for excretion.

Exchange Vessels Characteristics of capillaries for good

exchange:

thin capillary walls

large number of capillaries

slow blood flow through the capillaries

Capillary Forces

Certain forces push and pull nutrients and waste in and out of the capillaries:

Diffusion-primary process causing substances to move across the capillary wall.

(movement from an area of high concentration to an area of lower concentration)

Filtration-Osmosis-holes or pores in the capillaries allow water and small substances to squirt into the interstitium.

Edema

Edema occurs when there is a disruption in the forces that push and pull water across the capillary walls.

Diseases that may cause disruptions: Heart failure severe burn kidney disease blocked lymphatic drainage

Blood Flow• Vasodilation and

vasoconstriction also participate in the distribution of blood flow.

• Resting state, skeletal muscles receive 20% of total blood flow, kidneys and abdomen receive 19% and 24%.

• During exercise, blood is redirected and the % of blood flow to the skeletal muscles is greatly increased.

Sum It Up! Functions of the circulatory system:

acts as a delivery system regulates blood pressure engages in exchange of nutrients and

waste within the cells distributes blood in response to

changing body needs helps in the regulation of body

temperature

As We Age Walls of the arteries thicken and become

less elastic and thicker. Blood flow to vital organs decreases. Blood pressure increases. Elderly are more prone to varicose veins. More prone to thrombus. Cardiovascular adjustment to changes in

position are slowed, may cause dizziness, increase in falls.