BLOOD VESSEL STRUCTURE, BLOOD PRESSURE AND SYSTEMIC VESSELS

Blood Vessels: The Vascular System• Types of blood vessels:

– Arteries (in direct contact with the heart) and Arterioles

• Carry blood away from the heart

– Capillaries• Where substance exchange (gases, nutrients,

hormones, etc) between other tissues and the blood occurs

– Venules and Veins (in direct contact with the heart)• Return blood toward the heart

Arteries and Arterioles1. Arteries are strong, elastic vessels adapted for

carrying high-pressure blood.2. The inside space of an artery through which blood

flows is the lumen.3. The wall of an artery has 3 layers. From the inside to

the outside they are:• Tunica interna (endothelium)- Elastic tissue• Tunica media- Smooth muscle and elastic tissue• Tunica externa (adventitia)- Elastic tissue

4. The structure of an artery helps it propel blood onward while the ventricles are relaxing.

5. Arterioles are very small (almost microscopic) arteries

Arteries and Arterioles continued..6. When the sympathetic nervous system (fight

or flight) is active, the smooth muscle of arteries contract, which narrows the lumen (less blood flow). This is called vasoconstriction. When the parasympathetic nervous system is active, the smooth muscle relaxes, which increases the lumen diameter. This is called vasodilation. *When would vasoconstriction occur? Vasodilation?

Artery – Cross section

Tunica Interna

Tunica Media

Tunica Externa

Capillaries1. Capillaries are the smallest vessels, consisting

only of one cell layer through which substances are exchanged with tissue cells. Consist only of the tunica intima.

2. The number of capillaries throughout the body varies, depending on metabolic activity. Tissues with high metabolic requirements include the muscles, liver, kidneys and nervous system.

3. Because they are so numerous, blood flows more slowly through them which helps with substance exchange.

4. Precapillary sphincters (rings of smooth muscle) regulate the flow of blood into capillaries.

Capillary Beds

Exchanges in Capillaries1. At the arteriole end of a capillary, the blood

pressure is high, which forces oxygen, water and nutrients out of the capillary. This is called filtration.

2.At the venule end of a capillary, the blood pressure is lower, which causes most water and solutes that were forced out before to diffuse back into the capillary. This is called reabsorption. About 85% of the fluid filtered is reabsorbed. The carbon dioxide from the surrounding cells gets absorbed as well.

Filtration Reabsorption

Venules and Veins1.Venules leading from capillaries merge to form

veins that return blood to the heart.2. Veins have the same three layers as arteries,

but are much thinner. They do not carry the same high pressure blood.

3. Veins have flap-like valves inside to prevent backflow of blood.

4. Veins use the milking action of skeletal muscles to move blood because they are not lined with the same amount of smooth muscle as arteries.

Movement of Blood Through Veins

Varicose Veins• In people with weak vein

valves, gravity forces blood backwards through the valve. This increases venous blood pressure, which pushes the vein’s wall outward. After this repeatedly happens, the walls lose their elasticity and become stretched and flabby. This is called varicose veins.

Main Differences Between Blood Vessels

• Walls of arteries are the thickest and their smooth muscle helps move blood

• Lumens of veins are larger because walls are thinner

• Larger veins have valves to prevent backflow• Skeletal muscle “milks” blood in veins toward

the heart• Walls of capillaries are only one cell layer thick to

allow for exchanges between blood and tissue

Blood Pressure• Blood pressure is the pressure exerted by blood on the

walls of a blood vessel. It is highest in the aorta and large arteries branching off of the aorta.

• Blood pressure is affected by the distance from the left ventricle , the total volume of blood, vasoconstriction/vasodilation and blood viscosity.– Pressure in an artery is approximately 93 mm Hg, in a

capillary is 35 mm Hg and in a venule is 16 mm Hg.– Loss of blood would lower bp as water retention would raise

bp.– Vasoconstriction raises bp as vasodilation lowers bp.– Blood viscosity is “thickness” of blood. The greater the # of

blood cells and solutes, the greater the bp.

Comparison of Blood Pressures in Different Vessels

Systolic/Diastolic PressureA healthy blood pressure reading is 120 mm Hg/80 mm Hg.

• Systolic Blood Pressure is the top number of a blood pressure reading (120). This is the pressure that the blood is putting on the arteries as the ventricles contract, forcing blood out of the heart.

• Diastolic Blood Pressure is the bottom number of a blood pressure reading (80). This is the pressure that the blood is putting on the arteries as the ventricles relax.

• The surge of blood that occurs with ventricular contraction can be felt at certain points in the body as a pulse. The pulse rate normally is about 70-80 bpm.

Measuring Arterial Blood Pressure

Pulse

• Pulse - Pressure wave of blood

• Monitored at “pressure points” in arteries where pulse is easily felt

• Pulse averages 70–76 beats per minute at rest

Variations in Blood Pressure

• Normal human range is variable:– Normal

• 140–110 mm Hg systolic• 80–70 mm Hg diastolic

– Hypotension• Low systolic (below 110 mm HG)• Often associated with illness

– Hypertension• High systolic (above 140 mm HG)• Can be dangerous if it is chronic

What helps maintain normal blood pressure?

• Baroreceptors- Pressure receptor nerve cells which are located in the aorta and other large arteries and send messages to the brain.

• Chemoreceptors- Measure the chemical composition (O2 and CO2) of blood. These cells send messages to alter respiration rate.

• Hormones- Regulate blood flow and pressure– Renin, Adrenaline, ADH

Systemic CirculationThe systemic circuit includes the aorta and its branches leading to all body tissues as well as the system of veins returning blood to the right atrium.

Major Arteries of Systemic CirculationAreas that they feed

1. External carotid-external to skull2. Internal carotid- internal to skull3. Common carotid- branches into

external and internal4. Vertebral- posterior brain5. Brachiocephalic trunk-branches

into right subclavian and right common carotid

6. Brachial-arm7. Renal-kidney8. Radial-radial side of forearm9. Common iliac-branches into

internal and external iliac10. Internal iliac- pelvis

11. Subclavian- parts of brain, spinal cord, neck, chest, shoulder

12. Axillary- shoulder 13. Ulnar- ulna side of forearm14. External iliac- lower limbs15. Femoral- groin and thigh16. Posterior tibial- posterior muscles

and bones of leg and foot17. Popliteal- knee and posterior leg

muscles18. Anterior tibial-anterior muscles

and bones of leg and foot

Major Arteries of Systemic Circulation

Parts of the Aorta• The aorta has 4 parts:

– Ascending aorta- Emerges from the left ventricle; where the coronary arteries branch to feed the heart.

– Arch of the aorta- As the name implies, where the aorta “arches” to the left. The brachiocephalic trunk, left common carotid artery and left subclavian arteries branch off of this.

– Thoracic aorta- The descending portion that is begins at the 4th/5th thoracic vertebrae and continues until the diaphragm opening.

– Abdominal aorta- The descending portion between the diaphragm opening and the 4th lumbar vertebra.

Label the 4 parts of the aorta

Major Veins of Systemic CirculationAreas that they drain

1. Internal jugular- head2. Vertebral- neck, cervical

vertebrae3. Brachiocephalic-dumps into the

SVC4. Brachial-forearm, elbow, and

humerus5. Renal- kidney6. Radial- radius side of forearm7. Common iliac- Pelvis and upper

leg8. Internal iliac- pelvis9. Greater saphenous-longest in

the body- femur region10. Posterior tibial- back side of

lower leg

11. Subclavian- arms, neck, thoracic wall

12. Axillary- arms and upper chest13. Cephalic- lateral upper limbs14. Hepatic-liver15. Median cubital-elbow16. Ulnar- ulna side of forearm17. Femoral- thigh18. Popliteal- knee19. Small saphenous-Foot and

posterior leg20. Anterior tibial-anterior portion of

leg, ankle and knee

Major Veins of Systemic Circulation

Common Blood Vessel Disorders

• Hypertension- High blood pressure– Systolic greater than 140 mm Hg and Diastolic

greater than 90 mm Hg– Effective treatments include: lose weight, limit

alcohol intake, exercise, reduce sodium intake, don’t smoke and manage stress.

• Aneurysm- A thin, weakened section of the wall of an artery or a vein. If it bursts, massive hemorrhaging could result.

• Aneurysm video• Endovascular aneurysm repair

Abdominal Aortic Aneurysm- EEEKKK!!!