Chapter 21

Blood Vessels

Direction of Flow

Heart to aorta to arteries to arterioles to capillaries.

Capillaries to venules to veins to vena cava to heart.

ArteriesVeins

• Capillaries form Microcirculation• Microscopic vessels that connect arterioles to venules• Found near every cell in the body but more extensive in

highly active tissue (muscles, liver, kidneys & brain)•entire capillary bed fills with blood when tissue is active•lacking in epithelia, cornea and lens of eye & cartilage

• Function is exchange of nutrients & wastes between blood and tissue fluid

• Structure is single layer of simple squamous epithelium and its basement membrane

Capillaries:

1. Continuous

2. Fenestrated

3. Sinusoid

Venous valves

Blood Distribution

• 12% pulmonary vessels

• 8 % = heart

• 15% = systemic arteries and arterioles

• 5% = capillaries

• 60% = systemic veins and venules

Venous flow occurs by:

1. muscle contraction

2. respiratory pump

3. valve assistance

4. Ventricular relaxation

Varicose Veins

• Twisted, dilated superficial veins– caused by leaky venous valves

• congenital or mechanically stressed from prolonged standing or pregnancy

– allow backflow and pooling of blood• extra pressure forces fluids into surrounding tissues

• nearby tissue is inflamed and tender

• Deeper veins not susceptible because of support of surrounding muscles

Anastomoses• Union of 2 or more arteries supplying the same body

region– blockage of only one pathway has no effect

• circle of willis underneath brain• coronary circulation of heart

• Alternate route of blood flow through an anastomosis is known as collateral circulation– can occur in veins and venules as well

• Alternate routes to a region can also be supplied by nonanastomosing vessels

Pulse Pressure

• Pulse pressure = systole - diastole

• MAP = diastolic pressure + pulse pressure/3

• MAP = mean arterial pressure

• MAPB = diastole + 1/3 (systole – diastole)

• MAPB = mean arterial blood pressure

Blood PressureInfluenced by:

• Peripheral resistance

• Heart efficiency

• Blood viscosity

• Total blood vessel length

• Arteriole elasticity

• Blood volume

Hormones that affect BP

• Renin angiotensin

• Epinephrine and norepinephrine

• Antidiuretic hormone

• Atrial natriuretic peptide

Autoregulation of BP

• Physical changes

• Vasodilating and constricting chemicals

Major Branches of the Aorta

• Coronary arteries• Brachiocephalic• Left common carotid• Left subclavian• Celiac• Superior mesenteric artery• Renals• Ovarian / testicular• Inferior mesenteric

Minor Branches of the Aorta

• Pericardial Thoracic

• Bronchial Lumbar

• Esophageal Suprarenal

• Mediastinal

• Intercostal

• Phrenic

Celiac circulation

Abdominal arteries

Arterial supply and venous drainage of the liver

Hypertension

• Systole > 140

• Diastole > 90

• Causes: diet high in fat and sodium, obesity, older age, race, heredity, stress, and smoking.

Words to Learn

• Aneurysm Shock• Angiogram Sphygmomanometer• Diuretic Korotkoff sounds• Phlebitis Angiogenesis• Phlebotomy Hypotension• ThrombophlebitisOcclusion• Syncope White Coat Hypertension• Tachycardia Edema