chapter 21 blood vessels. direction of flow heart to aorta to arteries to arterioles to capillaries....

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