• The walls of blood vessels are composed of three layers.

   The outer layer is the tunica adventitia.
   The middle layer is the tunica media.
   The inner layer is the tunica intima.
• The passageway within the vessel is called the lumen.

• Arteries carry blood away from the heart are under high pressure located deep

There are 3 types (levels)
   1) elastic: large, thick walled, near the heart
   2) musclular: distributing arteries; from 10 mm to 0.3 mm in diameter
   3) arterioles: from 0.3 mm to 10 micrometers in diameter
• Capillaries: very small (from 8-10 micrometers in diameter); they are woven together in a network called a capillary beds exchange sites ... where oxygen and nutrients are released from the blood and carbon dioxide and wastes enter the blood
• There are 3 types (structurally) of capillaries.

   1) continuous
       a) most common
       b) found in the skin and muscles
       c) though they don’t have holes in the lining, adjacent cells usually don’t match up correctly and leave gaps for materials to pass through
   2) fenestrated - have holes (fenestrations) in the lining
   3) sinusoidal
       a) large and irregular
       b) very leaky
• Veins: carry blood to the heart thin walls; are under low pressure; have one-way valves so that blood doesn’t flow backwards small veins, called venules; exit the capillary beds and are 8 to 100 micrometers in diameter

TERMS
 

• Blood flow - volume of blood flowing through an area in a certain amount of time
• Blood pressure (BP) - pressure exerted on the blood vessel by the blood
• Resistance - the friction encountered by blood as it passes through the vessels; it comes from viscosity, blood vessel length and diameter
• Blood viscosity - how well the blood flows ... its “thickness”

• Systolic pressure - when the heart contracts and BP is at its highest
• Diastolic pressure - when the heart relaxes and BP is at its lowest Pulse pressure - systolic pressure minus diastolic pressure

• Blood pressure can be increased by certain chemicals (epinephrine, ADH, etc.).
• Blood pressure can be lowered by certain chemicals (alcohol, nitric oxide, etc.)

• In the long run, BP is controlled by the kidneys, which regulate how much water is taken from the blood.
• If more water is removed, BP goes down; if more water is retained, BP goes up.

• High blood pressure is known as hypertension.
• Hypertension can be caused by: diet, obesity, age, race, heredity, stress, and smoking.

• Low blood pressure is known as hypotension.  It can be orthostatic (temporary, such as when you stand rapidly) or chronic.

• Pulse is a pressure wave transmitted through the arteries.
• It can be best detected from certain pressure points [see Fig. 20.10 on p. 659].
• The same pressure points, areas where an artery is near a bone, can be pressed to stop profuse bleeding.

• Circulatory Shock - a condition in which blood vessels are inadequately filled and blood cannot circulate properly.
• Hypovolemic shock - most common; results from large-scale loss of blood volume

Homeostatic Imbalances in the Circulatory System Caused by Behavior & Chemicals

• Atherosclerosis - blockage of the arteries
• Stroke - artery to the brain is blocked … killing nerve tissue in the brain
• Heart attack (myocardial infarction) - coronal artery is blocked … killing heart muscle tissue
• Alcohol decreases the atherogenic plaques both in humans and experimental animals.
• Hypotension - low blood pressure
  Orthostatic hypotension - temporary condition caused when rising suddenly; more common in the elderly
  Chronic hypotension - continuous condition that can be caused by poor nutrition, Addison’s disease, hypothyroidism, etc.
• Hypertension - high blood pressure
  Contributing factors include: 
     Diet: too much or too little of certain nutrients can increase hypertension
     Obesity: increases hypertension
     Age: chances of hypertension increase as you get older (esp. over 40)
     Race: darker races get hypertension more often than lighter races
     Heredity: if it runs in your family, you have a better chance of getting it
     Stress: stress can increase hypertension
     Smoking: nicotine constricts the blood vessels, increasing blood pressure
• Alcohol decreases myocardial contractility and reduces cardiac energy.
• Numerous studies have demonstrated a causal association between chronic intake of 30 g or more alcohol per day and elevated blood pressure in men and women.
• Alcohol intake can lead to stroke (hemorrhagic and ischemic). Heavy alcohol consumption increases the risk of hemorrhagic stroke.
• Cardiomyopathy, a degenerative disease of the heart in the absence of coronary artery disease, is a well-established complication of chronic alcohol abuse.
• Excessive drinking, however, is associated with higher mortality risk. However, consumption of 5 or more drinks per day increases risk of stroke by 250 to 450 percent.

BUT,  a large number of epidemiologic studies have consistently shown that moderate alcohol intake is associated with decreased risks of coronary artery disease (CAD).
WHY?  Not sure … perhaps:
     • HDL/LDL?      • Ischemia/reperfusion      • PKC      • Platelets       • Fibrinolysis