BLOOD VESSELS

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BLOOD VESSELS BLOOD PRESSURE

• Chapters 18 19

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Overview

• Idea of blood circulation 300 years ago
  William Harvey
• 3 general types of vessels
• Arteries ----arterioles ----capillaries
  ----venules ----- veins
• Direct tissue contact is with capillaries only

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Structure

• (except capillaries ) vessels composed of 3
  layers (tunics) surrounding an opening (lumen)
• Tunica intima or interna (innermost) composed
  of outer layer of endothelium (continuation of
  endocardium) and supported by a basement layer
  slick to reduce friction

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• Tunica media circularly arranged smooth muscle
  cells and elastic connective tissue muscle is
  regulated by vasomotor fibers from autonomic
  nervous system

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• Tunica adventitia or externa composed of
  collagen fibers to protect and anchor vessel
  infiltrated with nerve and lymph vessels and vasa
  vasorum (vessels of the vessels)

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Arteries

• Transport away from heart 3 groups
• Elastic arteries large, thick walled, close to
  heart, little vasomotor action elasticity
  provides support from pressure due to pumping
  heart

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• Muscular arteries medium size, more vasomotor
  and less elasticity found in the extremities

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• Arterioles lumen less than 0.5 mm much
  vasomotor control composed of almost all smooth
  muscle
• Pulse pressure point area where an elastic
  artery is close to the skin surface

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Elastic Artery
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Arteriole
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Capillaries

• Thin walled
• composed of tunica intima (no muscle or
  connective tissue)
• sometimes one endothelial cell thick

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• lumen just large enough for RBCs to pass through
  in single file
• most tissues are vascularized directly by
  capillaries (except tendons, ligaments,
  cartilage, cornea and lens of eye)

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• 3 types (based on structure)
• Continuous
• abundant in the skin and muscles
• interspersed with large intercellular clefts to
  allow passage of fluids

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• Fenestrated
• endothelial cells of capillaries are joined by
  gap junctions
• have pores
• found where absorption and filtration occurs
• intestinal mucosa, endocrine organs, filtering
  units of kidneys

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• Discontinuous
• extremely porous
• endothelial cells do not provide a continuous
  covering
• large gaps between cells
• allows large molecules to pass
• found in bone marrow liver and spleen

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• Capillary beds can be of 3 types based on
  function regulated by vasomotor and chemical
  control depending upon body conditions
• Thoroughfare vessels that connect arterioles
  with venules no blood/tissue exchanges occur here

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• True capillaries actual blood/tissue exchanges
  occur here.
• Sinusoids special capillary beds that flow into
  liver and lymphatic tissue blood flows slowly
  here where vessels are lined with phagocytic
  cells so blood can be processed carefully

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Veins

• Composed of tunic intima and tunica adventitia
• little tunica media (muscle) due to being on the
  back side of circulation
• Have large lumens and thin walls to accommodate
  large blood reservoirs

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• dont have to withstand pressure from heart and
  are therefore, usually collapsed when not filled
  with blood
• contain valves to prevent backflow

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• Venules
• created from uniting capillaries
• drain into veins
• Venous valves
• formed from the tunica adventitia skeletal
  muscle also adds to this pumping of blood back to
  heart

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• Varicose veins tortuous and dilated due to
  incompetent valves hemorrhoids

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Blood Pressure

• Force/unit area exerted on vessel wall by blood
• Expressed in mmHg (ex 120/80 mm Hg)

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• Refers to systemic arterial blood pressure in
  largest arteries near heart
• Resistance (opposition to flow), measures amount
  of friction blood encounters in vessels 3
  sources

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• Blood viscosity thickness or stickiness of
  blood
• Vessel length longer the vessel greater the
  resistance
• Vessel diameter (is dynamic) smaller the lumen
  greater the friction

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• Blood pressure results when flow is opposed by
  resistance
• Left ventricle contracts and pushes blood into
  the aorta systolic arterial blood pressure
  average in adults is 120 mmHg.

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• Left ventricle relaxes diastolic arteriole
  blood pressure average in adults is 80 mmHg.
• Blood pressure measurement is to check the
  relative health of the blood vessel wall.

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Factors Affecting Blood Pressure

• Cardiac output changes in the amount of blood
  put out/minute and or changes in heart rate
• Peripheral resistance vessel diameter is single
  most important influence on blood pressure and
  flow

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• Blood volume problems during hemorrhaging or
  fluid retention.

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Regulation of Blood Pressure

• Nervous Control maintains blood pressure and
  alters blood distribution as needed.
• Vasomotor fibers release NE (vasoconstrictor) and
  sometimes ACh (vasodilator)

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• Vasomotor center sympathetic nerves in the
  medulla oblongata
• Pressoreceptors receptors found in carotid
  arteries, and other large vessels, trigger
  vasodilation when stimulated by high pressure.

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• Chemoreceptors sensitive to O2 and H ion
  levels when triggered, increases pressure to
  speed blood to lungs

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Diseases

• Cardiovascular diseases are one of the leading
  causes of death and disability in the U.S.
• 2 Main Types Hypertension and Atherosclerosis.

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Hypertension

• High Blood Pressure
• Forces the heart to work harder, which may weaken
  it and weaken blood vessels.
• Increases the risk of heart attack and stroke.

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Atherosclerosis

• Plaque build up in arteries
• Can cut off oxygen flow to the heart (heart
  attack)
• Clots due to plaque build up can break loose and
  block blood vessels leading to the brain (stroke).

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Circulatory System Health

• How to help prevent cardiovascular disease
• Exercise strengthens the heart
• Balanced diet low saturated fat and cholesterol
• DO NOT SMOKE!!!!!!!!!!!!!