Chapter 19- Blood Vessels

• Cardiovascular System consists of the blood, heart and blood vessels.

  • 60,000 miles of blood vessels in the body.
  • Blood vessels made of living cells
• Three main kinds of blood vessels:

  1. Arteries - away from heart
  2. Veins - toward the heart
  3. Capillaries - gas exchange (1 tunica interna, tight junctions)
• The walls of arteries & veins have 3 layers: *Lumen - space inside blood vessel*

  1. Tunica Interna - innermost (lymphatics), may elastic
  2. Tunica Media - Muscle (vasoconstruction/vasodilation), elastic fiber.
  3. Tunica Externa - outermost, plastic fibers (lymphatics).
• Tunica Media - Muscle (vasoconstruction/vasodilation), elastic fiber.

  Vasoconstruction = decrease diameter of blood vessel

  Vasodilation = increase diameter of blood vessel

  Less tunic media, lots of elastic fibers -> aorta/pulmonary trunk

  • constrict
  • dilate
• Venous System:

  1. Large Veins
  2. Small Veins
  3. Venules
• Arterial System:

  1. Elastic Arteries (ex: aorta)

  * elastic fibers, no constrict/dilate "conducting arteries"

  2. Muscular Arteries "disturbing arteries"

  * ex: ulnar/radial

  3. Arterioles

  * ex: resistance vessels

  4. Capillaries

  * tunica interna, thinnest, exchange vessels, left-communication
• The arterial system - high pressure, thickest layer is tunica media, all layers have more elastic fibers.

  (a) Elastic arteries stretch during ventricular contraction. (ex: aorta)

  (b) Elastic arteries recoil during ventricular relaxation. (ex: brachial, radial)
• The tunica media allows muscular arteries and arterioles to constrict and dilate:

  • Muscular arteries therefore can regulate blood flow into blood supply to specific organs.
  • Arterioles therefore can regulate blood flow into capillaries.
• The capillaries are the exchange vessels:

  • 5-10 micrometers in diameter
  • Tunica interna only - thin walls
  • Tight junctions join cells together
  • Clefts - gaps between neighboring cells
• There are 3 types of capillaries:

  1. Continuous Capillaries - least permeable, no pores (slow exchange)

  • Locations: throughout body, skin, muscle

  2. Fenestrated Capillaries - very permeable, has pores (fast exchange)

  • Locations: small intestine, kidneys

  3. Sinusoids - extremely permeable, large pores and clefts (fastest exchange)

  • Locations: Liver (krupfter cells), bone marrow, spleen, sinusoids
• Capillary Exchange - movement of substances between blood plasma and interstital fluid.
• Capillary exchange is aided by:

  • Diffusion - going from high to low concentration
  • Transcytosis - ex: exocytosis, pinocytosis
  • Bulk flow - passive process by which large numbers of ions, molecules or particles in a fluid move together in the same direction.
• Capillary transport mechanism

  1. Diffusion through plasma membrane.
  2. Bulk flow through clefts
  3. Bulk flow through fenestrations
  4. Transcytosis using vesicles
• Bulk flow is directional : High -> Low

  • Filtration

  (high pressure in capillaries > low pressure in interstitial fluid)

  • Reabsorption

  (high pressure in interstital fluid > low pressure in capillaries)

  *pressure differences determine the direction of bulk flow*
• Definitions

  • Hydrostatic Pressure (HP) <- ->

  forced exerted by a fluid against a wall.

  • Osmotic Pressure (OP) -> <-

  force opposing hydrostatic pressure due to non-diffusing molecules

  • Net Filtration Pressure (NFP)

  calculated using several HP and the OP

  
  

  (a) when blood HP > blood OP, then filtration occurs at the beginning of capillary (≈ 20 L of fluid/day)

  (b) when blood OP > blood HP, then reabsorption occurs at the end of capillary (≈ 17 L of fluids reabsorbed day)
• • Filtration occurs at the beginning of capillary (NFP is +10 mmHg)
  • Reabsorption occurs at the end of capillary (NFP is -9mmHg)
• Venous System

  • Low pressure system compared to arterial system
  • Has thinner walls and wider lumens than arteries (tunica externa is thickest layer) compared to arterial system.
  • Blood reservoirs of vascular system (veins)
• The Venous System consists of :

  • Venules (smallest diameter) - connect cap, to veins
  • Veins (large diameter) ex:

  valves present in veins

  • Venous sinuses - specialized, broad veins supported by surrounding tissue ; only has the tunica interna.

  ex: coronary sinus

  ⬇️⬇️⬇️⬇️

  deoxygenated blood

  going outwards in

  different directions
• Anastomoses provide detours for blood flow.

  (a) The major coronary artery : anatomosis

  (b) The major cardiac : coronary sinus
• Blood pressures drop along the vascular system

  • Arterial system - highest pressure (120 -> 35 mmHg)
  • *must know* capillaries (35 -> 16 mmHg)
  • Venous system - lowest pressure (16 -> 0 mmHg)
• Blood Pressure moves areas of high pressure -> low pressure

  1. Aorta
  2. Arteries ex: muscular arteries
  3. Arterioles
  4. Capillaries
  5. Venules
  6. Veins
  7. Venae Cavae (back to RA)
• Venous return of blood is aided by:

  • Muscular pump

  (squeeze deep veins -> heart)

  • Respiratory pump

  (squeeze local veins -> heart)

  • Valves

  (back flow, ex. varicose veins 'incompetent valve')

  Also large lumens (decrease resistance)
• Some definitions:

  • Blood flow (F) = ml/min
  • Blood pressure (P) = mmHg
  • Resistance (R)
• F = ΔP/R

  F: blood flow per min.

  ΔP: change in BP *hydrostatic

  Smaller Lumen/diameter:

  As resistance ⬆️

  Flow ⬇️

  Larger Lumen/diameter:

  As resistance ⬇️

  Flow ⬆️

  ΔP⬆️,F⬆️ (vice versa)
• Contraction of the ventricles increases blood pressure -> increase blood flow. (blood pressure)
• Increases in the resistance decrease blood flow :

  • Greater blood viscosity (thickness) increases resistance.

  ⬆️Plasma p vot. (ex: polycythemia)

  • Greater total blood vessel length increases resistance.
  • Vasoconstruction increase resistance
  • Vasodilation decreases resistance
• Systolic P (≈120)

  • max P when ventricle contracting

  Diastolic P (80 mmHg)

  • max P when ventricle is resting

  Mean arterial P

  • diastolic P
  • pulse pressure (systolic - diastolic)
• Blood Pressure - hydrostatic pressure exerted by blood.

  • Systolic Pressure
  • Diastolic Pressure
  • Pulse Pressure (systolic P - diastolic P)
  • Mean Arterial Pressure (MAP)

  diastolic P

  avg pressure from arterial system
• Neural Regulation of Blood Pressure (BP) is short-term

  ⬆️HR, ⬆️BP (sympathetic), vasoconstrict (sym ON/activated)

  ⬇️HR, ⬇️BP (parasympathetic), vasodilation (sym OFF/deactivated)

  *Only the sympathetic division of the autonomic nervous system can change the diameter of blood vessels*
• Hormonal Regulation of BP is short-term.

  
  

  Hormones that raise BP:

  • Angiotensin II
  • Epinephrine & norepinephrine
  • Antidiuretic Hormone (ADH)

  (opposite dehydration)

  bp med: for hypertension ⬇️BP ex: diuretic ⬆️dehydration ⬇️BP

  
  

  Hormones that lower BP:

  • Atrial natriuretic peptide (ANP)

  change in NA (decrease)
• Renal Regulation of BP is long-term:

  • Kidneys increase BP by increasing blood volume.
  • Kidneys decrease BP by decreasing blood volume.

  Short-term regulation by:

  • Nervous system (para + sym)
  • Hormones

  Long-term regulation by:

  • Kidneys adjusting blood volume
• Normal BP is about 120/80

  Disorders of the Vascular System:

  • Hypertension - high blood pressure

  (>140/90)

  • Hypotension - low blood pressure

  (systolic pressure < 100 mmHg)
• Hypotension may be due to different causes:

  • Orthostatic hypotension, due to position of body
  • Chronic hypotension (circulatory shock), allergies, bacterial infections *hives
  • Acute hypotension (sudden)
• Circulatory shock - condition when there is not enough blood in the blood vessels and blood cannot circulate normally.

  • Hypovolemic shock - loss of volume
  • Vascular shock - vasodilation
  • Cardiogenic shock - weak heart
• Hypertension

  • ⬆️ Afterload
  • High pressure in SL valves
  • Harder for the heart to reopen

  valve in next contract.