Chapter 19 - Blood Vessels

1
Chapter 19 - Blood Vessels

• Circulation is divided into the systemic and
  pulmonary circulation.
• At rest 84 of blood is in the peripheral
  circulation.

2
Function of Circulation

• Transport nutrients to tissues,
• Transport waste,
• Transport hormones,
• Maintain tissue fluid environment.

3
Parts of Circulation

• Arteries withstand high pressure,
• Arterioles dilate and constrict in response to
  tissue needs (smooth muscle) determine flow into
  capillary beds
• Capillaries are permeable to materials carried in
  the blood,
• Venules collect blood and serve as a reservoir.

4

• I. Blood Vessel Structure Function
• A. Vessel Walls
• 1. Three tunics around a central blood
  containing space - the lumen.
• 2. Tunica interna (intima) contains the
  endothelium and is continuous with endocardial
  lining of the heart.
• 3. Turnica media circular smooth muscle
  regulated by
• sympathetic motor division responsible for
  vasoconstriction (narrow vessel) vasodilation
  (widen vessel) maintains blood pressure and
  blood circulation.
• 4. Tunica externa (adventitia) collagen fibers
  that protect and anchor vessel to surrounding
  structures.

5
Artery
6
(No Transcript)
7
Tunica media
lumen
Tunica interna
Tunica adventitia
8

• B. Arteries
• 1. Elastic Arteries
• a. Large, thick-walled conducting arteries near
  the heart
• b. Aorta and its branches
• c. Elastin for pressure
• 2. Muscular Arteries
• a. Distributing arteries deliver blood to body
  organs
• b. Smooth muscle vasoconstriction
• 3. Arterioles
• a. Largest of these have all three tunics with
  little elastin in the media
• b. Determine blood flow to capillary beds

9
(No Transcript)
10
Pressure produced by ventricular contraction is
stored in elastic walls of arteries and released
by recoil
11
(No Transcript)
12

• C. Capillaries
• 1. General
• a. Tunica interna only thin walls
• b. Exchange between plasma and cells
• c. No capillaries in
• tendons, ligaments
• cartilage
• d. High density in muscles, glands ( more
  metabolic activity)

13
(No Transcript)
14

• 2. Types of Capillaries
• a. Continuous capillaries
• 1) Skin muscle (most common) whose cells are
  tightly joined
• b. Fenestrated capillaries
• 1) Large pores so fluid can pass rapidly between
  plasma and interstitial fluid
• 2) Found in small intestine, kidneys for
  absorption
• c. Sinusoidal capillaries
• 1) Highly modified - leaky
• 2) Large molecules blood cells can move
  between blood and tissues
• 3) Found in liver, bone marrow, lymphoid tissues
  some endocrine organs

15
(No Transcript)
16

• 3. Capillary Beds
• a. Precapillary sphincter at metarteriole
  regulates flow into the bed
• b. Interweaving networks of thin vessels
• c. Vascular shunt - connects arteriole venule
  with true capillaries
• d . Terminal arteriole ----gt metarteriole ----gt
  capillary ----gt venule
• e. 10-100 true capillaries per capillary bed,
  depending on the needs of the tissue. At rest,
  there is little to no blood flow thru the muscle
  capillaries.

17

• D. Venous System
• 1. Venules blood flow converges from
  capillaries to small venules
• 2. Venules join to form Veins
• a. Thinner walls with larger lumen than
  arteries blood pressure in veins is low and they
  contain up to 65 of blood volume at one time
• b. Venous valves prevent backflow
• c. Varicose veins due to incompetent valves
• E. Vascular Anastomoses
• 1. Where vascular channels unite
• 2. Arterial anastomoses many organs receive
  blood from more than 1 pathway, if 1pathway is
  blocked.
• 4. Venous anastomoses most common

18
Vein and a valve
(Notice that a vein often has a larger lumen)
19
ConclusionHeart is a pump, the arteries are
conduits, the arterioles are resistance vessels,
the capillaries are exchange sites, and the veins
are conduits and blood reservoirs.Why Does
Blood flow?Liquids flow down a pressure
gradient. Blood only flows when one region
develops a higher pressure than another region.
High pressure is created in the chambers of the
heart when it contracts. Blood flows out of the
heart (highest pressure) into the closed loop of
blood vessels (lower pressure). As it moves,
pressure is lost because of friction between the
fluid and the vessel walls. So pressure falls as
we move farther from the heart.
20
II. Physiology of Circulation

• A. Blood Flow, Pressure Resistance
• 1. Terminology
• a. Blood flow volume of blood flowing through
  vessel, organ, or entire circulation in a period
  of time (mL/min)
• b. Blood pressure
• 1) Force exerted by the fluid on the wall of a
  vessel
• 2. Pressure decreases over distance and force is
  in all directions.
• 3) Pressure is measured in mm of mercury (Hg)
  the hydrostatic pressure exerted by a 1 mm high
  column of mercury on an area of 1 cm2
• c. Resistance
• 1) Tendency of the cardiovascular system to
  oppose blood flow. Resistance impedes flow
  friction
• 2) Peripheral resistance (PR)

21

• Blood Pressure and resistance determine flow
  through a blood vessel (Flow changes when these
  factors change).
• Pressure difference between 2 ends of a vessel
  pushes blood through the vessel.
• Resistance impedes flow because of friction of
  molecules along the inside of the lumen of the
  vessel.
• Q change P
• R
• where blood flow(Q) is directly proportional to
  difference in pressure (P) and inversely
  proportional to resistance R.

22
Use increase of decrease

• Vasoconstriction will ____________
• resistance and therefore_________________flow
  if the
• pressure stays the same.

23
Flow changes when pressure and/or resistance
change.

• Factors of Resistance
• a. Blood viscosity internal resistance related
  to the viscosity and determines blood flow. What
  happens with excess red blood cells?
• b. Total blood vessel length longer more
  resistance.
• c. Blood vessel diameter changeable factor,
  unlike above smaller diameter more resistance.
• A small change in the diameter of a vessel can
  have a large impact on the flow through the
  vessel.

24
Explain

• T or F
• Changes in vessel diameter have little affect on
  resistance to blood flow.

25
Blood Viscosity

• Determines flow.
• Normal blood with a hematocrit of 42 requires
  about 3X pressure to move it as water.
• Polycythemia (excess red blood cells) hematocrit
  of 70 would require 10X the pressure to move the
  blood.

26
Vessel DiameterPoiseuilles Law - flow is
proportional to the 4th power of the diameter of
the vessel.
Diameter of a vessel is 2X the radius plays a
major role in blood flow
27

• B. Systemic Blood Pressure
• 1. Arterial Blood Pressure
• a. 1). Distensibility of elastic arteries and
  2). volume of blood
• b. Systolic pressure ventricles contract (120
  mm Hg)
• c. Diastolic pressure aortic pressure drops to
  lowest level as elastic arteries recoil to
  maintain pressure (80 mm Hg)
• d. Pulse pressure difference between systolic
  and diastolic. Felt in elastic arteries
• e. Mean arterial pressure MAP diastolic 1/3
  of pulse pressure
• 2. Capillary Blood Pressure
• a. Dropped to 35 mm Hg ----gt 10 mmHg to venules
• b. Capillaries are fragile and permeable

28

• 3. Venous Blood Pressure
• a. Steady 20 mm Hg
• b. Factors in venous return
• 1) Respiratory pump inhaling increases
  abdominal pressure thoracic pressure drops
• 2) Muscular pumps skeletal muscles around
  veins
• 3) Venous valves

29
Venous resistance

• Veins are a reservoir and propel blood back to
  the heart via a venous pump.
• Veins distend so they have little resistance to
  flow.
• When standing pressure in veins of feet is 90mm
  Hg.

30

• 5. Neural control blood pressure integrating
  center for neural control or BP is the medulla
  oblongata. Vasomotor center
• a. 1) Sympathetic neurons in cardiac center
  of medulla
• 2) Neural input will cause a change in vessel
  diameter, thus change resistance.
• 3) Innervates smooth muscles of blood vessels

31

• b. Baroreceptor reflexes that control BP
• 1) In walls of carotid artery and aortic arch
• 2) If BP drops, firing rate or receptor
  increases this changes cardiac output and
  peripheral resistance

32

• c. Chemoreceptor-initiated reflexes
• 1). In aortic arch and large arteries of neck
• 2) Respond to low oxygen or pH levels or a rise
  in carbon dioxide
• 3) Results in reflex vasoconstriction and
  increase heart rate to speed blood return

33

• T F
• Vasoconstriction increases resistance and
  decrease blood flow

34

• 6. Short-Term Chemical Controls
• a. Epinephrine and norepinephrine (NE) from the
  adrenal medulla increase vasoconstriction and
  cardiac output during stress. Vasoconstriction
  increases resistance and decrease flow if
  pressure stays the same.
• b. Antidiuretic hormone (ADH) water
  conservation and vasoconstriction during
  hemorrhage.
• c. Alcohol inhibits ADH and depresses
  vasomotor center vasodilation of skin.
• 7. Long-Term Renal Regulation
• a. Kidneys directly regulate BP by regulating
  blood volume.
• b. Rising BP enhances fluid loss in urine
  falling BP causes kidney to retain water,
  increasing blood volume
• c. Indirect release of a hormone complex
  renin-angiotensin that causes salt and water to
  be retained affecting BP

35
Image of an arteriole before(a) and after (b) a
drop of NE was applied.
36

• C. Monitoring Circulation
• 1. Vital signs pulse, blood pressure,
  respiratory rate and temperature
• 2. Pulse radial is most commonly used, but
  there are many others also called pressure
  points that are compressed to stop bleeding
• 3. Blood pressure sphygomomanometer used to
  hear sounds of Korotkoff

37

• D. Blood Pressure Alterations
• 1. Hypotension
• a. Systolic pressure lt100
• b. May be within normal limits or sign of poor
  nutrition . . .
• 2. Hypertension
• a. Chronically elevated BP systolic gt140,
  diastolicgt 90
• 1) Increased peripheral resistance
• b. Primary or essential hypertension 90 have
  no known cause
• 1) Factors include diet, obesity, age, race,
  heredity, stress, smoking
• 2) Treated with diuretics, diet restrictions,
  other medications
• c. Secondary hypertension arteriosclerosis,
  hyperthyroid, etc.
• Key feature of both is adaptation of aortic
  baroreceptors to higher pressure so no reflex
  reduction occurs!

38
III. Blood Flow Through Tissues

• A. Tissue Perfusion each tissue has the
  ability to control local blood flow to meet
  the needs of the specific tissue.
• B. Velocity of Blood Flow
• 1. Inversely related to cross-sectional area of
  vessels.
• 2. Slowest in capillaries

39
At rest, skeletal muscle receive 20 of the
cardiac output exercising 85 of cardiac
output.
40

• C. Autoregulation- Automatic adjustment of blood
  flow to each tissue proportional to its
  requirements
• Intrinsic control modify diameter of local
  arterioles feeding the capillaries
• 1. Metabolic controls oxygen is the strongest
  stimuli
• immediate vasodilation of the arterioles serving
  the capillary beds of the needy tissue so the
  blood goes through capillaries to these tissues
• 2. Myogenic controls - response is smooth muscle,
  increased blood pressure stretches the vessels.
• 3. Collateral circulation - when a vessel,
  artery, or vein is blocked, new vessels develop
  around the blockage.

41
IV. Blood Flow Through Capillaries

• A. Capillary Exchange
• 1. Once blood reaches capillaries, exchange
  takes place between plasma and cells.
• 2. Capillaries have the thinnest walls and have
  pores that allow water gases, and most dissolved
  solutes to pass
• 3. Movement is by diffusion aided by hydrostatic
  pressure

42
2 Fluid Movements in Capillaries

• 1. Capillary hydrostatic Pressure (HPc) - Force
  exerted by a fluid against a wall the blood
  pressure against capillaries that pushes fluid
  out of capillary pores.
• 2. Interstitial fluid hydrostatic pressure (HPif)
  - opposing force acting outside the capillaries
  pushes fluid in.

43

• 2. Osmotic Pressures
• 1. Created by presence of non-diffusible
  molecules in fluid such as plasma proteins
• 2. Colloid osmotic pressure osmotic pressure
  created by proteins
• 3. Because colloid osmotic pressure is higher in
  the plasma because of the large protein
  molecules, water moves from the interstitial
  fluid to the capillary.
• Hydrostatic-Osmotic Pressure Interactions
• 1. Net filtration pressure (NFP) considers all
  forces responsible for fluid flow at the
  capillary depending on the difference between the
  opposing forces.

44
(No Transcript)