Circulation: Blood vessels,
Blood pressure & Tissue fluid
Colston’s School
There are
3 Types of Blood Vessels






Arteries
Arterioles
Capillaries
Venules
Veins
Arteries
 Take blood AWAY
from the heart.
 Branch repeatedly
 Smallest ones are the
arterioles
 Typically oxygenated
–...
See the atrium

Coronary blood
vessels
Capillaries
 Smallest
 Most abundant
– Billions
– Huge surface area

 Connect A’s and V’s
 RBC only just fit through, ...
Veins





Take blood TO the heart.
Converge
Smallest – venules
Typically deoxygenated
– Exceptions
 Pulmonary veins
...
Blood Vessel Structure
 Blood vessels have 3 layers:
– Tunica intima
– Tunica media – most important for you!! This is
th...
Tunica
intima

LUMEN

Tunica
adventitia

Tunica
media
LUMEN

Can you see the endothelium?
What type of tissue is it? Why?
T. intima

T. media
The squiggly black things are elastic fibres
Elastic Arteries
 Aorta and major
branches
 Act as AUXILLARY
PUMPS.
 How do they do
this???
What layer would be
most pronounced in a
muscular artery?
Arterioles – highly innervated, good tunica media
Site of resist...
 Arteriosclerosis
– Situation where vessel walls get thick, hard, and lose elasticity.

 Atherosclerosis
– Type of arter...
Capillaries
 Billions – providing a huge Surface Area
 Thin and one cell thick, short difusive
pathway – Fick’s Law
 Fo...
Types of Capillaries
 Continuous
– Most common and most permeable
– No “holes” in the endothelial membrane
so, selectivel...
Notice how red blood cells just fit
through vessels
Some red blood cells become deformed, bend to fit capillary
Why are capillaries
organised into beds?

If you were running,
1.

The precapillary
sphincters in your
hamstrings would be...
Capillaries converge to form
venules, the smallest of the veins.
Veins




All 3 tunics present. TA is the largest.
Contain valves
Distensible
– Contain 60% of body’s blood supply
– Ca...
Compare the vein and the arteries in this image.
1.

What similarities are there? & What differences
do you see?
What do valves do?
Why are they necessary?
Varicose veins
become visible
Blood Pressure
 Arteries
 Capillaries
 Veins

Why is there a
Blood Pressure
value in all 3
vessels
Aorta

Ejected Blood

When the Left Ventricle contracts more
blood enters the arterial system than gets
pushed onward. Thi...
Recoil of the elastic artery

As the LV relaxes, the stretched arterial walls
recoil and push the contained blood onward
t...
What’s an anatomical reason
for why the pressure
fluctuation disappears here?
Pulse Rate = Heart Rate
Pulse Pressure = Systolic Pressure – Diastolic Pressure
 Suppose you measured the pulse rate
and pulse pressure at the carotid
artery and at the tibial artery.
– Would pulse rat...
What happens to BP if:
 Blood volume increases?
 Cardiac output increases?
 Peripheral resistance decreases?
Capillary Blood Pressure




Low
Vessels are less likely to burst
Low pressure means slow flow which
means more time fo...
Moving Blood Thru the Veins

Skeletal Muscle Pump

Respiratory Pump

Why are these 2 auxiliary pumps necessary?
Circulation & Ventillation
 What happens when we breathe?
Deep Inspiration

Thoracic Cavity
Expands
Pressure in thoracic
cavity drops
Pressure in thoracic
veins drops

Abdominal Ca...
Controlling BP

Short
term

Long
term
Brain Centres involved in Short Term
BP Control
 Vasomotor
– Adjusts peripheral resistance by adjusting
sympathetic outpu...
Increased vasomotor center
activity
Increased sympathetic output to
arterioles
Vasoconstriction

Increased peripheral resi...
Baro-receptors
measure changes
in blood pressure
as determined
by deformation
BP rises

Detected by
baroreceptors in
aortic arch &
carotid sinus

Info sent to cardiac
and vasomotor
centers

Decreased
...
Increased blood CO2,
H+ (i.e., decreased
blood pH)
Sensed by chemoreceptors
Info sent to respiratory and
cardiac centers i...
Short Term Chemical Controls
– Epinephrine and norepinephrine
 Adrenal medulla
 ↑HR, SV, CO, PR, and thus BP

– ADH


...
Decreased
BP

Sensed by special
renal baroreceptors

Kidneys release the
enzyme renin

Renin causes increased plasma level...
DRUGS!

Primary

Hypertension
-140/90
-Aneurysm
-Heart Attack

Hypotension
-100/60
-Causes?

Secondary
Diuretics

Calcium
channel
blockers

Beta
blockers

Increase
urine
output

Decrease tension
in vascular smooth
muscle

Pre...
Why doesn’t
it regain its
initial
velocity?
Autoregulation  the automatic adjustment of blood flow to
each tissue in proportion to the tissue’s requirements at any
i...
Tissue fluid formation
 4 forces can impact the exchange of water
between capillary plasma and interstitial
fluid.
– Capi...
Most substances are
exchanged via diffusion
 Capillary osmotic pressure
– Mostly due to what protein?
– Pulls water from the ISF into the capillary.

 Capillary hyd...
ISF OP

CAPILLARY HP
CAPILLARY OP
ISF HP

Extra Cellular Fluid
If capillary BP is greater than capillary
OP, there will be net movement of fluid out
of the capillary.

If capillary BP i...
Capillary BP
Filtration

Pressure

Capillary OP
Reabsorption

Arterial end

Venous end

Distance along the capillary
Excess tissue fluid
is returned to the
blood vessels via the
lymphatic system!
Failure to return excess
interstitial fluid

EDEMA
Hypertension

↑ ISF
formation

↑ capillary BP

Starvation
Lack of
dietary
protein
Histamine

↑ capillary
permeability

↓ i...
Burn/crush
injury

↑ ISF protein
content

Backup of blood in
pulmonary circuit

↑ ISF OP

↑ pulmonary
capillary BP

↑ ISF
...
Hemorrhage
Diarrhoea

Large-scale Fluid Loss

Vomiting
Hypovolemic
Shock
1.

Rapid weak pulse

2.

Cold, clammy skin

WHY?...
Failure to maintain
vasomotor tone.

Excess vasodilation.

Neurogenic Shock
Inability of the heart to
efficiently pump blood.

Cardiogenic Shock
Unique Aspects of Foetal
Circulation
 Blood flow to and from the placenta
 Blood flow within the heart (pulmonary
circui...
Blood Flow to and from the
Placenta

Internal Iliac A.

Umbilical A.’s

Umbilical V.
Ductus Venosus

Inferior vena cava

L...
Blood Flow within the Foetal Heart
Right atrium

Foramen ovale

Left atrium

(Most of the blood)
Right ventricle

Pulmonar...
Foramen Ovale

Fossa Ovalis
Ductus Arteriosus

Ligamentum Arteriosum
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
Circulationbloodtissuefluid colstons
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Circulationbloodtissuefluid colstons

  1. 1. Circulation: Blood vessels, Blood pressure & Tissue fluid Colston’s School
  2. 2. There are 3 Types of Blood Vessels      Arteries Arterioles Capillaries Venules Veins
  3. 3. Arteries  Take blood AWAY from the heart.  Branch repeatedly  Smallest ones are the arterioles  Typically oxygenated – Exceptions  Pulmonary arteries  Umbilical arteries
  4. 4. See the atrium Coronary blood vessels
  5. 5. Capillaries  Smallest  Most abundant – Billions – Huge surface area  Connect A’s and V’s  RBC only just fit through, often deform to fit!
  6. 6. Veins     Take blood TO the heart. Converge Smallest – venules Typically deoxygenated – Exceptions  Pulmonary veins  Umbilical veins
  7. 7. Blood Vessel Structure  Blood vessels have 3 layers: – Tunica intima – Tunica media – most important for you!! This is the region of elastic fibres which in arteries stretch and recoil – Tunica externa
  8. 8. Tunica intima LUMEN Tunica adventitia Tunica media
  9. 9. LUMEN Can you see the endothelium? What type of tissue is it? Why?
  10. 10. T. intima T. media
  11. 11. The squiggly black things are elastic fibres
  12. 12. Elastic Arteries  Aorta and major branches  Act as AUXILLARY PUMPS.  How do they do this???
  13. 13. What layer would be most pronounced in a muscular artery? Arterioles – highly innervated, good tunica media Site of resistance and direction!!!!
  14. 14.  Arteriosclerosis – Situation where vessel walls get thick, hard, and lose elasticity.  Atherosclerosis – Type of arteriosclerosis where fatty plaques form on the tunica interna
  15. 15. Capillaries  Billions – providing a huge Surface Area  Thin and one cell thick, short difusive pathway – Fick’s Law  Found almost everywhere  3 types – Continuous – this one we need to know!! – Fenestrated – Sinusoidal
  16. 16. Types of Capillaries  Continuous – Most common and most permeable – No “holes” in the endothelial membrane so, selectively permeable – Abundant in skin and muscle  Fenestrated – “Holes” in the endothelial membrane – Found in intestines and kidney  Sinusoidal – Most permeable and least common – Big ‘holes” in endothelial membranes – Big clefts between cells – Liver, spleen, and bone marrow especially
  17. 17. Notice how red blood cells just fit through vessels Some red blood cells become deformed, bend to fit capillary
  18. 18. Why are capillaries organised into beds? If you were running, 1. The precapillary sphincters in your hamstrings would be… 2. The precapillary sphincters in your large intestine would be…
  19. 19. Capillaries converge to form venules, the smallest of the veins.
  20. 20. Veins    All 3 tunics present. TA is the largest. Contain valves Distensible – Contain 60% of body’s blood supply – Capacitance vessels/Blood reservoirs  Low pressure  Often collapsed in section
  21. 21. Compare the vein and the arteries in this image. 1. What similarities are there? & What differences do you see?
  22. 22. What do valves do? Why are they necessary?
  23. 23. Varicose veins become visible
  24. 24. Blood Pressure  Arteries  Capillaries  Veins Why is there a Blood Pressure value in all 3 vessels
  25. 25. Aorta Ejected Blood When the Left Ventricle contracts more blood enters the arterial system than gets pushed onward. This causes the arteries to stretch and pressure within them to rise. The highest pressure achieved is known as the systolic pressure.
  26. 26. Recoil of the elastic artery As the LV relaxes, the stretched arterial walls recoil and push the contained blood onward through the system. As they recoil, the amount of contained blood decreases as does pressure. The lowest pressure achieved just before the next contraction is the diastolic pressure.
  27. 27. What’s an anatomical reason for why the pressure fluctuation disappears here?
  28. 28. Pulse Rate = Heart Rate Pulse Pressure = Systolic Pressure – Diastolic Pressure
  29. 29.  Suppose you measured the pulse rate and pulse pressure at the carotid artery and at the tibial artery. – Would pulse rate be the same in both places? – What about pulse pressure?  Does body position play a role in pulse pressure?  If systolic BP is 118 and pulse pressure is 41, what’s the diastolic BP?
  30. 30. What happens to BP if:  Blood volume increases?  Cardiac output increases?  Peripheral resistance decreases?
  31. 31. Capillary Blood Pressure    Low Vessels are less likely to burst Low pressure means slow flow which means more time for exchange
  32. 32. Moving Blood Thru the Veins Skeletal Muscle Pump Respiratory Pump Why are these 2 auxiliary pumps necessary?
  33. 33. Circulation & Ventillation  What happens when we breathe?
  34. 34. Deep Inspiration Thoracic Cavity Expands Pressure in thoracic cavity drops Pressure in thoracic veins drops Abdominal Cavity gets smaller Pressure in abdominal cavity rises Pressure in abdominal veins rises We have a pressure gradient moving blood towards the heart!
  35. 35. Controlling BP Short term Long term
  36. 36. Brain Centres involved in Short Term BP Control  Vasomotor – Adjusts peripheral resistance by adjusting sympathetic output to the arterioles  Cardio-inhibitory  Cardioacceleratory
  37. 37. Increased vasomotor center activity Increased sympathetic output to arterioles Vasoconstriction Increased peripheral resistance Increased blood pressure What about a decrease in vasomotor activity?
  38. 38. Baro-receptors measure changes in blood pressure as determined by deformation
  39. 39. BP rises Detected by baroreceptors in aortic arch & carotid sinus Info sent to cardiac and vasomotor centers Decreased vasomotor activity Decreased NE release on arterioles Vasodilation Decreased PR Increased cardioinhibitory activity Increased vagus activity Decreased BP Increased ACh release on heart Decreased cardioacceleratory activity Decreased NE release on heart Decreased SV and HR Decreased CO
  40. 40. Increased blood CO2, H+ (i.e., decreased blood pH) Sensed by chemoreceptors Info sent to respiratory and cardiac centers in medulla Increased respiration rate and depth Increased SV, HR, and CO
  41. 41. Short Term Chemical Controls – Epinephrine and norepinephrine  Adrenal medulla  ↑HR, SV, CO, PR, and thus BP – ADH    Made in the hypothalamus but stored in posterior pituitary ↓ urine output and thus promotes an ↑in BV and BP ↑ PR and thus BP – Histamine  Mast cells and basophils  ↓ PR and thus BP – Nitric oxide  Potent vasodilator and thus ↓ BP – Alcohol  Inhibits ADH and ↓PR. Thus it ↓ BP.
  42. 42. Decreased BP Sensed by special renal baroreceptors Kidneys release the enzyme renin Renin causes increased plasma levels of angiotensin II AgII is a potent vasoconstrictor Increased peripheral resistance AgII causes the pituitary to release ADH AgII causes the adrenal cortex to release aldosterone Decreased urine output Increased BP Increased blood volume AgII activates thirst centers
  43. 43. DRUGS! Primary Hypertension -140/90 -Aneurysm -Heart Attack Hypotension -100/60 -Causes? Secondary
  44. 44. Diuretics Calcium channel blockers Beta blockers Increase urine output Decrease tension in vascular smooth muscle Prevent NE and Epi from binding to the heart Decrease BV Decrease PR Decrease HR Decrease SV Decrease BP Decrease CO
  45. 45. Why doesn’t it regain its initial velocity?
  46. 46. Autoregulation  the automatic adjustment of blood flow to each tissue in proportion to the tissue’s requirements at any instant. Example: Working Muscle Tissue Tissue temp. rises Tissue CO2 levels rise Tissue O2 levels fall Arterioles serving tissue vasodilate Lactic acid levels rise Increased blood flow to tissue CO2 removed Lactic acid removed Heat removed O2 delivered
  47. 47. Tissue fluid formation  4 forces can impact the exchange of water between capillary plasma and interstitial fluid. – Capillary osmotic pressure – Capillary hydrostatic pressure – Interstitial osmotic pressure – Interstitial hydrostatic pressure
  48. 48. Most substances are exchanged via diffusion
  49. 49.  Capillary osmotic pressure – Mostly due to what protein? – Pulls water from the ISF into the capillary.  Capillary hydrostatic pressure – i.e., the blood pressure of the capillary. – Pushes water from the capillary to the ISF.  ISF osmotic pressure – Usually inconsequential due to the low protein content of the ISF. – It would pull water from the capillary into the ISF.  ISF hydrostatic pressure – Usually inconsequential due to the lack of a high volume of interstitial fluid. – It would push water from the ISF into the capillary.
  50. 50. ISF OP CAPILLARY HP CAPILLARY OP ISF HP Extra Cellular Fluid
  51. 51. If capillary BP is greater than capillary OP, there will be net movement of fluid out of the capillary. If capillary BP is less than capillary OP, there will be net movement of fluid into the capillary.
  52. 52. Capillary BP Filtration Pressure Capillary OP Reabsorption Arterial end Venous end Distance along the capillary
  53. 53. Excess tissue fluid is returned to the blood vessels via the lymphatic system!
  54. 54. Failure to return excess interstitial fluid EDEMA
  55. 55. Hypertension ↑ ISF formation ↑ capillary BP Starvation Lack of dietary protein Histamine ↑ capillary permeability ↓ in plasma albumin Vasodilation ↓ capillary OP ↑ capillary BP ↑ ISF formation ↑ ISF formation
  56. 56. Burn/crush injury ↑ ISF protein content Backup of blood in pulmonary circuit ↑ ISF OP ↑ pulmonary capillary BP ↑ ISF formation ↑ ISF formation L. Ventricle failure Decreased blood flow in systemic circuit ↓ systemic capillary BP ↓ ISF formation
  57. 57. Hemorrhage Diarrhoea Large-scale Fluid Loss Vomiting Hypovolemic Shock 1. Rapid weak pulse 2. Cold, clammy skin WHY???
  58. 58. Failure to maintain vasomotor tone. Excess vasodilation. Neurogenic Shock
  59. 59. Inability of the heart to efficiently pump blood. Cardiogenic Shock
  60. 60. Unique Aspects of Foetal Circulation  Blood flow to and from the placenta  Blood flow within the heart (pulmonary circuit bypass)
  61. 61. Blood Flow to and from the Placenta Internal Iliac A. Umbilical A.’s Umbilical V. Ductus Venosus Inferior vena cava Liver Placenta
  62. 62. Blood Flow within the Foetal Heart Right atrium Foramen ovale Left atrium (Most of the blood) Right ventricle Pulmonary trunk Pulmonary circuit Left ventricle Ductus arteriosus Aorta Systemic circuit
  63. 63. Foramen Ovale Fossa Ovalis
  64. 64. Ductus Arteriosus Ligamentum Arteriosum

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