1. Circulation: Blood vessels,
Blood pressure & Tissue fluid
Colston’s School

2. There are
3 Types of Blood Vessels





Arteries
Arterioles
Capillaries
Venules
Veins

3. Arteries
 Take blood AWAY
from the heart.
 Branch repeatedly
 Smallest ones are the
arterioles
 Typically oxygenated
– Exceptions
 Pulmonary arteries
 Umbilical arteries

4. See the atrium
Coronary blood
vessels

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. Veins




Take blood TO the heart.
Converge
Smallest – venules
Typically deoxygenated
– Exceptions
 Pulmonary veins
 Umbilical veins

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. Tunica
intima
LUMEN
Tunica
adventitia
Tunica
media

9. LUMEN
Can you see the endothelium?
What type of tissue is it? Why?

10. T. intima
T. media

13. The squiggly black things are elastic fibres

16. Elastic Arteries
 Aorta and major
branches
 Act as AUXILLARY
PUMPS.
 How do they do
this???

20. What layer would be
most pronounced in a
muscular artery?
Arterioles – highly innervated, good tunica media
Site of resistance and direction!!!!

21.  Arteriosclerosis
– Situation where vessel walls get thick, hard, and lose elasticity.
 Atherosclerosis
– Type of arteriosclerosis where fatty plaques form on the tunica interna

23. 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

24. 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

27. Notice how red blood cells just fit
through vessels
Some red blood cells become deformed, bend to fit capillary

28. 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…

29. Capillaries converge to form
venules, the smallest of the veins.

30. 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

31. Compare the vein and the arteries in this image.
1.
What similarities are there? & What differences
do you see?

32. What do valves do?
Why are they necessary?

34. Varicose veins
become visible

35. Blood Pressure
 Arteries
 Capillaries
 Veins
Why is there a
Blood Pressure
value in all 3
vessels

36. 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.

37. 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.

38. What’s an anatomical reason
for why the pressure
fluctuation disappears here?

39. Pulse Rate = Heart Rate
Pulse Pressure = Systolic Pressure – Diastolic Pressure

40.  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?

41. What happens to BP if:
 Blood volume increases?
 Cardiac output increases?
 Peripheral resistance decreases?

42. Capillary Blood Pressure



Low
Vessels are less likely to burst
Low pressure means slow flow which
means more time for exchange

43. Moving Blood Thru the Veins
Skeletal Muscle Pump
Respiratory Pump
Why are these 2 auxiliary pumps necessary?

45. Circulation & Ventillation
 What happens when we breathe?

46. 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!

48. Controlling BP
Short
term
Long
term

49. Brain Centres involved in Short Term
BP Control
 Vasomotor
– Adjusts peripheral resistance by adjusting
sympathetic output to the arterioles
 Cardio-inhibitory
 Cardioacceleratory

50. Increased vasomotor center
activity
Increased sympathetic output to
arterioles
Vasoconstriction
Increased peripheral resistance
Increased blood pressure
What about a decrease in vasomotor activity?

52. Baro-receptors
measure changes
in blood pressure
as determined
by deformation

53. 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

54. 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

56. 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.

57. 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

58. DRUGS!
Primary
Hypertension
-140/90
-Aneurysm
-Heart Attack
Hypotension
-100/60
-Causes?
Secondary

60. 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

61. Why doesn’t
it regain its
initial
velocity?

62. 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

63. 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

64. Most substances are
exchanged via diffusion

66.  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.

67. ISF OP
CAPILLARY HP
CAPILLARY OP
ISF HP
Extra Cellular Fluid

68. 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.

69. Capillary BP
Filtration
Pressure
Capillary OP
Reabsorption
Arterial end
Venous end
Distance along the capillary

70. Excess tissue fluid
is returned to the
blood vessels via the
lymphatic system!

71. Failure to return excess
interstitial fluid
EDEMA

72. 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

73. 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

74. Hemorrhage
Diarrhoea
Large-scale Fluid Loss
Vomiting
Hypovolemic
Shock
1.
Rapid weak pulse
2.
Cold, clammy skin
WHY???

75. Failure to maintain
vasomotor tone.
Excess vasodilation.
Neurogenic Shock

76. Inability of the heart to
efficiently pump blood.
Cardiogenic Shock

77. Unique Aspects of Foetal
Circulation
 Blood flow to and from the placenta
 Blood flow within the heart (pulmonary
circuit bypass)

78. Blood Flow to and from the
Placenta
Internal Iliac A.
Umbilical A.’s
Umbilical V.
Ductus Venosus
Inferior vena cava
Liver
Placenta

82. 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

84. Foramen Ovale
Fossa Ovalis

85. Ductus Arteriosus
Ligamentum Arteriosum