Summary Lecture 1 Hypertentsion and the vascular system

Pathophysiology of heart and circulation – Lecture 1 –
Hypertension and the vascular system

Anatomy and function
Anatomy artery
Inside to outside: endothelial cell  internal elastic lamina 
smooth muscle cell  external elastic lamina  adventitia

Vascular network
Circulation divided into 3 parts
1. Distribution/resistance: aorta  large artery  small artery  arteriole
Aorta: pulse dampening and distribution
Large arteries: capable of constricting and dilation – but have no significant
role in the regulation of pressure and blood flow – distribution
Small arteries: distribute blood flow within the organ – distribution and
resistance
Arterioles: diameter <200 micrometer – resistance

Small arteries + arterioles  primary resistance vessels. Innervated by
autonomic nerves and are richly endowed (voorzien) with receptors that bind
circulation hormones (echolamines, angiotensin II) which can alter vessel
diameter

2. Exchange: capillaries  small venules
Capillaries: only endothelia cells and a basement membrane no smooth
muscle – exchange
Small venules: when capillaries join together they still have no smooth muscle
– exchange

Capillaries  primary exchange vessels

3. Capacitance (most blood volume is found and regional blood volume is
regulated): large venules  vein  vena cava
Large venules: small venules converge now there
is smooth muscle – capable of dilating and
constricting – collection and capacitance
Vein: large venules conserve – capacitance
Vena cava: collection

Large venules + vein  primary capacitance
vessels

Distribution of pressures and volumes
Pressure
Contraction of the heart  pressure increases  given
rise to systolic pressure (120 mm Hg)
Relaxation of the heart  pressure decreases  given rise to
diastolic pressure (80 mm Hg)

Pulse pressure = Psystolic – Pdistolic

, Mean aortic pressure (MAP) is 95 mm Hg and this decreases as the blood flow
further away from the heart because of energy is lost as heat
MAP = Pdiastolic + 1/3 (Psystolic – Pdiastolic)

Large arteries: blood pressure does not fall much because these vessels have low
resistance and therefore little loss of pressure energy
Small arteries and arterioles: large fall in blood pressure because these vessels have
high resistance
Capillaries: important that blood pressure is low otherwise large amounts of fluid
would leak through the capillaries causing tissue edema
Vena cava: blood pressure is close to 0

Blood pressure is affected by hydrostatic pressure
differences:
 Everything below the heart: increase in hydrostatic
pressure
 Everything above the heart: decrease in hydrostatic
pressure

Giraffe needs a very high blood pressure to compensate for
the highly negative hydrostatic pressure (because neck high
above the heart).

Organs that determine blood pressure:
 Kidney: resorbs salts and water – affects volume of blood
 Brain: nerve fibers that innervate various organs and blood vessels
 Circulation hormones: affect the contractile blood vessels and inflammatory
factors

EQUATION: DeltaP = F (blood flow) * R (vascular resistance)
Blood flow is equal in the whole blood circulation
Vascular resistance refers to the resistance that must be overcome to push blood
through the circulatory system and create flow
P drops? More resistance

EQUATION: R = n (blood viscosity) * L (vessel length) / r^4 (vessel radius --
diameter)
The vascular diameter is very dynamic (dilate and contract)
Increase in vessel radius? Less resistance

Something to think about: capillaries have the smallest
diameter so why don’t they have the most resistance
instead of the small arteries and arterioles?
This is because capillaries have many parallel
pathways  resistance in parallel decreases

Volume
The greatest volume of blood is found in the venous part