Lecture 8.1: Special Circulations Flashcards
What are the 2 Main Circulatory Systems in the Body?
1) Pulmonary
2) Systemic
Pulmonary Circulation
- ‘Managed’ by the right side of the heart
- Deals with the oxygenation of venous blood
- Delivery of ‘good to go’ arterial blood to the left
side of the heart
Systemic Circulation
- Managed by the left side of the heart
- Delivers oxygenated arterial blood to the body * Returns it via the venous system back to the
right side of the heart
Pulmonary Artery Pressure
- Low Pressure
- Low Resistance
- 15-30mmg/4-12mmHg
- Short, wide vessels
- Lots of capillaries (in parallel)
Local Hypoxia effect on Pulmonary & Systemic Circulation
- Causes vasodilation in the systemic circulation
- Causes vasoconstriction in the pulmonary
circulation
What can happen if pulmonary capillary pressure increases?
- Pulmonary oedema can form
Why is Pulmonary Oedema bad? What relieves the systems?
- Pulmonary oedema impairs gas exchange
- Mainly at base when upright
- Throughout lung when lying down
- Diuretics relieves the symptoms
- But treat the cause
Consequences of Failure of Cerebral Circulation (4)
- Neurons very sensitive to hypoxia
- Loss of consciousness after a few seconds of
ischaemia - Irreversible Damage in ~ 4 minutes
- Strokes/Cardiac Events
Blood supply to brain is via…? (carotid…..to penetrating arteries)
- Internal Carotid Arteries
- Vertebral Arteries (from which the basilar artery
originates) - Carotids and basilar anastomose to form a
circle around the optic chiasm (circle of Willis) - Anterior, middle and posterior cerebral arteries
arise from the circle of Willis - The cerebral arteries divide to form the pial
arteries that run over the surface of the brain - From pial arteries, smaller arteries are formed
that penetrate
What is an anastomose?
A surgical connection between two structures
Why are Anastomoses important in younger people?
- In younger people, the anastomoses ensure
cerebral perfusion if a carotid fails - In older individuals, this process is less
effective
What is Autoregulation?
The intrinsic ability of an organ to maintain blood flow at a nearly constant rate despite changes in arterial perfusion pressure
Do Cerebral Arteries show Autoregulation?
- Cerebral vessels show considerable
autoregulation to maintain proper flow - If BP drops and perfusion is threatened,
cerebral resistance vessels dilate - The brain is extremely selfish, brainstem
responses can interrupt flow to other vascular
beds to preserve itself!
What does local hypoxia results in cerebral arteries?
Local hypoxia results in cerebral vasodilation via adenosine
What is the Cushings Reflex/Cushings Response?
- It is a physiological nervous system response
to acute elevations of intracranial pressure
(ICP)
Results in Cushing’s Triad of:
* Widened pulse pressure (increasing systolic,
decreasing diastolic)
* Bradycardia
* Irregular Respirations
What problems space occupying lesions cause in terms of the cerebrum?
- Impaired CSF drainage
- Raises intracranial pressure with displacement
of brainstem down into foramen magnum - Compression of brainstem produces activation
of vasomotor centres - Cushing’s Reflex is caused
- Also evoke bradycardia mediated via.
baroreceptor reflex
What substances can move through the Blood Brain Barrier?
- Lipid soluble substances able to move freely
from blood to brain - Lipid insoluble eg salts do not
Brain capillaries have specialised tight junctions, what are they made of?
- Made of cadherin-10, claudin-1 and occluding
amongst others - Unbroken seal between cells
- Aided by feet of astrocytes
In what places is the BBB defective?
- Circumventricular Organs (allows Na+/Cl- to
access osmoreceptors) - Area Postrema (medulla) (allows emetics to
access vomiting centre)
Coronary Circulation
- Right and left coronary arteries arise in the
aorta from dilatations called the sinuses of
Valsalva - Left coronary artery (left ventricle and
interventricular septum) - Right coronary artery (right ventricle)
- Venous drainage primarily to the right atrium via
the coronary sinus
When does most coronary blood flow occur?
- ~80% of coronary blood flow occurs during
diastole - Many vessels are compressed during systole
What does continuous production of NO by endothelium do?
- Maintains a high basal flow
- Flow reduced by NO synthase inhibitors
Additional demand of exercise met by metabolic..?
- Additional demand of exercise met by metabolic
hyperaemia - Adenosine prime contender
What is Hyperaemia?
It is the process by which the body adjusts blood flow to meet the metabolic needs of its different tissues in health and disease
What are the 3 Ways Heat is Lost?
- Radiation
- Conduction/convection (air next to skin warmed
up and moved on) - Evaporation
What is the Importance of Cutaneous Circulation?
- Important role in temperature regulation
- Cutaneous heat loss matched to core heat
production - Cutaneous blood flow is the principal factor in
regulating heat loss by the aforementioned
mechanisms
The skin itself is Poikilothermic, what does this mean?
It has variable temperature/temperature changes
What does Homeothermic mean?
Having a relatively uniform body temperature maintained nearly independent of the environmental temperature
What are Arteriovenous Anastomoses (AVAs)? Where are they found?
- They are specialised structures that are direct
connections between small arteries and small
veins - Acral (Apical) Skin
- Fingers/toes/lips/nose/ie exposed regions
What part of the nervous system are AVAs controlled by?
- Show little basal tone
- Controlled almost exclusively by SANS
influenced by hypothalamic temperature
regulating centre
What happens when core temp increases to encourage heat loss?
- Sympathetic drive is reduced
- Leads to vasodilation
- Blood flows into skin increasing blood flow and
heat delivery = heat loss
