Circulation: Special Circulations Flashcards
What is meant by Special circulations?
Circulations that are able to adapt to the needs of certain end organs or tissues, like that in the brain, heart, skin, skeletal muscle, kidneys, lungs.
CUTANEOUS/SKIN CIRCULATION:
What are the 3 special requirements of this circulations?
How is the temperature regulated?
What does the skin temperature depend on?
- • Used for defence against environment,
• Involved in the Lewis triple response to trauma (↑blood flow)
• Help regulate body temperature - By Radiation, Conduction, Convection (removed by air/water), Sweating - skin is a poikilothermic organ, so it can only withstand short periods of very high or low temperatures.
- Cutaneous blood flow
What is the structural feature of this circulation? What does it do?
What are the nerve fibres present on the arteries? What are they driven by?
LOOK AT DIAGRAM!
- Arterio-Venous Anastomoses (AVAs) - direct connections of arterioles and venules to expose blood to lots of surface area.
- Sympathetic vasoconstrictor and Sudomotor vasodilator fibres - driven by temperature regulatory nerves in Hypothalamus.
What are the functional features of this circulation?
- Responsive to ambient (environmental) and core temperatures:
• ↑Ambient temperature = Vaso/venodilation = ↑Heat LOSS
• ↓Ambient temperature = Vaso/venoconstriction = ↓Heat LOSS - Severe colds → Paradoxical cold vasodilation
- Core temperature receptors in hypothalamus control sympathetic activity to skin to controls skin blood flow.
Describe Cold-induced Vasoconstriction
Describe Paradoxical (absurd) Cold Vasodilation
LOOK AT DIAGRAM!
- Conserves heat - occurs due to abundance of α2-receptors on VSMCs in skin - NA binds at low temp.
- Protects skin from damage - occurs due to paralysis of sympathetic transmission - Long-term exposure leads to oscillations/fluctuations of contraction and relaxation.
How does an increase in core temperature lead to vasodilation?
It stimulates warmth receptors in Hypothalamus, which will cause:
• Sweating - ↑sympathetic activity (ACh) to sweat glands
• Vasodilation - ↑sympathetic Sudomotor (Ach act on endothelium to release NO) activity to arterioles in extremities
Other functional specialisations:
Baroreflex/RAAS/ADH stimulated vasoconstriction:
What does it do?
What is the process mediated by?
What does it cause?
- Causes vasoconstriction of skin circulation to direct blood to the more important organs during a ↓BP e.g. haemorrhage, sepsis.
- Sympathetic vasoconstrictor fibres, Adr, ADH, Ang II
- PALE, COLD skin of patient in SHOCK
Lewis Triple Response:
What is it in response to?
What fibre is involved in this response?
What does it cause?
What is the importance of this response?
LOOK AT DIAGRAM!
- Skin trauma
- Nociceptive C fibre
- Local redness, Inflammatory swelling, Vasodilation spreading from trauma site (FLARE)
- Increased delivery of immune cells and antibodies to the trauma site - deals with invading pathogens
What are the 3 special problems with this circulation? Explain them.
How can prolonged obstruction be avoided?
- Prolonged obstruction of blood flow by compression:
• Can lead to severe tissue necrosis e.g. bed sores on weight bearing areas
• Avoided by moving position - causes Reactive Hyperaemia (excessive blood flow) - skin has high tolerance to ischaemia. - Postural hypotension/oedema due to gravity:
• Standing for ages in hot weather will ↓CVP and ↑Capillary permeability
• Will feel faint - Raynaud’s disease:
• Due to sustained cold-induced vasoconstriction in fingers
• Cause local tissue ischaemia
PULMONARY CIRCULATION:
What are the 2 special requirements of this circulation?
- Gaseous exchange:
• Receives entire CO from RV
• Needs a low pressure and to occur very fast - Area for metabolic function:
• Since it receives the entire CO from RV, the pulmonary circulation is a good system to produce/remove a substance
What are the structural features of this circulation?
Very capillary dense and there’s a very short diffusion pathway
What are the functional features of this circulation?
- Low vascular resistance:
• Less sympathetic influence
• Low pressure system - aid gas exchange - Hypoxia pulmonary vasoconstriction (HPV):
• Hypoxia (low O2) leads to Vasoconstriction - prevents blood flow to poorly ventilated areas - maintains a good V/Q ratio.
• Hypoxia = ↑Excitability and contractibility of VSMCs
• Normally hypoxia would cause vasodilation in the systemic circulation - Metabolic functions:
• Since it receives all CO from RV, it contains ACE to convert Ang I → Ang II
What are the 3 special problems that can occur in this circulation? Explain them
- Gravity:
• When standing, pulmonary arterial pressure at the lung apex is low due to gravity
• Poor perfusion to apex can lead to vessel collapse and impaired blood oxygenation - Chronic HPV:
• Occur in high altitudes for a long time or have respiratory diseases, like COPD
• Chronic HPV will lead to pulmonary hypertension and RV failure. - Pulmonary Oedema:
• Thin barrier between capillary and alveoli can cause a leak
• Conditions like Mitral stenosis will ↑Pulmonary capillary pressure = ↑Filtration = Oedema - poor lung function
SKELETAL CIRCULATION:
What are the 2 special requirements of this circulation?
- Exercise:
• Delivery of oxygen and nutrients has to be equal to the amount of work occurring
• Blood flow has to be proportional to exercise intensity - Controls arterial pressure:
• Vascular resistance is a main contributor to TPR - Vasodilation/Vasoconstriction of this circulation can have large effects on BP
What are the structural features of this circulation?
Capillary density differs in different muscles - constantly active muscles will have a higher capillary density
