Flashcards in Cardio L7 Tissue blood flow Deck (54)
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1
• The Key role of the vascular system is to
distribute the cardiac output according to the metabolic needs of the tissues.
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• The distribution of blood flow is
is not fixed, for example at rest skeletal muscle receives about 20% of the cardiac output. During heavy exercise this may increase to 80%.
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Arterioles: function
3. Regulate local blood flow according to local metabolic need.
4. Large amount of Smooth muscle
5. Exhibit:
a. Vasoconstriction
b. Vasodilation
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Vascular Smooth Muscle (VSM briefly allow
constriction dilation
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VSM cell shape
1. Spindle shaped cells
2. Approx 50 nanometers x 4um
3. Thick (myosin) and thin (actin) filaments.
4. Actin → inserts into dense bands (inner membrane and dense bodies (cytoplasm)
5. Function syncytium: cells are linked by gap junctions
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VSM Contraction: process
1. Calcium (from SR or calcium channels) forms a complex with calmodulin
2. Ca-calmodulin regulates an enzyme called myosin light chain kinase (MLKC)
3. MLCK regulates action myosin interaction by phosphorylating the light chain of the myosin head.
4. Latch state of prolonged crossbridge formation (energy efficient tone).
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VSM contraction stimuli:
VSM contraction stimuli:
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VasoConstriction controlled by 3 and process
Noradrenaline (alpha 1 receptor)
Angiotensin (ATII receptors action)
Endothelin (act via ETA receptors)
Act via phosphplipase C (PLC) to produce vasoconstriction
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Vasodilation controlled by
Adrenaline (Beta2) acts via a cAMP dependent pathway to inhibits MLCK and cause vasodilation
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Beta 2 receptors
Found on skeletal muscle e.g. during exercise increase vasodilation to increase blood flow
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Vasodilation controlled by
Endothelium derived relaxing factor (EDRF) and atrial natriuretic peptide (ANP) act via cGMP to produce vasodilation.
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ANP acts via
Acts via cGMP = vasodilation
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Alpha 1 receptor is for
Vasoconstriction
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NO
Acts via cGMP causing relaxation
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Control of Blood Vessels:
local and global control
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local control
a. Mechanical
b. Metabolites
c. Autocoids
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Global control
SNS
Hormones
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Mechanical
A high external pressure may impede blood flow
E.g.
→ Left coronary flow pattern.
→ Pressure sores
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Mechanical Process of action in arterioles
Raising the internal pressure in arterioles would initially distend them before they reacting by contracting i.e. myogenic response.
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Metabolites: action
Many products of metabolism cause vasodilation and allow local blood flow to be matched to local metabolite rate
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Metabolites: examples
Carbon dioxide
Lactate
Adenosine
Potassium ions
Hypoxia
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Metabolites: clinical
COPD → increase of Co2 pathologically
1. Bounding pulse
2. Headaches
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Active hyperaemia
Skeletal muscle during exercise. Metabolites increases and so vasodilation occurs and more blood flow.
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Reactive hyperaemia
After a period of ischemia. E.g cuff
Build up of metabolites that has occurined during ischemia
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Autocoids (local hormone) Function
These are vasoactive chemicals that are produce locally, released locally and act locally
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Autocoids (local hormone) Examples
Histamine
Serotonin (5-HT)
Bradykinin
Prostaglandins
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Thromboxane
Predominantly produce by platelets → platelet aggregation and vasoconstriction
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Prostacyclin
Produce by endothelium. Inhibits platelet aggregation and causes vasodilation
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Aspirin
Inhibit production of thromboxane. Acute treatment of MI
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