Cardio L7 Tissue blood flow Flashcards
• The Key role of the vascular system is to
distribute the cardiac output according to the metabolic needs of the tissues.
• 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%.
Arterioles: function
- Regulate local blood flow according to local metabolic need.
- Large amount of Smooth muscle
- Exhibit:
a. Vasoconstriction
b. Vasodilation
Vascular Smooth Muscle (VSM briefly allow
constriction dilation
VSM cell shape
- Spindle shaped cells
- Approx 50 nanometers x 4um
- Thick (myosin) and thin (actin) filaments.
- Actin → inserts into dense bands (inner membrane and dense bodies (cytoplasm)
- Function syncytium: cells are linked by gap junctions
VSM Contraction: process
- Calcium (from SR or calcium channels) forms a complex with calmodulin
- Ca-calmodulin regulates an enzyme called myosin light chain kinase (MLKC)
- MLCK regulates action myosin interaction by phosphorylating the light chain of the myosin head.
- Latch state of prolonged crossbridge formation (energy efficient tone).
VSM contraction stimuli:
VSM contraction stimuli:
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
Vasodilation controlled by
Adrenaline (Beta2) acts via a cAMP dependent pathway to inhibits MLCK and cause vasodilation
Beta 2 receptors
Found on skeletal muscle e.g. during exercise increase vasodilation to increase blood flow
Vasodilation controlled by
Endothelium derived relaxing factor (EDRF) and atrial natriuretic peptide (ANP) act via cGMP to produce vasodilation.
ANP acts via
Acts via cGMP = vasodilation
Alpha 1 receptor is for
Vasoconstriction
NO
Acts via cGMP causing relaxation
Control of Blood Vessels:
local and global control
local control
a. Mechanical
b. Metabolites
c. Autocoids
Global control
SNS
Hormones
Mechanical
A high external pressure may impede blood flow
E.g.
→ Left coronary flow pattern.
→ Pressure sores
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.
Metabolites: action
Many products of metabolism cause vasodilation and allow local blood flow to be matched to local metabolite rate
Metabolites: examples
Carbon dioxide Lactate Adenosine Potassium ions Hypoxia
Metabolites: clinical
COPD → increase of Co2 pathologically
- Bounding pulse
- Headaches
Active hyperaemia
Skeletal muscle during exercise. Metabolites increases and so vasodilation occurs and more blood flow.
Reactive hyperaemia
After a period of ischemia. E.g cuff
Build up of metabolites that has occurined during ischemia
Autocoids (local hormone) Function
These are vasoactive chemicals that are produce locally, released locally and act locally
Autocoids (local hormone) Examples
Histamine
Serotonin (5-HT)
Bradykinin
Prostaglandins
Thromboxane
Predominantly produce by platelets → platelet aggregation and vasoconstriction
Prostacyclin
Produce by endothelium. Inhibits platelet aggregation and causes vasodilation
Aspirin
Inhibit production of thromboxane. Acute treatment of MI
Auto-regulation: function
Over a range of perfusion pressures blood flow remains remarkably constant.
2. Brain, kidney, myocardium, intestine → flow doesn’t obey straight line increase pressure increase flow
auto-regulation 3. Underlying mechanisms
that changes resistance with change in pressure: Probably involves myogenic response and effects of local metabolites.
Endothelial Derived Relaxing factor (EDRF):
- Shear stress, Ach and substance P will cause relaxation of arterial vessels.
a. Achieved via: Stimulates endothelial production of EDRF (nitric Oxide)
b. EDRF stimulates guanylate cyclase in VSM and produces relaxation.
Patho: of EDRF
Septic shock → production of NO is abnormally elevated = abnormal dilation and therefore TPR falls and a fall in blood pressure.
NO vasodilators
GTN (increased production of NO and so vasodilation).
Sympathetic Nervous system:
- Tonic activity (noradrenaline release) contributes to the maintenance of vessel tone
- A fall in sympathetic tone =
dilation
- A rise in sympathetic tone =
arteriolar vasoconstriction (raises TPR and afterload) and venoconstriction (raises CVP and preload)→ therefore stroke volume.
Hormones:
- Renin angiotensin aldosterone system
- Vasopressin (Anti-diuretic hormone
- Adrenaline
- ANP
Renin-Angiotensin-Aldosterone Important in
Control of ECF and blood volume
Renin-Angiotensin-Aldosterone Function
Decreased afferent arteriolar pressure
Increased renal sympathetic tone
Renin-Angiotensin-Aldosterone Important in
Response to haemorrhage
Renin-Angiotensin-Aldosterone Secreted by
The juxtaglomerular cells (afferent arterioles) in response to: decreased solute NaCL load at the macula densa.
Renin-Angiotensin-Aldosterone Process
ACE converts Angiotensin 1 to angiotensin 2
Angiotensin 2
Constricts vascular smooth muscle and so increases resistance and increased afterload.
Increased water and sodium retention via aldosterone stimulation → Increased preload.
Vasopressin (ADH) Produced by
the magnocellular neurones of the supraoptic and paraventricular nuclei of the hypothalamus
Vasopressin (ADH) Released from
The posterior lobe of the pituitary
Vasopressin (ADH) Stiimulated by
Increased osmoarity or fall in BP
Vasopressin (ADH) Outcome
Vasoconstriction (except cerebral and coronary vessles)
Renal water retention
Adrenaline vs Noradrenaline Both function
Increases cardiac contractility and hert rate via the Beta 1 adrenoceptor → positive chronotrophs
Adrenaline vs Noradrenaline Both Cause
Arteriolar vasoconstriction via the alpha 1 adrenoceptor
Adrenaline alone
Has a high affinity for Beta 2 receptors and produces vasodilation in skeletal muscle, myocardial and liver vessels.
Local Anaesthetics:
- A mixture of adrenaline and local anaesthetics is often used to cause vasoconstriction and reduced bleeding but should never be used in distal regions e.g.s fingers/toes (ischemia).
Coronary Circulation:
LCA flow is greatest during diastole.
As myocardium contracting → the LCA perforating branches are occluded.
Lewis Triple Response:
- Response to skin trauma → wheel and flare reaction
2. Abolished by sensory denervation.
