Please enable JavaScript.

Coggle requires JavaScript to display documents.

Circulatory system and BP, Endothelium Elastin fibers Smooth muscle …

- - - - Vasoregulation
        Vasodilation
        Increased blood flow in the arteriole wall
        ↓ O2
        ↑ CO2
        ↑ Nitric oxide (very potent)
        ↓ Sympathetic activity
        Histamine
        Heat
        Vasoconstriction
        Decreased blood flow in the arteriole wall
        ↑ O2
        ↓ CO2
        ↑ Endothelin (very potent)
        ↑ Sympathetic activity
        Cold
        Vasopression and angiotensin II (potent vasoconstrictor)
      - Local control of arteriolar (arterioles)
        radius
      - The fraction of the total CO delivered to each organ varies depending on demands for blood
      - Differences in flow to organs are determined by differences in vascularization and differences in resistance offered by arterioles supplying each organ
      - Extrinsic Control of arteriolar radius
        
        Extrinsic control of arteriolar radius is important in regulating blood pressure, and influence of total peripheral resistance (TPR, total resistance offered by systemic peripheral vessels) on mean arterial pressure
        
        Sympathetic fibers supply arteriolar smooth muscle everywhere
        
        Increased sympathetic activity leads to generalized vasoconstriction
        
        Decreased sympathetic activity leads to generalized vasodilation
        
        Cardiovascular control center control the sympathetic output
        
        Adrenal hormones
        
        Norepinephrine produces generalized vasoconstriction
        
        Epinephrine reinforces local vasodilatory mechanisms in tissues
        
        Vasopression and angiotensin II
        
        Vasopressin maintains water balance
        
        Angiotensin II regulates salt balance
        
        Local controls overriding
        sympathetic vasoconstriction
        E.g. Riding bicycle (exercise)
        → increased sympathetic activity
        → generalized vasoconstriction, but...
        → local metabolic activity in leg muscle induces vasodilation (override)
        → more blood to leg muscle
        → lesser blood to arm muscles and viscera etc
        No parasympathetic innervation
        to arterioles
      - Blood Pressure
        
        Affected by cardiac output (heart rate, stroke volume) and
        total peripheral resistance (arteriol radius, blood viscosity)
        
        Needs to be closely regulated
        
        High enough (adequate pressure) to maintain blood flow and tissue perfusion (fluid exchange)
        
        Not too high to overwork heart and cause vascular damage and rupture of small vessels
  - - - Venous return affected by sympathetic innervation
        
        Vasoconstriction leads to higher venous return, as it is "squeezed" more.
      - Skeletal Muscle activity
        
        When muscle contracts during activity
        
        Compress veins
        
        Decreases venous capacity
        
        Increasing venous return
      - Gravity
        
        Lying down, equal
        
        Standing up
        
        Vessels below heart subject to gravity (pressure caused by weight of blood from heart to vessel)
        
        Distensible veins yield under hydrostatic pressure, leading to ↑ capacity
        
        In leg, post-capillary blood pools in extended veins, hence ↓ VR, ↓CO
        
        Blood to brain reduced, resulting in fainting
        
        Walking helps to push blood to heart
        
        Postural Hypotension
        
        Triggers sympathetic venous vasoconstriction, driving some of the pooled blood forward
        
        Skeletal muscle pump “interrupts” column of blood
        
        Sympathetic venous vasoconstriction cannot completely compensate without skeletal pump
        
        Valves stop blood from going backwards:
        
        One-way valves spaced 2-4 cm away
        
        Also help counteract gravity (minimize back flow)
        
        Varicose veins
        
        Incompetent venous valves (can no longer support the column of blood above it and collapse)
        
        Aggravated by frequent, prolonged standing
      - Other factors:
        
        Respiratory activity
        
        Pressure within chest cavity is 5 mmHg less than atmospheric pressure
        
        External pressure gradient between the lower veins (atmospheric pressure) and chest veins (less than atmospheric pressure)
        
        Cardiac suction
        
        Ventricular contraction
        
        AV valves closed but drawn downward, enlarging atrial cavity so atrial pressure transiently drops lower than 0mmHg – sucking more blood into atria
        
        Ventricular relaxation
        
        AV valves open, rapid expansion of ventricles creates a suction effect sucking blood from atrium and veins