7 - Vascular physiology part 2 Flashcards
What are the two types of passive exchange of the capillaries?
- Diffusion (movement of solute due to concentration gradient)
- Bulk flow (movement of water and solutes together due to pressure gradient)
Why is blood flow slow through capillaries?
- To allow enough time for exchange of materials
- The velocity is proportional to total cross-sectional area of all vessels at any given level of circulatory system
What are capillary pores?
- Narrow, water-filled gaps (pores) that lie at junctions between cells
- Permit passage of water soluble substances
- Lipid soluble substances readily pass through endothelial cells
Describe the effect of contracted and relaxed sphincters.
When the sphincters are relaxed, there are more open capillaries
When theres arteriolar vasolidation, there is increased capillary blood flow
What forces influence bulk flow?
- Capillary blood pressure:
- Fluid or hydrostatic pressure exerted on the inside of the capillary walls by blood, forces fluid out of capillaries - Plasma-colloid osmotic pressure
- A force caused by colloidal dispersion of plasma proteins
- Encourages water movements into capillaries - Interstitial fluid hydrostatic pressure
- Is the fluid pressure exerted on the outside of the capillary wall by interstitial fluid - Interstitial fluid-colloid osmotic pressure
- Does not contribute significantly to bulk flow
- Small fraction of plasma proteins that leak across the capillary walls are normally returned to blood by lymphatic system
What does this diagram show?
Inward pressure: Plasma-colloid osmotic pressure and interstitial fluid hydrostatic pressure
Outward pressure: Interstitial fluid-colloid osmotic pressure and Capillary blood pressure
What is the Blood Brain Barrier (BBB)?
- A network of blood vessels and tissue that is made up of closely spaced cells and helps keep harmful substances from reaching the brain
- The capillaries in the brain are joined by tight junctions (no pores)
What can penetrate: - Lipid soluble substances (O2, CO2, steroid hormones) and small water molecules
What can’t penetrate: - Glucose, amino acids, ions
- Downside: Many drugs cannot penetrate BBB
What is the lymphatic system and what are its functions?
- Extensive network of one-way vessels
- Functions:
1. Return of excess filtered fluid
2. Defence against disease (Lymph nodes have phagocytes that destroy bacteria filtered from interstitial fluid)
3. Transport of absorbed fat
4. Return of filtered protein
What are the 3 components of the lymphatic system?
- Initial lymphatics:
- Small, blind-ended terminal lymph vessels
- Permeate almost every tissue of the body - Lymph
- Interstital fluid in lymphatic vessel - Lymph vessels
- Formed from convergence of initial lymphatics
- One way valves spaced at intervals direct flow of lymph towards venous outlet in right atrium
What is edema and what causes it?
- Swelling of tissues when too much interstitial fluid accumulates
- Causes:
1. Reduced concentration of plasma proteins
2. Increased permeability of capillary wall
3. Increased venous pressure
4. Blockage of lymph vessels
Where is most blood volume located?
In veins (aka blood reservoir)
What is venous return and what affects it?
- Venous return is the rate of blood flow back to the heart. Affected by: - Cardiac contraction - Sympathetic induced venous vasoconstriction - Skeletal muscle activity - Effect of venous valves - Respiratory activity - Effect of cardiac suction
What is Skeletal Muscle Pumping?
- Many large veins lie between skeletal muscles
- When skeletal muscle contracts, the veins are compressed and blood in the veins is squeezed forward toward the heart
- Increased sympathetic NS stimulation and skeletal muscle pumping during exercise enhances venous return
What is the function of venous valves?
- Counteracts gravity
- Minimizes backflow of blood
*Venous vasoconstriction and external venous compression (muscle pump) drives blood towards the heart
What does the Respiratory Pump do?
- Inhalation and exhalation changes the pressure within our chest cavity
- On average the pressure within our chest cavity is less than atmospheric
- The venous system in our limbs and abdomen is subject to normal atmospheric pressure
- This pressure difference squeezes blood from the veins in our lower extremities into the right atrium
What factors increase venous return?
- Venous valves
- Cardiac suction effect
- Pressure from cardiac contraction
- Sympathetic vasoconstrictor activity
- Skeletal muscle pump
- Respiratory pump
- Blood volume
What regulates blood pressure?
- Cardiac output
- Total peripheral resistance
-> Mean arterial pressure (cardiac output x total peripheral resistance)
How does the Baroreceptor reflex work?
- Short-term control adjustments
- Occur within seconds
- Adjustments made by alterations in cardiac output and total peripheral resistance
- Mediated by means of autonomic nervous system influences on heart, veins and arterioles
- Long-term control adjustments
- Require minutes to days
- Involve adjusting total blood volume by restoring normal salt and water balance through mechanisms that regulate urine output and thirst
What does increased arterial pressure signify?
Increased firing rate in afferent neuron arising from carotid sinus baroreceptor
What causes circulatory shock?
- When blood pressure falls so low that adequate blood flow to the tissues can no longer be maintained
Types:
- Hypovolemic shock (low volume)
- Cardiogenic shock (heart produced)
- Vasogenic shock (vessel produced)
- Neurogenic shock (nerve produced)
