Session 1 - Introduction to Histology of the CVS Flashcards
How does exchange occur between blood and tissues?
Diffusion
Give three factors which affect rate of diffusion
Area available for exchange
Diffusion ‘resistance’
Concentration gradient
What affect does increased capillary density have and why?
Increased rate of diffusion as larger surface area for diffusion
What do highly metablolically active tissues have?
A high capillary density
Why is area available for exchange conisdered a maximum?
Because not all capillaries are perfused
In the body is area
a) Rate Limiting
or
b) Not rate limiting
It is b, not rate limiting
What are the three factors which affect diffusion resistance?
Nature of molecules crossing the capillaries
Nature of the barrier
Path length
How do lipophillic molecules reach cells from capillaries?
By directly crossing capillary wall due to the nature of the lipid bilayer of endothelial cells
How do hydrophillic molecules reach cells?
Pass through pores, which offer little resistance
What property do small moleules posses when compared to large?
Diffuse more easily
How the nature of the barrier affect diffusion?
Increasing pore size and number facilitates the diffusion of large and hydrophillic molecules
What does path length depend on?
Capillary density and interstitial space
How does conc gradient affect diffusion?
The greater the concentration gradient, the greater the rate of diffusion. Must be maintained in order for exchange to continue.
What is the conc gradient in capillaries between?
Capillary contents and nearby cells
What is the most important variable in conc grad?
The flow of blood
What happens if blood is not supplied at appropriate rate?
Conc grad driving exchange will dissipate, and nutrients will not be supplied at the right rate
What is the cardiac output of an average male at rest?
5 l/min
What is the minimum rate of blood flow required by the brain?
750 ml/min
What three organs must have blood at ALL times?
Kidney, heart muscle and brain
What are the four main components of circulation?
Pump
Distribution vessels
Flow control
Capacitance
What is the bodies pump?
Take a guess, wise guy.
What is the bodies main distribution vessels for circulation?
Arteries
What type of vessels are used in flow control?
Resistance vessels, such as arterioles and pre-capillary sphincters
What two things do resistance vessels ensure?
Blood flow to areas of the body which are difficult to perfuse
Blood flow is restricted to areas which are easy to perfuse
What is capacitance?
Store of blood to be called upon to cope with temporary imbalances between the amount of blood returning to the heart and the amount that is required to pump out.
Where is capacitance generated?
In the veins
What is the function of an artery?
Carry blood away from the heart to the capillary beds
Give two types of artery
Elastic (conducting) or muscular (distributing)
What are arterioles?
Arteries with a diameter of less than 0.1mm
What are capillaries?
Vessels 7-10 micrometers in diameter
What is a post capillary venule?
Receive blood from capillaries, have a diameter of 10-30 micrometers and are even more permeable than capillaries
What is a merging venule?
Diameter more than 50 micrometers. Tunica media reappears
describe a vein
Very large diameter
Thin wall with more connective tissues
Fewer elastic and muscle fibres
Usually have semi-lunar valves
What are veins and arteries comprised of?
Three layers
Tunica intima, media and adventitia
Describe the tunica intima of elastic arteries
Endothelial cells with long axes parallel to axis of artery
Narrow subendothelium of CT with discontinuous internal elastic limina
Why do epithelial cells in tunica intima of elastic arteries have endothelial cells with long axes parallel to axis of artery
to reduce friction
Why does the tunica intima of elastic arteries have a narrow subendothelium of CT with discontinuous internal elastic lamina?
to allow for expansion
Describe the structure of the media of elastic arteries
40-70 layers of fenstrated elastic membrane, with smooth muscle and collagen between these lamellae.
How is the smooth muscle in the media of elastic arteries controlled?
Smooth muscle is involuntary and allows for controlled contraction in order to move the blood through the lumen
Describe the adventitia of elastic arteries
Thin layer of fibroelastic CT containing lymphatic vessels and nerve fibers
Describe the intima of muscular arteries
Endothelium, subendothelium, thick internal elastic lamina
Describe the media of muscular arteries
40 layers of smooth muscle cells connected by gap junctions
Prominent external elastic lamina
Why is does the media of muscular arteries have 40 layers of smooth muscle cells connected by gap junctions?
For coordinated contraction
Describe the structure of the adventitia of muscular arteries
Thin layer of fibroelastic CT with nerve fibers
Vasa vasorum
Why does the adventitia of the arteries have nerves?
For vasoconstriction and dilation
What are vasa vasorum?
Dekiever blood to tissues in muscular artery which are inadquately nourished by luminal blood
Describe the structure of the intima of arterioles
Endothelium and thin subendothelium
Describe the structure of the media of arterioles
1 to 3 layers of smooth muscle
Describe the structure of the adventitia of arterioles
Hardly present
How do metarterioles differ from arterioles?
Smooth muscle layer discontinuous. spaced apart and encircle endothelium of capillary arising from metarterioles, forming pre-capillary sphincter
What is a pre-capillary sphincter?
Formed from metarterioles, can contract and prevent blood flow into capillary bed
Describe the structure of capillaries
Single layer of endothelium with basement membrane
Give three types of capillary
Continous, fenstrated and sinusoidal
what is a fenstrated capillary?
Interruptions between thin parts of endothelium
What is a sinusoidal capillary?
Where are they found?
Large diameter, special linings and an incomplete basal lamina which allows blood cells to enter tissue space.
Liver, spleen and bone marrow
Why are venules more permeable than capillaries?
Lower pressure so fluids tend to drain into them
Describe the structure of merging venules
Intima - endothelium or thin smooth muscle form thin wall
Valves which are thin extensions of intima and prevent backflow
Media - 2 to 3 layers of smooth muscle
Describe the intima of veins
Thicker tunica intima than venules (smooth muscle, valves)
Describe the media of veins
2 to 3 laers of smooth muscle
When does the media of veins differ?
In superficial veins of leg, where muscle thick to resist distension caused by gravity
Adventitia of veins?
Well developed
What is a vena comitante?
A vein or usually a pair of veins found either side of and artery whose pulsations aid venous return
What happens to veins if pressure is not maintained?
They collapse
How is pressure in arteries maintained?
Systolic blood flow
How is blood pressure in veins maintatined?
The muscle pump action in the leg and pressure factor in abdominal and thoracic cavity
Name three structures blood vessels do not reach in body
Cartilage, epithelia and cornea
