5. Blood Vessels Flashcards
Describe the structure of the tunica intima
Endothelium lining made of simple squamous epithelial cells.
- contains a basal lamina of the epithelial cells.
- Subendothelial connective tissues.
Describe the structure of the Tunica media
Smooth muscle fibres in loose connective tissue.
Contains elastic fibre sometimes.
Describe the structure of the Tunica externa/adventitia
- Connective tissue
- stabilises blood vessel
- Comprised mainly of Collagen
- Merges with surrounding connective tissue
- Can contain vaso vasorum.
Examples of the elastic conducting arteries
Brachiocephalic
Common carotid
Aorta.
Name two examples of muscular distributing arteries
Brachial and femoral
State the structural adaptations of elastic conducting arteries
Thick tunica media
Many elastic fibres
Few smooth muscle cells
Elastic fibres recoil when the heart relaxes.
State the strucural adaptations of the muscular distributing arteries
Thick tunica media
thick tunica externa.
Lots of smooth muscle cells.
Distinct internal and external elastic laminae
Diameter = 0.5mm
What is the diamter of the muscular distributing arteries
0.5-0.4cm
State the diameter of the elastic conducting arteries
diameter can be up to 2.5 cm
State the diameter of the arterioles
< 30uM
Which of the 3 arteries has the largest diameter
The elastic conducting arteries
What are the structural adaptations of the aterioles
one to two layers of smooth muscle in the tunica media
poorly defined tunica externa
What is the size of the capillaries
8 micrometers in diameter
State the general features of capillaries
connects arterioles and venules via microcirculation
sites of gaseous exchange
thin walls facilitate diffusion
blood blow through capillaires is slow
Structure permits 2 way exchange
8 micrometers
found near every cell
What does the capillary sphincter do, and what does contraction and relaxation of the capillary do.
Capillary sphincter guards the entrance to each capillary
contraction narrows the entrance
relaxation dilates the entrance
What is the arteriovenous anastomoses and what does this structure permit
Forms direct communication between the arteriole and the venule
When dilated blood bypasses the capillary bed and flows directly to venous circulation
3 Types of Arteries
Elastic (Conducting) Artery
Muscular (Distributing) Artery
Arterioles (resistance vessels)
Describe the Elastic (Conducting) Artery. Give examples
Withstand changes in pressure during the cardiac cycle and ensure continuous blood flow - when the heart is contracts the pressure is very high in vessel.
Diameter: up to 2.5 cm
e.g. aorta, brachiocephalic & common carotid
Describe the Arterioles (resistance vessels).
Capable of vasoconstriction & vasodilation
Control blood flow to organs
Involved in blood pressure control
Diameter: ≤ 30 µm
Structural Adaptations of Arterioles (resistance vessels)
one to two layers of smooth muscle cells in tunica media
poorly defined tunica externa
Describe a Capillary
- Connect arterioles and venules (microcirculation)
- Site of gaseous exchange
- Thin walls facilitate diffusion – endothelium & basement membrane
- No Tunica media or Tunica externa/adventia
- Structure permits 2-way exchange
- 8-μm (micrometres) in diameter
- Blood flow through capillaries is slow, so gas exchange can occur.
What are the 3 types of Capillaries?
Continuous
Fenestrated
Sinusoids
What is a Continuous Capillary?
- Majority are continuous*
- Found in skeletal and smooth muscle, CT and the lungs
What is a Fenestrated Capillary?
- Pores penetrate the endothelium
- Allow rapid exchange of water or larger solutes (e.g. small peptides)
- Found in kidney, choroid plexus and endocrine glands - more permeable
What is a Sinusoid Capillary?
- Spaces between endothelial cells - Very leaky
- Incomplete or absent BM
- Exchange of large solutes i.e. plasma proteins
- Slow flow
- Found in the liver
What controls the flow through capillary beds?
Metarterioles
Precapillary sphincters
Arteriovenous Anastomoses
Describe Metarterioles
Metarterioles supply whole capillary beds
Each metarteriole continues as a thoroughfare channel which leads directly to a vein and has numerous capillaries leading off it
Constriction of the metarteriole can reduce flow to a whole capillary bed
Describe Precapillary Sphincters
Precapillary sphincters guard the entrance to each capillary
Contraction narrows the entrance and reduces flow
Relaxation dilates the entrance and increase flow
Describe Arteriovenous anastomoses
Form direct communication between the arteriole and venule
When dilated blood bypasses the capillary bed and flows directly to venous circulation
Define Capitance
the word explaining the relationship between the volume of blood in a vessel and the blood pressure
What is the systemic Circulation?
- High pressure system (arterial side)
- Takes oxygen rich blood from the left side of the heart to the body tissues
- Returns oxygen poor blood from the tissues to the right side of the heart
What is Pulmonary Circulation?
- Low pressure system
- Takes blood low in oxygen from the right side of the heart to the lungs
- Takes blood rich in oxygen from the lungs to the left side of the heart
- Pulmonary arteries carry blood AWAY from the heart therefore oxygen poor
- Pulmonary veins carry blood TOWARDS the heart therefore are oxygen rich
What is interstitial fluid?
In the capillary the fluid is termed plasma, in the interstitial space it is called interstitial fluid
How does fluid move in and out of the interstitial space?
Fluid moves from the arterial end of the capillary into the interstitial space
Fluid moves from the interstitial space back into the capillary at the venous end
What happens in capillary exchange?
Capillary blood pressure is greater than Blood Colloid Osmotic Pressure at arterial end. Filtration occurs, pushing fluid out of capil into interstitial fluid
BCOP is greater than CBP at arterial end. Reabsorbtion occurs, pulling fluid back into capillary.
BCOP is mainly due to plasma proteins
How much fluid is reabsorbed in capillary exchange?
85%
How is excess interstitial fluid removed?
- Lymph capillaries are blind ended tubes that are located adjacent to capillary beds
- The excess interstitial fluid enters the lymphatic capillary and is called lymph
- Lymph passes through the lymphatic circulation and returns to the blood vascular system
How is Lymph Drained?
From the Lymph capillaries, to lymph vessels, goes through the lymph nodes, to the lymph trunks, to the thoracic duct or to the right lymphatic duct
Role of the Right lymphatic duct in lymph drainage
It Drains lymph from the right side of the head & thorax and right upper limb.
Drains into the right subclavian vein
Role of the Thoracic duct in lymph drainage
It Drains lymph from the remainder of the body into the left subclavian vein
