Transcript lesson 20 arteries and veins

Arteries and Veins
Learning Outcomes
Arteries have an outer layer of connective tissue containing elastic
fibres and a middle layer containing smooth muscle with more elastic
fibres. The elastic walls of the arteries stretch and recoil to
accommodate the surge of blood after each contraction of the heart.
The smooth muscle can contract or relax causing vasoconstriction or
vasodilation to control blood flow.
Veins have an outer layer of connective tissue containing elastic fibres
but a much thinner muscular wall than arteries. Function of valves.
Structure and Function of Blood Vessels
The central cavity of a blood vessel is called the lumen
The lumen is lined with a thin layer of cells called the endothelium
The composition of the vessel wall surrounding the endothelium is
different in arteries, veins and capillaries
Artery
Arteries carry blood away from the heart
Arteries have a thick middle layer of smooth muscle
They have an inner and outer layer of elastic fibres
Elastic fibres enable the artery wall to pulsate, stretch and recoil,
thereby accommodating the surge of blood after each contraction of
the heart
Smooth Muscle
Smooth muscle can contract or become relaxed
This contraction or relaxation brings about vasodilation or
vasoconstriction to control blood flow
During strenuous exercise the arterioles leading to the muscles undergo
vasodilation – the circular muscle in the arteriole wall is relaxed and the
lumen is wide
This allows an increased blood flow to the skeletal muscles
the gut . . . .
At the same time, the arterioles leading to the small intestine undergo
vasoconstriction
The circular muscles are contracted and the lumen is narrow
As a result, this reduces the blood flow to the gut
Veins
Veins carry blood back to the heart
The muscular layer and layers of elastic fibres in the vein wall are
thinner than those in an artery because blood flows along a vein at low
pressure
The lumen of a vein is wider than that of an artery
Valves are present in veins, to prevent the backflow of blood
Following two slides compare an artery and vein
Try these questions . . .
1.
2.
3.
4.
Give two structural differences between an artery and a vein
Give one functional difference
Name the central cavity of a blood vessel
What term is used when the circular muscle in a blood capillary is
contracted and the central cavity is narrow?
5. Describe a blood capillary during vasodilation
Answers . . . .
1. Wall of artery is thicker than that of vein and veins have valves
2. Arteries carry blood away from the heart, veins carry blood back to
the heart
3. Lumen
4. Vasoconstriction
5. Circular muscle relaxed, lumen is wide
1. Give two structural differences between an artery and a vein
Wall of artery is thicker than that of vein and veins have valves
2. Give one functional difference
Arteries carry blood away from the heart, veins carry blood back to the
heart
3. Name the central cavity of a blood vessel
lumen
4. What term is used when the circular muscle in a blood capillary is
contracted and the central cavity is narrow?
vasoconstriction
5. Describe a blood capillary during vasodilation
Circular muscle relaxed, lumen is wide