IB biology: topic 6: blood vessels

what are the layers of an artery (from the lumen outwards)

tunica intima, tunica media, tunica externa

what is the role of the tunica externa?

tough outer layer of connective tissue, often made of collagen, prevents artery from stretching too wide

what is the role of the tunica media?

thick layer of muscle and elastic fibres (elastin)

what is the role of the tunica intima?

smooth endothelium

what is an aneurysm?

bursting of an artery

artery: diameter?

larger than 10 micrometres

vein: diameter?

variable but much larger than 10 micrometers

capillary: diameter?

around 10 micrometres

artery: relative thickness of wall and diameter of lumen?

relatively thick wall and narrow lumen

capillary: relative thickness of wall and diameter of lumen?

extremely thin wall

vein: relative thickness of wall and diameter of lumen?

relatively thin wall with variable but often wide lumen

artery: number of layers in wall?

three layers (tunica externa, media and intima - can be subdivided into more layers)

vein: number of layers in wall?

three layers (tunica externa, media and intima)

capillary: number of layers in wall?

only one layer - tunica intima which is an endothelium consisting of a single later of very thin cells

artery: muscle and elastic fibres in the wall

abundant

capillary: muscle and elastic fibres in the wall

none

vein: muscle and elastic fibres in the wall

small amount

artery: valves?

none

capillary: valves?

none

vein: valves?

present in many veins

what is the role of arteries?

convey blood at high pressure from ventricles to tissues.

what tissues make up arteries?

elastic tissue, muscle tissue

what do elastic tissues contain that allow them to be elastic?

contains elastin fibres which stretch then recoil

what does the recoiling of elastin fibres in arteries do to the blood?

recoil helps propel blood forwards and maintain BP.

what type of muscle makes up muscle tissue?

smooth muscle

what is the role of the muscle tissue in the arteries?

determines diameter of lumen and to some extent the

rigidity of the arteries, controlling flow through them.

what is the purpose of the tissue types in the arteries?

contribute to toughness of walls which must withstand high pressure without bulging or bursting.

what are the two types of arterial blood pressure?

systolic pressure and diastolic pressure

what is systolic pressure?

caused by surge of blood at high pressure entering from the heart -

wall of artery is pushed outwards, widening lumen and stretching elastic fibres in wall, thus storing potential energy.

in terms of blood pressure, what is systolic pressure?

the highest pressure reached in the artery.

what is diastolic pressure?

drop in pressure at end of heartbeat allows stretched elastic fibres to squeeze blood in lumen.

(saves energy & prevents pressure becoming too low).

in terms of blood pressure, what is diastolic pressure?

the lowest pressure inside the artery

what is vasoconstriction?

when smooth muscle contracts narrowing lumen so blood pressure increases

what does vasoconstriction of arterioles do in terms of blood flow?

restricts blood flow to the part of the body they supply.

what is vasodilation?

when smooth muscle relaxes widening lumen so blood pressure decreases.

what does vasoconstriction of arterioles do in terms of blood flow?

promotes blood flow to the part of the of the body they supply.

what is the role of capillaries?

blood flows through tissues in capillaries with permeable walls that allow exchange of materials between cells and blood.

what is the diameter of the capillaries?

10μm.

how do capillaries form a network?

repeatedly branch and re-join

what are capillary walls like?

wall consists of one layer of very thin endothelial cells, coated by a filter-like protein gel, with pores between.

what do pores in the capillary walls mean?

permeable walls allow part of plasma to leak out forming tissue fluid (this flows between cells before re-entering blood)

what parts of capillaries vary between tissues?

permeability and density of networks

how can capillaries respond to damage to the tissue?

continually repair and remodel themselves in response to the needs of the tissues.

what is the role of veins?

veins collect blood at low pressure from the tissues and return it to the heart.

how is blood flow assisted in the veins?

by gravity and pressure exerted by skeletal muscle.

why do veins not require thick walls?

much lower pressure

what are risks of the low pressure in the veins?

backflow of blood

what do pocket valves do?

prevent backflow – blood gets caught in three cup-shaped flaps, filling them and blocking lumen.

why can veins dilate/hold more blood more than arteries?

as there are far fewer muscle and elastic fibres