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Lesson 2

Blood vesselsCardiac cycleHeart Sounds

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Blood vessels

There are three types of blood vessels:ArteriesCapillariesVeins

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Blood vessels

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Arteries

Carry blood away from the heartThick muscular wall to withstand

high pressure of bloodNarrow lumenMost collagen (tough fibrous

protein)- tough and durableElastic fibres and smooth muscle-

allows stretch & recoil

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Arteries… cont

No valvesBranch into smaller and smaller

vessels- arteriolesContraction of smooth muscle of

arterioles allows blood to be diverted to different parts of the body

e.g. fight or flight more blood to skeletal muscles and less to digestive system

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Arteries… cont

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Capillaries

Tiny vessels- 1 cell thick wall 10m in diameter

Exchange of nutrients and waste with tissues occurs here

Extensive branching network (capillary bed) throughout body tissues

Only certain capillary beds open at one time to allow shunting of blood from one area to another

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Capillaries… cont

Most numerous type of blood vessel in the body

Permeable wallsCarry blood at low pressure and low flow

rate Reduces fluid loss through permeable

capillary walls Allows sufficient time for exchange of

materials

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Veins

Carry blood back to the heartThin muscular wall as blood at low

pressureWide lumen- reduces resistance to

blood flowLess collagen, elastic fibres and

smooth muscle

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Veins… cont

Have valvesBlood at low pressure- return blood

against gravity- so lie close to muscles- when muscle contract they squeeze the veins to temporarily increase the blood pressure

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Veins… cont

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Describe three things that this graph shows.

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Major Blood VesselsNB heart muscle itself

is supplied with blood by coronary arteries

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Cardiac Cycle

A pattern of contraction (systole) and relaxation (diastole) by heart in 1 heart beat

Lasts about 0.8 seconds (based on heart rate of 75bpm)

Chambers alternately contract and relaxBlood always flows towards low pressure

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Cardiac Cycle…cont

3 phases to the cycle:1. Atrial systole2. Ventricular systole3. Diastole

Decrease in volume

Increase in pressure

Blood forcedout

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Atrial systole

Blood flows into LA and RA under low pressure

LA & RA contract simultaneously AV (bicuspid & tricuspid) valves

open Blood forced into LV & RV At this point LV & RV in diastole & SL

valves closed

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Ventricular systole

0.1 secs later AV (bicuspid & tricuspid) valves

close Blood forced into LV & RV which

contract & push blood through open SL

valves to arteries High pressure in ventricles

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Diastole

Atria & ventricles relax Elastic recoil of relaxing heart walls

lowers pressure in atria & ventricles Blood under high pressure in

arteries drawn back into heart from veins

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Heart Sounds

Lub dub Lub- closing of AV valves Dub- closing of SL valves

Human heart sounds

Feline heart sounds