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A young vampire bat came flapping in from the night, covered in fresh blood and perched himself on the roof of the cave to get some sleep. Before long, all the other bats smelled the blood and began hassling him about where he got it. He was tired and needing a rest, so he told them to please leave him alone. However, it was clear that he wasn't going to get any sleep until he satisfied their curiosity.

"OK!" he said with exasperation, "follow me," and he flew out of the cave with hundreds of bats following close behind him.

Down through the valley they went, across the river and into the deep forest. Finally he slowed down and all the other bats excitedly gathered around him.

"Do you see that tree over there?" he asked.

"Yes, yes, yes!" the bats all screamed in a frenzy.

"Good," said the first bat, "Because I DIDN'T!"

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Some Exam Howlers…

Three kinds of blood vessels are arteries, vanes and caterpillars.H2O is hot water, and CO2 is cold water.Water is composed of two gins, Oxygin and Hydrogin. Oxygin is pure gin. Hydrogin is gin and water.Blood flows down one leg and up the other.The body consists of three parts- the brainium, the borax and the abominable cavity. The brainium contains the brain, the borax contains the heart and lungs, and the abominable cavity contains the bowels, of which there are five - a, e, i, o, and u.

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Copyright Notice

BioSciences

Circulation

Professor Geoff Shaw

School of BioSciencesBiosciences-4

g.shaw@zoology.unimelb.edu.au

Ref: KLES

5th Ed: Chapter 24: Pp 566-567,572-586; Figures 24.6-8,12,13; Table 7.3 b,c (p159)

4th Ed: Chapter 23: p532, 539 – 551, Fig 23.8-10, 12, 13, Table 7.3c (p149)

Plus resources on LMS

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Why have circulation?

• distribution– oxygen– CO2

– nutrients– wastes– heat

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Animals with circulatory systems

mollusc - slug

insect - butterfly

annelid –earthworm

echinoderm – starfishmammal – human

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Animals without circulatory systems

porifera – sponge

coelentrate – sea anemone

platyhelminth (flatworm) – “magic carpet ride”

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Circulation

• Function• Types• Structure in vertebrates• The heart

Open circulatory system

cells bathed directly in blood plasma

eg crab, beetle cell

pump (heart)

cell cell

cell

cell

cell

cell

cell

cell

cell

cellcellcell

cell

body wall

extracellular fluid ≡ blood

Closed circulatory system•blood in vessels•extracellular fluid bathes cells

•exchange b/w blood and extracellular fluid

•Blood and extracellular fluid are separate. eg. earthworm, vertebrates

cell

pump (heart)

cell

cell

cell

cellcellcellcell

cell

cell

cell

body wall

extracellular fluid

cell

bloo

d

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Providing oxygen by diffusion only

O2 used by cells

O2 diffusing into animal

No O2 reaches here

The theoretical size limit for an animal if only diffusion occurs is a diameter of about 1 mm.

≈1 mm

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• Convection is the bulk movement of fluid• Movement of substances to or from cells by

diffusion is usually assisted by convection• Convection is much faster than diffusion

Convection: To move 1 metreBlood in an arteryBlood in a capillary

DiffusionOxygen in water

5 sec17 min

3 years

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Convection and Diffusion work together• In closed circulation, the convected blood is separated

from the cells by the wall of the blood vessels and by extracellular fluid, as follows:

Blood

Capillary

CellsDiffusion shown as

Note diffusion across capillary wall into extracellular fluid, then into cells.

Extracellular fluid

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The heart powers convection of the blood

• Metabolic energy (muscle)

• Energy in the blood – potential energy = pressure – kinetic energy = flow

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Features of hearts

Hearts often have:• Several chambers in sequence

• first chamber pumps blood into second,

etc.

• Sequential contraction

• One-way flow Valves

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Cardiac contraction cycle

• Contraction– systole (pronunciation sis-toh-le)– expels blood

• Relaxation– diastole (pronunciation dia-

stoh-le)– allows heart to refill with blood

• Source of contraction– muscle - myogenic– nerves - neurogenic

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Vertebrate cardiac muscle• specialised type of striated muscle

• electrical depolarisation contraction

• muscle cells interconnected intercalated discs– strong connections

– electrical connections

• electrical connections between cells allow propagation of contraction

• pacemaker activity

intercalated discs

muscle cells

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and Systole

Blood flow in heart during contraction cycle

Diastole

KLES5 24.6a

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Blood flow in heart during contraction cycle

KLES5 24.6b

pulmonary artery

aorta

Systole

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KLES5 Fig 24.8

Sinoatrial node Atrioventricular node

AV bundle

Purkinjefibres

10 ms. SA node starts AP in atrium 80 ms. Contraction over atrium.AP triggers AV node 0.1 sec delay

170 ms: rapid conduction down AV bundle & Purkinje fibres

190 ms: ventricular contraction propagated from apex expels blood from heart systole

PacemakerConduction of the AP in the mammalian heart

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Blood Vessels

artery

arteriole

capillaries

venule

vein

From Heart To Heart

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blood vessel structure

• arteries – thick walled to cope with pressure; elastin; smooth muscle; endothelium

• veins – thinner walled (lower pressure); less muscle/elastin; endothelium; valves

KLES5 fig 24.12Appear white in

dissectionsAppear dark

in dissections

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Blood vessel functions• Arteries

– high pressure and velocity– elastic reservoir - damps the flow pulse

• Arterioles– smooth muscle - to regulate blood flow (and blood

pressure) • Capillaries = exchange vessels

– low pressure, low velocity– thin wall (<1 µm) - endothelium only– surface area : volume ratio high

• SA / Vol = 2prl / pr2l = 2 / r• Veins

– low pressure, high-ish velocity– smooth muscle to regulate volume

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KLES fig 24.13

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“Pull out, Betty, Pull out! … You’ve hit an artery!”

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arteries and disease• arteriosclerosis - hardening of arteries• atherosclerosis - fatty deposits

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capillary wall transfer - diffusion - pinocytotic (active) transfer- filtration through special

fenestrae (windows)

T.S. capillary

The wall is formed by a rolled endothelial cell

see KLES5 fig 24.15 pinocytosis

Lumen (ca 8 µm)

Tight junction

Fenestra(Latin: window)in some tissues

diffusion

filtration

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Capillary

• most capillaries don’t leak much – eg blood brain barrier

• leaky capillaries in certain sites, eg kidney

• active transport in certain sites – eg placenta

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Fish circulation

Heart

Gill Bodyblood picks up O2

and loses CO2

blood loses O2 and picks up CO2

low pressure

high pressure

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Mammal circulation

LungBody

R atrium

R ventricle L ventricle

L atrium

blood picks up O2 and loses CO2

blood loses O2 and picks up CO2

high pressure

low pressure

low pressure

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Control of heart rate and blood pressure

• baroreceptors (pressure)– great veins– aortic arch– carotid body

• chemoreceptors (chemicals)– carotid body : O2

– aortic body: CO2 and pH

• feed into vasomotor centre in brain stem- regulation of – respiration– heart rate; cardiac output– blood pressure– vascular tone (constriction of blood

vessel walls)

Brain

vagus nerve

Heart

vasomotor centres in brainstem

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regulation of blood flow

• heart rate and strength of beat– affected by emotion, exercise, hormones,

temperature, pain, age, and stress • relaxation or constriction of blood

vessels– affected by emotion, exercise, hormones,

temperature, pain, age, and stress – local effects eg inflammation

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What do I expect you to learn from this lecture?

• Why do animals have circulatory systems?• Open and closed circulatory systems; roles of

convection and diffusion• Structure and function of the heart

– muscle, chambers, valves, pacemaker, conduction, contraction cycle

• Differences between arteries, capillaries and veins in structure and function– Why do arteries have elastic walls? Why are capillaries

tiny? Why do veins have valves?

• How is circulation regulated?- central and local control- neural signals to heart and vessels- hormonal and local regulators