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!"
BioSciences
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.
BioSciences
Copyright Notice
BioSciences
Circulation
Professor Geoff Shaw
School of BioSciences
Biosciences-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)
BioSciences Plus resources on LMS
Why have circulation?
• distribution
– oxygen
– CO2
– nutrients
– wastes
– heat
BioSciences
Animals with
circulatory systems
annelid –
earthworm
mollusc - slug
BioSciences
insect - butterfly
echinoderm – starfish
mammal – human
Animals without circulatory systems
porifera –
sponge
coelentrate –
sea anemone
BioSciences
platyhelminth (flatworm) –
“magic carpet ride”
Circulation
•
•
•
•
Function
Types
Structure in vertebrates
The heart
BioSciences
Open circulatory system
cells bathed
directly in
blood plasma
pump (heart)
cell
cell
cell
cell
eg crab, beetle
cell
cell
cell
cell
cell cell
cell
cell
cell
cell
extracellular fluid ≡ blood
body wall
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
pump (heart)
cell
cell
cell
cell
cell
cell
cell
cell
cell
cell
extracellular fluid
body wall
cell
cell
Providing oxygen by diffusion only
O2 diffusing
into animal
No O2
reaches here
O2 used
by cells
≈1 mm
BioSciences
The theoretical size limit for an animal
if only diffusion occurs is a diameter of
about 1 mm.
• 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:
Blood in an artery
Blood in a capillary
Diffusion
Oxygen in water
BioSciences
To move 1 metre
5 sec
17 min
3 years
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:
Extracellular fluid
Capillary
Diffusion shown as
BioSciences
Blood
Cells
Note diffusion across capillary wall into
extracellular fluid, then into cells.
The heart powers convection of
the blood
• Metabolic energy (muscle)
• Energy in the blood
– potential energy = pressure
– kinetic energy = flow
BioSciences
Features of hearts
Hearts often have:
• Several chambers in sequence
• first chamber pumps blood into second, etc.
• Sequential contraction
• One-way flow  Valves
BioSciences
Cardiac contraction cycle
• Contraction
– systole
– expels blood
(pronunciation sis-toh-le)
• Relaxation
– diastole
(pronunciation dia-stoh-le)
– allows heart to refill with blood
• Source of contraction
– muscle - myogenic
– nerves - neurogenic
BioSciences
Vertebrate cardiac muscle
• specialised type of striated muscle
• electrical depolarisation  contraction
• muscle cells interconnected  intercalated discs
– strong connections
– electrical connections
muscle cells
• electrical connections between cells
allow propagation of contraction
• pacemaker activity
intercalated discs
BioSciences
Blood flow in heart during contraction cycle
Diastole
BioSciences
and
Systole
KLES5 24.6a
Blood flow in heart during contraction cycle
aorta
pulmonary artery
Systole
BioSciences
KLES5 24.6b
Conduction of the AP in the mammalian heart
Pacemaker
Sinoatrial node
Atrioventricular node
10 ms. SA node starts AP in atrium
80 ms. Contraction over atrium.
AP triggers AV node 0.1 sec
delay
AV bundle
Purkinje
fibres
BioSciences
170 ms: rapid conduction
down AV bundle &
Purkinje fibres
KLES5 Fig 24.8
190 ms: ventricular contraction
propagated from apex expels
blood from heart  systole
From Heart
Blood Vessels
To Heart
vein
artery
arteriole
capillaries
BioSciences
venule
blood vessel structure
• arteries – thick walled to cope with
pressure; elastin; smooth muscle;
endothelium
• veins – thinner walled (lower pressure);
less muscle/elastin; endothelium; valves
Appear white in
dissections
BioSciences
Appear dark
in dissections
KLES5 fig 24.12
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
BioSciences
KLES fig 24.13
BioSciences
“Pull out, Betty, Pull out! … You’ve hit an artery!”
BioSciences
arteries and disease
• arteriosclerosis - hardening of arteries
• atherosclerosis - fatty deposits
BioSciences
T.S. capillary
Tight junction
diffusion
The wall is formed by a
rolled endothelial cell
capillaryLumen
wall transfer
(ca 8 µm)
- diffusion
- pinocytotic (active) transfer
- filtration through special
fenestrae (windows)
filtration
Fenestra
BioSciences
see KLES5 fig 24.15
pinocytosis
(Latin: window)
in some tissues
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
BioSciences
Fish circulation
low pressure
blood picks up O2
and loses CO2
Gill
Body
blood loses O2
and picks up CO2
high pressure
Heart
BioSciences
Mammal circulation
Body
blood loses O2
and picks up CO2
low
pressure
Lung
blood picks up O2
low
and loses CO2
pressure
R atrium
R ventricle
BioSciences
L atrium
high pressure
L ventricle
Control of heart rate and blood pressure
• baroreceptors (pressure)
– great veins
– aortic arch
– carotid body
vasomotor
centres in
brainstem
• chemoreceptors (chemicals)
Brain
– 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)
BioSciences
Heart
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
BioSciences
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?
BioSciences
- central and local control
- neural signals to heart and vessels
- hormonal and local regulators