All the organs of the human body were having a meeting, trying to decide who should be
the one in charge.
"I should be in charge," said the brain , "Because I run all the body's systems, so without
me nothing would happen."
"I should be in charge," said the blood, "Because I circulate oxygen all over so without
me you'd all waste away."
"I should be in charge," said the stomach," Because I process food and give all of your
energy."
"I should be in charge," said the legs, "because I carry the body wherever it needs to go"
"I should be in charge," said the eyes, "Because I allow the body to see where it goes."
"I should be in charge," said the rectum, "Because I'm responsible for waste removal."
All the other body parts laughed at the rectum and insulted him, so in a huff, he shut
down tight. Within a few days, the brain had a terrible headache, the stomach was
bloated, the legs got wobbly, the eyes got watery, and the blood was toxic. They all
decided that the rectum should be the boss.
So what's the moral of the story?
The asshole is usually in charge!
Copyright Notice
Figures and images indicated by KLES are taken from the
subject textbook R B Knox, P Y Ladiges, B K Evans and R Saint,
Biology, An Australian Focus 4th Ed, McGraw-Hill, 2009, with
permission of the publisher. Diagrams and images without that
designation are © Geoff Shaw, or are from public domain
BioSciences sources as indicated.
Strategies for Learning
• Revise early, Revise often.
Number of students downloading L19 notes from LMS (by 24/4, 06:30 AM)
Total students who have accessed at least one form of notes
Students who had NOT accessed any notes from LMS
<700
>1200
http://services.unimelb.edu.au/academicskills/undergrads/
top_resources
BioSciences
… continued from lecture 19
• Diverse gas exchange surfaces
• Exchange rate  area x pressure / distance (Fick’s
Law)
• Structure and function of respiratory structures
– large surface area; rich blood supply; counter current flows;
surfactant
• Roles of convection and diffusion for gas exchange
• Mechanisms of breathing and significance of dead
space
BioSciences
Transport of oxygen
1. O2 dissolves in water (or blood plasma)
2. O2 combines reversibly with haemoglobin
(Hb)
3. In 100 mL of oxygenated human blood, there
is about 0.3 mL dissolved O2 and 20 mL O2
bound to Hb (40 mL in whale).
BioSciences
Iron-based
respiratory
pigments
The oxygen-binding
unit is haeme - based
on Fe++.
Oxygen binding is not
an oxidation.
Colour change
BioSciences
Haemoglobin
• In vertebrate haemoglobin, 4 globins (2
alpha, 2 beta) form a tetramer, MW ca
68,000.
– (Earthworm haemoglobin has MW ca 1,000,000.)
• Binds and transports O2
- reversible
• binds carbon monoxide
http://en.wikipedia.org/wiki/Hemoglobin
Oxygen transport in the blood
•
The amount of oxygen carried by blood is largely determined by the oxygen
dissociation curve for haemoglobin, and by the local partial pressure of oxygen (PO2).
98%
100
100%
The right-ward
shift of the
curve at low
pH is called
the Bohr
effect.
% saturation of HHb with O2
Arterial
blood
75
50
Venous blood
- high [CO2] & more acidic,
- low [O2],
25
(tissue)
(alveoli)
(air)
0
40
BioSciences Note 1 Torr = 1 mm Hg
120
160
Blood PO2 (Torr)
160
PO2 (Torr)
120
80
40
0
0
2000
4000
6000
8000 10000
altitude (m)
BioSciences
Control of heart rate, blood pressure, and
breathing
vasomotor and
respiratory
centres in
brainstem
• baroreceptors (pressure)
– great veins
– aortic arch
– carotid body
• chemoreceptors (chemicals)
• feed into vasomotor centre in brain stem
- regulation of
–
–
–
–
respiration
heart rate; cardiac output
blood pressure
vascular tone (constriction of blood
vessel walls)
Heart
Lungs
BioSciences
phrenic and thoracic nerves
to diaphragm and intercostal muscles
Brain
– carotid body : O2
– aortic body: CO2 and pH
Circulatory control and exercise
EXERCISE
of skeletal
muscle
incr. local
metabolites
decr O2,
incr CO2
increased gas
exchange
in lungs
Chemoreceptors:
- carotid bodies
- aortic bodies
increased rate
and strength
of heartbeat
baroreceptors
in carotid and aortic
bodies
BioSciences
vasoconstriction
of some ateries
increased blood
to muscles
local dilation
blood vessels
Awareness in
higher centres
of brain
vasodilation of
arteries to muscle
Adapted from
KLES5 fig 24.18
What drives ventilation?
% CO2 in inhaled air
breathing rate (L/min)
1
2
3
4
5
6
7
8
9
10
a small amount of
CO2 in inhaled air
stimulates a large
increase in
breathing rate
80
•Note - experiments
with rebreathing air.
60
40
a small
amount of O2
in inhaled air
has little
effect on
breathing rate
20
18
16
14
12
10
8
6
4
% O2 in inhaled air
BioSciences
•Air-breathing tetrapods
like us are very
sensitive to CO2.
2
0
•Note - danger of
hyperventilation before
unassisted diving.
•Chemoreceptors
(CO2/pH, O2) in carotid
and aortic bodies and
(CO2/pH) in medulla of
brainstem
Cells, Tissues and Organs
Professor Geoff Shaw
School of BioSciences
g.shaw@unimelb.edu.au
Refs (list also includes some material covered in Lec 21):
KLES5: Chap 7 esp. Tables 7.1-7.3 on pp 157-159, pp 163-174, Chap 28:
pp 680-685
KLES4: Chap 7: esp. Tables 7.1-3, pp 153-163, Chap 27:636-640
Resources on LMS
Examples of cells, tissues, organs, and their function and control
mechanisms in Lectures 18,19,21,22,23 (and others)
BioSciences
Our bodies are made up of ….
• organ systems
– skeleton
– muscles
– nervous system
– digestive system
– circulatory system
– respiratory system
– ….. and lots lots
more
BioSciences
And organs are made up of cells
and tissues
• Many different sorts
– connective tissue
– muscle
– epithelium
– glandular
– neural
– …. and so on…
BioSciences
Examples of tissues/cells
mouse uterus
blood
muscle
connective tissue
epithelium
BioSciences
Coordination
• at the inter-cellular level
– example – NO and vascular control
• at the tissue/organ level –
– eg signalling in the heart – coordinated
contraction…
• At the whole organism level –
– eg cardiovascular coordination
– endocrine  reproduction
BioSciences
How do cells communicate?
• local
– cell-cell contacts
– chemical signals
• distance
– neural
– endocrine
BioSciences
fast
slower
Homeostasis
• from the Greek
– homoios same
– stasis
standing still
• a tendency to maintain a
constant internal environment
– also spelled Homoeostasis
BioSciences
Body Temperature
Balance between heat
generation and heat loss
HEAT
generation
“Cold Blooded” animal
increase heat loss or
decrease heat production
 cooler
decrease heat loss or
increase heat production
 hotter
“Warm Blooded” animal
Balance:
heat loss = heat made
 const Temp
BioSciences
lizard sunning itself
on a rock…
BioSciences
Why do we maintain
homeostasis?
waste energy
risk of predation
etc etc
BioSciences
Why do we maintain
homeostasis?
waste energy
risk of predation
etc etc
BioSciences
metabolic
efficiency
less dependent
on environment
etc etc
Control Mechanisms
SET POINT
INTEGRATORY
SYSTEM
SENSOR
BioSciences
RESPONSE
(EFFECTOR)
SYSTEM
NEGATIVE FEEDBACK
• Responses cause changes that tend to
return to desired set-point
sweating
panting
vasodilation
Goosebumps
(pilo-erection)
shivering
vasoconstriction
seek shade/cool
movement
remove clothes
warm clothes
resting
seek warm place
BioSciences
POSITIVE FEEDBACK
• When responses increase the change
from the set point
– eg severely hypothermic person may
undress…
– LH surge in female reproductive cycle
(discussed in a later lecture)
– Birth (later in this lecture)
BioSciences
Homeostasis:
body temperature
• costs:
– metabolic energy needed to stay warm in
too cool environment
– water loss for cooling (sweat, panting) in
too warm environment
BioSciences
Homeostasis:
body temperature
• benefits:
– cellular enzymes optimised for one
temperature, ↑ efficiency
– can remain active in cold
• more time to forage
• less risk of predation
– able to use wider range of environments
BioSciences
Homeostasis: blood gas
Breathing and exercise:
breathing
circulation
exercise
air
O2
blood
O2
input  output?
BioSciences
tissues
O2 + sugar  CO2
Homeostasis: blood gas
• hold your breath – what happens
– ↓ blood O2 and ↑ CO2
– CO2 ↔ carbonic acid  pH sensor …
urge to breathe too great.
Deep breaths taken…
Blood CO2
excess CO2 lost quickly
hold breath
Time
BioSciences
“overshoot” and responses to
correct (reduced breathing)
Hyperventilation
• rapid deep breathing
–loss of CO2  increased pH
 light headed, dizzy, tingling …
If ↑ CO2 = ↓ O2  dilation of arteries to brain
then ↓ CO2 = ↑ O2  contraction of arteries to brain
BioSciences
Homeostasis: blood glucose
Food
metabolism
storage
absorption
gycogenolysis
storage
absorption
transport
glucose + glucose +…  glycogen
glycogen  glucose +…
release
glucose+O2 CO2+H2O
transport
metabolism
BioSciences
transport
Homeostasis: blood glucose
BioSciences
eat chocolate
eat chocolate
blood glucose
If no “feedback” regulation…. (…diabetes…)
time
4.5 mmol/L
Insulin and glucagon
• peptide hormones
• made by islet cells in pancreas
blood
glucose
glucose
glucose
glucose
glucose
glucose
glucose
glucose
Liver cells
glucose
glucose
glucose
BioSciences
INSULIN
GLYCOGEN
GLUCAGON
Homeostasis: blood glucose
eat chocolate bar
BioSciences
high glucoseinsulin
insulinglucose stored
in glycogen
eat chocolate bar
blood glucose
With “feedback” regulation…. (normal)
low glucoseglucagon
glucagonglucose released
from glycogen
time
4.5 mmol/L
Multiple regulatory mechanism…
• endocrine:
–
–
–
–
insulin
glucagon
adrenaline
cortisol, …
• behavioural
– hunger  eating
– satiety  fasting
– activities
• burn off sugar
• lethargy, to conserve sugar
• etc etc etc…
BioSciences
Birth, an example of a
non-homeostatic processes
oxytocin release
Pituitary
gland
neural reflex
Ferguson Reflex
contractions
stretch cervix
BioSciences
uterine
contractions
What do I expect you to learn from this lecture?
• Levels of organization within an organism
– cells, tissues and organs
– communication between cells / tissues/ organs
– endocrine and neural control
• What is homeostasis?
• What are some costs and benefits of
homeostasis?
• How do feedback systems work ?
(sensors  integrators  response systems)
• Negative and positive feedback
• Examples of some homeostatic systems
– body temperature
– blood gases
– blood glucose