Metabolism I - St. Bonaventure University

mistaureolinMechanics

Oct 27, 2013 (3 years and 9 months ago)

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Metabolism

Mechanistic view tells us living matter obeys the
ordinary, (universal) laws of physics and
chemistry

Laws of thermodynamics

Conservation of mass

Conservation of momentum

Gravitation

Chemical properties of elements

Laws of thermodynamics



Second Law


Whenever anything actually
happens, the entropy (disorder) of the system (or
of the universe) increases (cannot decrease)



In any
isolated system

(no matter or energy can
enter or leave), including the
entire universe
:



First Law: total amount of energy is constant, though it can
change form

Laws of thermodynamics

Disorder may be in the arrangement of matter or
energy


Heat (thermal energy) is disordered
energy

“Time’s Arrow” points in the direction of increasing
entropy of the universe

Mowing the Lawn & Thermodynamics


2
nd

law energy dispersed and
isn’t available to produce
initial fuel and do work



Given amount of chemical
energy in gas

1
st

law
-

energy transferred to
blades, noise, heat (exhaust,
engine)

How can life exist?

Violates the 2
nd

law of thermodynamics!!

Life is an organization of matter

A systematic
DECREASE

in entropy

Organizing processes require energy

What is the isolated system?


The Universe as a whole not the Earth



Steady input of energy from the sun
(sun is losing energy it will burn out)



Life is a series of energy transfers

The sun is losing energy
-

it will burn out


Peter Ward
, Professor of Geological Sciences at the
University of Washington in Seattle:



“The presence of complex life on the Earth will end in no
more than a
billion years

(and perhaps much sooner), due
to a sequentially predictable breakdown of habitable
systems on our planet. The systems in question are those
that serve to regulate the Earth's temperature and
atmospheric carbon dioxide content”


Food as Energy

Two hypotheses about animals’

use of food

1.
Assimilation

-

2.
Combustion

-

Aristotle and Animal Nutrition
(assimilation)


Animals composed of the four elements



Different organs


different proportions



Food


same four elements
-

added to the body

(“assimilated”)



Food processed (“concocted”) to proportions of
different organs

Food


Function and relationship
to anatomy

Human Dissections and Vivisection


http://www.karlloren.com/ultrasound/p39.htm

Post
-
mortem examinations
rare well into Middle Ages,
largely due to religious and
intellectual scruples

This early representation
(c. 1300) of a dissection
shows a surgeon and a
monk.



Galen of Pergamum (ca. 130
-
ca. 200)



Dissected dead
animals; served as
physician to gladiators



Observed blood vessels
(tubes) connecting
intestines to liver, liver
to heart, and heart to
lungs

www.malaspina.com/jpg/galen.jpg


Galen’s Model


Digestion consisted of series
of concoctions to “refine” food



Food absorbed by intestines



1
st

concocted in liver


flows
to heart



Further refinement in heart to
make blood


out to tissues



Additional concoction in brain


more highly refined fluid

Galen’s Model


Before blood leaves heart


exchange of material with
lungs



Blood flow right to left
ventricles via little holes



Waste material right ventricles
to lungs



Lungs take in air


left
ventricle exposed to blood
producing
pneuma

(‘vital
spirit’


‘vital heat’)

14th century anatomist: Vesalius


Spent a good deal of his time
sneaking into graveyards and
stealing bodies



Would dissect corpses make
detailed notes & illustrations



Later commisioned artist Titan
to do illustrations for his book
Di Humani Corporis Fabrica



Book and illustrations
revolutionary in the field of
medicine and art



Contradicted Galen


http://www.search.com/reference/Vesalius

Di Humani Corporis Fabrica

tyranny.com/graphics/jpegs/vsel1.jpg

tyranny.com/graphics/jpegs/vsel7.jpg

The Anatomy Lecture of Dr. Nicolaes Tulp by
Rembrandt van Rijn (1632)

mathiasbynens.be/images/anatomy
-
lecture.jpg

The Anatomy Lecture of
Dr. Nicolaes Tulp by
Rembrandt van Rijn



Reveals significant changes in the
way anatomy taught, illustrates a
major conceptual & methodological
development in the understanding of
the natural world



Notably changed in the portrait is
the placement of the text, which had
directed the observations of earlier
anatomists



Focus of lecturer & students on
corpse, with text in shadows at foot
of dissecting table



Close observation by the students is
emphasized, and the dissection
itself reveals the hidden underlying
structures of the human form


mathiasbynens.be/images/anatomy
-
lecture.jpg


William Harvey


Performed a series of
experiments on blood
flow



Observed heart as it
beat in a living animal



Heart is muscular
tissue with valves

Members.aol.com/ldaucourt/Histmed.htm

Heart as a
muscular
“pump”

www.med.umich.edu/1libr/aha/hrtflow.gif

William Harvey


Calculated heart pumps out 2 oz blood with each
contraction



If blood is absorbed


would provide ~ ___ lbs of
blood / minute (don’t eat that much)


[equals ~ _____________ / day]



Blood must circulate

William Harvey Studies on Blood Flow

www.life.uiuc.edu/ib/494/harvey.html

Opposition to William Harvey


Against long
-
held views



Inability to explain
HOW

blood provides
nourishment



Connection between arteries and veins?

Marcello Malpighi (1661)

“De pulmonibus observationes anatomicase”


Left
-

frog's lung external view



Right
-

lung cut longitudinally



Alveoli connected with tracheo
-
bronchial tubes by capillary
network.



Established connection
-

veins
and arteries which anatomists had
been looking for but never found


http://www.scienzagiovane.unibo.it/English/scientists/malpighi
-
2.html

Alveoli and capillary network


The respiratory tubes, or
bronchioles, end in
minute alveoli, each of
which is surrounded by
an extensive capillary
network.


Artery




Capillaries






Vein

http://nmhm.washingtondc.museum/news/healthyheart.html

www.daviddarling.info/images/capillaries.jpg

Blood Flow

Nutrition as replacement of lost material


Food replace tissue lost from “wear and tear”


lubricate muscles & joints



Tissues made of cells / “globules” in blood


tissue growth = assimilation of globules



“Globularist” hypothesis rejected



-

blood “globules” not same size as cells



-

muscle cells long fibrous



-

how do blood “globules” get out of blood vessels



But 1830’s nutrition still assimilation



Nutrition as Combustion


Life dependent on “inner fire”



~ Warm when alive


cold when die



~ Aristotle


“innate heat” needed by animals



~ Galen


“vital heat” associated with pneuma



Like gunpowder (potassium nitrate & sulfur)



~ “aerial nitre” breathed in produces heat when reacts


with sulfurous material in tissue



Descartes and others


heat arising from friction due to
movement of body parts




Combustion hypothesis


Leonardo da Vinci (1500’s) compared animal heat to
burning candle

suggested food served as fuel



Lavoisier (late 1700’s) stated flames and animals
consume oxygen (O
2
)
-

produce carbon dioxide (CO
2
)



What do flames and animals have in common?




Lavoisier & Laplace


“slow combustion”

Lavoisier

Laplace

http://historyofscience.free.fr/Lavoisier
-
Friends/a_tab2_lavoisier_alone.html

www.sjsu.edu/faculty/watki ns/Laplace.gif

Lavoisier and Laplace’s
“Ice Bucket Calorimeter”



Produced CO
2

by
burning coal or
respiration from
guinea pig



Measured O
2

used
CO
2

and heat
produced


http://www.chem.yale.edu/~chem125/125/history99/2Pre1800/Lavoisier/Instruments/calorimeter.html


Observations on combustion and animals


produced ~ same amount of heat

[ice melted per in
3

CO
2

produced]



produced ~ same volume of CO
2
per in
3

O
2

consumed

[0.81 vs 0.75 cubic inches]



difference


air carried in fur of guinea pig as it was
thrust through mercury into the sealed chamber



concluded


production of heat and CO
2

were linked
and that underlying process was the same in
combustion as in respiration

“respiration is therefore a combustion, very slow it is
true, but otherwise perfectly similar to that of
charcoal”

“it occurs in the interior of the lung, without
producing perceptible light, because the liberated
matter of fire is immediately absorbed by the
humidity of these organs”

“Slow combustion”


They hypothesized that animals carry
out a “slow combustion” of fuel (now
called cellular respiration).



They believed that the function of
cellular respiration was to make heat.


How do we use food?



thermodynamics of chemicals centered on release
of heat


wood, coal, other organic chemicals



heat is one form of energy



any substances burned releasing heat must
contain energy in their chemical make
-
up



food molecules source of energy because they
have relatively weak, less stable chemical bonds
therefore high potential energy



How do we use food?


CO
2

& H
2
O have especially strong chemical bonds
therefore relatively low potential energy




to synthesize high
-
energy food molecules from
more stable, lower
-
energy molecules (CO
2

&
H
2
O), a source of energy is needed → light energy
from the sun



food molecules are sources of energy


now view

photosynthesis and respiration simple energy
transfers

How do we use food?



The eventual fate of most of the energy
released from food molecules is indeed heat
(as Lavoisier thought), but it is the
intermediate uses of that energy that make
life possible





Cellular Respiration