Biology Lecture #4 - Metabolism.docx

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Published on 22 Apr 2013
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Biology Lecture #4 Metabolism
Topics to be covered, Homeostasis and the control of energy balance, metabolic rate and
temperature
Homeostasis
Process that allows animals through behaviour and physiology to maintain an acceptable state of
body while facing external and internal challenges
Involves number interactions of metabolic and cellular processes in an animal such as negative and
positive feedback loops
Example : being exposed to the cold
Sensor in neurons
Integrator in brain realizes due to sensor that temperature is under 37 degrees
Effector, the activation of skeletal muscles
Response, shivering, which increases heat production
Example of a negative feedback
Negative feedback a variable being regulated that brings responses that move the variable
towards the opposite direction
Eg. Decrease in body temperature leads to responses that result in an increase body
temperature
May occur at either the organ, cellular or molecular level
Important in organisms as it prevents homeostatic responses from overcompensating
Homeostatic challenge that initiates process a, process a activates process b, which turns
down process a
Looping around as b reduces strength of a, which reduces activation b which causes soft
landing effect
Positive feedback far less common, essentially accelerates a process
Instead of inhibiting a process, it accelerates a process by reinforcing the direction of the change
via an explosive system
Example birth in mammals
Head of baby will stretch cervix, stretch receptor neurons send a signal up to the brain
which activates a hormone, oxytoxin which increases the contraction of the smooth muscles
in the cervix which further reinforces the stretch receptor neurons and the cycle will
continue until delivery of the baby
Homeostatic Strategies
Animals differ to extent to which they maintain internal constancy in physiological conditions, as
they all operate based on variables
Conformers allow a physiological process to change based on their environment
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Regulators control physiological variables within a narrow range, despite their external conditions
Thermo-conformers/regulators
Poikilotherms (heterotherms) and homeotherms differ in the constancy of body
temperature (variable vs constant respectively)
Also have to consider how/where heat comes from,
ectotherms and endotherms differ in source of body heat (ex vs in respectively)
Metabolism
refers to all bodily activities and chemical reactions in an organism that maintain life
all the processes contributing to homeostatic processes are referred to as the bodies metabolism
the metabolic rate is therefore the rate at which organisms use energy to contribute to the
reactions
always being in an alert and active state requires metabolism, but organism cannot always pull
energy from environment
one of main ways is to consume food
what if cant get food, how does it get energy for metabolism?
Another problem is that metabolic fluctuates, determines in environment and type of activities
that the organism is performing
Essentially a supply and demand issue
An organisms metabolism is very closely linked to its body temperature, purely chemistry issue
Temperature is thermodynamic variable that affects the rate of biochemistry reactions
As you raise temperature, it also raises the metabolic demands as they occur faster
To solve the first issue of energy storage, animals don’t consume nutrients and use them as they
need
Multiple processes to deal with and store the nutrients
Absorptive state energy ingested is being used for energetic demands, rest is stored in
complex molecules, essentially storing what it needs and using the rest
Eg. Glucose broken down into glycogen to store, same with breaking triglycerides into
adipose and absorbing all protein for cell usage
Postabsorptive state uses the body’s stores to meet energy needs
Glycogenolysis - Glycogen stored into liver becomes glucose to be put back into blood
stream
Gluconeogenesis of adipose adipose tryglycerides into glycerol and fatty acids, the
components
Gluconeogenesis of the muscle takes protein and breaks down into amino acids,
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