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Summary BBS1002 Homeostasis and Organ systems
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A good summary of all cases of this block. Notes from the lectures are integrated in this summary.
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BBS1002 - Learning targets Homeostasis and Organ systemsBy Cédric Pluis 2019-2020
1
,Introduction lecture about the homeostasis
Input of our body:
▪ Oxygen
▪ Water (intracellular: cytosolic / extracellular = plasma)
▪ Food, which can be divided into two categories:
o Macronutrients are needed in large amounts, such as: carbohydrates, proteins,
lipids, water and fibres
o Micronutrients are needed in small amounts, such as trace minerals and
vitamins
o Essential nutrients (= can’t be synthesised by the body itself) are required for
physiological function, such as micronutrients (trace minerals and vitamins) for
energy, certain amino acids and certain fatty acids (omega-3: alpha-linoleic acid
and omega-6: linoleic acid)
What happens with the input?
o The body produces energy out of oxygen, water and food in the
cellular respiration reaction in the mitochondria
o Daily energy requirement = 70% Resting Daily Energy
Expenditure + 20% Physical activity + 10% Digestion
Heat is a rest product of the energy production in the body:
o We cannot stop producing heat. It is part of life
o We need to maintain our body temperature.
Exercise and the temperature of the environment can influence
the daily required energy.
Energy process:
▪ The surplus of free energy from exergonic reactions is released as heat (∆G)
▪ Exergonic reaction (spontaneous): there is more energy released than needed to let the
reaction occur, heat (energy) is released for maintaining body temperature
▪ Humans are using this heat to maintain a stable body temperature
▪ Humans are using this heat (released energy) to maintain a stable body temperature.
The released energy from exergonic reactions (mostly using ATP) is used to drive
endergonic reactions (such as biosynthesis in the)
Output of our body
▪ Carbon dioxide
▪ Urine
▪ Feces
2
, Metabolism: Substance X → Substance Y
Total amount of Substance X in the body =
Existing body load
+ Intake or Metabolic production
– Excretion or Metabolic removal
Secretion and excretion
▪ The body secretes saliva and gastric juice and it excretes carbon dioxide.
o Secreting is releasing products which perform other functions of the body (for
example: sweat)
o Excreting is releasing metabolic waste or substances (which don’t have a
function anymore in the body)
• Excreting occurs via the following patways: Integumentary
system, Respiratory system, Excretory system and Digestive
system (CO2 = 900 g/da, urine 1.5 L/day, feces 150 g/day)
The definition of homeostasis
▪ The term homeostasis refers to the ability of the body to maintain a stable internal
environment despite changes in external conditions (the body can deal with normal
health and with health challenge but not with a disease or death)
o ECF (extracellular fluid) is a transport and mixing system that surrounds
the cells
o ECF constitutes the internal environment.
o The internal environment is largely determined by the composition of ECF
o Homeostasis requires the control the ECF constituents
▪ Controlled variables have a normal value and range. Setpoint is the normal value,
change = error + correction. The gain indicates the effectiveness of the negative or
positive feedback to control system
3
, Mass balance:
▪ The human body is an open system that exchanges heat and materials with the outside
environment. To maintain homeostasis, the body must maintain mass balance. The law
of mass balance says that if the amount of a substance in the body is to remain constant,
any gain must be offset by an equal loss. The amount of a substance in the body is also
called the body’s load, as in “sodium load.”
▪ For example, water loss to the external environment (output) in sweat and urine must be
balanced by water intake from the external environment plus metabolic water production
(input). The total amount of substance x in the body = intake + production – excretion –
metabolism
▪ To maintain mass balance, the body has two options for output:
o The simplest option is simply to excrete the material. Excretion is defined as the
elimination of material from the body, usually through the urine, feces, lungs, or
skin.
o A second output option for maintaining mass balance is to convert the substance
to a different substance through metabolism.
o Mass flow = concentration of substance y x volume flow
o Clearance is usually expressed as a volume of blood cleared of substance x per
unit of time. For this reason, clearance is only an indirect measure of how
substance y is eliminated.
Control mechanism of homeostasis via a sensor, an effector and an integrator
4
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