Homeostasis in humans
Introduction
• Homeostasis is the process of maintaining a
constant, internal environment within
narrow limits, despite changes that take
place internally and externally.
• Cells can only perform life processes if
conditions around them are kept within
optimum narrow limits.
• The conditions within cells depend on the
conditions within the internal environment
(the tissue fluid)
• Factors such as carbon dioxide, glucose, salt
and water concentration, temperature and
pH must be kept constant in the internal
environment (tissue fluid)
Homeostasis through negative feedback
Function of negative feedback is to maintain homeostasis.
Negative feedback is when some condition in the body changes,
mechanisms in the body produce opposite effect so the body returns
to normal.
• You must know the negative feedback mechanism controlling the
concentration of:
• Glucose
• Carbon dioxide
• Water
• Salts
An example of a negative feedback loop
Negative feedback mechanism controlling the concentration of glucose
You must be able to
describe this process – with
or without a diagram
Negative feedback mechanism controlling the concentration of carbon
dioxide
You must be able to
describe this process –
with or without a
diagram
Negative feedback mechanism controlling the concentration of water
and salts
• Water and salt concentrations are controlled through the process of
osmoregulation (a function of the kidneys).
osmoregulation
• process that controls [water] and [salt/solutes] in body.
• a function of the kidneys – they regulate and keep [water] and
[solutes] at correct levels.
in blood and tissue fluid
• solutes such as glucose and salts are dissolved in water.
• gives blood and tissue fluid a particular osmotic pressure (how much
solute is in solution).
• must be kept constant.
ADH and Aldosterone work together to control water and salt balance
Control of salt balance of body (works together with water balance)
Always refer to more or
less Aldosterone being
secreted
Thermoregulation
• process in which body continually adjusts to keep temperature
constant, between 36°C and 37,5°C
• optimum temperature for body’s enzymes – 36,9°C
• Body gains heat
• absorbing heat from environment through skin
• from hot foods and drinks
• producing it through metabolic processes
• Body loses heat
• through skin radiation of heat energy
• evaporation of sweat
• gains and losses must be balanced to keep body temp. at 36,9°C
Hypothermia and hyperthermia
• occurs when temperature control mechanisms no longer work
properly
• Hypothermia
• too low body temp – metabolic activity slows down – brain’s
functioning slows down – can cause death
• Hyperthermia
• too high body temp – enzymes denature – stop working
completely – affects brain which controls all body functions death
Basic structure of the skin
Epidermis:
Protects underlying organs
against damage, water loss, UV
radiation and bacteria.
Includes germinal layer (stratum
germinativum), oil glands and
hairs.
Dermis:
Made of loose connective
tissue.
Includes sweat glands, blood
vessels, nerves and temperature
receptors.
Hypodermis (subcutaneous
layer):
Mainly adipose tissue for
insulation.
Physiological control of body temperature
• Body temperature is controlled through sweating, vasodilation and
vasoconstriction.
• The Hypothalamus of the brain is the temperature control centre.
• As blood flows through hypothalamus is determines the temperature.
• Hypothalamus uses negative feedback mechanisms to control body
temperature by stimulating behavioural as well as physiological
changes.
• Cold and heat receptors in skin detect temperature changes, sensory
nerves send impulses to hypothalamus.
• Hypothalamus stimulates voluntary changes in behaviour.
• Cold
• More clothes, huddling, exercising, hot drink
• Hot
• Move to shade, in cool water, cold drink
Physiological changes
In warm conditions - Vasodilation
• ↑ body temp – blood temp ↑ – flows through hypothalamus – nerve
impulses sent to blood vessels, sweat glands and erector muscles –
causes vasodilation
• Surface blood vessels dilate – more blood flows near surface of skin – lose
heat energy through radiation (from blood to surroundings)
• Sweating also occurs
• sweat glands become more active – produce more sweat –
evaporation – causes cooling, because evaporation needs heat energy
– this heat energy is removed from blood in surface capillaries – blood
cools down
Vasoconstriction in cold conditions
• When body temperature drops – cooler blood flows through hypothalamus,
causing vasoconstriction
• Surface blood vessels constrict – reduced blood flow to skin surface – less
heat loss from blood.
• Most blood flows through vessels in hypodermis – fat insulation reduces
heat loss.
• Sweat glands are inactive so there is no evaporative cooling
• Hypothalamus also stimulates:
• rapid skeletal muscle contraction – shivering – produces heat
• adrenal and thyroid glands – large amounts of adrenalin and thyroxin - ↑
metabolic rate of liver – more heat produced.