Homeostasis
• Physiological state of the body
• Internal physical and chemical conditions are
maintained within a tolerable range (balance)
– Internal temperature, hormone levels, pH, pressure,
concentrations of glucose and other solutes in the blood,
water balance (osmoregulation)
Extracellular Fluid
• Interstitial fluid
– Surrounds fills the spaces
between cells and tissues
– Approx 10L
– Consists of water, sugars,
salts, FA, AA, coenzymes,
hormones, neurotransmitters,
waste products
– Regulates flow of chemicals
and allows cells to function
properly
• Blood plasma
– Helps movement of water and
electrolytes throughout the
body
– Approx 3L
Internal Environments
• Changes in Extracellular
Fluid has negative
effects on cellular
function
• Body uses organ systems
to regulate internal
conditions
– Nervous system
– Endocrine system
– Muscular system
– Integumentary system
– Excretory system
– Reproductive system
Nervous System (Communication)
•
•
•
•
Brain, spinal cord, peripheral nerves, sensory organs
Receives sensory data from the environment
Informs body of external conditions
Transmits signals throughout the body
Endocrine System (Communication)
• Pituitary, thyroid, pancreas, adrenal (glands)
• Regulates levels of hormones and other chemicals
Excretory System (Protect the Body)
• Kidneys, bladder, urethra, ureters
• Rids the body of waste
• Maintains clean internal environment
Integumentary System (Protect the Body)
• Skin, sweat glands, hair, nails
• Maintains a constant body temperature
Immune System (Protect the Body)
• White blood cells
• Protects/fights infection
Digestive System (Acquire Energy)
• Liver
• Breaks down amino
acids
• Detoxifies harmful
chemicals (alcohol)
• Manufactures
important proteins
• Stores glucose
Circulatory System (Acquire Energy)
• Transports important substances, including food
molecules, oxygen, carbon dioxide, hormones
throughout the body
Respiratory System (Acquire Energy)
• Exchanges oxygen and
carbon dioxide between
the lungs and the
atmosphere.
• Oxygen is needed to
release energy from food
molecules
• Carbon dioxide is a waste
gas
Skeletal System (Support and Move Body)
• Includes bones,
ligaments, cartilage
• Bones protect
organs and are
points of
attachment for
muscles
Muscular System (Support and Move Body)
• Provide movement
for the body
• 3 types
– Skeletal muscle –
move skeleton
– Smooth muscle –
organs
– Cardiac muscle –
heart
Reproductive System (Produces Next Generation)
• Includes organs that produce and transport sperm
and eggs
• Enables female to give birth
Mechanisms used in Homeostasis
• Respond to internal
and external
conditions
• Feedback systems
– Positive/Negative
• Help bring the body
back into balance
• Breathing rate,
heart rate, internal
temperature, blood
glucose levels
Negative Feedback
• Reduces the output or activity of an organ or system back to its normal
range
• Include 3 elements
1. Sensor
– tissues or organs - detects change
2. Integrator - hypothalamus
– control centre – compares conditions from environment with to optimal
conditions in the body
– Set points – ranges of values which need to be maintained
3. Effector
– returns measured condition back to set point – response
– Antagnositc effectors – produce opposite effect of change detected
Positive Feedback Mechanisms
• Increases change in
environmental condition
• Does not result in
homeostasis
• Cause system to become
unstable
• “fight or flight” response
• reproduction
• fever
• Positive feedback
mechanisms operate
within negative
feedback mechanisms
• Allows body to be
brought back into
balance
Thermoregulation
• Internal temperature
regulation
• Negative feedback
mechanism
• Thermoreceptors
– compare external temp
with internal set point
– Found throughout
integumentary system
• Trigger responses (2)
– Rate of exothermic
reactions in body
(metabolism)
– Rate of thermal energy
exchange through
surface of body
Hypothalamus
• Body’s thermostat
• Maintains body
temperature
• Optimal body
temperature
– 35⁰ - 37.8⁰
• Signals from
hypothalamus
make us aware of
our own
temperature
Mechanism
• Body temp rises above
hypothalamus set point →
blood vessels dilate/induce
vasodilation/sweating →
increase blood flow→
increase thermal energy
loss to environment
(radiation)→ sweat glands
activated → body temp
decreases
• Body temp falls below
hypothalamus set point →
vasoconstriction in skin/
skeletal muscles start
shivering→ reduced blood
flow→ less thermal energy
lost to environment →
body temp increases
Mechanisms of Thermal Energy Exchange
• Occurs at the surface
where body comes
into contact with the
external environment
• Exchange of thermal
energy occurs
through 1 of 4
mechanisms
–
–
–
–
Conduction
Convection
Radiation
Evaporation
• All of these
mechanisms act
simultaneously
Thermal Energy
• Conduction
– Flow of thermal energy
between molecules
that are in direct
contact
• Convection
– Transfer of thermal
energy within a fluid
(liquid or gas)
• Radiation
– Thermal energy is
transferred
electromagnetically
• Evaporation
– Absorbs thermal
energy from skin via
water/sweat
Homeotherms
• Animals that maintain a stable internal
temperature regardless of external conditions
• Includes
– Poikilotherms
– Endotherms
– Ectotherms
Poikilotherms
• Fish, amphibians, reptiles, and most
invertebrates
• Body temperature varies with and often matches
the temperature of the external environment
Endotherms
• Warm blooded animals
(mammals, birds)
• Homeotherms that use
internal physiological
mechanisms
(metabolism) to
generate thermal energy
and maintain body temp
• Remain fully active over
a wide range of
temperatures
• Need a constant supply
of energy
Ectotherms
• Cold blooded animals
(reptiles, amphibians, fish)
• Homeotherms that use
external sources of energy to
absorb thermal energy and
regulate body temperature
• Temperature fluctuates with
environmental temperature
• Inactive when temp are too
low
• Undergo thermal
acclimatization
– Gradual adjustment to
seasonal temp
Torphor, Hibernation, Estivation
• Adaptations to survive
extreme climates by
conserving energy
• Torphor
– Sleeplike state
– Metabolic rate and body
temperature drop in
response to daily temp
(nocturnal animals,
hummingbird)
• Hibernation
– State of inactivity over an
extended period of time
• Estivation
– Seasonal torphor –
environment is hot and
water is scarce
Water Balance
• Extracellular fluid needs to maintain a constant
volume (~15L) of water and balance of solute
within the body
• Mechanism
– Osmosis
Osmosis
• Water molecules move
from a high
concentration to a
region of lower
concentration across a
selectively permeable
membrane
• Osmotic pressure
– Results from a
difference in water
concentration gradient
between the two sides
of the selectively
permeable membrane
• Hyperosmotic
• Hypoosmotic
• Isoosmotic
Osmotic Environments (Cell)
• Hyperosmotic
– Solution with higher
concentration of solute
molecules than water
molecules
– Water tends to move
to this side
• Hypoosmotic
– Solution with lower
concentration of solute
molecules than water
molecules
– Water tends to move
from this solution
• Isoosmotic
– Solution with equal
solute and water
concentrations on both
sides of cellular
membrane
Osmoregulation
• Process of actively
regulating the osmotic
pressure of bodily
fluids
• Osmole (osmol)
– Contributes to
osmotic pressure of
solution
• Extracellular fluid =
intracellular fluid
(isoosmotic)
– [solute] remains the
same across cellular
membrane
– [water] remains the
same across cellular
membrane
The Excretory System
• Main functions (with the help of osmoregulation)
– Concentrate wastes and expel them from the body
– Regulate fluids and water within the body
• Organs included
– Kidney
– Adrenal gland
– Ureter
– Urinary bladder
– Urethra
Removal of Metabolic Waste
Waste
Origin of Waste
Organ of Excretion
Ammonia
Breakdown of amino acids in the liver
kidneys
Urea
Conversion of ammonia in the liver
kidneys, skin
Uric Acid
Breakdown of purines in food and drink
kidneys
Carbon Dioxide
Cellular respiration (breakdown of glucose)
lungs, intestines, skin
Bile Pigments
Breakdown of porphyrin ring (hemoglobin)
intestines
Lactic Acid
Cellular respiration (breakdown of glucose)
kidney
Solid Waste
Breakdown of food
intestine
Mechanism
• Thirst
– Physiological sensation to drink water
• Stimuli to Thrist
– Hypertonicity – cellular dehydration is monitored
by the hypothalamus via osmoreceptors
• Mechanism
– Hypothalamus sends a signal to pituaitry gland to
release ADH (anti-diuretic hormone/vasopressin)
– ADH acts on collecting tubules in nephrons making
them more permeable to water
– >1% of filtered water is excreted
– Reabsorption of water reduces [Na⁺]
– Osmoreceptors send signal to hypothalamus
stopping release of ADH
Kidneys
• Removes waste
• Balances blood pH
• Maintain body’s water
balance
• Blood is supplied to
kidney via renal artery
• Re-enters circulatory
system via renal vein
Nephrons
• Functional unit of
the kidney
• (1 000 000 per
kidney)
• Regulate water
balance
• Conduct excretion
• Different sections
of the nephron
have specialized
functions in
formation of urine
and conservation
of water
Urinary Bladder
• Renal pelvis connects the kidney to the ureter
which fills the bladder
• Holds ~300mL-400mL of urine before exiting the
urethra
Deamination
• Occurs in the liver
– breakdown of protein
• Removal of amino
group from amino acid
• Creates ammonia NH₃
(toxic to body)
• Urea Cycle
– Ammonia reacts with
bicarbonate and 2 ATP
molecules to form urea
– Transported to kidneys
where excretion occurs
via blood
Bicarbonate Buffer System (Kidneys)
• Maintains pH of blood
(acid-base homeostasis)
• Regulates the excretion of
H⁺ ions in the urine and
reabsorption of
bicarbonate into
bloodstream
– TOO ACIDIC – hydrogen
ions are excreted
– TOO BASIC – less hydrogen
ions are excreted
• CO₂ dissolved in blood
reacts with water to form
carbonic acid (H₂CO₃)
Formation of Urine
• Ultimate goal
– conserve water, balance salts,
concentrate wastes
• Urine
– hypoosmotic to surrounding body
fluids
– water tends to move from urine
into the body fluids
• 3 Feature of nephron interact to
achieve ultimate goal
– Arrangement of loop of Henle
– Difference in permeability
– Concentration gradient of
molecules and ions
• 3 processes interact to achieve
formation of urine
– Filtration
– Reabsorption
– Secretion
Formation of Urine: Overall Process
Filtration
• Begins at Bowman’s capsule
(selectively permeable
membrane)
• Receives water, ions, glucose,
AA and urea from glomerulus
• Difference of pressure allows
for transfer of molecules and
ions into capsule
• 1400L of blood pass through
kidneys every day
• Bowman’s capsule filters ~180L
from blood
• ~1.5L is excreted as urine daily
Reabsorption
• Occurs as fluid from
Bowman’s capsule enters
proximal convoluted tubule,
Loop of Henle and distal
convoluted tubule
• Water, ions and nutrients are
transferred back into
interstitial fluid and
peritubular capillaries via
passive and active transport
• Microvilli inside tubules
increase surface area
• Difference in solute
concentration allows water to
move across the membrane
and back into interstitial fluid
via osmosis (aquaporins)
Secretion
• Removal of waste products from
the blood and interstitial fluid and
secreted into the nephron
• Include – detoxified poisons, water
soluble drugs, metabolites, H⁺
• Secretion of H⁺ ions balances
acidity in body
• Reabsorption of HCO₃⁻ occurs
simultaneously
• Buffer system controls pH levels of
blood
– Increased acidity – H⁺ excreted as
urine
• Urine reaches bottom of collecting
ducts, flows into renal pelvis,
through ureters, into urinary
bladder and exits through urethra
Kidneys Regulate Blood Oxygen Levels
• Kidneys monitor
blood oxygen levels
(RBC’s)
• If too low – kidneys
release
erythropoetin (EPO)
into the blood
stream which
stimulates the
production of red
blood cells
Kidney Diseases
• Renal Failure
• 2 types
1. Acute
–
rapid progressive loss
of renal function
– Injuries, accidents,
complications from
surgery
2. Chronic
– slow progressive with
long term consequences
– Diabetes mellitus,
uncontrolled
hypertension, polycystic
kidney diseases
• Treatments
– Dialysis
– Kidney transplant