Homeostasis
Chapter 9
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/homeo/homeosts.shtml
Homeostasis
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Physiological state of the body
Internal physical and chemical conditions are maintained
within a tolerable range
Includes
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Temperature, hormone levels, pH, pressure, concentrations of
glucose and other solutes in the blood
Internal Environment
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Extracellular fluid
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Interstitial fluid – fills the spaces between cells and tissues (e.g. plasma)
Consists of water, sugars, salts, FA, AA, coenzymes, hormones,
neurotransmitters, waster products
Regulates flow of chemicals and allows cells to function properly
Lymphatic system transports fluid throughout the body
Internal Environments
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Changes in Extracellular Fluid has negative effects on cellular
function
Body uses organ systems to regulate internal conditions
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Nervous system
Endocrine system
Muscular system
Integumentary system
Excretory system
Reproductive system
Nervous System
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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
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Pituitary, thyroid, pancreas, adrenal (glands)
Regulates levels of hormones and other chemicals
Excretory System
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Kidneys, bladder, urethra, ureters
Rids the body of waste
Maintains clean internal environment
Integumentary System
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Skin, sweat glands, hair, nails
Maintains a constant body temperature
Immune System
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White blood cells
Protects/fights infection
Digestive System
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Liver
Breaks down amino acids
Detoxifies harmful chemicals (alcohol)
Manufactures important proteins
Homeostatic Mechanisms
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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
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Reduces the output or activity of an organ or system back to its
normal range
Include 3 elements
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Sensor
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Integrator - hypothalamus
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tissues or organs - detects change
control centre – compares conditions from environment with to optimal
conditions in the body
Set points – ranges of values which need to be maintained
Effector
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returns measured condition back to set point – response
Antagnositc effectors – produce opposite effect of change detected
Hypothalamus
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Body’s thermostat
Maintains body temperature
Optimal body temperature – 35⁰ - 37.8⁰
Body temp falls → vasoconstriction in skin/shivering→ reduced
blood flow→ less thermal energy lost to environment → body
temp increases
Body temp rises → blood vessels dilate/induce
vasodilation/sweating → increase blood flow→ increase thermal
energy loss to environment→ body temp decreases
Signals from hypothalamus make us aware of our own
temperature
Positive Feedback Mechanisms
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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
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Internal temperature
regulation
Negative feedback mechanism
Thermoreceptors – compare
external temp with internal
set point
Trigger responses (2)
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Rate of exothermic reactions in
body (metabolism)
Rate of thermal energy
exchange through surface of
body
Mechanisms of Thermal Energy Exchange
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Occurs at the surface where body comes into contact with the
external environment
Exchange of thermal energy occurs through 1 of 4 mechanisms
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Conduction
Convection
Radiation
Evaporation
All of these mechanisms act
simultaneously
Conduction
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Flow of thermal energy between molecules that are in
direct contact
Convection
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Transfer of thermal energy within a fluid (liquid or gas)
Radiation
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Thermal energy is transferred electromagnetically
Evaporation
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Absorbs thermal energy from skin via water/sweat
Homeotherms
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Animals that maintain a stable internal temperature
regardless of external conditions
Includes
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Poikilotherms
Endotherms
Ectotherms
Poikilotherms
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Fish, amphibians, reptiles, and most invertebrates
Body temperature varies with and often matches the
temperature of the external environment
Endotherms
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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
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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
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Gradual adjustment to seasonal temp
Torphor, Hibernation, Estivation
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Adaptations to survive extreme
climates by conserving energy
Torphor
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Hibernation
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Sleeplike state
Metabolic rate and body temperature
drop in response to daily temp
(nocturnal animals, hummingbird)
State of inactivity over an extended
period of time
Estivation
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Seasonal torphor – environment is hot
and water is scarce
Water Balance
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Extracellular fluid needs to maintain a constant volume
(~15L) of water and balance of solute within the body
Mechanism
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Osmosis
Osmosis
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Water molecules move from a high concentration to a region of
lower concentration across a selectively permeable membrane
Osmotic pressure
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Results from a difference in water concentration gradient between the
two sides of the selectively permeable membrane
Hyperosmotic
Hypoosmotic
Isoosmotic
Hyperosmotic
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Solution with higher concentration of solute molecules
Water tends to move to this side
Hypoosmotic
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Solution with lower concentration of solute molecules
Water tends to move from this solution
Isoosmotic
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Solution with the same solute and water concentrations
Osmoregulation
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Process of actively regulating the osmotic pressure of
bodily fluids
Extracellular fluid = intracellular fluid (isoosmotic)
[solute] remains the same
[water] remains the same
The Excretory System
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Main functions (with the help of osmoregulation)
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Concentrate wastes and expel them from the body
Regulate fluids and water within the body
Organs included
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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
Kidneys
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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
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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
http://www.youtube.com/watch?v=oXcEAH_yesY
Urinary Bladder
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Renal pelvis connects the kidney to the ureter which fills
the bladder
Holds ~300mL-400mL of urine before exiting the urethra
Deamination
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Occurs in the liver – breakdown of
protein
Removal of amino group from amino
acid
Creates ammonia NH₃ (toxic to
body)
Urea Cycle
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Ammonia reacts with bicarbonate and 2
ATP molecules to form urea
Transported to kidneys where
excretion occurs via blood
Bicarbonate Buffer System
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Maintains pH of blood (acid-base homeostasis)
Formation of Urine
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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
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Arrangement of loop of Henle
Difference in permeability
Concentration gradient of molecules and ions
3 processes interact to achieve formation of urine
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Filtration
Reabsorption
Secretion
Formation of Urine: Overall Process
Filtration
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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
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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
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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
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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
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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
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Renal Failure
2 types
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Acute – rapid progressive loss of renal function
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Chronic – slow progressive with long term consequences
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Injuries, accidents, complications from surgery
Diabetes mellitus, uncontrolled hypertension, polycystic kidney diseases
Treatments
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Dialysis
Kidney transplant