Homeostasis

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Homeostasis
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What is Homeostasis?

• Body cells work best if they have the correct set
  points for
• Temperature
• Water levels
• Waste levels
• Glucose concentration (blood glucose)
• Your body has feedback mechanisms to keep the
  cells in a constant environment.

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What is Homeostasis?

• The maintenance of a constant internal
  environment in the body.
• Negative feedback animation
• The ability or tendency of an organism or cell to
  maintain internal equilibrium by adjusting its
  physiological processes.
• Physiology is the study of the mechanical,
  physical, and biochemical functions of living
  organisms

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Glossary

• Maintain keep up.
• Constant the same.
• Internal inside the body.
• Environment surroundings of the body.

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• Our bodies attempt to maintain an internal
  balance called HOMEOSTASIS. There are many
  conditions in which life processes are limited
• Eg. Most enzymes in our bodies work best at
  37ºC.
• pH of blood is maintained between 7.35 and 7.45.
  (recall 7 is neutral, blood is slightly basic)
  
• Too low, acidosis
• Too high, alkalosis

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http//timlinn.edublogs.org/2011/03/24/worlds-bigg
est-dog-tongue/
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Negative Feedback

• Body responds to change in such a way as to
  reverse the direction of a change in set point.
• Because this tends to keep things constant
  (stabilizing effect), it allows us to maintain
  homeostasis.
• Most common

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Positive Feedback

• Body responds to change in such a way as to
  change even more in the same direction of set
  point change.
• This has a de-stabilizing effect, so it does not
  result in homeostasis.
• Positive feedback is used in certain situations
  where rapid change is desirable (adrenalin in
  fight or flight).
• Not very common

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Feedback Loops (3 Major Components)

• Sensor (receptor)
• Detects variation in the set point
• Sends message to coordinating center (CC)
• Coordinating Center (Hypothalamus)
• Receives message from receptor
• Sends message to effector to rectify deviation in
  set point (nervous or hormonal mechanism)
• Effector
• Receives message from CC
• Carries out instructions to rectify deviation in
  set point

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Negative Feedback Loop

• Control Center (Hypothalamus)
• Sensor/Receptor Effector
• Change Change
• Cause
• Normal Condition

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http//wps.aw.com/bc_martini_eap_5/105/27046/69238
09.cw/index.html
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MAJOR HOMEOSTATIC ORGAN

• Hypothalamus (brain) Homeostasis
• The main function of the hypothalamus is
  homeostasis, or maintaining the body's status
  quo.

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MAJOR HOMEOSTATIC ORGAN

• The following factors are held to a precise value
  called the set-point
• blood pressure,
• blood sugar
• body temperature,
• fluid and electrolyte balance,
• and body weight
• Although this set-point can migrate over time,
  from day to day it is remarkably fixed.

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Receptors and Effectors

• To achieve this task, the hypothalamus must
• receive inputs about the state of the body from
  nerve fibers/endings called receptors/sensors
• Send a response to these changes to nerve endings
  called effectors i.e. if anything drifts out of
  whack.

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Intrinsic Receptors

• The hypothalamus has some intrinsic receptors,
  including
• thermoreceptors (sense degree of hotness and
  coldness) and
• osmoreceptors (sense electrolyte balance).
• The hypothalamus sends signals to effectors
  (nerve endings that respond) which can control
  heart rate, vasoconstriction, digestion,
  sweating, etc.

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The Brain
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• We will concentrate on FOUR homeostatic
  processes
• thermoregulation
• osmoregulation
• blood glucose management
• waste management
• The first two and last two of these homeostatic
  processes are closely interrelated.

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Thermoregulation

• The process of keeping the body at a constant
  temperature.
• We are homiotherms (warm blooded).
• Heat is constantly produced through metabolism
  (25 remains in the body) and lost (75)
• If your body is in a hot or cold environment your
  body temperature is 37ºC.

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Thermoregulation

• Processes affected by temp.
• enzyme function, disease control, metabolic rate
• Body heat depends on metabolic rate (how the body
  uses nutrients, activity)
• At rest muscles produce up to 30 of our body
  heat (brain)
• During exercise, our muscles produce 40X more
  body heat than other tissues (only 25 efficient)
• Normal body temp. 98.6ºF or 37ºC

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Controlling body temperature

• Animals with a large surface area compared to
  their volume will lose heat faster than animals
  with a small surface area.

Volume _______ Surface area ______ Volume
Surface area ratio ___________
Volume _______ Surface area ______ Volume
Surface area ratio ___________
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Controlling body temperature
Volume Surface area 16
Volume Surface area 15
For every 1 unit of heat made, heat is lost out
of 6 sides
For every 1 unit of heat made, heat is lost out
of 5 sides
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Controlling body temperature
Volume Surface area 16
Volume Surface area 15
The bigger the Volume Surface Area ratio is,
the faster heat will be lost.
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Penguins huddling to keep warm
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THERMAL RANGESProfessor Alan Hedge, Cornell
University, January 2007

• SKIN (Shell)
• gt45C (gt113F) Burns
• 42C (108F) Pain
• 40C (104F) Uncomfortably hot
• 25C (77F) Uncomfortably cold
• 5C (41F) Numbness
• 0C (lt32F) Frostbite
• -0.6C (lt31F) Skin freezes

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BODY (Core)

• gt42C (108F) Fatal
• 41C (106F) Coma, convulsions
• 39.5C (103F) Upper acceptable limit -
  drowsiness
• 37C (98.6F) normal
• 35.5C (96F) Lower acceptable limit - mental
  dullness
• 34.5C (94F) Shivering diminishes - extreme
  mental slowness
• 33C (91F) Coma
• lt33C (91F) Deep Coma. Death
• 27C (81F) Heart stops. Death

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What mechanisms are there to cool the body down?

• Sweating
• When your body is hot, sweat glands under the
  skin are stimulated to release sweat.
• The liquid sweat turns into a gas (it evaporates)
• To do this, it needs heat.
• It gets that heat from your skin.
• As your skin loses heat, it cools down.
• animation

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Sweating
The skin
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What mechanisms are there to cool the body down?

• Vasodilation/Vasoconstriction
• Your blood carries most of the heat energy around
  your body.
• There are capillaries underneath your skin that
  can swell/dilate if you get too hot.
• This brings the blood closer to the surface of
  the skin so more heat can be lost.
• This is why you look red when you are hot!

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This means more heat is lost from the surface of
the skin
If the temperature rises, the blood vessel
dilates (gets bigger).
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What mechanisms are there to warm the body up?

• Vasoconstriction
• This is the opposite of vasodilation
• The capillaries underneath your skin get
  constricted/shrink (shut off).
• This takes the blood away from the surface of the
  skin so less heat can be lost.

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This means less heat is lost from the surface of
the skin
If the temperature falls, the blood vessel
constricts (gets shut off).
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What mechanisms are there to warm the body up?

• Piloerection
• This is when tiny muscles in the skin contract,
  causing the hairs on your skin stand up .
• It is sometimes called goose bumps or chicken
  skin!
• The hairs trap a layer of air next to the skin
  which is then warmed by the body heat
• The air becomes an insulating layer.

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What mechanisms are there to warm the body up?

• Shivering
• Muscles contract and expand in speedy bursts
  producing heat

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OSMOREGULATIONWater Regulation

• Water makes up 60 of total body composition, of
  this.
• Water is constantly required and removed.
• 73 of lean body mass (LBM) is composed of water
• essential for survival
• required for all cell functions
• used for thermoregulation
• major component of blood volume

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OSMOREGULATION

• Not enough water in the body dehydration.
• In dehydrated states, water is lost from the
  blood, electrolyte imbalance
• Too much water in the body edema (water
  retention swelling), electrolyte imbalance

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Homeostasis of Heat and Water

• Body temp. monitored by the hypothalamus.
• Skin surface
• 32 000 heat receptors/sq. inch
• concentrated in fingertips, nose, elbows, upper
  lip, chest.
• Brain and blood vessels contain the thermal
  receptors for sensing core body temperature

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Heat Loss Mechanisms at Rest

• Radiation at rest 60 of heat loss from a nude
  body
• Convection air movement past body. Two ways,
  natural (air molecules) and forced (eg. Fan) (up
  to 30 lost through head and neck)
• Evaporation water loss through skin 15 of heat
  loss

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Heat Loss Mechanisms at Rest

• Inhalation/Exhalation 10 loss of heat and water
  loss (exhalation)
• Conduction skin contact with objects such as
  chairs, floors, etc. about 3
• Excretion of urine and feces, both water (major
  component, 400 800 mL/event) and heat loss (3)
• Winter survival

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SWEAT BASICS

• Each sq. inch of skin has 32 000 nerve fibers, 98
  sebaceous glands 650 sweat glands
• Heat and emotions affect sweating
• Emotional tears are more toxic - healing
• Men sweat 50 more than women. Older people (esp
  males) and children sweat ineffectively

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Sweat Composition

• Eccrine glands produce sweat
• 99 water
• NaCl
• Other electrolytes
• traces of urea, lactic acid,
• fatty acids and proteins
• Colorless and odorless

http//www.sweathelp.org/English/PFF_Hyperhidrosis
_Overview.asp
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SWEAT BASICS

• Eccrine glands produce
• between 200 ml 10 L per day depending on
  activity level and climate
• 200 ml/hr at room temperature, and up to 1.5 L/h
  in extreme heat climates
• The greatest number of sweat glands are on the
  forehead, neck, back of hand, forearm, back and
  front trunk lowest on thighs, soles of feet,
  palms of the hands.

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Sweat Glands
E Epidermal Layer D - Dermis H Hair
Follicles G Sweat/Eccrine Glands S Sebaceous
Glands

• http//www.nature.com/milestones/skinbio/images/su
  bject_index_02.gif

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http//vrc.belfastinstitute.ac.uk/resources/skin/s
kin.htm
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Hair Follicle
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SWEAT BASICS

• Apocrine gland/ducts (sebaceous glands)
• Secrete protein, oils and water. These open onto
  hair follicles
• Highest density in underarms, nipples, pubic
  area, lips, chin and head, eyelids, outer ear.
• Bacteria decompose apocrine secretions (within an
  hour) and create individually characteristic
  body odor (BO)

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Sweat Exercise

• High intensity exercises or exercises lasting
  more than 1 h can result in 2.0 L/h of water loss
  (usually 1.0 L/h is more common).
• This depends on environmental conditions,
  humidity, clothing, intensity, fitness level, and
  acclimation to climate.

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Sweat Exercise

• 24 h prior to major activity
• consume fruits, veggies, and carbs to promote
  hydration.
• Avoid, caffeines, alcohols (which promote
  dehydration).

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Sweat Exercise

• 2 h before - 2 cups of water (not juice/pop)
• during more water about every 15 minutes.
• After (if over 1 hr) replace electrolytes
• (ie Gatorade which balances sugars, NaCl, and K
  ions lost through sweating).
• Make your own salt, fruit juice, water

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Other ways we lose heat and water

• Expectoration (cough) Sternutation (sneeze)
• Salivation Ejaculation
• Menstruation Parturition (Birth)
• Lactation Epilation (hair loss)
• Lacrimation (tears) Eructation (burps)
• Flatulation Regurgitation
• Spontaneous exanguination (blood loss)
• Sweat Gland Video clips
• http//www.britannica.com/EBchecked/topic/453087/p
  erspiration
• skin

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What Causes Prickly Heat
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Controlling Glucose levels

• Your cells also need an exact level of glucose in
  the blood.
• Excess glucose gets turned into glycogen in the
  liver
• Regulated by two pancreatic hormones
• Insulin
• Glucagon

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Glycogen
Too much glucose in the blood Insulin converts
some of it to glycogen
Insulin
Glucose in the blood
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Glycogen
Not enough glucose in the blood glucagon
converts some glycogen into glucose.
Glucagon
Glucose in the blood
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Diabetes

• Some people do not produce enough insulin.
• When they eat food, the glucose levels in their
  blood cannot be reduced.
• This condition is known as DIABETES.
• Diabetics sometimes have to inject insulin into
  their blood. They have to be careful of their
  diet.

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Glucose levels rise after a meal.
Insulin is produced and glucose levels fall to
normal again.
Glucose Concentration
Normal
Time
Meal eaten
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Glucose levels rise after a meal.
Glucose Concentration
Diabetic
Insulin is not produced so glucose levels stay
high
Time
Meal eaten
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The glucose in the blood increases.
Glycogen
But there is no insulin to convert it into
glycogen.
Insulin
Glucose concentration rises to dangerous levels.
Glucose in the blood
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Blood Sugar Feedback Loop
Liver Glycogen
Glucagon
Insulin
Blood Glucose
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http//dtc.ucsf.edu/types-of-diabetes/type1/treatm
ent-of-type-1-diabetes/how-the-body-processes-suga
r/the-liver-blood-sugar/
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Osmoregulation

• Control of water levels
• Carried out by the KIDNEYS.
• Closely linked to the excretion of urea.
• Waste product made when the LIVER breaks down
  excess proteins
• Why might you have to get up to go the washroom
  at night if you had a late night steak?
• Contains Nitrogen.

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The kidneys

• Cleans the blood of waste products
• Controls water retention
• Waste products and water make up urine
• excreted via the ureter.
• Dirty blood enters the kidney through renal
  artery and exits through renal vein
• Several things happen to clean the blood...

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1. Filtration
Blood enters the tubule area in a capillary.
The capillary forms a small knot near the
kidney tubule (glomerulus more about this
later).
The blood is filtered so all the small particles
go into the tubule.
The capillary then carries on to run next to the
tubule.
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The kidney tubule now contains lots of blood
components including Glucose Ions Water Ur
ea
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2. Reabsorb sugar
The body needs to have sugar in the blood for
cells to use in respiration. So all the sugar is
reabsorbed back into the capillary.
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2. Reabsorb sugar
The body needs to have sugar in the blood for
cells to use in respiration. So all the sugar is
reabsorbed back into the capillary.
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3. Reabsorb water
Water and ions are the next to be absorbed. It
depends on how much is needed by the body.
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3. Reabsorb water
Water and ions are the next to be absorbed. It
depends on how much is needed by the body.
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Reabsorbing water
If you have too little water in your blood, you
will produce very concentrated urine. (very
little water in it because most was reabsorbed)
If you have too much water in your blood, you
will produce very dilute urine. (lots of water
in it)
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5. Excrete the waste

• Everything that is left in the kidney tubule is
  waste
• All the urea
• Excess water

This waste is called urine. It is excreted via
the ureter and is stored in the bladder.
The clean blood leaves the kidney in the renal
vein.
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Summary of urine production

• Urea is a waste product made in the LIVER.
• Water content of the body is controlled in the
  KIDNEYS.
• Urea, water and other waste makes up URINE.
• Urine travels down the URETER and is stored in
  the BLADDER.
• Urine is excreted through the URETHRA.