HOMEOSTASIS


  • Feedback Loops: Organisms respond to changes in their bodies with processes that will bring their bodies back to normal (homeostasis).


NEGATIVE FEEDBACK LOOP 

Stimulus: spark a change in the variable

Receptor: sensor, detects the change in variable 

Input: sending the sensed information to the brain

Output: going out of the brain to tell the effector

Effector: decides what the response to the change should be

Response: The effector feeds back to the variable to make it back into homeostasis

Homeostasis: When your body functions properly

Counteractive response: the variable that made it unbalanced in the first place causes a counteractive response that counters that unbalanced variable to return back to the straight line (into homeostasis)


  1. What is a NEGATIVE feedback loop?

  • A negative feedback loop is when (returns to a median value - set point) there is a variable that causes a counter-reaction turning the body back to homeostasis.

  1. Use the trend in the data to describe how the data demonstrates negative feedback:

  • When there’s an imbalance everything goes crazy, until the control center and receptors (sensors) bring it to a balanced point, so it returns to its homeostasis.


POSITIVE FEEDBACK LOOP


The variable is more intensified  allowing the response to be as sudden.

Ex: a baby pushing on the cervix → causes more hormone which in turn causes a LOT OF CONTRACTIONS`


  1. What is a POSITIVE feedback loop?

  • A positive feedback loop (also a cascading effect) allows an organism (severity → from an intensified variable) to return to its homeostasis in a more intensified way.

  1. Use the trend in the data to describe how the data demonstrates positive feedback:

  • Factor 2 went up more since the (mL) was an intensifying variable due to the abundant amount of it reflected positively over time.


Sohan Remarks:

Keywords: Cascading, intensifying, severity

NOT going back to a set point


Performance Task 3: How do the body systems work together to maintain homeostasis?


Body Temperature:

  1. Imagine you are outside on a hot hot summer day, what will your body start to do?

SWEAT

  1. Now imagine there is a fire drill right now and you are standing around the oval and you don’t have a jacket on, what will your body start to do? SHIVER

  2. This is called “thermoregulation.” Take apart the word and figure out its meaning:

  1. The prefix thermos mean: temperature or heat

  2. The ending regulation means: ability to maintain or control

  3. So thermoregulation in our body would be: the body’s ability to control or maintain a stable internal temperature.

 

  • Endotherm: (warm-blooded) needs to maintain an internal temperature. 

  • Ex. humans (any mammals)

  • Ectotherm: (cold-blooded) temperature fluctuations do not need to maintain a constant internal body temperature.

  • Ex. snakes (reptiles)



Blood Clotting:

  1. Imagine that the corner of the paper made a cut on the skin of your finger. The cut will make you bleed until a clot forms.

  2. Platelets and fibrin are two components that form a clot. Platelets are enucleated cells (a cell that had its nucleus replaced with a different nucleus) fragments in the bloodstream. Fibrin (made from a fibrinogen protein found in a blood vessel) is a protein in which its strands help in weaving the clot together.

  3. This is how the process works. In the blood plasma, there is an enzyme named thrombin.

  4. The collagen protein outside of the broken blood vessels has a tissue factor that activates the thrombin enzyme. The activation of just one thrombin enzyme signals a cascading effect of many activated rapidly turning many fibrinogen proteins into many strands of fibrin.

  5. The many strands of fibrin and platelets stick together to form a matrix, hence forming a clot.


Spiked platelets: Make the sticky stuff to stick the platelets and fibrin strands together 



Blood Glucose: 

  1. If you haven’t eaten in a while, you will start to feel hungry/dizzy, making you want some food in your body.

  2. Imagine you don’t have access to food(maybe if you're in class for a long time) you may start to feel tired/weak. 

  3. The main energy molecule your body needs in order to make ATP(energy needed by cells) is glucose.

  4. If you do not get enough food into your body over a long period of time, your body starts to look for a new source of energy and may begin to break down your fats, in this way your body constantly has a source of energy.

  5. What do you think would happen if you eat lots of and lots of sugar and have too much glucose?

→ Stored as glycogen (a complex sugar that stores glucose, the body’s main source of energy, for later use).

  1. When glucose levels are low in the bloodstream, the alpha cells in the pancreas release glucagon. When the liver detects glucagon in the bloodstream, it breaks down the stored molecule, glycogen, into glucose for the bloodstream.

  2. When glucose levels are high in the bloodstream, the beta cells in the pancreas release insulin. With insulin in the bloodstream, the glucose can get absorbed by body cells to make ATP and/or the liver releases an enzyme, glycogen synthase, to make glycogen, a chain of glucose molecules for storage. The glycogen molecules can be delivered to the liver, muscle cells, or fat cells as storage. 




Feedback systems in your body - class notes


Feedback systems have 3 key features:


  1. A receptor that can evaluate the stimulus(change in environment) and sends a message to…

  2. An integrator/control center (brain) that processes the information and sends a message to…

  3. An effector that acts on the stimulus and causes a response (reaction) in the organism


  • Feedback Loops can be NEGATIVE or POSITIVE, based on the response to the stimulus. Most feedback loops in living things are negative. 



  1. What is an example of a NEGATIVE feedback loop?

  • An example would be you shivering on a cold winter day which is a counteractive response to return back to homeostasis.

  1. Describe the process: A variable that causes a body to go out of homeostasis and then react with a counteractive response to be put back.

  2. What is an example of a POSITIVE feedback loop?

  • An example of this would be a baby pushing on a mother’s cervix causing an overload of hormones → causing more contractions which is a MORE intensifying response.

  1. Describe the process: A variable that causes a reaction and countless more intensifying ones to return back to homeostasis in a body.


Performance Task 4: What do acids and bases have to do with homeostasis?


DISSOCIATION OF WATER

Water molecules themselves can break apart and form ions, but this is very rare. The majority of water molecules in any sample of water are covalently bound together. Only approximately 2 in a billion of water molecules in any sample will dissociate. This process is also reversible.







  1. When it dissociates, the proton breaks away, but the electron is left behind with the remaining OH. This single proton is also called a hydrogen ion (H+) 


  1. The remaining OH- that is left after the hydrogen ion breaks away is referred to as the hydroxide ion. 


  1. In pure water, the number of hydrogen ions would equal the number of hydroxide ions. This results in a neutral solution.

Ex: If a beaker of pure water has 50 hydrogen ions, then it will have 50 hydroxide ions. 

(50 hydrogen ions = 50 hydroxide ions)

  1. The free hydrogen ion is attracted to another water molecule which forms a hydronium ion. (H3O) 2 water molecules + hydrogen ion = hydronium ion








ACIDS

Acid - a substance that increases the H+ ion concentration in water. Since an acid is a substance that adds H+ ions to a solution when it dissociates it is called a hydrogen ion donator. When acids add H+ are attracted to water molecules and form hydronium ions (H++H2O → H3O+). Acids increase the number of hydronium ions (H3O+) in a solution. The H+ also binds to OH- forming H2O. This decreases the OH- ions.

HCl →← Na+  +  OH-


BASES

Bases - a substance that decreases the H+ concentration (or the hydronium ion concentration-H3O+) of a solution. A base can attract the extra proton on the hydronium ion which results in the production of a water molecule. Because the hydronium ion concentration decreases we tend to say that the hydrogen ion concentration has decreased. Bases are therefore called hydrogen ion acceptors.


Notes: Acids lower the pH of a solution because an increase in hydrogen ions lowers pH. Ex. if a pH of a solution goes from 7 to 4 the hydrogen ion concentration has increased.

Many bases donate hydroxide ions which bind to (accept) hydrogen ions.

Examples:

NaOH → Na+   +    OH- NaOH dissociates in water.


OH-  + H3O+(H+)  → 2 H2O

The hydroxide ion (OH-) accepts a H+ ion and water is formed. This reduces the concentration of H+ (H3O+) in the solution.



Note: Not all the bases release hydroxide ions but they can accept and bind to hydrogen ions: ex. Ammonia (NH3) is a base.


NH3 +  H3O+ (H+) → NH4  + H2O   

 NH3 accepts a H+ ion and water is formed. This reduces the concentration of H+ (H3O+) in the solution


Note: Bases raise the pH of a solution because decrease in hydrogen ions raises pH. Ex. if the pH of a solution goes from 7 to 10 hydrogen ions concentration has decreased.


MORE ON BASES AND ACIDS


Some acids and bases are considered to be strong, and some considered to be weak. Strong acids or bases tend to dissociate completely into separate ions, while weaker acids or bases tend to only partially dissociate. In other words, some of the acidic or basic compounds will remain intact (not dissociate) in water. This would put fewer hydrogen ions or hydroxide ions into solution, which would make it weaker acid or base solution. Hydrochloric acid (HCI) is a strong acid, which dissociates completely, and sodium hydroxide is a strong base, which also dissociates completely. 


Strong acids completely dissociate in water, forming H+ and an anion (negative ion leftover from the dissociation of H+). There are only six strong acids (don't memorize these) (Note: all others are considered weak acids) 


Strong bases dissociate 100% into the cation and OH- (hydroxide ion). 


Weak bases do not provide OH- ions by dissociation. Instead, they react with water to generate OH- ions. • Ammonia (NH,) is an example of a weak base. 

Ex. NH, + H,0 <=> NH4+ + OH Remember, the term "alkaline" can also be used to refer to basic substances



Properties of Water


The water molecule is polar. 

It has a (+) side and a (-) so that it can attract each other like magnets.

Most of the electrons hang out around oxygen in the middle, so the oxygen is slightly negative (-).

The hydrogens are slightly positive (+).

This attraction leads to a Hydrogen bond (not as strong as covalent bonds and ionic bonds).

Hydrogen bond - the attraction between a hydrogen atom with a slightly positive charge and another atom with a negative charge.


Hydrogen bonds gives water specific properties:

Universal Solvent

Cohesion

Adhesive

Surface Tension

Capillary

Density

pH



PIVOT INTERACTIVE: