Tuesday, December 4, 2007

Regulating The Internal Environment Part 2

~Maintaining Homeostasis~

Homesostasis in the body is maintained through a series of different actions trigured by different internal and external stimuli.

The Negative Feedback Loop is one of the most essential actions. It starts with a stimulis, sensors within the body monitor these changes and immdeiately send information to the corresponding intergrating sensor such as an organ or a gland. From there chemicals are released to return the condition to its normal state. Once the response is complete sensors stop sending information and the chemical is stopped, thus allowing the system to enter a state of rest until it must perform its' function again.

An example of this is the action your body goes through when you are threatened or excited. The pituitary gland releases a hormone that causes your adrenal glands to release adrenaline which allows your body to perform basic functions at a heightened level. Adrenaline effects your heartrate and general awareness, giving you abilities that you don't normally have.
The endocrine system also plays a large role in regulating homeostasis. Blood pressure and osmolarity are regulalted by the endocrine system, specifically the brain and kidneys. The pituitary gland monitors these conditions and when something happens to the levels of either osmolarity or BP then action is immediately taken.

-If blood osmolarity rises to high meaning it becomes hypertonic the pituitary gland trigures the release of an anti-diuretic hormone a.k.a. ADH. This increases the permeability of the collecting ducks in the kidneys allowing for increased water absorption. This dilutes the blood bringing it back down to a more stable level.

-If blood pressure drops too low renin is released which removes part of the protein angiotensinogen already found in the blood exposing its' reaction site allowing it to cause the kidneys to release aldosterone. This causes increased water and salt absorption replacing missing components of the blood so pressure is restored.

The other key system to maintaining homeostasis is the

Nervous System.

The most important cell of the nervous system is the neuron. The neurons in the body work very similar to a line of dominoes. A signal starts the reaction like knocking over the first one. A wave is then sent through each single cell until it reaches its predetermined destination. The only way it can occur again is if you reset the axons in a neuron or the lines of dominoes.

Nerve cell live in a sea of charged ions. Ions with negative charges (anions) are found more within the cell, and ions with positive charges (cations) are more common outside the cell. When a nerve is stimulated Sodium channels in the cell membrane open allowing the diffusion of positively charged ions into the cell. At this point the charge on the cell is reversed. Following the first wave another wave of channels is opened this time allowing cations to move out of the cell causing the repolarization of the nerve cell. This is the way messages are sent from anywhere in your body to your brain within milliseconds. After all channels have been closed again and the cell is stabalized it is ready to fire again.

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