Biology‎ > ‎

Homeostasis.

posted Jan 27, 2015, 10:00 PM by ranmini@charliesresearch.com   [ updated Sep 14, 2017, 10:51 PM by Upali Salpadoru ]






Fig.1. Homeostasis is maintaining  a balanced internal environment..

°


    Life originated in water. The reptiles, mammals, and birds  evolved from the adventurous creatures that migrated into an aerial environment. 
    These animals have developed very efficient body structures and miraculous physiological trends, yet every living cell in their bodies still has to be bathed in a liquid medium. 
     Unlike in the sea the environmental conditions on land fluctuate  much more. In spite of these changes, the ability to maintain the consistency of the body fluid has been termed ‘homeostasis’


.  Homeostasis of Temperature

Animals capable of temperature regulation are called homotherms. They achieve this by taking corrective action. [Such actions are called negative feed back.]

Heres how they do it.

The hypothalamus acts as a receptor  in regulation, by detecting changes in body temperature. [These receptors are better known as thermo-receptors.)

  • Skin also possesses thermo-receptors  which can detect the temperature of the external environment.
  • This information is then relayed to the hypothalamus which can in turn transmit nerve pulses for corrective actions.

Corrective actions to lose heat. [Negative feed back]

  • Increased sweating will donate a lot of heat for the water to evaporate from the skin.. [Latent Heat}
  • Vasodilation , where the blood vessels close to the skin surface become enlarged, giving a larger surface area for heat to be lost to the external environment from the blood vessel carrying over-heated blood.
  • Erecting hair to lose heat.
  • Drop in metabolic rate. [ Low cellular activity]

Actions to conserve heat    [This is also negative feed back.]

  • Reduce sweating.
  • Vasoconstriction:Reduce blood flow to the skin.
  • ‘Hair stands on end’ A layer of air between the hair and the skin gets trapped.. This insulation of warmer air next to the skin reduces heat lost.
  • Shivering. [Increased metabolic activity]
Temperature fluctuations.

Fig.2. A man need not worry.

1.  Homeostasis of Temperature.

    The average temperature of a human being is 37° C. It is quite  normal to fluctuate it between 35°. and 38°. The body can make adjustments to lower it from a maximum of 41. 

Once these limits are passed there can be positive feedbacks that can lead to death.

  

 Corrective actions are called negative feed back

 Positive feed backs are actions  that can upset a steady state

Fig.2
Positive Feed back

These actions will make things worse.
A temperature above 41. or below 35 will induce positive feed backs. A high temperature will produce a higher rate of metabolism which will further increase the temperature and even cause the death. Lowering of temperature excessively will make metabolism almost impossible and cause the condition known as hypothermia.

                                                                       Fight or Flight  …..A positive feed back


In emergencies, adrenaline is released by the body to fight or  'flight reactions'.
Adrenaline is secreted by the adrenal glands. The secretion of it leads to increased metabolism, breathing and heart rate. Once the emergency is over, and adrenaline levels drop, the homeostatic controls prevail.

2.   Homeostasis of Water …Osmoregulation


Osmoregulation is the regulation of water concentrations in the bloodstream, effectively controlling the amount of water available for cells to absorb. Osmoreceptors that are capable of detecting water concentration are situated on the hypothalamus.

#

1

2

3

4

5

Marks

1.0

90 mg.

Eating

Insulin

Release glucagons.

Glycogen

10

2.0

d

c.

b.

e

b.

10


  • The hypothalamus sends chemical messages to the pituitary gland next to it.
  • The pituitary gland secretes anti-diuretic hormone (ADH), which targets the kidney responsible for maintaining water levels. If more water is required in the blood stream, high concentrations of ADH make the tubules more permeable.
  • When the hormone reaches its target tissue, it alters the tubules of the kidney to become more / less permeable to water.
  • If less water is required in the blood stream, low concentrations of ADH make the tubules less permeable
3.   Blood / Sugar Homeostasis



Pancreas Receptors

The receptors of the pancreas are responsible for monitoring glucose levels in the blood, since it is important in every cell for respiration.
Two types of cell release two different hormones from the pancreas, insulin and glucagon. These hormones target the liver, one or the other depending on the glucose concentration
  • In cases where glucose levels increase, less glucagon and more insulin is released by the pancreas and targets the liver
  • In cases where glucose levels decrease, less insulin and more glucagon is released by the pancreas and targets the liver

The Liver

The liver acts as a storehouse for glycogen, the storage form of glucose. When either of the above hormones target the liver, the following occurs
  • Insulin - Insulin is released as a result of an increase in glucose levels, and therefore promotes the conversion of glucose into glycogen, where the excess glucose can be stored for a later date in the liver
  • Glucagon - Glucagon is released as a result of an decrease in glucose levels, and therefore promotes the conversion of glycogen into glucose, where the lack glucose can be compensated for by the new supply of glucose brought about from glycogen
Diabetes

Diabetes insipidus is a condition where excess urine is excreted caused by the sufferers inability to produce ADH and promote the retention of water.

Diabetes Mellitus is another form of diabetes where the sufferer does not have the ability to produce sufficient insulin, meaning that glucose cannot be converted into glycogen. Anyone who has this condition usually has to take injections of insulin after meals and snacks to maintain their storage of glucose needed in emergencies.

 

Question 1.0

1.    What is the mass of glucose on 100cm3 of normal blood?
2.    What can make the normal blood sugar level to increase in a healthy person?
3.    What is the hormone, secreted by pancreas, that can bring about a negative feed back when the glucose level rises?
4.    What is the expected negative response when fasting?
5.    Name the product formed as a result of the above negative response.


Question 2.0

1. Which of the following is the best definition of homeostatis.?

  1. Control of temperature.
  2. Control of water and ions.
  3. Independence of the external environment.
  4. Maintenance of a constant internal environment.
  5. Maintenance of constant body functions by the external environment.

2. Which of the following is a physiological method of cooling the body?

  1. sitting in an air conditioned room.
  2. Taking a cold shower.
  3. Producing more sweat on the skin.
  4. Drinking hot tea.
  5. Eating less food.

3. Which of the following will lose heat at a faster rate?

  1. Tall thin men in the tropics.
  2. Tall thin men in the Arctic.
  3. Short fat men in the tropics.
  4. Short fat men in the Arctic.
  5. Short thin men in the tropics.

4. An increase in the CO2 concentration in the blood of a man results in ………

a.          negative feed back and a slower breathing rate.

b.          Positive feed back and a slower breathing rate.

c.          No feed back and normal breathing rate.

d.          Positive feed back and a faster breathing rate.

e.          Negative feed back and a faster breathing rate.

5.0  Which one of the following will aid the heat loss on a hot day?

 

a.        Subdermal fat.

b.        Dermal blood vessels.

c.        Light clothing.

d.        Hair.

e.        Sebaceous glands.

 

#

1

2

3

4

5

Marks

1.0

90 mg.

Eating

Insulin

Release glucagons.

Glycogen

10

2.0

d

c.

b.

e

b.

10


#

1

2

3

4

5

Marks

1.0

90 mg.

Eating

Insulin

Release glucagons.

Glycogen

10

2.0

d

c.

b.

e

b.

10

The body requires volumes of glucose in order to create ATP. The amount of ATP demanded will fluctuate, and therefore the body regulates the availability of glucose to maximise its energy making potential.

Comments