This document discusses homeostasis and negative feedback mechanisms in the human body. It explains that homeostasis is the process of maintaining a constant internal environment through negative feedback loops. The hypothalamus acts as a control center, detecting changes in factors like temperature and blood sugar levels. It then stimulates responses to restore balance, like vasodilation/constriction, sweating, shivering or glucagon/insulin secretion. Negative feedback mechanisms work to regulate temperature, blood sugar levels, and water content in the body.

1. HOMEOSTASIS
NEGATIVE FEEDBACK MECHANISMS

2. WHAT IS HOMEOSTASIS?
• Homeostasis is the process of maintaining a constant internal
environment within the body.
• Core body temperature is normally 37°C no matter what the
temperature of the surroundings or the activity level of the
individual. It is controlled by a negative feedback system.
• The hypothalamus is the temperature-regulating centre of the brain.
It contains receptors which are sensitive to the temperature of the
blood flowing through the brain.

3. NEGATIVE FEEDBACK MECHANISM.
• Negative feedback mechanisms operate in the human body to detect
changes or imbalances in the internal environment and to restore the
balance.
• GENERAL SEQUENCE OF NFM.
• An imbalance is detected
• A control centre is stimulated.
• Control centre responds.
• Message sent to target organs/s.
• he target organ responds.
• It opposes/reverses the imbalance.
• Balance is restored.

4. TEPARATURE REGULATION IN THE BODY:
WARM.
• ON A HOT DAY the hypothalamus is stimulated and sends impulses
to the blood vessels. Blood vessels dilate (become wider). This is
called vasodilation.
• The hairs of the body lie flat to avoid trapping an insulating layer of
air.
• More blood flows to the skin.
• More heat is lost from the skin.
• More blood is sent to the sweat glands.. Sweat gland becomes more
active. More sweat is released. Evaporation of the sweat cools the
skin.

5. COLD TEMPARATURE.
• ON A COLD DAY the hypothalamus is stimulated and sends
impulses to the blood vessels Sweat gland becomes less active.
Less sweat is released. There is less evaporation of sweat and
less cooling of the skin. Blood vessels constrict (become
narrower). This is called vasoconstriction.
• the hairs are raised by small muscles to trap a layer of air near the
skin giving the appearance of goose bumps. Air is an insulator so
this helps to keep heat in. Shivering starts, when the muscles
contract fast and involuntarily. This produces more heat and,
during shivering, there is usually an increase in the rate of
respiration, which also warms the surrounding tissues.
• Less blood flows to the skin.
• Less heat is lost from the skin.
• Less blood is sent to the sweat glands.

6. MAINTAINING THE BLOOD SUGAR LEVEL.
• THE HORMONE INSULIN IS REPONSIBLE FOR LOWERING THE GLUCOSE LEVELS
IN THE BLOOD.
• WHEN GLUCOSE LEVELS ARE TOO HIGH INSULIN REDUCE GLUCOSE LEVELS
BY.
1. PROMOTING ABSORBTION OF GLUCOSE INTO CELL, FOR USE IN CELLULAR
RESPIRATION.
2. IT STIMULATE THE LIVER AND MUSCLES TO CONVERT GLUCOSEINTO
GLYCOGEN, FOR STORAGE ON THE LIVER AND MUSCLES.
- SOME PEOPLE HAVE A SHORTAGE OF THE HORMONE INSULIN PRODUCTION,
THIS COUD BE DUE TO DAMAGE OR DISEASES IN THE BETA CELLS OF ISLETS
LANGERHAN, SUCH PEOPLE SUFFER FROM DISEASE CALLED DIABATES
MELLITUS.
1.WHEN THE BLOOD SUGAR IS LOW AND IN EMERGANCY SITUATION, THE
HORMONE GLUCAGON INCREASE THE BLOOD GLUCOSE LEVELS BY
CONVERTING STORED GLYCOGEN FROM THE LIVER OR MUSCLES INTO
GLUCOSE.

7. MAITAINING WATER LEVELS
(OSMOREGULATION)
• WHEN THE BODY HAS LOST TOO MUCH WATER ( FOR AN EXAMPLE
AFTER A STRENUOUS ACTIVITY ON A HOT DAY)
• THE VOLUME OF WATER IN THE BLOOD DECREASE.
• OSMORECEPTORS ON THE HYPOTHALAMUS ARE STIMULATED AND
THE MASSEGE IS SENT TO THE PITUTARY GLAND WHICH SECRET
MORE ADH, THE WALL OF THE DISTAL CONVULATED TUBULE AND
COLLECTING TUBULE BECOME MORE PERMEABLE.
• MORE WATER WILL BE RE-ABSORBED AND THE AMOUNT OF WATER
IN THE BLOOD THUS INCREASE, CONCETRATED URINE IS FORMED
AND LESS WATER IS EXCRETED FROM BODY.

8. OSMOREGULATION.
• WHEN THE BODY HAS ACCUMULATED TOOO MUCH WATER.( FOR AN EXAMPLE
ON A COLD DAY DURING INACTIVITY OR TOO MUCH LIQUID HAS S BEEN TAKEN
IN.
• THE VOLUE OF WATER IN THE BLOOD INCREASE.
• OSMORECEPTORS IN THE HYPOTHALAMUS ARE STIMULATED AND THE
MESSAGE IS SENT TO PITUTARY GLAND WHICH SECRETS LESS ADH INTO BLOOD.
• THE WALLS OF DISTAL CONVULUTED TUBULE AND COLLECTING TUBLES
BECAOME LESS PERMEABLE.
• THIS WILL CAUSE LESS WATER TO LEAVE THE TUBULES BY OSMOSIS AND ENTER
THE MEDULLA AND THE SMALL AMOUNT OF WATER ISNOT QUICKLY RE-
ABSORBED BY BLOOD CAPPILLARIES.
• WATER IS EXCRETED FROM THE BODY IN THE FORM OF VERY DILUTED URINE.