REGULATION OF INTERNAL ENVIRONMENT
The body fluids which include the blood, the lymph and the intercellular or tissue fluids surround the cells of
the body. They constitute the internal environment of the living organism. The composition and concentration
of these fluids must be kept fairly constant to keep the body healthy and maintain proper growth and proper
functioning of the cells.
The maintenance of a steady internal environment is called Homeostasis.
What is Homeostasis ?
The maintenance of a constant or steady internal environment by organisms in spite of the changing external
environment.
The organs involved in the maintenance of a steady internal environment are called homeostatic organs.
Homeostatic organs includes:
i.
ii.
iii.
iv.
Kidneys
Liver
Skin
Endocrine system.
PRINCIPAL OF HOMEOSTASIS/NEGATIVE FEEDBACK MECHANISM
STIMULUS
(CHANGES IN INTERNAL
ENVIRONMENT)
RECEPTOR
( DETECTS CHANGES IN
THE ENVIRONMENT)
CONTROLLED
MECHANISM
NEGATIVE
FEEDBACK
NORMAL
CONDITION
THE KIDNEYS
The kidneys performs two main functions in the body of vertebrates including humans;
1. Excretory functions
2. Osmoregulatory functions
As an osmoregulatory and excretory organ, it performs the following functions;
a) It removes toxic wastes and harmful substances
b) It produces heat during cold
c) It regulates nitrogeneous waste like urea
d) It regulate water level in the body
e) It assists to regulate pH of the body
f) It maintains salt or ion – balance in the body
The first three are excretory functions while the last three are osmoregulatory functions of the kidneys.
OSMOREGULATORY FUNCTIONS OF THE KIDNEYS
- Maintenance of Water Balance
When the solute concentration of blood increases either by ;
consumption of too much salt,
drinking of too little water,
profuse sweating,
or a combination of all the three, it leads to an increase in the osmotic pressure of the blood . This
condition, that is high osmotic pressure of the blood is picked up by the osmoreceptors in the
hypothalamus region of the brain which then sends impulses which are transmitted to the posterior
pituitary gland.
-
-
The posterior pituitary gland is stimulated to produce anti – diuretic hormone (ADH).
This is transported to the kidneys through the blood stream.
The ADH causes an increase in water re-absorption from the filtrate by the kidneys tubules into the
blood. This reduces the osmotic pressure of the blood and this continues until the osmotic pressure of
the blood becomes normal.
The normal osmotic pressure is also picked up by the osmoreceptors in the hypothalamus which stops
the sending of impulses to the posterior pituitary gland, and production of ADH is equally stopped.
This process is known as homeostatic feedback mechanism.
Thirst is a sensation that indicates high osmotic pressure of the blood and hence, the need to drink
more water. The intake of water will help regulate the osmotic pressure of the blood.
When the body is hydrated ( too much water in the body ) which results from drinking a large quantity
of water or on cold days when we sweat less, the osmotic pressure of the blood is lowered and less
ADH is secreted and the wall of the kidneys becomes less permeable and more water is lost from the
body as dilute urine.
Regulation of Sodium level.
If the sodium ion level in the blood is low, the brain stimulate the production of the hormone
aldosterone by the adrenal cortex. This hormone stimulate the active uptake of sodium ions from the
glomerular filtrate by the distal convoluted tubules and collecting ducts into the blood. When the
sodium ion of the blood is higher than normal, the excess is passed out with urine.
Regulation of blood pH
The normal pH of the blood is almost neutral, about 7.4. If the pH of the blood rises above 7.4 and
becomes alkaline, the hydrogen trioxocarbonate (IV) ions which makes the blood alkaline are excreted
while hydrogen ions are retained in the distal convoluted tubules. This will lower the pH of the blood
while alkaline urine is produced.
If however the pH is low, that is slightly acidic, hydrogen ions are excreted while hydrogen
trioxocarbonate (IV) ions are retained . This leads to the production of acidic urine and an increase in
the blood pH.
FACTORS THAT AFFECT THE FUNCTIONING OF THE KIDNEYS.
1. Change in optimum temperature of the environment.
2. Change in normal habitats.
3. Drugs intake.
4. Diseases.
DISEASES OF THE KIDNEYS
1. Nephritis : The inflammation of the blood vessels in the Bowman’s capsule of the nephron caused by
bacteria. The blood vessels become porous and useful materials from the blood are leaked into
glomerular filtrate.
2. Diuresis : This is a condition in which large quantities of dilute urine are produced because the cells of
the kidneys are not reabsorbing water from the glomerular filtrate. This condition is common in
patients suffering diabetes insipidus( production of large quantity of dilute urine )
3. Kidney stones : These are stony masses of materials and organic matter formed in the urinary tubules.
Low water intake with high salt consumption predisposes someone to this disease by causing
crystallization of mineral salts which disturb the free flow of urine.
4. Dropsy (oedema) : This is a condition in which the cells of the Bowman’s capsule are unable to absorb
water from the blood in the urinary tubules. This causes water retention in the blood resulting to
swelling of some body parts.
REMEDY TO KIDNEYS DISEASES
1. Use of drugs e.g antibiotics ( nephritis), diuretics ( oedema )
2. Kidney transplant ( diuresis, nephritis )
3.
4.
5.
6.
7.
8.
Dialysis: use of dialysis machine ( artificial kidney) to filter waste out of the patient’s blood.
Reduction in water intake (oedema )
Taking excess water, and avoiding excessive intake of food containing calcium (kidney stone )
A surgical operation called nephrectomy (kidney stones)
Dietary control
Rest and warmth.
THE LIVER
The liver is the largest organ in the body of a mammal with a weight of about 1.25kg. It is reddish brown, soft
with two lobes and it is located below the diaphragm on the right side of the abdomen. It partly overlaps the
stomach and has bile duct connecting it to the duodenum. The duct is attached to the gall bladder. The liver
gets supply of blood from the hepatic artery and hepatic portal vein. This makes the liver the only organ in the
body that receives blood from two sources. Blood is drained from the liver by the hepatic vein.
Structure of the Liver
FUNCTIONS OF THE LIVER
The liver performs homeostatic functions and also receives digested food from the intestine, screens it and
release the amount needed by the body into the circulatory system.
The functions include the following;
a) Regulation of blood glucose level
The blood glucose level of a healthy person is 90mg/100cm3. A level higher than the started, it is
termed excess. Excess glucose is converted to glycogen under the control of the hormone called
insulin. With low glucose level, glycogen is converted to glucose under the influence of hormone,
glucagon. Both insulin and glucagon are produced by the pancreas.
b) Regulation of blood protein
The liver regulates the amount of amino acid in the blood by releasing the amount required by the
body into the blood. Excess amino acid is broken down into amino group and carboxylic acid. The
amino group is converted to urea which is excreted by the kidney and the sweat glands. The carboxylic
group is converted to glycogen and stored in the liver.
This process is called deamination.
c) The liver also manufacture essential blood proteins like fibrinogen, prothrombin, globulus which are
involved in blood clothing.
d) Lipid metabolism
The liver converts fats to glucose to be oxidised to release energy in case of shortage of glucose in the
body. The liver also converts excess glucose to fats for storage.
e) Production of bile.
The bile is mainly water, bile salts , bilirubin, inorganic salts and cholesterol. The bile is stored in a gall
bladder. The function of the bile is for emulsification of fats.
f) Formation of red blood cells in foetus and breakdown of red blood cells in adult.
g) Storage of vitamins
The liver stores vitamins A, B, D, E and K in its cells and release them into the blood streams when they
are required by the body.
h) Storage of minerals
The liver stores minerals like iron, potassium, copper and zinc in its cells.
i) Storage of blood
The liver stores up to 1,500cm3 of blood. It also regulates blood volume and pressure in general
circulation.
j) Production of heat
The liver, because of its numerous metabolic activities, generates a lot of heat which is passed round
the body to help maintain the body temperature.
k) Inactivation of hormones
The liver inactivates excess hormones, thereby ending their period of activities.
l) Detoxification
The liver converts toxic compounds like alcohols, drugs, food additives into harmless compounds
which are passed out of the body with urine.
DISEASES OF THE LIVER
i.
Hepatitis : This is the inflammation and destruction of the liver cells. This is caused by a virus and
is spread through contaminated food, water, infected blood and sharing of sharp objects.
ii.
Liver cirrhosis : This is a liver condition in which the liver becomes hard and stiff. The damaged
liver cells are replaced by useless fibrous tissues. It may be caused by prolonged consumption of
toxic substances like excessive drinking of alcohol. It can also be caused by viral infection or
untreated hepatitis.
iii.
Gall stones: These are stony masses formed in the gall bladder or bile duct. These are mostly
precipitation of cholesterol. The gall stones obstruct the flow of bile, subjecting the gall bladder to
infections.
iv.
Amoebic liver abscess: This infection is caused by Entamoeba histolytica, the same parasitic
amoeba that causes amoebic dysentery. It is usually transported with digested food from the small
intestine to the liver through the hepatic portal vein.
v.
Cancer of the liver: This is a malignant growth of the liver. It is also called carcinoma. The growth
sends out a network of long processes much like the limbs of a crab. This growth prevents the liver
from carrying out its normal functions.
vi.
Jaundice: Caused by increase in the blood bilirubin level due to excessive breakdown of red blood
cells . The symptoms of jaundice is yellowing of skin or eye white.
REMEDY
The liver cells have the natural capacity of regenerating ( dividing and producing new cells ). The liver can
therefor heal itself with the aid of the following procedures:
1. A long period of bed rest
2. Low fat controlled diet
3. Avoiding drinking alcohols
4. Removing the cause of the disease
5. Liver transplant can be done in progressive liver cirrhosis and cancer of the liver
THE SKIN
The skin is the largest organ of the body which forms the outer covering of many animals especially the
vertebrates. It is the toughest tissue in the body after the bones and the cartilages. An average skin is between
1 – 2 mm thick. The skin is either naked as in amphibians or covered with scales as in fishes and reptiles or with
feathers as in bird or with hairs as in mammals.
The Structure of the Skin
The mammalian skin consists of two main layers; the epidermis and the dermis.
I.
The Epidermis
The epidermis is the first layer of the skin which varies in thickness depending on the part of the
body. It consists of three sublayers namely;
a) Cornified layer
b) Granular layer
c) Malpighian layer
A) Cornified layer
This is the outermost layer of the epidermis which consists of dead cells, fats and deposits of
keratin pigment. The keratin makes the layer tough, flexible and water – proof; it prevents
microbial entrance as well as reduces water loss from the body.
B) Granular layer
This is a layer under the cornified layer. It consists of round living cells. These cells are
constantly being pushed up by the new cells produced by the malpighian layer under it.
C)
II.
Malpighian layer
This is third sub – layer of the epidermis called the germinative layer because it consists of
actively dividing long and narrow meristermatic cells. The malpighian layer contains the
pigment melanin, which gives colour to the skin. It also absorb harmful ultraviolet rays from
the sun. This prevents the skin/body from injury. The pigment melanin is lacking in the skin
of albinos.
The malpighian layer folds inward in many places and sometimes penetrating deep into
the dermis to form the hair follicles and the sebaceous glands.
The Dermis
The second layer of the skin, the dermis, is much thicker than the epidermis. It composed mainly
of connective tissues, these include;
A) Blood capillaries
A network of blood capillaries is found in the dermis. They supply food and oxygen as well as
remove waste.
B) Sweat glands
These glands begin as coiled tubes called sweat glands deep down the dermis and continue as
straight tubes called the sweat ducts and open outside as the sweat pore. It absorbs water
and salts from the surrounding capillaries which when release outside evaporate and cools
the body.
C) Hair follicles
The hair follicles are epidermal in origin but their bases are found deep down in the
dermis. Attached to each hair follicle is a hair erector muscle. When the hair erector
muscle contracts, it pulls the hair shaft and makes it stand erect. This is what result to
goose pimples. When the hair erector muscle relaxes, the hair shafts fall on the skin
surfaces thereby expelling all air that act as insulator making the body lose heat.
D) Sensory nerve endings and receptors
The skin is also a sense organ. This is because it contains four different sensory
receptors. These receptors are found mainly in the dermis with some very close to the
epidermis. They are able to receive stimuli, convert them to impulse and send them to
the central nervous system.
They include; touch receptors or meissner’s corpuscles, pain receptors, thermoreceptors and
pressure receptors or pacinian corpuscles.
E) Sebaceous gland
Sebaceous gland secret an oily substance called sebum which repels water and also
prevents microbes from multiplying.
F) Subcutaneous layer ( adipose tissue )
It act as a long term food store and an insulating layer preventing heat loss from the
body. The thickness of this layer varies depending on the part of the body.
Structure of the skin
FUNCTIONS OF THE SKIN
1. Protection : The skin protects the body against dehydration , invading microbes, mechanical
damages and poisonous chemicals.
2. Sensitivity : It controls receptors sensitive to heat, cold, touch and pressure in response to
stimuli.
3. Excretion: It removes excess water and nitrogenous waste(urea) from the body.
4. Temperature regulation: Through vasodilation and vasoconstriction the skin regulate the body
temperature.
5. Production of vitamin D: The skin produces vitamin D when exposed to mild morning sunlight.
6. Storage : The skin stores fats in the adipose tissues which forms an insulating layer.
DISEASES OF THE SKIN
Skin diseases are caused by viruses, bacteria, protozoa or fungi.
These include;
1. Chicken pox
2. Measles
3. Pimples
4. Skin rashes
5. Eczema
6. Boil
CARE OF THE SKIN
1. Do not scratch your skin with sharp objects.
2. Avoid the use of injurious creams and soaps like bleaching creams because it destroy the
melanin pigment.
3. Taking bath regularly
4. Clean clothes should be worn
5. Eat balance diet to keep the skin healthy
6. Exposure to fresh air and ultraviolet rays ( vitamin D )
7. Regular exercise
8. Use of deodorants and anti – perspirants which may control excessive sweating and unpleasant
odour.
THE HOMEOSTATIC FUNCTION OF THE SKIN( TEMPERATURE REGULATION )
Mammals like human maintain a constant body temperature. This allows them to live in any type of
weather. Heat gained or loss from the body caused a rise or fall from the normal body temperature
which is approximately 37 .
The hypothalamus monitors, receives information and stimulates processes for balance.
 On a hot day;
The body temperature rises.
It may be caused by hot weather , vigorous exercise, high fever or exposure to solar radiation. An
increase in body temperature stimulates temperature receptors in the hypothalamus to send nerve
impulses to the skin. These impulses stimulate processes that get rid of excess body heat.
These processes include;
1. Vasodilation ( vaso = vessel, dilation = widening )
The blood capillaries close to the surface of the skin dilates while the ones deep down the skin
constrict. This allows more blood flow near the surface of the skin and heat is lost to the
environment by conduction, convection and radiation thus reducing the temperature.
2. Sweating
Sweating is another way the skin assists the body to lose heat. Sweat glands are stimulated by
impulses to secrete large amount of sweat which evaporates and cools the body. Other animals
lose heat by panting i.e evaporation of water through the mouth, nose and tongue.
3. Lowering of the hair shaft
The hair erector muscles relax making the hair to be flat on the body. This process expels
most of the air which is trapped by the hair and thus removing the insulation which they offer
to the body.
4. Decrease metabolic rate
The body slows down its metabolic activities so that less heat is generated.
 On a cold day
Fall in body temperature.
Due to cold weather, the following processes occur;
1. Vasoconstriction ( constriction = narrowing )
The blood capillaries close to the surface of the skin constrict, narrow while the ones deep
down dilate. Little quantity of blood flows near the surface of the skin thereby reducing the
amount of heat lost from the body by conduction, convection or radiation.
2. Less sweating
The sweat glands produce little or no sweat so that little or no heat is lost from the body by
the evaporation of sweat.
3. Raising of hair shaft
The hair erector muscles contract making the hair shaft to stand erect. The raised hair shaft
trap a layer of air on the surface of the skin. This acts as an insulator thereby reducing the
amount of heat that is lost from the body.
4. Shivering
The muscles cells undergo involuntary contractions, this generates heat that raises the
temperature of the body.
5. Increase metabolic rate
The thyroid gland is stimulated by the hypothalamus to produce thyroxine which increases the
metabolic rate, hence more heat is produced especially by the liver.