Download The Liver Although skin is considered to be the largest organ of the

The Liver
Although skin is considered to be the
largest organ of the human body,
liver is known to be the largest
internal organ and the largest gland
in the human body. One may wonder
as to what a gland is and what a
purpose it serves. A gland is an
organized group of cells or tissues
specialized to secrete or excrete certain substances to be used elsewhere in the body. Glands are broadly
classified into two major groups i.e. endocrine and exocrine glands. A normal liver weighs about 1.2 to 1.5
kg and performs both endocrine and exocrine functions.
The liver has many complex metabolic functions that are discussed below:
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Liver is the organ which receives almost all the nutrients that are ab sorbed from our
digestive tract. Liver processes all the nutrients derived from the food we eat then stores the
energy and when necessary it mobilizes the stored energy to be used throughout the body so in
a sense liver acts like an interface between the circulatory blood and the digestive system.
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The liver is a site where large quantities of blood can be stored. When the total volume of
the blood increases in the body, the liver being the largest internal gland is readily expandable
and can act like a blood reservoir. In instances of cardiac failure, high pressure in the right
atrium of the heart causes backpressure in the liver; this forces the liver to expand; the liver
can then store about 500 to 1000 ml of extra blood within its own tissues. The liver can also
supply the body with this extra stored blood in times of diminished blood volume in the body.
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The liver plays key role in carbohydrate metabolism by converting glucose to glycogen
thus preventing hyperglycemia (elevated blood glucose) after a meal rich in carbohydrate.
Liver converts stored glycogen to glucose and releases them into the blood when needed in
order to maintain a stable blood glucose level during fasting state and between meals. Liver
can also convert non-carbohydrate compounds such as lactic acid, amino acid to glucose.
Inappropriately high output of hepatic glucose is seen in patients with diabetes mellitus; certain
antidiabetic drugs are used to reduce hepatic glucose output.
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Liver synthesizes various plasma proteins. Liver replaces the plasma proteins in days to
weeks after a major blood loss.
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Liver removes ammonia from the blood by converting it to a less toxic compound called
urea. Accumulation of ammonia and other toxins may eventually cause hepatic encephalopathy.
In liver cirrhosis, blood ammonia is increased to toxic level due to impair ed liver function.
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Liver detoxifies poisons, alcohol, and drugs from the blood.
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Uptake and storage of vitamins A, D, B12 and folic acid are employed in the liver.
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Liver stores certain minerals such as iron and copper.
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The liver serves as a filter between the blood that comes from the gut and the blood that
circulates in the rest of the body. Liver clears the bacteria, antigens, damaged cells, proteins,
hormones and drugs from the circulation.
The Kidneys
There are two bean-shaped kidneys
in the human body. A normal kidney
is about 2.5 cm thick, 10 cm long
and 5 cm wide. They are reddish-brown
in color and each weighs approximately
130 gm in adults. Both kidneys receive
blood from the renal artery; in a resting
adult approximately 1.2 to 1.4 Liters
of blood flows through both kidneys
in one minute which means every 4 to 5 minutes all the circulating blood in the body passes through
the kidneys. Kidneys help remove excess salt, water and waste products from the bloodstream. Like
other endocrine organs, kidneys also secrete important hormones such as rennin and erythropoietin
into the circulation. These hormones play significant roles in the production of blood cell and in the
regulation of blood pressure.
Other functions of Kidneys:
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Kidney excretes harmful metabolic waste products especially nitrogenous compounds (urea,
uric acid and creatinine), metabolites of various hormones and end products of hemoglobin
breakdown. It also eliminates drugs, pesticides, food additives and other foreign toxic
substances from the body.
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Kidney maintains the acid-base balance by controlling the synthesis and excretion of
bicarbonate and hydrogen ions. It can generate enough bicarbonate ions to neutralize net acid
production from metabolism. All the renal tubules are capable of secreting increased amount of
hydrogen ions into the urine thus eliminating excess hydrogen ions from the blood.
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Kidney reabsorbs essential nutrients such as glucose, amino acids from the filtered blood.
During prolonged fasting kidneys can synthesize glucose from amino acids and then release
glucose into the blood.
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Kidney maintains calcium homeostasis by reabsorbing more than 90% of the filtered calcium in
the proximal convoluted tubule and in the thick ascending limb of loop of Henle. Parathyroid
hormone and vitamin D are the major hormones that influence calcium balance in the body.
Parathyroid hormone acts on the distal convoluted tubule to increase calcium reabsorption into
the blood.
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Kidney regulates water balance within the body either by concentrating or diluting the urine.
Sodium is reabsorbed along the entire length of the nephron to a varying degree; very little
sodium is lost in the urine. More than 67% of the filtered sodium is reabsorbed in the proximal
convoluted tubule. Antidiuretic hormone (ADH) is released from the pituitary gland when the
sodium ion concentration becomes too high; this causes kidney to retain more water. Increased
water dilutes the excess sodium back to normal. Increased water also increases the blood
volume which in turn increases the arterial pressure in the kidney thus causing it to excrete more
water and along with it excess sodium in the urine.
The Lungs
Lungs are the major organ of our
respiratory system, helping us to obtain
oxygen and get rid of carbon dioxide.
Our chest cavity houses a pair of lungs
which are connected to the external
environment through the nose and
mouth. A cylindrical tube, called
trachea, is the main link between the
lungs and the nose and mouth. When we breathe in, air travels through the trachea to our lungs.
As the trachea moves down the chest, it splits into two branches called bronchus, one for each
lung. Each bronchus then further subdivides into several smaller tubes called bronchioles. Thus,
each lung contains many bronchioles spread all over in order to ensure an even distribution of
oxygen in the lungs.
For oxygen to be able to reach all the parts of our body, it has to be dissolved into the blood. The
blood stream then distributes oxygen to the entire body. Therefore, there has to be a supply of
blood vessels in the lungs. These blood vessels are present on minute, sac-like structures called
alveoli found at the end of bronchioles. There are numerous alveoli in each lung in order to
provide the maximum surface area for the exchange of oxygen as well as carbon dioxide between
the lungs and the blood stream.
Lungs play a role in the function of respiration in our body. Oxygen is taken in when we breathe
in. The inhaled air travels from the external air passages (mouth and nose) down the trachea and
finally into the lungs through the bronchus and bronchioles. This oxygen dissolves into the layer
of moisture found around each alveoli and is finally dissolved into blood capillaries. In this way,
our lungs play a vital role in providing oxygen to all the parts of our body.
It is important for our bodies to get rid of carbon dioxide which is produced as a waste product of
respiration. Once again, lungs are the organs which help in the elimination of this toxic waste
product. The path of carbon dioxide from the blood to the external environment through our lungs
is the reverse of the path taken by oxygen to enter the blood stream.

The size of both of the lungs in a pair is not the same. The left lung is smaller and is divid ed
into two lobes. On the other hand, the right lung is larger and consists of three lobes.

The combined surface area of all the tiny alveolar sacs found in the lungs is equal to the area
of an entire tennis court.

It is possible for a person to survive with just one lung. However, he would be weaker than
normal individuals with both of their lungs functioning properly.

On average, the volume of air taken in every day by the lungs is approximately 9,000 liters.

The lungs of newly born babies breathe at a faster rate as compared to the lungs of adults.
The Brain
Made up of about 100 billion neurons
and contributing nearly 2% of
body-weight, brain is the supreme
structural and functional unit and
control center of the body and the
superior-most region of CNS
(Central Nervous System). Broadly
speaking, major part of the brain is
comprised of the hemispheres (left & right) of cerebral cortex. Cerebellum, the horizontally
furrowed structure of brain's rear part, is located behind brainstem that is attached to cerebrum.
Primary components and associated structures of brain work in coordination with one another and
execute a number of vital functions, viz. growth, maintenance, reproduction, sexual maturity,
alarming and responding to environmental hazards, and personal & behavioral developments.
Being the master/head organ of your body, brain is assigned a multitude of vital tasks that are
regulated and accomplished quite efficiently. From a mild feeling of touch to the complex
phenomenon of sublime thoughts and critical decision-making capabilities, all fall under the
domain of this central part of the Central Nervous System that is enclosed in the hard shell, the
skull, beautifully placed at the top of your body. To list all the functions and responsibilities of this
white & gray matter, you need to compose a whole book. However, for the basic understanding of
the subject, here follow some of the major tasks of brain:
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Reasoning and thinking
Movements
Sensory perception (touch, smell, sight, tastes, and feel)
Communication and language
Visual processing
Problem solving
Emotions
Auditory processing
Memory
Learning
Breathing control
Regulation of heartbeat
Blood pressure control
The Colon (large intestine)
Last major segment of the digestive system
consists of a long, convoluted and
comparatively wide canal that performs
the finishing task of gastro-intestinal
mechanism by absorbing the leftover
fluids, salts and vitamins, etc. Also known
as large bowel, it joins the posterior end
of small bowel at caecum and runs in the same direction to reach rectum where it opens out of the
body through anus.
There are many tasks assigned to the last region of digestive tract which can be
summarized as follows:
Absorption
Leftover fluids, salts/mineral ions, vitamins, etc.
Feces Formation
Conversion of indigestible material into faeces for excretion.
Habitation For Bacteria
Providing a shelter and maintaining the population of more than 500 bacterial species that
synthesize a number of useful products for human body.
Fermentation
The waste and indigestible food is fermented with the help of bacterial action present
therein.
Feces Storage
Temporary storage of the waste material before it is emptied out of the body through anus.
Excretion
Elimination of stool (indigestible and fermented part of dietary components) through anal
opening (the posterior most part of the digestive tract).
The Pancreas
Pancreas is one of the extrinsic glands of
the digestive system since it is located
outside the wall of the digestive tract. It
has mixed endocrine and exocrine
functions. The exocrine part secrets
pancreatic juice into the duodenum; the
juice contains a number of digestive
enzymes and pro-enzymes that help
digest the food. The endocrine part produces hormones such as insulin that play significant role in
the absorption, metabolism and storage of nutrients such as glucose. Dysfunction in the endocrine
part of the pancreas leads to diabetes mellitus.
Measuring about 12 to 15 centimeter in length, pancreas is a glandular organ lying behind stomach
in the abdomen and performing both endocrine as well as exocrine functions. The exocrine
secretions (pancreatic juice) are released into the duodenum of small intestine through pancreatic
duct. The pancreatic fluid is of great importance for the digestive system as it contains a number of
biological catalysts (enzymes) that carry out breakdown of carbohydrates, fats, proteins and other
components of chyme into simpler absorbable molecules. The internal or endocrine functions
include the secretion of vital hormones, viz. somatostatin, glucagon, insulin and pancreatic
polypeptide that carry out a number of important functions in the body.
About 1500 ml of pancreatic juice is secreted everyday which contains many digestive enzymes,
water and various ions such as bicarbonate, sodium, potassium.

pH of the pancreatic juice is alkaline in nature which helps neutralize the gastric
content entering the duodenum from the stomach.

Pancreatic enzymes and pro-enzymes (zymogens) are essential for the digestion of
protein, carbohydrate and fat constituents of food that we eat every day.

Endocrine part of pancreas secrets two important hormones - insulin and glucagon
- both of which are secreted reciprocally from pancreas and also act reciprocally in
most circumstances. In a nutshell, insulin increases storage of glucose, fatty acids
and amino acids. On the other hand glucagon is a catabolic hormone so it
mobilizes glucose, fatty acids and amino acids from stores into the bloodst ream.
The Skin
Skin is the outer covering which protects
all the delicate body parts lying underneath
it. It is the largest organ of our body which
consists of several tissues including sweat
glands, hair follicles, and Meissner's
corpuscles. Our skin not only provides
protection to the internal body parts,
but also gives us our sense of touch.
Skin is not just the largest, but also one of the most important organs of our body since it performs
an array of various significant functions. Protecting the inner parts from diseases, regulating the
body temperature, moisture retention, removal of toxins and Vitamin D production are some of the
most important functions which are performed by the skin.
The most important function of the skin is protection. It prevents harmful pathogens and toxic
substances from entering the body. Unless there is a cut on the skin, nothing can penetrate the skin
as this layer assures the protection of different inner parts as well. Therefore, our skin is deemed as
our body's first line of defense. This largest organ of the body resists the absorption of water when
we are in rain. This resistance is because of the outer most part of the skin which is known as
epidermis. The health of epidermis is utterly necessary as it also fights bacteria, virus and other
harmful germs.
Our skin helps our body maintain a constant internal temperature. When the temperature of the
environment rises, the blood vessels present in the skin dilate. In this way, more heat is lost from
the body. On the other hand, in response to a cold environment, these blood vessels constrict,
thereby cutting down the body's heat loss. Sweat glands present in the skin also play an important
role in the regulation of temperature. More sweat is produced when the temperature of the
surroundings rises. The evaporation of this sweat from the skin creates a cooling effect.
Our skin contains a substance called ergosterol, which is responsible for the synthesis of vitamin D.
On exposure to sunlight, ergosterol is converted into vitamin D2 which is one form of five types of
vitamin D. Vitamin D is a steroid vitamin and it promotes the absorption of calcium and
phosphorous together with their metabolism.