HUMAN DIGESTIVE SYSTEM
(Simple & Explanative Note)
(Simple & Explanative Note)
By learningcentury.blogspot.com
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| Human Digestive System I Image by pixabay |
ALIMENTARY CANAL:
The human alimentary canal or digestive tract is
differentiated into the following parts.
1.
Oral cavity
2.
Pharynx
3.
Esophagus
4.
Stomach
5.
Small intestine
6.
Large intestine
1. ORAL CAVITY (BUCCAL CAVITY):
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1) It
is the first part of digestive tract which receives the food.
2) The
process of lubrication and digestion starts in oral cavity.
ORGANS:
There are three important
organs in oral cavity.
1) Teeth
2) Tongue
3) Salivary
glands
1.
TEETH:
i.
Teeth help in grinding
of food.
ii.
Permanent teeth are of
four main types i-e
A) INCISOR:
Incisor teeth are adapted for cutting or
biting.
B) CANINE:
Canine teeth are adapted for tearing.
C) PREMOLAR:
Premolar teeth are adapted for grinding and
mastication.
D) MOLAR:
Molar teeth are also adapted for grinding
and mastication of food or the mechanical digestion of food.
2.
TONGUE:
1) Tongue
is a fleshy structure that contains taste buds.
2) Taste
buds create a desire for food to eat and help us to sense taste.
3) Tongue
also helps during the grinding of food by keeping food between teeth.
4) It
also helps in the swallowing process.
3.
SALIVARY
GLANDS:
1) Salivary
glands secrete saliva.
2) There
are three pairs of salivary glands in our oral cavity.
3) The
saliva contains salts like Sodium bicarbonate (NaHCO3), water, mucous
and enzyme.
4) Sodium
bicarbonate is antiseptic; it kills the germs and makes the food
alkaline.
5) Mucus
lubricates the food.
6) The
enzyme salivary amylase chemically digests starch and glycogen into
maltose.
7) The
secretion of saliva called watering of mouth is a reflex action.
8) Even
sight, smell, hearing of food can stimulate secretion of saliva.
9)
In the oral cavity, food
turns in the form of a ball.
2. PHARYNX AND SWALLOWING:
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| Human Digestive System I Image by pixabay |
1) Pharynx
is a cavity behind the soft palate, in which the oral cavity opens.
2) Tongue
pushes back the food (bolus) in the pharynx.
3) The
downward movement of food, from the oral cavity, is called swallowing.
4) Swallowing
is voluntary in the oral cavity and below the oral cavity, it becomes automatic (reflex
action/involuntary).
5) From
pharynx, the food is forced into the esophagus by peristalsis.
6) Pharynx
is a passage for both air and food.
7) It
provides passage to food from the oral cavity to esophagus.
8) It
also provides passage to air from the nasal cavity to the trachea through an opening
called glottis.
9) During
swallowing a flap called epiglottis closes the glottis to prevent the entry
of food particles in the trachea.
10) During
swallowing the soft palate and uvula more superiorly to close the
nasopharynx.
11) Thus
uvula prevents food from entering the nasal cavity.
3. ESOPHAGUS:
1) Esophagus
or food pipe is a muscular tube extending from pharynx to stomach.
2) It
is about 10 inches long.
3) It
runs through the neck and thorax between trachea and vertebral column.
4) Food
is passed rapidly through the esophagus by peristalsis.
PERISTALSIS:
1) Wave
like contraction and relaxation of muscles of alimentary canal is called
peristalsis.
2) The
peristalsis helps the food to move along the alimentary canal.
3) It
starts from esophagus and move along the whole alimentary canal.
ANTI PERISTALSIS:
1) Sometimes
due to irritation in esophagus or stomach, the peristalsis is reversed and
vomiting occurs.
2) This
reversal of peristalsis is called antiperistalsis.
4. STOMACH:
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| Human Digestive System I Image by pixabay |
The stomach is a sac-like
muscular part of the digestive system.
Stomach is discussed as
under;
1.
SHAPE:
The human stomach is pear-shaped.
2.
SIZE:
The human stomach is about 12 inches
long and 6 inches wide.
3.
LOCATION:
1) It
is located between the esophagus and intestine.
2) It
is present crosswise in the abdominal cavity beneath the diaphragm.
4.
CAPACITY:
The food holding capacity of stomach is 1
liter (1kg).
5.
CARDIAC
SPHINCTER:
1) Food
enters the stomach from the esophagus.
2) At
the junction of the stomach and esophagus there are muscles called cardiac
sphincter.
3) They
prevent food from passing back to esophagus.
6.
MUSCULAR
WALLS OF STOMACH:
1)
The walls of stomach
are thick and muscular.
2)
Stomach churn the
food into smaller particles by contraction of its muscular walls
3)
This churning of food
is also called mechanical digestion.
4)
Churning produce heat
which helps to melt lipids in food.
7.
GASTRIC
GLANDS:
1) The
inner walls of the stomach have many gastric glands.
2) They
secrete gastric juice into the stomach.
3) Gastric
juice contains mucus, pepsinogen enzyme, and hydrochloric acid.
4) HCl converts the inactive pepsinogen into an
active enzyme called pepsin.
5) Pepsin
breaks large protein molecules into shorter chains of amino acids called peptides.
6) HCl
also kills bacteria present in food.
7) In
stomach the food is converted into a thick soup-like fluid called chyme.
8) Mucus in gastric juice forms a coating on the
inner walls of the stomach.
9) it
protects the inner walls of the stomach from HCl and enzymatic action of pepsin,
8.
PYLORIC
SPHINCTER:
1)
The other end of
stomach called pyloric end, opens into the first part of small intestine called duodenum.
2)
Pyloric sphincter is
the muscles which separate the stomach form duodenum.
3)
Food usually remains
stomach for 3-4 hours.
4) Each
time pyloric sphincter opens, about 5-15ml chyme enter the small intestine.
5. DIGESTION IN SMALL INTESTINE:
1) The
stomach opens into the small intestine through the pyloric sphincter.
2) It
is the longest part of the human digestive system.
3) It
is an elongated and coiled narrow tube.
PARTS OF SMALL INTESTINE:
Small intestine is divided
into the following three parts;
1) Duodenum
2) Jejunum
3) Ileum
1)
DUODENUM:
i.
Duodenum is the first
part of small intestine.
ii.
It is about 12
inches long and curved like ‘C’.
iii.
It receives chyme from
stomach.
iv.
In duodenum the chyme
mixes with the bile and pancreatic juice.
v.
Bile comes from liver
and pancreatic juice from pancreas.
vi.
Both, bile and
pancreatic juice is alkaline.
2)
JEJUNUM:
i.
Jejunum comes after
duodenum and passes into ilium.
ii.
The jejunum is about 2.4m
long.
3)
ILEUM:
i.
It is about 2.6m
long.
ii.
The glands of ileum
secrete intestinal juice.
iii.
The intestinal juice
contains enzymes and over undigested materials.
iv.
So the digestion of
food is completed in the small intestine.
LIVER AS DIGESTIVE GLAND:
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| Human Digestive System I Image by pixabay |
Liver acts as digestive gland
and is discussed under the following headings.
1.
COLOUR:
Liver is a large reddish-brown gland.
2.
LOBES:
Liver consist of two main lobes, which
are further divided into smaller lobes.
3.
BILE:
1)
Bile is a green
alkaline liquid produced by liver and is stored in gallbladder.
2)
Bile contains water,
sodium bicarbonate, excess of calcium and broken hemoglobin.
3)
From gall bladder,
bile is secreted in duodenum by common bile duct.
4.
FUNCTION
OF BILE:
1) The
bile helps in the emulsification of fats.
2) It
neutralizes the acidity of chyme.
3) It
kills the germs and bacteria present in food.
4) Emulsification
is the process by which large globules of fats are broken down into smaller
globules, soluble in water.
PANCREASE:
Pancreas acts as a digestive
gland and discussed under the following headings.
1.
COLOUR:
Human pancreas is a yellowish organ.
2.
SIZE:
It is about 7inches long and 1.5inches
wide.
3.
LOCATION:
The pancreas lies beneath the stomach and
is connected to the duodenum.
4.
FUNCTION:
i.
Pancreas secretes
pancreatic juice into pancreatic duct, which join common bile duct before
entering the duodenum.
ii.
Pancreatic juice
contains sodium bicarbonates and enzyme.
iii.
Sodium bicarbonate neutralizes
the chyme acidity.
5.
ENZYMES
SECRETTED BY PANCREASE:
Pancreas secretes pancreatic juice, which
contains the following three enzymes
a)
Trypsinogen (Trypsin)
b) Amylase
c)
Lipase
A) TRYPSINOGEN (TRYPSIN):
i.
Trypsin is the active
form of trypsinogen.
ii.
Trypsin converts
proteins into peptides and then into amino acids.
iii.
It completes the
digestion of proteins.
B) AMYLASE:
I.
Pancreatic amylase act
on the starch, which have escaped the action of salivary amylase.
II.
It converts starch
into simple sugars.
C) LIPASE:
I.
Lipase acts on emulsified
fats and convert them into fatty acids and glycerol.
II.
Thus the digestion of fats
is completed.
ABSORPTION OF FOOD IN SMALL INTESTINE
1.
The uptake of soluble
and diffusible food from the digestive tract into the cells or blood is called
absorption.
2.
After completion of
digestion of food, the end products i-e amino acids, simple sugars, glycerol
and fatty acids are absorbed from small intestine into blood.
3.
The structure of small
intestine is in accordance with its absorptive function.
4.
Its inner lining has
large folds.
5.
These folds have
millions of finger like projections called villi.
6.
Single cell thick
epithelium of villus also contains microscopic projections called microvilli.
7.
The microvilli greatly
increase the surface area of villus.
8.
Inside villus, there
are
a)
Blood capillaries
b) Small
lymphatic vessels called lacteal.
ABSORPTION OF FOOD BY VILLUS:
1.
During absorption, the
simple sugars, amino acids, vitamins, minerals and water enter the blood
capillaries in the villi.
2.
These capillaries open
in the hepatic portal vein, which carries the nutrients to liver.
3.
Fatty acids and
glycerol are majorly absorbed into lymph vessel, which pour them into
blood stream.
6. FUNCTIONS OF LARGE INTESTINE:
Various functions of large are given below;
1) It
absorbs certain vitamins.
2) It
absorbs water and maintains the balance of fluids in body.
3) It
processes undigested food into faeces.
4) It
stores the waste materials before it is eliminated.
PARTS OF LARGE INTESTINE:
1) Large
intestine is that part of digestive system where undigested materials is
collected and processed into faeces.
2) It
is about 1.5 meter long and consists of three following parts;
a)
Caecum
b) Colon
c)
Rectum
a)
CAECUM:
1)
Caecum is the first
part of the large intestine which is located in the right lower abdomen.
2)
It is a connection
between small intestine and colon.
3)
Caecum receives and
stores the mixture from the small intestine and forwards it to the colon.
4)
The caecum contains a
mixture of
a)
Undigested food fiber
b)
A little bit water
c)
Some vitamins
d)
Some mineral salts
5)
A small projection
emerging from caecum is called appendix.
6)
In human beings, it
has no known function.
7)
Its infection is
called appendicitis.
b)
COLON:
1) It
is the longest part of the large intestine.
2) It
has shape like inverted ‘U’.
3) Colon
has following parts;
a.
Ascending colon
b.
Transverse colon
c.
Descending colon
d.
Sigmoid colon
c)
RECTUM:
1) It
is the final part of the large intestine.
2) It
is the part where stool (faeces) is stored before being passed out from
anus. It is called egestion.
Q1: Write a note on colon?
Ans: COLON:
1) Colon
is the longest part of large intestine.
2) The
colon has four sections
a.
Ascending colon
b.
Transverse colon
c.
Descending colon
d.
Sigmoid colon
FUNCTION:
1) As
the material travels through the colon, the lining of the colon absorbs most of the
water, some vitamins, and minerals.
2) The mixture of undigested materials, water dead cells of the alimentary canal, bile
pigments etc. mixes with mucus and take the form of feces.
3) Through
muscular movements of colon, faeces are pushed into the rectum.
4) Bacteria
are present in colon.
5) They
use some fibers as nutrients.
6) They
also, nourish the cells of the colon.
7) Some
vitamins are also produced by them.
Q2: Define the following.
A. DIGESTION
B. ABSORPTION
C. ASSIMILATION
D. EGESTION
A. DIGESTION:
The conversion of large, complex,
non-diffusible and insoluble food into small, simple, diffusible and soluble
form by the action of enzymes is called digestion.
B. ABSORPTION:
The uptake of soluble and diffusible food
from the digestive tract into the cells or blood is called absorption.
C. ASSIMILATION:
a)
The digested food is
carried to the cells by the blood.
b) The
cells absorb ad convert nutrients into the fluid or solid substance of the
body.
c)
This process is known
as assimilation.
D. EGESTION:
1) Not
all the food we eat is digested.
2) Some
amount of food is not digested and is changed to waste materials, which must be
removed from the body.
3) This
elimination or removal of undigested food (feces) from the body is called
egestion.
HUMAN DIGESTIVE SYSTEM (Simple & Explanative) (The End)
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