Human Digestive
System
Introduction
The
task of the digestive tract is the physical
and chemical breakdown of food.
Following ingestion food and fluids are processed by the digestive organs so that the nutrients can be absorbed from the
intestine and circulated around the body. Any residue of food i.e., not digested is solidified and eliminated
from the body in the form of faeces
(excreta).
Digestive tract
The process of digestion begins
when food enters the mouth and is largely completed at the end of small
intestine.
Digestive organs
It is composed of mouth, pharynx, oesophagus, stomach, intestine, rectum and anus which is
basically a food processing pipe about 9metres
(30ft) long.
Associated digestive structure
includes three pairs of salivary
glands,the pancreas,the liver and gall
bladder each of which has an important role.The appendix – a short blind ended tube attached to large intestine has
no known function.
Digestive Enzymes
They are protein molecules that increase the speed of chemical reactions in
the body. These are secreted by the gland cells present in the wall of
digestive system along with other substances in the form of juice.
Role of Enzymes in digestive system
They add a molecule of water and
split the chemical bonds in complex molecules. This process of splitting a
molecule with the addition of water molecule known as hydrolysis.
·
Enzymes containing hydrolytic reactions known as
hydrolytic enzymes (or) hydrolases.
·
The complex molecule on which enzyme acts – Substrate.
·
The simple molecules formed from complex
molecule – Products.
One type of enzyme acts only on one
substrate but not on other substrate of another enzyme.
Example: LIPASE acts on LIPIDS but not on PROTEINS
Enzymes will be
active basing on the concentration of
hydrogen ions, temperature and amount of
substrate. Some will be inactive when they are secreted, they will be
active in the lumen of digestive system.
Digestive Glands
·
Mouth
: Salivary glands
§
Parotid
§
Sub-mandibular
§
Sub-lingual
·
Stomach:
Liver (largest gland) and Pancreas (Second largest gland).
·
Intestine:
Duodenum, Jejunum and Ileum.
Digestion
The process of
converting complex molecules (Carbohydrates) into simple molecules (sugars)
known as digestion.
The digestive
process breaks down the food by chemical
and mechanical action into
substances that can pass into the bloodstream
and be distributed to the body cells.
Types of digestion
Intercellular Digestion ·
Digestion
occurs in the food vacuoles within cells. ·
Lysosomal
enzymes are secreted into the food vacuole. ·
Products
of digestion diffuse into cytoplasm through vacuolar membrane. ·
Ingestion
occurs through pinocytic vesicle, ·
E.g.
protozoans, sponges and coelenterates.
Extracellular Digestion ·
Digestion
occurs outside of cells in the lumen of the alimentary canal. ·
Salivary,
gastric pancreatic and intestinal enzymes are secreted into the digestive
cavity. ·
Digested
food materials are absorbed into blood through gut epithelia. ·
Ingestion
occurs through mouth. ·
E.g. coelenterates to chordates.
Detailed Description
The digestive
system of human beings comprises of ·
Alimentary canal: Mouth, Buccal cavity, Pharynx, Oesophagus, Stomach, Intestine (small & large), Rectum and Anus. ·
Digestive glands:Salivary glands, Gastric glands and Intestinal glands. Ø
Mouth It
is a transverse slit like opening covered with upper and lower lips which helps
in taking the food materials – Ingestion
process. Ø
Buccal Cavity This
is the space or cavity present inside the mouth bounded dorsally by pellate, ventrally by throat and laterally by jaws composed of o
Pellate
It acts as a roof
and divisible into anterior hard pellate
and posterior soft pellate behind
this, UVULA is present.
o
Tongue It
is a thick muscular sensory organ present on the floor of buccal cavity
consisting voluntary muscles, blood vessels and sensory nerves.The
functions of tongue are it helps in ingestion,
chewing swallowing, tasting, cleaning the teeth and mixing the food
with saliva.
o
Teeth It
is the hardest material of the body which helps in cutting, tearing, chewing and grinding the food.
The
teeth present in the buccal cavity constitute dentition. In human beings teeth are thecodont (embedded in jaws), heterodont
(different types) and diphyodont
(two sets).
o
Types of teeth
According
to their shape and function they are divided into 4 types as follows:
§
Incisors: Flat shaped with
sharp edges,
helps in cutting
§
Canines: Pointed edges,
helps in tearing.
§
Pre molars: Ridged shaped,
helps in grinding.
§
Molars: Flat shaped,
helps in crushing, grinding.
o
Using the Jaws
The process of
digestion starts as soon as food enters the mouth. Food is chewed, lubricated
by saliva and processed by the tongue. The flexible temperomandibular joint attaches the jaw bone to the skull which
allows moving in different directions. With the help of tongue food moves in
the mouth and by the teeth until it is formed into soft lump as a bolus for
swallowing.
o
Structure of Tooth
The teeth are
enclosed in sockets in the jaw bone and held in place by ligaments and shock
absorbent gums. At the centre of each tooth, a soft pulp is present with blood
vessels and nerves surrounded by a layer of sensitive tissue known as dentine. Above the gum tooth has an
outer covering of hard enamel and
below the gum a bone like tissue is present known as cementum forms the tooth’s outer layer. The important parts of this
are
§
Crown: Present above the
gum.
§
Root: Embedded in the
gum.
§
Neck: Narrow part of
the gum line.
Tooth Structure
It is
represented by D.F = N/D
Where
N stands for no. and kind of teeth
in the upper part.
D
stands for no. and kind of teeth in the lower part.
§ Dental formula in adults : I
2/2, C 1/1, P 2/2, M 3/3 (x2=
32)
The format will be 2:1:2:3/2:1:2:3
Where the numbers correspond to I: C: P: M (upper)/I: C:
P: M (lower).
§ Dental formula in children’:
2/2, C 1/1, P 2/2, M 3/3 (x2= 32)
The
format will be 2:1:2:0/2:1:2:0
Where the numbers correspond to I: C: P: M (upper)/I: C: P: M (lower).
` The primary
set of teeth developed during childhood known as Milk or Deciduos teeth
and is replaced as a permanent teeth
in adults.
The total set of teeth in the
buccal cavity constitutes Dentition. o
Salivary
glands The saliva contains an enzyme amylase and is carried by the ducts into the mouth. It is composed
three pairs of salivary glands:
o
Parotid glands – Stenson’s gland
These are located in front of the ear and the duct opens
inside the cheek opposite to the second upper molar tooth.
o
Sub-mandibular glands – Wharton’s gland
These are located deep into the mouth on each side of the
jaw bone and the duct opens into small swelling on the underside of the tongue.
o
Sub-lingual glands – Rivinus gland
These are located under the tongue and the duct open into
the floor of the mouth.
Salivary
Glands Continuation......... Next file
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