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DIGESTION AND ABSORPTIONINTRODUCTION: Nutrition is the sum total of the process in involved in the supply and the utilization of essential
organic and inorganic compounds for growth, repair and maintenance of the body. In animals it involves
ingestion (taking in), digestion (breaking down), absorption, assimilation and egestion (removal of undigested
food). Nutrition is basically of following two types:
(i) Autotrophic nutrition: Autotrophs are capable of synthesizing their organic food from inorganic materials
using light and chemical energy.
According to type of energy they utilize for synthesis of food autotrophs are classified as –
(a) Photoautotrophos: All chlorophyll bearing organisms have developed special mechanism to trap solar energy
and utilizing it for synthesis of their own organic food by photosynthesis.
𝑠𝑢𝑛𝑙𝑖𝑔ℎ𝑡
6𝐶𝑂2 + 12 𝐻2 𝑂 → 𝐶6 𝐻12 𝑂6 + 6𝐻2 𝑂+6𝑂2
𝐶ℎ𝑙𝑜𝑟𝑜𝑝ℎ𝑦𝑙𝑙
(b)Chemoautotrophs: They synthesize their food by utilizing energy produced during oxidation of chemicals. Ex-
Sulphur bacteria, nitrite bacteria, nitrate bacteria etc.
Nitrite bacteria (Nitrosomonas) 𝑁𝐻4 + 2𝑂2 → 2𝑁𝑂3 + Energy
(ii) Heterotrophic nutrition: Heterotrophs cannot synthesize their food. Hence directly or indirectly they have to
depend upon autotrophs for their food.
Nutrition in Man: Man is omnivorous and its nutrition is holozoic.
Digestive system of Man: Digestive system of Man consists of alimentary canal and associate glands. The
alimentary canal of man consists of following main parts.
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,(i)Mouth
(ii)Buccal cavity Nasopharynx
(iii)Pharynx Oropharynx
Laryngopharynx
(iv)Oesophagus
(v)Stomach Cardiac
Fundus
Body
Pylorus
(vi)Small intestine Duodenum
Jejunum
Ileum
(vii)Large intestine Caecum
Colon
Rectum
(i)Mouth: Mouth is a crescentic opening bounded by a pair of muscular lips provided with mucous glands. Upper
lip has a depression called philtron. Orbicularis oris muscle helps in movement of lips. Internal to lips, jaws are
present. The space between lips and jaws is called vestibule.
(ii)Buccal cavity: Mouth leads to spacious cavity called buccal cavity. Its roof is formed by palate, lateral walls
by cheeks, on the floor there is a long muscular tongue, anteriorly bounded by jaws and with teeth and posteriorly
leads in to pharynx.
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, Palate: The anterior part of the palate is called hard palate supported by maxilla and palatine bone and provided
with palatine rugae to grip food at the time of chewing. The posterior smooth part is called soft palate postriorly
narrows down forming a fleshy conical process called uvula or velam palati.
Tongue: Tongue is a muscular organ of taste present on the floor of the buccal cavity. Its base is remains attached
to the floor of the buccal cavity by a membranous fold called frenulum or frenulum linguae. It is narrowing infront
and broad at the back. It is formed of connective tissue, striated muscle, blood vessels and Ebner’s gland. Surface
of the tongue is uneven due to presence of minute projections called papillae. In man three types of lingual papillae
are present i.e. filiform(smallest,most abundant,conical in shape and distributed over anterior 2/3 part of tongue ),
fungiform(large mushroom shaped present at the anterior and lateral part of the tongue) and circumvallate(largest ,
less in number (8-12) arranged in inverted-V shaped row located at the back of the tongue). Sense organs located
around the papillae are called taste buds which recognize different types of tastes of food. In man following four
types of taste buds are present in the tongue. In man, the taste buds present at anterior tip of the tongue feel sweet
taste, at the posterior part feel bitter taste; on the side feel sour taste and a small area just behind taste bud for
sweetness feel salty taste.
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