The digestive system consists of digestive tract and associated organs of digestion.
It provides water, electrolytes, vitamins and nutrients to the body with the help of the circulatory system.
Functions of the digestive system are :-
- Ingestion: Taking in food through mouth.
- Mastication: Movement of the lower jaw during chewing.
- Deglutition: Swallowing of food so that it passes from mouth to stomach.
- Digestion: Chemical breakdown of food material.
- Absorption: Nutrient molecules are absorbed into circulatory system through mucous membrane of small intestine.
- Defecation: Elimination of solid/semisolid/liquid waste material of food through anus.
The digestive tract extends from mouth to anus.
It is a tubular passage and measures about 10 m (30 ft) in length.
(Proximal to distal ) GIT consists of following parts:-
- Small intestine
- Large intestine
- Anal canal
Mouth (oral cavity)
It is the first part of the digestive tract.
It is bounded anteriorly by lips, laterally by cheeks, superiorly by palate and inferiorly by a muscular floor.
The teeth are embedded in the sockets of alveolar process of mandible and maxilla.
In an adult individual, there are 32 teeth, 16 in each jaw.
• Tongue is a mobile muscular organ in the oral cavity, which bulges upwards from the floor of the mouth.
•It is a mass of skeletal muscle covered by mucus membrane.
•The muscle mass is separated into right and left halves by a midline fibrous septum.
•Tongue is separated from teeth by a deep alveololingual sulcus.
Functions of Tongue are:-
External Features of Tongue
- A root.
- A tip.
- A body.
Shape :Tongue is conical in shape.
Muscles of Tongue
• The musculature of tongue consists of extrinsic and intrinsic muscles.
• The intrinsic muscles are within the tongue and have no attachment outside the tongue.
• Whereas extrinsic muscles take origin from outside the tongue and enter the tongue to be inserted.
• The intrinsic muscles change the shape of tongue whereas extrinsic muscles move the tongue (such as protrusion, retraction and side-to side movements) as well as alter its shape.
|INTRINSIC MUSCLE||EXTRINSIC MUSCLE|
|1. Superior longitudinal||1. Genioglossus|
|2. Inferior longitudinal||2. Hyoglossus|
|3. Transverse||3. Styloglossus|
|4. Vertical||4. Palatoglossus|
1. Branches of lingual artery (chief artery of tongue).
2. Tonsillar branch of the facial artery.
3. Ascending pharyngeal artery.
Deep lingual vein.
All the muscles of tongue (intrinsic and extrinsic) are supplied by the Hypoglossal nerve except Palatoglossus which is supplied by cranial root of accessory via Pharyngeal Plexus.
Anterior 2/3 of the tongue is supplied by:-
(a) Lingual nerve carrying general sensations.
(b) Chorda Tympani nerve carrying special sensations of taste.
Posterior 1/3 of the tongue is supplied by:-
(a) Glossopharyngeal nerve, carrying both general and special sensations of taste.
(b) Posterior most part (base of the tongue) is supplied by the Internal Laryngeal branch of the Superior Laryngeal carrying special sensations of taste.
•Pharynx is a funnel-shaped fibromuscular tube.
•it extends from base of the skull to esophagus.
•It is lined throughout with mucous membrane.
•Pharynx acts as a common channel for both food (deglutition) and air (respiration).
•Length: 12-14 cm,
•Width: 3.5 cm at its base, and 1.5 cm at pharyngoesophageal junction.
•Esophagus is a narrow muscular tube extending from pharynx to stomach.
•It is about 25 cm long and provides passage for chewed food (bolus) and liquids during the third stage of deglutition.
•The anatomy of esophagus is clinically important because of its involvement in various diseases such as Esophagitis, Esophageal varices and Cancer.
•It begins with lower part of the neck and terminates in the upper part of the abdomen by joining the upper end of the stomach.
PARTS OF ESOPHAGUS
•Cervical part (4 cm in length).
•Thoracic part (20 cm in length).
•Abdominal part (1-2 cm in length).
•Normally, there are four sites of anatomical constriction/narrowing in esophagus. The distance of each constriction is measured from the upper incisor teeth.
1. First constriction, at the pharyngo-esophageal junction, 9 cm (6 inches) from the incisor teeth.
2. Second constriction, where it is crossed by the arch of aorta, 22.5 cm (9 inches) from the incisor teeth.
3. Third constriction, where it is crossed by the left principal bronchus, 27.5 cm (11 inches) from the incisor teeth.
4. Fourth constriction, where it pierces the diaphragm, 40 cm (15 inches) from the incisor teeth.
To be continued in part 2…
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