GIT/Alimentary Canal

Dr. AHAD HUSSAIN; PT

MS-SPT, MSPH

DIPLOMA IN PHARMACY

Mouth

• The mouth or oral cavity is bounded by muscles and bones:
• Anteriorly – by the lips Posteriorly – it is continuous with the oropharynx
• Laterally – by the muscles of the cheeks
• Superiorly – by the bony hard palate and muscular soft palate
• Inferiorly – by the muscular tongue and the soft tissues of the floor of the mouth.

• The palate forms the roof of the mouth and is divided into the anterior hard palate and the posterior soft palate
• Hard palate is formed by the maxilla and the palatine bones.
• soft palate is muscular
• uvula is a curved fold of muscle covered with mucous membrane, hanging down from the middle of the free border of the soft palate.

Tongue

• The tongue is a voluntary muscular structure that occupies the floor of the mouth.
• It is attached by its base to the hyoid bone
• and by a fold of its mucous membrane covering, called the frenulum, to the floor of the mouth

• Superior surface consists of stratified squamous epithelial cells
• contain sensory receptors (specialised nerve endings) for the sense of taste in the taste buds.

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�Blood supply�

• lingual branch of the external carotid artery.
• Venous drainage is by the lingual vein, which joins the internal jugular vein.

Nerve Supply

• Hypoglossal nerves (12th cranial nerves), which supply the voluntary muscle.
• lingual branch of the mandibular nerves, which arise from the 5th cranial nerves, are the nerves of somatic (ordinary) sensation, i.e. pain, temperature and touch

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Functions of the tongue

• The tongue plays an important part in:
• chewing (mastication)
• swallowing (deglutition)
• speech
• taste

Teeth

• teeth are embedded in the alveoli or sockets of the alveolar ridges of the mandible and the maxilla.
• Babies are born with two sets
• the temporary or deciduous teeth and the permanent teeth

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Functions of the teeth

• Teeth have different shapes depending on their functions.
• Incisors and canine teeth are the cutting teeth and are used for biting off pieces of food,
• whereas the premolar and molar teeth, with broad, flat surfaces, are used for grinding or chewing food

• Although the shapes of the different teeth vary, the structure is the same and consists of: the
• crown – the part that protrudes from the gum
• the root – the part embedded in the bone
• the neck – the slightly narrowed region where the crown merges with the root.

Blood Supply

• maxillary arteries.
• The venous drainage is by a number of veins which empty into the internal jugular veins.

Nerve Supply

• upper teeth is by branches of the maxillary nerves
• lower teeth by branches of the mandibular nerves.
• These are both branches of the trigeminal nerves (5th cranial nerves).

Salivary glands

• Salivary glands release their secretions into ducts that lead to the mouth.

Parotid glands

• These are situated one on each side of the face just below the external acoustic meatus.
• Each gland has a parotid duct opening into the mouth at the level of the second upper molar tooth.

Submandibular glands

• These lie one on each side of the face under the angle of the jaw.
• The two submandibular ducts open on the floor of the mouth
• one on each side of the frenulum of the tongue

Sublingual glands

• These glands lie under the mucous membrane of the floor of the mouth in front of the submandibular glands.
• They have numerous small ducts that open into the floor of the mouth.

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Blood supply

• Arterial supply is by various branches from the external carotid arteries and
• venous drainage is into the external jugular veins.

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Composition of saliva

• Saliva is the combined secretions from the salivary glands and the small mucus-secreting glands of the oral mucosa.
• About 1.5 litres of saliva is produced daily and it consists of:
• water
• mineral
• Salts
• a digestive enzyme: salivary amylase
• mucus
• lysozyme (special enzyme found in tears, saliva, sweat)
• immunoglobulins
• blood-clotting factors.

Functions of saliva

• Chemical digestion of polysaccharides
• Lubrication of food
• Cleaning and lubricating the mouth
• Non-specific defence
• Taste

Pharynx

• Divided into three parts, the nasopharynx, oropharynx and laryngopharynx.
• The nasopharynx is important in respiration.
• The oropharynx and laryngopharynx are passages common to both the respiratory and the digestive systems.

• The lining membrane (mucosa) is stratified squamous epithelium
• The middle layer consists of connective tissue which becomes thinner towards the lower end and contains blood and lymph vessels and nerves
• The outer layer consists of a number of involuntary muscles that are involved in swallowing

�Blood supply�

• The blood supply to the pharynx is by several branches of the facial arteries.
• Venous drainage is into the facial veins and the internal jugular veins.

Nerve Supply

• Parasympathetic supply is mainly by the glossopharyngeal and vagus nerves.
• and sympathetic from the cervical ganglia.

Oesophagus

• oesophagus is about 25 cm long and
• about 2 cm in diameter
• lies in the median plane in the thorax in front of the vertebral column behind the trachea and the heart.
• Pharynx above, continues to oesophagus
• just below the diaphragm it joins the stomach
• at the level of the 10th thoracic vertebra

• it curves upwards before opening into the stomach.
• sharp angle prevents the regurgitation (backflow) of gastric contents into the oesophagus
• The upper and lower ends of the oesophagus are closed by sphincters.

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• upper cricopharyngeal or upper oesphageal sphincter prevents air passing into the oesophagus during inspiration and the aspiration of oesophageal contents.
• cardiac or lower oesophageal sphincter prevents the reflux of acid gastric contents into the oesophagus.

Blood Supply

• Arterial
• The thoracic region is supplied mainly by the paired oesophageal arteries, branches from the thoracic aorta.
• The abdominal region is supplied by branches from the inferior phrenic arteries and the left gastric branch of the coeliac artery

Venous d arainage

• From the thoracic region venous drainage is into the azygos and hemiazygos veins.
• The abdominal part drains into the left gastric vein

Bolus

• When food is taken into the mouth it is chewed (masticated) by the teeth and moved round the mouth by the tongue and muscles of the cheeks.
• It is mixed with saliva and formed into a soft mass or bolus ready for swallowing.

�Swallowing (deglutition)�

• It is initiated voluntarily but completed by a reflex (involuntary) action.
• The mouth is closed and the voluntary muscles of the tongue and cheeks push the bolus backwards into the pharynx
• Involuntary contraction of Phayrnx muscles muscles propels the bolus down into the oesophagus.
• The presence of the bolus in the pharynx stimulates a wave of peristalsis that propels the bolus through the oesophagus to the stomach

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Stomach

• The stomach is a J-shaped dilated portion of the alimentary tract situated in the epigastric, umbilical and left hypochondriac regions of the abdominal cavity.

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Organs associated with the stomach

• Anteriorly – left lobe of liver and anterior abdominal wall
• Posteriorly – abdominal aorta, pancreas, spleen, left kidney and adrenal gland
• Superiorly – diaphragm, oesophagus and left lobe of liver
• Inferiorly – transverse colon and small intestine
• To the left – diaphragm and spleen
• To the right – liver and duodenum.

Structure of the stomach

• The stomach is divided into three regions:
• the fundus,
• the body and
• the pylorus.
• At the distal end of the pylorus is the pyloric sphincter, guarding the opening between the stomach and the duodenum. When the stomach is inactive the pyloric sphincter is relaxed and open, and when the stomach contains food the sphincter is closed

Blood Supply

• by the left gastric artery, a branch of the coeliac artery, the right gastric artery and the gastroepiploic arteries.

Venous drainage

• through veins of corresponding names into the portal vein.

• Stomach size varies with the volume of food it contains.
• 1.5 litres or more in an adult.
• When a meal has been eaten the food accumulates in the stomach in layers
• the last part of the meal remaining in the fundus for some time.
• Mixing with the gastric juice takes place gradually

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• The activity of gastric muscle consists of a churning movement that breaks down the bolus and mixes it with gastric juice
• peristaltic waves that propel the stomach contents towards the pylorus.

Gastric Juice

• Gastric juice About 2 litres of gastric juice are secreted daily by specialised secretory glands in the mucosa
• It consists of:
• mucus secreted by mucous neck cells in the glands and
• surface mucous cells on the stomach
• surface inactive enzyme precursors:
• pepsinogens secreted by chief cells in the glands.

Functions of Gastric juice

• Water further liquefies the food swallowed.
• Hydrochloric acid
• acidifies the food and stops the action of salivary amylase
• kills ingested microbes
• provides the acid environment needed for effective digestion by pepsins.
• Pepsins act most effectively at a very low pH, between 1.5 and 3.5.

Functions of the stomach

• These include:
• temporary storage allowing time for the digestive enzymes, pepsins, to act chemical digestion –
• pepsins convert proteins to polypeptides mechanical breakdown –
• the three smooth muscle layers enable the stomach to act as a churn, gastric juice is added and the contents are liquefied to chyme.
• Gastric motility and secretion are increased by parasympathetic nerve stimulation