The digestive system Flashcards
What are the main functions of the digestive system?
Continuous supply of water.
Electrolytes, vitamins and nutrients.
Remove the toxic residues.
What is the digestive system formed from?
Alimentary canal / gastrointestinal tract
Starts at mouth and ends at anus
Accessory organs:
Teeth and gums
Tongue
Salivary glands
Liver and biliary tract
Pancreas
What are the structures of the oral cavity?
Oral orifice - anterior opening of oral cavity
Oral vestibule - space between teeth and lips.
Oral cavity proper - area of tongue and teeth
What is the roof of the oral cavity?
Anteriorly it is made by hard palate because it has palatine bone, and is covered in mucosa.
Posteriorly it is a soft palate because it is made of muscles and soft tissues.
What is the function of the oral cavity?
It acts as a flutter valve that can:
Swing up to close the pharyngeal isthmus, and seal off the nasopharynx from the oropharynx (prevents food into the nose).
Swings down to close the oropharyngeal isthmus and seal the oral cavity from the oropharynx.
What is the tongue?
It is the floor of the mouth.
It is a mass of skeletal muscle covered in mucous membrane.
It is innervated by the hypoglossal nerve.
What is the main functions of the tongue?
Articulation
Directing food into the oropharynx during deglutition.
Taste
How does the tongue produce taste?
Papillae are mucosal elevations on the tongue.
Fungiform, foliate and vallate papillae are taste buds.
Filiform papillae do not have taste buds, increase area of absorption and sensitivity of the tongue.
What is the terminal sulcus?
Has a V form which divides the tongue into:
Anterior 2/3s - innervated by the facial nerve and trigeminal nerve.
Posterior 1/3 - by glossopharyngeal nerve.
Taste sensations in the posterior 1/3 are carried by the vagus nerve.
What are the salivary glands?
Saliva is produced by the goblet cells and by the salivary glands - parotid, submandibular and sublingual gland.
What is the parotid gland?
Largest and main salivary gland.
Located anterior to the ear.
Parotid duct opens in the cheek opposite the upper molar.
It is innervated by the Glossopharyngeal nerve.
What is the submandibular gland?
Located under the mandibular bone.
Innervated by the facial nerve.
What is the sublingual gland?
Smallest and deepest gland.
Located beneath the tongue.
Innervated by the facial nerve.
Ducts open in the floor of the mouth.
What is the pharynx?
A musculofascial half-cylinder that links the oral and nasal cavities to the larynx and oesophagus.
It is attached to the base of the skull, and at the vertebra C6 level, then becomes the oesophagus.
What are the regions of the pharynx?
Nasopharynx - anteriorly attached to nasal cavities throug choanae.
Oropharynx - anteriorly opens into oral cavity (oropharyngeal isthmus).
Laryngopharynx - anteriorly attached to larynx through superior aperture of larynx.
What is the oesophagus?
Muscular tube connecting the pharynx and stomach.
It begins at the cartilage opposite the C6 vertebra.
It continues through the thorax then ends at the cardiac opening of the stomach at the T10 vertebra.
What are the areas of natural constriction in the oesophagus?
The lumen is smaller at the junction of oesophagus with pharynx.
Where the left bronchus crosses the oesophagus.
Where the oesophagus crosses the diaphragm.
What are the structures around the oesophagus?
Anteriorly: left atrium, left bronchus, right pulmonary artery.
Posteriorly: Thoracic duct, hemi-azygous vein, aorta
What is the arterial supply to the oesophagus?
Thorax - branches of thoracic aorta and bronchial arteries.
Abdomen - ascending branches of the left gastric artery.
What is the venous drainage of the oesophagus?
Azygos vein and hemiazygos vein.
Oesophageal branches to the left gastric vein.
What is the lymphatic drainage of the oesophagus?
Posterior mediastinal and left gastric nodes.
What is the foregut?
Starts at the abdominal oesophagus.
Contains the spleen, liver, stomach and pancreas.
Ends below the major duodenal papilla in duodenum.
Blood is supplied by the celiac trunk.
What is the midgut?
Begins below the major duodenal papilla.
Contains the small intestine.
Ends at the junction between the proximal 2/3 and distal 1/3 of the transverse colon.
Supplied by the superior mesenteric artery.
What is the hindgut?
Begins before the colic flexure.
Contains distal 1/3 of transverse colon, descending colon, sigmoid, rectum, and ends midway through the anal canal.
Supplied by the inferior mesenteric artery.
What are the tissue layers of the gastrointestinal tract?
Mucosa - innermost layer.
Submucosa
Muscularis Externa
Serosa - outermost layer.
What is the mucosa?
This is the inner most layer, made from epithelium.
It secretes mucous, which is important for food travelling through the canal.
What is the submucosa?
This has simple columnar epithelium.
Lamina propria - connective tissue, arteries, veins, lymphatics and nerves
What is the muscularis externa?
Smooth muscles which keeps the mucous moving.
This has a circular layer and a longitudinal layer
What are smooth muscles?
Involuntary contraction
Spindle shaped, uni-nucleated and non-striated.
Arranged in sheets - circular or longitudinal
