List the layers of tissue in the GI tract
- serosa
- muscularis externa
- submucosa
- mucosa
What is the embryological origin of the upper GIT?
Foregut
List teh muscles of the oral cavity (and their innervation)
- walls of the oral cavity are comprised of the buccinator, which holds the cheek against the alveolar arches
- the floor is comprised of the mylohyoid and geniohyoid, which together help depress the mandible to open the mouth
The innervation of these muscles is VII, V, C1 resp
Describe teh surfaces of the tongue
- superior or oral part: covered in hundreds of papillae
- inferior, covered in mucosal folds, site of frenulum
- pharyngeal, composed of lymphoid tissue, site of lingual tonsil
Distinguish and describe intrinsic and extrinsic tongue muscles
- intrinsic: refers to muscles that originate and insert within the tongue e.g. , work to lengthen and shorten, curl and flatten the tongue
- extrinsic: refers to muscles originating from structures outside the tongue, and insert within the tongue. Includes mylohyoid and geniohyoid as well as…
- styloglossus: retracts tongue
- palatoglossus: elevates back of tongue, moves arches towards midline, depresses soft palate
- hyoglossus: depresses tongue
- genioglossus(most superior): depresses central part and protrudes anterior part
List the functions of the extrinsic tongue muscles
- styloglossus: retracts tongue
- palatoglossus: elevates back of tongue, moves arches towards midline, depresses soft palate
- hyoglossus: depresses tongue
- genioglossus(most superior): depresses central part and protrudes anterior part
List the salivary glands and their innervation
- sublingual and submandibular (sits outside oral cavity floor), innervated by CN VII
- parotid gland, innervated by CN IX
Describe the pharynx, and the blockagae of food from nasal cavity and larynx
- the common pathway for food via the oesophagus, and air via the trachea
- spans base of skull to C6
- food is blocked
- from nasal cavity by soft palate
- from larynx by epiglottis
List and describe the two layers of striated muscle in the pharynx
- constrictors (superior middle and inferior) - the external layer, contracts sequentially to push food bolus down to oesophagus for swallowing
- superior attaches to pterygomandibular ligament: site for administration of inferior alveolar nerve block
- longitudinal muscles/internal layer: palat0/salpingo/stylopharyngeus, elevate the pharynx
- salpingo: eustachian tube and constrictors
Describe the sites of constriction in the oesophagus and their clinical significance
The oesophagus has three constrictions, as it passes various anatomical structures:
- at junction with pharynx i.e. upper sphincter - cervical C6/7
- crossing with aortic arch and L main bronchus - T3/4 / bronchoaortic
- passing oesophageal hiatus: diaphragmatic - T10/11
Clinical significance:
- common site of damage
- foreign bodies
- passing endoscope
- estimating distance of nasogastric tube
List the three portions of the oesophagus
There are three parts to the oesophagus:
- cervical: C6 to jugular notch
- thoracic: jugular notch to oesophageal hiatus, longest portion
- abdominal: hiatus to cardia, shortest portion
List some anatomical structures close to the cervical and thoracic oesophagus
Anatomical relationships:
- cervical: posterior to the trachea, lateral: carotid sheath (Artery, IJ vein, vagus n.)
- thoracic: in posterior mediastinum i.e. posterior to the heart, left atrium; anterior and right to aorta
Describe the musculature of the oesophagus
The regions of the oesophagus have unique musculature, blood supply and lymphatics:
- upper third is striated muscle
- middle third is a mix
- lower third is smooth muscle
Describe the arterial supply of the oesophagus
- upper third of the oesophagus is supplied by inferior thyroid arteries (branch of thyrocervical trunk, branch of subclavian)
- middle third is supplied by oesophageal arteries (2-5 unpaired), branches of the thoracic aorta
- lower third is supplied by left gastric artery (branch of coeliac trunk, branch of abdominal aorta)
Describe the venous drainage of the oesophagus
- upper third is drained by inferior thyroid veins, which drain into brachiocephalic veins and SVC
- middle third is drained by oesophageal veins, which drain into azygos vein and into SVC
- lower third is drained by left gastric vein, which drains into portal vein
- note that oesophageal and left gastric vein anastomose
- NOTE ALSO: portal hypertension and oesophageal varices (As a consequence of anastomoses)
Describe the lymphatic drainage of the oesophagus
- upper third drained by deep cervical nodes
- middle third drained by superior and posterior mediastinal nodes
- lower third drained by left gastric nodes and coeliac nodes
- clinical significance: cancer of the lower third often spreads to coeliac nodes and all regions that drain into the coeliac nodes i.e. stomach, duodenum, spleen, omenta
Describe the sources of oesophagus innervation
Two main sources of innervation
- oesophageal plexus
- vagal trunks (vagus nerve – parasympathetic, and somatic motor in upper oesophagus)
- cervical and thoracic sympathetic trunks (sympathetic)
- enteric nervous system, see [[Anatomy B5 - Lecture 2]]
Describe the LOS and its role
- a high pressure zone between
- the positive pressure of the abdomen
- negative pressure of the thorax
- Both the oesophageal muscle and diaphragm play a a role in LOS to move contents into stomach
- Note the “Z” line at squamo-columnar junction
- Malfunction of LOS: GORD
- No voluntary control as opposed to UOS
Descrube the regions and composition of the stomach
- is comprised of four parts: cardia, fundus, body or corpus, and pyloric region - which can be further divided into antrum and canal
- two borders: greater and lesser curvature
- two openings: cardial orifice or entrance, pylorus or exit
- three muscle layers from outer surface: longitudinal, circular and oblique - different direction fibres help move in different ways to move food
- longitudinal is more superficial
- followed by circular
- oblique is deepest
Describe the parts and broad function of the duodenum and pancreas
- The duodenum has a ‘c’ shape and is comprised of four parts: superior, descending, inferior, ascending (in that order)
- pancreas also has four parts: head neck body and tail
- it has exocrine function: excretes through main and accessory ducts
- it also has endocrine function: produces insulin and glucagon
- outflow: ampulla of Vater, surrounded by sphincter of Oddi, inserts into greater duodenal papilla and opens into duodenum-
List the main arteries of the GIT
- foregut is supplied by celiac trunk
- midgut is supplied by superior mesenteric artery
- hindgut is supplied by inferior mesenteric artery
Breakdown the major arteries of the upper GIT and their branches
- celiac trunk
- left gastric artery
- splenic artery (tortuous to accommodate for stomach movement inferior to it)
- pancreatic
- L gastroepiploic/gastro-omental (anastomoses with R counterpart)
- short gastrics
- common hepatic artery
- right gastric
- proper hepatic
- gastroduodenal (R omental)
Describe the main veins of the GIT and their drainage
- ‘special K’: Portal vein, into which drains
- SMV (continuous with portal vein)
- Splenic vein, which enters SMV
- IMV, which drains into splenic, into SMV, ultimately into portal vein
- Note also pancreaticoduodenal, gastric, pancreatic veins
Describe the broad innervation of the GIT
- sympathetic: thoracic splanchnic nerves
- parasympathetic: vagal trunks: anterior and posterior
- enteric
