What is the GI tract?
A continuous tube that starts at the oral cavity and ends at the anus
What is the structure of the GI tract?
The tube is lined by mucosa which is made up of epithelium and lamina proper
Also smooth and skeletal muscle in the walls
What are the components of the GI tract?
Head: Oral cavity, pharynx Neck: Pharynx, oesophagus Chest: Oesophagus Abdomen: Stomach, small intestine, large intestine Pelvis: Rectum, anal canal Perineum: Anus
What is the function of the oral cavity?
Sensing, salvation, chewing, initiating swallowing
What is the function of the pharynx?
Defence against infection, swallowing, airway protection
What is the function of the oesophagus?
Transit from the pharynx to the stomach
What is the function of the stomach and small intestine?
Transit, defence against infection (acid in stomach), digestion and absorption
What is the function of the large intestine and anus?
Transit, re-absorption of water and electrolytes, stool formation, waste excretion
What divides the upper and lower GI tract?
The ileocecal junction - between the small intestine and large intestine
What is the main principle of the upper gi tract?
To ensure that solids and liquids can safely get in and out of our stomach
What are the dangers that the upper GI tract protects us from?
Poisons: sensory receptor
Sharp or hot/cold: sensory receptors
Bacteria/virus: Saliva, tonsils, stomach acid
Obstruction: Chewing, lubrication, swallowing, peristalsis
Aspiration: Cough reflex
What are the structures present in the oral cavity?
Nasal cavity, hard palate, teeth, mandible, muscle of floor of mouth, hyoid bone, epiglottis, pharynx, dens of C2, tongue
How do we chew?
The muscles of mastication - there are 4 muscles at each TMJ - 3 close and 1 open
What are the close muscles?
Temporalis
Masseter
Medial pterygoid
What is the open muscle?
Lateral pterygoid
How is drooling prevented?
The muscles of facial expression, lies between superficial fascia and facial skeleton
What is the name of the muscle that prevents drooling?
Orbicularis oris which is a circular muscle that surrounds the mouth and prevents dribbling during chewing and swallowing
What is the oral cavity lined internally by?
Mucosa which has a stratified squamous epithelium for protection.
Where is keratin present?
On the gingivae and hard palate
What are the structures present in the mouth?
Hard palate, soft palate, arches of soft palate, palatine tonsils, upper dental arch, uvula, lower dental arch, gingiva, tongue
What are the 4 types of papilla on the tongue?
Foliate papillae, vallate papillae, fungiform papillae and filiform papillae
What papillae are taste buds?
Foliate, vallate, fungiform
What does the tongue not have?
A skeleton
What do the extrinsic muscles of the tongue do?
4 pairs that attach the tongue to the bony skeleton which allows movement of the tongue during mastication, speech and swallowing
What do the intrinsic muscles do?
4 pairs that change the shape of the tongue during function
What does saliva do?
A solute that allows tasting to occur, contains a lubricant (mucin) the aid swallowing and speech for keeping the mucosa moist. Buffer for plaque acids and contains antimicrobial elements
What are the major salivary glands?
Parotid (near ear)
Subandibular
Sublingual
What will stimulate salivation?
Thought, sight or smell of food
Painful oral conditions such as teething or a fractured mandible
Where is the parotid gland located and where does the duct go?
Found next to ear and the duct runs across the face and secretes into the mouth by the upper 2nd molar
Where is the sub-mandibular gland located and where does the duct go?
Under the mandible, the duct enters the floor of the mouth and secretes via the lingual caruncle
Where is the sublingual gland located and where does the duct go?
Under the tongue, lays in the floor of the mouth and will secrete via several ducts superiorly
What is the function of the pharynx?
Swallowing, breathing, defence against infection
What is the pharynx lined by?
Mucosa - non-keratinised stratified squamous epithelium
What are the 3 parts to the pharynx?
Nasopharynx - posterior to nasal cavity but superior to soft palate
Oropharynx - posterior to oral cavity between soft palate and epiglottis
Laryngopharynx - posterior to layrnx, between the epiglottis and oesophagus
What is the laryngeal inlet?
The opening into the airway
How is aspiration reduced?
The raising of the layrnx towards the oesophagus reduces the change of aspiration, but if it does occur the cough reflex will engage
What is the structure of the oesophagus?
Muscular tube that has a gradual transition of skeletal muscle to smooth muscle. Lined with non-keratinised stratified squamous epithelium
What is the function of the oesophagus?
To transmit food and liquids from the pharynx to the stomach
Where does the oesophagus travel?
Inferiorly through the thoracic cavity, pierces the diaphragm at T10 vertebral level and then joins the stomach within the abdominal cavity
What is the abdominal cavity formed by?
Bone (ribs, spine, pelvis)
Muscle (diaphragm, back and anterolateral wall)
How many layers of skeletal muscle are there in the abdominal wall?
3
What is the peritoneum?
A continuous serous membrane that secretes lubricating peritoneal fluid into the peritoneal cavity. It lines the abdominal cavity and invests viscera (organs)
What are the 2 layers to the peritoneum?
Visceral - invests an organ
Pariteal - touches the internal body wall
What is peritonitis?
The inflammation of the peritoneum which is caused by infection, surgery or trauma. This will lead to guarding
How are the abdominal organs organised -
4 quadrants?
Right Upper Quadrant Left Upper Quadrant Right Lower Quadrant Left Lower Quadrant Separated by the level of umbilicus and a straight line down from the sternum to anus
How are the abdominal organs organised - 9 regions?
Right and left hypochondrium Right and left lumbar Right and left inguinal Epigastric Umbilical Pubic
What are the planes that separate the regions?
Mid-clavicular planes
Subcostal plane
Transtubecular plan
What is the shape and position of the stomach?
J shaped organ that connects the oesophagus to the small intestine. Located mostly in the left lower quadrant
What is the function of the stomach?
Defence against infection by the production of stomach acid
Digestion and absorption
“Blender”
What separates the stomach from the small intestine?
The pyloric sphincter which connects the stomach to the duodenum of the small intestine
What is the function and location of the small intestine?
Responsible for transit, digestion and absorption
Attached to the body wall by mesentery and is located in all four quadrants
What are the 3 parts of the small intestine?
DJ Ileum
Duodenum
Jejunum
Ileum
What is mesentery?
A double layer of peritoneum that connects the small intestine to the body wall. It allows the passage of nerovasculature
What is the function of the large intestine?
Transit
Reabsorption of water and electrolytes
Stool formation
Where is the large intestine found and what makes it up?
All 4 quadrants Caecum Ascending colon Transverse colon Descending colon Sigmoid colon
What is the rectum and anus and what is their function?
The terminal end of the large intestine that forms stool and excretes waste
What is the structure of the rectum and anal canal?
The rectum and anal canal is made up of smooth muscle but the sphincter that forms the anus is skeletal - allowing voluntary faecal excretion
What is peristalsis?
Waves of simultaneous shortening of the length of a segment of the tube plus the narrowing of the luminal diameter in that segment. The outer longitudinal layer of smooth muscle shortens the tube and the inner circular layer of smooth muscle constricts the diameter
What are the kinds of blockage that can occur in the GI tract?
External compression: An expanding tumour in an adjacent structure
Internal obstruction: A mucosal tumour that expands within the lumen e.g. an ingested foreign body
What is the body’s response to an obstruction?
Increased peristalsis proximal to the site of the obstruction in an attempt to remove it
What is colicky pain?
When peristalsis occurs in waves causing pain to remove a blockage
What are the types of mucosa and where are they found?
Protective in the oral cavity, oesophagus and anus - the areas of greatest mechanical friction
Stomach - secretory - minimally absorptive
Small intestine - absorptive for nutrients
Large intestine - absorptive for water and electrolytes
How is flow controlled through the GI tract?
Cricopharyngeal sphincter - junction between larynopharynx and oesophagus to prevent regurgitation
Pyloric shpincter at the junction between the stomach and duodenum to control release of chyme from stomach
External anal shpincter that controls release of stool from anal canal
What are the 3 areas of the GI tract that have different blood supplies?
Foregut
Midgut
Hindgut
What is in the forgut?
Oesophagus to mid-duodenum
Liver and gall bladder
Spleen
Half of pancreas
What is in the midgut?
Mid-duodenum to proximal 2/3rds of transverse colon
Half of pancreas
What is in the hindgut?
Distal 1/3rd of transverse colon to proximal 1/2 of anal canal
Where does the inferior vena cava travel?
Ascends in the retroperitoneum then passes through the diaphragm to drain into the right atrium
Where does the aorta travel through?
Leaves the left ventricle and passes through the diaphragm then descends into the retroperitoneum
What are the 3 branches of the abdominal aorta?
Coeliac trunk - foregut organs
Superior mesenteric artery - midgut organs
Inferior mesenteric artery - hindgut organs
What are the veins that drain the GI tract?
Splenic vein drains forgut
Inferior mesenteric vein drains the hindgut organs
Superior mesenteric vein drains the midgut
Hepatic portal vein is formed from the superior mesenteric vein and splenic vein
What are the two venous systems?
Portal venous system - drains for the absorptive parts of GI tract to liver via hepatic portal vein. Blood is deoxygenated and nutrient rich
Systemic venous system - drains deoxygenated lood from body to right atrium, this includes blood from the liver