Overview of the alimentary system Flashcards
Overall function of digestive system
digest and absorb food
Definition of absorption
Transferring nutrients to the circulation
Which two groups of organs make up the alimentary system?
Digestive tract (oesophagus, stomach, small and large intestine) and accessory organs (salivary glands, gall bladder, liver, pancreas)
What are the three major pairs of salivary glands?
Parotid, submandibular, sublingual
What are the possible consistencies of saliva secretions?
Serous (watery), mucous (thick) or seromucous (mixed)
Function of the gall bladder
Stores concentrated bile (produced by the liver) and releases it into the duodenum when fatty food is consumed (bile emulsifies lipids and neutralises acid).
Description and function of the pharynx
a 12-15cm long muscular tube responsible for the passage of food and air - digestive and respiratory role
Description of oesophagus
a 20-25cm muscular tube which extends from the pharynx to the stomach, passing behind the trachea and the heart)
Description and function of stomach
muscular organ found in UL of abdomen. Churns food and drink to form chyme and secretes HCl and enzymes to digest food.
Function of sphincters
regulates the release of secretions e.g. from oesophagus to stomach or from stomach to small intestine.
What are the 3 parts of the small intestine?
Duodenum, jejunum, ileum
Parts of the large intestine
caecum, appendix, ascending, transverse and descending colon, rectum, anus
What are the layers of the gastrointestinal histology?
Mucosa, submucosa, muscularis externa/propria, adventitia/serosa
Which layers make up the mucosa?
Epithelium, lamina propria, muscularis mucosae
What is the epithelium type in the oral cavity, pharynx and oesophagus and why?
Non-keratinised stratified squamous epithelia - protective against mechanical abrasion
What is the lamina propria?
Thin layer of connective tissue found in the mucosa beneath the epithelial layer. Contains inflammatory cells and provides support and nutrients to the epithelium.
What is the muscularis mucosae?
Layer of smooth muscle continuous throughout the alimentary system (from oral cavity to anal canal). Found in the mucosa beneath the lamina propria, above the submucosa.
What is the submucosa?
Dense irregular connective tissue containing large blood vessels, nerves and lymphatic vessels.
What is the muscularis propria/externa?
Smooth muscle found below the submucosa made up of an inner circular layer and outer longitudinal layer of muscle. Contracts to aid digestion and movement of food via peristalsis.
What is the difference between adventitia and serosa?
Either one is found encapsulating an organ. Adventitia is a fibrous CT layer while serosa is a serous membrane which secretes serous fluid to reduce friction.
Which parts of the digestive system have adventitia?
Oral cavity, upper oesophagus, ascending and descending colon and rectum. Everything else has serosa
What is GORD?
Gastro-Oesophageal Reflux Disease. Continuous reflux of acid from stomach into oesophagus which may cause Barrett’s oesophagus.
Metaplasia definition
When epithelium changes from one type to another - can be part of normal maturation or pathological.
What is Barrett’s oesophagus?
The pathological change of oesophageal-epithelium from stratified squamous to simple columnar epithelium.
What is the risk of having Barrett’s oesophagus?
Risk of dysplasia and oesophageal cancer
What is dysplasia?
The abnormal growth of cells resulting in unequal cell size, abnormally-shaped cells, excess pigment and higher number of mitotic figures.
Which organ of the alimentary system has a secretory function?
Stomach
What are the names of the glands in the stomach?
Gastric glands - cardiac, fundic, pyloric glands
Which layer of the mucosa are glands located?
Lamina propria
What do the secretory cells secrete in the stomach?
HCl, mucus, enzymes, bicarbonate
What is the epithelium type in the stomach?
Simple columnar epithelium
Which organs of the alimentary system have an absorptive function?
Small (and large) intestine
What is the epithelium type in the small intestine?
Simple columnar epithelium
What is the apical specialisation of epithelium in the small intestine?
Villi - finger-like extensions
Function of villi
Increase surface are of the small intestine by about 30 times to aid digestion and absorption in the duodenum, jejunum, ileum.
What is Coeliac disease and how does it affect the small intestine?
Autoimmune response when gluten is consumed. Causes villous atrophy, hyperplastic crypts and an increase in lymphoid cells.
What is villous atrophy?
Destruction of villi causing a flattening appearance of the mucosa. Reduces surface area so small intestine unable to absorb nutrients.
What are hyperplastic crypts?
When the grooves between the villi become stretched and elongated
What are lymphoid cells?
Chronic inflammatory cells found in the lamina propria
What is the function of the epithelium in the large intestine?
Absorb water and vitamins created by colonic bacteria (e.g. vit K - blood clotting), and secrete mucous to protect itself from undigestible materials.
What are colonic crypts?
Intestinal glands in invaginations of the large intestine
What is IBD?
Inflammatory Bowel Disease - divided into Crohn’s disease and ulcerative colitis
What is Crohn’s disease?
Lifelong inflammation of tract lining which results in collection of granulomas (chronic inflammatory cells). Can affect anywhere in the GIT - e.g. lesions in the oral cavity. Symptoms of abdominal pain, vomiting, altered bowel habits…
What is ulcerative collitis?
Inflammation and ulceration of the colon and rectum only. Symptoms of abdominal pain, diarrhoea…
What are the 5 different roles of the alimentary system?
Secretory (lubrication too), Digestion, Motility, Absorption, Excretion
What is the total amount of fluid (external and internal from secretions) that enters the GIT in a 24 hr period?
7600 ml (-100 ml of faeces = 7500 ml)
What are some of the secretions that enter the GIT?
Saliva (600ml), Gastric juices (2000ml), Bile (500ml), Pancreatic juice (1500ml), Intestinal juice (1500ml)
What are the two forms of digestion?
Mechanical and chemical
What does the mechanical aspect of digestion involve?
Churning, mixing, propulsive motility
What does the chemical aspect of digestion involve?
Mainly enzymes secreted at different points in the GIT e.g. amylase in saliva, trypsin, amylase and lipase from the pancreas. Also HCl
What is the motility occurring at each stage in the GIT?
Chewing and swallowing in the mouth -> churning and mixing in the stomach with acid, enzymes, bicarbonate -> peristalsis in the intestine -> defaecation
How much fluid is absorbed in the GIT?
7500 ml (equal to secretions and intake).
Where in the GIT does most absorption occur?
Most absorption occurs in the small intestine with some in stomach and large intestine.
Functions of the mouth
Sensory function, motor functions, salivation, immunity (lymphoid tissue - tonsils), reflexes (protective)
What are the sensory functions of the mouth?
Nociception (pain), mechanoreception (movement), thermoreception (temperature), gustation (taste), higher level perceptions e.g. evoke feelings/responses
What are the motor functions of the mouth?
Feeding (breakdown, deglutition/swallowing into pharynx), Communication (speech, facial expressions)
What is the function of saliva?
Protect the mucosa, lubricate, digest
What is the name of the muscle that forms a hammock at the floor of the mouth?
mylohyoid
What is the difference between the hard and soft palate?
The hard palate is made of bone whereas the soft palate is made of muscle, with mucous membrane on top. The soft palate is posterior to the hard palate.
What is the lowest part of the soft palate?
Uvula
What is the name of the pillars in the posterior part of the mouth?
Fauces
Which tonsils are located on the fauces?
Palatine tonsils
Function of palatine tonsils
Primary line of defence against pathogens
Where is the sublingual duct found?
Under tongue
Which two salivary glands release their secretions into the sublingual duct?
Submandibular and sublingual glands
What is the name for the folds under the tongue?
Plica fimbriata
What is the function of the lingual vein?
Drains the floor of the mouth
What is the name of the structure which holds the tongue in place?
Lingual frenulum
What might being tongue-tied / difficulty to eat and speak be caused by?
A short lingual frenulum
What are the three groups of general muscles in the mouth?
Jaw muscles, facial muscles, buccinator
What are the names and locations of the two jaw muscles?
Temporalis helps close the mouth - located over the side of the temple/scalp. Masseter helps close the mouth too - located over the jaw angle.
What is the name of the facial muscle that surrounds the mouth?
Orbicularis oris
Where is the buccinator located?
Cheeks
Function of the buccinator
puffs out cheeks, moves food into the centre of the oral cavity during chewing
What type of saliva secretion is produced by the parotid gland?
Serous
What type of saliva secretion is produced by the submandibular gland?
seromucous
What type of saliva secretion is produced by the sublingual gland?
mucinous
How can mumps (paramyxovirus) affect salivary glands?
Swelling of parotid gland
What is the name of the condition involving calculus /stone forming in a salivary gland?
Sialolithiasis
Which salivary gland is typically affected by sialolithiasis?
Submandibular
What is the name of the condition of inflamed salivary glands?
Sialoadenitis
What must surgeons be cautious of when when removing a tumour near the parotid gland?
Facial nerve is close to parotid gland. Located first to avoid damage.
