Flashcards in STRUCTURE AND FUNCTION OF THE GUT Deck (115):
What is the cell type that lines the entire mouth?
Stratified squamous epithelial cells
How many teeth do adults normally have?
How many teeth do children normally have?
20 deciduous teeth
Where do the teeth arise from?
Where on the tongue are the receptors for sweet foods found?
Towards the front
Where on the tongue are the receptors for salty foods found?
Anterior middle portion
Where on the tongue are the receptors for sour foods found?
Posterior middle portion
Where on the tongue are the receptors for bitter food found?
Towards the back
What attached the anterior part of the tongue to the floor of the mouth?
What are the roles of saliva?
Lubricate food to aid swallowing
Begin digestion of starches (amylase)
Break down of fats to help tongue analyse fragments (Lipases)
How much saliva an adult produce per day?
1500 ml, most is swallowed and recycled
What is the enzyme found in the saliva which starts the breakdown of starch?
What are the names of the three main salivary glands found in the mouth?
Which salivary gland in the mouth produces the highest percentage of saliva?
The submandibular gland - 70%
What is the specific role of the parotid gland?
Produces watery secretions lacking mucus
Secretes the alpha amylase
What is the specific role of the submandibular gland?
Is saliva isotonic, hypertonic or hypotonic?
What is the oesophageal hiatus?
The point where the oesophagues passes through the diaphragm and hence enters the abdomen
What proportion of the oesophagus is made of striated muscle?
The upper third
What proportion of the oesophagus is made of smooth muscle?
Lower two thirds
At what spinal level does the oesophageal hiatus sit?
What is the name of the oesophageal sphincter that closes off the entrance to the stomach?
Cardio sphincter or lower oesophageal sphincter
Which nerve controls the sphincters of the oesophagus?
Describe the nervous pathway of swallowing.
Sensory endings in the mouth signal presence of food
Sends signal to nucleus of the tractus solitarius (solitary tract, NTS)
Activates motor neurones in nucleus ambiguus
Controls muscles of soft palate, larynx and epiglottis
What is the capacity of the average adult stomach?
What do we call the superior part of the stomach where the bolus enters?
What is the name of the folds in the stomach that allow it to expand?
What are the functions of the stomach?
Temporary storage of food
Mechanical breakdown of food
Pepsin digestion of proteins
Controlled passage of chyme into small intestine
Secretion of intrinsic factor
What is chyme?
The name used for the semi-digested material which is passed on from the stomach to the small intestine.
What is the role of intrinsic factor?
It protects vitamin B12 from the very low pH of the stomach. It is absorbed with the vitamin in the ileum.
What is the name of the additional muscle layer in the stomach wall not found in other parts of the GI tract? What is its function?
Inner oblique muscle
Churn up the food
What is the primary barrier which prevents the digestive enzymes from digesting the stomach wall?
A very thick layer of mucus
Which cells secrete gastrin from the stomach wall?
Which cells secrete HCl from the stomach wall?
Parietal (oxyntic) cells
Which cells secrete intrinsic factor from the stomach wall?
Parietal (oxyntic) cells
What are pepsinogens and which cells are responsible for secreting them from the stomach wall?
Pepsinogens are inactive precursors of pepsin secreted from the chief cells (or peptic cells)
What is the role of gastrin?
Stimulates the release of acid from the parietal cells.
What are the components of gastric juice?
What are the three ions channels/transporters found on the lumen side of the parietal cells, used in the secretion of acid?
Proton pump - K+ in for H+ out - active transport
K+ and Cl- co-transporter - passive transport
Where do the protons used to make acid come from?
How are the OH- ions, made as a by product of acid secretion, dealt with?
They are deposited in the blood as bicarbonate.
What is the pH of the blood in the gastric vein? What do we call this?
What is the pH in the lumen of the stomach?
pH ~ 1.3
What are the roles of stomach acid?
Denatures connective tissue and muscle fibres of meat
Combines with calcium and iron in the food to form soluble salts that can be digested
Activates inactive pepsinogens
Optimizes pH for pepsins
What do we call pepsinogens wrapped up in membrane-bound granules?
Does the stomach secrete lipase?
Yes, however not much fat digestion occurs in the stomach
What is secreted with the mucus to prevent the digestion of the stomach wall?
Bicarbonate to shield wall from acid
What prevents stomach acid from getting under the epithelium?
What increases mucus production?
Prostaglandins increase mucus production and increase blood flow to the mucosa, bringing bicarbonate with it.
How much gastric juice is made in the adult stomach on an average day of eating?
What are the three phases that regulate gastric secretion?
What triggers the cephalic phase of gastric secretion?
Smell, sight, taste of food, chewing
What transmits the signal in the cephalic phase?
What triggers the gastric phase of the gastric secretion?
Distension of the stomach
What triggers the intestinal phase of gastric secretion?
Protein digestion products in the duodenum
What inhibits gastric secretion?
Intestinal phase - Secretion of secretin, CCK and GIP
What are the two parts of the stomach's motor system?
Proximal motor unit
Distal motor unit
How does the stomach churn up and mix the contents?
Through a peristaltic wave mainly from the distal motor unit
What are the three parts of the small intestine?
What is the average length of the small intestine in an adult?
What is the average width of the small intestine in an adult?
What are the main two functions of the small intestine?
What is particular about the folds in the small intestine in terms of how the chyme is passed through?
The folds force the chyme to take a spiral pathway
What is the brush border of the small intestine?
The wall of the small intestine contains villi, which themselves have microvilli. These microvilli increase surface area and are sometimes referred to as the brush border.
What is the name of the glands found in between the villi in the small intestine?
Crypts of Lieberkuhn
How far do the Crypts of Lieberkuhn extend through the wall of the small intestine?
Down to the muscularis mucosa
What do the endocrine cells of the Crypts of Lieberkuhn in the small intestine produce?
What is the pH of the fluid secreted into the lumen of the small intestine?
What stimulates the secretion of secretin in the small intestine?
What stimulates the secretion of cholecystokinin in the small intestine?
Fat digestion products
What is the length of the duodenum?
Is the duodenum contained within mesentery?
Other than the chyme, what else enters the duodenum?
What is the name of the sphincter that separates the duodenum from the bile and pancreatic ducts?
Sphincter of Oddi
How does the duodenum protect itself from the bile and the pancreatic juices?
It secretes an alkaline mucus
Are the jejunum and ileum supported by mesentry?
What is the arterial supply to the jejunum and ileum?
Superior mesenteric artery
What is particular about the mucosal thickness of the jejunum and ileum?
As you move distally, there is a gradual reduction in the mucosal thickness
Is the pancreas an endocrine or an exocrine gland?
What are the endocrine functions of the pancreas?
Secretion of insulin and glucagon
What cells secrete digestive enzymes from the pancreas?
The acinar cells
Innervation of the endocrine islets of the pancreas is supplied by what?
Parasympathetic vagal nerve
What is the role of the duct cells in the exocrine ducts?
Regulated by secretin, they release a HCO3- rich secretion which is added to the enzyme and Cl- rich secretion from the acinar cell above.
What are the enzymes released from the pancreas that are responsible for the digestion of protein?
What is the enzyme released from the pancreas that is responsible for the digestion of sugars?
What are the enzymes released from the pancreas that are responsible for the digestion of oils and fats?
What is the major activator of most of the enzymes released from the pancreas?
What is the zymogen of trypsin?
What emulsifies fat before digestion?
What is the enzyme used as the catalyst in bicarbonate ion production?
How are bicarbonate ions secreted into the lumen of the pancreatic ducts?
How are the protons left behind as a by product of bicarbonate ion production removed from the cell?
Na+ ions are countertransported at the non-lumenal side.
What regulates the secretion of the aqueous component of pancreatic juices?
What is the first part of the large intestine?
How much passes into the large intestine everyday in the average healthy adult?
About 500 ml
What are taeniae coli?
Thickened bands of longitudinal muscle
What are haustra?
Pockets formed by the smooth muscle action of the taeniae coli.
What is the function of the large intestine?
Storage of residues before elimination
Secretion of mucus to lubricate faeces
Absorption of remaining water and electrolytes
Where in the GI tract is most of the water reabsorbed?
The small intestine
How much water is reabsorbed in the large intestine?
What happens if the large intestine fails to reabsorb the water?
How does re-absorption by the large intestine occur?
Sodium ions actively taken up, under control of aldosterone.
What otherwise indigestible things are digested by flora in the large intestine?
Some carbohydrates and lipids
Give an example of an aerobic microbe found in the flora of the large intestine.
Give an example of an anaerobic microbe found in the flora of the large intestine.
How do microbes naturally found in the flora of the large intestine contribute to the bilirubin cycle?
Convert bilirubin into non-pigmented urobilinogens.
What are the vitamins synthesized by the microbes naturally found in the flora of the large intestine?
Why might antibiotics lead to an increased risk of bleeding?
Vitamin K synthesized by microbes naturally found in the flora of the large intestine is a cofactor in the production of blood clotting factors.
How long does stuff end up staying in the large bowel in an average adult?
What muscle layer contracts in the mixing movements of the large intestine?
Which parts of the large intestine have peristaltic movements occur and different points throughout the day?
The transverse colon and descending colon
What is a mass movement of the large bowel?
Portion of the colon that contracts is longer than a normal peristaltic wave. Material is moved out of the proximal colon. When the mass movement happens in the descending colon we experience the need to defecate.
Does the rectum normally contain anything?
No, not unless we need to defecate.
Which sphincter in the rectum is under voluntary control?
The external anal sphincter