OC5 - digestive system Flashcards
what are the layers of the digestive system?
mucosa
submucosa
muscularis
serosa
what are the tissues in the mucosa?
epithelial
connective
muscle
what is the function of the mucosa?
lines the gut
what are the tissues in the submucosa?
connective
nervous
what is the function of the submucosa?
blood supply, glands and nerves
what are the tissues in the muscularis?
skeletal muscle - top
smooth muscle - circular and longitudinal
what is the function of the muscularis?
peristalsis
myenteric plexus - autonomic control
what are the tissues in the serosa?
epithelial
connective
what is the function of the serosa?
connects the alimentary canal to the peritoneum
what are the activities within the digestive system?
propulsion
chemical digestion
mechanical digestion
absorption
what is propulsion within the digestive system?
swallowing - oropharynx
peristalsis - oesophagus, stomach, small intestine, large intestine
where does chemical digestion occur?
mouth
stomach
small intestine
what is mechanical digestion wthin the digestive system?
chewing - mouth
churning - stomach
segmentation - small intestine
what is absorbed in the digestive system?
nutrients - to lymph vessels by the small intestine
water - to blood vessels by the large intestine
what are the components of the alimentary canal?
mouth
oesophagus
stomach
small intestine
large intestine
what is the function of the mouth?
start of the alimentary canal
mechanically breaks down food using teeth
swallowing is voluntary but after this point muscular control is involuntary
what are the three salivary glands?
parotid
submandibular
sublingual
where is the parotid gland located?
inside the cheeks
where is the submandibular gland located?
beneath the jaw
where is the sublingual gland located?
under the tongue
what are the components of saliva?
saliva production is under control of the autonomic nervous system
amylase
bicarbonates & phosphates
chlorides
mucin
lysosyme
what is the function of amylase in saliva?
digests starch
what is the function of bicarbonates and phosphates in saliva?
act as buffers
what is the function of chlorides in saliva?
activate amylase
what is the function of mucin in saliva?
forms mucous when dissolved in water
what is the function of lysosyme in saliva?
destroys bacteria
what is the function of the oesophagus?
food forms a bolus and moves down the oesophagus by peristalsis
no digestion or absorption occurs here
what are the components of the stomach?
cardia
fundus
body
pylorus
what is the function of the cardia in the stomach?
where food passes from the oesophagus to the stomach
what is the function of the fundus in the stomach?
dome-shaped
stores undigested food and gasses from chemical digestion
what is the function of the body in the stomach?
main part of the stomach where the majority of the mixing takes place and where chyme is formed.
what is chyme?
a thick semi-fluid mass of partially digested food and digestive secretions
what is the function of the pylorus in the stomach?
connects the stomach to the duodenum
what are the components of the pyorus in the stomach?
pyloric antrum - connects to the body of the stomach
pyloric canal - connects to the duodenum and contains the pyloric sphincter which controls stomach emptying.
what are the gastric cell types in the stomach?
mucus
pariteal
zymogenic
enteroendocrine
what is the function of mucus cells in the stomach?
secrete mucus
what is the function of pariteal cells in the stomach?
secrete hydrochloric acid (HCl)
what is the function of zymogenic cells in the stomach?
secrete pepsinogen
what is the function of enteroendocrine cells in the stomach?
secrete gastrin
what is the function of the muscles in the stomach?
the stomach contains three layers of smooth. muscle: oblique, circular and longitudinal
this allows multidirectional contractions which mix and churn chyme
what is the function of the small intestine?
chyme moves from the stomach into the duodenum
most chemical digestion and absorption occurs here
consists of: duodenum, jejunum, ileum.
chyme moves through the the small intestine by peristalsis
what is the absorption model?
mucosa - folded into villi which are very thin to allow for rapid absorption. each villi is supplied with blood vessels to recieve the absorbed nutrients - glucose, amino acids, vitamins and minerals
epithelial cells - folded into microvilli
lacteal - absorbs fats and products of fat digestion
what is segmentation within the small intestine?
the small intestine relaxes and contracts the circular muscle to thoroughly mix chyme with digestive juices and brings it into contact with the intestinal wall.
what are the glands in the small intestine?
contains intestinal glands (krypts of lieberkuhn) which are found between villi. they secrete a slightly alkaline fluid containing water, mucus and enzymes.
pancreatic juice - alkaline
bile - emulsifies fats
pancreatic duct and bile duct join at hepatopancreatic ampulla (ampulla of vater)
what is the function of the large intestine?
chyme moves from the small intestine to the large intestine through the ileocecal valve
water absorption
excretion of waste
there is no villi
mucosa - goblet cells secrete mucus and columnar epithelial cells for water absorption
what is haustral churning within the large intestine?
passage of food along the colon
material accumulates in pouches called haustra which contract when full to squeeze the contents from one haustrum to another - peristalsis.
what are the accessory organs?
liver
pancreas
gallbladder
what is the function of the liver?
produces bile salts which emulsify fats aiding their digestion and absorption
removes toxins and drugs by secreting them into bile
what is the function of the liver with carbohydrates?
the liver stores excess glucose as glycogen when glucose levels are high
what is the function of the liver with proteins?
deamination of excess amino acids to ammonia and then to urea
transamination to convert one amino acid to another that is needed
what is the function of the liver with lipids?
stores some triglycerides
converts fatty acids to acetyl CoA
converts excess acetyl CoA to ketone bodies
what is the function of the pancreas?
produces digestive enzymes and bicarbonate
islets of langerhans secrete insulin and glucagon
acinar cells secrete digestive enzymes - secretin and cholecystokinin
controlled by parasympathetic impulses via the vagus nerve
what is the function of secretin in the pancreas?
produced due to acid in the duodenum
stimulates the acinar cells of the pancreas to secrete water and bicarbonate into the pancreatic duct that trains into the duodenum to dilute and neutralise the HCl secreted by the stomach.
what is the function of cholecystokinin in the pancreas?
produced due to fats in the small intestine
secreted by cells of the upper small intestine
stimulates the gallbladder to contract and release stored bile into the small intestine
stimulates the secretion of pancreatic juice and may induce satiety
what is the function of the gallbladder?
stores concentrates and releases bile
releases bile into the two-way cystic duct when it is needed by the small intestine
what is the cephalic phase?
initiated by the sight, smell, taste or thought of food
results in stimulation of parasympathetic impulses by the vagus nerve
increases gastric secretions and gastric motility
what is the gastric phase?
initiated by stretch receptors and chemoreceptors
stimulation of parasympathetic impusles - waves of peristalsis
secretion of gastrin - secretion of gastric juices
what is the intestinal phase?
initiated by chyme entering the duodenum
release of hormones: GIP - inhibits gastric secretion and motility, secretin - decreases gastric secretion, CCK- secretion of bile and pancreatic juices
enterogastric reflex - increases sympathetic, decreases parasympathetic
