The Journey through the GI tract Flashcards
Why is digestion important?
The majority of the food we eat is not in the form which can be used by the body
Food and drink must be changed into smaller molecules of nutrients before they can be absorbed into the blood and carried to cells throughout the body
Our digestive system is a highly evolved set of organs which facilitate the coordinated breakdown and absorption of nutrients and fluids
Organs of the GI tract
Oesophagus
Stomach
Small intestine (duodenum, jejunum, ileum)
Large intestine (descending colon, ascending colon, rectum, anus)
Accessory organs of the GI tract
Oral cavity
Liver
Ball bladder
Pancreas
What’s the advantage of a long tube over a sack?
Large surface areas
Sequence and control of speed
Sphincters
1) lower oesophageal sphincter/cardiac sphincter
2) pyloric sphincter
3) ileocecal sphincter
4) internal anal sphincter
5) upper oesophageal sphincter
6) sphincter of Oddi
What does the term GI tract actually refer to
alimentary canal; muscular tube that extends from oral cavity to anus
Oesophagus function
transit
Stomach function
H+/Chemical and physical breakdown
Secretion of intrinsic factor (glycoprotein)
Intrinsic factor
Important for absorbing vitamin B12, which is really important for red blood cells
Pernicious anaemia
autoimmune destruction of parietal cells lead to B12 not being absorbed (ask Mum bc I think this is the one she has)
Small intestine function
Fat, protein, carbohydrate digestion & absorption
Water and electrolyte abs.
Bile salt transport vitamin B12 absorption
Large intestine function
Storage/water and electrolyte transport
Defecation
Colonised by bacteria
Changing pH
Stomach - 1.5
Colon - 6.7
Oesophagus
23-30 cm long
extends down from pharynx
immediately behind trachea
outer longitudinal muscle and an inner circular muscle (both skeletal) work together to generate peristalsis
Peristalsis
the automatic wave-like movement of the muscles that line your gastrointestinal tract. Peristalsis moves food through your digestive system, beginning in your throat when you swallow and continuing through your oesophagus, stomach and intestines while you digest
The stomach
Entry = cardiac sphincter
3 main regions -> fundus (top), body, antrum (bottom)
Pyloric sphincter = exit into duodenum
longitudinal and circular muscle layers + oblique muscle layer
Strong contractions initiate by pacemaker zone
keeps contents “chyme”
What hormone is produced in the cells of the stomach to stimulate hunger?
Ghrelin
Chyme
the pulpy acidic fluid which passes from the stomach to the small intestine, consisting of gastric juices and partly digested food.
What happens when stomach is full?
pyloric sphincter opens
Histology of the stomach
rugae increase surface area
gastric glands lined by columnar epithelial cells
flat surface w gastric pits
mucus lining prevents self destruction by acid
What do mucus cells secrete?
alkaline mucus (glycoprotein) protects lining (epithelium) against the acidity
What do parietal cells produce?
gastric acid
intrinsic factor
What do enterochromaffin cells secrete?
histamine; stimulates parietal cells to produce gastric acid
Chief cells
pepsin
gastric lipase
What do D-cells secrete?
somatostatin; inhibit gastric acid, affecting cell proliferation
What do G-cell secrete?
gastrin; stimulate parietal cells to secrete gastric acid and chief cells to release prepsinogen
Exocrine cells
secrete into the lumen
endocrine cells
secreted internally, affecting cells nearby release site
Stomachs of newborn infants produce what that is absent in adults?
Rennin and gastric lipase
