Gastro-Intestinal Tract (GIT) 2 Flashcards
Describe the bile produced by the liver - what it contains and its role
contains sodium & potassium salts - these emulsify lipids within fat to form globules which can be broken down further by pancreatic lipase
Describe the path of bile from the liver
Bile drains through the right and left hepatic ducts into the common hepatic duct then passes through the common bile duct into the small intestine
Describe what happens to the sphincter and bile between meals
the sphincter closes and bile is stored in the gall bladder as it cannot enter the intestine
Describe the mucosa in the small intestine and its role and also describe the walls of the small intestine
the mucosa contains Brunner’s glands which secrete mucous to neutralise gastric acid, the walls of the SI have deep crevices lined with glandular epithelium - these form intestinal glands called Crypts of Lieberkuhn which secrete intestinal juice
Describe what intestinal juice and pancreatic juice together does
this aids absorption of constituents of chyme
Describe the role of epithelial cells in the small intestine and what its aided by
epithelial cells begin absorption and brush border enzymes aid this
Dextrinase, Maltase, Sucrase, Lactase = carbohydrates
Peptidase = proteins
Nucleotide digesting enzymes
Describe the mucosa lining of the inner walls of the small intestine
covered with villi - finger-like projections - increases surface area for digestion, the villi house an arteriole/venule & lymphatic vessel - because the walls are so thin, the passage of nutrients (results of food breakdown) is possible, there are also goblet cells which secrete mucous aiding digestion
Describe the role of Paneth Cells
these regulate the number of microbes - keeps the environment at its optimum
Describe the micro-villi found on the walls of the SI
smaller than villi, increase surface area further to aid digestion, estimated 200 million per square mm
Describe Plicae Circulares and its role
these are deep folds within the intestine, increase surface area for successful digestion, enables the chyme to spiral rather than travel in straight line
Describe Segmentation
the movement of the intestine to bring the food contents in close contact with the mucosa, the food is sloshed back and forth approx. 12 times per minute in the duodenum and 8 times per minute in the ileum
What does intestinal distention trigger
nerve impulses to stimulate motility
What is peristalsis called in the small intestine and what is its role
migrating motility complex (MMC), moves food through GIT 1cm/1min, controlled by nerve impulses
How long does it take food to move from the stomach to the end of the SI
120 minutes
ABSORPTION - carbohydrates
all become monosaccharides for absorption, Fructose & Glucose = monosaccharides and are absorbed by diffusion or active transport through the lumen of the villi
ABSORPTION - proteins
become amino acids and are absorbed by active transport through the lumen of the villi
Monosaccharides and amino acids ….
enter the bloodstream and are transported to the liver
ABSORPTION - fats
Tri/Di glycerides become monoglycerides by the action of bile, monoglycerides are converted to glycerol & fatty acids by lipase - these recombine with proteins to become phospholipids which are too large to pass into the bloodstream - enter the lymphatic system and drain eventually into the bloodstream through the subclavian vein - transported to the liver for further breakdown
ABSORPTION - electrolytes
absorbed by sodium/potassium pumps, diffusion & secondary transport
ABSORPTION - vitamins
mostly by simple diffusion but Vit B12 needs intrinsic factor and needs active transport for absorption
ABSORPTION - water
via osmosis but fluctuates as it is dependent on the concentration of electrolyte balance within water, approx. 8.3 litres of water absorbed, 90% of absorption takes place in the small intestine
Describe Alcohol Absorption - 4 points
can begin in the stomach, absorbed more quickly in SI because theres a larger surface area, presence of fat slows gastric emptying so blood alcohol level rises slower because it remains in the stomach longer so less enters the bloodstream
Describe the role of gastric alcohol dehydrogenase enzyme and where its found
found in the stomach, breaks down alcohol into non-intoxicating elements
Describe the basic features of the Large Intestine (LI)
1.5m length, 6.5cm diameter, commences at ileo-caecal valve and finishes at anal orifice, consists of caecum and appendix, ascending/transverse/descending/sigmoid colon, Rectum & Anal Column
Describe the position of the caecum
hangs below the ileo-caecal valve
Describe the appendix
small coiled tube, 8cm
Describe the passage of food through the LI
ascends up the right side of the abdomen via the ascending colon & turns left under the liver at the hepatic flexure, then travels across to the left side of the abdomen via the transverse colon, then turns through the splenic flexure to travel down the left side of the abdomen via the descending colon, at the level of the iliac crest it travels towards the midline via the sigmoid colon, terminating at the 3rd sacral vertebrae where it becomes the rectum
Describe the Rectum - 3 points
20cm long, has good blood supply, has internal & external muscular sphincter
Describe the Mucosa lining in the walls of LI
no villi, no permanent folds but do have goblet cells which secrete mucus to assist passage through intestine
Describe the Muscularis lining in the walls of LI
external, longitudinal fibres
internal, circular fibres
Describe the Taeniae Coli lining in the walls of the LI
bands of muscle fibre which run the length of the LI and gather it into haustral folds during contraction
Name the 4 functions of the LI
Haustral Churning
Peristalsis
Mass Peristalsis
Chemical Digestion
Describe Haustral Churning in the LI
process movement of food contents from 1 haustra to the next
Describe Peristalsis in the LI
12 contractions/min to move food along
Describe Mass Peristalsis in the LI
move food from mid transverse colon to rectum in a strong peristaltic movement
Describe Chemical Digestion in the LI
by bacterial action, breaks down any remaining carbohydrates and prepares waste products (faces) for elimination
Describe Pressure Receptors in the Rectal Walls
recognise the need for expulsion although (fortunately) voluntary control of external sphincter which controls rate of release
Prior to expulsion, the LI is responsible for …
absorption of remaining water - approx. 100mls along with electrolytes such as sodium
