Gastrointestinal System Flashcards
Ingestion
The intake of food into the GI tract via the mouth
Mechanical Processing
Physical breakdown of food by the teeth, stomach and intestines
Increases the surface area of food, allowing enzymes to work more efficiently
Chemical Processing
Breakdown of complex molecules (polymers) into monomers using enzymes and other substances
Secretion and Absorption and Egestion
Secretion: release of water, acid, enzymes, buffers and salts which aid in chemical digestion and absorption
Absorption: uptake of useful molecules across the epithelium of the GI tract and into interstitial fluid
Egestion: removal of waste products
Breaking down of polymers
we cannot absorb polymers such as proteins, lipids and carbohydrates so they must be broken down by chemical and physical digestion
Proteins are broken down into amino acids
Lipids are broken down into fatty acids and glycerol
Carbohydrates are broken down into monosaccharides
What is someone lacking if they are lactose intolerant
lactase enzyme
Layers of the GI tract wall
Serous: fibrous connective tissue - structure and support
Muscularis: two layers of smooth muscle. Antagonist pair. Lognitudinal muscle (down GI tract) and circular (around circumference of GI tract). creates peristalsis
Submucosa: connective tissue layer which contains blood vessels, lymph vessels and nerves
Mucosa: inner lining, cells get replaced every 5-7 days
Lumen
Chemical and Physical processing in the mouth
Chemical: amylase breaks down starch into maltose, saliva makes food softer and helps form a bolus. Taste sensation increases to prepare the rest of the digestive system = stimulation of gastric juices
Mechanical: teeth. Food is broken down into smaller pieces creating a larger surface area for enzymes to act on. helps mix food with saliva
Voluntary phase of swallowing (deglutition)
tongue pushes bolus into the pharynx whilst oesophagus is kept closed. Bolus travels down the oesophagus via peristalsis
Involuntary phase of swallowing (deglutition)
soft palate rises to close the passage to the nasal cavity and the epiglottis decompresses over the trachea
How does peristalsis occur?
circular muscle contracts behind bolus and longitudinal muscle contracts in front of bolus
Where are these 4 sphincters
Oesophageal
Pyloric
ileo-caecal
Odi
oesophageal = Between the oesophagus and cardia part of the stomach
pyloric = connects the stomach to the duodenum
ileo-caecal = small intestine to caecum
Odi = bile duct
What is food mixed with in the stomach?
hydrochloric acid and gastric juices to create chyme
How many muscle types in the stomach & name them
3
circular, longitudinal and oblique
4 parts of the stomach
cardia, fundus, body and pylorus
Functions of the stomach
storage area
mechanical and physical processing
Protective - hydrochloric acid kills bacteria
Mechanical and chemical processing in the stomach
Mechanical: 3 layers of muscle. stomach folded into rugae to expand as it fills
Chemical: gastric juices (hydrochloric acid, lipases, intrinsic factor and mucus
What is intrinsic factor?
helps with the absorption of vitamin B12
Vitamin B12 is a water soluble vitamin with an important role in the functioning of the brain, nervous system and blood
What would happen if insulin was taken as a tablet?
Would have less of an affect because it would get broken down in the stomach by pepsin since it is a hormone and hormones are proteins
What reflex regulates stomach emptying?
Enterogastric reflex
Why does chyme need to be neutralised in the small intestine?
because the stomach has a pH of 2 and the small intestine has a pH of 7-8
What are the 3 parts of the small intestine
Duodenum, jejunum and ileum
Mechanical and chemical processing in the small intestine
Mechanical: peristalsis, segmentation
Chemical: microvilli secrete enzymes such as maltase, sucrase and peptidases. Other secretions from accessory organs also help break down complex molecules
Villi and Microvilli
on the walls of the small intestine - majority of nutrients are absorbed
Create a larger surface area for absorption
highly vascular to maintain a diffusion gradient
Absorption
nutrients are absorbed through epithelial cells in microvilli and enter the bloodstream via capillaries or the lymphatic system via lacteals
Where are amino acids and glucose taken after they are absorbed
to the liver via the hepatic portal vein
Where are fats absorbed
into lacteals to enter the lymphatic system. They eventually enter the bloodstream at the subclavian vein
Order of segments in the large intestine
ascending colon, transverse colon, descending colon and sigmoid colon
Functions of large intestine
absorption of water, ions and vitamins
formation of faeces
What is faeces made of
water, inorganic salts, undigested food and epithelial cells
Cause of diarrhea and constipation
Diarrhea = bacteria inside stomach increase the rate of peristalsis
Constipation = codeine slows peristalsis. Too much water absorbed
Appendix
attached to the posteromedial surface of the caecum
little function in humans but is painful when inflammed
Process of excretion
rectal walls stretch = activation of the parasympathetic nervous system = we can ignore signals until another mass enters the rectum
long rectal muscles contract = increased pressure = voluntary contraction of diapghram and accessory muscles = relaxation of internal anal sphincter
Where is bile produced and what is it’s function
Liver
emulsified fats making them more water soluble
bile enters the duodenum when we are eating
When we are not eating the sphincter of Odi closes and bile backs up into the gall bladder
Functions of the pancreas
Endocrine (directly into bloodstream) and Exocrine gland (into gland)
Insulin - beta cells
Glucagon - alpha cells
secretes enzymes such as amylases and lipases
produces sodium bicarbonate (reduces acidity of stomach contents)
What are the following processes
deamination
transamination
protein synthesis
Deamination: removal of amino acids to enable the conversion into carbohydrates
Transamination: converting one amino acid to another
protein synthesis: making proteins from amino acids
What is the livers role in lipid metabolism
fatty acids are oxidised to form ATP
liver is involved in the synthesis of lipoproteins, cholesterol and phospholipids and is responsible for breaking down cholesterol to form bile salts
True or false
as the rectum fills, the rectal walls stretch and activate the sympathetic nervous system
False
Activates the parasympathetic nervous system
