Digestion Flashcards
What is digestion?
the breaking down of ingested food into useable nutrient molecules that can enter the vascular or lymphatic system.
What does the digestive system consist of?
- digestion achieved by gastrointestinal tract (tube from mouth to anus which breaks down food)
- The accessory structures (digestive organs)- not part of the tract - (e.g. teeth, tongue, liver, pancreas that help by mechanical or chemical means - things which we can absorb into the vascular or lymphatic system)
What is our food composed off?
the major nutrients:
- Carbohydrates
- Protein
- Fats (glycerol and fatty acids)
Vitamins- act as co-enzymes.
they can be either fat soluble A,D,E,K) OR wake soluble. (B AND C)
Minerals/trace elements- body requirements of 7 minerals- calcium, phosphorous, potassium, sulphur, sodium, chloride, magnesium) and trace amounts of. about aa dozen others. They serve other functions such as CA: bone, Fe- haemoglobin, Ca/Na/K- nerve/muscle)
What are the 6 processes of digestion consist of?
Ingestion- take food in
Propulsion- propel food through gastrointestinal tract
Mechanical Breakdown-in the stomach with teeth (accessory structure)
Digestion- chemically
Absorption- into vascular system
Defecation- get rid off it
What is the structure of the GI tract?
4 layers
- Inner layer known as mucosa
- Under sub mucosa
- Layer of muscle
- Outer serosa - tough outer protective connective tissue
What does mucosa contain of?
- Mucosa usually consists of a simple columnar epithelium
- layer of mucous which secrete many goblet cells to protect and lubricate the passage of food
- in stomach and small intestine, the mucosa also contains cells secreting digestive enzymes and hormones
- epithelial cells (simple columnar epithelium)
- Lamina propria- contains aereolar connective tissue and containing protective lymphoid follicles
What is a lamina propria in the mucosa?
Lies underneath the epithelium which is aerolar connective tissue
-have lymphatic vessels of lymphatic system- protect body.
What is the submucosa?
- loose areolar c.t
- has layer of lymph and blood vessels
- abundant nerve supply
- elastic fibres/tissue due to the gastrointensital needs to be elastic as it needs to expand when we intake food.
What is in the muscular layer of the GI tract?
-2 layers of smooth muscle (inverted by autonomic system) : inner circular and outer longitudinal.
What is the function of this muscular layer?
- Shove food along by the process of peristalsis.
- Food turned into a bolus (balls) and that is then pushed through GI tract by contraction of the muscle.
What is the main function of the mouth?
-responsible for ingestion
What is the structure of the mouth?
lined with stratified squamous epithelium
- Has tongue which mixes the food with saliva, forming a bolus
- tongue contains taste buds
- teeth macerate the food (mastication- crush food)
- mouth is connected to a number of glands whose secretions form saliva
What are the 3 salivary glands properties?
- exocrine- into ducts
- contain both mucous and serious secreting cells
What are the 3 salivary glands?
-Parotid glands
-Submandiular gland
-Sublingual gland
(they produce saliva)
What do these secretions of saliva serve to?
- dissolve the food so we can taste it
- help form the food into a bolus
- lubricate the mouth
- begin digestion of starch and fats by producing amylase and lipase.
Where does the food end up once gone through mouth?
- Back of throat- Pharynx- which can be divided into various regions
What is the Pharynx?
Where the food, fluids and air leave the mouth
What is the epiglottis?
allows air to pass down the trachea and is normally open
- If food gets stuck it will cause you to choke / lead to death
What happens when swallowing?
- The epiglottis closes
- ensuring food and liquids to not enter the trachea but instead enter the oesophagus
What is the oesophagus?
a 25cm tube connecting the mouth to the stomach
What does the oesophagus consist of?
4 layers (previous layers stated)
What does the submucosa contain in the oesophagus?
contains mucous -secreting oesophageal glands, that aid the passage of the food.- LUBRICATE
What is bolus in the oesophagus?
propelled by peristalsis ( about 8 seconds)
- drinks take 2 seconds
What does the stomach serve to do?
- store food
- mixed food into’chyme’ (semi fluid)- continually going through contractions and mixed with digestive enzymes
- begin the digestion of proteins and fats-carbs digestion happens in mouth
Whats the stomach structure?
15-25cm long
Has a volume of 500ml
- When had a meal a volume can be up to 4L
- Is guarded at either end by a sphincter muscle
-An empty stomach has multiple longitudinal folds (rugae)
-Folds in stomach increases S.A
- Has the usual 4 layersof the GI tract
What is on the surface on the stomach?
-has gastric pits- these are connected to gastric glands. opening to glands
What does the gastric glands secrete?
mucous
-produce HCL
-Produce pepsinogen
-Secret Lipases
both HCL and pepsinogen combine to form pepsin which is a digetsive enyme that can digest proteins.
- Lipases digests fats
- Covered in a whole layer of thick mucous so it protects the stomach from acidiy and protein sigesting enzymes
What does the smooth muscle of the stomach have?
both the normal circular and longitudinal layers as well as a 3rd layer, oblique layer
What do these smooth muscle layers serve to do as part of the stomach?
to mix, grind and propel the food in the stomach ( constant contractions)
What does the sympathetic activity do?
is decreased in digestion
What does the parasympathetic activity?
-increases digestion
What does the longitudinal muscle layer contain ?
enteric pacemaker cells
What do the enteric pacemaker cells do?
they depolarise spontaneously, causing 3 slow waves of contraction (causing a.p) in the stomach every minute.
- generates its own action potential
- Leaky to Na ions
What are the PACEMAKERs connected to?
the pacemaker of the stomach are connected to the surrounding smooth muscle by gap junctions, a.p spreads evenly throughout the stomach
Where is the basic rhythm of contraction?
generated in the stomach
-can be modulated by the autonomic system as wells as by local tissue factors such as stomach stretch receptors and gastric secretions
What is the small intestine?
where food leaves the stomach and enters in the small intestine
What does the small intestine consist of?
Duodenum (25cm)
jejunum (2.5m)
ileum (3.6m)
What does the small intestine do?
- produces digestive juices
- linked to liver, gall bladder and pancreas
- They produce digestive enzymes that break down all categories of foodstuffs (e.g amylase., lipase, nuclease)- Pancreas
- The liver and gall bladder act together to produce bile and bile emulsifies fat.
What is emulsification
breaking fats into small bits via bile salts
What is the small intestine for?
are specialised for absorption
- surface area increased x600
- 1cm tall circular folds of the mucosa and submucosa
- 1mm tall villi(containing blood and lymph vessels)
- microvilli on the absorptive epithelial cells(brush border)
total absorptive area of the small intestine = 200m2
What is the structure of the small intestine?
- same 4 layers as other areas of the GI tract - mucosa, subucosa, muscular layer and outer serosa
- simple columnar epithelium= specialised for absorption
- cells in mucosa which produce enzymes involved in carb and protein digestions
- the epithelium also contains many mucous secreting goblet cells
- Pits- connected to tubular glands which secrete intestinal juice
- these contain mucous, antibacterial agents and other protective components of the immune system
What is the large intestine?
it frames the small intestine on 3 sides
What is the size of the large intestine?
What is the main function of the large intestine?
To remove water from the food and store solid faces
- retain water in body
- little digestion occurs here
What else does the large intestine contain?
bacteria that ferment any remaining carbs
- carb digestion
- involved in synthesis of vitamins B and K
What is the structure of the large intestine?
- Made of the same 4 layers as the GI tract
- No villi o increase SA
- Intestinal glands contain goblet cells that produce mucous- to ease the path of the faeces and protect the intestinal wall.
- Most of the large intestine is lined by simple columnar- however the anal canal has stratified squamous epithelium
What is the digestion of carbohydrates?
- either monosaccharides, disaccharides or polysacchruides.
- NEED to be broken down into monosaccharides to be absorbed in the vascular system
Process of digestion of carbs?
- Happens in mouth
- Amylase from the salivary gland begins the breakdown of starch in the mouth, forming shorter oligosaccharides- taste sweet
- This process is completed by amylase from the pancreas
- Remaining carbs are digested by amylase from pancreas in small intestine
- These short chain sugar molecules are then converted to monosaccharides by the brush border enzymes (produced on microvilli) in the small intestine, where they are absorbed.
- –Glucose and fructose get absorbed by the wall of the small intestine and into vascular system.
What is the digestion of proteins?
-Proteins are chains of amino aids which need to be converted into dipeptides or single a.a before they can be absorbed.
Process of digestion of amino acids
- doesnt occur in mouth, occurs in stomach
- pepsin (pepsinogen+hcl) in the stomach breaks proteins into polypeptides and free a.a
- pancreatic enzymes continue this breakdown
- which is completed by brush border enzymes in the small intestine.
- individual a.a absorbed in the epithelial cells in the small intestine and end up in the vascular system.
What is the digestion of fats?
-most ingested fats are triglycerides that need to be broken down into monoglyercides and fatty acids
Process of digestion of fats?
Limited digestion of fats occurs in mouth and stomach
- As fat is not soluble in water it would form big globules in water that could not be digested by enzymes
- It is therefore emulsified (broken into smaller bits) by bile salts
- These small fat spheres are split into monoglycerides and fatty acids by pancreatic lipases which form ‘micelles’ , that are absorbed.
What is different about the digestion of fats?
fats absorbed in small intestine BUT put into lymphatic system.
- While the breakdown products of carbs and protein digestion are absorbed into blood capillaries in the villi o the small intestine, monglycerides and fatty acids enter lacteals (lymphatic vessels)
What is a lacteal?
villi in small intestine that contains lymphatic vessels
