Digestion & Absorption Flashcards
Define Digestion
Sequential ordered process with physiological links between each stage. Each specific stage allows the interaction of fluid and emulsifying agent, acid-base exchange, enzyme and substrate contact. Each stage is regulated and integrated.
Why is digestion important?
Food contains a mix of nutrients, often within a complex chemical / compound that cannot be directly absorbed and digestion allows for access to the desired nutrients
What are the two types of digestion
Chemical & Mechanical
What is the first part of digestion called
Mastication
Name the functions of the mouth in digestion?
Mechanical Digestion -> chewing
Chemical Digestion -> salivary lipases & amylase
Propulsion of food into oesophagus
Give 3 functions of saliva in digestion
Moistens food
Buffers pH of food
Antibacterial (immunoglobulins and lysozymes)
How does the oesophagus move food from mouth to stomach
Peristalsis (oesophagus tissue can secrete mucous for aid)
Give 3 cell types in the stomach
Epithelial, Parietal Epithelial, Chief Cells
What is the function of epithelial stomach cells?
Produce mucous and bicarbonate which makes an alkaline barrier to protect the epithelium and stomach from the acid produced -> i.e. cytoprotective
What is the function of stomach parietal epithelial cells
Secrete hydrogen and chloride ions to form HCl acid and also secretes intrinsic factor
What are the functions of stomach chief cells
Secretion of zymogens and enzymes (pepsinogen, chymosin (carbohydrate enzymes) and gastric lipase).
Give 4 function of the stomach
Stores chyme Absorbs ethanol and lipid soluble drugs Mechanical digestion -> churning Chemical digestion -> gastric enzymes and acid Sterilisation of food stuff Inactivation of salivary amylase
What is absorbed in the stomach?
Ethanol
Lipid soluble drugs
Explain the structure of the small intestine in regards to surface area
Mucosal folds forms villi
Apical villi contain further folds called microvilli
Give 3 functions of the duodenum
Receives chyme from the stomach
Receives digestive juices from sphincter of Oddi (pancreatic, gall bladder and liver)
Duodenal gland cells secrete mucous and bicarb for lubrication and neutralisation
Fatty acid absorption
Give the main function of the jejunum
Bulk of absorption takes place here - particularly carbs and amino acids
Give 3 main functions of the ileum
Reabsorption of bile salts
Absorption of vitamins (+ particularly Vit B12 bound to IF)
Transport undigestible matter into colon via ileocaecal valve
Give 2 function of gall bladder/liver secretions in the lumen
pH neutralisation & fat emulsification
Give 2 main functions of pancreatic secretions in the lumen
pH neutralisation, chemical digestion (lipase, amylase and proteases)
Give the 3 main parts of the large colon along with one function
Caecum - receives undigested food
Colon - home of intestinal flora, absorbs water & mineral salts
Rectum - storage of faeces until defecation
What is starch made up of?
Two polysaccharide chains called Amylose & Amylopectin
What is the bonding involved with amylose?
unbranched alpha 1-4, glycosidic bonds
What is the bonding involved with amylopectin?
alpha 1-4 glycosidic bonds with alpha 1-6 branching glycosidic bonds every 12 subunits of glucose
Explain the digestion of starch
Amylases in saliva and pancreatic juice breaks alpha-1,4 bonds in starch down into oligosaccharides, disaccharides (maltose), dextrins (smaller units containing the alpha-1,6 bonds).
What type of enzymes are found in the brush-border that digests carbohydrates / disaccharides?
Hydrolase enzymes
Name the three most common brush border enzymes involved in disaccharide digestion and their targets with breakdown products
Maltase -> Maltose -> 2 x glucose
Sucrase -> Sucrose -> 1 glucose & 1 fructose
Lactase -> Lactose -> 1 glucose & 1 galactose
What brush border enzyme can break down dextrin and why?
Sucrase-Isomaltase -> can hydrolyse both the 1,6 and the 1,4 glycosidic bonds
What transporters are important in the absorption of monosaccharides
SGLT-1 = Glucose & Galactose into enterocyte GLUT5 = Fructose into enterocyte GLUT2 = All 3 out of cell basolaterally
Does GLUT2 require ATP?
Yes
How efficient is protein digestion & absorption
Extremely efficient, 1g of nitrogen is excreted out of faeces every day regardless of intake (0-250g)
What part of protein digestion cycle is recyclable
Most enzymes used in the digestion of protein are all reabsorbed and recycled
Where is protein mostly absorbed?
upper two thirds small intestine
What is the ‘classification’ of enzymes involved with protein digestion? (Edwards question)
Protease & Peptidase
Protease digests proteins in peptides
Peptidases digest peptides but are a subclass of protease
The two terms are used interchangeably
What is the first sight and stage of protein digestion?
Stomach