The GI tract Flashcards
Mechanical function of the GI tract
To breakdown and propel food to sites of absorption and expulsion
Membrane transport in the GI tract
Large surface area for absorption - fat-soluble substances diffuse through GI tract walls, and water-soluble substances are transported by transport proteins
Immunological function of the GI tract
Generates protective inflammatory response to protect against toxins and pathogens
Gastointestinal associated lymphoid tissue (GALT) - Peyer’s patches and plasma cells
Secretory function of the GI tract (4)
- hormones that aid and regulate digestion
- acid that helps in breakdown and sterilisation of food
- mucous that protects GI tract’s inner wall
- secretions that neutralise stomach acid
Function of the mouth (4)
- Digests mechanically (chewing) and chemically (amylase - carbs)
- Secretes saliva
- Absorbs drugs
- Has immunological properties
3 stages of swallowing
- Voluntary - bolus passes to oropharynx
- Pharyngeal - involuntary passage of bolus through the pharynx into the oesophagus
- Oesophageal - involuntary passage of bolus through the oesophagus into the stomach
How is food in the airway prevented?
As the tongue moves upwards against the palate, it causes the epiglotis to move over the trachea
Functions of the oesophagus (2)
- Food is moved via peristalsis
2. Secretes mucus to aid passage of food
Gastric secretions chemically aid digestion of…
fats and proteins
Protein digestion is aided by…
hydrochloric acid, which is controlled by histamine, gastrin, and acetylcholine
Functions of the stomach (3)
- Motility - makes chyme from saliva, food and gastric juice
- Secretion - gastric juice, pepsin, intrinsic factor, lipase, mucus, gastrin
- Absorption - water, alcohol and drugs
Pepsin
Breaks proteins down into peptides, then again into essential, dispensible, and conditionally dispensible amino acids
Lipase
Active in an acidic environment
Breaks down triglycerrides into di- and monoglycerrides
Saturated vs unsaturated fats
Saturated fats have no double bonds and form in a straight structure; unsaturated have double bonds and form a bend structure
Amylase
Breaks carbohydrates into simple sugars or monosaccharides so they can be transported across membranes
Villi
Developed surface of the epithelium in the small intestine
Increase surface area to aid absorption
Microvilli on villi surface agitate fluid around villi to ensure micronutrients can access cell surface
Functions of the small intestine
Digestion: so substances can be facilitated across membrane
Absorption
Protection: Paneth cells are immunological tissues
Hepatic portal system
- Small intestine absorbs products of digestion
- Nutrients travel via the hepatic portal vein to the liver
- Liver liberates or stores nutrients according to blood levels
- Nutrents enter general circulation via the hepatic vein
Functions of the large intestine
Removes water from chyme to produce faeces
Contents is dryer and with more fibrous material than small intestine
Positive feedback loop of defecation
- Peristalsis forces faeces into rectum
- Stretch receptors in spinal cord send signal to spinal cord
- Involuntary muscle in rectum contracts
Neural control of the GI tract
ANS - parasympathetic nervous system, using acetylecholine
SNS inhibits via adrenaline/noradrenaline
Institial cajal cells
‘Pacemakers’
Stimulated by acetylecholine and stretch
Myenteric plexus
Network of nerve fibres between circular and longitudinal GI muscle layers - coordinates peristalsis contraction
Muscularis mucosae
Muscle tissue between GI epithelium and submucosa that agitates epithelial layer to liberate glandular crypts and enhance contact between epithelium and tract contents
