1. Digestive System Flashcards
Structure and Function of the System Control of GI Motility and Secretion
Name the 7 main parts that make up the digestive system
Mouth, Pharynx, Oesophagus, Stomach, Small intestine, Large Intestine and Rectum
Name the 4 accessory organs of the digestive system
Salivary Gland, Liver, Gall Bladder and Pancreas
Why digest?
Fuel cells, break down large molecules to smaller ones which can then diffuse into cells and bloodstream for usage
What are the 4 main phases of gastrointestinal system?
Motility, Secretion, Digestion and Absorption
Which of the 4 phases are not controlled?
Absorption
What can be secreted into the lumen?
Enzymes (for digestion), salt, water, Mucus, HCl, HCO3
What is the inner-most layer of the lumen wall?
Mucosa
What is the function of the mucosa?
Increase surface area due to folded membrane, protective surface, secretes enzymes, defence against bacteria.
Name the three layers of the mucosa and their function
Mucous Membrane (protect surface, contains exocrine and endocrine gland cells), Lamina Propria (lyphoid tissue - important for defence) and Muscularis Mucosa (smooth muscle)
What is the function of the submucosa?
Thick layer of connective tissue for distensibility and elasticity. Contains larger blood and lymph vessls and contains nerve network which stimulates contraction and hormonal release.
Name the nerve network of the submucosa and muscularis externa
Submucosal plexus and myentric plexus
Name the muscle that makes up the muscularis externa
Smooth muscle
What affect do each layer in the muscularis externa have on the lumen when contracted?
Circular layer (contraction decreases diameter of lumen) and longitudinal layer (contraction shortens tube).
What does contraction of muscularis externa result in?
Produces mixing and propulsive movement
What is the function of the serosa?
Secrete serous fluid for lubrication - prevents friction
What is the function of mesentry?
Holds lumen to body wall - fIxation in the body and allows movement for mixing.
What does enteric innervation mean?
Within tract (involves myentric and submucosal plexus) and is interconnected (motor, secretory and sensory neurones)
What does extrinsic innervation mean?
Brain innervation - further away.
What effect does parasympathetic innervation have on the activity of the gut
Increases activity - rest and digest
What is the function of villi?
Increases surface area due to folded epithelial layer (e.g. Small intestine: 300m2) - shedding (whole new lining every 5 days) - absorption via capillaries (except for fats (lacteal))
What is secreted by the salivary gland and why?
Salt, water, mucus, amylase - lubraication and polysaccharide (starch) digestion
Which part of the digstive system secretes lingual lipase?
Tongue for lipid digestion
Why is mucus secreted by the oesophagus?
Lubrication - prevents friction
Why is HCl secreted by the stomach?
Activates Pepsin to pepsinogen which digests proteins.
What is the function of HCO3?
Bicarbonate neutralises chyme and adjusts pH after stomach.
Where is bile salts stores?
Gall Bladder
What is secreted by the liver?
Bile slats, HCO3 and waste
Where is most of digestion taken place?
Small Intestine
Where is water reabsorpted to prevent loss?
Large Intestine
Is mucus secreted in the large Intestine?
Yes for lubrication
What is the function of the rectum?
Defecation
What makes up carboydrates?
Monosaccharides
Fatty Acids and Glycerol form what?
Lipids (fats)
Name a polysaccharide?
Glycogen, Cellulos, Amylopectin, amylose (strach)
What does amylase do and where is it secreted?
Amylase breaks down strach in the mouth
How is glucose transported into epithelial cells?
Via cotransport with Na+ ions
How is fructose transported into epithelial cells?
Via protein channel straight into cell
How does pepsinogen digest proteins?
Breaks bonds between amino acids
What is the difference between endopeptidases and exopeptidases?
Endopeptidases break bonds between AAs, Exopeptidases act on the ends of chains
What type of molecule is moved into epithelial cells via endocytosis
Small peptides
How is amino acids transported into epithelial cells?
Via co-transport with Na+ ions
Name the 3 lipases and what do they act on?
Lingual, gastric and pancreatic lipases and they act on lipids (fats)
Where is most lipids digested?
Small intestine
What is the problem with large lipid droplets?
Small surface area: volume ratio - not many enzymes can act on the lipids at once.
What do bile salts do?
Increase SA:V ratio by creating several small droplets from one big one creating more sites for enzymes to act upon. They also prevent reaggregation of droplets together.
What are micelles?
Small droplets which act as reservoir to store FAs and glycerol
How are FAs and glycerol secreted out of epithelial cells and where to?
Exocytosis (vesicles) into lacteal.
How is water absorbed?
Osmosis via channel transporters down osmotic graident.
How are fat soluble vitamins absorbed?
Follow fat absorption
How is vitamin B12 absorbed?
Bind to intrinsic factor.
What does the control of the GI respond to?
Distension, osmolarity and acidity and concentration of molecules
Name the 3 types of control systems
Neural, Hormonal and Local muscle response
what does submucosal plexus control?
Exocrine and endocrine secretions
What does the myenteric plexus control?
Control of peristaltic secretions
What is the effect of thinking about food?
Causes changes in CNS and affect enteric NS so you start to produce hormones and saliva.
Do short reflexes involves the brain?
No but long reflexes do
What stimulates hormonal release?
Receptors in contact with the luminal contents detect extremes in distension, osmolarity and acidity etc…
How is hormones secreted into blood?
Endocrine gland secretion
What are the two families of hormones?
Gastrin and Secretin
Name the 3 phases of GI control
Cephalic, Gastric and Intestinal.
Which part of the body is the site of cephalic phase
Head
Name the two phases of GI control which affected by hormonal control
Gastric and Intestinal
Control of gastric phase happens in response to what?
Distension, Acidity and Peptides
What influences cephalic phase?
Touch, sight, taste, thought
What is mastication?
Chewing phase
Is mastication voluntary?
Yes but eventually you swallow due to excess saliva
Which parts of the mouth contain receptors that produce a reflex
Gums and Hard Palate
Saliva in mouth is secreted in response to what?
Presence of food in mouth
How is food prevented from entering the lungs
Glottis closes to prevent food going down trachea, aryno-oesophageal opens to allows food into oeophagus to stomach
What is peristalsis?
Constriction and shortening of tube, which moves contents though intestinal tract, mixing an propelling food though.
What is secondary peristalsis?
Oesophageal distension and it occurs when indigested food has been left behind after primary peristalsis.
What causes mixing?
Reduction in lumen diameter moves some parts forward and other parts in reverse.
Name the 3 parts of stomach
Fundus, Body and Antrum
What is the function of stomach?
Acts as a store for food, mixing, breaks down big molecules into smaller ones, more manageable liquid (chyme)
What does the pyloric sphincter do?
Prevents food coming back from small intestine.
What prevents food re-entering oesophagus?
Oesphageal sphincter
Name the 3 cells in stomach and what do they secrete?
Mucous (mucus), parietal (HCl) and chief (pepsinogen)
What is receptive relaxation?
Take extra volume of food with little rise in stomach pressure stimulated by eating
What is the function of the body in the stomach?
Storage
Where does mixing take place in the stomach?
Antrum
What controls emptying in the stomach?
Factors in the duodenum
Why does excess fat slow emptying of stomach?
Fat digestion is slow and so to reduce build up of fats in small intestine and less waste emptying is reduced
Name two factors that affect gastric emptying.
Amount of chyme, Fat, Acid, Hypertonicity and distension.
Does intense pain inhibit motility?
Yes
What membrane potential change causes contraction?
Parasympathetic depolarisation.
What secretes gastric juice
Oxyntic mucosa and pyloric gland areas.
What stimulates chief cells?
ACh, Gastrin
What is the postprandial alkaline tide?
They secrete bicarbonate ions into blood causing temporary increase in pH - maintain plasma’s electrical balance. Back optimal pH.
Which of the 3 phases causes a decrease in HCl
Intestinal Phase
How is pepsinogen converted to pepsin
Pepsinogen released by chief cells, mixes with HCl, causing pepsinogen activation to become pepsin (change conformation)
What is secreted from pancreas?
HCO3 and enzymes
Where does most digestion take place?
Small intestine
What is secreted when pH lowers in the small intestine
Plasma secretin levels increases, and pancreas increases bicarb concentration and that neutralises acid in small intestine.
What does CCK do?
Increased levels increases enzymes released by pancreas which increases rate of digestion of fats and proteins.
What stimulates the release of HCO3 from epithelial cells of bile duct?
Secretin.
What is the sphincter of Oddi
Smooth muscle which relaxes when we eat to allow bile and pacreatic juice to flow into small intestine.
Does contraction of gall bladder release or inhibit the release of bile salts
Releases.
Does peristalsis occur in the small intestine?
Yes
What does Gastro-ileal reflex do?
Increases segmentation which stimulates colonic peristalsis and provides an urge to defecate.
What is the migrating mobility complex?
Short peristaltic waves which pushes indigestible foods through the small intestine. (2hrs)
What does motilin do?
Increase peristaltic mobility.
What does relaxation of ileocecal sphincter result in?
Chyme moving into large intestine.
What is intestinal segmentation?
Causes mass movement through large intestine
Which part of the anus is voluntarily controlled?
External Anal sphincter.
Describe renal distension.
Internal sphincter relaxes, external contracts, increased peristalsis in sigmoid colon and increases rectal pressure.
