week 1 - basic structures and processes Flashcards
how many layers does gut wall have? name them inner to out?
4 layers: Mucosa (innermost) Submucosa Muscularis externae Serosa (outermost)
what does mucosa contain?
epithelium, lamina propria, muscularis mucosae
what is the submucosa layer?
CT layer with glands, nerves, veins and arteries
what does the muscularis externae layer contain?
2 smooth muscle layers:
outer longitudinal
inner circular
what is the serosa layer?
outermost serous membrane:
CT (inner), simple squamous epithelium (outer) – mesentery between 2 layers lubricate on containing arteries, veins, nerves
what is the overall process of GI?
Point of entry for food into body
Mechanically breakdown food
Temporary store food – stomach
Chemically digest food: salivary amylase & lipase, pancreatic amylase
Kill pathogens in food
Move food along GI tract – cilia
Absorb nutrients from resultant solution – small intestines
Eliminate residual waste materials – rectum & anus
what is digestion?
conversion of what we eat by physical & chemical disruption, into a sterile, neutral pH, isotonic solution (absorb), from which we absorb nutrients (sugars, fatty acids, AA, minerals, vitamins
what does the alimentary canal contain within GI?
Mouth, tongue, pharynx, oesophagus, stomach, small intestine, colon of large intestine, appendix, rectum, anus
what are accessory organs of the GI?
liver, gallbladder, pancreas
what is the function of the mouth in digestion?
Saliva: Starts digestion (salivary amylase & lipase - chemical), bacteriostatic (IgA), high Ca2+ (protect teeth), assists swallowing Physical: teeth, tongue, muscles of mastication (chewing) Forms bolus (chewed food) to enter oesophagus
oesophagus - function in digestion?
Upper end oesophagus (voluntary), lower end oesophagus (involuntary)
Rapid peristaltic transport (mouth to stomach in 8-9 seconds)
Fastest GI transport: oesophagus (entry) & rectum/anus (exit)
structure of oesophagus?
mucosa (epithelium, lamina propria, muscularis mucosae), submucosa, muscularis externa
innervation of oesophagus?
myenteric plexus (between 2 layers of muscularis externae), submucosal plexus (between submucosa and muscularis externae)
stomach - how does it digest food??
Physical: churning (3 muscle layers & mucosal rugae)
Chemical: acid (HCl) & enzymes
function of the stomach?
Acts as food store – eat faster than digest
Contracts rhythmically: mix & disrupt food
Secretes acid & proteolytic enzymes – breakdown tissues & disinfect
Protects epithelium – secreting mucus
Produce hypertonic chyme – combined action of acid, enzymes & agitation (stir disturbance) (hypertonic: more molecules greater osmotic strength)
Brings incompletely digested chime to duodenum
what is receptive relaxation of the stomach?
wall relaxes - pressure doesn’t rise as volume increases
structure of stomach (from lumen out)?
rugae, gastric mucosa, muscularis mucosae, submucosa, muscularis externa
what is rugae?
folds of gastric mucosa
what is the function of the gastric mucosa in stomach?
secretes acid, digestive enzymes & hormone gastrin
describe the muscularis externa in stomach
3 layers of smooth muscle: oblique, circular, longitudinal
which epithelium lines the stomach?
Simple columnar epithelium all the way along stomach
what does liver secrete? into where?
Liver secretes bile into duodenum (of small intestine – pylorus end of stomach), some bile stored in gallbladder
what does pancreas secrete? where into? via?
pancreas secretes pancreatic juice into duodenum (pancreatic duct)
where does pancreas and liver secrete into? why?
All into 2nd part of duodenum (major duodenal papilla)
all alkali to neutralise acid chyme
function of duodenum?
dilation & neutralisation of chyme
structure of duodenum?
Structure: 25cm, C-shaped, proximal SI, curves round head of pancreas
what does bile contain?
water, alkali (isotonic balance acidic HCl), bile salts (emulsify fat)
what happens in terms of the undigested food in the duodenum?
Water drawn in from ECF to render hypertonic chyme, isotonic
Liver release bile (from gall bladder)
Pancreas, liver & intestine secrete enzymes: act with bile to complete digestion of chyme
how does enzymes form pancreas and intestine complete digestion?
Cleave peptides to AA
Cleave polysaccharides to monosaccharides
Breakdown & re-form lipids
Breakdown nucleic acids
what does absorption require in order to occur properly?
active process – requires lots of energy
Requires large SA
Good blood supply / drainage – energy (glucose, ATP), oxygen etc.
how does the gut provide a large surface area?
gut is folded/villi/micro-villi, adequate contact time (control gut transit)
structure of the jejunum (from in to out)?
Plicae circulares (end of villi, circular folds of mucosa & submucosa project into gut lumen) Jejunal mucosa Muscularis mucosae, submucosa, muscularis externa (inner circular, outer longitudinal)
what does microvilli contain?
goblet cells
what does jejunal mucosa contain?
simple columnar epithelium, lamina propria, MM
what has happened by small intestine (duodenum / jejunum / ileum)?
most active absorption proximally, by terminal ileum (nutrients absorbed, water still to be absorbed)
describe the large intestine (structure) from appendix end
caecum, ascending colon, (right hepatic flexure), transverse colon, (left splenic flexure),descending colon, sigmoid colon, rectum
structure of large intestine?
Mucosa, submucosa, muscularis externa
what does mucosa of large intestine contain?
has crypts of Lieberkühn – simple columnar epithelium – produce mucus & absorb water & electrolytes
what is the function of the large intestines?
continues water recovery – contents semi-solid by end of large intestine
Contents await expulsion in colon (not yet rectum)
how do contents travel from colon to rectum?
At certain times, rapid propulsion into the rectum (stretches rectum gives the urge to defaecate)
fluid balance of gut - how many litres of fluid in 1kg of ingested food?
Ingest 1kg: mouth 1.5L saliva, stomach 2.5L gastric secretions, small intestine 9L of water/alkali – making a total of 14L (including ingested 1kg)
of the 14L, how much is reabsorbed and how much is excreted?
small intestine: absorb 12.5L, large intestine: absorbs 1.35L
Leaving 0.15kg faeces
what does decrease absorption / increase secretion results in?
- Life threatening dehydration (depletion of body fluids, not just what we drank because of osmosis (hypertonic, isotonic))
- Life threatening electrolyte imbalance
Motility & secretion precise control by what?
neural (nerves), paracrine & endocrine
how does the neural control function?
divided into somatic and ANS
what does somatic neural control?
Somatic (innervates striated muscle): ingestion (mouth & first 1/3 oesophagus), excretion (last sphincter of anus)
what does ANS neural control?
ANS controls the rest:
a. Post ganglionic neurones from plexuses
b. ‘gut nervous system’ – gut brain
c. range of neurotrasmitters
describe the post ganglionic neurones from plexus (control of ANS neural on the gut)
- Submucosal plexus: between muscle layers of gut (ME)
2. Myenteric plexus: beneath muscle but on top of submucosa
what are the paracrine control over the gut
Paracrine control (act locally):
- histamine
- vasoactive substances
what does histamine control?
control acid production in stomach
what do vasoactive substances control?
affect blood flow in gut
describe endocrine control over the gut
Range of hormones control:
- secretion of stomach acid
- alkali secretion from liver & pancreas
- enzyme secretion
what do all hormones of the gut belong to?
All hormones are peptides of 2 structurally related families (gastrin & secretin groups)
