9.1 The Digestive System Flashcards
Four layers of the gut wall
Mucosa, submucosa, muscularis externae, serosa
Passage from mouth to anus?
Mouth, oesophagus, stomach, small intestine(duodenum, jejunem, ileum), large intestine (caecum, ascending, transverse, descending, sigmoid), rectum, anus
Function of GI tract?
Port of entry for food Disrupt, store, digest food Kill pathogens Move food along tract Absorb nutrients Remove waste
Function of the mouth?
1) physical - teeth, tongue and muscle of mastication chew food.
2) chemical - salivary amylase and lipase break down food
3) forms bolus assisted by saliva which enters oesophagus
What is the function of the saliva? (4)
1) digestion starts by amylase and lipase
2) it is bacteriostatic containing immunoglobulin A antibody (IgA)
3) protects teeth and gum decay and mouth using high calcium
4) assists swallowing
What can be said about the upper and lower ends of the oesophagus?
Upper end - voluntary control, some striated muscle
Lower end - involuntary control, solely smooth muscle
What is peristalsis?
Contraction and relaxation of muscles creating wave-like contractions transporting bolts to stomach from oesophagus in 8 seconds
Function of the stomach?
Physical - churning
Chemical - forms hypertonic chyme from food, HCl acid and proteolytic enzyme
Storage of food as we eat faster than we digest
Why doesn’t the stomach digest itself?
It produces mucous which contains HCO3- ions that neutralise the acid. It is resistant to the pepsin too.
What causes mucus release?
Distension, food contents, gastric gland secretions
What structure are the following cells a part of? Isthmus, parietal, chief and enteroendocrine cells?
What are their functions?
Gastric Gland
Isthmus - stem cells divide and populate gland
Parietal - secrete H+ ions into lumen, HCO3- ions into blood which then move into surface mucous cells
Chief cells - secrete Pepsinogens which convert into pepsin
Enteroendocrine - secrete gastrin
Function of the duodenum? (2) What two organs are associated with it and its function?
1) Dilution and neutralisation of hypertonic chyme making it isotonic. It brings in water from ECF.
2) absorption of iron
Pancreas and liver
Function of liver in association to duodenum?
Releases bile to emulsify fat
Assists duodenum to neutralise hypertonic chyme as bile is made of water, alkali and bile salts
Function of pancreas in association to duodenum?
Secretes digestive enzymes
- cleave peptides to AA
- cleave polysaccharides to monosaccharides
- break down and reform lipids
- break down nucleic acids
Helps with neutralisation
The small intestine is in charge of absorption of different things. What is the duodenum, jejunum and ileum responsible for absorbing?
Duodenum - absorbs iron
Jejunum - sugars, AA, fatty acids
Ileum - Vit B12, bile acids, remaining nutrients
How does the small intestine increase its surface area and why would it need to?
Villi and microvilli maximise absorption
What is the function of the large intestine?
Water recovery from the isotonic chyme so its semi solid near end
It stores faeces
Contains most of GI tracts bacteria which are involved in
-the synthesis of vitamins K, B12, thiamine and riboflavine.
-breakdown of primary bile to secondary bile
-conversion of bilirubin to non-pigmented metabolites (all readily absorbed)
Where are most of the GI tracts bacteria found and what are their functions?
The large intestine
Synthesis of Vit K, B12, thiamine, riboflavine
Breakdown of primary bile to secondary
Breakdown of bilirubin (yellow) to non-pigmented molecules which are all readily absorbed
Why is fluid balance so important in the body?
Gut is dealing with large quantities of water (14L without drinking) and so if this is messed with, life threatening dehydration and electrolyte imbalance.
Its also why diarrhoea and constipation are so common
Precise control in the digestive system are achieved by which 3 systems?
Neural, paracrine, endocrine
Explain neural control of the digestive system.
1) somatic Nervous system controls ingestion - the mouth and top 1/3 of oesophagus
2) autonomic controls the rest by postganglionic plexuses in two areas
- between muscle layers and Gut wall
- between submucosa and muscularis externae
Explain paracrine control of the digestive system.
Substances act locally
Histamine - controls production of acid in stomach
Vasoactive substances - affect blood flow in gut
Explain endocrine control of the digestive system
1) secretin
- HCO3- secretion from duct cells of pancreas
- bile production by the liver
- inhibition of acid by parietal cells in stomach
2) Cholecystokinin (CCK)
- enteroendocrine cells of duodenum (gastric glands)
- promotes release of digestive enzymes by pancreas
- promotes release of bile from gall bladder
- Hungersuppressant
3) Gastrin
- released by pancreas, duodenum
- promotes production of HCl by parietal cells of stomach
If stools are pale and greasy, what could account for this?
No bile production
Why dont we inhale what we swallow?
The Epiglottis and Upper Esophageal Sphincter (UES) open and close as required.
When we swallow a bonus, epiglottis closes airway (larynx) and soft palate blocks the nasal cavity
When we breath, UES closes and blocks esophagus
