Digestive System Flashcards
What are the four layers of the gut wall, starting from the innermost?
Mucosa
Submucosa
External muscle layers (muscularis externae)
Serosa
What does the submucosa contain?
Layer of CT bearing glands, arteries, veins and nerves
How many layers of smooth muscle does the muscularis externa contain and what are they?
2
Outer longitudinal layer
Inner circular layer
What does the muscularis externa do?
Creates successive peristaltic waves to move luminal contents along the gut
What makes up the serosa? (2)
Simple squamous epithelium (mesothelium)
Connective tissue
What are the major functions of the GI tract? (8)
- Port of entry for food into body
- Mechanically disrupt food
- Temporarily store food
- Chemically digest food
- Kill pathogens in food
- Move food along tract
- Absorb nutrients from resultant solution
- Eliminate residual waste
Complete the sentence:
Digestion is the conversion of what we eat by ________ and ________ disruption into a solution (relatively sterile, _______ in pH and _______) from which we can absorb our nutrients.
Physical
Chemical
Neutral
Isotonic
Which enzymes in saliva start digestion?
Amylase
Lipase
Saliva is bacteriostatic, what does this mean?
Prevents bacteria multiplying without destroying them
Why does saliva have a high calcium content?
Protects teeth
Complete the sentence:
Physical disruption starts in the mouth by the action of _____, ______ and muscles of _____________.
Teeth
Tongue
Mastication
True or false: the fastest GI transport is on entry and exit
TRUE
Complete the sentence:
The mouth forms a _____ which enters the oesophagus and is transported to the stomach.
Bolus
True or false: the upper end of the oesophagus is solely smooth muscle so involuntary control
FALSE - lower end, upper end has some striated skeletal muscle so control is voluntary
Which type of epithelium is found in the oesophagus?
Stratified squamous non-keratinised (withstands abrasion)
What does the lamina propria of the oesophageal mucosa contain?
Loose CT with blood and lymph vessels, some smooth muscle cells and many immune cells
Complete the sentence:
Physical disruption continues in the stomach by _______ (_ muscle layers and ________ ______)
Churning
3
Mucosal rugae
What is receptive relaxation?
Stomach wall relaxes so pressure doesn’t rise
Why does the stomach secrete acid and proteolytic enzymes?
To break down tissues and disinfect
How does the stomach protect its epithelium?
By secreting mucus
Complete the sentence:
The stomach produces hypertonic ______ by combined action of acid, ________ and agitation
Chyme
Enzymes
What is chyme?
Partially digested stomach content
What are the layers of smooth stomach muscle?
Oblique
Circular
Longitudinal
What are rugae?
Fold of gastric mucosa forming longitudinal ridges in the empty stomach
True or false: surface mucous cells are abundant in the gastric pits but infrequent in the tubular gastric glands below
TRUE
Mucus is released by surface mucous cells in the stomach in response to what? (3)
Distension
Stomach content
Acid secretion by gastric glands
What can damage the surface mucous cells of the stomach?
Alcohol or aspirin
How is the stomach lining protected?
Mucus secreted by surface mucous cells in the stomach contain HCO3- ions which neutralise the effect of H+ ions and thereby protect the stomach lining
What is the isthmus?
Region in which stem cells divide to populate a gland by upward or downward migration
What do chief cells do?
Secrete pepsinogens which are converted into pepsin which partly hydrolyse proteins
What do enteroendocrine cells do?
Include G cells which secrete gastrin
How long is the duodenum?
20-25cm
True or false: the duodenum is the shortest and most proximal portion of the small intestine
TRUE
What do the walls of the duodenum contain?
Brunner’s glands which secrete bicarbonate-rich mucus to neutralise acidic chyme
What does bile contain?
Water
Bile salts (to emulsify fats)
Alkali
True or false: pancreas and liver secrete alkali to neutralise acidic chyme
TRUE
What do the enzymes from the pancreas and intestine do? (4)
- Cleave peptides to AA
- Cleave polysaccharides to monosaccharides
- Break down and re-form lipids
- Break down nucleic acids
What does absorption require?
Lots of energy
Large surface area
Good blood supply/drainage
Drainage during absorption occurs via which vessel?
Hepatic portal vein
What is a lacteal?
Dilated lymphatic capillary vessel
What are the three parts of the small intestine called?
Duodenum
Jejunum
Ileum
What does the duodenum absorb?
Iron
What does the jejunum absorb?
Most sugars
AAs
Fatty acids
What does the ileum absorb?
Vitamin B12
Bile acids
Remaining nutrients
What are the different parts of the large intestine, going in a clockwise motion and ending with the rectum?
Caecum Ascending colon Transverse colon Descending colon Sigmoid colon
True or false: colon contains most of the GI tract’s bacteria
TRUE
What are the bacteria in the colon involved in? (3)
- Synthesis of vitamins K, B12, thiamine and riboflavine
- Breakdown of primary to secondary bile acids
- Conversion of bilirubin to non-pigmented metabolites
Decreased absorption or increased secretion can result in what?
Life threatening dehydration
Life threatening electrolyte imbalance
Motility and secretion need precise control and this is achieved by what three types of overlapping mechanisms?
Neural
Paracrine
Endocrine
What are the two types of neural control?
Somatic
Autonomic
Which two processes are involved in somatic control?
Ingestion
Excretion (last sphincter of anus)
What do post ganglionic neurones form?
Plexuses
Name two locations of plexuses
Between muscle layers of gut wall (myenteric plexus)
Between submucosa and muscularis externa (submucosal plexus)
What are two types of paracrine control and what do they do?
Histamine - controls production of acid in stomach
Vasoactive substances - affect blood flow in gut
What do the range of endocrine hormones involved control?
Secretion of stomach acid
Alkali secretion from liver and pancreas
Enzyme secretion
What does secretin promote? (2)
HCO3- secretion from duct cells of the pancreas
Bile production by the liver
What does secretin inhibit?
Secretion of acid by parietal cells of the stomach
What does CCK stand for?
Cholecystokinin
What does CCK do? (3)
Promotes release of digestive enzymes from pancreas.
Promotes release of bile from gall bladder (stimulates it to contract).
Hunger suppressant.
Where is CCK made?
Enteroendocrine cells of duodenum
Where is gastrin released? (3)
- G cells of pyloric antrum of stomach
- Pancreas
- Duodenum
What does gastrin do?
Promotes the production of HCl (gastric acid) by parietal cells of the stomach
What are the overall roles of the gut? (3)
Secretion
Movement
Absorption
