Digestive System Flashcards
What are the accessory organs of the digestive system?
liver, pancreas, gallbladder, salivary glands
Name the 4 layers of the gut wall.
Mucosa
Submucosa
External muscle layers (2)
Serosa
Outline the structure of the mucosa in the alimentary tract.
- Epithelium - simple columnar
- Lamina propria - mucosal glands and peyer’s patches
- Muscularis mucosae
What is present in the submucosa?
Glands
Veins, arteries and nerves
What are the 2 layers of external smooth muscle in the gut wall?
Inner circular
Outer longitudinal
What is the serosa of the gut wall called and what is it comprised of?
Connective tissue and simple squamous epithelium = mesothelium.
Outline major functions of the GI tract.
- Chemical and physical disruption of food
- Food storage
- Kills pathogens
- Absorb nutrients
- Excrete waste material
What are the properties of saliva?
- High in calcium
- Lipases and amylases - begins digestion
- Alkali
- Aids swallowing
- Protects the mouth
- Bacteriostatic (IgA)
What innervates the GI tract?
Myenteric plexus and submucosal plexus
What muscle types control the oesophagus?
Upper 1/4 - skeletal muscle, voluntary
Lower end- smooth muscle, involuntary
What epithelium lines the oesophagus and its characteristics?
Stratified squamous non - keratinized epithelium.
Withstands abrasion.
What does the submucosa contain?
Mucus secreting glands
What is the food entering the oesophagus called?
Bolus
What is receptive relaxation?
Distension of the stomach wall in order to prevent pressure rising
There are 3 layers of smooth muscle in the stomach wall, what are they?
Oblique, circular and longitudinal
The stomach contains longitudinal ridges, what are these called?
Rugae
What are some of the functions of the stomach?
Chemically (HCl, stomach acid) and physically (churning) disrupt the food.
Secretes acid and proteolytic enzymes
Food store
What does the stomach produce?
Hypertonic, acidic chyme
What classification are gastric glands?
Long, straight tubular glands
What cells dominate the pit of the gland?
Mucus- secreting cells
Parietal cells are in gastric glands, what is their function?
Secrete H+ ions into the lumen and HCO3- into the capillaries which move it to the surface mucous cells.
What do chief cells of the gastric gland secrete?
Pepsinogens which are converted into pepsins which hydrolyse proteins.
Enteroendocrine cells at the bottom of the gastric gland include G-cells, what do these secrete?
Gastric, which stimulates acid secretion.
What section of the small intestine has brunner’s glands, what do they do?
Duodenum.
They secrete bicarbonate- rich mucus to neutralise the acidic chyme from the stomach.
How else does the duodenum neutralise the chyme?
Alkali secretions from the pancreas and liver
What does the duodenum do to the tonicity of the chyme?
Hypertonic to Isotonic by drawing water from ECF.
What structures increase the surface area of the small intestine?
pilcae circulares
Villi
Microvilli
What is absorbed in each of the parts of the small intestine?
Duodenum - Iron
jejumum - fatty acids, amino acids and sugars
Ileum- Vit B12, bile acids and remaining nutrients
What is the main function of the large intestine?
Water and electrolyte absorption
What functional role does the large population of bacteria in the colon have?
- synthesises vitamin K, B12, histamine and riboflavin.
- breakdown of bile acids
- conversion of bilirubin to non-pigmented metabolites
What are crypts of lieberkuhn?
Mucus secreting tubular glands between villi.
What does bile contain?
Water, alkali and bile salts
How do paracrine substances contribute to control of the gut?
Histamine - controls acid production
Vasoactive substances affect blood flow to gut
What 3 endocrine molecules control the gut?
Gastrin
Secretin
Cholecystokinin
What does gastrin do?
Promotes HCl production by parietal cells
What does secretin do?
Inhibits acid secretion by parietal cells
Stimulates bicarbonate secretion from pancreatic ducts
Promotes bile production by the liver
What does cholecystokinin do?
promotes release of digestive enzymes from pancreas
Promotes release of bile from the gallbladder
Hunger suppressant
Where are plicae circulares and what is their function?
Small intestine, increase SA for absorption
Which section of the intestine is lined with villi?
Small intestine only
