Gastrointestinal System Flashcards
List the functions of the GI/digestive system. (7)
- Ingestion
- Mechanical processing
- Digestion
- Secretion
- Absorption
- Compaction
- Defecation
List the organs/components of the digestive tract. (6)
- Oral cavity
- Pharynx
- Oesophagus
- Stomach
- Small intestine
- Large intestine
List the accessory organs of the GI system.
- Salivary glands
- Liver
- Gallbladder
- Pancreas
Which stain would be typically be used in investigation of the digestive tract?
H&E (haematoxylin and eosin)
List the typical layers of the digestive tract (internal to external).
- Mucosa
- Submucosa
- Muscularis propria
- Adventitia/serosa
What role does the oral cavity play in relation to the GI system?
Ingestion, mechanical processing and some digestion.
List the extrinsic salivary glands.
- Parotid
- Submandibular
- Sublingual
Which cranial nerve is involved in mastication?
CN V - trigeminal
Where is the oesophagus located?
Between the pharynx and the stomach.
What is the function of the oesophagus?
To transport food from pharynx to stomach.
What is found within the mucosa of the oesophagus?
- Non keratinising stratified squamous epithelium
- Lamina propria
- Muscularis mucosae
What is found within the submucosa of the oesophagus?
- Glands
2. Lymphoid follicles
Describe the muscle layer of the oesophagus.
- External layer is longitudinal muscle and inner layer is circular muscle.
- Superior third = voluntary striated muscle (skeletal)
- Middle third = voluntary striated and smooth muscle
- Inferior third = smooth muscle
Where is the stomach located?
Between the oesophagus and duodenum of small intestine. (Epigastric, left hypochondrium and umbilical regions).
What is the function of the stomach?
List the major functions of the stomach.
- Acting as a mixing compartment to produce chyme.
- Storage/emptying
- Secretes gastric juice to contribute to digestion.
List the regions of the stomach.
- Cardiac region
- Fundus
- Body
- Pyloric antrum
- Pyloric canal
- Pyloric sphincter
- Pylorus
Which curvature of the stomach is lateral and which is medial?
Lateral: greater
Medial: lesser
What are the three layers of the mucosa of the stomach?
- Epithelium
- Lamina propria
- Muscularis mucosae
Describe the submucosa of the stomach.
- Connective tissue
- Vascular plexus that supplies mucosa
- Allows mucosa to move freely over deeper structures
List the muscle layers of the muscularis of the stomach from deepest to most superficial.
- Oblique muscular layer
- Circular muscular layer
- Longitudinal muscular layer
The outer surface of the stomach is covered in a layer of…
Peritoneum
What is the peritoneum of the stomach continuous with?
Superiorly: lesser omentum
Inferiorly: greater omentum
Which cells are found within the epithelium of the stomach? (6)
- Surface mucous cells
- Mucous neck cells
- Parietal (oxyntic) cells
- Chief cells
- G cells
- Stem cells
Describe the surface mucous cells of the stomach.
Tall, thin, columnar epithelial cells
What is the function of the surface mucous cells of the stomach?
- Secrete mucin which combines with water to form mucus
2. Mucous protects underlying mucosa from self abrasion that may result from stomach acid
Describe the mucous neck cells of the stomach.
Low columnar epithelial cells
What is the function of the mucous neck cells of the stomach?
To secrete a soluble mucous in the active stomach
Describe the parietal (oxyntic) cells of the stomach.
- Oval epithelial cells
2. Contain canaliculi with irregular microvilli edges
What do the canaliculi of the parietal stomach cells contain?
H+/K+ ATPase antiporters
What is the function of the parietal cells of the stomach?
- Secrete hydrochloric acid
2. Secrete an intrinsic factor which is essential for vitamin B12 absorption
Describe the chief cells of the stomach.
Cuboidal epithelial
What is the function of the chief cells of the stomach?
- Secrete pepsinogen which is converted to pepsin by HCl
- Secrete gastric lipase
- Secrete rennin in infants
Describe the G cells of the stomach.
Large, round enteroendocrine cells
What is the function of the G cells of the stomach?
- Secrete gastrin which stimulates parietal and chief cell secretions
- Increase motility of the stomach
- Relax the pyloric sphincter
Describe the stem cells of the stomach.
Low, columnar epithelial cells with short microvilli on apical surfaces
What are the three sections of the small intestine?
- Duodenum
- Jejunum
- Ileum
Where is the duodenum located?
Between the pylorus of the stomach and duodenojejunal junction.
When chyme reaches the duodenum, what does it trigger the release of?
- Hormones that stimulate the gall bladder and liver to secrete bile
- Enzymes from the pancreas
Where do chemicals enter the duodenum?
On the medial side via the hepatopancreatic ampulla (ampulla of Vater)
List the functions of the duodenum.
- Mixing secretions from liver, pancreas and duodenum with food
- Neutralisation of acid
- Further digestion
- Absorption
List the functions of the jejunum.
- Completing breakdown of chyme
2. Nutrient absorption
What is the function of the ileum?
Nutrient absorption
What surface specialisations does the mucosa of the small intestine have?
Villi
What are the three layers of mucosa in the small intestine?
- Epithelium
- Lamina propria
- Muscularis mucosae
Describe the epithelial cells of the small intestine.
Columnar epithelium specialised for digestion and absorption of nutrients.
Where are Brunner’s glands found and what is their function?
- Submucosa of small intestine
2. Produce alkaline mucus that acts by neutralising the acidic chyme from the stomach
Where does the myenteric plexus lie?
Between the circular and longitudinal muscle layers of the muscularis of small intestine.
What is the serosa of the small intestine composed of?
Simple squamous epithelium
Describe the absorptive epithelial cells of the small intestine.
- Tall, thin, simple columnar epithelial cells
- Present on surface of villi
- Covered in microvilli
What is the function of the absorptive epithelial cells of the small intestine?
Uptake of nutrients and to produce digestive enzymes in the small intestine.
Describe the goblet cells of the small intestine.
- Columnar epithelial cells
2. Mucus filled goblet shaped spaces
What is the function of the goblet cells of the small and large intestine?
- Synthesise an alkaline mucus that lines mucosal wall to provide lubrication
- Prevent digestive enzymes from eroding cell walls
Where are the crypts of Lieberkuhn found and what do they contain?
- Found in grooves between intestinal villi
2. Hormone secreting cells, Paneth cells, constantly dividing epithelial cells
Describe the enteroendocrine cells of the small intestine.
- Large, triangular and hormone secreting
2. Large, irregular nuclei surrounded by granules
What is the function of the enteroendocrine cells of the small intestine?
To secrete hormones
What is the function of the Paneth cells of the small intestine?
They secrete lysozyme which protects the gut wall by rupturing bacterial cell walls.
List the enzymes found at the brush border of the small intestine. (9)
- Aminopeptidases
- Dextrinase
- Dipeptidase
- Enteropeptidase
- Lactase
- Maltose
- Nucleosidase
- Phosphatases
- Sucrase
What is the function of aminopeptidases?
- Cleave proteins
- Breaking down peptide chains in to small peptide chains
- In the presence of metal ions
What is the function of dextrinase?
Breaks down dextrin, a short chain glucose polymer
What is the function of dipeptidase?
Breaks down dipeptides in to single amino acids
What is the function of enteropeptidase?
- Cleaves amino acids from trypsinogen in to active form, trypsin
- Activates chymotrypsin, elastase and carboxypeptidase
What is the function of lactase?
Breaks down lactate in to glucose and galactose
What is the function of maltose?
Breaks down maltose in to two glucose molecules
What is the function of nucleosidase?
- Breaks down nucleotides
- Removes phosphate group
- Yields pentode sugar and free bases
What is the function of phosphatases?
Remove phosphate groups from their substrates.
What is the function of sucrase?
Break down sucrose in to fructose and glucose
What is the function of the large intestine?
- Absorb water and salts
2. Eliminate waste
What is the first part of the large intestine?
The caecum
What is the function of the absorptive cells of the large intestine?
Absorption of mainly water and salts
What is the difference between the mucosa of the small and large intestine?
Small: circular folds or villi for increased surface area
Large: long, tubular intestinal glands so less surface area
What are haustral contractions?
Slow segmental contractions that occur every 30 minutes to move faeces from caecum to rectum for expulsion.
Which structures are covered by the peritoneum?
- Stomach
- Liver
- Jejunum
- Ileum
What are the sections of the colon?
- Ascending colon
- Transverse colon
- Descending colon
- Sigmoid colon
What is the function of the colon?
- To remove further water, nutrients and electrolytes
2. Move chyme/faeces to rectum