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What are the 9 segments of the GI tract
- Small Intestine
- Large intestine
- Anal canal
What occurs in the stomach
Food is broken down and mixed with fluids to become chyme
What is the order of the 3 segments of the small intestine and how long is each segment
- Duodenum 25cm
- Jejunum 2.5m
- Ileum 3.5m
What is an accessory organ and what are the accessory organs of the GI tract
An organ associated with the GI tract but not part of the tube itself.
e.g. pancreas, liver, salivary glands, gallbladder
What do the accessory organs do
Synthesise and deliver material to the lumen of the GI tract via a duct system
What are the three pairs of salivary glands, what does each pair secrete, and where are they located?
Parotid glands secrete watery serous fluid and are located just below the ear
Submandibular glands secrete mucous fluid as well as serous fluid and are located below the mandible (jaw bone)
Sublingual glands secrete mucous fluid and are located below the tongue
The opening from the mouth into the oropharynx is defined as?
The lumen of the mouth is called the...
Type of epithelium in the oesphagus? Why is this necessary?
Stratified squamous epithelium. Multiple layers prevent damage from food
Junction where oesphagus joins the stomach.
Describe the mucosa of the GI tract
- Epithelium lines the lumen
- Lamina propria supports the epithelium
- Muscularis mucosa underlies the lamina propria
- * Epithelium and lamina propria are folded to allow the tract to distend *
Describe the submucosa of the GI tract
- Lies beneath the mucosa
- Connective tissue
- Contains glands and ducts as well as larger blood vessels, nerves and lymphatics
Define the Muscularis of the GI tract
- Two layers of smooth muscle.
- - Inner cicular layer. Contraction leads to deacrease in diameter of the lumen
- - Outer longitudinal layer. Contraction leads to a decrease in length.
Describe the adventitia of the GI tract
- Surrounds the outside of the GI tract
- Fibrous connective tissue
- Adventitia + peritoneum = serosa
Define the peritoneum in the GI tract. What is the cavity between the two layers of the peritoneum?
- Two layers of serous membrane
- - Outer parietal layer lines the abdominal wall
- - Inner visceral layer wraps around most organs
- Cavity = peritoneal - contains serous fluid
What are the mesentaries and what are they composed of
- Double layer of visceral peritoneum.
- Attaches organs loosely to the posterior abdominal wall
What is the function of the omenta and what are they composed of?
- Lesser omentum: two layers of peritoneum
- Greater omentum: four layers of peritoneum - protective layer, prevent spread of infection
Functions of the stomach:
- Temporary storage of food and fluids
- Mechanical digestionL requires muscle
- Chemical digestion (enzymes and chemicals are secreted from stomach epithelium)
- Mixing of food: requires muscle
(6 bullet points)
- - Made up of the fundus, body and pylorus
- - Increases in size to accomodate large volume (1-1.5L)
- - Three layers of muscle
- - Right border = lesser curvature
- - Left border = greater curvature
- - Folded surface (rugae) increase surface area
Inferior to diaphragm and liver
Stomach structural components of wall (serosa, muscularis, submucosa and mucosa)
- Serosa: supportive CT lined by SSE
- Muscularis: outer longitudinal, middle circular, inner oblique
- Submucosa: CT contains blood vessels and nerves
- Muscosa: muscalaris mucosae next to the submucosa, gastric glands open into the lumen via gastric pits, on top of the muscalaris mucosae is the lamina propria (carries blood vessels), then a final layer of simple columnar epithelial cells.
Most of the absorption in the GI tract occurs in the...
The epithelial cells on the surface of the villi in the small intestine are of what kind?
Simple columnar epithelial cells, specialised for absorption
The ileum and caecum are seperated by which valve? Is this valve tight or loose?
Ileocaecal valve. It is loose and allows free passage of material into the LI without preventing backflow into the SI
Ascending, transverse and descending parts of the large intestine: intraperitoneal or retroperitoneal?
- Ascending: retroperitoneal
- Transverse: intraperitoneal
- Descending: retroperitoneal
Describe the muscalaris layer in the large intestine
- Outer longitudinal layer is divided into 3 bands: taeniae coli
- Inner circular layer forms semilunar folds that divide the large intestine into pouches called haustra
Variations to the basic four-layerd structure in the LI
- Mucosa: contains mucous secreting glands. Lamina propria of the mucosa contains collagen and immune cells
- Muscularis layer is discontinuous
- Peritoneum forms fat-filled pouches called apendices epiploicae
Describe the sphincters of the anal canal
- Internal: thickened smooth muscle, relaxes involuntarily
- External: thickened skeletal muscle, relaxes voluntarily
Describe the lining of the anal canal
- Upper portion is lined with columnar epithelium
- Lower portion is lined with stratified squamous epithelium
Describe the flow of bile in the GI system
- Half of the bile flows into the duodenum via the common bile duct
- The other half is diverted to the gallbladder via the cystic duct for storage (which then flows through the common bile duct when required)
Where do the common bile duct and pancreatic duct meet
Ampulla of Vater at the greater duodenal papilla
What does the sphincter of Oddi do?
Muscular valve which controls the flow of secretions from the liver, gallbladder and pancreas from the ampulla into the duodenum
What happens to the blood draining from the GI tract?
It drains into the portal venous system which carries it to the liver sinusoids for processing and detoxification.
Propelling of food along the GI tract. Occurs due to sequential contraction of adjacent segments of smooth muscle
Occurs only in the intestines. Involves simultaneous contraction of certain regions of smooth muscle which results in mixing of food and exposure to absorptive surfaces
Explain the Basic electrical rhythm (or slow wave)
- Spontaneous variations in membrane potential.
- When the slow wave reaches threshold an AP will fire and muscle contraction will result.
- The frequency varies in different parts of the GI tract...
- - Stomach contracts 3 times/min
- - Duodenum contracts 12 times/min
- - Ileum contracts 9 times/min
Explain the migrating motor complex including the duration of the 3 distinct phases
- Occurs 4-5 hours after a meal and is repeated every 2 hours after that until the next meal
- - Waves of motility from stomach to SI clear the GI tract.
- 3 distinct phases
- - Inactivity ~hour
- - Intermittent activity ~50mins
- - Intense activity 5-10mins
How often do segmentation movements occur in the large intestine? Why?
Every 30 minutes. Only a small amount of extraction of electrolytes and water occurs in the large intestine.
What is gastrin secreted in response to and what are its actions
- In response to stomach distension, partially digested proteins, vagal stimulation
- Actions: increase HCl and pepsin secretion, increase stomach motility
What is the Gastric inhibitory peptide secreted in response to and what are its actions
- In response to the presence of fatty acids and glucoseActions: Stimulate insulin secretion, affect fatty acid metabolism
What is secretin secreted in response to and what are its actions
- In response to presence of acid and partially digestion proteins and fatty acids
- Actions: Inhibit acid secretion, increase HCO3- secretion, bile ejection from gallbladder
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