Digestive System Flashcards
What are the major valves in the digestive system?
- cardiac sphincter
- pyloric sphincter
- illeocaecal valve
What does the pyloric sphincter do?
Controls emptying rate of stomach
What does the cardiac sphincter do?
Prevents reflux of stomach contents into eosphagus
What does the illeocaecal valve do?
Prevents reflux of large intestine contents into the small intestine
What does the celiac trunk supple blood to?
- lower oesophagus
- stomach
- duodenum
- pancreas
- liver
- spleen
What does the superior mesenteric artery supply blood to?
- most of the small intestine
- proximal half of the large intestine
What does the inferior mesenteric artery supply blood to?
- distal half of large intestine
- rectum
Define ingestion
The selective intake of food
Define digestion
Mechanical and chemical breakdown of food
Define absorption
Uptake of nutrient molecules into epithelial cells of the digestive tract and then to blood and lymph
Define compaction
Absorption of water and consolidation of the indigestible residue
Define defamation
Elimination of waste
What is peristalsis?
Waves of contraction of circular muscle behind the food bolus and relaxation of muscle in front of the bolus
What does peristalsis do?
Moves food along the gut
What is segmentation?
Alternate contraction of rings of smooth muscle
What does segmentation do?
Divides and squeezes back and forth, mixes food within the gut
What epithelium are the lips and cheeks lined with?
Non keratinised stratified squamous epithelium
What is mastication?
Chewing, mechanical digestion
What are the purposes of mastication?
Makes food easier to swallow, exposes more surface area of food for the action of digestive enzymes which increases the rate of chemical digestion
What are the two phases of swallowing?
- buccal - voluntary
- pharyngoesophagal - involuntary
Why is the pyloric sphincter so important?
It limits the flow of highly acidic stomach contents into the duodenum so that the submucosal glands and pancreatic secretions can neutralise the contents
Epithelium of the digestive tract
- oral cavity: non-keratinised stratified squamous
- esophagus: non-keratinised stratified squamous
- stomach: simple columnar
- small intestine: simple columnar
- large intestine: simple columnar
Digestion of carbohydrates
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Digestion of proteins
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Digestion of fats
…
Embryological development of the digestive system
Endoderm forms lining of gut
Mesoderm forms Ct and surrounding muscle
What cells are found in the stomach?
- mucous cells & mucous neck cells
- chief cells
- parietal cells
What do chief cells secrete?
- pepsinogen
- gastric lipase
What do parietal cells secrete?
- HCl
- intrinsic factor
How does the production and action of pepsin work?
- chef cells secrete pepsinogen (inactive form of pepsin)
- parietal cells secrete HCl
- HCl removes some of the amino acids from pepsinogen to for pepsin
How is pepsin autocatalytic?
It causes more pepsinogen to convey to pepsin
Why does the stomach have 3 layers of muscular is externa?
- helps with segmentation
- allows the stomach to stretch
What do tight junctions in the stomach epithelium do?
Prevents stomach juices from digesting the connective tissue of the lamina propria
What is gastric juice made up of?
- water
- HCl
- pepsin
What is the pH of gastric juice?
0.8
How much gastric juice is produced everyday?
2-3L
What are the three ways that the small intestine increases surface area?
- plica circulares
- villi
- microvilli
Characteristics of plica circulares
- circular folds of the mucosa and submucosa
- form transverse spiral pathways
- occur from the duodenum to the middle of the ileum
What is the function of plica circulares?
- causes chyme to flow in a spiral path which increases contact with mucosa
- slows passage of chyme
- promotes more thorough mixing and nutrient absorption
- increases surface are by a factor of 2-3
What are villi?
- fingerlike projections
- folds of the epithelium
What is the function of villi?
- increase surface area by a factor of 10
What are microvilli?
- folds of the epithelia cell membrane
What is the function of microvilli?
- increase the surface area by a factor of 20
- contain brush border enzymes for contact digestion
Epithelium of the rectum and anal canal
- simple columnar
- non-keratinised stratified squamous
What primary tissues types is the digestive tract derived from?
- endoderm: forms lining of the gut
- mesoderm: forms CT and muscle that surround the gut
What is formed from the foregut?
Lining of the mouth, pharynx, esophagus, stomach and 1st third of duodenum
What is formed from the midgut?
Last 2 thirds of the duodenum, jejunum, ileum, ascending colon and part of the transverse colon
What is formed from the hind gut?
Transverse colon, descending colon, rectums and anal canal
Embryological development of the liver, gallbladder and pancreas
Form as a diverticula (bud) of the endoderm tube at the junction of the foregut and the midgut
What are the layers of the digestive tract?
- lumen
- mucosa
- submucosa
- muscularis externa
- adventitia or serosa
Mucosa
- epithelium
- lamina propria (CT)
- muscularis mucosa
Submucosa
Layer of loose CT containing nerves, blood, mucus secreting glands and lymphatic cells
Muscularis externa
Usually 2 layers of smooth muscle: in ed circular layer, outer longitudinally layer
Serosa
Thin layer of CT and mesothelium
Adventitia
Fibrous CT
What are the 2 neural networks in the digestive tract?
- myocentric plexus
- submucosal plexus
Myocentric plexus
- between the 2 layers of muscularis externa
- controls frequency & strength of contractions of muscularis externa
Submucosal plexus
- controls glandular secretions
- controls movement of muscularis mucosa
Intrinsic salivary glands
- lingual, buccal and labial glands
- produce lingual lipase, lysozyme and secrete saliva
Extrinsic salivary glands
- paratoie, submandibular and sublingual glands
- secrete salivary
What is the function of saliva?
Moistens and lubricates food
What are the parts of the small intestine?
Duodenum, jejunum, ileum
Where does most of the digestion and nutrient absorption occur?
Jejunum
Parts of the villi where nutrients are absorbed:
Capillary: carbohydrates and proteins
Lacteal: lipids
Digestion of carbohydrates
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Digestion of proteins
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Digestion of fats
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Muscularis externa of the large intestine
Taenia coli form haustra coli
Gastro-esophageal junction
Epithelium goes from stratified squamous to simple columnar
