BL S8 The Digestive System Flashcards
What is the alimentary canal?
The whole passage along which food passes through the body from mouth to anus during digestion.
What are the four layers to the gut wall?
Mucosa
Submucosa
Muscularis externae
Serosa or adventia
What are the 3 layers of the mucosa?
Epithelium
Lamina propria
Muscularis mucosae
What is found in the lamina propria?
Aggregations of lymph tissue called lymphatic nodules.
What is the submucosa made of and what is found in it?
Connective tissue
Glands Arteries Veins Lymphatics Nerves
GAVLN
What are the 2 layers of the smooth muscle in the muscularis externae and how can they be distinguished between?
Inner circular layer and outer longitudinal layer.
Inner layer - central circular nuclei
Outer layer - elongated cigar shaped
What is the structural difference between adventitia and serosa?
Adventitia consists of loose connective tissue only.
Whereas serosa consists of a layer mesothelium and a layer of loose connective tissue.
What is the difference in where adventitia is compared to serosa?
Adventitia is found covering retroperitoneal organs, whereas serosa is found covering intreaperitoneal organs.
What is the functional difference between adventitia and serosa?
Serosa secretes fluid for lubrication, whereas adventitia is mainly there to bind to structures.
Name the visceral and parietal layers of the serosa.
Visceral layer is the loos connective tissue membrane.
Parietal layer is the mesothelium.
What are the functions of the GI tract?
Entry point for food Mechanically disrupt Store food Chemically digest Kill pathogens Move food along tract Absorb nutrients from resultant solution Elimination/ defecation - residual waster
Define digestion
The conversion of food by physical and chemical disruption into a sterile, isotonic and neutral pH solution from which we will absorb nutrients.
What are some properties of saliva?
Enzymes - amylase and lipase - chemically digests
Bacteriostatic - IgA - halts/ prevents bacterial growth
High in calcium - protect teeth and calcium from leeching out
Alkaline - pH buffers
Assist swallowing - lubrication
What is physical disruption in the mouth carried out by?
Teeth, tongue and muscle of mastication.
Peristalsis works independant of gravity, true or false?
True
Where is the fastest GI transport?
Entry -oesophagus
Exit - rectum/ anus
What type of epithelium is the in the oesophagus?
Stratified squamous non-keratinised.
What type of gland is found within the submucosa of the oesophagus?
Mucus secreting glands
As stomach fills with food, its walls relax. What is this called?
Receptive relaxation.
How does the stomach seal protect?
Secrets mucus
Through the combined action of what does the stomach produced chyme?
Acid- HCl
Physical disruption - 3 muscle layers + rugae
Enzymes - proteolytic enzymes
Acid and enzymes = chemical disruption
What can be said about the tonicity of the chyme produced?
Hypertonic
Where is chyme from stomach delivered to?
Duodenum
What is the function of the gastric rugae?
Allow for expansion of the stomach upon new food contents entering.
What is the third layer of smooth muscle in the muscularis externae of the stomach called?
Oblique
What four regions are gastric glands compromised of?
Pit
Isthmus
Neck
Base
What is found in the pit?
Surface mucous cells
What is found in the isthmus?
Stem cells, mucous cells and parietal cells
What is found in the neck of a GG?
Enteroendocrine cells, parietal cells and mucous neck cells.
What is found in the base?
Parietal, Enteroendocrine cells, chief cells.
What are the roles of stem cells?
Divide to populate gland by upward or downward migration.
What is the function of parietal cells?
Secrete H+ ions into lumen and HCO3- ions into capillaries from where they will diffuse into the surface mucous cells.
What is the function of chief cells?
Release pepsinogens which are converted into pepsin extracellularly.
Pepsinogens partially hydrolyse proteins.
What is the functions of Enteroendocrine cells?
Secrete hormone gastrin.
The gastric mucosa reacts to this by secreting acid.
What are the properties of mucous secreted?
Resistant to degradation from pepsin
Contains HCO3- ions to neutralise the effects of nearby H+ ions - protecting the stomach lining.
What is mucus released in response to?
Distension
New stomach contents
Acid secretion from gastric glands
What is aspirin’s effect on surface mucous cells?
Impairs mucous production from these cells, eventually leads to their damage.
How will damaged cells within a gastric gland be replaced?
Mitosis of stem cell in the isthmus.
How long is the duodenum?
20-25cm
How is the duodenum involved in the dilution and neutralisation of chyme?
Brunners gland - secrete bicarbonate rich mucous to neutralise.
H20 drawn in from ECF - hypertonic to hypotonic
Bile from liver - contains water, alkalis and bile salts - neutralisation and emulsification.
Pancreas secrete alkali to neutralise.
How is digestion of chyme completed?
Pancreatic, liver and intestinal enzymes which act with bile.
What is needed for absorption?
Energy - active process
Large SA - gut folded VIII - microvilli
Goo blood supply and drainage.
What is the length, SA and diameter of the small intestine
22 feet long
1 inch diameter
25m^2
What does the duodenum absorb?
Iron
What does the Jejunum absorb?
Sugars
Amino acids
Fatty acids
What does the ileum absorb?
Vit B12
Bile acids
Remaining nutrients
What type of cells line the small intestine?
Simple columnar epithelium, with microvilli.
Goblet cells.
What is a lacteal?
A dilated lymphatic capillary vessel.
Who long in and wide in the large intestine?
1.2m and 6-9cm wide
What are the crypts of Lieberkühn and where are they found?
Intestinal glands
Found in the small and large intestine.
What do surface epithelial cells of the large intestine do?
Absorb water and Electrolytes.
Where is faeces stored?
In colon.
If urge to defecate is not acted upon what will happen?
Rectum contents are returns to the colon via reverse peristalsis.
If faeces is stored for too long in the colon what will be the result?
More water will be reabsorbed - harden - constipation.
What roles do GI tract bacteria carry out?
Synthesis of vit K, B12 and riboflavin W.
Breakdown of primary to secondary bile acids.
Convert bilirubin to non-pigmented metabolites.
What can problems with fluid balance result in?
Dehydration and electrolyte imbalance.
What areas of the GI tract are under somatic control?
Mouth and 1/3 of oesophagus
Last sphincter of anus.
Where do the autonomic post-ganglionic neurones form plexuses?
Between muscle layers of muscularis externae - myentric plexus
Between submucosa and muscularis externae - submucosal plexus.
How is gut under paracrine control?
Histamine - controls acid production in stomach
Vasoactive - substances affect the blood flow in the gut
How is the gut under endocrine control?
Range of hormones control
Secretion of stomach acid
Alkali secretion from liver and pancreas
Enzyme secretion
Generally the gut is controlled by enzymes it makes itself, true or false?
True.
