The Digestive System Flashcards Preview

ESA 1 - Body Logistics > The Digestive System > Flashcards

Flashcards in The Digestive System Deck (47)
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1
Q

Where is most of the digestive system located?

A

In the abdominal cavity:

  • peritoneal cavity - surrounded by peritoneum
  • retroperitoneal space - posterior to peritoneum
2
Q

What is the difference between intraperitoneal and retroperitoneal organs?

A

Intraperitoneal organs = organs having a mesentery
- eg stomach, jejenum and ileum, transverse colon, liver and gallbladder.

Retroperitoneal organs = organs without a mesentery
- eg pancreas, duodenum, ascending and descending colons.

3
Q

What are mesenteries?

A

Portions of peritoneum that suspend the gut and provide paths for blood vessels and nerves to viscera.

4
Q

What are the 4 layers of the gut wall?

A
  1. Serosa
    • mesothelium (simple squamous epithelium)
    • thin layer of CT
  2. Muscularis externa - 2 layers of smooth muscle:
    • outer longitudinal layer
    • inner circular layer
  3. Submucoa - layer of CT
  4. Mucosa
    • muscularis mucosae
    • lamina propria (CT containing mucosal glands and Peyer’s patches)
    • epithelium
5
Q

What is digestion?

A

The conversion of what we eat by physical and chemical disruption into a solution that is:

  • relatively sterile
  • neutral in pH
  • isotonic (same osmolarity as bodily tissues)
  • from which we can absorb nutrients.
6
Q

Which process occurs in the mouth?

A

Physical and chemical disruption of food:

  • physical: action of teeth, tongue and muscles of mastication
  • chemical: action of salivary amylase and lipase
7
Q

By what is saliva produced?

A

Exocrine salivary glands:

  • parotid
  • submandibular
  • sublingual
8
Q

What are the 4 functions of saliva?

A
  1. Starts digestion (amylase and lipase)
  2. Assists swallowing
  3. Protects mouth (e.g. High calcium protects teeth)
  4. Is bacteriostatic
9
Q

What is food moving from the mouth to the oesophagus called?

A

Bolus

10
Q

What is the function of the oesophagus?

A

Rapid peristaltic transport of bolus to stomach.

11
Q

What helps food move down the oesophagus rather than the trachea?

A

Epiglottis

12
Q

What control do we have over the oesophagus?

A
  • Upper 1/3 under voluntary control (some striated skeletal muscle)
  • Lower 2/3 under involuntary control (solely smooth muscle). Innervated via myenteric plexus and submucosal plexus.
13
Q

What type of epithelium lines the oesophagus?

A

Stratified squamous non-keratinised… withstands abrasion.

14
Q

What are the functions of the stomach?

A
  1. Continued disruption
    • physical: churning (3 muscle layers and mucosal rugae)
    • chemical: acid (HCl) and proteolytic enzymes (e.g. Pepsin)
  2. Storage
    • eat faster than digest
    • wall relaxes so that pressure doesn’t rise (= receptive relaxation)
  3. Disinfection
15
Q

What does the combined action of acid, enzymes and agitation produce to be delivered to the duodenum?

A

Incompletely digested, hypertonic chyme.

16
Q

From the stomach onwards, what type of epithelium lines the GI tract?

A

Simple columnar epithelium

17
Q

What is special about the muscularis externa in the stomach?

A

Composed of 3 layers of SM: oblique, circular and longitudinal.

18
Q

What structures does the muscosa in the stomach form?

A
  • Shallow gastric pits: lined by surface mucous cells.

- Long, straight tubular gastric glands: extend downwards from the gastric pits towards the muscularis mucosae.

19
Q

What is the function of surface mucus cells?

A
  • Secrete mucus in response to distension, stomach content and acid secretion.
  • Mucus is:
    1. resistant to pepsin degradation
    2. contains HCO3- ions which neutralise the effects of H+ ions
      So protects the stomach lining from self-degradation.
20
Q

What is the effect of alcohol/aspirin on the stomach?

A

Damages mucous cells.

But these are quickly replaced by mitosis in deeper cells in the neck of the gastric pit.

21
Q

What is the function of parietal cells?

A

Secrete H+ ions into the lumen and HCO3- ions into nearby capillaries which move them to surface mucous cells.

22
Q

What is the function of Chief cells?

A

Secrete pepsinogens which are converted into pepsins (once passed the mucus barrier to protect stomach) - partly hydrolyse proteins.

23
Q

What is the function of enteroendocrine cells?

A

Include G cells which secrete gastrin- stimulates acid secretion from the wider gastric mucosa.

24
Q

What are the 3 parts of the small intestine?

A
  1. Duodenum
  2. Jejenum
  3. Ileum
25
Q

How long is the small intestine and what is its surface area?

A
  • ~7 m

- >25 m2

26
Q

What is the main function of the small intestine and how is it adapted for this process?

A

Absorption

  • Large surface area: plicae circularis, villi and microvilli
  • Adequate contact time
  • Good energy/blood supply and drainage (via hepatic portal vein)
27
Q

What is the duodenum and what are its functions?

A
  • 20-25 cm long, C-shaped, proximal portion of the small intestine that curves head of pancreas.
  • Functions:
    1. Dilution and neutralisation of acidic chyme
    2. Completion of digestion
28
Q

With which organs does the duodenum interact with to complete its functions?

A

Liver
Gallbladder
Pancreas

29
Q

How does the duodenum dilute and neutralise acidic chyme?

A

Neutralise:

  1. Walls contain Brunner’s glands: secrete bicarbonate-rich mucus.
  2. Pancreas and liver secrete alkali (e.g. In bile).

Dilute (hypertonic chyme to isotonic chyme):

  1. Water is drawn in from extracellular fluid.
  2. Bile released from liver contains water.
30
Q

How do the pancreas, liver and duodenum function in completion of digestion?

A

Pancreas and duodenum secrete specific enzymes which act with bile from liver:

  • cleave peptides to aa
  • cleave polysaccharide to monosaccharides
  • break down and re-form lipids
  • break down nucleic acids
31
Q

Where does most active absorption occur?

A

Jejenum

32
Q

What is absorbed in each part of the small intestine?

A
  • Duodenum: iron
  • Jejenum: most of sugars, aa and fatty acids
  • Ileum: vitB12, bile acids and remaining nutrients
33
Q

What does the small intestine not absorb?

A

Water

34
Q

What structure does the mucosa and submucosa form in the jejenum?

A

Plicae circulares (circular folds projecting into gut lumen)

35
Q

What are lacteals?

A

Dilated lymphatic vessel in small intestine which absorbs digested fats.

36
Q

What is the large intestine composed of?

A
  • Caecum
  • Ascending colon
  • Transverse colon
  • Descending colon
  • Sigmoid colon
37
Q

How long/large is the colon?

A

1.2 m long

6-9 cm wide

38
Q

What is the function of the colon?

A
  1. Water (and electrolyte) reabsorption (over 20hr transit) - content is semi-solid by end of large intestine.
  2. Content awaits expulsion.
39
Q

What type of lymphoid tissue does the colon’s surface contain?

A

Peyer’s patches

40
Q

Where are most of the GI tract’s bacteria located?

A

Colon (99% are anaerobic, most are lost in faeces)

41
Q

What are bacteria in the colon involved in?

A
  1. Synthesis of vitamins K and B12, thiamine and riboflavin
  2. Breakdown of bile acids
  3. Conversion of bilirubin to non-pigmented metabolites
42
Q

How is bacterial invasion of the colonic wall and underlying tissue prevented?

A

Viscoelastic mucus gel separates luminal bacteria from epithelial surface.

43
Q

Describe the neural control of the GI tract.

A
  1. Somatic control (innervating striated muscle) during ingestion and (mouth and 1st 1/3 of oesophagus) and excretion (last sphincter of anus).
  2. Autonomic nervous system controls the rest.
44
Q

Describe the ANS innervation of the GI tract.

A

Post-ganglionic neurones form plexuses:

  1. Myenteric plexus (in muscularis externa)
  2. Submucosal plexus (in submucosa)
45
Q

Describe the paracrine control of the GI tract.

A

Substances act locally:

  • histamine - controls acid production in stomach
  • vasoactive substances - affect blood flow in gut by dilating blood vessels
46
Q

Describe the endocrine control of the GI tract.

A

Gut generally controlled by hormones it makes itself. Regulate:

  • stomach acid secretion
  • alkali secretion from liver and pancreas
  • enzyme secretion
47
Q

Give examples of hormones regulating GI function.

A
  1. Secretin (secreted in duodenum)
    - promotes bicarbonate secretion from pancreatic duct cells
    - promotes liver bile production
    - inhibits secretion of acid by parietal cells of stomach
  2. Cholecystokinin (synthesised and secreted by enteroendocrine cells of duodenum)
    - promotes bile release from gallbladder
    - promotes digestive enzyme release from pancreas
    - hunger repressant
  3. Gastrin (released by G cells of pyloric antrum of stomach, pancreas and duodenum)
    - promotes production of HCl (gastric acid) by parietal cells of stomach