GIT Flashcards

1
Q

Describe the structure of the GIT (in order, including all accessory organs)

A
  1. Mouth (tongue, salivary glands - parotid, sublingual, submandibular)
  2. oesophagus
  3. Stomach
  4. Small intestines (gall-bladder, liver, pancreas)
  5. Large intestine
  6. Rectum
  7. Anus
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2
Q

What is a sphincter?

A
  • an opening/entryway that opens/closes a tube when required
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3
Q

Discuss the properties of the basic architectural components of the GIT (mucosa and submucosa)

A
Mucosa:
- epithelial cells
- lamina propria
- muscularis mucosa 
Submucosa:
- circular muscle
- longitudinal muscle 
- nerve plexus: intrinsic (submucosal, myenteric) and extrinsic (parasympathetic - vagus and pelvic nerves - and sympathetic - T8-L2)
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4
Q

Discuss the borders of the fore-, mid- and hind-gut

A

Foregut: oral cavity to mid-duodenum
Mid-gut: duodenum to initial 2/3rds of transverse colon
Hind-gut: later 1/3rd transverse colon to the upper portion of anus

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5
Q

What is the function of the oral cavity in the GIT?

A

Physical digestion
Chemical digestion:
- saliva (mucin, buffers (carbonic acid, antibacterial)
- amylase (action: hydrolyses starch and glycogen to smaller poly-saccharides and maltose)
Tongue:
- taste buds and propulsion of food bolus

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6
Q

How does the bolus move through the oesophagus into the stomach?

A

Peristalsis - waves of muscular contraction

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7
Q

Discuss the functions of the stomach

A
  • gastric juice and smooth muscles help digestion further (gastric juice = acid (pH 2) and pepsin)
  • pepsin - hydrolyses proteins
  • mucus
    (regions of stomach, fundus, corpus, antrum-pylorus)
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8
Q

Discuss the functions of the liver

A
  • bile production
  • storage
  • nutrient interconversion
  • detoxification and first-pass
  • phagocytosis
  • synthesis
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9
Q

What is the function of the gall-bladder (biliary system)?

A
  • concentrates bile
  • secretory/resorptive function (particularly large ducts)
  • highly resistant to concentrated bile acids
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10
Q

What causes the urge to defecate?

A

When the descending colon becomes full and stool passes into the rectum

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11
Q

What glands produce what secretions?

A

Parotid: (25% - serous, amylase)
Submandibular: (70% - mixed, lysozyme and lactoperoxidase)
Sublingual: (5% - mucus, lingual lipase)

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12
Q

What are the functions of the following enzymes: amylase, lipase, lysozyme, lactoperoxidase?

A

Amylase: poly-> di and trisaccharide
Lipase: TG -> glycerides and FA
Lysozyme: antibacterial
Lactoperoxidase: bactericidal

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13
Q

Which cranial nerves and parts of the brain are involved in taste?

A
  • CNVII, CNIX, CNX
  • thalamus
  • medulla
  • gustatory center in cerebral cortex
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14
Q

What are the functions of the following gastric mucosa cell types: parietal, chief, APUD, G-cells, Mucus secreting cells, ECL?

A

Parietal - HCl and intrinsic factors
Chief - pepsin
APUD - somatostatin (inhibits acid secretion)
G-cells - gastrin (stimulates acid secretion)
Mucus-secreting cells - alkaline mucus
ECL - histamine to activate parietal cells

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15
Q

How is gastric secretion controlled?

A
Primary activators:
- 10th nerve, gastrin and histamine
Primary inhibitors:
- secretin and somatostatin
Regulation:
- cephalic
- gastric
- intestinal
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16
Q

Discuss gastric acid secretion

A
  • uptake of CO2, Cl-, Na+ and water
  • active secrete HCl into lumen of stomach (ACH, Gastrin, Histamine)
  • carbonic acid into blood
17
Q

What are the three components of the small intestine, and what are the primary purposes?

A

Duodenum - chyme mixes with bile and pancreatic juice
Jejunum - absorption (amino acids, lipids, CHOs, Fe and Ca2+)
Ileum - B12 and bile salts absorption

18
Q

What are the different duodenal mucosal cells and their functions?

A

Columnar - absorption
Goblet - mucus
Brunner’s glands - alkaline, mucus

19
Q

What are the different routes of cellular absorption?

A
  • ATP energy source
  • transcellular (in cell)
  • paracellular (between cells)
  • water absorption against an osmotic gradient
20
Q

What are some similarities between bile and pancreatic secretion?

A
  • simulation via CCK (cholecystokinin - a hormone)

- 10th nerve stimulation

21
Q

Describe the process of carbohydrate absorption

A

Dietary polysaccharide conversion

  1. Disaccharides in brush border
  2. Na+ and energy-dependent secondary active transport
  3. Monosaccharide fructose enters cell by passive facilitated diffusion
  4. Glucose, galactose and fructose exit the cell at the basal membrane by passive facilitated diffusion
  5. Simple diffusion moves monosaccharides
22
Q

Describe the process of protein absorption

A

Na+ and energy-dependent secondary active transport via a symporter

  1. Na+ and amino acids enter cell through lumen
  2. Hydrogen and small peptides also brought into cell
  3. Intracellular peptidases converts small peptides into amino acids
  4. Amino acids exit the cell at the basal membrane via various passive carriers
  5. Amino acids enter the blood via simple diffusion
23
Q

Describe the process of fat absorption

A
  1. Bile salts undergo lipid emulsion, become pancreatic lipase
  2. Pancreatic lipase breaks down into monoglycerides and free fatty acids
  3. Become bile salts again - micellar diffusion?
  4. Fatty acids and monoglycerides are then passively absorbed through the microvillus and into the cell
  5. Monoglycerides + fatty acids = triglycerides
  6. Triglycerides are aggregated and coated with lipoprotein - become chylomicrons
  7. Then exit basal membrane by exocytosis
24
Q

Describe the process of iron absorption

A

(Absorbable iron = heme and ferrous)
(Iron in feces = iron not absorbed by cells, iron lost as cell is sloughed)
1. Energy dependent transport of heme and ferrous iron into cell
2. Heme carrier protein 1 and divalent metal transported 1 -> iron absorbed into blood
3. Ferroportin exits basal membrane
4. Iron absorbed into blood, bound to transferrin
5. Ferritin - pool of iron not absorbed into blood
6. Iron lost as cell is sloughed
7. Dietary iron
etc. etc.

25
Q

Discuss absorption in the large intestine

A
  1. Na+ enters colonic cells by multiple pathways
  2. The Na+-K+-ATPase pumps Na+ into the ECF (reabsorbed)
  3. Na+ and Cl- enter by cotransport
  4. Cl- enters lumen through Cystic Fibrosis Transmembrane Conductance Regulator channel
  5. Na+ is reabsorbed
  6. Negative Cl- in lumen attracts Na+ by paracellular pathway; water follows.
26
Q

What is the role of bacteria in the large intestine?

A
  • fermentation of undigested CHOs and short chain FA
  • production of vitamin B and K
  • recycle bile
  • prevent growth of pathogenic bacteria
  • immunity
27
Q

What is known about ulcerative colitis + what are some risk factors?

A
  • It is chronic relapsing inflammatory bowel disease
  • has genetic factors
  • altered epithelial barriers
  • abnormal T-cell responses to normal microflora and other antigens
  • chronic condition
  • affects younger age groups
  • involves any part from mouth to anus and involves transmural lesions

Risk factors:
- family history, Jewish, Caucasians in Northern European countries, smoking is a life saver!!

28
Q

Describe the pathophysiology of ulcerative colitis

A
  • no skip lesions
  • limited to mucosa
  • impaired epithelial barrier
  • rectum - milder cases: hyperaemic, velvety and oedematous
  • severe case - haemorrhagic, erosions and ulcers
  • abscesses
  • necrosis (death of body tissue - occurs when little blood flow to tissue)
  • inflammatory (pseudo-) polyps
29
Q

What is Crohn’s Disease?

A
  • idiopathic, affecting anywhere from mouth to anus

- commonly affected sites: distal small intestine and proximal large intestine

30
Q

What are the aetiologies and pathogenesis of Crohn’s Disease?

A
  • family history, tobacco use, Jewish, urban residence, gene mutation
31
Q

What is the pathophysiology of Crohn’s Disease?

A
  • begins in submucosa
  • neutrophil infiltration
  • Ileocolon most commonly involved
  • skip lesions
32
Q

Summarise some differences in UC and CD

A

UC:
- blood in stool
mucus
- occasional stricture

CD:

  • (occasionally) blood in stool
  • (occasionally) mucus
  • fistulas (hole in wall of gut - opens to external environment)
  • cobble-stoning
    (frequently) stricture