GI Tract

Question 1

Secretion of: Mucous neck cell

Answer 1

mucus (protects lining) & bicarbonate

Question 2

Secretion of: Parietal cells

Answer 2

Gastric acid (HCl)

Question 3

Secretion of: Chief cell

Answer 3

Pepsinogen (converted into Pepsin by HCL) & gastric lipase

Question 4

Secretion of: D Cells

Answer 4

Somatostatin (inhibits HCL production)

Question 5

Secretion of: G Cells

Answer 5

Gastrin (stimulates acid production)

Question 6

What do the Crypts of Lieberkühn contain?

Answer 6

Paneth cells: defensins, antimicrobial, lysozyme, phagocytic.
Stem cells: Regeneration.
Goblet cells: Mucous.

Question 7

Functions of: Salivary Glands

Answer 7

-Mucus acts as lubricant
-Produces thiocyanate & lysosomes for anti-microbial defences
-Digestion (amylase & lipase)

Question 8

Function of Pancreas:

Answer 8

Makes enzymes to digest proteins, fats, & carbohydrates.
Produces the hormones e.g. insulin & glucagon.
And produces HCO3- which neutralises the acid from the stomach.

Question 9

Swallowing Reflex

Answer 9

Stimulated when a food bolus stimulates pressure receptors in the back of the throat & pharynx, signalling the swallowing centre in the medulla, triggering nerve impulses, innervating skeletal muscles, causing involuntary contraction pushing food into the oesophagus.

Question 10

Gastric Motility in the Stomach

Answer 10

Mixing wave initiated towards the pyloric sphincter. The more fluid chyme is pushed towards the pyloric sphincter, with the more solid region being pushed back by peristaltic waves, which then reverse to mix more thoroughly. The movement of liquid & solid is repeated, with the most liquid chyme passing through the pyloric sphincter, as mixing continues.

Question 11

Defaecation

Answer 11

Faeces stretches rectum & stimulates stretch receptors, signalling the spinal chord, which causes a reflex in the rectum, relaxing the internal anal sphincter. Impulses prevent from untimely defecation, by keeping the external anal sphincter contracted, defecation occurs when this sphincter relaxes.

Question 12

Vomitting

Answer 12

Heart rate & salvation increases, food enters the stomach via reverse peristalsis, & the pyloric sphincter relaxes to allow food to fill the stomach. Involuntary retching occurs, alongside muscle contraction in abdomen & diaphragm forcing the contents into the oesophagus, as the epiglottis closes, & vomiting occurs. Epiglottis remains closed, for a period after.

Question 13

Fat digestion

Answer 13

Fatty acids pass through epithelial cell layer, where they’re converted to triglycerides. These combine with cholesterol, phospholipids & protein to form chylomicron, which is water soluble & enters lacteal, then to the bloodstream.

Question 14

Hepatic First Pass Effect

Answer 14

During first passage through liver, a fraction of amount of drug absorbed is transformed into metabolite(s), which can reduce bioavailability if the metabolites are inactive.

Question 15

Efflux Pumps

Answer 15

Cellular proteins which can prevent intracellular accumulation of drugs by pumping drugs that enters cell right back out. An example is P-glycoprotein, which requires an inhibitor for some drugs to be absorbed.

Question 16

Stomach - Degradation & Metabolism

Answer 16

Hydrochloric acid – degrades some drugs, so gastro-resistant coatings are used to protect the drug & delay release. Pepsin – a powerful digestive protease. Destroys polypeptide drugs, but small peptides survive.

Question 17

Duodenum - Degradation & Metabolism

Answer 17

Enzymes which degrade some large proteins to small peptides.

Question 18

Small intestine - Degradation & Metabolism

Answer 18

High expression of cytochrome P450 enzymes (& others), in the intestinal epithelial cells. Highest [in] the villus tips of the duodenum& jejunum of the intestine.

Question 19

Colon - Degradation & Metabolism

Answer 19

Metabolic activity gradually decreases from the duodenum to the colon. Absorption remains good, however, potential to bypass metabolic degradation & target colonic delivery.
Gut flora can metabolize & inactivate drugs.

Question 20

Gastric Emptying:
The stomach gradually releases its contents into the small intestine. Numerous factors affect gastric emptying and subsequent drug absorption:

Answer 20

• Meal size: bigger meal, faster initial emptying
• Type of meal: Fatty acids (chain length dependent), carbs & proteins ([dependent]) reduce emptying rate
• Physical state: smaller empty faster
• Chemicals: acids & [high] alkalis reduce emptying rate ([dependent]) while [low] alkalis increase emptying rate
• Drugs: some reduce emptying rate e.g. narcotics
• Body position: lying on left side reduces
• Disease: emptying rate reduced by ulcers & in some diabetics.
• Exercise: reduces emptying rate.

Question 21

Gastric transit & drug absorption :
Passage of drug through pylorus is an important element with respect to rate of GI absorption

Answer 21

• Drug A : Drug is rapidly released from dosage form into gastric fluid. Drug can rapidly leave through the pylorus in a fasting subject.
• Drug B: Gastro-resistant dosage forms too large to pass the pylorus, must wait for «house-keeper» wave, causing a lag-time before the drug arrives at the intestines.