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HAP > GASTROINTESTINAL > Flashcards

GASTROINTESTINAL Flashcards

1
Q

What is the role of amylase, lysozyme and mucus in the mouth?

A

Amylase begins starch digestion
Lysozyme has an antibacterial action (protects mouth and teeth)
Mucus functions as lubricant and glue

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2
Q

Which cells do gastric glands contain and what do they secrete?

A

Mucus producing cells
Chief cells which secrete enzymes (pepsinogen)
Parietal cells which secrete HCl and intrinsic factor
Endocrine cells which secrete hormones

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3
Q

What is the secretion of HCl promoted by and inhibited by?

A

Promoted by cephalic and gastric phases
Inhibited by intestinal phase

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4
Q

Where are gastric glands found and what is their role?

A

Below gastric pits
Secrete most of the gastric juice

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5
Q

What is the role of the stomach?

A

Serves as a food reservoir until it can be partially digested and moved along into duodenum

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6
Q

How is food digested in the stomach?

A

Food is churned, breaking it into small particles and mixed with gastric juice

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7
Q

What does the rate of emptying of the stomach depend upon?

A

The type and amount of food in the stomach and amount of chyme in duodenum

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8
Q

What is the role of intrinsic factor?

A

B12 absorption

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9
Q

What hormones does the stomach produce and what is their role?

A

Gastrin which regulates digestion (HCl and pepsin)
Ghrelin which stimulates appetite and slows metabolism

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10
Q

What is the role of HCl?

A

Activates pepsinogen secretion
Stimulates duodenum to secrete hormones which in turn stimulates release of bile and pancreatic juice into duodenum

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11
Q

What is the role of mucus?

A

Protects against mechanical damage and corrosive action of HCl

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12
Q

How does gastrin stimulate HCl secretion?

A

Enters blood stream and circulates back to stomach where it binds to histamine H2 receptors on parietal cells
Also stimulates pepsin secretion

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13
Q

What are the three phases of deglutition (voluntary / involuntary)?

A

Oral stage: voluntary action, formation of food bolus
Pharyngeal stage: involuntary, bolus hits oropharynx and pushed down to oesophagus
Esophageal stage: involuntary, skeletal and smooth muscle move bolus down to stomach via peristalsis

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14
Q

What is the role of deglutition?

A

Changing physical state of ingested food (chewing, mixing with saliva, segmentation)

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15
Q

How does the voluntary phase of deglutition work?

A

Tongue rises and presses bolus against hard palate into oropharynx where involuntary phase begins

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16
Q

How does the involuntary phase of deglutition work?

A

Reflexes close soft palate, epiglottis, glottis
Upper esophageal sphincter relaxes
Peristalsis initiated in oesophagus

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17
Q

How are stomach contents mixed? What is gastric emptying controlled by?

A

Propulsion and retropulsion
Hormonal and nervous mechanisms (increased by parasympathetic nerve stimulation)

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18
Q

What is peristalsis and segmentation?

A

Peristalsis is wavelike muscle contraction
Segmentation is a mixing movement in which digestive reflexes cause a forward-and-backward movement with a single segment of the GI tract

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19
Q

Why is segmentation effective for absorption?

A

Increases food contact with the intestinal mucosa

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20
Q

What is intestinal motility controlled by?

A

Intrinsic stretch reflexes and cholecystokinin

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21
Q

How does digestion occur on the chemical level?

A

Enzymes in digestive juices which speed up hydrolysis

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22
Q

What is an enzyme?

A

A protein that accelerates chemical reactions without appearing in the final product and functions optimally at a specific pH

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23
Q

How are carbohydrates digested?

A

Via amylase which is found in saliva and pancreatic juice (hydrolyses these compounds)

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24
Q

What are examples of carbohydrate digestive enzymes and where are they located?

A

Sucrase, lactase, maltase
Located in the intestinal brush border

25
Q

What is the point of chemical digestion?

A

To break down compounds into their absorbable units (e.g. carbohydrates into glucose)

26
Q

What is the role of amylase in saliva and pancreatic juice?

A

To hydrolyse polysaccharides into disaccharides

26
Q

Where are disaccharides broken down into monosaccharides?

A

In the brush border (promote hydrolysis)

27
Q

What are the main proteases, where are they located and what is their role?

A

Pepsin (gastric juice)
Trypsin / chymotrypsin (pancreatic juice)
Peptidases (intestinal brush border)
To hydrolyse proteins into absorbable units (amino acids)

28
Q

What is the order of breaking down a protein?

A

Pepsin and trypsin / chymotrypsin hydrolyse proteins to proteoses and peptides
Trypsin / chymotrypsin and intestinal peptidases break down proteoses and peptides into amino acids

28
Q

What are the emulsifiers found in bile? Why is emulsification essential?

A

Lecithin and bile salts
Since fats are insoluble in water

29
Q

What does the formation of micelles allow for?

A

Digestion of fats into fatty acids and simpler compounds, monoglycerides and glycerol

29
Q

What is the role of colipase and lipase?

A

Colipase anchors lipase molecules to the inner face of each micelle
Lipase facilitates hydrolysis of emulsified fats

30
Q

Where are intestinal digestive enzymes produced?

A

In villus covered by ultra-fine microvilli (brush border)

31
Q

What is the role of microvilli?

A

Primary surface of nutrient absorption in the GI tract
Packed with enzymes that aid in the breakdown of complex nutrients into simpler compounds that are more easily absorbed (e.g. glycosidases are present at high concentrations on the surface of enterocyte microvilli)

32
Q

What is the two-fold benefit of microvilli?

A

Not only increase the surface area for absorption, they also increase the number of digestive enzymes that can be present on the cell surface.

33
Q

What are the crypts of Lieberkuhn? What is their role? What is the role of glands at the base of villi? What is the role of goblet cells on villi and in crypts?

A

Deep pits at the base of villi
Produce new cells / bacterial enzymes
Secrete intestinal juice
Secrete mucus

33
Q

What do intestinal crypts contain?

A

A base of replicating stem cells, Paneth cells of the innate immune system and goblet cells

34
Q

What is the role of the small intestine?

A

Chemical digestion and mechanical breakdown of chyme
Absorption of nutrients and transport of undigested material into the large intestine

35
Q

What is the role of the large intestine?

A

Reabsorbs remaining water, Na+ and glucose (proximal half)
Prepares and stores solid wastes for elimination (distal half)

36
Q

What causes the feeling of needing to defecate?

A

A mass movement forces the contents of the sigmoid colon into the rectum and the nerve endings in its walls are stimulated by stretch

37
Q

What is the peritoneum?

A

Large continuous sheet of serous membranes, lines entire abdominal cavity (parietal layer) + forms the visceral layer (serous layer)

38
Q

Where is the greater omentum?

A

Runs along the greater curvature and the first part of duodenum to the transverse colon

39
Q

Where is the lesser omentum?

A

Runs from the liver to the lesser curvature of the stomach and the first part of duodenum

40
Q

What does each lobule contain?

A

A branch of the hepatic vein and hepatic cells (hepatocytes)

41
Q

How is the liver segmented?

A

Consists of two lobes separated by the falciform ligament and each lobe is divided into lobules

42
Q

What are the functions of the liver?

A

Manufactures and secretes bile
Detoxifies various substances (bacteria, drugs, toxins)
Hepatocytes help metabolise proteins, fats and carbohydrates
Stores many substances including iron, vitamins A, B12 and D
Produces important plasma proteins (albumin) and clotting factors
Serves as a site of haematopoiesis in foetal development

43
Q

How much bile can the gallbladder hold and where is it in the body?

A

30-50 ml of bile
Lies on under surface of liver

44
Q

What is the common bile duct made up of? Where does this duct open into?

A

Hepatic duct and cystic duct (from gallbladder)
The duodenum

45
Q

What is the role of the gallbladder?

A

Stores and concentrates bile which enter duodenum via common bile duct

46
Q

What is the role of bile?

A

Emulsifies fat and enables its absorption

47
Q

What is bile made up of?

A

Water, bile salts, bile pigments, lecithin, and cholesterol

48
Q

Where does the pancreas lie? What protease does the pancreas release?

A

Behind the stomach, between the spleen and duodenum
Trypsin

49
Q

What is the role of trypsinogen?

A

Functions as storage of an inactive form of trypsin so that it may be kept in pancreas and released in significant amounts when required for protein digestion

50
Q

What might happen if trypsinogen is activated to trypsin in the wrong location?

A

This can be destructive and may trigger a series of events that lead to pancreatic self-digestion

51
Q

What other substances does the pancreas release?

A

Lipases that digest emulsified fats
Nucleases that digest nucleic acids i.e. DNA and RNA
Amylase which digests starches
Sodium bicarbonate which increases pH

52
Q

Why does old age result in constipation?

A

Fewer digestive juices produced, absorption is less efficient, peristalsis slows

53
Q

Why are many elderly citizens poorly nourished?

A

Taste and smell changes which lead to a loss of appetite

54
Q

Why is enzyme production altered in old age?

A

Changes to acinar cells within exocrine pancreas

55
Q

How is the common hepatic duct formed?

A

Small bile ducts in the liver join up to form the right and left hepatic duct, which then join to form the common hepatic duct

HAP (12 decks)

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