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M2 GI/Nutrition > Upper GI Structure & Function - Battle > Flashcards

Upper GI Structure & Function - Battle Flashcards

1
Q

What happens to food in the following parts of the digestive tract?

  1. Mouth
  2. Stomach
  3. Duodenum
  4. Small Intestine
  5. Large Intestine
A
  1. Mouth- mechanical and chemical breakdown of food, lubrication of bolus with saliva
  2. Stomach- bolus is broken down via mechanical, chemical means to form liquid chyme
  3. Duodenum- pancreatic enzymes and bile are added to chyme
  4. Small Intestine- nutrient absorption
  5. Large Intestine- fluid absorption
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2
Q
  1. Where is voluntary muscle seen in the GI tract?
  2. Where is involuntary muscle seen in the GI tract?
A
  1. oral cavity, upper third of the esophagus, and presumably the rectum
  2. essentially the entire length of the GI tract (peristalsis)
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3
Q

What are the four tunic layers in the GI tract?

A

(from apical to basal)

  • Mucosa
  • Submucosa
  • Muscularis externa
  • Adventitia/Serosa
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4
Q

What are the three layers of the mucosa?

A

(from apical to basal)

Epithelium

Lamina propria

Muscularis mucosae

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5
Q
  1. What is the main purpose of the epithelium?
  2. What structural variants can be seen?
A
  1. main site of secretion, absorption
  2. stratified squamous, simple columnar
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6
Q
  1. What is the purpose of the lamina propria?
  2. What makes up the lamina propria?
A
  1. Supports the epithelium
  2. connective tissue, with extremely dense lymphatics and capillaries (this is likely the source of the mucosal immunity)
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7
Q

What is the muscularis mucosae?

A

Thin layer of smooth muscle required for mucosal folding and movement

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8
Q
  1. What is the purpose of the submucosa?
  2. What does the submucosa contain?
A
  1. Support the mucosa
  2. collagenous and adipose tissue (physical support); blood, lymphatic vessels (nutritional support); submucosal/Meissner’s plexus (neural regulation)
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9
Q

What is seen in the submucosa of the duodenum and esophagus?

A

Mucous secreting glands

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10
Q
  1. Where is the muscularis externa?
  2. What does the muscularis externa do?
A
  1. The ME is basal to the submucosa
  2. The ME is responsible for movement of the GI tract
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11
Q
  1. What muscle layers make up the muscularis externa?
  2. What controls the muscularis externa?
A
  1. An inner, circular layer and an outer, longitudinal layer
  2. controlled by the myenteric/auerbach’s plexus
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12
Q
  1. What is the adventitia/serosa?
  2. What does it do?
A
  1. Outermost covering of the GI tract
  2. protects the GI tract
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13
Q

What is the difference between adventitia and serosa?

A

Adventitia is a loose connective tissue that is outside of the peritoneal cavity

Serosa is connective tissue with a simple squamous epithelium. The epithelium lubricates the peritoneal interfaces and prevents friction damage of the GI tract.

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14
Q

What is the enteric nervous system?

A

The neurons that control movement of the GI tract AKA the submucosal and myenteric plexuses

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15
Q

How is the enteric nervous system controlled?

A
  • neurotransmitters and neuromodulators
  • hormones

INDEPENDENT OF BRAIN AND SPINAL CORD

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16
Q
  1. What does the parasympathetic system do in the GI tract?
  2. What does the sympathetic system do in the GI tract?
A
  1. stimulates secretion and peristalsis
  2. represses peristalsis, activates sphincters
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17
Q
  1. What does the submucosal plexus do?
  2. What does the myenteric plexus do?
A
  1. controls mucosal movement, secretion, and blood flow
  2. controls peristalsis and gut movements
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18
Q
  1. What does protective epithelium look like on histology?
  2. Where is protective epithelium found in the GI tract?
A
  1. stratified squamous epithelium
  2. found in the upper GI and the anus
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19
Q
  1. What does secretory epithelium look like on histology?
  2. Where is secretory epithelium found in the GI tract?
A
  1. Fan-shaped, with lots of tubular glands
  2. found in the stomach
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20
Q
  1. What does absorptive epithelium look like on histology?
  2. Where is absorptive epithelium found in the GI tract?
A
  1. Villi with empty space in between the villi
  2. found throughout the small intestine
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21
Q
  1. What does the hybrid absorptive/protective epithelium look like on histology?
  2. Where is absoprtive/protective epithelium found in the GI tract?
A
  1. villi closely packed together, lots of mucous granules
  2. lines the large intestine
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22
Q

What is seen in the mucosal layer of the esophagus?

A

Epithelium: stratified squamous epithelium with langerhans cells

Lamina propria: esophageal cardiac glands

Muscularis mucosae: very thin, hard to identify

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23
Q

What is seen in the submucosa layer of the esophagus?

A

mucous and serous glands

remember, only the duodenum and the esophagus have glands in the submucosa

24
Q

What is seen in the muscularis externa of the esophagus?

A
  • inner layer of circular muscle
  • an outer layer of longitudinal muscle skeletal muscle is seen in the upper third
25
Q

What is seen in the adventitia/serosa of the esophagus?

A
  • Above the diaphragm, the esophagus is covered with adventitia;
  • below the diaphragm, it turns into serosa.
26
Q

What histological change is noted at the gastoesophageal junction?

A

Sharp change from stratified squamous (protective) epithelium to a simple columnar (secretory) epithelium.

27
Q
  1. Name two physiological sphincters in the upper GI tract that serve to prevent reflux.
  2. Why are they considered “physiological” spincters instead of “anatomical” sphincters?
A
  1. Pharyngoesophageal & Gastoesophageal sphincters
  2. They are not “anatomical” because there is no obvious thickening of muscle seen with other sphincters. But they still serve a clear purpose as sphincters: thus, “physiological”.
28
Q
  1. When the stomach is empty, what macroscopic anatomical feature is seen?
  2. About how much can a fully distended stomach hold?
A
  1. Rugae - prominent folds of mucosa and submucosa. These dissapear as the stomach distends to accomadate food.
  2. About 1.5L
29
Q
  1. Describe the makeup of gastic juice.
  2. Where is gastric juice secreted from?
A
  1. Composition:
    • HCl
    • Digestive Enzymes
      • Pepsin
      • Rennin
      • Gastric lipase
    • Mucus
  2. Gastric Glands
30
Q

Name and describe the four anatomical regions of the stomach.

A

From proximal to distal:

  1. Cardia: Small area at gastroesophageal junction.
  2. Fundus: Upper left to cardia; secrete acid and enzymes
  3. Body (corpus): Central area; secrete acid and enzymes
  4. Pylorus: Constricted region at base; regulates release of chyme into duodenum (via pyloric sphincter); secretes gastrin
31
Q
  1. Describe the histological appearance of stomach mucosa epithelium.
  2. What is the function of stomach mucosa epithelium?
A
  1. Simple columnar
  2. These cells generate a thick mucous covering that traps bicarbonate ions, protecting the mucosa from the stomach’s low pH. It also produces a **soluble **mucous that acts as a lubricant.
32
Q
  1. Describe the makeup of the stomach mucosa’s lamina propria.
  2. What special secretory cell, whose purpose is to increase acid production, is found in this layer?
  3. What product of these cells mediates this function?
A
  1. Loose connective tissue layer, densely packed with gastric glands.
  2. Enterochromaffin-type cells
  3. Histamine
33
Q
  1. Describe the makeup and function of the stomach mucosa’s muscularis mucosae.
  2. What component of the lamina propria layer extend into this muscular layer?
A
  1. Smooth muscle; influences gastric gland outward flow
  2. Gastric glands
34
Q

What are gastric pits?

A

Invaginations of the stomach mucosa’s epithelium into the lamina propria; denote entrances to the tubular-shaped gastric glands.

35
Q

Describe the makeup of the stomach’s submucosa.

A
  • Thick layer of dense connective tissue
  • Numerous wandering immune cells
  • Vascular & lymphatic structures
  • Submucosal (Meissner’s) plexus
36
Q
  1. Name the layers of the stomach’s **muscularis externa **from internal to external.
  2. Contraction of these muscular layers is mediated by what?
A
  1. Internal to external:
    1. Oblique (if present)
    2. Circular
    3. Longitudinal
  2. Myenteric (Auerbach’s) Plexus
37
Q
  1. How many gastric glands open into a single gastric pit?
  2. What are the three regions of each tubular-shaped gastric gland?
A
  1. One to seven
  2. Regions:
    • Base (deepest)
    • Neck
    • Isthmus (empties into gastric pit)
38
Q
  1. Name the six cell types found within gastric glands and the region of the pit/gland that each is found in (pit, isthmus, neck, or base).
  2. What type of epithelium is every one of these cell types?
A
  1. Surface mucus / lining cells
    • Pit
  2. Parietal (oxyntic) cells
    • Isthmus, neck, and base
  3. Neck mucous cells
    • Neck and base
  4. Chief (zymogenic, peptic) cells
    • Base
  5. Enteroendocrine cells
    • Base
  6. Stem cells
    • Neck
39
Q

What two gastric gland cells types produce mucous?

How are the two types of mucous different?

How would you tell the cells types apart using EM?

A
  1. Surface lining cells produce a thick, dense mucous that protects against acid digestion (binds bicarbonate ions).
    • EM shows practically pitch-black secretory glands (dense!)
  2. Mucous neck cells produce a soluble mucous that **lubricates **the stomach contents to aid digestion.
    • EM shows varyingly gray secretory granules
40
Q
  1. What are enteroendocrine cells?
  2. In what fashion do their products act on other cells?
A
  1. Small ovoid or pyramidal cells between the base of neighboring epithelial cells. Generaly secrete a single characteristic bioactive agent.
  2. Either paracrine of endocrine
41
Q

How many types of enteroendocrine cells are there?

List their shorthand names and their products.

A

Five types:

  1. G cells - gastrin
  2. EC cells - serotonin
  3. D cells - somatostatin
  4. A cells - enteroglucagon
  5. ECL cells - histamine
42
Q
  1. Parietal cells generate what product(s)?
  2. How are they distinctive by H&E staining?
  3. How are they distinctive morphologically?
A
  1. HCl & Intrinsic Factor
  2. Cytoplasm is heavily eosinophillic
  3. Presence of a secretory canaliculus
43
Q

Describe the appearance and function of a parietal cell’s secretory canaliculus.

A

Structure: An invagination of the apical surface which can almost encircle the nucleus, filled with a dense network of microvilli.

Function: Hugely increases the secretory surface area of the cell.

44
Q
  1. What is the tubulovesicular network of parietal cells?
  2. Explain its relationship with the secretory canaliculus.
  3. Explain why its abundance is inversely correlated with HCl secretion.
A

As per Wikipedia…

  1. The tubulovesicular network is a collection of canalicular precursors.
  2. The tubulovesicles can be fused with the cell membrane to form additional secretory canaliculus, or parts of the canaliculus can be endocytosed to reform the tubulovesicles. In this way, the parietal cell can up- or downregulate HCl secretion as needed.
  3. Because the canaliculus represents active secretory surface area and the tubulovesicles are inactive, a more abundant tubulovesicular network would indicate less active secretory canaliculus and thus decreased HCl secretion.
45
Q

What cell organelle are parietal cells particularly rich in? Why?

A

Mitochrondria! They provide energy for HCl secretion.

46
Q
  1. What is the principal cell type at the base of the gastric glands?
  2. Again, what do these cells secrete?
A
  1. Chief cells
  2. Pepsinogen, rennin, and gastric lipase
47
Q

Where in the chief cell are the secretory granules located?

The nucleus?

What cell organelles are rich in chief cells? Why?

A

Granules: apical

Nucleus: basal

Rich in rER and golgi to accomplish high volume protein production.

48
Q

Describe two mechanisms by which chief cells can be stimulated to release their secretory granules.

A
  1. Binding of the hormone secretin to receptors on chief cells leads to rapid exocytosis of the granules.
  2. Neural stimulation via CNX (vagus) also causes enzyme release
    • The “more significant” release method
49
Q
  1. Again, where are gastric stem (regenerative) cells found?
  2. How can gastric stem cells be idenified in stained sections?
A
  1. The neck of the gastirc glands.
    • Daughter cells differentiate and migrate upward or downward along the gland to replace all epithelial cell types.
  2. Presence of mitotic figures
50
Q
  1. What is the demand on the gastric stem cells?
  2. How can the surface epithelium of the stomach be quickly repaired following injury?
A
  1. Complete renewal of the mucosa every three days
  2. Rapid migration of epithelial cells that were lying deep in the protected environment of the gastric pits can replace the damaged epithelium (mucosal restitution)
51
Q

Describe the differences in the appearance of gastric pits/glands in the different areas of the stomach.

A

Fundus & Body (indistinguishable from each other): straight tubular glands

Pylorus: Branched glands, predominance of mucous neck cells (extra lubrication as the chyme is squeezed though the relatively smaller pylorus?)

**Cardiac **region: Shallower gastric pits, highly coiled glands. Abundance of enteroendocrine cells (want to send signals to the rest of the stomach at the start of digestion?)

52
Q

Name and broadly describe the three phases of the stomach’s response to a meal.

A
  1. Cephalic phase: brain anticipates food & sends signals to prepare the stomach
  2. Gastric phase: food enters the stomach; chemical & mechanical digestion
  3. Intestinal phase: Chyme release into duodenum, suppression of gastric activity
53
Q

Describe how the brain readies the stomach for digestion during the cephalic phase of digestion?

A
  • Smells & visual cues cause brain to send parasympathetic signals via CNX.
  • Vagus nerve causes ACh release, leading to gastrin secretion by G cells
  • Gastrin, ACh, and histamine stimulate ~30% of total gastric acid release from parietal cells.
54
Q

About how much of total secreted gastric acid is released during the gastric phase of digestion?

When is the remainder secreted? How much is the remainder?

A

~60% of the total to be secreted.

30% cephalic + 60% gastric = 90% of total has been released up to this point

The remaining 10% is released during the intestinal phase.

55
Q

Describe the enterogastric reflex.

A

Inhibition of gastric digestion and emptying by distension of the small intestine, mediated by the ENS.

56
Q

Name two enzymes that suppress gastric activity (during the intestinal phase of digestion.)

A
  1. Cholecystokinin
  2. Secretin
    • N.B. Although secretin **increases **secretion of digestive enzymes from chief cells, it also reduces acid secretion from the stomach by inhibiting gastrin release from G cells.

M2 GI/Nutrition (43 decks)

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