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SF3- EXAM 3 (Camelita) > Histology of Digestive Tract I+ II > Flashcards

Histology of Digestive Tract I+ II Flashcards

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10
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11
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Functions of the digestive system

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  • Ingestion
  • Propulsion
  • Mechanical digestion
  • Chemical digestion
  • Absorption
  • Defecation
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12
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What are the main divisions of the digestive system? What are the organ components of each?

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Alimentary Canal

  • Organs: Mouth, Pharynx, Esophagus, Stomach, Small and Large Intestines

Accessory Digestive Organs

  • Organs: Teeth, Tongue, Gallbladder, Salivary Glands, Liver, and Pancrease
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13
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The ________ is a continuous, muscular digestive tube winding thorughout the body.

A

Alimentary Canal

*Component that digests and absorbs food particles

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14
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What are the four basic processes of the digestive system?

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  • Digestion
    • ​Mechanical and chemical breakdown of food
  • Motility
    • ​Movement of material along the GI tract
  • Secretion
    • ​Release of substances from salivary glands, GI epithelial cells, hepatocytes or pancreatic acinar cells into the GI tract lumen or ECF
  • Absorption
    • ​Active or passive transfer of substances from the lumen of the GI tract to ECF
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15
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Which components of the GI tract added chyme to food?

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GI epithelium, liver and pancreas

NOTE: Chyme is soupy mixture designed to assist with secretion

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16
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Anatomy of the Digestive System

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17
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General Structure of Wall of the GI Tract

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18
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What are the four layers of the GI tract?

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  • Mucosa
    • ​Secretory and absorptive layer
  • Submucosa
    • ​Absorption is complete when nutrients enter blood vessels of the submucosa
  • Muscularis externa
    • ​Segmental contractions and peristalic movements
  • Serosa
    • ​Visceral peritoneum in abdominal region
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19
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General Organization and Structure of the Digestive/Alimentary Tube

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20
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Function of the esophagus

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  • Conducts food from oral cavity to stomach (using peristalsis)
  • Secretes mucus

NOTE: If acid from the stomach gets in here that’s heartburn.

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21
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Function of the stomach

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  • Fragmentation of food
  • Initiates digestion
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22
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Function of the small intestine

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  • Digestion is completed
  • Main absorption occurs
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23
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Function of large intestine

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  • Water absorption (20%) to reduce liquid content of solids
  • Production and absorption of Vitamins B and K
    • Synthesized by bacterial flora
  • A holding chamber for feces prior to defecation via the anal canal
  • Elimination
  • Bacterial digestion
    • Ferments carbohydrates
    • Protein breakdown
  • Concentrates waste

NOTE: 80% of water reabsorption occurs in the small intestine

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24
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Where does chemical digestion occur?

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Mouth, stomach, and small intestine

NOTE: Brush-border enzymes of the small intestine complete the final hydrolysis of carbohydrates, proteins and nucleotides prior to their absorption

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25
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Which enzymes break down carbohydrates in chemical digestion and where?

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  • Salivary amylase
    • ​Mouth
  • Pancreatic amylase
    • ​Small intestine
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26
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Which enzymes break down proteins in chemical digestion and where?

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  • Pepsin
    • ​Stomach
  • Pancreatic proteases
    • ​Small intestine
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27
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Which enzymes break down lipids in chemical digestion and where?

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  • Lingual lipase
    • ​Mouth
  • Gastric Lipase
    • ​Stomach
  • Pancreatic Lipase
    • ​Small intestine

NOTE: Bile significantly increases the rate of hydrolysis

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28
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Which enzymes break down nucleic acids in chemical digestion and where?

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  • Pancreatic nucleases
    • Small intestine
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29
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What are the 3 stages of the digestive system?

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  1. Cephalic
  2. Gastric
  3. Interstinal

*Stages names based on location of the food

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30
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Function of Cholecystokinin

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  • Slows down emptying of the stomach by acting on the pyloric sphincter
  • Stimulates bile release from the gall bladder and the secretion of pancreatic enzymes
  • Inhibits gastric acid secretion

NOTE: Site of production is duodenum and jejunum

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31
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Function of secretin

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  • Stimulate pancreatic bicarbonate secretion
  • Enhances insulin secretion by B cells of the islet of Langerhans
  • Inhibits gastric acid secretion

NOTE: Site of production id duodenum

32
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Function of gastrin

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  • Stimulate the secretion of HCl by parietal cells
  • Stimulates insulin secretion by B cells of Islet of Langerhans
  • Stimulates gastric motility and growth of the mucosal cells

NOTE: Site of production is stomach

33
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How does contraction the muscularis externa cause motility?

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  • Peristalsis
    • ​Occurs over long distances is the esophagus to move food from the pharynx to the stomach and within the stomach where it contributes to the mixing of food
    • Occurs over a short distance in the small intestine
  • Segmentation
    • ​characterized by short segments of the small and large intestines alternately contracting and relaxing which mixes contents and keeps them in contact with absorptive epithelium
34
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Peristalsis

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Adjacent areas of the GI tract alternatively contract and relax which keeps moving food along the tract distally (propulsion).

35
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Segmentation

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Nonadjacent segments of the intestine alternatively contract and relax, moving the food forward and backward.

NOTE: This results in food mixing rather than food propulsion.

36
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What are the major feautures of the esophagus?

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  • Skeletal muscle
    • (upper third for swallowing)
  • Smooth muscle
    • (lower third) for peristalsis
  • Esophageal glands
    • produce mucus to lubricate bolus
  • Esophageal sphincter
    • prevents backflow into oral cavity
  • Cardiac sphincter
    • prevents backflow into esophagus
37
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38
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Food found in the stomach is called ________.

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chyme

NOTE: The stomach can hold 2 L of food and water when completely filled.

39
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When the stomach is empty, the mucosa folds into _____________.

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rugae

NOTE: When filled, the expanded wall of the stomach causes these folds to disappear (flatten).

40
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The stomach is divided into 3 regions based on what?

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The type of mucosal glands found in each

  • Cardiac glands
    • ​Surface mucus-secreting cells and mucus-secreting, tubular, coiled glands
  • Pyloric glands
    • Pits deeper than in cardiac and fundic region
    • Glands lined mostly with mucous cell
  • Fundus (gastric) glands
    • ​Chief cells and parietal cells of gastric glands secrete substances into the lumen of the stomach which combine to make gastric juice
41
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Function of Chief Cells

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  • RER in basal cytoplasm – pepsinogen synthesis and packaging
  • Exocytosis of pepsinogen is stimulated by acetylcholine after feeding
  • Pepsinogen is converted in acid environment to pepsin, a proteolytic enzyme
42
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How is acid secretion regulated in parietal cells?

A
  • Parasympathetic stimulation and the hormone gastrin leads to fusion of the tubulo-vesicles with the canaliculi, and an increase in the secretion of HCl acid
  • Histamine potentiates these effects
43
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Where are enteroendocrine cells located?

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Dispersed in mucosal epithelium throughout GI tract

44
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Function of enterendocrine cells?

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  • Produce peptide hormones that regulate GI tract
  • Enzyme secretion and electrolyte metabolism
  • Gastrointestinal motility & mucosal growth
  • Release of other peptide hormones

NOTE: The secretions are released basally and enter the blood

45
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Hepatic and pancreatic secretions enter the lumen of the small intestine at the duodenum through a duct which is guarded by the contracted ___________.

A

Sphinctor of Oddi

NOTE: The Sphinctor of Oddi functions to keep the pancreated and hepatic secretions from entering the small intestine except during the intestinal phase of digestion

46
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The presence of food in the small intestine detected by ______ stimulates a combination of segmental and peristaltic contractions.

A

Mechanoreceptors

NOTE: The stimulation of segmental and peristaltic contractions mixes the chyme with pancreatic juice and bile and moves it toward the large intestine

47
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Small intestines are roughly ______ long.

A

7 meters

48
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Function of villi in instenine walls?

A

To increase surface

*The villi are covered in microvilli which further increases surface area for absorption

49
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Crypts of Lieberkuhn

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Secrete intestinal juice and special lysozymes that protect against bacteria

50
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Peyer’s Patches

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Aggregated lymphoid tissues containing lymphocytes

51
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Which four compoents amplify the total surface of the mucosa?

A
  1. Plicae
    1. Evagination of the mucosa and submucosa
  2. Villi
    1. Evagination of the mucosa
  3. Glands or crypts of Lieberkuhn
  4. Microvilli
    1. Evagination of apical domain of the enterocytes
52
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Structure of the Small Intestine

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53
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Individual epithelial cells of the small intestinal mucosa have highly folded apical cell membrane. Each fold is called a _________.

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Microvillus

NOTE: Each microvillus increases the # of integral membrane proteins for digestion and absorption that can be exposed to the membrane

54
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The intestinal mucosa is lined by simple columnar epithelium. What the four main types of cells found in the simple columnar epithelium?

A
  • Absorptive cells (enterocytes)
  • Goblet cells
  • Paneth cells
  • Enteroendocrine cells

NOTE: The paneth cells, enteroendocrine cells and stem cells are found only in the crypts of Lieberkuhn

55
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Functions of Lacteals

A

Uptake and transport of lipoproteins and chylomicrons

56
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Where does apoptosis occur in the small intestine?

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Apoptosis of the intestinal epithelial cells occurs at the tips of the villi

57
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Where does mitosis of stem cells occur within the epithelial cells in the small intestine?

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Mitosis of stem cells occurs within the mucosal glands/crypts of Lieberkuhn

58
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Functions of the duodenum

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  • To receive chyme from stomach
  • To neutralize acids before they can damage surfaces of the small intestine
59
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60
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How does the jejunum differ from the duodenum?

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  • Few or no submucosal glands
  • Submucosa is folded into plicae circulari
  • The musosal glands (crypts of Lieberkuhn) are much less prominent in the jejunum

NOTE: Both the duodenum and the jejunum have villi to increase surface area

61
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This part the small intestine is the location of the most chemical digestion and nutrient absorption.

A

Jejunum

62
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63
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64
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65
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Lymphocytes in intestinal epithelium of peyer’s patches perform immunlological surveillance of luminal antigens presented by ___ cells.

A

M

66
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Mechanism by which M cells play a role in immune response

A
  1. M cells take up antigen from intestinal lumen
  2. B-Lymphocytes occupy M cell cytoplasm. Antigen binds to Ig receptors on the sruface of the B-lymphocytes
  3. B-Lymphocytes exposed to antigen from the SI lumen, migrate to regional lymph nodes
  4. Migration to thoracic duct
  5. Migration to blood stream and circulation
  6. B- cells home to the lima propria of the gut, develop into plasma cells, secrete IgA
67
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Ileocecal junction

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68
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Teniae Coli

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Bands of smooth muscle that create pcoket-like sacs in the large intestine

69
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What type of epithelium is found in the large intestine?

A

Simple columnar epithelium

EXCEPT: In the anal canal where there is stratified squamous

NOTE: There are no villi or digestive-secreting cells in the large intestine

70
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71
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Components of the epithelial cells in the mucosal lining of the large intestine

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  • Few absorptive cells
  • Numerous goblet cells
  • Enteroendocrine cells
  • Stem cells
  • NO Paneth cells
72
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73
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Innervation of the GI tract

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  • Submucosal plexus of Meissner
  • Myenteric plexus of Auerbach
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76
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SF3- EXAM 3 (Camelita) (23 decks)

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