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Human Structure > Histology: GI Tract > Flashcards

Histology: GI Tract Flashcards

1
Q

Overview of Digestive System

A

Gastrointestinal Tract:

  • Oral Cavity
  • Pharynx
  • Esophagus
  • Stomach
  • Small Intestine
  • Large Intestine
  • Anal Canal

Accessory Digestive Organs:

  • Salivary Glands
  • Liver
  • Gallbladder
  • Pancreas
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2
Q

Oral Cavity

A

Lining Mucosa

  • Stratified squamous non-keratinized epithelium
  • Insides of cheeks, floor of mouth (under tongue)
  • Covers striated muscle

Masticatory Mucosa

  • Stratified squamous parakeratinized epithelium
    • Surface cells retain pyknotic (condensed) nuclei
  • Roof of mouth, dorsum of tongue, gums

Lamina Propria/Submucosa

  • Dense, irregular CT
  • Large bands of collagen (type I)
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3
Q
A

Lining Mucosa of Oral Cavity

  • Stratified squamous non-keratinzed epithelium
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4
Q
A

Masticatory Mucosa of Oral Cavity

  • Stratified squamous parakeratinized epithelium
  • Dorsum of tongue
  • Roof of mouth/gums
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5
Q
A

Lamina Propria of Oral Cavity

  • Dense, irregular CT
  • Contains minor salivary glands (purple in middle of slide)
  • Nerves
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6
Q
A

Lip

  • Transition from dry epithelium to wet epithelium (Vermillion – red part of lips)
    • Keratinized stratified squamous epithelium
    • Thin
    • Rich capillary bed (why they appear red)
  • Skin on right (hair follicles and keratinized)
  • Oral mucosa on left
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7
Q

Tongue

A
  • Striated Muscle
    • ​Intrinsic Muscles (arranged in 3 planes: up/down, in/out, longitudinally)
    • Extrinsic Muscles
      • Attachments outside tongue
  • Specialized oral mucosa
    • ​Taste sensation
    • Papillae
      • ​Filiform
      • Fungiform
      • Foliate
      • Vallate
    • Taste Buds
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8
Q

Filiform Papillae

A
  • Most numerous
  • Anterior aspect of tongue (in front of sulcus terminalis)
  • Heavily Keratinized
  • Conical projections with tips pointing backwards
  • NOOO taste buds
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9
Q
A

Fungiform Papillae (mushroom shaped)

  • Scattered among filiform papillae
  • Lightly keratinized
  • Contain tastebuds on dorsal surface
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10
Q
A

Foliate Papillae

  • Lateral edges of tongue
  • Rudimentary in humans
  • Taste budes on lateral walls
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11
Q
A

Vallate Papillae

  • 8-12 large papillae
  • Anterior V-Shape to Sulcus Terminalis
  • Thinly keratinized
  • Dome shaped surrounded by a moat
    • Tast buds on lateral sides
  • In lamina propria: von Ebner glands open into base of papilla to dissolve substances
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12
Q

Taste Buds

A
  • Pale-staining oval bodies within epithelium
  • Surface opening: taste pore
    • ​Neuroepithelial (gustatory cells)
      • ​Extend microvilli through taste pore with sensory receptors
      • Synapse with sensory neurons
      • 10-day turnover rate
    • Support Cells (“squiggly nucleus”)
    • Basal Cells
      • ​Stem cells
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13
Q

Teeth

A
  • 32 Permanent Teeth
  • Parts of Tooth
    • Crown (covered by enamel; above gumline)
    • Neck
      • ​Gingival sulcus b/w neck and gum
    • Root
      • ​Extends into dental alveoli
      • Covered by cementum
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14
Q

Enamel

A
  • Hardest substance in body (96% hydroxyapetite)
  • Covers crown of tooth
  • Produced by ameloblasts (formed as tooth is developing)
    • Secrete matrix which then becomes mineralized

Image (Developing tooth):

  • CT on left
  • A: ameloblasts
  • E: developing tooth
  • D: dentin
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15
Q

Cementum

A
  • Calcified tissue that covers root of tooth
  • Similar to bone: avascular, no Haversion system
  • Produced by cementocytes
  • Anchors periodontal ligaments to tooth

Image:

  • B: alveolar bone
  • L: periodontal ligament (anchor tooth to bone)
  • C: cementocytes
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16
Q

Dentin

A
  • Calcified tissue that makes up the majority of the tooth
    • ​Harder than bone (70% hydroxyapetite)
  • Produced by odontoblasts
    • ​Derived from neural crest cells
    • Line pulp cavity in center of tooth
    • Secrete predentin (non-mineralized)
      • Dentinal processes extend into canals called dentinal tubules that dentin mineralizes around
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17
Q

Pulp Cavity

A
  • Contains dental pulp
    • Highly vascularized
    • Well-innervated
  • Narrows at root to form root canal
    • ​Apical Foramen is opening at tip of root canal
    • Blood vessels and nerves enter pulp cavity
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18
Q

Periodontium

A
  • Supporting structure for teeth:
    • Gingiva (gums)
    • Periodontal ligament (fibrous CT with collagen)
      • ​Binds cementum to alveolar bone
      • Weakened by vitamin C deficiency (cannot make collagen) –> Scurvy
    • Alveolar Bone
      • Lacks lamellar pattern
      • Continuously remodeling
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19
Q

Major Salivary Glands

A
  • Parotid
  • Submandibular
  • Sublingual

Compound branched tubuloacinar glands

  • Branching duct system
  • Mucous tubules
  • Serous acini

Also:

  • Myoepithelial Cells
  • Surrounded by dense CT capsule
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20
Q

Salivary Gland Acini

A
  • Serous acini
    • Produce watery, protein-rich secretion
      • Zymogen granules (inactive enzymes)
    • Nucleus in basal part of cell (basophilic)
  • Mucuous Tubules
    • Produce thick, mucous secretion
      • Mucinogen granules (don’t stain well)
  • Mixed Acini
    • Serous Demilunes
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21
Q

Salivary Gland Ducts

A
  • Intercalated Ducts
    • ​Simple cuboidal epithelium
    • Smaller than acini
    • Secrete bicarbonate into saliva
    • Absorbs Cl- from saliva
  • Striated Ducts (basal membrane folded)
    • ​Simple columnar epithelium with centrally located nuclei
    • Larger than acini
    • Reabsorb Na+
    • Secrete K+ and bicarbonate
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22
Q

Excretory Ducts

A
  • Ultimately empty into oral cavity
  • Named: parotid duct, submandibular duct

As duct size increases, epithelium changes:

  • becomes Pseudostratified columnar, Stratified columnar, and finally stratified squamous (at entrance to oral cavity)
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23
Q

Parotid Gland

A
  • Largest salivary gland
  • Completely serous (all serous acini)
  • Intercalated ducts, Conspicuous striated ducts
  • Adipose Tissue

Mumps: viral infection of parotid gland

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24
Q

Submandibular Gland

A
  • Mixed serous and mucous gland (mostly serous)
  • Many striated ducts
  • Produced 2/3 of saliva
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25
Q

Sublingual Salivary Glands

A
  • Smallest
  • Mixed, mostly mucous
    • Some serous demilunes
  • Few striated ducts (not as prominant)
26
Q

General Organization of GI Tract

A

4 Layered Wall:

  • Mucosa (lines lumen)
  • Submucosa (CT layer)
  • Muscularis
    • ​2 layers (usually) of smooth muscle
  • Serosa (mesolthelial lining) or Adventitia (connective tissue)
    • ​Visceral peritoneumis serosa (intraperitoneal)
    • Adventitia near organs that are retroperitoneal
27
Q

Mucosa

A

Epithelium

  • Changes along course of GI tract

Lamina Propria

  • Loose CT, GALT
  • Glands

Muscularis Mucosae

  • Thin layer of smooth muscle
28
Q

Esophagus

A
  • Muscular tube
  • Longitudinal mucosal folds
  • Surrounded by ADVENTITIA (no serosa)
29
Q

Esophageal Mucosa

A
  • Stratified squamous non-keratinized epithelium
  • Lamina Propria:
    • Lymphocytes
    • Esophageal Cardiac Glands
      • Distal esophagus (near stomach)
      • Secrete mucous
  • Muscularis Mucosae
    • ​Longitudinal smooth muscle (along length of tube)
    • Thicker in proximal portion to aid with swallowing
30
Q

Gastroesophageal Reflux Disease

A

Acid Reflux

  • ​Stomach contents enter esophagus
  • Heartburn (pyrosis)
  • Risk Factors:
    • Obesity, pregnancy, smoking, hiatal hernia

Chronic GERD causes changes in epithelium (metaplasia)

  • Stratified squamous epithelium replaced by simple columnar with goblet cells (similar to lower GI tract)
  • Called Barrett’s Esophagus (higher risk of esophageal cancer)
31
Q

Esophageal Submucosa

A
  • Dense, irregular CT
    • Blood/lymphatic vessels
  • Submucosal/Meissner’s Plexus
    • ​Parasympathetic ganglia
    • Unmyelinated
  • Esophageal Glands (Proper)
    • Secrete mucous (lubricate food)
    • In upper 1/2 of esophagus
32
Q

Esophagus: Muscularis Externa

A
  • 2 layers of muscle
    • Inner circular layer
    • Outer longitudinal layer
    • Myenteric Plexus b/w layers (parasympathetic to smooth muscle)
  • Upper 1/3:
    • Striated Muscle (skeletal)
  • Middle 1/3:
    • Both striated and smooth muscle
  • Lower 1/3:
    • Smooth muscle
33
Q

Gastroesophageal Junction

A
  • Stratified squamous (esophagus) to simple columnar (stomach)
34
Q

Stomach

A

Histologically divided into 3 Regions:

  • Cardia
  • Fundus (Body)
  • Pylorus

Rugae:

  • Transient folds of mucosa and submucosa
35
Q

Gastric Mucosa

A
  • Simple Columnar Epithelium
    • ​Has Gastric Pits
  • Lamina Propria:
    • Gastric Glands
  • Muscularis Mucosae

Image (stains mucus)

36
Q

Gastric Pits/Glands

A

Surface Mucous Cells

  • Secretes thick, alkaline mucous

Mucous Neck Cells

  • Thinner, less alkaline mucous
  • In isthmus/neck

Parietal Cells

  • “Fried egg” appearance
  • Secrete HCl and intrinsic factor (needed to absorb B12, without –> pernicious anemia)
    • Acid secretion stimulated by histamine/gastrin

Chief Cells

  • Basophilic cells (image)
  • Digestive enzymes –> zymogen granules
    • Pepsinogen (converted to pepsin in stomach lumen) and gastric lipase

Enteroendocrine Cells

  • Do not stain well
  • Secrete into blood
  • Secrete gastrin in stomach (fxn vary through GI tract)
  • Secrete hormones from basal surface

Stem Cells (in the isthmus/neck)

37
Q

Fundic Region

A
  • Short gastric pits
  • Longer gastric glands
  • Parietal cells numerous in neck
  • Chief cells numerous at bottom of gland
38
Q

Pyloric Region

A
  • Long gastric pits
  • Short, wider glands
  • Mucous cells predominate
39
Q

Stomach Submucosa

A
  • Dense, irregular CT
  • Adipose
  • Large blood vessels
  • Submucosal (Meissner’s) Plexus
    • Picture inlay
40
Q

Stomach Muscularis Externa

A

3 Layers of Muscle

  • Inner Oblique
  • Middle Circular
    • Enlargement leads to Pyloric Sphinctor
  • Longitudinal Layer

Innervated by:

  • Myenteric Aurbach’s Plexus (parasympathetic)

Entire stomach covered by a serosa (intraperitoneal)

41
Q

Peptic Ulcers

A
  • Erosion in lining of stomach
  • Epigastric pain
  • Caused by:
    • H. Pylori
    • NSAIDs
  • Treatments:
    • Acid Blockers (proton-pump inhibitors)
    • Antibiotics
42
Q

Small Intestine

A
  • Principle site of digestion and absorption of food
  • Plicae Circularis
  • Villi
  • Microvilli
43
Q

Plicae Circularis

A
  • Folds of mucosa and submucosa
  • Increase intestinal surface area 3 fold
  • Most prominent in jejunum (slide)
44
Q

Villi

A
  • Projections of epithelium and lamina propria
  • Fibroblasts and smooth muscle
  • Central lacteal (lymphatic capillary)
  • Increase surface area 10-fold
45
Q

Microvilli

A
  • Covered by glycocalyx
    • Enzymes for digestion
  • Increase surface area by 20-fold
46
Q

Intestinal Glands

A
  • Extensions of epithelium down into lamina propria
  • “Crypts”
47
Q

Cell Types in Intestinal Epithelium

A
  • Enterocytes
  • Goblet Cells:
    • Unicellular, mucous-secreting glands
  • Paneth Cells
  • M (microfold) cells
  • Enteroendocrine cells
48
Q

Enterocytes

A
  • Absorptive Cells
    • Transcellular pathway (tight junctions b/w cells)
  • Active transport
    • Na+/K+ exchange pumps (Na+ out)
    • Glucose transporters
49
Q

Lipid Absorption

A
  • Lipids broken down by lipases and emulsified by bile in lumen of gut
    • Lipid diffuses across microvilli
  • Triglycerides resynthesized in SER
    • Packaged into chylomicrons
      • Transported across basolateral membrane into central lacteal
50
Q

Paneth Cells

A
  • In basal portion of intestinal crypts
  • Eosinophilic secretory granules
  • Secrete lysozyme and alpha-defensins
  • Regulate bacterial flora
51
Q

M (microfold) Cells

A
  • Overlie lymphatic nodules
    • Basal plasma membrane invaginations
      • APCs and lymphocytes
  • Microfolds on apical surface detect and endocytose antigens
  • Predominantly in ileum
52
Q

Duodenum

A
  • Leaf-shaped villi
  • Brunner’s glands in submucosa
53
Q

Jejunum

A
  • Finger-like villi
  • Prominent plicae circularis
  • No glands in submucosa
54
Q

Ileum

A
  • Shorter, leaf-shaped villi
  • Fewer plicae circularis
  • Peyer’s Patches (outlined in image)
55
Q

Outer Small Intestine

A
  • Submucosa
    • Meissner’s Plexus
    • Brunner’s Glands (duodenum)
    • Peyer’s Patches (ileum)
  • Muscularis Externa
    • Myenteric (Auerbach’s Plexus)
  • Serosa
    • Except posterior aspect of duodenum (has adventitia)
56
Q

Large Intestine Mucosa

A
  • Aborbs water and electrolytes
  • Eliminates waste, undigested food
  • No Villi
    • We DO have intestinal glands (simple tubular glands)
  • GALT in lamina propria
57
Q

Cell Types in Colon Epithelium

A
  • Colonocytes
  • Goblet Cells
    • More in distal colon
  • Enteroendocrine Cells
  • M Cells
  • No Paneth cells
58
Q

Large Intestine: Muscularis Externa

A
  • Inner Circular Layer
    • Penetrated by teniae colie (allows segments to contract independently)
  • Discontinuous Outer Longitudinal Layer
    • ​Teniae Coli
      • ​Continuous layer in appendix, rectum, anal canal
59
Q

Polyps

A
  • Abnormal growths in colon
  • Usually benign
  • Common in low-fiber diets
60
Q

Appendix

A
  • Large lymphatic nodules in lamina propria/submucosa
61
Q

Anal Canal

A

3 Zones:

  • Colorectal Zone
    • Simple Columnar Epithelium
  • Anal Transitional Zone
    • Simple columnar to stratified columnar
  • Squamous Zone
    • Stratified Squamous Epithelium continuous with skin

Muscularis Externa:

  • Inner circular layer becomes internal anal sphinctor

External Anal Sphinctor:

  • Striated (voluntary) muscle

Human Structure (30 decks)

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