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Human Structure > Histology: GI Tract > Flashcards

Histology: GI Tract Flashcards

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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
Sublingual Salivary Glands
* Smallest * Mixed, **mostly mucous** * Some serous demilunes * Few striated ducts (not as prominant)
26
General Organization of GI Tract
4 Layered Wall: * **Mucosa** (lines lumen) * **Submucosa** (CT layer) * **Muscularis** * **​**2 layers (usually) of smooth muscle * **Serosa** (mesolthelial lining) or **Adventitia** (connective tissue) * **​****Visceral peritoneum**is serosa (**intraperitoneal**) * Adventitia near organs that are **retroperitoneal**
27
Mucosa
Epithelium * Changes along course of GI tract Lamina Propria * Loose CT, GALT * Glands Muscularis Mucosae * Thin layer of smooth muscle
28
Esophagus
* Muscular tube * **Longitudinal mucosal folds** * **Surrounded by ADVENTITIA** (no serosa)
29
Esophageal Mucosa
* **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
Gastroesophageal Reflux Disease
**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
Esophageal Submucosa
* 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
Esophagus: Muscularis Externa
* 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
Gastroesophageal Junction
* Stratified squamous (esophagus) to **simple columnar** (stomach)
34
Stomach
Histologically divided into **3 Regions**: * Cardia * Fundus (Body) * Pylorus Rugae: * **Transient folds** of **mucosa and submucosa**
35
Gastric Mucosa
* **Simple Columnar Epithelium** * **​**Has **_Gastric Pits_** * Lamina Propria: * **Gastric Glands** * Muscularis Mucosae Image (stains mucus)
36
Gastric Pits/Glands
**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
Fundic Region
* **Short** gastric pits * **Longer** gastric glands * Parietal cells numerous in **neck** * Chief cells numerous at **bottom** of gland
38
Pyloric Region
* **Long** gastric pits * **Short, wider** glands * Mucous cells predominate
39
Stomach Submucosa
* Dense, irregular CT * Adipose * Large blood vessels * Submucosal (**Meissner's**) Plexus * Picture inlay
40
Stomach Muscularis Externa
**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
Peptic Ulcers
* Erosion in lining of stomach * **Epigastric pain** * Caused by: * **H. Pylori** * **NSAIDs** * Treatments: * **Acid Blockers (proton-pump inhibitors****)** * Antibiotics
42
Small Intestine
* **Principle site of digestion and absorption of food** * **Plicae Circularis** * **Villi** * **Microvilli**
43
Plicae Circularis
* Folds of **mucosa** and **submucosa** * Increase intestinal surface area 3 fold * **Most prominent in jejunum** (slide)
44
Villi
* Projections of epithelium and lamina propria * **Fibroblasts** and **smooth muscle** * **Central lacteal** (lymphatic capillary) * Increase surface area 10-fold
45
Microvilli
* Covered by **glycocalyx** * Enzymes for digestion * Increase surface area by 20-fold
46
Intestinal Glands
* Extensions of **epithelium** down into **lamina propria** * "Crypts"
47
Cell Types in Intestinal Epithelium
* Enterocytes * Goblet Cells: * Unicellular, mucous-secreting glands * Paneth Cells * M (microfold) cells * Enteroendocrine cells
48
Enterocytes
* **Absorptive Cells** * Transcellular pathway (**tight junctions** b/w cells) * Active transport * Na+/K+ exchange pumps (Na+ out) * Glucose transporters
49
Lipid Absorption
* 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
Paneth Cells
* In basal portion of **intestinal crypts** * Eosinophilic secretory granules * Secrete **lysozyme and alpha-defensins** * Regulate bacterial flora
51
M (microfold) Cells
* Overlie **lymphatic nodules** * Basal plasma membrane **invaginations** * APCs and lymphocytes * **Microfolds** on apical surface detect and endocytose **antigens** * **Predominantly in ileum**
52
Duodenum
* Leaf-shaped villi * **Brunner's glands** in submucosa
53
Jejunum
* Finger-like villi * **Prominent plicae circularis** * No glands in submucosa
54
Ileum
* Shorter, leaf-shaped villi * Fewer plicae circularis * **Peyer's Patches** (outlined in image)
55
Outer Small Intestine
* 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
Large Intestine Mucosa
* Aborbs **water and electrolytes** * Eliminates waste, undigested food * No Villi * We DO have **intestinal glands (****simple tubular glands)** * GALT in lamina propria
57
Cell Types in Colon Epithelium
* Colonocytes * Goblet Cells * More in distal colon * Enteroendocrine Cells * M Cells * **No Paneth cells**
58
Large Intestine: Muscularis Externa
* 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
Polyps
* Abnormal growths in colon * Usually benign * Common in low-fiber diets
60
Appendix
* Large **lymphatic nodules** in lamina propria/submucosa
61
Anal Canal
**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

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