Histology of the Upper GI Tract: Esophagus & Stomach (Test 1) Flashcards
(37 cards)
1
Q
General Organizations of the Digestive/ GI/ Alimentary Tract
A
- Swallowing, digestion and absorption take place in the GI tract
- Swallowing is the function of the Oral Cavity and the Esophagus
- Digestion converts food into a soluble form of Absorption (In the Small Intestine)
- Epithelial modifications (Villi) to INCREASE Surface Area facilitate Absorption
- Segments do not function as Independent units
- Excepto for the Oral Cavity, the digestive tube has a uniform Histologic Organization
- This organization is characterized by distinct and significant structural variations reflecting changes in Functional Activity
- After the Oral Cavity (in Head and Neck), the digestive tube is differentiated into four major organs: Esophagus, Stomach, Small Intestine, and Large Intestine
- Each of these Organs is made up of FOUR Concentric Layers:
1) The Mucosa
2) The Submucosa
3) The Muscular
4) The Adventitia or Serosa
2
Q
Upper GI Tract Component and Function
A
Swallowing/ Digestion:
- Mouth, Oral Cavity
- Esophagus
- Stomach
Absorption:
- Small Intestine (Duodenum, Jejunum, Ileum)
- Large Intestine (Ascending, Transverse, Descending and Sigmoid)
3
Q
Four Layers of the GI Tract
A
1) Muscosa:
- Epithelium
- Lamina Preprint
- Muscular Mucosa
2) Submucosa:
- Connective Tissue
- Contains glands, Blood Vessels, nerves
3) Muscular Externa:
- Smooth Muscle
- Two to Three Layers
4) Adventitia (Esophagus and most of Duodenum) or Serosa (Rest of GI Tract)
- Connective Tissue
- Supports and binds organs to others
4
Q
Mucosa
A
Shows significant variations along the length of the GI Tract
Mucosa has Three components:
1) A Lining epithelium with Mucosal and Submucosal Glands and Ducts
2) An underlying Lamina Propria consisting of a vascularized Loose Connective Tissue
3) A Thin Layer of Smooth Muscle, the Muscular Mucosae!!!
5
Q
Epithelium
A
Epithelium:
1) STRATIFIED SQUAMOUS:
- Oral Cavity, Oropharynx, Esophagus, Anal Canal
2) SIMPLE COMPLUMNAR:
- Stomach, Small Intestine, Large Intestine, and Rectum
Function:
- SELECTIVE PERMEABLE Barrier
- Transport, Digestion, Absorption
- Produce Hormones
6
Q
Lamina Propria
A
- Vascularized Loose Connective Tissue
- Lymphatic Nodules and Scattered IMMUNOCOMPETENT Cells (Lymphocytes, Plasma Cells, and Macrophages)
- Lamina Propria of the Small and Large Intestines is a relevant site of Immune Response (Peyer’s Patch or GALT)
7
Q
Muscular Mucosae
A
- A thin double layer of Smooth Muscle is often present- the Muscular Mucosa for LOCAL MOVEMENT of the Mucosa
- Increases CONTACT AREA with Food
- Propel and mix food in GI Tract
8
Q
Submucosa
A
- The Submucosa consists of a DENSE IRREGULAR Connective Tissue with Large Blood Vessels, Lymphatics, and Nerves branching into the Mucosa and Muscular. Glands are present in the Submucosa of the ESOPHAGUS and DUODENUM
9
Q
Mucosa
A
- In the Stomach and Small Intestine, both the Mucosa and Submucosa extend into the Lumen as folds, called RUGAE and PLICAE, respectively
- Mucosa alone can extend into the lumen as Fingers or Villi
- Mucosal Glands INCREASE the SECRETORY Capacity
- Mucosal Villi INCREASE the Absorptive Capacity of the Digestive Tube
- The Mucosa shows significant variations from Segment to Segment of the Digestive Tract
10
Q
Folds
A
- In Stomach and Small Intestine, folds of the Mucosa/ Submucosa extend into the lumen as:
1) RUGAE (Stomach)
2) PLICAE (Small Intestine)
3) VILLI (Mucosae alone)
- INCREASE Surface Area for Absorption
11
Q
Muscular Externa
A
- Contains TWO LAYERS of Smooth Muscle:
1) CIRCULAR LAYER: Inner Layer is arranged around the Tube Lumen
2) LONGITUDINAL LAYER: Fibers of the Outer Layer are disposed along the Tube
- CONTRACTION of the Smooth Fibers of the CIRCULAR Layer REDUCES the Lumen
- CONTRACTION of the Fibers of the LONGITUDINAL Layer SHORTENS the Tube
12
Q
Adventitia and Serosa
A
Adventitia:
- Outside the PERITONEAL CAVITY
- Binds to the Body Wall
- Loose Connective Tissue
- Blood vessels and Nerves
Serosa:
- Within the Peritoneal Cavity
- Loose Connective Tissue
- Simple Squamous Epithelium
- Blood Vessels, Nerves, Adipose Tissue
13
Q
Innervation- Enables GI Tract to respond to BOTH Local Stimuli and ANS Input
A
EXTRINSIC (ANS):
1) Sympathetic (TL):
- DECREASES Motility/ Secretions
2) Parasympathetic (VAGUS):
- INCREASES Motility/ Secretions
INTRINSIC/ ENTERIC:
- Distinct, Interconnected Neuronal Circuits
1) Submucosal Plexus (Meissner)
2) Myenteric (Auerbach)
- Between Inner and Outer layers of Muscular Externa
** 1) PERISTALTIC Contractions to move Food Bolus
** 2) Secretory activity of MUCOSAL. SUBMUCOSAL Glands
14
Q
Esophagus
A
- The Esophagus is a hollow Muscular Tube about 25 cm in Length
- It lies POSTERIOR to the Trachea in the Thoracic Cavity, except for its Distal End, which passes through the Diaphragm into the Abdominal Cavity
- The Esophagus carries food from the Oropharynx to the Stomach, by a STRONG PERISTALTIC Reflex
- The Lower Esophageal Sphincter (LES), just ANTERIOR to the GASTROESOPHAGEEAL JUNCTION, helps prevent Reflux and Regurgitation of Stomach contents through Contraction and must Relax to ALLOW FOOD PASSAGE with Swallowing
- There is also an UPPER ESOPHAGEAL SPHINCTER (UES), near the CRICOPHARYNGEUS MUSCLE
15
Q
Esophagus Cont 2
A
- MUCOSA: The lumen of the Esophagus is lined by a non-keratinized STRATIFIED SQUAMOUS EPITHELIUM. This layer so NON-ABSORPTIVE and FRICTION-RESISTANT
- A THIN LAMINE PROPRIA lies below. It contains THIN ELASTI Connective Tissue and a limited number os SUPERFICIAL MUCOSAL GLANDS. In the Upper Esophagus, the Muscular Mucosae consists of THIN ELASTIC FIBERS instead of Smooth Muscle Cells
- The Lower Esophagus contains SMOOTH MUSCLE FIBERS. When Relaxed, the Mucosa is deeply folded to allow extensive distention when a Bolus of Food passes through
- Esophageal glands secrete a lubricating layer of Mucus on the Epithelial surface to aid swallowing
- The next layer is a THICK MUSCULAR PROPRIA or EXTERNA, which transitions fro Skeletal Muscle in the Upper Third of the Esophagus for VOLUNTARY SWALLOWING to Smooth Muscle in the Lower two-thirds that CONTROLS PERISTALSIS
16
Q
Esophagus Cont 3
A
- At the GASTROESOPHAGEAL JUNCTION, the Mucosa transitions from the STRATIFIED SQUAMOUS EPITHELIUM of the Esophagus to Simple Columnar Epithelium and Glandular Secretory Mucosa. The MUSCULAR MUCOSA, SUBMUCOSA, and MUSCULAR PROPRIA are continuous through this Junction
17
Q
Portal Caval Anastomoses
A
- Increase in PORTAL VENOUS PRESSURE results in Dilation of Veins (Esophageal Variaces)
18
Q
Mucosal and Submucosal Glands
A
- Continuously produce a THIN LAYER of Mucous to LUBRICATE the Epithelial Surface
- Additional Mucus Glands (Cardiac Glands) are found in the Lamina Propria near the Esophagus/ Stomach Junction
19
Q
Esophagus- Muscular Externa
A
- Inner Circular and Outer Longitudinal
- Segment dependent variation
- Upper 1/3 = SKELETAL MUSCLE
- Middle 1/3 = Transition, PRIMARILY SMOOTH MUSCLE
- Lower 1/3 = SMOOTH MUSCLE
20
Q
Clinical Significance Swallowing and Dysphagia
A
- Esophagus as 2 Sphincters
- UPPER (UES): ANATOMICALLY defined, CRICOTHYROID
- LOWER (LES): FUNCTIONALLY defined, GASTROESOPHAGEAL Sphincter
- LES PREVENTS GASTRIC REFLUX!!!!!!!!
- GERD: Change in Epithelium to Columnar (Like Stomach), Chronic Esophagitis/ ulceration, Dysphagia, Fibrosis a/o Esophageal Strictures
21
Q
Barrett’s Esophagus
A
- Barrett’s Esophagus is a condition in which an ABNORMAL COLUMNAR Epithelium REPLACES the Stratified Squamous Epithelium that normally lines the Distal Esophagus
- It is most SEVER HISTOLOGIC Consequences of CHRONIC GASTROESOGEAL REFULX and predisposes to the development of ADENOCARCINOMA of the Esophagus
- The mean age of development of Barrett’s Esophagus is estimated to be 40 years, yet the mean age of Diagnosis is 63 years
- This suggests that a PREMALIGNANT disorder may be present up to 20 years before it is Clinically recognized
22
Q
Hernias
A
- Movement of Esophagus through Esophageal Hiatus of Respiratory Diaphragm in the Thorax
- Sliding or Paraesophageal
- Treatment: ANTACIDS!!!!!
23
Q
Stomach
A
- Between Esophagus and Duodenum
- Function: Homogenize and Chemically process the Swallowed Semisolid fluid
- Facilitated by CONTRACTION of Muscular Wall and Secretion of Acids and Enzymes
- Four Regions: Cardia, Fundus, Body, and Pylorus
- Based on Motility: ORAD (Relax during Swallowing) and CAUDAD (Regulation of Gastric Emptying) area!!!!!
24
Q
Stomach Cont 2
A
- RUGAE
- Gastric Glands/ pits
- Protective layer of Mucous protects Surface Epithelium from:
1) Mechanical Erosion by Ingested foods
2) Destructive effects of Acids and Hydrolytic Enzymes
25
Gastric Glands- Cardia Regions
- Cardiac Glands are lined by MUCUS-SECRETING CELLS and have a structure similar to the Esophageal Cardiac Glands found in the Mucous of the Esophagus
26
Gastric Glands
- Glands are Major contributors to GASTRIC JUICE
- 15 Million Glands, 2- 7 Glands per Gastric Pit
- House five Major Cell Types:
1) Mucous Neck Cells
2) Chief Cells (also called Peptic Cells)
3) Parietal Cells (also called Oxyntic Cells)
4) Stem Cells
5) Gastroenteroendocrine Cells
27
Mucous Cells
- The Gastric Mucousa of the Fundus-body has two classes of Mucus-producing cells:
1) The Surface Mucous cells lining the Pit
2) The mucous neck cells located at the OPENING of the Gastric Gland into the pit
- Both Cells produce MUCINS, GLYCOPROTEINS with High Molecular Mass
- A Mucus Layer, contains 95% Water and 5% Mucins, forms an Insoluble Gel that attaches to the Surface of the Gastric Mucosa, forming a 100 micro molar thick Protective Gastric Mucosal Barrier
- This protective Mucus blanket traps Bicarbonate ions and NEUTRALIZES the Microenvironemnt adjacent tot eh Apical region of the surface Mucous Cells to an ALKALINE pH!!!
28
Chief Cells
- Chief Cells predominate in the LOWER THIRD of the Gastric Gland
- Chief cells are not present in Cardiac Glands and are seldom found in the PYLORIC ANTRUM
- PEPSINOGEN containing Secretory Granules (ZYMOGEN GRANULES) are observed n the apical region of the Cell. PEPSINOGEN, a PROENZYME stored in the Zymogen Granules, is released into the Kumen of the Gland and converted in the Acid environment of the Stomach to PEPSIN, a Proteolytic Enzyme capable of DIGESTING MOST PROTEINS
- Exocytosis of Pepsinogens is RAPID and Stimulated by FEEDING (After Fasting)
29
Parietal Cells
- Parietal Cells or Oxyntic Cells, which secrete HYDROCHLORIC ACID and INTRINSIC FACTOR in Humans.
- The Cytoplasm of PARIETAL CELLS displays numerous TUBULOVESICLES and an INTRACELLULAR CANALICULUS continuous with the Lumen of the Gastric Gland
30
Autoimmune Gastritis
- Autoimmune Gastritis is caused by Autoantibodies to the H+, K+ Dependent ATPase, a Parietal Cell Antigen, and Intrinsic Factor
- Destruction of PARIETAL CELLS causes a Reduction in Hydrochloric Acid in the Gastric Juice (ACHLORHYDRIA) and a LACK of Synthesis of INTRINSIC FACTOR
- The resulting VITAMIN B12 DEFICIENCY disrupts the formation of Red Blood Cells in the Bone Marrow, leading to PERNICIOUS ANEMIA
31
Secretion fo Hydrochloric Acid
- PARIETAL CELLS produce an Acidic Secretion (pH 0.9 to 2.0) rich in Hydrochloric Acid
- The Parasympathetic Mediator ACETYLCHOLINE and the Peptide GASTRIN, produced by ENTEROENDOCRINE Cells of the Pyloric Antrum, stimulate Parietal Cells to secrete HCL
- ACETYLCHOLINE stimmalte the release of GASTRIN
32
Helicobacter Pylori
- The Gastric Juice is a combination of two separate Secretions:
1) An ALKALINE MUCOSAL GEL PROTECTIVE Component, produced by Surface Mucous Cells and Mucous Neck Cells
2) HCL and PEPSIN, Two Parietal- Chief Cell - derived potentially Aggressive components
- The protective component is CONSTITUTIVE; it is always present
- The Aggressive component is FALCUTATIVE because Hydrochloric Acid and Pepsin levels INCREASE above Basal Levels after Food Intake
- However, the Mucus Blanket lining the gastric Epithelium, in particular in the Pyloric Antrum, is the site where the FLAGELLATED Bacterium HELICOBACTER PYLORI resides in spite of the HOSTILE ENVIRONMENT
- H. pylori survives and replicates in the Gastric Lumen. Its presence has been associated with ACID PEPTIC ULCERS and ADENOCARCINOMA of the Stomach
- About 20% of the population is infected with H. pylori by age 20 years. The incidence of the Infection INCREASES to about 60% by age 60
- Most infected Individuals do not have Clinical Symptoms
33
Gastroenteroendocrine Cells
- The function of the Alimentary Tube is regulated by PEPTIDE Hormones, produced by Gastroenteroendocrine Cells, and Neuroendocrine Mediators, produces by Neurons
- peptide Hormones are Synthesized by Gastroenteroendocrine Cells dispersed throughout the Mucosa from the Stomach through the Colon. The population of Gastroenteroendocrine Cells is so Large that the Gastrointestinal Segment is regarded as the LARGEST Endocrine Organ in the body
- Gastroenteroendocrine Cells are members of DNES (for Diffuse Neuroendocrine System)
- Peptide Hormones (6) produces y Gastrointestinal Endocrine Cells have the follow General Functions:
1) Regulation of Water, Electrolyte Metabolism, and Enzyme Secretion
2) Regulation of Gastrointestinal Motility and Mucosal Growth
3) Stimulation of the release of other peptide Hormones
34
Peptide Hormones- Secretin
- SECRETIN is released by Cells in the Duodenal Glands of LIEBERKÜHN when the Gastric contents enter the Duodenum
- Secretin stimulates PANCREATIC and DUODENAL (Brunner's Glands) BICARBONATE ad Fluid release to Control the Gastric Acid Secretin (Antacid Effect) and regulate the pH of the DUODENAL Contents
- SECRETIN, togeth with CCK, Stimulates the GROWTH of the EXOCRINE PANCREAS. In addition, Secretin (and Acetylcholine) stimulate Chief Cells to Secrete PEPSINOGEN, and inhibits Gastrin release to REDUCE HCL SECRETION in the Stomach
35
Gastrin
- Gastrin is produced by G Cells located in the PYLORIC ANTRUM
- Three forms of Gastrin have been described
- The MAIN FUNCTION of Gastrin is to stimulate the production of HYDROCHLORIC ACID by PARIETAL CELLS
- Gastrin can also activate CCK to stimulate GALLBLADDER Contraction
36
Peptide Hormones
1) CCK is produced by the Duodenum. CCK Stimulates GALLBLADDER Contraction and Relaxation of the Sphincter of ODDI when Protein and Fat-rich Chyme enters the Duodenum
2) GLUCOSE-DEPENDENT INSULINOTROPIC PEPTIDE (GIP), formerly called Gastric- Inhibitory Peptide, is produced in the Duodenum. GIP stimulates INSULIN release (Insulinotropic effect) when Glucose is detected in the Small Intestine
3) MOTILIN is released Cyclically (every 90 Minutes) during FASTING from the Upper Small Intestine and stimulated GASTROINTESTINAL MOTILITY. A NEURAL Control Mechanism Regulates the release of MOTILIN
4) GHRELIN is produced in the Stomach (Fundus). GHERKIN binds to its receptor present in Growth Hormone- secreting Cells of the ANTERIOR HYPOPHYSIS. Gherkin stimulates the Secretion of GROWTH HORMONE. Gherkin Plasma levels INCREASE during Fasting triggering Hunger by acting on HYPOTHALAMIC FEEDING CENTERS
37
Mucosa, Submucosa and Muscular Externa
- Reticular and Collagen Fibers predominate in the Lamina Propria, and Elastic Fibers are Rare. The cell components of the Lamina Propria include Fibroblasts, Lymphocytes, Mast Cells, Eosinophils, and a few Plasma Cells
- The Submucosa consists of DENSE IRREGULAR CONNECTIVE TISSUE in which COLLAGENOUS and ELASTIC FIBERS are Abundant. A large number of Arterioles, Venous Plexuses, and Lymphatics are present in the Submucosa. Also present are the Cell Bodies and Nerve Fibers of the SUBMUCOSAL PLEXUS of MEISSNER!!!!!!!
- The MUSCULAR (Or Muscular Externa) of the Stomach consists of THREE poorly defined layers of Smooth Muscle orientated in Circular, Oblique, and Longitudinal Directions
- At the level of the Distal Pyloric Antrum, the CIRCULAR MUSCLE layer thickens to form the ANNULAR PYLORIC SPHINCTER
