Lecture 21: Abdominal Viscera I Flashcards
What is the esophagus? What cavities does it pass through?
Muscular tube 23-25 cm that travels through neck, thorax, abdomen. Connects pharynx to the stomach.
What are the muscular layers of the esophagus?
Internal circular muscles, outer longitudinal muscle
Identify the indicated structures
Where does the esophagus begin? What is it attached to?
The beginning partially blends with the pharyngeal constrictor muscles.
In which cavity is most of the esophagus located?
Thoracic
Describe esophageal position in superior mediastinum.
intermediate position between vertebral column (posterior) and trachea (anterior)
Describe esophageal position in inferior thoracic cavity.
Located in posterior mediastinum: pushed forward by the descending aorta. Passes through the diaphragm.
Through what opening does the esophagus pass through the diaphragm?
Esophageal hiatus
What is the cardiac region of the stomach?
The last 2 centimeters before the opening in the stomach.
What type of tissue is the inner layer of the esophagus composed of?
Stratified squamous non-keratinized epithelium.
How does esophagus move food to stomach.
Peristalsis - muscular contractions
What is the stomach, and its main function? What does it change food into?
A distensible organ that functions as a blender and reservoir.
It temporarily stores and digests food with strong acid and changes bolus of food into chyme
Describe location and shape of the stomach.
- J-shaped dilation distal to esophagus
- Variable shape due to ability to distend
- Has lesser curvature (concave)
- Greater curvature (convex)
What muscular strucures prevent reflux of food into the esophagus?
Voluntary muscles of diaphragm
Esophageal sphincter - smooth muscle surrounding opening to stomach
What are rugae, and their explain their function?
- Muscular folds lining the luminal surface of the stomach
- Increase surface area.
What action passes chyme into the small intestine? What controls the output of chyme?
- Peristalsis
- Pyloric sphincter - controls output of chyme
What are the 4 regions of the stomach?
- Cardia
- Fundus
- Body
- Pylorus & pyloric sphincter
Describe location of cardia, and what does it produce?
1.5-3 cm wide transition zone between the esophagus and the stomach
Its glands primarily produce mucus
Location and function of fundus and body?
histologically identical. Gastric glands releasing acidic gastric juice are located there
Location and function of pylorus.
funnel-shaped region that opens into the small intestine. Its glands primarily produce mucus
What are the 4 layers of the wall of the stomach?
- Mucosa
- Submucosa
- Muscle
- Serosa
What type of tissue is the mucosa of the stomach composed of?
Simple columnar epithelium = secretory epithelium
What protects the stomach epithelium from secreted acids?
Alkaline mucus
What are the invaginations in the stomach epithelium called?
Gastric pits
What is located at the bottom of the gastric pits?
Tubular glands, which project into lamina propria.
1-7 glands open into the bottom of each pit.
What do the gastric glands secrete?
Pepsinogen, lipase and
hydrochloric acid
What happens to pepsinogen in acidic pH?
Converted to pepsin for protein digestion.
Identify the indicated structures.
Identify the indicated structures
Where is this tissue located?
Identify the indicated structures.
The stomach
Identify indicated structures.
From what region of the stomach is the below tissue?
Identify indicated structures
From what region of stomach is tissue? Name the structures.
What region of stomach is below tissue sample? Identify structures.
Notice difference in epithelial shape between different regions.
Where is the beginning and end of the small intestine?
What are the 3 sections?
- Extends from pylorus of stomach to ileocecal junction
- Duodenum
- Jejunum
- Ileum
What are plicae circulares and their function?
Where are they most abundant?
Circular folds beginning in duodenum; composed of mucosa and submucosa.
Increase surface area for absorption
Most abundant in the jejunum and disappear in the distal ileum.
What is the plicae circulares composed of?
Mucosa and submucosa
Describe the shape and length of the duodenum. Where does it begin and end?
- C-shaped organ and cradles the head of the pancreas
- About 12 inches (name after its length)
- It extends from the pylorus to the duodenojejunal flexure, junction
What are the 4 parts of the duodenum?
- Superior
- Descending
- Horizontal
- Ascending
What is the major duodenal papilla and where is it located?
Opening for main pancreatic duct and common bile duct.
Located on left side of descending duodenum
Which part of the small intestine is retroperitoneal?
The duodenum
Which parts of the small intestine are intraperitoneal?
The Jejunum and Ileum
Location of the jejunum: where does it begin and end?
is continuous with duodenum proximally and the ileum distally
no clear demarcation from ileum; it is the proximal 2/5 of combined length of jejunum and ileum
Location of the Ileum: Where does it begin and end?
is continuous with jejunum proximally, cecum distally
It is the distal 3/5 of combined length of jejunum and ileum
Which parts of the small intestine form the mesentery?
The jejunum and ileum attach to the posterior abdominatl wall by the mesentery (mesointestine).
What is the main function of the small intestines?
secretion of enzymes and hormones, and nutrient absorption
What are the 4 layers to the intestinal epithelium?
- Mucosa
- Submucosa
- Muscular Layer
- Serosa
What are villi, and in which layer of the epithelium are they located? What is their function?
Finger-like projections extending from the epithelium and lamina propria.
Increased surface area for absorption.
What are the crypts of Liberkuhn, and where are they located?
Intestinal glands deep between the villi that secretes intestinal juice to aide digestion, as well as a germinative site for epithelial cell production.
Contains germ cells that can differentiate into many different cell types.
Extend from lamina propria to muscularis mucosae.
What are the cells lining the intestinal lumen? Describe their structure and function.
Enterocytes - simple columnar epithelium w/ microvilli covering apex
Absorb nutrients from intestinal lumen
What border do the microvilli form collectively? What is their function?
The Brush Border
Increase surface area.
What becomes of sugars, proteins and lipids once absorbed by enterocytes?
- Sugars and proteins pass into the blood capillaries
- lipids pass into the central lacteal in the core of the villus
What are Goblet cells, and where are they located?
What is their function?
scattered between enterocytes, increasing in number distally (most numerous in the ileum)
Goblet cell granules contain acid glycoprotein which are secreted onto the luminal surface, and which lubricate and protect the lining of the intestine
- Tissue type in intestinal lamina propria
- What structures does it contain
- Where is it located
- Loose connective tissue
- Blood and lymph vessels, and nerves
- Composes core of each villus
What is the muscularis mucosae, its location and function?
- Smooth muscle with two layers. The inner layer is circular, the outer layer is longitudinal.
- Smooth muscles extend into the villi facilitating their rhythmic movements.
What is the submucosa?
Dense connective tissue rich in collagen and elastic fibers.
What glands are located in the submucosa of the duodenum? What do they secrete?
Duodenum
What are Peyer’s patches? Where are they located?
Ileum
What is the muscularis externa?
Outer ring of smooth muscle with a circular inner and longitudinal outer layer.
Identify which section of the intestines the following tissues come from.
Contrast the epithelial differences between the different intestinal regions, and identify labelled structures.
What is the outer layer of the duodenum?
Adventitia
What is the outer layer of the jejunum and ileum? Why are they called the mesenteric intestine?
Serosa
Jejunum and ileum invested by the mesentery proper
This is why they’re called mesenteric intestines.
What is the total absorptive area of the intestines?
- Total absorptive area of over 200 m2 (2153 ft2 – approximately, the size of a tennis court!)
What are the 6 sections of the large intestine?
What’s the main function of the Colon?
Water Absorption - extracts water from chyme, turning it into feces
What are the 3 distinct surface features of the large intestine?
- Tenia coli are three bands of longitudinal smooth muscle fibers.
- Haustra are sacculations of the colon that bulge out between tenia coli.
- Omental (epiploic) appendices are fat-filled appendices.
What are semilunar folds?
Mucosal folds lining the interior of the large intestine?
Describe mucosa of the large intestine
- Mucosa of the large intestine lacks villi and has a smooth interior surface.
- The surface epithelium invaginates into the lamina propria to form the intestinal glands of Lieberkuhn (crypts in small intestine and glands in large intestine)
What type of cells line the lumenal surface of the colon?
- simple columnar epithelium consisting of intestinal
absorptive cells and goblet cells - goblet cells are dominant cell type, and their number
increases in more distal parts of the large intestine
Describe lamina propria and muscularis mucosae of colon?
- Lamina propria typically contains lymphoid tissue
- Muscularis mucosae has inner circular and outer longitudinal smooth muscle layers
Describe submucosa of colon. Does it have glands?
Submucosa – usually dense CT, similar to the small intestine. No glands are present
Describe structure of muscularis externa. What are taeniae coli?
- Inner circular and outer longitudinal layers of smooth muscle
- The outer longitudinal layer is discontinuous forming three separate longitudinal bands of smooth muscle called taeniae coli
What is the outer layer of the colon?
Serosa / adventitia
The cecum, transverse and sigmoid colon are covered by serosa.
Describe the structure of the cecum.
Length, where does ileum enter, what valve?
Cecum is a blind pouch 6-7cm long.
I. Ileum enters cecum at ileocecal orifice. Ileocecal valve guards the orifice.
II. Appendicular orifice also in cecum
Describe structure of the vermiform appendix.
Vermiform appendix – 2-20 cm long, usually ~8 cm
I. Position of the rest of the appendix varies
II. Frequently inflamed – appendicitis
Describe structure of ascending colon. Extends from where to where?
a. From cecum proximally to right colic (hepatic) flexure distally.
b. Narrower than cecum
Describe structure of transverse colon. Extends from where to where?
a. Largest and most mobile portion of the large intestine.
b. From right colic (hepatic) flexure to left colic (splenic) flexure
Describe structure of descending colon. Extends from where to where?
a. From left colic flexure to sigmoid colon
b. Narrowest portion of colon
Describe the structure of the sigmoid colon.
S-shaped loop from descending colon to rectum
What are the rectum and anal canal?
Rectum and anal canal – located within true pelvis
a. Rectum is continuous with sigmoid colon
b. The Anal canal is the inferior 1.5 in of the GI tract; it is continuous with rectum at anorectal junction.
Describe the changes that occur at the anorectal juntion:
1. Epithelial change
2. Vasculature
3. Inner circular layer
4. External anal sphincter composition
- changes from simple columnar to non-keratinized stratified squamous
- The combined lamina propria-submucosal layer (muscularis mucosae disappears) contains large thin-walled veins.
- When these veins dilate, they are called internal hemorrhoids - The inner circular layer of the muscularis externa enlarges to form the internal anal sphincter (smooth muscle)
- Defecation involves voluntary muscles comprising external anal sphincter.
Where is the following tissue located, and identify the indicated structures.
Identify indicated structures.
Identify structures on the right
