Digestive 2 Flashcards
Digestive process
- Ingestion
- Propulsion
- Mechanical Breakdown
- Digestion
- Absorption
- Defecation
Peristalsis:
Adjacent segments of GI tract alternately contract and relax, moving food along the tract distally. (Esophagus, stomach, small and large intestine)
Segmentation:
Nonadjacent segments of GI tract alternately contract
and relax, moving food forward then backward. Food is mixed and slowly propelled. (Small intestine)
Layer of walls of the GI
- Mucosa
- Submucosa
- Muscularis Externa
- Serosa
mucous membrane that consists of 3 sublayers
- Lining epithelium
- Highly differentiated along the regions of the GI tract
- Functions include: absorbing nutrients and secreting mucus - Lamina propria
- Connective tissue whose capillaries nourish the lining
epithelium and absorb digested nutrients - Muscularis mucosae
- Layer of smooth muscle that produces local movements of the mucosa – can dislodge sharp food particles that become embedded in the mucosa
- Submucosa
A layer of connective tissue.
• Contains major blood and lymphatic vessels, and
nerve fibers.
• The many elastic fibers in the submucosa enable the alimentary canal to return to its shape after food material passes through it.
- Muscularis Externa
Consists of two layers of smooth muscle that work together to perform peristalsis and segmentation.
- An inner circular layer – fibers orient around the circumference of the canal. Functions to squeeze the gut tube. In some places, this layer thickens to form sphincters ie. Cardiac sphincter and pyloric sphincter
Consists of two layers of smooth muscle that work together to perform peristalsis and segmentation.
2.An outer longitudinal layer; fibers orient along the length of the canal. Functions to shorten the gut tube.
- Serosa
Very thin outer layer of moist tissue (mesothelium). As the alimentary canal expands and contracts, the serosa helps reduce friction against adjacent structures.
Also called visceral peritoneum.
Esophagus
A muscular tube that connects pharynx to stomach.
• Passes through esophageal hiatus in diaphragm.
• Joins stomach at cardial orifice where cardiac sphincter closes off lumen
Gastroesophageal reflux disease
A malfunctioning cardiac sphincter results in gastroesophageal reflux disease. This allows stomach acids to erode the wall of the esophagus causing a burning pain (heart burn).
Hiatal Hernia
Abdominal esophagus or superior part of stomach pushes through an enlarged esophageal hiatus. Symptoms: heartburn.
Stomach functions
• A temporary storage tank where food is churned
into a paste called chyme
• Produces pepsin, a protein digesting enzyme that functions only under acidic conditions.
• Substances absorbed directly from stomach: water, electrolytes, and some drugs (aspirin and alcohol).
• Food remains in stomach for approx. 4 hours. Can hold up to 4 liters of food! Functions:
stomach has 4 major regions
Cardia • Encircles the cardial orifice. Contains cardiac sphincter. Fundus • Part of stomach that rises above cardia. • Gas bubbles accumulate here. Body • Majority of stomach Pyloric region • Composed of 2 parts: canal and antrum. • Contains pyloric sphincter.
Stomach: Histology
Mucosa
• Simple columnar epithelium with mucus glands
Submucosa
• Contains blood and lymphatic vessels, lymph
nodes, and nerves
Muscularis externa
• Contains 3 layers:
1. Innermost oblique
2. Inner circular
3. Outer longitudinal
• Gives the wall of the stomach a very muscular
function to move and mix food around.
Serosa
• Attached to mesenteries – talk about in
next lecture
Gastric pit
• Lining of surface epithelium is mucous cells
that secrete bicarbonate-buffered mucous.
• Same throughout the different regions of
stomach.
Gastric gland
• Lining cells vary among different regions of
stomach.
• Pyloric and cardiac regions: cells of gastric glands are primarily mucous cells.
• Fundus and body regions: gastric glands contain four types of cells…..
Peptic ulcers
Craterlike erosions of the mucosa.
• Caused by acid resistant H. pylori bacteria.
• H. pylori secrete urease – an enzyme that produces
ammonia, which damages the gastric mucosa.
• Ammonia also neutralizes acid to allow H. pylori to live in stomach.
Stomach: Arterial supply
Abdominal aorta with major branches: Celiac trunk Provides blood supply to the stomach: 1. Left gastric artery 2. Common hepatic artery 3. Splenic artery
- Left gastric artery
Lesser curvature of stomach
- Common hepatic artery
- Right gastric artery – lesser curvature
* Right gastroepiploic artery – greater curvature
- Splenic artery
- Left gastroepiploic artery– greater curvature
* Short gastric artery– Fundus
Small intestine
site of enzymatic digestion and absorption of nutrients.
• Undergoes active segmentation to maximize absorption.
• Peristalsis propels chyme through small intestine in ~3-6 hours.
• 6 meters in length.
• Continuous but divided into three regions:
- Duodenum
- Shortest part: 25 cm long
* Most features of interest
- Jejunum
- 2/5 of total length
* Superior left portion of coils
- Ileum
- 3/5 of total length
* Inferior right portion of coils
Duodenum receives:
• Digestive enzymes from the PANCREAS via main
pancreatic duct.
• Bile from LIVER and GALLBLADDER via bile duct.
hepatopancreatic ampulla
pancreatic duct + bile duct
This hepatopancreatic ampulla opens into duodenum at major duodenal papilla
Plicae circulares - small intestine
- Circular folds of mucosa and submucosa.
* Swirl chyme through intestine, slowing movement to allow more time for absorption.
- Villi - small intestine
- Finger-like projections of mucosa.
* Increase surface area.
Microvilli - small intestine
- Cover apical surface of enterocytes.
- Long and densely packed, amplifying surface area.
- Contain enzymes on cell membrane that help breakdown nutrients.
Small intestine cells
• Enterocytes: contain microvilli, specialized for
absorption.
• Goblet cells: secrete mucus – provides lubrication and
protects intestinal wall from enzymatic digestion.
• Enteroendocrine cells: secrete hormones – signal
gallbladder to release bile, and pancreas to release
digestive enzymes and bicarbonate rich juice.
Intestinal Crypt
contains intestinal stem cells as well as specialized immune cells (Paneth cells) that protect from bacterial
pathogens.
Vessels in Lamina Propria
- Blood vessels: carry absorbed products of proteins and carbohydrates.
- Lacteals: large lymphatic capillary, carry absorbed fats.
Muscle in Lamina Propria
Muscularis mucosa: small layer of smooth muscle cells in the lamina propria. Help to keep mucosal layer moving (e.g. help get contents out of crypt).
- Submucosa. - histology
• Connective tissue that supports the mucosa.
• In duodenum only: duodenal glands open into
intestinal crypts. Secrete alkaline mucus that neutralizes acidity of chyme and helps protect mucosa.
• In distal jejunum and ileum: huge areas of lymphoid nodules (Peyer’s patches) – monitor bacteria in intestines.
Intestinal Obstruction
- Mechanical
• Blockage of the lumen of the intestine by:
Hernia Twist Tumor Foreign object - Non-mechanical
• Occurs when peristalsis halts.
• Trauma, or when intestine is touched during surgery
Crohn’s disease
A subtype of inflammatory bowel disease.
• Chronic inflammation of the intestinal wall.
• Abnormal immune response to bacteria normally present in the intestine.
• Deep ulcers and fissures along entire intestine, but primarily in ileum.
