lec10 anatomy

Anatomy Dr.Israa H. Mohsen
Lec10
Digestive System
Digestive System Function
• Acquires nutrients from environment
• Anabolism
Uses raw materials to synthesize essential compounds
• Catabolism
Decomposes substances to provide energy cells need to function
Digestive (GI) Tract
Histological Structure of the Digestive (GI) Tract
Functions of Oral Cavity
• Sensory analysis
Of material before swallowing
• Mechanical processing
Through actions of teeth, tongue, and palatal surfaces
• Lubrication
Mixing with mucus and salivary gland secretions
• Limited digestion
Of carbohydrates and lipids
Esophagus
• A hollow muscular tube
• About 25 cm (10 in.) long and 2 cm (0.80 in.) wide
• Conveys solid food and liquids to the stomach
• Begins posterior to cricoid cartilage
• Is innervated by fibers from the esophageal plexus
Stomach Function
• Major Functions of the Stomach
Storage of ingested food
Mechanical breakdown of ingested food
Disruption of chemical bonds in food material by acid and enzymes
Production of intrinsic factor, a glycoprotein required for absorption of vitamin B12 in small intestine
Gastric Anatomy
Digestion in the Stomach
• Stomach performs preliminary digestion of proteins by pepsin
Some digestion of carbohydrates (by salivary amylase)
Lipids (by lingual lipase)
• Stomach contents
Become more fluid
pH approaches 2.0
Pepsin activity increases
Protein disassembly begins
• Although digestion occurs in the stomach, nutrients are not absorbed there
Small Intestine
• 90% of absorption occurs in the small intestine
Small Intestine
• The Duodenum
The segment of small intestine closest to stomach
25 cm (10 in.) long
“Mixing bowl” that receives chyme from stomach and digestive secretions from pancreas and liver
Functions of the duodenum
To receive chyme from stomach
To neutralize acids before they can damage the absorptive surfaces of the small intestine
Small Intestine
• The Jejunum
Is the middle segment of small intestine
2.5 meters (8.2 ft) long
Is the location of most
Chemical digestion
Nutrient absorption
Has few plicae circulares
Small villi
Small Intestine
• The Ileum
The final segment of small intestine
3.5 meters (11.48 ft) long
Ends at the ileocecal valve, a sphincter that controls flow of material from the ileum into the large intestine
Small Intestine
Small Intestine
• Intestinal Secretions
Watery intestinal juice
1.8 liters per day enter intestinal lumen
Moisten chyme
Assist in buffering acids
Keep digestive enzymes and products of digestion in solution
• Intestinal Movements
Chyme arrives in duodenum
Weak peristaltic contractions move it slowly toward jejunum
• Myenteric reflexes
• Not under CNS control
• Parasympathetic stimulation accelerates local peristalsis and segmentation
Pancreas
• Lies posterior to stomach
From duodenum toward spleen
• Is bound to posterior wall of abdominal cavity
• Is wrapped in thin, connective tissue capsule
Functions of the Pancreas
1. Endocrine cells of the pancreatic islets:
Secrete insulin and glucagon into bloodstream
2. Exocrine cells:
Acinar cells and epithelial cells of duct system secrete pancreatic juice
Pancreas
Liver
Liver
• Hepatocytes
Are liver cells
Adjust circulating levels of nutrients
Through selective absorption and secretion
In a liver lobule form a series of irregular plates arranged like wheel spokes
Many Kupffer cells (stellate reticuloendothelial cells) are located in sinusoidal lining
As blood flows through sinusoids
Hepatocytes absorb solutes from plasma
And secrete materials such as plasma proteins
Gallbladder
• Is a pear-shaped, muscular sac
• Stores and concentrates bile prior to excretion into small intestine
• Is located in the fossa on the posterior surface of the liver’s right lobe
• The Cystic Duct
Extends from gallbladder
Union with common hepatic duct forms common bile duct
Large Intestine
• Is horseshoe shaped
• Extends from end of ileum to anus
• Lies inferior to stomach and liver
• Frames the small intestine
• Also called large bowel
• Is about 1.5 meters (4.9 ft) long and 7.5 cm (3 in.) wide
Parts of Large Intestine
• The Cecum
Is an expanded pouch
Receives material arriving from the ileum
Stores materials and begins compaction
• Appendix
Also called vermiform appendix
Is a slender, hollow appendage about 9 cm (3.6 in.) long
Is dominated by lymphoid nodules (a lymphoid organ)
Parts of Large Intestine
• The Colon
Has a larger diameter and thinner wall than small intestine
The wall of the colon
Forms a series of pouches (haustra)
Haustra permit expansion and elongation of colon
Parts of Colon
• Ascending Colon
Begins at superior border of cecum
Ascends along right lateral and posterior wall of peritoneal cavity to inferior surface of the liver and bends at right colic flexure (hepatic flexure)
• Transverse Colon
Crosses abdomen from right to left; turns at left colic flexure (splenic flexure)
Is supported by transverse mesocolon
Is separated from anterior abdominal wall by greater omentum
Parts of Colon
• The Descending Colon
Proceeds inferiorly along left side to the iliac fossa (inner surface of left ilium)
Is retroperitoneal, firmly attached to abdominal wall
• The Sigmoid Colon
Is an S-shaped segment, about 15 cm (6 in.) long
Starts at sigmoid flexure
Lies posterior to urinary bladder
Is suspended from sigmoid mesocolon
Empties into rectum
Parts of Colon
Parts of Large Intestine
• The Rectum
Forms last 15 cm (6 in.) of digestive tract
Is an expandable organ for temporary storage of feces
Movement of fecal material into rectum triggers urge to defecate
• The anal canal is the last portion of the rectum
Contains small longitudinal folds called anal columns
• Anus
Also called anal orifice
Is exit of the anal canal
Has keratinized epidermis like skin