Small Bowel Flashcards
Outline the gross anatomy of the small bowel
- continuous with pyloric antrum
- 5.3m in length
- ends st the ileo-cæcal valve
- 3 sections: duodenum, jéjunum and ileum
- arranged in loops
- lies centrally in the abdominal cavity
3 sections of small bowel
Duodenum
Jéjunum
Ileum
Structure of small bowel
4 layers:
Mucosa- secretory epithelium
Submicosa- areolar connective and elastic tissues
Muscular- smooth muscular. Outer longitudinal and inner circular
Serosa- peritoneum
Functions of serosa
2 layers, visceral and parietal.
Visceral covers abdo organs
Parietal covers abdo wall
Produces and secrets serous fluid
Mucosa Sub-Layers
Mucous membrane
Lamina Propria
Muscularus Mucosa
Duodenum
C shape around head of pancreas
Hepatopancratic opens into second part
Subdivided into four sections
Duodenal relation - 1st part
Ant- liver and gallbladder
Post- portal vein and common bile duct
Infer - head of pancreas
Duodenal relations - 2nd part
Rt latéral- rt kidney and hepatic flexure
Med- head of pancreas
Duodenal relations -3rd part
Pos- right psoas muscle, IVC and abdominal aorta
Ant- root of mesentery
Sup- head of pancreas
Duodenal relations-4th part
Ant- transverse colon
Sup- head of pancreas
Post- left psoes muscle, left renal vein
Jéjunum Gross anatomy
Second portion of small bowel
Approx 2m long
Continuous with dudenojejunal flexure and ilium
Calibrea wider than ilium
Ilium gross anatomy
Final portion of small bowel and also the longest
3m approx
Continuous with jéjunum although no obv point when one become the other
Terminated at ilio-caecal valve- controls flow of contents into ceacum
Blood supply
Superior mesenteric artery supplies ALL of the small bowel
Duodenum received blood from hepatic artery
Venous drainage superior mesenteric artery
Functions of small bowel
Onward movement of food bolus via peristalsis Movement allows mixing of content Secretion of intestinal juice (enzymes) Carbohydrate, protein and fat digestion Protection against bacterial infection Secretion of hormones (CCK and SECRETIN)
What is CCK?
CCK-Cholecystokinin
Secreted in response to fat in chyme
What is Secretin?
secreted in response to acidic chyme
Chemical digestion in small bowel
Acid chyme in first part of duodenum, mixes with pancreatic just and intestinal juice
The mixture is in contact with enterocyts of villi
Digestion of ALL nutrients completes in small bowel
Intestinal Juice (Succus entericus)
Secreted by intestinal glands
What makes up intestinal juice (Succus entericus)
Water
Mucous
Mineral salts
Digestion functions of intestinal juice
Enterokinase- converts tripsinogen to trypsin
Chymotrypsinogen to chymotrypsin
Eripson- peptides and polypeptides into amino acids
Lipase- fats to fatty acids and glycerol
Analyse- starch to maltose
Maltase- converts maltose to glucose
Sucrase and lactase- converts dissachardies (sucrose and lactose) into glucose and other monosaccharides
Carbohydrate digestion
Pancreatic amylase converts all digestible polysaccharides to disaccharides
Sucrase, maltase and lactase produce and secreted by microbilli complete digestion of carbohydrates by converting disaccharides and sugars into monosaccharides
Protein digestion’s
Trypsinogen and chymotrypsinogen are inactive enzymes found in pancreatic juice
Come into contact with enterokinase and become activitated as tripsin and chymotrypsin
Fat digestion
Cholecystokinin secreted in the duodenum as soon as acidic chime from the stomach is present which tigers the release of bile and pancreatic juice
Bile salts emulsify fats
Lipase converts fats to fatty acids and glycerol
Absorption of nutrients
Monosaccharides- passive diffusion
Disaccharides, dipeptides and tripeptides- active transport
Monosaccharides and amino acids- pass directly into capillaries
Fatty acids- pass into lymphatic vessels
