Small Bowel

Question 1

Outline the gross anatomy of the small bowel

Answer 1

• 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

Question 2

3 sections of small bowel

Answer 2

Duodenum
Jéjunum
Ileum

Question 3

Structure of small bowel

Answer 3

4 layers:
Mucosa- secretory epithelium
Submicosa- areolar connective and elastic tissues
Muscular- smooth muscular. Outer longitudinal and inner circular
Serosa- peritoneum

Question 4

Functions of serosa

Answer 4

2 layers, visceral and parietal.
Visceral covers abdo organs
Parietal covers abdo wall

Produces and secrets serous fluid

Question 5

Mucosa Sub-Layers

Answer 5

Mucous membrane
Lamina Propria
Muscularus Mucosa

Question 6

Duodenum

Answer 6

C shape around head of pancreas
Hepatopancratic opens into second part
Subdivided into four sections

Question 7

Duodenal relation - 1st part

Answer 7

Ant- liver and gallbladder
Post- portal vein and common bile duct
Infer - head of pancreas

Question 8

Duodenal relations - 2nd part

Answer 8

Rt latéral- rt kidney and hepatic flexure

Med- head of pancreas

Question 9

Duodenal relations -3rd part

Answer 9

Pos- right psoas muscle, IVC and abdominal aorta
Ant- root of mesentery
Sup- head of pancreas

Question 10

Duodenal relations-4th part

Answer 10

Ant- transverse colon
Sup- head of pancreas
Post- left psoes muscle, left renal vein

Question 11

Jéjunum Gross anatomy

Answer 11

Second portion of small bowel
Approx 2m long
Continuous with dudenojejunal flexure and ilium
Calibrea wider than ilium

Question 12

Ilium gross anatomy

Answer 12

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

Question 13

Blood supply

Answer 13

Superior mesenteric artery supplies ALL of the small bowel
Duodenum received blood from hepatic artery
Venous drainage superior mesenteric artery

Question 14

Functions of small bowel

Answer 14

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)

Question 15

What is CCK?

Answer 15

CCK-Cholecystokinin

Secreted in response to fat in chyme

Question 16

What is Secretin?

Answer 16

secreted in response to acidic chyme

Question 17

Chemical digestion in small bowel

Answer 17

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

Question 18

Intestinal Juice (Succus entericus)

Answer 18

Secreted by intestinal glands

Question 19

What makes up intestinal juice (Succus entericus)

Answer 19

Water
Mucous
Mineral salts

Question 20

Digestion functions of intestinal juice

Answer 20

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

Question 21

Carbohydrate digestion

Answer 21

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

Question 22

Protein digestion’s

Answer 22

Trypsinogen and chymotrypsinogen are inactive enzymes found in pancreatic juice

Come into contact with enterokinase and become activitated as tripsin and chymotrypsin

Question 23

Fat digestion

Answer 23

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

Question 24

Absorption of nutrients

Answer 24

Monosaccharides- passive diffusion
Disaccharides, dipeptides and tripeptides- active transport
Monosaccharides and amino acids- pass directly into capillaries
Fatty acids- pass into lymphatic vessels

Question 25

What is peristalsis

Answer 25

Waves of contraction and relaxation in the muscular layer
Longitudinal and circular fibres act as antagonistic pairs
Pyloric sphincter remains closed whilst bolus travels along small bowel