The Small Intestine

Question 1

Retroperitoneal Organs

Answer 1

Not covered by peritoneum
• Pancreas
• Duodenum
• Ascending and descending colon
• Rectum

Question 2

Small Intestine

Answer 2

• Longest segment of the alimentary canal
• Most of the digestion
• Most of the absorption
• Uses peristalsis to move chyme along the canal
• 3 subdivisions: Duodenum, Jejunum, ileum

Question 3

Duodenum

Answer 3

• Receives digestive enzymes and chemicals from the
accessory digestive organs:
-Pancreas, Gallbladder, Liver
• All enter through the hepatopancreatic ampulla which
opens into the duodenum through the major duodenal
papilla

Question 4

Absorption in Small Intestine

Answer 4

• Very large surface area:
• Long length
• Circular folds: force chyme to spiral
• Villi: contain blood and lymphatic vessels, absorptive
cells
• Microvilli: on the surface of epithelial cells, contains
enzymes to complete final digestion

Question 5

Lacteals

Answer 5

• Absorb digested fats
• Go into general circulation before reaching the liver
unlike other digested material
• Bypasses “first pass metabolism”

Question 6

Small Intestine Cells

Answer 6

• Absorptive Enterocytes
• Absorb digested material
• Goblet cells
• Secrete lubricating mucus
• Enteroendocrine cells
• Secrete hormones for bile and enzyme release

Question 7

how does the duodenum receive digestive enzymes from the pancreas and bile from liver/gall bladder

Answer 7

via the main pancreatic duct and bile from the liver and gallbladder via the bile duct. These ducts enter the wall of the duodenum where they form a bulb called the hepatopancreatic ampulla

Question 8

major duodenal papilla

Answer 8

how the hepatopancreatic ampulla opens into the duodenum

Question 9

Arterial supply to the small intestine comes primarily via

Answer 9

the superior mesenteric artery

Question 10

from the superior mesenteric vein, the nutrient-rich venous blood from the SI drains into the what and is carried where?

Answer 10

hepatic portal vein, which carries it to the liver.

Question 11

The small intestine is innervated by what enteric neurons.

Answer 11

Parasympathetic fibers from the vagus and sympathetic fibers from the thoracic splanchnic nerves

Question 12

The wall of the small intestine has three structural modifications that amplify its absorptive surface enormously:

Answer 12

circular folds, villi, and extensive microvilli
(Because most absorption occurs in the proximal region of the small intestine, these specializations decrease in number toward the distal end.)

Question 13

The circular folds

Answer 13

• > permanent, transverse ridges of the mucosa and submucosa
• > Besides increasing the absorptive surface area, these folds force the chyme to spiral through the intestinal lumen, slowing its movement and allowing time for complete absorption of nutrients.

Question 14

Villi are

Answer 14

• fingerlike projections of the mucosa
• covered by a simple columnar epithelium made up primarily of absorptive cells, called enterocytes, specialized for absorbing digested nutrients
• Within the core of lamina propria in each villus is a network of blood capillaries and a wide lymphatic capillary called a lacteal

Question 15

The end products of the digestion of carbohydrates and proteins enter ?

Answer 15

the blood capillaries of the core of lamina propria in each villus and go to liver

Question 16

absorbed fats enter ?

Answer 16

the lacteals of the core of lamina propria in each villus
-do not go directly to the liver, but rather travel through the lymphatic vessels and empty into the venous system near the brachiocephalic vein

Question 17

microvilli function/location

Answer 17

The apical surfaces of the absorptive enterocytes have many microvilli
-Besides amplifying the absorptive surface, the plasma membrane of these microvilli contains enzymes that complete the final stages of the breakdown of nutrient molecules.

Question 18

Absorptive enterocytes structure

Answer 18

• contain many mitochondria because the uptake of digested nutrients is an energy-demanding process.
• They also contain an abundant endoplasmic reticulum, which assembles the newly absorbed lipid molecules into lipid-protein complexes called chylomicrons

Question 19

Goblet cells

Answer 19

secrete onto the internal surface of the intestine a coat of mucus that lubricates the chyme and forms a protective barrier that prevents enzymatic digestion of the intestinal wall.

Question 20

Enteroendocrine cells

Answer 20

The enteroendocrine cells of the duodenum secrete several hormones, which signal the gallbladder to release stored bile and the pancreas to secrete digestive enzymes and a bicarbonate-rich juice to neutralize the acidic chyme entering the duodenum.

Question 21

intestinal crypts location/function

Answer 21

Between the villi, the mucosa contains invaginations called intestinal crypts
-The epithelial cells that line these crypts secrete intestinal juice, a watery liquid that mixes with chyme in the intestinal lumen

Question 22

Two other cell types(besides epithelial cells) are found within the intestinal crypts:

Answer 22

1. Undifferentiated epithelial cells: line the intestinal crypts and renew the mucosal epithelium by dividing rapidly and moving continuously onto the villi

Question 23

why is such rapid replacement of the inner epithelium of the small intestine necessary (renewed every 3–6 days)

Answer 23

epithelial cells cannot withstand the destructive effects of the digestive enzymes in the intestinal lumen for long.

Question 24

Mature Paneth cells location/function

Answer 24

• found at the base of the crypt.
• These epithelial cells secrete enzymes that destroy certain bacteria and may help determine which kinds of bacteria live in the intestinal lumen.

Question 25

duodenal glands location/function

Answer 25

• The submucosa of the small intestine is a typical connective tissue. In the duodenum only, it contains a set of compound tubular duodenal glands, whose ducts open into the intestinal crypts
• secrete an alkaline, bicarbonate-rich mucus that helps neutralize the acidity of the chyme from the stomach and contributes to the protective layer of mucus on the inner surface of the small intestine.