12.3.4 Human Nutrition: Absorption

Question 1

Human Nutrition: Absorption

Answer 1

• The small intestine is lined with folds that contain even smaller folds within them called villi. These villi greatly increase the surface area of the small intestine for the absorption of nutrients. Amino acids and monosaccharides pass through the
epithelial cells of the villi and enter the bloodstream.
• Glycerol and fatty acids enter the epithelial cells where they are used to reform triglycerides and are packaged into chylomicrons. The chylomicrons enter the lymphatic system through the lacteal, a vessel of the lymphatic system found in the interior of a villus.
• The regulation of digestion by hormones is necessary to ensure that digestive juices are present only when needed.

Question 2

villi

Answer 2

• The lining of the small intestine is highly folded, resulting in an increased surface area that maximizes nutrient uptake. Within the folds of the lining of the small intestine are more folds called villi. Villi are covered with specialized epithelial cells that have microscopic projections on the surface called microvilli.

Question 3

lacetal and chylomicrons

Answer 3

• Molecules enter and pass through the microvilli and enter the capillaries or the lacteal, which transports them throughout the body.
• Amino acids and monosaccharides enter the bloodstream through capillaries located within a single villus.
• Triglycerides, on the other hand, are broken down into
  glycerol and fatty acids, which are absorbed by the epithelial cells. In the epithelial cells, as shown in the diagram to the left, glycerol and fatty acids will be reformed into triglycerides, which are then mixed with cholesterol and coated with proteins to form chylomicrons. Chylomicrons are then transported out of the cells and enter the lacteal. The chylomicrons will travel through the lymphatic system and eventually enter the bloodstream.

Question 4

note

Answer 4

• The regulation of digestion is necessary to ensure that
  digestive juices are present only when needed.
• The smell and taste of food stimulates the stomach to secrete gastric juice. Substances in food then stimulate the stomach to secrete the hormone gastrininto the bloodstream. Gastrin will stimulate the stomach to continue producing gastric juice.
• As acid chyme enters the small intestine from the stomach, the duodenum secretes the hormone secretin. Secretin stimulates the pancreas to produce bicarbonate, which neutralizes acid chyme.
• When amino acids and/or fatty acids enter the small intestine the hormone cholecystokinin (CCK) is secreted. CCK stimulates the pancreas to release pancreatic enzymes and stimulates the gall bladder to release bile.

Question 5

Initial circulation of amino acids and monosaccharides occurs through the __________, and that of triglycerides occurs through the __________.

Answer 5

• blood stream, lymphatic system

Question 6

Which of the following best describes the role of enterogastrones?

Answer 6

• They are secreted in the small intestine, travel through the bloodstream, and exert an effect on the pancreas.

Question 7

Prior to absorption by the epithelial system, triglycerides

Answer 7

• are broken down into glycerol and fatty acids.

Question 8

Ingestion of food stimulates the secretion of

Answer 8

• gastrin by the stomach.

Question 9

Which of the following is / are not stimulated by the hormone cholecystokinin?

i. release of pancreatic amylase
ii. release of bile
iii. production of gastric juice
iv. production of bicarbonate by the pancreas

Answer 9

• iii, iv

Question 10

The role of the villi in the small intestine is analogous to

Answer 10

• alveoli in the lungs.

Question 11

Donating blood two or three hours after eating a bacon double cheeseburger, a large order of french fries, and a shake might not be the best idea. It may shock both the donor and the phlebotomist—why?

Answer 11

• The presence of chylomicrons in the blood will give it a milky appearance.

Question 12

Once food is digested, nutrients need to be absorbed into the bloodstream. There are numerous ways to move nutrients from the lumen of the intestine into the blood. Which nutrient cannot be moved into the bloodstream by diffusion or active transport?

Answer 12

• lipids