Nutrition: Digestion 1

Question 1

Main features of small intestine?

Answer 1

Small intestine = Duodenum, Jejunum and the Ileum

• The MUCOSA is folded and its surface is made up of Villi.
• The villi are covered by Enterocytes
• ENTEROCYTES are columnal epithelial cells
• Thousands of MICROVILLI are present on the luminal surface of each of the ENTEROCYTES

• The enterocytes are responsible for ABSORPTION and some DIGESTION

• These features lead to an INCREASED surface area for absorption of nutrients

Question 2

How are Molecules Transported Across Membranes?

Answer 2

• SIMPLE DIFFUSION e.g. small non-polar molecules and uncharged polar molecules

• FACILITATED DIFFUSION e.g. via binding to transmembrane proteins, no energy required

• ACTIVE TRANSPORT: Movement against the concentration gradient, requires energy and a carrier protein Primary active transport – movement is directly linked to energy use Secondary active transport – indirectly linked to an electrochemical gradient set up using energy

• RECEPTOR MEDIATED ENDOCYTOSIS - movement into the cell via a specific receptor

• PINOCYTOSIS – ‘cell drinking’ (cell takes in extracellular fluid and soluble molecules)

• EXOCYTOSIS – secretory, movement out of the cell

Question 3

What is Endocytosis and why is it fundamental?

Answer 3

Endocytosis is RECEPTOR mediated, therefore SPECIFIC and SATURABLE

FUNDAMENTAL to neurotransmission, signal transduction and regulation of plasma membrane activities

(EXPLOITED by viruses, bacteria and toxins to gain entry to cells)

Question 4

What is Triacylglycerol (TAG) composed of?

Answer 4

Triacylglycerol (TAG) (or Triglyceride) Composed of three fatty acids (FA) and one molecule of glycerol

Question 5

Name some Monosaccharides, Disaccharides, Polysaccharides.

Answer 5

Monosaccharides e.g. glucose, galactose, fructose Disaccharides e.g. sucrose, maltose, lactose Polysaccharides e.g. starch and glycogen