3.3 Digestion + Absorption Flashcards

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1
Q

Define digestion

A

The hydrolyisis of polymers to monomers for absorption across cell membranes

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2
Q

What do all membrane-bound disaccaridases do to disaccharides

A

Hydrolyse glycosidic bonds within the disaccharide to form the two monosaccharides

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3
Q

What does maltase hydrolyse into what

A

Maltose into two glucose molecules

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4
Q

What does lactase hydrolyse into what

A

Lactose into glucose and galactose

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5
Q

What does sucrase hydrolyse into what

A

Sucrose into glucose and fructose

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6
Q

Function of amylase

A

Hydrolysises glycosidic bonds within starch to form maltose

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7
Q

Outline the three stages to absorption of glucose

A
  • Sodium ions activly transported out of ileum epithelial cell into blood
  • Glucose co-transported with sodium ions from gut to ileum epithelial cell
  • Glucose moves by faccilitated diffusion from ileum epithelial cell to blood
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8
Q

Explain the first stage of abosoption of glucose

A
  • Sodium ions actively transported out of ileum capillary cell into blood by sodium-potassium pump
  • ATP hydrolysis changes the carrier proteins shape, to allow movement of sodium ions
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9
Q

Explain the second stage of glucose absorption

A
  • Maintains a diffusion gradient for sodium ions to enter the ileum epithelial cell from the gut through carrier proteins by faccilitated diffusion
  • Glucose is co-transported with sodium ions
  • Glucose moved into ileum epithelial cell through a co-transport protein by facillitated diffusion
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10
Q

Explain the third stage of glucose absorption

A

Glucose moves by faccilitated diffusion from ileum epithelial cell to blood capillary through a carrier protein

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11
Q

Explain the function of lipase

A

Hydrolyses ester bonds within triglycerides to form monoglycerides and fatty acids

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12
Q

What are the functions of bile salts

A
  • Emulsify lipids into smaller droplets
  • Form micelles
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13
Q

Why do bile salts emulsify lipids into smaller droplets

A
  • Increase their surface area
  • Faster hydrolysis by lipase
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14
Q

Describe and explain how bile salts form micelles, and their function

A
  • Formed of bile salts, monoglycerides and fatty acids
  • Micelles allow fatty acids to become more soluble
  • Transports monoglycerides and fatty acids to ileum cell wall, to be absorbed into the ileum epithelial cell
  • Fatty acids diffuse through the cell membrane
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15
Q

Explain the first process of lipid absorption

A
  • Micelles contain bile salts and monoglycerides
  • Movement of ileum brings micelles into contact with ileum epithelial cell where it breaks down
  • Monoglycerides and fatty acids are absorbed by epithelial cell via simple diffusion
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16
Q

Outline the stages of lipid absorption

A
  • Micelles
  • Modification
  • Chylomicrons
17
Q

Explain the second stage of lipid absorption

A
  • Monoglycerides and fatty acids transported to smooth endoplasmic reticulum, where they are reformed to triglycerides
  • Triglycerides transported to SER where associated with cholestrol and proteins to form lipoproteins
  • They form chylomicrons
18
Q

Explain the third stage of lipid absorption

A
  • Chylomicrons transported by vesicles to cell-surface membrane
  • **Vesicles fuse with cell-surface membrane **and are released by exocytosis
  • Chylomicrons enter lacteal
19
Q

Function of endopeptididases

A
  • Hydrolyse internal peptide bonds in the middle of polypeptide chains
  • Create more terminal ends and smaller polypeptide chains
  • Increase the surface area for exopeptididases to act
19
Q

Function of exopeptididases

A

Hydrolyse peptide bonds at terminal ends of polypeptide chains

20
Q

Describe the apperance of dipeptidases and where they are produced

A
  • Membrane-bound
  • Duodenum wall
21
Q

Outline the three stages to amino-acid absorption

A
  • Sodium ions activly transported out of ileum epithelial cell into blood
  • Amino-acids move co-transported
  • Amino-acids move into blood
22
Q

Explain the first stage of amino-acid absorption

A
  • Sodium ions activly transported out of ileum epithelal cells into blood by sodium-potasium pump
  • ATP hydrolysis changes the carrier proteins shape, to allow movement of sodium ions
23
Q

Explain the second stage of amino acid absorption

A
  • Maintains a diffusion gradient for sodium ions to move into the ileum epithelial cell from the gut by facillitated diffusion
  • Amino-acids are co-transported with sodium ions
  • Amino-acids move into ileum epithelial cell from the gut through a co-transport protein via facilitated diffusion
24
Q

Explain the final stage in amino-acid absorption

A

Amino-acids move by faccilitated diffusion from the ileum epithelial cell to the blood capillary by a protein carrier