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Biology A Level > Digestion > Flashcards

Digestion Flashcards

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1
Q

Amylase

A
  • optimum pH: 7
  • starch -> maltose
  • produced in the salivary glands, released into the mouth
  • produced in the pancreas, released into the duodenum
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2
Q

Pepsin

A
  • optimum pH: 1.5
  • protein -> polypeptide
  • produced by the gastric glands, released into the stomach
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3
Q

Describe the pH of the stomach

A
  • provided by HCl

* mucus lining provides protection

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4
Q

Maltase

A
  • optimum pH: 7
  • maltose -> glucose
  • produced in the pancreases, released into the duodenum
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5
Q

Lipase

A
  • optimum pH: 7
  • lipid -> lipid components
  • produced in the stomach and pancreas, released into duodenum
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6
Q

Trypsin

A
  • optimum pH: 7

* polypeptides -> amino acids

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7
Q

Bile function

A
  • neutralises pH
  • sodium hydrogencarbonate (hydrogencarbonate ions -> alkaline)
  • secreted by the pancreas and by Brunner’s glands in the duodenum
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8
Q

Brunner’s glands

A

• lead to crypts of Lieberkuhn

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9
Q

Crypts of Lieberkuhn

A
  • tubular invaginations of glandular epithelia at the base of vili
  • close to the base, there are actively dividing stem cells
  • Paneth cells
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10
Q

Paneth cells

A

secrete microbial agents to protect stem cells in crypts of Lieberkuhn from infection

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11
Q

Bile

A
  • produced by the liver
  • stored in the gall bladder
  • released via the bile duct
  • neutralises HCl
  • bile salts emulsify fats
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12
Q

Emulsification of fats

A

Break fat globules into tiny droplets, increasing SA

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13
Q

Ileum function

A

Absorption

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14
Q

Ileum adaptations

A
  • many folds, convolutions and twists to increase SA
  • thin walls
  • high capillary density -> carries sugars, AAs, minerals, vitamins (A, C and E) and water-soluble substances
  • villi
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15
Q

Villi adaptations

A
  • épithélial cells with lots of mitochondria

* microvilli project themselves into the lumen of the small intestine -> forms a brush border

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16
Q

Absorption

A

Takes place via diffusion and active transport

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17
Q

Why is absorption of lipids hard?

A
  • large and hydrophobic long-chain fatty acids are not easily suspended in the watery intensional chyme
  • bile salts and lecithin enclose them in a micelle
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18
Q

Micelle

A
  • tiny polar sphere with hydrophilic ends facing the watery environment and hydrophobic tails turned into the interior
  • creates a receptive environment for long-chain fatty acids
  • can easily squeeze between microvilli and get v. Close to the luminal cell surface
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19
Q

Why are micelles necessary?

A

lipids would sit on the surface of the chyme and never come into contact with the absorptive surfaces of the epithelial cells

20
Q

Leaving the micelle

A

Having reached the cell surface, lipid substances exit the micelle and are absorbed by simple diffusion

21
Q

The process of lipid exocytosis from epithelial cells

A

1) fatty acids and monoglycerides leave micelle and enter epithelial cells
2) fatty acids link to form triglycerides
3) fatty globules combine with proteins to form chylomicrons, inside the Golgi
4) chylomicrons are extruded from the epithelial cells and enter a lacteal
5) lymph in the lacteals transports chylomicrons away from intestine; exocytosis

22
Q

Describe the stomach

A
  • dotted with pits leading to tubular gastric glands

* gastric glands secrete gastric juices

23
Q

Gastric juices

A
  • mainly water
  • mucus
  • HCl
  • pepsinogen
24
Q

Mucus

A
  • from goblet cells

* protection and lubrication

25
Q

HCl

A
  • from oxyntic cells

* aka pariétal cells

26
Q

Pepsinogen

A
  • from chief cells
  • aka. peptic, zymogen cells
  • a precursor; inactive form of an enzyme that is converted by HCl to pepsin (active enzyme)
27
Q

Pepsin

A
  • large polypeptides -> small polypeptides

* endopeptidase

28
Q

Endopeptidases

A
  • breaks the peptide links within a polypeptide chain; does not break the terminal peptide links
  • produces almost no individual AAs
  • creates more ends on which exopeptidases can work, with increased SA
  • e.g. pepsin, trypsin
29
Q

Trypsin

A

Derived from trypsinogen

30
Q

Mechanical digestion

A

Muscles in the stomach wall churn contents, covering them in enzymes

31
Q

Acid chyme

A
  • uniform creamy paste

* creates by combining chemical and mechanical digestion

32
Q

Exopeptidases

A
  • break the terminal peptide bonds
  • e.g. aminopeptidase
  • e.g. carboxypeptidase
33
Q

Aminopeptidase

A

Acts on terminal peptide bonds at the amino end of the polypeptide chain

34
Q

Carboxypeptidase

A

Acts on terminal peptide bonds at the carboxyl end of the polypeptide chain

35
Q

Dipeptidases

A
  • secreted by enterocytes into the small intestines
  • hydrolyse dipeptides
  • membrane-bound
36
Q

Enterocytes

A

Intestinal lining cell

37
Q

Nucléase

A

Nucleic acids -> nucleotides

38
Q

Chymotrypsin

A

Proteins -> small polypeptides

39
Q

Entérokinase

A

Trypsinogen -> trypsin

40
Q

Sucrase

A

Sucrose -> α-fructose + α-glucose

41
Q

Lactase

A

Lactose -> α-glucose + β-galactose

42
Q

Peptidases

A

Peptides -> amino acids

43
Q

Proteases

A

Proteins -> polypeptide chains

44
Q

Nucleotidases

A

Nucleotides -> bases, sugars and phosphates

45
Q

Water in digestion

A
  • essential for hydrolytic breakdown of food

* transport medium for secretions

Biology A Level (45 decks)

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