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BIOM20002 - HSF > Lecture 46 - Absorption of Nutrients > Flashcards

Lecture 46 - Absorption of Nutrients Flashcards

0
Q

Describe the nutrient makeup of a carrot

A

Even though it seems bland, it contains:

Lipid: cell membrane

Protein: structures in the cell

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1
Q

What are the basic food groups

A

Carbohydrates
Proteins
Fats
Vitamins and minerals

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2
Q

Describe what has to happen before nutrient absorption?

Describe how this is overcome

A

1/ get to the right location (Jejunum)
- peristalsis

2/ broken down into small enough molecules

  • chemical
  • mechanical

3/ physical contact with the mucosa
- villi for increased SA

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3
Q

Describe the overall process of digestion

A

Macronutrients –> molecules

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4
Q

How is food chemically digested?

Where is this happening?

A

Must first be broken up to increase surface area

Digestive enzymes coming into contact with the small food particles

Motor activity to mix the enzymes with the food

Most prominent in duodenum and upper Jejunum

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5
Q

Where do digestive enzymes come from?

A

Exocrine Pancreas

To a lesser extent: mucosal epithelial cells

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6
Q

Describe the function of digestive enzymes from the mucosal epithelial cells

A

Enzymes embedded in the membrane of the mucosa

Exposed to the food particles in the lumen for digestive action

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7
Q

Where does intestinal epithelium begin and end?

A

Inside of lip

Anus

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8
Q

Describe the epithelium in the mouth and oesophagus

A

Impervious
Doesn’t absorb anything
Doesn’t secrete anything

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9
Q

Describe the requirements of the epithelium of the stomach

A

Secretory

Protective (against acid)

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10
Q

What is the name for the cells in the small bowel?

A

Enterocytes

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11
Q

Describe the surface epithelium of the small bowel

A

Crypts/ pits and villi

Connected by tight junctions –> strong barrier

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12
Q

Describe the life of an enterocyte

A 
Stem cells at base of the crypt
Continually made
Migrate up to tip of villous
- change function as they move up
Shed off
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13
Q

What is the structure of an enterocyte?

A

Apical surface

  • brush border
  • absorption

Basolateral surface
- diffusion of molecules out into Lamina propria

Different functions at each side

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14
Q

What is the function of enterocytes in the crypt and at the tip of the villous?

How does this change?

A

Crypt: secretory

Villous: absorption

Change in the protein expression in the cell as they migrate up

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15
Q

What is gluten?

A

Protein found in most grains

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16
Q

What is coeliac disease?

A

Autoimmune reaction in some people when gluten is eaten

Shedding of the epithelium from the villous in the small bowel

The symptoms resolve quickly after a few days

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17
Q

What is in saliva that starts to break down food?

Describe how this functions

A

Amylase

Breaks some of the bonds within sugars and starches (polysaccharides)

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19
Q

What is the role of secretin?

What causes its release?

A

Release: acid in the small intestine

Function:

  • HCO3- secretion
  • inhibits acid secretion
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19
Q

Which sugars can be absorbed by the intestinal epithelium?

A

Glucose
Fructose
Galactose

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20
Q

What is the role of CCK?

A

Brings about release of:

  • bile (gall bladder contraction)
  • pancreatic enzymes
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21
Q

Can disaccharides be absorbed?

A

No, only monosaccharides can be absorbed

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22
Q

What is happening in lactose intolerance?

A

No lactase gene
Can’t break down lactose (a disaccharide)
Diarrhoea

As we age, we have reduced tolerance of lactose

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23
Q

How is glucose transported across the apical surface of the enterocyte?

A

Na+/glucose linked transporter
SGLT

Across apical surface of enterocyte

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24
Q

How is galactose transported into the enterocyte?

A

Same as glucose

SGLT

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25
Q

How is fructose transported across the apical surface of the enterocyte?

A

GLUT 5

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26
Q

How is glucose transported across the basal surface of the enterocyte?

A

GLUT2

27
Q

How is fructose transported across the basal surface of the enterocyte?

A

GLUT 2

28
Q

How is galactose transported across the basal surface of the enterocyte?

A

GLUT 2

29
Q

What is important about high fructose diets?

A

Skews expression towards GLUT 5 transporters

Associated with disease

30
Q

How can protein be absorbed?

A

Must be first broken down into short peptides and amino acids

31
Q

What are endopeptidases?

What are some examples?

A

Breaks peptide bonds within an amino acid chain

Trypsin
Pepsin
Cymotrypsin

32
Q

Where is protein first broken down?

A

In the stomach

No pepsin in the mouth

33
Q

What happens to lipids in the stomach?

A

Chyme is separated out

Lipids float to the top (fundus

34
Q

Describe the release of pepsin

A
  1. Vagal activity and gastrin bring about release
  2. Released by chief cells as pepsinogen
  3. Activated the acid in the stomach
35
Q

What is the function of exopeptidases?

List some examples

A

Cleave terminal amino acids on peptides

Carboxypeptidases
Aminopeptidases

36
Q

Which enzymes can break a peptide down into single amino acids?

A

Exopeptidases

37
Q

What secretes pepsin?

A

Chief cells

38
Q

Describe the release of trypsin

A
  1. Released by pancreas under CCK signalling
  2. Initially inactive - PROTRYPSIN (so as to prevent digestion of pancreas)
  3. Endopeptidase activity
39
Q

What is pancreatitis?

A

Blockage of pancreatic duct
Proteases activated whilst still in the pancreas
Start to break down the pancreas

Acute then extreme pain
Death

40
Q

How are amino acids absorbed across the apical surface?

A

Na+ coupled cotransporters

41
Q

How do di and tri peptides cross the apical surface?

A

H+ coupled transporters

42
Q

How do amino acids cross the basal surface?

A

Na+ coupled co transporters

44
Q

How can polypeptides get across the apical surface?

A

Endocytosis

45
Q

Describe the general digestion of fat

A

Triglycerides:

  • Lipases break TGs into:
  • monoglyceride + free fatty acids

Phospholipids:
broken down by phospholipases

Cholesterol:
down not require breakdown

46
Q

What is the structure of a triglyceride?

A

Glycerol + 3 fatty acids

47
Q

What leads to the release of bile into the duodenum?

A
  1. Fat in the stomach
  2. Release of CCK from duodenum
  3. Contraction of gall bladder
  4. Release of bile from common bile duct
48
Q

How does cholesterol get into cells?

A

Active transport

49
Q

Describe the breakdown and subsequent uptake of fat

A
  1. Bile coats large fat droplets –> emulsification
  2. Pancreatic lipase & Colipase break down fats into monosaccharides –> micelles
    3a. Monoglycerides, fatty acids diffuse into cells
    3b. Cholesterol transported in
50
Q

What is Colipase?

How is it activated?

A

Trypsin activates Colipase

Colipase activates lipase

51
Q

What happens to free fatty acids, cholesterol and monoglycerides once inside the enterocyte?

A

Combine to form chylomicrons

Chylomicrons cross basolateral membrane via exocytosis

Chylomicrons enter lymphatic lacteals

52
Q

What is a lacteal?

A

A lymphatic capillary that absorbs fats in the villi

53
Q

What happens to water in the lumen of GIT?

A

Mostly reabsorbed:

  • jejunum
  • ileum
  • colon
54
Q

How much water is reabsorbed per day?

How much is excreted in the faeces?

A

8-9 L

200 ml

55
Q

Which diseases occur when there is a failure to control water transport?

A

Cholera
Typhoid
Clostridium difficile
Rotavirus

56
Q

How is cellulose digested?

Where?

A

Not digested
Fermented

Commensal bacteria carry this out

Caecum and proximal colon

57
Q

What are the products of cellulose fermentation?

A

Short chain fatty acids (SCFAs)

58
Q

Where does the energy required by the colonic mucosa come from?

A

The fermentation of cellulose

59
Q

What else do the bacteria of our microbiome produce?

A

Neurotransmittes

Other bioactive substances

60
Q

What are some of the pancreatic enzymes that CCK brings about the release of?

A
  • protrypsin
  • chymotrypsinogen
  • procarboxypeptidase
61
Q

How is the acid maintained as acidic?

A

Parietal cells of the stomach pump H+ into the lumen of the stomach

62
Q

Describe the release of trypsin

A
  1. CCK stimulates pancreas
  2. Protrypsin released from pancrease
  3. Activated by a protein in the brush border
63
Q

Describe the release of chymotrypsinogen and procarboxypeptidase

A
  1. CCK stimulates pancreas
  2. Release from pancreas into duodenum
  3. Activated by trypsin
64
Q

Where is CCK released from?

A

Enteroendocrine cells of the duodenum

65
Q

List the proteases

A 
Pepsin
Trypsin
Chymotrypsin
Carboxypeptidase
Aminopeptidase

BIOM20002 - HSF (60 decks)

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