Macronutrients: Carbs, proteins and fats [Theme 1]

Question 1

Dietary fat

• Hormone regulation
• Function

Answer 1

Triacyglycerol- primary energy storage in adipose tissue.
- Releases fatty acids during fasting

Influx into adipose tissue mediated lipoprotein lipase
- Regulated by insulin

Question 2

Fat digestion in the mouth

- Gland

Answer 2

Lingual lipase

- Secreted by serous glands

Question 3

Fat digestion in the stomach

- Cell secreted from

Answer 3

Gastric lipase

• Secreted from gastric chief cells
• In fundic mucosa

Optimum pH of 3-6
- No need for bile acid or colipase

Question 4

Importance of fat digestive enzymes

Answer 4

Lingual lipase and gastric lipase accounts for:
- 50% of lipid hydrolysis in neonates

• 30% of lipolysis in adults.

Question 5

Bile acids in fat digestion

Answer 5

These acids/ salts are released from the liver.

Amphipathic molecules: cholic and chenodeoxycholic acid.

They dissolve lipids to from mixed micelles.

Question 6

Fat digestion in the small intestines

Answer 6

Pancreatic lipase is secreted with pro-colipase.

Pancreas and activated colipase hydrolyse TG.

Products of hydrolysis passively diffuse across the apical membrane of the microvilli.
- Also through lipid protein transporter mechanisms.

Question 7

Pancreatic lipase

Answer 7

Digestive enzyme in pancreatic juice into the duodenum.

Released with pro-colipase which stabilises it when activated by trypsin into colipase.

Hydrolyses TG to—->

• MG
• Fatty acids
• Glycerols

Question 8

Dietary carbohydrates.

• Polysaccharides
• Disaccharides
• Monosaccharides

Answer 8

Polysaccharides:

• Starch
• non starch: cellulose, chitins, glucans

Disaccharides:

• Lactose
• Sucrose

Monosaccharides:

• Glucose
• Fructose

Question 9

Initial digestion of starch

Answer 9

In the salvia and pancreas by alpha-amylase.
- Forms maltose, maltotriose and alpha-dextrins.

Further digestion by brush border enzymes:

• Gluco-amylase
• Alpha-dextrinase
• Sucrase
• Maltase
• ——> releases glucose and fructose.

Question 10

Sucrase

Answer 10

Brush border digestive enzyme that breaks down sucrose—–> glucose and fructose.

Question 11

Maltase

Answer 11

Brush border digestive enzyme that breaks down maltose—–> 2 alpha glucose molecules

Question 12

Carbohydrate absorption

Answer 12

Only monosaccharidies can be absorbed in the small intestines.

Glucose and galactose absorbed apically through Na+ co-transport.
- Fructose via GLUT-5

All monosaccharides absorbed basolaterally via GLUT-2.

Question 13

Fructose absorption

Answer 13

Fructose enters the small intestinal membrane at the apical side via GLUT-5.

This capacity is limited so excess fructose passes to the colon and can cause osmotic diarrhea.

Question 14

Carbohydrates no absorbed in small intestines

Answer 14

Non-starch polysaccharides- like fibre.
- Soluble fibre like pectin and gum are fermented by bacteria in the colon.

Most oligosaccharides.

Soluble fibre like pectin and gum are fermented by bacteria in the colon.

Question 15

Fibre

Answer 15

A non-starch polysaccharide.

Both soluble and insoluble starch both enhance peristalsis and gastric motility.

• Reduces cholesterol absorption
• Balances population of commensal bacteria

Examples:
Pectin, Gum (soluble)

Question 16

Non-starch polysaccharides

Answer 16

Dietary fibre

Responsible for maintaining weight and colon health.

They can be fermented microbialy to produce gas

Question 17

Short chain fatty acids

Answer 17

These enhance microbial growth in the gut that is ferments NSP.

Acetate- enters peripheral circulation.

Propionate—-> enters liver

butyrate—-> used by colonic cells

Question 18

Daily requirement for protein in diet

Answer 18

0.8g of protein per kg of weight a day.

Question 19

Uses of protein in the body

Answer 19

Maintenance:
to keep us alive

Growth:
Positive tissue accretion (muscles, connective tissue, etc.)

Reproduction:
Growth in reproductive tissue (milk, eggs etc)

Question 20

Protein value in diet

Answer 20

The more similar the source of protein is to the body proteins, the more likely it is to contain all the amino acids required.

Varying the range of protein source is very important for people who have diets missing food groups.

Question 21

Protein digestion in the stomach

Answer 21

HCl and Pepsinogen released in response to gastrin and vagal stimulation.

Protein digested by pepsin.

• Pepsinogen is the inactive form released from chief cells in the stomach.
• Activated as pepsin in pH 2-3

HCl secreted by gastric parietal cells.

Digestion terminated by bicarbonate neutralisation.

Question 22

Pepsin

Answer 22

Gastric protease released by gastric chief cells in its inactive form: pepsinogen.
- Triggered by gastrin and vagal stimulation.

It is activated in the presence of HCl where pH 2-3.

Pepsin is the protease that can break down collagen.

Question 23

Protein digestion by the pancreas

Answer 23

Pancreas releases pro-enzymes:

• Trypsinogen
• Chymotrypsinogen

Pro-enzymes are activated by enterokinase secreted by Brunner glands in the duodenum:

• Trypsin
• Chymotrypsin

Trypsin inhibitor in the secretory vesicles prevent inappropriate activation of trypsin in the pancreas/ pancreatic duct.

Question 24

Absorption of amino acids

Answer 24

Amino acids are enter the cell via cotransport with Na+, on the apical membrane.

The basolateral membrane contains transporters no dependent on Na+.

Question 25

Absorption of Di/tripeptides

Answer 25

They enter the enterocyte in the small intestines apically, co transported with H+.

In the cell, they are cleaved by cytoplasmic peptidase into amino acids.

Amino acids leave basolaterally via transporters not dependent on H+.

Question 26

Absorption of intact proteins

Answer 26

Only very few proteins can go through the membrane bound proteases intact.
- Normal enterocytes do not have the transporters to facilitate the transport.

Neonates can absorb intact proteins in the SI
- immunoglobulins from colostrum

Question 27

Closure of small intestines

Answer 27

Occurs when the small intestine loses its capacity to absorb intact proteins.

Seen after babies stop being able to absorb immunoglobulins.