- Dietary CHO, fats and proteins are large complex molecules that cannot be absorbed. - They must be digested to small simple molecules (monosaccharides, monoglycerides and amino acids) which are easily absorbed from the intestine.

Biochemistry 🧪 Flashcards by Ahmed Farag

Introduction

Dietary CHO, fats and proteins are large complex molecules that cannot be absorbed.
They must be digested to small simple molecules (monosaccharides, monoglycerides and amino acids) which are easily absorbed from the intestine.

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CHO digestion

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Triglycerides digestion

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Triglycerides digestion

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triglycerides digestion

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phospholipids digestion

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cholesterol esters digestion

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Protein digestion

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Protein digestion

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protein digestion

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what is the PH of salivary secretions?

6.2 - 7.6

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what are the components of salivary secretions?

Electrolytes: mainly Na+, K+, Ca++, Cl-.

Organic contents: Salivary enzymes (salivary amylase, lingual lipase) and mucus.

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what are the effects of salivary secretions?

Starts the digestion of CHO and fat:

Salivary amylase:
- partially digests starch and glycogen to dextrin and few maltose.
- It acts on cooked starch.

Lingual lipase:
- It is secreted by the dorsal surface of the tongue (Ebner’s glands).
- It helps fat digestion in new-born infants (their pancreatic lipase is still not developed).

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effect of salivary secretions on CHO digestion

Salivary amylase:
- partially digests starch and glycogen to dextrin and few maltose.
- It acts on cooked starch.

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effect of salivary secretions on Fat digestion

Lingual lipase:
- It is secreted by the dorsal surface of the tongue (Ebner’s glands).
- It helps fat digestion in new-born infants (their pancreatic lipase is still not developed).

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what is the PH of gastric secretions?

1 - 3

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what are the components of gastric secretions?

Inorganic: mainly HCl

organic: Gastric enzymes (lipase, pepsin, gelatinase, renin), mucus, Intrinsic factor.

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what are the effects of gastric secretions?

affects CHO, dietary fat (triglycerides) & proteins

effect of gastric secretions on CHO

No carbohydrate digesting enzymes available in gastric juice.
Only, HCl can partially hydrolyze the disaccharides and polysaccharides.

effect of gastric secretions on fat (triglycerides digestion)

Ingested triglycerides are emulsified then undergo enzymatic hydrolysis by lipase enzymes.
Gastric lipase (pH 3-6) hydrolyses triglycerides containing only the unsaturated fatty acids at the third ester bond to form FFA and α, ꞵ(1, 2)-diglycerides.

what is emulsification?

Breakdown of large fat globule into small ones. In the mouth (chewing), in the stomach (peristaltic contractions) and in intestine (peristaltic movement, bile salts and by lyso-phospholipids).

effect of gastric secretion on proteins

Protein digestion begins in the stomach by:
- gastric HCL
- Pepsin
- rennin
- gelatinase

role of gastric HCL in protein digestion

It causes denaturation of proteins to the easily digested metaproteins.
It activates pepsinogen to pepsin.
It makes pH in the stomach suitable for the action of pepsin.

PH & role of Pepsin in protein digestion

PH: 1.5 - 2.2

An endo-peptidase acting on central peptide bond in which NH2 belongs to aromatic amino acids e.g. phenyl alanine, tyrosine and/or tryptophan.
Secreted as inactive pepsinogen.
Activated by HCL then by autoactivation.

PH and role of rennin in protein digestion

**PH: 4** - A milk-clotting enzyme in the stomach of infants and young animals. - Acts on casein converting it to soluble paracasein, which binds calcium ions forming insoluble calcium paracasinate. - Calcium paracaseinate is then digested by pepsin.

role of gelatinase in protein digestion

liquefies gelatin.

what does the digested food passing from the stomach to duodenum contain?

1) Products of protein digestion: proteoses, peptones and large polypeptides. 2) Products of fat digestion: FFA, 1,2 diglycerides and emulsified undigested fat. 3) Products of CHO digestion: some dextrin, maltose, uncooked partially hydrolyzed starch.

what is the PH of bile secretions?

7.5 - 8.8

what are the contents of bile secretions?

**Inorganic:** includes Na +, K +, Cl-, HCO3-, Ca ++ and Mg++ **Organic:** - Bile salts - bile pigments - Cholesterol - Phospholipid as lecithin - Fatty acids

what are the effects of bile secretions?

- Bile salts assist emulsification of fat by lowering surface tension and exposing large area of triglycerides to the action of pancreatic lipase. - Bile salts are required for the activity of pancreatic phospholipase A2 & cholesterol esterase.

what is the PH of pancreatic secretions?

7.1 - 8.2

what is the composition of pancreatic secretions?

**Inorganic constituents:** mainly NaHCO3 **Organic constituents:** - pancreatic enzymes (amylase, lipase, colipase trypsin & other protein digesting enzymes) - Trypsin inhibitor

what do pancreatic secretions affect?

they affect the digestion of CHO, Triglycerides, phospholipids, cholesterol esters & proteins

effect of pancreatic secretions on CHO

**Pancreatic amylase:** - completely digests starch, glycogen, and dextrin into the disaccharide maltose and few glucose. - It acts on cooked and uncooked starch.

effect of pancreatic secretions on dietary fat (digestion of triglycerides)

**Pancreatic lipase and colipase:** - Pancreatic lipase (the most active lipase) hydrolyzes the 1st and 3rd ester bonds with the production of 2 FFA and β (2ry) monoglyceride (The major digestion products of TG). - β (2ry) monoglyceride may be converted to α (1ry) mono-glyceride by isomerase (slow ineffective process)

effect of pancreatic secretions on digestion of fat (phospholipids)

**Phospholipase A2:** - It is activated by trypsin & requires bile salts and Ca++ for activity. - It hydrolyzes glycero-phospholipids by removing FA in position 2 (ꞵ) to form lyso-phospholipids.

effect of pancreatic secretions on fat (digestion of cholesterol esters)

**Pancreatic cholesterol esterase (cholesterol ester hydrolase):** - It hydrolyzes cholesterol ester into FA and free cholesterol. - It requires bile salts for its activity

pancreatic secretions affecting on protein digestion

what is the PH of intestinal secretions?

7 - 8

what are the contents of intestinal secretions?

Alkaline fluid containing Na+, K+, CL-, HCO3, Mucus and Enzymes

what are the effects of intestinal secretions?

affects CHO, fat & proteins

effect of intestinal secretions on CHO

Maltase, lactase and sucrase hydrolyze the corresponding disaccharides to produce glucose, fructose, and galactose.

effect of intestinal secretions on fat

**Intestinal lipase:** Act within intestinal mucosal cells where it hydrolyze the absorbed primary monoglyceride forming glycerol and FFA. **Intestinal phospholipase:** complete the hydrolysis of lysophospholipids to glycerol, FA, phosphoric acid and nitrogenous base.

effect of intestinal secretions on protein