digestive enzymes and hormones

DIGESTIVE ENZYMES AND DIGESTIVE ENZYMES AND HORMONES

Jessica C. Largado

Camille Lee R. Mananggit

Functions of SecretoryGlands

1. Secretion of digestive enzymes

2. Production of mucus

Lubrication

Protection of alimentary tract Protection of alimentary tract

A. SALIVARY SECRETION

Saliva-mixed secretion of salivary glands

MAIN SALIVARY GLANDSMAIN SALIVARY GLANDS

1. Parotid

2. Submaxillary or Mandibular

3. sublingual

Sublingual gland

Major Types of Secretion

1. Serous secretion- ptyalin or salivary amylase

-starch splitting enzyme

Major Types of Secretion

2. Mucus secretion- mucus

-for lubrication

B. GASTRIC SECRETION

Components:

1. pepsinogen-active form of pepsin

-protein digestion

2. mucus- lubricated ingested food

-protects mucosa

3. HCO3- protects mucosa against acid and pepsin

4. Intrinsic factor- absorption of Vit B12

5. Rennin- milk coagulation

6. Gastric lipase- hydrolyze fats

Types of Glands

1. Cardiac Gland

-secrete mucus

2. Fundic gland

-gastric/oxyntic gland-gastric/oxyntic gland

Types of Glands

-has five types of cells

1. parietal cells-secrete HCl

2. chief cells or peptic cells-secrete pepsinogenpepsinogen

3.mucous cells-secrete mucus

4. endocrine D cells-secrete somatostatin

5. entero-chromaffin-like cells-histamine

Types of Glands

3. Pyloric gland-has G cells

Types of Glands

Cardiac gland

Fundic gland

Types of Glands

Pyloric gland

Types of Glands

Types of Glands

Stimulation of Acid Secretion

1. Gastrin

-from G cells

-stimulated by

protein products inprotein products in

the stomach

Stimulation of Acid Secretion

2. Acetylcholine

-released from cholinergic neurons

-stimulates acid production in the same way as gastrin

3. Histamine

-released from ECL cells

-directly contacts the parietal cells

INHIBITION OF ACID SECRETION

Stomach secretes acids at mealtime

Antrum contents approaches Ph 2.0

Stomach secretes acids at mealtime

Antrum contents approaches Ph 2.0

D cells secrete somatostatin

Inhibition of gastrin & histamine release

Inhibition of acid production

D cells secrete somatostatin

Inhibition of gastrin & histamine release

Inhibition of acid production

C. Secretion of the Small Intestine

1. Crypt of Lieberkuhn-secrete enterokinase and amylase

-has two types of cells

1.Goblet cells - secrete

mucusmucus

2. Enterocytes – secrete

water and electrolytes

Stimulation of Acid Secretion

Brunner’s Gland

-duodenal gland

-secrete large amount of alkaline mucus in response toresponse to

1. tactile or irritating stimuli

2. vagal stimulation

3. GI hormone-secretin

Stimulation of Acid Secretion

Digestive Enzymes

1. Peptidase-split small peptides into AA

2. Four enzymes that split disaccharide into monosaccharide

a. sucrase

b. maltaseb. maltase

c. isomaltase

d. lactase

3. Intestinal lipase-split neutral fats into glycerol and FA

HorMones

1. Gastrin- stimulates gastric glands to secrete pepsinogen and hydrochloric acid

-presence of peptides and amino acids in gastric lumenin gastric lumen

2. Secretin- signals the secretion of sodium bicarbonate in the pancreas

-stimulates bile secretion in the liver

-acidic pH in the lumen of small intestine

HorMones

3. Cholecystokinin- stimulates the release of digestive enzymes in the pancreas

-emptying of bile in the gall bladder

-presence of fatty acids and amino -presence of fatty acids and amino acids in the small intestine

4. Gastric Inhibitory Peptide- decrease the stomach churning

-slowing the emptying of the stomach

-presence of fat and glucose in small intestine

HorMones

5. Motilin- increase the migrating myoelecticcomponent of gastrointestinal motility

-secretion is associated with fasting

6. Ghrelin- appears to be a strong stimulant for 6. Ghrelin- appears to be a strong stimulant for appetite and feeding

-secretion peaks prior to feeding and diminishes with gastric filling

D. EXOCRINE PANCREAS

1. Endocrine-hormone secreting

2. Exocrine- enzyme and bicarbonate secreting partsparts

Secretion of Sodium Bicarbonate

Carbon dioxide combines with water through carbonic anhydrase to form carbonic acid

Carbonic acid dissociates into bicarbonate (actively transported into lumen) and hydrogen

Hydrogen ion exchanged for sodium ion

Sodium ion diffuses into lumen

Sodium and bicarbonate attract water, forming bicarbonate solution

Secretion of Pancreatic Enzymes

1. Zymogen granules

a. inactive zymogen -attack membranes

eg. Proteases

b. active zymogen -do not attack membranesb. active zymogen -do not attack membranes

eg. Lipase, amylase

Secretion of Pancreatic Enzymes

2. Proteolytic enzymes

1. trypsin

2. chymotrypsin

3. carboxypeptidase3. carboxypeptidase

4. ribonucleases

5. deoxyribonuclease

Regulations of Pancreatic Secretion

1. Nervous Regulation

2. Hormonal Regulation

1. Cholecystokinin (CCK)

2. Secretin2. Secretin

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