Digestion of a MealDigestion of a Meal

Digestion of a MealDigestion of a Meal

time taken for food to pass through the digestive system depends on:

1. type of diet

2. amount of fibre present

Digestion of CarbohydratesDigestion of Carbohydratescarbohydrases:

general name for all enzymes that break down carbohydrates

stored in: various glands ex.

salivary pancreas small intestine

liver and muscles to: break down glycogen

Digestion of CarbohydratesDigestion of Carbohydrates

polysaccharides

maltose

maltase→

glucose

→amylase

…..1000’s

starch

glycogen

→ disaccharides → monosaccharides

GluGlu

- made in salivary glands

& pancreas

- works in mouth &

duodenum

- made in duodenum

- work in duodenum

Digestion of CarbohydratesDigestion of CarbohydratesNote: Other disaccharides are also chemically digested into monosaccharides in the duodenum.

sucrose

lactose

sucrase→

lactase→

fructose

glucosegalactose

F Glu

GluGal

glucose

Digestion of ProteinsDigestion of Proteins

proteases: general name for all enzymes

that break down proteins

cannot be stored in active form because:

it would digest organ parts

therefore stored as inactive enzymes

when secreted into the digestive tract, chemicals present activate enzyme

Digestion of ProteinsDigestion of Proteins

Example:

Stomach: + →(inactive enzyme) (active

enzyme)

HClpepsinogen

pepsin

Digestion of ProteinsDigestion of Proteins

protein peptides amino acids

100’s ….- made in stomach

- works in stomach

pepsin trypsin

- made by pancreas

- works in small intestine

Digestion of LipidsDigestion of Lipidslipases:

general name for all enzymes that break down lipids

stored in: various glands: ex.

pancreas small intestine

fatty tissue under the skin

Digestion of LipidsDigestion of Lipids

glycerol fatty acid

fat globulesmaller

fat globule

glycerol &

3 fatty acids

lipase

(chemical digestion)

bile

(physical digestion)

emulsification

- made by liver

- works in duodenum

-made by pancreas

- works in duodenum

Exocrine vs. Endocrine GlandsExocrine vs. Endocrine Glandsgland:

organ that produces & releases a secretion

exocrine gland:organs that release their secretions

into ducts (tubes) such as:

sweat glands

Exocrine vs. Endocrine GlandsExocrine vs. Endocrine Glandsexocrine glands: (continued)

mammary glands

digestive organs: ex. salivary glands

pancreas

liver

Endocrine vs. Exocrine GlandsEndocrine vs. Exocrine Glands

endocrine gland: organs that release hormones

directly into the blood (not through ducts)

examples: testes → testosterone ovaries → estrogen pancreas → insulin

Hormonal Control of DigestionHormonal Control of Digestion important so that secretions are only released

when the appropriate food is present hormones (chemicals that control metabolic

pathways) get to their target tissue via the blood stream

stimulus: target tissue: response:

action that triggers a responsetissue that is affected by hormone

action tissue produces as a result of hormone binding

Hormonal Control of Protein DigestionHormonal Control of Protein DigestionHormonal System

Gastrin Secretin

Gland

Stimulus

Target Tissue

Response

Role of Released Substance

cardiac sphincter cellsprotein in food

stomach lining

Release:1. HCl2. pepsinoge

n

Release:sodiumbicarbonate

1. activates pepsin2. digest amino

acid chains

duodenal gland cells

acidic chyme

pancreas cells

neutralizes acidity in chyme

HomeworkHomework

Complete ‘Chemical Digestion

of Nutrients’ Handout