6.1 Digestion

Question 1

Two major organs groups in digestive system

Answer 1

Alimentary canal: food actually passes (esophagus, stomach, small / large intestine

Accessory organs: aid in digestion but don’t trasnport food (salivary glands, pancreas, gall bladder, liver)

Question 2

Explain the components of alimentary canal and their functions

Answer 2

• esophagus: connects oral cavity and stomach, food with saliva via peristalsis is moved down
• stomach: temporary storage, food is mixed by churning, protein digestion begins, lined with gastric pits which release digestive juices
• small intestine: long highly folded tube, food substaces absorbed, epithelium invaginations - villi
• large intestine: water and dissolved minerals absorbed

Question 3

Explain the accessory organs and their functions

Answer 3

• salivary glands: secrete saliva for chemical breakdown in mouth (amylases - starch)
• pancreas: secrete enzymes into small intestine (amylases, lipases), secrete hormones for blood sugar regulation (insulin, glucagon)
• liver: uses substances absorbed by small intestine to compose new compounds (detoxification, haemoglobin breakdown, bile production, metabolism, storage - glycogen)
• gall bladder: stores bile (emulsification of fats) produces by liver, via bile duct released into small intestine (fats absorbed in small intestine into lacteals inside villi)

Question 4

Mechanical vs chemical digestion

Answer 4

Mechanical: food physically broken down into smaller pieces - chewing, churning (stomah), segmentation (small intestine)

Chemical: food is broken down by chemical agent action - saliva (salivary glands - enzymes), stomach juice (gastric glands- enzymes and pH), bile (bile salts intearct with fats - emusification into small droplets - available for lipase)

Question 5

Explain peristalsis vs segmentation

Answer 5

Peristalsis - mechanism of movement in esophagus, stomach, small / large intestine

Continous segmentation of longitudinal smooth muscle - rynthmically contract and relax - food _moved unidirectionall_y along the alimentary canal

Segmentation - contractions of circular smooth muscle - moves chyme (food paste) in both directions for greater mixing with digestive juices

Question 6

Where are most of enzymes produced

Answer 6

In the PANCREAS

Question 7

Explain digestion of each macromolecule

Answer 7

CARBOHYDRATES: begins in mouth, amylase from salivary glands and pancreas - further digestion in small intestine (enzymes immobilised in epithelium), humans don’t have cellulase

PROTEINS: begins in the stomach - proteases (acidic), smaller proteins digested in small intestine - endopeptidases (neutral)

FATS: begins in intestines - bile emulsification, small droplets digested by lipases (secreted by pancreas)

NUCLEIC ACIDS: pancrease releases nucleases

Question 8

What are the main tissues of small intestine?

Answer 8

• serosa: protective layer
• muscle layer: longitudinal (peristalsis) and circular (segmentation) muscles
• submucosa: connective tissue separating muscle and innermost layer
• mucosa: highly folded innner layer which absorbs nutrients from intestine lumen into the blood stream and lacteal

Question 9

Features of villi

Answer 9

Question 10

How are nutrients absorbed by villi?

Answer 10

Between epithelial cells tight junctions - nutrients can pass only through specific membrane transport machanisms

• co-transport: active translocation is coupled with passive movement - glucose + am a are co-transported by active Na+ translocation
• facilitated diffusion: channel proteins - located near immobilised enzymes - localised concentration gradient - fructose, vitamins
• osmosis: water uptake
• simple diffusion: hydrophopic may diffuse - fats - straight into lacteals
• bulk transport: pinocytosis - in intestines vesicles can form to absorb fluids with dissolved nutrients

Question 11

What is the digestion sequence of starch?

Answer 11

STARCH - amylose (linear) or amylopectin (branched)

• in mouth machanically and chemically - salivary amylase, in intestines - pancreatic amylase = amylose -> maltose, amylopectin -> dextrin = both digested by maltase (hydrolysis) which is fixed on the epithelium of small intestine +> glucose used for ATp or stored as glycogen in liver

Question 12

How does the pancreas control blood sugar?

Answer 12

Pancreas secretes amylase in exocrine glands to intestine for primary digestion of starch - secretes insulin and glucagon hormones by endocrine glands into blood

Insulin (stimulates glycogen formation -liver and adipose) and glucagon (stimulates glycogen breakdown) regulate blood sugar levels

Question 13

How can digestion be modelled?

Answer 13

By dialysis tubing - selective by size - small pass, large dont