Download VCE_Yr11_BIOLOGY_Functions of the digestive system

Step 2:Mechanical breakdown of food
 Digestion video
(To be played in Winamp as the file would not insert as a link).
Digestive system
 FRED (Human digestive system model)
(To be pulled apart & discussed with students).
Mechanical breakdown of food &
secretion of enzymes
Where does mechanical breakdown of food begin?
Where does it continue?
What enzyme is secreted in the mouth? Its purpose?
What is the ball of food called that is swallowed?
How does it move down the oesophagus?
What is secreted in the stomach?
What are the components of gastric juice?
What does pepsin/pepsidase do?
What is food called once it mixes with gastric juice?
What organs does the stomach signal to that food is
coming?
How does it do this?
What muscle controls the flow of food to the small
intestine? What is the 1st section of the small intestine
called?
Mechanical breakdown of food &
secretion of enzymes
Mechanical breakdown of food begins in the mouth, &
amylase (an enzyme) is secreted to begin breakdown of
starch to simpler sugars
The bolus (ball of food & saliva) is swallowed, & moves
down the oesophagus by peristalsis
Further mechanical breakdown occurs in the stomach, &
food is mixed with secreted gastric juice (mucus, pepsin
(enzyme), HCl & H20) to make chyme
Pepsidase breaks proteins into peptides (smaller
fragments)
The stomach produces hormones that signal the pancreas
& gall bladder that food is coming
The pyloric sphincter regulates chyme exiting the
stomach to the small intestine
Duodenum, pancreas & gall bladder
What is the 1st section of the intestine called that chyme
exits the stomach into?
What does the pancreas secrete into the duodenum?
What does the gall bladder secrete into the duodenum?
Duodenum, pancreas & gall bladder
From the stomach chyme enters the small intestine
(duodenum, jejunum, ileum), 1st the duodenum
The gall bladder & pancreas then secrete into the
duodenum
Pancreas
> bicarbonate neutralises the HCl from the stomach
Gall bladder
> amylases break down carbohydrates
> trypsin further digests proteins into peptides
> lipases break fats & phospholipids into glycerol & fatty acids
> nucleases break down nucleic acids
> bile:
salts emulsify fats into smaller drops in aqueous solution
the smaller droplets of fat aid digestion by increasing SA:vol ratio
allows lipases (from the pancreas) to break fats down into fatty acids &
glycerol
Absorption in the small intestine:
Jejunum & Ileum
What now occurs in the small intestine?
What enzymes are still present/working?
> peptides
amino acids
> carbohydrates
> lipids
glucose
fatty acids & glycerol
Absorption in the small intestine:
Jejunum & Ileum
What occurs in the small intestine after food has been
broken down into its constituent macromolecules?
(Biology, 4th Ed. Campbell)
What features of the small intestine assist absorption?
How do nutrients move through the wall of the small
intestine?
Absorption in the small intestine:
Jejunum & Ileum
Into where do sugars & amino acids diffuse?
(Biology, 4th Ed. Campbell)
Into where do glycerol & fatty acids diffuse?
How do nutrients move through the wall of the small
intestine?
Absorption in the small intestine:
Jejunum & Ileum
Food is further broken down into macromolecules
that can be absorbed through the wall of the small
intestine
The jejunum & ileum have structural features that
assist absorption:
> thin wall, allowing diffusion of nutrients
> villi & microvilli greatly increase the surface area
for absorption
Glucose & amino acids are absorbed through
capillaries lining the microvilli
Glycerol & fatty acids are absorbed through lacteals
& into the lymph fluid, which drains out into the
bloodstream in the neck
The LARGE intestine: colon & rectum
What moves into the colon?
What happens in the colon?
Fibre?
Bacteria break down 30-40% into fatty acids &
glycerol.
Some vitamins (Vitamin K)
Enzymes, H2O, electrolytes?
What action continues to move contents through the gut?
What moves into the rectum?
faeces
The LARGE intestine: colon & rectum
What does faeces contain?
What macromolecular contents are in food that we
need?
Is it possible to absorb all of the nutrients in our
food?
Sugars/starches completely absorbed
10% fat remains
15% protein remains
~35% fibre gets digested in the colon
Overall ~ 90% energy in food has been absorbed
Digestion in herbivores
(adjunct)
What do herbivores eat?
What form is the major form of stored carbohydrate in plants?
Can animals break cellulose down?
Bacteria ferment the cellulose, & herbivores have large
expanded sections in their gut to accommodate them
What are the two classifications of herbivores:
foregut fermenters & hindgut fermenters
Obtaining Energy & Nutrients for Life
Students to concept map what they have learnt in
this unit on the whiteboard!
(Otherwise titled: “The crowd goes wild”)