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Digestion of Nutrients
Digestion video
(To be played in Winamp as the file would not insert as a link).
Step 2:Mechanical breakdown of food
Digestive system
FRED (Human digestive system model)
(To be pulled apart & discussed with students).
Where does mechanical breakdown of food begin?
Mechanical breakdown of food & secretion of enzymes
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 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
Mechanical breakdown of food & secretion of enzymes
Duodenum, pancreas & gall bladderWhat 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 bladderFrom 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
> amylases break down carbohydrates
> trypsin further digests proteins into peptides
> lipases break fats & phospholipids into glycerol & fatty acids
> nucleases break down nucleic acids
Gall bladder > 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 & IleumWhat now occurs in the small intestine?
What enzymes are still present/working?
> peptides amino acids
> carbohydrates glucose
> lipids fatty acids & glycerol
Absorption in the small intestine:Jejunum & IleumWhat occurs in the small intestine after food has been
broken down into its constituent macromolecules?
What features of the small intestine assist absorption?
How do nutrients move through the wall of the small intestine?
(Biology, 4th Ed. Campbell)
Absorption in the small intestine:Jejunum & IleumInto where do sugars & amino acids diffuse?
Into where do glycerol & fatty acids diffuse?
How do nutrients move through the wall of the small intestine?
(Biology, 4th Ed. Campbell)
Absorption in the small intestine:Jejunum & IleumFood 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?
Enzymes, H2O, electrolytes?
What action continues to move contents through the gut?
Bacteria break down 30-40% into fatty acids & glycerol.
Some vitamins (Vitamin K)
What moves into the rectum? faeces
The LARGE intestine: colon & rectum
What does faeces contain?
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
What macromolecular contents are in food that we need?
Is it possible to absorb all of the nutrients in our food?
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”)