1. Human DigestiveDigestive System - YouTube.flv System
Video link
Human
DigestiveDigestive System - YouTube.flv System
Click digestive system to see video

2. 5 Digestion Processes (IDAAE)
Ingestion: taking in of food into the body.
Digestion: breaking down of food into simpler substances
Absorption: diffusion of food from small intestine into the blood
Assimilation: using digested nutrients to make new material
Egestion: removal of undigested waste material

3. Recall. . . What are the main organs of the alimentary canal? Mouth
Oesophagus
Stomach
Small intestine
Large intestine
Anus
Although not part of the alimentary canal, the liver, gall bladder and pancreas are closely associated with it. They play an important role in digestion by secreting digestive enzymes.

4. Digestion
Mechanical / physical digestion physically breaks down the food in the mouth (chewing). Smaller pieces of food increase surface area for digestion. It also takes place in the stomach (churning of food by the muscular stomach walls)
Chemical digestion uses enzymes to chemically break down complex food substances into their simplest form. e.g.
Starch maltose
amylase

5. Starch (carbohydrate) digestion: in mouth and small intestine.
Chemical digestion:
Starch (carbohydrate) digestion: in mouth and small intestine.
Protein digestion: in stomach and small intestine
Fat digestion: only in small intestine
Why must food be digested???
Large molecules of food are unable to pass through cell membranes, thus must be broken down into small molecules so that they can diffuse through cell membranes into the blood stream

6. Mouth (Ahhh....) Mouth ingests food
Teeth masticates food into small pieces to increase surface area for digestion
Saliva (pH 7) moisten and soften food
Starch maltose
Tongue mixes food with saliva and rolls food into a bolus before swallowing
Saliva - water, mucus, salivary amylase
Salivary amylase

8. https://vimeo.com/76306735 Swallowing
(1)The initial stages of eating and swallowing are under voluntary control.
(2)Once food enters the mouth the teeth break it down into smaller and smaller pieces. This has the dual function of making the food easier to swallow and increasing the surface area of food on which the saliva can act.
The tongue, lips and cheeks assist the teeth in the process by allowing the food to be "rolled" around the oral cavity.
The mechanical action described above produces a softened bolus of food which is now ready to be swallowed. The correct biological term for swallowing is deglutition.
(3) shows the voluntary stage of deglutition. Here the bolus is pushed into the upper part of the pharynx (known as the oropharynx) by the action of the tongue. 
The pharyngeal stage of deglutiton is stimulated when the bolus enters the oropharynx. This stage of swallowing is mainly due to a reflex response. Various nerve receptors send messages to the deglutition centre of the brain stem. (see medulla and pons in your notes on the central nervous system).
(4)This sets off muscular contractions in the pharynx. The soft palate closes off the nasopharynx. The vocal cords in the larynx are moved up and towards the front of the throat thus closing it off to the passage of food. This is extremely important in preventing food from entering the airway.I am sure we have all experienced the unpleasant feeling of food or drink going the "wrong way"!!
Another effect of the process is to widen the opening of the oesophagus thus making the passage of the bolus along the alimentary canal easier.
(5) As the bolus pushes it's way into the oesophagus it automatically pushes the epiglottis downwards further closing off the airway.
(6) The bolus then enters the oesophagus and the final stage of swallowing begins.
This final stage is known as the oesophageal stage of deglutiton.

9. What Happens During Breathing and Swallowing?
Normally, air passes into the trachea (windpipe) while food passes into the oesophagus.
pharynx
During breathing, the larynx is lowered and the glottis is open.
air
larynx (voice-box)
Figure 6.4 page 92
oesophagus
glottis
trachea (windpipe)

10. What Happens During Breathing and Swallowing?
During swallowing, the larynx is raised and the glottis is covered by the epiglottis. This prevents food particles from entering the trachea.
pharynx
food particles
Figure 6.4 page 92
epiglottis
oesophagus
glottis
larynx (voice-box)
trachea (windpipe)

11. What Happens During Breathing and Swallowing?
Occasionally, small particles of food or water may get into the larynx or trachea.
food particles
Figure 6.4 page 92
larynx (voice-box)
trachea (windpipe)

12. What Happens During Breathing and Swallowing?
This automatically induces violent coughing to force the food particles or water out and to prevent choking.
food particles
Figure 6.4 page 92
larynx (voice-box)
trachea (windpipe)

13. Oesophagus Minimal digestion
Carries food from mouth to stomach by peristalsis
Oesophagus has circular and longitudinal muscles which are antagonistic.
When circular muscles contract, longitudinal muscles relax and vice-versa.

14. Peristalsis
Part of the gut wall
The two layers of muscles cause rhythmic, wave-like contractions of the gut walls. Such movements are known as peristalsis.
Peristalsis:
enables food to be mixed with the digestive juices; and
moves the food along the gut.
circular muscles
Figure 6.6 page 93
longitudinal muscles

15. Direction of movement of food Circular muscles relax
Wall here dilates
Direction of movement of food
Circular muscles relax
Wall here constricts. Circular muslces contract; longitudinal muscles relax
Longitudinal muscles
contract

16. Peristalsis – Move the food down!
When circular muscles contract, longitudinal muscles relax. Gut wall constricts i.e. gut becomes narrower and longer. Food is squeezed or pushed forward.
Gravity and slippery mucous lining helps push food down too.

17. Stomach Stores food temporarily
Stomach muscles churns and mixes food (also by peristalsis) with gastric juice to form chyme.
Gastric juice contains hydrochloric acid (HCl) and enzymes like rennin and pepsin
HCl is very acidic (pH2), thus it kills bacteria and other microorganisms, as well as stopping the action of salivary amylase
Provides acidic medium for gastric enzymes to work
Only protein digestion here

18. The stomach is “guarded” at the entrance and exit points by sphincter muscles which control the amount of food entering and leaving the stomach.
Compare the stomach wall n oesophagus wall? Which is thinker? Why? ( pro
Click stomach or video link to see video

19. Small Intestine Subdivided into duodenum, jejunum and ileum
In the small intestine, chyme stimulates
Pancreas to secrete pancreatic juice
Gall bladder to secrete bile
Intestinal glands to secrete intestinal juice
All three juices secreted are alkaline,
pH 8.5

20. Pancreatic and intestinal juice contain many digestive enzymes.2
bile 1
bile duct
pancreatic juice
Pancreatic and intestinal juice contain many digestive enzymes.
Bile does not contain
enzymes. Bile emulsifies fats, increasing the
surface area for lipase
action
pancreatic duct 3
intestinal juice

22. Villi – absorption by diffusion
To liver
From intestine To

23. Large Intestine (colon)
Large inverted U shaped tube.
No digestion takes place here
Absorbs water and minerals salts
Stores the faeces (dead cells, mucus, germs, undigested food)

24. Is the colon the main region for water absorption?
No! About 94% of the total amount of water passing through the alimentary canal is absorbed by the small intestine! The large intestine absorbs most of the remaining 6% of water.
Rectum – temporarily stores faeces
Anus – egests (= removal of undigested matter) faeces

25. Organs associated with the alimentary canal
These organs do not digest food but aid in digestion
Gall bladder
Pancreas
Liver

26. One cell thick epithelium – for efficient absorption of food particles
Blood capillaries –
transport sugars and amino acids away from the small
intestine
Lacteal – fatty acids
and glycerol recombine
in the epithelium to
form fat which then
enters the lacteal as
fine fat droplets
This continual transport of digested food substances
maintains the concentration gradient for the absorption
of digested food substances.

27. Gall bladder
Temporarily stores bile (smelly green substance) secreted by liver.
Secretes bile in the presence of chyme.
Bile breaks up large fat droplets into very small fat droplets to increase surface area for lipase action (Emulsification) Bile emulsifies fats
*Bile is not an enzyme, so it is not affected by temperature

28. Pancreas Connects to small intestine by pancreatic duct
Produces pancreatic juice
Secretes hormones like insulin (controls blood glucose concentration) and glucagon (controls carbohydrate metabolism)
Liver
Produces bile, which is stored in the gall bladder

30. Absorption Adaptations of the small intestine
Small intestine is very long (~5 m)
Internal surface of the small intestine has many folds.
On these folds, there are many finger-like projections called villi
These 3 adaptations increase surface area for absorption

31. Assimilation
After travelling through the blood stream to the rest of the body, cells can now make use of
glucose as source of energy
amino acids to build new cytoplasm and tissue cells
fatty acids to build new cell membranes