human digestive digestive system - youtube.flv system
DESCRIPTION
Human Digestive Digestive System - YouTube.flv System. http://vimeo.com/76306734 Video link. 5 Digestion Processes (IDAAE). Ingestion : taking in of food into the body. Digestion : breaking down of food into simpler substances - PowerPoint PPT PresentationTRANSCRIPT
1
Human Human
DigestiveDigestDigestiveDigestive System - ive System - YouTube.flv YouTube.flv
SystemSystem
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 maltoseamylase
5
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
7
8
Swallowing https://vimeo.com/76306735
9
trachea (windpipe)
glottis
During breathing, the larynx is lowered and the glottis is open.
pharynx
oesophagus
larynx (voice-box)
air
What Happens During Breathing and Swallowing?
Normally, air passes into the trachea (windpipe) while food passes into the oesophagus.
10
During swallowing, the larynx is raised and the glottis is covered by the epiglottis. This prevents food particles from entering the trachea.
pharynx
trachea (windpipe)
oesophagus
glottis
epiglottis
food particles
larynx (voice-box)
What Happens During Breathing and Swallowing?
11
Occasionally, small particles of food or water may get into the larynx or trachea.
trachea (windpipe)
larynx (voice-box)
food particles
What Happens During Breathing and Swallowing?
12
What Happens During Breathing and Swallowing?
This automatically induces violent coughing to force the food particles or water out and to prevent choking.
trachea (windpipe)
larynx (voice-box)
food particles
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
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.
Part of the gut wall
Peristalsis
circular muscles
longitudinal muscles
15
Wall here constricts. Circular muslces
contract; longitudinal muscles relax
Wall here dilates
Direction of movement of food
Circular 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.
• http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/basics/peristalsis.html
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.
https://vimeo.com/76306734
19
Small Intestine
• Subdivided into duodenum, jejunum and ileum
• In the small intestine, chyme stimulates1. Pancreas to secrete pancreatic juice
2. Gall bladder to secrete bile
3. Intestinal glands to secrete intestinal juice
• All three juices secreted are alkaline,
pH 8.5
20
bile
intestinal juice
pancreatic duct
pancreatic juicebile duct1
3
2•Pancreatic and intestinal juice contain many digestive enzymes.
•Bile does not containenzymes. Bile emulsifies fats, increasing thesurface area for lipase action
21
22
Villi – absorption by diffusion
DiffusionDiffusion
From intestine
To
To liver
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 faecesAnus – 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
Lacteal – fatty acids and glycerol recombine
in the epithelium toform fat which then enters the lacteal as
fine fat droplets
Blood capillaries – transport sugars and amino acids away from the
small intestine
One cell thick epithelium – for efficient absorption of
food particles
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
29
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