Download digestive system - Bakersfield College

DIGESTIVE SYSTEM
Professor Andrea Garrison
Biology 11
Illustrations ©2010, 2013 Pearson
Education, Inc.
Digestive System
• Digestive system = digestive
tract plus associated glands
and organs
• Function = digestion
– Breaks down food to simple
molecules that can be
absorbed by the lining of the
intestine
Digestive System
2
Glands in lining
of stomach and
intestine
Modified by A. Garrison
Digestive System
3
Stages of Digestion
Digestive System
4
Stages of Digestion
Digestive System
5
Stages of Digestion
Digestive System
6
Stages of Digestion
Digestive System
7
Ingestion
Digestive System
8
Digestion
• Mechanical digestion
– Breaks chunks of food into small pieces
• Allows chemical digestion to be effective
• Chemical digestion
– Digestive enzymes and assisting chemicals break
food into smaller molecules for absorption
Digestive System
9
Glands in lining
of stomach and
intestine
Modified by A. Garrison
Digestive System
10
Digestion in Mouth
• Mouth
– Ingestion
– Mechanical digestion
• Food is chewed
– Pressure on gums creates
reflex
• Bolus is formed by tongue,
teeth, cheeks
Digestive System
11
Digestion in Mouth
• Mouth
– Chemical digestion
• Taste buds detect sweet,
sour, salty, bitter
• Clue to spoiled food
• Smell, sight, taste of food
prepares stomach
Digestive System
12
Digestion in Mouth
• Mouth
– Chemical digestion
• Salivary glands secrete saliva
– Parotid glands
– Sublingual glands
– Submandibular glands
• Saliva
– 99% water
– 1% salts and proteins
» Mucins produce
mucus
» Amylase breaks down
starch
Digestive System
13
Swallowing
• Bolus pushed to pharynx to esophagus
– Food swallowed via reflex in pharynx
Digestive System
14
Swallowing
• Bolus pushed to pharynx to esophagus
– Food swallowed via reflex in pharynx
Digestive System
15
Swallowing
• Bolus pushed to pharynx to esophagus
– Food swallowed via reflex in pharynx
Digestive System
16
Peristalsis
• Food moves through
digestive tract from
esophagus to anus via
peristalsis
– Waves of involuntary
muscle contractions
– Push materials forward
– Different rates in
different regions of
digestive tract
– Triggered by stretch of
muscular walls as
material moves in
Digestive System
17
Esophagus
• Muscular tube from
pharynx to stomach
• Esophageal sphincter
at top
• Penetrates diaphragm
Digestive System
18
Stomach
• Sphincters keep food
and gastric juices in
stomach until desired
release
– Cardiac sphincter
• Prevents backflow into
esophagus
– Pyloric sphincter
• Controls movement
into small intestine
Digestive System
19
Stomach -- Digestion
• Serves for:
– Food storage
– Formation of
chyme
• Slurry of food,
mucus, gastric
enzymes
– Initiation of
protein digestion
Digestive System
20
Stomach -- Digestion
• Muscles of
stomach wall
contract to mix
the chyme
Digestive System
21
Stomach -- Digestion
• Gastric glands secrete
mucus, pepsin, acid
– Very acidic
– Deactivates salivary amylase
– Acid + pepsin breaks down
proteins → amino acid chains
Digestive System
22
Small Intestine
• Peristalsis in stomach
and relaxation of pyloric
sphincter
• Chyme enters small
intestine a little bit at a
time
Small intestine
Digestive System
23
Small Intestine
• 3 sections
– Duodenum -- first 10 inches
– Jejunum -- 8 feet
– Ileum --12 feet
Small intestine
Digestive System
24
Small Intestine -- Digestion
• Chyme
– Carbs have barely
started digestive
process
– Protein segments
from stomach
digestion
– Fats not yet
digested
Digestive System
25
Small Intestine -- Digestion
• Role of liver
– Produces bile to
assist in fat digestion
• Role of gall bladder
– Stores bile from liver
• Role of pancreas
– Produces
bicarbonate
– Produces digestive
enzymes
Digestive System
26
Small Intestine -- Digestion
• Duodenum receives
– Chyme
– Mucus from intestinal
cells
– Secretin and CCK from
glands in intestinal lining
• Stimulate liver,
gallbladder and
pancreas
– Bile from liver via
gallbladder
– Bicarbonate from
pancreas
– Digestive enzymes from
pancreas
Digestive System
27
Small Intestine -- Digestion
• Bicarbonate neutralizes acid
• Bile emulsifies fats
– Increases surface area for digestive
enzymes
Digestive System
28
Small Intestine -- Digestion
• Pancreatic enzymes work once pH neutralized
– Pancreatic amylase
• Digests carbohydrates to monosaccharides (sugars)
– Proteases
• Digest proteins to amino acids
– Lipases
• Digest fats to fatty acid + glycerol
Digestive System
29
Small Intestine -- Digestion
Digestive System
30
Small Intestine -- Digestion
(protease)
Digestive System
31
Small Intestine -- Digestion
Digestive System
32
Small Intestine
• Most of absorption
occurs here
• Maximizes surface
area
– Folds, folds, more
folds
– Villi and microvilli
most abundant in
duodenum and
jejunum, also present
in ileum
Digestive System
33
Small Intestine
Digestive System
34
Small Intestine
Digestive System
35
Small Intestine
Digestive System
36
Absorption
• Most of water
• Amino acids & sugars
– actively transported
into cells and then to
blood capillaries
• Fats
– Diffuse into cells
– Built back into
triglycerides
– Attached to proteins
(lipoproteins)
– Expelled via exocytosis
– Absorbed into
lymphatic vessel and
carried to blood
Digestive System
37
Ulcer-causing Bacteria
Digestive System
38
What’s left?
• Mostly wastes
– Never absorbed into cells of body
• Exception is bile, made from breakdown products of
red blood cells
• Some water
– Will be absorbed in large intestine
Digestive System
39
Ileocecal Sphincter
• Peristalsis moves
materials into large
intestine
• Small intestine joins
large intestine at
ileocecal sphincter
Digestive System
40
Large Intestine
• Large intestine
– Colon
•
•
•
•
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
– Rectum
– Anus
Transverse
colon
Ascending
colon
Sigmoid
colon
Descending
colon
Rectum
Anus
Digestive System
41
Large Intestine -- Absorption
• Large anaerobic bacteria population (E. coli)
– Breaks down remaining nutrients
– Synthesize some B vitamins and vitamin K
• absorbed in large intestine
Digestive System
42
Large Intestine -- Absorption
• Most remaining water absorbed
– Prevents dehydration
– Peristalsis too fast
• Diarrhea
– Peristalsis too slow
• constipation
Digestive System
43
Egestion
• Peristalsis moves wastes into rectum
• Stretch of rectal walls triggers urge to defecate
• Wastes removed from body through anus
– 2 sphincters
• Internal anal sphincter -- involuntary
• External anal sphincter -- voluntary
Digestive System
44