Transcript Digestive System - Sonoma Valley High School

Digestive
System
Digestive system functions
1.
2.
Ingestion
Mixing and
movement of food.
–
3.
Digestion of foods.
–
–
4.
5.
Peristalysis
Chemical
Mechanical
Absorption of
digested foods.
Defecation.
Layers of the GI tract
• Alimentary canal vs
Accessory organs.
• Wall of GI tract is
composed of four
layers (inside->outside)
–
–
–
–
Mucosa
Submucosa
Muscularis
Serosa
• Peritoneum
• Mesentery
Layers of the GI tract
Salivary Glands
• Saliva is secreted from 3
pairs of glands
• Parotid glands (back)
• Submandibular glands (jaw)
• Sublingual (below tongue)
• Composition of saliva:
– 99.5% water
– 0.5% solutes
• Salivary amylase- (digestive
enzyme for starch)
• Mucus (lubrication)
• lysozyme (kills bacteria)
Tortora
516
Control of
Salivary Glands
– Parasympathetic ANS
stimulates production
of saliva.
– Stimuli:
• Food touching the
tongue
• Smell
• Taste
• Thought of food.
Chewing
• Mechanical digestion
involves
– Muscular manipulation
by the tongue
– Teeth grind food into
smaller pieces
– Saliva mixes in
Result: a soft, flexible,
easily swallowed mass
called a bolus
Swallowing
• Voluntary stage
– Bolus is pushed to
back of mouth by
tongue.
• Pharyngeal stage
– Breathing stops.
– Bolus passes through
pharynx
• Esophageal stage
– Peristalysis
– Heartburn
Tortora
Pages 519-520
Esophagus
• Connects mouth to
stomach.
• Lies behind the
trachea (flat side)
• Passes through the
diaphragm
• Contains two layers
of smooth muscle.
• Food has to pass over
trachea @ epiglottis
Tortora
Pages 518-520
Stomach
• J shaped, lies under
diaphragm.
• A mixing chamber and
holding reservoir- size
varies
• Divided into four
areas:
–
–
–
–
Cardia
Fundus
Body
Pylorus/ Pyloric
sphincter
• Rugae
520-521
Wall of Stomach
•
•
•
•
4 layers:
Mucosa
Submucosa
Muscularis: 3
layers of muscle
– Longitudinal layer
– Circular layer
– Oblique layer
• Serosa
Tortora
Pages 439-443
Gastric Gland
secretions
• Mucous cells
– Mucus
• Chief cells
– Pepsinogen
• Parietal Cells
– HCL
– Intrinsic factor (B12)
• G cells
– Gastrin (hormone)
Tortora Page 522
Stomach & Digestion
• Mechanical digestion
– Bolus converted to
chyme.
– Mixing waves push
chyme into duodenum.
– Pyloric sphincter
releases into SI
• Chemical digestion
– Pepsin breaks down
proteins into
peptides.
– Lipase digests
triglycerides (in acid)
into diglycerides
Tortora
522-523
Stomach & Absorption
• Mucus protects the
stomach lining from
being digested itself
• Little absorption of
nutrients here
• Stomach wall does
absorb:
–
–
–
–
Water
Electrolytes
Some drugs (aspirin)
Alcohol
Tortora
523
Pancreas
• Pancreas lies behind
the stomach
• Secretions pass
through pancreatic
duct into duodenum
• Pancreatic juice:
Bicarbonate
counteracts acid from
chyme
• Digestive enzymes
• Islets of Langerhans
produce hormones:
insulin
Tortora 523
Enzymes produced by the pancreas
that work in the small intestine:
1.
2.
3.
4.
5.
6.
Pancreatic amylase – turns starches to dissacharides
Trypsin
- proteins to polypeptides.
Chymotrypsin
- proteins to peptides.
Carboxypeptidase - proteins to peptides.
Pancreatic lipase - triglycerides to fatty acids &
monoglcerides
Ribonuclease
-nucleic acid digestion
Liver
• Heaviest gland in the
body: 3 lbs.
• Involved in filtration,
storage (glycogen),
protein metabolism,
and excretion
• Produces bile
– Emulsifies lipids
(fats)
– Bile leaves liver
through cystic duct.
Tortora
524-525
Gall Bladder
• Bile (made in the liver) is
stored in the gall
bladder.
• Carried by cystic duct to
common bile duct, then
released into duodenum.
• Bile emulsifies lipids
Gall stones (crystallized cholesterol)
Tortora 525526
Small Intestine
• Composed of
– Duodenum
– Jejunum
– Ileum
• Food is released
through ileocecal
sphincter into the
cecum
Tortora
526-527
Small Intestine
• Mucosa
• Villi extend from wall
of sm. intestine.
– Capillary network
– Lacteal- lymph
– Duodenal glandssecrete alkaline
mucus
– Microvilli-increases
surface area for
absorption
Enzymes produced by small
intestine
•
•
•
•
•
•
Maltase
maltose to glucose
Sucrase
sucrose to glucose & fructose
Lactase
lactose to glucose & galactose
Peptidases
peptides to amino acids
Ribonuclease
RNA to sugar & bases
Deoxyribonuclease DNA to sugar & bases
Absorption in the Small
Intestine
• Carbohydrates &
proteins move into
capillaries.
• Fatty acids &
monoglycerides move
into the lacteal
(lymph capillaries)
Tortora
530
Large Intestine/ colon
• 5 ft in length/2.5 inches
diameter
• Ileocecal sphincter:
allows material to pass
from sm. intestine to the
colon
• Has ascending,
transverse, descending,
and sigmoid portions.
• Puckered due to
contraction of muscular
bands (teniae coli)
Tortora
532-533
Digestion and
absorption
– Bacteria ferment &
digest foodreleasing H2, CO2,
methane gases
(flatulence)
– Bacteria produce
vitamin B & K
(absorbed by colon)
– Bacteria break down
bilirubin- brown
color
– Absorbs much of
the water and ions,
forming feces.
Appendix
• Structure:
– Short finger-like
extension of the lg.
intestine
– Attaches to the
cecum
– Stores a sample of
healthy colon
bacteria, to recolonize the colon
after an intestinal
disease.
Appendicitis:
inflammation requiring
removal of the
appendix
Tortora
532
Inflamed appendix
Defecation reflex
– Mass peristalysis pushes
contents from the sigmoid
colon to the rectum
– Stretch receptors initiate
the defecation reflex
– Initiated by food in the
stomach/ ANS controlled.
– Internal sphincter(involuntary) opens
– External sphincter releases
(voluntary control)
+ downward pushing of the
diaphragm push out the feces
Tortora
533-534
Colon cancer
Healthy colon
• One of the deadliest
cancers
• Detected by stool
samples, or
sigmoid/colonoscopies
• Polyp removal using a
wire snare