Download Digestion

Chapter 12 – Digestive System
Digestion: changing food into forms that can be absorbed through cell membranes
Layers of alimentary canal:
1. Mucosa: innermost, protects tissues beneath it; carries on absorption and secretion
2. Submucosa: nourishes surrounding tissue and carries away absorbed material
3. Muscular layer: two layers of smooth muscle; circular (diameter)and longitudinal (short)
4. Serosa: moistens and lubricates outer tube so organs will slide freely over it
Alimentary canal – 9 meters long; openings at each end
Organ
Mouth
Components
Teeth
Deciduous – primary
teeth, 10 per jaw
Permanent – secondary
teeth, 16 each jaw
Incisors – front bite,
used on large pieces of
food
Cuspids – canine,
grasping or tearing
Bicuspids – premolars;
grinding
Molars - grinding
Tongue
Function
Receives food and reduces it
Breaks food into smaller pieces to increase
surface area for digestive enzymes
Crown – above gingiva
Root – below gingiva
Gingiva – gum
Composed of dentin
Disease / Disorder
Dental caries (decay): decalcification of
enamel and destruction of dentin; causes a
cavity – caused by bacteria on dirty teeth
and a diet high in sugar; causes bacteria to
produce acids that decay the teeth
Skeletal muscle connected to floor by
frenulum; mixes food particles; anchored
to hyoid and lingunal tonsil
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Palate
Cheeks
Lips
Salivary glands
Pharynx
Roof of oral cavity (hard and soft); during
swallowing uvula covers entrance to nasal
cavity; contains palatine tonsils
Chewing
Sensory receptors for temperature and
texture
Moistens food and binds it together
Secretions – serous, moistens, submandibular s.g. (floor of mouth);
amylase, begins starch digestion, - parotid
s.g. (below ear); mucus, binds food, –
sublingual s.g. (under tongue)
Connects nasal and oral cavities with
larynx and esophagus; swallowing
1. food chewed and mixed with saliva,
mixture turns into a bolus, forced into
pharynx by tongue
2. bolus reaches pharynx and stimulates
sensory receptors to trigger swallowing
reflex > soft palate, uvula raised
preventing food from entering nasal
cavity>hyoid bone and larynx elevated so
food won’t enter trachea, epiglottis covers
opening to trachea (glottis)> muscles in
lower part of pharynx relax opening of
esophagus > peristaltic waves begins and
forces food into esophagus
3. food transported to stomach by
esophagus
Tonsillitis – infection most commonly of
the palatine tonsils
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Esophagus
Passageway for food from mouth to
stomach straight collapsible tube 25 cm
long
Hiatal hernia – weak place in diaphragm,
abdominal organs may protrude through
the esophagus cause the person to feel a
choking sensation.
Heartburn – gastric juice refluxes into
esophagus
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Stomach
Capacity of 1 liter; receives food; initiates
protein digestion; mixes food with gastric
juice; carries on limited absorption (water,
glucose, certain salts, alcohol, lipid soluble
drugs) moves food into the small
intestine;regions: cardiac, fundic, body,
pyloric
Gastric secretions
Mucous cells – mucus and alkaline
substance
Parietal cells – HCl + intrinsic
factor=gastric juice
Chief cells – digestive enzymes,
pepsinogen + HCl = pepsin, protein
splitting enzyme, intrinsic factor aids in
absorption of vitamin B12, controlled by
hormonal and neuronal mechanisms – ACh
stimulates gastric glands to secrete gastric
juices, gastrin also secreted by some
stomach cells > stimulates gastric glands
even more; gastrin also stimulates cell
growth in mucosa to repair tissue;
Ulcer – open sore in mucosa; commonly
caused by bacterial infection
Vomiting – triggered by irritation or
distention of alimentary canal; emetic
center in medulla oblongata; response
cause the stomach to squeeze from all
sides
Chyme – paste of food particles + gastric
juice
Chyme is pumped into the small intestine a
little at a time; liquids pass through
rapidly, fatty foods remain 3-6 hours,
proteins and carbohydrates pass through
quickly
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Pancreas
Gallbladder
Closely associated with the small intestine;
Pancreatic juice
Pancreatic amylase: splits starch or
glucagen into disaccharides
Lipase ; breaks triglycerides into fatty
acids and glycoxol
Proteinase: (trypsin, chymotrypsin,
carboxypeptidase) splits bonds b/w
different combinations, activated by other
enzymes in sm. Int.
Nucleases: breaks down nucleic acids
into nucleotides
Attached to ventral surface of liver by
cystic duct which joins hepatic duct; stores
bile b/w meals; common bile duct – union
of hepatic and cystic ducts
Pancreatitis – blocked duct, cuases back
up in portions of pancrease, may become
digested
Gallstone: crystal of cholesterol; blocks
the flow of bile into the sm. int; remove
stones or gallbladder
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Liver
2 lobes: right (larger),
left (smaller); bile
secreted by hepatic cells
Metabolic activities; carbohydratesmonitors level of glucose, protein
metabolism used in blood filtering; most
vital is deamination; stores glycogen, iron,
vit. A,D,B12 detoxification
Jaundice: excretion on bile is prevented
causing a yellowish tinge
Hepatitis: inflammation of liver, caused
by a virus
Type A – children or young adults; spread
by touching contaminated 0virus
containing feces) objects; nausea, jaundice,
abdominal pain, complete recovery no
liver damage
Type B – symptoms similar to type A,
effects last longer; spread by body fluids
(STD) most recover, but some become
carriers
Non A and non B – blood transfusions,
drugs, alcohol, chronic (6 months or
longer) may have liver damage
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Small
intestine
Large
intestine
Receives pancreatic secretions, completes
digestion of nutrients in chyme; regions –
duodenum, jejumum, ileum; suspended
from posterior abdominal cavity wall by
mesentery; contains many intestinal villi,
mostly in duodemum and jejumum; most
important absorbing organ, mixing and
peristalsis
Enzymes: stilumalted by direct contact
with chyme
1. peptidases: split peptides into amino
acids
2. sucrase, maltase, lactase: split
disacchrides into monosaccharides sucrose
> glucose, maltose > fructose, lactose >
galactose
3. intestinal lipase: fats > fatty acids and
glycerol
Absorption of water and salts; concentrates
chyme into feces
Lactose intolerance: insufficient
quantities of lactase to break down milk
sugar; remains undigested causes an
increase in osmotic pressure; water drawn
into intestine; intestinal bacteria produce
organic acids and gases bloating, diarrhea,
cramps
Blocked colon,
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