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Page 3 : Notes
Digestive System: Path of food
Alimentary canal:
Open at both ends
 Irregular tube about 29 ft. (9m) long
 Also called gastrointestinal tract or
GI tract
 Food travels: mouth -> pharynx ->
esophagus -> stomach -> small
intestine -> large intestine ->
rectum
 Food does not travel through: liver
or pancreas

Two forms of digestion:

Mechanical – teeth tear food into
smaller pieces and stomach churns

Chemical – enzymes break large
molecules into smaller molecules
(molecular level)

Foods undergo digestion, absorption
and metabolism.
Digestive System:
Functions in altering food in to a form
that can be absorbed by cells
 Serves as a system that also
eliminates wastes (feces)
 Composed of main organs and
accessary organs:

Main organs – food passes through
 Accessary organs – can secrete into the
GI tract (teeth, tongue, salivary glands,
liver, gallbladder, pancreas & appendix)

Walls of the digestive tract:




Mucosa - lines inside of
GI tract
Submucosa - connective
tissue with blood
vessels + nerves
Muscularis – circular
and longitudinal muscle
layers; perform
peristalsis
Serosa – outermost
covering connects to
mesentery
Path of food: Mouth
Where digestion begins!
 Roof has hard and soft palates with
the uvula (prevents food from
entering nasal cavity)
 Floor has tongue and muscles,
attached by the frenulum
 Tongue surface has papillae (bumps
on tongue), largest is vallate

Accessory glands:

Salivary glands:

Produce saliva
 Contains
mucus and
digestive enzymes
Salivary amylase –
Carb. Digestion


Three pairs:
 Parotid
– largest, back of throat
 Submandibular – under jaw
 Sublingual – under tongue
Teeth:



Incisors – sharp,
cutting
Canines (cuspids) –
tear or pierce
Premolars (bicuspids)
And

Molars (tricuspids) –
tricuspids

Both have large, flat
surfaces for grinding
or crushing
How many teeth?
Deciduous teeth (baby teeth)
 20 teeth
 6 months: average age for first eruption
 Complete set at about 2 years of age

Permanent teeth (adult teeth)
 32 teeth
 6 years: average age for first eruption
 Complete set between 17-24 years of age

Sections of a typical tooth
Crown
Neck
Root
Pharynx:
Tubelike structure made of muscle
and lined with mucous membrane
 Food is small rounded mass, called
bolus
 Three regions:

Nasopharynx
 Oropharynx
 Laryngopharynx

Esophagus:
Muscular, mucus-lined tube
 Connects the pharynx to stomach
 About 10 inches long
 Cardiac sphincter:

Ring of muscle
tissue at end that
leads to stomach

Stomach:
Pouch that stores food
 Muscular walls mix food with gastric
juice that contains hydrochloric acid
and enzymes (produced by gastric
glands)
 Empty – folds line inside called rugae

Chyme – food is a
semi-solid mixture when
it exits
Pyloric sphincter – ring
of muscle tissue

Muscularis of stomach:
Small intestine:
20 feet long
 3 sections:

Duodenum – first section – 12 in.
 Jejunum – middle section
 Ileum – last section

Small intestine:
Internal – mucus lining has intestinal
glands and circular folds called plicae
 Covered by small projections called
villi
 Microvilli are small projections on villi


Increase surface area for absorption of
nutrients
Villi and microvilli:
Liver:



Largest gland in
the body
Secretes bile,
yellowish-brown
liquid
Emulsifies fats and
eliminates
cholesterol from
body
Pancreas:




Lies behind stomach
Secretes pancreatic
juice that contains
enzymes
Breaks down
proteins, lipids, +
carbs
Secretes sodium
bicarbonate (alkaline
substance that
neutralizes HCl
The Ducts
Large intestine:

5 feet long with regions (cecum,
ascending, transverse, descending,
sigmoid and rectum)
Large intestine:
Undigested and unabsorbed food is
acted on by bacteria
 Absorbs vitamins (K + B-complex)
 No villi here
 Absorption of salts and water
 Ileocecal valve is doorway in to the
large intestine


Appendix:
Wormlike tubular structure
 Contains lymphatic tissue
 May be involved in immunity


Peritoneum:
Large, moist slippery sheet of serous
membrane
 Lines abdominal cavity + covers organs
 Has two extensions:

 1.
mesentery - giant, pleated fan that
encloses the small intestine and attaches it
to the posterior abdominal wall
 2. greater omentum – pouchlike extension,
shaped like an apron, hangs over the
intestines (lace apron)