Download The Digestive System

The
Digestive
System
Chapter 15
Terminology…
• Digestion: breaking down food
molecules so the body can use the
nutrients
• Gastroenterology: branch of science
dealing with S/F/D of stomach &
intestines
• Peritoneum: serous membrane of
abdomen
• Visceral: surrounds organs
• Parietal: lines abdominal cavity
Digestive System
• 2 parts
• Gastrointestinal (GI) tract (alimentary canal)
• Accessory digestive organs
• 6 functions
• Ingestion: taking in food/liquids
• Secretion: water, enzymes, buffers
• Mixing & propulsion: muscular contraction &
peristalsis
• Digestion: chemical=enzymes; mechanical=teeth
& churning
• Absorption: small nutrients enter cells
• Defecation: output of undigested material
(feces); mainly cellulose
GI Tract
• Continuous tube from mouth to
anus through which food passes
• Mouth  pharynx  esophagus
 stomach  small intestine 
large intestine (colon)
accessory
accessory
accessory
accessory
Accessory Organs
• Aid in digestive process, but food
does NOT pass through the structure
• Teeth: mastication
• Tongue: swallowing, food movement
• Salivary glands: moistening food
• Liver
• Gallbladder
• pancreas
Mouth/Oral Cavity
•
•
•
•
•
•
Lips
Hard palate
Soft palate with uvula
Tongue
Frenulum
Salivary glands
• Saliva=water, solutes, amylase
• Teeth
Teeth
• a/k/a dentes
• for mastication
• Chewed food + saliva = BOLUS
• Gum = gingiva
• Deciduous = baby teeth
• 6 months – 6 years
• 20 teeth
• Permanent = adult teeth
• 6 years – adulthood
• 32 teeth
• 4 kinds:
•
•
•
•
Incisors (flat): cutting
Cuspids (canines): shredding
Bicuspids (premolars): crushing/grinding
Tricuspids (molars): crushing/grinding
Pharynx
• Oropharynx
• Laryngopharynx
• Swallowing causes…
• Soft palate to close nasopharynx
• Epiglottis to close larynx
Esophagus
• Food passageway
• Collapsable tube
• rings of muscle
• Cardiac sphincter: at base of
esophagus where it meets
stomach
• Faulty sphincter may cause heart
burn and/or GERD
Stomach
• Rugae: internal folds
• 4 parts
•
•
•
•
Cardia (with sphincter)
Fundus
Body
Pylorus (with sphincter)
• Cells
• Chief cells: make pepsinogen
• Parietal cells: make HCl to convert pepsinogen
into pepsin
*Food remains here 2-6 hours
*Liquid food as it leaves the stomach is called
CHYME
*Forcible explusion of upper GI contents =
vomiting
Pancreas*
• Pancreatic duct connects
pancreas to duodenum (1st
section of small intestine)
• Secretes pancreatic juices
• Water, salts, enzymes, sodium
bicarbonate (buffer)
Liver* & Gallbladder*
• Liver
•
•
•
•
~ 3 lbs (2nd largest organ)
Makes bile (emulsifies fats)
2 lobes (right & left)
Detoxifies blood
• Gallbladder
• Hangs on liver
• Stores bile
• Gallstones may develop if bile
crystallizes
Small Intestine
• 1 inch in diameter
• Approx. 10 feet long
• 3 segments
• Duodenum (~10 inches)
• Jejunum (~3 feet)
• Ileum (~6 feet)
• Lined with villi & microvilli
(projections that increase surface
area by 600x)
• Chyme remains here 3-5 hours
• 90% of nutrient absorption occurs
here
Large intestine
• 2.5 inches in diameter
• Approx. 5 feet long
• 4 parts
• Cecum (pouchlike with appendix)
• Colon (ascending, transverse,
descending, sigmoid)
• Rectum
• Anal canal
• Food remains here 3-10 hours
• Water absorption occurs here
Defecation reflex
• Emptying the anus is a spinal cord
reflex
• Internal sphincter is relaxed
• External sphincter is controlled by YOU
• Food passes too
large intestine =
stool)
• Food passes too
large intestine =
stool)
quickly through
diarrhea (watery
slowly through
constipation (dry
Disorders
• Appendicitis: inflammation of appendix
• Removal = appendectomy
• Hepatitis: inflammation of liver
• Classified as STD
• A, B, C, D, E
• Ulcers: sores in GI tract
• Duodenal = occur in duodenum
• Peptic/Gastric = stomach
• Anorexia: eating disorder resulting from
lack of eating
• Bulemia: eating disorder resulting from
binging & purging
Healthy liver
Hepatitis liver
Nutrition
• Macronutrients are broken
down by the digestive system
into micronutrients
• Carbohydrates (digest fastest) 
simple sugars
• Proteins  amino acids
• Fats/Lipids (digest slowest)  fatty
acids
Carbohydrates
• Main energy source for the body
• Food sources: fruits, vegetables
& grains
*Cellulose is a complex carb that
humans cannot break down; it
makes up fiber/roughage
Proteins
• Needed for repair, enzyme
production, building muscle,
making hormones
• Food sources: meat, dairy, nuts
*some essential amino acids
come from food
Lipids
• Main source of energy storage
• Food sources: fats, oils, lipids,
cholesterol
Vitamins (p. 434)
• Organic compounds that are
required in small amounts for
proper metabolism
• 2 types:
• Fat soluble – A, D, E, K
• Water soluble – B, C
Minerals (p. 435)
• Inorganic elements that are
required in small amounts for
proper metabolism
• 2 types:
• Major minerals – Ca, P, K, S, Na,
Cl, Mg
• Trace minerals – Fe, Mn, Cu, I, Co,
Zn, F, Se, Cr