3d-human digestive system 2009
TRANSCRIPT
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Human Digestive
System
Chapter 10.2
Ms. Ho
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Ingestion
Digestion Absorption
Excretion
Functions of the Digestive
System
*Note: alternate terms for the Digestive Tract are GI
(gastrointestinal) Tract & Alimentary Canal
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Mouth and Oral Cavity
Mouth opens to the
Oral Cavity
Teeth
Salivary Glands
Tongue
Other Structures:
uvula, soft palate,
hard palate, tonsils
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Teeth Structure & Function
Mechanical digestion
OR breakdown of food
Incisors: bite & cut
Canines: tearing &
shreading
Bicuspids/Premolars:
pierce & tear Molars: crush & grind
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How are teeth modified in
organisms?
Carnivore Herbivore Omnivore
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Salivary Glands
Food is mixed with saliva that is produced by
3 pairs of salivary glands
Parotid (largest)
Sublingual (smallest)
Submandibular
Uses ducts (tubular
canals) to transportsecretions to mouth
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Saliva
Presence of food triggers nervous reflex insalivary glands release saliva via ducts
Saliva is 99% water, mucus (glycoprotein)& enzymes (i.e. salivary amylase)
Function:
protects lining of oral cavity from abrasion &lubricates food for easier swallowing
chemical digestion: amylase breaks downpolysaccharide (amylose maltose)
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Functions of the Tongue
Helps mix saliva &food together
Positions food on
molars for chewing Moves food around
until it forms a bolus(food ball) & pushes
it back to pharynx Primary organ for
taste
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Tongue & Taste Buds
Muscle containing
papillae pimple-like
structure on upper
surface of tongue thathouses the taste buds
4 sensory tastes:
Sweet
Salty Sour
Bitter
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Location of Taste Buds
Q: Are you a
Super-taster?
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Other Oral Cavity structures
Uvula: flap of tissue covering nasal cavity
when swallowing food
Tonsils: lymphoid tissue on either side of
uvula in back of throat that produces
antibodies
Hard Palate: roof of mouth, hard ridges
Soft Palate: further back in mouth endingin the uvula
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Pharynx Common passageway for
food, liquids, and air
Pharynx muscles assist in
swallowing of bolus
Region connecting oralcavity & pharynx is the
Oropharynx
Epiglottis: flap of tissue
that covers over openingof trachea (glottis)
prevents food from
entering airway
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Swallowing
Food
Trachea moves up
against epiglottis to
close the opening
& prevent food from
entering the trachea
Mucin is secretedby back of throat &
esophagus wall
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Structure of the Esophagus
Muscular, flexible
tube, ~25cm long
3 layers:
Mucosa (inner): lining
covered in mucus
Submucosa (middle):
nerves, blood & lymph
vesselsMuscularis (outer):
circular & longitudinal
muscle
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Function of the Esophagus
Cross-sectional
View
To conduct food from the pharynx to the stomach
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Peristalsis
A series of
wave-like
contractions
that propelsfood along the
digestive tract
Q: What is it
called when
food moves
upwards?
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Structure of the Stomach
J-shaped muscular sac, stretches with food
3 layers of muscles: Longitudinal (outside), Circular
(middle) & Oblique (inner folds)
Inner lining is folded into accordion-like ridges called
rugae inc SA
Ridges contain gastric glands that produce gastric
juice (enzymes, mucus, HCl) for chemical digestion
Cardiac sphincter: ring of muscle controlling
entrance into stomach
Pyloric sphincter: ring of muscle controlling exit out
of stomach
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Stomach
Q: How many litres
of food can the
stomach hold when
fully expanded?
Q: How long does
it take your stomach
to empty after ameal?
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Bulk storage of undigested food
Mechanical breakdown of food via
rhythmic contractions (mixing of fluids)
Chemical Digestion: breaks chemical
bonds via hydrochloric acid (pH 2) and
enzymes (pepsin & lipase)
End product is chyme partially digestedfood in a semi-liquid state
Functions of the stomach
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Stomach Lining
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Mixing & Rhythmic Contractions
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Consist of a series of loops loosely attachedto the back of the abdomen
Name is from small diameter (approx. 2.5 to
3cm diameter, 7m in length) Mesentery: layer of connective tissue that
holds small intestine together to prevententangling of intestine in abdominal cavity
Ileocecal valve: ring of muscles (sphincter)that controls movement of material fromsmall intestine to large intestine
Structure of the Small Intestine
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3 Sub-regions of Small Intestine
Duodenum
Jejunum
Ileum
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Function of the Small Intestine
Most of the chemicaldigestion ofmacromolecules &absorption ofnutrients occurs here
90% of products areabsorbed in smallintestines
Other 10% absorptionoccurs in stomach &large intestines
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Structure of Intestinal Wall
Lining has folded finger-like projections
called villi increase SA
Each villus has many microscopic foldscalled microvilli further increase SA
to maximize absorption
Network ofcapillaries & tiny lymph vessel
called lacteal extend into hollow core ofeach villus
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The Intestinal Wall
*Note: only 2 layers of muscles (circular & longitudinal muscle)
instead of 3 like the stomach (no oblique muscle)
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Cross-section of Small Intestines
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Surface of Intestinal Wall
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Cross-section of Villus
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Absorption within Small Intestines
Nutrients are absorbed
across Intestinal cells
(Villus) either via the:
Blood Capillaries amino acids &
monosaccharides
Lacteal glycerol &
fatty acids
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Functions within each Region
Duodenum: (first 25cm, U-shaped)chemical digestion occurs here, chymemixes w/ digestive juices from pancreas,
liver, gall bladder & intestinal wall Jejunum: (~3m long) most absorption of
nutrients occur here, highly folded innerlining contains lots villi & intestinal glands
Ileum: (~4m long) contains fewer & smallervilli, absorb nutrients & push undigestedmaterial into large intestine
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Intestinal Movements
Peristalsis: series of
wave-like muscular
contractions &
relaxations Rhythmical
Segmentation:
mixing contractions
that knead materialback and forth without
propelling it forward at
a very fast rate
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Structure of the Large Intestine
Large upside-down U-shaped organ
Approx. 1.5m in length & 8cm in diameter
Three main sections: ascending colon,transverse colon & descending colon
Chyme enters caecum a small pouchconnected to ascending colon host to
large # of bacteria that breakdowncellulose
Appendix a finger-like projection at the tipof caecum function is still a mystery
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3 sections of the Large Intestine
Ascending
Transverse
Descending
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Complete absorption of nutrients
Reabsorb water, minerals & other useable
materials prevents dehydration
Absorb vitamins K & B (biotin, folic acid)
produced by bacteria (E. coli)
Form, compact & store fecal matter (waste &
undigested material) prior to defecation
*Note: movement of material via peristalsis
Functions of the Large Intestine
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Structure of the Large Intestines
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Last portion of the digestive tract:
Rectum: where feces are stored until
eliminated
Anal Canal: between rectum & anus
passageway for feces, ends in Internal
(involuntary) and External (voluntary) anal
sphincters allows body to control timingof elimination
Rectum & Anal Canal
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Digestive Questions
How long does it take to
digest a meal?
How is gas produced
within along thedigestive tract (2 ways)?
How does one get
diarrhea & how does it
happen?
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Accessory Organs
Pancreas, Liver &
Gall Bladder
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Accessory Organs
Large organs outside the digestive tract
that aids in chemical digestion
Chemical secretions are carried by ducts
that empties into the digestive tract
3 Main Accessory Organs:
Liver
Gall Bladder
Pancreas
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Liver, Gall Bladder & Pancreas
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Structure of the Liver
Largest internal organ, brownish-red in colour,divided into 2 large lobes (L & R)
Located just beneath the diaphragm
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Function of the Liver
Liver performs over 500 functions:
Produces bile (greenish-yellow liquid) that
contains bile salts from cholesterol that helps to
emulsify large fat globules into smaller fatdroplets (easier fat digestion & lipase action)
Emulsification: is a process that involves
molecules attracted to water at one end and fats
at the other end creating a suspension of smallfat dropletsstable emulsion
Bile released via hepatic duct
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Functions of the Liver
Plays major role in metabolism (set ofchemical reactions that maintains life):
Demolition: breaks down old RBC
Recycler: parts of decomposed Hb arerecycled to make bile salts
Storehouse: collects excess chemical inblood (i.e. fat soluble vitamins, glucose
glycogen)Detoxification centre: detoxifies poisons
ingested in food & water (i.e. alcohol)
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Hollow, pear-shaped organ on the
underside of the liver
Not involved in enzyme production
Storage warehouse for bile, release is
triggered by hormone via cystic duct
Gall Bladder
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Gall Bladder
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Structure of the Pancreas
Leaf-shaped gland, ~20cm in length
Located close to curve of stomach,
attached to the duodenum
Pancreatic juice enters duodenum via
pancreatic duct
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The Pancreas
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Produces over28 digestive enzymes thatbreaks down lipids (lipase), carbohydrates(amylase) & proteins (trypsin, peptidase)
Produces pancreatic juice, alkalinesubstance (NaHCO3) that neutralizesacidic chyme, so other enzymes canfunction
Produces insulin (hormone that regulatesblood glucose levels), allows glucose toenter cells
Pancreas
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Pancreas & Diabetes Hypoglycemic: abnormally low-levels of
glucose in blood (pancreas sends out too
much insulin to break down sugar)
Hyperglycemic: extremely high glucoselevels or diabetes (pancreas cant make
enough insulin or body cant use insulin)
Type 1: insulin dependent
Type 2: non-insulin dependent
Type 3: gestinational diabetes
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AccessoryOrgans &
their ducts
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Summary of the Digestive System