Transcript The Digestive System

The Digestive System
Chapter 48
INTRODUCTION
Digestion is the mechanical and chemical
breakdown of food into forms that cells can absorb.
The FUNCTIONs of the Digestive System include
1. Breakdown food
2. Convert it into a usable form
3. Form and expel solid wastes
HUMAN
DIGESTIVE
SYSTEM
THE ALIMENTARY CANAL
If stretched out, the alimentary
canal is about 8 meters long.
That’s 26 feet!
OVERVIEW
•
https://www.youtube.com/watch?v=nM5kMSjBrmw
THE MOUTH (ORAL CAVITY)
• The mouth:
• Receives food
• Mechanically breaks up solid particles using TEETH & TONGUE
• Chemically digest food using saliva.
• This action is called mastication
• Makes a BOLUS (wet ball of food)
• The mouth also functions as an organ of
speech, and sensory reception.
TEETH & TONGUE
TEETH
Incisors- bite or cut off
Canines- grasp and tear
Premolars – grinding food
Molars – grinding food
TONGUE
• Position food between
teeth
• Push food back to pharynx
SALIVARY GLANDS
• Secrete saliva
Saliva moistens the food, and
begins the digestion of
carbohydrates
Three pairs of major
salivary glands.
THE PALATE AND UVULA
During swallowing,
muscles draw the soft
palate and the uvula
upward preventing food
from entering the nasal
cavity.
PHARYNX
• The back of the
throat.
• Deglutition
(swallowing)
SWALLOWING
• Epiglottis
• flap of cartilage
• closes trachea (windpipe) when swallowing
• food travels down esophagus
ESOPHAGUS
• Moves food down
to stomach by
PERISTALSIS
• involuntary muscle
contractions to
move food along
STOMACH
• 2 sphincters (valves)
• 3 layers of muscle
• Secretes gastric juices
(enzymes + HCl)
• Mechanically and
chemically breaks
down food
GASTRIC JUICE
• Acidic (pH 1.5-2.5)
(HCl)
• Pepsin- an enzyme
that breaks down
large proteins into
amino acids.
• HCl activates pepsin
• BOLUS + GASTRIC
JUICE = chyme.
• Heartburn
• Acid Reflux
ACCESSORY ORGANS
ACCESSORY ORGANS
•Pancreas
•Gall Bladder
•Liver
PANCREAS
Secretes PANCREATIC JUICE which contains enzymes to
digest all major nutrient types.
• Alkaline (base) neutralizes acidic chyme coming from
stomach.
LIVER
LIVER
• Function: produces bile
• BILE breaks up fats
GALL BLADDER
• It stores bile between meals
• Bile duct –
• Connects the liver, pancreas, and gall bladder to the
duodenum (small intestine)
GALLSTONES
• GALLSTONES – an accumulation of hardened
cholesterol and/or calcium deposits in the
gallbladder
• Can either be “passed” (OUCH!!) or surgically
removed
SMALL INTESTINE
• Function
• Digestion & absorption
• over 6 meters!
• small intestine has huge
surface area ~size of
tennis court
• Structure
• 3 sections
• duodenum = most digestion
• jejunum = absorption of
nutrients & water
• ileum = absorption of
nutrients & water
ABSORPTION IN THE SI
•
Much absorption is thought to occur directly through
the wall without the need for special adaptations
•
Almost 90% of our daily fluid intake is absorbed in the
small intestine.
•
Villi - increase the surface area of the small intestines,
thus providing better absorption of materials
Villi increase surface area.
More surface area = More absorption
LARGE INTESTINES
(COLON)
• Function
• re-absorb water
• use ~9 liters of water every
day in digestive juices
• > 90% of water reabsorbed
LARGE INTESTINE
• Solid materials pass through
the large intestine.
• These are undigestible solids
(fibers).
• Water is absorbed.
• Vitamins K and B are
reabsorbed with the water.
• Rectum- solid wastes exit the
body.
BACTERIAL FLORA
• Living in the large intestine is
a community of helpful
bacteria
• Escherichia coli (E. coli)
• produce vitamins
• vitamin K; B vitamins
• generate gases
• by-product of bacterial
metabolism
• methane, hydrogen sulfide
FECES
• Poop, excrement, solid waste, etc…
• Feces is composed of materials not digested or
absorbed, and include: Water, Electrolytes, Mucus,
Bacteria, and Bile pigments
• Approximately 1/3 of the dry weight of feces is
bacteria.
.
• The color of feces is provided by bile pigments
altered by bacteria
DIARRHEA
• a gastrointestinal
disturbance characterized
by decreased water
absorption and increased
peristaltic activity of the
large intestine.
• This results in increased,
multiple, watery feces.
• This condition may result in
severe dehydration,
especially in infants
CONSTIPATION
• a condition in which the
large intestine is emptied
with difficulty
• Too much water is
reabsorbed
• Solid waste hardens
RECTUM
• Last section of colon
(large intestines)
• eliminate feces
• undigested
materials
• extracellular
waste
• mainly cellulose
from plants
• roughage or
fiber
• masses of
bacteria
ANAL CANAL / ANUS… LAST STOP
• Exit or opening for solid
wastes
• Regulated by anal
sphincter (valve)
• Anal sphincter surrounded
by muscles
• Elimination aided by
abdominal muscles
HEMORRHOIDS
•Very common, especially during pregnancy and after
childbirth.
•Result from increased pressure in the veins of the anus. The
pressure causes the veins to bulge and expand, making them
painful, particularly when you are sitting..
Symptoms
Pain during bowel
• Anal itching
movements
• Anal ache or pain,
One or more hard
tender lumps near the
especially while sitting
anus
• Bright red blood on
toilet tissue, stool, or
in the toilet bowl