Download Digestive System

Do Now
• What do you already know about the
digestive system? List 3 things!
• What would happen if you were tied
upside down, would you still be able to
eat? Explain.
• List the components of the alimentary
canal.
The Digestive System!
Chapter 15
Objectives
• To compare and contrast chemical vs.
mechanical digestion.
• To explain the general characteristics of the
alimentary canal.
• To explain the process of swallowing and
peristalsis.
• To identify the structures of the mouth and
explain their function.
• To understand the necessity of salivary glands
and name each type.
Digestion
• Chemical digestion- complex molecules are
broken down into smaller molecules
• Mechanical digestion- physical movement of
food that breaks it down into smaller pieces
– Ex. Chewing, grinding, mashing
– Chewing is called “mastication”
Components of Digestive System
• Alimentary Canal
– “digestive tract”
– Mouth, pharynx,
esophagus, stomach, small
intestine, large intestine,
rectum and anus
• Accessory Structures:
– Salivary glands, liver,
gallbladder, & pancreas
Alimentary Canal
• Muscular tube that
passes through the
body’s ventral
cavity
• About 9 meters
long
• Contains 4 layers
Alimentary Canal
1) Mucosa (innermost):
– Protects the tissues beneath it & carries out secretion
and absorption
– Consists of epithelium, underlying CT, and a little bit of
smooth muscle
2) Submucosa:
– Nourishes surrounding tissue and carries away
absorbed materials
– Consists of loose connective tissue, blood vessels,
glands.
Alimentary Canal
3) Muscular Layer:
– Layer which moves the tube
– Contains two coats of smooth muscle tissue & nerves (plexus)
– Fibers of the inner coat (circular) surround the tube
• When they contract the tube’s diameter decreases
– Fibers on the outer muscular coat (longitudinal) run lengthwise
• When they contract the tube shortens
4) Serosa:
– Protects underlying tissues and secrete serous fluid
Alimentary Canal
Movements of the Alimentary Canal
• Mixing Movement
– Occurs when smooth
muscle in small units of the
tube contract rhythmically
– Mixes food with digestive
juices secreted by the
mucosa
• Propelling Movement
– Known as peristalsis
Do Now
-Which layer of the alimentary canal is
responsible for moving the tube? What type
of tissue is this layer?
- List the 3 macromolecules found in your food
and what they’re broken down into.
Alimentary Canal Length
Organs of the Digestive System
•
•
•
•
The Mouth
Receives food and begins
digestion mechanically
Reduces the size of solid
particles and mixes them
with saliva
Oral cavity - Lips, cheeks,
tongue & palate
Vestibule - Narrow space
between teeth, cheeks, &
lips
Salivary Glands
• Secrete saliva
• Contain 2 types of
secretory cells:
*Major glands:
1. Parotid
2. Submandibular
3. Sublingual
– Serous cells:
produce salivary
amylase (breaks
down carbs)
– Mucous cells:
produce mucus to
bind to food and
lubricate during
swallowing
Pharynx
• Connects nasal and
oral cavities with
larynx and
esophagus
• Contains 3 parts:
– Nasopharynx
– Oropharynx
– Laryngopharynx
Swallowing Mechanism
1. Food is chewed and mixed with saliva,tongue
rolls this into a mass or bolus and forces it into
the pharynx
2. Food stimulates sensory receptors around the
pharyngeal opening, triggering the swallowing
reflex
3. Momentarily inhibits breathing, peristalsis
transports food into the esophagus and to the
stomach
Esophagus
• Connects pharynx to
the stomach
• Separated from the
stomach by the
cardiac sphincter
• Contracts and closes
the sphincter to
prevent regurgitation
Stomach
• J shaped with about a
1 liter capacity
• Contains rugae, which
allow it to expand
• Divided into 4 regions
–
–
–
–
Cardiac
Fundic
Body
Pyloric
• Contains cardiac and
pyloric sphincters
Stomach Juices
“Gastric Juice” consists of:
• HCl
•Mucus
•Viscous alkaline secretion
that coats the stomach
•Enzymes:
–Proteases such as
Pepsin- digests protein
(starts as pepsinogen
and when mixed with
HCl makes pepsin)
Stomach Juices
• The mixture of gastric
juice and the bolus gives
us chyme
• Chyme pushed into the
small intestine
• Type of food can affect
rate of emptying:
– Fatty food 3-6 hrs. in
stomach
– Proteins move more
quickly
– Carbs go through the
fastest!
Gastric Absorbtion
• The stomach mostly breaks things down
• Can absorb only small amounts of water,
certain salts, alcohol, and some lipidsoluble drugs.
– EX: Aspirin
Pancreas
• Secretes pancreatic
juice into the duodenum
• Pancreatic enzymes:
– Pancreatic amylase
• Digests carbs
– Pancreatic lipase
• Digests fats
– Nucleases
• Digests nucleic
acids
– Proteases:
•Digest protein
Liver
• Effects carbohydrate,
lipid, and protein
metabolism
• Produces bile:
– Contains bile salts,
bile pigments
(bilirubin and
biliverdin)
– **bile salts emulsify
fats and also
increase absorption
of fat-soluble
vitamins (A,D,E, & K)
Liver
• Also involved in…
– Blood sugar
regulation
– Storage of iron,
vitamins A, D, B12
– Detoxifies blood
(ex: removes
alcohol, H202)
Small Intestine
• 3 sections: Duodenum, Jejunum, Ileum
• Receives secretions from pancreas and liver
• Contain intestinal “villi”- increase surface
area for absorption
*Most of the absorption occurs here!
Large Intestine
• Contains cecum
(appendix attached),
colon, rectum, anal
canal
• Main function is to
absorb water and
electrolytes from
remaining chyme,
and forms and stores
feces.
Feces
• Contains materials
not digested or
absorbed
• Water
• Electrolytes
• Mucus
• Shed intestinal cells
• Bacteria (makes it
smell!)
Review
• What is the process that occurs after
swallowing?
• What is the scientific name for the
digestive tract?
• How many layers is this tract?
• What are the 3 parts of the pharynx?
• What is absorbed in the stomach?
• What does the pancreas do?