Biology 2
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http://www.youtube.com
/watch?v=Wu2iJseYlOQ
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The mechanical and chemical breakdown of
foods and the absorption of the resulting
nutrients by cells
◦ Mechanical digestion- breaks large pieces into smaller
ones without altering their chemical composition
◦ Chemical digestion- breaks food into simpler chemicals
Explain how both types of
digestion occur in the mouth…
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Alimentary canal:
◦ Extends from the
mouth to the anus
◦ 8-9 meters long (or
about 30 feet)
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Accessory organs:
◦ Secrete substances
used in the process of
digestion into the
canal
1.
2.
3.
4.
5.
6.
7.
8.
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Rectum
Anus
1.
2.
3.
4.
Salivary Glands
Liver
Pancreas
Gallbladder
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Mucosa: innermost layer, bordering lumen
◦ Mostly epithelial with tiny projections extending
into the lumen to increase surface area to enhance
absorption
◦ Glandular epithelium that secrete digestive
enzymes
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Submucosa:
◦ Connective tissue
◦ Nervous tissue
◦ Blood vessels
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Muscular Layer - smooth muscle
◦ Contracts resulting in peristalsis
◦ Circular fibers and longitudinal fibers
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Serosa – outermost layer
◦ Connective tissue and epithelium
◦ Protection
◦ Secretes serous fluid which moistens and lubricates
tube so organs within abdominal cavity freely slide
against eachother
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Mixing movements
◦ Smooth muscles in small segments contract
rhythmically
◦ Such as a wave of contractions from one end of the
stomach to another to mix digestive juices and food
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Propelling movements
◦ Peristalsis- wavelike motion when a ring of
contraction appears in the wall of the tube but a
section of the tube ahead is relaxed
◦ Pushes food along the tube from one end to the
other such as in the esophagus
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https://www.youtube.com/watch?v=_QYwscALNng
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Take about 30 minutes to complete the jot
chart for all the parts of the digestive system.
◦ Be sure to use details (write small)
◦ We will discuss the anatomy & physiology of each
part and potentially add to your jot chart
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Lips, tongue, cheek, and palate surround the
oral cavity
Tongue- skeletal muscle with raised papillae
and taste buds found in pores
Palate- bony roof of oral cavity
Teeth- 20 primary teeth; 32 secondary teeth
◦ Composed of outer enamel, hard dentin, & root
with canal of nerves and blood vessels
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Receives food, beginning
mechanical digestion with
reducing solid particles and
mixing them with saliva in a
process called mastication
Tongue- moves and mixes food,
while rough papillae create
friction, further breaking down
food
Teeth- increase the surface area
of the food by breaking it down
for further chemical digestion
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Has lymphatic structures,
such as tonsils and adenoids
◦ These are common sites of
infection and can interfere with
breathing and swallowing when
infected
◦ Tonsillectomy- removal of
tonsils due to repeated infection
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Dental caries- when acid
forming bacteria decay tooth
enamel
◦ Arises when sticky, sweet food
is not brushed off the teeth
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3 pairs of salivary glands:
1. Parotid glands- large amylase
secreting glands b/w skin of cheek
and masseter muscle, slightly below
ears
2. Submandibular glands- located on
floor of mouth on lower jaw & consists
of serous and mucous cells
3. Sublingual glands- small on floor of
mouth below tongue, consisting of
mucous cells
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Secrete saliva that moistens food particles
and begins chemical digestion of
carbohydrates (sugar)
Cleanses mouth and teeth
Dissolves food so it can be tasted
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Contains two types of cells:
◦ Serous cells- make salivary amylase enzyme that
breaks down complex carbs into simpler
disaccharides
◦ Mucous cells- make mucus to bind and lubricate
food for swallowing
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Cavity posterior to mouth from where the
esophagus leads to the stomach
Connects the nasal and oral cavities
Muscular passageway that functions
in swallowing
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3 stages of swallowing:
1. Voluntary stage in which food is chewed and
mixed with saliva, tongue rolls food into ball
(bolus) and forces it into the pharynx
2. Food stimulates sensory receptors, triggering
swallowing reflex
3. Peristalsis transports food through esophagus to
stomach
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Straight muscular food
tube from pharynx to
stomach
Lies posterior to trachea
Penetrates the
diaphragm
Lower esophageal
sphincter remains
contracted until
peristalsis waves open it
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Simply a muscle to pass food through
peristalsis
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Reflux of gastric juices from the stomach
through the esophageal sphincter causes
heartburn
◦ Can even lead to esophageal cancer if continuous
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J-shaped pouch-like organ in upper left
portion of abdominal cavity
Can hold 1L or more
Regions of stomach:
◦ Cardiac region- near esophageal opening
◦ Fundic region- balloons superior to cardiac region
for temporary storage
◦ Body- main part of the stomach
◦ Pyloric region – narrows into the pyloric canal,
which ends at a muscular pyloric sphincter valve
that empties into the small intestine
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Mixes food with gastric juice, initiates protein
digestion, carries on limited absorption, &
moves food to the small intestines
◦ Pepsinogen from chief cells mixes with HCl to form
pepsin and break down protein
◦ Intrinsic factor is released to help absorb vitamin
B12
◦ Chyme, mixed gastric juices and food, get pushed
to pyloric region of stomach
Inner lining of the stomach has 3 cell types:
1. Mucous cells- secrete mucus, coating walls
to protect them from strong stomach acid
2. Chief cells- secrete digestive enzymes
3. Parietal cells- release hydrochloric acid
(HCl)
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Lining has many gastric pits (grooves) and
is very thick
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Extends horizontally across the posterior
abdominal wall in C-shaped curve of
duodenum
C cells produce pancreatic juice that empties
into the pancreatic duct
The pancreatic duct connects to the
duodenum
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Exocrine function is to secrete pancreatic
digestive juices
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Amylase- digest carbs
Lipase- breaks down lipids (fats)
Nucleases- break down nucleic acids
Trypsin- main enzyme that breaks down protein
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In cystic fibrosis, defective chloride channels
in cells draws in water, drying out the lungs
and pancreas specifically
◦ Causes sticky mucus that can make breathing
difficult and blocks secretions of the pancreas
◦ Can cause malnutrition
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Upper right quadrant
of abdominal cavity
Heaviest organ in the
body at 3 pounds
Reddish brown and
surrounded by blood
vessels
Separated into 2
lobes
Hepatic duct releases
bile into duodenum
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Aids in carbohydrate metabolism by breaking
down glycogen into glucose when blood
sugar is low
Functions in lipid metabolism, where fats
made in the liver get transported away to
adipose tissue for storage
Protein metabolism & makes clotting proteins
found in blood plasma
Stores substances, detoxifies body, destroys
damaged RBCs & WBCs
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Livers digestive function is the secretion of
bile, which is contain bile salts that emulsify
fats, breaking them down into smaller
droplets
Hepatitis- inflammation of the liver and can
be caused by virus, alcoholism, or various
drugs
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Muscular pear-shaped sac in a depression on
the liver’s interior surface
Connects to cystic duct that joins to hepatic
duct
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Stores bile between meals, reabsorbs water to
concentrate bile, and contracts to release bile
into the small intestine
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Gallstones- caused by cholesterol
precipitating out of bile, forming crystals
◦ Can block bile flow into the small intestine, causing
pain
◦ Cholescystectomy can surgically remove the
gallbladder when gallstones are obstructive
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Long tubular, looping organ extending from
pyloric sphincter of stomach to large intestine
3 portions
1. Duodenum- follows a C shaped path and is fixed in
place
2. Jejunum- mobile portion of the s.i. with thicker wall
more active in absorption
3. Ileum- last stretch of s.i. that joins the large intestine
Mesentery- double layered
fold of membrane that
suspends s.i. from
abdomen walls w/
blood vessels & lymph
tissue
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Intestinal villi cover the inner wall of s.i. that
increase surface area for absorption
Goblet cells secrete mucus to further dissolve
chyme
Peptidases- enzymes that break down ______
Sucrase, maltase, and lactase- enzymes that
break down ______
Intestinal lipase- enzyme that breaks down ___
Mixing and peristalsis
◦ Peristalsis is much slower in s.i., taking about 3-10
hours to go from one end to the other
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In malabsorption, the s.i. digests but doesn’t
absorb all nutrients
◦ Symptoms- weight loss, vitamin deficiency, anemia,
diarrhea
◦ Causes could be obstructions, reaction to gluten
(protein in grains), microvilli are damaged
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Ileoceccal sphincter joins the ileum of the s.i. to the
cecum of the large intestine
Much larger in diameter than s.i.
Parts of Large Intestine:
◦ Cecum- beginning pouch that hangs below the ileoceccal
sphincter
 Appendix projects down from it
◦ Colon- ascending, transverse, descending, and sigmoid
colons
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Lacks villi
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Little or no digestive function
Goblet cells that function in mucus secretion,
protecting the intestinal walls from abrasion
Absorbs water and electrolytes
Intestinal flora- many bacteria species that
break down some of the molecules that
humans cannot digest, such as cellulose from
plants
◦ This creates gas as a by-product
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Mixing and peristalsis movements
◦ Usually peristalsis only occurs 2-3 times a day in l.i.
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Why can antibiotics often times cause digestive
problems, such as diarrhea and/or stomach
cramping?
What can be done to prevent or help circumvent
this?
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Attaches to the sigmoid colon and ends about
5 cm below the tip of the coccyx
Simply a canal to rid the body of waste
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Colorectal cancer
screenings are
recommended for those
over 50
◦ Polyps and tumors are
recognized and removed
◦ Fiberoptic colonoscopyinvasive and requires a
sedative
◦ Virtual/tomographic
colonoscopy- much less
invasive but if a polyp is
found, then the fiberoptic
procedure must take place
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An opening at the inferior end of the
alimentary canal to expel wastes
Internal anal sphincter muscle under
involuntary control
External anal sphincter muscle under
voluntary control
Expels feces
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Feces includes materials that were not
digested or absorbed, plus water,
electrolytes, mucus, shed intestinal cells, and
bacteria
◦ 75% water
◦ Color is due to bile pigments altered by bacterial
action
◦ Odor due to bacterial breakdown of nutrients and
their byproducts
◦ Diversity of gut bacteria is
linked to good health