Download Digestive System

Digestive System
Digestive System
• Also called the gastrointestinal tract
• Major components
– Mouth
– Pharynx
– Esophagus
– Stomach
– Intestine
– Rectum
– Anus
Digestion
• The mechanical and chemical
processes that breaks down
large food molecules into
smaller ones.
Absorption
• When the small food molecules
pass through the cells of the small
intestine into the blood stream and
lymphatic system. Water, minerals
(salts), and some vitamins enter the
blood stream via the large
intestine.
Activities of Digestion
• Ingestion, or eating
• Peristalsis, or involuntary, sequential
contractions that move ingested nutrients
along the digestive tract.
• Digestion, or the conversion of large
nutrient molecules into small molecules.
• Absorption, or the passage of usable
nutrients into the blood stream and
lymphatic system
Activities of Digestion
• Defecation- the elimination
from the body of undigested
and unabsorbed material as
solid waste.
Chemical Digestion
• Breaks down food particles
through a series of metabolic
reactions involving enzymes.
Mechanical Digestion
• Physical processes such as
chewing, peristalsis, and the
churning movement of the
stomach and small intestine
of mix the food with
enzymes and digestive juices.
MOUTH
• Also known as the ORAL CAVITY
• Includes: Outer vestibule or Buccal cavity
– Lips, cheeks, teeth and gums
• Oral cavity proper
– Opening (cavity),
– fauces (L. throat)
FAUCES
A sensory nerve ending that
triggers the involuntary phase
of swallowing. Also
stimulates the gag reflex.
MOUTH
• 1 to 2 liters of saliva each day
• 1st food breaks apart by chewing
• Chemical digestion starts with starch being
broken down.
• Chewing mixes the food with saliva
• Saliva is mostly water
• Mixture (lubricated ball is called BOLUS
Lips consists mainly of fibroelastic
connective tissue and skeletal muscle covered
by epithelium.
• Orbicularis oris muscle makes the lips
capable of movement.
• Lips are sensitive and abundantly supplied
with blood vessels, lymphatic vessels, and
sensory nerve endings coming from the
trigeminal nerve.
•
• labial frenulum- fold of mucous membrane that
connects each lip to the gum.
• lingual frenulum- limits backward movement of
tongue.
• red free margin- lips are covered by thin
translucent epidermis that allows capillaries
underneath to show, to give lips a reddish color.
• Lips place food in mouth to keep food
in proper position.
• Contain sensory receptors to identify
specific textures of food.
• Moist mucous membrane of inner
surface of lips leads to mucous
membrane of inner surface of cheeks.
CHEEKS
• Cheeks- fleshy part of either side of face, below
eyes and between nose and ear.
• The mucous membrane lining the lips and cheeks
is a thick squamous epithelium.
• When surface cells are worn away, they are
replaced by rapid dividing cells underneath.
• Muscle of cheeks contribute to chewing process,
and help hold food in position.
• Roof of mouth
• 2 Sections
- hard palate (anterior)
formed by part of palatine bones &
maxillae
- soft palate (posterior)
posterior border of hard palate,
extends b/w the oral & naval parts of
pharynx
• The small, fleshy, hard cone in center is
called the uvula
- keeps food from entering nasal
passages when swallowing
• Two curved folds of mucous membrane
extending laterally & downward from soft
palate
- palatoglossal arch
- palatopharyngeal arch
• The palatine tonsils lie b/w the arches.
• When food is chewed & moistened by
saliva, the tongue pushes it up against
the surface of the hard palate, crushing
& softening it.
• The hard palate is covered
with a firm mucous
membrane, the soft palate
composed of interlacing
skeletal muscles allowing it
to move up & down over the
nasopharynx.
BABIES:
20 TEETH
10 ON EACH JAW
EACH JAW HOLDS:
ADULTS:
4 CUTTING TEETH
(INSCISORS)
32 PERMANENT
2 CANINES
16 ON EACH JAW
4 PREMOLARS
SIX MOLARS
THIRD MOLARS
(WISDOM TEETH)B/W
AGES 17-21, NO BABY
TOOTH BEFORE.
Root-embedded in a
socket in alveolar process
of a jaw bone.
Crown- projecting
upward from the gum.
Neck- b/w root and
crown, which is
surrounded by the gum.
Dentine- is extremely sensitive yellowish portion surrounding the
pulp cavity. (bulk end of tooth)
Enamel-is the insensitive white covering of the crown. (hardest
substance in the body)
Cement- bonelike covering of neck and root
Pulp- soft core of connective tissue; contains the nerves and blood
vessels of the tooth.
Gum- firm connective tissue. Covered with mucous membrane.
EYETEETH
•Why are canine
teeth called
“eyeteeth”?
Tongue
• Tip of tongue functions in chewing
• Base of tongue helps move food from the
mouth to the pharynx
• Important for speech
• Helps to taste food
• Composed of skeletal muscle
• Covered by smooth mucous membrane on
underside
• Dorsal surface contains papillae (taste buds)
•
•
•
•
Mucous membrane is divided in two
The oral part, anterior two-thirds
Pharyngeal part, posterior third
Delineated by the V-shaped sulcus terminalis
Three types of papillae
• Filiform papillae, appear
whitish and contain no
taste buds
• Fungiform papillae,
located on the tip of the
tongue, contain taste buds
• Circumvallate papillae, in
shape of a V on posterior
of oral part of tongue,
contain taste buds
The Pharynx
The Esophagus
Pharynx
•Air passage way during breathing & a food
passage during swallowing.
•3 parts:
•Nasopharynx- superior to soft palate
•Oropharynx- soft palate to the epiglottis
•Laryngopharynx- posterior to the
epiglottis, joins the espophagus
Esophagus
•Muscular, membranous tube( about 25 cm long), which
food passes from the pharynx into the stomach
•Located in front of the vertebral column and behind the
trachea
•Each end closed by sphincter muscle-rest & collapsed
•Irritation in lining of esophagus-heartburn
•Epiglottis-goes to stomach or lungs-moves so that
you can swallow food
The stomach is the most expandable part
of the digestive tract. It stores, mixes,
and digests ingested nutrients.
*Food enters the stomach through
the lower esophageal orifice.
*Partially digested nutrients leave
the stomach and enter the opening
at the other end of the stomach
called the pyloric orifice.
1. The stomach stores ingested nutrients until they
can be released into the small intestine.
2. The stomach churns ingested nutrients, breaks
them up into small particles, and mixes them
with gastric juices to form a liquid called
chyme.
3. The stomach secretes hydrochloric acid and
enzymes that initiate the digestion of proteins
and kill most of the bacteria that enter the
stomach in food.
1. After food enters the stomach slow
peristaltic mixing waves start in the
fundus and body. Basic Electrical Rhythm
(BER).
2. After the pyloric region fills, peristaltic
waves chop the chyme and push it toward
the pyloric canal toward the pyloric orifice.
3. As the stomach empties, peristaltic waves
,move farther up the body of the stomach,
so that all the chyme is pushed into the
pyloric region.
*Gastric emptying is regulated
by both neural and hormonal
mechanisms.
*Gastric emptying in inhibited by
the presence of fat, acid,
hypertenosity, or distension in
the duodenum.
*A neural response is mediated
by the enterogastric reflex, which
decreases stomach motility and
gastric secretion.
*The hormonal response inhibits
gastric motility by releasing
hormones collectively known as
enterogastrones.
***Gastric juice is a
clear, colorless fluid
secreted by the
stomach mucosa in
response to food.
*1.5L of gastric juice
is secreted daily.
Gastric juice is composed of
hydrochloric acid, mucus, and
several enzymes. That
enzymes being pepsinogen.
Small amounts of gastric
lipase are secreted in the
stomach, and the digestion of
fats begins there, though only
minimally.
Gastric juice also contains an intinsic
factor that combines with Vitamin B12
from digested food to form an
antianemic factor necessary for the
formation of red blood cells.
***Pepsin, assisted by hydrochloric
acid, breaks down large protein
molecules into smaller molecule
peptones,proteoses, and amino acids.
1. Cephalic (“head”) phase.- When food is
seen, smelled, tasted, chewed, or
swallowed, the stomach is stimulated by
activity of the vagus nerve, gastric juice is
secreted before the food is swallowed.
•Chyme moves into the small intestine after 1
to 3 hrs.
•Takes 1 to 6 hrs to move through the 6-m
(20ft) intestine.
•Absorbs almost all the digested molecules of
food into the blood and
lymph.
•Lies within the abdominopelvic cavity
•Separated into three parts the duodenum,
jejunum, and ileum
•Duodenum- is the C-shaped initial segment and is
about 25cm long the
Shortest of the three
•Jejunum is about 2.5 m (8ft) long. Ileum extends
from the jejunum to the
cecum. Both are suspended from the posterior
abdominal wall by the
Mesentery.
•A sphincter that ordinarily remains constricted,
regulating the entrance
Of chyme into the large intesine and preventing the
SPHINCTER
• A sphincter that ordinarily remains
constricted, regulating the entrance
of chyme into the large intestine and
preventing the contents of the cecum
from flowing back into the ileum
Mucosa has three distinctive features that enhance
the digestion and absorption processes known as
plicae circulares, and villi and glands that secrete
intestinal juice.
Plicae circulares- are circular folds that increase the surface area
available for absorption and cause the chme to spiral rather than move in
a straight line; the spiraling motion enhances absorption.
-The large intestine’s
primary functions are to
reabsorb any remaining
water and some salts, and
the accumulation and
movement(excretion) of
undigested substances like
feces.
Large Intestine
-The part of the digestive tract between the ileocecal
orifice and the anus.
-7 parts of the Large Intestine
-Ascending colon
-cecum
-Transverse colon
-veriform appendix
-Descending colon -rectum
-Sigmund colon
• Muscles are arranged so it can move side to side,
up and down, and in and out.
• Three bilateral pairs of extrinsic muscles
• Hypoglossus
• Genioglossus
• Styloglossus
• Four pairs of intinsic muscles
•
•
•
•
Longitudinalis superior
Longitudinalis inferior
Transversus lingual
Verticalis lingual
• The extrinsic muscles move food within the
mouth to form it into a round mass, or
bolus, and the intrinsic muscles assist in
swallowing
Uvula
• Hanging down from the center
of upper soft palate.
• Helps keep food from entering
the nasal passages during
swallowing.
Large Intestine
-The
part of the digestive tract between the ileocecal
orifice and the anus.
-4 parts of the Large Intestine
-Ascending colon
-Transverse colon
-Descending colon
-Sigmund colon
-The large intestine’s primary functions are to reabsorb any remaining
water and some salts, and the accumulation and movement(excretion) of
undigested substances like feces.