Download Digestive System

Digestive System
• Carries out the chemical and mechanical
breakdown of foods and the absorption
of the resulting nutrients by cells.
(Digestion)
_________________________ Digestion–
breaks large pieces into smaller ones without
altering their chemical composition.
Chemical Digestion– breaks food into
simpler chemicals.
Alimentary Canal
• Includes mouth, pharynx, esophagus,
__________________, small intestine, large
intestine, rectum and anus
• Plus accessory organs such as salivary
glands, liver, gallbladder, and pancreas.
• Approximately 8 meters long
• Know the structure of the alimentary canals..
The different layers and what they do.
• Lumen– tiny projections in the mucosa that
extend into the passageway of the digestive
tube to increase the absorptive surface area.
Movements of the Tube
• Mixing movements and propelling
movements
• _______________________– a ring of
contraction appears in the wall of the tube,
at the same time the muscular wall ahead
of the ring relaxes. As the wave moves
along, it pushes tubular contents ahead of
it.
Mouth
• Receives food and begins digestion by
mechanically reducing the size of the solid
particles
• Called _________________________.
Tongue
• Lingual frenulum– a membranous fold
connects the midline of the tongue to the floor of
the mouth.
• Mostly ___________________ muscle
• Mixes food with saliva during chewing and
moves food toward the pharynx during
swallowing
• ________________________– rough
projections on the surface provide friction which
helps handle food and bear taste buds.
• The root of the tongue is anchored to the hyoid
bone in the back
Palate
• Roof of the oral cavity
• Consists of a hard palate (bony part of roof
of mouth) and soft palate (muscular
posterior part)
• _______________ – part of soft palate,
cone-shaped projection in back of mouth.
• Palatine tonsils– masses of lymphatic
tissue on either side of tongue in soft
palate
• Pharyngeal tonsils– (adenoids) found
above border of the soft palate
Cleft Palates
Teeth
• Begin mechanical digestion by breaking pieces
of food into smaller pieces
• Primary teeth (deciduous teeth)– erupt thru
gums between ages 6 months and 2 to 4 years
-- 20 deciduous teeth
• _____________________ teeth (permanent
teeth)– push primary teeth out of their sockets
(after the primary teeth roots are resorbed)
• Usually appear between ages 6 years to and
may not be complete until 17 and 25 years. -- 32
permanent teeth
Salivary Glands
• Secrete saliva which begins the chemical
digestion of carbohydrates
• Is a solvent to dissolve foods so they can
be tasted
• __________________ cells secrete the
enzyme salivary amylase which splits
starch and glycogen molecules into
disaccharides
• Mucus cells secrete mucus which binds
food particles and lubricates the food
during swallowing
Types of Salivary Glands
Parotid Glands– ______________ salivary gland
– Anterior and somewhat inferior to each ear
– Secretes a clear watery fluid rich in amylase
Submandibular glands
• located in the floor of the mouth on
the inside surface of the lower jaw
•Secrete both mucus and serous
Sublingual glands
• located on the floor of the mouth
inferior to the tonuue
•Primarily mucus, thicker
Pharynx
• A cavity posterior to the mouth from which
the tubular esophagus leads to the stomach
• Connects the nasal and oral cavity to larynx
and esophagus
Bolus– tongue rolls food mixed with saliva into
a mass and forces it into pharynx
• Food stimulates sensory receptors around
pharyngeal opening which triggers
swallowing reflex ( page 410)
• ____________________ – closes of the top
of larynx so that food is less likely to enter
trachea (windpipe)
Esophagus
•
•
•
•
Straight, collapsible tube about 25 cm long
Food passageway from pharynx to stomach
Behind trachea
Mucus glands scattered throughout to
lubricate lining
• Has lower esophageal ______________
just before the stomach which remains
contracted and close entrance to stomach to
prevent regurgitation of stomach contents
• When peristaltic wave reaches end of
esophagus, muscle fibers temporarily relax
and allow swallowed food to enter stomach.
Stomach
• J-shaped pouch-like organ that hangs
inferior to the diaphragm in upper left
portion of abdominal cavity
• Thick folds (called rugae) of mucosal and
submucosal layers mark the stomach’s
inner lining and disappear when the
stomach wall is __________________
• Receives food from esophagus, mixes
food with gastric juices, initiates protein
digestion, moves food into the small
intestines and some absorption
Stomach
• Pyloric sphincter – muscle at end of
stomach controls movement from stomach to
small intestines
• 3 types of gastric glands release different secretions
which make up the:
– ______________________ juices– contains
digestive enzymes, mucus and hydrochloric acid
• Pepsin– most important enzyme– begins digestion
of all types of dietary proteins into polypeptides
• Mucus cells release a thick, alkaline secretion which coats the
inside of stomach
• Prevents stomach from digesting itself
Regulation of Gastric secretions
1. When a person tastes, smells or sees
appetizing food or when food enters
stomach, parasympathetic impulses
stimulate release of _____________
(Ach)
2. Ach stimulates gastric glands to secrete
abundant gastric juices
3. As food moves into small intestine, acid
triggers nerve impulses that inhibit
gastric juices
Mixing and Emptying Stomach
Actions
• Mixing movements of the stomach produce a
semifluid paste of food particles and gastric juices
called __________________.
• When peristaltic waves push chyme toward
pyloric sphincter, the muscle begins to relax and
stomach contractions push chyme into small
intestine a little at a time.
• Fatty foods may remain in stomach 3- 6hrs
• Foods high in protein move thru more quickly
• Carbohydrates usually pass thru faster than
proteins
Pancreas
• As chyme enters the duodenum, the
pancreas, liver and gallbladder add their
secretions
• Mostly involved in lymphatic system
• Connects with the duodenum at the same
place where the bile duct and gallbladder
join
• Pancreatic juice contains enzymes that
digest carbohydrates, fats, nucleic acids
and proteins
Pancreas
• Pancreatic amylase – enzyme that splits
starch or glycogen (carbs) into disaccharides
• Pancreatic lipase– enzyme that digests fats
• Secretin – As acidic chyme, enters the
duodenum, the hormone secretin is released
into bloodstream… this stimulates secretion
of pancreatic juices that have a high
concentration of bicarbonate ions to
neutralize the acidity of chyme before it
enters small intestines
Liver
• Found in upper right quandrant of the
abdominal cavity, just inferior to the
diaphragm
• Has various functions, but only _________
secretion is important to digestion
• Look on page 419 and list the functions of
liver
• Bile– yellowish green liquid continuously
secreted from hepatic (liver) cells
Bile and Gallbladder
• ______________________– pear-shaped sac in a
depression on the liver’s inferior surface (behind the
liver)
• Gallbladder stores bile from liver, contracts to
release bile into small intestine
• Bile salts break fat globules into smaller droplets
(Emulsification)
• Fat splitting enzymes (lipases) can then digest fat
molecules more effectively
• Bile also enhance absorption of fatty acids,
cholesterol and fat-soluble vitamins A, D, E, and
K…. Lack of bile results in poor lipid absorption and
vitamin deficiencies
Small Intestine
•
Tubular organ that extends from the
pyloric sphincter to the beginning of the
large intestine
1. Completes the digestion of nutrients in
chyme
2. Absorbs the products of digestion
3. Transports the residues to the large
intestines
• Consists of the duodenum (1st part),
jejunum (2nd part is mobile) and ileum
(last part)
Structure of Intestinal Wall
• Mesentery– is the peritoneal membrane
that suspends the jejunum and ileum from
the posterior abdominal wall
• The inner wall of the small intestine has
many tiny projections of mucus membrane
called intestinal ________________
• Villi greatly increase the surface area of
the intestinal lining, aiding the absorption
of digestive products
• Mucus secreting goblet cells are abundant
throughout the small intestine
Small intestines
1. The enzyme peptidases is secreted… to
split peptides into amino acids
2. The enzymes sucrase, maltase and
lactase are secreted… to split the
disaccharides (sucrose, maltose and
lactose) into ____________________
(glucose, fructose and galactose)
3. The enzyme intestinal lipase is secreted
to split fats
Small intestine
• Distension of the intestinal wall triggers
release of small intestine secretion
• Small intestine is the most important
absorbing organ of alimentary canal
• The villi absorbs the monosacharides,
amino acids and fat molecules and send
them by blood to the cells to be used or
lymphatic system
• Also absorbs _____________ and
electrolytes
• Food takes 3 to 10 hrs to travel the length
Small intestine to large intestine
• If small intestine becomes overdistended
or irritated, a strong peristaltic rush may
pass along organ’s length
• This sweeps contents into large intestine
so quickly that water, nutrients and
electrolytes are not absorbed, this is
_________________ characterized by
watery stools and frequent defecation.
• Ileocecal sphincter– joins small intestine
to large intestine
Large intestine
• Diameter is greater than small intestine
• 1.5 meters long
• Consists of the cecum, colon, rectum
and anal canal
• 4 Colon parts: ascending,
___________________, descending and
sigmoid colon (page 427, picture)
• Anal canal is last 2.4-4.0 cm of LI
• Anus– opens to the outside
Large intestine
•
•
•
Wall lacks villi
Has little or no digestive function
Mucus is only significant secretion which:
1. protects wall against abrasive materials
2. binds particles of fecal matter
•
•
Absorbs water and electrolytes and
proximal end
Stores fecal matter at distal end
Large intestines
• Intestinal _____________ – bacteria that
break down some molecules that escape
human digestive enzymes
• Cellulose (complex carbohydrates) do not
get digested by human enzymes
• Bacteria break it down and use it as
energy, and make vitamins K, B12,
thiamine and riboflavin which the
intestines absorb
• Bacterial actions may produce gases
Large intestines
• Peristaltic waves of large intestines only
happen 2 or 3 times a day.
• Mass movements in which a large section
of the intestinal wall constrict vigorously,
forcing the intestinal contents toward the
rectum (usually follow a meal)
• Feces– include materials that were not
digested or absorbed, plus water,
electrolytes, mucus, shed intestinal cells
and bacteria
– odor results from a variety of compounds that
bacterial produce
Large intestines
• Have 2 sphincter muscles:
– Internal anal sphincter– involuntary
– External anal sphincter– voluntary
• A person can initiate defecation reflex by
holding a deep breath and contracting the
abdominal muscles
• This forces feces into rectum and as rectum
distends, triggers the defecation reflex that
stimulate peristaltic waves in the descending
colon