Transcript Digestive_System

DIGESTIVE
SYSTEM
Digestion is the mechanical and chemical breakdown of
food into nutrients that cell membranes can absorb.
The system digestive consists of the alimentary canal
and several accessory organs.
The alimentary canal is a 9 meter long muscular tube
that passes through the body’s ventral cavity.
DIGESTIVE PROCESSES
Ingestion
Movement
/ peristalsis
Digestion (chemical &
mechanical)
Absorption
Defecation
STRUCTURES OF THE WALL
1. Mucosa (mucus membrane)
composed of:
surface epitheleum
underlying connective tissue
small amount of smooth muscle
contains:
folds and projections that extend into the lumen to
increase absorptive surface area
mucus and digestive secreting gland
Function:
secretes and absorbs
protects the tissues beneath
2. Submucosa
contains:
loose connective tissue
glands
blood vessels
lymphatic vessels
nerves organized into a network called a
plexus
Function:
nourish surrounding tissues and carry
away
absorbed materials
3. Muscular Layer
contains:
2 coats of smooth muscle tissue
nerves organized into a plexus
function:
move the tube
movement:
circular muscle fibers contract to decrease
the tubes diameter
longitudinal muscle fibers contract to
shorten the tube
4. Serosa (serous layer)
composed of:
visceral peritoneum
function:
* protect underlying tissues
* secretes serous fluid which moistens and
lubricates the tube’s outer surface
so that organs
within the abdominal
cavity slide freely against one
another
MOVEMENTS OF THE TUBE
1.
Mixing movements
smooth muscles in small segments of the tube
contract rhythmically
2. Propelling movements
wavelike motions called peristalsis
MOUTH
1.
Cheek
consists of:
* outer layers of skin
* pads of subcutaneous fat
* muscles associated with expression
chewing
* inner linings of moist stratified
squamous epitheleum
and
2. Lips
contain:
skeletal muscle
sensory receptors
used to judge foods temp &
texture
many blood vessels
give lips reddish color
3. Tongue
* covered by a mucus membrane and a
membraneous fold called the frenulum
which connects the midline of the tongue
to the floor of the mouth
* composed of skeletal muscles
* rough projections called papillae provide
friction and contain taste buds
* posterior region, or root, is anchored to the
hyoid bone and covered with a rounded mass
of lymphatic tissues called lingual tonsils
4. Palate - forms the roof of the oral cavity
consists of:
* hard palate – anterior part
* soft palate – posterior part; forms a
muscular arch which extends
downward as a cone-shaped
projection called the uvula
During swallowing, muscles draw the soft palate
and uvula upward, closing the opening
between the nasal cavity and pharynx.
Palate cont….
In the back of the mouth, and on either side of
the tongue and closely associated with the
palate, are masses of lymphatic tissue called
palatine tonsils, which protect the body
against infections.
Pharyngeal tonsils, or adenoids, are on the
posterior wall of the pharynx, above the border
of the soft palate. Enlargement can block the
passage between the pharynx and the nasal
cavity, and must be removed.
TEETH
Two different sets of teeth form during
development.
Primary teeth (deciduous teeth) erupt
between the ages of six months and two to
four years. 20 teeth, 10 in each jaw.
Secondary teeth (permanent teeth) consists
of 32 teeth, 16 in each jaw. Appearance
begins around 6 years in age and is not
complete until the third molars appear
between 17 and 25.
Teeth cont….
The function of teeth is to break food into smaller pieces,
thus increasing the surface area of the food particles,
enabling digestive enzymes to react more effectively.
DIFFERENT TEETH ARE ADAPTED TO
HANDLE FOOD IN DIFFERENT WAYS:
1.
2.
3.
4.
Incisors (8) – chisel shaped, and their sharp edges
bite off large pieces of food
Cuspids (4) – cone-shaped, and they grasp and tear
food
Bicuspids (8) – flat surfaces, grind food
Molars (12) – flat surfaces, grind food
TOOTH STRUCTURE
2 main portions:
1. Crown – projects beyond the gum
2. Root – anchored to the alveolar process of the
jaw
SALIVARY GLANDS
Secretes saliva
 Moistens and binds food particles
 Begins chemical digestion of carbohydrates
 Solvent – dissolves food to be tasted
 Cleanses the mouth and teeth

SALIVARY SECRETIONS
2 Types of secretory cells:
1. serous cells – produce the watery fluid
that contains amylase which splits
starch and glycogen molecules into
dissaccharides
2. Mucous cells – produces a thick liquid called mucus
which binds food particles and lubricates for
swallowing
When a person sees, smells, tastes, or even thinks about
food, parasympathetic nerve impulses elicit the
secretions of a large volume of watery saliva.
Unpleasant senses inhibit parasympathetic activity so
less saliva is produced, and swallowing may become
difficult.
MAJOR SALIVARY GLANDS
1.
2.
3.
Paratid glands – largest; lies in front and
somewhat below each ear; secrete a clear
watery fluid containing amylase
Submandibular glands – located in the floor
of the mouth on the inside surface of the
lower jaw; predominately serous cells;
secretions is more viscuous because of the
presense of mucous cells also
Sublingual glands – smallest; on the floor of
the mouth under the tongue; primarily
mucous cells; secrete a thick stringy mucus
PHARYNX
Cavity behind the mouth
 No digestive aspect
 Passageway whose muscular walls function in
swallowing
 Connects the nasal and oral cavities with the
larynx and esophagus

PHARYNX
1.
Nasopharynx – communicates with the
nasal cavity and provides a passageway
for air during breathing
2.
Oropharynx –opens behind the soft
palate into the nasopharynx;
passageway for food and air moving
downward from the mouth
3.
Laryngopharynx – just below the
oropharynx; passageway to the
esophagus
SWALLOWING MECHANISM
Swallowing reflexes have 3 stages:
1st
* initiated voluntarily
* food is chewed and mixed with saliva
* tongue rolls mixture into a mass
(bolus)
* bolus forced into the pharynx
2nd
* begins as food stimulates sensory receptors
around the pharyngeal opening triggering
the
swallowing reflex:
a. soft palate rises, preventing food from entering the
nasal cavity
b. hyoid bone and larynx elevate; flaplike structure of
the larynx called the epiglottis, closes off the top of the
trachea
c. tongue presses against the soft palate, sealing off the
oral cavity from the pharynx
d. longitudinal muscles in the pharyngeal wall contract
pulling the pharynx upward toward the food
e. muscles in the lower part of the pharynx relax,
opening the esophagus
f. peristaltic waves begin in the pharyngeal muscles
and force food into the esophagus
The swallowing reflex briefly inhibits breathing.
3rd
peristalsis transports the food in the esophagus
to the stomach
ESOPHAGUS
 Straight,
collapsible tube about 25cm long
 Passageway from pharynx to the stomach
 Penetrates the diaphragm through an opening
called the esophageal hiatus
 Just above the stomach, circular smooth
muscle fibers in the esophageal wall thicken
forming the lower esophageal sphincter
(cardiac sphincter). These fibers contract and
close the entrance to the stomach preventing
regurgitation.
 Cardiac sphincter relaxes and allows food to
enter the stomach
 Mucous glands are scattered throughout the
submucosa
STOMACH
 Pouch-like,
J-shaped organ that hangs under
the diaphragm in the upper left portion of the
abdominal cavity.
 Capacity of about 1L or more
 Thick folds (rugae) of mucosal and submucosal
layers mark the stomach’s lining. These folds
disappear when the stomach wall distends.
 Mixes food with gastric juices
 Initiates protein digestion
 Limited amount of absorbtion
 Moves food into the small intestines
PARTS OF THE STOMACH
1.
2.
3.
4.
Cardiac region – small area near the esophageal
opening
Fundic region – balloons above the cardiac region;
temporary storage area
Body region – dilated and is the main part of the
stomach
Pyloric region – narrows and becomes the pyloric
canal as it approaches the small intestine. At the
end of the pyloric canal the muscular wall thickens
to form a powerful circular muscle, the pyloric
sphincter (pyloris). This muscle is a valve that
controls the gastric emptying into the small
intestine.
GASTRIC SECRETIONS
Many small openings, called gastric pits, stud the
surface of the mucus membrane. These pits are
at the end of tubular gastric glands.
Gastric glands generally contain three types of
secretory cells who’s products form gastric juices.
GASTRIC SECRETORY CELLS
1.
Mucous cells
* occur in the neck of the glands near
opening of the gastric pits
* secrete mucus
* release a more viscuous and alkaline
secretion which coats the inside
stomach wall preventing pepsin from
digesting proteins in the stomach
lining
the
GASTRIC SECRETORY CELLS
2. Chief Cells
* secrete digestive enzymes
* pepsin is the most important of these
enzymes
* pepsin is secreted as pepsinogen and is
snipped off when it comes in contact with
the hydrochloric acid secreted by the parietal
cells
* begins digestion of nearly all types of
dietary proteins
* secretes Gastric lipase that begins the
digestion of triglycerides (fats, oils…)
GASTRIC SECRETORY CELLS
3. Parietal Cells
* secrete hydrochloric acid
* secretes intrinsic factor that is needed for
vitamin B12 absorption from the small
intestines
GASTRIC SECRETORY CELLS
4. Enteroendocrine cells
*secrete the peptide hormone gastrin which increases
the secretory activity of gastric glands
REGULATION OF GASTRIC SECRETIONS
Gastric juice is secreted continuously, but
the rate varies considerably and is
controlled both neurally and hormonally.
When a person tastes, smells, or even sees
pleasant food, or when food enters the
stomach, parasympathetic impulses on
the vagus nerves stimulate acetcholine
(Ach) release from nerve endings.
This release causes gastric glands to secrete
large amounts of gastric juice (rich in HCl
& pepsin) and gastrin.
REGULATION OF GASTRIC SECRETIONS
Food moving into the small intestine
inhibits gastric juice secretion due to
sympathetic nerve impulses that are
triggered by acid.
Proteins and fats in the upper part of the
small intestine cause the intestinal wall to
release the peptide hormone
cholecystokinin, which decreases gastric
motility as the small intestine fills with
food.
GASTRIC ABSORPTION
Gastric enzymes begin breaking down proteins, but
the stomach wall is not well-adapted to absorb
digestive products.
The stomach absorbs only small quantities of water
and certain salts, as well as alcohol, and some
lipid soluble drugs.
VOMITING
Results from a complex reflex that empties the stomach through the
esophagus, pharynx, and mouth.
Irritation or distension in the stomach or intestines can trigger
vomiting.
Sensory impulses travel from the site of the stimulation to the
vomiting center in the medulla oblongata, and several motor
responses follow:
1.
Taking a deep breath
2.
Raising the soft palate and thus closing the nasal cavity
3.
Closing the opening of the trachea
4.
Relaxing the cardiac sphincter
5.
Contracting the diaphragm so that it presses downward over
the stomach
6.
Contracting the abdominal muscles so that pressure inside the
abdominal cavity increases
As a result, the stomach is squeezed from all sides, forcing its
contents upward and out.
PANCREAS
5% Endocrine Function
95% Exocrine Function
Secretes digestive juices called pancreatic juice.
STRUCTURE OF THE PANCREAS
Extends horizontally across the posterior
abdominal wall in the C-shaped curve of the
duodenum (first segment of the small
intestine).
Pancreatic acinar cells make up the bulk of the
pancreas.
Small tubes unite to form larger tubes which
give rise to the pancreatic duct extending the
length of the pancreas, and connecting with
the duodenum at the same place where the
bile duct joins.
A hepotopancreatic sphincter controls the
movement of pancreatic juices into the
duodenum.
PANCREATIC SECRETIONS
Pancreatic juices contain enzymes that digest
carbohydrates, fats, nucleic acids, and
proteins
1.
Pancreatic amylase – carbohydrate digesting
enzyme
2.
Pancreatic lipase – fat digesting enzyme
3.
Nucleases (2)– break nucleic acids into
nucleotides
4.
Trypsin, chymotrypsin, and
carboxypeptidase – protein-splitting
(proteolytic) enzymes; no single enzyme can
split all amino acid combinations therefore
REGULATION OF PANCREATIC SECRETIONS
 Regulated
by the nervous and endocrine
systems
 Parasympathetic impulses stimulate the
release of pancreatic juices
 As acidic chyme enters the duodenum its
mucus membrane releases the peptide
hormone secretin into the bloodstream which
stimulates secretions of pancreatic juices high
in bicarbonate ions, which neutralize the acid.
 Proteins and fats in chyme within the
duodenum also stimulate the intestinal wall to
release cholyecystokinin, which travels via the
bloodstream to pancrease
LIVER
 Upper
right quadrant of the abdominal cavity
 Reddish brown and well supplied with blood
vessels
LIVER STRUCTURE
Enclosed by a fibrous capsule
 Large right lobe and smaller left lobe are divided by
connective tissue
 Each lobe is separated into many tiny hepatic lobules
which are the liver’s functional units.
 A lobule consists of many hepatic cells radiating
outward from a central vein.
 Vascular channels called hepatic sinusoids separate
platelike groups of these cells from each other.

Structure cont…..
Blood from the digestive tract, which is carried
in the portal vein, brings newly absorbed
nutrients into the sinusoids and nourishes the
hepatic cells.
Large phagocytic macrophages called Kupffer
cells are fixed to the inner linings of the
hepatic sinusoids, and remove bacteria or
other foreign particles that enter the blood in
the portal vein through the intestinal wall.
Within the hepatic lobules are many fine bile
canals, which receive secretions from the
hepatic cells.
These canals merge to become the hepatic ducts,
which merge to form the common hepatic duct.
LIVER FUNCTION
1.
2.
3.
Carbohydrate metabolism – polymerizes
glucose to glycogen, breaks down glycogen to
glucose, and changes noncarbohydrates to
glucose
Lipid metabolism – oxidizes fatty acids,
synthesizes lipoproteins, phospholipids, and
cholesterol; changes portions of
carbohydrates and protein molecules into
fats
Protein metabolism – deaminates amino
acids; forms urea; synthesizes plasma
proteins; changes certain amino acids to
other amino acids
LIVER FUNCTION CONT….
4. Storage – stores glycogen, iron, and vitamin A,D, and
B12
5. Blood Filtering – removes damaged red blood cells and
foreign substances by phagocytosis
6. Detoxification – removes toxins from the blood
(alcohol, ammonia, drugs & hormones)
7. Synthesis of bile salts and heparin
8. Secretion of bile
BILE
Yellowish green liquid
 Bile consists of water, bile salts, cholesterol,
phospholipids, bile pigments (bilirubin and biliverdin)
and ions.
 Bile pigment are products of red blood cell breakdown
and consists of iron, globin, and bilirubin (from the
heme). Iron and globin are recycled, some bilirubin is
excreted in bile.

BILE CONT….
Bile salts are the most abundant and are the only
substance with a digestive function (breaks down
fat globules into smaller droplets, emulsification)
 Enhances absorption of fatty acids, cholesterol,
and the fat soluble vitamins A,D,E, and K
 Lack of salts results in poor lipid absorption and
vitamin deficiencies

JAUNDICE
Turns the skin and eye whites yellow
 Buildup of bile pigments
 Causes:
1. obstructive jaundice – blocked bile
ducts
2. hepatocellular jaundice – liver is diseased
3. hemolytic jaundice – red blood cells are
destroyed too rapidly

GALLBLADDER
Pear-shaped sac in a depression on the liver’s inferior
surface
 Connects with the cystic duct and joins the common
hepatic duct
 Lined with epithelial cells and has a strong muscular
layer in its wall
 Stores bile between meals, reabsorbs water to
concentrate bile, and releases bile into the small
intestine through the hepatopancreatic sphincter

GALLSTONES
Cholesterol precipitates and forms crystals
 May block flow into the small intestine and cause
considerable pain
 Cholecystectomy removes the gallbladder when
gallstones are obstructive

SMALL INTESTINE

Receives secretions from the pancreas and the
liver as well as completing digestion of the
nutrients in chyme, absorbing the products of
digestion, and transporting the residues to the
large intestine.
PARTS OF THE SMALL INTESTINE
Duodenum
* 25cm long and 5cm in diameter
* Lies behind the parietal peritoneum
* 1st section and most fixed portion
2. Jejunum and Ileum
* remainder of the small intestine
* mobile and lie freely in the peritoneal
cavity
* proximal two-fifths is the jejunum; greater
diameter, thicker walls, more vascularized,
and more active
1.
PARTS OF THE SMALL INTESTINE
CONT….
3. Mesentary
* double-layered fold of peritoneal membrane that
suspends the jejunum and ileum from the
posterior abdominal wall
* supports the blood vessels, nerves, and lymphatic
vessels that supply the intestinal wall.
4. Greater Omentum
* filmy, double-layered fold of the peritoneal
membrane
that drapes like an apron from the
stomach over the
transverse colon and the folds
of the small intestine
* If infection occurs in the alimentary canal, cells from
the omentum may adhere to the inflamed region and
help wall it off so the infection is less likely to
enter
the peritoneal cavity.
STRUCTURE OF THE SMALL
INTESTINAL WALL
 Appears
velvety due to many tiny projections
of mucous membrane called intestinal villi.
 Intestinal villi are densest in the duodenum
and the proximal portion of the jejunum.
 Villi project into the lumen of the alimentary
canal, contacting the intestinal contents.
 Villi increase the surface area of the intestinal
lining, aiding absorption of digestive products.
STRUCTURE OF THE SMALL
INTESTINAL WALL CONT…..
1.
2.
Villi – consists of a layer of simple columnar
epithelium and a core of connective tissue
containing blood capillaries, a lymphatic
capillary called a lacteal, and nerve fibers
Intestinal glands – tubular and lie between the
base of adjacent villi, extending downward into
the mucous membrane
SECRETION OF THE SMALL INTESTINE
1.
2.
Goblet cells – abundant throughout the
mucosa of the small intestine and secrete
mucus
Mucus-secreting glands – located in the
submucosa within the proximal duodenum and
secrete large quantities of thick, alkaline
mucus in response to stimuli
SECRETION OF THE SMALL
INTESTINE CONT…
3. Intestinal glands – secrete large amounts of
watery fluid that has a neutral pH (6.5-7.5) and
it lacks digestive enzymes
4. Epithelial cells of the intestinal mucosa – have
digestive enzymes embedded in membranes of
microvilli on their luminal surfaces. These
enzymes break down food molecules just before
absorption.
a. peptidases – splits peptides into amino
acids
b. sucrase, maltase, and lactase – split the
disaccharides sucrose, maltose,
and lactose
into the monosaccharides
glucose, fructose,
and galactose
c. intestinal lipase – splits fats into fatty
acids and
glycerol
REGULATION OF SMALL INTESTINE
SECRETIONS


Goblet cells and intestinal glands secrete their
products when chyme provides both chemical and
mechanical stimulation.
Distension of the intestinal wall activates the nerve
plexuses within the wall and stimulates
parasympathetic reflexes that also trigger release of
small intestine secretions.
ABSORPTION IN THE SMALL INTESTINE
Nutrient
Absorption Mechanism
Means of
Transport
Monosaccharides
Facilitated diffusion & active transport
Blood in capillaries
Amino Acids
Active transport
Blood in capillaries
Fatty acids &
glycerol
Facilitated diffusion of glycerol; diffusion of
fatty acids into cells
a. Most fatty acids are resynthesized
into fats and incorporated in
chylomicrons
b. Some fatty acids with relatively
short carbon chains are
transported without being
changed back into fats
Lymph in lacteal
Blood in capillaries
Electrolytes
Diffusion & active transport
Blood in capillaries
Water
Osmosis
Blood in capillaries
MALABSORPTION
In malabsorption, the small intestine digest, but does
not absorb, some nutrients.
 Causes include:
1. surgical removal of a portion of the SMI
2. obstruction of lymphatic vessels due to tumor
3. Interference with the production and release of bile
as a result of liver disease
4. Reaction to gluten (found in grains), called
celiac disease. Damages microvilli, sometimes
destroys them. Reduces absorptive surface of the
SMI preventing absorption of some nutrients.

Symptoms include diarrhea, weight loss, weakness,
vitamin deficiencies, anemia, and bone
demineralization.
MOVEMENTS OF THE SMALL
INTESTINE
 Mixing
and peristalsis
 Mixing movements include small, periodic,
ringlike contractions that cut chyme into
segments and move it back and forth.
 Weak peristaltic waves propel chyme short
distances through the SMI.
 3 to 10 hours to travel the length
 Over distension or irritation of the wall can
cause a strong peristaltic rush along the entire
length of the SMI, emptying it into the LI
without absorption taking place, results in
diarrhea.
SMALL INTESTINE


At the distal end of the SMI is a sphincter muscle
called the iliocecal valve, which joins the SMI’s
ileum to the LI’s cecum.
After a meal, a gastroileal reflex increases
peristalsis in the ileum and relaxes the sphincter,
forcing some of the contents of the SMI into the
cecum
LARGE INTESTINE
 About
1.5m long
 Begins in the lower right side of the abdominal
cavity where the ilium joins the cecum.
 Extends upward on the right, crosses obliquely
to the left, and descends into the pelvis.
 At its distal end it opens to the outside of the
body as the anus.
 Functions to reabsorb water and electrolytes
from chyme remaining in the alimentary
canal.
 Forms and stores feces.
PARTS OF THE LARGE INTESTINE
1.
Cecum – dilated, pouchlike structure that hangs
below the iliocecal opening; projecting downward
from it is a narrow tube with a closed end called the
vermiform appendix (has no digestive function, but
contains lymphatic tissue)
PARTS OF THE LARGE INTESTINE
CONT…
2. Colon
a. Ascending colon – begins at the cecum and
travels upward against the posterior
abdominal wall to a point just below the liver.
It then turns sharply to the left and becomes:
b. Transverse colon – longest and most
moveable
part; suspended by a fold of
peritoneum and sags in
the middle below
the stomach; as it approaches the spleen, it
turns abrptly downward and becomes:
c. Descending colon – descends to the brim of
the
pelvis and then makes an S-shaped
curve called the:
d. Sigmoid colon
PARTS OF THE LARGE INTESTINE
CONT…
3. Rectum – continuous from the sigmoid colon; lies
next to the sacrum and follows its curvature. The
peritoneum firmly attaches it to the sacrum, and
the rectum ends about 5cm below the tip of the
coccyx
4. Anal canal – last 2.5 to 4 cm of the LI; the
mucous membrane folds into a series of six to
eight longitudinal anal columns; At its distal end,
the canal opens to the outside as the:
5. Anus – 2 sphincter muscles guard the anus – an
internal anal sphincter muscle composed of
smooth muscle under involuntary control and an
external sphincter muscle composed of skeletal
muscle under voluntary control
STRUCTURE OF THE LARGE INTESTINE
WALL
Composed of the same type of tissues as other parts of
the alimentary canal
 Does not contain the villi
 Longitudinal muscles are not uniform, but instead,
form three distinct bands (teniae coli) that extend the
length of the colon.
 Teniae coli exert tension lengthwise on the wall,
creating a series of pouches (haustra)

FUNCTIONS OF THE LARGE
INTESTINE
Little to no digestive function
 Mucus is only significant secretion to protect the wall
from abrasion of the material passing through it
 Mucus binds particles of fecal matter
 Mucal alkalinity helps control the pH
 Absorbs water and electrolytes in the proximal half of
the tube.
 Stores feces for a time in the distal portion.

MOVEMENTS OF THE LARGE
INTESTINE
 Mixing
and peristaltic movements are
more sluggish.
 Peristaltic waves should happen 2 to 3
times a day.
 A person can usually initiate a defecation
reflex by holding a deep breath and
contracting the abdominal wall muscles.
 The internal sphincter will relax as
pressure increases in the rectum.
 Contracting the external anal sphincter
allows voluntary inhibition of defecation.
FECES

Contains:
Undigested or absorbed material
 Water
 Electrolytes
 Mucus
 Bacteria
Usually feces is about 75% water, and its color derives from
bile pigments that bacterial action has altered somewhat.
Its odor results from a variety of compounds bacteria produce.

SUMMARY CHART ON DIGESTION