Download The Digestive System

The Digestive
System
ST 120
Objectives
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Sequence of component parts
List and describe layers of the tract
Mouth to Small Intestines
Structure
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Irregular tube
Open at both ends
Called the alimentary canal or the
gastrointestinal tract (GI)
~29 feet long in the adult
Passageway that moves through the body
like a hallway
Lined with mucous membrane
Structure
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Food must be digested to be used by the body
The process of altering the chemical and physical
composition of food so that it can be absorbed
and used by body cells is known as digestion
Food undergoes three kinds of processing:
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Digestion
Absorption
Metabolism
Organs of the Digestive System
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Main
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Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Rectum
Anal canal
Organs of the Digestive System
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Accessory
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Teeth and tongue
Salivary glands
Liver
Gallbladder
Pancreas
Vermiform appendix
Wall of the Digestive Tract
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4 layers of tissue
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Mucosa or mucous membrane
Submucosa
Muscularis
Serosa
Inside or hollow space is the lumen
Wall of the Digestive Tract
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Mucosa: in the esophagus it is tough and
stratified abrasion-resistant epithelium. In
the remainder of the tract, it is a delicate
layer of simple columnar epithelium.
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It produces mucus that coats the alimentary
canal.
Wall of the Digestive Tract
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Submucosa: connective tissue layer that
lies just below the mucosa. It contains
many blood vessels and nerves.
Wall of the Digestive Tract
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Muscularis: composed of two layers of
muscle tissue. Food material is moved
through the digestive system by a wavelike,
rhythmic contraction of the muscular coat
called peristalsis.
Also, the contraction of the muscularis
assists in mixing food with digestive juices.
Wall of the Digestive Tract
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Serosa: outermost covering. In the
abdominal cavity it is composed of the
visceral peritoneum.
Wall of the Digestive Tract
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The loops of the digestive tract are
anchored to the posterior wall of the
abdominal cavity by a large double fold of
peritoneal tissue called the messentery.
Blood supply to the bowel runs through
this.
Mouth
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Aka oral cavity
Lined with mucous membrane
Roof of mouth is formed by the hard and
soft palates
Uvula is the structure that hangs in the
back of the throat
Uvula and soft palate prevent food and
liquid from entering the nasal cavities
Mouth
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Hard palate is formed by parts of the
palatine and maxillary bones
The tongue is made of skeletal muscle
covered with mucous membrane
Frenulum attaches the tongue to the floor
of the mouth
Papillae are the bumps that contain taste
buds
Teeth
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4 major types:
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Incisors
Canines
Premolars
Molars
Teeth
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Incisors have a sharp cutting edge for
mastication
Canines are sometimes called cuspids and
they pierce or tear food to be eaten
Premolars or bicuspids and molars or
tricuspids have flat surfaces for grinding or
crushing
Typical Tooth
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3 main parts:
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Crown
Neck
Root
Typical Tooth
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Crown- visible portion that is covered in
enamel (hardest substance in the body)
and dentin and cementum.
Neck- narrow portion surrounded by the
pink gingiva or gum tissue that joins the
crown to the root.
Root- fits into the socket of the upper and
lower jaw.
Typical Tooth
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Periodontal membrane lines each tooth
socket.
Dental caries is a disease of the enamel,
dentin, and cementum that results in the
formation of a permanent defect called a
cavity.
Salivary Glands
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Three pairs of these glands secrete most of
the saliva produced each day
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Parotids
Submandibulars
Sublinguals
Parotids
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Largest
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Lie just below and in front of each ear at
the angle of the jaw
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People with mumps complain when they
chew or open their mouths
Submandibular Glands
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Ducts open into the mouth on either side of
the lingual frenulum
Sublingual Glands
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Open into the floor of the mouth
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Sublingual means under the tongue
Saliva
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Contains mucus and a digestive enzyme
called salivary amylase
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Mucus moistens the food and allows it to
pass without friction
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Salivary amylase begins the chemical
digestion of carbs
Pharynx
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Tubelike structure made of muscle and
lined with mucous membrane
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Functions in respiratory and digestive
systems
Esophagus
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Muscular, mucus-lined tube that connect
the pharynx with the stomach
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~10 inches long
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Serves as a passageway for food
Stomach
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Lies in upper part of the abdominal cavity
just under the diaphragm
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Serves as a pouch that food enters into
after it has been chewed, swallowed and
passed through the esophagus
Stomach
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Food enters the stomach by passing through the
gastroesophageal or cardiac sphincter at the end
of the esophagus
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Sphincters are rings of muscle tissue
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Cardiac sphincter keeps food from reentering the
esophagus when the stomach contracts
Stomach
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If the opening in the diaphragm is enlarged,
there may be a bulging of the diaphragm
and part or maybe even all of the stomach
will move upward into the chest. This is
known as a hiatal hernia.
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May result in gastroesophageal reflux
disease.
Stomach
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Contraction of the stomach wall mixes food with
gastric juices and breaks it down into a substance
called chyme.
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Gastric juice contains hydrochloric acid.
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Mucous membranes line the stomach and it
contains thousands of microscopic gastric glands
that secrete gastric juice and HCl acid
Stomach
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When the stomach is empty, its lining lies in
folds called rugae.
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3 divisions of the stomach
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Fundus
Body
Pylorus
Stomach
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Partial digestion occurs after food is held in
the stomach by the pyloric sphincter
muscle.
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Stays closed most of the time thereby
closing off the opening of the pylorus into
the small intestine.
Small Intestine
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~7 meters
Small in diameter
Composed of 3 sections
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Duodenum
Jejunum
Ileum
This is the order in which food moves through them
Small Intestine
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The mucous lining of the small intestine contains
1000’s of microscopic glands called intestinal
glands that secrete intestinal digestive juice.
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Wall is not smooth, but has multiple circular folds
called plicae. (plicate- to fold) These folds are
covered with 1000’s of tiny fingers called villi.
Small Intestine
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Villi contain capillaries that absorb sugars and
amino acids.
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Villi greatly increase the surface area for contact
between the capillaries and the intestinal lining.
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Each villus has a lacteal (lymphatic vessel) that
absorbs lipid or fat materials from the chyme.
Small Intestine
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Each villus is covered by epithelial cells
that have a brush-like border composed of
microvilli.
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Microvilli further increase the surface area
for absorption.
Small Intestine
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Most chemical digestion occurs in the duodenum.
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The duodenum is C-shaped and curves around the
pancreas.
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The middle 3rd of the duodenum has openings in it
where pancreas empties digestive juice and the liver
empties bile into the small intestine. These openings
are the minor and major duodenal papillae.
Day 2 Objectives
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Liver to Extensions
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Digestion
Liver and Gallbladder
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Liver cells secrete bile into ducts, so it is
considered the largest gland in the body.
Hepatic ducts drain bile out of the liver.
The common bile duct (CBD) drains bile
into the small intestine, and is formed by
the union of the cystic duct and the
common hepatic duct.
Liver and Gallbladder
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Bile contains substances that emulsify or
chemically break up fats.
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Fats in chyme signal the release of
cholecystokinin from the mucosa of the
duodenum. This stimulates the contraction
of the gallbladder and bile flows into the
duodenum.
Liver and Gallbladder
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Gallbladder functions to store bile
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Bile gives feces its color
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Jaundice is a yellowish skin discoloration
Pancreas
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Lies behind the stomach
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Exocrine gland that secretes pancreatic
juice into ducts and an exocrine gland that
secretes hormone into the blood
Pancreas
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Pancreatic juice is the most important digestive
juice because it contains enzymes that digest all
three major kinds of food.
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Also contains sodium bicarbonate that neutralizes
hydrochloric acid
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Enters the duodenum where bile enters
Large Intestine
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Only ~5 feet long
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Larger in diameter than the small intestine
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Forms lower portion of the digestive tract
Large Intestine
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Undigested and unabsorbed food material enters
the large intestine after passing through a
sphincter-like structure called the ileocecal valve.
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This is no longer chyme because chyme is soupy.
The material here is the consistency of fecal
matter because water and salts are reabsorbed
during its passage through the small intestine.
Large Intestine
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Material that escaped digestion in the small
intestine is acted on by bacteria which
results in additional nutrients and other
fibers are absorbed.
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These bacteria also synthesize vitamin K
and some B-complex vitamins
Large Intestine
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Not ideal for absorption- no villi
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Normal passage takes 3-5 days
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Diarrhea results when the rate of passage
quickens
Large Intestine
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Subdivisions in order of food passage:
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Cecum
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Rectum
Anal canal
Large Intestine
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2 sphincter muscles stay contracted to
keep the anus closed
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The inner anal sphincter is smooth or
involuntary muscle
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The outer one is voluntary muscle
Appendix
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Wormlike, tubular structure
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Attached directly to the cecum
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1. base 2. mesoappendix
Appendicitis is the inflammation of the
mucous lining of the appendix
Peritoneum
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Large, moist slippery sheet of serous
membrane that lines the abdominal cavity
and covers the organs located in it
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Parietal portion lines the abdominal cavity
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Visceral portion forms the outer layer of
each organ
Peritoneum
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Small space between the parietal and
visceral layers is called the peritoneal
space.
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Contains fluid to keep both layers moist
and able to slide over one another.
Extensions
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2 most prominent:
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Mesentery, mesocolon
Greater omentum
Extensions
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Mesentery: an extension between the
parietal and visceral layers of the
peritoneum and is shaped like a giant fan.
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It anchors the small intestine to the
posterior abdominal wall. Blood supply runs
through.
Mesocolon for Colon
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Extensions
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Greater omentum: a pouch-like extension
of the visceral peritoneum from the lower
edge of the stomach, part of the
dupdenum, and the transverse colon.
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Shaped like a large apron and hangs down
over the intestines. Called the lacy apron.
Digestion
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A complex process that occurs in the
alimentary canal and consists of physical
and chemical changes that prepare food for
absorption.
Digestion
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Mechanical digestion breaks food into tiny
particles, mixes them with digestive juices, moves
them along the alimentary canal, and finally
eliminates the wastes.
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Main processes of mechanical digestion:
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Mastication
Deglutition
Peristalsis
Defecation
Digestion
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Chemical digestion: breaks down large,
nonabsorbable food molecules into smaller,
absorbable molecules.
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Consists of numerous chemical reactions
catalyzed by enzymes in saliva, gastric
juice, pancreatic juice, and intestinal juice.
Carbohydrate Digestion
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Very little digestion occurs before the small
intestine.
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Pancreatic and intestinal juice enzymes
digest carbs.
Carbohydrate Digestion
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Pancreatic enzyme breaks polysaccharides
into disaccharides.
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3 intestinal enzymes digest disaccharides
by changing them to monosaccharides.
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Most abundant monosaccharide is glucose.
Protein Digestion
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Starts in the stomach
Pepsin causes large protein molecules to
be broken down into somewhat smaller
molecules
In the intestine, other enzymes finish the
job
The end product is amino acids
Fat Digestion
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Most fats are undigested until after
emulsification by bile in the duodenum.
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After this, pancreatic lipase splits up the fat
molecules into fatty acids and glycerol
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End product is fatty acids and glycerol
Absorption
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After food is digested, it is absorbed, that is, it
moves through the mucous membrane lining of
the small intestine into the blood and lymph
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Food absorption is the process by which
molecules of amino acids, glucose, fatty acids,
and glycerol go from the inside of the intestines
into the circulating fluids of the body.