Transcript Digestive System

Digestive System
Function

The function of the digestive system is
to change complex nutrient molecules
that can be absorbed into the blood or
lymph to be transported to cells
Divisions of digestion
1.The alimentary tube extends from the
mouth to the anus. It consist of the oral
cavity, pharynx, esophagus, stomach,
small intestine, and large intestine.
2. The accessory organs of the digestion
are the teeth, tongue, salivary glands,
liver, gallbladder, and pancreas.
Types of digestion
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2.
Food is broken down in two
complementary processes
Mechanical digestion is the physical
breaking up of food into smaller pieces
Chemical digestion uses enzymes to
break up food particles, and turn them
into something the body can utilize
Oral Cavity
Food enters the oral cavity by way of
the mouth
 The boundaries are the hard and soft
palates, the cheeks, and the floor of the
mouth
 Within the oral cavity are the teeth and
tongue
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Teeth
The function of the teeth is to chew
 Individuals develop two sets of teeth
1) deciduous and 2) permanent
 Deciduous teeth arrive around 6 months
of age, and are a set of 20 teeth
 Permanent teeth begin to replace
deciduous teeth at the age of six, and
consist of 32 teeth
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Teeth
Enamel is the hard outer covering of the
tooth, and is more resistant to decay
than other parts of the tooth
 Dentin is within the enamel, and is very
similar to bone; dentin also forms the
root of tooth
 The innermost portion of a tooth is the
pulp cavity, which contains the blood
vessels and nerve endings
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Tongue
The tongue is made of skeletal muscle
 On the upper surface are small
projections called papillae, which
contain taste buds
 Sensory nerves for taste are the cranial
nerves
 Elevation of the tongue is the first step
in swallowing, and is a voluntary action
 The mass of food, called a bolus, is
pushed backward toward the pharynx
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Salivary glands
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Saliva is the digestive secretion in the oral
cavity produced by three pairs of glands
1. Parotid glands are just below the ears
2. Submandibular are posterior to the
mandible
3. Sublingual are on the floor of the mouth
Each gland has at least one duct to take saliva
to the oral cavity
Cont.
Secretion of saliva is continuous, but
varies
 The presence, sight, or smell of food
increases the amount saliva
 Stressful situations decrease the
amount of saliva
 Salivary amylase is the digestive
enzyme that breaks down starch
molecules
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Pharynx
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No digestion takes place in the
pharynx, its only related function is
swallowing
The reflex center for swallowing is the
medulla
The medulla coordinates:
Constriction of the pharynx
Closure of the epiglottis
Peristalsis of the esophagus
Esophagus
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The esophagus is a muscular tube that takes
food from the pharynx to the stomach; no
digestion takes place
 Peristalsis of the esophagus propels food
 The lower esophageal sphincter relaxes to
permit food to enter the stomach, then
contracts to prevent backup
 If contraction is not complete gastric juices
may splash up, I.e. heartburn
Layers of alimentary tube
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2.
3.
4.
4 layers
Mucosa
Submucosa
External muscle layer
serosa
Mucosa
The mucosa, or lining, is made of
epithelial tissue and smooth muscle
 The epithelium secretes mucus, which
lubricates the passage of food, and
secretes digestive enzymes
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Submucosa
The submucosa is made of connective
tissue
 Meissner’s plexus is the nerve network
that regulate secretions
 Also known as the brain of the gut
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External muscle layer
The external layer has two layers, inner
and outer
 Contractions of the external layer help
break up food and mix it with digestive
juices
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Serosa
The outermost layer, is fibrous
connective tissue
 The serosa is the mesentary lining the
abdominal cavity
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Stomach
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The stomach is a sac that extends from the
esophgus to the small intestine
Both mechanical and chemical digestion
take place in the stomach
Parts of the stomach:
Cardiac is the opening of the esophagus
Fundus is the level above the opening
Body is the large central portion
Pylorus is where most digestion takes place
Cont.
The folds within the stomach called
rugae allow the stomach to stretch
without tearing
 Parietal cells secrete hydrochloric acid,
which begins the digestion of proteins
 Mucus cells secrete mucus, which coats
the stomach, and prevents the erosion
of gastric juices
 The pH of the stomach is around 1,
which helps to kill microorganisms
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Small intestine
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2.
3.
Extends from the stomach to the large
intestine
The small intestine has 3 parts
Duodenum
Jejunum
Ileum
-Digestion is completed in the small
intestine
-Peyer’s patches are lymph nodes that
destroy pathogens in the sm. intestine
Liver
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Consist of two large lobes, right and left
The capillaries of the liver are called
sinusoids
The only digestive function of the liver is the
production of bile
Bile carries bilirubin and excess cholesterol to
the intestines for elimination
Bile salts emulsify fats in the small intestine;
this a mechanical process
The hormone secretin, stimulates the
production of bile
Gallbladder
Is located on the underside of the liver
 Bile from the liver is stored in the
gallbladder until needed
 Cholecystokinin is the hormone that
stimulates the contraction of the smooth
muscle in the gallbladder, which forces
out bile
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Gallstones
Are caused by cholesterol crystals, that
if large enough cannot pass out of the
gallbladder
 The backing up of bile can cause
juandice
 Lithotripsy is the generation of shock
waves that break down gallstones into
smaller pieces
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Pancreas
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Pacreatic enzymes
1. Amylase- digest starch
2. Lipase- converts fats to fatty acids
3. Trypsin- digest polypeptides to amino acids
The pancreas also produces bicarbonate juice,
which neutralizes the gastric acid that come
from the stomach
Secretin stimulates the production of
bicarbonate juice in the pancreas
Disorders of the stomach
Pyloric stenosis means that the opening
of the pyloric sphincter is narrowed,
blocking the emptying of the stomach
 A gastric ulcer is an erosion of the
mucosa of the stomach; it is the result
of over secretion of HCl
 The bacteria Helicobacter pylori causes
most gastric ulcers
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Large Intestine
Extends from the small intestines to the
anus
 The first portion is called the cecum; the
ileocecal valve prevents fecal matter
from back flowing into the small
intestine
 The appendix is attached to the cecum
 Infection of the appendix caused by the
fecal matter is called appendicitis
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Cont.
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The last portion of the large intestine is called
the colon; no digestion occurs here
The only secretion of the colon is mucus that
coats for the passage of feces
The functions of the colon are the absorption
of minerals, water, and vitamins
About 80% of the water that enters the colon
is absorbed
The flora of the colon prevents the growth of
pathogens
Disorders of the Intestines
Duodenal ulcers are erosions of the
intestinal wall, caused by gastric juices
 Lactose intolerance is the inability to
digest lacose; when lactose is not
digested it undergoes fermentation
within the intestine
 Salmonella is caused by a bacteria
found in meats and eggs, they cause
the intestines to secrete large amounts
of fluid
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Cont.
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Paralytic ileus is the ceasing of contraction of
the smooth muscle layer of the intestine,
causing intestinal blockage
 Infant botulism is caused by the ingestion of
bacterial spores; an infant’s stomach does not
produce enough HCl to destroy spores
 Diets high in fiber have been thought to
reduce the frequency of certain diseases
Absorption
Most absorption takes place in the small
intestine
 Absorption needs a large surface area,
projections called villi help increase
surface area
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Elimination of feces
Feces consist of cellulose and other
undigestible material, and water
 A spinal cord reflex called the
defecation reflex controls the elimination
of feces
 The relaxation of the internal anal
sphincter permits defecation to occur
 The external anal sphincter makes it
possible to delay defecation
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Problems of the Liver
Hepatitis is the inflammation of the liver
caused by viruses
 Hepatitis A is an intestinal virus that is
spread by the digestion of fecal matter
 Hepatitis B is contracted by exposure to
body fluids of an infected person (blood,
semen)
 Hepatitis C virus is spread through body
fluids, blood, and mucus membranes
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Other Functions of Liver
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Carbohydrate metabolism- excess glucose
is stored as glycogen
Amino acid metabolism- amino acids are
changed to carbohydrates
Lipid metabolism- synthesis of cholesterol
Formation of bilirubin- old RBC’s are
phagocytized and bilirubin is formed
Phagocytosis- phagocytized old RBC’s and
bacteria are absorbed by the colon
Detoxification- liver enzymes change
poisons to less harmful substances