Digestive System
Digestive System

The organs that break down food to molecular
size before it can be absorbed by the digestive
system and used by the cells
Digestive System

Composed of the GI tract and accessory
structures
Digestive System

GI tract – a tube open at both ends for the
transit of food and wastes during processing
Digestive System

1.
2.
3.
4.
5.
6.
GI tract includes
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Digestive System

Acessory structures contribute to food
processing
Digestive System

1.
2.
3.
4.
5.
6.
Accessory structures include
Teeth
Tongue
Salivary glands
Liver
Gallbladder
pancreas
Digestive System

Includes six basic processes
Layers of GI Tract
1.
2.
3.
4.
Mucosa
Submucosa
Muscularis
Serosa
Mucosa
Consists of
1. Epithelium
2. Lamina propria
3. Muscularis mucosa
Epithelium

Non-keratinized stratified squamous epithelium
in the esophagus
Epithelium

Simple columnar in the rest of the tract
Lamina propria

Contains loose connective tissue
Lamina Propria

Blood and lymph vessels
Lamina Propria

Nerves and sensors
Muscularis Mucosa

Causes local folding of the mucosal layer to
increase surface area for digestion and
absorption
2. Submucosa

Consists of areolar connective tissue
Submucosa

Submucosal plexus
Submucosa

Glands and lymphatic tissue
3. Muscularis

The mouth, pharynx, and superior part of the
esophagus contains skeletal muscle that
produces voluntary swallowing
Muscularis

Skeletal muscle forms the external (voluntary)
anal sphincter
Muscularis

Consists of smooth muscle in an inner sheet of
circular fibers and an outer sheet of longitudinal
fibers
Muscularis

Stomach contains an inner oblique layer also
3. Serosa

Superficial layer of the GI tract
Serosa

The esophagus is covered by an adventitia
instead of serosa
Serosa

Inferior to the diaphragm also called the visceral
peritoneum
Peritoneum

Largest serous membrane of the body
Peritoneum

Two layers
Peritoneum
1.
2.
Parietal peritoneum
Visceral peritoneum
Parietal Peritoneum

Lines the wall of the abdominal cavity
Visceral Peritoneum

Covers some of the organs
Peritoneal Cavity

The space between the parietal and visceral
portions that contains serous fluid
Mouth

Oral cavity
Mouth

Formed by the cheeks, hard and soft palate, lips,
and tongue
Mouth

The space extends from the gums and teeth to
the fauces
Mouth

Fauces – opening between the oral cavity and
pharynx
Salivary Glands

Lie outside the mouth and pour their contents
into ducts that empty into the oral cavity
Salivary Glands

Produce saliva
Salivary Glands

1.
2.
3.
Three pairs
Parotid
Submandibular
Sublingual
Salivary Glands

Saliva lubricates and dissolves food
Salivary Glands

Saliva start the chemical digestion of carbs
Salivary Glands

Parasympathetics stimulate secretion of watery
saliva
Salivary Glands

Sympathetics stimulate the secretion of thick,
tacky, saliva
Mumps

Inflammation and enlargement of the parotid
gland
Mumps

Symptoms include fever, pain, and swelling of
one or both glands
Tongue

Composed of skeletal muscle covered with
mucous membrane
Tongue

The upper surface and sides are covered with
papillae
Tongue

Some papillae contain taste buds
Tongue

On the dorsum of the tongue are glands that
secrete lingual lipase
Teeth

Adapted for mechanical digestion
Teeth

1.
2.
3.
Consists of
Crown
Neck
Root
Teeth

Teeth composed of dentin
Teeth

Dentin – calcified connective tissue that gives
the tooth its basic shape and rigidity
Teeth

Dentin of the crown is covered by enamel
Teeth

The dentin of the root is covered by cementum
Teeth

Cementum – attaches the root to the
periodontal ligament
Teeth

The dentin encloses the pulp cavity in the crown
and the root canals in the root
Teeth

1.
2.
Two sets of teeth
Deciduous (primary)
Pemanent (secondary)
Teeth

Salivary amylase – converts polysaccharides
(starches) to disaccharides (maltose)
Pharynx

Composed of skeletal muscle and lined by
mucous membrane
Pharynx

1.
2.
3.
Consists of
Nasopharynx
Oropharynx
laryngopharynx
Pharynx

Swallowing moves food from the mouth to the
stomach
Esophagus

Behind the trachea
Esophagus

Connects the pharynx to the stomach
Esophagus

Serosa called the adventitia
Esophagus

Contains an upper and lower esophageal
sphinchter
Esophagus

Highly coordinated, propulsive contractions
(peristalsis) of the muscularis push the bolus
distally
Stomach

J-shaped
Stomach

Begins at the bottom of the esophagus and ends
at the pyloric sphincter
Stomach

Pyloric sphincter – separates the stomach from
the duodenum
Stomach

Mixing and holding area for food
Stomach

Begins the digestion of food
Stomach

Water, HCL, and pepsin covert the bolus of
food to a clear liquid called chyme
Stomach

Can absorb water, alcohol, and apirin
Stomach

1.
2.
3.
4.
Three regions
Cardiac
Fundus
Body
Antrum
Stomach

When stomach is empty, the mucosa lies in folds
called rugae
Stomach

Surface of the mucosa is a layer of simple
columnar epithelium
Stomach

Epithelial cells extend down into the lamina
propria forming gastric pits and the narrower
and deeper continuations of the these, called
gastric glands
Stomach

1.
2.
3.
Gastric glands consist of 3 types of exocrine
glands
Mucous neck cells
Chief cells
Parietal cells
Stomach

1. Mucous neck cells – secrete mucous
Stomach

Mucous rich in bicarbonate and prevents gastric
acid from damaging the epithelium
Stomach

2. Chief cells secrete pepsinogen and gastric
lipase
Stomach

Pepsinogen is activated by HCL into pepsin
Stomach

Pepsin can also activate pepsinogen
Stomach

Pepsin digests protein
Stomach

Gastric lipase splits certain molecules in
butterfat of milk into fatty acids and
monoglycerides
Stomach

Gastric lipase has a VERY limited role in the
adult stomach
Stomach

3. Parietal cells secrete HCL and intrinsic factor
Stomach

Intrinsic factor is important for absorption of
vitamin B-12
Stomach

Parietal cells contain H2 receptors, gastrin
receptors, and Ach receptors
Stomach

H2 blockers such as Tagamet, Zantac , and
Pepcid work here
Stomach

Parietal cells also have receptors for
somatostatin which decrease acid secretion
Stomach

G cells in the antrum secrete the hormone
Gastrin which increases acid secretion and
motility
Stomach

Near parietal cells are mast cells that releases
histamine in responses to gastrin or stimulation
by the vagus
Stomach

Ach is released by parasympathetic fibers
Stomach

The serosa is a part of the visceral peritoneum
Stomach

Above the lesser curvature, the visceral
peritoneum becomes the lesser omentum
Stomach

Below the greater curvature, the visceral
peritoneum becomes the greater omentum
Regulation of Gastric Secretion and
Motility

Gastric secretion is regulated by nervous and
hormonal secretions
Regulation of Gastric Secretion and
Motility

1.
2.
3.
Stimulation occurs in three overlapping phases
Cephalic
Gastric
Intestinal
Cephalic Phase

Consists of reflexes initiated by sensory
receptors in the head, such as when you see,
smell, or think about food
Cephalic Phase

Stimulates salivary flow, gastric secretion and
motility
Gastric Phase

Begins when food enters the stomach
Gastric Phase

Distension of stomach and increase in pH
stimulate gastric secretion via parasympathetic
neurons
Gastric Phase

This results in increase in HCL secretion
Gastric Phase

Protein, high pH, alcohol, and coffee also
stimulates gastrin secretion
Gastric Phase

Histamine enhances the effects of Ach and
gastrin
Gastric Phase

Gastrin secretion is limited by negative feedback
Gastric Phase

Low pH under 2 decreases it secretion
Gastric Phase

Somatostatin from endocrine cells in the gastric
wall inhibit the secretion of gastrin and
histamine
Gastric Phase

Somatostatin also inhibits acid secretion in
parietal cells
Intestinal phase

Stimulated by distension, low pH, and increase
in fats
Intestinal Phase

Long and short neural reflexes inhibit gastric
acid secretion
Intestinal Phase

Hormones released by the intestinal tract such
as Gastric inhibitory peptide (GIP), secretin, and
cholecystokinin (CCK) inhibit gastric acid
secretion
Regulation of Gastric Emptying

Gastric emptying – the periodic releases of
chyme from the stomach into the duodenum
Regulation of Gastric Emptying

Stimulated by nerve impulses in response to
distention of the stomach and gastrin
Regulation of Gastric Emptying

Most food leaves the stomach 2-6 hours after
ingestion
Regulation of Gastric Emptying

Carbs leave first, then proteins, then fats
Regulation of Gastric Emptying

Gastric emptying is inhibited by CCK and GIP
and short and long neural reflexes
Regulation of Gastric Emptying

GIP also promotes insulin secretion in pancreas
Pancreas

It is connected to the duodenum via the
pancreatic duct and accessory duct
Pancreas

The pancreatic duct fuses with the common bile
duct ate the ampulla of Vater
Pancreas

The pancreatic islets secrete hormones
Pancreas

Exocrine cells (acini) secrete a mixture of fluid
and digestive enzymes called pancreatic juice
Pancreas

Pancreatic juice contains bicarbonate and
enzymes that digest starch, proteins, fats, and
nucleic acids
Pancreas

Bicarbonate converts the acid stomach contents
to a slightly alkaline pH (7.1-8.2)
Pancreas

This halts pepsin acitvity and promotes the
activity of pancreatic enzymes
Pancreas

Pancreatic amylase digests starch
Pancreas

Trypsin, chymotrypsin, and carboxypeptidase
digest proteins
Pancreas

Pancreatic lipase digest fats
Pancreas

Ribonuclease and deoxyribonuclease digest
nucleic acids
Pancreas

These enzymes are secreted as inactive
precursors
Pancreas

Trypsinogen is activated by duodenal
enterokinase, producing kinase
Pancreas

Trypsin then activates the other precursor
enzymes
Pancreas

CCK from the duodenum stimulates the
pancreas to secrete digestive enzymes and
ejection of bile into the duodenum via
contraction of the gall bladder
Pancreas

Secretin stimulates the pancreas to secrete
bicarbonate
Liver and Gallbladder

Heaviest gland in the body
Liver and Gallbladder

Second largest organ in the body
Liver and Gallbladder

The liver is divisible into left and right lobes,
separated by the falciform ligament
Liver and Gallbladder

The gallbladder is a sac located in a depression
on the posterior surface of the liver
Liver and Gallbladder

The right and left hepatic duct combine to form
the common hepatic duct which binds with the
cystic duct to form the common bile duct
Liver and Gallbladder

Functions of the gall bladder are to store and
concentrate bile until it is needed by the small
intestine to help digest fats
Liver and Gallbladder

The muscularis of the gallbladder ejects bile into
the cystic duct
Liver and Gallbladder

The liver receives a double supply of blood
from the hepatic artery and the hepatic portal
vein.
Liver and Gallbladder

The hepatic portal vein receives venous blood
from the intestines.
Liver and Gallbladder

All blood leaves the liver the liver via the hepatic
veins to the inferior vena cava.
Liver and Gallbladder

Hepatocytes produce bile that is stored in the
gallbladder
Liver and Gallbladder

Bile contains bilirubin, cholesterol, and bile acids
Liver and Gallbladder

Bile emulsifies triglycerides
Functions of the Liver

Carbohydrate, lipid, and protein metabolism
Functions of the Liver

Removal of drugs and hormones from the
blood
Functions of the Liver

Excretion of bilirubin
Functions of the Liver

Synthesis of bile salts
Functions of the Liver

Storage of vitamins and minerals
Functions of the Liver

Phagocytosis
Functions of the Liver

Activation of vitamin D
Small Intestine

Extends from the pyloric sphincter to the
ileocecal sphincter
Small Intestine

1.
2.
3.
Divided into
Duodenum
Jejunum
ileum
Small Intestine

The mucosa forms fingerlike villi
Small Intestine

Lacteals – lymphatic capillaries embedded in the
villi for fat absorption
Small Intestine

1.
2.
3.
4.
Mucosal epithelium contains
Absorptive cells
Goblet cells
Enteroendocrine cells
Paneth cells
Small Intestine

The free surface of absorptive cells contains
microvilli
Small Intestine

Crypts of Lieberkuhn – cavities lined by
glandular epithelium in the mucosa
Small Intestine

Duodenal glands – located in the submucosa
and secrete an alkaline mucus
Small Intestine

Peyer’s patches – aggregated lymphatic nodules
in the submucosa of the ileum
Small Intestine

Brush border enzymes break down dipeptides
and disaccharides on the surface of microvilli
Small Intestine

Segmentation – localized contraction in areas
containing food
Small Intestine

Peristalsis – propels the chyme onward through
the intestinal tract
Chemical digestion in the Small
Intestine

Pancreatic amylase breaks down starches into
maltose
Chemical digestion in the Small
Intestine

Maltase – breaks down maltose to 2 glucoses
Chemical digestion in the Small
Intestine

Lactase – breaks down lactose to glucose and
galactose
Chemical digestion in the Small
Intestine

Sucrase – breaks down sucrose to glucose and
fructose
Chemical digestion in the Small
Intestine

Glucose, fructose, and galactose are absorbable
Chemical digestion in the Small
Intestine

Maltase, sucrase, and lactase are brush border
disaccharidases
Chemical digestion in the Small
Intestine

Trypsin and chymotrypsin break down proteins
Chemical digestion in the Small
Intestine

Brush border enzymes split dipeptides to amino
acids
Chemical digestion in the Small
Intestine

Most dipeptides are split into amino acids inside
epithelial cells.
Chemical digestion in the Small
Intestine

Bile salts break the globules of triglycerides into
droplets
Chemical digestion in the Small
Intestine

Pancreatic lipase hydrolyzes triglycerides into
fatty acids and monoglycerides
Chemical digestion in the Small
Intestine

Infants have low levels of pancreatic lipase
Chemical digestion in the Small
Intestine

Infants have lipase mainly derived from chief
cells
Chemical digestion in the Small
Intestine

Breast milk also contains lipase
Large Intestine

Extends from the ileocecal valve to the anus
Large Intestine

1.
2.
3.
4.
Subdivisions
Cecum
Colon
Rectum
Anal canal
Large Intestine

Appendix – hangs inferior to the cecum
Large Intestine

1.
2.
3.
4.
Colon divided into
Ascending
Transverse
Descending
Sigmoid portions
Large Intestine

The mucosa has no villi
Large Intestine

The mucosa has simple columnar epithelium
with numerous goblet cells
Large Intestine

Taeniae colie – Three strips of longitudinal
muscles in the muscularis
Large Intestine

The taeniae coli contract and gather the colon
into a series of pouches called haustra
Large Intestine

The last stages of chemical digestion occur in
the large intestine through bacterial action
Large Intestine

Some vitamins (K and folic acid) are synthesized
by bacterial action and absorbed by the large
intestine
Large Intestine

Absorbs water, electrolytes, and some vitamins
Large Intestine

Feces consist of water, inorganic salts, sloughedoff epithelial cells, bacteria, products of
bacterial decomposition, and undigested parts
of food
Large Intestine

An important organ in maintaining the body’s
water balance
Defecation

Elimination of feces
Defecation

Aided by voluntary contractions of the
diaphragm and abdominal muscles
Defecation

The external anal sphincter can be voluntarily
controlled
Diarrhea

Frequent defecation of liquid feces
Diarrhea

Caused by increased motility of the intestine and
can lead to dehydration and electrolyte
imbalances
Constipation

Refers to infrequent or difficult defecation
Constipation

Causded by decreased motility of the intestines
Constipation

May be alleviated by increasing one’s intake of
dietary fiber and fluids
Hepatitis

Inflammation of the liver
Hepatitis

Caused by viruses, drugs, and chemicals,
including alcohol