Transcript Lecture 7
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