2. LECTURES OUTLINE
• The Gastrointestinal System
• Control Mechanisms in Gastrointestinal
Physiology
• The Mouth and Esophagus
• The Stomach
• The Pancreas
• The Liver
• The Small Intestine
• The Large Intestine
• Enteric Motility
3. • The gastrointestinal system consists of
the gastrointestinal tract and the accessory
exocrine glands
4. Copyright 2009, John Wiley & Sons,
Inc.
Functions of the digestive system
1. Ingestion
2. Secretion of water, acid, buffers, and enzymes
into lumen
3. Mixing and propulsion
4. Digestion
• Mechanical digestion churns food
• Chemical digestion – hydrolysis
5. Absorption – passing into blood or lymph
6. Defecation – elimination of feces
5. • the mouth
• the esophagus
• the stomach
• the small intestine
• the large intestine
The gastrointestinal tract includes:
6. The major accessory glands are:
• the salivary glands
• the liver
• the gallbladder
• the pancreas
8. Processes of the Digestive System:
• Motility
• movement of food
through the digestive
system
• Secretion
• release of substances to
enhance breakdown of
food
• Digestion
• physical and chemical
breakdown of food
• Absorption
• transfer of materials to
internal environment
9. • The GI tract has four layers:
From deep to superficial:
• Mucosa
Epithelial cells
Lamina propria
Muscularis mucosae
• Submucosa (elastic connective tissue
contains lymph and blood vessels)
• Muscularis externa (smooth muscle
arranged in circular and longitudinal layers)
• Serosa ( outer connective tissue)
Histological organization of the digestive tract
12. Smooth Muscles show rhythmic cycles of
activity that generates contraction that spreads
• Peristalsis is waves or contractions that move
and propel food (bolus) along the GI tract
• Segmentation
• Segmentation is the contraction that is
produced in small intestine and some portion
of large intestine.
• This contraction leads to mixing of food and
fragment a bolus
Movement of digestive materials
14. • Movement of materials along the digestive tract is
controlled by:
• Neural mechanisms
• Parasympathetic and local reflexes
• Hormonal mechanisms
• Enhance or inhibit smooth muscle
contraction
• Local mechanisms
• Coordinate response to changes in pH or
chemical stimuli
Control of the digestive system
16. Copyright 2009, John Wiley & Sons,
Inc.
Neural innervation
• Enteric nervous system (ENS)
• Intrinsic set of nerves - “brain of gut”
• Neurons extending from esophagus to anus
• 2 plexuses
• Myenteric plexus – GI tract motility
• Submucosal plexus – controlling secretions
• Autonomic nervous system
• Extrinsic set of nerves
• Parasympathetic stimulation increases secretion and
activity by stimulating ENS
• Sympathetic stimulation decreases secretions and activity
by inhibiting ENS
17. THE ENTERIC NERVOUS SYSTEM
is composed mainly of two plexuses:
(1)an outer plexus lying between the longitudinal
and circular muscle layers, called the myenteric
plexus or Auerbach’s plexus
(2) an inner plexus, called the submucosal plexus or
Meissner’s plexus, that lies in the submucosa.
18. Copyright 2009, John Wiley & Sons,
Inc.
Organization of the enteric nervous
system
20. • Its functions include:
• Analysis of material before swallowing
• Mechanical processing by the teeth, tongue,
and palatal surfaces
• Lubrication
• Limited digestion e.g. salivary amylase initiates
digestion of complex carbohydrates
The Oral Cavity
The mouth opens into the oral or buccal cavity
21. • primary functions include:
• Mechanical processing
• Assistance in chewing and swallowing
• Sensory analysis by touch, temperature, and
taste receptors
The tongue
23. • There are 3 pairs of salivary glands:
• Parotid
• Sublingual
• Submandibular
SALIVARY GLANDS
24. • In the mouth cavity open three pair of big salivary
glands and a lot of small buccal glands.
• Parotid glands consist of the serum types cells
and secrete serous type of saliva.
• Submandibular and sublingual glands consist
of the cells of serum and mucous types and secrete
serous and mucus types of saliva.
• Small buccal glands consist of mucous types of
cells; produce mucous saliva with a big quantity of
water.
SALIVARY GLANDS
26. Quantity, composition and properties of
saliva
• In the case of dream produce nearly 0,05
mL/minute, in the normal condition – 0,5
mL/minute, in the case of maximal secretion – near
5 mL/minute. By day produce 0,8-1,5 L of saliva.
Composition of saliva: water, organic – alfa-
amilase, lipase, phosphatase, RNAase, DNAase,
mucin, substances for protective – lisocim,
thiocianates, antibodies – and unorganic
substances – sodium, potassium, calcium, chlorites,
etc.
27. Functions of saliva
• Lubrication, moistening, and dissolving
• Initiation of digestion of complex
carbohydrates
• Help to control bacterial population in the oral
cavity
28. Mechanism of saliva forming
• In acinars' cells produce primary saliva in which
synthesis necessary amino acids, glucose, mineral
substances (for example, Ca++).
• In the cells of salivary glands occur passive
processes, which provide moving of water and
electrolits from blood to the glands’ ductus (strait).
In the ductus occur reabsorption of sodium,
chlorine, secretion of potassium, HCO3
–.
• This is the secondary saliva. Aldosterone increase
reabsorption of sodium and secretion of potassium.
29. Influence of vegetative nerves on secretor
activity of salivary glands
Stimulation of the parasympathetic nerve supply
causes profuse secretion of watery saliva with a
relatively low content of organic material.
Stimulation of the sympathetic nerve supply causes
profuse secretion of saliva with small quantity of water
with a relatively big content of organic material.
30. Swallowing
• After chewing, the food (now called a bolus)
is swallowed.
• Swallowing (known scientifically as deglutition) is
the process in the human body that makes some
things pass from the mouth, to the pharynx, and
into the esophagus, while shutting the epiglottis.
31. • Pharynx:
• Movement of food bolus in esophagus (and
rest of GI tract) via peristalsis
• Esophagus:
• Carries solids and liquids from the pharynx to the
stomach
• Passes through esophageal hiatus in diaphragm
• The wall of the esophagus contains mucosal,
submucosal, and muscularis layers
Swallowing
33. • Storage - bulk storage of undigested food
• Releases small amounts to small intestine
• Mechanical processing of the food (forms chyme )
• Chemical processing of the food – e.g. disruption
of chemical bonds via acids and enzymes
• Secretion – e.g. production of intrinsic factor, HCl,
pepsinogen and gastrin
Stomach
Functions of the stomach:
35. Anatomically, the stomach is usually
divided
into two major parts:
The proximal (“orad”) part:
•Cardia
•Fundus
•Body
The distal (“caudad” ) part:
•Pylorus
36. • Cardia –portion of the
stomach that connects
to the esophagous
• Fundus – portion
superior to stomach-
esophageal junction
• Body – area between
the fundus and the
curve of the J
• Pylorus – antrum and
pyloric canal adjacent
to the duodenum
(portion of the stomach
that connects to the
duodenum)
Anatomy of the stomach
39. Secretory activity of stomach
• Production of stomach juice per day – near 2,5 L
of juice.
• Their main components – enzymes, HCl and
mucin.
• pH of morning saliva is neutral, after eating –
sour – 0,8-1,5.
40. • In Fundus and Body of the stomach there are gastric pits
• Each gastric pit communicate with several gastric gland
• Gastric glands are dominated with two types of secretary
cells:
• Parietal cells
• Secrete Intrinsic factor, and HCl
• Intrinsic factors are needed for vitamin B12 absorption
• HCl kill most acteria, denature proteins, inactivate food enzymes,
breakdown plant cells and connective tissue in meat, activate
pepsinogen to pepsin.
• Chief cells
• Secrete Pepsinogen (inactive porenzyme) that converts to pepsin (active
form) in the presence of acid.
• Pepsin breaks down proteins
• In kids chief cells also produce lipase and rennin (help milk digestion)
Gastric Secretion
41. • Pyloric glands
• Primarily produces mucous containing several
hormones
• Enteroendocrine cells
• G cells secrete gastrin
• Gastrin stimulates paraietal cells and chief
cells to secrete HCl and pepsinogen i.e. HCl
and pepsinogen is produced in response to
gastrin
• D cells secrete somatostatin
• Somatostatin inhibits gastrin secretion
Gastric Secretion
44. Role of the hydrochloric acid in the
digestion
• 1. To promote the swell of protein;
• 2. To promote the change of pepsinogen in
pepsins;
• 3. To make optimal conditions for actions of
pepsins;
• 4. To fulfill protective role from bacteria;
• 5. To promote motor and evacuated
functions of stomach;
• 6. To stimulate production of duodinum
hormon – secretin.
45. • Gastric control and production is done in 3
phase:
• Cephalic phase - prepares stomach to receive ingested
material
• Begins when one sees, smells, tastes or thinks of food
• Increases gastric juice production
• Gastric phase - begins with the arrival of food in the
stomach
• Neural, hormonal, and local responses further increase secretion
• Intestinal phase - controls the rate of gastric emptying
i.e. control the rate of chime entry into duodenum
• Inhibit gastric acid and pepsinogen production
Regulation of gastric activity
46. • Preliminary digestion of proteins
• Pepsin –enzyme that digests proteins
• However due to time limit digestion of protein can not be completed
• Permits digestion of carbohydrates by enzyme
lipase until the pH falls to 4.5
• Absorption does not occur in stomach because:
• Epithelial cells are not exposed to chime (covered by alkaline
mucus)
• Epithelial cells lack transport mechanism
• Gastric lining is impermeable to water
• Digestion is not completed
• Some drugs, however, are absorbed
Digestion and absorption in the stomach
47.
48. • Plays Important role in digestion and absorption
• Mucosa of SI produce few enzymes, and buffer to
neutralize chime
• Divided into three part:
• Duodenum – receives chime from stomach, bile from
gall bladder, and digestive secretion from pancreas
• Digestion continues in duodenum
• Jejunum – digestion and absorption takes place here
• Ileum
• Ileocecal sphincter
• Transition between small and large intestine
SMALL INTESTINE (SI)
52. 1. Peristalsis
the wave-like form of muscle contraction, moves
chyme along the intestine and causes only a
small amount of mixing. These contractions are
weak and slow in the small intestine so that time
is sufficient for complete digestion and
absorption of the chyme as it moves forward.
2. Segmentation
mixes chyme with digestive juices and exposes it to
the intestinal mucosa for absorption. This form
of motility causes only a small degree of forward
movement of the chyme along the small
intestine
INTESTINAL MOVEMENTS
53. Composition and properties of intestine juice
• Mucine
• Enzymes:
• Proteolytic
• Lipolytic
• Amilolytic
• Nuclealytic
• Immunoglobulins; ions; leukocytes
• pH of intestine juice is 7,5-8,0; production per day
– near 1,8-2,5 L.
• Functions: ending hydrolyses of all nutritive
substances; protective of mucus wall; support of
chyme in fluid condition; formed of base reaction of
intestine contents.
Increase secretion: parasympathetic nerves,
secretine, and glucagons.
54. • Pancreas is both an endocrine and exocrine gland
• Endocrine functions
• Secretes Insulin and glucagons
• Exocrine functions
• Produces majority of pancreatic secretions
• Pancreatic juice secreted into small intestine contain
THE PANCREAS
56. • Performs metabolic and hematological regulation
and produces bile
• Histological organization
• Consist of two lobes
• Each lobe is divided into lobules
• Lobule is the functional unit of liver
• Lobules unite to form common hepatic duct
• Duct meets cystic duct to form common
bile duct
The liver
58. Liver lobule is the basic functional unit of the
liver
• Hepatocytes form irregular plates arranged in
spoke-like fashion
• Bile canaliculi carry bile to the bile ductules
• Bile ductules lead to portal areas
60. BILIARY SYSTEM
• Bile is a complex fluid secreted by the liver and consists of
organic molecules in an alkaline solution. The biliary tract
consists of a series of ducts that convey bile from the liver to
the duodenum. Bile has three functions:
• It facilitates the assimilation of dietary lipid;
approximately 50% of dietary lipid appears in feces if bile
is excluded from the small intestine. Bile facilitates fat
digestion by promoting its emulsification and
solubilization. This is achieved through the formation of
mixed micelles, which enhance lipase action and then
assist in the delivery of the digestive products to be
absorbed by the enterocytes.
• It provides a pathway to excrete hydrophobic
molecules that may not be readily excreted by the
kidney.
• It assists in neutralizing gastric acid because it is an
alkaline solution.
61. Composition of bile:
• bilirubin,
• bile acids,
• cholesterol,
• leukocytes,
• some epitheliocytes,
• cristalls of bilirubin,
• calcium.
62. BILE PRODUCTION AND BILE SECRETOIN
• Secretion of bile occur all time and increase by
influences of bile acids, cholecystokinin-
pancreasemin, secretin.
• Bile secretion in the duodenum depends from take
food (minerals water, HCl, fatty acids increase bile
formation).
• It depends of nervus vagus (increase bile
formation) and humoral influences – concentration
of cholecystokinin-pancreasemin (increase bile
formation and ejection), secretin, gastrin.
63. • Functions of gall bladder are that it:
• Stores bile
• modifies bile and
• concentrates bile
• Bile slat break large droplet of fat for digestion
THE GALLBLADDER
Animation: Accessory Organ (see tutorial)
67. • Begins in the mouth
• Salivary and pancreatic enzymes:
• Oligosachrides, Disaccharides and
trisaccharides
• Brush border enzymes
• Monosaccharides
• Absorption of monosaccharides occurs across the
intestinal epithelia
Carbohydrate digestion and absorption
68. Absorption and intracellular processing of fats
A. Diffusion of micelles.
B. Intracellular synthesis of triglyceride and formation of chylomicrons. C.
Exocytosis of chylomicrons to lymphatic vessels.
69. •Bile salts improve chemical digestion by emulsifying lipid
drops (lipids interact with bile salts and form
emulsification droplets)
•pancreatic lipases break emulsified fat into free fatty acids
and monoglycerides
•Lipid-bile salt complexes called micelles are formed
•Micelles diffuse into intestinal epithelial cells
• Reform triglycerides in epithelial cells
• Combined w/ protein to form chylomicrons
• Chylomicrons released via exocytosis into lymphatic
system
• Then its transported to blood
Lipid digestion and absorption
70. • Water
• Nearly all that is ingested is reabsorbed via
osmosis
• Ions
• Absorbed via diffusion, cotransport, and active
transport
• Vitamins
• Water soluble vitamins are absorbed by
diffusion
• Fat soluble vitamins are absorbed as part of
micelles
• Vitamin B12 requires intrinsic factor
ABSORPTION WATER, IONS, VITAMINS
71. LARGE INTESTINE
• is the region of the digestive tract from the
ileocecal valve to the anus. Approximately 1.5 m
in length, it has a larger diameter than the small
intestine. The mucosa of the large intestine is
composed of absorptive cells and mucus-secreting
goblet cells and
• does not form villi. The large intestine consists of
the following structures:
Cecum collects and stores material from ileum
Appendix
Colon consist of four regions: ascending colon,
transverse colon, descending colon and sigmoid
colon
Rectum – it is expandable
73. FUNCTIONS OF THE LARGE INTESTINE
• Major functions:
1. absorption of water
2. absorption of vitamins produced by bacteria
3. storage of fecal material prior to defecation
• The colon’s absorption of most of the water and
salt from the chyme results in this “drying” or
concentrating process. As a result, only about 100
ml of water is lost through this route daily. The
remaining contents, now referred to as feces, are
“stored” in the large intestine until it can be
eliminated by way of defecation.
74. Role of the microflora of large intestine
• 1. Ending decompose of all nutritive substances, which are
do not digested in small intestines.
• 2. Synthesis of some vitamins – of B group, vitamin K.
• 3. Take place in metabolic processes.
• 4. Stimulates absorption of water and amino acids.
• 5. Inactivate enzymes of small intestines.
• 6. Forms normal reaction in large intestine.
• 7. Decompose organic substances of chyme.
• 8. Have protective role to the pathogenic microorganisms.
75. QUESTIONS
1. Functions of the gastrointestinal tract. Structure of the GI.
2. Types of Movement of digestive materials.
3. Oral cavity.
4. Salivary glands. Composition of saliva.
5. Mechanism of secretion of saliva. Regulation of Salivary secretion.
6. Chewing.
7. Esophagus.
8. Stomach. Structure and innervation of the stomach.
9. Gastric secretion. Types of gland cells.
10. Composition of gastric juice.
11. Mechanism of hydrochlolic acid secretion. Substances that stimulate
and ihibite of HCL secretion.
12. Regulation of gastric secretion.
13. Small intestine. Structure. Functions. Types of motility in SI.
14. Digestion and absorption carbohydrates, proteins, lipids in SI.
15. Large intestine. Structure. Functions. Role of the microflora of large
intestine.
