 Human Digestive System
 Digestive System is divided to
1- Gastrointestinal tract and accessory organs
A. Gastrointestinal Tract
1. Also known as "alimentary canal"
2. All organs through which food passes (mouth to
anus)
B. Accessory Structures
1. Assist in digestion
2. Includes teeth, tongue, salivary glands, liver,
gall bladder, pancreas.
1
The gastrointestinal
tract (GIT) consists of
a hollow muscular
tube starting from the
oral cavity, where
food enters the mouth,
continuing through
the pharynx,
esophagus, stomach
and intestines to the
rectum and anus,
where feaces is
expelled.
2
Accessory organs : assist the
tract mechanically or by
secreting enzymes to help break
down food into its component
nutrients.
Food is never found within the
accessory organs, only within
the tract itself.
3
A diet must supply chemical energy,
organic molecules, and essential nutrients
• A diet provides:
– Chemical energy, which is converted into ATP to
power cellular processes.
– Organic building blocks, such as organic carbon
and organic nitrogen, to synthesize a variety of
organic molecules.
– Essential nutrients (essential amino acids,
essential fatty acids, vitamins & minerals), which
are required by cells and must be obtained from
dietary sources.
•Ingestion
Taking food
into the
mouth.
•Mastication:
•Peristalsis
•Deglutition
Functions of the GI Tract

1-Motility:
– Movement of food through the GI tract.
• Ingestion:
– Taking food into the mouth.
• Mastication:
– Chewing the food and mixing it with saliva.
• Deglutition:
– Swallowing the food.
• Peristalsis:
– Rhythmic wave-like contractions that move food
through GI tract.
– Valves called sphincters regulate the movement of
material between compartments
Functions of the GI Tract (continued)
• 2-Secretion:
– Includes both exocrine and endocrine
secretions.
• Exocrine:
– Hydrochloric acid (HCl), Water, (H2O), bicarbonate (HCO3-) ,
bile, Digestive Enzymes (lipase, pepsin, amylase, trypsin,
and elastase), are secreted into the lumen of the GI tract.
• Endocrine:
– Stomach and small intestine secrete hormones to help
regulate the GI system.
» Gastrin, secretin, CCK (cholecystokinin), GIP (gastric
inhibitory peptide), GLP-1 (glycogen-like peptide-1),
guanylin, VIP (vasoactive intestinal peptides), and
somatostatin.
Functions of the GI Tract (continued)
• 3-Digestion is the process of breaking food down into
molecules small enough to be absorbed.
digestion is an extracellular process that occurs mainly in the
stomach and small intestine where proteins, fats and carbohydrates
are chemically broken down into their basic building blocks.
It is of 2 types:
• A-Mechanical digestion, including chewing, which increases
the surface area of food
• B-Chemical digestion splits food into small molecules that can
pass through membranes; these are used to build larger
molecules
• In chemical digestion, the process of enzymatic hydrolysis
splits bonds in molecules with the addition of water
• 4-Absorption:
– Process of the passage of digested end products
(chemical subunits) into the blood or lymph.
– Smaller molecules are absorbed across the epithelium
of the small intestine and subsequently enter the
circulation.
– The large intestine plays a key role in reabsorbing
excess water.
• 5-Storage and elimination:
– Temporary storage and elimination of indigestible
material out of the digestive system.
– undigested material and secreted waste products,
bacteria, unabsorbed digested material, cells sloughed
from the GI tract are excreted from the body via
defecation (passing of faeces).
•Esophagus
Layers of the GI
1- Mucosa
• Lines the lumen of GI tract.
– Depending on its function, the epithelium may be simple columnar
epithelium or stratified (multiple layers).
• Lamina propria:
– Thin layer of connective tissue containing lymph nodules.
• Muscularis mucosae:
– Thin layer of smooth muscle responsible for the folds.
– Folds increase surface area for absorption.
• Goblet cells:
– Secrete mucus.

Mucosa’s functions are
1- Secrets mucus, digestive enzyme, and hormones.

2-Absorption of the end products of digestion into the blood

3- Protection against infectious diseases (lymph nodes

2-Submucosa
• Thick, highly vascular layer of connective tissue.
• Absorbed molecules enter the blood and lymphatic vessels.
• Submucosal plexus (Meissner’s plexus):
– Provide autonomic nerve supply to the muscularis mucosae.
3-Muscularis
• Responsible for segmental contractions and
peristaltic movement through the GI tract.
–Inner circular layer and outer longitudinal layer of
smooth muscle.
• Contractions of these layers move food through the
tract; mix the food.
• Myenteric plexus (Auerbach’s) located between the 2
muscle layers.
–Major nerve supply to GI tract.
•Fibers and ganglia from both sympathetic and
parasympathetic nervous systems.
4-Serosa / or Adventitia
• Binding and protective outer layer.
• Consists of areolar connective tissue covered with
simple squamous epithelium.
Layers of the gastrointestinal tract
Copyright 2009, John Wiley &
Sons, Inc.
Neural innervation
• Enteric nervous system (ENS)
– Intrinsic set of nerves - “brain of gut”
– Intrinsic sensory neurons which form network within
the walls of the gut from esophagus to anus
– 2 plexuses
• Myenteric plexus – GI tract motility
• Submucosal plexus – controlling secretions
• Autonomic nervous system
– Extrinsic set of nerves
– Parasympathetic stimulation: Vagus and sacral spinal
nerves increase GI secretions and activity by
stimulating ENS
– Sympathetic stimulation decreases secretions and
activity by inhibiting ENS
From Mouth to Stomach
The first stage of digestion is mechanical that takes place in the oral
cavity. It includes:
• Mastication (chewing):
– Mixes food with saliva which contains salivary amylase.
• Salivary glands deliver saliva to lubricate food
• Teeth chew food into smaller particles that are exposed to salivary
amylase, an enzyme that can catalyze the partial digestion of starch.
• Saliva also contains mucus, a viscous mixture of water, salts, cells,
Antimicrobial agents and glycoproteins.
•
•
•
•
•
The tongue shapes food into a bolus and provides help with swallowing
The throat, or pharynx, is the junction that opens to both the
esophagus and the trachea
The esophagus conducts food from the pharynx down to the stomach
by peristalsis
Swallowing causes the epiglottis to block entry to the trachea
Coughing occurs when the swallowing reflex fails and food or liquids
reach the windpipe.
From Mouth to Stomach
•
Deglutition (swallowing):
– Begins as a voluntary activity.
– Involves 3 phases:
• Oral phase is voluntary.
• Pharyngeal and esophageal phases are involuntary (autonomic)
and controlled by the swallowing center in the medulla. So, it
cannot be stopped.
–
–
–
–
•
(continued)
During swallowing
Soft palate lifts to close off the nasopharynx
Larynx is raised and vocal cords close off the opening to the larynx.
Epiglottis covers the entrance to respiratory tract.
The upper esophageal sphincter relaxes.
Esophagus:
– Connects pharynx to the stomach.
• Upper third contains skeletal muscle.
• Middle third contains a mixture of skeletal and smooth muscle.
• Terminal portion contains only smooth muscle.
Esophagus
• Peristalsis: Wave-like
muscular contractions:
– Circular smooth muscles
contract behind, relaxe
in front of the bolus.
– Followed by longitudinal
contraction (shortening
passage way ahead of
the bolus) of smooth
muscle.
• Rate of 2-4 cm/sec.
– After food passes into
stomach, lower
esophageal sphincter
constricts.
Insert 18.4a
Figure 41.10-3
Tongue
Bolus of
food
Pharynx
Epiglottis
up
Glottis
Larynx
Trachea
Esophageal
sphincter
contracted
Esophagus
To lungs To stomach
Relaxed
muscles
Contracted
muscles
Sphincter
relaxed
Stomach
Stomach
• Most distensible part of GI tract.
– Empties into the duodenum.
• Functions of the stomach:
– Stores food.
– Initiates digestion of proteins.
– Kills bacteria.
– Moves food (chyme) into intestine.
• Contractions of the stomach churn chyme.
– Mix chyme with gastric secretions.
– Push food into intestine.
• Gastric mucosa has gastric pits in the folds.
Figure 41.11
Esophagus
Sphincter
Stomach
10 m
Sphincter
Gastric pits on
interior surface
of stomach
Small
intestine
Folds of
epithelial
tissue
Epithelium
3
Pepsinogen
Pepsin
2
Gastric gland
Mucous cell
Chief cell
Parietal cell
HCl
Chief
cell
1
Cl
H
Parietal
cell
gastric pits contain four major secretory
cells:
a. chief cells Secret pepsinogen :
1. pepsinogen is activated by low pH to
form pepsin
2. pepsin is a protease for protein
digestion
24
b. Parietal cells involved in
1-HCl secretion: HCl secretion is enhanced by
histamine, gastrin,
HCl
a-Kills microbes;
b-denatures proteins (hydrolyzes peptide bonds) ;
c-breakdown of cell wall
d- reduce pH = 2 activates pepsinogen 
pepsin (partial protein digestion)
E-activates pepsin
2- Intrinsic factor secretion
It is a polypeptide that binds to and allows B12
absorption in the intestine
25
c. G-cell secretes gastrin hormone
Gastrin :
1-activates gastric juice secretion
2-stimulates parietal cells to secrete HCl
3- stimulates chief cell secrete to pepsinogen;
4- stimulates Enterochromafin like cells (ECL) to
secret histamine
5- stimulate stomach wall contraction
d. D-cell secrets Somatostatin Reduce gastrin
release  inhibits acid
E-Enterochromafin like cells (ECL) secrets
histamine (stimulates acid)
F. Goblet cell secretes mucus ( contains HCO3-)
which has a protective role against acids and
digestive enzymes
26
Gastric Glands Summery
Secrete gastric juice:
– Goblet cells: mucus.
– Parietal cells: HCl and intrinsic
factor needed for the absorption of
vitamin B12.
– Chief cells: pepsinogen.
– Enterochromaffin-like cells (ECL):
histamine and serotonin which act
as paracrine regulators of the GI
tract.
– G cells: gastrin hormone.
– D cells: somatostatin hormone.
– Stomach: ghrelin hormone that
regulates hunger.
HCl Functions
Insert fig. 18.9
Digestion and Absorption in the Stomach
•
•
•
Proteins are partially digested by pepsin.
Carbohydrate digestion by salivary amylase is inactivated by acidity.
Alcohol and aspirin are the only commonly ingested substances
absorbed.
Protective Mechanisms of Stomach
Q2-Why pepsin and HCL can not damage the stomach lining?
•
•
•
•
•
•
Parietal and chief cells impermeable to HCl.
Alkaline mucus contains HCO3-.
Tight junctions between adjacent epithelial cells.
Rapid rate of cell division (entire epithelium is replaced in 3 days).
Prostaglandins inhibit gastric secretions.
Pepsin is secreted in an inactive form.
•
Gastric ulcers: lesions in the lining, are caused mainly by the
bacterium 1-excessive gastric acid secretion in respose to high levels of
gastrin which is secreted by pancreatic tumer
2-infection by Helicobacter pylori bacteria.
3- inadequate HCO3- secretion in doudenum
•
•
•Propulsion in the Stomach
- Food must first be well mixed.
- Rippling peristalsis occurs in the lower stomach.
- The pylorus meters out chyme into the small intestine (30
ml at a time).
- The stomach empties in four to six hours.
Small Intestine
• In SI the partially digested food coming from the stomach
is mixed with three other liquids here:
1. Bile, a substance that is released by the gallbladder to help
in the digestion of fat.
2. Pancreatic juice and enzymes (released into the intestine
by the pancreas).
3. Other alkaline intestinal enzymes, such as maltase, lactase
and sucrose, which help to further break down different
types of sugars (this is why some people have reactions to
dairy products – they lack, or have very low levels of
lactase, so can’t break down lactose, the main sugar in
dairy products).
• The major functions of small intestine are:
• 1- Segmentation: major contraction activity that
results in mixing chyme with Bile & pancreatic juices
and other digestive enzymes.
• 2-Completes digestion of carbohydrates and proteins.
lipid digestion Begins then fats are broken down to
glycerol and fatty acids
• 3-Absorption of 90% of all nutrients: Glucose, Amino
Acids, Fatty Acids, Vitamin B12, Vitamin K, Water,
Na+ Ca++ Fe++ K+ Cl32
Intestinal Contractions and Motility
• 2 major types of
contractions occur in the
small intestine:
(a) Peristalsis – Alternating
waves of contraction (occurs
throughout digestive
system). Moving bolus then
chyme forward.
(b) Segmentation – Moving
materials back and forth to
aid in mixing chyme (mostly
in small intestine and colon)
Special structural features increase surface
area for digestion and absorption
– Circular folds
•
•
Permanent ridges of mucosa and submucosa
Cause chyme to coil
– Villi
•
•
•
Fingerlike projections of mucosa
Contains arteriole, venule, blood capillary, and
lacteal
Each villus is covered with columnar epithelial cells
interspersed with goblet cells.
– Microvilli
•
•
Projects of apical membrane of absorptive cells
Brush border with brush border enzymes
Vein carrying
blood to liver
Villi
Microvilli (brush
border) at apical
(lumenal) surface
Epithelial
cells
Blood
capillaries
Muscle layers
Villi
•
Intestinal wall
Epithelial
cells
plicae circularis Large
circular
folds
Basal
surface
Lacteal
Key
Nutrient
absorption
Lymph
vessel
Lumen
Plicae circularis folds increase the
surface area and speeds up absorption
process.
36
Small Intestine
•Epithelial cells at the
tips of villi are exfoliated
and replaced by mitosis.
•Paneth cells---lysozyme
(anti-bacterial).
•Lamina propria contain
lymphocytes, capillaries,
and central lacteal.
The mucosa of the small intestine contains
several specialized cells.

Some are responsible for absorption, others
secrete digestive enzymes and mucous to
protect the intestinal lining from digestive
actions.
•Histology
mucosa has intestinal glands for secretion of
intestinal juice
mucosa and submucosa has large folds called
Plicae circularis.

Each plicae has numerous villi (folds of
mucosa) and each villus is covered by
epithelium with projecting microvilli (brush
border).

This increases surface area and speeds up
the absorption process.
39
“brush border” has many enzymes :
i.
Several carbohydrate-digestive enzymes such as
maltase, sucrase, lactase
i.
Protein-digestive enzymes : Peptidases such as
aminopetidase, dipeptidase
ii.
Nucleosidases and phosphatases.
Nucleosidase an enzyme that catalyzes the splitting of a nucleoside to
form a purine or pyrimidine base and a sugar
alkaline phosphatase---removes phosphate group from organic
compounds.
40
 1. As chyme enters the duodenum, Peristalsis propels
chyme through small intestine.
2-Chyme’s proteins and carbohydrates are partly digested
but no fat digestion occurred yet.
• 3. Additional digestion is aided by secretions from the liver
(Bile) and the pancreas.
• a. Bile is a secretion of the liver temporarily stored in the
gallbladder before being sent to duodenum; bile emulsifies
fat (allows fat droplets to disperse in water).
41
• Each villus contains blood vessels and a lymphatic
capillary, called a lacteal.
• a. A lacteal aids in the absorption of fats.
• 6. Sugars and amino acids enter villi cells and are absorbed
into bloodstream.
• 7. Glycerol and fatty acids enter villi cells; reassembled
into fat molecules, they move into lacteals.
• 8. After nutrients are absorbed, the hepatic portal vein
carries nutrient-rich blood from the capillaries of the villi
to the liver, then to the heart.
• The liver regulates nutrient distribution, interconverts
many organic molecules, and detoxifies many organic
molecules.
• nutrients are eventually carried throughout the body by
the bloodstream.
42
•Digestion and Absorption of Nutrients
43
Nutrient Absorption Summery
1. Carbohydrates
a. enzymaticaly digested to form
monosaccharides (glucose, fructose,
galactose)
b. absorbed in SI by active transport or
facilitated diffusion
c. enter blood capillary in villi, then
directed to hepatic portal vein
44
2. Proteins
a. enzymatically digested to amino
acids or di- and tri-peptides
b. absorbed in SI by active transport or
facilitated diffusion.
c. enter blood capillary in villi, then
directed to hepatic portal vein
45
3. lipids
a. enzymatically digested to short or long
chain fatty acids
b. suspended in SI in form of micelles ‫جزيئة‬
‫غرويّة‬with bile salts
c. micelle formation aids lipid diffusion into
SI epithelial lining
d. inside epithelial cells, lipids bound into
chylomicrons for transport
e. chylomicrons are transported to lacteal
villi; then into lymphatics and then to
venous blood
46
47
Carbohydrate digestion
Oral cavity,
Polysaccharides Disaccharides
pharynx,
esophagus
Salivary amylase
Smaller
Maltose
polysaccharides
Stomach
Protein digestion
Proteins
Pepsin
Small polypeptides
Small
intestine
(enzymes
from
pancreas)
Pancreatic amylases
Nucleic acid digestion
Fat digestion
DNA, RNA
Fat (triglycerides)
Pancreatic trypsin and
chymotrypsin
Pancreatic
nucleases
Disaccharides
Smaller
polypeptides
Nucleotides
Pancreatic lipase
Pancreatic carboxypeptidase
Glycerol, fatty acids,
monoglycerides
Small peptides
Small
intestine
(enzymes
from
epithelium)
Disaccharidases
Nucleotidases
Dipeptidases, carboxypeptidase, and
aminopeptidase
Nucleosides
Nucleosidases
and
phosphatases
Monosaccharides
•
Amino acids
Nitrogenous bases,
sugars, phosphates
The portion of a nucleotide without the phosphate group is called a nucleoside
Large Intestine
•
•
•
Outer surface bulges outward to form pouches called haustra, does not
contain villi.
Appendix: immune function. Inflammation of appendix is called appendicitis.
Little absorptive function.
– Absorbs H2O, electrolytes, several vitamin B complexes, vitamin K, and
folic acid.
– The colon houses anaerobic bacteria (e.g., Escherichia coli) which live
on unabsorbed organic material; some produce vitamins. So, they form
mutualistic or commensal relationships with humans.
• Bacteria ferment indigestible molecules to produce short-chain fatty
acids.
• Intestinal microbiota (microflora) produce significant amounts of folic
acid and vitamin K and B vitamins.
• Reduces the ability of pathogenic species to colonize the intestine.
• Excessive use of antibiotics kills the normal flora.
Fluid and Electrolyte Absorption
• The small intestine receives 7-9L fluid from different
secretions and diet and most of this fluid and
electrolytes are absorbed by small intestine.
• Absorption of H2O occurs passively as a result of the
osmotic gradient created by active transport.
• Aldosterone stimulates NaCl and H2O absorption in the
ileum.
• Large intestine:
– Absorbs about 90% of the remaining volume.
• Secretion of H2O occurs passively as a result of
the osmotic gradient created by active transport
of Na+ or Cl- to the intestinal lumen.
• Diarrhea---excessive water secretion in feces.
• Constibation---decreased water secretion in
feces.
•The rectum



Last portion of the digestive tract
Terminates at the anal canal
Internal and external anal sphincters
51
52
Defecation
• Feces, including undigested material and bacteria,
become more solid as they move through the colon.
• Feces is stored in the rectum until they can be
eliminated through the anus
• The anus has two sphincters:
 Internal anal sphincter
 External anal sphincter

Internal anal sphincter is composed of smooth
muscle (relaxation causes the urge feeling)
External anal sphincter is composed of skeletal
muscle (relaxation causes defecation)
These sphincters are closed except during defecation


• Defecation reflex:
– Longitudinal rectal muscles contract to increase rectal pressure.
_ Relaxation of internal anal sphincter.
– Excretion is aided by contractions
of abdominal and pelvic skeletal
muscles that push feces from the
rectum.
• Defecation occurs when rectal pressure rises and external anal
sphincter relaxes.
Liver
The liver is a large, reddish-brown organ
situated in the right upper quadrant of the
abdomen.
It is surrounded by a strong capsule and
divided into four lobes namely the right,
left, caudate and quadrate lobes. The liver
has several important functions.
55
Liver
•liver is largest
•gland in body
56
All
nutrients absorbed by the intestines pass through the liver and
are processed before traveling to the rest of the body.
1.
Capillary in
intestine
1.
Liver
receives
nutrient-rich
blood from
SI via the
hepatic
portal vein
2.
Capillary
3.
Hepatic vein
4.
Inferior vena
cava
57
Capillaries of the digestive tract drain into the hepatic portal vein, which
carries blood to liver.
Portal system: capillaries---vein--- capillaries---vein.
• The hepatic portal vein
is not a true vein,
because it does not
conduct blood directly
to the heart.
• It is a vessel in the
abdominal cavity that
drains blood from the
gastrointestinal tract and
spleen to capillary beds
in the liver.
58
Enterohepatic Circulation
•Some compounds
re-circulate between
liver and intestine.
So, they have
enterohepatic
circulation
•e.g bile salts,
cholesterol.
Hepatic blood flow
• Liver receives blood
from
• Hepatic artery
carrying oxygenated
blood
• Hepatic portal vein
carrying
deoxygenated blood
with newly absorbed
nutrients and possibly
drugs, microbes or
toxins from GI tract
•The Role Of Liver
1-It acts as a mechanical filter by filtering blood that travels from the
intestinal system
– 2-It detoxifies several metabolites including the breakdown of
bilirubin, ETOH, detoxification and other dietary toxins. Chemical
alteration of the molecules such as ammonia. Ammonia is
produced by deamination of amino acids in the liver. It is very
toxic. So, the liver converts it into urea that is excreted in urine.
– other molecules that are cleared from blood are eliminated in the
feces.
3-The liver has synthetic functions, producing albumin and blood
clotting factors and cholesterol
4-Regulates carbohydrate metabolism
a. glucose secretion into blood/absorption from blood into glycogen
storage
b. regulated by insulin & glucagon
61
•The Role Of Liver
5-However, its main roles in digestion are in
the production of bile and metabolism of
nutrients.
The bile produced by cells of the liver, enters
the intestines at the duodenum.
Here, bile salts break down lipids into smaller
particles so there is a greater surface area for
digestive enzymes to act
62
Major Categories of Liver Function
Functional
category
Actions
Detoxification of
blood
Phagocytosis by kupffer cells
Chemical alteration of biologically active molecules (hormones &
drugs)
Production of urea, uric acid & other molecules that are less toxic
than parent compounds
Excretion of molecules in bile
Carbohydrate
metabolism
Conversion of blood glucose to glycogen & fat
Production of glucose from liver glycogen & from other molecules
(amino acids,…) by gluconeogenesis
Secretion of glucose into blood
Lipid metabolism
Synthesis of triglycerides & cholesterol
Excretion of cholesterol in bile
Production of ketone bodies from fatty acids
Protein synthesis
Production of albumin, clotting factors and plasma transport
proteins
Secretion of bile
Synthesis of bile salts
Gallbladder
• Sac-like organ attached to the inferior surface of the
liver.
• Functions to Stores and concentrates bile.
• When gallbladder fills with bile, it expands.
– Contraction of the muscularis layer of the
gallbladder ejects bile into the common bile duct
into duodenum.
• When small intestine is empty, the sphincter of
ampulla (sphincter of Oddi) closes.
– Bile is forced up to the cystic duct to gallbladder.
• Gallstones: small hard deposits that can produce
painful symptoms by obstructing the cystic or
common bile duct. Also, they contain cholesterol as
their major component.
•The sphincter of
ampulla or sphincter
of Oddi is a muscular
valve that controls the
flow of digestive
juices (bile and
pancreatic juice)
through the ampulla
of Vater (is formed
by the union of the
pancreatic duct and
the common bile
duct) into the
duodenum.
•Pancreas
Pancreas
Finally, the pancreas is a
lobular, pinkish-grey organ
that lies behind the stomach.
Its head communicates with
the duodenum and its tail
extends to the spleen.
The organ is approximately
15cm in length with a long,
slender body connecting the
head and tail segments.
67
The pancreas has both exocrine and
endocrine functions. Endocrine refers to
production of hormones which occurs in the
Islets of Langerhans.
The Islets produce insulin, glucagon and
other substances and these are the areas
damaged in diabetes mellitus.
The exocrine (secretory) portion makes up
80-85% of the pancreas and is the area
relevant to the gastrointestinal tract.
68
It is made up of numerous acini (small glands) that secrete
contents into ducts which eventually lead to the
duodenum.
 The pancreas secretes fluid rich in carbohydrates and
inactive enzymes. Secretion is triggered by the hormones
released by the duodenum in the presence of food.
Pancreatic enzymes include carbohydrases, lipases,
nuclease, and proteolytic enzymes that can break down
different components of food.
These are secreted in an inactive form zymogens
(inactive enzyme) to prevent digestion of the pancreas
itself. The enzymes become active once they reach the69
duodenum.
 E. Role Of The Pancreas In Digestion
 approx 1.5L/day pancreatic secretions are
produced
 secretions enter duodenum via two
pancreatic ducts
 many different components in these
secretions
 a. NaHCO3 – buffers pH of chyme
 b. Pancreatic amylase
70
c. Trypsinogen: is activated by
enterokinase to become trypsin
trypsin acts on other proteases to activate
them
d. lipases
e. ribonucleases (a type of nuclease
that catalyzes the degradation of RNA into
smaller components. )
71
Fig. 18.29
EN: Enterokinase
Pancreatic juice Summery
– 1200-1500ml daily
– Mostly water
• Sodium bicarbonate – buffers acidic stomach
chyme
• Enzymes
– Pancreatic amylase
– Proteolytic enzymes – trypsin (secreted as
trypsinogen), carboxypeptidase
– Pancreatic lipase
– Ribonuclease and deoxyribonuclease