Transcript Digestive System

• 6 Processes of Digestion
– Ingestion
– Mechanical Digestion
Ingestion
Mechanical
digestion
• Chewing (mouth)
• Churning (stomach)
• Segmentation
(small intestine)
Chemical
digestion
Food
Pharynx
Esophagus
Propulsion
• Swallowing
(oropharynx)
• Peristalsis
Stomach
(esophagus,
stomach,
small intestine,
large intestine)
Absorption
Lymph
vessel
Small
intestine
Large
intestine
Defecation
Blood
vessel
Mainly H2O
Feces
Anus
• Chewing, swallowing
• Peristalsis
• Segmentation
– Chemical Digestion
• Enzymes breaking
chemical bonds
– Secretion
• Goblet cells secreting
mucus
• Organs secreting
enzymes
– Absorption
• Nutrients pass into blood
stream
– Defecation
• Removal of solid waste
Salivary
glands
Accessory Organs
to S. Intestines
stomach
Small Intestine
Blood
stream
Large Intestine
Histology of Digestive Tract
• Stratified squamous
– Mouth, pharynx &
esophagus
• Simple Columnar
– Stomach thru L.I.
– Goblet cells
• Villi
Microvilli
Mouth
• Main Functions
– Ingestion
– Physical digestion
• Tongue, teeth
– Chemical digestion
• Saliva and salivary
glands
Accessory Organs of Mouth
• Tongue
– Taste buds
– Responsible for
gripping food
– Mixes food with saliva
– Initiates swallowing
From
mouth
(a) Peristalsis: Adjacent segments of
alimentary tract organs alternately contract
and relax, which moves food along the tract
distally.
(b) Segmentation: Nonadjacent segments
of alimentary tract organs alternately
contract and relax, moving the food
forward then backward. Food mixing and
slow food propulsion occurs.
Salivary Glands
Parotid, submandibular and sublingual
• Functions
– Produce saliva
•
•
•
•
99% water
Contains enzyme amylase
Mucin – forms mucus
Growth Factor
• Functions of Saliva
– Cleanses mouth
• Growth factor and lysosomes
– Dissolves food for taste
– Moistens food; creates bolus
– Enzyme amylase begins the
chemical digestion of starch
Amylase
• Starch (polysaccharide)
disaccharides
Pharynx and Esophagus
• Pharynx
– Back of throat
– Passage way for
food
• Esophagus
– Food chute
– Stratified squamous
tissue
Stomach
• Four Primary Functions
– Temporary storage tank for food
– Mechanically break down food
• Food is converted into creamy paste called chyme
– Chemical breakdown of protein begins
– Production of intrinsic factor; necessary for
absorbing Vitamin B12.
Regions of the Stomach
• Cardiac region
– Upper area around
cardiac sphincter
• Fundus
– Dome-shaped part of
stomach
• Body
• Pylorus- inferior
portion
• Pyloric sphincter:
controls the emptying
of the stomach into the
S.I.
Stomach Physiology
• Rugae
• Peristalsis
– Controlled by
pacemaker cells
– Becomes more
forceful closer to
the pyloric region
• Gastric Pit
– Gastric gland
• Secretes mucus and
enzyme pepsinogen
• Parietal cells
– Secrete HCl and
instrinsic factor
– HCl is needed to
convert pepsinogen
into pepsin
– Kills bacteria that is
ingested with food
– Rennin
• Chief cells – produce
pepsinogen; inactive
form of pepsin
Pepsinogen
Pepsin
Converting Pepsinogen
to
Pepsin
HCl
Mitochondria
Parietal cell
Chief cell
Enteroendocrine
cell
(c) Location of the HCl-producing parietal cells and
pepsin-secreting chief cells in a gastric gland
Regulation of Gastric Activity
1. Cephalic phase
– prepares stomach to receive food
– Sight, smell, taste of food
– Controlled by vagus nerve and
parasympathetic system
– Only lasts a short time
2. Gastric Phase
– Stimulation of stretch receptors and
chemoreceptors stimulate the release of
hormone gastrin
– Gastrin causes release of HCl and
pepsinogen
– Increase in stomach contraction intensity
– Small amounts of caffeine and alcohol
stimulate chemoreceptors causing an
increase in gastric secretions
3. Intestinal phase
– Begins when food starts to enter S.I.
– Controls the rate of gastric emptying
– Slows down gastric activities by releasing
three hormones
•
•
•
Cholecystokinin (CCK)
Secretin
Gastric inhibitory peptide (GIP)
Small Intestine
• Digesting &
Absorbing Organ
• Anatomy
– Consists of 3
sections
• Duodenum
• Jejunum
• Ileum
– ileocecal spincter:
controls flow into
colon
– Mesentary
Modifications for Absorption
• Folds
– Mixes chyme
and slows
down
movement
• Villi
– Fingerlike
projections
increases
surface area
• Microvilli
Lining of Small Intestine
Regulation with Intestinal Hormones
• Secretin: released when pH falls in duodenum
(Why would this happen?)
– Result: causes water and buffers to be secreted into
S.I. by pancreas
• Cholecystokinin (CCK): secreted when protein
and lipid dense chyme arrives in S.I.
– Result: increases the secretion of digestive enzymes
from the pancreas and bile from the liver
• Gastric Inhibitory Peptide (GIP): released when
food begins to enter S.I.
– Result: inhibit digestive activity in stomach; causes
release of insulin from pancreas
1
Chyme entering duodenum
causes release of
cholecystokinin
(CCK) and
secretin from
duodenal
cells.
4 Bile salts and,
to a lesser extent,
secretin
transported via
bloodstream
stimulate liver to
produce bile
more rapidly.
5
2
CCK (red
dots) and
secretin (yellow
dots) enter the
bloodstream.
3
CCK induces
secretion of
enzyme-rich
pancreatic juice.
Secretin causes
secretion of
HCO3–-rich
pancreatic juice.
CCK (via
bloodstream)
causes
gallbladder to
contract ; bile enters
duodenum.
6
During
cephalic and
gastric phases,
vagal nerve
stimulation
causes weak
contractions of
gallbladder.
Chemical Digestion
• Brush Border
Enzymes
– Intestinal juice is
water, mucus and
enzymes
– Sucrase
– Lactase
– Maltase
– Peptidases/proteases
Lactose Intolerance
• Segmentation: movement of food through S.I.;
moves very slowly so chemical digestion can
occur
• Chemical Digestion:
– Very few Enzymes come from S.I.
– Need assistance from accessory organs
• Absorption: the building blocks of food are
passed into blood stream by Active Transport
– Most absorption is completed b4 it reaches the ileum
• Ilieum’s main function is to return bile salts to liver
– Mesentary
Accessory Organs: Pancreas
• Endocrine Gland
– Produces hormones
• Exocrine Gland
– Produces digestive
enzymes
• Empties into
duodenum
• Pancreatic
duct fuses
with Common
bile duct and
enters the
duodenum
Pancreatic Secretions
• Secretes (Exocrine Gland)
– Bicarbonate ions (NaHCO3-); turns acidic
chyme from stomach into basic solution (ph 78)
– Enzymes
•
•
•
•
Trypsinogen (inactive form)
Amylase
Lipase
Nucleases
Conversion of Trypsinogen into Trypsin
• Increase in pH
from bicarbonate
ions and another
enzymes converts
trypsinogen into its
active form trypsin
• Trypsin is a
protease and
continues protein
digestion
Digestion of Lipids
•
Lipase breaks down
lipids into fatty acids and
glycerol.
Fatty acids and glycerol
can then be absorbed
into the blood stream
Bile assists in this
process by physically
breaking down fats into
smaller droplets.
• Endocrine Gland
– Islets of Langerhans
are specialized cells
• Responsible for
secreting 2 hormones
– Glucagon
– Insulin
Anatomy of Liver and gall bladder
• Liver
– Hepatic duct allows
bile to leave the liver
• Gall Bladder
– Lies under liver;
appears like a slightly
inflated green balloon
– Stores bile
• Bile leaves the liver via
the cystic duct
• Cystic duct and hepatic
duct join to make
Common Bile Duct.
• Bile Production
– Only digestive process
– Physically separates
fats into smaller
droplets; allows lipase
to digest faster
– (Remember fats don’t
dissolve in water)
• I.e. scatters fat droplets
throughout solution
• Metabolic Regulation
– Processes all nutrients absorbed into blood
– Helps regulate cholesterol levels
– Forms nonessential amino acids; byproduct is
ammonia (toxic)
– Converts ammonia into urea (less toxic)
– Stores glucose as glycogen (polysaccharide)
– Stores fat soluble vitamins (A,D,E,K)
– Detoxifies alcohol and drugs (both legal and illegal)
• Blood leaving liver has fewer waste products
than the blood that enters it.
• Assists in Regulating
Blood
– Produces plasma
proteins
– Conserves iron from
old RBC’s
• Cirrhosis
– Chronic inflammation of
liver
– Results from severe
alcoholism or chronic sever
hepatitis
– Liver cells die are replaced
scar tissue and fat
deposits.
• Hepatitis
– Inflammation of liver
– Caused by a virus, sewage
contaminated water or
feces-mouth
• Cholesterol in
Bile salts
crystallize;
• Gets stuck in
duct; causes
extreme pain
Protein digestion
Foodstuff
Protein
Large polypeptides
Small polypeptides,
small peptides
Amino acids
(some dipeptides
and tripeptides)
Enzyme(s)
and source
Pepsin
(stomach glands)
in presence
of HCl
Pancreatic
enzymes
(trypsin, chymotrypsin,
carboxypeptidase)
Brush border
enzymes
(peptidases, proteases)
Site of
action
Path of absorption
• Amino acids are absorbed
by cotransport with
Stomach
sodium ions.
• Some dipeptides and
tripeptides are absorbed
via cotransport with H++
Small
and hydrolyzed to amino
intestine
acids within the cells.
• Amino acids leave the
epithelial cells by
Small
facilitated diffusion, enter
intestine
the capillary blood in the
villi, and are transported
to the liver via the hepatic
portal vein.
Carbohydrate digestion
Foodstuff
Enzyme(s)
and source
Site of
action
Starch and disaccharides
Oligosaccharides
and disaccharides
Lactose Maltose Sucrose
Galactose Glucose Fructose
Salivary
amylase
Pancreatic
amylase
Brush border
enzymes in
small intestine
(lactase,maltase
and sucrase)
Mouth
Small
intestine
Small
intestine
Path of absorption
• Glucose and galactose
are absorbed via
cotransport with
sodium ions.
• Fructose passes via
facilitated diffusion.
• All monosaccharides
leave the epithelial
cells via facilitated
diffusion, enter the
capillary blood in the
villi, and are
transported to the liver
via the hepatic portal
vein.
Fat digestion
Foodstuff
Enzyme(s)
and source
Site of
action
Unemulsified
fats
Emulsification by
the detergent
action of bile
salts ducted
in from the liver
Pancreatic
lipases
Monoglycerides Glycerol
and fatty acids
and
fatty acids
Small
intestine
Path of absorption
• Fatty acids and monoglycerides
enter the intestinal cells via
diffusion.
• Fatty acids and monoglycerides
are recombined to form
triglycerides and then
combined with other lipids and
Small
intestine proteins within the cells.
• Some short-chain fatty acids
are absorbed, move into the
capillary blood in the villi by
diffusion, and are transported
to the liver via the hepatic
portal vein.
Nucleic acid digestion
Foodstuff
Enzyme(s)
and source
Nucleic acids
Pentose sugars,
N-containing bases,
phosphate ions
Pancreatic ribonuclease and
deoxyribonuclease
Brush border
enzymes
(nucleosidases
and phosphatases)
Site of
action
Path of absorption
• Units enter intestinal cells
by active transport via
Small
intestine membrane carriers.
• Units are absorbed into
capillary blood in the villi
Small
and transported to the
intestine
liver via the hepatic portal
vein.
What remains in Small Intestine?
•
•
•
•
Indigestible food materials (cellulose)
Lots of bacteria
Water
Passes through ileocecal valve into Large
Intestine
Large Intestine/Colon
Anatomy
• Cecum
• Appendix
• Colon
–
–
–
–
Ascending
Transverse
Descending
Sigmoid
• Rectum
• Anal Canal
Microscopic Anatomy
• No villi or microvilli
• No cells which secrete
enzymes
• Many goblet cells lining
the simple columnar
tissue for lubrication
• Rectum tissue
becomes stratified
squamous
Main functions
• Absorbs water and
electrolytes (Na, Cl,
K)
• Absorbs water soluble
vitamins
• Eliminates undigested
food; defecation
Haustra = wall pockets
(seen in picture)
Other Inhabitants
• Bacteria
– Responsible for
fermenting undigested
food
– Product of these
reactions is gas (H2,
N2, CO2, H2S, CH4)
– Assist in synthesizing
vitamin B and vitamin
K.