Transcript Slide 1 - e

Gastrointestinal tract
activities
GI tract activities include ingestion,
mechanical digestion, chemical
(enzymatic) digestion propulsion,
absorption, and defecation. Sites of
chemical digestion are also sites
that produce enzymes or that
receive enzymes or other secretions
made by acessory organs outside
the alimentary canal. The mucosa of
the GI tract secretes mucus, which
protects and lubricates.
(E. Marieb, HA&P, 2004)
The regulation of
digestive activities
The major factors
responsible for
regulating digestive
activities:
1) neural
mechanisms
2) hormonal
mechanisms
3) local mechanisms
(F. Martini, A&P, 2004)
The salivary glands
(a) A lateral view, showing the relative positions of the salivary glands and ducts
on the left side of the head
(b) The submandibular gland secretes a mixture of mucins, produced by mucous
cells, and enzymes, produced by serous cells (LM X 303)
(F. Martini, A&P, 2004)
The swallowing
process
This sequence based
on a series of X rays,
shows the stages of
swallowing and the
movement of materials
from the mouth to the
stomach.
(F. Martini, A&P, 2004)
The swallowing
process (continue)
This sequence based
on a series of X rays,
shows the stages of
swallowing and the
movement of materials
from the mouth to the
stomach.
(F. Martini, A&P, 2004)
The stomach lining
(a) A surface view of the gastric mucosa of the full stomach, showing the
entrances to the gastric pits (SEM X 35)
(b) A section through gastric pits and gastric glands (LM X 300)
(F. Martini, A&P, 2004)
The stomach lining
(c) The organization of the stomach wall, (d) A gastric gland (F. Martini, A&P, 2004)
The secretion of
hydrochloric acid
An active parietal cell
generates H+ by the
dissociation of carbonic
acid within the cell. The
bicarbonate is exchanged
for Cl- in the interstitial
fluid; the chloride ions
diffuse into the lumen of
the gastric gland as the
hydrogen ions are
transported out of the cell.
(F. Martini, A&P, 2004)
The phase of the gastric secretion
(F. Martini, A&P, 2004)
The phase of the gastric secretion
(F. Martini, A&P, 2004)
The phase of the gastric secretion
(F. Martini, A&P, 2004)
The intestinal wall. (a) A section
of the intestine (LM X 2.5), (b) A
single plica and multiple villi, (c)
The organization of the intestinal
wall (F. Martini, A&P, 2004)
The intestinal wall
(d) Internal structures in a single villus, showing the capillary and lymphatic
supplies
(e) A villus in sectional view (LM X 252)
(F. Martini, A&P, 2004)
The pancreas. (a) The gross anatomy of the
pancreas. The head of the pancreas is tucked into a
C-shaped curve of the duodenum that begins at the
pylorus of the stomach. The cellular organization of
the pancreas is shown (b) diagrammatically and (c)
in a micrograph (LM X 86) (F. Martini, A&P, 2004).
Liver histology. (a) A single liver lobule and its cellular components,
(b) A diagrammatic view of liver structure, showing relationships among
lobules (F. Martini, A&P, 2004).
Liver histology
(c) A section through liver lobules from a pig liver (LM X 38)
(d) A portal area (LM X 31)
(F. Martini, A&P, 2004)
The gallbladder. (a) A view of the inferior surface of the liver, showing the
position of the gallbladder and ducts that transport bile from the liver to the
gallbladder and duodenum. (b) An interior view of the duodenum, showing the
duodenum ampulla and related structures (F. Martini, A&P, 2004).
The activities of
major digestive
tract hormones
The primary actions
of gastrin, secretin,
CCK, GIP and VIP
(F. Martini, A&P, 2004)
Digestive secretion and absorption
of water
The green arrows indicate secretion and
the white arrows indicate reabsorption.
(F. Martini, A&P, 2004)
Ion and vitamin absorption
by the digestive track
(F. Martini, A&P, 2004)
Protein digestion and
absorption in the small
intestine
Proteins and protein fragments
are digested to amino acids by
the action of pancreatic
proteases (trypsin, chymotrypsin,
and carboxypeptidase), and by
brush border enzymes of the
intestinal mucosal cells. The
amino acids are then absorbed by
active transport into the capillary
blood and villi.
(E. Marieb, HA&P, 2004)
Role of bile salts in fat
emulsification
As large aggregates of fats enter
the small intestine, bile salts cling
via their nonpolar parts to the fat
molecules (triglycerides). Their
polar parts, facing the aqueous
phase, interact with water and
repel each other, causing the fatty
globule to be physically broken
up into small fat droplets.
(E. Marieb, HA&P, 2004)
Fatty acid absorption
Digestion products of fat
breakdown, lecithin, and
cholesterol associate with bile
salts to form micelles, which
serve to “ferry” them to the
intestinal mucosa. They then
dissociate and enter the mucosa
cells by diffusion. In the
mucosal epithelial cells, they are
recombined to lipids and
packaged with other lipoid
substances and protein to form
chylomicrons. The
chylomicrons are extruded from
the epithelial cells by exocytosis
and enter the lacteal for
distribution in the lymph. Free
fatty acids and monoglycerides
enter the capillary bed.
(E. Marieb, HA&P, 2004)