Download Liver and Gallbladder

Liver and
Gallbladder
• Liver is one of the body’s most important organs and
has many metabolic and regulatory roles. The
digestive function is to produce bile for export to the
duodenum.
• Bile is stored in the gall bladder
• Bile emulsifies fats  physically breaks fats into tiny
particles so they are more accessible to digestive
enzymes
Composition of Bile
• Yellow-green alkaline solution
• Contains bile salts, bile pigments,
cholesterol, triglycerides,
phospholipids, and a variety of
electrolytes.
• Only bile salts and phospholipids aid
in the digestive process.
Composition of Bile
• Bile salts emulsify fats distributes fat
throughout the water intestinal contents, just as
a dish detergent breaks up a pool of fat drippings
in a roasting pan.
• As a result, large fat globules are physically
separated into millions of small, more accessible
fatty droplets that provide a large surface area for
fat-digesting enzymes to work on.
• Bile salts also help with fat and cholesterol
absorption
Composition of Bile
• Bilirubin  chief bile pigment. A waste
product of the heme of hemoglobin formed
during the breakdown of RBCs.
• It is metabolized by bacteria in the small
intestine and one of the products is
stercobilin, which gives the brown color.
• When bile is absent, feces are gray-white in
color and have fatty streaks because
essentially no fats are digested or absorbed.
Pancreas
• Soft, tadpole-shaped gland that extends
across the abdomen.
• Produces enzymes (collectively called
pancreatic juice) that break down all
categories of foodstuffs.
• Pancreatic juice (pH ~8)consists of water,
enzymes and electrolytes. High pH helps to
neutralize acidic chyme.
Pancreas
• Enzymes:
– Trypsinogen  activated to trypsin by a brush
border enzyme
– Amylase  Carbohydrates
– Lipases  fats
– Amylase and lipase are secreted in active form but
– require ions or bile be present for optimal activity
Large Intestine
• Frames the small intestine on 3
sides
• Extends from the ileocecal valve
to the anus.
• Lumen diameter ~7cm (2 ¾ in)
• Length 1.5 meter (5 ft)
Large Intestine
• Major function is to absorb most of the
remaining water from the indigestible food,
stores the residue temporarily, and then
eliminate them from the body in the form of
feces.
• Because the colon doesn’t secrete digestive
enzymes, chemical digestion officially ends in
the small intestine.
Large Intestine
• Cecum (“blind pouch”)
– lies below the
ileocecal valve. First
part of the large
intestine.
Large Intestine
• Appendix –
• attached to the
cecum.
• Contains lymphoid
tissue and plays an
important role in
body immunity
Large Intestine
• Ascending colon –
• travels up the right
side of the abdominal
cavity
• Transverse colon • travels across the
abdominal cavity
Large Intestine
• Descending colon
• travels down the
left side of the
abdominal cavity
• Sigmoid colon
• when colon enters
the pelvis
• s-shaped
• travels transverse
Large Intestine
• Rectum –
• travels down, just in
front of the sacrum
• Anal canal –
• last portion of large
intestine
• about 3 cm long.
• Has the sphincters that
open and close the
anus during defecation
Large Intestine
• Since most food is absorbed before reaching
the large intestine, there are no circular folds,
no villi, and virtually no cells that secrete
digestive enzymes.
Large Intestine
• The mucosa is thicker, and abundant crypts
are deeper and there are lots of goblet cells
that produce mucus.
• The mucus eases the passage of feces and
protects the intestinal wall from irritating
acids and gases released by resident bacteria
Large Intestine - Bacterial Flora
• Most bacteria entering from the small
intestine are dead, but some are still alive.
• These and the bacteria that enter the GI tract
from the anus, these constitute the bacterial
flora of the large intestine over 700 species!
Large Intestine - Bacterial Flora
• Metabolize some proteins and ferment some
indigestible carbohydrates (cellulose, xylan,
and others), releasing irritating acids and a
mixture of gases (including dimethyl sulfide,
H2, N2, CH4, and CO2).
• Some are quite
odorous
• (dimethyl sulfide)!
Large Intestine - Bacterial Flora
• About 500 ml of gas (flatus) is produced each
day. More when certain carbohydrate rich
foods (beans) are eaten.
• Bacteria also synthesize B complex vitamins
and most of the vitamin K that the liver needs
to make some of the clotting proteins.
• Also found in the large intestine are viruses
and protozoans. Of these at least 20 are
known pathogens.
Large Intestine - Bacterial Flora
• Most enteric bacteria are
commensals (no harm and no
benefit to the host)
• that coexist peacefully with their
host as long as they remain in the
lumen.
• Bacteria break down and
metabolize the residual complex
carbohydrates further, adding
much to their own nutrition but
essentially nothing to ours.
Large Intestine - Motility
• Haustral contractions
– Slow segmenting
movements mainly
occuring in the
transverse and
descending colon.
– Last about 1 minute and
occur every 30 minutes
or so
Large Intestine - Motility
• Mass movements
– Long, slow-moving, powerful contractile waves
that move over large areas of the colon 3-4 times
daily and force the contents towards the rectum.
– Typically occurs during or just after eating.
– Bulk, or fiber, in the diet increases the strength of
colon contraction and softens the stool, allowing
the colon to act like a well-oiled machine.
Homeostatic Imbalance - Diverticulosis
• When the diet lacks bulk, and the
volume of the residues in the colon is
small, the colon narrows and its
contractions become more powerful,
increasing the pressure on its walls.
• This promotes the formation of
diverticula, small herniations of the
mucosa through the colon walls.
• Most commonly occurs in the sigmoid
colon. Affects over half of people over
the age of 70.
Defecation
• The semisolid product delivered to the rectum
is called feces or stool, contains undigested
food residues, mucus, sloughed-off epithelial
cells, millions of bacteria, and just enough
water to allow for smooth passage.
• The rectum is usually empty, but when mass
movements force the feces into it, the
defecation reflex is triggered.
Homeostatic Imbalance
• Watery stools
• Results from any condition that rushes food
residue through the large intestine before that
organ has had sufficient time to absorb the
remaining water.
• Prolonged diarrhea may result in dehydration
and electrolyte imbalance.
Homeostatic Imbalance
• When food remains in the colon
for extended periods
• too much water is absorbed and
the stool becomes hard and
difficult to pass.
• May result from a lack of fiber in
the diet, improper bowel habits
(holding it), lack of exercise,
emotional upset, or laxative
abuse