Lecture 18 Malabsorption
Means bad absorption of everything: fats, carbs, and proteins. Diagnosis point of view we look for
increased fat in the stool = steatorrhea = screening test for malabsorption.
1) Need lipases to break down fat into 2 monoglycerides and FA’s, so you need a functioning
2) Need villi of the small intestine b/c if we didn’t, the small intestine would have to be a mile
long. Villi increase the overall absorptive surface without increasing the length. So, if you don’t
have them, you decrease the absorptive surface, and will lose the monoglycerides and FA’s.
Therefore, you need a functioning SI with villi.
3) Need bile salts to emulsify the fat and break it down to micelles (tiny particles that are 1 micron in
diameter) and chymlomicrons. Emulsifying agents are many times in dishwashers b/c need to get fat off
plates. Fat will come to the surface and break up into micelles, which are easier to absorb.
So, need functioning pancreas, bile salts, small intestine that has villi in order to reabsorb fat.
Bile salts are made in the liver from cholesterol. Cholesterol cannot be degraded; it either
solubilized in bile (therefore run the risk of cholesterol stones) or is converted to bile acids.
Cannot break down cholesterol. \
Bile salt deficiency is seen in: a) liver dz; b) anything that obstructs bile flow will produce bile
salt def; c) bacterial overgrowth can eat and breakdown bile; d) terminal ileal dz, ex. Crohn’s dz
cannot recycle; and e) Cholestyramine: resins – used for treatment of hyperlipidemia, can
produce bile salt def. This is the MOA of resins, by binding and then excreting them, b/c if you
are not recycling them, you will make more. What’s happening in the liver? Upregulation of LDL
receptors synthesis, b/c need to make more bile salts, therefore need to suck more out of the
blood and will make more LDL receptors. These drugs will eventually take more cholesterol out
of the blood and lower it, so you can make more bile salts. It also takes drugs with it, so it’s not
good for people taking meds, b/c you will lose these meds in the stool, along with bile salts.
Dz’s: screening test is looking for fat in stool (steatorrhea) – let’s say it is positive. So, we have
to figure which if the 3 areas is the cause of the malabsorption – pancreatic def, bile salt def, or
something wrong with the small bowel (MC).
Pic of small bowel lesion and a skin zit that has an association with it. This is celiac dz
(autoimmune dz), and the skin zit is dermatitis herpetiformis. Celiac dz is an autoimmune dz
against gluten wheat, esp. gliadin. It is very common and is the MCC of malabsorption in this
country. So, when you eat wheat products, the gluten is reabsorbed into the villi and there are
Ab’s against gliadin, and leads to destruction of the villi (just like Ab’s against parietal cells or
intrinsic factors, which destroy everything around it). So, the Ab’s attack gluten that has just
been reabsorbed by the food, which will cause destruction of the villus. And there are no villi
here – it is flat; blunting of villus – so you are not able to reabsorb fat, proteins, or carbs. There
is no villus surface. The glands underneath are fine, however. The villi are absent. There is a 100% chance of dermatitis herpetiformis association with underlying celiac dz. Dermatitis
herpetiformis is an autoimmune dz, and it is a vesicular lesion of the skin –looks like herpes of
the skin. They will show pic of a dermatitis herpetiformis, and will ask what the cause of
diarrhea is? Ab’s against gluten (gliadin). Whipple’s
An infection of the small infection due to an organism that you cannot gram stain. T. whippelii
only seen with EM; cannot be cultured. See flat blunted villi and foamy macrophages (look like
Niemann pic bubbly macrophages; can also be from an HIV “+” b/c it looks like Whipple’s, but
isn’t). The macrophages have distinctive PAS-positive stains.
HIV positive pt and acid fast stain – pt with helper T cell count of 100. Have an acid fast stain
with the foamy macrophages – due to MAI (this is more common that TB), and can cause
Whipple like dz with malabsorption.
Whipple’s, being an infection, has systemic signs and symptoms: fever, lymphadenopathy,
polyarthritis, generalized pain. It’s an infection therefore can be treated with antibiotics.
So, there are 2 dz’s that cause malabsorption: celiac dz and Whipple’s dz. Other dz’s are dz’s of
the pancreas – chronic pancreatitis (MC in alcoholics – 2 reasons for malabsorption in alcoholics
– a lipase def related to chronic pancreatitis, or bile salt def due to cirrhosis, or both in an
Best way to classify is to subdivide into 3 types: