ANAT 261 Lecture Notes - Duodenum, Elastase, Catabolism

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Naveen Sooknanan McGill Fall 2011
1
Liver:
The liver is one of the glands in the digestive system. It does not contain any hormones.
It has both endocrine and exocrine properties
o Exocrine: secretes bile, which goes to the gall bladder and then the intestines
o Endocrine: secreted into the bloodstream
The liver is the largest gland in the body. It is located right under the diaphragm
The liver is surrounded by a capsule CT which is very touch and rich in collagen fibers
o When you take a blow to the liver, the
capsule tears and the doctor must stich
it back together because the liver
would fall apart without it
The porta hepatis is a layer of CT which
divides the liver into lobes and smaller
lobules
o This CT is accompanied by 2 pairs of
each portal veins and hepatic arteries
o They come from the abdominal
cavity, particularly the area that drains
the spleen, and also from the digestive
system
Portal veins come from various areas
including those mentioned above
o Chylomicrons from the digestive tract come in from the portal veins to be
digested
o They have a functional circulation rather than a typical nutritional circulation
Hepatic arteries are paired with the portal veins and just run in the opposite direction
o They oxygenate the liver
The hepatic vein has a typical nutritional function
o It takes carbon dioxide produced in the liver back to the heart
o It drains directly into the inferior vena cava
The exocrine secretion of the liver consists of many bile ducts converging into one
hepatic duct
o This hepatic duct will continue to the gall bladder where it will place all of the
liver’s exocrine secretions
o It will eventually reach the intestines
The liver has several important functions:
The first is endocrine secretion into the blood stream. Secretion includes:
o Albumin, a typical protein in the body
o Fibrinogen and prothrombin are coagulation proteins
o Transferrin binds to free-floating iron in the blood, which is toxic, and brings it
wherever it needs to go
o VLDL and LDL (very) low density lipoproteins
Lipids combined with proteins can travel in the aqueous cytoplasm
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Naveen Sooknanan McGill Fall 2011
2
Cholesterol is necessary for growth of the PM, but it can be bad when
circulates in the blood for too long
Exocrine secretion is mainly to the gall bladder
o Bile acids
o Bilirubin, which is a pigment coming from dead red blood cells
o Phospholipids and cholesterol (travel with bile)
Inactivation/elimination of substances:
o Glucuronyl transferase combine glucuronic acid and bilirubin, but also produces
barbiturates, antihistaminics, anticonvulsants, insecticides and other drugs
Bilirubin is a product that can emulsify fats
Barbiturates are anaesthetics
o Endocytosis of hormones and LDL (cholesterol) particles
They undergo receptor mediated endocytosis (RME) and then destruction
Cholesterol can become oxidised in the blood, which is bas, so the liver
needs to unoxidize these by RME
Otherwise, they get eaten by macrophages, which deposit in artery
walls and can cause a heart attack
A hormone, problactin, in females, cannot be in the blood for too long and
needs to be absorbed by the liver
Conversion of substances:
o Tetra-iodothyronine T4 (thyroxine) Tri-iodothyronine T3 (which is more
potent)
T4 is a thyroid hormone
o The liver generally converts certain products into more potent compounds
Hemopoiesis, production of blood cells:
o The liver is the first organ to produce blood, but this only happens during fetal
development
o Mature hemopoiesis is done in the bone marrow
Storage of substances:
o Sugar monosaccharides are linked together in the liver and stored as glycogen
o Cholesterols that are absorbed by RME can be stored as phospholipids
o Lipids can also be stored in the liver
o When sugar levels are high in the blood, insulin stimulates the liver to absorb
sugar and turn them into glycogen
The liver can slowly release sugar by breaking up glycogen as we sleep, or
between meals
This sugar can then be used as energy
for the cells
Hepatic lobules are individually wrapped by CT.
Eventually; differentiation causes the disappearance of
lobules
Interlobular space contains hepatic arteries (red),
portal veins (blue), and bile ducts (green)
o Interlobular tissue in the liver is referred to a
portal space
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Naveen Sooknanan McGill Fall 2011
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A central vein penetrates into the middle of every hepatocyte
o From this vein, sinusoids branch off and divide the lobule into septi, or trabeculae
Remember what sinusoids are? They’re a type of fenestrated capillary.
They are very disorganized, unlike regular capillaries that we are used to
seeing
A sublobular vein runs parallel to rows of hepatocytes
o All of the central veins drain into the sublobular vein which
o “Sub” in this case does not necessarily mean below, as long as it is parallel to a
row of hepatocytes
The portal space, which means interlobular tissue for the liver, can be thickened at some
places because of the presence of bile ducts
We will now focus in onto one hepatic lobule and its components:
The central vein is an important landmark when looking for a hepatic lobule in a slide
o These veins have no proper wall (i.e. adventitia, etc.), only an endothelium
o Sinusoids, which divide the hepatic lobule into septi, or trabeculae, converge into
one central vein
Portal venules and hepatic arterioles can also be seen, but they are not to be confused
with the central vein
o The portal venules is responsible for functional circulation while the hepatic
arterioles bring in oxygen
o These two systems mix as they both open into the sinusoids, which use the blood
and then drain into the central vein
o Portal venules can often be confused with lymphatic, but we don’t need to know
the different
Anything with just an endothelium is a portal venule and anything with
SMCs is a hepatic arteriole
The sinusoids themselves appear to just be empty spaces between hepatocytes
o There are very little cells in a sinusoid, and fixation removes all of the RBCs form
the lumen
o Therefore ,they are not
much more then empty
spaces on the slide
o This is because they rest
on a discontinuous BM
and have no tight junctions
between endothelial cells
o Sinusoids branch at all
levels and can travel
between septi
Bile ducts are perhaps the easiest
structures to see because they are
lined by a single layer of cuboidal
cells in smaller structures and
columnar cells in larger ones
o They are interlobular ducts because they lie in the CT of portal space
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