[151111]lymphatic system and git
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IN THE NAME OF ALLAH
LYMPHATIC SYSTEM
THYMUS(cont)
We stop discussing thymus gland and if you remember I mentioned that thymus gland consist of
cortex and medulla. And it consists of incomplete lobules. The cortex (dark in color) and the medulla
(light in color). Why?? Because there are a lot of undifferentiated lymphocytes in the cortex and we
know the histology of lymphocyte is almost a nucleus surrounded by a lymphocytoplasmic. So the cell
looks flat due to abundant of lymphocytes. We have also reticular cell and macrophages. Almost 10% of
mature lymphocytes are found in medulla. While the percentage of reticular epithelial cell increased in
number, in addition the macrophages are also increased in number. So this is why medulla appeared
light (low no of lymphocytes and large number of reticular epithelial cells and macrophages).
In medulla, which I will not discussed too much, the reticular epithelial cells as I mentioned
before, they come from different origins of thymus, they come from epidermal origin. There are six
types but Im concerned about one of this types which is cell became flattened (in medulla) and it
become a ring around each other(surround each other). They give me a round structure called Hassall
corpuscles. This cell increased by age so we expect to find many Hassall Corpuscles in the adult of
mature thymus (age of puberty), while they are a few in the immature thymus. So it is a diagnostic of
the thymus gland, the Hassall corpuscles.
SPLEEN
Spleen is the largest single accumulation of lymphoid tissue in the body and the only one
involved in infiltration of blood. There is no cortex or medulla in the spleen. The spleen is surrounded by
dense connective tissue capsule which partially subdivide the parenchyma into compartments. The
connective tissue inside the spleen we called it trabeculae. This is by which blood vessels redistributed
inside the spleen. The main blood vessels was splenic artery. It enters the spleen and branching into
small trabecular arteries. As you can see, there are round dark area in the light end represent lymphatic
nodules which is the descriptive form of collection of lymphocytes. The function of thymus is only the
production of T-lymphocytes not an immune organ in addition is a gland that produce hormones and no
antigen-antibody reactions.
But here in spleen as you can see (refer to slide) the whole inside the spleen we called it splenic
pulp. It can be divided into white pulp and red pulp. We called it white pulp because we can make
specimen and we can find white spots and they are collections of white blood cells (WBC). While the
red pulp represent collection of red blood cells (RBC) and they look red because they are full with fresh
blood while white pulp full of fresh lymphocytes. White pulp applied to all round structure, while red
pulp applied to everything else. In the magnification of white pulp structure, I will find in the middle of
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each one there is an open circle which represents central arterioles. This is one of the characteristics of
spleen in the middle of white pulp.
Last time when I read about antigens interstudy with the body through the mouth, we think and
consider that it is a first line defense and the lymph nodes all over the body is the second line defense.
Lymph node is an effectors called lymph of antigens while the spleen is the opposite effectors of blood.
It filter the blood from antigens. What happened?? Blood enter the spleen through splenic artey then
divided into many branches and this branches divide into smaller and smaller branches called central
arterioles. Around each central arteriole there is lymphatic nodule. The type of lymphocyte in this area is
T-lymphocytes. And on the other side or area there is B-lymphocytes. So we have two types of
lymphocytes in the lympathic nodules in the spleen and it has immunological background.
The antigen that under the spleen via circulation is the effector of blood. Once the antigen reach
here and once again these are small arteries, so the antigens can freely leave the circulation. And once it
leaves the circulation, the antigens will be attack by T-lymphocytes. There is of antigens that will
continue in the artery to this end here. At the end, each artery is end with a dilated capillary we called it
sinusoid capillary or at the theory, they said that the artery is in splungy(?) and the blood leaves the
artery at this end. So the blood in the central artery has two possibilities to flow. First either in end of
sinusoid (closed circulation) or the blood leaves the artery at the end here and it pass around (open
circulation).
In either way, I have antigens (in closed circulation or open circulation). What will happened
here? Here, it is attack by T-lymphocytes. After it leaves the nodules, the antigens will leave and pass
here. It will returned back to this area which represent between what and what? (white pulp and red
pulp) and the area between them is called marginal zone. It is a close area between those pulp
everywhere in the spleen. It is characterized by abundance of macrophages. This is the most
immunogenic area in the spleen to attack the antibodies. So this is simply what I would like you to
understand about the spleen.
I told you something on the lymph node on lymphatic nodules, general speaking. All lymphatic
nodules made of B-lymphocytes. And each lymphocyte formed a nucleus.
In the stimulated to the lymphatic chain into plasma cell, if you aware about histology of plasma
cell it consists of a nucleus in one area and this region according to the nucleus, a large cytoplasm
compared to the lymphocytes. But if I have a collection of plasma cells, they will look white in color or
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light in color. So I expect an antigens comes to lymphatic nodules to stimulate the B-lymphocyte to
change or differentiate into plasma cells. And now I have collection of plasma cells that secrete
antibodies and the light area represents active lymphatic nodules. I said upon that all lymphatic
nodules are dark in color(inactive lymphatic nodules). Once I dont need more plasma cells, they will
degenerate and die.
This diagram shows open circulation and closed circulation.
GASTROINTESTINAL TRACT
GIT
What are the functions of GIT?
y Absorption of food
y Digestion
y Metabolism
Whats more?
One other function of the GIT system is acid-base balance. GIT system also synthesise and
secrete hormone. For example, secretin, cholecystokinin and gastrin.
In addition, how intestine can absorb vitamin B12. We must have what we called intrinsic factor
which secreted by the stomach which help absorption of the vitamin B12. So, this is the other function
regarding GIT system.
Anatomically speaking, what makes one GIT system? There are mouth, pharynx, esophagus,
stomach, small intestine, large intestine, for GIT system to perform good function it must be help and
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supported by accessories organ. What are the accessory organs? We have liver, pancreas and salivary
gland and once again, the pancreas and liver support the function of GIT system.
Generally speaking, the GIT system, it is simply a tube, from the beginning, the mouth down to the
anal canal, simply it is a tube. This tube, from the beginning to the end, it consists of 4 layers. From the
inside to outside we have first layer is the mucosa (just like epithelial layer). We have second layer thesubmucosa (underneath the mucosa). We have third layer, muscularis or the muscle layer of the GIT
and finally we have serosa, the outer covering of the GIT. So, this is the principle layer for all GIT from
the mouth down to the anal canal BUT with some exception! This will be discussed in a minute.
1. The first part is mucosa. The mucosa generally speaking it is simple columnar epithelial cell and
underneath there is basal membrane, there is small area of loose connective tissue (named
lamina propia) and finally we have a very thin layer of smooth muscle fiber (which called
muscularis mucosa). All of these form the mucosa.
2. When we come to submucosa, it is a dense connective tissue area and mainly this called
support, protection of the GIT. At the end of the mucosa , we have what we called mucosal
gland which gland that are found in the mucosa. In addition, this is the submucosa, sometime
we can find submucosal gland (gland in submucosa).
3. When it comes to the third layer muscularis, generally speaking, it consist of two muscle layer.
One of them, it is longitudinal (along the length of GIT) and the other muscle which is circular
(surrounding the lumen) of the tract.
4. And last layer which is serosa, it consist of loose connective tissue and is surrounded from
outside by a layer of simple squamous epithelium.
ESOPHAGUS
The first exception in oesophagus is you will find the epithelium is stratified squamous
epithelium, non-keratinized. Anatomically speaking, we can divide the esophagus into 3 portion. Upper,
middle and lower portion. When it comes to the muscle layer , the upper consist of skeletal muscle
fiber. In the middle portion, there is a mixture of skeletal and smooth muscle fiber. While in the lower
portion is smooth muscle fiber. This is one of exception of esophagus.
Another exception, we have talked about the gland in mucosa and sub mucosa. In esophagus,
we in the upper portion we have submucosal gland while in the lower portion I have mucosal gland and I
called them esophageal gland but they are in deep mucosa not in submucosa. The upper portion I have
submucosal gland, in the lower portion I have mucosal gland, we called them esophageal gland. All of
these gland, they secrete the mucus for lubrication of esophagus.
Where we could find the peritoneum? In the abdomen. esophagus? Where we could find? In
thorax. Is there peritoneum in thorax? No peritoneum in thorax. So, there is no serosa in esophagus.
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Generally speaking, in the esophagus there is another exception. There is no serosa and it is
replaced by what we called adventitia, so, these are almost the characteristics of esophagus.
If follow the pointer, the epithelium will change into something different. There is different
epithelium, which present the gland and we can see that the gland is at the level of the ending of the
epithelium and we see something new here. And this is the connection between the esophagus and the
stomach.
STOMACH
So, here we will begin with the stomach. Now, in the stomach is the same. Just like we have said
before, the epithelium made of simple columnar epithelium, have mucosal gland but we do not have
submucosal gland. We have 3 muscle layer in stomach. So, this is the exceptional. Instead of 2 muscle
layer, I have 3 muscle layer. About gland, I only have mucosal gland in stomach, no submucosal gland.
So, I will just concentrate on the mucosal gland in stomach. Anatomically speaking, stomach is divided
into how many parts? We have cardia, fundus, body and pylorus. Histologically speaking, the cardia andthe pylorus, they have common histology, while the body and fundus have the same histology. But,
both, they are different.
It is a mixed gland. What is the meaning of mixed gland? Ya3ni it is endocrine and exocrine. The
exocrine they has duct and the endocrine they has duct and both of them are found in the stomach. The
mucosal gland, in the duct they secrete direct into the stomach and endocrine gland they secrete
hormone that distributed in blood.
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This is the mucosal gland. From here to here it is a gland and it has subdivided into portion. This
is the pit of the gland. Next to the pit here, we have the neck of the gland. And next to the neck,
somewhere here, we called it the ithmus of the gland. And down here, we have the body of the gland.
So, in stomach I have a pit, neck, isthmus and body.
This is a schematic diagram for this. This is the pit (gastric pit) of the gland. It is covered by
simple columnar epithelium and they mainly are mucus secreting cell. They secrete mucus. This is the
mucus neck cell, this is the isthmus (represent the area where is present the stem cell). They have theability to divide by mitosis and to replace all type of cell in the gland.
Down in the body I can differentiate to another type of cells. Some of them are red and some of
them are blue. The red cells they have the parietal cell or oxyntic cell. These are cells that specialized in
secretion of HCL. The blue cells, these are protein synthesizing cell named chief cell or zymogenic cell.
They synthesize and secrete proteins. Again, HCL secreting cell, they are found in which part of the cell?
It is in the lower part of the body. The cluster of cell, they are enteroendocrine cells which synthesize
and secrete hormone.
____________________________________THE END _____________________________________
Alhamdulillah. If theres anything that you dont understand please go back to the book. We tried to
type back what Dr Ziad said almost everything. And forgive us if theres mistakes in our notes. And sorry
for being late >.< Wish all of you good luck in the exams. enshaAllah ( )/