4.lymphatic system

Compiled by: Prof. Anwar
Baig- AIKTC-SOP
4. Lymphatic system
Presented by: Prof.Mirza Anwar Baig
Asisstant Professor,AIKTC-School of Pharmacy,New
Panvel,Mumbai

Baig- AIKTC-SOP
Contents:
1.Introduction
2.Organization of lymph vessels
3.Formation and flow of lymph
4.Lymphatic organs and tissues

Baig- AIKTC-SOP
1. Introduction:
Important terms:
lymphatic system:
lymph, lymphatic vessels, lymphatic tissues, and red
bone marrow.
lymph:
Clear fluid, is interstitial fluid but located within
lymphatic vessels and lymphatic tissue.
Lymphatic tissue:
Specialized form of reticular connective tissue that
contains large numbers of lymphocytes. Two types
of lymphocytes participate in adaptive immune
responses: B cells and T cells.

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Functions of Lymphatic system:
Three primary functions:
1. Drains excess interstitial fluid.
Lymphatic vessels drain excess interstitial fluid from
tissue spaces and return it to the blood.
2. Transports dietary lipids.
Lymphatic vessels transport lipids and lipid-soluble
vitamins (A, D, E, and K) absorbed by the gas-
trointestinal tract.
3. Carries out immune responses.
Lymphatic tissue initiates highly specific responses
directed against particular microbes or abnormal cells.

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2. Organization of lymph vessels
• lymphatic capillaries. tiny
vessels,located in the spaces
between cells, are closed at
one end , lymphatic capillaries
unite to form larger lymphatic
vessels , resemble veins in
structure but have thinner
walls and more valves.
• At intervals along the
lymphatic vessels, lymph flows
through lymph nodes,
encapsulated bean-shaped
organs consisting of masses of
B cells and T cells.
• lie in the subcutaneous tissue
of skin.
• Tissues that lack lymphatic
capillaries include avascular
tissues (such as cartilage, the
epidermis, and the cornea of
the eye), the central nervous
system, portions of the spleen,
and red bone marrow.

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Baig- AIKTC-SOP
EDEMA
• Edema is the excess
accumulation of fluids
in tissue spaces. as a
result of decreased
plasma protein,
increased capillary
permeability or
lymphatic blockage,
can result in swelling and
congestion of the
extravascular
compartment.

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Lymphatic trunk and ducts:
• The principal trunks are the lumbar,
intestinal, bronchomediastinal, subclavian,
and jugular trunks.
1. The lumbar trunks: lower limbs, the wall
and viscera of the
pelvis, the kidneys, the adrenal glands,
and the abdominal wall.
2. The intestinal trunk drains lymph from
the stomach, intestines,
pancreas, spleen, and part of the liver.
3. The bronchomediastinal trunks: drain
lymph from the thoracic wall, lung, and
heart.
4. The subclavian trunks drain the upper
limbs. The jugular trunks
drain the head and neck.
5. The jugular trunks drain the head and
neck.

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Formation and Flow of Lymph
1. Most components of blood plasma filter freely through the
capillary walls to form interstitial fluid, but more fluid
filters out of blood capillaries than returns to them by
reabsorption.
2. The excess filtered fluid—about 3 liters per day—drains
into lymphatic vessels and becomes lymph.
3. interstitial fluid contains only a small amount of protein.
Proteins that do leave blood plasma cannot return to the
blood by diffusion because the concentration gradient.
4. The proteins can, however, move readily through the
more permeable lymphatic capillaries into lymph.
5. Thus, an important function of lymphatic vessels is to
return the lost plasma proteins to the bloodstream.

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Schematic diagram showing the relationship of
the lymphatic system to the cardiovascular
system.

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Two “pumps
• Aid the return of venous blood to the heart maintain
the flow of lymph.
1. Skeletal muscle pump:
The “milking action” of skeletal muscle contractions
compresses lymphatic vessels (as well as veins) and
forces lymph toward the junction of the internal
jugular and subclavian veins.
2. Respiratory pump.
Lymph flow is also maintained by pressure changes
that occur during inhalation (breathing in).
• Lymph flows from the abdominal region, where the
pressure is higher, toward the thoracic region, where
it is lower.
• When the pressures reverse during exhalation
(breathing out), the valves prevent backflow of lymph.
In addition, when a lymphatic vessel.

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2. Lymphatic organs and tissues
Classified into two groups based on their functions.
1. Primary lymphatic organs:
Sites where stem cells divide and become
immunocompetent, that is, capable of mounting an
immune response.
Examples red bone marrow (in flat bones and the
epiphyses of long bones of adults) and the thymus.
The pre-T cells in turn migrate to the thymus, where
they become immunocompetent T cells.
2. Secondary lymphatic organs:
Most immune responses occur.
They include lymph nodes, the spleen, and lymphatic
nodules (follicles).

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Thymus gland:

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Thymus
• Capsule: separates the two lobes
• Trabeculae: Extensions of the capsule, penetrate inward and divide
each lobe into lobules
• Cortex: Immature T cells (pre-T cells) migrate from red bone marrow
to the cortex of the thymus, where they proliferate and begin to
mature.
• Composed of
1. Dendritic cells: derived from monocytes, assist the maturation
process.
2. Epithelial cells help “educate” the pre-T cells in a process known
as positive selection. Additionally, they produce thymic hormones
that are thought to aid in the maturation of T cells. Only about 2%
of developing T cells survive in the cortex. The remaining cells die
via apoptosis (programmed cell death).
3. Thymic macrophages: clear out the debris of dead and dying cells.
The surviving T cells enter the medulla.

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The medulla:
Consists of
1. Mature T cells
2. Epithelial cells
3. Dendritic cells
3. Macrophages
4. Thymic (Hassall’s) corpuscles.
Some of the epithelial cells become arranged into
concentric layers of flat cells that degenerate and
become filled with keratohyalin granules and keratin.
may serve as sites of T cell death in the medulla.
T cells that leave the thymus via the blood migrate
to lymph nodes, the spleen, and other lymphatic
tissues where they colonize parts of these organs and
tissues.

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Lymph node:

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Lymph Nodes
• Located along lymphatic vessels are about 600 bean-shaped
lymph nodes. scattered throughout the body, both superficially
and deep, and usually occur in groups.
• Large groups of lymph nodes are present near the mammary
glands and in the axillae and groin.
• Lymph nodes are 1–25 mm (0.04–1 in.) long.
Fuction:
1. Lymph nodes function as a type of filter.
2. As lymph enters one end of a lymph node, foreign substances
are trapped by the reticular fibers within the sinuses of the
lymph node.
3. Macrophages destroy some foreign substances by phagocytosis
4. Lymphocytes destroy others by immune responses.
5. The filtered lymph then leaves the other end of the lymph node.

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Spleen
• The oval spleen, largest lymphatic
tissue, about 12 cm (5 in.) in
length.
• Located in the left hypochondriac
region between the stomach and
diaphragm.
• The superior surface of the spleen
is smooth and convex and
conforms to the concave surface of
the diaphragm.
• Impresions —the gastric impression
(stomach),the renal impression (left
kidney), and the colic impression
(left colic flexure of large
intestine).
• Hilum: Through it pass the splenic
artery, splenic vein, and efferent
lymphatic vessels.

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Spleen
1. A capsule of dense connective tissue surrounds the spleen.
2. Trabeculae extend inward from the capsule.
3. The capsule plus trabeculae, reticular fibers, and fibroblasts
constitute the stroma of the spleen.
4. Parenchyma of the spleen consists of two different kinds of
tissue called white pulp and red pulp.
5. White pulp is lymphatic tissue,consisting mostly of lymphocytes
and macrophages.
6. The red pulp consists of blood-filled
venous sinuses and splenic cords.
i. Splenic cords consist of red
blood cells, macrophages, lymphocytes,
plasma cells, and granulocytes.
7. Veins are closely associated with
the red pulp.

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White pulp consist of
i) B cells and T cells carry out immune functions
ii) Spleen macrophages destroy blood-borne pathogens by
phagocytosis.
Functions of Spleen
(1) Removal by macrophages of ruptured, worn out, or
defective blood cells and platelets;
(2) Storage of platelets, up to one-third of the body’s
supply.
(3) Production of blood cells (hemopoiesis) during fetal
life.

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Lymphatic Nodules
• Egg-shaped masses of lymphatic tissue that are not
surrounded by a capsule.
• Scattered throughout the lining of the gastrointestinal,
urinary,and reproductive tracts and the respiratory
airways, also referred to as mucosa-associated
lymphatic tissue (MALT).
• Among these are the tonsils in the pharyngeal region.
• Usually there are five tonsils, which form a ring at the
junction of the oral cavity and oropharynx and at the
junction of the nasal cavity and nasopharynx.
• The tonsils are strategically positioned to participate in
immune responses against inhaled or ingested foreign
substances.

4.lymphatic system

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