For medical, nursing and physiotherapy undergraduates, and postgraduates

1. LYMPHATIC
SYSTEM
DR. SUNDIP CHARMODE
ASSOCIATE PROFESSOR
DEPARTMENT OF ANATOMY
AIIMS RAJKOT

2. INTRODUCTION
• It consists of a closed system of vessels which ramify in the tissue spaces
in and around the blood capillaries and conveys the tissue fluid into the
blood vascular system by acting as an alternate route.
• Lymphatic system is auxiliary to the venous system.
• The lymphatics are intercepted by chains of lymph nodes which filter
lymph and add lymphocytes.

3. COMPONENTS
• The lymphatic system consists of:
1. Lymph
2. Lymph vessels
1. Lymph capillaries
2. Lymph vessels proper
3. Terminal lymph ducts
3. Lymphoid organs
4. Epithelio-lymphoid system
5. Bone marrow

4. LYMPH
• Clear and colourless watery fluid except ?
• Tissue fluid when enters lymphatic system is known as Lymph.
• Tissue fluid is derived from the blood plasma via microcirculation.
• Much of this fluid is returned to the venous system.
• Colloids and particulate matter of the tissue fluid are absorbed into the
lymphatic system through highly permeable endothelial wall of lymph
capillaries.

5. LYMPH
• Lymphatic vessels take up this residual fluid by passive diffusion and
the transient negative pressures in their lumina, generated
intrinsically by contractile activity of smooth muscle in the largest
lymphatic vessel walls, and extrinsically by compression of the
lymph vessels due to contraction of adjacent muscle or arterial
pulsation.

6. LYMPH
• Formation of lymph is directly proportional to the formation of tissue
fluid.
• The unidirectional flow of lymph is maintained by the presence of
valves in the larger vessels.

7. MECHANISM OF FORMATION OF LYMPH
1. At the arterial end of capillary:
• Hydrostatic pressure – 30 mm of Hg
• Protein osmotic pressure – 25 mm of Hg
• Filtration pressure – (30-25) = 5 mm of Hg
Most of the crystalloids and oxygen of blood appear in tissue space for
nutrition of the tissue cells.
2. At the venous end of capillary:
• Hydrostatic pressure – 12 mm of Hg
• Protein osmotic pressure – 25 mm of Hg
Hence, most of crystalloids and micro-molecules of colloids of tissue fluid
along with Co2 are reabsorbed through semi-permeable endothelial wall of
venous end.

8. FUNCTIONS OF LYMPHATIC SYSTEM
1. Help venous system to drain colloid components and particulate
matters of the tissue fluid.
2. Helps in absorption of digested fat directly into cisterna chyli.
2/3rd of the fat is digested by the lymphatic system.
3. Filters the particulate matters and noxious agents of lymph by
the phagocytic action of the macrophage cells of the lymph nodes.
4. Produces lymphocytes by the lymphatic follicles of the lymph
nodes.

9. FUNCTIONS OF LYMPHATIC SYSTEM
5. Produces immune substances (antibodies) by the plasma cells of
the lymph nodes
6. Under pathological conditions, it provides channels for the spread
of infection or malignant cells.

10. LYMPH - CONTENTS
1. Lymphocytes
2. Fats
3. Proteins
4. Particulate matter

11. LYMPH CAPILLARIES
• Begin as dilated, blind end tubes with large diameters and less regular
cross sectional appearances.
• They begin in tissue spaces around blood capillaries, form network
and communicate freely with adjacent lymph capillaries and are
valveless.
• Lymph capillaries don’t collapse due to anchoring filaments which
tether their walls to surrounding connective tissue structures and exert
radial traction.
• More permeable to bigger molecules – proteins, particulate matter
and colloids.

12. LYMPH CAPILLARIES - STRUCTURE
• Lined by single layered flattened endothelial cells.
• Definite basal lamina is absent or incomplete.
• They lack pericyte cells and are anchored to the fibers of connective
tissue.
• The endothelial cells of capillaries are not connected to one another by
tight junctions.
• The walls of the capillaries are highly permeable to the
macromolecules of colloids.

15. LYMPH CAPILLARIES
• The direction of lymph in lymph capillaries is multifugal.
• More numerous in skin, glands, mucous and serous membranes.
• Lymph capillaries join into larger vessels which pass to local lymph
nodes.

18. LYMPH CAPILLARIES
• Sites where lymph capillaries are absent are :
1. Avascular structures: Epidermis, cornea and articular hyaline
cartilage
2. Hair and Nails
3. Liver lobule and lung units
4. Brain and spinal cord
5. Splenic pulp and Bone marrow

19. Sl.
no
Lymph capillaries Blood capillaries
1 Absence of basal lamina and pericytes;
presence of flap valves in between the
endothelial cells
Presence of definite basal lamina
and pericytes
2 Permeable to macromolecules of colloids and
particulate matters
Permeable to soluble crystalloids
and micro-molecules of colloids.
3 The capillary wall is anchored to the
connective tissue fibers.

20. FACTORS HELPING TISSUE FLUID TO
ENTER INTO LYMPH CAPILLARIES
1. Filtration pressure of the tissue fluid
2. Diffusion of crystalloids through the semi-permeable membrane
3. Colloids enter the lumen of capillaries through the flap valves in
between the endothelial cells by a sort of suction action.

21. LYMPH VESSELS PROPER
• Thin walled with beaded appearance
• Presence of numerous semilunar valves (even more than the veins)
maintains unidirectional flow of lymph.
• Pass through series of lymph nodes
• Two set of veins:
1. Superficial veins lie in the sub-cutaneous areolar tissue and
accompany the veins
2. Deep veins are situated under cover of deep fascia and accompany
the arteries or veins.

22. LYMPH VESSELS PROPER -
STRUCTURE
• Three coats (from within outwards):
1. Tunica intima lined by endothelium
2. Tunica media consists of circularly arranged plain muscle
3. Tunica externa consists of fibrous tissue
• The endothelial cells of smaller lymphatic vessels contain numerous
transcytotic vesicles within their cytoplasm, and so resemble blood
capillaries.

23. LYMPH VESSELS PROPER
• Unlike blood capillaries, their endothelium is quite permeable to much
larger molecules:
1. Readily permeable to large colloidal proteins and
2. Readily permeable to particulate matter such as cell debris and
microorganisms
• Permeability is facilitated by gaps between the endothelial cells, which
lack tight junctions and by pinocytosis.
• Valves are semilunar, generally paired, and composed of extension of
intima.

24. LYMPH VESSELS PROPER
• The edges of the valves point in the direction of the current, and the
vessel wall downstream is expanded into a sinus, which gives the
vessels a beaded appearance when they are distended.

25. PECULARITIES OF LYMPH VESSELS
1. Lymph flows in one direction only, guided by the valves
2. Retrograde flow may take place if the vessels are obstructed, by the
separation of the valves
3. Sometimes lymph vessels terminate into remote lymph nodes and
bypass the immediate nodes via pericapsular plexus.
4. Lymphatic drainage of certain organs under pathological condition
is different from the drainage when the organs are healthy.

26. PECULARITIES OF LYMPH VESSELS
5. Lymphatic vessels repair easily and new vessels readily form after
damage.

27. TERMINAL LYMPH DUCTS
• Thoracic duct and Right lymphatic duct which terminate
respectively into left and right brachiocephalic veins.
• The thoracic duct drains the lymph from the entire body except the
right side of the head and neck, right upper limb, right thoracic wall,
right lung , right side of the heart, and a part of the convex surface of
the liver.

28. FACTORS RESPONSIBLE FOR DRAINAGE
OF LYMPH
1. Massaging action of skeletal muscles
2. Filtration pressure in tissue spaces
3. Transmitted pulsations of the arteries
4. Gravity
5. Valves of lymph vessels convert them into small segments and direct
the flow
6. Respiratory movements and suction action of diaphragm
7. Negative pressure in brachio-cephalic vein

29. LYMPHOID TISSUE
1. Primary lymph follicles
2. Lymph nodes
3. Haemolymph and haemal nodes
4. Thymus

30. LYMPH NODE
• Usually arranged in groups and are frequently situated along the
blood vessels.
• Variable in shape and size.
• Bean shaped, hilum gives attachment to single efferent lymph vessel.

32. FUNCTIONS OF LYMPH NODE
1. Filter the lymph and remove particulate matter
2. Plasma cells of the primary follicle produce antibodies which block
the action of the antigens of bacteria or other foreign agents.
3. Produce various types of lymphocytes
4. Provide portal of entry for lymphocytes into lymphatic channels
5. B lymphocytes settle in superficial zone of cortex and T
lymphocytes in midzone and deep zone of cortex.

33. FUNCTIONS OF SPLEEN
1. Filter the blood from antigens and microorganisms
2. Trigger immunological response against antigens
3. Produce various types of lymphocytes ( B and T)
4. Removes old and abnormal RBC’s
5. Removes bacteria by phagocytosis
6. Stores blood
7. Forms blood cells during foetal life

34. FUNCTIONS OF THYMUS
1. It is the site of production of T lymphocytes
2. It secretes a hormone ‘Thymosin’ which supports the activity of T
lymphocytes throughout the body

35. EPITHELIO-LYMPHOID SYSTEM
• Large amount of uncapsulated lymphoid tissue exists in walls of
alimentary, respiratory and genitourinary tracts.
• Collectively called as Mucosa associated lymphoid tissue (MALT)
1. Gut associated lymphoid tissue (GALT)
2. Bronchus associated lymphoid tissue (BALT)

36. EPITHELIO-LYMPHOID SYSTEM
• Notable aggregations and collections of MALT are :
1. Pharyngeal tonsils
2. Tubal tonsils
3. Palatine tonsils
4. Lingual tonsils
5. Peyer’s patches
6. Abdominal tonsils

37. RETICULO-ENDOTHELIAL SYSTEM
• The cell of this system are concerned with phagocytosis.
• They are important for local and general defence mechanisms.

38. RETICULO-ENDOTHELIAL SYSTEM
Cells Site of location
Macrophages Connective tissue, bone marrow, suprarenal
gland
Pericytes Capillaries
Monocytes Blood
Dust cells (alveolar macrophages) Lungs
Reticular cells Spleen and lymphoid tissue
Kupffer cells Liver
Microglia Central nervous system

39. FUNCTIONS
1. Drains excess fluid to the venous system which could not be drained
by the venous system.
2. Absorbs fat (2/3rd)
3. Provides immunity by producing lymphocytes – through lymph
nodes
4. Provides immunity by producing antibodies by plasma cells.
5. Under pathological conditions, it provide channels for spread of
infection or malignant cells.

40. THANK YOU