Lymph channels of the body - Formation and composition of lymph

LYMPH CHANNELS OF THE BODY

Lymphatic system consists of lymph channels such as lymph capillaries, collecting vessels, lymphatic trunks and lymphatic ducts. Lymph vessels are thin walled, valved vessels which carry lymph fluids. Lymphatic vessels begin as lymphatic capillaries, which combine to form lymphatic vessels. Lymphatic trunk is formed by joining of large lymphatic vessels. Lymphatic trunk is opens into two large lymphatic duct –

1. right lymphatic duct.

2. thoracic (left lymphatic)duct.

Lymph capillaries :

• made up of single layered endothelial cells.

• It contain minivalve- flap like structure formed by overlapping of adjacent endothelial cells. Minivalves allow lymph flow only in one direction (towards the thorax).

• Lymphatic capillaries are attached to the neighbouring tissue by anchoring filaments, that contain collagen filaments and elastic fibres.

• It has greater permeability than blood capillaries.

Lymphatic vessels

• Similar to veins

• It has 3 layers

1) Tunica intima – inner layer-made up of single squamous epithelium.

2) Tunica media—middle layer consist of smooth muscles n elastic tissue-arranged in circular shape around endothelium.

3) Adventitia – outer layer contain fibrous tissue.

• Afferent lymphatic vessels ➡️lymph node ➡️ Efferent lymphatic vessel.

Lymphatic trunk

• Lymphatic vessels exit lymph nodes and join to form lymphatic trunks.

• Major lymphatic trunks are

a) Lumbar trunks (right and left lumbar trunk)- drain lymph from lower limbs, wall n viscera of pelvis, kidneys, adrenal glands n abdominal wall.

b) Intestinal trunk – drains lymph from intestines, stomach, spIeen , part of liver n pancreas.

c) Broncho mediastinal trunks (right and left) –carry lymph from heart, thoracic wall n lung.

d) Subclavian trunks (right and left) –lymph from upper limbs.

e) Jugular trunks (right and left) -- drain lymph from head and neck.

Lymphatic duct

• Lymphatic ducts helps to return lymph fluid into blood.

• 2 lymphatic ducts of body are

1) Right lymphatic duct --- 1.2 cm length.

• Receives lymph from the right jugular, right subclavian, and right bronchomediastinal trunks.

• Drains lymph into venous blood at the junction of the right internal jugular and right subclavian veins.

2) .Thoracic duct/ left lymphatic duct -- larger duct - for lymph drainage from whole body except for right sides of head , neck ,thorax, and the right upper extremity.

• 38-45 cm long 2-5mm in diameter.

• It contains valves -- unicuspid, bicuspid( common), or tricuspid prevents backflow.

• It runs from superior part of cisterna chyli(enlarged lymph sac at the L2 vertebral level to lower spine, it receives lymph from right and left lumbar trunks and intestinal trunk).

• It receives lymph from cisterna chyli, left jugular, left subclavian, and left Broncho mediastinal trunks.

LYMPH NODES

• It is small, bean- shaped organ ,Located along lymph vessels.

• 1–25 mm length.

• Function as filtering and processing center of immune system.

• It filter lymph before it is returned to the blood.

• Nearly 600 lymph nodes in body , occur as groups.

 Lacteals- specialized lymphatic capillaries In small intestine. Which absorb dietary lipids into lymphatic vessels n at last into the blood.

 Chyle -- creamy white lymph -- deposition of lipids causes lymph leaking from the small intestine

 Tissues that lack lymphatic capillaries

 avascular tissues (cartilage, epidermis, and cornea of eye).

 central nervous system.

 Teeth.

 portions of the spleen.

 red bone marrow.

 endomysium of muscles n bones.

These tissues have minute interstitial channels called prelymphatics through this interstitial fluid can flow this fluid eventually enters into lymphatic vessels or, in the case of the brain, into the cerebrospinal fluid and then directly back into the blood.

FORMATION OF LYMPH

• Interstitial fluid is a precursor of prenodal lymph -produced by ultrafiltration of capillary microcirculation

• Starling principle state that microvascular ultrafiltration is determined by net balance b/w osmotic and hydrostatic pressure across microvascular endothelium.

• Pressure gradient between arterial and venous valves of capillary beds induce the fluid filtering from the arterial end into interstitial space and reabsorption into venous system.

• This concept is revised

• Osmotic and hydrostatic pressure provide low level of fluid filtration from microcirculation at both arterial and venous ends towards interstitial fluid.

• Fluids, proteins and small molecules pass through microvessels, it get filtered from microvessels into interstitium.

• This exchange occurs in glycocalyx – matrix of glycoproteins and glycosaminoglycan. It has a thickness of 50 to 500 nm. Present on the luminous surface of endothelium. Extend to intercellular cleft.

• Glycocalyx act as a sieve of different size.-it influences filtration rate.

 FACTORS EFFECTING LYMPH FORMATION

• Capillary pressure – if capillary Pressure increased formation of lymph increases.

• Permeability of capillary walls – when permeability increases then more tissue fluid will be form and that increases lymph formation.

• Rise in temperature increases capillary permeability- ⬆️ lymph formation.

• Reduced oxygen supply - increases capillary permeability- ⬆️ lymph formation.

• Increased metabolic activity increases lymph formation.