1. It consists of lymphatic tissues and lymphatic vessels.
The lymphatic (lymphoid) system is essentially a drainage system, which is concerned with return of a fluid called "lymph" back to the blood stream.
It consists of lymphatic tissues and lymphatic vessels.
Its components are not in continuous order, but are scattered throughout the body and it services almost all regions.
Lymphatic tissues are a type of connective tissue that contains large numbers of lymphocytes.
Lymphatic tissue is organized into the following organs: the thymus, lymph nodes, spleen, and lymphatic nodules.
Lymphatic tissue is essential for the immunologic defenses of the body against bacteria and viruses.
Lymphatic vessels are tubes that assist the cardiovascular system in the removal of tissue fluid from the tissue spaces of the body; the vessels then return the fluid to the blood.
Lymphatic vessels are found in all tissues and organs of the body except:
Central nervous system.
Eyeball & internal ear.
Epidermis of skin.
Cartilage & bone.

2. Lymph vessels are either superficial or deep:
Superficial lymphatics: more numerous than veins in the subcutaneous tissue and anastomosing freely, converge toward and follow the venous drainage.
These vessels eventually drain into deep lymphatics that accompany the arteries and also receive the drainage of internal organs.
Both superficial and deep lymphatics traverse lymph nodes as they course proximally, becoming larger as they merge with vessels draining adjacent regions.
The lymphatics that carry lymph to a lymph node are referred to as afferent vessels; those that transport it away are efferent vessels.
The larger lymphatics enter large collecting vessels, called lymphatic trunks, which unite to form either the right lymphatic duct or the thoracic duct:
Right lymphatic duct.
Thoracic duct.

3. Functions of the lymphatic system
The functions of the lymphatic system are just as varied as its locations. These functions fall into 3 categories:
Fluid balance:
The small lymphatic capillaries pick up excess interstitial fluids and proteins, which accumulate in the tissue spaces. These capillaries then drain into larger vessels, which return these materials to the venous system near the heart.
Absorption and transport of dietary fat:
Many digested fats are too large to enter the blood capillaries and are instead absorbed into lymphatic capillaries. Special lymphatic capillaries, called lacteals (L. lacteus, milk), receive all lipid and lipid-soluble vitamins absorbed by the intestine. Visceral lymphatics then convey the milky fluid, chyle (G. chylos, juice), to the thoracic duct and into the venous system.
Formation of a defense mechanism for the body:
When foreign protein drains from an infected area, antibodies specific to the protein are produced by immunological cells (lymphocytes) and dispatched to the infected area.

4. Peritoneal covering: Blood supply: Lymph drainage:
The spleen is surrounded by peritoneum, which passes from it at the hilum to the:
Greater curvature of the stomach as the gastrosplenic ligament (carrying the short gastric and left gastroepiploic vessels).
Left kidney as the splenicorenal ligament (carrying the splenic vessels and the tail of the pancreas).
Blood supply:
Arteries
The large splenic artery is the largest branch of the celiac artery. It has a tortuous course as it runs along the upper border of the pancreas. The splenic artery then divides into about 6 branches, which enter the spleen at the hilum.
Veins
The splenic vein leaves the hilum and runs behind the tail and the body of the pancreas. Behind the neck of the pancreas, the splenic vein joins the superior mesenteric vein to form the portal vein.
Lymph drainage:
The lymph vessels emerge from the hilum and pass through a few lymph nodes along the course of the splenic artery and then drain into the celiac nodes.

5. Clinical Notes Splenic Enlargement Trauma to the Spleen
A pathologically enlarged spleen extends downward and medially.
The left colic flexure and the phrenicocolic ligament prevent a direct downward enlargement of the organ.
As the enlarged spleen projects below the left costal margin, its notched anterior border can be recognized by palpation through the anterior abdominal wall.
Trauma to the Spleen
Although anatomically the spleen gives the appearance of being well protected, automobile accidents of the crushing or run-over type commonly produce laceration of the spleen.
Penetrating wounds of the lower left thorax can also damage the spleen.

6. Lymphatic drainage of the upper limb
Superficial lymph vessels:
The superficial lymph vessels draining the superficial tissues of the upper arm pass upward to the axilla.
Those from the lateral side of the arm follow the cephalic vein to the infraclavicular group of nodes; those from the medial side follow the basilic vein to the lateral group of axillary nodes.
The deep lymphatic vessels: draining the muscles and deep structures of the arm drain into the lateral group of axillary nodes.

7. Axillary Lymph Nodes Efferent Afferent Site Anterior (pectoral) group
Central group
Apical group
Lat. part of breast
Front of trunk (above umbilicus)
At the lower border of pect. minor (along lat. thorathic artery)
Anterior (pectoral) group
Few lymph vessels pass to deep cervical LN
Most of lymphatics of UL
Along the lateral wall of axilla (along axillary vein)
Lateral
(Brachial)
group
Back of trunk (above iliac crest)
Tail of breast
From the previous 3 groups
Along lower border of subscapularis (along subscapular artery)
Posterior
(subscapular)
At the base of axilla in fat of axilla (closely related to intercosto-brachial N
Lymph vessels of this group unite to form subclavian lymph trunk which opens into:
on left side: in thoracic duct
on right side: in right lymph duct
From previous groups
Upper part of breast
Near the apex of axilla (behind clavi-pectoral fascia)

8. Lymphatic drainage of the lower limb
Inguinal lymph nodes: are divided into superficial & deep groups.
Superficial inguinal LNS
They lie in the superficial fascia below the inguinal ligament and can be divided into a horizontal and a vertical group.
The horizontal group lies just below and parallel to the inguinal ligament.
The medial members of the group receive superficial lymph vessels from the anterior abdominal wall below the level of the umbilicus, perineum, urethra, external genitalia of both sexes (but not the testes) and lower 1l2 of anal canal.
The lateral members of the group receive superficial lymph vessels from the back below the level of the iliac crests.
The vertical group lies along the terminal part of the great saphenous vein and receives most of the superficial lymph vessels of the lower limb.
The efferent lymph vessels from the superficial inguinal nodes pass through the saphenous opening in the deep fascia and join the deep inguinal nodes.

9. Lymphatic drainage of the thorax
Thoracic Wall:
 to the anterior axillary nodes.
The lymph vessels of the skin of the anterior thoracic wall drain
 to the posterior axillary nodes.
The lymph vessels of the skin of the posterior thoracic wall drain
 to the internal thoracic nodes (along the internal thoracic vessels)  to the thoracic duct on Lt.side and the bronchomediastinal trunk on Rt. side.
The deep lymph vessels of the anterior parts of the intercostal spaces drain
 to the posterior intercostal nodes (lying near the heads of the ribs(  to the thoracic duct.
The deep lymph vessels of the posterior parts of the intercostal spaces drain

10. Lymphatic drainage of the abdomen
Abdominal Wall:
 to the anterior axillary nodes.
The lymph vessels of the skin of anterior abdominal wall above the level of the umbilicus drain
Superficial lymph vessels
 to the superficial inguinal nodes.
The lymph vessels of the skin of anterior abdominal wall below the level of the umbilicus drain
 to the posterior axillary nodes.
The lymph vessels of the skin of the back above the level of the iliac crests drain
The lymph vessels of the skin of the back below the level of the iliac crests drain
 into the internal thoracic, external iliac, posterior mediastinal and para-aortic nodes.
The deep lymph vessels follow the arteries and drain
Deep lymph vessels

11. Abdominal cavity: Lymph nodes Lymph vessels
The lymph nodes are closely related to the aorta and form a preaortic and a Rt. & Lt. lateral aortic (para-aortic) chain.
The preaortic lymph nodes lie around the origins of the celiac, superior mesenteric & inferior mesenteric arteries and are called as the celiac, superior mesenteric & inferior mesenteric lymph nodes, respectively. They drain the lymph from the gastro-intestinal tract, extending from the lower 1/3 of esophagus to halfway down the anal canal, and from the spleen, pancreas, gallbladder, and greater part of the liver. The efferent lymph vessels form the large intestinal trunk.
The para-aortic lymph nodes drain lymph from the kidneys and suprarenals; from the testes in the male and from the ovaries, uterine tubes, and fundus of the uterus in the female; from the deep lymph vessels of the abdominal walls; and from the common iliac nodes. The efferent lymph vessels form the right and left lumbar trunks.
Lymph nodes
The thoracic duct starts in the abdomen as an elongated lymph sac, the cisterna chyli, which receives the intestinal trunk, the right and left lumbar trunks & some small lymph vessels that descend from the lower part of the thorax.
Lymph vessels

12. They receive lymph from
Regional nodes: are arranged as follows:
They receive lymph from
Site
Name
Back of the scalp.
Over occipital bone on the back of skull.
Occipital nodes
Scalp above the ear, auricle & the ext. auditory meatus.
Behind ear over mastoid process.
Retroauricular nodes
Scalp above the parotid gland, eyelids, parotid gland & auricle.
On or within the parotid gland.
Parotid nodes
Lateral side of scalp & face.
Over buccinator muscle.
Buccal nodes
Front of scalp, nose, cheek, upper lip & lower lip (except the central part), frontal, maxillary & ethmoid sinuses, upper & lower teeth (except the lower incisors); anterior 2/3 of tongue (except the tip), floor of mouth & gums.
Superficial to the submandibular gland just below the lower margin of jaw.
Submandibular nodes
Tip of tongue, floor of anterior part of mouth, incisor teeth, center part of the lower lip, and skin over the chin.
In submental triangle just below the chin
Submental nodes

13. They receive lymph from
Site
Name
Nasal pharynx, the auditory tube, and the vertebral column.
behind pharynx & infront of vertebral column.
Retropharyngeal nodes
Larynx.
in front of the larynx
Laryngeal nodes
Neighboring structures, including the thyroid gland.
alongside the trachea.
Paratracheal nodes
Skin and superficial tissues of the front of the neck.
Along the course of ant. jugular veins.
Anterior cervical nodes
Skin over the angle of the jaw, the skin over the lower part of the parotid gland, and the lobe of the ear.
Along course of ext. jugular vein superficial to sternomastoid.
Superficial cervical nodes
All the groups of regional nodes.
Form a vertical chain along the course of IJV within the carotid sheath
Deep cervical nodes
The efferent lymph vessels from the deep cervical lymph nodes join to form the jugular trunk, which drains into the thoracic duct or Rt. lymphatic duct.

14. Clinical Notes Disease of the Lymphatic System
Lymphangitis, Lymphadenitis, and Lymphedema:
Lymphangitis and lymphadenitis: are 2ry inflammation of lymphatic vessels and lymph nodes, respectively.
These conditions may occur when the lymphatic system is involved in chemical or bacterial transport after severe injury or infection.
The lymphatic vessels, not normally evident, may become apparent as red streaks in the skin, and the nodes become painfully enlarged.
Lymphedema or edema: is a localized accumulation of interstitial fluid, occurs when lymph does not drain from an area of the body, e.g. if cancerous lymph nodes are surgically removed from the axilla, lymphedema of the limb may occur.
Spread of cancer:
Cancer invades the body by growing into adjacent tissue or by dissemination of tumor cells to sites distant from the original or primary tumor) metastasis).
Metastasis occurs by one of three ways:
Direct seeding of the serous membranes of body cavities.
Lymphogenous spread via lymphatic vessels.
Hematogenous spread via blood vessels.
Lymphogenous spread is the most common route for the initial dissemination of carcinomas (epithelial tumors), the most common type of cancer.
Hematogenous spread is the most common route for the metastasis of the less common (but more malignant) sarcomas (C.T. cancers. Because veins are more abundant and have thinner walls that offer less resistance, metastasis occurs more often by venous than arterial routes. Since the blood-borne cells follow venous flow, the liver and lungs are the most common sites of secondary sarcomas.