适用课程: 人体解剖学(0232000810),人体解剖学(0232000910),人体解剖学(0232001010),人体解剖学(双语)(0232001011),人体解剖学(双语)(0232001111),人体解剖学(0232005610),人体解剖学(23058001),人体解剖学(23058004)【访问量:1461964】
SYSTEMATIC ANATOMY

Chapter 2  Lymphatic System

Section 1  Introduction

 

Lymphatic systemis composed of lymphatic vessels, lymphatic tissuesand lymphatic organs. In the tissue spaces, some fluid elements filter through the wall of the capillaries into tissue space to become tissue fluid, which is mostly taken up by the blood capillaries, partly, the rich protein-containing fluid, taken up by the lymphatic capillaries to become the lymph. The lymph has a composition quite similar to blood plasma. Lymph is colorless except some appear milky because of its fatty content. Lymph tissues include diffused lymphatic tissues and lymphatic nodules. Lymph nodes, tonsils, thymus and spleen are lymph organs serve as both filters and sources of lymphocytes. So in addition to act as accessory system of cardiovascular, lymph system can also transports fats from digestive tract to blood, produce lymphocytes and develop antibodies.

Lymph vessels arise from lymphatic capillaries that pass through lymph nodes then converge to form nine lymphatic trunks. Each trunk drains a definite part of body and empty into lymphatic ducts. Two great terminal vessels are thoracic and right lymphatic ducts. They return lymph to blood circulation at left and right venous angles separatelyFig.III-2-1.

 

Fig.III-2-1  The structure and match of lymphatic system of human body

 

 . Lymphatic Vessels

They originate from lymphatic capillaries, just as blood capillaries converge to form venules and veins, lymph capillaries unite to form the lymphatic vessels, and then lymphatic trunks. These lymphatic trunks empty into the great veins in the root of the neck through lymphatic ducts.

1. Lymphatic capillaries 

Lymphatic capillaries are microscopic vessels in tissue space, and they anastomosis each other to form networks. Their structures have been revealed that the endothelial cells making up the capillaries wall are not tightly joined; their edges loosely overlap each other and form the opening junctions. These arrangement permits fluid to enter easily into the lymphatic capillaries but prevents the flow out of the capillary much like a one-way valve would operate. They are slightly larger and more permeable than blood capillaries(Fig.III-2-2). So lymphatic capillaries are structurally adapted to ensure the return of proteins to the circulation when they leak out of blood capillaries. Lymphatic capillaries exist throughout the body, except the splenic pulp, bone marrow, epidermis, hair, nails, cornea, lens, articular some cartilages, and the central nervous system.

 

Fig.III-2-2   The comparison of lymphatic capillary and blood capillary                     

       The open and overlapping junctions may be seen on the lymphatic capillary. And blood capillary is in the right inferior corner.

 

2. Lymphatic vessels

 Lymphatic capillaries unite to form lymphatic vessels which resemble veins in structure, but have thinner walls and more valves. In the path of the lymphatic vessels there are number of  lymph nodes at various intervals. In general, the lymphatic vessels of the skin travel in loose subcutaneous tissue following the superficial veins, however, the deep lymphatic vessels of the trunk and viscera travel with the deep arteries. There are widespread communicating branches between the superficial lymphatic vessels and the deep lymphatic vessels. Speed of lymph circulation is slow, only as slow as one tenth of that in veins. In order to maintain the circulation of lymph, the quantity of lymphatic vessels and their valves are many times of these of veins.

3.  Lymphatic trunks Fig.III-2-3

Lymphatic trunks are formed by the union of the larger lymphatic collecting vessels and named mostly for the regions from which they collect lymph. The nine major trunks are the paired lumbar trunks , brochomediastinal trunks , subclavian trunks, jugular trunks and the single intestinal trunk.

4.  Lymphatic ducts

Lymph is finally delivered to one of two large ducts in thoracic and cervical  region. These two ducts are named thoracic duct and right lymphatic duct. details will be considered in section 2Fig.III-2-3.

 

Fig-III-2-3 Lymphatic trunks and ducts

Fig.III24 Lymph Nodes

 

. Lymph Nodes

Lymph nodes are small round or bean-shaped structures located along lymphatic vessels. In general, they are grayish pink with length range from 5 to 25mm. Lymph nodes contain slight depression on one side called hilus where blood vessels, nerve and efferent lymphatic vessels pass. Lymph enters the convex surface of lymph nodes through afferent lymphatic vessels, and leaves by efferent lymphatic vessels at hilus. There are fewer efferent lymphatic vessels than afferent lymphatic vessels, so the rate of lymph flow through the nodes is slowed and efferent lymphatic vessels are wider than afferent lymphatic vessels. However, the efferent lymphatic vessels of one lymph node may be afferent lymphatic vessels of another node. Lymph nodes often get together and classed by deep fascia into superficial group and deep group. Superficial groups can be easily touched, but deep groups often located near the hilus of viscera or the branch of blood vessels in abdomen and pelvis. They are often named by their location or nearby blood vesselsFig.III24

.

Clinic Notes

In addition, to act as filter of lymph, lymph nodes also product lymphocytes and plasmocytes, and play a role in activating the immune system.

Lymph of an organ or region will flow to some lymph nodes which is called regional nodes of this organ or region. Knowledge of regional nodes may be helpful in diagnosing the site of an infection if there are infected lymph nodes. The location of lymph nodes and direction of lymph flow are also important in the diagnosis and prognosis of cancer with metastasis.

Section 2  Lymphatic Ducts

 

The principal trunks pass their lymph into two large ducts, thoracic duct and right lymphatic duct. Each duct empties lymph into venous circulation at the junction of the internal jugular vein and subclavian vein on its own side of the body. Thus, lymph is drained back into blood.

 

.  Thoracic Duct

Thoracic duct is the largest lymphatic vessel of human with about 30 to 40cm in length and 3mm in diameter(Fig.III-2-3). This duct begins as dilation in front of the first lumber vertebra called cisterna chyli. Cisterna chyli receives intestinal trunk and a pair of lumbar trunks. Begins from cisterna chyli, thoracic duct then passes the aortic hiatus of the diaphragmbehind the aorta and enters the posterior mediastinum in where it lies between vertebral column and oesophagus. At the level of the fifth thoracic vertebra it crosses to the left of the vertebral column. At the root of the neck, the duct forms arch of thoracic duct, and enters the left venous angle (junction of the left internal jugular and subclavian veins). At the root of the neck, it also receives subclavian trunk, left jugular trunks, left bronchomediastinal trunk. Through these six lymphatic trunks, thoracic duct receives lymph from the left side of the head, neck and chest, the left upper limb, abdomen, pelvis and two lower limbs, about 3/4 parts of the whole body.

 

. Right Lymphatic Duct

Right lymphatic duct is a short duct about 1 to 1.5cm long, and 2mm in diameter. It is united by right jugular trunk, right subclavian trunk, and right bronchomediastinal trunk. Sometimes the three lymphatic trunks may open separately into right internal jugular or subclavian veins. Right lymphatic duct receives lymph from the right side of head, neck, chest, and the right upper limb, about one fourth of the whole body(Fig.III-2-3).

Fig.III-2-5  Lymph nodes of head and neck

 

Section 3  Lymph nodes and lymph drainage of whole Body

 

.  Lymph Nodes and lymph drainage of Head and Neck

1.  Lymph nodes and lymph drainage of head.

Most of the lymph nodes  of the head are located in the junction of head and neck. They are the occipital lymph nodes, mastoid lymph nodes, parotid lymph nodes, submandibular lymph nodes, submental lymph nodes from posterior to anterior. These lymph nodes receive the lymph of the head and face ,and then empty to deep lateral cervical lymph nodes (Fig.III-2-5).

(1) Occipital lymph nodes  They locate on the surface of the insertion of trapezius,and receive lymph from occipital portion and nape.

(2) Mastoid lymph nodes  They lie behind ear and on surface of the attachment Mastoid of sternocleidomastoid,and receive lymph from the parietal, temporal region and retroauricular region.

(3) Parotid lymph nodes  They can be classed into the superifical and deep groups, which locate on the surface of parotid gland and in the substance of the gland respectively, and receive lymph from forehead, temple, auricle, external auditory canal, tympaanic membrane, cheek and parotid gland.

(4) Submandibular lymph nodes  They locate in submandibular triangle, near submandibular gland. Receive lymph from face, orbit, nasal part, and oral cavity.

(5)Submental lymph nodes  They lie in submental triangle. Receive lymph from chin, lower lip, and tip of tongue.

2.  Lymph nodes and lymph drainage of neck

Lymph nodes of neck can be divided into anterior cervical lymph nodes and lateral cervical lymph nodes.

(1). Anterior cervical lymph nodes  They lie in front of larynx, thyroid gland, and trachea, under the hyoid bone.

1) Superficial anterior cervical lymph nodes They arrange along the superficial jugular vein and receive lymph from superficial layer of anterior neck.

2)  Deep anterior cervical lymph nodes They lie in front of the larynx and receive lymph from larynx, thyroid gland, and trachea. Efferent vessels of these two groups of lymph nodes empty into lateral cervical lymph nodes.

(2). Lateral cervical lymph nodes  They are divided into the superficial lateral cervical lymph nodes and the deep lateral cervical lymph nodes(Fig.III-2-6).

1) Superficial lateral cervical lymph nodes  They arrange along the superficial jugular vein and receive the lymph from superficial layer of neck and the  efferent vessels of mastoid lymph nodes, occipital lymph nodes, and submandibular lymph nodes. Their efferent vessels empty into deep cervical lymph nodes.

2) Deep lateral cervical lymph nodes(Fig.III-2-6)  There are as many as 10 15 lymph nodes in number, and they locate along internal jugular vein from base of skull to root of neck. Some of them lie along the accessory nerve and the transverse cervical blood vessels. They may be divided into the superior and inferior groups bounded by the omohyhoid.

  The superior deep lateral cervical lymph nodes lie on the upper part of the internal jugular vein, they receive the efferent lymph vessels of the lymph nodes of the head and the superficial lateral cervical lymph nodes, also receive the lymph from the nose, tongue, pharynx, larynx, thyroid gland, trachea and the esophagus.

The inferior deep lateral cervical lymph nodes surround the lower part of the internal jugular vein, some of them lie along the transverse cervical blood vessels which are called the supraclavicular lymph nodes. Some lymph nodes locate just in front of scalenus anteriorthe left ones of them are called Virchow’s lymph node, which may be involved in the cancer of the stomach or esophagus.

 

Fig.III-2-6 The deep cervical lymph nodes

Lymph Nodes and lymph Drainage of Upper Limb

Lymphatic system of upper limb is composed of superficial lymphatic vessels, deep lymphatic vessels, and lymph nodes. Superficial lymphatic vessels drain lymph of skin and subcutaneous fascia; deep lymphatic vessels drain lymph of muscles, tendons, bones, and joints. These lymphatic vessels empty mainly into regional lymph nodes. Lymph nodes of upper limb concentrated mainly at elbow and axillary fossa.

1. Cubital lymph nodes Yhey are one or two lymph nodes in number, and locate near elbow and medial epicondyle of humerus. They receive lymph of lymphatic vessels along basilic vein and ulnar blood vessel, and then empty into axillary lymph nodes.

2. Axillary lymph nodes(Fig.III-2-7解剖图谱311)  There are about 15 20 lymph nodes in axillary fossa around axillary blood vessels, and are divided into five groups.

1) Lateral lymph nodes They locate along axillary vein. Receive lymph from superficial and deep lymphatic vessels of upper limb.

2) Pectoral lymph nodes They lie along inferior border of the pectoralis minor muscle, receive lymph of anterior and lateral thoracic walls and central and lateral portions of mammary gland.

3) Subscapular lymph nodes They locate along subscapular artery, receive lymph from posterior part of neck and thoracic wall.

4) Central lymph nodes They are embedded in fat near the base of axillary, receive lymph from lateral lymph nodes, pectoral lymph nodes, and subscapular lymph nodes.

5) Apical lymph nodes Locate along axillary artery and vein, the apical lymph nodes receive lymph from central lymph nodes and superior portions of mammary gland. The efferent lymphatic vessels of these lymph nodes empty into subclavian trunk.

 

Fig.III-2-7  axillary lymph nodes and lymph Drainage of breast

Fig.III-2-8  Parietal lymph nodes  of thorax

 

Lymph Nodes and Lymph Drainage of Thorax

Lymph nodes of the thorax are divided into two groups named parietal lymph nodes and visceral lymph nodes

1. Parietal lymph nodesThe superficial lymphatic vessels of thoracic wall empty mainly into axillary lymph nodes. However, the deep lymphatic vessels of it drain into the parietal lymph nodeswhich include parasternal lymph nodes, intercostal lymph nodes, and superior phrenic lymph nodes(Fig.III-2-8).

(1)Parasternal lymph nodes They locate along internal thoracic artery and veinreceive lymph from anterior wall of thorax and abdomen above umbilicus, medial part of mammary gland, superior surface of diaphragm and liver. The efferent lymphatic vessels of these lymph nodes empty into bronchomediastinal trunk or empty directly into thoracic duct and right lymphatic duct.

(2) Intercostal lymph nodes they locate in the posterior part of the intercostal spacesreceive lymph from deeper layer of the posterior aspect of the chest and parietal pleura. Their efferent lymphatic vessels empty into thoracic duct.

(3) Superior phrenic lymph nodesThey locate on the superior surface of diaphragm and can be divided into three group named as anterior, middle and posteriorand receive lymph from diaphragm, pericardium心包, pleura and superior surface of liver. Their efferent lymphatic vessels empty into parasternal lymph nodes and anterior mediastinal lymph nodes.

2. Visceral lymph nodes  Visceral lymph nodescan be divided into three groups as anterior mediastinal lymph nodes, posterior mediastinal lymph nodes and lymph nodes of the trachea, bronchi and lungs(Fig.III-2-9;312)

      Fig. Superior phrenic lymph nodes

(1)Anterior mediastinal lymph nodes  They locate in the front of pericardium and the blood vessels arise from aortic arch, receive lymph from thymus, heart, pericardium, diaphragm, and superior surface of liver. Their efferent lymphatic vessels empty into right and left bronchomediastinal trunks.

(2)Posterior mediastinal lymph nodes  They lie around oesophagus and thoracic aorta, and receive lymph from oesophagus and tissues around thoracic aorta. Efferent lymphatic vessels empty into thoracic duct.

(3)Lymph nodes of the trachea, bronchi and lungs (Fig.III-2-10;313)

Pulmonary lymph nodes locate in lung substance and receive lymph from lung. Their efferent lymphatic vessels empty into bronchopulmonary lymph nodes, which locate in the hilus of each lung and receive lymph from lung. Their efferent lymphatic vessels empty into trachobronchial lymph nodes. The trachobrochial lymph nodes can be divided into superior and inferior two groups and locate near the bifurcation of trachea. Their efferent lymph nodes empty into paratracheal lymph nodes and then empty into right and left bronchomediastinal trunks and finally drain to thoracic duct and right lymphatic duct.

 

       

 

Lymph Nodes and Lymph Drainage of Abdomen

Lymph nodes of abdomen are divided into parietal lymph nodes and visceral lymph nodes.

1. Parietal lymph nodesThe superficial lymphatic vessels of the anterior wall of abdomen above and below umbilicus empties into the axillary lymph nodes and the superficial inguinal lymph nodes, and the deep lymphatic vessels drain upwards to the parasternal lymph nodes and downwards to the deep inguinal lymph nodes respectively. The lymph from posterior wall of abdomen is emptied into lumbar lymph nodes. Lumbar lymph nodes locate around inferior vena cava and abdominal aorta, and receive lymph from posterior wall of abdomen and the abdominal paired viscera.

2. Visceral lymph nodes Lymphatic vessels of paired abdominal viscera drain into lumbar lymph nodes, these of unpaired viscera drain into celiac lymph nodes, superior mesenteric lymph nodes, and inferior mesenteric lymph nodes.

                  Gig. celiac lymph nodes

 

    

  Visceral lymph nodes and Lymphatic vessels  

(1)Celiac lymph nodes locate near the origin of celiac trunk(Fig.III-2-11), receive lymph from stomach, liver, duodenum, gallbladder, pancreas and spleen, their efferent lymphatic vessels empty into intestinal trunk. This group of lymph nodes including right and left gastric lymph nodes, right and left gastroepiploic lymph nodes pyloric lymph nodes, hepatic lymph nodes, and pancreaticosplenic lymph nodes. These lymph nodes locate along arteries with same name and receive lymph of similar area supplied by the arteries with the same name.

(2)Superior mesenteric lymph nodes locate around the origin of superior mesenteric artery (Fig.III-2-12),and receive lymph from lymph nodes of mesentery, ileocolic, right colic and middle colic lymph nodes. These lymph nodes locate along the corresponding vessels.

(3)Inferior mesenteric lymph nodes Locate around the origin of inferior mesenteric arteryand receive lymph from left colic, sigmoid colic, and superior rectal lymph nodes.

                     Fig. The superior and inferior mensteric lymph nodes

 

The Efferent lymphatic vessels of celiac lymph nodes, superior mesenteric lymph nodes, and inferior mesenteric lymph nodes unite into intestinal trunk, and then empty into cisterna chyli.

3.  Lymph Nodes and Lymph Drainage of Pelvis (Fig.III-2-13,14;)

Lymph nodes of pelvis are composed of the internal iliac lymph nodes, sacral lymph nodes, external iliac lymph nodes, and common iliac lymph nodes.

(1). Internal iliac lymph nodes locate along internal iliac arteryand receive lymph from wall of pelvis, pelvis organs, gluteal region, perineum, and posterior part of thigh. Their efferent lymphatic vessels empty into common iliac lymph nodes.

(2). Sacral lymph nodes locate along middle sacral arteryand lateral sacral arterythey receive lymph from posterior wall of pelvis, rectum, prostate or uterus. Their efferent lymph nodes of these lymph nodes empty into internal iliac lymph nodes or common iliac lymph nodes.

(3). External iliac lymph nodes locate along external iliac arteryand receive efferent lymphatic vessels of the inguinal lymph nodes and the lymph of anterior wall of abdomen, bladder, prostate or cervix. Their efferent lymphatic vessels empty into common iliac lymph nodes.

(4). Common iliac lymph nodes locate along the common iliac blood vessels and receive the efferent lymphatic vessels of above three groups. They also receive lymph from lower limb, the wall of pelvis, pelvis organs, and inferior part of abdomen. Their efferent lymphatic vessels empty into right and left lumbar lymph nodes.

 

  Fig.lymphatic vessels and lymph nodes of the pelvis(female)

Lymph Nodes and lymph Drainage of Lower Limb

Lymphatic system of lower limb is composed of superficial lymphatic vessels, deep lymphatic vessels and lymph nodes. Superficial lymphatic vessels receive lymph from skin and subcutaneous fascia; deep lymphatic vessels receive lymph nodes from muscles, tendons, bones, and joints. These lymphatic vessels empty into regional lymph nodes. Finally, these lymphatic vessels empty into inguinal lymph nodes. There are communicating branches between these two kinds of lymphatic vessels.

1. Popliteal lymph nodeslocate in popliteal fossaand receive lymph from lateral border of foot, and posterior part of leg. The efferent lymphatic vessels of these lymph nodes empty into deep inguinal lymph nodes.

2. Inguinal lymph nodes locate below the inguinal ligament and can be divided into two groups.

 

 

(1)Superficial inguinal lymph nodes(Fig.III-2-14)

  are composed of 8 to 10 lymph nodes and can be divided into the upper and lower groups. The upper group locate below inguinal ligament and the lower group locate around the terminal part of great saphenous vein. These lymph nodes receive lymph from the lower part of abdominal wall, external genitalia, gluteal region, perineum and lower limb with the exception of region drained by popliteal lymph nodes.

(2) Deep inguinal lymph nodes locate around the femoral vein(Fig.III-2-15) and are composed of 2 to 5 lymph nodes. They receive lymph from deep lymphatic vessels of lower limb and the efferent lymphatic vessels of superficial inguinal and popliteal lymph nodes. Their efferent lymphatic vessels empty into external iliac lymph nodes.

 

 

 

 

           Fig.III-2-15 The deep inguinal lymph nodes

Section 4  Lymph drainage of some organs

Lymph drainage of some important organs must be known in order to diagnosis and treat correctly.

. Lymph drainage of esophagus

Lymph drainage of esophaguscan be divided into three parts: lymph from cervical esophagus flow into deep cervical nodes; lymph from thoracic esophagus flow into tracheobronchial lymph nodes or posterior mediastinal lymph nodes; most of the lymph from abdominal esophagus flow into left gastric lymph nodes. Sometimes, lymph from esophagus can flow into thoracic duct directly.

. Lymph drainage of breast(Fig.Ⅲ-27)

Lymphatic drainage of breast can be divided into four parts, among which more than 75% of the lymph flow into axillary lymph nodes. Lymph fluids from the lateral part of breast empty into pectoral group of axillary lymph nodes, this is the main way of breast lymph drainage. Lymph fluids from the upper part of breast empty into apical group of axillary lymph nodes. Lymph from the medial part empty into parasternal lymph nodes. Lymph fluids from infra-medial part empty into superior phrenic lymph nodes

 

. Lymph drainage of heart

Lymphatic drainage of heart can be divided into two parts. There are 1-2 left lymphatic trunks of heart receiving lymph from the left ventricles and atrium, and usually empty into inferior tracheobronchial lymph nodes. 1-3 right lymph trunks of heart receiving lymph from right atrium and ventricle and usually empty into lymph nodes of aortic arch.

 

. Lymph drainage of stomach(Fig.Ⅲ-211)

Lymphatic drainage of stomach has four directions. Lymphatic vessels from lesser curvature, right side of gastric fundus and cardiac part empty into left gastric lymph nodesLymph Nodes and cardiac lymph nodes. Lymphatic vessels from most part of gastric fundus and left part of greater curvature empty into left gastroomental lymph nodes and pancreaticosplenic lymph nodes. Lymphatic vessels from pyloric part and right part of greater curvature empty into right gastroomental lymph nodesand infrapyloric lymph nodes. Lymphatic vessels from lesser curvature side of pyloric part empty into suprapyloric lymph nodes.

All the efferent lymphatic vessels of above lymph nodes empty into celiac lymph nodes.

 

. Lymph drainage of liver

Lymphatic drainage of liver can be divided into superficial and deep system. Superficial hepatic vessels drain lymph in four directions. Lymph of superficial hepatic vessels can empty into lymph nodes around inferior vena cava, hepatic lymph nodesand celiac lymph nodes. Deep hepatic lymphatic vessels from two trunks named as ascending and descending trunks. Ascending trunk empty into lymph nodes around inferior vena cava, superior phrenic lymph nodes, mediastinal lymph nodes, while descending trunk empty into hepatic lymph nodes, gastropancreatic lymph nodes, and their efferent lymphatic vessels empty into celiac lymph nodesFig.III217.

 

Fig.III217  Lymphatic drainage of liver

. Lymph drainage of uterus

Lymphatic drainage of uterusis widespread along with blood and ligament. Lymph  from fundus of uterusand upper part of uterine body empty into lumbar lymph nodes along suspersory ligament of ovary. Some of the lymph fluids from upper part of uterine body empty into superficial inguinal lymph nodes along round ligament of uterus. Most of the lymph from inferior part of uterus body and neck of uterus empty into internal iliac lymph nodes and external iliac lymph nodes, a few of them empty into sacral lymph nodes(Fig.III216).

 

. Lymph drainage of rectum

Lymphatic drainage of rectum can be divided into two parts by dentate line. Most of the lymphatic vessels above dentate line empty into superior rectal lymph nodes, while a few of the lymphatic vessels empty into internal iliac lymph nodes. Lymphatic vessels of rectum under dentate line empty into superficial inguinal lymph nodes

 

                Fig.III216.Lymph drainage of rectum

.

 Section 5  Spleen and thymus

. Spleen

As a key lymphatic organ, spleen is also the largest lymphatic organ. In addition to take part in immune reaction, spleen carries on several functions, which are unique to the spleen: forms erythrocytesin the embryo, filters the blood, and serves as a blood reservoir.

Spleen lies in the left hypochondriac regionbetween the fundus of stomachand diaphragm, situated in the deep surface of the left ninth to eleventh rib. Its long axisis coincidence with the tenth rib, so spleen cannot be touched in normal people under the left costal arch. Its location will change with breath, posture and filling degree of stomach. The spleen is purplish in color and is fragile . It is the most frequently damaged organ in cases of abdominal trauma( Fig.III-2-19).

Spleen is described as having two ends, anterior and posterior; two borders, superior and inferior; and two surfaces, diaphragmatic and visceral. There are two or three splenic notcheson the superior border of the spleen and can be used as the marker of palpation. The diaphragmatic surface is smooth and convex and conforms to the concave surface of diaphragm to which it is adjacent. The visceral surface is concave and adjacent to the fundus of stomach, left kidney and left flexure of colon. There is a long fissure near the center of the visceral surface, which is called the hilum of spleen, through which the blood vessels and nerves pass into the spleen.

Spleen is surrounded by a capsule of visceral peritoneum and is fixed by ligament structured by peritoneum. About 10 percent to 40 percent of the population has accessory spleenwith vary size and number.

 

                   Fig.III-2-19   The Spleen

 

. Thymus

As a lymphatic organ, thymus also has the function of endocrine. It locate between manubrium of sternumand superior mediastinum, near the brachiocephalic vein and arch of aorta. Thymus has the shape of cone, and can be divided into two lobes as right and left. Its substance is soft and these two lobes are connected by connective tissue(Fig.III-2-20).

The size of thymus varies with age. Prominent in newborns, then it continues to increase in size until puberty, after which its growth stops and starts to atrophy Thymus of adult keeps its shape but has been almost replaced entirely by fibrous and fatty tissue.

 

              Fig.III-2-20   The thymus

 

 

Liu Zhiyu  Shandong University School of Medicine