Spleen, Thymus and Tonsils Dr Rania Gabr

objectives Discuss the gross features of the spleen Give its blood supply Discuss the gross anatomy of the thymus and tonsils Give their function and blood supply

Position of spleen The spleen lies in the left hypochondrium between the stomach and diaphragm. It has two ends, three borders and two surfaces.

Measurements: -1 inch (thickness) x 3 inches (Breadth) x 5 Inches (length). - Weight: 875 gram (7 ounces). - Surface anatomy: Behind left 9, 10, 11 ribs.

Surface anatomy : It lies parallel to the ribs number 9, 10 , and 11 on the left side. The long axis of the spleen lies parallel to the 10th rib. Its medial end lies 1 1/2 inches from the spine of T. 10, while the lateral end lies just behind the mid- axillary line.

Shape : 3 borders, 2 ends, 2 surfaces. A. Ends 1) lateral end (Broad) 2) medial end (tapering) B. Borders Upper(Anterior) border: Sharp & notched Lower (Posterior)border: (Broad) Intermediate border: thick, incomplete. Extends from the medial end till the hilum).

Surfaces 1- Diaphragmatic surface: Convex, Related to the diaphragm which separates it from 3 structures :------- - Lower part of left pleura, - Base of left lung, - Left 9, 10, 11 ribs.

2- Visceral surface: Concave, irregular, directed to the abdominal cavity. Contains the hilum and impressions for 4 abdominal organs: 1- Gastric impression (related to posterior wall of fundus of stomach). 2- Renal impression. 3- Colic impression (left colic flexure). 4- Pancreatic impression (tail of pancreas).

Peritoneal relations The spleen is completely covered by peritoneum of the greater sac except at the hilum. It is attached and related to the following ligaments: 1- Gastro-splenic ligament 2- Lieno-renal ligament.

Peritoneal connections 1- Gastrosplenic ligament: From the fundus and the greater curvature of stomach to the hilum of spleen. 2- Lienorenal ligament: From the lower border of the hilum of spleen to the anterior surface of kidney.

CONTENTS The gastrosplenic ligament contains: - Short gastric vessels - Left gastroepiploic vessels - Lymph nodes The lieno-renal ligament contains: - Splenic vessels - Tail of pancreas - Lymph nodes

Arterial Supply: Splenic artery (branch of the coeliac trunk). It has a tortuous course at the upper border of the pancreas. It passes with the tail of the pancreas in the lieno-renal ligament. At the hilum it divides into 5 or 6 splenic branches.

Venous drainage: The spleen is drained by the splenic vein that passes on the posterior surface of the pancreas to unite with superior mesenteric vein to form the portal vein posterior to the neck of the pancreas.

Clinical notes: Splenomegaly It is an enlargement of the spleen beyond its normal size. Many disorders, including infections, anemias, can cause an enlarged spleen. Enlarged spleen extends downward and medially (due to the presence of the phrenico-colic ligament that prevents its direct downward descent). The splenic notch(s) may be felt by palpation through the anterior abdominal wall. Injury of the spleen is common due to fracture of the 9, 10, 11 ribs, automobile accidents, during playing contact sports, or due to penetrating wounds of the lower left thorax.

Accessory spleens Accessory spleens are common (10- 15% of people). They are found at the hilum of spleen, the lieno-renal, or the gastro-splenic ligaments. The tail of pancreas is in close relation to the hilum of spleen so it could be injured during splenectomy (surgical removal of the spleen).

Thymus Roughly a bi-lobed structure DEVELOPMENT- bilateral 3rd pharyngeal pouches EVOLUTION- largest at birth or during infancy Increases slightly during 1st decade of life and decreases thereafter.

Thymus Introduction It is a flattened lymphoid organ located in the upper anterior mediastinum & lower part of the neck

Thymus It consists of two lateral lobes placed in close contact along the middle line, situated partly in the thorax, partly in the neck.

Con . . In the thorax, It is covered by the sternum. Below, it rests upon the pericardium, being separated from the aortic arch and great vessels by a layer of fascia In the neck it lies on the front and sides of the trachea.

The two lobes generally differ in size; they are occasionally united, so as to form a single mass; and sometimes separated by an intermediate lobe. The thymus is of a pinkish-gray color, soft, and lobulated on its surfaces. It is about 5 cm. in length, 4 cm. in breadth below, and about 6 mm. in thickness. At birth it weighs about 15 grams, at puberty it weighs about 35 grams; after this it gradually decreases to 25 grams at twenty five years, less than 15 grams at sixty, and about 6 grams at seventy years.

Vasculature Blood Supply A rich arterial supply to the thymus is derived mainly from the: 1.Anterior intercostal & 2.Mediastinal branches of the internal thoracic arteries Veins of the thymus end in the left brachiocephalic, internal thoracic & inferior thyroid veins. The lymphatic vessels of the thymus end in the parasternal, brachiocephalic & tracheobrochial lymphnodes.

The Tonsils Definition: - Ovoid lymphoid tissue with fibrous capsule laterally over the “superior constrictor “muscles. Its surface is covered with stratified squamous epithiluim & crypts. It has a medulla & cortex like all other lymphoid tissues. It is part of the Waldeyer`s ring.

The Tonsils Waldeyer's ring is a continuous band of lymphoid tissue that surrounds the upper pharynx. The superior portion of the ring is located in the nasopharynx and is composed of the adenoids, Laterally the palatine tonsils and, Anteriorly the lingual tonsils to complete the ring. Tonsillar crypts extend deeply into the body of the tonsil and are surrounded by lymphoid nodules. Debris and foreign particles collect within the crypts.

Function: Concerned with immune mechanism. - 1st line of defense. The lymphoid tissues produce lymphocytes. - T-cells produce plasma cells & help in antibody formation. Active phase lasts until 8-10 years of age. This function should not alter the decision to remove the tonsils if a valid indication for tonsillectomy exists.

Blood Supply: Arterial supply: - Tonsilar branch of facial artery from the ext. carotid. - Descending palatine -------- > internal maxillary artery. - Ascending palatine -------- facial artery - Ascending pharyngeal ---- external carotid. - Dorsalis linguae ------- lingual artery

to the tonsil is from the glossopharyngeal nerve. Venous drainage : occurs through the Para tonsillar vein, and the vessels also pass through to the pharyngeal plexus or facial vein after piercing the superior constrictor.  Nerve supply : to the tonsil is from the glossopharyngeal nerve. Tonsillar tumors or infections may result in ear pain due to referred pain conducted by cranial nerve IX: Glossopharyngeal nerve.