tailieunhanh - Ebook Textbook of human histology (With colour atlas and practical guide - 6th edition): Part 2

(BQ) Part 2 book "Textbook of human histology" presents the following contents: Lymphatics and lymphoid tissue, skin and its appendages, respiratory system, oral cavity and related structures, oesophagus, stomach and intestines, the liver and pancreas, the urinary organs, the male reproductive organs, the female reproductive organs,. | 11 Lymphatics and Lymphoid Tissue Introductory Remarks When circulating blood reaches the capillaries part of its fluid content passes into the surrounding tissues as tissue fluid. Most of this fluid re-enters the capillaries at their venous ends. Some of it is however returned to the circulation through a separate system of lymphatic vessels usually called lymphatics . The fluid passing through the lymphatic vessels is called lymph. The smallest lymphatic or lymph vessels are lymphatic capillaries that join together to form larger lymphatic vessels. The largest lymphatic vessel in the body is the thoracic duct. It drains lymph from the greater part of the body. The thoracic duct ends by joining the left subclavian vein at its junction with the internal jugular vein. On the right side there is the right lymphatic duct that has a similar termination. Scattered along the course of lymphatic vessels there are numerous small bean-shaped structures called lymph nodes that are usually present in groups. Lymph nodes are masses of lymphoid tissue described below. As a rule lymph from any part of the body passes through one or more lymph nodes before entering the blood stream. There are some exceptions to this rule. For example some lymph from the thyroid gland drains directly into the thoracic duct . Lymph nodes act as filters removing bacteria and other particulate matter from lymph. Lymphocytes are added to lymph in these nodes. Each group of lymph nodes has a specific area of drainage. For the location of various groups of lymph nodes and the areas of the body drained by them see a book on gross anatomy. Aggregations of lymphoid tissue are also found at various other sites. Two organs the thymus and the spleen are almost entirely made up of lymphoid tissue. Prominent aggregations of lymphoid tissue are present in close relationship to the lining epithelium of the gut. Such aggregations present in the region of the pharynx constitute the tonsils. Isolated nodules of .