Lymphatics Anatomy Flashcards
Functions of Lymphatic System
- Returns interstitial fluid to the cardiovascular system
- Screen lymph for microbes and foreign proteins
Composition of Lymph
- Excess interstitial fluid
- Ions in a concentration similar to that of plasma
- Proteins usually in lower concentration than plasma as larger proteins less likely to leave blood vessels
- Cells are mainly lymphocytes but also some macrophages
- Microbes and other particulate matter
- Lipid molecules from digestion via lacteals
Thoracic Duct and Cysterni Chyli
Main channel for returning lymph to body. Is a continuation of cysterni chyli in the abdomen. Thoracic duct crosses left of aorta at 5th thoracic vertebrae and continues across oesophagus. Can be easily ruptured causing leakage.
Cysterni chyli is an expanded bipartite sac which is a collection point within the abdomen for lymph from the lumbar area, hind quaters and viscera. Continuous cranially with thoracic duct.
Lymph Node Structure
Dense outer capsule, cortex, medulla and hilus. Generally pink and reddish brown and embedded in fat. Contain sinuses, supporting CT tissue stroma with many reticular fibres and blood vessels and parenchyma of mainly lymphocytes, macrophages, reticular and plasma cells. Structured to allow filtration. Circulating lymphocytes interact with antigen.
Lymph Flow
Lymph enters via afferent vessels, through subscapular sinus, cortical and trabeculae sinuses, medullary sinuses, efferent lymphatic vessels via hilus where th valves prevent back flow.
Structure of Primary and Secondary Lymph Nodes
Lymph nodes contain cortex, paracortex and medulla (inwards to outwards) with follicles spread in the medulla.
Primary follicles have tightly packed B lymphocytes and stain darly. They have no germinal centre as they are not activated.
Secondary follicles have responded to antigen stimulation and hence have a light staining germinal centre with proliferating B lymphocytes and macrophages surrounded by a corona (marginal zone) which contains non-dividing B cells and helper T cells.
Interfollicular cortical tissue contains T cells.
Lymph Centres of the Head and Neck
Mandibular lymph centre - Occur in intermadibular space or angle of the jaw.
Lateral Retropharyngeal - Drain deep structures and part of the neck. Lymph may drain from here to tracheal trunks or may go to the deep cervical lymph centre.
Superficial cervical - Front of shoulder joint, drains superficial parts of neck and proximal part of forelimb, drains to tracheal trunk.
Axillary - not usually easy to palpate in many species except cats and humans. Drains deep structure of entire limb and superficial parts of distal limb goes mostly to thoracic duct.
Lymph Centrea of Hindlimb, Pelvis and Abdominal Wall
Politeal - in popliteal fossa caudal to stifle. Drains distal part of limb towards deep ingional node.
Superficial Inguinal - Palpable nodes either mammary or scrotal. Drain the male reproductive tract and udder/caudal mammary glands.
Attachments of Spleen
Gastrosplenic ligament attaches visceral surface of spleen to stomach/rumen. All species have gastrosplenic ligament. Usually formed by greater omentum, except in ruminants where it is a reflection of peritoneum.
Phrenicosplenic ligament present in all ruminants, horse and attaches parietal surface of spleen to diaphragm.
Renosplenic ligament attaches dorsal spleen to left kidney. Present only in the horse.
Functions of Spleen
In foetus, produces all types of blood cells, in adult produces lymphocytes, removes effete red blood cells, stores iron from red cells, removes foreign material from blood, produces antibodies, stores blood especially in horse, dog and cat.
Function of Thymus
Most developed in young animals. Major role is the production of T lymphocytes, where T cells undergo negative and positive selection before being let out into blood flow.
Structure of Thymus
Cortex - mainly densly packed lymphocytes on a framework of epithelial cells
Medulla - Fewer lymphocytes and more epithelial cells and have charactersitc Hassall’s corpuscles in medulla
Macrophages present in both cortex and medulla.
