Capsule, trabeculae, and reticular fibers.
Approximately 75%.
The thymus is a bi-lobed organ with a lumpy surface. The outer cortex is densely packed with immature T-cells, and the inner medulla contains mature T-cells along with Hassall’s corpuscles (flattened epithelial cells).
Lymph nodes are supported by trabeculae and a reticular meshwork made of reticular cells and fibers.
Lymph flows from the afferent lymphatic vein to the subcapsular sinus, then to the trabecular sinus, followed by the medullary sinus, and exits through the efferent lymphatic vein at the hilum.
Maturation of B-lymphocytes (B-cells).
Peyer's patches.
Once tissue fluid enters the lymphatic capillaries, it becomes lymph.
The white pulp triggers immune responses, while the red pulp breaks down old, abnormal, and damaged red blood cells and serves as a blood reservoir, releasing blood in emergencies.
Lymph, macrophages, and reticular cells.
Palatine, pharyngeal, lingual, and tubal tonsils.
Maturation of T-lymphocytes (T-cells).
Single lacteal surrounded by capillaries.
To trap bacteria and help migrate pathogens into lymphoid tissue.
It drains into lymphatic capillaries.
The spleen is dark purple due to its high blood content and receives blood supply from the celiac trunk via the splenic artery. The surface near the diaphragm is smooth and convex, while the other side is closely associated with other organs.
The outer cortex consists of the paracortical and superficial layers. The superficial layer contains B-cells and macrophages, while the paracortical layer contains T-cells.
Spleen, lymph nodes, tonsils, and lymphatic nodules.
The pharyngeal tonsil (adenoid) is located on the roof of the pharynx, posterior to the nasal cavity.
To form a ring of lymphoid tissue, collect and remove pathogens entering the body from inhaled air via the nasal cavity and swallowed food via the oral cavity.
Lymph is the interstitial fluid contained inside lymphatic vessels.
The thymus matures T-cells, which are then distributed to other lymphatic organs to trigger immune responses. It is most active during youth and degenerates after puberty, with fat accumulating in the thymus causing it to turn yellow.
Begins at the cisterna chyli and extends vertically between the thoracic aorta and azygos vein to the root of the neck.
Palatine tonsil.
1. Macrophages detect antigens in lymph. 2. Phagocytic cells engulf and digest antigens, transforming into antigen-presenting cells. 3. The phagocytic cells release chemicals to activate helper T-cells, which trigger B-cells to divide into plasma cells and memory B-cells. 4. Plasma cells produce antibodies that bind to the antigen. 5. Chemicals released also activate cytotoxic T-cells, which attack the antigen-presenting cells directly, causing apoptotic cell death.
The tonsils are located in the pharyngeal region at the top of the throat.
Palatine tonsils.
Aggregations of lymphatic nodules in the ileum of the small intestine.
The thymus is located between the sternum and the upper heart.
Drains lymph from the right upper quadrant of the body (right arm, right side of head, and neck).
Drains lymph from the entire left side of the body and the right lower body.
The sinuses in lymph nodes include subcapsular, trabecular, and medullary sinuses, which are protected by macrophages and lymphocytes that clear pathogens.
In the small intestine’s intestinal villus.
To kill harmful bacteria and generate memory lymphocytes by sampling different antigens, contributing to long-term immune response.
Lymphatic capillaries are small, closed-ended vessels made of endothelial cells that form minivalves, which open under pressure from accumulated tissue fluid.
The spleen is located in the upper left abdomen, near the diaphragm.
Recognition of pathogens, phagocytosis, and antigen presentation.
They trap and destroy pathogens entering the pharynx and produce immune cells.
The primary function of lymph nodes is to kill pathogens in lymph.
A lymphatic nodule consists of a germinal center surrounded by a mantle zone.
Tissue fluid is formed when plasma exits capillaries into tissues, containing ions, nutrients, gases, and water.
The spleen contains white pulp (lymphoid tissue) and red pulp (blood-filled sinuses and cords containing macrophages, lymphocytes, and plasma cells).
Approximately 25%.
Small, encapsulated, bean-shaped organs ranging from 1 mm to 2 cm in length, distributed along lymphatic vessels.
Tonsils are lymphatic tissue located in the pharyngeal region.
Red bone marrow and thymus.
Behind the openings of the Eustachian tubes, slightly below the adenoid.
On the lateral walls of the pharynx, behind the mouth and palate.
Lymphatic nodules are small, localized clusters of dense tissue formed by lymphocytes; an example location is the mucosa of the gastrointestinal tract.
On the posterior surface of the tongue.
Clusters of lymphocytes in the connective tissue of easily infected mucous membranes.
Interstitial fluid pressure prevents backflow by pushing the flaps together.
40 cm.
To trap and destroy bacteria and other pathogens.
In mucous membranes in vulnerable areas of the body, such as the digestive tract.
1. Moves to larger lymphatic vessels. 2. Passes through lymph nodes. 3. Eventually drains into lymphatic ducts.
1. Drains lymph from the rest of the body. 2. Empties into the left subclavian vein. 3. Larger and longer than the right lymphatic duct. 4. Begins at the cisterna chyli.
Primary and secondary lymphatic organs.
1. The diaphragmatic surface faces the diaphragm. 2. The visceral surface faces the stomach and kidney.
1. Superficial cortex. 2. Paracortical area.
T lymphocytes.
Lymphoid follicles and crypts.
Absorb and transport lipids and chylomicrons, and empty them into the lymph nodes.
1. A clear fluid that circulates through the lymphatic system. 2. Contains white blood cells, especially lymphocytes.
1. Large lymphatic vessels. 2. Drain lymph into the venous system.
1. Located along lymphatic vessels. 2. Filter lymph and house lymphocytes.
1. Thin walls. 2. Numerous valves to prevent backflow.
1. Most active during childhood. 2. Begins to shrink after puberty. 3. Degenerates into fatty tissue in adults.
One-way valves in the lymphatic capillaries prevent backflow.
1. Drains lymph from the right upper body. 2. Empties into the right subclavian vein. 3. Shorter than the thoracic duct.
1. Filters blood. 2. Removes old and damaged red blood cells. 3. Stores platelets. 4. Recycles iron from hemoglobin.
1. Contraction of surrounding muscles. 2. One-way valves prevent backflow.
Because they play roles in the production and maturation of lymphocytes.
1. Dark purple and oval-shaped. 2. Blood arrives via the splenic artery.
1. Splenic cords in red pulp. 2. Splenic sinusoids in red pulp. 3. Lymphoid follicles in white pulp.
1. B lymphocytes. 2. Germinal centers. 3. Follicular dendritic cells. 4. Macrophages.
1. They have thin walls. 2. Overlapping endothelial cells act as one-way valves. 3. Tissue fluid enters through gaps between cells.
Because they transport chyle, which is rich in fats.
Maturation of T lymphocytes.
1. Found along lymphatic vessels. 2. Filter lymph and initiate immune responses.
1. Outer cortex. 2. Inner medulla. 3. Germinal centers in the cortex.
1. Maintains fluid balance in the body. 2. Absorbs and transports fats from the digestive system. 3. Defends the body against pathogens. 4. Removes waste products from tissues.
1. Right lymphatic duct into the right subclavian vein. 2. Thoracic duct into the left subclavian vein. 3. Near the junction of the internal jugular and subclavian veins. 4. Ensures lymph returns to the bloodstream.
1. Consists of two lobes. 2. Each lobe has an outer cortex and inner medulla. 3. Contains thymic epithelial cells and lymphocytes.
Lymphatic vessels have lower pressure and need more valves to ensure unidirectional flow.
Along the vertebral column.
Enters through afferent lymphatic vessels, passes through the cortex and medulla, and exits through efferent lymphatic vessels.
1. They absorb excess tissue fluid and proteins. 2. Located throughout the body, especially in tissues.
1. Right lymphatic duct. 2. Thoracic duct.
1. Absorb dietary fats. 2. Located in the villi of the small intestine. 3. Transport chyle to the lymphatic system.
1. A primary lymphatic organ. 2. Located in the upper chest, behind the sternum.
1. In the upper left abdomen. 2. Below the diaphragm and behind the stomach.
1. Red pulp: filters blood and removes old red blood cells. 2. White pulp: contains lymphocytes and monitors blood for pathogens.
1. Small, bean-shaped structures. 2. Filter lymph and house lymphocytes.
