- Found only in closed lymphatic vessels - Transparent, slightly yellow, watery flood, resembles blood plasma but more dilute
Function of the Lymph System
1. Drain interstitial fluid (15% total volume capillary fluid) (also collected: cell debris, bacteria, dead cells, lymphocytes) 2. Transport lipid and lipid soluble vitamins from GI tract to vascular system 3. Filtration & immunological defense
Lymphoid tissue is a ____ ________ ____________
- Specialized connective tissue - Characterized by large # lymphocytes (T & B cells) w/ additional cells (APC)
Different types of Lymphoid Tissue
- Diffuse (exist freely, not encapsulated) -> MALT, GALT, BALT - Dense (encapsulated) -> Lymphoid organ (nodes, tonsils, thymus, spleen)
- Structural unit lymphoid tissue - Made of clusters of lymphocytes
Diffuse Lymphoid Tissue
- Occur throughout body, under WET EPITHELIAL MEMBRANES where loose CT is INFILTRATED by LYMPHOID CELLS - Lymphoid cells scattered randomly to make lymphoid nodules - Transient structures
Examples of Lymph Nodes
- Parotid Lymph Nodes - Jugular Lymph Nodes - Pre-aortic Lymph nodes - Axillary lymph nodes - Para vertebral and para sternal lymph nodes - Name based on location
What are the shape of lymph nodes?
Characteristics of Lymph
- Convex surface which receives afferent lymph vessels (several openings) - Have hilum where blood vessels enter and efferent lymph vessels leave - DENSE IRREGULAR CONNECTIVE tiSSUE CAPSULE - Connective tissue septa (derived from capsule), subdivide cortex into incomplete compartments - Cortex has lymphatic nodules (primary/inactive, secondary/active) - Paracortex zones: separates cortical area from medulla, mostly T Cells and MACROPHAGES
Picture Lymph Nodes. Can you spot the capsule, afferent vessels, medulla, cortex, paracortex, and efferent lymphatic?
- Afferent lymph vessels: several afferent openings - Septum: extensions of capsule - Cortex is deep to the capsule, mostly B cells
Lymph Node Light Microscope Image
Can you spot the germinal centre?
Lymphatic Nodules are made of mostly what
- B cells accompanied by macrophages
Lymphatic Nodule Activation
- Spherical dense aggregations of mostly B cells accompanied by macrophages - Activated when introduced to antigen - B lymphocytes PROLIFERATE in LYMPHOID NODULES -> Germinal centre (look more pink)
Difference between primary and secondary lymph nodule
Primary -> Inactive B cells, mature, not exposed to antigens, purple Secondary -> Active B cells, immature, exposed to antigens, pink
T, B, and plasma cells in medullary region
- Areas between medullary cords - Part of the rich network of interconnected lymphatic sinuses
Lymph Circulation in Lymph Node
Afferent lymphatic vessel -> subcapsular sinus -> trabecular sinus -> medullary sinus -> efferent lymphatic vessels - T & B cells added to the lymph - Lymph is filtrated (damaged/old lymphocytes and antigens or other debris destroyed)
Lymph circulation image
- Need to know: Afferent lymph vessel, capsule, subcapsular sinus, medullary sinus, efferent lymphatic vessel, capillary bed, trabecular sinus, trabecula,
Maturation t cells in Lymph Node
- APCs activated via cytokines (contact w/ organisms) - Activated APCs from mucosal membranes to lymph nodes - Immature T cells made in bone marrow -> brought by blood vessels - T cells scan peptides carried by APCs -> recognition -> activation/maturation/proliferation - If no recognition, return to lymph flow by efferent lymph vessel
- Encapsulated lymph tissue (organ) situated @ PHARYNX - Made of -> pharyngeal, palatine, lingual
- Produce ANTIBODIES against antigens in vicinity - Has CRYPTS (10-20 invaginations) -> have desquamated epithelial cells (dead cells)
Can you see the Crypts, lymphoid nodules, and the capsule?
- Crypts: Collects samples of content of oral cavity - B cells detect for antigens from lymph nodules, produce antibodies if necessary
Endoderm - Located below thyroid gland, above the heart
- Composed 2 soft pinkish gray lobes - Surrounded by DENSE IRREGULAR CT - Give rise to interlobular trabeculae -> divide gland into incomplete lobules - Thymus usually gets replaced by loose CT and fat ~ 13-15
Each lobule in the thymus is composed of 2 portions
Cortex and Medulla
- No lymphatic nodule or plasmic cells - Composed of EPITHELIAL RETICULAR CELLS, macrophages (positive selection)
How many different types of epithelial reticular cells are there?
6. 3 in cortex, 3 in medulla
I: Surround blood vessels, separate immature T lymphocytes from antigens (no access) II: Framework. Prevent clusters of T lymphocytes to pass information III: Separate coffee from medulla on the cortex side IV: Separate cortex from medulla on the medulla side V: Act as macrophages to digest undeveloped T cells (positive selection) VI: Dying cells, dead (form thymic (Hassall's) corpsucles)) - All ERC make different hormones (Thymosin) -> facilitate transformation of Thymocytes to T cells
Main function thymus
- Expose immature T cells to the antigens
2 Phased Elimination of Thymus
- Positive -> in cortex -> caused by macrophages (those that produce proteins that are abnormal) - Negative -> in medulla -> caused by ERC V -> to kill autoreactive T cells - About 98% will be killed by macrophages
- Contain plasma cells, lymphocytes, macrophages, reticuluar cells (in negative selection) - No LYMPHATIC SINUSOID in thymus
- Not 100% complete - Some auto reactive T cells escape -> releasted into circulation - Additional mechanisms present (regulatory T cells) - If these fail, autoimmune diseases my arise
What is the largest lymphoid organ? Where does it arise from?
What are the major lymphatic vessels connected to the spleen?
There are none. - A capsule made of CT surrounds the organ & sends trabeculae that travel within parenchyma
The spleen is subdivided into ______ and _______ ________
Red and white pulps
What is white pulp made of?
- Lymphoid tissue organized around arteries (PALS) -> housed as T cells - Lymphatic nodule housing B cells - 20% of spleen
- White pulp (20% spleen) -> clusters lymphocytes (dense basophilic aggregates) -> site of immune surveillance & production T & B cells, antibodies - Red pulp -> filter blood and invading micro-organisms
- Between white and red pulp - Contains heavy concentration macrophages - Site where blood brought to spleen is released, and functions initiated
Movement of Blood from PALS to Red Pulp
- Central artery of PALS -> Lymphoid nodule -> Branches into sinusoids -> blood goes into sinusoids and leak out and enter red pulp (open circulation)
How macrophages kill old blood cells
- Macrophages kill old blood cells (RBC live for ~120 days) - Need open blood circulation so macrophages can phagocytose RBC - Abnormal RBCs that are too rigid can't pass through
- Path of blood that leaves open ended capillaries in marginal zone & is heading for sinuses through open ends/slits in walls of those sinuses
Can you find the sinusoid, capsule, lymph nodule, secondary sinusoids, PALS, and the central artery?
- Big spleen that can compress other organs - Results from antigenic stimulation, obstruction blood flow, underlying functional abnormality, infiltration, viral infection - Splenoctamy: Removing the spleen