6. Histology and Cell Biology of Lymphatics Flashcards
Functions of the Lymphatic System
1. Production and distribution of lymphocytes: – Primary and secondary lymphoid organs
2. Maintenance of normal blood volume and
chemical composition of the interstitial fluid:
– Drainage system: Returns excess interstitial fluid back to the blood, preventing ____, the excess accumulation of
fluid around tissues.
3. Alternative route for the transport of hormones,
nutrients and waste:
– E.g.: In the intestine, lymphatic capillaries (____)
transport absorbed fat from the small intestine to the blood stream.
edema
lacteals
Organization of the Lymphatic System
• Lymphatic Vessels:
– Capillaries (or Terminal Lymphatics)
– Collecting Vessels
• Lymphoid Tissues and Organs (see Foundation Sciences I,
module 3, for a refresher in Immunology):
– Primary Lymphoid Organs - Produce the cell components of
the immune system:
• ____
• ____
– Secondary Lymphoid Organs and Tissues - Where immune
responses occur:
• Lymphoid Organs:
– ____
– ____
• Lymphoid Tissues:
– ____
– ____
– ____
bone marrow
thymus
lymph nodes
spleen
tonsils
gut-associated lymphatic tissue (GALT)
diffuse lymph nodules
The Lymphatic Vessels
• Range from lymphatic capillaries to large-diameter lymphatic ducts.
• Lymphatic endothelium lacks ____:
– “Leaky”: Allows entry of high molecular weight molecules (e.g. albumin).
• In ____, muscular contraction: opening of spaces for uptake of cell debris, pathogens, and cancer cells.
• In the intestine: absorption of ____ and transport to the blood stream.
• Fluid movement – ____ way flow:
– ____ contraction: SMCs in vessel wall contract in response to lymph filling (peristaltic pump effect) and opening/closure of valves.
– ____ contraction: contraction of surrounding muscles and respiratory movements.
• Lymphatics connect peripheral tissue (interstitial volume) with the venous
○ Lymphatic ducts transporting from tissues to return fluid to circulation
○ Venous > low pressure
§ High pressure of arterial would push lymphatic fluid backwards
• Traffic occurs in the capillaries
○ ____ will always occur at this level
○ Formation of ____ (slide 5)
tight junctions inflammation lipoproteins one intrinsic extrinsic
leakage of fluid
edema
Histology of the Lymphatic Capillaries • \_\_\_\_ (sacs), small diameter vessels that collect the lymph in peripheral tissues. • Structure: • Endothelium with little or no \_\_\_\_. • \_\_\_\_ outline. • Anchored to surrounding CT by \_\_\_\_. ---• \_\_\_\_ fibers.
blind-ended basal lamina irregular anchoring filaments elastic
Histology of the Lymphatic Capillaries
• Lymphatic structures end up in a ____
○ Not ____ like circulatory vessels
• Lined by endothelium lacking ____
○ Also lacking a BL
• Whenever capillary bed is present
○ ____ from blood plasma into interstitial space of tissues
§ Osmotic pressure
○ Capillaries reabsorb fluid in interstitial space into the collecting lymphatics and into the thoracic duct
• Anchoring filaments
○ Attach to collagen fibers in regular tissue
○ Prevent ____ of capillaries
§ Very ____ pressure
§ Surrounded by fluid
§ Maintain tubes in an ____ conformation
• Histology
○ Look like “holes” within tissue, surrounded by “nothing”
○ ____ shape - do not have high abundance of muscle and collapse
§ Small veins have a similar morphology in terms of shape
○ Diagnosis doesn’t mean if you don’t see RBC you assume it’s definitely a ____
§ Must look closer at the entire structure
blind-ended sac continuous tight junctions leakage of fluid collpase low open irregular lymphatic
• Diagnostic: Only the lumen of ____ and ____ may contain RBCs.
arterioles
venules
Lymphatic Collecting Vessels • Largest lymph vessel – thoracic duct: \_\_\_\_ mm diameter • Tunica Intima: • Smooth endothelium. • \_\_\_\_ valves to prevent fluid backflow. • Tunica Media: • Very \_\_\_\_. • SM and elastic fibers. • Tunica Adventitia: • \_\_\_\_, inconspicuous. • CT with collagen and elastic fibers. • Attaches lymphatic vessels to other underlying tissues: \_\_\_\_.
• Semilunar valves are similar to those seen in smaller diameter \_\_\_\_ • TI ○ Leaky • TM ○ Essentially \_\_\_\_ in this kind of vessel • TA ○ Produces elastic fibers (anchoring filaments) and collagen to which they attach
4-6 semilunar thin thin anchoring filaments
veins
non-existant
Lymphatic Collecting Vessels: Fluid Movement
- Lymphangion: ____ of the lymphatic system, segment between two ____ valves in a vessel.
- Fluid movement: ↑ lymph pressure due to ____ or ____ contraction → valve opening → lymph moves into next chamber → drop in ____ → valve closing → no backwards flow.
• Mechanism also applies to small veins • Movement of fluid is induced by: ○ Contraction of SM around tissue ○ Contraction of \_\_\_\_ around tissue § Compress lymphatic capillaries, pushing unidirectionally
functional unit semilunar filling SMC pressure
skeletal tissue
Lymphoid Tissues and Organs – Primary Lymphoid Organs - Produce the \_\_\_\_ of the immune system: • \_\_\_\_ • \_\_\_\_ – Secondary Lymphoid Organs and Tissues - Where \_\_\_\_ responses occur: • Lymphoid Organs: – \_\_\_\_ – \_\_\_\_ • Lymphoid Tissues: – \_\_\_\_ – \_\_\_\_ – \_\_\_\_
cell components
bone marrow
thymus
immune lymph nodes spleen tonsils gut-associated lymphatic tissue (GALT) diffuse lymph nodules
Primary Lymphoid Organs: Thymus
• Primary lymphatic tissue, located in the midline of the body, above the ____.
• Maturation of ____ cells.
• Greatest size at ____: decreases in size as
functional cells die and are replaced by
fibrous CT and adipose.
Morphology: – Two lobes divided into \_\_\_\_ lobules. – Surrounded by a CT \_\_\_\_. – CT from capsule continues into \_\_\_\_ (pl. of trabeculum). – Two histological regions: • Cortex • Medulla
• Cortex ○ Outside of tissue ○ Within CT • Medulla ○ Center of tissue • Both regions \_\_\_\_ differently, and are different in \_\_\_\_ composition
heart
T
puberty
incomplete
capsule
intralobular traceula
stain
cellular
Primary Lymphoid Organs: Thymus • Morphology: – \_\_\_\_ cortex with abundant \_\_\_\_ (thymocytes). – Cortex shows NO \_\_\_\_. – Less basophilic medulla, with \_\_\_\_. – Stromal cells of \_\_\_\_ origin. – Highly \_\_\_\_: capillaries.
• Medulla ○ More eosinohpilic § Binds eosin ○ More \_\_\_\_ § Fewer \_\_\_\_ • Stroma/parenchyma is epithelial in origin ○ Most other lymphoid organs are \_\_\_\_ cells § Fibroblasts
basophilic T lymphocytes lymphatic nodules Hassall's corpuscles epithelial vascularized
protein
nuclei
reticular
The Thymic Cortex
• Large number of ____
○ Single T lymphocyte
§ ____ within the tissue
§ >90% of lymphocyte is the ____
• Highly vascularized
○ Lymphocytes immigrate from regular ____
• Cortical epithelial cells
○ Composition of the thymus (epithelial)
○ Lymphocytes aren’t the only cell-type present
• Trabeculae from CT capsule
○ Stain ____
§ Like medulla
○ High abundance of ____
nuclei
“thymocytes”
nuclei
circulatory capillaries
red
ECM
A Diagnostic Thymic Structure: The Medullary Hassall’s Corpuscle
• Made up of \_\_\_\_ cells ○ \_\_\_\_ § The end-stage § Dead • Highly keratinized show the deepest \_\_\_\_ in stain • These cells cannot be shed off like keratinized cells on skin ○ Instead, form a corpuscle § \_\_\_\_ depository • Corpuscle vs BV ○ BV § Full of \_\_\_\_ § Very different structure • Can see them at low magnification • Only present within the \_\_\_\_
epithelial keratinized red waste RBC medulla
Reminder: T-cell Selection in the Thymus
• Positive and Negative selection of T cells to recognize foreign antigens:
– Positive selection allows only those T cells that are able to bind to self-MHC molecules in the thymus to mature. Positive selection results in ____.
–Negative selection removes T cells whose TCR strongly recognize (high affinity) self-MHC + self-antigen. Die by ____ within the thymus. Negative selection results in ____.
• Differentiate between T cells ○ CD4/CD8 antigens • During selection: ○ Double-positive ○ And then selected to individual antigens
MHC restriction
apoptosis
self-tolerance
Cellular Organization of the Thymus • Cortex: – Locus of T-cell selection: Immature T cells. – Branched cortical epithelial cells. – Macrophages. • Medulla: – Mature T cells. – Medullary epithelial cells. – Macrophages. – Dendritic cells.
• Process of selection takes place in \_\_\_\_ ○ Both for and against § Apoptosis is occurring due to double-negative • Double-negative located in the outer cortex ○ Close to \_\_\_\_ ○ Immature • During selection, becoming double and single-positive ○ Deeper and deeper within \_\_\_\_ • Single-positive will migrate into circulation, into \_\_\_\_
cortex
capsule
cortex
medulla
