Lymphatic system
BLANK returns fluids leaked from blood vessels back to blood; consists of three parts
Parts of Lymphatic System
1. Network of lymphatic vessels (lymphatics)
2. Lymph: fluid in vessels
3. Lymph nodes: cleanse lymph
Lymphatics
Network of lymphatic vessels
elaborate network of drainage vessels
-Circulates ~ 3L interstitial fluid per day
-Once interstitial fluid enters lymphatics, it is called lymph
Lymph
Fluid in vessels
Lymph nodes
Cleanse lymph
Lymphoid organs and tissues
provide structural basis of immune system by housing phagocytic cells and lymphocytes
Lymphoid organs and tissues
spleen, thymus, tonsils, lymph nodes, other lymphoid tissues
Lymphatic system
returns interstitial fluid and leaked plasma proteins back to blood via lymphatic vessels
Lymphatic Vessels
�BLANK offer a one-way system, ensuring lymph flows only toward heart
�Lymph vessels (lymphatics) include:
-Lymphatic capillaries
-Larger lymphatic vessels
Lymphatic capillaries
-Blind-ended vessels that weave between tissue cells and blood capillaries
-----Absent from bones, teeth, bone marrow, and CNS (CNS uses CSF for drainage)
-Similar to blood capillaries, but more permeable
-Can take up larger molecules and particles that b
permeability
Lymphatic Capillaries: Increased BLANK due to two specialized structures
1. Endothelial cells
2. Minivalves
-----Decreases in ECF cause minivalves to close
Endothelial cells
overlap loosely to form one-way minivalves
Minivalves
are anchored by collagen filaments to matrix, so increases in ECF volume opens minivalves even more
Lacteals
Specialized lymph capillaries present in intestinal mucosa
-----Absorb digested fat and deliver fatty lymph (chyle) to the blood
Larger lymphatic vessels
-Lymph capillaries drain into increasingly larger vessels called collecting lymphatic vessels
-Consist of collecting vessels, trunks, and ducts
-Have structures and tunics similar to veins, except:
-----Have thinner walls, with more internal valves
-----A
Lymphatic trunks
which are formed by union of largest collecting vessels, drain large areas of body
Lymphatic trunks
Named for regions of body they drain
-Paired lumbar
-Paired bronchomediastinal
-Paired subclavian
-Paired jugular trunks
-Single intestinal trunk
lymphatic ducts
Lymph is delivered from trunks into one of two large BLANK
�Each empties lymph into venous circulation at junction of internal jugular and subclavian veins on its own side of body
Right lymphatic duct
drains right upper arm and right side of head and thorax
Thoracic duct
Drains rest of body
-----In about half of individuals, starts out as an enlarged sac, cisterna chyli
Lymph Transport
�The lymphatic system lacks a pumping organ
�Uses the same methods as veins to propel lymph
Methods to propel lymph
-Milking action of skeletal muscle
-Pressure changes in thorax during breathing
-Valves to prevent backflow
-Pulsations of nearby arteries
-Contractions of smooth muscle in walls of lymphatics
Physical activity
BLANK increases flow of lymph; immobilization of area keeps needed inflammatory material in area for faster healing
Lymphoid Cells
BLANK consist of
(1) immune system cells found in lymphoid tissue and
(2) supporting cells that form lymphoid tissue structures
Immune system cells
Lymphocytes
T cells and B cells
Macrophages
Dendritic cells
Reticular cells
Lymphocytes
cells of the adaptive immune system; mature into one of two main types
-T cells (T lymphocytes)
-B cells (B lymphocytes)
T cells and B cells
Protect against antigens (anything the body perceives as foreign)
-Examples: bacteria, toxins, viruses, mismatched RBCs, cancer cells
T cells
manage immune response, and some also attack and destroy infected cells
B cells
produce plasma cells, which secrete antibodies
-Antibodies mark antigens for destruction by phagocytosis or other means
Macrophages
phagocytize foreign substances; help activate T cells
Dendritic cells
capture antigens and deliver them to lymph nodes; activate T cells
Reticular cells
produce reticular fiber stroma that supports other cells in lymphoid organs
Lymphoid Tissue Function
-Houses and provides proliferation sites for lymphocytes
-Offers surveillance vantage points for lymphocytes and macrophages as they filter through lymph
Lymphoid Tissue Composition
Largely reticular connective tissue, a type of loose connective tissue
-Macrophages live on reticular fibers
-Spaces between fibers offer a place for lymphocytes to occupy when they return from patrolling body
Two types of lymphoid tissues
Diffuse lymphoid tissue
Lymphoid follicles (nodules)
Diffuse lymphoid tissue
Loose arrangement of lymphoid cells and some reticular fibers
-----Found in virtually every body organ
-----Larger collections in lamina propria of mucous membranes
Lymphoid follicles (nodules)
solid, spherical bodies consisting of tightly packed lymphoid cells and reticular fibers
-----Contain germinal centers of proliferating B cells
-----May form part of larger lymphoid organs (nodes)
-----Isolated aggregations of Peyer's patches and in appen
Two categories of Lymphoid Organs
Primary lymphoid organs
Secondary lymphoid organs
Primary lymphoid organs
Areas where T and B cells mature�red bone marrow and thymus
-----T and B cells originate in bone marrow, but only B cells matures there; T cells mature in thymus
Secondary lymphoid organs
Areas where mature lymphocytes first encounter their antigen and become activated
-----Nodes, spleen, MALT (mucosa-associated lymphoid tissue) and diffuse lymphoid tissues
Lymph nodes
Principal secondary lymphoid organs of body
Hundreds of nodes are found throughout body
-----Most are embedded deep in connective tissue in clusters along lymphatic vessels
-----Some are nearer to body surface in inguinal, axillary, and cervical regions o
Two main functions of lymph nodes
1. Cleansing the lymph: act as lymph "filters"
2. Immune system activation
Cleansing the Lymph
Act as lymph "filters"
�Macrophages remove and destroy microorganisms and debris that enter lymph
------Prevent unwanted substances from being delivered to blood
Immune System Activation
offer a place for lymphocytes to become activated and mount an attack against antigens
Structure of a Lymph Node
�Vary in shape and size, but most are bean shaped
-----Small, less than 2.5 cm (~1 inch)
�Surrounded by external fibrous capsule
�Capsule fibers extend inward as trabeculae that divide node into compartments
histologically distinct regions of node
1. Cortex
2. Medulla
Cortex
-Superficial area of cortex contains follicles with germinal centers that are heavy with dividing B cells
-Deep cortex houses T cells in transit
-----T cells circulate continuously among blood, lymph nodes, and lymph
-Abundant numbers of dendritic cells a
Medulla
-Medullary cords extend inward from cortex and contain B cells, T cells, and plasma cells
Lymph sinuses
BLANK are found throughout node
-Consist of large lymphatic capillaries spanned by criss crossing reticular fibers
-Macrophages reside on fibers, checking for and phagocytizing any foreign matter
Circulation in the Lymph Nodes
�Lymph enters convex side of node via afferent lymphatic vessels
�Travels through large subcapsular sinus and then into smaller sinuses found throughout cortex and medulla
�Lymph then enters medullary sinuses
�Finally exits concave side at hilum via effer
Spleen
BLANK is blood-rich organ about the size of a fist, located in left side of the abdominal cavity, just below the stomach
�Largest lymphoid organ
�Served by splenic artery and vein, which enter and exit at the hilum
Functions of the Spleen
-Site of lymphocyte proliferation and immune surveillance and response
-Cleanses blood of aged blood cells and platelets; macrophages remove debris
functions of spleen
1.Stores breakdown products of RBCs (e.g., iron) for later reuse
2.Stores blood platelets and monocytes for release into blood when needed
3.May be site of fetal erythrocyte production
Spleen
BLANK is encased by fibrous capsule and also has trabeculae
Two components of the spleen
-White pulp
-Red pulp
White pulp
Site where immune function occurs
�Contains mostly lymphocytes on reticular fibers
�White pulp clusters are found around central arteries; appear as islands of white in a sea of red pulp
Red Pulp
Site where old blood cells and bloodborne pathogens are destroyed
�Rich in RBCs and macrophages that engulf them
�Composed of splenic cords (reticular tissue) that separate blood-filled splenic sinusoids (venous sinuses)
Mucosa-associated lymphoid tissue
MALT
MALT
-Lymphoid tissues in mucous membranes throughout body
�Protects from pathogens trying to enter body
�Found in mucosa of respiratory tract, genitourinary organs, and digestive tract;largest collections of MALT found in
-----Tonsils
-----Peyer's patches
---
Tonsils
Simplest lymphoid organs
�Form ring of lymphatic tissue around pharynx; appear as swellings of mucosa
�Named according to location
Palatine tonsils
at posterior end of oral cavity
�Largest of tonsils and most often infected
Lingual tonsil
lumpy collection of follicles at base of tongue
Pharyngeal tonsil
also called adenoids; located in posterior wall of nasopharynx
Tubal tonsils
surround openings of auditory tubes into pharynx
Tonsils function
BLANK is to gather and remove pathogens in food or air
Tonsils
�Contain follicles with germinal centers and scattered lymphocytes
�Are not fully encapsulated
�Overlying epithelium invaginates, forming tonsillar crypts
-Bacteria or particulate matter enters crypts, where they are trapped and destroyed
�Risky to lure b
Peyer's patches
Clusters of lymphoid follicles in wall of distal portion of small intestine
-Also called aggregated lymphoid nodules
Peyer's patches
Structurally similar to tonsils
Location
BLANK aids in functions of Peyer's patches
1.Destroy bacteria, preventing them from breaching intestinal wall
2.Generate "memory" lymphocytes
Appendix
offshoot of first part of large intestine
Appendix
Contains a large number of lymphoid follicles
functions
Location aids in BLANK of Appendix
1.Destroy bacteria, preventing them from breaching intestinal wall
2.Generate "memory" lymphocytes
Thymus
bilobed lymphoid organ found in inferior neck
-----Extends into mediastinum and partially overlies heart
Functions as lymphoid organ where T cells mature
-Most active and largest in size during childhood
-Stops growing during adolescence, then gradually atrophies
-Still produces immunocompetent cells, though more slowly
Thymus
BLANK differs from other lymphoid organs in important ways
1.Has no follicles because it lacks B cells
2.Does not directly fight antigens
-----Functions strictly in T lymphocyte maturation
----------Contains blood thymus barrier:
3.Stroma is made up of ep
blood thymus barrier
keeps immature T lymphocytes isolated from any antigens to prevent premature activation
Developmental Aspects of the Lymphatic System
-Beginnings of lymphatic vessels and main clusters of lymph nodes seen by week 5 of embryonic development
-Except for spleen and tonsils, lymphoid organs are poorly developed at birth
-After birth, high numbers of lymphocytes appear; their development par
True
Interstitial fluid and lymph are identical except for their respective locations in the body.
False
True
Lymphatic collecting vessels
What part of the lymphatic system is most closely associated with capillary beds?
Lymphatic trunks
Lymph nodes
Lymph ducts
Lymphatic collecting vessels
Lymphatic collecting vessels
BLANK are most closely associated with capillary beds. The BLANK filter lymph through the lymph nodes. Vessels that bring lymph to the nodes are called afferent vessels, and vessels that carry lymph away from the nodes are called efferent vessels. From th
D
How are lymphatic collecting vessels different from veins?
A. Lymphatic collecting vessels have thicker walls than do veins.
B. Lymphatic collecting vessels do not form branches; veins do form branches.
C. Lymphatic collecting vessels have fewer tunics th
veins
Like BLANK, lymphatic collecting vessels have three tunics and they are able to form branches (anastomoses). However, the lymphatic vessels anastomose more than BLANK. BLANK and lymphatic collecting vessels both have valves, but lymphatic vessels have mor
pulmonary trunk
All lymph is eventually returned to circulation via the:
vena cava.
pulmonary trunk.
subclavian veins.
aorta.
subclavian veins
From the lymph nodes, lymph travels to lymphatic trunks and then to lymph ducts. From the terminal lymphatic ducts, lymph rejoins the venous blood supply via the BLANK.
Delivery of nutrients to tissues
Which of the following is not a function of lymphatic vessels?
Transportation of absorbed fat from the intestines to the blood
The return of tissue fluid to the bloodstream
The return of leaked proteins to the blood
Delivery of nutrients to tissues
blood vessels
Lymphatic vessels have a role in carrying tissue fluid, leaked proteins, and absorbed fats to the blood. They do not deliver nutrients or gases to the tissues; that is the role of BLANK.
False
Reticular connective tissue is found in all lymphoid organs and tissues.
False
True
Lymph nodes produce lymph
Which of the following is not a characteristic of lymph nodes?
Lymph nodes activate the immune system.
Lymph nodes have a capsule.
Lymph nodes filter lymph.
Lymph nodes produce lymph.
lymph
BLANK are rich with macrophages, B cells, and T cells, and are strategically located for activating the immune system. Structurally, BLANK nodes have a capsule, medullary cords, and sinuses that serve to filter BLANK fluid. BLANK is not produced by lymph
C
Which of the following is not a role of the spleen?
A. Store platelets
B. Break down erythrocytes
C. Serve as a site of T cell maturation
D. Serve as an immune system surveillance organ
spleen
The BLANK serves as an immune system surveillance organ; it also stores platelets and breaks down erythrocytes. There are plenty of T cells in the white pulp of the BLANK, but the T cells do not mature there; the exclusive role of the thymus is to foster
A
Choose the true statement about the thymus.
A. After puberty, the thymus begins to decrease in size.
B. The thymus contains reticular fibers.
C. The thymus directly fights foreign antigens.
D. B cells and T cells mature in the thymus.
thymus
The BLANK is prominent in newborns, and continues to increase in size until the child is about a year old. After puberty, the BLANK begins to diminish in size. Unlike other lymphoid tissues or organs, the BLANK does not directly combat foreign antigens. I
B
The main role of the tonsils is to:
A. help B cells mature.
B. gather and remove pathogens entering through the pharynx.
C. help T cells mature.
D. filter lymph.
tonsils
The main role of the BLANK is to gather and remove pathogens entering through the pharynx.
The spleen
Which of the following is not a part of the mucosa-associated lymphatic tissue (MALT)?
The spleen
The appendix
Peyer's patches
The tonsils
appendix
The mucosa-associated lymphatic tissue (MALT) includes the Peyer's patches, tonsils, BLANK, and the lymphoid follicles of the respiratory and genitourinary tracts. The spleen is not a MALT tissue.