Ch. 22: Lymphatic System and Immunity Flashcards
Innate immunity.
Non-specific, defences are present at birth, early warning system, prevent microbes from entering body, eliminate microbes that do enter the body.
First line of defence of innate immunity.
Physical and chemical barriers of skin and mucous membranes. Epidermis has many layers of closely packed keratinized cells, periodic shedding of epidermal cells removes microbes from skin surface, mucous membranes secrete mucous that traps microbes, lacrimal apparatus of eyes produces and drains away tears in response to irritants, washing action of tears dilutes microbes and stops them from settling on eyeball surface, saliva washes microbes from teeth and mouth, cleansing of urethra by flow of urine slows microbial colonization, vaginal secretions expel microbes, vomiting expels microbes, defecation expels microbes, unsaturated FAs in sebum on skin surface inhibit bacteria growth, sweating flushes microbes from skin, gastric juice in stomach destroys bacteria.
Second line of defence of innate immunity.
Antimicrobial substances, NK cells, phagocytes, inflammation, fever.
Adaptive immunity.
Specific recognition of microbes, specific response, adapts or adjusts to handle a specific microbe, lymphocytes.
Lymphatic system is responsible for which immunity?
Adaptive.
Lymphatic system contains…
Lymph, lymphatic vessels, structures and organs containing lymphatic tissue, and red bone marrow.
Lymphatic tissue.
Specialized form of reticular connective tissue that contains large numbers of lymphocytes.
3 functions of lymphatic system.
1) Drains excess interstitial fluid from tissue spaces back into blood
2) Transports dietary lipids from GI
3) Carries out immune responses
Lymphatic capillaries.
Located between cells, closed at one end, unite to form lymphatic vessels, greater permeability and larger diameter than blood capillaries, one-way structure that permits interstitial fluid to flow into them but not out.
Lymphatic vessels.
Resemble small veins, thinner walls, more valves.
Lymph nodes.
Encapsulated bean-shaped organs consisting of masses of B-cells and T-cells. Covered by a capsule of dense connective tissue that extends into the node. Capsular extensions (trabeculae) divide the node into compartments, provide support, and provide a route for blood vessels into the interior of the node. Internal to the capsule is a supporting network of reticular fibres and fibroblasts. Parenchyma of a lymph node is divided into a cortex and medulla, and the cortex consists of an outer cortex and inner cortex.
Where are lymphatic vessels in the skin and in the viscera?
Skin: Lie in subcutaneous tissue and follow the same route as veins.
Viscera: Follow the same route as arteries and form plexuses around them.
Which tissues lack lymphatic capillaries?
Avascular tissues (cartilage, epidermis, cornea), parts of spleen, and red bone marrow.
Describe the epithelial cell wall of lymphatic capillaries.
The cells overlap, and when the pressure is greater in interstitial fluid than in lymph, the cells separate slightly so interstitial fluid enters the lymphatic capillary. When the pressure is greater in the lymphatic capillary, the cells adhere more closely so lymph cannot escape back into interstitial fluid. Pressure is relieved as lymph moves further down the lymphatic capillary.
Anchoring filaments.
Attach to lymphatic capillaries, contain elastic fibres, extend out from the capillary attaching lymphatic endothelial cells to surrounding tissues. When excess interstitial fluid accumulate and cause tissue swelling, the anchoring filaments are pulled, making the openings between cells even larger so that more fluid can flow into the lymphatic capillary.
Lacteals.
Specialized lymphatic capillaries, carry dietary lipids into lymphatic vessels and into blood in the small intestine.
What colour is lymph?
Clear pale yellow. Lymph draining from the small intestine is creamy white.
How does lymph travel?
Through lymphatic capillaries –> lymphatic vessels –> lymph nodes.
Lymph trunks.
As lymphatic vessels exit lymph nodes in a particular region of the body, they unite to form lymph trunks.
What are the principal lymph trunks?
Lumbar trunks, intestinal trunks, bronchomediastinal trunks, subclavian trunks, jugular trunks.
Lumbar trunks.
Drain lymph from lower limbs, wall and viscera of pelvis, kidneys, adrenal glands, abdominal wall.
Intestinal trunks.
Drain lymph from stomach, intestines, pancreas, spleen, part of the liver.
Bronchomediastinal trunks.
Drain lymph from thoracic wall, lung, heart.
Subclavian trunks.
Drain lymph from upper limbs.
Jugular trunks.
Drain lymph from head and neck.
Lymph from the upper right quadrant of the body returns to the…
Superior vena cava from the right brachiocephalic vein.
Lymph from the upper left side of the body and entire body below diaphragm returns to the…
Superior vena cava from the left brachiocephalic vein.
An important function of lymphatic vessels is to…
Return the lost plasma proteins and plasma to the bloodstream.
Lymph drains into venous blood through the…
Right lymphatic duct and the thoracic duct at the junction of the internal jugular and subclavian veins.
Respiratory pump.
Lymph flow is maintained by pressure changes that occur during inhalation. Lymph flows from the abdominal region (high pressure) to the thoracic region (low pressure). When the pressures reverse during exhalation, the valves in lymphatic vessels prevent back flow.
Skeletal muscle pump.
Milking action of skeletal muscle contractions compresses lymphatic vessels and forces lymph toward the junction of the internal jugular and subclavian veins.
Primary lymphatic organs.
Sites where stem cells divide and become immunocompetent. Red bone marrow (flat bones, epiphyses of long bones) and thymus.
Secondary lymphatic organs and tissues.
Sites where most immune responses occur. Lymph nodes, spleen, lymphatic nodules.
Which lymphatic structures are organs and which are tissues?
Organs: thymus, lymph nodes, spleen (each is surrounded by a connective tissue capsule.
Tissue: nodules (lack a capsule).
Describe the structure of the thymus.
Located in mediastinum between sternum and aorta. An enveloping layer of connective tissue holds the 2 lobes together, and a connective tissue capsule encloses each lobe separately. Extensions of the capsule (trabeculae) penetrate inward and divide each lobe into lobules.
Each thymic lobule consists of a…
Deeply staining outer cortex and lighter staining central medulla.
Outer cortex of thymus.
Composed of large numbers of T-cells and scattered dendritic cells, epithelial cells, macrophages.
Describe T-cells and the thymus.
Pre-T-cells migrate from red bone marrow to the thymus cortex where they proliferate and mature. T-cells then enter the medulla. T-cells that leave the thymus via the blood migrate to lymph nodes, spleen and other lymphatic tissues where they colonize parts of these organs and tissues.
What is the role of thymic macrophages?
Clear out debris of dead and dying cells.
Inner medulla of thymus.
Consists of widely scattered mature T-cells, epithelial cells, dendritic cells, macrophages. Some epithelial cells cluster and degenerate and are filled with keratohyalin granules and keratin. These clusters are called thymic corpuscles and they serve as sites of cell death for T-cells in the medulla.
Why does the thymus appear red?
High content of lymphoid tissue and rich blood supply.
Large groups of lymph nodes are present near the…
Mammary glands, and in the axillae and groin.
Stroma of a lymph node.
Capsule, trabeculae, reticular fibres and fibroblasts.
Outer cortex of lymphatic node.
Consists of lymphatic nodules.
Lymphatic nodules.
Masses of lymphatic tissue that are not surrounded by a capsule. Scattered throughout lamina proprietor of mucous membranes lining the GI, urinary tract, reproductive tract, and respiratory airways. Nodules consisting of mainly B-cells are primary lymphatic nodules, but most of the lymphatic nodules in the outer cortex of nodes are secondary lymphatic nodules which form in response to an antigen and are sites of plasma cell and memory B-cell formation. After B-cells in a primary lymphatic nodule recognize an antigen, the primary lymphatic nodule develops into a secondary lymphatic nodule. The germinal center of a secondary lymphatic nodule contains a region of light staining cells (B-cells, follicular dendritic cells, macrophages). When follicular dendritic cells present an antigen, B-cells proliferate and develop into antibody producing plasma cells or memory B-cells. The region of a secondary lymphatic nodule surrounding the germinal center is composed of dense accumulations of B-cells that have migrated away from their site of origin within the nodule.
Inner cortex of lymphatic node.
Does not contain lymphatic nodules. Consists mainly of T-cells and dendritic cells that enter a lymph node from other tissues. Dendritic cells present antigens to T-cells. Newly formed T-cells migrate from lymph node to other areas of the body.
Medulla of lymphatic node.
Contains B-cells, antibody producing plasma cells that have migrated out of cortex, and macrophages.
How does lymph enter a lymph node?
Through several afferent lymphatic vessels which penetrate the convex surface of the node, and contain valves that open toward the center of the node. Once inside the node, lymph flows into subcapsular sinuses, then trabecular sinuses, then medullary sinuses.
How does lymph exit a lymph node?
Efferent lymphatic vessels contain valves that open away from the center of the lymph node to convey lymph, antibodies secreted by plasma cells, and activated T-cells out of the node.
Hilum.
Slight depression on one side of the lymph node where efferent vessels emerge from. Blood vessels can also enter and exit the node here.
How does a lymph node act as a filter?
Lymph enters one end –> foreign substances are trapped by reticular fibres within sinuses –> macrophages and lymphocytes destroy foreign substances.
Spleen.
Largest single mass of lymphatic tissue. Soft, encapsulated, located between stomach and diaphragm. Splenic artery, splenic vein and efferent lymphatic vessel pass through its hilum. A capsule of dense connective tissue surrounds the spleen and is covered by a serous membrane. Trabeculae extend inward from the capsule.
Stroma of the spleen.
Capsule, trabeculae, reticular fibres, fibroblasts.
Parenchyma of the spleen consists of 2 different kinds of tissue:
1) White pulp (lymphatic tissue, lymphocytes, macrophages, arranged around branches of splenic artery).
2) Red pulp (blood-filled venous sinuses and cords of splenic tissue, cords consist of RBCs / macrophages / lymphocytes / plasma cells / granulocytes, veins are closely associated with red pulp).
What are the roles of B-cell, T-cells and macrophages within white pulp?
B-cells and T-cells carry out immune responses. Macrophages destroy blood borne pathogens.
What are the 3 functions of the red pulp related to blood cells?
1) Macrophage removal of ruptured and defective blood cells and platelets.
2) Storage of platelets.
3) Production of blood cells during fetal life.
Tonsils.
5 tonsils form a ring at the junction of the oral cavity and oropharynx, and at the junction of the nasal cavity and nasopharynx. Tonsils are strategically positioned to participate in immune responses against inhaled/ingested foreign substances.
Single pharyngeal tonsil.
Adenoid. Embedded in the posterior wall of the nasopharynx.
Two palatine tonsils.
Posterior region of oral cavity (one on either side). The tonsils commonly removed in a tonsillectomy.
Paired lingual tonsils.
Base of tongue. May require removal.
Which enzyme is capable of breaking down cell walls of bacteria, and is present in tears, saliva, perspiration, nasal secretions and tissue fluids?
Lysosome.
Antimicrobial substances.
Discourage microbial growth. Interferons, complement system, iron-binding proteins, antimicrobial proteins.
Interferons.
Lymphocytes, macrophages, and fibroblasts infected with viruses produce IFNs. Once released, they diffuse to uninfected neighbouring cells where they induce synthesis of antiviral proteins that interfere with viral replication.
Complement system.
Defensive system made up of 30+ normally inactive proteins produced by the liver and found in blood plasma and on plasma membranes. These proteins enhance immune reactions, causing cytolysis, phagocytosis, inflammation, and prevent excessive damage to body tissues.
