10.6 The Lymphatic System Flashcards
What is the lymphatic system?
a system closely associated with the circulatory system and consists of lymphatic vessels and the lymphoid organs
What are the 3 main functions of the lymphatic system that contributes to homeostasis?
- lymphatic capillaries absorb excess tissue fluid and return it to the bloodstream
- lymphatic capillaries absorb fats from the digestive tract and transport them to the bloodstream
- lymphoid organs help to defend the body against disease
What do lymphatic vessels do?
- form a one-way system that begins with lymphatic capillaries
- drain excess fluid from the tissues and return it to the circulatory system
- have valves to prevent backflow
What are lymphatic capillaries?
tiny, closed-ended vessels whose walls consist of simple squamous epithelium, richly supplied in most regions of the body
What do lymphatic capillaries do?
absorb excess tissue fluid
What is tissue fluid?
mostly water, but contains solutes (ie. nutrients, electrolytes, oxygen) derived from the plasma and cellular products (ie. hormones, enzymes, wastes) secreted by cells
What is lymph?
tissue fluid contained within lymphatic vessels
What do lymphatic capillaries join to form?
form lymphatic vessels that merge before entering one of two ducts, the thoracic duct or the right lymphatic duct
What does the larger, thoracic duct do?
returns lymph collected from the body below the thorax and the left arm and the left side of the head and neck, into the left subclavian vein
What does the right lymphatic duct do?
returns lymph from the right arm and right side of the head and neck into the right subclavian vein
What does lymph do on its way back to the circulatory system?
percolates through various lymph nodes, where any foreign material present can be recognized by the immune system
What is the structure of the larger lymphatic vessels similar to?
circulatory veins
What is the movement of lymph within lymphatic capillaries largely dependent on?
skeletal muscle contraction
What happens to lymph forced through lymphatic vessels as a result of muscular compression?
prevented from flowing backward by one-way valves
What is edema?
a localized swelling caused by the accumulation of tissue that has not been collected by the lymphatic system
When does edema occur?
if too much tissue fluid is made and/or if not enough is drained away
What can edema lead to?
- tissue damage
- death
What are lymphoid organs?
organs that contain large numbers of lymphocytes
What are lymphocytes?
the type of white blood cells that is mainly responsible for adaptive immunity
What are primary lymphoid organs?
where lymphocytes develop and mature
ie. red bone marrow and thymus
What are secondary lymphoid organs?
where some lymphocytes become activated
ie. lymph nodes and spleen
What is red bone marrow?
contains a network of connective tissue fibres, along with stem cells that are ever capable of dividing and producing blood cells
Describe the cells produced by the red bone marrow.
- some become the various types of white blood cells
- packed around thin-walled sinuses filled with venous blood
- differentiated blood cells enter the bloodstream at these sinuses
Where is red bone marrow present in children?
most bones
Where is red bone marrow present in adult?
mainly in the bones of the skull, sternum, ribs, clavicle, pelvis, and vertebral column
What are B cells (B lymphocytes)?
lymphocytes that remain in the bone marrow until they mature
What are T cells (T lymphocytes)?
lymphocytes that migrate from bone marrow through the bloodstream to the thymus where they mature and differentiate
What is thymus?
soft, bilobed, primary lymphoid organ that secretes the hormone thymosins, which aids in the differentiation of T cells
Where is the thymus located?
in the thoracic cavity between the trachea and the sternum above the heart
When does the thymus grow the largest, and shrink?
grows around the time of puberty
shrinks as we get older
What does connective tissue do for the thymus?
divides the thymus into lobules, which are filled with T cells and supporting cells
What are the lobules of the thymus lined with?
epithelial cells that secrete hormones called thymosins
What does thymosin do?
aid in the differentiation of T cells packed inside the lobules
How many T cells exit the thymus?
about 5%
What is apoptosis?
involves a cascade of specific cellular events leading to the death and destruction of the cell
What undergoes apoptosis?
T cells that are capable of reacting to the body’s own cells
What are T cells that leave the thymus capable of?
reacting to foreign molecules
What happens in secondary lymphoid organs?
- may encounter foreign molecules or cells, after they proliferate and become activated
- these activated cells usually reenter the bloodstream, where they search for sites of infection and inflammation
Where is the spleen?
upper left side of the abdominal cavity behind the stomach
What does most of the spleen consist of?
- blood vessels and sinuses where macrophages remove old and defective blood cells
- small areas of lymphoid tissue, where lymphocytes can react to foreign invaders in the blood
What happens to a person with no spleen?
- more susceptible to certain types of infections
- because the spleen also removes older red blood cells and platelets, the numbers of both types of cells may increase
What are lymph nodes?
small, ovoid strictures occurring along lymphatic vessels, through which the lymph must pas
What does connective tissue do for nodes?
divide the nodes into nodules
What are nodules packed with?
B and T cells, contains sinus
What happens as lymph courses through the many sinuses?
resident macrophages engulf pathogens
What are pathogens?
disease-causing agents such as viruses and bacteria, as well as any debris present in the lymph
What are lymph nodes named for?
their location
ie. inguinal nodes are in the groin, axillary nodes are in the armpits
What do physicians feel for as evidence the body is fighting an infection?
swollen or tender lymph nodes
What is metasis?
the spreading of cancer far from its place of origin
Why does the lymphatic system sometimes inadvertently assist metasis?
cancer cells sometimes enter lymphatic vessels and move undetected to other regions of the body, where they may produce secondary tumours
