Lymphatic System Physiology Flashcards
What does the lymphatic system consist of?
- Lymph nodes and other lymphoid tissues (spleen [red & white pulp], tonsils, Peyer’s patches, thymus)
- Lymph vessels
- Lymph
What is lymph?
The circulating fluid found in the lymphatic vessels
How many directions does lymph move in?
1 (due to valves)
slide 1
What is the function of the lymphatic system?
slide 3
What is a CCL receptor?
a receptor on WBCs that binds to HEV
A primary function of the lymphatic system is to prevent the accumulation of ____ in the _____.
an accumulation of large molecules (usually proteins) in the interstitum.
Excess of capillary filtration over reabsorption is balanced by ____ ____.
lymph flow
How does the blood capillary filtrate leave the interstitium?
Either by reabsorption or through the lymphatic system.
What is the only route for the reuptake of filtered plasma proteins?
the lymphatic system
What prevents backflow of lymph?
valves
In a given tissue, which is higher: intralymphatic pressure or intravenous pressure?
intralymphatic pressure
What are the 2 main determinants of lymph flow?
- Filling pressure (preload)
- outflow resistance (afterload)
What happens when afterload, preload, or both levels are increased?
The lymph vessel is stretched, and the rate and strength of contraction is increased
What is increased due to complete obstruction of a lymph vessel?
the amplitude and frequency of contractions- this is to raise peak lymphatic pressure
What 3 things affect the rate and strength of contraction in a lymph vessel?
- hormones
- vasoactive substances
- nerves
What 3 things stimulate motor activity and local lymph flow?
- Norepinephrine
- Epinephrine
- α-adrenergic sympathetic nerves
Does gravity affect lymph flow?
No. Content is propelled by smooth muscle activity
Lymph vessels are also called ___ ___.
Lymphatic capillaries
What are the two types of lymphatic vessels, and where do they travel?
- Afferent (toward- unfiltered fluid from body tissues to lymph nodes)
- Efferent lymphatic vessels (away- filtered fluid from lymph nodes to subsequent lymph nodes or into the venous system)
Lymph capillaries start from _____ as large blind ended (not open, can only do diffusion) terminals called ____ ____.
tissue spaces; capillary buds
United lymph capillaries form:
Large lymphatic vessels
What are lymph capillaries lined by?
endothelial cells
Endothelial cells of the lymph capillaries are:
overlapped on one another
The large lymph vessels ultimately form the:
right and left lymphatic duct
the left, larger duct is alsos known as the thoracic duct
The right lymphatic duct opens into the:
And the left into the:
- right subclavian vein
- left subclavian vein
What 4 regions of the body are lymph vessels NOT found in?
- superficial layers of the skin
- CNS
- Cornea and bones
- Alveoli of the lungs
What are the blind ended vessels permeable to?
- proteins (large molecuels)
- cells
- fluids
- dissolved molecules
Describe lymph:
- clear
- contains less protein than blood plasma
- contains few RBCs
- contains high amounts of lymphocytes
What does lymph carry?
- glucose
- salts
- fats (chylomicra from intestine)
- fibrinogen
Is lymph movement passive or active?
passive
What are the 4 ways lymph moves through vessels?
- muscle movement (exercise, etc.)
- breathing
- heart beat
- tissue massage
The lymphatic system propels its contents by ____ muscle activity.
smooth muscle activity
When no lymph is present in the vessels, the lymph pressure falls to __.
zero
What causes rhythmic contractions of the lymphatic vessels?
stretching of the vessels by the lymph
What generates lymphatic pulse pressures?
contraction of the lymphatic vessel smooth muscles (diaphragm)
Where does the protein in the interstitium come from?
blood
How are lymphatic pulse pressures generated and facilitated?
- generated by contraction of the lymphatic vessel smooth muscles
- facilitated by contractile actomyosin filament present in the lymphatic capillary endothelial cells (composed of actin and myosin proteins)
Myosin motors pull on actin filaments, causing them to slide past each other, resulting in contraction
What are lacteals?
- Special lymph capillaries
- The sites of absorption of digested fats (lipids) (in chylomicrons).
Artery -> vili -> vein -> hepatic portal vein (the path of fats that are collected?)
slide 19 cass notes
What is the path of thoracic lymphatic drainage?
duct -> vein -> vena cava
Where does fluid enter the lymphatic system?
the interstitial fluid
- moves to the subclavian veins at the base of the neck
What does the right lymphatic duct drain?
- drains the upper right portion of the body, returning lymph to the bloodstream via the right subclavian vein
What does the left lymphatic duct drain?
- the rest of the body into the bloodstream via the left subclavian vein
What is lymphedema? What causes it?
The accumulation of fluid in the tissues
- due to tumor pressure, parasites, or surgery
What are the 3 parts of a lymph node?
- cortex
- paracortex
- medulla
The cortex of a lymph node contains primary and secondary ____ ____, with a dense population of:
- p & s lymphoid follicles;
- dense pop. of B lymphocytes and macrophages
The paracortex of a lymph node contains _____.
T lymphocytes
The medulla of a lymph node contains:
B and T lymphocytes and macrophages
What is the function of a lymph node?
To host defense (& macrophages)
At the venous end of the capillaries, __/___ of the blood and the interstitial fluid move into lymph vessels, while __/____ move into venous end of the arterial capillaries.
- 1/10ths: blood and ISF
- 9/10ths: venous end of arterial capillaries
Where does the concentration of the lymph take place?
in the lymph nodes by water absorption
What do lymph nodes desroy?
Bacteria and other toxins by phagocytosis
Essentially, lymph is composed of:
proteins and other macromolecules which escaped reabsorption at the venous end of the capillaries
What are the 2 primary ways cells enter lymph nodes?
- lymph
- afferent lymphatic vessels (for lymph-associated cells)
What are the major cells in lymph?
lymphocytes
What does HEV stand for?
High endothelial venules
How do lymphocytes generally enter lymph?
through HEVs
What do HEVs contain?
A single layer of endothelial cells. These cells possess:
- surface receptors for chemokines (CCL19 & CCL21)
- receptors specific for naive T lymphocytes (CCR7)
What happens as lymphocytes pass through HEVs?
the lymphocytes bind to the surface receptors of the HEVs and are carried into the paracortex of the lymph node
What is the role of CCR7 (C-C Chemokine Receptor 7)?
- guiding the migration and homing of immune cells to lymphoid organs. (specifically T cells and dendritic cells)
- immune surveillance
- initiation of the adaptive immune response
Which chemokine receptor is a key for the initiation of the adaptive immune response?
CCR7
Where are CCL21s expressed?
- HEVs
- In lymphatic vessels
Where is CCL19 primarily produced?
In the T cell zones of lymphoid tissues
(also expressed on HEVs)
Why is intralymphatic pressure greater than intravenous pressure?
Where can CCL19 and CCL21 be found in the body?
Secondary lymphoid tissues- lymph nodes, the spleen, and the thymus.
(this is where they guide the migration of cells expressing CCR7 receptors)
What is the role of CCR7? (located on lymphocytes)
to direct naive T cells to lymphoid tissues through HEVs, which allows them to encounter antigens presented by dendritic cells or other APCs
Most of the lymphocytes within a node are ______.
naive. They have yet to encounter an antigen and must migrate to regions where they will be most effective to recognize one.
(they migrate from the cortex -> paracortex -> medulla)
What is the migration path for B lymphocytes?
- enter paracortex through HEVs
- migrate into the outer cortex;
- join specialized dendritic cells and macrophages
- Their joining creates primary follicles
- surrounding them are tightly packed dendrites = germinal center
- antigen-dependent B cells mature
- Activated B cells migrate from paracortex to the medulla
- proliferation as antibody-secreting plasma cells
What do primary follicles consist of?
A resting B cell surrounded by a loose network of dendritic cells
What happens in primary follicles when a foreign antigen is encountered?
- The B cell becomes activated and is surrounded by a more tightly packed association of dendritic cells and macrophages
- This forms a germinal center
What encloses a germinal center?
A mantle zone- a ring of resting B cells and dendritic cells
What do the germinal center and mantle zone together create?
a secondary follilcle
(site of antigen-dependent B-cell maturation)
What is the migration path for T lymphocytes?
- Enter the lymph node through HEVs
- remain in the paracortex
- Cortical macrophages and dendritic cells present antigen peptides to NAIVE T cells
- They are stimulated and become activated helper or cytotoxic lymphocytes
- Move to medulla
All activated lymphocytes migrate where? And through which type of lymphatic vessel?
through the medulla and enter the lymphatic circulation
- through the EFFERENT lymphatic vessel (drains either into adjacent lymph nodes or ultimately into the thoracic duct)
slide 39
What are the 5 functions of lymph?
- returns the proteins that leaked into tissue spaces back to the blood
- important role in redistribution of fluid in the body
- removes bacteria, toxins, and other foreign bodies from tissues
- serves as an important route for intestianl fat absorption (lipids)
- plays an important role in immunity by transport and storage of T and B lymphocytes
What does the lymphatic system of the udder help with?
regulating proper fluid balance within the udder and combating infection (helps with fluid drainage and supply)
Lymph travels from the udder to the _______ and empties into the blood system
thoracic duct
What causes edema of the lymphatic system?
High pressure in the vascular system results in the pooling of interstitial fluid
(The lymphatic system is passive with low pressure; high vascular pressure adds too much to ISF that the lymph is not able to drain quickly enough.)
Is lymphatic dysfunction hereditary?
(Some lymph nodes may become fibrous.)
Yes; can be herediatry and congenital
What is lymphedema caused by?
- malformation of the lymphatic system, which may be due to aplasia, valvular incompetence, or lymph node fibrosis
- Potential causes also include:
-Heart disease: mitral valve disease, which can cause left-side heart failure,
-Trauma to lymphatic vessels or lymph nodes
-Heat or radiation exposure
slide 44 (not on exam)
What is the largest lymphatic organ?
the spleen
What are some features of the spleen?
- rich blood supply
- filters blood and reacts immunologically to blood-borne antigens
- contains large amounts of lymphocytes
- contains meshwork of reticular cells, fibers, and a rich supply of macrophages
- provides a site for lymphocyte maturation
- Good (major) environment for destruction of RBCs (mononuclear phagocytic system)
What do the red and white pulp of the spleen contain?
White:
- thick accumulation of lymphocytes surrounding an artery
Red:
- large numbers of red blood cells that are filtered and degraded
Circulation within the red pulp of the spleen allows macrophages to:
Screen antigens that are in the blood
What occurs in the spleen?
- Activation and proliferation of B and T lymphocytes
- Secretion of antibodies
How does the spleen contribute to making and destroying RBCs?
- Iron is removed from erythrocyte hemoglobin during RBC catabolism
- It removes and destroys senescent, damaged, and abnormal red blood cells and platelets
- it forms RBCs during the early fetal life
- it stores blood, especially RBCs, in most species
What is the bilobed organ located in the superior mediastinum, anterior to the heart and great vessels?
The thymus
The thymus parenchyma (functional tissue of the thymus gland) contains:
Developing T cells (in an extensive meshwork formed by epithelioreticular cells)
What happens when the thymus function reduces (at around the time of puberty)?
- T cell differentiation and proliferation is reduced
- most of the lymphatic tissue is replaced by adipose tissue (involution)
What is involution?
the shrinkage of an organ in old age or when inactive
the organ is turned into fat
During the involution of the thymus, connective tissue surrounds the thymus and subdivides it into ______.
thymic lobules (bilobes)
Which types of epithelioreticular cells are found in which parts of the thymus?
Cortex: Types 1, 2, and 3
Medulla: types 4 and 5
What protects developing lymphocytes in the thymus from premature exposure to antigens?
The blood-thymus barrier
Where is the site of T-cell education?
the thymus
During fetal life, the thymus is populated by:
multipotential lymphoid stem cells that originate from the bone marrow; they are destined to become immunocompetent T cells
What is T cell education?
The maturation and differentiation of stem cells into immunocompetent T cells.
It is characterized by the expression and deletion of specific surface CD (cluster differentiation) agents.
Which lymphoid organs house T lymphocytes?
- Tonsils
- Peyer’s patches
- Vermiform appendix
Which lymphoid organ forms a ring of lymphatic tissue at the entrance of the oropharynx?
The tonsils
Where are Peyer’s patches located?
The ileum (instestines)
Where does the Veriform appendix arise from?
The cecum (pouch that connects the small intestine to the colon)
