Lecture 20: The Lymphatic System

Question 1

what is the lymphatic system and its components

Answer 1

LS returns fluids leaked from blood vessels back to blood
-Consists of:
1. Lymphatic vessels (lymphatics)
-Carry lymph from peripheral tissues to veins
2. Lymph – fluid similar to plasma
-Lack plasma proteins
3. Lymphoid tissues and organs – cleanse lymph
-Scattered throughout the body
4. Lymphoid cells
-Lymphocytes, phagocytes and other cells

Question 2

what are the functions of the lymphatic system

Answer 2

-Produce, maintain, and distribute lymphocytes and other lymphoid cells – performs immune responses
-Drain interstitial fluid – to form lymph
-Maintain normal blood volume
-Transport dietary fats and vit. A, D, E, K from GIT
-Transport hormones and wastes

Question 3

what are lymphatic vessels

Answer 3

-Provide a one-way system, ensuring lymph flows only toward heart
-Lymphatics include lymphatic capillaries and larger lymphatic vessels

Question 4

what are lymphatic capillaries

Answer 4

-Blind-ended vessels that weave between tissue cells and blood capillaries
-Absent from bones, teeth, bone marrow, and CNS
-Similar to blood capillaries, but more permeable -absorb larger molecules

Question 5

what are the two specialized structures that allow for increased permeability of lymphatic capillaries

Answer 5

1. Endothelial cells overlap loosely to form one-way minivalves
2. Minivalves are anchored by collagen filaments to matrix
   -So, increase in ECF volume opens minivalves even more
   -Decrease in ECF cause minivalves to close

Question 6

what are lacteals (lymphatic capillaries)

Answer 6

Specialized lymph capillaries present in intestinal mucosa
-Absorb digested fat and deliver fatty lymph (chyle) to the blood

Question 7

describe the larger lymphatic vessels

Answer 7

-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
-Anastomose more frequently
-Collecting vessels in skin travel with superficial veins, but deep vessels travel with arteries

Question 8

describe the lymphatic trunk and ducts

Answer 8

lymph passes from the lymphatic vessels-> lymph nodes-> lymph trunks
named for regions of body they drain

Question 9

what are the main lymphatic trunks

Answer 9

1. intestinal trunk
2. Right & left lumbar trunk
3. right & left broncho-mediastinal trunk
4. right & left subclavian trunk
5. right & left jugular trunk

Question 10

what are the main lymphatic ducts

Answer 10

lymphatic trunk merges to form either the thoracic or the right lymphatic duct
1. the right lymphatic duct: drains lymph from the right upper limb and the right side of the head and thorax, empties into the junction of the right intestinal jugular and subclavian veins
2. the thoracic duct: drains lymph from the rest of the body, empties into the blood at the junction of the left internal jugular and subclavian veins

Question 11

describe the formation and flow of lymph

Answer 11

Blood capillaries (blood) → Interstitial space (ISF) → lymphatic capillaries (lymph) → lymphatic vessels (lymph) → lymphatic trunks (lymph) → lymphatic ducts (lymph)→ junction btw subclavian and internal jugular veins (blood)

Question 12

flow of lymph

Answer 12

-blood plasma is filtered from blood capillaries into interstitial spaces to become interstitial fluid
-lymphatic capillaries absorb interstitial fluid and pass lymph to afferent lymphatic vessels
-afferent lymphatic vessels carry lymph from lymphatic capillaries to lymph nodes
-lymph nodes remove foreign substances through filtering lymph, phagocytosis, and immune reactions
-efferent lymphatic vessels carry lymph from lymph nodes
-lymphatic vessels pass lymph to lympahtic ducts
-lymphatic ducts (thoracic & right lymphatic duct) empty lymph into the junction of the jugular and subclavian veins of jugular and subclavian veins of the cardiovascular system

Question 13

describe lymph transport

Answer 13

-Lymph system is a low-pressure system like venous system
-Lymph is propelled by same mechanisms:
* 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 increases flow of lymph

Question 14

what are the primary lymphatic organs

Answer 14

-Where immune cells divide and become immunocompetent
* Red bone marrow
* Thymus

Question 15

what are the secondary lymphatic organs

Answer 15

Site of activation of immune cells → immune response
* Lymph nodes
* Spleen
* MALT
* Lymphatic nodules (follicles)

Question 16

what is the thymus

Answer 16

-Bilobed organ within mediastinum
-Atrophies (waste away) after puberty – diminishes immune system effectiveness
* Lobes wrapped with capsule, invaginations → trabeculae – separate lobes into lobules

Question 17

what are the lobules of the thymus

Answer 17

a) Cortex: pre-T cells (from red bone marrows), dendritic cells (aids T cell maturation), epithelial cells (pre-T cell education – pos. selection, secrete thymic hormones), macrophages (clear dead cells and debris)
b) Medulla
* Contains fewer lymphocytes and thymic corpuscles
* Thymic corpuscles are where regulatory T cells (Tregs) develop

Question 18

describe lymphocytes

Answer 18

-Divide in cortex
-Migrate into medulla
-Mature T cells leave thymus by medullary blood vessels

Question 19

what are thymic hormones

Answer 19

-Thymosin— an extract from thymus
-Several hormones: thymosin-a, thymosin-b, thymosin V, thymopoietin, thymulin
-Promotes development and maturation of T cells

Question 20

what are the main functions of the lymph nodes

Answer 20

1. 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
2. Immune system activation – offer a place for lymphocytes to become activated and mount an attack against antigens

Question 21

what are the two components of the lymph nodes

Answer 21

1. Stroma (framework of CT) Capsule, trabeculae, reticular fibers, fibroblasts
2. Parenchyma (functional part)
   - Cortex
   - Medulla

Question 22

what is the route of flow through a lymph node

Answer 22

afferent lymphatic vessel-> subcapsular sinus-> trabecular sinus-> medullary sinus-> efferent lymphatic vessel

Question 23

describe the spleen

Answer 23

-Attached to stomach by gastrosplenic ligament
-Contacts diaphragm and left kidney
-Splenic veins, arteries, and lymphatic vessels: Communicate with spleen at hilum

Question 24

describe the anatomy of the spleen

Answer 24

-Stroma: capsule, trabeculae, reticular fibers, fibroblasts
-Parenchyma consists of:
* White pulp – lymphocytes and macrophages, surrounds central artery
* Red pulp – venous sinuses, splenic cords (RBCs, free and fixed macrophages, granulocytes)

Question 25

what are the functions of the spleen

Answer 25

-Removal of abnormal BCs and other blood components by phagocytosis
-Storage of platelets, and iron recycled from red blood cells
-Initiation of immune responses by B- and T cells
-Hemopoiesis in fetal life

Question 26

describe the lymphatic nodules

Answer 26

-Masses of lymphatic tissue that are not surrounded by a capsule
-Scattered throughout the lamina propria of mucous membranes lining the GI, urinary, and reproductive tracts and respiratory airways – mucosa-associated lymphatic tissue (MALT)
-Usually solitary, aggregates form in tonsils, lymphatic follicles (Peyers patches) in ileum, appendix

Question 27

what are peyer’s patches and their function

Answer 27

-Clusters of lymphoid follicles in wall of distal portion of small intestine
-aka aggregated lymphoid nodules
-Structurally similar to tonsils
-Location aids in functions:
1. Destroy bacteria, preventing them from breaching intestinal wall
2. Generate “memory” lymphocytes

Question 28

what is the appendix

Answer 28

-Offshoot of first part of large intestine
-Contains a large number of lymphoid follicles
-Location aids in functions (like Peyer’s patches)
1. Destroy bacteria, preventing them from
breaching intestinal wall
2. Generate “memory” lymphocytes

Question 29

describe the tonsils

Answer 29

-Simplest lymphoid organs
-Function to gather and remove pathogens in food or air
-Contain follicles with germinal centers and scattered lymphocytes
-Form ring of lymphatic tissue around pharynx; appear as swellings of mucosa

Question 30

how are tonsils named

Answer 30

Named According to Location:
-Palatine tonsils: posterior end of oral cavity, Largest of tonsils and most often infected
-Lingual tonsil: lumpy collection of follicles at base of tongue
-Pharyngeal tonsil: aka adenoids; located in posterior wall of nasopharynx
-Tubal tonsils: surround openings of auditory tubes into pharynx

Question 31

what is lymphangitis

Answer 31

lymphatic vessels appear as painful red lines under the skin
-Caused by inflammation of larger lymphatic vessels that contain vasa vasora
-Become congested with blood

Question 32

what is lymphedema

Answer 32

-severe localized edema
-Causes: anything that prevents normal return of lymph to blood
* Examples: tumors blocking lymphatics or removal of lymphatics during cancer surgery

Question 33

what is buboes

Answer 33

Inflamed, swollen, tender lymph nodes that result when nodes are overwhelmed by what they are trying to destroy

Question 34

what is a splenectomy

Answer 34

-Surgical removal of ruptured spleen
-When removed, liver and bone marrow take over most of its functions
- In children younger than 12, spleen will regenerate if a small part is left