Title: Human Anatomy and Physiology, Eleventh Edition
URL Source: blob://pdf/0734cbe8-3a94-4af8-892b-5c491205b2ab
Markdown Content:
Human Anatomy and Physiology
Eleventh Edition
# Chapter 20
The Lymphatic System and
Lymphoid Organs and
Tissues
PowerPoint Lectures Slides prepared by Karen Dunbar Kareiva, Ivy Tech Community College
Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Lymphatic System and Lymphoid Organs
# and Tissues
Lymphatic system returns fluids leaked from blood vessels back to blood; consists of
three parts
1. Network of lymphatic vessels (lymphatics)
2. Lymph : fluid in vessels
3. Lymph nodes : cleanse lymph
Lymphoid organs and tissues provide structural basis of immune system by housing
phagocytic cells and lymphocytes
Structures include spleen, thymus, tonsils, lymph nodes, other lymphoid tissues Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# 20.1 Lymphatic System
Lymphatic system returns interstitial fluid and leaked plasma proteins back to blood via:
Lymphatic vessels (lymphatics): elaborate network of drainage vessels
Circulates ~ 3L interstitial fluid per day
Once interstitial fluid enters lymphatics, it is called lymph Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Distribution and Structure of Lymphatic
# Vessels
Lymphatic vessels offer a one -way system, ensuring lymph flows only toward heart
Lymph vessels (lymphatics) include lymphatic capillaries and larger lymphatic vessels
Lymphatic capillaries
Blind -ended vessels that weave between tissue cells and blood capillaries
Absent from bones, teeth, and bone marrow
Once thought to be absent from CNS, but now found to be present but limited
to locations in meninges where they help to drain interstitial fluid and CSF .
Similar to blood capillaries, but more permeable
Can take up larger molecules and particles that blood capillaries cannot
Example: proteins, cell debris, pathogens, and cancer cells
Can act as route for pathogens or cancer cells to travel throughout body Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Distribution and Structure of Lymphatic
# Vessels
Lymphatic capillaries (cont.)
Increased permeability due to two specialized structures
1. Endothelial cells overlap loosely to form one -way minivalves
2. Minivalves are anchored by collagen filaments to matrix, so increases in
ECF volume opens minivalves even more
Decreases in ECF cause minivalves to close
Lacteals : specialized lymph capillaries present in intestinal mucosa
Absorb digested fat and deliver fatty lymph ( chyle ) to the blood Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
Figure 20.1b Distribution and special features of lymphatic capillaries. Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Distribution and Structure of Lymphatic
# Vessels
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
Anastomose more frequently
Collecting vessels in skin travel with superficial veins, but deep vessels travel with
arteries Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Distribution and Structure of Lymphatic
# Vessels (5 of 6)
Larger lymphatic vessels (cont.)
Lymphatic trunks , which are formed by union of largest collecting vessels, drain
large areas of body
Named for regions of body they drain:
Paired lumbar
Paired bronchomediastinal
Paired subclavian
Paired jugular trunks
Single intestinal trunk Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Distribution and Structure of Lymphatic
# Vessels
Lymph is delivered from trunks into one of two large lymphatic ducts
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
Each empties lymph into venous circulation at junction of internal jugular and
subclavian veins on its own side of body Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Lymph Transport
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; immobilization of area keeps needed
inflammatory material in area for faster healing Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Clinical Homeostatic Imbalance 20.2
Lymphedema : severe localized
edema
Caused by anything that prevents
normal return of lymph to blood
Examples: tumors blocking
lymphatics or removal of
lymphatics during cancer
surgery
Lymphedema may improve if
some lymphatic pathways
remain and enlarge Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# 20.2 Lymphoid Cells, Tissues, and
# Organs Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Lymphoid Cells
Lymphoid cells consist of (1) immune system cells found in lymphoid tissue and (2)
supporting cells that form lymphoid tissue structures
1. Immune system cells
Lymphocytes : cells of the adaptive immune system; mature into one of two
main types
T cells (T lymphocytes)
B cells (B lymphocytes)
Other lymphoid immune cells
Macrophages phagocytize foreign substances and help activate T cells
Dendritic cells capture antigens and deliver them to lymph nodes; also
help activate T cells
2. Supporting lymphoid cell
Reticular cells produce reticular fibers called stroma in lymphoid organs
Stroma: network -like support that acts as scaffolding for immune cells Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Reticular Connective Tissue in a Human
# Lymph Node
Figure 20.4 Reticular connective tissue in a human lymph node. Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Lymphoid Tissue
Main functions of lymphoid tissue
Houses and provides proliferation sites for lymphocytes
Offers surveillance vantage points for lymphocytes and macrophages as they filter
through lymph
Largely composed of 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 Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Lymphoid Organs
Two main types of lymphoid tissues
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 Peyers patches and in appendix Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Lymphoid Organs
Lymphoid organs are grouped into two functional categories
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 Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# 20.3 Lymph Nodes (1 of 2)
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 of body
where collecting vessels converge into trunks Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# 20.3 Lymph Nodes (2 of 2)
Two main functions of lymph nodes
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 Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Clinical Homeostatic Imbalance 20.3
Buboes : inflamed, swollen, tender lymph nodes that result when nodes are overwhelmed
by what they are trying to destroy
Condition often referred to as swollen glands
Buboes are sometimes pus -filled
Bubonic plague was named after chief clinical feature of this disease
Lymph nodes can become secondary cancer sites if metastasizing cancer cells become
trapped in node
Cancer -infiltrated lymph nodes are swollen but usually not painful, a fact that helps
distinguish cancerous nodes from those infected by microorganisms Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# 20.4 Spleen (1 of 3)
Spleen is blood -rich organ about size of fist, located in left side of abdominal cavity, just
below stomach
Largest lymphoid organ
Served by splenic artery and vein , which enter and exit at the hilum
Functions
Site of lymphocyte proliferation and immune surveillance and response
Cleanses blood of aged blood cells and platelets; macrophages remove debris Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
Figure 20.7c The spleen. Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# 20.4 Spleen
Histologically, consists of two components: white pulp & red pulp
1. 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
2. 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) Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
Figure 20.7b The spleen. Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
Figure 20.7d The spleen. Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Clinical Homeostatic Imbalance 20.4
The spleen has a thin capsule, so direct blow or severe infection may cause it to rupture,
spilling blood into peritoneal cavity
Splenectomy : surgical removal of ruptured spleen
Once standard treatment to prevent hemorrhage and shock, but has been
discovered spleen can often repair itself
Frequency of emergency splenectomies has decreased dramatically
If spleen must be 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 Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# 20.5 MALT
Mucosa -associated lymphoid tissue (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
Peyers patches
Appendix Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Tonsils (1 of 2)
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 Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Tonsils (2 of 2)
Tonsils function is to gather and remove pathogens in food or air
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 bacteria into tissues, but allows immune cells to become
activated and build memory cells against these potential pathogens Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
Figure 20.8 Histology of the palatine tonsil. Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Peyers Patches
Peyers patches : clusters of lymphoid follicles in wall of distal portion of small intestine
Also called aggregated lymphoid nodules
Structurally similar to tonsils
Location aids in functions
1. Destroy bacteria, preventing them from breaching intestinal wall
2. Generate memory lymphocytes Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
Figure 20.9 Peyers patch (aggregated lymphoid nodules). Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Appendix
Appendix : 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 Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# Appendix Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# 20.6 Thymus (1 of 3)
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 Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# 20.6 Thymus (2 of 3)
Thymus is broken into lobules that contain outer cortex and inner medulla
Cortex contains rapidly dividing lymphocytes (the bulk of thymic cells) and
scattered macrophages
Medulla contains fewer lymphocytes and thymic corpuscles
Thymic corpuscles are where regulatory T cells develop
Regulatory T cells: type of T cell that helps to prevent autoimmunity Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# 20.6 Thymus (3 of 3)
Thymus 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 : keeps immature T lymphocytes isolated
from any antigens to prevent premature activation
3. Stroma is made up of epithelial cells, not reticular fibers
Provide environment in which T lymphocytes become immunocompetent Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
# The Thymus
Figure 20.10 The thymus. Copyright 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
Table 20.1 Summary of Lymphoid Organs and Tissues.