Ch. 22 Lymphatic System Flashcards
1
Q
What is a pathogen?
A
A disease-causing organism
2
Q
What is the lymphatic system?
A
The cells, tissues, and organs responsible for defending the body
3
Q
What are the primary cells of the lymphatic system?
A
Lymphocytes
4
Q
What are lymphocytes vital to?
A
The body’s ability to resist or overcome infection and disease
5
Q
Define immunity
A
The ability to resist infection and disease
6
Q
All the cells and tissues involved in producing immunity are part of the ____ ____
A
Immune system
7
Q
What is the immune system?
A
A functional system that includes parts of the integumentary, skeletal, lymphatic, cardiovascular, respiratory, and digestive systems
8
Q
How do vaccines work?
A
A vaccine, containing weakened or dead forms of the infecting microbe is administered. The antigens are not virulent enough to cause the disease, but they provoke the adaptive immune response in the body. This immune response involves B cells that differentiate into plasma cells and make antibodies. It also involves cytotoxic T cells and helper T cells. Regulatory T cells moderate the immune response. Memory T cells and memory B cells help the body remember the antigen so when the protected person is exposed to the real disease, a strong secondary immune response occurs
9
Q
What forms of the virus are vaccines given as?
A
Some vaccines are given as live, attenuated (greatly weakened) forms of a virus. Others are given as inactivated antigens, made from small pieces of killed bacteria. Some require booster shots to boost the secondary immune response and keep immune memory alive
10
Q
What is “herd” immunity?
A
Herd immunity, or community immunity, is when a large part of the population of an area is immune to a specific disease. If enough people are resistant to the cause of a disease, such as a virus or bacteria, it has nowhere to go. While not every single individual may be immune, the group as a whole has protection.
11
Q
Is immunity to chickenpox, developed after vaccination, innate immunity, or adaptive immunity? Why?
A
Innate immunity is genetically determined and present at birth. For example, skin and mucous membranes provide an innate physical and chemical barrier to infecting organisms. All humans are susceptible to chickenpox, an infectious disease. The immunity developed after a chickenpox vaccination is artificially acquired adaptive immunity, developed to a specific antigen, the varicella- zoster virus (VZV).
12
Q
What does the lymphatic system consist of?
A
- Lymph
- A network of lymphatic vessels
- An array of lymphoid tissues and lymphoid organs
- Lymphoid cells
13
Q
Define lymph
A
Interstitial fluid that has entered lymphatic vessels
14
Q
Where does lymphatic vessels begin and connect to?
A
Begin in peripheral tissues and connect to veins
15
Q
What do lymphoid cells include?
A
Lymphocytes and smaller numbers of phagocytes and other cells
16
Q
What are primary lymphoid tissues and organs?
A
Sites where lymphocytes are formed and mature
17
Q
What does primary lymphoid tissues and organs include?
A
Red bone marrow and the thymus
18
Q
What is red bone marrow?
A
Where other defense cells, the monocytes and macrophages, are also formed
19
Q
What is activated in secondary lymphoid tissues and organs?
A
Lymphocytes
20
Q
What does secondary lymphoid tissues and organs include?
A
The tonsils, MALT, lymph nodes, and the spleen
21
Q
What does MALT stand for?
A
Mucosa-associated lymphatic tissue
22
Q
What is the primary function of the lymphatic system?
A
To produce, maintain, and distribute lymphocytes and other lymphoid cells that provide defense against infections and foreign substances. It also helps maintain blood volume.
23
Q
What do lymphocytes do?
A
To provide an effective defense, lymphocytes must detect problems, and they must be able to reach the site of injury or infection. Lymphocytes and other cells circulate within the blood. They are able to enter or leave the capillaries that supply most of the body’s tissues
24
Q
Capillaries normally deliver more fluid to _____ _____ than they carry away
A
Peripheral tissues
25
Where does the excess fluid delivered by capillaries to peripheral tissues go?
The bloodstream through lymphatic vessels
26
The continuous circulation of extracellular fluid helps...?
- Transport lymphocytes and WBCs from one organ to another
- To maintain normal blood volume
- Eliminate local variations in the composition of the interstitial fluid by distributing hormones, nutrients, and wastes from their tissues of origin to the general circulation
27
What do lymphatic vessels do?
Carry lymph from peripheral tissues to the venous system
28
What is the pathway of lymph?
First enters lymphatic capillaries and then drains into larger major lymph-collecting vessels, known as trunks and ducts
29
What does the lymphatic network begin with?
Lymphatic capillaries, which branch through peripheral tissues
30
How do lymphatic capillaries differ from blood capillaries?
- They are closed at one end rather than forming continuous tubes
- Have larger luminal diameters
- Have thinner walls
- Typically have a flattened or irregular outline in sectional view
31
Fluid moves from the plasma through the tissues as _____ _____, and into the lymphatic system as _____
Interstitial fluid
| Lymph
32
What are lymphatic capillaries lined by?
Endothelial cells
33
What are lymphatic capillaries either missing or are incomplete?
The basement membrane
34
How are the endothelial cells of a lymphatic capillary structured?
They are not bound together, but they do overlap
35
In lymphatic capillaries, what does the region of overlap act as?
A one-way valve
36
What does the valve in lymphatic capillaries permit and prevent?
It permits fluids and solutes (including proteins) to enter, along with viruses, bacteria, and cell debris, but it prevents them from returning to the intercellular spaces
37
Where are lymphatic capillaries present?
In almost every tissue and organ in the body
38
Define lacteals
Lymphatic capillaries in the small intestine that transport lipids absorbed by the digestive tract
39
Where are lymphatic capillaries absent?
In areas without a blood supply, such as the cornea of the eye
40
From the lymphatic capillaries, where does lymph flow?
Into larger lymphatic vessels that lead toward the body’s trunk
41
What is the structure of the walls of larger lymphatic vessels?
Contain three layers, comparable to veins
42
What do small to medium-sized lymphatic vessels contain?
Valves which are close together and produce noticeable bulges
43
What is unusual about the appearance of lymphatic vessels and why?
Lymphatic vessels have a beaded appearance due to an irregular lumen
44
What is the purpose of valves in lymphatic vessels?
They prevent the backflow of lymph within lymphatic vessels, especially in the limbs
45
What is pressure like in the lymphatic system and how do valves contribute?
Minimal. The valves are essential to maintaining normal lymph flow toward the thoracic cavity
46
What aids lymph flow in lymphatic vessels?
Contractions of skeletal muscles surrounding the lymphatic vessels
47
What feature do lymphatic vessels share with veins that allows lymph to flow in only one direction?
Valves
48
What distinguishes lymphatic vessels from arteries and veins?
Differences in size, general appearance, and branching pattern
49
What color are arteries, veins, and lymphatic vessels?
Arteries - bright red
Veins - dark red
Lymphatic vessels - pale gold
50
A tissue contains many more ____ than ____, but the _____ are smaller
Lymphatic vessels
Veins
Lymphatic vessels
51
What are the two sets of lymphatic vessels that collect lymph from lymphatic capillaries?
Superficial lymphatics
| Deep lymphatics
52
Where are superficial lymphatics located?
- In the subcutaneous layer deep to the skin
- In the areolar tissues of the mucous membranes lining the digestive, respiratory, urinary, and reproductive tracts
In the areolar tissues of the serous membranes lining the pleural, pericardial, and peritoneal cavities
53
What are deep lymphatics?
Larger lymphatic vessels that accompany deep arteries and veins supplying skeletal muscles and other organs of the neck, limbs, and trunk, and the walls of visceral organs
54
What converges to form lymphatic trunks?
Superficial lymphatics
| Deep lymphatics
55
Where do lymphatic trunks empty into?
The thoracic duct and the right lymphatic duct
56
What does the thoracic duct do?
Collects lymph from the body inferior to the diaphragm and from the left side of the body superior to the diaphragm
57
Where does the thoracic duct begin?
Inferior to the diaphragm at the level of vertebra L2
58
What is cisterna chyli?
An expended, saclike chamber at the base of the thoracic duct
59
Where does cisterna chyli receive lymph from?
The inferior part of the abdomen, the pelvis, and the lower limbs by way of the right and left lumbar trunks and the intestinal trunk
60
Where does the thoracic duct collect lymph from and where is it emptied?
It collects lymph from the left bronchomediastinal trunk, the left subclavian trunk, and the left jugular trunk, and then empties into the left subclavian vein near the left internal jugular vein
61
Where does lymph reenter the venous circulation?
From the left side of the head, neck, and thorax, as well as from the entire body inferior to the diaphragm
62
Where does the smaller right lymphatic duct collect lymph from?
The right side of the body superior to the diaphragm
63
What merges to create the smaller right lymphatic duct?
Formed by the merging of the right jugular, right subclavian, and right bronchomediastinal trunks in the area near the right clavicle
64
Where does the right lymphatic duct empty?
Empties into the right subclavian vein, delivering lymph from the right side of the body superior to the diaphragm
65
Define lymphedema
Swelling as a result of lymphatic vessel obstruction, especially in subcutaneous tissues; large amounts of lymph accumulate
66
What do lymphoid cells consist of?
Immune system cells found in lymphoid tissues and the cells that support those tissues
67
Immune system cells that function in defense include _____ and _____
Phagocytes and lymphocytes
68
Immune system phagocytes include ____ and ____
Macrophages and microphages
69
In lymphoid cells, what do macrophages and microphages function as?
A general first line of defense against pathogens (bacteria or viruses)
70
What do lymphocytes respond to?
Specific invading pathogens, as well as abnormal body cells and foreign proteins
71
How do lymphocytes eliminate threats from invading pathogens?
Through a combination of physical and chemical attacks
72
Lymphocytes account for ____ of circulating lymphocytes
20-40%
73
3 classes of lymphocytes in blood
T cells
B cells
NK cells
74
Define lymphoid tissues
Connective tissues dominated by lymphocytes
75
What is a lymphoid nodule?
Lymphocytes that are densely packed in an area of areolar tissue
76
Where do lymphoid nodules occur?
In the connective tissue deep to the epithelia lining the respiratory tract, where they are known as tonsils, and along the digestive, respiratory, urinary, and reproductive tracts. Also found within more complex lymphoid organs, such as lymph nodes or the spleen
77
What is the central zone called in a nodule, and what does it contain?
A germinal center, which contains dividing lymphocytes
78
What are the tonsils?
Large lymphoid nodules in the walls of the pharynx
79
Name the 5 tonsils
A single pharyngeal tonsil
Left and right palatine tonsils
A pair of lingual tonsils
80
When are lingual tonsils visible?
When they become infected and swollen
81
What is tonsillitis?
An inflammation of the tonsils
82
Which tonsils are typically affected by tonsillitis?
The palatine tonsils
83
When do tonsils reach their largest size?
Puberty, then they begin to atrophy
84
What does MALT stand for?
Mucosa-associated lymphoid tissue
85
What is MALT?
The collection of lymphoid tissues that protect the epithelia of the digestive, respiratory, urinary, and reproductive systems
86
Define aggregated lymphoid nodules
Clusters of lymphoid nodules deep to the epithelial lining of the intestine
87
Define appendix
A tube-shaped sac opening into the junction between the small and large intestines with walls containing a mass of fused lymphoid nodules
88
What do lymphoid organs include?
The lymph nodes, thymus, and spleen
89
What separates lymphoid organs?
A fibrous connective tissue capsule
90
Where are the greatest number of lymph nodes located?
In the neck, axillae, and groin
91
What covers each lymph node?
A dense connective tissue capsule
92
Describe the interior of a lymph node
Bundles of collagen fibers extend from the capsule into the interior
93
Shape of a lymph node
Kidney beam
94
What are the two sets of lymphatic vessels?
Afferent lymphatics
| Efferent lymphatics
95
What do afferent lymphatics do?
Bring lymph to the lymph node from peripheral tissues
96
What do efferent lymphatics do?
Carry lymph away from the lymph node and toward the venous circulation
97
What happens in secondary lymphoid tissues and organs?
It is where lymphocytes are activated and cloned
98
What do lymphatic vessels carry?
Lymph
99
Lymph flows along a network of _____, the smallest of which are the _____
Lymphatic vessels
| Lymphatic capillaries
100
What are lymphoid cells?
Immune system cells found in lymphoid tissues and the cells that support these tissues
101
What are immune system cells that function in defense?
Phagocytes and lymphocytes
102
What is the significance of where lymphoid tissues/organs are located?
They are distributed in areas that are vulnerable to injury or invasion
103
What is a lymph node?
Encapsulated masses of lymphoid tissue
104
What is the paracortex dominated by?
T cells
105
What type of cell do the cortex and medulla contain?
B cells
106
Where is the thymus found?
Behind the sternum, in the anterior mediastinum
107
What do epithelial reticular cells regulate?
T cell development and function
108
What does the adult spleen contain?
The largest mass of lymphoid tissue in the body
109
What do the cellular components of the spleen form?
Pulp
110
What does red pulp contain?
Large numbers of RBCs
111
What does white pulp resemble?
Lymphoid nodules
112
The lymphatic system is a major component of the body's defenses, which are classified as either:
1
2
1. Innate (nonspecific) immunity
| 2. Adaptive (specific) immunity
113
What is innate (nonspecific) immunity?
Protects without distinguishing one threat from another
114
What is adaptive (specific) immunity?
Protections against particular threats only
115
What is the immune response?
The body's reaction to infectious agents and other abnormal substances
116
Where do lymphocytes continuously migrate?
Into and out of the blood through the lymphoid tissues and organs
117
What is lymphocytopoiesis?
Lymphocyte production
118
What does lymphocytopoiesis involve?
The red bone marrow, thymus, and peripheral lymphoid tissues
119
What do innate (nonspecific) defenses do?
Prevent the approach, deny the entry, or limit the spread of living or nonliving hazards
120
In innate defenses, what do physical barriers include?
Skin, mucous membranes, hair, epithelia, and various secretions of the integumentary and digestive systems
121
What are the two types of phagocytes?
Microphages and macrophages
122
What are microphages?
Neutrophils and eosinophils in circulating blood
123
How do phagocytes leave the bloodstream?
By emigration - migration between adjacent endothelial cells
124
What do phagocytes exhibit?
Chemotaxis - sensitivity and orientation to chemical stimuli
125
What do NK cells attack?
Foreign cells
Normal cells infected with viruses
Cancer cells
126
What do NK cells provide?
Immune surveillance
127
What does immune surveillance involve?
Constant monitoring of normal tissues by NK cells that are sensitive to abnormal antigen on the surfaces of otherwise normal cells
128
NK cells kill cancer cells that have ____ on their surfaces
tumor-specific antigens
129
What are interferons?
Small proteins released by cells infected with viruses
130
What do interferons trigger?
The production of antiviral proteins, which interfere with viral replication inside the cell
131
What are cytokines?
Chemical messengers released by tissue cells to coordinate local activities
132
What are interferons classified as?
Cytokines
133
How many complement proteins make up the complement system?
30
134
What do complement proteins interact with each other in cascades to do?
Destroy target cell walls
Enhance phagocytosis
Stimulate inflammation
135
What are the 3 ways the complement system can be activated?
Classical pathway
Lectin pathway
Alternative pathway
136
What is inflammation?
A localized tissue response to injury
137
What is fever?
A body temperature greater than 37.2°C or 99°F
138
What does fever do to the body?
Inhibit pathogens and accelerate metabolic processes
139
What do pyrogens do?
Reset the body's thermostat and raise the temperature
140
What are T cells responsible for?
Cell-mediated (cellular) immunity
141
What are the 4 primary types of T cells?
Cytotoxic
Helper
Regulatory
Memory
142
What type of immunity do B cells provide?
Antibody-mediated (humoral) immunity
143
What do B cells differentiate into?
Plasma cells, which secrete antibodies
144
What is the immune response triggered by?
The presence of specific antigens and includes cell-mediated and antibody-mediated defenses
145
What are the 2 types of immunity?
Innate immunity
| Adaptive immunity
146
What are the 2 types of adaptive immunity?
Active immunity and passive immunity
147
What is innate immunity?
Innate (nonspecific) immunity is a type of body defense that you are born with and does not distinguish among different threats
148
What is adaptive immunity?
Adaptive (specific) immunity is acquired after birth and after exposure to a particular antigen
149
What is active immunity?
Develops after exposure to an antigen
150
What is passive immunity?
Produced by transferring antibodies from another source
151
What are the 2 types of active immunity?
Naturally acquired active immunity
| Artificially acquired active immunity
152
What are the 2 types of passive immunity?
Naturally acquired passive immunity
| Artificially acquired passive immunity
153
What is naturally acquired active immunity?
Normally begins to develop after birth
| Continues to build as you encounter new pathogens or other antigens
154
What is artificially acquired active immunity?
Stimulates the body to produce antibodies under controlled conditions so you will be able to overcome natural exposure to the pathogen in the future
155
What is naturally acquired passive immunity?
A baby receives antibodies from the mother, either by crossing the placenta or through breast milk
156
What is artificially acquired passive immunity?
A person receives antibodies to fight infection or prevent disease. Ex. rabies virus
157
Which immunity is provided by receiving a vaccine?
Artificially acquired active immunity
158
What are the four general properties exhibited by immunity?
Specificity
Versatility
Memory
Tolerance
159
Why does specificity occur?
Because T cells and B cells respond to the molecular structure of specific antigens
160
What is versatility based on?
The large diversity of lymphocytes in the body and from variability in the structure of synthesized antibodies
161
What do memory cells enable?
The immune system to remember previous target antigens
162
What is tolerance?
The ability of the immune system to ignore some antigens, such as those of normal body cells
163
When does antigen presentation occur?
When an antigen-glycoprotein combination appears in the plasma membrane of an antigen-presenting cell (typically a macrophage or dendritic cell). T cells sensitive to this combination are activated if they contact the membrane of the antigen-presenting cell
164
What does MHC stand for?
Major histocompatibility complex
165
What is MHC?
A group of genes that code for proteins found on the surfaces of cells that help the immune system recognize foreign substances
166
What are APCs (antigen-presenting cells) involved in?
Antigen stimulation
167
What do lymphocytes respond to?
An antigen bound to either a class I or a class II MHC protein in a process called antigen recognition
168
Where are class I MHC proteins located?
In all nucleated body cell
169
Where are class II MHC proteins located?
Only in APCs (antigen-presenting cells) and lymphocytes
170
Whether a T cell responds to antigens held in class I or class II MHC proteins depends on what?
The structure of the T cell plasma membrane
171
What are the proteins within T cell plasma membranes?
CD markers
172
Which markers are present on all T cells?
CD3 markers
173
What markers are present on cytotoxic and regulatory T cells?
CD8 markers
174
What markers are on all helper T cells?
CD4 markers
175
What happens when each type of CD8 cell responds quickly to a class I MHC-bound antigen?
One type of CD8 cell gives rise to large numbers of cytotoxic T cells and memory T cells. The other type of CD8 cell responds more slowly, giving rise to small numbers of regulatory T cells
176
What do cytotoxic T cells do?
Seek out and destroy abnormal and infected cells
177
What are the 3 ways the cytotoxin T cell may destroy the target cell?
1. Release perforins to destroy the target cell’s plasma membrane
2. Release cytokines and activate genes in the target cell’s nucleus telling that cell to undergo apoptosis
3. Secrete a poisonous lymphotoxin to kill the target cell
178
What does cell-mediated immunity result from?
The activation of CD8 cells by antigens bound to class I MHCs
179
During cell-mediated immunity, what happens when the CD8 cells are activated?
Most of these T cells divide to generated cytotoxic T cells and memory T cells
180
What do regulatory T cells moderate the responses of?
Other T cells and B cells
181
Helper T cells respond to antigens presented by _____
Class II MHC proteins
182
What happens when helper T cells are activated?
They secrete cytokines that aid in coordinating adaptive and innate defenses and also regulate cell-mediated and antibody-mediated immunity
183
What are cytokines?
Chemical messengers coordinated by the immune system
184
What do interleukins do?
- Increase T cell sensitivity to antigens exposed on macrophage membranes
- Stimulate B cell activity, plasma cell formation, and antibody production
- Enhance innate defenses
- Moderate the immune response
185
What do interferons (IFNs) do?
Slow the spread of a virus by making the synthesizing cell and its neighbors resistant to viral infections
186
What do tumor necrosis factors (TNFs) do?
Slow tumor growth
Kill tumor cells
Act as pyrogens
187
What are colony-stimulating factors (CSFs)?
Factors produced by active T cells, cells of the monocyte-macrophage group, endothelial cells, and fibroblasts
188
When do B cells become sensitized?
When antibody molecules in their plasma membranes bind antigens. The antigens are then displayed on the class II MHC proteins of the B cells, which become activated by helper T cells activated by the same antigen
189
What can an active B cell differentiate into?
A plasma cell or produce daughter cells that differentiate into plasma cells and memory B cells
190
What are produced by plasma cells?
Antibodies
191
What does a Y-shaped antibody molecule consist of?
Two parallel pairs of polypeptide chains containing constant and variable segments
192
What are the five classes of antibodies (immunoglobulins)?
```
IgG
IgE
IgD
IgM
IgA
```
193
What do IgG do?
They are responsible for resistance against many viruses, bacteria, and bacterial toxins
194
What do IgE do?
They release chemicals that accelerate local inflammation
195
What do IgD do?
It is an individual molecule on the surface of B cells, where it can bind antigens in the extracellular fluid
196
What do IgM do?
They are the first type of antibody secreted after an antigen arrives
197
What do IgA do?
Attack pathogens before they gain access to internal tissues
198
Where are IgA found?
On glandular secretions such as mucus, tears, saliva, and semen
199
What is it called when antibody molecule bind to an antigen?
An antigen-antibody complex
200
What are the affects that appear after an antibody molecule binds to an antigen?
```
Neutralization
Precipitation
Agglutination
Opsonization
Stimulation of inflammation
Preventing of bacterial or viral adhesion
```
201
What is neutralization?
Antibody binding that prevents viruses or bacterial toxins from binding to body cells
202
What is precipitation?
The formation of an insoluble immune complex
203
What is agglutination?
The formation of large complexes
204
What is opsonization?
The coating of pathogens with antibodies and complement proteins to enhance phagocytosis
205
What is the primary response?
The initial immune response to an antigen?
206
What is the secondary response?
All following contacts with the same antigen after the initial immune response; the most important feature of immune systems
207
Why does the primary response take time to develop?
Because the antigen must activate the appropriate B cells. These cells must then differentiate into plasma cells. As plasma cells differentiation and begin secreting, the concentration of circulating antibodies makes a gradual, sustained rise
208
How long does the primary response take to develop peak antibody levels?
About 2 weeks
209
In humoral immunity, the antibodies first produced by plasma cells are the agents of the ______
Primary response
210
During which response does the maximum antibody level appear during?
The secondary response to antigen exposure
211
Are the initial steps in the immune responses to viral and bacterial infections the same or different?
Different
212
What is immunocompetence?
The ability to produce an immune response after exposure to an antigen
213
What type of immunity does a developing fetus acquire?
Passive immunity from antibodies in the maternal bloodstream
214
What type of immunity does an infant develop after delivery?
Active immunity following exposure to environmental antigens
215
What is released during periods of stress?
Interleukin-1 is released by active macrophages, which triggers the release of ACTH by the anterior lobe of the pituitary gland
216
What is produced by the adrenal cortex that moderates the immune response? What happens to their long-term secretion?
Glucocorticoids. Their long-term secretion can lower a person's resistance to disease
217
What are hypersensitivities?
Allergies. Inappropriate or excessive immune responses to allergens
218
What are allergens?
Antigens that trigger allergic reactions
219
What are the 4 types of allergies?
Type 1 - Immediate hypersensitivity
Type 2 - Cytotoxic reactions
Type 3 - Immune complex disorders
Type 4 - Delayed hypersensitivity
220
What happens during anaphylaxis?
A circulating allergen affects mast cells throughout the body
221
When do autoimmune disorders develop?
When the immune response inappropriately targets normal body cells and tissues
222
What happens during an immunodeficiency disease?
Either the immune system does not develop normally, or the immune response is blocked
223
What happens to the immune system during aging?
It becomes less effective at combating disease
224
Which system has extensive interactions with the nervous and endocrine systems?
The lymphatic system
225
If you are immunocompetent, what do you have?
A normal immune response
226
People have autoimmune diseases because they don't have ______
Immunocompetence
227
Where do B cells mature?
The red bone marrow
228
Where do T cells mature?
The thymus
229
What is the protein responsible for the development into B cells and NK cells?
Interleukin 7
230
Which cells are responsible for immunological surveillance?
NK cells
231
B cells become _____
Plasma cells
232
What is the lymphocyte timeline of T cells?
1. Hemocytoblast
2. Lymphoid stem cell
3. Travels to thymus
4. T cell maturation
5. Differentiation of one of the 4 types of T cells
233
What is the lymphocyte timeline of B cells?
1. Hemocytoblast
2. Lymphoid stem cell
3. Interleukin-7
4. Mature in red bone marrow and enter bloodstream; move into peripheral tissues
234
What is the function of the spleen?
Removes dead or damaged RBCs
