ch 21 lymphoid and immune systems Flashcards
microbiome
microorganisms that reside on and in the human body
microbiome
many are beneficial but some have potential to be
harmful
microbiome
also constantly exposed to potentially
harmful microorganisms from external environment
microbiome
body is protected by the
immune system
immune system
not an organ system
but a cell population that inhabits all organs and defends the body from agents of disease
immune system
immune cells concentrated in a true organ system
lymphoid system
immune system: lymphoid system
network of organs vein-like vesseles that recover
fluid
immune system: lymphoid system
inspect it for
disease agents
immune system
activate immune
responses
immune system
return fluid to the
bloodstream
the lymphoid system & fluid recovery
lymphoid (lymphatic) system
lymphatic vessels that penetrate nearly every tissue and a
collection of lymphoid tissues and organs that produce immune cells
the lymphoid system & fluid recovery
fluid recovery
fluid continually filters from the blood capillaries into the tissue spaces
the lymphoid system: fluid recovery
blood capillaries reabsorb ____ and the rest ____ enters the lymphatic vessel
85%
15%
the lymphoid system: fluid recovery
lymphedema
swelling due to interference in lymphatic drainage
functions of the lymphatic system: immune surveillance
excess filtered fluid picks up
foreign cells and chemical from the tissues
functions of the lymphatic system: immune surveillance
passes through lymph nodes where
immune cells stand guard against foreign matter
functions of the lymphatic system: immune surveillance
activates a protective immune
response
functions of the lymphatic system: lipid absorption
lacteals
special vessels in small intestine absorb dietary lipids that are not absorbed by the blood capillaries
components of the lymphoid system
lymph
the recovered fluid
components of the lymphoid system
lymphatic vessels
transport the lymph
components of the lymphoid system
lymphoid tissue
aggregates of lymphocytes and macrophages that populate many organs of the body
components of the lymphoid system
lymphoid organs
organs where lymphoid cells are concentrated
surrounded by connective tissue capsules
lymph vs blood plasma
lymph
clear
colorless fluid
similar to plasma
but low in protein
lymph vs blood plasma: lymph
orginates as tissue fluid taken up by
lymphatic vessels
lymph vs blood plasma: lymph
chemical composition varies in
different places
(in intestines, after lymph nodes)
lymph and the lymphatic vessels
lymph flows through a system of
lymphatic vessels
(lymphatics)
lymph and the lymphatic vessels
lymphatic capillaries are also called
terminal lymphatics
lymph and the lymphatic vessels: lymphatic capillaries
microscopic vessels that penetrate nearly every
tissue of the body
lymph and the lymphatic vessels: lymphatic capillaries
absent from
cartilage
cornea
bone
bone marrow
lymph and the lymphatic vessels: lymphatic capillaries
capillary wall
endothelial cells overlapping each other like roof shingles
lymph and the lymphatic vessels: lymphatic capillaries
closed at one end
cells tethered to surrounding tissue by anchoring filaments
lymph and the lymphatic vessels: lymphatic capillaries
gaps (intercellular cells)
between the cells are large enough to allow bacteria and cells to enter lymphatic capillary
lymph and the lymphatic vessels: lymphatic capillaries
endothelium creates
valve-like flaps that open when interstitial fluis pressure is high and close when it is low
lymph and the lymphatic vessels
larger lymphatic vessels composed of 3 layers
- tunica interna: endothelium and valves
- tunica media: elastic fibers, smooth musce
- tuncia externa: thin outer layer
lymph and the lymphatic vessels
lymphatic capillaries merge to form
collecting vessels
which converge to form larger lymphatic trunks
* solitary intestinal trunk
* paired jugular
* subclavian
* bronchomediastinal
* intercostal
* lumbar trunks
each drains a major portion of body
lymph and the lymphatic vessels: lymphatic vessels
lymphatic trunks converge to form
2 collecting ducts
lymph and the lymphatic vessels: collecting ducts
right lymphatic duct
receives lymph from right arm
right side of head and thorax
empties into right subclavian vein
lymph and the lymphatic vessels: collecting ducts
thoracic duct
larger and longer
begins as a sac in abdomen called the cysterna chyli
receives lymph from below diaphragm, left arm, left side of head, neck, and thorax
empties into left subclavian vein
lymph and the lymphatic vessels: collecting ducts
subclavian veins collect from
collecting ducts
lymph and the lymphatic vessels: collecting ducts
summary of path from the tissue fluid back to the bloodstream
- lymphatic capillaries
- collecting vessels
- 11 lymphatic trunks
- two collecting ducts
- subclavian veins
lymph passes through lymph nodes along the way
lymph and the lymphatic vessels: flow of lymph
lymph flows under forces similar to those that govern
venous return
except no pump (heart)
lymph and the lymphatic vessels: flow of lymph
lymph flows at low pressure and slower speed than
venous blood
lymph and the lymphatic vessels: flow of lymph
stretching of vessels stimulate their
contraction
lymph and the lymphatic vessels: flow of lymph
moved along by rythmic contractions of
- lymphatic vessels
- squeezing of skeletal muscles
- rhythmic pulsations of nearby arteries
- a thoracic (respiratory) pump
- rapidly flowing blood in subclavian vein draws lymph into it
glymphatic system of the brain
glymphatic system
lymphatic-resembling vessels associated with neuroglia
glymphatic system of the brain
arteries that penetrate the brain tissue are surrounded in perivascular tunnels containing a mix of cerebrospinal fluid (CSF) and interstitial fluid (ISF)
- arterial pulsation help drive fluid mix into brain tissue
- CSF-ISF composition is regulated by astrocytes
lymphoid cells
neutrophils
antibacterial
lymphoid cells
natural killer cells
lymphocytes that attack and destroy infected host cells and cancerous cells
lymphoid cells
T lymphocytes (T cells)
mature in thymus
lymphoid cells
B lymphocytes
activation causes proliferation and differentiation into plasma cells that produce antibodies
lymphoid cells
macrophages
large phagocytic cells
are APCs
lymphoid cells
antigen presenting cells
they displat antigens on surface to alert other immune cells
lymphoid cells
dendritic cells
APCs found in skin, mucous membranes, and lymphoid organs
lymphoid tissues
lymphoid tissue
aggregations of lymphocytes in the connective tissues of mucous membranes and various organs
lymphoid tissues
dense lymphoid tissue
lymphocytes are scattered (not densely clustered)
* Prevalent in body passages open to the exterior: respiratory, digestive, urinary, and reproductive tracts
* In mucous membranes, diffuse lymphoid tissue is called mucosa-associated lymphoid tissue (MALT)
Lymphoid
Lymphoid nodules (follicles
lymphocytes and
macrophages gather in dense masses
* May be temporary or permanent features of some tissues
* Aggregated lymphoid nodules (formerly Peyer patches)—large
clusters of nodules in the small intestine
Lymphatic organs
Have connective tissue capsule that
separates lymphatic
tissue from neighboring tissues
Lymphatic organs
Primary lymphoid organs
include red bone marrow and
thymus
* Sites where T and B cells become immunocompetent—able to
recognize and respond to antigens
Lymphatic organs
Secondary lymphoid organ
include lymph nodes, tonsils,
and spleen
* Locations where immunocompetent cells migrate and populate
Lymphoid Organs
Red bone marrow
soft, loosely organized, highly vascular
material separated from osseous tissue by endosteum of
bone
* Involved in hematopoiesis (blood formation) and immunity
* Blood-forming cells attached to reticular cells and other
elements of marrow stroma
* Secrete colony-stimulating factors that stimulate stem cells to
produce the formed elements
* As blood cells mature, they push their way through the
reticular and endothelial cells to enter the sinus and flow
away in the bloodstream
Thymus: Lymphoid Organs
Thymus
member of the endocrine, lymphoid, and immune
systems
* Bilobed organ located in superior mediastinum between
sternum and aortic arch
* Houses developing T cells and secretes hormones
regulating their activity
* With age, exhibits large degree of involution—
degeneration, shrinkage
* By age 65, unable to make new T cells
* State of immunosenescence leaves older people vulnerable to
infections, cancer
Thymus
thymus
- Fibrous capsule gives off trabeculae (septa) that divide the
gland into several lobes - Lobes have cortex and medulla populated by T cells
- Thymic epithelial cells involved in T cell development
- Secrete signaling molecules thymosin, thymopoietin, thymulin,
interleukins, and interferon - Cortical epithelial cells—along with pericytes, surround capillaries
to form blood-thymus barrier
Lymphoid Organs
Lymph nodes
bean-shaped structures that cleanse lymph
and are sites of lymphocyte activation
* Most numerous lymphoid organs, about 450 in typical
young adult
* Enclosed with fibrous capsule with trabeculae that divide
interior into compartments
* Parenchyma divided into cortex and medulla
* Germinal centers in cortex—where B cells multiply and
differentiate into plasma cells
* Several afferent lymphatic vessels lead into the node
along its convex surface
* Lymph leaves the node through one to three efferent
lymphatic vessels that leave the hilum
Lymphoid Organs
Lymph nodes Concentrated in the following locations:
- Cervical lymph nodes in neck
- Axillary lymph nodes in armpit
- Thoracic lymph nodes in thoracic cavity, especially mediastinum
- Abdominal lymph nodes in posterior abdominopelvic wall
- Intestinal and mesenteric lymph nodes in mesenteries and near
appendix and intestines - Inguinal lymph nodes in groin
- Popliteal lymph nodes in back of knee
Lymphoid Organs
Lymphadenitis
swollen, painful lymph node responding
to foreign antigen
Lymphoid Organs
Lymphadenopathy
collective term for all lymph node
diseases
Lymph Nodes and Metastatic Cancer
Metastasis
cancerous cells break free from original primary
tumor, travel to other sites in the body and establish new
tumors
* Metastasizing cells easily enter lymphatic vessels
* Tend to lodge in the first lymph node they encounter,
multiply there, and eventually destroy the node
* Cancerous nodes usually swollen, firm, painless
* Tend to spread to the next node downstream
* Treatment of breast cancer is lumpectomy, mastectomy,
along with removal of nearby axillary nodes
Lymphoid Organs
Tonsils
patches of lymphoid tissue located at the entrance
to the pharynx
* Guard against ingested or inhaled pathogens
* Covered with epithelium and has deep pits—tonsillar
crypts, lined by lymphoid nodules
* Incomplete fibrous capsule
* Three main sets of tonsils:
* Single pharyngeal tonsil (adenoids) on wall of pharynx
* Pair of palatine tonsils at posterior margin of oral cavity
* Numerous lingual tonsils concentrated on each side of base of
tongue
* Tonsillitis—acute inflammation of palatine tonsils
Lymphoid Organs
Spleen
the body’s largest lymphoid organ
* Inferior to diaphragm and posterolateral to stomach
* Medial hilum for passage of splenic artery and vein, and
lymphatic vessels
* Parenchyma exhibits two types of tissue:
* Red pulp—sinuses filled with erythrocytes
* White pulp—lymphocytes, macrophages surrounding small
branches of splenic artery
Lymphoid Organs
Functions of the spleen:
- For old, fragile RBCs, spleen is “erythrocyte graveyard”—
macrophages recognize and phagocytize them - Blood cell production in fetus (and very anemic adults)
- Lymphocytes, macrophages of white pulp monitors blood for foreign
antigens, maintains army of monocytes for release when needed - Stabilizes blood volume through plasma transfers to lymphoid
system - Spleen is highly vascular and vulnerable to trauma and
infection - Ruptured spleen requires splenectomy, but this leaves person
susceptible to future infections, premature death
Innate ImmuInnate
Pathogens
agents capable of producing disease, including
viruses, bacteria, fungi, and other microbes
Three lines of defenses against pathogens:
* First line of defense—skin and mucous membranes,
which serve as barriers
* Second line of defense—protections against pathogens
that break the skin, mucous membrane barriers
* Leukocytes and macrophages, antimicrobial proteins, natural killer
cells, fever, and inflammation
* Third line of defense—adaptive immunity, mechanisms
that defeat a specific pathogen and leave the body with a
memory of it
Innate Immunity
Immune system
widely distributed population of cells, diverse
chemicals, physical barriers, and physiological responses
Divided into two broad forms of defense:
* Innate immunity—defenses we are born with (innate); protect
us from broad spectrum of disease agents
* It has a local effect: defends at point of invasion, but there are
exceptions (fever)
* It is nonspecific: defenses are against a broad spectrum of
disease agents, rather than one particular pathogen
* Lacks memory: does not “remember” exposure to a specific
pathogen
* Adaptive immunity—defenses against specific pathogens,
developed only upon exposure (adaptive), and maintains
immune memory
External Barriers
First line of defense: skin and mucous membranes
Protective features of the skin:
- Toughness of keratin, difficult to penetrate
- Too dry and nutrient-poor to support much microbial growth
- Microbes adhered to skin are continually shed with dead
keratinocytes - Presence of an acid mantle—thin film of lactic and fatty acids from
sweat and sebum that inhibits bacterial growth - Dermcidin, defensins, and cathelicidins: peptides in the skin that
kill microbe
Leukocytes and Macrophages
When skin and mucous membranes are penetrated, cellular
defenses await:
- Phagocytes—cells that engulf foreign matter
Five types of leukocytes (some of which are phagocytes): - Neutrophils
- Eosinophils
- Basophils
- Monocytes
- Lymphocytes
Leukocytes:
Neutrophils
- Wander in connective tissue killing bacteria
- Can ensnare bacteria by releasing a neutrophil extracellular trap
(NET)—web of nuclear chromatin and proteins - Can kill by phagocytizing and digesting microbe, or by release of
bactericidal chemicals to create killing zone around neutrophi
Leukocytes
Eosinophils
- Found especially in mucous membranes
- Guard against large parasites: tapeworms, roundworms
- Participate in inflammation
- React to allergens and participate in allergic reactions
Leukocytes
Basophils
- Secrete chemicals that aid mobility and action of other leukocytes
- Leukotrienes: activate and attract neutrophils and eosinophils
- Histamine: a vasodilator; increases blood flow and speeds delivery
of leukocytes to the area - Heparin: inhibits clot formation that would impede leukocyte mobility
- Mast cells also secrete these substances; similar to basophils but
found in connective tissues
Leukocytes
Lymphocytes
- Includes T cells and B cells, which participate in adaptive immunity
- Also includes natural killer (NK) cells, part of innate immuniy
Leukocytes
Monocytes
- Emigrate from the blood into connective tissues and transform into
macrophages - Macrophage system—all the body’s avidly phagocytic cells, except
leukocytes; includes monocytes, macrophages, dendritic cells, and
others - Some macrophages are wandering cells; others are fixed in place
- Examples of specialized forms in specific locations: microglia,
alveolar macrophages, and stellate macrophages
Antimicrobial Proteins:Three outcomes of complement activation:
Inflammation
- C3a stimulates mast cells and basophils to secrete histamine and
other inflammatory chemicals - Activates and attracts neutrophils and macrophages
Antimicrobial Proteins:Three outcomes of complement activation:
Immune clearance
- C3b binds with antigen–antibody (Ag-Ab) complexes to red blood
cells that circulate through liver and spleen - Macrophages of those organs strip off and destroy the Ag–Ab
complexes leaving RBCs unharmed
Antimicrobial Proteins:Three outcomes of complement activation:
Phagocytosis
C3b coats microbial cells (opsonization) and serves as binding
sites for phagocyte attachmen
Antimicrobial Proteins:Three outcomes of complement activation:
Cytolysis
- Complement C3b initiates formation of C5b
- C5b aggregates with other complement proteins within plasma
membrane of microbe - Form membrane attack complex—a hole in the target cell
membrane - Electrolytes leak out, water flows in rapidly, cell ruptures
(cytolysis)
Natural killer (NK) cells
continually patrol body looking for
pathogens and diseased host cells
NK cells attack and destroy microbes, transplanted cells,
cells infected with viruses, and cancer cells
* Recognize infected cell and bind to it
* Release proteins called perforins, which polymerize to
form a ring and create a hole in its plasma membrane
Secrete a group of protein-degrading enzymes—granzymes
* Enter through pore and degrade cellular enzymes and
induce apoptosis (programmed cell death)
Fever
Fever (pyrexia)
an abnormal elevation of body
temperature
* Febrile—pertaining to fever
* Results from trauma, infections, drug reactions, brain
tumors, and other causes
* Defense mechanism that, in moderation, does more good
than harm
* Promotes interferon activity
* Elevates metabolic rate and accelerates tissue repair
* Inhibits reproduction of bacteria and viruses
* Recovery is sometimes faster when allowing fever to take
its course, rather than taking antipyretics—fever-reducing
medications
Fever
fever usually triggered by
exogenous pyrogens—fever-
producing agents originating outside the body
* Examples: glycolipids on bacterial and viral surfaces
* Endogenous pyrogens—fever-producing agents
originating from within body (peptides secreted by
neutrophils, macrophages)
* These raise hypothalamic set point for body temperature
* Neurons in the anterior hypothalamus secrete prostaglandin 2E ,
which also raises set point
* Stages of fever: onset, stadium, defervescence
Inflammation
Inflammation
local defensive response to tissue injury,
including trauma and infection
* General purposes of inflammation
* Limit spread of pathogens, then destroys them
* Remove debris from damaged tissue and initiate tissue repair
* Four cardinal signs of inflammation:
* Redness, swelling, heat, pain
* Involves numerous cytokines—small proteins that
function in chemical communication between cells
* Alter physiology of receiving cell
* Include interferon, interleukins, tumor necrosis factor, chemotactic
factors, and others
Inflammation
Mobilization of defenses:
- Most immediate requirement after tissue injury is to get
defensive leukocytes to the site quickly - Achieved by local hyperemia—increasing blood flow
- Local vasodilation due to vasoactive chemicals
- Histamine, leukotrienes, and other cytokines
- Secreted by basophils, mast cells, cells damaged by trauma,
toxins, or organisms triggering inflammation - Hyperemia also washes toxins and metabolic waste from the site
more rapidly
Inflammation
mobilization of defenses continued
- In the mobilization events so far, we can see the basis for
the four cardinal signs of inflammation: - Heat: results from hyperemia
- Redness: due to hyperemia, and extravasated RBCs in the tissue
- Swelling (edema): due to increased fluid filtration from the
capillaries - Pain: from direct injury to the nerves, pressure on the nerves from
edema, stimulation of pain receptors by prostaglandins, bacterial
toxins, and bradykinin
Inflammation
Containment and destruction of pathogens:
- Another priority of inflammation is to prevent pathogens
from spreading throughout body - Fibrinogen filters into tissue fluid, clots to form a sticky
mesh that walls off microbes - Heparin prevents clotting at site of injury
- Pathogens are in a fluid pocket surrounded by clot
- Attacked by antibodies, phagocytes, and other defenses
- Neutrophils accumulate at the injury site within an hour
- After leaving the bloodstream, they exhibit chemotaxis—attraction
to chemicals such as bradykinin and leukotrienes that guide them
to the injury site
Inflammation
Containment and destruction of pathogens (continued)
- Neutrophils quickly respond to and kill bacteria
- Phagocytosis
- Respiratory burst
- Secrete cytokines for recruitment of macrophages and additional
neutrophils - Macrophages and T cells secrete colony-stimulating factor to
stimulate leukopoiesis (production of more leukocytes) thereby
raising WBC counts in blood - Neutrophilia—5,000 cells/μL to 25,000 cells/μL in bacterial infection
- Eosinophilia—elevated eosinophil count in allergy or parasitic
infection
Inflammation
Tissue cleanup and repair:
- Primarily involves monocytes, which arrive in 8 to 12 hours
and become macrophages - Engulf and destroy bacteria, damaged host cells, and dead and
dying neutrophils - Edema contributes to tissue cleanup
- Swelling compresses veins and reduces venous drainage
- Forces open valves of lymphatic capillaries, promoting lymphatic
drainage of bacteria, dead cells, and debris - Pus—yellow accumulation of dead neutrophils, bacteria,
cellular debris, and tissue fluid - Abscess: accumulation of pus in a tissue cavity
inflammation
tissue cleanup and repair (continued)
- Platelet-derived growth factor is secreted by blood
platelets and endothelial cells in injured area - Stimulates fibroblasts to multiply, synthesize collagen
- Hyperemia delivers oxygen, amino acids, and other
necessities for protein synthesis - Increased heat increases metabolic rate, speeds mitosis
and tissue repair - Fibrin clot forms a scaffold for tissue reconstruction
- Pain makes us limit the use of a body part so it has a
chance to rest and heal
Adaptive Immunity
Adaptive immunity serves as the third line of defense; has
three characteristics distinguish immunity from innate
immunity
- It has a systemic effect: acts throughout the body
- It exhibits specificity: generates protection and immunity
to specific pathogens on an individual basis - It has a memory: when re-exposed to the same pathogen,
the body reacts so quickly that there is no noticeable illness
Forms of Adaptive Immunity
Two types of adaptive immunity:
Cellular (cell-mediated) immunity
- Lymphocytes directly attack and destroy foreign cells or diseased
host cells - Rids the body of pathogens that reside inside human cells where
they are inaccessible to antibodies - Also acts against parasitic worms, cancer cells, and transplanted
cells
Forms of Adaptive Immunity
Two types of adaptive immunity:
Humoral (antibody-mediated) immunity
- Mediated by antibodies that do not directly destroy a pathogen but
tag it for destruction - Effective against extracellular viruses, bacteria, yeasts, protozoans,
and molecular (noncellular) disease agents such as toxins, venoms,
and allergens
