Lymphatic System

Ch. 22

What are the main components of the Lymphatic system?

1. Lymph

2. Lymphatic Vessels

3. Lymphatic Tissues

Lymph

Fluid (similar to IF)

• between tissue cells & lymph vessels

Lymphatic vessels

Help transport Lymph

Lymphatic Tissue

Specialized reticular C.T.

• contains many Lymphocytes (T & B cells)

What are the main functions of the Lymphatic system?

1. Draining— removes/returns excess IF to the blood to maintain blood volume

2. Transporting— dietary fats ("Lacteals”) from the GI tract

3. Immune responses— Cell-mediated or Antibody-mediated

Lacteals

Specialized lymphatic capillaries (small intestine) that carry dietary fats

Where can Lymph structures be found in the skin?

Veins

Where can Lymph structures be found in the viscera?

Arteries

Lymph Circulation

1. Capillaries

2. Vessels

3. Nodes

4. Trunks

5. Ducts

What are the main Lymph Trunks (drains)?

1. Lumbar— lower limbs (+ pelvis, kidneys, adrenal glands, & abdominal wall)

2. Intestinal— stomach, intestines, pancreas, spleen, & part of liver

3. Bronchomediastinal— thoracic wall, lung, & heart

4. Subclavian— upper limbs

5. Jugular— head & neck

Which Lymph trunk drains the wall & viscera of the Pelvis?

Lumbar trunk

Which Lymph trunk drains the Lungs?

Bronchomediastinal trunk

Which Lymph trunk drains the Spleen?

Intestinal trunk

Which Lymph trunk drains the Head + Neck?

Jugular trunk

Which Lymph trunk drains the Upper limbs?

Subclavian trunk

Thoracic ("left") Duct

Main duct for returning lymph → blood

• Drains everything, BUT the right upper side

Routes of the Thoracic (“left”) Duct

Receives lymph:

• R/L Lumbar & Intestinal trunks

• L Bronchomediastinal, Subclavian, & Jugular trunks

Empties lymph into:

• L Brachiocephalic vein

Routes of the Right Lymphatic Duct

Receives lymph:

• R Bronchomediastinal, Subclavian, & Jugular trunks

Empties lymph into:

• R Brachiocephalic vein

What is the function of Filtration at the Blood capillaries?

• Turns excess filtered fluid (~3L/day) into Lymph

• Returns any lost plasma proteins

Primary lymphatic organs

Stem cells divide → Mature Immunocompetent T & B cells

• Red bone marrow

• Thymus

Secondary lymphatic organs

Site of Immune responses

• Lymph nodes

• Lymph modules

• Spleen

Thymus

In mediastinum (between sternum & aorta)

→ Site of pre-T cell maturation (immunocompetent)

Why is the Thymus known as a “Bilobed” organ?

Because it contains…

Capsule + Trabeculae (cortex, medulla) = 2 Lobules

Thymic Cortex (#bootcamp)

Pre-T cells migrate from the RBM to here = Maturation

• dendritic cells + specialized epithelial cells help w/ the process

• macrophages clear out the dead cells

Thymic Medulla (#graduation)

Contains the newly Mature T cells

• eventually migrates/colonizes lymph nodes, spleen, & etce

What is the percentage of T-cells that actually mature & make it to the Medulla?

~2%

• most die via apoptosis or by macrophages :(

Lymph Nodes

~600 beans located alongside Lymph vessels

• Helps filter lymph (macrophages/lymphocytes will destroy the filtered microbes)

Stroma

Supporting framework for the “Parenchyma” (immune cells)

Outer Cortex (Lymph nodes)

Aggregates B cells (“lymphatic nodules”) in response to an Antigen

• dendritic cells help present antigen to B cells → proliferates into Ab producing plasma cells

When does a Primary lymphatic nodule → Secondary lymphatic nodule?

After a B cell (in primary LN) recognizes the antigen

Inner Cortex (Lymph nodes)

T cells

• dendritic cells help present antigens to T cells

Medulla (Lymph nodes)

B cells & Plasma cells (antibody producers)

• macrophages are always cleaning up debris from apoptosis

Lymph Nodes Flow

1. Afferent lymphatic vessels

2. Subcapsular sinus

3. Trabecular sinus

4. Medullary sinus

5. Efferent lymphatic vessels

Why are there more afferent > efferent lymphatic vessels?

Slows the flow of lymph = more time to be filtered

• macrophages/lymphocytes can destroy foreign substances

Hilum

Indented, concave part where blood vessels & efferent lymphatic vessels enter/exit

Parenchyma

Functional, internal tissue made up of immune cells

• filters lymph fluid

• launches immune responses

Spleen

Largest single mass of lymphatic tissue

White Pulp (Spleen)

Lymphatic tissue with macrophages/lymphocytes around CENTRAL ARTERIES

Function of White Pulp (Spleen)

Filters/destroys microbes in blood (via T & B cells)

Red Pulp (Spleen)

Blood-filled venous sinuses + splenic cords

Functions of Red Pulp (Spleen)

• Removes ruptured/old RBCs & platelets

• Stores platelets

• Produces blood cells during fetal life

What happens to a ruptured Spleen?

*Most damaged in abdominal trauma

→ Hemorrhage (bleeding) & Shock

What happens to people with removed Spleens?

Must take prophylactic antibiotics before procedures

• no spleen = decreased immune functions

Lymphatic Nodules

Scattered throughout the mucous membranes lining tracts + airways (mainly small/solitary)

• “Mucosa-associated lymphatic tissue”

Tonsils (Pharynx)

Strategically positioned to fight off inhaled/ingested foreign substances

• pharyngeal (1), palatine (2), & lingual (2)

Peyer’s patches (Small intestine)

Large/multiple aggregations

• Immune sensors of the gut-associated lymphoid tissue (GALT)

Innate (nonspecific) immunity

Body's natural defense mechanisms that provide immediate, but general protection against pathogens.

• Physical barriers (skin, mucous membranes)

• Immune cells

1st Line of Defense

Protects against entry into the body

• Physical & Chemical barriers (external)

Physical barriers (1st Line of Defense)

• Epidermis— protects/sheds

• Mucous membranes— traps microbes & foreign substances

• Cilia (upper respiratory tract)— propels inhaled microbes towards pharynx to swallow

Chemical barriers (1st Line of Defense)

• Sebum

• Lysozyme

• Gastric juice

• Vagina

Sebaceous glands (Chemical barrier)

Sebum— oil forms a protective film over the skin (pH 3-5)

Tears & Saliva (Chemical barrier)

Lysozyme— digests cell wall of bacteria

Gastric Glands (Chemical barrier)

Gastric juices— acidity destroys microbes

Vagina (Chemical barrier)

Vaginal secretions— slight acidity discourages bacterial growth

Adaptive (specific) immunity

Body's defense system that adapts to specific pathogens over time, providing long-lasting immunity

• Lymphocytes

• Antibodies

2nd Line of Defense

Required when the 1st defense is penetrated (internal barriers)

• Antimicrobial substances

• NK cells

• Phagocytes

• Inflammation

• Fever

Antimicrobial substances

1. Interferons (IFNs)

2. Complement system

3. Iron-binding proteins

Interferons (IFNs)

Proteins produced by viral-infected cells

• induces neighboring cells into producing proteins that’ll interfere w/ viral replication

Complement system

Inactive proteins circulating in the blood

• reactivated to enhance immune, allergic, & inflammatory reactions

Iron-binding proteins

Inhibits bacterial growth by reducing iron available

• transferrin, ferritin, & hemoglobin

Natural Killer (NK) cells

5-10% of lymphocytes in the blood

• Kills any infected body cells & some tumor cells

• Attacks cells w/ abnormal plasma membrane proteins

• Binds/releases toxic substances (perforins, granzymes)

Perforins

Creates holes in the plasma membrane

→ Cytolysis to release toxic substances

Granzymes

Induces Apoptosis to kill toxic substances

Phagocytes

Perform Neutrophils (ingests microbes/cell debris)

• Wandering/fixing macrophages

Phases of phagocytosis

1. Chemotaxis

2. Adherence

3. Ingestion

4. Digestion

5. Killing

Chemotaxis (Phagocytosis)

Chemically stimulated movement of phagocytes to site of damage (toxin from bacteria, damaged tissue)

Adherence (Phagocytosis)

Phagocyte binds to foreign material/microbe

Ingestion (Phagocytosis)

Plasma membrane projections (pseudopods) engulf the microbe

→ “phagosome”

Digestion (Phagocytosis)

Phagosomes + lysosomes → phagolysome (breaks down lethal oxidants)

Inflammation

Nonspecific, defensive response to tissue damage (cut, burn, bacterial invasion)

• disposal of microbes at the site of injury

Redness (Symptom of Inflammation)

Increased blood flow to the affected area (vasodilation)

Heat (Symptom of Inflammation)

Increased blood flow + rate of metabolic reactions

Swelling (Symptom of Inflammation)

Increased BV permeability = excess accumulation of IF

Pain (Symptom of Inflammation)

Release of chemicals + damage to neurons

• kinins, prostagladins

1st stage of Inflammation

Vasodilation + Increased BV Permeability

• more blood flow to the site & leaky capillaries

• histamines, kinins, prostaglandins

2nd stage of Inflammation

Emigration of Phagocytes

• Chemotaxis

• Neutrophils → Leukocytosis → Monocytes

Pus

Dead phagocytes & damaged tissue

3rd stage of Inflammation

Tissue Repair

• damaged/dead cells are replaced

• Scar tissue = more collagen fibers + less flexible

Fever

Abnormally high body temperature

• intensifies the action of Interferons

• inhibits microbial growth

• speeds up reactions that repair

What is the relationship between an antigen & an antibody?

“Lock & Key”

• Antigens are the specific triggers → antibodies are the specialized proteins that match, bind to, & disarm them.

Cell-Mediated (Adaptive Immunity)

Cytotoxic T cells (CD8+ cells)

Cytotoxic T cells (CD8+

Attacks infected body, cancer, & foreign cells (organ transplants)

→ INTRACELLULAR pathogens (fungi, parasites, viruses)

What’s the difference between NK cells vs. Cytotoxic T cells?

Similar to NK cells, but…

• Receptors for a specific microbe = Cytotoxic T cells only kill target cells infected with that particular microbe type

Immunological Surveillance

The body’s immune system patrols tissues to detect/destroy foreign pathogens (self v. non-self)

Antibody-mediated (Adaptive Immunity)

B cells (Plasma cells)

B cells (Plasma)

Synthesizes Antibodies that attack Antigens

→ EXTRACELLULAR pathogens (fungi, parasites, viruses OUTSIDE cells)

Effector clone cells

Destroys/inactivates antigens

• active Helper/Cytotoxic T cells, Plasma cells

Memory clone cells

Lingers to initiate faster reactions to the same antigen in the future

• Memory Helper/Cytotoxic T cells, Memory B cells

Antigen

Proteins that trigger immune responses

• whole/parts of a microbe or non-microbial

Epitopes

Small parts of a large antigen that trigger an immune response by binding to T/B cell antigen receptors

Major Histocompatibility Complex (MHC) Antigens

Helps the body NOT attack its own cells

• presents antigens to help T cells recognize the foreign antigen

MHC-I Molecules

On the surface of ALL body cells (besides RBCs)

MHC-II Molecules

ONLY on the surface of special antigen-presenting cells (APCs)

• B cells, dendritic cells, & macrophages

What is the difference between the processing of antigens?

• B cells → directly recognize/bind antigens in lymph, blood, or IF

• T cells → must be processed (broken down into peptide fragments) + presented (inserted on cell membrane)

Exogenous Antigen Processing

APCs

• ingests/digests bacteria, toxins, parasitic worms, pollen, dust

• Antigen-MHC-II complex (helper T cells)

Which Antigens are Exogenous cells present on?

MHC-II self antigen

Endogenous Antigen Processing

ALL body cells (except RBCs)

• digests intracellular viral or cancerous proteins → peptide fragments

• Antigen-MHC-I complex (cytotoxic T cells)

Which Antigens are Exogenous cells present on?

MHC-I self antigen

Cytokines

Small, local mediators that stimulate/inhibit many normal cell functions

• proliferation

• differentiation

Interleukins-2 (IL-2)

Acts as a growth factor that drives the expansion of activated T lymphocytes after antigen recognition