Immune + Lymphatic System

Pathogens

microscopic organisms that cause disease (bacteria, viruses, fungi, parasites)

Lymphatic System

protects against disease, works with the circulatory system

What do lymph system cells respond to?

Environmental pathogens; Toxins; Abnormal body cells, such as cancers

What structures are included in the lymph system?

series of nodes, ducts, vessels

Lymphocytes

part of the immune response; identify, attack, develop immunity

Immunity

ability to resist infection and disease

Components of lymphatic system

lymph, lymphatic vessels, lymphoid tissues, lymphoid organs, lymphoid cells

Lymph

similar to plasma but without plasma proteins; contains WBC, some bacteria and waste

Lymphatic Vessels

Carry lymph from peripheral tissues to veins

Lymphoid tissues and organs

scattered throughout the body

Lymphoid cell examples

lymphocytes, phagocytes

Where are lymphocytes produced?

primary lymphoid tissues and organs; red bone marrow, thymus

Where are lymphocytes activated?

secondary lymphoid tissues and organs; tonsils, MALT, lymph nodes, spleen

Lymphatic System Functions

– Produce, maintain, and distribute lymphocytes and other lymphoid cells

– Return excess fluid to bloodstream

– Maintain normal blood volume

– Manipulate blood pressure

– Transport hormones, nutrients, and wastes

Lymphatic vessels

carry lymph from peripheral tissues to the venous system

What happens to lymph that leaks from blood capillaries into the vessels?

conducted to the large veins of the neck at the junction of the internal jugular vein and the subclavian vein

Lymphatic Capillaries

• Differ from blood capillaries in several ways

• Closed at one end rather than forming a tube

• larger luminal diameters

• thinner walls

• flat or irregular outline in sectional view

• Endothelial cells loosely bound together

• Overlap of endothelial cells acts as one-way valve

• Allows fluids, solutes, viruses, and bacteria to enter

• Prevents their return to intercellular spaces

How does lymph flow?

From lymphatic capillaries to larger lymphatic vessels containing one-way valves

Lacteals

Special lymphatic capillaries in small intestine; Transport lipids from digestive tract

Types of lymphatic vessels

Superficial lymphatics, deep lymphatics

Deep lymphatics

larger vessels that accompany arteries and veins

Where are lymphatic vessels located?

skin, mucous membranes, serous membranes lining body cavities

Lymphatic trunks

joining lymphatic vessels; empty into collecting vessels

Two major collecting vessels

Thoracic duct, right lymphatic duct

Thoracic duct base

expands to form cisterna chyli; recieves lymph from right and left lumbar trunks, intenstinal trunk

Thoracic duct inferior segment

collects lymph from left bronchomediastinal trunk, Left subclavian trunk, Left jugular trunk

Where does the thoracic duct empty?

Left subclavian vein

Where does the right lymphatic duct collect from?

Right jugular trunk, Right subclavian trunk, Right bronchomediastinal trunk

Where does the right lymphatic duct empty?

right subclavian vein

What is lymphedema?

Blockage of lymph drainage from a limb

What does lymphedema cause?

severe swelling

What does lymphedema interfere with?

immune system function

Lymphoid cells

Immune system cells and supportive cells in lymphoid tissues

Lymphocytes

Make up 20–40 percent of circulating leukocytes; Most are stored, not circulating

Types of lymphocytes

T cells, B cells, NK cells

Where do T cells mature?

thymus

Where are B cells derived?

bone marrow

Lymphoid tissue components

connective tissues dominated by lymphocytes

Lymphoid nodule composition

Areolar tissue with densely packed lymphocytes

Lymphoid nodule germinal center

contains dividing lymphocytes

Lymph node function

filter the lymph that passes through the vessels and add lymphocytes to it

B cell lymphocyte function

produce antibodies that target foreign cells and attack them

Where are lymphoid nodules distributed?

lymph nodes, spleen, respiratory tract (tonsils), digestive tract, urinary tract, reproductive tract

Where are tonsils located?

5 in the wall of the pharynx

List the tonsils

• Pharyngeal tonsil (adenoid)

• Left and right palatine tonsils

• Two lingual tonsils

• Lymphoepithelial tissue in mouth and throat

Tonsillitis

inflammation of tonsils, especially the palatine tonsils

Mucosa-associated lymphoid tissue (MALT)

Lymphoid tissues associated with various systems but primarily digestive

Aggregated lymphoid nodules

Clustered deep to intestinal epithelial lining, MALT

Appendix (vermiform appendix)

Contains a mass of fused lymphoid nodules

List the lymphoid organs

• lymph nodes

• thymus

• spleen

How are lymphoid organs separated from surrounding tissues?

fibrous connective tissue capsule

Lymph node structures

• Trabeculae

• Hilum

• Afferent lymphatics

• Efferent lymphatics

Trabeculae

Bundles of collagen fibers, Extend from capsule into interior of lymph node

Hilum

Shallow indentation where blood vessels and nerves reach lymph node

Afferent lymphatics

Carry lymph from peripheral tissues to lymph node

Efferent lymphatics

Leave lymph node at hilum, Carry lymph to venous circulation

Order of lymph flow through nodes

afferent lymphatics → subcapsular space → outer cortex → paracortex → core (medulla) → efferent lymphatics

Subcapsular space

Contains macrophages and dendritic cells

Outer cortex

Contains B cells within germinal centers

Paracortex

dominated by T cells

Core (medulla)

Organized into medullary cord, Contains B cells and macrophages

Lymph node function

Purify lymph before return to venous circulation, Remove 99 percent of antigens

Antigens released due to infection

Enter lymph and stimulate macrophages and lymphocytes in lymph nodes, carried by dendritic cells to lymph nodes

Lymphoid tissues and nodes together

Monitor peripheral infections, Respond before infections reach vital organs

Lymph nodes of gut, trachea, lungs, thoracic duct

protect against pathogens in digestive and respiratory systems

Largest lymph nodes

In groin, axillae, and base of neck; swell in response to infection

Lymphadenopathy

chronic or excessive enlargement of lymph nodes, may indicate infections or cancer

Thymus location

mediastinum (above heart)

Thymus atrophy

occurs after puberty, diminishing effectiveness of immune system, replaced by adipose tissue

Thymus structure

divided into 2 thymic lobes, fibrous septa divide lobes into smaller lobules

Thymic lobule structure

dense outer cortex, pale central medulla

Lymphocyte-Thymus interaction

lymphocytes divide in cortex, migrate to medulla, mature T cells leave thymus by medullary blood vessels

Epithelial reticular cells

Surround lymphocytes in cortex

Form layered structures in medulla known as thymic (Hassall’s) corpuscles

Maintain blood thymus barrier in cortex (absent in medulla)

Thymic hormones

thymosin

Thymosin

extract from thymus containing several hormones, promotes development and maturation of T cells

Largest organ in lymphatic system

spleen

Splenic functions

1. Removal of abnormal blood cells and other blood components by phagocytosis

2. Storage of iron recycled from red blood cells

3. Initiation of immune responses by B cells and T cells

If the spleen is removed, the ___ can take over removal of abnormal blood cells by phagocytosis.

liver

Why have iron storage in the spleen?

keep reserve RBCs incase of hemorrhage, produce new RBCs in developing fetus

When is B cell/T cell immune response initiated?

antigens in circulating blood

Splenic anatomy

• Attached to stomach by gastrosplenic ligament

• Contacts diaphragm and left kidney

• Splenic veins, arteries, and lymphatic vessels

Where do splenic veins, arteries, and lymph vessels communicate with the spleen?

splenic hilum

Splenic histology

Cellular components within capsule make up pulp

Red pulp

contains many RBC, circulating blood elements, fixed and free macrophages; stains pink

White pulp

dominated by lymphocytes, resembles lymphoid nodules; stains purple

Trabecular arteries

• Branch and radiate toward capsule

• Finer branches surrounded by white pulp

• Capillaries discharge red blood cells into red pulp

Splenic circulation

trabecular arteries → blood passes though network of reticular fibers → enters large sinusoids lined by macrophages → empty into trabecular veins

Splenectomy

removal of a severely ruptured spleen

Immunity

ability to resist and defend against infectious organisms and other damaging substances

resistance

ability of the body to maintain immunity

immune response

Body’s reaction to infectious agents and other abnormal substances

Innate (nonspecific immunity)

Always works the same way, Against any type of invading agent

Adaptive (specific) immunity

Protects against specific pathogens, Depends on activities of lymphocytes, Develops after exposure to environmental hazards

Lymphocyte distribution

Tissues maintain different T cell and B cell populations

Lymphocyte transport

through blood vessels or lymphatics

Lymphocyte life span

many years

Immune surveillance

NK cells, secrete chemicals that lyse the plasma membrane of targeted cells

Antibody-mediated immunity

B cells, differentiate to plasma cells → release antibodies → attach to pathogen

Cell-mediated immunity

cytotoxic T cells, attack and destroy foreign or virus infected cells