lymphatic system

valves

medium and large veins, as well as lymph vessels have _________

medium and large veins

(especially in the limbs) contain internal VALVES formed from folds of the tunica intima (the innermost layer). These pocket-like valves prevent blood from flowing backward against gravity.

lymphatic vessels

(collecting vessels, trunks, and ducts) feature abundant, closely spaced VALVES. Because the lymphatic system lacks a central pump like the heart, lymph flow relies heavily on skeletal muscle contraction, breathing, and these one-way valves to prevent backflow as fluid moves toward the subclavian veins.

lymph nodes

______ _______ are strategically distributed throughout the body, but they are concentrated in high densities in specific regional clusters—primarily where lymphatic vessels converge near body trunk junctions, organ entrances, and areas exposed to external pathogens

INCLUDES:

Cervical Nodes

Axillary Nodes:

Inguinal Nodes

Mesenteric / Intestinal Nodes

Mediastinal & Bronchial Nodes

Iliac Nodes

lymph node regional clusters

Cervical Nodes

Axillary Nodes:

Inguinal Nodes

Mesenteric / Intestinal Nodes

Mediastinal & Bronchial Nodes

Iliac Nodes

Cervical Nodes

Located along the neck. They drain and filter lymph from the head and neck region, monitoring for airborne or swallowed pathogens.

Axillary Nodes

Located in the armpit (axilla). They drain lymph from the upper limbs, mammary glands, and upper chest wall.

Inguinal Nodes

Located in the groin area. They filter lymph from the lower extremities, external genitalia, and lower abdominal wall.

Mesenteric / Intestinal Nodes

Located within the mesenteries (peritoneal folds) supporting the small and large intestines. These monitor antigens absorbed through the digestive tract.

Mediastinal & Bronchial Nodes

Located in the chest cavity along the trachea and primary bronchi, filtering lymph from the lungs and heart.

Iliac Nodes

Located along the iliac blood vessels in the pelvic cavity, draining pelvic organs and the lower limbs before lymph ascends to the abdominal trunks.

Cisterna Chyli

a dilated, sac-like lymphatic pouch located in the posterior abdominal cavity, typically anterior to the bodies of the L1 and L2 vertebrae, just inferior to the aortic hiatus of the diaphragm.

cisterna chyli

serves as the main collecting reservoir for lymph and nutrient-rich lipid emulsion (chyle) coming from the lower body and gastrointestinal tract. It receives lymph from: Left and Right Lumbar Trunks and Intestinal Trunk

origin of the thoracic duct

The cisterna chyli marks the ________ ___ ___ ________ ______ (the body's primary, largest lymphatic vessel

left internal jugular and left subclavian veins

Lymph/chyle collected in the cisterna chyli ascends through the diaphragm via the thoracic duct, ultimately discharging into the venous circulation at the junction of the ___ _______ ______ ___ ___ __________ ___ (left venous angle).

Mucosa-Associated Lymphoid Tissue

What does MALT stand for?

MALT

is a widespread collection of unencapsulated, diffuse aggregates of lymphoid tissue (containing T cells, B cells, macrophages, and plasma cells) located within the mucous membranes lining the respiratory, digestive, urinary, and reproductive tracts.

mucous membranes

MALT stands for Mucosa-Associated Lymphoid Tissue. It is a widespread collection of unencapsulated, diffuse aggregates of lymphoid tissue (containing T cells, B cells, macrophages, and plasma cells) located within the ________ ________ lining the respiratory, digestive, urinary, and reproductive tracts.

MALT

Because mucous membranes line body cavities that open to the outside world, _______ serves as an essential first line of immune defense against pathogens ingested, inhaled, or brought into contact with epithelial surfaces.

Locations of Significant MALT Concentration

Tonsils

Peyer’s Patches (Aggregated Lymphoid Nodules)

appendicular Lymphoid Tissue (The Appendix)

tonsils

Located in the pharynx (throat) region, tonsils form a ring of lymphoid tissue (Waldeyer's ring) around the entrance to the respiratory and digestive tracts to trap and destroy airborne and ingested pathogens:

palatine

lingual

pharyngeal

Tubal

Palatine Tonsils

• Pair located on either side of the posterior oral cavity (the ones most frequently removed during a tonsillectomy)

Lingual Tonsil

Collection of lymphoid follicles located at the base of the tongue

Pharyngeal Tonsil (Adenoid)

Single node located in the posterior wall of the nasopharynx.

Tubal Tonsils

Tiny clusters surrounding the openings of the auditory (Eustachian) tubes into the nasopharynx.

Peyer’s Patches

large, prominent clusters of lymphoid follicles located in the submucosa of the distal small intestine, specifically concentrated in the ileum.

Because the ileum is densely populated with gut bacteria, Peyer's patches prevent bacteria from penetrating the intestinal wall and entering the bloodstream. Specialized microfold cells (M cells) sample intestinal antigens and present them to underlying lymphocytes.

ileum

Peyer’s patches are large, prominent clusters of lymphoid follicles located in the submucosa of the distal small intestine, specifically concentrated in the ______

prevent bacteria from penetrating the intestinal wall

Because the ileum is densely populated with gut bacteria, Peyer's patches _______ ________ ______ _________ ___ _________ ______ and entering the bloodstream. Specialized microfold cells (M cells) sample intestinal antigens and present them to underlying lymphocytes.

appendix

• a tubular offshoot attached to the cecum (the beginning of the large intestine) in the lower right quadrant of the abdomen.

• Function: High concentrations of lymphoid follicles fill its wall, allowing it to monitor intestinal contents and generate memory lymphocytes.

cecum

The appendix is a tubular offshoot attached to the ________ (the beginning of the large intestine) in the lower right quadrant of the abdomen.

appendix

High concentrations of lymphoid follicles fill its wall, allowing it to monitor intestinal contents and generate memory lymphocytes.

GALT

Gut-Associated Lymphoid Tissue

Peyer's patches (ileum), Appendix, esophagus, stomach, colon

BALT

Bronchus-Associated Lymphoid Tissue

Walls of the respiratory tract (trachea, bronchi, bronchioles)

NALT

Nasopharynx-Associated Lymphoid Tissue

Tonsils and nasal passages

SALT / CALT

Skin/Conjunctiva-Associated Lymphoid Tissue

Epithelial surfaces of skin and eyes

spleen

1. Immune Surveillance and Response (White Pulp)

2. Blood Filtration, RBC Recycling, and Storage (Red Pulp)

White Pulp

• consists of lymphatic tissue (mostly lymphocytes and macrophages) arranged around central arteries, resembling lymphoid follicles.

• Function: It acts as the site for immune surveillance of the blood. As blood flows through, lymphocytes and macrophages detect blood-borne antigens, initiating immune responses (producing antibodies and activating T cells) against pathogens.

lymphatic tissue

White pulp consists of ___________ __________ (mostly lymphocytes and macrophages) arranged around central arteries, resembling lymphoid follicles.

white pulp

It acts as the site for immune surveillance of the blood. As blood flows through, lymphocytes and macrophages detect blood-borne antigens, initiating immune responses (producing antibodies and activating T cells) against pathogens.

red pulp

makes up the majority of the spleen's volume and consists of venous sinuses and splenic cords (cords of Billroth) rich in macrophages.

red pulp function

• Hemocatheresis: Macrophages phagocytize and destroy aged, rigid, or damaged red blood cells and platelets, recycling iron from hemoglobin.

• Reservoir: It stores blood platelets (about 30-40% of the body's total) and monocytes to be released during times of physiological stress or hemorrhage.

thymus

the maturation and differentiation of T lymphocytes occurs here

Key Functions of the Thymus

T Cell Maturation & Immunocompetence

Thymic Selection (Quality Control):

Endocrine Secretion:

T Cell Maturation & Immunocompetence

Immature precursor T cells (thymocytes) originate in the red bone marrow and migrate to the thymic cortex. As they travel from the cortex to the medulla, they are exposed to hormones and chemical signals that force them to develop immunocompetence (the ability to recognize specific foreign antigens).

thymic selection

• Positive Selection: Ensures T cells can successfully recognize self-MHC (Major Histocompatibility Complex) molecules. Those that fail undergo apoptosis (programmed cell death).

• Negative Selection: Eliminates self-reactive T cells that would attack the body's own healthy tissues (preventing autoimmune disease). Only about 2% of developing T cells survive this rigorous screening process.

thymic Positive Selection

Ensures T cells can successfully recognize self-MHC (Major Histocompatibility Complex) molecules. Those that fail undergo apoptosis (programmed cell death).

thymic negative selection

Eliminates self-reactive T cells that would attack the body's own healthy tissues (preventing autoimmune disease). Only about 2% of developing T cells survive this rigorous screening process.

Endocrine Secretion

The epithelial reticular cells of the thymus secrete hormones—such as thymosin, thymopoietin, and thymulin—which promote the maturation and proliferation of T cells.

childhood

The thymus is uniquely active and largest during __________, when the immune system is actively learning to recognize pathogens. After puberty, the thymus undergoes involutions, gradually shrinking in size and being replaced largely by adipose (fat) tissue, though it continues to produce T cells at a reduced rate throughout adulthood.