Unit II - The Lymphatic, Immune, and Respiratory Systems

Net Filtration Pressure

Hydrostatic Pressure (HP_C) - Osmotic Pressure (OP_C)

Hydrostatic Pressure (HP_C)

The physical pressure of water / blood pushing out of the capillary into the tissue

Osmotic Pressure (OP_C)

The pulling force created by the plasma that retains / draws water into the capillary

HP_C > OP_C

A positive NFP forces fluid out of the capillary

HP_C < OP_C

A negative NFP pulls fluid into the capillary

Function of the Lymphatic System

Maintain fluid balance inside the body by collecting extra interstitial fluid

Lymphatic Vessels

• A one-way system in which lymph travels towards the heart

• Contains…

  • Capillaries

  • Lymphatic Collecting Vessels

  • Trunks / Ducts

Lymphatic Capillaries

• Permeable

• Loosely joined endothelial minivalves

  • Allows IF to enter w/o letting lymph escape

• Withstands interstitial pressure and remains open

Function of Lymphatic Capillaries

Cells in the lymph nodes collect and examine these during inflammation

• Cell Debris

• Pathogens

• Cancer Cells

Lacteals

Specialized lymph capillaries present in intestinal mucosa, that absorb digested fat and deliver chyle to the blood

Lymphatic Collecting Vessels

• Contain the same three tunics as veins w/ thinner walls

• Branch more frequently

Lymphatic Trunks

• Formed by the union of the largest collecting ducts

• Include

  • Paired Lumbar

  • Bronchmediastinal

  • Subclavian

  • Jugular

Right Lymphatic Duct

Drains the right upper arm and the right side of the head and thorax

Thoracic Duct

Arises from the cisterna chyli and drains the body, with the exception of the right upper arm, right side of the head and the right side of the thorax

The Source of Lymph Fluid

Comes from excess interstitial fluid that is then collected

Lymph Transport

• Vessels are low-pressure conduits

• Uses…

  • Pulsations of nearby arteries

  • Contractions of smooth muscle in the walls of the lymphatics

Lymphoid Tissue

Contain…

• Lymphocytes: protect against antigens

  • B - Cells: produce antibodies

  • T - Cells: manage immune response

• Macrophages

• Dendritic Cells: capture antigens

• Reticular Cells: produce supporting network

Diffuse Lymphoid Tissue

• Made up of mostly T - Cells, Macrophages, and Plasma Cells

• Provides an immediate first-line defense against pathogens

• Found in the GI tract, respiratory tract, and urinary tractz

Follicular Lymphoid Tissue

• Made up of mostly B - Cells

• Serves as the site for antibody production

• Found in lymph nodes, white pulp, tonsils, and Peyer’s patches

Location of Lymph Nodes

Found all over the body, but clusters can be found in the inguinal, axillary, and cervical regions of the body

Histological Structure of Lymph Nodes

The Function of Lymph Nodes

The body’s biological filtration centers and immune activation stations

The Pathway of Lymph Flow

• The Afferent Lymphatic Vessels

• The Subcapsular Sinus

• The Trabecular Sinuses

• The Medullary Sinuses

• The Efferent Lymphatic Vessels

  • There are more AFFERENT than EFFERENT lymphatic vessels

White Pulp

• Contains mostly lymphocytes

• Suspended in reticular fibers

• Involved in immune function

• Stains PURPLE

Red Pulp

• Remaining tissue

• Gets rid of worn-out RBCs

• Gets rid of bloodborne pathogens

• Stains RED

Function of the Spleen

• Site of lymphocyte proliferation

• Immune surveillance and response

• Cleanses the blood

• Stores breakdown products of RBCs

• Site of fetal erythrocyte production

• Stores blood platelets

Structure of the Thymus

Contains…

• An outer cortex with densely packed lymphocytes and scattered macrophages

• An inner medulla with fewer lymphocytes and thymic corpuscles

Function of the Thymus

• Secretes hormones that cause T - Cells to become immunocompetent

• Does NOT directly fight antigens

Function of Mucosa - Associated Lymphatic Tissue (MALT)

Protects the digestive and respiratory systems from foreign matter

Components of Mucosa - Associated Lymphatic Tissue (MALT)

• Contains…

  • Peyer’s Patches

  • Tonsils

  • Appendix

  • Lymphoid Nodules

Surface Membrane Barriers

• Barriers that prevent pathogens from entering the body

• The first line of defense

• Contain…

  • Skin

  • Mucosa

  • Sebum

  • Saliva

  • Earwax

  • Mucous

  • Stomach Acid

  • Vaginal Fluid

Importance of Phagocytosis to Innate Defense

• Immediate pathogen eradication

• Clearance of cellular waste and debris

• Initiation and orchestration of the inflammatory response

• The critical bridge to adaptive immunity

Importance of Natural Killer Cells to Innate Defense

• Rapid, non-specific surveillance

• Detects when a cells does not have “self”

• Targeted, clean cell destruction

• Orchestrates the broader immune response

Importance of Fever to Innate Defense

• Inhibits pathogen reproduction

• Sequesters critical nutrients

• Accelerates immune cell function

• Enhances tissue repair

The Inflammatory Process

• Injury: physical harm to the body

• Chemical Alarm: histamines, cytokines, etc…

• Vascular Changes: increased blood flow to injury site, causes redness, heat, and swelling

• Leukocytic Response: neutrophils, macrophages, etc…

• Phagocytic Response: leukocytes perform phagocytosis, engulfing foreign debris

• Clean - Up: invading pathogens, cellular debris, and dead tissue are disposed of

• Resolution: macrophages release growth factor that signal end of inflammation response

• Healing: excess fluid is drained by lymphocytes and fibroblasts start forming scar tissue

Signs of Inflammation

• SHARP

• Swelling - Edema - Controls the Degree of Injury

• Heat - Increased Blood Flow

• Altered Function - Controls the Degree of Injury

• Redness - Increased Blood Flow

• Pain - Brings Attention to Injury

Inflammatory Chemicals

• Histamines: cause rapid vasodilation and increase capillary permeability

• Prostaglandins: cause vasodilation, contribute to swelling, and trigger fever

• Platelet - Activating Factor: causes platelet aggregation and amplifies leukocyte adhesion

• Interleukin - 1: promotes inflammation and serves as a pyrogen

• Interleukin - 6: stimulates the liver to aid in system-wide defense

• Bradykinin: dilates blood vessels and stimulates pain receptors

Antigen

Any substance or molecule that can be recognized by the immune system and has the potential to trigger an immune response

How Antigens Affect the Adaptive Defenses

• Antigen Presentation: MHC - II

• Humoral ( Antigen-Mediated ) Immunity: B - Cells create antibodies

• Cellular Immunity: MHC - I

• Immunological Memory: retains a blueprint of that specific antigen

Complete Antigen

A large, structurally complex molecule that is capable of inducing a specific immune response by itself

Hapten

A small, structurally simple foreign molecule that cannot trigger an immune response on its own, but can react with antibodies once an immune response is established

Antigenic Determinant

The specific, microscopic region on the surface of an antigen that is physically recognized and bound by the immune system

B - Cells

• Origin: red bone marrow and hematopoietic stem cells

• Maturation Process:

  • Phase A: Central Maturation (Bone Marrow — Antigen-Independent)

  • Phase B: Peripheral Maturation ( Spleen — Antigen-Dependent)

• General Function: orchestrate antigen - mediated immunity

T - Cells

• Origin: red bone marrow and hematopoietic stem cells

• Maturation Process:

  • Receptor Generation

  • Selection (Helper vs. Cytotoxic vs. Apoptosis)

• General Function: orchestrate cell - mediated immunity

Immunocompetence

The ability of an immune cell to recognize and bind to a single, specific foreign antigen

Development of Immunocompetence in T - Cells

• Occurs in the thymus

• Unique T - Cell Receptors are constructed

• TCRs are tested for successful binding to MHC proteins

• If the T - Cell can bind, then it is allowed to live

Development of Immunocompetence in B - Cells

• Occurs in red bone marrow

• Unique B - Cell Receptors are constructed

• If a cell can build and display a successful BCR, it is allowed to live

Self - Tolerance

The ability of the immune system to recognize the body’s own normal tissues and remain unresponsive to them

Development of Self - Tolerance in T - Cells

• Occurs in the thymus

• T - Cells are tested for successful binding to self - antigens

• If the T - Cell binds too tightly, it is killed

Development of Self - Tolerance in B - Cells

• Occurs in the red bone marrow

• BCRs exposed to self - antigen

• If the B - Cell binds too tightly, it is killed

Antigen - Presenting Cells

• Dendritic Cells: engulf surrounding fluid and pathogens via phagocytosis

• Macrophages: engulf extracellular pathogens to clear up local infections

• B - Cells: bind to specific antigens to dispose of them

• MHC - I: forces cells to identify themselves

• MHC - II: forces other cells to identify other foreign cells

Cellular Immunity

The arm of the adaptive immune defense network that protects the body by destroying the infected, mutated, or abnormal body cells

Process of Activation for T - Cells

• Antigen Binding: the T - Cell must lock onto its exact matching antigen

• Co - Stimulation: the T - Cell must receive a separate signal to kill the antigen

• Cytokine Signaling: the T - Cell produces and responds to cytokines and begins dividing

• Clonal Selection: the T - Cell rapidly divides into the thousands

• Differentiation: the T - Cells divide into effector or memory cells

Clonal Selection of T - Cells

• The Pre-Existing Pool: there are already millions of T - Cells existing in the body

• The Selection: only one T - Cell will have a receptor to fit a specific antigen

• The Expansion: that T - Cell is multiplied