Lymphatic System

Exam Information

Next exam covers:
- Chapter 22: Lymphatic System
- Chapter 23: Respiratory System
- The exam only covers 2 chapters but they are big.

Extra Credit Opportunity

Based on a drawing from lecture.
Due tonight by 11:00 PM.
Use SBCC email address to submit.
Two questions.
One point each.
Based on identifying blood type from the drawing.
QR code closes 06/23 at 11 PM.
Submissions after close will not be accepted.
QR codes differ between sections, so use the correct one for your section.

Chapter 22: Lymphatic System

Functions of the Lymphatic System

Collect Excess Fluids:
- Collects excess fluids from tissues and returns them to the circulatory system.
- Helps combat fluid accumulation in peripheral tissues.
- Fluid is emptied into the venous side of blood.
- If the lymphatic system cannot collect fluids, peripheral edema (tissue swelling) may occur due to fluid accumulation.
- Blockage or issues in lymphatic system.
Absorb Lipids:
- Absorbs lipids from the intestine using lacteals.
- Lacteals are structures of the lymphatic system that absorb lipids.
- Carbohydrates and proteins are absorbed through the circulatory system via capillaries.
Immune System:
- The lymphatic system is a large part of the immune system.
- Composed of cells, tissues, and organs.
- Lymphocytes are a type of white blood cell found in the lymphatic system.
- Lymphocytes are agranulocytes.

Components/Structures of the Lymphatic System

Lymphatic Fluid (Lymph):
- Fluid gathered from tissues, returned to the circulatory system.
Tonsils:
- Collections of lymphatic tissues in the oral cavity and pharynx.
- Three types of tonsils in the throat region.
Lymph Nodes:
- Nodes belonging to the lymphatic system, found throughout the body.
- Cervical lymph nodes (cervical region).
- Axillary lymph nodes (armpit region).
- Lymph nodes are interconnected by lymphatic vessels.
Thymus Gland:
- Located in the mediastinum, posterior to the sternum and anterior to the great vessels of the heart.
- Regulates the immune system (Thymosin hormone).
Spleen:
- Part of the lymphatic system.

Fluid Circulation

During ventricular systole, stroke volume (approximately $63$ mL) of blood is sent into the ascending aorta and aortic arch.
Some fluids are returned to the venous side of blood via the lymphatic system.
Lymphatic capillaries collect lymph fluid and move it toward lymph nodes.
Lymph drains into two major vessels (ducts), depending on the collection site.

Lymphatic Ducts

Right Lymphatic Duct:
- Drains lymph from the right half of the hip, right side of the neck, right side of the chest (thorax), and right upper extremity.
Thoracic Duct (Left Lymphatic Duct):
- Drains lymph from the left half of the head, left half of the neck, left half of the thorax, left upper extremity, entire abdomen and pelvis, and both lower extremities.

Lymphatic Drainage

Whether lymph drains into the right lymphatic duct or the thoracic duct depends on the body part.
Right Lower extremity → Thoracic duct
Right Lymphatic Duct drains directly into the right subclavian vein.
Thoracic Duct drains into the junction between the left internal jugular vein and the left subclavian vein.
- Veins merge, arteries branch.

Thoracic Duct Origin

Starts in the lower aspect of the thorax, where it meets the abdomen.
Between T12 and L1, there is a sac called the cisterna chyli.
The thoracic duct starts from the cisterna chyli.

Vessels in the Lymphatic System

contributing to these two major ducts, there are minor trunks.

Lymphocytes: Cells of the Lymphatic System

Lymphocytes are leukocytes produced in the red bone marrow.
Originate from hemocytoblasts.
Hemocytoblasts differentiate into:
- Myeloid stem line.
- Lymphoid stem line.

Lymphoid Stem Line

Produces two types of cells:
- Pre-B cells.
- Pre-T cells.
Both are immature cells produced in the bone marrow; maturation location differs.

Cell Maturation Table

Cells	Site of Production	Site of Maturation
Pre-B cells	Bone marrow	Bone marrow
Mature B cells	Bone marrow	Bone marrow
Pre-T cells	Bone marrow	Thymus gland
Natural killer cells	Bone marrow	Bone marrow

Pre-B Cells: Mature in the bone marrow to become B cells. "B" stands for bone marrow.
Pre-T Cells: Migrate to the thymus gland to mature into T cells. "T" stands for thymus (not thyroid).
*Mature B and T cells are sent to different parts of the lymphatic system.
*B cells also referred to as B lymphocytes and T cells are referred to T lymphocytes.

Maturation Process

Involves exposing cells to two types of surface antigens:
1. Self Antigens:
  - Found on normal cells of the body.
  - Examples: surface antigen B, surface antigen Rh
2. Non-Self Antigens (Foreign Antigens):
  - Found on infectious agents like bacteria, viruses, fungi, etc.
  - Immune system recognizes these as foreign and mounts an immune defense.

Maturation Process Involves Two Types of Selection

Positive Selection:
- Cells with a strong reaction against nonself antigens are retained.
- Immune system responds against nonself antigens to eliminate them, while self antigens are preserved.
Negative Selection:
- Cells reacting against self antigens are eliminated to prevent autoimmune diseases.
- Auto immune diseases = immune system destroying our own cells.
- Examples: lupus, psoriasis.
- Cells undergo programmed cell death (apoptosis).

Apoptosis

Programmed cell death.
Cells are programmed for self-destruction through their genes.

Lymphocyte Types: B Cells

If there is an infection, the B cells will be activated.
Activated B cells are called plasma cells.
The purpose of plasma cells is to produce antibodies.
B cells do not produce antibodies; Plasma cells produce them.
Involved in antibody-mediated immunity (humoral immunity).

Lymphocyte Types: T Cells

Pre-T cells mature in the thymus gland through positive and negative selection, becoming mature T cells.
T cells are subdivided into:
- CD4 Cells (Helper T cells).
- CD8 Cells (Cytotoxic T cells).
- Memory T cells
- Suppressor T cells
Are involved in cell-mediated immunity
T cells encounter the cause of the disease or the pathogen directly
Because B cells produce antibodies, they do not use cell mediated immunity.

Lymphocyte Types: Natural Killer (NK) Cells

Produced and mature in the red bone marrow.
Provide immunological surveillance.
Punch holes in pathogens using proteins called perforins.