Biology 242 – Lab
LAB #6
(6th/19 Lab Sessions for Winter Quarter, 2008)
TOPICS TO BE COVERED:
DESIRED OUTCOMES:
After completing the activities described for this lab session, students should:
»Be able to identify structures of the lymphatic system on anatomical models and preserved
specimens.
»Be able to describe the role of the immune system in processing lymphatic fluid as it is returned
to the heart.
»Be able to trace the pathway of lymphatic fluid as it is returned to the heart.
MATERIALS NEEDED:
»Anatomical models: Various human torsos, intestinal villi,
»Dissection cats
»Dissection tools
Overview:
The Lymphatic/Immune System is the only system in the body with “two names” – the first name encompasses the structural components of this system and the second name encompasses its functional capabilities. Overall, this system serves numerous homeostatic functions in the body. For one, it serves protective and
defensive functions, combating harmful agents in the internal and external environments. It also works with the
cardiovascular system to maintain fluid balance in the interstitium, and with the gastrointestinal system to
absorb fats.
The activities in today’s Lab session will introduce you to this diverse system. It consists of a diverse
group of chemicals, cells, tissues, and organs that have three primary functions:
(1) Transport of excess interstitial fluid back to the heart. In the cardiovascular system, hydrostatic pressure
(the force of blood on the blood vessel wall) is stronger than colloidal osmotic pressure (the force of proteins and other
non-diffusible entities in blood). This creates a gradient to push fluid out of the capillaries and into the interstitial
spaces. Approximately 1.5 ml/min of fluid is lost out of the circulation in this manner. This may not sound like
a great deal, but if this fluid were NOT returned to the blood vessels, we could lose our entire plasma volume in
about 1 day! Luckily, the lymphatic system picks up this excess fluid and, through a series of lymphatic structures, returns it to the cardiovascular system at the junction where the internal jugular vein joins the subclavian
vein to form the brachiocephalic vein on each side. The fluid is dealt with by a series of specialized lymphatic
channels, starting with those that are microscopic in size and progressing to those that are macroscopic and visible in our cat dissections. The smallest of these, lymphatic capillaries, surround capillary beds. These lymph
capillaries are separate and distinct from blood capillaries and contain highly permeable walls. Once collected
into the lymph capillaries, the fluid, now called lymph, flows into larger channels called lymphatic vessels;
which flow toward and into nine major lymphatic trunks; and these finally empty into one of two lymphatic
ducts before being returned to the circulation.
(2) Activation of immune system. Several of the lymphatic organs function to activate the immune system.
These include the thymus, an organ in which T lymphocytes mature; the spleen, which houses phagocytes, and
the tonsils, aggregates of unencapsulated lymphoid tissue found in the oropharynx and nasopharynx. In addition, lymphoid organs called lymph nodes are found along all the lymphatic vessels. The vessels deliver lymph
into the nodes, where it is filtered so it can trap pathogens, toxins, and cells (such as cancer or virus-infected
cells.)
(3) Absorption of dietary fats. Fats are not absorbed from the small intestine directly into the blood stream.
Instead, fats enter a specialized lymphatic vessel called a lacteal, after which they travel with the lymph to be
deposited in the blood at the junction of the internal jugular vein and subclavian veins via either the Right or the
Left Lymphatic Duct.
Activity #1: Anatomical Structures of the Lymphatic System
See Figures 13.1, 13.4, 13.6, and 13.10 in your lab Atlas for reference. Locate the following structures
of the Lymphatic System on anatomical models, on charts, or on diagrams:
1. Lymph channels: a. Left Lymphatic Duct (aka Thoracic Duct)
b. Right Lymphatic Duct
c. R + L Bronchomediastinal trunks
d. R + L Jugular trunks (aka Cervical trunks)
e. R + L Axillary trunks
f. R + L Inguinal trunks
g. Intestinal trunk
h. Lacterals
i. Cisterna Chyli
2. Lymph Nodes:
a. Cervical lymph nodes
b. Axillary lymph nodes
c. Inguinal lymph nodes
d. Mesenteric lymph nodes
3. Spleen
4. Thymus (this is best viewed on a young cat specimen)
5. Mucosal-associated lymphoid tissue (See Small Intestine Model)
6. Vermiform appendix
7. Tonsils (aka: “Waldeyer’s Ring”)
a. Lingual tonsils, b. Palatine tonsils c. Pharyngeal tonsil (adenoids)
Activity #2: Cat Structures of the Lymphatic System
The thymus degenerates in adults, so it often is not represented on anatomical models and torsos.
Therefore, it is advantageous to view the thymus and other lymphatic organs in a preserved specimen as well.
Young cats are particularly well-suited to this task, as they have a prominent thymus.
Open the chest-plate of your cat to view the thymus. Also, if the peritoneal cavity has been entered, you
will be able to examine the spleen. Describe the location, texture, and appearance of each of these two organs.
Activity #3: Trace the Flow of Lymph Through the Body
Trace the pathway of lymph flow from the starting point (given below) to the point at which the lymph
fluid is returned to the cardiovascular system. Trace the flow through the major lymph-collecting vessels,
trunks, and ducts, highlighting clusters of lymph nodes through which the lymph passes as it travels. First, write
the sequence of the flow, and then use the diagram provided in the to show this flow. Trace the flow from the
following locations:
1. Right foot
2. Left forearm
3. Right cervical region