Chapter 18 - Lymphatic System And Immunity

Question 1

Identify the major components of the lymphatic system

learner objective

Answer 1

The lymphatic system is made of many vessels, including lymphatic pathways, capillaries, trunks, and collecting ducts. It transports a fluid called lymph, which is filtered in a variety of ways.

Lymph nodes are structures important in filtering the lymph, and the spleen is important in filtering the blood.

The thoracic duct drains lymph mostly from the left side of the body and the right lymphatic duct drains lymph mostly from the right side of the body.

Question 2

Describe the structure of lymphoid tissues, vessels, and organs
(learner objective)

Answer 2

Lymphoid tissues and organs are composed primarily of squamous epithelium, which allows tissue fluid to enter.

Lymphatic vessels are similar to veins but have thinner walls and valves that prevent the back flow of lymph.

Question 3

Describe the major functions of the lymphatic system

learner objective

Answer 3

The lymphatic system transports the lymph and other fluids so interstitial fluid does not accumulate in tissue spaces.

It also absorbs digested fats and sends them to the venous circulation.

It coordinates the destruction of infectious microorganisms of many types, as well as toxins and cancer cells. Lymphocytes and macrophages are used to engulf and destroy them.

Question 4

primary functions of the lymphatic system

Answer 4

production, maintenance, and distribution of lymphocytes.

Transport excess fluid out of interstitial spaces in tissues and return it to the blood stream. May be up to to 3 litres of fluid a day.

Question 5

without the lymphatic system

Answer 5

fluid would accumulate in tissue spaces

Question 6

the production of lymphocytes is called?

Answer 6

lymphopoiesis

Question 7

what do the biochemicals and cells of the lymphatic system do?

Answer 7

They attack “foreign” particles in the body, allowing the destruction of infectious microorganisms and viruses, toxins, and cancer cells.

Question 8

the lymphatic system is…

Answer 8

the structural base of our immune system

Question 9

lymphoid organs and tissues contain…

Answer 9

lymphocytes and phagocytic cells.

together these play essential roles in how the body defends itself and resists disease.

Question 10

our immune system is divided into two parts:

Answer 10

the innate or non-specific defence system

the adaptive or specific defence system

Question 11

the innate defence system

Answer 11

protects the body continuously and quickly from foreign substances.

The skin and mucous membranes comprise the first line of defence against pathogens.

When either of these are compromised, the second line of defence uses phagocytes, antimicrobial proteins, and various other cells that attack invaders. Inflammation is the most important feature of the second line of defence.

Question 12

the adaptive or specific defence system

Answer 12

provides a third line of defence.

focus’s on certain foreign substances.

acts slower then the innate or non-specific defence system.

The term ‘specificity’ refers to the activation of needed lymphocytes and production of antibodies to achieve targeted effects.

Question 13

organisation of the lymphatic system: lymphatic pathways

Answer 13

Lymphatic capillaries for tiny tubes called lymphatic pathways, which merge to form larger vessels, eventually uniting with veins in the thorax.

Question 14

organisation of the lymphatic system: Lymphatic capillaries

Answer 14

microscopic lymphatic capillaries extend into interstitial spaces in complex networks.

The walls of lymphatic capillaries are a single layer of squamous epithelium that allows tissue fluid to enter.

The fluid inside these capillaries is called lymph.

They are found in loose connective tissue between cells and blood capillaries.

Not found in bones, bone marrow, teeth and all of the central nervous system.

In the CNS excess tissue fluid drains into the CSF.

Question 15

Inflammation effect on lymph capillaries

Answer 15

proteins easily enter lymph capillaries but cannot enter blood capillaries.

inflammation of tissues cause lymphatic capillaries to develop opening through which larger particles can pass.

These particles may include cancer cells, cell debris, and pathogens.

The pathogens can then use the lymphatics to travel elsewhere in the body. However because lymph moves through the lymph nodes, the particles are usually removed and evaluated by the immune system cells.

Question 16

Lacteals

Answer 16

specialised lymphatic capillaries located in the small intestine’s lining that absorb digested fats and carry them to the venous circulation.

The name lacteal comes from the appearance of the lymph, which resembles milk.

It is actually fatty lymph, known as chyle, that drains from the intestinal mucosa villi, which are finger-like in appearance.

Question 17

organisation of the lymphatic system: Valves similar to veins

Answer 17

Lymphatic vessels have valves preventing back-flow of lymph.

Therefore lymph moves through them in one direction: toward the heart.

Larger vessels lead to specialised organs known as lymph nodes and then continue on to form larger lymphatic trunks.

Question 18

organisation of the lymphatic system: tunics

Answer 18

Similar to veins the collecting lymphatic vessels have three tunics but with thinner walls.

The vessels also have more internal valves and experience anastomoses more frequently.

Question 19

anastomosis (plural anastomoses)

Answer 19

An anastomosis (plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf veins, or streams.

Question 20

major lymphatic trunks of the body are the paired:

Answer 20

lumbar trunks

Bronchomediastinal trunks

Subclavian trunks

Jugular trunks

and the single Intestinal trunk.

Question 21

lymphatic ducts

Answer 21

The lymph form lymphatic vessels drains as they join one of two collecting ducts.

The right lymphatic duct - lymph drainage of the right side of the head and thorax. It empties into the right subclavian vein near the right jugular vein.

The thoracic duct - is larger and longer, receiving lymph from the lower limbs, abdominal regions, left upper limb, and the left side of the head, neck, and thorax. It empties into the left subclavian vein near the left jugular vein.

Lymph then moves from the two collecting ducts into the venous system, becoming part of the plasma. This occurs just before the blood is returned to the right atrium.

Question 22

difference between lymph and tissue fluid

Answer 22

Lymph is basically the same as tissue fluid but is referred to as lymph once it has entered a lymphatic capillary.

Tissue fluid is made up of water and dissolved substances from the blood capillaries. It is very similar to blood plasma, containing gases, hormones, and nutrients.

However, it lacks plasma proteins because their size does not permit them to leave the blood capillaries.

Plasma colloid osmotic pressure helps to draw fluid back into the capillaries using the process of osmosis.

Question 23

Lymph formation

Answer 23

Lymph forms because filtration from blood plasma occurs at a higher rate than does reabsorption.

The hydrostatic pressure of tissue fluid is increased, inducing tissue fluid movement into the lymphatic capillaries.

Most of the small proteins the blood capillaries filtered earlier are returned to the bloodstream via the lymph.

Lymph also carries foreign particles, including bacteria and viruses, to the lymph nodes.

Question 24

Movement of lymph

Answer 24

The movement of limb is influenced by muscular activity because the lymphatic system has no organ that pumps lymph throughout its vessels.

Lymph itself is under low hydrostatic pressure, and it moves similarly to how blood moves through the veins.

Without contraction of skeletal muscles, smooth muscle contraction in the larger lymphatic trunks, and breathing related pressure changes, lymph may not flow easily.

Skeletal muscles, for example, compress lymphatic vessels to move the lymph inside, with valves preventing any backflow.

Breathing creates a relatively low thoracic cavity pressure during inhalation, aiding lymph circulation. The diaphragm increases abdominal cavity pressure, squeezing lymph out of abdominal vessels and into thoracic vessels.

Increased passive movements or physical activity cause lymph to flow more quickly. This balances the increased rate of fluid loss from the blood. Therefore, if a part of the body has a serious infection, immobilisation results in decreased flow of inflammatory material out of it.

The continuous movement of lymph stabilises fluid volume in the bodies interstitial spaces. When tissue fluid accumulates in the interstitial spaces, known as the edema, it is because of interference with lymph movement.

Edema commonly occurs after surgery when lymphatic tissue is removed, such as when a breast tumour is removed. In this example, axillary lymph Notes may be removed as part of the surgery to prevent cancer cells from being transported via nearby lymphatic vessels. This can obstruct upper limb draining, resulting in edema.