BIOL1019 Chap.8 Lymphatics and Innate Immunity
Lymphatics and Innate Immunity
The lymphatic system returns excess tissue fluid to the blood, absorbs dietary fat and hosts much of the immune response. This chapter follows fluid from blood capillaries into blind-ended lymphatic capillaries with one-way flaps, through vessels and ducts with no pump of their own, back to the subclavian veins, and explains how blocked drainage produces lymphedema.
It separates primary lymphoid organs, red bone marrow and thymus, from secondary organs such as lymph nodes and spleen. The second half covers innate immunity, which works the same way against any pathogen: physical barriers as the first line, then phagocytes, natural killer cells, interferons, complement, inflammation and fever as the second.
Lymphatics and immunity are the last topic examined in Test 1, and the lecture concept checks ask you to identify lymphatic structures, explain lymph formation and movement, relate blocked drainage to lymphedema and describe the barriers and internal defences in turn.
What this chapter covers
- 01
Lymph formation and lymphatic capillaries
- 02
How lymph moves without a pump
- 03
Primary and secondary lymphoid organs
- 04
Lacteals and fat absorption
- 05
First line: physical barriers
- 06
Phagocytes, natural killer cells and interferons
- 07
Complement, inflammation and fever
- 08
Lymphedema when drainage fails
Worked example · free
Why a blocked lymphatic causes swelling
- +1Fluid leaves blood capillaries into the interstitial spaces and enters blind-ended lymphatic capillaries, becoming lymph.
- +1Overlapping endothelial cells act as one-way flaps, so fluid enters but cannot return to the tissues.
- +1With no pump, lymph is moved by smooth muscle in vessel walls, skeletal muscle contraction and breathing.
- +1When drainage is blocked, interstitial fluid accumulates and stagnates, producing the swelling of lymphedema.
Key terms
- Lymph
- Tissue fluid once it lies inside lymphatic vessels, low in protein and rich in lymphocytes.
- Lymphedema
- Swelling caused by blocked lymph drainage, in which interstitial fluid accumulates and stagnates.
- Interferon
- A cytokine released by a virus-infected cell that helps neighbouring cells resist viral replication.
- Opsonisation
- The coating of a pathogen by complement proteins that increases its uptake by phagocytes.
- Natural killer cell
- An innate lymphocyte that destroys abnormal cells with perforin without needing prior exposure.
Lymphatics and Innate Immunity FAQ
What is the difference between primary and secondary lymphoid organs?
Primary lymphoid organs produce and mature lymphocytes: red bone marrow, where all lymphocytes originate and B and NK cells mature, and the thymus, where T cells mature and are selected for self-tolerance. Secondary organs, such as lymph nodes, the spleen and nodules like the tonsils and Peyer's patches, are where antigens are encountered and responses begin.
What are the first and second lines of defence?
The first line is physical: the skin, the epithelial linings of internal passageways, flushing secretions such as tears, mucus and urine, and killing secretions such as stomach acid. The second line is internal and still non-specific: phagocytes, immunological surveillance by natural killer cells, interferons, complement, the inflammatory response and fever.
Why does inflammation cause redness, heat and swelling?
Injured tissue releases mediators that cause vasodilation, increasing blood flow to the area, which produces redness and heat. Vascular permeability then increases, letting fluid leak into the interstitial space, which causes swelling, and pain follows. Phagocytes recruited to the site clear pathogens and debris, which is the purpose of the response.
How do lacteals connect the lymphatic system to digestion?
Lacteals are the lymphatic capillaries found inside each intestinal villus. Dietary lipids, packaged as chylomicrons, and fat-soluble vitamins enter the lacteals rather than blood capillaries, then travel through lymphatic vessels and the thoracic duct before reaching the bloodstream. This is one of the three functions of the lymphatic system the course lists.
Exam move
Draw the fluid loop from blood capillary to subclavian vein and annotate the flaps, the three forces moving lymph and the two ducts. Make a table of lymphoid organs with columns for primary or secondary and capsule. Then list the seven innate defences and write one sentence each on how it removes a pathogen without any prior exposure.
Practise one inflammation answer as a strict sequence, from tissue injury through vasodilation and permeability to phagocyte recruitment, and link each step to the sign it produces.
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