Anatomy and Physiology of the Lymphatic and Immune Systems

Question 1

LYMPHATICS

List the 3 main functions of the lymphatic system.

Answer 1

1. Immunity
2. Lipid Absorption
3. Fluid recovery

Question 2

LYMPHATICS

How does Immunity work within the lymphatic system?

Answer 2

Fluids from all capillary beds are filtered at lymph nodes by immune cells

Immune cells stand ready to respond to foreign cells or chemicals encountered

Question 3

LYMPHATICS

How does Lipid absorption work within the lymphatic system?

Answer 3

Lacteals in small intestine absorb dietary lipids

Question 4

LYMPHATICS\

How does Fluid recovery work within the lymphatic system?

Answer 4

Fluid recovery absorbs a small amount of plasma proteins and 2-4L/day of fluid from tissues and returns it to the bloodstream via the subclavian veins

Question 5

LYMPHATICS

What happens when Fluid Recovery does not function correctly?

Answer 5

Interference with lymphatic drainage leads to severe oedema (swelling)

Question 6

LYMPHATICS

Describe the structure of lymph and lymphatic vessels.

Answer 6

Lymph is:

• clear, colourless fluid, similar to plasma but with much less protein
• formed from fluid that has leaked out of the capillaries

Lymphatic capillaries are:
- smallest of the lymphatic vessels
- closed at one end
- endothelial cells loosely overlapped
- allow bacteria and other cells entrance to
- lymphatic capillary
- creates valve-like flaps that open when interstitial
fluid pressure is high, and close when it is low
- slightly larger in diameter than blood capillaries

Question 7

LYMPHATICS

Order the flow of lymph from smallest to largest of lymphatic vessels.

Answer 7

1. Lymphatic capillaries converge to form collecting vessels
2. Collecting vessels: course through many lymph nodes and travel with veins and arteries
   
   • Collecting vessels converge to form lymphatic trunks
3. Lymphatic trunks: 6 of them drain major portions of body and converge to form collecting ducts
4. Collecting ducts :
   
   • right lymphatic duct – receives lymph from R arm, R side of head and thorax; empties into R subclavian vein
   • thoracic duct - larger and longer, begins as a prominent sac in abdomen called the cisterna chyli; receives lymph from below diaphragm, L arm, L side of head, neck and thorax; empties into L subclavian vein

Question 8

LYMPHATICS

Study the integration of the lymphatic system and the cardiovascular system.

Answer 8

Question 9

LYMPHATICS

List 5 mechanisms by which lymphatic return is achieved.

Answer 9

1. Rhythmic contractions of lymphatic vessels
   stretching of vessels stimulates contraction
2. Skeletal muscle pump
3. Thoracic pump aids flow from abdomen to thoracic cavity
4. Valves prevent backward flow
5. Rapidly flowing blood in subclavian veins, draws lymph into it

NB Exercise significantly increases lymphatic return

Question 10

LYMPHATICS

Name the major types of lymphatic cells and state their function.

Answer 10

1. T lymphocytes (T cells)
2. B lymphocytes (B cells)
3. Natural killer (NK) cells (another type of lymphocyte)
4. Antigen Presenting Cells (APCs)

Question 11

LYMPHATICS

What are T Lymphocytes (T Cells)?

Answer 11

Function to recognise & attack foreign antigens

Mature in the Thymus

Question 12

LYMPHATICS

What are B Lymphocyte cess (B Cells)?

Answer 12

Activation causes proliferation and differentiation into plasma cells that produce antibodies

Mature in Bone

Also memory B cells that do not differentiate

Question 13

LYMPHATICS

What are Natural killer (NK) cells?

Answer 13

Another type of lymphocyte

Attack bacteria, transplanted tissues and infected host cells

Question 14

LYMPHATICS

Describe structure and function of lymph nodes.

Answer 14

Are the most numerous lymphatic organs

Elongated kidney bean shaped structure of 3 cm in length

Their two functions are to filter the lymph and act as a site of T and B cell activation

Fewer efferent vessels exiting compared to afferent vessels entering slows flow through node to aid filtering

Contain reticular and dendritic cells and also macrophages which phagocytise foreign matter

Approx 450 nodes found widespread throughout the body but tend to be concentrated in groin, axilla, cervical region, abdomen and behind knee.

Question 15

LYMPHATICS

Describe structure and function of thymus.

Answer 15

Lymphatic organ in superior mediastinum

Houses developing lymphocytes and secretes hormones

Contains epithelial cells which;
- form blood thymus barrier
- isolates developing T lymphocytes from foreign
antigens
- secretes hormones (thymopoietin, thymulin and
thymosins)
- to promote development and deployment of T
lymphocytes
Very large in foetus; after age 14 begins involution
- in elderly mostly fatty and fibrous tissue

Question 16

LYMPHATICS

Describe structure and function of spleen.

Answer 16

Largest lymphatic organ located between diaphragm, stomach and left kidney

Primarily an open microcirculation!

Functions include - blood production in foetus and blood reservoir, RBC disposal (“red blood cell graveyard”, macrophages engulf worn out RBCs) and immune surveillance with its large numbers of WBCs

Question 17

IMMUNE SYSTEM - INNATE IMMUNITY

What are the two major categories of immune mechanisms.

Answer 17

Innate immunity:

consists of defences we’re born with and that protect us from a broad spectrum of disease agents;

- encompasses the first and second lines of 
  defence. 

Adaptive immunity:

constitutes the third line of defence and is distinguished by its capacity for immune memory.
- Itadaptsthe body to the presence of a pathogen
so we become less vulnerable to the illness it could
otherwise cause.

NB There is extensive interaction between the two, they’re not entirely separable or independent.

Question 18

IMMUNE SYSTEM - INNATE IMMUNITY

What are the mechanical and chemical barriers of defence?

Answer 18

Skin features that aid in defence:

- Surface composed mainly of keratin, a tough protein few pathogens can penetrate. 
- Microorganisms continually cast off as we shed surface keratinocytes.
- Dry and poor in nutrients limits microbial growth (exceptions e.g. axillary and pubic areas). 
- Coated with diverse antimicrobial chemicals. 
       - Sweat and sebum create and acidic environment that inhibits bacterial growth. 
       - Skin-produced peptides destroy bacteria, viruses, and fungi. 
       - Defenses are enhanced by vitamin D (calcitriol).

Mucous membranes protect digestive, respiratory, urinary, and reproductive tracts.

- Sticky mucus traps microorganisms. 
- In respiratory system mucus are moved by cilia to the pharynx, swallowed, and destroyed by stomach acid. 
- Flushed from the upper digestive tract by saliva and from the lower urinary tract by urine. 
- Mucus, tears, and saliva containlysozyme,an enzyme that destroys bacteria by dissolving their cell walls.

Areolar tissue beneath the skin and mucous membranes contains hyaluronic acid.

- Difficult for microorganisms to pass through this sticky tissue gel. 
- Some pathogens (and snake venom) produce the enzyme hyaluronidase, aiding invasion of the connective tissues.

Question 19

IMMUNE SYSTEM - INNATE IMMUNITY

Categorise the components of innate (non-specific) immunity, identifying the white blood cells associated with this defence.

Answer 19

1. Antimicrobial Proteins
2. Neutrophils
3. Eosinophils
4. Basophils
5. Monocytes & Macrophages

NB Neutrophils, eosinophils and basophils are granulocytes.

Question 20

IMMUNE SYSTEM - INNATE IMMUNITY

RECALL FROM MICROBIOLOGY

What is a Pathogen?

Answer 20

Disease-causing microorganisms (also known as infectious agents). Only about 3% of known microbes are pathogenic.

Question 21

IMMUNE SYSTEM - INNATE IMMUNITY

RECALL FROM MICROBIOLOGY

What is non-pathogens?

Answer 21

Microbes that do not cause disease. The vast majority of microorganisms are non-pathogens.

Question 22

IMMUNE SYSTEM - INNATE IMMUNITY

What are the 3 lines of defence against pathogens and other threats?

Answer 22

Thefirst line of defenceconsists of epithelial barriers and secretions
- Skin and mucous membranes, impenetrable to
most of the pathogens that daily assault us.

Thesecond line of defenceconsists of protections against pathogens that break through those external barriers.
- Include leukocytes and macrophages,
antimicrobial proteins, natural killer cells, fever, and
inflammation.

Thethird line of defenceis adaptive immunity.
- Group of mechanisms that defeat a specific
pathogen AND leave the body with memory.
- Memory enables rapid defeat of pathogens so
future encounters with pathogen cause no illness.

Question 23

IMMUNE SYSTEM - INNATE IMMUNITY

What are the 3 characteristics of INNATE immunity?

Answer 23

1. It’slocal: targets pathogens at the
   point of invasion. Fever is an exception, having
   asystemic(body-wide) effect.
2. It’snon-specific:Each mechanism
   of innate immunity acts against a broad spectrum
   of disease agents, not against one particular
   pathogen
3. Lacks memoryof any prior exposure to a
   pathogen, so it is no easier to defeat that
   pathogen on later exposures than it
   was the first time.

Question 24

IMMUNE SYSTEM - INNATE IMMUNITY

What are the 3 characteristics of ADAPTIVE immunity?

Answer 24

1. Adaptive immunity has systemic effects:acts
   throughout the body to defeat that pathogen
   wherever it may be found.
2. Adaptive immunity has specificity:Directed against
   antigens. Immunity to one disease e.g. chickenpox
   doesn’t confer immunity to others e.g. tetanus.
3. Adaptive immunity has memory:When re-exposed
   to the same antigen, the body reacts more quickly
   and efficiently. The reaction time for innate
   defences, by contrast, is just as long for later
   exposures as for the initial one.

Question 25

IMMUNE SYSTEM - INNATE IMMUNITY

What are the 3 basic defences of INNATE immunity?

Answer 25

1. Protective proteinssuch as keratin, interferons, and complement;
2. Protective cellssuch as neutrophils and macrophages (not lymphocytes); and
3. Protective processessuch as fever and inflammation.

Question 26

IMMUNE SYSTEM - INNATE IMMUNITY

What are the 2 defences of the ADAPTIVE immunity and the 2 lymphocytes that are involved?

Answer 26

Humoral immunity from antibodies
- made by B cells (plasma cells)

Cell-mediated immunity
- from T cells.

Question 27

IMMUNE SYSTEM - INNATE IMMUNITY

What are the two families of blood-borne antimicrobial proteins?

Answer 27

Interferon and Complement system.

Question 28

IMMUNE SYSTEM - INNATE IMMUNITY

Function of Interferons in Immune System.

Answer 28

Interferons are secreted by virus-infected cells and act to ‘warn’ surrounding cells to protect themselves.

- Break down viral genes
- Prevent viral replication 
- Activate NK cells and macrophages to destroy infected cells before they release virions. 

Interferons also confer resistance to cancer, since the activated NK cells destroy malignant cells.

Question 29

IMMUNE SYSTEM - INNATE IMMUNITY

Function of Complement system in Immune System.

Answer 29

The complement system contributes to both innate and adaptive immunity.

Inactive complement proteins circulate in the blood and are activated by pathogens:

- Classical pathway - requires antibodies (adaptive immunity). 
- Alternative pathway - viruses, bacteria, and yeasts (and tumour cells).
- Lectin pathway - carbohydrates on a microbial cell surface. 

Activated complement helps destroy pathogens by four methods:

- Enhances inflammation;
- Mediates immune clearance (clears away antigen–antibody complexes);
- Stimulates phagocytosis (coats microbial cells making them ‘sticky’ to phagocytes);
- Perform cytolysis (proteins formmembrane attack complex (MAC) thatpunches holes in the target cell.

Question 30

IMMUNE SYSTEM - INNATE IMMUNITY

Role of Antimicrobial Proteins in immune system.

Answer 30

Many proteins inhibit microbial reproduction providing short-term, non-specific resistance to pathogens.

Question 31

IMMUNE SYSTEM - INNATE IMMUNITY

Role of Neutrophils in immune system.

Answer 31

Found particularly in the connective tissues killing bacteria.
Phagocytosis and digestion
Degranulation produces a cloud of bactericidal chemicals.
When bacteria are detected lysosomes migrate to cell surface andrelease enzymes that surround pathogen.
Enzymes catalyse chemical reactions that form a killing zonearound the neutrophil, destroying many bacteria.
These oxidising agents are also damaging to connective tissues.

Question 32

IMMUNE SYSTEM - INNATE IMMUNITY

Role of Eosinophils in immune system.

Answer 32

Reside especially in the mucous membranes.

Accumulate at sites of allergy, inflammation, or parasitic infection.

Degranulation of superoxide and hydrogen peroxide helps to kill parasites too big to phagocytise.

Also produce toxic proteins including a neurotoxin which paralyses parasites such as tapeworms and roundworms.

Secrete enzymes that degrade and limit histamine and other inflammatory chemicals (control excessive effects of inflammation) that could damage tissue.

Question 33

IMMUNE SYSTEM - INNATE IMMUNITY

Role of Basophils in immune system.

Answer 33

Secrete chemicals (cytokines) that aid the mobility and action of other leukocytes.

- leukotrienesactivate and attract neutrophils and eosinophils
- the vasodilatorhistamine increases blood flow and delivers leukocytes to the area
- the anticoagulantheparin inhibits blood clotting that would impede leukocyte mobility. 

These substances are also produced bymast cells,a type of connective tissue cell similar to basophils.

Question 34

IMMUNE SYSTEM - INNATE IMMUNITY

Role of Monocytes & Macrophages in immune system.

Answer 34

Leukocytes that migrate from the blood into the connective tissues and mature into macrophages.

Macrophages are widely distributed in the loose connective tissues.

Specialised forms with more specific localities:

- microgliain the central nervous system
- alveolar macrophagesin the lungs
- stellatemacrophagesin the liver
- Langerhans cells in the skin.

Act as antigen presenting cells – introduces antigens to T and B lymphocytes.

Question 35

IMMUNE SYSTEM - INNATE IMMUNITY

Describe the defensive functions of various types of leukocytes and macrophages

Answer 35

NK cells circulate detecting pathogens or diseased host cells.

Target bacteria, cells of transplanted organs and tissues, cells infected with viruses, and cancer cells.

Question 36

IMMUNE SYSTEM - INNATE IMMUNITY

Define fever.

Answer 36

The abnormal elevation of body temperature AKA Pyrexia.

- Shivering generates heat and cutaneous arteries constrict to reduce heat loss. 
- Pyrogen secretion stops when the infection is resolved and the hypothalamic thermostat is reset back to normal. 
- Heat-losing mechanisms e.g. cutaneous vasodilation and sweating are activated. 
- Excessively high temperature can be dangerous - speeds up enzymatic pathways causing cellular dysfunction. 
- Above 40.5°C  can cause delirium, convulsions and coma, and death or brain damage common from fevers from 44° to 
  46°C

Question 37

IMMUNE SYSTEM - INNATE IMMUNITY

What does Fibrile mean?

Answer 37

Pertains to fever

- Usually beneficial because it: 
      - promotes interferon activity
      - inhibits reproduction of bacteria and viruses and 
      - elevates metabolic rate and accelerates tissue repair

Question 38

IMMUNE SYSTEM - INNATE IMMUNITY

What are Exogenous pyrogens?

Answer 38

Fever-producing agents from outside the body (e.g. surface molecules of bacteria and viruses)

 - Neutrophils and macrophages attack such pathogens, secreting a variety endogenous pyrogens (fever-producing 
   agents that come from inside the body)

 - These stimulate neurons of the anterior hypothalamus to raise the set point for body temperature.

Question 39

IMMUNE SYSTEM - INNATE IMMUNITY

What is Inflammation and its purpose?

Answer 39

Local defensive response to tissue injury of any kind, including trauma and infection.

Purposes are to:

 - limit the spread of pathogens and ultimately destroy them;
 - remove the debris of damaged tissue; and 
 - initiate tissue repair.

The suffix’-it is’means inflammation of specific organs and tissues:e.g. arthritisanddermatitis

Question 40

IMMUNE SYSTEM - INNATE IMMUNITY

What 4 cardinal signs is inflammation characterised by?

Answer 40

Redness
Swelling
Heat
Pain

Impairment (loss of function) may or may not occur, mostly caused by the pain.

Question 41

IMMUNE SYSTEM - INNATE IMMUNITY

What are the 3 major processes that occur in inflammation?

Answer 41

Mobilization of defences

Containment and destruction of pathogens

Tissue clean-up and repair.

Question 42

IMMUNE SYSTEM - INNATE IMMUNITY

Where can inflammation occur?

Answer 42

Inflammation occurs anywhere, most common and observable in trauma prone skin.

Question 43

IMMUNE SYSTEM - INNATE IMMUNITY

What are the types of cells and chemicals that regulates inflammation?

Answer 43

Cytokines - small proteins that regulate inflammation by forming a communication network among immune cells.

Cytokines include:

- interferons
- interleukins
- tumour necrosis factor
- chemotactic factors.

Question 44

IMMUNE SYSTEM - INNATE IMMUNITY

Explain the mobilisation of defences in innate immunity.

Answer 44

Vasoactivechemicals dilate the blood vessels in the area of injury.
- Histamine, leukotrienes, and other cytokines secreted by basophils, mast cells, and damaged cells.

Increased local blood flow delivers leukocytes, and washes toxins and metabolic wastes from the tissue.

Vasoactive chemicals stimulate increased permeability of blood vessels

Movement of fluid, leukocytes, and plasma proteins including complement, antibodies, and clotting factors which help combat pathogens into surrounding tissue.

Question 45

IMMUNE SYSTEM - INNATE IMMUNITY

Explain containment and destruction of pathogens.

Answer 45

Fibrinogen* filters into injured tissue fluid and clots form adjacent to the injury, isolating pathogens.

Heparin prevents clotting in the immediate area of the injury, pathogens are trapped in a fluid pocket surrounded by a capsule of clotted fluid.

Pathogens are attacked by antibodies, phagocytes, and other defences.

NB Remember fibrinogen from the blood clotting lecture

Question 46

IMMUNE SYSTEM - INNATE IMMUNITY

Explain tissue clean-up and repair in inflammation.

Answer 46

Monocytes mature into macrophages and are major agents of tissue clean-up and repair.

Macrophages phagocytise bacteria, damaged host cells, and dead and dying neutrophils.

Macrophages also act as antigen-presenting cells, activating the processes of adaptive immunity.

Oedema contributes to tissue clean-up: compressing veins and reducing venous drainage, promoting lymphatic drainage.

Neutrophils and most macrophages die, combining with tissue debris and fluid to form pus.

Fibroblasts multiply and synthesize collagen for tissue repair

Question 47

IMMUNE SYSTEM - ADAPATIVE IMMUNITY

Describe the types of adaptive immunity.

Answer 47

Two types of adaptive immunity, cellular and humoral immunity, interact extensively and often respond to the same pathogen.

Cellular (cell-mediated) immunity – T cells:
- Lymphocytes directly destroy foreign cells or diseased host cells.
- Means of ridding the body of pathogens that reside inside human cells, where they are inaccessible to antibodies e.g.
intracellular viruses, bacteria, yeasts, and protozoans.
- Acts against parasitic worms, cancer cells, and cells of transplanted tissues and organs.

Humoral (antibody-mediated) immunity – B cells:
- Antibodies don’t directly destroy pathogens but tag them for destruction
- Humoralrefers to antibodies dissolved in the body fluids.
- Humoral immunity is effective against extracellular viruses, bacteria, yeasts, protozoans, and molecular (noncellular)
disease agents such as toxins, venoms, and allergens.
- In a mismatched blood transfusion, it also destroys foreign erythrocytes.

Question 48

IMMUNE SYSTEM - ADAPTIVE IMMUNITY

Describe the four properties of adaptive immunity.

Answer 48

Active Immunity - the body makes its own antibodies and T cells against a pathogen, providing lasting protection.
Passive Immunity - acquired from another person or animal immune to the pathogen
Natural Immunity - a result of natural exposure to an antigen
Artificial Immunity - results artificial exposure to an antigen, e.g. vaccination

Question 49

IMMUNE SYSTEM - ADAPATIVE IMMUNITY

Describe the four combinations of properties of adaptive immunity.

Answer 49

Natural active immunity - production of own antibodies or T cells as a result of natural exposure to an antigen.

Artificial active immunity - production of own antibodies or T cells as a result ofvaccination.

Natural passive immunity - temporary immunity from acquiring antibodies produced by another person. Foetal acquisition of maternal antibodies through the placenta, or baby may acquire them during breast-feeding.

Artificial passive immunity - temporary immunity from injection of immune serumfrom another person or animal with antibodies against a pathogen. Immune serum used for emergency treatment of snakebites, botulism, tetanus, rabies, and other diseases.

Question 50

IMMUNE SYSTEM - ADAPATIVE IMMUNITY

Explain the roles of B cells in adaptive immunity defence.

Answer 50

B cells recognise specific antigens and produce the antibody against that particular antigen.

When stimulated, the B cell starts dividing, making copies of itself (clonal expansion).

Most of these B cells mature into plasma cells which produce antibodies.

Some B cells remain as memory B cells, for the next time the antigen is encountered – this provides immunological memory.

Question 51

IMMUNE SYSTEM - ADAPATIVE IMMUNITY

Explain the roles of T cells in adaptive immunity defence

Answer 51

T lymphocytes directly attack and destroy diseased or foreign cells, and the immune system remembers the antigens of those invaders and prevents them from causing disease in the future

Question 52

IMMUNE SYSTEM - ADAPATIVE IMMUNITY

Describe the 4 principal types of T lymphocytes.

Answer 52

Cytotoxic T (TC) cells(or CD8+ T cells) carry out the attack on foreign cells. (TC recognize diseased or foreign cells and release chemicals that will destroy it).

Helper T (TH) cells(or CD4+ T cells) promote the action of TCcells as well as play key roles in humoral and innate immunity.

Regulatory T (TR) cellsinhibit multiplication and cytokine secretion by other T cells, down-regulating TCactivity when pathogens are defeated.

Memory T (TM) cellsare descended from TCcells and are responsible for memory in cellular immunity.

Question 53

IMMUNE SYSTEM - ADAPATIVE IMMUNITY

List the five classes of immunoglobulins (antibodies).

Answer 53

IgA
IgD
IgE
IgG
IgM

Question 54

IMMUNE SYSTEM - ADAPATIVE IMMUNITY

Compare the five classes of immunoglobulins

Answer 54

IgA: in blood plasma and in mucus, tears, milk, saliva, and intestinal secretions. Prevents pathogens adhering to epithelia and penetrating underlying tissues. Provides passive immunity to the newborn through breast milk and colostrum. Dimer structure.

IgD: activation of B cells by antigens, surface protein on B cells.

IgE: basophils and mast cells. Stimulates release histamine and other inflammatory mediators; immediate hypersensitivity reactions, eosinophils mobilisation in parasitic infections.

IgG: ~80% of circulating blood plasma antibodies; main antibody in 2o immune response; e.g. Anti-D antibodies of the Rh blood group (crosses placenta).

IgM: ~10% of circulating antibodies in plasma. Main antibody in the 1o immune response; e.g. anti-A and anti-B agglutinins of the ABO blood group. Pentamer structure.

Question 55

IMMUNE SYSTEM - ADAPATIVE IMMUNITY

Explain the functions of antibodies.

Answer 55

Antibodies use four mechanisms to render antigens harmless:
- Neutralization:masking critical regions of an antigen molecule by antibodies.
- Complement fixation:antibodies bind complement proteins to an enemy cell, leading to its destruction.
- Agglutination:clumping of enemy cells by antibodies, effective as a defence against bacteria. An antibody molecule has
2 to 10 binding sites so it can bind to antigen molecules on many enemy cells at once and stick them together.
Neutrophils and macrophages can phagocytize agglutinated clusters of bacteria more efficiently than phagocytizing
bacteria one at a time.
- Precipitation:antigen molecules (not whole cells) are clumped by adhesion to antibodies creating large Ag–Ab
complexes that can be removed by immune clearance or phagocytized by eosinophils

Question 56

IMMUNE SYSTEM - ADAPATIVE IMMUNITY

Explain Memory in Humoral Immunity.

Answer 56

The humoral immune reaction to first exposure to the antigen is theprimary response.
Protective IgM antibodies appear first after 3 to 6 days, as naive B cells must multiply and differentiate into plasma cells. Replaced by IgG antibodies later.
Antibody titre(level in the blood plasma) begins to rise.
The primary response leaves an immune memory of the antigen.
When re-exposed to the same antigen plasma cells form quickly, IgG titre rises sharply and to a greater extent and peaks within a few days.
IgG remains elevated for weeks to years, conferring lasting protection.