Infection and immunity Flashcards
What are the 3 roles of the lymphatic system?
Fluid balance
Fluid absorption
Defence
Describe the composition of the lymphatic system
The lymph capillaries and vessels
Lymph tissue and organs.
Why are lymph vessels more permeable than blood vessels?
They lack a basement membrane.
How do the lymph vessels promote the movement of fluid within them towards the heart?
One way semilunar valves,
Thin layer of muscle contained within the wall
Pressure from skeletal muscle contraction.
Describe the lymph drainage into the major veins.
Right arm, axillary region, and right side of heart drain into right sub-clavian. The rest of the body drains into the left sub-clavian.
Name the lyphoid organs
Lymph nodes, Tonsils, Spleen, Thymus gland
Describe the structure and function of a lymph node.
Rounded structures distributed along the lymphatic vessels composed of a cortex and a medulla.
Cortex contains lymphocyte germinal centres and medulla contains the phagocytic macrophages.
Functions include;
Fluid balance- 10% of fluid that leaves the blood returns to the heart via the lymph (3 litres)
Fat absorption- This is via lacteals in the GI tract. The lymph lacks a basement membrane so allows for easy permeability relative to blood vessels. A chyle is lymph milky in appearance from the presence of fat.
Defence- Drainage from sites of inflammation allows APCs to identify any pathogens by the lymphocytes aiding the immune response.
Describe Lymphadenopathy
Collective term for all lymph enlargement.
This can be lymphadenitis from infection (painful) or as a SOL due to metastasis from a tumour (firm and usually painless)
Describe the tonsils
Small masses of lymphoid tissue around the pharynx. They trap and remove bacteria however congestion with causes tonsillitis.
Describe the spleen
Largest lymphoid organ with two main tissue types
Red pulp- Receives Arterial blood and removes old RBCs and recycles the iron though macrophages.
White pulp- Contains T and B cell compartments. Recognise/removes pathogens and activates T and B cells.
It contains a store of blood for in the case of hemorrhagic shock and although its possible to live without a spleen it leaves the body open to certain infections more readily.
Spleen also produces opsonins to enhance phagocytosis and properdin which activates the alternative pathway complement system by binding to and promoting the hydrolysis of C3 into C3a and b.
Describe the thymus
Larger in infancy and puberty and shrinks in adults eventually getting fibrosed. Secretes thymosins and is a site of T lymphocyte maturation and production.
What is the role of hepcidin?
A chemical mediator that is released from the liver in response to inflammatory markers in the blood. It results in the sequestering of Iron to inhibit bacterial infection growth and proliferation. In chronic inflammation of neoplasia where there is a release of the markers it can lead to anemia of chronic disease.
Define an infection
An invasion of a host’s tissues by microorganisms and it can result in a loss of homeostasis of the body by a number of mechanisms i.e mutiplication, host response and toxins.
Provide an example of an intermediary transmission of an infection
An individual carrying MRSA on their skin and infecting someone else with it.
How can a patient get infected by a disease they are carrying?
Ordinary microbiota/ commensals that have a normal role in the right place. They can cause harm if they go into a new place.
What is horizontal transmission?
Contact, inhalation and ingestion.
What is vertical transmission?
from mother to child either at or before birth.
what are the 5 stages of an infection getting established in a host
exposure, adherence, invasion, multiplication and dissemination. The rate it occurs depends on a number of factors both of the patient and of the pathogens. These are known as virulence factors.
