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What layers are there to the skin and what cells/structures are found in these layers

The outer layer of the skin is the epidermis, it consists of tightly packed dead cells, keratin and phagocytic immune cells. The inner layer is the dermis, it consists of a thick layer of connective tissue, collagen and blood vessels as well as more phagocytic immune cells.


What chemical defenses does the skin have? How do they work?

Antimicrobial peptides (skin definsins), these are active against bacteria, fungi and viruses and often work by forming pores in the microbial membrane.
Lysozyme, an enzyme which breaks down bacterial cell walls.
Sebum, this produces a low pH, making microbial colonisation difficult.
Salt, creates a hypertonic environement, dehydrating pathogens.


What is the structure of the mucous membranes? Where are they found?

Consists of 1-2 layers of tightly packed live cells which are constantly renewed as well as mucus producing goblet cells. The layers are the mucus layer on the vulnerable side of the mucus membrane, this mucus layer is produced by the goblet cells and moved by epithelial cells which make up the epithelium layer, behind this is fibrous connective tissue.
Mucus membranes are found throughout the body essentially anywhere where a semi internal contact environment is e.g ocular (eyes), respiratory, oral and urogenital/rectal areas.


What is the mucociliary escalator?

A pathway involving the movement of mucus towards the pharynx (throat) by the epithelial columnar cells' cilia in the lungs.


How is the gastrointestinal tract protected from microbes?

The stomach has a low pH, digestive enzymes are produced by the intestines, bile from the gall bladder inhibits growth of some microbes and there is a mucus layer in the stomach as well.


How do the eyes have added defense?

The tears contain lysozyme and are also flushed into the throat which can be swallows, killing the microbes by digestion?


How does the urogenital tract have extra defense?

Urine has a high osmolarity (draining microbes of water), contains lysozyme, has a low pH and the urine flow helps expel microbes.


Where are cilia found on the mucus membranes?

In the trachea and uterine tubes.


What types of responses does a pathogen infection provoke? What do these do?

Anti microbial peptide production (defensins or cathelicidins, produced by epithelial cells lining mucosal surfaces and keratinocytes in the skin, interfere with growth and reproduction of microbes (causing death and can act as chemo attractants for inflammatory cells.))

Interferon production: main type is type 1 interferon, a protein (chemical messenger/cytokine) produced by host cells to combat viruses, produced by virus infected cells to prevent infection in neighbouring cells for 3-4 days but can have side effects (e.g muscle aches, chills, headache and fever).
Also activates the complement system (a cascade of enzymatic reactions which leads to killing of microbes).


What is the proper name for white blood cells? What are the three lineages of blood cells and what is the common link?

Leukocytes.is the poper name for white blood cells. The three blood cell lineages are the Erythroid (red blood cells/erythrocytes),
the myeloid (granulocytes, monocytes, dendritic cells and platelets, these are innate immune cells)
and the lymphoid (B and T lymphocytes (adaptive immune cells)).
All of these cells are derived from the same hematopoietic stem cells found in the bone marrow.


What cells are granulocytes? What do they do?

Neutrophils: The most abundant granulocyte in the blood, a highly phagocytic cell with a short half life, the numbers increase hugely during a bacterial infection.

Eosinophils: one of the lower proportion cells in the blood, does some phagocytosis but mainly releases toxic granules to kill and break down microbes and parasites (like worms), these are responsible for allergic reactions and indicate a parasitic infection if levels are high.

Basophils: very low numbers in the blood (the lowest), conduct no phagocytosis but do release granules which can cause allergic reactions or fight worm infections.

Mast cells: line the mucosal surfaces (not found in blood) and release granules that attract other white blood cells to areas of tissue damage.


What are monocytes and macrophages? What do they do?

Monocytes are the form of macrophages before they reach the blood, in this form they don't do much phagocytosis, once they leave the blood (enter tissues) however they become macrophages. These macrophages become resident (known as sessile) or move through tissues (migratory) and conduct phagocytosis, release chemical messengers and show information about pathogenic microbes to T cells.


What are dendritic cells?

A cell found in low numbers in the blood and all tissues which are exposed to the environment. They are phagocytic and are the most important cell for the triggering of the adaptive immune response.


How do immune cells move around the body?

The cells are carried in the blood and in the lymph vessels, they can leave from the blood to enter tissues. If they enter the lymphatic vessels from tissue they will drain into lymph nodes.


What are the signs of inflammation and why do these occur?

heat, redness, swelling and pain. These occur because mast cells will secrete chemicals upon damage to the tissue, these are histamine (vasodilation), prostaglandins (vascular permeability) and leukotrienes (vascular permability), the extra permability and vasodilation (as well as a single for white blood cells to arrive) leads to more cells in the tissue than normal, causing the symptoms experienced.


What is a fever? Why does it occur?

A fever is when the core body temperature is over 37 degrees celcius, caused by a resetting of the body's thermostat in the hypothalamus due to pyrogens (interleukin-1) which are released after ingesting bacteria, once the phagocytosis stops the signal stops and the thermostat resets to normal.