Overview of Immune system Part 2

Immune system

Innate immune defenses 

The immune system isn't like the other systems in their description. In other words, the immune system is not a full/specific organ like the other systems for example when we recall the digestive system we know we are talking about the stomach, small intestines, esophagus and so on, when we say the respiratory system we know we are talking about the lungs, alveoli sacs and etc..

The immune system is the lymph nodes, vessels, tracts & trunks, also lymphocytes and bone marrow, the immune system's job is a prerequisite in order to live, the immune system helps our body keep foreign invaders outside of our bodies such as bacteria, virus, and fungi that are waiting for any chance to use you and your body's resources to divide, so our body needs to develop special soldiers in order to avoid these bad guys, for example, our first line of defense like our external barricades is our skin, the skin is made of three layers 1)epidermis *the outermost layer* 2) dermis *the inner layer* 3) Hypodermis *the deeper layer*

1)Epidermis,  several layers of epithelial cells, Stratum(corneum, lucidum, granulosm& germinativum) at the surface of this layer where the exterior cells exists are dead keratinocytes cells exists which makes up the substance of skin called Keratin, at the base of its inner layer, there are pigment cells which secrete granules responsible for the color of the skin through cells called melanocytes, the darker is your skin the more active melanin you have and vice versa.

2)Dermis, lies beneath the epidermis, consisting of connective tissues, also is crucial since it contains blood capillaries, nerve endings, lymphatics, sweat glands, fat glands, fatty cells and hair follicles, the sweat gland is one of the various points we will talk about as something related to our immune system, these sweat glands through coiled tubes that reaches the skin surface through a pore secretes sweat which mainly consists of NaCl + water, some bacteria cannot bear the acidity of such secretions our skin releases, therefore our skin has sort type of immunity to our body so we categorize it in our innate immune defenses, also the presences of some peptides called defensins 
( antimicrobial polypeptides, they invade microbes )that also provides an immunity function by attacking any bacteria or fungi by binding to their membrane and increases their membrane permeability.

The presence of mucous membranes in our body that covers all the tracts that lead to the outside world such as digestive, respiratory, urinary & reproductive systems also have an immune function, mucous mainly composed of Mucin( mucin is a family of large heavily glycosylated proteins, ''glycosylation'' as a definition means the reaction in which a carbohydrate molecules ( glycosyl donor) is attached to any functional group of another molecule ( glycosyl acceptor) it is more likely a type of covalent bonding, these molecules or membranes tends to protect you from the outside world.

For example, your nasal passages containing mucous protect you from any harmful foreign invaders (airborne vectors) that you may inhale frankly as well as the presence of cilia which work on kicking out any tiny objects such as dust.

The saliva which your salivary glands secrete mucin, salts, and lysozymes among other things help protect you from anything you may take in while eating or through a mouth breath, lysozymes also known as bacteria-fighting enzymes destroys the bacteria's cell wall.

Your lacrimal eye fluid(tears) also has an immune function, it consists of water, electrolytes such as sodium & potassium, proteins such as lysozymes, immunoglobulins ( antibodies), mucin, defensins, and lipids among other things.

Your stomach which is a main digestive organ, any type of vector that somehow made it to your stomach can be eliminated due to the presence of acids secreted by the stomach in order to digest food such as HCl, pepsin, and enzymes secreted by the pancreas that tends to break down lipids, carbohydrates and proteins also tend to help in immunity.

In case any successful vector such as Staphylococcus bacteria( gram +ve bacteria) made it to through any cut you have made accidentally while peeling an orange, this induces your internal innate immune defenses where your body tends to activate a sort of weapons that work against these foreign objects such as fever, chemical signals, and inflammation,

What happens in the case of an infection?

It is a beautiful day until you accidentally cut your skin, nearby bacteria seize the opportunity and enters through your wound starting to divide, your body's first line of defense that arrive to the scene are phagocytes such as neutrophils which are the most abundant type of your innate immune cells they range in percentage of 40 to 70% they mainly destroy the bacteria and any toxins secreted by them their nucleus has two to six lobes also they tend to commit a suicide right after destroying any foreign invaders.

Another type of phagocytes which are bigger are Macrophages meaning big eaters, they have two types, mobile and fixed, the fixed ones such as those found in the liver where they are fixed on the liver cells tissues and others are mobile which has the ability to move around, they kill bacteria by engulfing them through cytoplasmic extensions through a process called phagocytosis, where the bacteria is eaten and digested due to the presence of various and more lysosomes ( lysosome is a cell organelle found in eukaryotic cells functions in digestion and waste removal so it has enzymes) these lysosomes tends to surround the bacteria and releases its enzymes, what characterizes the macrophages unlike the neutrophils they can devour many bacteria, fungi or viruses up to 100, macrophages are derived from immune phagocytic immune cells known as monocytes comprises about 3 to 8%, these cells that has left the bloodstream.

Natural killer cells, these cells aren't phagocytic, these immune cells patrol all your body cells looking up for any infected cells that has been infected by any sort of a vector, through cell signaling by sending messenger proteins which tends to activates a process known as apoptosis '' program cell death'' induces the cell to kill itself, the way the natural killer cells identify the infected or cancerous cells is that each normal cell has a special antigen called MHC1 '' Major histocompatibility complex'' also known as human leukocyte antigen ( are group of genes that expresses proteins found on the surface of cells that help the immune cells to identify any foreign invaders) but when any normal healthy cell gets infected they lose this antigen.

So back to the cut you had when you were peeling the orange, bacteria nearby embrace the opportunity and gets through, your body innately tends to protect you from any loss or any breach from foreign invaders into your body, so your damaged skin cells that have been affected by the cut releases chemicals known as chemokines ( small protein molecules, chemo>>chemical, kines>>kinetic*movable*) which tends to inform your body that something has gone wrong then this launches inflammatory response through chemicals, redness, swelling, heat, and pain for example in your dermis skin layer exactly in the connective tissue of this layer has specialized cells called mast cells ( are cells filled with basophils granules that releases histamine molecules & other substances during allergic reactions and inflammatory responses) mast cells basically fight worms, communicate with other cells, activate cells and causes inflammation as well among other things, histamine molecules one of the main factors of causing the inflammatory response, it goes to the capillaries feeding the skin cells with oxygen & nutrients  deeper into the endothelial cells layer stimulating them to widen & separate between each other to make the capillaries larger leading to what we call vasodilation which makes you feel with enlargement or swelling, this is helpful and are actual signs of healing since it helps increase the blood flow to the damaged tissue, platelets start to clot the wound in order to prevent more blood loss, fibroblasts found in the connective tissues secrete collagen( main structural protein found in the connective tissues of animals) towards the cut to take the shape of the original worn out tissue.
Since the capillaries are vasodilated and capillaries contain blood which in our case has lymphocytes and white blood cells that pass by, they will squeeze through the separated/widened capillaries moving towards the site of infection through a process called leukocytosis it is also a sign of inflammatory response where the number of white blood cells increases in number during an infection but when the foreign invaders are overwhelming the macrophages and neutrophils releases fever-inducing substances called pyrogen ( low molecular weight protein, endogenous since it is produced from the leucocytes) in response to the exogenous pyrogen released from the bacteria (foreign invaders) released into the blood circulation which stimulates the hypothalamus.
The hypothalamus is a section of the brain responsible for the production of many essential hormones that control different organs and cells, in our case the hypothalamus among other things is responsible for temperature regulation, thirst, and hunger, so when the pyrogen chemicals are released they stimulate the hypothalamus to increase the body temperature resulting in a higher metabolism of your cells making them consume more oxygen& nutrients leading to a faster healing, also this induces the liver and spleen to hold their iron and zinc in order to prevent the contribution of these materials to the growth of these foreign invaders that's why the person infected with any bacteria or virus tends to breathe heavily, lose appetite and feels sleepy among other things.

Thanks to the following websites and youtube channels for making this overview possible and I really hope you get educated and I am hoping you give me your feedback in the comments section, Thanks a lot.
References used:
http://www.healthline.com/human-body-maps/hypothalamus
http://medical-dictionary.thefreedictionary.com/pyrogen
https://www.britannica.com/science/major-histocompatibility-complex
https://www.boundless.com/physiology/textbooks/boundless-anatomy-and-physiology-textbook/integumentary-system-5/accessory-structures-of-the-skin-65/sweat-sudoriferous-glands-397-4497/
http://www.nature.com/eye/journal/v17/n8/fig_tab/6700566t1.html#figure-title
http://www.medicinenet.com/script/main/art.asp?articlekey=26300
https://www.youtube.com/channel/UC4a-Gbdw7vOaccHmFo40b9g  (Khan Academy)
https://www.youtube.com/channel/UCX6b17PVsYBQ0ip5gyeme-Q (CrashCourse)

Stay tuned for the next part, we will talk about some adaptive immune defenses!!

Diagram showing the existence percentage of some white blood cells in the blood

Capillary tube contents after centrifuge, discussing the presence of platelets that clots the damaged tissues, lymphocytes and white blood cells 

Capillary beds and the exchange of gases and nutrients to the damaged tissues