The tedious process of muscle contraction

I'm pretty sure my body knows more biology then I do.

So muscle contraction requires ATP and Ca, Na, K, Cl ions. In order to acquire these, we have to eat food. Food enters our digestive system and encounters digestive enzymes. The nutritions are then absorbed in jejunum, and minerals like Ca, Na, K and Cl are absorbed in large intestine. All of these nutritions will then enter the blood stream.
In order to acquire ATP, one have to have glucose, fructose and galactose first. After glucose, fructose and galactose enters the blood stream. They may break the homeostasis of glucose in blood and have too high of a glucose level. As a result, the Beta cells in pancreas will release insulin into blood.

The body will send chemicals to the Beta cells. The receptors on the surface of the Beta cells will receive these chemicals and signal the nucleus of the Beta cell, which contains DNA of insulin and secrets insulin. Insulin will stimulate the body cells to take up more glucose and store it as glycogen.
If the glucose level in blood is too low, the body will secret chemicals that signal the receptors on the surface of pancreas Alpha cells. The receptors will then send the chemicals to the nucleus of Alpha cell, which contains DNA of glucagon. Alpha cells produce glucagon, which stimulates the liver to break down glycogen and release glucose into blood.

Glucose goes through cell respiration, and then ATP is made. 

Now, here's what happens to Ca homeostasis. When the level of Ca in blood is too low, parathyroid will detect the low Ca level and secret PTH, which stimulates kidney to secret Ca and activate Vitamin D to help Ca absorbing. It also activates Osteoclast, which crushes bones to release Ca into blood. When Ca level is too high in blood, thyroid will secret Calcitonin, which signals the kidney to take in Ca and signal Osteoblasts to build bone matrix to lower Ca level. 

With Ca, Na, Cl, K and ATP in the system, muscles are able to contract in the following way:

Sodium and potassium is pumped through the plasma membrane to produce an electrical current, which repels Ca to move tropomyosin to move away from the actin binding sites. ATP binds to the tip of the cross bridges on myosin and turns into ADP and P. The cross bridges then binds to the exposed active sites and move the muscle and contracts it.

 
 

Quiz -- Immune System

... Why a quiz on something we haven't learned...

1. Immediate nonspecific response
The skin serves as an outer barrier that blocks out some of the microorganisms. If the microorganisms enter the body through the respiratory system, reactions like coughing, sneezing and tearing will clear out some of them. Mucus secreted by the respiratory system also helps trap microorganisms, and the enzymes in mucus digests microorganisms too. Inflammation is also one of the immediate nonspecific response. If microorganisms enters body tissue, cells around that area will secret eicosanoids and cytokines, which produce fever to slow down bacteria reproduction and attract white blood cells to attack bacteria.

The complement system works like this: antibodies attach to carbohydrates on the surfaces of microbs. The recognition signal will trigger the production of all kinds of protease. This produces a catalytic cascade, which results in the production of peptides that attract immune cells.

Phagocytosis: Cells called phagocytes engulf pathogens and then form a vesicle with the pathogen in it. The vesicle then combine with lysosome, and pathogen is digested by enzymes.

2. Activates T and B cells in response to an infection

T Cells and B Cells are major lymphocytes. Killer T Cells recognize non-self cells by detecting the type of antigen with its receptor. If the antigen does not match up to self, Killer T Cells produces enzymes that puts the non-self cell into apoptosis. The Helper T Cell does not kill non-self cells itself. It uses receptors to detect the type of non-self cells and help immune system to react in the correct way. B Cells attach the antibodies on its surface to the antigens of non-self cells and attract Helper T Cells. They then produces antibodies that specifically signals this type of non-self cell. The antibodies circulates in lymph system and blood and bind to these non-self cells as markers for the immune system to recognize and destroy.

3. Responds to a later exposure to the same infectious agent

Vaccines basically help to expose B Cells and Helper T Cells to virus and produce antibodies that would bind to the virus and mark them as non-self the next time they see it and help the immune system to react.

4. Receptors on the surface of cells can only recognize self antigens. When receiving a mismatching antigen, it recognize the thing as non-self.

When cancer cells forms a tumor, they usually carry different antigens, which would help Killer T Cells to recognize them as non-self and attack them. However, sometimes the immune system cannot recognize the tumor cells because they produces chemicals that inhibits the immune system responses.