Flu shots only protect against the most common flu viruses, and every now and then a slightly different type spreads more than expected. Usually when this happens, the existing flu shot gives some protection so that even if a person who had a flu shot catches it, they do not get as sick.
Some flu viruses are caught from animals. Bird flu, for example, is usually only caught by people in contact with sick birds (usually chickens). These types of flu virus are usually very limited, and while they can make a person very ill, usually other people do not catch the virus from the sick person.
Another way that the flu can change is when a person or animal catches two different flu viruses. The two viruses can exchange some of their genetic information, which can create a brand new flu that nobody has ever caught before.
If an animal flu virus changes in this way to one that can easily pass from human to human, many people become ill because nobody has any immunity to the new virus. Often, a brand new virus is more severe and kills more people.
New types of flu virus are usually what causes pandemics, and that is the reason many scientists have been following Bird Flu so closely—it kills six people out of every ten who catch it. This would be a very serious problem if it changes enough to spread easily between people.
This new flu virus got its name because it contains genetic parts that are commonly found in flu viruses that infect pigs. It is not spread by pigs or by eating pork—this is a new human virus being spread by humans. The name was the 2009 flu pandemic.
Although information is still coming out about swine flu, so far it does not seem to be as severe as bird flu or the flu that caused the influenza pandemic of 1918 (also known as Spanish flu), but it is much too early to predict whether it will cause the next flu pandemic.
Pancreas
The pancreas is an organ that makes hormones and enzymes to help digestion. The pancreas helps break down carbohydrates, fats, and proteins. The pancreas is behind the stomach and is on the left side of the human body.
The part of the pancreas that makes hormones is called the Islets of Langerhans. The Islets of Langerhans are a small part (2%) of the total cells in the pancreas. The Islets of Langerhans change which chemical they make depending on how much of other chemicals are already in the blood. So, the pancreas works to keep the level of chemicals in balance in the body. If the Islets of Langerhans stop working, a person will suffer from a disease called diabetes. Doctors are experimenting with taking the Islets of Langerhans cells from a donor body and putting them into the pancreas of a person with diabetes to make that person well.
The pancreas belongs to two systems of the body: the digestive system for its role in breaking down nutrients, and the endocrine system for producing hormones.
The pancreas releases these hormones:
The pancreas releases many different enzymes to help digestion:
Chloroplast
A chloroplast is a small organelles inside the cells of plants and algae. They absorb light to make sugar in a process called photosynthesis. The sugar can be stored in the form of starch. Chloroplasts contain the molecule chlorophyll, which absorbs sunlight for photosynthesis. In addition to chlorophyll, a chloroplast uses carbon dioxide (CO) and water (HO) to form sugar and gives off oxygen (O). Chlorophyll is what gives green plants their green colour. Chloroplasts also contain various yellow and orange pigments to assist in photon capture for photosynthesis.
Each chloroplast is surrounded by a double walled semi-permeable membrane. These are collectively known as peristromia. In the layered stacks are flat disk-shaped thylakoids. They contain light-absorbing pigments, including chlorophyll and carotenoids, as well as proteins which bind the pigments. Like mitochondria, chloroplasts also contain their own DNA and ribosomes.
Chloroplasts are one of the many different types of organelles in the cell. They are thought to have originated as endosymbiotic cyanobacteria. This was first suggested by Konstantin Mereschkowski in 1905 after an observation by Schimper in 1883 that chloroplasts closely resembled cyanobacteria. Almost all chloroplasts are thought to derive directly or indirectly from a single endosymbiotic event.
Mitochondria also had a similar origin, but chloroplasts are found only in plants and protista. In green plants, chloroplasts are surrounded by two lipid-bilayer membranes. They are thought to correspond to the outer and inner membranes of the ancestral cyanobacterium. Chloroplasts have their own genome, which is much smaller than that of free-living cyanobacteria. The DNA which remains shows clear similarities with the cyanobacterial genome. Plastids may contain 60–100 genes whereas cyanobacteria often contain more than 1500 genes. Many of the missing genes are encoded in the nuclear genome of the host.
In some algae (such as the heterokonts), chloroplasts seem to have evolved through a secondary event of endosymbiosis, in which a eukaryotic cell engulfed a second eukaryotic cell containing chloroplasts, forming chloroplasts with three or four membrane layers. In some cases, such secondary endosymbionts may have themselves been engulfed by still other eukaryotes, thus forming tertiary endosymbionts. In the alga "Chlorella", there is only one chloroplast, which is bell-shaped.
In some groups of mixotrophic protists such as the dinoflagellates and some sea slugs, chloroplasts are separated from a captured alga or diatom and used temporarily. These klepto (stolen) chloroplasts may only have a lifetime of a few days and are then replaced.
Chlorophyll
Chlorophyll is a chemical in the chloroplasts of plants. It allows plants to absorb and use light. Energy from the light is used in photosynthesis to make glucose. This contains lots of stored energy which the plant needs to release. It does this through respiration. This energy is then used when the plant grows or repairs damage. Chlorophyll also makes the stem and leaf of the plant green.
Chlorophyll is a green pigment in almost all plants, algae, and cyanobacteria. It absorbs light most strongly in the blue portion of the electromagnetic spectrum, followed by the red portion. However, it is a poor absorber of green and near-green portions of the spectrum. Chlorophyll was first isolated in 1817.
Chlorophyll is necessary for photosynthesis, which allows plants to obtain energy from light.
Chlorophyll molecules are arranged in and around the membranes of chloroplasts. It serves two main functions. The function of most chlorophyll (up to several hundred molecules per photosystem) is to absorb light and transfer that light energy to reaction centres. These pigments are named after the wavelength (in nanometers) of their red-peak absorption maximum. These chlorophyll pigments can be separated in a simple paper chromatography experiment.
The function of the reaction center chlorophyll is to use the energy transferred to it from the other chlorophyll pigments to undergo a specific redox reaction. In this reaction the chlorophyll gives an electron to an electron transport chain. This reaction is how photosynthetic organisms such as plants produce O gas, and is the source for practically all the O in Earth's atmosphere. Photosystem I typically works in series with Photosystem II.
The electron flow produced by the reaction center chlorophyll pigments is used to shuttle H ions across the membrane, setting up a chemiosmotic potential used mainly to produce ATP chemical energy; and those electrons ultimately reduce NADP to NADPH, a universal reductant used to reduce CO into sugars as well as for other biosynthetic reductions.
A green sea slug, "Elysia chlorotica", has been found to use the chlorophyll it has eaten to perform photosynthesis for itself. This process is known as kleptoplasty, and no other animal has been found to have this ability.