produce a variety of compounds that can be divided into primary metabolites and secondary metabolites. Primary metabolites are essential for the survival of the plant and include sugars, proteins and amino acids.
Secondary metabolites were once believed to be waste products. They are not essential to the plant’s survival, but the plant does suffer without them. Secondary metabolites also have many uses for us, too. Some are beneficial, and others can be toxic.
ALKALOIDS
Alkaloids are secondary metabolites. They are primarily composed of nitrogen and are widely used in medicine. They can also be highly toxic.
Papaver somniferum
Morphine was the first alkaloid to be found. Morphine comes from the plant Papaver sonniferum, or the opium poppy. It is used as a pain reliever in patients with severe pain levels and cough suppressant.
Another example of an alkaloid is cocaine. It can be highly dangerous and addictive. However, it has also been used as an anesthetic. Cocaine has long been used by the people of South America to alleviate hunger. Workers chew on the leaves while working, which is not dangerous because the leaves only contain a small amount of cocaine. However, cocaine derivatives are very dangerous when habitually used and can be deadly.
Perhaps the most loved and known alkaloid is caffeine. While we use it to stay alert, it has protective properties for the plants it comes from: cocoa, coffee and tea.
Coffee Beans
Seedlings of the coffee plant have a high concentration of caffeine. The high concentration is toxic and protects the seedlings from insects that want to snack on it.
Toxic caffeine levels also have another interesting defense mechanism. It prevents the germination of any other plants in the area. This is referred to as allelopathy. In humans, caffeine has also been thought to reduce the risk of diabetes and heart disease in addition to helping us face long days of work and school.
TERPENOIDS
Terpenoids are made of isoprene units and are found in all plants. They are the largest group of secondary metabolites and are very volatile, which means they evaporate easily.
Isoprene is a gas produced in the chloroplasts and released by the leaves. Isoprene is thought to protect the plant from heat.
Essential oils give plants their fragrance. In some plants, the scent is used to deter herbivores and protect the plant from dangerous pathogens. We use essential oils for aromatherapy and medicine. In aromatherapy, essential oils are thought to improve the mood and mental functioning. In alternative medicine, essential oils are thought to have quite a few benefits.
Most of the time, essential oils are dangerous if consumed so they are usually applied topically or inhaled. They can be used for skin issues, respiratory ailments and as antiseptics.
Next is taxol, which has become important in the medical field. It is used to treat ovarian and breast cancer. Taxol comes from the bark of the Pacific yew tree. The bark produced very small amounts of taxol and the process killed the tree. Other sources needed to be found.
Now, other sources of taxol include a fungusthat grows on the tree and needles of the European yew.
The final type of terpenoid is the one that is the most familiar to us: rubber. It is the largest of the terpenoids because it contains over 400 isoprene units. Rubber is obtained from latex, which is a fluid produced by Hevea brasilenis. The uses for rubber are numerous and go back hundreds of years. Today, we use rubber in shoes, erasers, tires, gloves, spandex and the beloved rubber ducky.
PHENOLS
The final type of secondary metabolites has recently become very popular due to their health benefits: the phenols.
The phenols consist of a hydroxyl group (–OH) attached to an aromatic ring. Phenols are found in nearly all parts of the plant and in nearly every plant on the planet.
The first group of phenols is the flavonoids. Flavonoids are water-soluble pigments found in the vacuoles of plant cells. Flavonoids can be further divided into three groups: anthocyanins, flavones and flavnols.
Anthocyanins range in color from red to blue and purple. The color depends on the pH of the environment. Anthocyanins are most commonly found in grapes, berries and have a wide range of health benefits. Anthocyanins are believed to protect against heart disease, diabetes and even cancer when they are consumed. They are also appearing in skincare products to slow down the aging process.
The next two groups have white or yellow pigments. They are called flavones and flavnols. As a group, the phenols attract pollinators to the plants and even impact how plants act with one another.
Aspirin Tablets
Yet another medically relative phenol is salicylic acid, which is the active ingredient in aspirin. It comes from the bark of the willow tree. It has been used to effectively treat aches and fevers since the days of Hippocrates. It also has cosmetic uses.
It is used in numerous skincare products to treat acne, large pores and dermatitis.The final type of phenol is important to the structure of the plant and is called lignin. It adds stiffness and strength to cell walls of the plant cells. Lignin is crucial to terrestrial plants because it supports the branches and size. It also allows the cell wall to be waterproof and protects the plant from fungal attacks.
Not only do the secondary metabolites have functions for the plants, they have proven to be pretty beneficial for us, too. Their effects have not only been cultivated in recent years, but for centuries. Be sure to eat your berries for their great health benefits, and remember where the active ingredient in that aspirin you took came from.
FUNCTIONAL ANATOMY OF THE KNEE: MOVEMENT AND STABILITY
The knee is a joint formed, stabilized and given mobility by the articulation of bones, ligaments and tendons. This joint is the largest joint in the body and is formed by the articulation of the femur bone in the thigh with the tibia in the lower leg.
There are 3 main types of joints: Fibrous – an immovable joint, Cartilagenous – partially moveable, and Synovial – a freely moveable joint. The knee joint is classified as a synovial joint for obvious reasons based on the definitions given.
Synovial joints or diarthroses are considered moveable joints. According to the Encyclopedia of Nursing and Allied Health, joint function, synovial joints can be further divided into 3 types, these are: Uniaxial – joints that hinge or pivot moving only in one plane, Biaxial – such as the saddle and condyloid joints. These joints move in two planes. And lastly, the Triaxial – which allows movement in three planes including the ball and socket joints and gliding joints
The knee falls under the uniaxial as it is a hinge joint and it moves in one plane with slight rotational movement, but the rotation is not enough to be considered significant.
ANATOMY & PHYSIOLOGY
The knee is the largest joint of the body and is often the site of pain and injury in athletes (the reason I am writing about this is that I strained my medial collateral ligament, more on that later), consists of the medial and lateral condyles (round projection at the end of the bone) of the lower femur (thigh bone) and the same condyles at the upper end of the tibia.
The patella (knee cap) covers the front of the joint, it is the protruding structure you see when you extend your knee. This structure slides along a groove on the femur.
Each of the 3 bones in the knee joint are covered with articular cartilage, which is a tough elastic material, that acts as shock absorbers and allows the knee joint to move with ease. Another cartilage tissue called the menisci separates the femur and tibia, divided into two crescent shaped discs located medially and laterally (inner and outer respectively). This cartilage also acts as shock absorbers, as well as enhancing stability.
In a normal knee joint, a synovium (synovial membrane) surrounds the knee jointand it produces synovial fluid that nourishes the surrounding cartilage in the knee. The synovium also functions in protecting and supporting the joint due to its tough outer layer.
STABILITY
The stability of the knee is due mainly to four ligaments. A ligament is several large fibrous bands of tissue, comparable to that of a rope, they support the knee on both sides and front to back. Ligaments connect bone to bone.
- Medial Collateral Ligament (MCL), also known as the Tibial Collateral Ligamentbecause it connects the Femur and Tibia, provides stability to the inner (medial) aspect of the knee.
- Lateral Collateral Ligament (LCL), also known as the Fibular Collateral Ligamentbecause it connects the Femur and Fibula, provides stability to the outer (lateral) aspect of the knee
- Anterior Cruciate Ligament (ACL), in the center of the knee, limits rotation and forward movement of the Tibia
- Posterior Cruciate Ligament (PCL), also in the center of the knee, and like the ACL secondarily limits rotation, while primarily limits backward movement of the Tibia.
MOVEMENT
Your knee is a hinge joint like your elbow, which we discussed already, which means it bends and straightens. We also said that it has the ability to slightly rotate as it moves.
The muscles in the thigh, the quadriceps and hamstrings perform movement of the knee joint, but these muscles need assistance from tendons to connect them to the muscles. Tendons are tough cords of tissue that connect muscle to bone. They are similar to ligaments in structure. The difference is in just what they articulate with.
When you straighten your leg, the quadriceps muscles contract pulling on the quadriceps tendon, which in turn pulls on the patella via the patellar tendon causing an extension of the knee. Please note the patellar tendon connects the patella to the tibia, so technically it is a ligament, but commonly called a tendon. On the posterior side of the knee the hamstring group of muscles contract pulling on the tendons associated with the hamstring, pulling on the femur, which causes the flexion of the knee.
LYMPHOPOIESIS: THE DEVELOPMENT OF LYMPHOCYTES
Fig.1 Lymphocyte
Lymphocytes are the smallest and the second most common type of white blood cell. They are known as the cells of immunity. Lymphocytes have large round/oval nuclei that occupies most of the cell with little cytoplasm. The nucleus will stain dark purple or blue when it is exposed to a certain stain called Wright’s stain (please see figure 1 ).
There are two types of lymphocytes T lymphocytes and B lymphocytes which the immune response depends upon. They are derived from the hematopoietic stem cell(HSC).
LYMPHOPOIESIS
As we already know, HSC can develop into common lymphoid progenitor (CLP) or common myeloid progenitor (CMP). CLP then will generate T and B lymphocytes while CMP generates myeloid elements. So, lymphocytes originate from CLP in the bone marrow.
One should note that during postnatal life, the bone marrow and thymus are the primary lymphoid organs. The secondary lymphoid organs in which specific immune response take place are the lymph nodes, spleen and lymphoid tissue.
B-LYMPHOCYTE DEVELOPMENT
B-cells originate in the bone marrow and circulate the peripheral blood until they recognize an antigen. There are various stages in the development of B lymphocytes:
Their development is altered by cytokines. Interleukin-7 interacts with stem cellfactor to begin the process. In order for the cells to function, they will express on their surface immunoglobulin (Ig).
Ig production begins at the Pro-B cell stage of B cell development. Ig is needed for the development and maturation of the B cell from CLP to pre-B cell.
First there will be an expression of IgM, then IgD and finally IgG or IgA. The termination of B cell will take place in the peripheral lymph organs such as the spleen and lymph nodes. In these organs B cells change into plasma cells and memory cells.
The plasma cells are capable of producing and releasing antibodies, while the memory cells remember antigens that they were once exposed to in the past.
T-LYMPHOCYTE DEVELOPMENT
T- Lymphocyte development begins with CLP cells that migrate to the thymus where they will differentiate into mature T cells. It is associated with the movement of the cells through the cortex and medulla of the thymus. Maturing begins in the cortex, and as the cells develop more they move towards the medulla.
During the developmental stages of T cells, the cells contain specific surface proteins. As the cell progresses through maturity, they are identified by antibodies that recognize the surface proteins. In other words, there are cell surface markers which are used by antibodies to identify the T cell.
T cell eventually differentiates into two types of T lymphocytes: cytotoxic T-cell and helper T-cell. Cytotoxic T-cell is important because they produce a substance called lymphokines which help B cells destroy foreign substances. Cytotoxic T-cells also have CD8 antigen.
Helper T-cell on the other hand produces CD4 antigen and functions to assists killer T cells with the protection of the body against invading organisms.
Like B-cells, T-cells depend on interleukin-7 and other interleukins. One should note that most of T-cell development occurs in the thymus; however the final steps in which cytotoxic and helper T-cell are produced occur in the peripheral blood.
INTRODUCTION TO THE SPINOTHALAMIC TRACT
I think it’s time to make a jump, and to look at the nervous networked that feeds the brain information about what’s going on with the body. There are two types of information relays.
There are pathways that transmit information that goes from the brain to the limbs (called descending tracks), and there are pathways that transmit the information from the limbs to the brain (called the ascending tracks).
But how do you know which track does what?
Ascending and Descending tracts. Image Credit: Mikael Hรคggstrรถm
LET’S BEGIN WITH THE SPINOTHALAMIC TRACT
First, look at the terminology: Spinothalamic. This gives you a hint as to the direction of the electrical signal. Spino-Thalamic. The information will travel from the spine up to the thalamus (which is situated in the brain). So yes, the spinothalamic tract is an ascending pathway.
At this point you already know that this pathway will have something to do with information about the body.
The spinothalamic tract is involved with perceptions of temperature, itch, touch, and pain.
We also said that the information is being relayed. The term relay applies really well to this situation because the electrical signal will be “relayed” from neuron to neuronas it ascends up to the thalamus.
Like most ascending pathways, there are 3 neuronal levels in the spinothalamic tract.
SPINOTHALAMIC TRACT – LEVEL 1
The level 1 neurons are called “primary neurons.” These primary neurons have free nerve endings that will translate pain, temperature, itch, or touch sensations into an electrical signal. These primary neurons can be pretty long and travel all the way from the bottom of the foot to the spinal cord.
The cell bodies of these primary neurons are located in dorsal root ganglions.Their axons enter the spinal cord through Lissauer’s fascicles, then go up one segment before synapsing. They will synapse in the posterior horn on the same side (ipsilateral side).
SPINOTHALAMIC TRACT – LEVEL 2
The secondary neurons begin in the posterior horn of the spinal cord (The primary neurons that we just talked about synapse on them).
At this point, there are two options for these neurons.
- They can travel up on the same side (ipsilateral ascension)
- Decussate and travel up on the opposite side (contralateral ascension). Most axons will mostly travel up on the contralateral side, but all will synapse in the thalamus (ipsilaterally or contralaterally).
The Contralateral Ascension
Decussation: the level 2 neurons send their axons across the midline before going up through the lateral spinothalamic tract. They will then synapse on the ventral post lateral nucleus of the thalamus.
It is interesting to note that axons from the lower limbs align themselves on the “lateral side” of the spinothalamic tract, whereas axons from the upper limbs align themselves more on the “central” side of the spinothalamic tract.
Along the way, some of these neurons branch out to the periaqueductal gray or to the reticular formation.
That’s pretty cool because pain can be down regulated at these levels. Which means that even if the body sends out a strong pain signal, the brain can actually modulate how much of that pain it will feel…..
Spinothalamic Tract – Level 3
The last level! The tertiary neurons begin in the ventral posterolateral nucleus of the thalamus. Their axons will travel through the internal capsule. They will keep on going through the corona radiate (I love that name). Their journey will end on the secondary sensory cortex.
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