The Body
Environmental Interactions
Chapters 13 & 14
Compendium Review I
I. Principles of Endocrinology
A. Target Cells, Tropic, Nontropic hormones, & Negative feedback
B. Pituitary & Hypothalamus www.mednote.co.kr
http://faculty.virginia.edu/bio202/lectures/Pituitary.gif
1. Hormones & functions
C. The Thyroid gland www.fccj.org
1. Thyroxine, Triidothyronine, Calcitonin
D. The Parathyroid glands & Pancreas
1. Glucagon & Insulin
2. Adrenal Medulla & Adrenal Cortex www.valleyhealth.com/images/image_popup/adrenal.jpg
3. Diseases of the Adrenal Cortex
E. Endocrine Disorders
II. The Immune System
A. Viruses & Bacteria
1. Treatments for Infections
B. First & Second Lines of Defense
1. Inflammatory Response
2. Pyrogens, Interferons, & Complement
C. Third Line of Defense
1. Antigens
2. T cells, B cells & Antibodies http://www.asu.edu/, http://www.uccs.edu/~rmelamed/MicroFall2002/Chapter%2017/B-Cells.jpg
3. Macrophages, active & Passive Immunity biomed.brown.edu
4. Tissue transplantation
D. Diseases of the Immunity System
1. Allergies www.personalmd.com
2. Autoimmune Diseases
The endocrine system is very complex that is made up of many small glands that are in various places in the body that produces hormones that are transported throughout the body via the bloodstream. Hormones effect our homeostasis, growth & development, reproduction, energy production and storage and behavior.
-The target cells contain receptors that are for specific hormones. Some receptors are found in the cells cytoplasm, or in the cells plasma membrane.
Hormones fall into two very broad categories.
-Tropic hormones stimulate the endocrine glands to produce and release hormones.
-Nontropic hormones are needed to help stimulate cell growth, metabolism, and other functions.
Chemical compositions are important when talking about hormones and their classification. There are three types of hormones that are made in the body and they are; steroids, proteins and polypeptides, and lastly, amines.
-There are two types of feedback loops that controls hormonal secretions in the body and they are negative feedback loops and positive feedback loops.
-The pituitary gland secretes hormones by the anterior and posterior lobes. It is pea shaped and hangs from the hypothalamus. The hypothalamus which is located in the brain controls and regulates the hormone production, nutrients and ions in the blood. When talking about the hypothalamus it is important to remember that it produces two types of hormones and they are the inhibiting and releasing hormones. The hypothalamus is triggered to produce the hormones by nerve impulses and chemical stimuli in the body. Below is a picture of the pituitary gland and the hypothalamus and how they cooperate with each other.
-Anterior Pituitary is in charge of the following hormones:
Growth hormone: breaks down fat in the body, growth in cells, muscles, and bones
Thyroid-stimulating hormone: releases throxine & triiodothyronine.
Andrenocorticotropic hormone: where hormones are secreted by the adrenal cortex and glucocorticoids.
Gonadotropins: gamete and hormone production takes place by the gonads.
Prolactin: stimulates milk production
Melanocyte-stimulating hormone: unknown the function of this hormone. How could we not know this?
-Posterior pituitary gland is in charge of the following hormones:
Antidiuretic hormone: which stimulates water reabsorption by nephrons of the kidney.
Oxytocin: stimulates the release of milk from breasts and contractions during birth.
-The thyroid gland is in the neck and it produces three different hormones. Depending on the person each thyroid is shaped differently wither U-shaped or H-shaped. The thyroid is important in balancing out the metabolism, heat production, and calcium levels in the blood. The thyroid gland is made up of a spherical shaped structure known as the follicles.
-The two hormones, thyroxin and triiodothyronine work together to accelerate the breakdown of glucose and also assist in the growth and development. Calcitonin decreases the elevations of calcium in the blood.
When thyroid activity is slowed down it is called hypothroidism and when it is increased it is called hyperthyroidism.
-Parathyroid glands are embedded into the back of the thyroid gland and they produce the hormone Para hormone. Its co-worker is calcitonin and when they work together it makes for a successful calcium level drop.
- The pancreas’ primary function is to produce insulin and glucagons that will control the glucose levels in the blood but it also produces digestive enzymes that it releases into the small intestine. It is located in the abdominal cavity. Below is a picture of the pancreas and a portion of the small intestine.
-Glucagon raises the glucose levels in the blood and directly goes against the actions of insulin. Insulin causes the blood sugar levels to drop after eating food. There are tests that can be conducted that help with finding out if the levels are balanced in the body it is called the glucose tolerance test. During this test the doctors give their patients glucose orally and then check the blood levels regularly.
The adrenal glands sit on top of the kidneys and each is made up of two parts.
-The adrenal medulla which is what raises your heart rate and accelerates the breathing when we get frightened or scared from the latest freaky movie at the theater. It produces our stress hormones called adrenaline and noradrenaline. This is what determines whether you are going to stay and fight or take flight. This is a picture of the kidneys with the adrenal glands nestled into the upper portion of them.
-The adrenal cortex produces three types of hormones and it is considered to be the outer part of the gland. The first group is called the glucocorticoids which are important in glucose metabolism and maintaining blood glucose levels. Several chemically secreted glucocorticoids are important and one of those is cortisol. Cortisol helps in the inflammation of the tissues when they are injured or damaged. The second group is called the mineral corticoids and they are involved in electrolyte or mineral salt balance. The most important one is aldosterone. It stimulates sodium reabsorption in sweat glands, saliva, and potassium excretion of the kidneys. Aldosterone helps to conserve body water.
-Endocrine disorders and their causes-
Hypersecretion = over production of something hyposecretion = under production of something
Giantism: hypersecretion of growth hormones (GH) starting at birth or early on in life.
Dwarfism: hyposecretion of growth hormone starting at birth or early on in life.
Acromegaly: hyper secretion of GH after bone growth has stopped
Hyperthyroidism: over activity of the thyroid gland
Hypothyroidism: under activity of thyroid gland
Hyperparathyroidism: excess parathyroid hormone secretion usually resulting from a benign tumor in the parathyroid gland.
Cushing’s syndrome: hyper secretion of hormones from adrenal cortex or from cortisone treatments
Hyporparathyroidism: hyposecretion of the parathyroid glands
Diabetes insipidus: hyposecretion of ADH
Diabetes mellitus: insufficient insulin production or inability of target cells to respond to insulin
Addison’s disease: gradual decrease in production of hormones from adrenal gland very common with that of an autoimmune reaction.
The immune system is a complex system in our body. It is what is necessary to fight off infections, viruses, and bacteria.
-Viruses are nonliving biological agents that invade cells. A virus has a nucleic core that consists of DNA or RNA. It contains a protein that is in the core that is known as a capsid. Viruses can’t multiply and divide on their own like cells can. A viruses main mission is to invade and conquer. Most viruses get into the body through the respiratory and digestive systems and also through sexual contact.
When an invasion like this takes place the immune system kicks into high gear usually wiping out the virus within 10 to 14 days.
-When we think of bacteria it is not always thought that there are good and bad bacteria but some bacteria are helpful to the body and others can be harmful. Bacteria are classified as living organisms that take over their hosts. Bacteria are prokaryotes. (no nucleus) Bacteria contains tiny circular chromosomal DNA called plasmids. Bacteria can enter into the body through the respiratory, upper GI tract, cuts and abrasions, and urinary system. Once they are inside the body they often use our own nutrients to make more their kind.
Treating viruses and bacteria they have to be treated differently. Bacteria can be combated with antibiotics by shutting down the protein synthesis.
-The first line of defense is a physical and chemical barrier. The skin is an important physical barrier in defending the body against foreign microorganisms. There is a layer of the skin called the dermis. It has epidermal cells are produced by cell division in the epidermis. The dead cells contain keratin. Keratin is what is used in waterproofing our bodies and providing protection for the tissues. The cells of the epidermis are joined by special structures known as tight junctions. The chemical barrier in the first line of defense is the hydrochloric acid that the stomach produces and that aids in destroying the bacteria that is ingested. Tears and saliva are contain the enzyme lysozyme which are used in destroying the cell wall of the bacteria.
-The second line of defense combats infectious agents that might get through the first lines of defense and it involves a huge array of chemical and cellular agents. There are four components in the second line of defense; inflammatory response, pyrogens, interferons, and complement.
Pyrogens are molecules released primarily by macrophages that have been exposed to bacteria. The pyrogens travel to the hypothalamus. The body’s temperature is controlled by a group of nerve cells kind of like an internal thermometer. Below is a picture of a macrophage attacking foreign cells. 
Interferons are a group of proteins that are released from cells that are infected by the virus. Interferons don’t protect the cells that are already infected by the different viruses they just help in stopping the spread of the viruses to other cells.
Blood proteins come together to give help to the antibodies to form what is called the complement system.
There are five proteins that join together to form a large protein complex called the membrane-attack complex. This membrane gets inside the plasma membrane of the cell and makes an opening for water to flow through. This in turn causes the bacteria to swell up and explode.
-The third line of defense is the immune system. The cells of the immune system selectively target foreign substances and foreign organisms. The immune system is extremely important in maintaining homeostasis by eliminating bacteria, viruses, single celled fungi and many parasites. The immune system is like the paper sorter of the body. Separating the good stuff from the bad stuff.
-Antigens are substances that trigger the immune response. Antigens stimulate two types of lymphocytes which are T cells and B cells.
-B cells react to microorganisms called bacteria toxins. When activated they produce antibodies. These cells mature in the bone marrow. Below is a picture of a T cell and its immune defense.
-T cells are formed in the thymus and each one will bind with another antigen.
Several million of the B & T cells are produced in the body early in life. Only a small percentage of these cells will be called into action during our lifetime. There are four types of that are important when thinking about T cells.
1. Cytotoxic T cells bind to the molecules in the membranes of the cells they attack and then they release a chemical substance known as perforin-1. These guys are housed in the membranous sacs in the cytoplasm of the cytotoxic T cells. The performing-1 are then released into the space between the killer cell and its prey.
2. Helper T-cells enhance the immune response and it releases interleukin 2 and this helps in increasing the activity of the cytotoxic T cells. These cells make up about 60% to 70% of the T cells that are moving around throughout the body.
3. Memory T cells are also produced when antigens are present. These guys form a cellular reserve and they protect the body in the event that the intrusion occurs at a later date.
4. Suppressor T cells are the cells that turn off the actions of the immune system. As the job of the other T cells begin to slow down and the suppressor T cells begin to increase.
Below is a picture of a B cell. It is interesting to see its way of responding.
-Antibodies are formed by the B cells dividing into what is known as lymphoblasts and then they work together to form a new cell called the plasma cell. Then these cells produce antibodies. Antibodies are proteins that get rid of bacteria and bacteria toxins. Antibodies fall into a class of blood proteins called globulins and they are specifically called immunoglobulins. It is T shaped and has four peptide chains.
When an antigen enters into the body it initiates a primary response and this response is pretty slow but effective. Antibodies kill of antigens different ways.
1. By neutralization and this where the antibodies bind to viruses or bacterial toxins by putting a clear coat around them.
2. Agglutination this occurs when antibodies bind to the antigens and clump together.
-Macrophages play a very important role in protecting the body. They help stimulate T and B cells to fight off bacteria toxins. The macrophages are the ones that cover the foreign toxins surround them and clump together and present them to the help T cells.
- There are two types of immunity that take place in the body.
One type is active immunity. Vaccines are considered to be an active immunity. Reason being is because the vaccine is injected into the patient and then the body produces memory cells in T and B cells that protect the body against futuristic infections. Vaccines has helped in combating serious diseases such as polio, and smallpox.
Another type of immunity is passive immunity. It is a temporary form of protection where the body is injected with immunoglobulins. The cells in the body are not activated and that is why it is considered passive. An example of this would be the injection of immunoglobulins after a poisonous snake bite. Infants can also get this type of protection through the placental sac while in the womb.
-Tissue transplants are very complicated for the immune system. There are three ways that tissue transplantation can be excepted. The first way is if you can actually use what you already have. An example of this would be with burn victims a lot of times the doctors will use tissue from other areas of the body cover a very damaged area. The second way is if the tissue that is being used comes from an identical twin. Because the twins have identical antigens and cells. The last way a tissue transplant may be excepted is if medication (immunity suppressant) is given to the patient. This medicine is usually continued throughout the lifetime of the patient. Unfortunately, this causes the patient to be vulnerable to many other viruses and bacteria in the environment.
When talking about the immune system you have to keep in mind that with every complex system in the body there can be malfunction. Two types of malfunction are autoimmune diseases as well as allergies. I did not realize that allergies were a malfunction of the immune system. Boy there is a lot of malfunctioning going on! Below is a picture of the way histamines are released and worked.
-Allergies are the body’s way of overreacting to environmental substances. Antigens that stimulate an allergic reaction are called allergens. Histamines cause the arterioles to dilate and then the bronchioles constrict which makes it hard for the person to breathe. When this happens it is called asthma. Most allergic reactions are not life threatening but if the allergic response occurs in the blood stream then it can be fatal if not treated right away. A drop in blood pressure and constriction of the bronchioles can result in anaphylactic shock. I have heard of this happening with bee stings and snake bites. Allergies can be treated three different way. The first way is easy stay away from what bothers. Second, administer antihistimines which counteract the effects of the body. Third, get allergy shots. With each shot that is given the level of the allergen is increased and by doing this it helps in reducing the body’s allergic reaction.
-Autoimmune diseases result from the body calling an attack on its own cells. This can take place in a number of ways. One way is if a body organ is injured in some way and then the normal body proteins are entered into the blood stream this then results in a immune system response. Also, a genetic or chemical mutation that the body no longer recognizes as belonging to the individual.
The immune system is a complex system made up of crime fighters and pacifiers. We all hold a little bit of good and evil when it comes to fighting off infections and diseases or excepting tissues and vaccines. Even sometimes we can have the dramatic consequences of mutiny. Like with each system in the human body they all come with the abilities to malfunction, which in turn can lead to serious consequences. Without this protective big brother, called the immune system, we would be lost in a world of sickness.
Table Of Contents
The Body
Environmental Interactions
Chapters 11 & 12
Compendium Review II
I. Senses
A. General & Special Senses
1. Naked Nerve Endings & Encapsulated Receptors www.visualsunlimited.com
B. Taste & Smell
1. Olfactory Epithelium
library.thinkquest.org
C. The Visual Sense : The Eye
1. Structures & Functions of the Eye www.emedicinehealth.com
2. Cones & Rods
3. Visual Problems
D. Hearing & Balance
1. Anatomy of the Ear
2. Structures & Functions of the Ear http://www.music.sc.edu/fs/bain/vc/musc726a/MUSC%20726%20Lecture/more%20ear-brain/01-ear.gif
II. The Skeleton & Muscles
A. Structure & Function of the Human Skeleton
1. Compact, Spongy Bones, & Joints bioweb.wku.edu
2. Injuries of Joints http://www.dropmachine.com/media/data/500/AC_JOINTS_BILAT_0001.jpg
B. Skeletal Muscles
1. Muscle Fibers Parts & Functions http://www.muscleandstrength.com/images/articles/musclefiber.jpg
The body has its own surveillance system. There are many receptors in the body that monitor all the things inside the body as well as outside of the body. The body contains two types of receptors that are made up of general senses and special senses. General senses are usually evoked by stimuli. When talking about general they consist of pain, touch, pressures, temperatures and limb positions. When talking about the special senses they consist of taste, smell, vision, hearing and balance. Receptors come in different sizes and shapes. All these senses working together give our body the ability to perceive the environment and our surroundings.
The first one is called the naked nerve ending receptors.
These nerve endings can detect pain, temperature, and light touching. There are two types of pain and they are called somatic and visceral.
Somatic pain is a result of injuries in the skin, joints, muscles and tendons. The response can be a result of many types of injuries that may occur such as pinching, cutting, breaking, crushing, or even hot and cold temperatures.
Visceral pain is a result from the stimulation of naked nerve endings in the body organs (viscera). Pain receptors are often stimulated by expansion. For example, pain in the intestinal track might be caused by gas stretching the naked nerve fibers in the walls of the intestines. In other body organs the pain receptors could be caused by a lack of oxygen. Somatic pain is easily identified (pinching) whereas visceral pain is often vague and hard to localize (chest pain is it the lungs, heart?) Visceral pain that appears on the body surface but away from the actual location of the pain is called referred pain. Below is a picture of a motor nerve. I think it kind of looks like some modern art I saw the other day or a face to the side. It kind of reminds me of the ink blot pictures.
Light touch two types of mechanoreceptors. The first type consists of nerve endings that are wrapped around the base of the hair follicles. The second type is a light touch mechanoreceptor which is made up of small cup-shaped cells and naked nerve endings that come in contact with them. They are on the outside layer of the skin. Temperature is extremely important one I think because it can detect hot and cold sensation. If the temperature is too hot or too cold the receptors are activated.
-Encapsulated receptors are made up of nerve endings that are surrounded by one or more layers of cells. The largest encapsulated nerve ending is the Pacinian corpuscle. It kind of looks like an onion that has been speared by a wire. They are located in the deep tissue layers of the skin. These are stimulated by pressure like that you feel when you are sitting on the couch. Another type of sensory receptor is called the Meissner’s corpuscle. They respond to a light touch and are located in the outermost layer of the dermis. They are the most abundant in the tips of the finger and on the lips. Proprioception is a sense of position. They are located in the joints and these receptors inform us of what our limbs are doing. Golgi tendon organs are made up of connecctive tissue fibers that are surrounded by nerve endings and encased in a capsule. It is helpful in muscle contraction and knee jerk reflexes.
All these receptors are subject to change which is called adaptation. This happens whent eh receptors stop sending impulses even though the stimulus is still happening. An example of this is when you first put on a pair of earrings, or put in a pair of contacts it was bothersome at first but then you got used to it.
-Taste buds respond to different foods differently depending on the chemicals that they possess. Below is a picture of the tongue in a cartoon format. It is showing where the taste buds are that deliniate the different tastes.
Taste buds are located on the tongue. Since the taste buds respond differently to different chemicals in foods they are referred to as chemoreceptors. At the end of each taste bud it has micovilli (taste hairs). Taste buds have five flavors; sweet (stimulated by sugars and amino acids), sour stimulated by acidic substances), bitter (stimulated by alkaloids), salty (stimulated by metal ions), and umami (stimulated by meat flavors MSG too). The taste of something we eat is determined by the amounts of the stimulus it contains.-The olfactory epithelium is a patch of receptors that detect different smells that are given off by various items. It is a chemical sense. These receptors are located in the roof of the nasal cavity. There are about 50 million olfactory receptor cells in the olfactory membrane. There are 1000 different protein receptor molecules that the olfactory hairs can bond with to create a specific odor. The receptors for smell adapt very quickly to its surrounding smells which is why a lot of times we can’t smell things that others can when they first time walk into a room. We have already adapted to the smell that is good or bad.
-Smell and taste go hand in hand. Molecules that re released by food they enter into your nasal cavity and dissolve in the watery substance in your olfactory membrane and stimulate receptor cells. It smells so good I think I could taste it is not too far off base. That is why food does not taste as good when you are sick as it does when you aren’t.
-The eye is my favorite of all the senses. Below is a picture of an eye inside and outside.
The eye is spherical shaped. The eye consists of three layers. The outer layer is made up of the sclera (eye muscles) which is the white part of the eye and the cornea which is the clear part inside the eye. The cornea allows light to come in. The middle layer consists of three parts; the choroid, ciliary body, and the iris. The choroid is the largest portion of the middle layer and it absorbs stray light and it provides that proper nutrients to the eye. The ciliary body contains smooth muscle fibers that control the shape of the lens, and permits us to be able to focus on incoming light and images. The iris is the colored potion of the eye and it also regulates the amount of light entering into the eye. The dark opening in the iris is called the pupil. The pupil allows light to come into the eye. The inner layer is called the retina. The outer layer of the retina is pigmented layer and the inner layer consists of photoreceptors and associated nerve cells. Two types of photoreceptors are in the retina called rods and cones. Rods are sensitive to light usually used for night vision and are located in the periphery of the retina. The cones are used for day vision and are in the macula and fovea. There are about 150 million rods in each EYE! And about 6 million cones. The images from our field of vision are brought into the eye and then into the retina and impulses are transmitted to the visual cortex of the brain. Some processing happens in the retina and the rest happens in the brain. When we see the image it is upside down brought onto the fovea and then the brain processes the information and gives us a right side up image. I think that is awesome! The cornea and lens focus light on the retina. The incoming light is focused on the photoreceptors of the retina by the lens.Perfect vision is 20/20. Meaning that objects further than 6 meters away are in perfect focus by the retina. -However there are a few types of vision problems.
Nearsightedness is when the eyeball is a bit elongated. Without glasses parallel light rays arising from distant images come into focus in the front of the retina which makes the image blurry. It can also be a result of the lens being too strong or too concave. It is genetic and it generally appears around the age of 12 and gets worse as the child gets to the age of 20.
Farsightedness is the opposite of nearsightedness. It results in the eyeballs being too short or the lens is too weak (too convex). Farsightedness is generally present from birth and tends to run in the families. With this type of seeing problem people can see things far away but things up close are fuzzy.
Another type of eye problem is called astigmatism. This is an unequal curvature in the eye. It is kind of shaped like a basketball. It causes the person to see things in a fuzzy manner. It is usually something that you have when you are born and it is not something that gets worst or goes away as you mature in age.
-Presbyopia is a condition that people over the age of 40 usually develop that makes it hard for people to focus on nearby objects. It can be corrected by wearing eye glasses during such needed activities such as reading, sewing, needlepoint etc.
-Color blindness is in about 5% of the population and it is hereditary and is more common in men then women. This defect is from as simple as not being able to distinguish certain shades of color to not even being able to perceive a color. If you have red-green colorblindness then the body is missing the red or green cones in the eye. If you don’t have enough red cones then you see red as green and if you are missing the green cones then green objects appear red. The only problem I could see this with is if you did not know the position of the stoplight colors. Red at top, yellow in middle and green on bottom then you would not know whether or not to stop or go.
The ear in a human is considered to be a special sense. It has two functions the most obvious one is to hear, and maintain balance and body position.
-The ear is made up of three parts; the outer ear, the middle ear, and the inner ear. Below is a picture of the ear and its parts to make it easier to identify what is being discussed.
The outer ear is basically that… the outside of the ear. It is an irregular shaped cartilage that is covered by skin and the earlobe. It also consists of a short tube called the external auditory canal and this tube moves airborne sound waves into the middle ear. This is where you will find the nice product called earwax. Earwax is helpful in combating bacteria or anything that might be trapped in the ear. Also it contains an antibiotic substance that helps reducing ear infections.
The middle ear is contained within the skull. The eardrum, or tympanic membrane separates the middle ear cavity from the external auditory canal. Inside the middle ear there are three minuscule bones called the ossicles and they transmit sound to the cochlea in the inner ear. Going from the outside to the inside they are as follows; hammered shaped malleus, incus, and the stirrup shaped bone stapes. When the membrane is struck by the sound waves it then vibrates and causes the malleus moves back and forth. Then the incus vibrates which causes the stapes to move in and out against the oval window. It kind of looks like the head of a drum.
The eustachian tube helps to equalize pressure in the middle ear. It helps to balance out the pressure internally and externally. When there is a change in elevation and the feeling of the ears popping this is the eustachian tube equaling out the pressure.
The inner ear occupies the large cavity in the temporal bone of the skull and contains two sensory organs, the cochlea (snail shaped) and the vestibular apparatus which is made up of two parts; the semicircular canals and the vestibule. The semicircular canals are three ringlike structures filled with fluid set at right angles to one another. They house the receptors that tell the body the position and movement. The receptors for head movement are located in there. There are two membranous sacs in the vestibule, the utricle and the saccule, contain receptors that respond to linear acceleration and tilting of the head.
The musculoskeletal system is made up of bones, joints, and muscles. In adults muscles make up about 50% to 60% of the body weight.
Bones have many functions for the body. They give internal support, create movement, and protect the internal organs. In addition to all those important functions they also produce blood cells and platelets, store fat, and help to regulate the blood calcium levels in the body.
-The skeleton consists of two parts. The axial skeleton consists of the skull, spine, and the rib cage. The second part is called the appendicular skeleton and this consists of the arms, shoulders, legs, and pelvis.
-Bones are made up of a dense outer layer and a less compact central region or spongy bone.
The outer layer of the compact bone is a layer of connective tissue. This tissue is called periostemon and it serves as a site of attachment for skeletal muscles by tendons and is filled with nerve fibers. Inside the bone is a large cavity called the marrow cavity. There is red marrow which is found in a fetus or in a newborn. As people age everyone’s marrow turns to yellow. Yellow marrow can be reactivated to produce blood cells under certain circumstances when an injury occurs. Bones are remodeled for strength when exposed to new stresses. Multinucleated cells that are present on the spongy bones are called osteoclasts. Osteoclasts are very large cells that digest bone with enzymes. Osteoclasts tear down some of the spongy bone whereas osteoblasts rebuild new compact bone, causing it to thicken to meet new stresses. Osteoporosis is a disease of the bone that is caused by a progressive loss of calcium in the bones. It makes the bones become brittle and weak which in turn can make for an easy break. It is most common among women that are going through menopause and are losing the estrogen hormone and it can also occur in people that are immobile for long periods of time. It can be reversed through calcium supplements, calcium rich foods, estrogen therapy and exercise.
-Joints permit varying degrees of mobility. Mobility occurs when bone and muscles work together. Joints are the structures that connect the bones of the skeleton. Some joints only allow little mobility and they are called slightly moveable (the vertebrae) and other joints that permit no mobility are called immovable joints (skull bones connecting together to form the skull) and the last bit of joints that allow free movement or synovial joints are called movable joints (arms). Joints have cartilage that are located on the surface of the bone and connective tissue that that form ligaments that join bone to bone together. Ligaments are not very flexible. Synovial fluid provides nutrients to the cartilage and it is like a lubricant. Tendons and muscles provide additional support in the joints. Two of the most common synovial joints are the hinge joints (knees and fingers) that have limited mobility and the ball-in-socket (hips and shoulders) that have a wider range of mobility. Below is a picture of a synovial joint along with all the parts that are of importance when thinking about it.
-Joints can be injured in one of three common ways. Dislocation which is caused by a fall or some other body movement that does not agree with the joint. It is when the joint “pops” out so to speak and is moved from its correct position. It is sometimes accompanied by a sprain, inflammation, and immobility. This often times happens with shoulders, fingers, or knees and it is necessary for it to be put back into place in order for the joint to function properly. A sprain is another common injury when we are talking about joints. It is usually a partially or completely torn ligament and it heals slowly. It has to be repaired a lot of times with surgery when the ligament is completely torn. Cartilage tears are another common joint injury. It can happen if the joints are twisted or when pressure is applied to them. Cartilage tears are usually done by surgically removing it and it sometimes makes the joints less stable and this usually occurs in the knee joints. Osteoarthritis is caused by wear and tear on the cartilage. One of the most common problems is called degenerative joint disease or osteoarthritis. Excessive wear and tear on the joints causes cartilage to crack and flake. It most of the time it occurs on weight bearing joints. There is also rheumatoid arthritis is another common disorder it is an autoimmune disease and it is the most crippling and painful form of arthritis. It occurs in people between the ages of 20 and 40. It is a permanent condition that can be with physical therapy, painkillers, anti-inflammatory drugs, and surgery. Below is a picture of a bone iwht muscle fibers and it also shows the marrow. Everything is labeled for easy understanding.
The skeletal muscles allow a wide range of movement. Skeletal muscles are controlled by the nervous system. Most skeletal muscles are stretched over one or more joints and so when they contract it then causes movement. Muscles often times work in groups to produce movement or different activities. Skeletal muscles are both excitable and contractile and they consist of long unbranched muscle fibers. They appear striped or striated if looked at under a microscope. These fibers are very elastic and are capable of returning to there regular position and look after they are flexed or released. Inside the muscle fibers can be found numerous myofibrils, bundles of contractile filaments like the proteins actin and myosin which are stimulated by nerve impulses. During muscle contraction or shortening the actin filaments are pulled by the myosin molecules that cause them to slide inward. The attachment of the myosin and actin molecules are stimulated by the release of calcium inside the muscle cells. ATP in the muscle provides the energy necessary to pull the actin filaments inward. ATP is used regularly when you are talking about muscle cells.
A single contraction followed by relaxing is called a switch. The engagement of additional muscle fibers during contraction is called recruitment. The motor neuron and the muscle fibers it supplies constitute a motor unit. Motor units account for the degree of control that various muscles put forth. In order for the force of the contraction to be stronger more motor neurons are stimulated. The strength of a muscle contraction can also be increased by a process called wave stimulation. The firmness that your muscle has is called muscle tone. It is essential for maintaining posture. It also generates heat in any warm blooded animals. Muscle tone results from the contraction of the muscle fibers during periods where you are not as active. The skeletal muscles have two types of muscle fibers called slow an dfast twitches. Slow twitch fibers contract relatively slow but have a lot of endurance. Fast-twitch muscle fibers contract swiftly. The muscles of sprinters and other athletes whose performance depends on quick bursts of activity contain a high proportion of fast-twitch fibers. Skeletal muscles have a pretty good ocmbination of slow and fast-twitch fibers giving the muscles overall a very good performance. Increasing muscle mass and endurance go hand and hand. Muscle protein is quickly made and destroyed. Half of the muscles you gain in lifting weights is lost within 2 weeks after stopping the exercise. High intensity exercise like weightlifting builds muscles relatively easy and takes very little of it to see a change. Whereas low intensity exercise such as aerobics and swimming don’t build bulk muscle but it does increase in our endurance. Increased endurance also is a result of improving the function of the respiratory system and blood flow.
The skeleton and the muscles that connect it are important in mobility and overall health. Any malfunction in one area or another may result in painful consequences. Just like with all systems in the body it is a complex network all working together to improve our overall performance.
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