Skeletal, Muscular and Articular Systems

Key hormones associated with bone formation in men/women are PTH (parathyroid hormone) produced by the parathyroid glands, and Calcitonin produced by C-cells. In children, HGH is important and is most involved in epiphyseal plate activity; in adolescents the sex hormones testosterone and oestrogen play an important role in bone growth, growth hormone (HGH) is modulated by the activity of the thyroid hormones, ensuring that the skeleton has proper proportions as it is growing.

Later in adolescence, the sex hormones testosterone and oestrogen induce epiphyseal plate closure in the long bones; an excess of growth hormone during this development phase can lead to gigantism, while a deficiency of HGH and/or the thyroid hormones would produce dwarfism. Low blood levels of ionic calcium will stimulate the release of PTH; in turn stimulating osteoclasts to resorb bone and thus releasing more calcium to the blood. Osteoclasts will break down both old and new bone matrices, osteoid escapes assimilation due to its lack of calcium salts.

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Rising levels of blood calcium will end the stimulus of PTH, declining levels of PTH will reverse these effects; causing the level of blood Ca2+ to fall, calcitonin only has a negligible effect on calcium homeostasis in humans. (Marieb & Hoehn, 2010, pp. 185-86) Task 1C The major supplements used to help sufferers of osteoporosis are calcium and vitamin D, aim for at least 700mg of calcium from food/drink intake; when using calcium and vitamin D to help osteoporosis then a formulation prescribed by a doctor should be sought.

Most over the counter calcium/vitamin D supplements do not contain the correct amount and ratio of calcium/vitamin D, to help treat osteoporosis a formulation containing 1. 2g of calcium and 800iu of vitamin D should be taken. (NHS , 2011) Other good dietary sources of calcium are small fish (with bones – sardines/pilchards), low-fat dairy products and dark green leafy vegetables (broccoli/cabbage/okra) as are tofu (soya) and nuts. (NHS, 2011) Good dietary sources of vitamin D include all oily fish, eggs; fortified spreads and liver.

It is also important to get the appropriate amount of sunlight, as the UVB rays penetrate skin where they are converted into pre-vitamin D3 by cutaneous 7-dehydrocholesterol. Aim for at least 5-30 minutes per day of UVB during the hours of 10am to 3pm, to the legs; face; back and arms for sufficient vitamin D production; cloud cover and darker skin tones will reduce the available UVB. (USA. Gov, 2011) Task 1D High impact sports, such as running; weight training; walking; aerobic exercise and squash are all good for increasing BMD, low impact sports such as swimming and cycling have no positive effect on BMD.

Exercise regimes should be undertaken at least twice per week, preferably three times p/w of 30 minutes or more, and of course should be supervised by a qualified individual. The level of intensity should be low at the start of the regimen, increasing the number of repetitions and/or weight over time. Any BMD gains achieved would be lost if the exercise regime is stopped, and thus regular face-to-face contact is important to help foster a positive mental attitude. (Todd & Robinson, 2003)

Individuals suffering from osteoporosis should be careful when undertaking vigorous high impact exercise, due to the weakness of the skeletal system; most importantly, an active lifestyle coupled with regular exercise should be followed to help combat osteoporosis in advancing years. Task 2 Task 2A - Axial Skeleton Eighty bones separated to form three regions (skull, vertebral column & thoracic cage) make up the structure of the axial skeleton. The parts of the axial skeleton form the longitudinal axis of the body, protect the brain/spinal cord and support the neck/head/trunk.

The skull formed of the cranial and facial bones is an exceptionally complex bony structure; the skull serves as a compound for the frail brain, and has connection positions for the head/neck muscles. The vertebral column comprises of 26 asymmetrical bones connected to form a curved flexible structure that supports the trunk; extending from the skull to the pelvis the vertebral column transmits weight to the lower limbs. Providing attachment points for the muscles of the neck/back and for the ribs, it also acts as protection for the spinal column.

The thorax, more commonly known as the chest consists of thoracic vertebrae; ribs; sternum and costal cartilages that secure the ribs onto the sternum. Forming a protective cage around vital organs, the thorax has a rough cone shape that is quite broad; the thorax also supports the shoulder girdles; upper limbs and provides the muscles of the back/neck/shoulders and chest with connection points. (Marieb & Hoehn, 2010, pp. 199,216) Task 2A - Appendicular Skeleton The appendicular skeleton is made up of the limbs and their girdles, the appendicular skeleton is appended to the axial skeleton; hence the name appendicular.

The upper limbs attached via a yoke like girdle (pectoral) to the trunk of the body; and the lower limbs secured by the pelvic girdle. The bones of the upper/lower limbs have different functionalities and mobility, but still have the same essential plane; that the limbs are constituted of three key divisions linked via alterable joints. The appendicular skeletal structure allows us movement such as taking a step, picking up a cup or kicking a ball. The pectoral girdle is comprised of an anterior clavicle and a posterior scapula; the shoulders formed from the associated muscles and the paired pectoral girdles.

Attaching the upper limbs to the axial skeleton, the pectoral girdles also present points of attachment for muscles that are responsible for moving the upper limbs; mobility is high as these girdles are very light. The upper limbs form from 30 bones, each bone described locally as a bone of the hand, arm or forearm; the arm is considered in an anatomical sense to be the upper limb between the shoulder and elbow. The lower limbs attach to the axial skeleton via the pelvic girdle and diffuse the weight of the upper body to the lower limbs, and provide support for the pelvic visceral organs.

Some of the strongest ligaments in the body attach the pelvic girdle to the axial skeleton, the pelvic girdle is very stable but lacks the mobility of the pectoral girdle; carrying the weight of the body the lower limbs are subject to astonishing forces. Compared to the bones of the upper limbs, the bones of the lower limbs are much thicker and stronger. (Marieb & Hoehn, 2010, pp. 223,233,237)

The thoracic cage is thinly attached to the pectoral girdle, not like the pelvic girdle that is affixed to the axial skeleton by some incredible strong ligaments, some of the strongest in the body.

The sockets of the pelvic girdle are deep and cuplike, the femur head is secured firmly in place in these sockets, the pectoral girdle is far more moveable but the pelvic girdle is much more table. The shoulders are formed from the paired pectoral girdles and their associated muscles, a girdle usually refers to a belt like structure that encircles the body, however in the case of the pectoral girdles this does not satisfy the said description. The medial end of each clavicle is joined anteriorly to the sternum and the distal ends encounter the scapulae laterally.

The scapulae do not perfect the girdle posteriorly, as their medial rims fail to join to each other or to the axial skeleton, however the scapulae attach to the thorax and the vertebral column via muscles that garb their exteriors. The upper limbs are attached to the axial skeleton via the pectoral girdles and also provide connection points for the upper limb muscles. The girdles are light and this allows a freedom of movement that is not accomplished elsewhere in the body, as only the clavicle fastens to the axial skeleton, this allows the scapulae to move easily across the thorax.

The hip joint being a ball and socket joint has a good range of motion; however, the shoulder has a wider range of motion. The joints strong ligaments limit movements, but do occur in all planes. Formed from the articulation of the femurs spherical head and the greatly cupped acetabulum of the hipbone is the hip joint. A circular lip of fibrocartilage (Acetabulor labrum) enhances the depth of the acetabulum; the diameter of the labrum is smaller than the head of the femur making for a snug fit of these articular surfaces; dislocations of the hip are a rare incident.

Extending from the brim of the acetabulum up to the stem of the femur, the heavy articular casing wholly surrounds the joint; there are several robust ligaments that reinforce the hip joint capsule. These ligaments include the iliofemoral ligament, an anteriorly placed v-shaped ligament, and the pubofemoral, which is a triangular condensing of the lesser fragment of the capsule, and the ischiofemoral ligament that is a coiling posterior ligament. On either side of the pelvic girdle, the iliolumbar ligament connects the pelvis and vertebral columns. (Marieb & Hoehn, 2010, pp. 225-226,233,267) Ligaments of the pelvic girdle: Iliolumbar ligament ? Anterior Sacroiliac ligament ? Sacrospinus ligament ? Sacrotuberous ligament ? Pubofemoral ligament ? Iliofemoral ligament ? Ischiofemoral ligament ? Sacroiliac ligament ? Ischiofemoral ligament ? Ligamentum teres Ligaments of the thoracic girdle: ? Capsular ligament ? Coracoclavicular ligament ? Costoclavicular ligament ? Coracohumeral ligament ? Glenohumeral ligament Task 2c – Lordosis, Kyphosis, Scoliosis Cervical and lumbar secondary curvatures being convex anteriorly, are associated with a Childs development, this is a result of reshaping of the intervertebral discs and not from modification of the vertebrae.

The cervical curvature being present at birth does not become distinct until 3 months when the baby will start to raise its head, whereas the lumbar curvature will develop when the baby begins to walk. During the early childhood years the vertebral problems of scoliosis or lordosis may appear as rapid growth of the long bones stretches muscles, lordosis is most often present during preschool years but is more often than not remedied when the abdominal muscle strengthen. This firming up tilts forward the pelvis and the thorax widens, thus developing the military posture in adolescence.

At the onset of old-age many parts of the skeleton are affected, principally the spine; the discs thin and loose elasticity and hydration resulting in a probable rise in disc herniation, at 55 years old it’s not uncommon to have a loss of up to several centimetres in stature. Osteoporosis can produce further shortening of the spine as can kyphosis, in the elderly this is referred to as a dowager’s hump, with age the thorax develops rigidity due to ossification of the costal cartilage, thus resulting in shallow breathing from a loss of rib cage elasticity.

Abnormal spine curvatures, of which some are congenital and some resulting from muscle weakness, disease and bad posture. In the thoracic region of the spine, an abnormal lateral curvature is referred to as scoliosis (twisted disease) most often presenting during adolescence and more common in girls. Scoliosis can also be a result of muscle paralysis, unequal lower limbs (length) or severe abnormal vertebra structure, non-functioning muscles on one side of the spine will cause the muscles of the opposite side to exert an unopposed pull; forcing the spine into a misaligned position.

Body braces and/or surgery are used to treat scoliosis during childhood and thus preventing a permanent deformity. Scoliosis can also cause breathing difficulties, due to the nature of the disease a compressed lung in not unusual. Kyphosis, often referred to as hunchback, is a thoracic curvature that is dorsally exaggerated; very common due to osteoporosis in elderly people and can also reflect rickets, osteomalacia or tuberculosis of the spine.

A prime mover or agonist is a muscle that has the chief responsibility of producing an explicit undertaking, for instance the biceps brachii is the fleshy muscle of the anterior arm that is the agonist of elbow flexion. An antagonist is a muscle that opposes the movements of agonists, an active agonist will result in a stretched or relaxed antagonist; however, antagonists usually help to regulate movement of the agonist with a slight tightening to provide resistance to slow or stop movement as not to overshoot the mark. Agonists and antagonists are located opposite each other on the joint of which they act, antagonists can also work as agonists and one example of this is the biceps brachii causing flexion of the forearm that is antagonised by the triceps brachii, the agonist for forearm extension.

In the sliding filament model of contraction, thin filaments will slide past thick filaments, and as a result, the actin and myosin strands will overlap to a larger gradation. Relaxed muscle fibres only have thick and thin fibres overlapping at the tips of the a-bonds, stimulation of the muscles fibres by the nervous system activates the myosin heads of the thick filaments to clasp onto the myosin fastening position on the actin of the thin filaments, and this process begins sliding.  In the course of contraction, these cross bridge connections are forced/broken numerous times, the attachments act like miniscule ratchets in order to create pressure and thus impel the thin filaments further toward the sarcomeres centre.

This contraction event occurs concurrently throughout all sarcomeres in a cell shortening the muscle cell, it should be noted as the thin filaments slide towards the centre; the z-disc to which they are attached to will be pulled toward the m-line. In an overall look at contraction, the muscle cell contracts as do the i-bonds and the distance between consecutive z-discs is reduced and the h-zones vanish, moving the contiguous a-bonds closer together; however, they do not change in length. (Marieb & Hoehn, 2010, p. 284) Task 6b Direct Phosphorylation The demand for ATP rises as we begin vigorous exercise, within a few contractions stored ATP is consumed, creatine phosphate is then used to egenerate ATP and this process is ongoing while the metabolic pathways acclimatize to the bodies demand for increased ATP. Pairing CP with ADP results in an almost instantaneous energy transfer, and a phosphate group to form ATP from the CP to ADP. Two to three times as much CP as ATP is stored in muscle cells, the CP-ADP feedback is incredibly efficient and the volume of ATP in muscle cells does not change by much during the preliminary contraction phase. Maximum muscle power can be provided for 14-16 seconds using stored CP and ATP, this is roughly long enough to invigorate muscle for a 100-metre surge; this reaction is reversible and CP resources are refilled during rest periods. (Marieb & Hoehn, 2010, pp. 298-99) Anaerobic Pathway

More ATP is engendered by catabolism as stored ATP and CP are expended; this catabolism of glucose is through the blood or from glycogen stored in muscle, glycolysis is the opening phase of glucose breakdown, glycolysis occurs in both the presence and absence of oxygen; however, it does not use oxygen and is therefore anaerobic. Glucose is destroyed to form two pyruvates during glycolysis, this releases enough energy to form some ATP (two ATP per glucose); usually, pyruvate manufactured would then enter the mitochondria and reacting with oxygen would provide even more ATP using the aerobic pathway. Vigorous muscle contraction at about 70% causes the bulging muscles to compress blood vessels, thus impairing blood flow and oxygen delivery.

During these anaerobic conditions, the majority of pyruvate produced is transformed into lactic acid, this process is referred to anaerobic glycolysis. Anaerobic glycolysis yields around 5% of the ATP produced via the aerobic pathway from each glucose molecule, however it produces ATP about 2. 5 times faster than the aerobic pathway. (Marieb & Hoehn, 2010, pp. 298-99) Aerobic Pathway Ninety-five percent of ATP used for muscle activity during moderate exercise and rest is produced via the aerobic respiration pathway. Occurring in the mitochondria, aerobic respiration requires oxygen and encompasses a series of chemical reactions. During these reactions, the links of fuel molecules are destroyed liberating energy for ATP production.

Glucose is broken down utterly to yield water, CO2 and great quantities of ATP, diffusing out of muscle tissue into the blood; the lungs remove CO2. With the onset of exercise, glycogen stored in the muscles provides a large amount of the fuel, briefly, after this circulating glucose, pyruvate and free fatty acids are the main source of fuel, roughly 30 minutes after this fatty acids will be the main energy source. Aerobic glycolysis provides a great deal of ATP (32), but is slow due to its numerous steps; it also requires a constant supply of oxygen and nutrients to continue.

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