Archive for January 2011
DNA is a long, double-stranded polymer that is made of a double chain of nucleotides. DNA is an important part of genetics that any allied health professional will be interested to know about. Adenine, guanine, cytosine and thymine and the pentose sugar deoxyribose are the bases found in DNA. Hydrogen bonds link the two nucleotide chains together into a ladder-like molecule. The backbone of this ladder is made of alternating sugar and phosphate components. The molecule coils into a spiral staircase-like structure called a double helix. Each nitrogen base bonds in a very specific manner. Adenine always bonds to thymine and guanine always bonds to cytosine. The base pairing rule is that ATGA on one DNA nucleotide strand would be bonded to TACT on the other side. RNA is different from DNA in that it is located primarily outside of the nucleus of a cell. RNA is responsible for carrying out the orders for protein synthesis directed by DNA. RNA molecules are also different from DNA because they have single strands of nucleotides. The nitrogen bases in an RNA strand are adenine, guanine, cytosine, and uracil instead of thymine which is found in DNA. The sugar that attaches to RNA is ribose instead of deoxyribose. There are three different types of RNA molecules that are distinguished by their size, shape and the specific role they play in carrying out DNA instructions for protein synthesis. Messenger RNA (mRNA) carries genetic information for a protein from DNA to the ribosomes. There are three gourps of nucleotides in a sequence of mRNA called codons. Each group of codons represents codes for a single amino acid. If the sequence is changed or interrupted at any point, it can change the composistion of the protein that is produced or result in no protein being produced at all. There are a total of sixty-four codons and only twenty amino acids. Ribosomal RNA (rRNA) are structural and functional components of the ribosomes where protein synthesis occurs. Transfer RNA (tRNA) translates the genetic code for the mRNA into the primary sequence of amino acids in the protein. There are two important steps that tRNA must perform. First, the tRNA must covalently bind a single specific amino acid to the end of its molecules. The covalently bound amino acid will eventually be transferred from the tRNA to a growing polypeptide chain during protein synthesis. Second, the tRNA must recognize the correct codon on the mRNA that calls for that specific amino acid. In addition to the three types of RNAs, there are small RNA molecules called microRNAs. These small RNA molecules are thought to control genetic expression by shutting down genes or altering their expression. All of the similarity and differences that are seen in any living thing are directed by DNA and carried out through RNA. These genetic codes produce thousands of different proteins that make each organism unique. Any changes that occur in the nucleotide sequence of a DNA molecule create mutations that damage the DNA.
Nucleic acids are made of carbon, oxygen, hydrogen, nitrogen, and phosphorus. They make up the largest molecules in the body and can be very complex. There are two major classes of nucleic molecules called deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Nuceotides are the structural units of nucleic acids. There are three components to every nucleotide. There is a nitrogen-containing base, a pentose sugar, and a phosphate group. There are also five different varieties of nitrogen containing bases that contribute to the structure of a nucleotide. Each nitrogen base is either a purine or a pyrimidine. Adenine (A) and Guanine (G): These two nitrogen containing bases consist of six-member rings fused to five-member rings. They are both purines. Thymine (T), Cytosine (C), and Uracil (U): These three nitrogen containing bases consist of smaller, single six-member rings. They are all pyrimidines. The synthesis of a nucleotide involves the attachment of a base to a pentose sugar. This attachment forms a nucleoside that is named after the nitrogenous base it contains. When a phosphate group bonds to the sugar of a nucleoside a nucleotide is formed.
DNA and RNA are both composed of nucleotides but differ in many ways. DNA is typically found in the nucleus of a cell. It makes up the genetic material and has two major roles: It replicates itself before a cell divides. This is important because this early division ensures that descendant cells receive identical genetic information. DNA also provides the instructions necessay for building every protein in the body. The information that DNA provides concerning protein synthesis is what determines the type of organism that will be created- tree, human, cat, frog, etc. Tomorrow we will learn more about the molecular structure of RNA and DNA.
Many premature infants end up with a common disorder called hyaline membrane disease (HMD). This disease mostly affects premature babies and is caused by a membrane covering the alveoli in the lungs. This membrane covering makes it difficult for proper gas exchange to occur. Radiographs are usually able to detect a vast majority of cases. There are four characteristic features of hyaline membrane disease that HMD radiographs will show:
-diffuse granularity
-uniform disease
-air bronchograms
-relatively small lung volume
Most radiographs will show at least three out of four of the above feature.
A lack of a lipid chemical surfactant that is synthesized by the alveolar lining cells of full term infants causes hyaline membrane disease. These important cells develop and mature during the third trimester of pregnancy. Infants that are born before the third trimester will be deficient in these cells. Without these surfactants, the surface tension around the alveoli will remain high making it difficult for them to remain expanded. Without this chemical surfactant, the alveoli in a neonate’s lungs will collapse.
This disease does not necessarily appear immediately after birth but may develop within a few hours after delivery. Signs of this disease include rapid, labored breathing, grunting and flared nostrils. The potential for lung collapse and respiratory failure increase the longer this disease goes untreated.
The incidence of this disease can be reduced by assessing the maturity of the fetal lung to determine the best time for delivery. Infants born before 37 weeks gestation increase their chances of hyaline membrane disease.
Below are the five stages of endochondral ossification:
Stage 1: A bone collar surrounds the long shaft of the hyaline cartilage. Osteoblasts, that are matrix-synthesizing cells responsible for bone growth, help to encase the hyaline cartilage in bone. This creates a layer of bone called the periosteal bone collar.
Stage 2: The center of the bone shaft begins to calcify and develop cavities. During the development of the bone collar in stage 1, mature cartilage cells called chondrocytes begin to enlarge and signal the surrounding area to calcify. This causes the mature cartilage cells to die because the calcification causes the matrix to become impermeable to diffusing nutrients. The deterioration in the surrounding area creates cavities. The hyaline cartilage is stabilized by the bone collar that was formed in stage 1. The cartilage continues to grow in the remaining healthy regions causing elongation.
Stage 3: The periosteal bud invades the internal cavity and spongy bone forms. This stage occurs during the third month of development. During this stage, the periosteal bud, which contains an artery, a vein, lymphatic vessels, nerve fibers, red marrow elements, osteoblasts, and osteoclasts, enters the internal cavity of the bone shaft. The entering osteoclasts help to erode the cartilage matrix, while the osteoblasts secrete osteoid. Osteoid is composed of proteoglycans and glycoproteins as well as collagen fibers that contribute to a bone’s structure, flexibility and tensile strength. The secreted osteoid forms trabeculae.
Stage 4: The diaphysis (long shaft) elongates and a medullary cavity begins to form. In the center of the diaphysis or long shaft, osteoclasts break down the spongy bone and open up a medullary cavity in the center. Between week 9 and birth, the epiphyses (bone ends) grow rapidly and consist primarily of cartilage. The hyaline cartilage models continue to elongate by division of viable cartilage cells at the bone ends. Ossification continues as the shaft elongates and cartilage calcifies, erodes and is replaced by bony spicules on the epiphyseal surfaces facing the medullary cavity.
Stage 5: The epiphyses (bone ends) ossify. At birth, most of the long bones in the body have a bony long shaft surrounding remnants of spongy bone, a widening medullary cavity, and two cartilaginous ends. Not long after birth secondary ossification centers appear. The long bones typically form these centers in both epiphyses. Small long bones typically form only one secondary ossification center. The epiphyses also start to gain bony tissues. Deterioration at the center of the cartilage in the epiphysis opens up cavities that also allow for a periosteal bud to enter. Bone trabeculae appear as well. The secondary ossification process is almost exactly the same as the primary ossification process, except that the spongy bone in the interior remains and no medullary cavity is formed. Once the secondary ossification is complete, there will only be two places that have hyaline cartilage. Epiphyseal surfaces, like articular cartilage, and the junction of the diaphysis and epiphysis, where the epiphyseal plates form, are the only two places where hyaline cartilage will be found.
Have you been exploring different allied health care professions? One similar profession to sonography is how to become a radiologist. Radiologists make similar amounts of money, similar types of machinery, and involves similar levels of education.
The human embryo is constructed entirely of fibrous membranes and hyaline cartilage for the first 7 weeks of development. Before week 8, bone tissue begins to develop and replace the fibrous membranes and hyaline cartilage that was previously in place. The process of bone development from a fibrous membrane is called intramembranous ossification and the resulting bone is called membrane bone. The replacement of hyaline cartilage into bone is called endochondral ossification and results in the formation of cartilage, or bone. The initial development of fibrous membranes and hyaline cartilages for the embryonic skeleton allows for mitosis, which would be far more difficult, less flexible and resilient than normal bone.
Intramembranous ossification forms the cranial bones in the skull. The frontal, parietal, occipital, and temporal bones are all created through this process as well as the clavicle bones. Most of the bones created in this process are flat bones that are thin, flattened and usually a bit curved.
Endochondral ossification is the process by which all of the bones of the skeleton below the base of the skull form, with the exception of the clavicle bones. This process usually begins during the second month of development. During this process the hyaline cartilage that was formed during the first weeks of development are used as models for bone construction. This process of bone development is more complex than intramembranous ossification because the hyaline cartilage must be broken down during the ossification process. Tomorrow we will outline the five stages of development.
Pediatricians, baby books, magazines, and every reliable source that knows anything about babies will tell you that breastfeeding your child is the better than formula feeding. Of course, as a mother with all of my natural motherly instincts, I whole heartedly agreed with every doctor, every book, every magazine and every reliable source that agreed with this sentiment. However, the real reason why I chose breastfeeding over formula feeding is a little more selfish than the typical reasons most “good” mothers would admit to.
I chose to breastfeed my babies for three completely selfish and totally justifiable reasons. If you are studying how to become a midwife, mothers may assess the positives and negatives related with breast feeding.
Reason #1: Formula is expensive.
I know it doesn’t sound very maternal, but the cost of formula is one great reason that kept me from considering formula feeding. I just couldn’t justify spending any money on something that wasn’t going to be able to provide the best nutrition, especially if it was going to be expensive. If breast milk is free, why spend money if you don’t have to?
Reason #2: I love my sleep.
Waking up in the middle of the night and having to find a bottle, warm water to the perfect temperature, add formula, and shake it all up until all the clumps are gone is a lot to think about. This is especially true if you have to do it every two to three hours a night. Being able to latch my baby onto my breast and not have to do anything more than change the side he nursed on and burp him occasionally was so easy in comparison to formula feeding. Plus, it got me back to sleep a lot faster and with less stress.
Reason #3: I hate cleaning bottles.
If you are an expectant first time mom, you have probably already received or purchased several baby bottles. It is almost like you don’t really believe you are about to have a baby until you have purchased these three important baby items- bottles, diapers, and burp clothes.
When I had my first child, I received and purchased several bottles. After my son was born, I went through every bottle and every nipple trying to find one he would suck out of. It was very frustrating. After spending quite a bit of money to find the perfect bottle for his occasional bottle feedings, I became even more annoyed with cleaning the bottles. If you don’t have a dishwasher, cleaning bottles can be a time consuming task. Getting the grim that cakes up around the base of the bottles if you don’t wash them immediately is no fun.
