Mutations

In genetics, a mutation is a permanent change of the nucleotide sequence of the genome of an organism, virus, or extrachromosomal genetic element. Mutations result from unrepaired damage to DNA or to RNA genomes (typically caused by radiation or chemical mutagens), errors in the process of replication, or from the insertion or deletion of segments of DNA by mobile genetic elements. Mutations may or may not produce discernible changes in the observable characteristics (phenotype) of an organism. Mutations play a part in both normal and abnormal biological processes including: evolution, cancer, and the development of the immune system.

Mutation can result in several different types of change in sequences. Mutations in genes can either have no effect, alter the product of a gene, or prevent the gene from functioning properly or completely. Mutations can also occur in nongenic regions. One study on genetic variations between different species of Drosophila suggests that, if a mutation changes a protein produced by a gene, the result is likely to be harmful, with an estimated 70 percent of amino acid polymorphisms that have damaging effects, and the remainder being either neutral or weakly beneficial. Due to the damaging effects that mutations can have on genes, organisms have mechanisms such as DNA repair to prevent or correct (revert the mutated sequence back to its original state) mutations

Myocardial Infarction

Myocardial infarction (MI; Latin: infarctus myocardii) or acute myocardial infarction (AMI), commonly known as a heart attack, occurs when blood stops flowing properly to a part of the heart, and the heart muscle is injured because it is not receiving enough oxygen. Usually, this is because one of the coronary arteries that supplies blood to the heart develops a blockage due to an unstable buildup of white blood cells, cholesterol and fat. The event is called "acute" if it is sudden and serious. Myocardial infarction differs from cardiac arrest, although cardiac arrest can be a consequence of MI.

A person having an acute MI usually has sudden chest pain that is felt behind the sternum and sometimes travels to the left arm or the left side of the neck. Additionally, the person may have shortness of breath, sweating, nausea, vomiting, abnormal heartbeats, and anxiety. Women experience fewer of these symptoms than men, but usually have shortness of breath, weakness, a feeling of indigestion, and fatigue. In many cases, in some estimates as high as 64%, the person does not have chest pain or has vague symptoms. These are called "silent" myocardial infarctions.

Important risks are previous cardiovascular disease, old age, tobacco smoking, abnormal blood levels of certain lipids, diabetes, high blood pressure, lack of physical activity, obesity, chronic kidney disease, excessive alcohol consumption, and the use of cocaine and amphetamines. The main ways to determine if a person has had a myocardial infarction are electrocardiograms (ECGs) that trace the electrical signals in the heart and testing the blood for substances associated with damage to the heart muscle. ECG testing is used to differentiate between two types of myocardial infarction based on the appearance of the tracing. An ST section of the tracing higher than the baseline is called an ST elevation MI (STEMI) which usually requires more aggressive treatment. If this is not the case, the diagnosis is confirmed with a blood test (usually troponin).

Immediate treatments for a suspected MI often include aspirin, which prevents further blood from clotting; nitroglycerin, sometimes given to treat chest pain; and oxygen. STEMI is treated by restoring circulation to the heart, called reperfusion therapy, and typical methods are angioplasty, where the arteries are pushed open, and thrombolysis, where the blockage is removed using medications. Non-ST elevation myocardial infarction (NSTEMI) may be managed with medication, although angioplasty may be required if the person is considered to be at high risk. who have multiple blockages of their coronary arteries, particularly if they also have diabetes, may also be treated with bypass surgery (CABG).Ischemic heart disease, which includes MI, angina, and heart failure when it happens after MI, was the leading cause of death for both men and women worldwide in 2011

Myofilament Contraction

Myofilaments are the filaments of myofibrils constructed from proteins. The principal types of muscle are striated muscle, obliquely striated muscle and smooth muscle. Various arrangements of myofilaments create different muscles. Striated muscle has transverse bands of filaments. In obliquely striated muscle, the filaments are staggered. Smooth muscle has irregular arrangements of filaments.

Muscle fiber contraction
The axon terminal of a motor neuron releases the neurotransmitter, acetylcholine.
Acetylcholine diffuses across the synaptic cleft and binds to the muscle fiber membrane.
This depolarizes the muscle fiber membrane, and the impulse travels to the muscle's sarcoplasmic reticulum via the transverse tubules.
Calcium ions are then released from the sarcoplasmic reticulum into the sarcoplasm and subsequently bind to troponin.
Troponin and the associated tropomyosin undergo a conformational change after calcium binding and expose the myosin binding sites on actin, the thin filament.
The filaments of actin and myosin then form linkages.
After binding, myosin pulls actin filaments toward each other, or inward.
Thus muscle contraction occurs, and the sarcomere shortens as this process takes place.

Muscle fiber relaxation
The enzyme acetylcholinesterase breaks down acetylcholine and this ceases muscle fiber stimulation.
Active transport moves calcium ions back into the sarcoplasmic reticulum of the muscle fiber.
ATP causes the binding between actin and myosin filaments to break.
Troponin and tropomyosin revert to their original conformation and thereby block binding sites on the actin filament.
The muscle fiber relaxes and the entire sarcomere lengthens.
The muscle fiber is now prepared for the next contraction.

Olfaction Sense of Smell

Olfaction, also known as olfactics. is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, which can be considered analogous to sensory cells of the antennae of invertebrates. In humans, olfaction occurs when odorant molecules bind to specific sites on the olfactory receptors. These receptors are used to detect the presence of smell. They come together at the glomerulus, a structure which transmits signals to the olfactory bulb (a brain structure directly above the nasal cavity and below the frontal lobe). Many vertebrates, including most mammals and reptiles, have two distinct olfactory systems—the main olfactory system, and the accessory olfactory system (used mainly to detect pheromones). For air-breathing animals, the main olfactory system detects volatile chemicals, and the accessory olfactory system detects fluid-phase chemicals. Olfaction, along with taste, is a form of chemoreception. The chemicals themselves that activate the olfactory system, in general at very low concentrations, are called odorants. Although taste and smell are separate sensory systems in land animals, water-dwelling organisms often have one chemical sense.

Volatile small molecule odorants, non-volatile proteins, and non-volatile hydrocarbons may all produce olfactory sensations. Some animal species are able to smell carbon dioxide in minute concentrations

Oogenesis

Oogenesis, ovogenesis, or oögenesis /ˌoʊ.əˈdʒɛnɨsɪs/ is the creation of an ovum (egg cell). It is the female form of gametogenesis; the male equivalent is spermatogenesis. It involves the development of the various stages of the immature ovum

Oogenesis in mammals

Diagram showing the reduction in number of the chromosomes in the process of maturation of the ovum. (In mammals, the first polar body normally disintegrates before dividing, so only two polar bodies are produced.)
In mammals, the first part of oogenesis starts in the germinal epithelium, which gives rise to the development of ovarian follicles, the functional unit of the ovary.

Note that this process, important to all animal life cycles yet unlike all other instances of cell division, occurs completely without the aid of oo spindle-coordinating centrosomes.

Oogenesis consists of several sub-processes: oocytogenesis, ootidogenesis, and finally maturation to form an ovum (oogenesis proper). Folliculogenesis is a separate sub-process that accompanies and supports all three oogenetic sub-processes.

Cell type ploidy Process Process completion
Oogonium diploid Oocytogenesis (mitosis) third trimester (forming oocytes)
primary Oocyte diploid Ootidogenesis (meiosis 1) (Folliculogenesis) Dictyate in prophase I for up to 50 years
secondary Oocyte haploid Ootidogenesis (meiosis 2) Halted in metaphase II until fertilization
Ovum haploid
Oogonium —(Oocytogenesis)—> Primary Oocyte —(Meiosis I)—> First Polar Body (Discarded afterward) + Secondary oocyte —(Meiosis II)—> Second Polar Body (Discarded afterward) + Ovum

The creation of oogonia
The creation of oogonia traditionally doesn't belong to oogenesis proper, but, instead, to the common process of gametogenesis, which, in the female human, begins with the processes of folliculogenesis, oocytogenesis, and ootidogenesis.

Human oogenesis
At the start of the menstrual cycle, some 12-20 primary follicles begin to develop under the influence of elevated FSH to form secondary follicles. The primary follicles have formed from primordial follicles, which developed in the ovary at around 10–30 weeks after conception. By around day 9 of the cycle, only one healthy secondary follicle remains, with the rest having undergone ovarian follicle atresia. The remaining follicle is called the dominant follicle and is responsible for producing large amounts of estradiol during the late follicular phase. Estradiol production depends upon co-operation between the theca and granulosa cells. On day 14 of the cycle, an LH surge occurs, which itself is triggered by the positive feedback of estradiol. This causes the secondary follicle to develop into a tertiary follicle, which then ovulates some 24–36 hours later. An important event in the development of the tertiary follicle occurs when the primary oocyte completes the first meiotic division, resulting in the formation of a polar body and a secondary oocyte. The empty follicle then forms a corpus luteum, which later releases the hormone progesterone.

Oocytogenesis[edit]
Oogenesis starts with the process of developing oogonia, which occurs via the transformation of primordial follicles into primary oocytes, a process called oocytogenesis. Oocytogenesis is complete either before or shortly after birth.

Number of primary oocytes[edit]
It is commonly believed that, when oocytogenesis is complete, no additional primary oocytes are created, in contrast to the male process of spermatogenesis, where gametocytes are continuously created. In other words, primary oocytes reach their maximum development at ~20[5] weeks of gestational age, when approximately seven million primary oocytes have been created; however, at birth, this number has already been reduced to approximately 1-2 million.

Recently, however, two publications have challenged the belief that a finite number of oocytes are set around the time of birth.The renewal of ovarian follicles from germline stem cells (originating from bone marrow and peripheral blood) has been reported in the postnatal mouse ovary.

Due to the revolutionary nature of these claims, further experiments are required to determine the true dynamics of small follicle formation.

Ootidogenesis
The succeeding phase of ootidogenesis occurs when the primary oocyte develops into an ootid. This is achieved by the process of meiosis. In fact, a primary oocyte is, by its biological definition, a cell whose primary function is to divide by the process of meiosis.

However, although this process begins at prenatal age, it stops at prophase I. In late fetal life, all oocytes, still primary oocytes, have halted at this stage of development, called the dictyate. After menarche, these cells then continue to develop, although only a few do so every menstrual cycle.

Meiosis I
Meiosis I of ootidogenesis begins during embryonic development, but halts in the diplotene stage of prophase I until puberty. The mouse oocyte in the dictyate (prolonged diplotene) stage actively repairs DNA damage, whereas DNA repair is not detectable in the pre-dictyate (leptotene, zygotene and pachytene) stages of meiosis. For those primary oocytes that continue to develop in each menstrual cycle, however, synapsis occurs and tetrads form, enabling chromosomal crossover to occur. As a result of meiosis I, the primary oocyte has now developed into the secondary oocyte and the first polar body.

Meiosis II
Immediately after meiosis I, the haploid secondary oocyte initiates meiosis II. However, this process is also halted at the metaphase II stage until fertilization, if such should ever occur. When meiosis II has completed, an ootid and another polar body have now been created.

Folliculogenesis
Main article: Folliculogenesis
Synchronously with ootidogenesis, the ovarian follicle surrounding the ootid has developed from a primordial follicle to a preovulatory one.

Maturation into ovum
Both polar bodies disintegrate at the end of Meiosis II, leaving only the ootid, which then eventually undergoes maturation into a mature ovum.

The function of forming polar bodies is to discard the extra haploid sets of chromosomes that have resulted as a consequence of meiosis.

In vitro maturation
Main article: In vitro maturation
In vitro maturation (IVM) is the technique of letting ovarian follicles mature in vitro. It can potentially be performed before an IVF. In such cases, ovarian hyperstimulation isn't essential. Rather, oocytes can mature outside the body prior to IVF. Hence, no (or at least a lower dose of) gonadotropins have to be injected in the body. However, there still isn't enough evidence to prove the effectiveness and security of the technique.

Oogenesis in non-mammals
Main article: Evolution of sexual reproduction
Many protists produce egg cells in structures termed archegonia. Some algae and the oomycetes produce eggs in oogonia. In the brown alga Fucus, all four egg cells survive oogenesis, which is an exception to the rule that generally only one product of female meiosis survives to maturity.

In plants, oogenesis occurs inside the female gametophyte via mitosis. In many plants such as bryophytes, ferns, and gymnosperms, egg cells are formed in archegonia. In flowering plants, the female gametophyte has been reduced to an eight-celled embryo sac within the ovule inside the ovary of the flower. Oogenesis occurs within the embryo sac and leads to the formation of a single egg cell per ovule.

In ascaris, the oocyte does not even begin meiosis until the sperm touches it, in contrast to mammals, where meiosis is completed in the estrus cycle.

Organs of Digestion

In the human digestive system, the process of digestion has many stages, the first of which starts in the mouth (oral cavity). Digestion involves the breakdown of food into smaller and smaller components which can be absorbed and assimilated into the body. The secretion of saliva helps to produce a bolus which can be swallowed in the oesophagus to pass down into the stomach.

Saliva also contains a catalytic enzyme called amylase which starts to act on food in the mouth. Digestion is helped by the mastication of food by the teeth and also by the muscular contractions of peristalsis. Gastric juice in the stomach is essential for the continuation of digestion as is the production of mucus in the stomach.

Peristalsis is the rhythmic contraction of muscles that begins in the oesophagus and continues along the wall of the stomach and the rest of the gastrointestinal tract. This initially results in the production of chyme which when fully broken down in the small intestine is absorbed into the blood. Most of the digestion of food takes place in the small intestine. Water and some minerals are reabsorbed back into the blood, in the colon of the large intestine. The waste products of digestion are defecated from the anus via the rectum

Osteoporosis

Osteoporosis ("porous bones", from Greek: οστούν/ostoun meaning "bone" and πόρος/poros meaning "pore") is a progressive bone disease that is characterized by a decrease in bone mass and density which can lead to an increased risk of fracture.[1] In osteoporosis, the bone mineral density (BMD) is reduced, bone microarchitecture deteriorates, and the amount and variety of proteins in bone are altered. Osteoporosis is defined by the World Health Organization (WHO) as a bone mineral density of 2.5 standard deviations or more below the mean peak bone mass (average of young, healthy adults) as measured by dual-energy X-ray absorptiometry; the term "established osteoporosis" includes the presence of a fragility fracture.[2] The disease may be classified as primary type 1, primary type 2, or secondary. The form of osteoporosis most common in women after menopause is referred to as primary type 1 or postmenopausal osteoporosis, which is attributable to the decrease in estrogen production after menopause. Primary type 2 osteoporosis or senile osteoporosis occurs after age 75 and is seen in both females and males at a ratio of 2:1. Secondary osteoporosis may arise at any age and affect men and women equally; this form results from chronic predisposing medical problems or disease, or prolonged use of medications such as glucocorticoids, when the disease is called steroid- or glucocorticoid-induced osteoporosis.

The risk of osteoporosis fractures can be reduced with lifestyle changes and in those with previous osteoporosis related fractures, medications. Lifestyle change includes diet, exercise, and preventing falls. A review by the U.S. Preventive Services Task Force (USPSTF) found insufficient evidence to recommend calcium and vitamin D supplements to prevent fractures.[3] Bisphosphonates are useful in those with previous fractures from osteoporosis but are of minimal benefit in those who have osteoporosis but no previous fractures. Osteoporosis is a component of the frailty syndrome