Meiosis

Meiosis

Mitosis provides a method for the asexual reproduction of singular cellular organism and a means of growth and cell replacement in multicellular organisms. An alternative to asexual reproduction, where the offspring are identical to the parent, is sexual reproduction where the genetic material from reproductive partners combines to produce offspring. Clearly such combination cannot involve all the genetic material of the parents, otherwise, with each successive generation we would see a doubling of the genetic material within each cell. To accommodate this the parents produce sex cells (eggs/sperm) called gametes that each contain half the parental genetic material, these fuse to produce offspring.

The gamete cells, then, are unusual in that they contain half the number of chromosomes of 'normal' cells and, as such, are termed haploid (normal cells, containing two sets of chromosomes, are termed diploid).

The normal number of chromosomes in human cells is 46 (in 23 pairs). These pairs originate from parental gamete cells containing 23 single chromosomes, 23 in the mother's egg and 23 form the father's sperm. These two sets of chromosomes are called homologues in that they carry genetic code for the same function, that is a particular chromosome from the mother may carry the genetic coding for hair colour, this is the partner chromosome for the paternal chromosome carrying the same genetic information. Each of the 23 chromosomes can be distinguished by its size, the position of its centromere and the pattern of dark bands. The process of identifying specific chromosomes is called karyotyping and you will undertake a karyotyping exercise in class - external visitors to this page can find the karyotyping exercise on the links page. You can learn more about karyotyping from the set.

The process of meiosis can be considered in two stages; Meiosis I and Meiosis II.

Meiosis I

As with mitosis, meiosis I is preceded by an interphase stage. During this stage chromosomal replication takes place resulting in two identical chromatids, attached by centromeres. Centrosomes are also replicated during this stage.

Interphase is followed by Prophase (I). Homologous pairs of chromosomes pair up and the chromatids of these (of which there are four) cross over one another (see diagram, set book page 140). This coming together of chromatids is important in understanding genetic inheritance. The alignment of chromatids seems random and during this cross over phase there is an exchange of genetic material from one chromatid to the other. In other words, segments of genetic code are exchanged - see Figure 8.18b, page 145 in the set book. This grouping of four chromatids is termed a tetrad. This exchange of genetic material results in chromatids that are uniquely different from that of the parent and ensures genetic variation from one generation to the next.

As this exchange of genetic material takes place, the rest of the cell prepares for division. The centrosomes, with their spindle mictrotubules, separate and the nuclear membrane dissolves. The chromosomes now move to the metaphase plate, as in mitosis, except now they arrive as pairs. Spindle fibres from one pole of the cell (cf mitosis where fibres from both poles) attach to one chromosome of each pair.

Anaphase I

As in mitosis, anaphase I sees the movement of chromosomes to opposite poles of the cell. Paired chromatids are attached by their centromere and so move together towards the poles, in effect the homologous pairs of chromosomes are separated and we have two individual sets of chromosomes at either end of the cell. This process of reducing the amount of genetic material to be passed onto the daughter cells is called reduction division.

Following Anaphase I are the stages of Teleophase I and Cytokinesis. Cell division begins with the formation of a cleavage furrow (in animals) or cell wall (in plants) and the two sets of chromosomes are separated into daughter cells. This is similar to mitosis but, unlike mitosis, there is no further duplication genetic material during the subsequent interphase.

Meiosis II

Meiosis II can follow meiosis 1 immediately or can be delayed by a period of interphase during which time the chromosomes decondense and the nucleus reforms. As in meiosis I, interphase is followed by stages called prophase, metaphase, anaphase, telophase and cytokinesis.

Prophase II

The chromosomes (containing two chromatids) condense, the spindle apparatus forms and the chromosomes move to the metaphase II plate.

Metaphase II

The chromosomes position themselves along the metaphase plate ready for separation.

Anaphase II

The sister chromids separate into individual chromosomes and move in opposite directions to the poles of the cell.

Teleophase II

The chromosomes decondense and nuclei of the (now four) cell(s) reforms. The new cells separate during cytokinesis.

Interphase II

Normal cellular activity continues but there is no further DNA replication and the gamete awaits fertilization.

Advantages of meiosis

The advantage of meiosis (sexual reproduction) lies in the shuffling and combination of genetic material. We have seen that homologous chromosomes code for certain characteristics - by exchanging DNA and combining different sources of genetic material we create a new set of genetic code. It is this generation of new code that results in variation within a population (such as eye colour etc.). This variation enables a population to evolve. Genetic diversity also enables populations to adapt and overcome threatening circumstances.

Mitosis

Mitosis

During mitosis, the cells undergo duplication and division, in other words, they produce copies of themselves. This duplication process is a normal function of cells and allows for growth and the replacement of worn or damaged cells. Some cells, such as the epithelial or skin cells, reproduce frequently, whilst others, such as mature nerve cells reproduce rarely if ever. Although cellular reproduction is a normal process, sometimes the process becomes uncontrolled and in such cases tumours and cancers develop, we shall see later that certain chemicals and radiation can promote such behavior.

Traditionally mitosis is divided into two main stages; interphase and mitosis (although each of these stages consist themselves of a number of phases).

Interphase: During interphase the cell prepares for reproduction by duplicating the cellular DNA. Much of this activity is invisible to the conventional light microscope and it is only during the mitosis stage itself that the frantic cellular activity becomes apparent.

 

Mitosis:

Diagrams in the set book will help you follow the process of mitosis. There is also an excellent animation of the process at San Diego State University This really is a must visit site. You can also download a copy of this animation. Kathleen M. Fisher, Professor of Biology at San Diego has produced an excellent biology site and her description of mitosis (better than mine!) and some ideas for lessons and exercises are available at her mitosis site - I strongly recommend you pay a visit.

Mitosis consists of a series of continuous processes; prophase, metaphase, anaphase and telophase (which itself leads to cytokinesis, the actual formation of daughter cells). It is important that you are able to describe each of these phases.

Prophase

During the prophase stage, the DNA containing chromatin condense and form chromosomes. Since the DNA has already been duplicated during the interphase, each chromatid consists of two chromosomes connected by a centromere. This, and other stages of mitosis, are illustrated in set book 1.

In the latter stages of prophase, spindle fibres form. These are attached to the chromatids and reach out in opposite directions. It is at this point that the chromosomes begin to move apart and the nuclear envelope breaks up and dissolves. The centrioles separate, each radiating microtubules called asters.

Metaphase

The chromosomes move apart and at metaphase they reach the central plane of the cell. Following the frantic activity which has gone before, this seems almost like a moment of rest for the cell as the chromosomes wait patiently for the next phase of mitosis.

Anaphase

During this phase the centrioles divide to form truly separate chromosomes, these are then drawn to their individual poles, where they wait to form the daughter cells. At this point we have a single cell containing two sets of individual yet identical chromosomes.

Telophase

Following anaphase, the two daughter cells begin to form. The nucleus (or nuclei since we now have two proto-cells), previously dissolved, begins to reform as does the nuclear membrane. The cytoplasm and organelles (duplicated earlier) are distributed between the emerging cells, the chromosomes disperse (as in the interphase) and the spindle is recycled to form the cytoskeleton.

The final phase is the separation of the two daughter cells (this is called cytokinesis) as the cytoplasm separates to form the two new cells.

Cell Division

Human Cell

The cell is the structural and functional unit of all known living organisms. It is the smallest unit of an organism that is classified as living, and is often called the building block of life. Some organisms, such as most bacteria, are unicellular (consist of a single cell). Other organisms, such as humans, are multicellular. (Humans have an estimated 100 trillion or 1014 cells; a typical cell size is 10 µm; a typical cell mass is 1 nanogram.) The largest known cell is an unfertilized ostrich egg cell.

In 1835 before the final cell theory was developed, Jan Evangelista Purkyně observed small "granules" while looking at the plant tissue through a microscope. The cell theory, first developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, states that all organisms are composed of one or more cells, that all cells come from preexisting cells, that vital functions of an organism occur within cells, and that all cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells.

The word cell comes from the Latin cellula, meaning, a small room. The descriptive name for the smallest living biological structure was chosen by Robert Hooke in a book he published in 1665 when he compared the cork cells he saw through his microscope to the small rooms monks lived in.

Nutrition

Nutrition

Frequency of eating per day

About 46.8 percent of the people could afford a three square meal per day at morning – afternoon – evening intervals. The average number of times children ate daily was 1.8. It is medically recommended to eat three times per day or whenever the body is hungry for food. This must be done with caution to give relief to the digestive system and the utilization of nutrients from the food taken. A medical fact is that the body needs nutritious food to undergo processes of growth and development and to meeting the challenges of body exercises and work. With the mean time of eating estimated at 1.8 times daily in the study locations, the healthiness of the population depends on the nutritious components of the food intake in vitamins, proteins and carbohydrates. Those who could afford twice meal per day engaged in child labour such as hawking of products

Types of foods intake

Child nutrition is a complex concept. Children need dozens of different vitamins, minerals, and other assorted nutrients each day, and those needs change as children grow. In fact, infant nutrition is quite different from child nutrition.
Nutrition guidelines recommended for adults are inappropriate for most children. This is because young children only have small tummies and so need plenty of calories and nutrients in a small amount of food to ensure they grow properly. While low-fat diets are recommended for older children and adults, under-fives need diets that contain good amounts of fat.
In this study, types of food intake were classified into different categories, carbohydrate, proteins and vitamins. Children were made to indicate the types / frequencies of specific food intake. Findings show that Yam remains the most staple food for the people in the study areas. Most inhabitants engage in yam cultivation in large quantities for consumption and commercial purposes. Over 88 percent took yam variety of foods daily. This is similar to the intake of rice, maize and cassava varieties food intake which recorded the highest percent of 37.5, 44.4 and 46.7 percent among the children. It can be inferred from findings that yam varieties intake had the highest percent of all food varieties intake among the people. Several reasons were adduced to this, included, availability, relatively cheap price, and the ability to grow them in at least consumable quantities at low costs. Findings further show that rice, maize and yams were taken in different varieties such as gaari, akpu, flour and fufu. The proteinous food intake was made of beans varieties. Beans was grown in subsistence quantities, among farmers. Some of these varieties include moinmoin, akara and beans cake. One-fifth of total sample (21.5 percent) took beans variety monthly between 1-10 times. The remaining 78.5 percent took food of beans varieties between 11-20 times monthly.

As food supplement, just a percent could afford tea with milk above 5 times monthly. Milk is a reliable source of multivitamins intake and normally taken in the morning before the days work. Maize is another source of carbonhydrate food intake. It is grown in large scale by most farmers not only for subsistence purposes but for market. A considerable proportion of those who engaged in farming earned their living from maize cultivation.

Major fruits in the research area include orange, cashew, carrot, mango and pineapple. Fruits are major source of vitamin supplements. Findings show that these fruits are common on seasonal basis and are largely grown in the Southern part of the research locations. The average number of times children took beans varieties, maize related foods and fruits were 7, 8, 10 times per month based on this survey. This indicates that daily, 0.2, 0.27, 0.3, proportion of sample food intakes were derived from proteins, vitamins and carbohydrate sources.

Cross Tabulation

In this sub-section, various socio-economic characteristics of the sample are correlated with their patterns of feeding to unearth the extent at which the influence or determine each other. The patterns of eating are classified into carbohydrate, and proteins and fruits. The criterion for carbohydrate intake was the consumption of yam, maize and cassava varieties of food while the intake of beans varieties of food was used for protein intake, fruits intake include cashew, mango, pawpaw and orange.

Age / food Intake

Carbohydrate

The data show that yam/yam related foods are among major foods for the people with an average intake of 22 times per month, 0.73 times per day. There is no significant relationship between age and yam intake. At a linear by linear Association value at 0.018, the Pearson chi-square test was found at 48.7, df (v) 15 and X2t = at 0.05 level of significance Yam is widely grown by indigenes. However, the higher the age, the higher the tendency for gaari intake and vice versa. This indicates that older children consume gaari more than the younger people. The general frequency of garri intake was higher than that of yam. The average number of garri intake per month was 34 per month indicating, 1.1 times per day. Maize related foods were consumed mostly by children between 8 - 14 years of age than those in other age cohorts.

Proteins Intake

The monthly average of the intake of proteins related foods was 15 times with the daily average of 0.5. This is lower than the daily/monthly average of cabonhydrate intake. There is no disparity between age and proteins intake, the monthly average spread across all age cohorts. While a little proportion of beans was grown in some study locations, some areas could not venture into the growth of beans because of the unfavorable climate and land composition.

Fruits Intake

The intake of fruits varieties varied directly with age. Older children have the tendency to take fruits more than the younger ones. Major fruits in the area are cashew, mango, orange, pineapple and banana. These fruits are grown in large quantities in the area. Research evidences have indicated that most of these fruits often waste in large quantities during season.

SELF CARE

Interventions (Nursing Interventions Classification)

The nurse may encounter the patient with a self-care deficit in the hospital or in the community. The deficit may be the result of transient limitations, such as those one might experience while recuperating from surgery; or the result of progressive deterioration that erodes the individual’s ability or willingness to perform the activities required to care for himself or herself. Careful examination of the patient’s deficit is required in order to be certain that the patient is not failing at self-care because of a lack in material resources or a problem with arranging the environment to suit the patient’s physical limitations. The nurse coordinates services to maximize the independence of the patient and to ensure that the environment that the patient lives in is safe and supportive of his or her special needs.

Defining Characteristics:
■Inability to feed self independently
■Inability to dress self independently
■Inability to bathe and groom self independently
■Inability to perform toileting tasks independently
■Inability to transfer from bed to wheelchair
■Inability to ambulate independently
■Inability to perform miscellaneous common tasks such as telephoning and writing
Related Factors:
■Neuromuscular impairment, secondary to cerebrovascular accident (CVA)
■Musculoskeletal disorder such as rheumatoid arthritis
■Cognitive impairment
■Energy deficit
■Pain
■Severe anxiety
■Decreased motivation
■Environmental barriers
■Impaired mobility or transfer ability
Expected Outcomes
■Patient safely performs (to maximum ability) self-care activities.
■Resources are identified which are useful in optimizing the autonomy and independence of the patient.

Microbiology

Microbiology

Microbiology (from Greek μῑκρος, mīkros, "small"; βίος, bios, "life"; and -λογία, -logia) is the study of microorganisms, which are unicellular or cell-cluster microscopic organisms. This includes eukaryotes such as fungi and protists, and prokaryotes, which are bacteria and archaea. Viruses, though not strictly classed as living organisms, are also studied. In short; microbiology refers to the study of life and organisms that are too small to be seen with the naked eye.

Microbiology is a broad term which includes virology, mycology, parasitology, bacteriology and other branches. A microbiologist is a specialist in microbiology.

Microbiology is researched actively, and the field is advancing continually. We have probably only studied about one percent of all of the microbe species on Earth. Although microbes were first observed over three hundred years ago, the field of microbiology can be said to be in its infancy relative to older biological disciplines such as zoology and botany.

History

Ancient
The existence of microorganisms was hypothesized for many centuries before their actual discovery in the 17th century. In 600 BCE, the ancient Indian surgeon Susruta held microbes responsible for several diseases and explained in Sushruta Samhita that they can be transmitted through contact, air or water. Theories on microorganisms was made by Roman scholar Marcus Terentius Varro in a book titled On Agriculture in which he warns against locating a homestead in the vicinity of swamps:

“ ...and because there are bred certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and there cause serious diseases.[4] ”

This passage seems to indicate that the ancients were aware of the possibility that diseases could be spread by yet unseen organisms.

In The Canon of Medicine (1020), Abū Alī ibn Sīnā (Avicenna) stated that bodily secretion is contaminated by foul foreign earthly bodies before being infected.[5] He also hypothesized on the contagious nature of tuberculosis and other infectious diseases, and used quarantine as a means of limiting the spread of contagious diseases.
When the Black Death bubonic plague reached al-Andalus in the 14th century, Ibn Khatima hypothesized that infectious diseases are caused by "minute bodies" which enter the human body and cause disease.

In 1546 Girolamo Fracastoro proposed that epidemic diseases were caused by transferable seedlike entities that could transmit infection by direct or indirect contact or even without contact over long distances.

All these early claims about the existence of microorganisms were speculative in nature and not based on any data or science. Microorganisms were neither proven and observed, nor correctly and accurately described until the 17th century. The reason for this was that all these early inquiries lacked the most fundamental tool in order for microbiology and bacteriology to exist as a science, and that was the microscope.

Toxinology

Toxinology

Toxinology is the specialized area of science that deals specifically with animal, plant, and microbial toxins. Prof. Dietrich Mebs has defined toxinology as "the scientific discipline dealing with microbial, plant and animal venoms, poisons and toxins". Additionally stating that "toxinology includes more than just the chemistry and mode of action of a toxin. It deals also with the biology of venom- or poison-producing organism, the structure and function of the venom apparatus, as well as the use of the venom or poison, the ecological role of these compounds." Prof. Jurg Meier has defined toxinology as "the science of toxic substances produced by or accumulated in living organisms, their properties, and their biological significance for the organisms involved".

There is an International Society on Toxinology, founded in 1962, catering for toxinologist and their research, with an international Congress every three years and regional sectional meetings in intervening years.

Toxins and toxinology
Toxins are natural substances, or substances produced by living organisms, in contrast to toxic substances from chemicals, which are toxicants. Living organisms producing or using toxins do so as either venoms or poisons. Venoms are toxins, or more commonly, collections of varying toxins, that are used actively against prey or predators, most commonly to subdue, kill and digest prey, or dissuade predators. Poisons of natural origin, that is containing toxins and used by living organisms, are passive and generally used for defence. A predator attempting to molest or eat a poisonous animal, plant or mushroom will suffer adverse effects from the toxins in the poison, varying from mild discomfort to rapid death. Particularly food poisons, but also for a few venoms, the component toxins are not produced by the deploying animal/plant, but are made by micro-organisms and concentrated and used by the deploying animal/plant. A good example is tetrodotoxin, used by a variety of poisonous animals and by a few venomous animals.

Toxins and toxinology is not solely focussed on adverse effects. An increasing number of toxins are important as research tools, unlocking secrets of disease, or as diagnostic agents in hospital laboratories, or as therapeutic agents to treat human disease, including anti-cancer agents, anti-epileptic agents, anti-clotting agents, analgesics, anti-hypertensive drugs, to name but a few. This is a very rich field for research.

Clinical toxinology
Within toxinology there is a clinical subgroup, clinical toxinologists, who focus on the medical effects in humans of exposure to the toxins in animal venoms or plant poisons. This includes such problems as venomous snakebite, currently considered to afflict >2.5 million people each year, with >100,000 deaths. Information on these medical consequences of toxins can be found in diverse sources, such as the Clinical Toxinology Resources Website and books such as Prof. Mebs book and the CRC book on toxinology.

ADVERSE REACTIONS TO DRUGS

ADVERSE REACTIONS TO DRUGS



An adverse reaction to a drug has been defined as any noxious or unintended reaction to a drug that is administered in standard doses by the proper route for the purpose of prophylaxis, diagnosis, or treatment. Some drug reactions may occur in everyone, whereas others occur only in susceptible patients. A drug allergy is an immunologically mediated reaction that exhibits specificity and recurrence on re-exposure to the offending drug.



Classification of adverse reactions to drugs

Reactions that may occur in anyone

Drug overdose -Toxic reactions linked to excess dose or impaired excretion, or to both
Drug side effect - Undesirable pharmacological effect at recommended doses
Drug interaction - Action of a drug on the effectiveness or toxicity of another drug

Reactions that occur only in susceptible subjects

Drug intolerance - A low threshold to the normal pharmacological action of a drug
Drug idiosyncrasy - A genetically determined, qualitatively abnormal reaction to a drug related to a metabolic or enzyme deficiency.
Drug allergy - An immunologically mediated reaction, characterised by specificity, transferability by antibodies or lymphocytes, and recurrence on re-exposure
Pseudoallergic reaction - A reaction with the same clinical manifestations as an allergic reaction (eg, as a result of histamine release) but lacking immunological specificity


Incidence

Adverse reactions to drugs are very common in everyday medical practice. A French study of 2067 adults aged 20-67 years attending a health centre for a check up reported that 14.7% gave reliable histories of systemic adverse reactions to one or more drugs. In a Swiss study of 5568 hospital inpatients, 17% had adverse reactions to drugs. Fatal drug reactions occur in 0.1% medical inpatients and 0.01% of surgical inpatients. The main drugs implicated are antibiotics and non-steroidal anti-inflammatory drugs. Adverse reactions to drugs occurring during anaesthesia (muscle relaxants, general anaesthetics, and opiates), although less common (1 in 6000 patients receiving anaesthesia), are life threatening, with a mortality of about 6%.

Numerous mechanisms have been implicated in adverse reactions to drugs. However, these mechanisms are not fully understood, which may explain the difficulty in differentiating drug allergy from other forms of drug reactions and in assessing the incidence of drug allergy, evaluating risk factors, and defining management strategies.

DEGREE OF IONISATION

Degree of ionisation

This is really important with regard to local anaesthetics. The essential fact to know is that highly ionized drugs cannnot cross lipid membranes (basically they can't go anywhere) and unionised drugs can cross freely. Morphine is highly ionised, fentanyl is the opposite. Consequently the latter has a faster onset of action. The degree of ionisation depends on the pKa of the drug and the pH of the local environment. The pKa is the the pH at which the drug is 50% ionised. Most drugs are either weak acids or weak bases. Acids are most highly ionised at a high pH (i.e. in an alkaline environment). Bases are most highly ionised in an acidic environment (low pH). For a weak acid, the more acidic the environment, the less ionised the drug, and the more easily it crosses lipid membranes. If you take this acid, at pKa it is 50% ionised, if you add 2 pH points to this (more alkaline), it becomes 90% ionised, if you reduce the pH (more acidic) by two units, it becomes 10% ionised. Weak bases have the opposite effect.

Local anaesthetics are weak bases: the closer the pKa of the local anaesthetic to the local tissue pH, the more unionised the drug is. That is why lignocaine(pKa 7.7) has a faster onset of action than bupivicaine (pKa 8.3). If the local tissues are alkalinised (e.g. by adding bicarbonate to the local anaesthetic), then the tisssue pH is brought closer to the pKa, and the onset of action is hastened.

GI SYSTEM ANATOMY and PROTEIN BINDING

INTERACTION BETWEEN HUMAN BODY AND DRUGS

Introduction

Drugs are the substance that are used to treat a disease. These are chemical substances derived from different sources (living or non- living things) which are sued to alter the functions of living/ bacterial tisseus by reacting with them.

Uses of drugs

Drigs are used for:

1. Diagnosis of diseases

2. Prevention of diesases

3. Treatment of diseases.

This chapter deals with the relationship between drug and the human body; the mechanism of drung' action, uses of drugs and the body's response to drugs.

Drugs are prepared in laboratories and experimented so that they are free of unacceable toxic substances which can harm the clients. Then only they are approved for use of human. The study of action of drug in man is called clinical pharmacology.

Clinical Pharmacology can be divided into two brances.

1. Pharmacokinetics.

Means what the human body dees to drungs it is the study of the movement of drugs in the body.

2. Pharmacodynamics

Means what a drug does to the human body. The knowledge about pharmacokinetics and pharmacodynamics is essential to know how the drugs are used for the best advantade of the patient.

Protein Binding

Most drugs bind to proteins, either albumin or alpha-1 acid glycoprotein (AAG), to a greater or lesser extent. Drugs prefer to be free, it is in this state that they can travel throughout the body, in and out of tissues and have their biological effect. The downside of this is that they are easy prey for metabolising enzymes.

As you would expect, more highly bound drugs have a longer duration of action and a lower volume of distribution. Generally high extraction ratio drugs' clearance is high because of low protein binding and, conversely, low extraction ratio drugs' clearance is strongly dependent on the amount of protein binding.

Why is this important? If a drug is highly protein bound, you need to give loads of it to get a theraputic effect; as so much is stuck to protein. But what happens if another agent comes along and starts to compete with the drug for the binding site on the protein? Yes, you guessed it, the amount of free drug is increased. This is really important for drugs that are highly protein bound: if a drug is 97% bound to albumin and there is a 3% reduction in binding (displaced by another drug), then the free drug concentration doubles; if a drug is 70% bound and there is a 3% reduction in binding, this will make little difference.

The drugs that you really need to keep an eye on are: warfarin, diazepam, propranolol and phenytoin. For example, a patient on warfarin is admitted with seizures, you treat the patient with phenytoin, next thing you know - his INR is 10.

The amount of albumin does not appear to be hugely relavent. In disease states such as sepsis, the serum albumin drops drastically, but the free drug concentration does not appear to increase