Basal-cell carcinomas develop in the basal cell layer of the skin. Sun light exposure leads to the formation of thymine dimers, a form of DNA damage. While DNA repair removes most UV-induced damage, not all crosslinks are excised. There is, therefore, cumulative DNA damage leading to mutations. Apart from the mutagenesis, sunlight depresses the local immune system, possibly decreasing immune surveillance for new tumor cells. Basal-cell carcinoma also develops as a result of Basal-Cell Nevus Syndrome, or Gorlin Syndrome, which is also characterized by keratocystic odontogenic tumors of the jaw, palmar or plantar (sole of the foot) pits, calcification of the falx cerebri (in the center line of the brain) and rib abnormalities. The cause of the syndrome is a mutation in the PTCH1 tumor-suppressor gene at chromosome 9q22.3, which inhibits the hedgehog signaling pathway. A mutation in the SMO gene, which is also on the hedgehog pathway, also causes basal-cell carcinoma.

Lesions of the skin
11.a Disorders of Pigmentation
11.b Melanoma
11.c Epidermal and Dermal Lesions
11.d Malignant Tumors

Epidermal organogenesis, the formation of the epidermis, begins in the cells covering the embryo after neurulation, the formation of the central nervous system. In most vertebrates, this original one-layered structure quickly transforms into a two-layered tissue; a temporary outer layer, the periderm, which is disposed once the inner basal layer or stratum germinativum has formed. This inner layer is a germinal epithelium that give rise to all epidermal cells. It divides to form the outer spinous layer (stratum spinosum). The cells of these two layers, together called the Malpighian layer(s) after Marcello Malpighi, divide to form the superficial granular layer (Stratum granulosum) of the epidermis. The cells in the granular layer do not divide, but instead form skin cells called keratinocytes from the granules of keratin. These skin cells finally migrate to form the cornified layer (stratum corneum), the outermost epidermal layer, where the cells become flattened sacks with their nuclei located at one end of the cell. After birth these outermost cells are replaced by new cells from the granular layer and throughout life they are shed at a rate of 1.5 g (0.053 oz) per day. Epidermal development is a product of several growth factors, two of which are: * Transforming growth factor Alpha (TGFα) is an autocrine growth factor by which basal cells stimulate their own division. * Keratinocyte growth factor (KGF or FGF7) is a paracrine growth factor produced by the underlying dermal fibroblasts in which the proliferation of basal cells is regulated.

Lesions of the skin
11.a Disorders of Pigmentation
11.b Melanoma
11.c Epidermal and Dermal Lesions
11.d Malignant Tumors

Melanoma  is a malignant tumor of melanocytes. Melanocytes are cells that produce the dark pigment, melanin, which is responsible for the color of skin. They predominantly occur in skin, but are also found in other parts of the body, including the bowel and the eye. Melanoma can occur in any part of the body that contains melanocytes. Melanoma is less common than other skin cancers. However, it is much more dangerous and causes the majority (75%) of deaths related to skin cancer. Worldwide, doctors diagnose about 160,000 new cases of melanoma yearly. The diagnosis is more frequent in women than in men and is particularly common among Caucasians living in sunny climates, with high rates of incidence in Australia, New Zealand, North America, and northern Europe. According to a WHO report about 48,000 melanoma related deaths occur worldwide per year. The treatment includes surgical removal of the tumor, adjuvant treatment, chemo- and immunotherapy, or radiation therapy. The chance of a cure is greatest when the tumor is discovered while it is still small and thin, and can be entirely removed surgically.

Lesions of the skin
11.a Disorders of Pigmentation
11.b Melanoma
11.c Epidermal and Dermal Lesions
11.d Malignant Tumors

In humans, melanin is the primary determinant of skin color. It is also found in hair, the pigmented tissue underlying the iris of the eye, and the stria vascularis of the inner ear. In the brain, tissues with melanin include the medulla and zona reticularis of the adrenal gland, and pigment-bearing neurons within areas of the brainstem, such as the locus coeruleus and the substantia nigra. The melanin in the skin is produced by melanocytes, which are found in the basal layer of the epidermis. Although, in general, human beings possess a similar concentration of melanocytes in their skin, the melanocytes in some individuals and ethnic groups more frequently or less frequently express the melanin-producing genes, thereby conferring a greater or lesser concentration of skin melanin. Some individual animals and humans have very little or no melanin in their bodies, a condition known as albinism. Because melanin is an aggregate of smaller component molecules, there are many different types of melanin with differing proportions and bonding patterns of these component molecules. Both pheomelanin and eumelanin are found in human skin and hair, but eumelanin is the most abundant melanin in humans, as well as the form most likely to be deficient in albinism.

Lesions of the skin
11.a Disorders of Pigmentation
11.b Melanoma
11.c Epidermal and Dermal Lesions
11.d Malignant Tumors

Sports injuries are injuries that occur to athletes participating in sporting events. In many cases, these types of injuries are due to overuse of a part of the body when participating in a certain activity. For example, runner's knee is a painful condition generally associated with running, while tennis elbow is a form of repetitive stress injury at the elbow. Other types of injuries can be caused by a hard contact with something. This can often cause a broken bone or torn ligament or tendon Injuries are a common occurrence in professional sports and most teams have a staff of Athletic Trainers and close connections to the medical community. Controversy has arisen at times when teams have made decisions that could threaten a players long-term health for short term gain. 

Related Videos
10.a Poisoning and Toxins
10.b Lifestyle Choices
10.c Drug Abuse
10.d Physical Injuries

Substance abuse, also known as drug abuse, refers to a maladaptive pattern of use of a substance that is not considered dependent. The term "drug abuse" does not exclude dependency, but is otherwise used in a similar manner in nonmedical contexts. The terms have a huge range of definitions related to taking a psychoactive drug or performance enhancing drug for a non-therapeutic or non-medical effect. All of these definitions imply a negative judgment of the drug use in question (compare with the term responsible drug use for alternative views). Some of the drugs most often associated with this term include alcohol, amphetamines, barbiturates, benzodiazepines (particularly temazepam, nimetazepam, and flunitrazepam), cocaine, methaqualone, and opioids. Use of these drugs may lead to criminal penalty in addition to possible physical, social, and psychological harm, both strongly depending on local jurisdiction. Other definitions of drug abuse fall into four main categories: public health definitions, mass communication and vernacular usage, medical definitions, and political and criminal justice definitions.

Related Videos
10.a Poisoning and Toxins
10.b Lifestyle Choices
10.c Drug Abuse
10.d Physical Injuries

The cytoplasm is a thick liquid residing between the cell membrane holding all the cell's internal sub-structures (called organelles), except for the nucleus. All the contents of the cells of prokaryote organisms (which lack a cell nucleus) are contained within the cytoplasm. Within the cells of eukaryote organisms the contents of the cell nucleus are separated from the cytoplasm, and are then called the nucleoplasm. In eukaryotic cells also, the cytoplasm contains organelles, such as mitochondria, which are filled with liquid that is kept separate from the rest of the cytoplasm by biological membranes. It is within the cytoplasm that most cellular activities occur, such as many metabolic pathways including glycolysis, and processes such as cell division. The inner, granular mass is called the endoplasm and the outer, clear and glassy layer is called the cell cortex or the ectoplasm.

Response to Cell Injury
2.a Causes of Cell Injury
2.b Cell Changes During Injury
2.c Cell Death
2.d Cell Adaptations
2.e Cell Alterations
3.a Acute Inflammation
3.b Importance of Neutrophils in inflammation
3.c Chemical Mediators in Inflammation
3.d Outcome of Inflammation
3.e Chronic Inflammation
3.f Tissue Response in inflammation

Cellular automata are often simulated on a finite grid rather than an infinite one. In two dimensions, the universe would be a rectangle instead of an infinite plane. The obvious problem with finite grids is how to handle the cells on the edges. How they are handled will affect the values of all the cells in the grid. One possible method is to allow the values in those cells to remain constant. Another method is to define neighbourhoods differently for these cells. One could say that they have fewer neighbours, but then one would also have to define new rules for the cells located on the edges. These cells are usually handled with a toroidal arrangement: when one goes off the top, one comes in at the corresponding position on the bottom, and when one goes off the left, one comes in on the right. (This essentially simulates an infinite periodic tiling, and in the field of partial differential equations is sometimes referred to as periodic boundary conditions.) This can be visualized as taping the left and right edges of the rectangle to form a tube, then taping the top and bottom edges of the tube to form a torus (doughnut shape). Universes of other dimensions are handled similarly. This is done in order to solve boundary problems with neighborhoods, but another advantage of this system is that it is easily programmable using modular arithmetic functions. For example, in a 1-dimensional cellular automaton like the examples below, the neighborhood of a cell xit—where t is the time step (vertical), and i is the index (horizontal) in one generation—is {xi−1t−1, xit−1, xi+1t−1}. There will obviously be problems when a neighbourhood on a left border references its upper left cell, which is not in the cellular space, as part of its neighborhood.
Response to Cell Injury
2.a Causes of Cell Injury
2.b Cell Changes During Injury
2.c Cell Death
2.d Cell Adaptations
2.e Cell Alterations
3.a Acute Inflammation
3.b Importance of Neutrophils in inflammation
3.c Chemical Mediators in Inflammation
3.d Outcome of Inflammation
3.e Chronic Inflammation
3.f Tissue Response in inflammation

Hematopathology is the study of diseases of blood cells (White blood cells, red blood cells, platelets) and cells/tissues/organs comprising the hematopoietic system. The term hematopoietic system refers to tissues and organs that produce and/or primarily host hematopoietic cells and include bone marrow, lymph node, thymus, spleen, and other lymphoid tissues. In the United States, hematopathology is a board certified subspecialty (American Board of Pathology) practiced by those physicians who have completed general pathology residency (anatomic, clinical, or combined) and an additional year of fellowship training in hematology. The hematopathologist reviews biopsies of lymph nodes, bone marrows and other tissues involved by an infiltrate of cells of the hematopoietic system. In addition, the hematopathologist may be in charge of flow cytometric and/or molecular hematopathology studies. After the hematopathologist makes the diagnosis, the hematologist or hemato-oncologist can make a decision about the best course of action.

Introduction to Pathology
1.a Definitions- Terms of Pathology
1.b Overview of Pathology
1.c Methods use in Pathology

Anatomical pathology (Commonwealth) or anatomic pathology (United States) is a medical specialty that is concerned with the diagnosis of disease based on the gross, microscopic, chemical, immunologic and molecular examination of organs, tissues, and whole bodies (autopsy). Anatomical pathology is itself divided in subspecialties, the main ones being surgical pathology, cytopathology, and forensic pathology. To be licensed to practice pathology, one has to complete medical school and secure a license to practice medicine. An approved residency program and certification (in the United States, the American Board of Pathology or the American Osteopathic Board of Pathology) is usually required to obtain employment or hospital privileges. Anatomical pathology is one of two branches of pathology, the other being clinical pathology, the diagnosis of disease through the laboratory analysis of bodily fluids and tissues. Often, pathologists practice both anatomical and clinical pathology, a combination known as general pathology. The distinction between anatomic and clinical pathology is increasingly blurred by the introduction of technologies that require new expertise and the need to provide patients and referring physicians with integrated diagnostic reports. Similar specialties exist in veterinary pathology.
Introduction to Pathology
1.a Definitions- Terms of Pathology
1.b Overview of Pathology
1.c Methods use in Pathology

One of the primary risk factors is poorly-controlled diabetes, particularly gestational diabetes (GD),[3] as well as preexisting diabetes mellitus (preexisting type 2 is associated more with macrosomia, while preexisting type 1 can be associated with microsomia). This increases maternal plasma glucose levels as well as insulin, stimulating fetal growth. The LGA newborn exposed to maternal DM usually has an increase only in weight. LGA newborns that have complications other than exposure to maternal DM present with universal measurements >90th percentile. Other determining factors include: Gestational age; pregnancies that go beyond 40 weeks increase incidence Fetal sex; male infants tend to weigh more than female infants Genetic factors; taller, heavier parents tend to have larger babies, with an obese mother greatly increasing the chances Excessive maternal weight gain Multiparity (have 2-3x the number of LGA infants vs. primaparas) Congenital anomalies (transposition of great vessels) - Hydrops Fetalis Erythroblastosis fetalis - Hydrops Fetalis Use of some antibiotics (amoxicillin, pivampicillin) during pregnancy - Hydrops Fetalis Genetic disorders of overgrowth (e.g. Beckwith-Wiedemann syndrome, Sotos syndrome) The condition is most common in mothers of African origin, partly due to the higher incidence of diabetes.

Trichotillomania, which is classified as an impulse control disorder by DSM-IV, is the compulsive urge to pull out one's own hair leading to noticeable hair loss, distress, and social or functional impairment. It is often chronic and difficult to treat.Trichotillomania may be present in infants, but the peak age of onset is 9 to 13. It may be triggered by depression or stress. Due to social implications the disorder is often unreported and it is difficult to accurately predict its prevalence; the lifetime prevalence is estimated to be between 0.6% (overall) and may be as high as 1.5% (in males) to 3.4% (in females). The name, coined by French dermatologist François Henri Hallopeau, derives from the Greek: trich- (hair), till(en) (to pull), and mania ("an abnormal love for a specific object, place, or action") Trichotillomania is defined as a self-induced and recurrent loss of hair.It is classified in DSM-IV as an impulse control disorder with pyromania, pathological gambling and kleptomania, and includes the criterion of an increasing sense of tension before pulling the hair and gratification or relief when pulling the hair.However, some people with trichotillomania do not endorse the inclusion of "rising tension and subsequent pleasure, gratification, or relief" as part of the criteria;because many individuals with trichotillomania may not realize they are pulling their hair, patients presenting for diagnosis may deny the criteria for tension prior to hair pulling or a sense of gratification after hair is pulled. Trichotillomania has been hypothesized to lie on the obsessive–compulsive spectrum, which is proposed to encompass obsessive–compulsive disorder, nail biting (onychophagia) and skin picking (dermatillomania), tic disorders and eating disorders. These conditions may share clinical features, genetic contributions, and possibly treatment response; however, differences between trichotillomania and OCD are present in symptoms, neural function and cognitive profile. In the sense that it is associated with irresistible urges to perform unwanted repetitive behavior, trichotillomania is akin to some of these conditions, and rates of trichotillomania among relatives of OCD patients is higher than expected by chance.However, differences between the disorder and OCD have been noted including differing peak ages at onset, rates of comorbidity, gender differences, and neural dysfunction and cognitive profile.When it occurs in early childhood, it can be regarded as a distinct clinical entity.Because trichotillomania can present in multiple age groups, it is helpful in terms of prognosis and treatment to approach three distinct subgroups by age: preschool age children, preadolescents to young adults, and adults.Trichotillomania is often not a focused act, but rather hair pulling occurs in a "trance-like" state; hence, trichotillomania is subdivided into "automatic" versus "focused" hair pulling. Children are more often in the automatic, or subconscious, subtype and may not consciously remember pulling their hair. Other individuals may have focused, or conscious, rituals associated with hair pulling, including seeking specific types of hairs to pull, pulling until the hair feels "just right", or pulling in response to a specific sensation.Knowledge of the subtype is helpful in determining treatment strategies

A parasitic twin (also known as an asymmetrical or unequal conjoined twin) is the result of the processes that produce vanishing twins and conjoined twins, and may represent a continuum between the two.[citation needed] Parasitic twins occur when a twin embryo begins developing in utero, but the pair does not fully separate, and one embryo maintains dominant development at the expense of the other. Unlike conjoined twins, one ceases development during gestation and is vestigial to a mostly fully formed, otherwise healthy individual twin. The undeveloped twin is defined as parasitic, rather than conjoined, because it is incompletely formed or wholly dependent on the body functions of the complete fetus. The independent twin is called the autosite. Conjoined-parasitic twins joined at the head are described as craniopagus or cephalopagus, and occipitalis if joined in the occipital region or parietalis if joined in the parietal region. Craniopagus parasiticus is a general term for a parasitic head attached to the head of a more fully developed fetus or infant.Fetus in fetu sometimes is interpreted as a special case of parasitic twin, but may be a distinct entity. The Twin reversed arterial perfusion, or TRAP sequence, results in an acardiac twin, a parasitic twin that fails to develop a head, arms and a heart. The parasitic twin, little more than a torso with or without legs, receives its blood supply from the host twin by means of an umbilical cord-like structure, much like a fetus in fetu, except the acardiac twin is outside the host twin's body. Because it is pumping blood for both itself and its acardiac twin, this causes extreme stress on the normal fetus's heart. This twinning condition usually occurs very early in pregnancy.A rare variant of the acardiac fetus is the acardius acormus where the head is well-developed but the heart and the rest of the body are rudimentary. While it is thought that the classical TRAP/Acardius sequence is due to a retrograde flow from the umbilical arteries of the pump twin to the iliac arteries of the acardiac twin resulting in preferential caudal perfusion, acardius acormus is thought to be a result of an early embryopathy.

The heart's electrical axis refers to the general direction of the heart's depolarization wavefront (or mean electrical vector) in the frontal plane. With a healthy conducting system the cardiac axis is related to where the major muscle bulk of the heart lies. Normally this is the left ventricle with some contribution from the right ventricle. It is usually oriented in a right shoulder to left leg direction, which corresponds to the left inferior quadrant of the hexaxial reference system, although −30° to +90° is considered to be normal. If the left ventricle increases its activity or bulk then there is said to be "left axis deviation" as the axis swings round to the left beyond -30°, alternatively in conditions where the right ventricle is strained or hypertrophied then the axis swings round beyond +90° and "right axis deviation" is said to exist. Disorders of the conduction system of the heart can disturb the electrical axis without necessarily reflecting changes in muscle bulk.

 

Suggestible states are very commonplace. Medical students who study frightening diseases for the first time routinely develop vivid delusions of having the "disease of the week"—whatever they are currently studying. This temporary kind of hypochondria is so common that it has acquired a name, “medical student syndrome.”

Hodges (2004), reviewing the literature, said that "the first descriptions of medical students' disease appeared in the 1960s." He may have been referring to the phrase, for the phenomenon itself was noted much earlier. George Lincoln Walton (1908) reported that

    Medical instructors are continually consulted by students who fear that they have the diseases they are studying. The knowledge that pneumonia produces pain in a certain spot leads to a concentration of attention upon that region which causes any sensation there to give alarm. The mere knowledge of the location of the appendix transforms the most harmless sensations in that region into symptoms of serious menace.

Hodges also said that it was suggested in the 1960s that:

    this phenomenon caused a significant amount of stress for students and was present in approximately 70 to 80 percent of students... papers written in the 1980s and 1990s conceptualized the condition as an illness in the psychiatric spectrum of hypochondriasis.... Marcus found that the dream content of year two medical students frequently involved a preoccupation with personal illness. Marcus's subjects reported many dreams in which they suffered illnesses of the heart, the eyes and the bowels, among others.

Hodges went on to describe work by Moss-Morris and Pétrie who saw medical students' disease as "a normal perceptual process, rather than a form of hypochondriasis." Learning about a disease "creates a mental schema or representation of the illness which includes the label of the illness and the symptoms associated with the condition. Once this representation is formed, symptoms or bodily sensations that the individual is currently experiencing which are consistent with the schema may be noticed, while inconsistent symptoms are ignored."

Howes and Salkovskis (1998) noted that "medical students frequently develop fears and symptoms of illness. This has been termed medical student's disease, nosophobia, hypochondriasis of medical students, and medicalstudentitis." They mentioned two studies, one concluding that about 70% of medical students have groundless medical fears during their studies, and one which found that 78.8% of a randomly chosen sample of medical students showed a history of "medical student disease." However, they cite a number of studies showing a similar incidence of hypochondria in law students and other non-medical students, which they said call into question "the widely held view that medical students are more likely than others to have excessive anxiety about their health.