Human skeleton »»

The human skeleton consists ofboth fused and individual bones supported and supplemented by ligaments , tendons , muscles and cartilage . It serves as a scaffold which supports organs, anchorsmuscles, and protects organs such as the brain , lungs and heart . [ citation needed ]
The biggest bone in the body is the femur in the thigh and the smallest is the stapes bone in the middle ear . Several factors contribute to the bone density and average mass of the human skeleton including; gender, race, hormonal factors, nutrition, physical activity and lifestyle behaviors.

[ 1 ] Because of these and other factors affecting an individual's weight the human skeleton may comprise between 12 and 20 percent of a person's total body weight with the average being 15 percent.

[ 2 ] Fused bones include those of the pelvis and the cranium . Not all bones are interconnected directly: there are three bones ineach middle ear called the ossicles that articulate only with each other. The hyoid bone , which is located in the neck and serves as the point of attachment for the tongue , does not articulate with any other bones in the body, being supported by muscles and ligaments.

Immune system »»

An immune system is a system of biological structures and processes within an organism that protects against disease . In order to function properly, an immune system must detect a wide variety of agents, from viruses to parasitic worms , and distinguish them from the organism's own healthy tissue .
Pathogens can rapidly evolve and adapt to avoid detection and destruction by the immune system. As a result, multiple defense mechanisms have also evolved to recognize and neutralize pathogens. Even simple unicellular organisms such as bacteria possess a rudimentary immune system, in the form of enzymes which protect against bacteriophage infections. Other basic immune mechanisms evolved in ancient eukaryotes and remain in their modern descendants, such as plants and insects. These mechanisms include phagocytosis , antimicrobial peptides called defensins , and the complement system . Jawed vertebrates , including humans, have even more sophisticated defense mechanisms, [ 1 ] including the ability to adapt over time to recognize specific pathogens more efficiently. Adaptive (or acquired) immunity creates immunological memory after an initial response to a specific pathogen, leading to an enhanced response to subsequent encounters with that same pathogen. This process of acquired immunity is the basis of vaccination .
Disorders of the immune system can result in autoimmune diseases , inflammatory diseases and cancer . [ 2 ] [ 3 ] Immunodeficiency occur when the immune system is less active than normal, resulting in recurring and life-threatening infections. In humans, immunodeficiency can either be the result of a genetic disease , such as severe combined immunodeficiency , or acquired conditions such as HIV / AIDS or the use of immunosuppressive medication. In contrast, autoimmunity result from a hyperactive immune system attacking normal tissues as if they were foreign organisms. Common autoimmune diseases include Hashimoto's thyroiditis , rheumatoid arthritis , diabetes mellitus type 1 , and systemic lupus erythematosus . Immunology covers the study of all aspects of the immune system.

Bone Marrow

Bone marrow ( Latin : medulla ossium ) is the flexible tissue found in the interior of bones . In humans , bone marrow in large bones produces new blood cells . On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg (143 lbs), bone marrow accounts for approximately 2.6 kg (5.7 lbs). The hematopoietic compartment of bone marrow produces approximately 500 billion blood cells per day, which use the bone marrow vasculature as a conduit to the body's systemic circulation.
[ 1 ] Bone marrow is also a key component of the lymphatic system , producing the lymphocytes that support the body's immune system .

Semen (disambiguation)

Semen is an organic fluid , also known as seminal fluid , that maycontain spermatozoa . It is secreted by the gonads (sexual glands) and other sexual organs of male or hermaphroditic animals and can fertilize female ova . In humans, seminal fluid contains several components besides spermatozoa: proteolytic and other enzymes as well as fructose are elements of seminal fluid which promote the survival of spermatozoa and provide a medium through which they can move or "swim".
Semen is produced and originates from the seminal vesicle , which is located in the pelvis. The process that results inthe discharge of semen is called "Ejaculation".

Smoking Damages DNA Within Minutes, Research Shows {{ HealthDay News ( 15 jan ) }}

Cigarettes start to destroy a smoker's DNA within minutes of inhaling, new researchindicates, suggesting that the habit causes immediate genetic damage and quickly raises the short-term risk for cancer.
"The results reported here should serve as a stark warning to those who are considering starting to smoke cigarettes," lead study author Stephen S. Hecht, from the Masonic Cancer Center and department of pharmacology at the University of Minnesota in Minneapolis, said in a news release from the American Chemical Society.
Hecht and his colleagues reportedtheir observations in the current issue of the journal Chemical Research in Toxicology .
In their research, the investigatorsfocused on a class of cancer-causing culprits found in cigarettesmoke called polycyclic aromatic hydrocarbons, or PAHs.
PAHs are known to inflict damage on DNA and are therefore thoughtto play a large role in the onset of lung cancer, a disease that the researchers pointed out has been linked to the loss of 3,000 lives a day worldwide, mostly as a consequence of smoking.
To date, however, little had been known about the exact mechanism by which PAH exposure causes disease.
To better understand the risks, Hecht's team conducted what they called a "unique" analysis, by labeling and tracking a single PAH -- phenanthrene -- through the bodies of 12 volunteer smokers.
The study authors noted that this approach was "the first to investigate human metabolism of a PAH specifically delivered by inhalation in cigarette smoke, without interference by other sources of exposure such as air pollution or the diet."
The results: having rapidly transformed in the body into a known toxin, the PAH in question began to cause havoc on the DNA of the smokers within just 15 to 30 minutes after smoking.
The velocity of the cancer-causing process surprised the research team. They said the speed with which the potentially lethal DNA assault began was comparable to having injected the PAH directly into an individual's bloodstream.

Menstrual cycle

The Menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purpose of sexual reproduction and fertilization .
This article focuses on the human menstrualcycle.

The menstrual cycle, under the control of the endocrine system , is necessary for reproduction . It is commonly divided into three phases:-
The follicular phase , Ovulation & The luteal phase ; although some sources use a different set of phases:
Menstruation , proliferative phase, and secretory phase.

[ 1 ] Menstrual cycles are counted from the first day of menstrual bleeding. Hormonal contraception interferes with the normal hormonal changes with the aim of preventing reproduction.
Stimulated by gradually increasing amounts of estrogen in the follicular phase, discharges of blood (menses) slow then stop, and the lining of the uterus thickens. Follicles in the ovary begin developing under the influence of a complexinterplay of hormones, and after several days one or occasionally two become dominant (non-dominant follicles atrophy and die). Approximately mid-cycle, 24–36 hours after the Luteinizing Hormone (LH) surges, the dominant follicle releases an ovum, or egg in an event called ovulation. After ovulation, the egg only lives for 24 hours or less without fertilization while the remains ofthe dominant follicle in the ovarybecome a corpus luteum ; this body has a primary function of producing large amounts of progesterone . Under the influence of progesterone, the endometrium (uterine lining) changes to prepare for potential implantation of an embryo to establish a pregnancy . If implantation does not occur within approximately two weeks, the corpus luteum will involute, causing sharp drops in levels of both progesterone and estrogen. These hormone drops cause the uterus to shed its lining and egg in a process termed menstruation.
In the menstrual cycle, changes occur in the female reproductivesystem as well as other systems (which lead to breast tenderness or mood changes, for example). A woman's first menstruation is termed "Menarche" , and occurs typically around age 12-13. The average age of menarche is about A.12.5 years in the United States B.12.72 in Canada C. 12.9 in the UK and D. 13.06 ± 0.10 years in Iceland .

The end of a woman's reproductive phase is called the "Menopause" , Which commonly occurs somewhere between the ages of 45 and 55.

Breast Cancer

Breast cancer ( malignant breast neoplasm ) is a type of cancer originating from breast tissue, most commonly from the inner lining of milk ducts or the lobules that supply the ducts with milk.

[ 1 ] Cancers originating from ducts are known as ductal carcinomas ; those originating from lobules are known as lobular carcinomas . Breast cancer is a disease of humans and other mammals ; whilethe overwhelming majority of cases in humans are women, men can sometimes also develop breastcancer.

[ 2 ] The size, stage, rate of growth, andother characteristics of the tumor determine the kinds of treatment. Treatment may include surgery , drugs ( hormonal therapy and chemotherapy ), radiation and/or immunotherapy.

[ 3 ] Surgical removal of the tumor provides the single largest benefit, with surgery alone being capable of producing a cure in many cases. To somewhat increase the likelihood of long-term disease-free survival, several chemotherapy regimens are commonly given in addition to surgery. Most forms of chemotherapy kill cells that are dividing rapidly anywhere in the body, and as a result cause temporary hair loss and digestive disturbances. Radiation is indicated especially after breast conserving surgery and substantially improves local relapserates and in many circumstances also overall survival.

[ 4 ] Some breast cancers are sensitive to hormones such as estrogen and/or progesterone , which makes it possible to treat them by blocking the effects of these hormones.
Worldwide, breast cancer comprises 22.9% of all cancers (excluding non-melanoma skin cancers ) in women.

[ 5 ] In 2008, breast cancer caused 458,503 deaths worldwide (13.7% of cancer deaths in women).

[ 6 ] Breast cancer is more than 100 times more common in women than breast cancer in men , although males tend to have poorer outcomes due to delays in diagnosis.

[ 7 ] Prognosis and survival rates vary greatly depending on cancer type, staging and treatment. However, survival rates across the world are generally good.

[ 8 ] Overall more than 8 out of 10 women (84%) in England that are diagnosed with the disease survive it for at least 5 years.

Our Brain

The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few invertebrates such as sponges , jellyfish , adult sea squirts and starfish do not have one, even if diffuse neural tissue is present. It is located in the head, usually close to the primary sensory organs for suchsenses as vision, hearing, balance, taste, and smell. The brain of a vertebrate is the most complex organ of its body. In a typical human the cerebral cortex (the largest part) is estimated to contain 15–33 billion neurons , [ 1 ] each connected by synapses to several thousand other neurons.These neurons communicate with one another by means of long protoplasmic fibers called axons , which carry trains of signal pulses called action potentials to distant parts of the brain or body targeting specific recipient cells.
From an evolutionary-biological point of view, the function of thebrain is to exert centralized control over the other organs of the body. The brain acts on the rest of the body either by generating patterns of muscle activity or by driving secretion ofchemicals called hormones . This centralized control allows rapid and coordinated responses to changes in the environment. Some basic types of responsiveness such as reflexes can be mediated by the spinal cord or peripheral ganglia , but sophisticated purposeful controlof behavior based on complex sensory input requires the information-integrating capabilities of a centralized brain.
From a philosophical point of view, what makes the brain special in comparison to other organs is that it forms the physical structure that generatesthe mind . As Hippocrates put it:"Men ought to know that from nothing else but the brain come joys, delights, laughter and sports, and sorrows, griefs, despondency, and lamentations." [ 2 ] In the early part of psychology, the mind was thought to be separate from the brain. However, after early scientists conducted experiments it was determined that the mind was a component of a functioning brain that expressed certain behaviours based on the external environment and the development of the organism. [ 3 ] The mechanisms by which brain activity gives rise to consciousness and thought havebeen very challenging to understand: despite rapid scientific progress, much about how the brain works remains a mystery. The operations of individual brain cells are now understood in considerable detail, but the way they cooperate in ensembles of millions has been very difficult todecipher. The most promising approaches treat the brain as a biological computer, very different in mechanism from electronic computers, but similarin the sense that it acquires information from the surrounding world, stores it, and processes it in a variety of ways.
This article compares the properties of brains across the entire range of animal species, with the greatest attention to vertebrates. It deals with the human brain insofar as it sharesthe properties of other brains. The ways in which the human brain differs from other brains are covered in the human brain article. Several topics that might be covered here are instead covered there because much more can be said about them in a human context. The most important is brain disease and the effects of brain damage, covered in the human brain article because the most common diseases of the human brain either do not show up in other species, or else manifest themselves in different ways.

Human Kidney

The kidneys are organs that serve several essential regulatory roles inmost animals , including vertebrates and some invertebrates . They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes , maintenance of acid–base balance , and regulation of blood pressure (via maintaining salt and water balance). They serve the body as a natural filter of the blood , and remove wastes which are diverted to the urinary bladder . In producing urine , the kidneys excrete wastes such as urea and ammonium , and they are also responsible for the reabsorption of water , glucose , and amino acids . The kidneys also produce hormones including calcitriol , erythropoietin , and the enzyme renin .
Located at the rear of the abdominal cavity in the retroperitoneum , the kidneys receive blood from the paired renalarteries , and drain into the paired renal veins . Each kidney excretes urine into a ureter , itself a paired structure that empties into the urinary bladder .
Renal physiology is the study of kidney function, while nephrology is the medical specialty concerned with kidney diseases . Diseases of the kidney are diverse, but individuals with kidney disease frequently display characteristic clinical features. Common clinical conditions involving the kidney include the nephritic and nephroticsyndromes , renal cysts , acute kidney injury , chronic kidney disease , urinary tract infection , nephrolithiasis , and urinary tract obstruction . [ 1 ] Various cancers of the kidney exist; the most common adult renal cancer is renalcell carcinoma . Cancers, cysts, and some other renal conditions can be managed with removal of the kidney, or nephrectomy . When renal function, measured by glomerular filtration rate , is persistently poor, dialysis and kidney transplantation may be treatment options. Although they are not severely harmful, kidney stones can be a pain and a nuisance. The removal of kidney stones includes sound wave treatment to break up the stones into smaller pieces, which are then passed through the urinary tract. One common symptom of kidney stones is a sharp pain in the medial/lateral segments of the lower back.

The duck-billed platypus, Ornithorhynchus anatinus , is a primitive Australian mammal (a monotreme ) that lays eggs. After an egg hatches, the tiny baby (called a puggle) drinks its mother's milk, which comes from tiny openings in the mother's belly. They have a life span of 10-17 years. Platypus live in burrows and spend much of their time in freshwater ponds and streams. The name platypus means "flat footed."