The
human body is composed of elements including
hydrogen,
oxygen,
carbon,
calcium and
phosphorus. These elements reside in trillions of cells and non-cellular components of the body. The adult male body is about 60%
total body water content of some . This is made up of about of
extracellular fluid including about of
blood plasma and about of
interstitial fluid, and about of fluid inside cells. The content,
acidity and composition of the water inside and outside cells is carefully maintained. The main
electrolytes in body water outside cells are
sodium and
chloride, whereas within cells it is
potassium and other
phosphates.
Cells The body contains trillions of
cells, the fundamental unit of life. At maturity, there are roughly 30 trillion cells, and 38 trillion bacteria in the body, an estimate arrived at by totaling the cell numbers of all the
organs of the body and
cell types. The skin of the body is also host to billions of commensal organisms as well as immune cells. Not all parts of the body are made from cells. Cells sit in an
extracellular matrix that consists of
proteins such as
collagen, surrounded by extracellular fluids. Each of the cells of the human body experiences, on average, tens of thousands of
DNA damages per day. These damages can block
genome replication or genome transcription, and if they are not
repaired or are repaired incorrectly, they may lead to
mutations, or other genome alterations that threaten cell viability. However, not all cells have DNA; some cells such as mature
red blood cells lose their nucleus as they mature.
Tissues in the body The body consists of many different types of
tissue, defined as cells that act with a specialised function. The study of tissues is called
histology and is often done with a
microscope. The body consists of four main types of tissues. These are lining cells (
epithelia),
connective tissue,
nerve tissue and
muscle tissue.
Cells Cells that line surfaces exposed to the outside world or gastrointestinal tract (
epithelia) or internal cavities (
endothelium) come in numerous shapes and forms – from
single layers of flat cells, to cells with small beating hair-like
cilia in the lungs, to column-like cells that line the
stomach. Endothelial cells are cells that line internal cavities including blood vessels and glands. Lining cells regulate what can and cannot pass through them, protect internal structures, and function as sensory surfaces.
Organs Organs, structured collections of
cells with a specific function, mostly sit within the body, with the exception of
skin. Examples include the
heart,
lungs and
liver. Many organs reside within
cavities within the body. These cavities include the
abdomen (which contains the stomach, for example) and
pleura, which contains the lungs.
Heart The heart is an organ located in the
thoracic cavity between the
lungs and slightly to the left. It is surrounded by the
pericardium, which holds it in place in the
mediastinum and serves to protect it from blunt trauma,
infection and help lubricate the movement of the heart via
pericardial fluid. The heart works by
pumping blood around the body allowing
oxygen,
nutrients,
waste,
hormones and
white blood cells to be transported. The heart is composed of
two atria and
two ventricles. The primary purpose of the atria is to allow uninterrupted venous blood flow to the heart during
ventricular systole. This allows enough blood to get into the ventricles during
atrial systole. Consequently, the atria allow a
cardiac output roughly 75% greater than would be possible without them. The purpose of the ventricles is to
pump blood to the lungs through the right ventricle and to
the rest of the body through the left ventricle. The heart has an
electrical conduction system to control the contraction and relaxation of the muscles. It starts in the
sinoatrial node traveling through the atria causing them to
pump blood into the ventricles. It then travels to the
atrioventricular node, which makes the signal slow down slightly allowing the ventricles to fill with blood before pumping it out and starting the cycle over again.
Coronary artery disease is the
leading cause of death worldwide, making up 16% of all deaths. It is caused by the buildup of
plaque in the
coronary arteries supplying the heart, eventually the arteries may become so narrow that
not enough blood is able to reach the
myocardium, a condition known as
myocardial infarction or heart attack, this can cause
heart failure or
cardiac arrest and eventually death. Risk factors for coronary artery disease include
obesity,
smoking,
high cholesterol,
high blood pressure,
lack of exercise and
diabetes.
Cancer can affect the heart, though it is exceedingly rare and has usually
metastasized from another part of the body such as the
lungs or
breasts. This is because the
heart cells quickly stop dividing and all growth occurs through
size increase rather than
cell division.
Gallbladder The gallbladder is a hollow pear-shaped organ located
posterior to the
inferior middle part of the
right lobe of the liver. It is variable in shape and size. It stores
bile before it is released into the small intestine via the
common bile duct to help with
digestion of fats. It receives bile from the
liver via the
cystic duct, which connects to the
common hepatic duct to form the
common bile duct. The gallbladder gets its blood supply from the
cystic artery, which in most people, emerges from the
right hepatic artery. Having gallstones is a risk factor for
gallbladder cancer, which, although quite uncommon, is rapidly fatal if not diagnosed early.
Systems File:Organ Systems I.jpg File:Organ Systems II.jpg -->
Circulatory system of the body The
circulatory system consists of the
heart and
blood vessels (
arteries,
veins and
capillaries). The heart propels the circulation of the blood, which serves as a "transportation system" to transfer
oxygen, fuel, nutrients, waste products, immune cells and signaling molecules (i.e.
hormones) from one part of the body to another. Paths of blood circulation within the human body can be divided into two circuits: the
pulmonary circuit, which pumps blood to the lungs to receive
oxygen and leave
carbon dioxide, and the systemic circuit, which carries blood from the heart off to the rest of the body. The blood consists of fluid that carries
cells in the circulation, including some that move from tissue to blood vessels and back, as well as the
spleen and
bone marrow.
Digestive system The
digestive system consists of the mouth including the
tongue and
teeth,
esophagus,
stomach, (
gastrointestinal tract,
small and
large intestines, and
rectum), as well as the
liver,
pancreas,
gallbladder, and
salivary glands. It converts food into small, nutritional, non-toxic
molecules for distribution and absorption into the body. These molecules take the form of
proteins (which are broken down into
amino acids),
fats,
vitamins and
minerals (the last of which are mainly ionic rather than molecular). After being
swallowed, food moves through the
gastrointestinal tract by means of
peristalsis: the systematic expansion and contraction of muscles to push food from one area to the next. Digestion begins in the
mouth, which
chews food into smaller pieces for easier digestion. Then it is
swallowed, and moves through the
esophagus to the
stomach. In the stomach, food is mixed with
gastric acids to allow the extraction of
nutrients. What is left is called
chyme; this then moves into the
small intestine, which absorbs the nutrients and water from the chyme. What remains passes on to the
large intestine, where it is dried to form
feces; these are then stored in the
rectum until they are expelled through the
anus.
Immune system The
immune system consists of the
white blood cells, the
thymus,
lymph nodes and
lymph channels, which are also part of the
lymphatic system. The immune system provides a mechanism for the body to distinguish its own cells and tissues from outside cells and substances and to neutralize or destroy the latter by using specialized proteins such as
antibodies,
cytokines, and
toll-like receptors, among many others.
Integumentary system The
integumentary system consists of the covering of the body (the
skin), including hair and
nails as well as other functionally important structures such as the
sweat glands and
sebaceous glands. The skin provides containment, structure, and protection for other organs, and serves as a major sensory interface with the outside world.
Lymphatic system female The
lymphatic system extracts, transports and metabolizes lymph, the fluid found in between cells. The lymphatic system is similar to the circulatory system in terms of both its structure and its most basic function, to carry a body fluid.
Musculoskeletal system The
musculoskeletal system consists of the
human skeleton (which includes
bones,
ligaments,
tendons,
joints and
cartilage) and attached
muscles. It gives the body basic structure and the ability for movement. In addition to their structural role, the larger bones in the body contain
bone marrow, the site of production of blood cells. Also, all bones are major storage sites for
calcium and
phosphate. This system can be split up into the
muscular system and the
skeletal system.
Nervous system The
nervous system consists of the body's
neurons and
glial cells, which together form the
nerves,
ganglia and
gray matter, which in turn form the
brain and related structures. The brain is the organ of
thought, emotion,
memory, and
sensory processing; it serves many aspects of communication and controls various systems and functions. The
special senses consist of
vision,
hearing,
taste, and
smell. The
eyes,
ears,
tongue, and
nose gather information about the body's environment. From a structural perspective, the
nervous system is typically subdivided into two component parts: the
central nervous system (CNS), composed of the brain and the
spinal cord; and the
peripheral nervous system (PNS), composed of the nerves and
ganglia outside the brain and spinal cord. The CNS is mostly responsible for organizing
motion, processing
sensory information, thought, memory,
cognition and other such functions. It remains a matter of some debate whether the
CNS directly gives rise to
consciousness. The
peripheral nervous system (PNS) is mostly responsible for gathering information with
sensory neurons and directing body movements with
motor neurons. The nervous system is subject to many different diseases. In
epilepsy, abnormal electrical activity in the brain can cause
seizures. In
multiple sclerosis, the
immune system attacks the
nerve linings, damaging the nerves' ability to transmit signals.
Amyotrophic lateral sclerosis (ALS), also known as
Lou Gehrig's disease, is a
motor neuron disease which gradually reduces movement in patients. There are also many other diseases of the nervous system. The
sex organs of the
male reproductive system and the
female reproductive system develops and mature at
puberty. These systems include the internal and external
genitalia. of the
female reproductive system Female puberty generally occurs between the ages of 9 and 13 and is characterized by
ovulation and
menstruation; the growth of secondary sex characteristics, such as growth of
pubic and
underarm hair,
breast,
uterine and
vaginal growth, widening hips and increased height and weight, also occur during puberty. Male puberty sees the further development of the
human penis and
testicles. The female inner sex organs are the two ovaries, their
fallopian tubes, the
uterus, and the
cervix. At birth there are about 70,000
immature egg cells that degenerate until at puberty there are around 40,000. No more egg cells are produced. Hormones stimulate the beginning of menstruation, and the ongoing
menstrual cycles. The female external sex organs are the
vulva (
labia,
clitoris, and
vestibule). a number of
disorders of the testicles including
testicular torsion, and a number of
sexually transmitted infections including
syphilis,
HIV,
chlamydia,
HPV and
genital warts.
Cancer can affect most parts of the reproductive system including
the penis,
testicles,
prostate,
ovaries,
cervix,
vagina,
fallopian,
uterus and
vulva.
Respiratory system The
respiratory system consists of the nose,
nasopharynx,
trachea, and
lungs. It brings oxygen from the air and excretes
carbon dioxide and water back into the air. First,
air is pulled through the trachea into the lungs by the
diaphragm pushing down, which creates a
vacuum. Air is briefly stored inside small sacs known as
alveoli (sing.: alveolus) before being expelled from the lungs when the diaphragm contracts again. Each alveolus is surrounded by
capillaries carrying deoxygenated blood, which absorbs oxygen out of the air and into the
bloodstream. For the respiratory system to function properly, there need to be as few impediments as possible to the movement of air within the lungs.
Inflammation of the lungs and excess
mucus are common sources of breathing difficulties.
Urinary system The
urinary system consists of the two
kidneys, two
ureters,
bladder, and
urethra. It removes waste materials from the blood through urine, which carries a variety of waste molecules and excess
ions and water out of the body. First, the
kidneys filter the blood through their respective
nephrons, removing
waste products like
urea,
creatinine and maintaining the
proper balance of
electrolytes and turning the waste products into
urine by combining them with water from the blood. The kidneys filter about 150 quarts (170 liters) of blood daily, but most of it is returned to the blood stream with only 1-2 quarts (1-2 liters) ending up as urine, which passes from the kidneys through the
ureters into the
bladder. The
smooth muscles lining the ureter walls continuously tighten and relax through a process called
peristalsis, forcing small amounts of urine into the bladder every 10–15 seconds. The bladder is a hollow balloon shaped organ located in the
pelvis. It stores urine until the brain signals it to relax the
urinary sphincter and release the urine into the urethra starting
urination. A normal bladder can hold up to 16 ounces (half a liter) for 3–5 hours comfortably. Numerous
diseases affect the urinary system including
kidney stones, which are formed when materials in the urine concentrate enough to form a solid mass,
urinary tract infections, which are infections of the urinary tract and can cause pain when urinating, frequent urination and even death if left untreated.
Renal failure occurs when the kidneys fail to adequately filter waste from the blood and can lead to death if not treated with
dialysis or
kidney transplantation.
Cancer can affect the
bladder,
kidneys,
urethra and
ureters, with the latter two being far more rare. ==Anatomy==