Descriptive
human anatomy often uses terminology that is fairly correct descriptive Latin. For example,
musculus gluteus maximus simply means the "largest rump muscle", where ''
was Latin for "little mouse" and applied to muscles; a frenum,
a structure for keeping something in place, is Latin for bridle; and a foramen'' is Latin for a passage or perforation.
Location and motion A standardised set of terminology is used in anatomy to describe relative and absolute location and movement of anatomical parts. The
standard anatomical position is the orientation that
anatomical terms of location and
motion are typically used in reference to.
Planes and axes Relative to the standard anatomical position, three
anatomical planes are widely used in medicine: • The parasagittal (Greek (), beside) or paramedian or
sagittal planes (Latin
sagitta, arrow), which include the
median or midsagittal plane and divide the body into left and right (in reference to the subject and not the observer). • The frontal or
coronal plane (Latin
corona, crown), which divide the body into front and back. • The axial or horizontal or
transverse plane (Latin
trans, across;
vetere, to turn), which is perpendicular to the other two planes. The
transpyloric plane, the
subcostal plane, and the
transumbilical plane planes are also considered in the division of the
torso into the
quadrants and regions of the abdomen. The three main axes of a human are the left-right (or horizontal or frontal), the craniocaudal (or rostrocaudal, longitudinal, or cephalocaudal), and the anteroposterior (or dorsoventral or sagittal) axes. Other
anatomical lines include the
axillary lines,
parasternal line, and
scapular line.
Location Many anatomical terms can be combined to indicate a position in two axes simultaneously or the direction of a movement relative to the body: Anterolateral indicates a position that is both anterior and lateral to the standard anatomical position (such as the bulk of the
pectoralis major muscle) or a named organ such as the
anterolateral tibial tubercle; anteromedial is used, for example, in the
anteromedial central arteries; proximodistal describes the axis of an
appendage such as an arm or a leg, taken from its tip at the distal part to where it joins the body at the proximal part. Combined terms were once generally hyphenated, but typically the hyphen is omitted. In
radiology, various X-ray views use
terminology based on where the X-ray beam enters and leaves the body, including the front to back view (anteroposterior), the back to front view (posteroanterior), and the side view (lateral).
Motion Circumduction is a conical movement of a body part, such as a
ball and socket joint or the
eye. Circumduction is a combination of flexion, extension, adduction and abduction. Circumduction may be performed at ball and socket joints, such as the
hip and
shoulder, as well as other parts of the body such as fingers, hands, feet, and head. For example, circumduction occurs when spinning the arm when performing a serve in
tennis or bowling a
cricket ball.
Integumentary The
integumentary system is the set of organs forming the outermost layer of the human body, comprising the
skin,
hair, and
nails. It acts as a protective physical barrier between the external environment and the internal environment, while maintaining water balance, protecting deeper tissue, excreting waste, and regulating
body temperature. The skin (or, integument) is a composite organ, made up of the outermost
epidermis and the inner
dermis. The epidermis comprises five layers: the
stratum corneum,
stratum granulosum,
stratum spinosum and
stratum basale. Where the skin is thicker, such as in the palms and soles, there is an extra layer of skin between the stratum corneum and the stratum granulosum known as the
stratum lucidum. The dermis comprises two sections, the papillary and reticular layers, and contains
connective tissues, blood vessels, glands, follicles,
hair roots, sensory nerve endings, and muscular tissue. Between the integument and the deep body musculature there is a transitional subcutaneous zone, the
hypodermis.
Musculoskeletal The
musculoskeletal system the
organ system that gives
humans the ability to move using their
muscular and
skeletal systems, and is described by the
anatomical terms of bone and
muscle. It is made up of the
bones of the
skeleton,
muscles,
cartilage,
tendons,
ligaments,
joints, and other
connective tissue that supports and binds tissues and organs together: • Bones are surrounded by a membrane known as the
periosteum (Greek (), around; Greek (), bone), and comprise multiple layers, depending on the type of bone, including
yellow and red
bone marrow, spongy bone, and the
endosteum. There are five general classifications of
bones: •
Long bones are characterized by a shaft known as the
diaphysis, which is much longer than its width, and an
epiphysis (Greek () upon, outside, over), a rounded head at each end of the shaft, connected to the diaphysis by the
epiphyseal plate. They are made up mostly of
compact bone, with lesser amounts of
marrow, located within the
medullary cavity, and areas of spongy, cancellous bone at the ends of the bones. •
Short bones are roughly
cube-shaped, and have only a thin layer of compact bone surrounding a spongy interior. Short bones provide stability and support as well as some limited motion. •
Flat bones are thin and generally curved, with two parallel layers of compact bone sandwiching a layer of spongy bone. •
Sesamoid bones are bones embedded in tendons. Since they act to hold the tendon further away from the joint, the angle of the tendon is increased and thus the leverage of the muscle is increased. •
Irregular bones do not fit into the above categories. They consist of thin layers of compact bone surrounding a spongy interior. As implied by the name, their shapes are irregular and complicated. Often this irregular shape is due to their many centers of ossification or because they contain bony sinuses. • A
tendon is a tough, flexible band of
fibrous connective tissue that connects muscles to bones. The extra-cellular connective tissue between muscle fibers binds to tendons at the distal and proximal ends, and the tendon binds to the
periosteum of individual bones at the muscle's origin and insertion. As
muscles contract, tendons transmit the forces to the relatively rigid bones, pulling on them and causing movement. Tendons can stretch substantially, allowing them to function as springs during movement. • Cartilage is a resilient and smooth type of
connective tissue that covers and protects the
ends of
long bones, and forms a structural component of many body parts including the
rib cage, the neck and the bronchial tubes, and the
intervertebral discs. It is classified into three types
elastic cartilage,
hyaline cartilage, and
fibrocartilage. •
Joints, also known as articulations, are structures that connect individual bones and may allow bones to move against each other to cause movement. Joints can be classified by structure and by function. Structurally,
synovial joints are joints that are not directly joined, which are lubricated by a solution called
synovial fluid;
fibrous, bony, and
cartilaginous joints are characterised by the presence of their respective connective tissues. There are three functional divisions of joints: •
Diarthroses, which allow extensive mobility between two or more articular heads. •
Amphiarthroses, which allow
some movement. • False joints or
synarthroses, which allow little or no movement and are predominantly
fibrous. • A
ligament is a small band of dense, white,
fibrous elastic tissue. Ligaments connect the ends of bones together in order to form a joint. Most ligaments limit
dislocation, and prevent certain movements, such as hyperextension and hyperflexion, which may lead to breaks. • An
enthesis is the connective tissue that attaches tendons and ligaments to bones. •
Fascia () is a generic term for
macroscopic membranous bodily structures. The human skeleton may be divided into two distinct divisions: the
axial skeleton, which includes the
vertebral column, and the
appendicular skeleton.
Action The action of muscles often involve antagonistic pairs of agonist muscles and antagonist muscles, which, respectively, cause and inhibit a movement. • Through the activation of agonist muscle, which produces most of the force and control of an action, movement occurs. • Antagonist muscles are the muscles that produce an opposing joint torque to the agonist muscles. • Synergist muscles, also called
fixators or
neutralisers, act around a joint to help, counter, or neutralise the action of an agonist muscle. Generally, as one muscle contracts, the other muscle relaxes in a process known as
reciprocal inhibition.
Muscle contraction may be concentric (i.e. shortening), eccentric (i.e. lengthening), or isometric (i.e. involving no change in length). Muscle groups (e.g. elbow flexors) are sometimes named based on the joint action they produce during concentric contraction. During muscle contraction, the insertion of a muscle is the structure that is moved and is typically a bone that is distal and lighter than the origin; the origin is the bone, typically proximal, that remains more stable during contraction; the head of a muscle is the end part of the muscle that attaches to its origin.
Vascular The
circulatory system is a
system of organs that includes the
heart,
blood vessels, and
blood which is circulated throughout the body. It includes the
cardiovascular system, which consists of the heart and blood vessels. Some sources use the terms
cardiovascular system, vascular system and
circulatory system interchangeably. The
lymphatic system (comprising
lymphatic vessels,
lymph nodes, lymphoid organs, lymphatic tissue and
lymph) is complementary to the circulatory system and forms part of the
immune system.
Circulatory system The network of blood vessels include the
great vessels (comprising large
elastic arteries and large
veins), other
arteries (which carry blood away from the heart) and veins (which carry blood to the heart), smaller
arterioles, and
capillaries, which join with
venules. Blood is a
fluid consisting of
plasma (comprising
serum and
clotting factors),
red blood cells,
white blood cells, and
platelets. Components of the blood include nutrients (such as
proteins and
minerals),
hemoglobin,
hormones, and
gases such as oxygen and
carbon dioxide. These substances provide nourishment, help the
immune system to fight
diseases, and help maintain
homeostasis through mechanisms such as
thermoregulation,
osmoregulation, and
acid-base regulation. The heart is lined by a double-layered sac known as the
pericardium. Further circulatory routes include the
coronary circulation to the heart itself, the
cerebral circulation to the
brain,
renal circulation to the
kidneys, and
bronchial circulation to the
bronchi in the lungs.
Lymphatic system The circulatory system processes an average of 20 litres of blood per day through
capillary filtration, which removes plasma from the blood. Roughly 17 litres of the filtered blood are reabsorbed directly into the
blood vessels. The lymphatic system provides an accessory return route to the blood for the remaining three litres of
interstitial fluid. •
Lymph is circulated in the body via muscle contraction and drains into the
lymphatic ducts, which empty into the
subclavian veins, returning fluid into blood circulation. • A
lymph node is an organised collection of lymphoid tissue through which the lymph passes on its way back to the blood. Lymph nodes are particularly numerous in the
mediastinum, neck, pelvis,
axilla, and
inguinal region. •
Gut-associated lymphoid tissue, including
Peyer's patch, plays a major role in the immune system. • The
spleen produces
immune cells to fight
antigens in its
white pulp, removes
particulate matter and aged blood cells, mainly
red blood cells in its
red pulp, and produces blood cells during fetal life.
Neuroendocrine The
nervous system coordinates the
actions and
sensory information of a person by transmitting
signals to and from different parts of the body, working in tandem with the
endocrine system to respond to environmental events. The endocrine system comprises
feedback loops of
hormones that are released by
glands directly into the
circulatory system, which target and regulate distant
organs. In
vertebrates, the
hypothalamus is the neural control center for all endocrine systems, being adjacent to the pituatary gland, and linking the two systems together as the
neuroendocrine system. in the human head and neck and their hormones
Nervous system The connections between
neurons, the primary cell of the nervous system, forms
neural pathways,
neural circuits, and
large-scale brain networks. Subsystems of the human nervous system include: • The
central nervous system (CNS), comprising the
brain and
spinal cord. Nerves that transmit signals from the CNS are called
motor nerves. Nerves that exit from the brain are called
cranial nerves while those exiting from the spinal cord are called
spinal nerves. • The
peripheral nervous system (PNS), comprising mainly
nerves, enclosed bundles of axons. The PNS is divided into: • The
somatic nervous system, which links the brain and spinal cord to sensory receptors and skeletal muscle. • The
autonomic nervous system, which is subdivided into: • The
sympathetic nervous system. • The
parasympathetic nervous system. • The
enteric nervous system, which controls the
gastrointestinal system. • The
neurovascular unit comprises the cells and vasculature channels within the nervous system that regulate cerebral blood flow.
Endocrine system The major
endocrine glands are the
thyroid,
parathyroid,
pituitary,
pineal, and
adrenal glands (Latin , kidney), and the
testis and
ovaries. The
thyroid secretes
thyroxine, the
pituitary secretes
growth hormone, the
pineal secretes
melatonin, the testis secretes
testosterone, and the
ovaries secrete
estrogen and
progesterone. The
hypothalamus,
pancreas, and
thymus also function as endocrine glands. The bones,
kidneys, liver, heart, and
gonads have secondary endocrine functions.
Glands that signal each other in sequence are often referred to as an axis, such as the
hypothalamic–pituitary–adrenal axis.
Endocrinology also comprises the study of the
exocrine glands (such as
salivary glands,
mammary glands, and
submucosal glands within the
gastrointestinal tract), which secrete hormones to the outside of the body, and of
paracrine signalling between cells over a relatively short distance. • The
thoracic cavity is protected by the
thoracic wall (comprising the
rib cage and associated skin, muscle, and
fascia), comprising the
mediastinum, heart and great vessels, and the bulk of the
respiratory tract. • The
abdominal cavity, lined by the
peritoneum, contains the bulk of the
gastrointestinal tract, the spleen and the
kidneys. Abdominal organs may be classified as solid organs or hollow organs. • The solid organs are the
liver,
pancreas, spleen, kidneys, and
adrenal glands. • The hollow organs of the abdomen are the
stomach,
intestines,
gallbladder,
bladder, and
rectum. • The
pelvic cavity contains the
urinary bladder,
internal reproductive organs, and
rectum.
Viscera are the internal organs of the ventral cavity. The term "visceral" is contrasted with the term "", meaning "of or relating to the wall of a body part,
organ or cavity". The two terms are often used in describing a membrane or piece of connective tissue, referring to the opposing sides.
Respiratory system The
respiratory system allows for
gas exchange, particularly of
carbon dioxide and
oxygen, in human beings. In the process of
breathing or ventilation, the
muscles of respiration pump air into the lungs, bringing it into close contact with the blood via millions of microscopic air sacs known as
alveoli. The upper respiratory tract includes the
nose,
nasal cavities,
sinuses,
pharynx and the part of the
larynx above the
vocal folds; the lower tract includes the lower part of the
larynx and the following aiways: the
trachea,
bronchi,
bronchioles and
alveoli. The lungs are surrounded by flattened closed sacs known as
pleura. • Contraction of the
diaphragm (an upwardly domed sheet of muscle that separates the thoracic cavity from the abdominal cavity) and of the
intercostal muscles (which lift up the ribs) increases the volume of the thoracic cavity. Because of this increased volume, the lungs (which comprise elastic connective tissue) begin to inflate. • Air, usually, enters from the nose. From the nose, air travels into the trachea (the largest of airways) into the two main bronchi, which branch into progressively narrower secondary and tertiary bronchi, which in turn branch into numerous smaller tubes known as the bronchioles, The process of "respiration" is used to describe three distinct but related processes in the human body:
cellular respiration,
physiological respiration, and ventilation (or, breathing).
Gastrointestinal system The
human digestive system, also known as the gastrointestinal system, comprises the
gastrointestinal tract and the accessory organs of digestion: the
tongue,
salivary glands,
pancreas,
liver, and
gallbladder.
Digestion involves the breakdown of food into smaller and smaller components, until they can be absorbed and assimilated into the body. The process of digestion has three stages: the
cephalic phase, the
gastric phase, and the
intestinal phase. •
Gallbladder: a hollow part of the
biliary tract that sits just beneath the liver, with the gallbladder body resting in a small depression. Commonly associated with
gallstones, or cholelithiasis.
Reproductive system The
reproductive system in humans is typically classified into the
male and
female reproductive systems.
Urinary system The
urinary system is the part of the
excretory system that removes waste in the form of
urine, comprising the
kidneys,
ureters,
bladder, and the
urethra. Other purposes of the urinary system include the regulation of blood volume and blood pressure; the control of
electrolyte and
metabolite levels; and the regulation of
blood pH. Each kidney consists of functional units called
nephrons. Following
filtration of blood and further processing, the
ureters carry
urine from the kidneys into the
urinary bladder. During
urination, the
urethra carries urine out of the bladder through the
penis or
vulva. The female and male urinary system are very similar, differing only in the length of the urethra. == Histology ==