and
gallbladder of a
sheep Except for
placozoans,
multicellular animals including humans have a variety of
organ systems. These specific systems are widely studied in
human anatomy. The functions of these organ systems often share significant overlap. For instance, the
nervous and
endocrine system both operate via a shared organ, the
hypothalamus. For this reason, the two systems are combined and studied as the
neuroendocrine system. The same is true for the
musculoskeletal system because of the relationship between the
muscular and
skeletal systems. •
Cardiovascular system: pumping and channeling
blood to and from the
body and
lungs with
heart,
blood and
blood vessels. •
Digestive system:
digestion and processing food with
salivary glands,
esophagus,
stomach,
liver,
gallbladder,
pancreas,
intestines,
colon,
mesentery,
rectum and
anus. •
Endocrine system: communication within the body using
hormones made by
endocrine glands such as the
hypothalamus,
pituitary gland,
pineal body or pineal gland,
thyroid,
parathyroids and
adrenals, i.e., adrenal glands. •
Excretory system:
kidneys,
ureters,
bladder and
urethra involved in fluid balance,
electrolyte balance and excretion of
urine. •
Lymphatic system: structures involved in the transfer of
lymph between
tissues and the
blood stream, the lymph and the
nodes and
vessels that transport it including the
immune system: defending against
disease-causing agents with
leukocytes,
tonsils,
adenoids,
thymus and
spleen. •
Integumentary system:
skin,
hair and
nails of
mammals. Also
scales of
fish,
reptiles, and
birds, and
feathers of birds. •
Muscular system: movement with
muscles. •
Nervous system: collecting, transferring and processing information with
brain,
spinal cord and
nerves. •
Reproductive system: the
sex organs, such as
ovaries,
oviducts,
uterus,
vulva,
vagina,
testicles,
vasa deferentia,
seminal vesicles,
prostate and
penis. •
Respiratory system: the organs used for
breathing, the
pharynx,
larynx,
trachea,
bronchi,
lungs and
diaphragm. •
Skeletal system: structural support and protection with
bones,
cartilage,
ligaments and
tendons.
Viscera In the study of
anatomy,
viscera (:
viscus) refers to the
internal organs of the
abdominal,
thoracic, and
pelvic cavities. The 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. In the
thoracic cavity, the
heart is a hollow, muscular organ.
Splanchnology is the study of the viscera. 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.
Origin and evolution The organ level of organisation in
animals can be first detected in
flatworms and the more derived
phyla, i.e. the
bilaterians. The less-advanced
taxa (i.e.
Placozoa,
Porifera,
Ctenophora and
Cnidaria) do not show unification of their tissues into organs. More complex animals are composed of different organs, which have evolved over time. For example, the liver and heart evolved in the
chordates about 550–500 million years ago, while the gut and brain are even more ancient, arising in the ancestor of vertebrates, insects,
molluscs, and worms about 700–650 million years ago. Given the ancient origin of most vertebrate organs, researchers have looked for model systems, where organs have evolved more recently, and ideally have evolved multiple times independently. An outstanding model for this kind of research is the
placenta, which has evolved more than 100 times independently in vertebrates, has evolved relatively recently in some lineages, and exists in intermediate forms in extant taxa. Studies on the evolution of the placenta have identified a variety of genetic and physiological processes that contribute to the origin and evolution of organs, these include the re-purposing of existing animal tissues, the acquisition of new functional properties by these tissues, and novel interactions of distinct tissue types. Reproductive organs are variable, and in
flowering plants, they are represented by the
flower,
seed and
fruit. In
conifers, the organ that bears the reproductive structures is called a
cone. In other divisions (
phyla) of plants, the reproductive organs are called
strobili, in
Lycopodiophyta, or simply gametophores in
mosses. Common organ system designations in plants include the differentiation of shoot and root. All parts of the plant above ground (in non-
epiphytes), including the functionally distinct leaf and flower organs, may be classified together as the shoot organ system. The vegetative organs are essential for maintaining the life of a plant. While there can be 11 organ systems in animals, there are far fewer in plants, where some perform the vital functions, such as
photosynthesis, while the reproductive organs are essential in
reproduction. However, if there is
asexual vegetative reproduction, the vegetative organs are those that create the new generation of plants (see
clonal colony). ==Society and culture==