Cat Anatomy
Click on an organ for more details
* Notice that the kidneys are not labeled on this picture. The kidneys are tucked up close to the liver
toward the spine.
Image modified from Hill's Pet Nutrition, Atlas of Veterinary Clinical Anatomy.
The organ systems include:
1. The cardiovascular system (cat) (dog) includes the heart and blood vessels. The cardiovascular system
performs the function of pumping and carrying blood to the rest of the body. The blood contains nutrients
and oxygen to provide energy to allow the cells of the body to perform work.
2. The lymphatic system includes the lymph nodes and lymph vessels. The lymphatic system is part of the
immune system that helps the body fight off disease. The lymphatic system also works with the
cardiovascular system to return fluids that escape from the blood vessels back into the blood stream.
3. The digestive system (cat) (dog) includes the mouth, teeth, salivary glands, esophagus, stomach,
intestine, pancreas, liver and gall bladder. The digestive system absorbs and digests food and eliminates
solid wastes from the body.
4. The integumentary system is the skin and fur that cover the animal's body. The skin protects the
underlying organs. The fur helps insulate against heat loss. Dogs and cats do not sweat through their
skin. They only sweat from their footpads and nose. They lose water by panting rather than sweating.
5. The musculoskeletal system includes all the muscles, bones and joints.
6. The respiratory system (cat) (dog) includes the mouth, nose, trachea, lungs and smaller airways
(bronchi and bronchioles). The respiratory system is responsible for taking in oxygen and eliminating
waste gases like carbon dioxide. Because dogs and cats do not sweat through the skin, the respiratory
system also plays an important role in regulation of temperature.
7. The urogenital system (cat) (dog) includes the kidneys, ureters, urinary bladder, urethra and the genital
organs of box sexes. The urinary system is responsible for removing waste products from blood and
eliminating them as urine. The genital organs are involved in reproduction.
8. The nervous system includes the brain, spinal cord and all the nerves that communicate between
tissues and the brain and spinal cord.
9. The endocrine system includes several glands that produce hormones. Hormones are substances that
travel through the blood stream and affect other organs. Endocrine organs include the thyroid glands,
parathyroid glands, adrenal glands and part of the pancreas.
10. The organs of special senses (cat) (dog) allow the animal to interact with its environment; sight, taste,
smell and hearing.
11. The hematopoietic system includes the bone marrow which is located inside the bones. Three types of
blood cells are made in the bone marrow: white blood cells that fight infection, red blood cells that carry
oxygen and platelets that are part of the blood clotting process.
Washington State University assumes no liability for injury to you or your pet incurred by following these
descriptions or procedures.
Morphology of a cat: carnivorous mammal of the feline family, with retractile claws. There are both wild
and domestic varieties. Felidae is the biological family of the cats; a member of this family is called a felid.
Head: foremost part of the cat.
Ear: organ of hearing.
Neck: part of cat that connects the head to the trunk.
Back: top part of the trunk.
Hip: joint connecting the rear leg to the pelvis.
Buttock: fleshy part lelow the tail.
Thigh: upper part of the rear leg.
Tail: extension of the spine.
Hind leg: rear limb.
Belly: lower part of the abdomen.
Chest: lower part of the thorax.
Fore leg: front limb.
Shoulder: joint connecting the arm with the body.
Lip: fleshy part covering the teeth.
Whiskers: hairs on the cats muzzle.
Nose: opening of the respiratory system.
Eye: sight organ of the cat
First trimester of the pregnancy
After a successful fertilisation, the first step is cell division. That one fertilised
ovum divides itself through mitosis into two cells. Mitosis is a cell division in
which two copies develop that each have the same cell core. Genetically, those
cells are identical to each other. In female cats this first division takes place after
60 to 68 hours after coitus. These first cells are called blastomeres. After this
first division, there will be a division every 10 to 14 hours. Division will soon
become asynchronous, so not every cell will divide if another divides too. It has
been established in different kinds of mammals that every one of the cells has the
complete ability to grow into a full-term individual at the two-cell or four-cell
stage. Identical "real" human twins are formed by the separation of two cells
after the very first division. Very rarely, but it seems to happen, identical
quadruplets occur in humans.
After the four-cell stage, not all cells are "totipotent" anymore. Therefore,
identical (monozygotic) octuplets will not occur. Divisions continue, there will
be more and more cells. This stage is called the cleavage stage, because little
growth takes place, only division (the embryo does not grow yet). Of course, the
amount of nuclear material will increase, because every new cell has a nucleus.
The lump of cells consisting of blastomeres is called a blastomerula. There are
approximately 30 cells that form a sphere, four days after fertilisation. This is
called the morula, "mulberry". The diameter is virtually the same as the diameter
of the blastomerula.
After about six days, the so-called blastula develops by forming a cavity,
surrounded by 60 to 80 cells, which are 0.6mm in diameter. This cavity is the
beginning of what will later become the digestive tract. The outer cells of the
blastula are called trophoblast; these cells are the beginning of the placenta. In
humans, implantation of the embryo takes places in the uterine wall at the end of
the first week. Whether this moment also applies to cat embryos, I do not know.
Before that time, trophoblasts produce gonadotropin, a hormone that ensures that
the endometrium is ready for implantation of the embryos. The embryos have
nestled themselves for the next, very important phase: gastrulatio. Gastrulatio is
an exceptional process. Different zones of the blastula fold, and form three more
or less distinguishable layers: the ectoderm, endoderm and mesoderm. Ectoderm
is the designation for the outer cells of the body: therefore, the skin (epidermis),
but the central nervous system also has an ectodermal origin. The endoderm
consists of cells that (will) make up the digestive tract, the gastrointestinal
system, then. The mesoderm, finally, are the cells, which will make up the
muscles, skeleton and internal organs. The first mesodermal structure that will be
formed is the chorda, the spinal column. Meanwhile, growth continues and the
embryo becomes egg-shaped. The dimensions are approximately 1.5mm by
1mm.
Gastrulatio is a vital and vulnerable moment in the existence of an embryo. At
this stage, the genetic material of the embryo itself is expressed. Before that
time, processes were mainly controlled by maternal influences (by the mother,
therefore) through the material in the egg-cell, originating from the mother.
Many embryos die at this stage because of lethal (deadly) gene combinations,
producing non-functioning or defective proteins. At this stage the cat's embryo is
1.5mm by 1mm.
During the next stage the organs are developed. The ectoderm forms a skin that
covers the entire body and a thickened plate develops, which folds into a groove:
the neural crest. Ultimately, this will become a tube, which will submerge below
the skin's surface and will differentiate to the central nervous system. We have
already (or just!) reached day 13.
Something surprising happens: concentrations of mesodermal tissue, "somites",
appear on either side of the neural crest, as a result of which the embryo is
divided into identical structures. The embryo has an elongated shape and a rodshaped structure across its middle, the notochord, the first skeletal element (the
spinal cord in development). The number of somites increases.
Dorsal and caudal (head and tail end) can be distinguished well, and already a
tail is showing. The endoderm is folded as a tubular structure, the beginning of
the gastrointestinal system. A primitive sort of blood circulation also develops.
At 15 to 17 days the cat's embryo is 2mm to 10mm big. The neural tube closes.
The head is prominently present and slightly bent towards the caudal side of the
embryo. Again, something surprising happens: the embryo develops gill arches,
four in total in the cat. The primitive gastrointestinal system is ready and there is
the beginning of a mouth. In the pharynx behind the mouth (the oesophagus)
deep grooves develop that reach to the ectoderm. Later on, these will disappear
again, but partly due to these gill arches, the thought arises that each embryo just
repeats evolution. At the same time the cerebellum develops. It is already clear
where the eyes and ears will be. The kitten has reached day 18 after the
conception. At days 18 and 19 forelegs and hind legs develop. The cerebrum and
brainstem are already present in a rudimentary form. The embryo is between
7mm and 18mm long, neck and tail are bent towards the trunk.
Everything happens quickly now. Until the 21st day the following things happen:
the front gill arch (left and right) deepens itself and ultimately forms the auditory
duct. The would-be eyes have a clear pigmentation and a duct for the olfactory
organ deepens itself. The cerebellum is divided by a groove. The forelegs are
now divided (as they are in the adult cat), with an internal skeleton, yet the hind
legs are still primitive protuberances. The tail lengthens and is curled towards the
body. Internally, veins differentiate for the blood circulation and nerves. The
larynx, bronchi and lungs can also be discerned. Oesophagus, stomach and
intestines are formed. Pancreas, thyroid gland, kidney and liver are also
developed. On the side of the back, vertebrae are formed. The primitive spinal
cord continues into the tail. Even the genital system is already present, albeit
primitively.
The embryo is now 10mm to 24mm long. It may be clear that, especially in the
early stages, people should be very careful with possible damaging substances.
Vaccination with a live (attenuated) virus can be harmful to the embryo and also
the use of, for example, remedies for fungi can be detrimental. Antibiotics are
only to be administered if strictly necessary. Particularly Baytril should be
avoided. Of course, the female cat's life takes precedence over the life of the
kittens and naturally the female should only be mated if she is 100 percent
healthy. But even pregnant cats can fall ill.
In the meantime the female cat shows signs that she is pregnant: her nipples
become slightly larger and pinker than they were before. After 21 days, an
experienced person can determine by way of palpation (a way of feeling and
touching carefully) if the female cat is pregnant. At this stage, the foetuses are
still so small (the size of a large pea), they can be distinguished among
themselves and can therefore be counted. Some female cats suffer from morning
sickness as a consequence of hormonal changes in their bodies.
Second trimester of the pregnancy
Over the next days (21 to 23 days) the upper lip is formed and eyelids begin to
develop. Earlobes are formed. At the end of the legs, toes can be distinguished as
a fan of dark matter against a lighter background. The genitalia are developed
further. Internally, the skeleton and the muscles differentiate further and the ribs
are formed, amongst others. The skeleton that is formed, still consists of
cartilage. The face develops, tongue and palate are formed. Thyroid gland,
parathyroid gland and heart develop, and an organ that most people at best only
know as "sweetbread" from haute cuisine. The common biomedical term for
sweetbread is thymus. This is situated in the chest cavity between the breast bone
and the heart. The thymus has a central function in the immune system and is
responsible for the production of so-called T-cells. If the thymus is absent in
newborn animals, they produce hardly any antibodies at all and are therefore
very susceptible to infections. But if the thymus is experimentally removed from
animals (mice) when they are a few days old, these problems will not occur so
much: the lymphocytes that are produced in the thymus and move on to the
spleen and lymph glands, probably have already passed on the necessary
information about what is foreign to spleen and lymph gland. The embryo now
measures 13mm to 30mm.
At 23 to 25 days, the toes of the foreleg, which were already visible, but still
formed a lump, start to separate from each other. On the hind legs, which are a
little behind in comparison with the forelegs, the would-be toes can be
distinguished like a fan of dark matter against a lighter background, as happened
before with the forelegs. Kidneys, adrenal glands and genitalia further
differentiate. Within the primitive spinal cord, grey and white matter is separated
and surrounded by a membrane. Grey matter mainly consists of nerve cells. The
grey colour comes from the nucleus of those cells. White matter consists of
attenuated nerve fibres, which contain a white, fatty substance, called "myelin".
This white matter shrouds the grey matter in the spinal cord. Axons and ganglia
differentiate. In the head the jaws, palate, tongue and salivary glands develop.
Within the brain the pituitary gland forms itself, an important organ that
produces several different hormones: Vasopressin, which is relevant to the
body's water balance, Oxytocin, which plays a role at birth and afterwards at
lactation and then a number of hormones involved with the regulation of other
glands: thyroid-stimulating hormone (TSH), adrenocorticotropic hormone
(ACTH), follicle-stimulating hormone (FSH) and luteinising hormone (LH),
which both have an effect on the sex glands. In addition to this the pituitary
gland also secretes growth hormone, which plays a very important, guiding role
in the growth (of the young animal) as well as in its metabolism.
Stage 25 to 28 days, 21mm to 40mm. At this stage the embryos are in fact
virtually complete mini cats and should rather be called foetuses. Everything
develops further and differentiates even more. The head develops cheeks, a chin,
a nose and a mouth. The area where the navel will be is reduced. The
peritoneum, the pulmonary membrane and the diaphragm are formed. The carpal
bones, toes and ribs are still cartilaginous, but are starting to calcify. The teeth
are formed (hidden away in the jaw).
Things are beginning to take shape. The foetuses are now also growing rapidly
and most "parts" are in their designated place. During the phase of 28 to 32 days,
they are 25mm to 50mm big and it becomes difficult to determine the number of
foetuses. Over the eye (that has been formed), an eyelid develops itself and there
are small, triangular ears. The inner ear starts to differentiate into a complicated
structure with which the animal can later hear; the eardrum is formed. On an
image, the foetus already looks like a kitten. The ossification of several parts,
still consisting of cartilage and where bone should usually be, goes on. The
bronchi differentiate more and more. In female foetuses the womb develops. The
liver, already present, is getting "lobed". The bladder develops. The size of the
foetus is now 25mm to 50mm.
The foetuses keep on growing, the head is and will stay relatively big. The
female cat now grows visually bigger, certainly if she carries multiple foetuses.
We have now arrived at the period of 32 to 38 days. The size of the foetuses is
now 35mm to 60mm. The skin feels smooth, there is no fur yet. The external
genitalia are formed. The toes develop nails. The eye differentiates further, the
iris is formed, amongst others.
Third trimester of the pregnancy
From days 38 to 44 the skin differentiates. It becomes thicker and starts to
wrinkle. The ears become bigger, the tail grows longer. The inner ear is formed,
but is still of cartilage. The alveoli are developed. The pituitary gland becomes
lobed. Within the intestines, intestinal villi are growing. The eyelids are
complete and present, the eyes are closed. The embryo is 50mm to 80mm in size.
On day 44 the embryo measures 59mm to 94mm and fur is developing, the
foetus is covered with a silky layer. From day 48 (65mm to 125mm), possible
pigmentation is visible.
At last, the final stage from day 58 on. This is the stage just before birth. All
organs are sufficiently fully-grown to make the foetus viable. A normal delivery
takes places between 59 and 69 days after conception. Before day 59, the kittens
will not yet be viable enough to survive without special medical help. If
gestation lasts longer than 69 days, it will be wise to consult a vet. If the female
cat does not mind that her temperature is taken rectally, you can take her
temperature every morning: from 12 to 24 hours before delivery her temperature
drops from its normal reading of 38.5 degrees Celsius to 37.5 degrees Celsius. A
normal delivery starts with cervical dilation. The cat will produce some mucus
from her vagina, but it is possible you will not notice this, because she will clean
this up herself, if she is able to reach with her big belly. This stage can last up to
36 hours, especially with a primipare female cat (i.e. a female cat that has her
first litter). It gets serious when she gets contractions. You can feel these strong
contractions very well, when you place a hand on her belly. The most important
thing you can do is: being there… Most female cats like it when you keep them
company. Delivery of the first kitten often takes the longest. Do not panic too
soon, just observe that the female cat stays calm. As long as the mother is not
agitated or panicky, most of the time there is nothing going on. It is always
pleasant, when both you and the female cat are inexperienced, to get support
from an experienced breeder.
However, giving birth is something that is very natural and most of time no
complications will happen. Still, it is wise to inform your vet about the
approaching happy event. If you should need veterinary assistance, it is good to
know who you can call (somehow, kittens like to be born in the middle of
night...).
And if everything has gone well... Congratulations...
Sources
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C. Darwin. In The Origin of Species by Means of Natural
Selection, or The Preservation of Favoured Races in the
Struggle for Life, First Edition. Chapter 13: Mutual Affinities of
Organic Beings: Morphology: Embryology: Rudimentary
Organs.
C. Knopse. Periods and Stages of the prenatal development of
the domestic cat. Anat. Histol. Embryol. 31,37-51, 2002
Blackwell Wissenschafts-Verlag, Berlin, ISSN 0340-2096.
PDF-file: http://www.vetmed.unimuenchen.de/anat1/english/2002_ck1.pdf.
C.H. WaddingtonGeorge Allen & Unwin LTD. Principles of
Embryology. 1954.