Essay/Term paper: The dog

Essay, term paper, research paper:  Science

The Dog


Domestic dog, carnivorous mammal, generally considered the first domesticated
animal. The domesticated dog has coexisted with human beings as a working
partner and household pet in all eras and cultures since the days of the cave
dwellers. It is generally believed that the direct ancestor of the domestic dog
is the wolf, originally found throughout Europe, Asia, and North America.
Remains of a dog, estimated to be 10,500 years old, have been found in Idaho.

TAXONOMY Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Carnivora
Family: Canidae Genus: Canis Species: Canis familiaris

ECOLOGY & HABITAT

Little is known about wild dogs of the past but that they are carnivores:
hunters and scavengers. This means that they are secondary consumers in web
chains. Eventhough they are carnivores they sometimes accept eating green plants.
The ecology of dogs right know is that it helps the human in many fields of life.
Since the cave dweller times, dogs have been domesticated by humans and it has
helped him to hunt, in herding, protection, etc. It has been very important as a
work animal and as a psychological support for humans. The habitat of the dog is
where it"s owner lives. Different dogs have different adaptations to their
ancestral habitat but nowadays, this is not applicable.

ANATOMY

SKELETON

The skeleton of the dog is the articulated structure, moved by the muscles, that
holds the dog"s body and protects some organs and the nervous system. It also
functions as mineral and blood deposit of the body. The skeleton of a dog is
made up of approximately 321 bones: 134 form the axial skeleton (skull,
vertebrae, ribs, etc.), and 186 form the appendicular skeleton (appendages). An
extra bone has to be added for male dogs which is the penile bone. The dog is a
digigraded animal (it walks with it"s toes). It lies on it"s third phalanges
which are protected by palm cushions. The dog"s toes are arranged in an angle
which gives more facility of rest after running or other activities. The teeth
of the dog is composed of 42 teeth which include canines, molars, incisors, etc.

JOINTS

Joints permit the movement of the bones. There are three types of joints in a
dog: fixed joints, movable joints, and semi-movable joints. Fixed joints, such
as the ones in the skull don"t permit any movement but keep the bones together.
The semi-movable joints are those that permit a little movement. They are
represented in the spinal column. The movable joints are those present in the
rest of the bones. Inside of this group of joints there are various types: the
hinge, the ball-and-socket, the pivot, and the gliding joints. The most movable
joints are present in the appendages. Joints are held together by a fibrous
wrapping, the joint capsule, which reinforced by ligaments. Muscles and tendons
also help keeping the bones together.

MUSCLES

There are three types of muscles in a dog: the skeletal muscle, cardiac muscle,
and smooth muscle. The skeletal muscle works in pairs, a flexor and an extensor.
It permits the movement of the skeleton and it also moves the skin of the dog
(cutaneal muscle is very developed in dogs). The cardiac muscle is the muscle
which is exclusively in the heart. The smooth muscle is the one present in the
walls of the digestive organs, arteries, veins, in the diaphragm (which
separates the two cavities of the body: the thorax and abdomen), and in some
other internal organs.

DIGESTIVE SYSTEM

The digestive system of a dog is very similar to a human one. It ensures the
ingestion of food and it"s transformation (by mechanical and chemical acts) to
simple substances which the dog"s body can absorb and assimilate. It all starts
in the mouth, where food is broken down mechanically and also a little
chemically (saliva and teeth). Then they pass through the esophagus to the
stomach to the small intestine (only 3 meters long but it has a very strong
digestion) and to the large intestine where the feces are made. Then excretion
is made through the rectum and then through the anus. A series of added glands
produce substances which are used in digestion and they perform various
important jobs. The most important one is the liver (which is an organ).

RESPIRATORY SYSTEM

In the respiratory system, air goes through the nostrils in the snout. In the
nasal cavity air is purified, moistened and warmed. Then it passes through
pharynx, larynx (where vocal cords for barking are), and then to the trachea.
Air is then canalized through the two bronchi and then inside the lung by the
bronchioles which are subdivisions of the bronchi. The last part are the alveoli
where oxygen diffuses to the blood.

URINARY SYSTEM

The urinary system, is composed by the kidneys and the urinary structures. The
blood is purified of toxins and excess water by the kidneys. Then the toxic
substances are diluted in urine which passes through the ureters to the urinary
bladder (deposit for urine). Then it is released through the urethra to the
exterior of the body.

GENITAL SYSTEM

It is composed of the genital glands (gonads) that produce the reproductive
cells, the genital conducts that ensure the transport of the sex cells, and the
copulation organs that permit the encounter of the gametes.

FEMALE

The gonads of the female dog are composed of the ovaries, which are under the
kidneys. The ovaries produce the eggs. The ovaries are active after the dog is 4
to 6 months old and the process occurs each 6 months more or less (this is
normally called "in heat"). After the egg is produce it goes to the oviduct
where it waits for a sperm cell to fertilize it. I f a zygote is formed then it
stays in the uterus for two weeks until it sticks to the wall. The vagina which
is quite long in dogs is used as birth and copulation canal.

MALE

The gonads of the male are the testicles which are inside a sac and the scrotum.
The sperm cells are produced here. The prostate is the gland that produces the
liquid in which sperm cells are carried. Sperm cells go out through the urethra,
which is surrounded by the penile bone, like urine does. The penis of the dog
has tissue around the urethra which capable of dilatation when extra blood is
pumped (for copulation).

CIRCULATORY SYSTEM

It includes a four chambered heart, arteries, veins, and lymphatic glands and
vessels. The circulation of blood provides the dog"s body with oxygen and
removes carbon dioxide from it. Oxygenated blood and deoxygenated blood
circulate separately

NERVOUS SYSTEM

The nervous system is composed of the central nervous system, the peripheral
nervous system, and the autonomous nervous system. The central nervous system is
composed by the brain and the spinal cord. The peripheral n. s. is made up of
the nerve cells and the autonomous one is made up of the sympathetic and the
parasympathetic systems. The autonomous nerve system is connected to the spinal
cord and the peripheral to the spinal cord or the brain.

SENSORY ORGANS

The eye of a dog consists of the cornea, the iris, the lens, the retina, the
choroid coat, the sclera, and the optic nerve which sends the image absorbed by
the retina to the brain. The ear of the dog is long and curved. It is composed
of the same structures as that of a human: the tympanic membrane, the series of
tiny bones such as the hammer, the semi circular canals, etc. The touch of the
dog is well developed specially in the legs and the tongue.

PHYSIOLOGY

CIRCULATION OF BLOOD

Deoxygenated blood from the right atrium, go to the right ventricle. It then
goes through the pulmonary arteries which go to the alveoli capillaries where
oxygen diffuses into the blood. Then it returns to the heart, to the left atrium,
by the pulmonary veins. From the left ventricle, the blood, rich in oxygen, go
to the Aorta, the principal artery which divides and divides into arterioles to
reach every cell of the dog"s body. Blood pressure is maintained in arteries by
the smooth muscle surrounding it. Through the capillaries, the oxygen and the
carbon dioxide exchange. Blood moves through veins because of the skeletal
muscle movement. In veins blood is prevented to go back by opening and closing
valves. Through the veins, to the vena cava, and then to the right atrium, the
blood reaches the heart again and the cycle is repeated. The lymphatic system
protects the organism from dangerous microorganisms (it produces and contains
white blood cells which produce antibodies against intruders) and drains the
intercellular spaces. The heart beat rate of dogs varies depending on the size
of the dog and it"s training but it is faster than that of a human.

RESPIRATORY SYSTEM

Air reaches the lungs by the same system as in humans. The diaphragm contracts,
decreasing the size of the lung and therefore expelling the air. Then it relaxes
and the change of pressure in the lungs compared to that of the outside, forces
air in and the lungs inflate. As heart beat, the respiration rate is faster than
in humans.

DIGESTION

INGESTION

The dog needs to drink huge amounts of water for it"s body needs since a lot of
it is lost in excretion, urine, and the evaporation of water in the respiratory
canals. The dog drinks by moving it"s tongue back and forth and in form of a
spoon. Like that it impulses the water into the mouth. The dog keeps the big
chunks of food still with it"s anterior paws which serve as "hands". To eat
solid food, the dog moves it"s head into the food source, penetrating the food
in it"s mouth. The teeth perform an indispensable job in mechanical digestion
eventhough it is not very effective in the dog since the mandible does not move
laterally. The secretion of saliva can be produced by the taste or smell
stimulus or when the dog perceive that food is present.

GASTRIC DIGESTION

The dog"s stomach only contracts when food is present to mix the food
intensively. The daily production of gastric juice is between 2 and 3 liters.
This mixture of hydrochloric acid and enzymes breakdown proteins and separate
the conjunctive tissue of meat. The production of gastric juice happens when
food is ingested or when it"s eating time in the dog"s schedule.

INTESTINAL DIGESTION

The chime, the product from the stomach, passes to the small intestine. The
pancreatic juice in the intestine contains enzymes that attack fats, proteins,
and starch. The volume of the bile from the liver secreted is of 25milliters per
kilogram of the dog"s weight each day. Bile helps to set favorable conditions
for the pancreatic juice to work and it eliminates different wastes. The gastric
juice finish the braking down of food. The products are then absorbed into the
blood in the small intestine. Some go to the blood (water, minerals, sugars,
amino acids, and some fats) and some go the lymph (fats). In puppies, digestion
of maternal milk is restricted to the stomach. A special enzyme which finishes
after lactancy is present for the breakdown of milk.

EXCRETION

The wastes pass through the large intestine where the feces are produced. Then
these feces go through the rectum and then to the anus where they finally leave
the body.

REPRODUCTION

The male reproductory system as well as the female one is controlled by the
hormones coming from the hypofisis and the nerve signals coming from the
hypothalamus.

THE MALE DOG

The reproduction organs of the dog function yearlong. One millimeter of sperm
contains 100,000 to 200,000 and the volume and concentration of these lower if
the dog copulates too much in a row. The testosterone, the sex hormone of the
male dog, is vital for the production of sperm cells, the definition of
secondary sex characteristics (bigger size and weight, and the bark is of a
lower pitch), and sexual behavior.

THE FEMALE DOG

The reproduction system of the female dog is much more complex than that of a
male dog. The female dog has estruation each six months more or less. There are
four periods in the sexual cycle: the proestruation, the menstruation, the
posestruation, and the anaestruation. The anaestruation is the period in which
the dog is not ready for reproduction. In the proestruation, which lasts for 9
days, the follicles grow in the ovaries. The dog"s vagina swells and it spills a
mucus type substance, later blood. The estruation comes next and it longs for 4
or 8 days. There is no more blood coming from the vagina but the dog is very
nervous. Ovulation occurs starts 3 to 5 days after the estruation starts. It
lasts 12 to 72 hours. The posestruation occurs if the dog is not pregnant and it
lasts for 2 months. The walls of the uterus widen because of the progesterone
secreted in the ovary. The anestro lasts 3 months and a half and it is the
resting of the female reproductive system.

MATING AND PREGNANCY

Copulation permits the contact of eggs and sperm cells to form zygotes. The
penis of the dog gets erect by the filling of erectal tissue with blood and the
penile bone. Then it is introduced into the relaxed and lubricated vagina of the
dog. Then the penis of the dog expands and the dog"s vagina muscles contract
trapping the penis in the vagina for a long time. The vagina then produces three
ejaculations in the male dog. The middle one with more sperm than the other two.
The female dog then liberates the male dog and there is a possibility of
offspring production. If the dog gets fertilized then it takes 2 months for the
parturition of the puppies. In the parturition, the female dog expels the puppy
after it releases the amniotic liquid and the fetal sacs. The female cleans the
puppy with its tongue to familiarize it with its mother and motivate its
physiological functions and then it licks its vagina carefully. After. The
placenta is released and it is eaten by the mother. The period between puppy is
between half and one hour. The puppies sucking of the mother"s breast is
essential for the further production of milk. The puppies" bumps, with their
heads, on their mother"s breasts is important for the production of hypofisiary
hormones in the dog.

THERMO-REGULATION

The dog is a ectothermic animal and its body temperature is of 38,5ºC. The
temperature regulators in young puppies is still imperfect so it needs the heat
of the mother or other siblings. The puppy regulates its temperature but it is
higher than that of an adult dog. When temperatures are low the dog uses two
different systems to prevent heat loss: lower the loss of heat or producing more
heat. The dog can lower the loss of heat by constricting the blood vessels of
peripheral regions (extremities, ears, skin). This lowers the amount of heat
exposed to the environment. The fur also isolate the body from cold. Little
muscles in the bases of the hairs make hairs stiffer, increasing the warm air
layer between the fur and the skin. The dog also arcs its body or goes near
other dogs to prevent heat loss. If this is not enough, the dog uses more energy
to keep the body temperature stable. The metabolism works more intensely
(specially in the liver) and fat and other energy sources are used. The contrary
situation is also possible, too much heat. The dog uses the blood vessels to
release extra heat. It dilates them in the peripheral regions to release the
extra energy to the surroundings. When heat is too much the dog seeks cool and
humid places to rest and release their heat. In other mammals evaporation of
sweat coming from sweat glands alleviate the heat but the sweat glands in dogs
are few and located in the feet cushions that makes them quite inefficient. As
compensation for the scarce sweat released, the dog has a cooling system based
in the mouth. The water of the mouth cavity, bronchi, and trachea evaporates
with an intense respiratory rate. This cools the body of the dog but water
losses are huge.

SENSE ORGANS

The smell is the most developed sense in the dog. A dog is capable of smelling a
drop of acetic acid which has been diluted in a thousand liters of water. A drop
of this solution is diluted in a thousand liters and the dog is still capable of
detecting the acetic acid. The olfactory capability of dogs depend on the type
of dog, the race. As comparison to the human smell, an average dog has 147
million smelling units… the human only has 500,000. The nose and the receptors
function as the ones of other mammals such as humans. The ear is also quite
developed in dogs. Dogs can hear very high pitched sounds such as ultrasonic.
The auditive range of dogs is between 20Hz and 60,000Hz. The human"s is from
16Hz to 20,000Hz. The functioning of the ear is the same as in a human. The
vision capability of the dog is not comparable to that of a human. They can
perceive changes of light but their ability to see clear forms is not much.
Concerning the color, not much study has been done on this. Dogs have a special
coating in the eye globe that permits the dog to see more light when it is
darker.

LOCOMOTION

(Look at the diagram to see how dogs move) Locomotion in dogs are the same as
most complex animals. Flexor and extensor muscles work in pairs to move the
structures.

BEHAVIOR

TERRITORIALITY

The male dog marks its "hunting" territory by odor signals produced by the anal
glands. The smell also attracts females into the territory. When dogs, male and
female, urinate at a certain place, that means that that is a common territory.
The dog defends it"s territory instinctively when an intruder that is not a
companion appears. This defense instinct makes it have a guardian quality.

THE CANINE HIERARCHY

Dogs that live in groups of dogs have hierarchies, inherited from their wild
ancestors. There are two types of dogs: dominant and submissive. This hierarchy
not only divides in into two categories, ranks in the canine society also exist.
Dogs do not have to live in groups to have these ranks, it is a natural instinct
that even exist in dogs living with owners in cities. In the relation with the
human owner, the owner is always dominant except in cases where the dog has
mental disorders.

SEXUAL BEHAVIOR

Dogs are polygamists, they don"t have a definite couple. When a female dog is in
heat, it is nervous and seeks desperately for a male. It releases ferormones in
its urine that a male can smell at kilometers of distance. When they meet, the
female exposes it"s vulva to the male. The sexual act goes after a series of
ritual games and a profound smell familiarization. Then comes the copulation. If
various dogs follow a female, disputes settle the hierarchy and the most
dominant one gets to reproduce.

SEXUAL PROBLEMS OF DOGS

Female and male dogs may feel frustrated when they can"t find a mating partner.
Dogs can get depressed and they may tend to escape from their home. Male dogs
relieve themselves by masturbating with an object. Female dogs may get very
nervous and develop a hysterical pregnancy in which the dog produces milk as an
expression of it"s needs to have puppies.

MATERNAL INSTINCT

Days before giving birth, a dog looks for a safe, warm, and comfortable place to
place her dogs to be born, a "nest". The dog looks for it"s puppies but those
who are deformed are killed by the mother herself (natural selection). A mother
cuts the umbilical cord and licks it"s new born puppies to stimulate
physiological functions. If a mother does not do this, then she lacks maternal
instinct. A mother is aggresive if she sees that something(an intruder) is
menacing its puppies. If the person is familiar, then she is pleased to have
them near its puppies. Very few male dogs care for puppies but some do.

THE DOG"S LANGUAGE

OLFACTORY COMMUNICATION

The dog uses it"s urine that contains glandular secretions as well as urine. A
dog uses this to transmit messages to others and to mark it"s territory. To
identify themselves, dogs smell each other profoundly especially the snout, the
genitals, and the anus. In sexual reproduction smell also plays an important
role as I explained above. The dog also can identify a prey by its smell.

THE VOICE

Dogs use to bark to advert others of danger. A howl in the middle of the night
is a concentration call. When a dog is in heat a male dog can howl for hours and
hours in desperation. The female responds with the same howl. Two dogs that may
encounter an bark are just imposing themselves. This makes them have more
confidence. The nature of dog sounds can be described as follows: a hoarse and
cut bark expresses a menace (a dare to another animal or an advice to an
intruder so that it moves out of the territory), a happy bark ( coming to its
owner or before going for a walk), a special bark to indicate a prey, etc. Then
there are the obvious sounds: cry, lament, howl, screams, and grunts.

THE EYES

The look of a dog can tell a lot. A fixed look means fear or malevolence. The
look of a dog to sheep or cows can control them and place them in order.

ATTITUDES AND MIMIC

Gestures of a dog to show happiness are the constant movement of the tail. A
tail between the legs means fear. A dog in an aggressive posture shapes and
moves its body to make it look bigger: it elongates, it"s hair gets straight up,
etc. To exhibit submission a dog often lies itself on the floor and with its
tail between its legs it shows its genitals. When a dog tries to play with
another it lies in a sphinx position, or it "dances" around the other dog, or it
gently bites the other"s tail, etc.