The DogDomestic dog, carnivorous mammal, generally considered the first domesticatedanimal. The domesticated dog has coexisted with human beings as a workingpartner and household pet in all eras and cultures since the days of the cavedwellers. It is generally believed that the direct ancestor of the domestic dogis 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: CarnivoraFamily: Canidae Genus: Canis Species: Canis familiarisECOLOGY & HABITATLittle is known about wild dogs of the past but that they are carnivores:hunters and scavengers. This means that they are secondary consumers in webchains. 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.

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Since the cave dweller times, dogs have been domesticated by humans and it hashelped him to hunt, in herding, protection, etc. It has been very important as awork animal and as a psychological support for humans. The habitat of the dog iswhere its owner lives.

Different dogs have different adaptations to theirancestral habitat but nowadays, this is not applicable.ANATOMYSKELETONThe skeleton of the dog is the articulated structure, moved by the muscles, thatholds the dogs body and protects some organs and the nervous system. It alsofunctions as mineral and blood deposit of the body. The skeleton of a dog ismade up of approximately 321 bones: 134 form the axial skeleton (skull,vertebrae, ribs, etc.), and 186 form the appendicular skeleton (appendages). Anextra bone has to be added for male dogs which is the penile bone. The dog is adigigraded animal (it walks with its toes).

It lies on its third phalangeswhich are protected by palm cushions. The dogs toes are arranged in an anglewhich gives more facility of rest after running or other activities. The teethof the dog is composed of 42 teeth which include canines, molars, incisors, etc.JOINTSJoints permit the movement of the bones. There are three types of joints in adog: fixed joints, movable joints, and semi-movable joints.

Fixed joints, suchas the ones in the skull dont permit any movement but keep the bones together.The semi-movable joints are those that permit a little movement. They arerepresented in the spinal column. The movable joints are those present in therest of the bones. Inside of this group of joints there are various types: thehinge, the ball-and-socket, the pivot, and the gliding joints. The most movablejoints are present in the appendages. Joints are held together by a fibrouswrapping, the joint capsule, which reinforced by ligaments.

Muscles and tendonsalso help keeping the bones together.MUSCLESThere 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 musclewhich is exclusively in the heart.

The smooth muscle is the one present in thewalls of the digestive organs, arteries, veins, in the diaphragm (whichseparates the two cavities of the body: the thorax and abdomen), and in someother internal organs.DIGESTIVE SYSTEMThe digestive system of a dog is very similar to a human one. It ensures theingestion of food and its transformation (by mechanical and chemical acts) tosimple substances which the dogs body can absorb and assimilate. It all startsin the mouth, where food is broken down mechanically and also a littlechemically (saliva and teeth). Then they pass through the esophagus to thestomach to the small intestine (only 3 meters long but it has a very strongdigestion) and to the large intestine where the feces are made. Then excretionis made through the rectum and then through the anus. A series of added glandsproduce substances which are used in digestion and they perform variousimportant jobs.

The most important one is the liver (which is an organ).RESPIRATORY SYSTEMIn the respiratory system, air goes through the nostrils in the snout. In thenasal cavity air is purified, moistened and warmed. Then it passes throughpharynx, 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 thebronchioles which are subdivisions of the bronchi. The last part are the alveoliwhere oxygen diffuses to the blood.URINARY SYSTEMThe urinary system, is composed by the kidneys and the urinary structures.

Theblood is purified of toxins and excess water by the kidneys. Then the toxicsubstances are diluted in urine which passes through the ureters to the urinarybladder (deposit for urine). Then it is released through the urethra to theexterior of the body.GENITAL SYSTEMIt is composed of the genital glands (gonads) that produce the reproductivecells, the genital conducts that ensure the transport of the sex cells, and thecopulation organs that permit the encounter of the gametes.FEMALEThe gonads of the female dog are composed of the ovaries, which are under thekidneys.

The ovaries produce the eggs. The ovaries are active after the dog is 4to 6 months old and the process occurs each 6 months more or less (this isnormally called “in heat”). After the egg is produce it goes to the oviductwhere it waits for a sperm cell to fertilize it. I f a zygote is formed then itstays in the uterus for two weeks until it sticks to the wall. The vagina whichis quite long in dogs is used as birth and copulation canal.MALEThe 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 theliquid 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 doghas tissue around the urethra which capable of dilatation when extra blood ispumped (for copulation).CIRCULATORY SYSTEMIt includes a four chambered heart, arteries, veins, and lymphatic glands andvessels. The circulation of blood provides the dogs body with oxygen andremoves carbon dioxide from it. Oxygenated blood and deoxygenated bloodcirculate separatelyNERVOUS SYSTEMThe nervous system is composed of the central nervous system, the peripheralnervous system, and the autonomous nervous system.

The central nervous system iscomposed by the brain and the spinal cord. The peripheral n. s. is made up ofthe nerve cells and the autonomous one is made up of the sympathetic and theparasympathetic systems.

The autonomous nerve system is connected to the spinalcord and the peripheral to the spinal cord or the brain.SENSORY ORGANSThe eye of a dog consists of the cornea, the iris, the lens, the retina, thechoroid coat, the sclera, and the optic nerve which sends the image absorbed bythe retina to the brain. The ear of the dog is long and curved.

It is composedof the same structures as that of a human: the tympanic membrane, the series oftiny bones such as the hammer, the semi circular canals, etc. The touch of thedog is well developed specially in the legs and the tongue.PHYSIOLOGYCIRCULATION OF BLOODDeoxygenated blood from the right atrium, go to the right ventricle. It thengoes through the pulmonary arteries which go to the alveoli capillaries whereoxygen 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, goto the Aorta, the principal artery which divides and divides into arterioles toreach every cell of the dogs body.

Blood pressure is maintained in arteries bythe smooth muscle surrounding it. Through the capillaries, the oxygen and thecarbon dioxide exchange. Blood moves through veins because of the skeletalmuscle movement. In veins blood is prevented to go back by opening and closingvalves.

Through the veins, to the vena cava, and then to the right atrium, theblood reaches the heart again and the cycle is repeated. The lymphatic systemprotects the organism from dangerous microorganisms (it produces and containswhite blood cells which produce antibodies against intruders) and drains theintercellular spaces. The heart beat rate of dogs varies depending on the sizeof the dog and its training but it is faster than that of a human.RESPIRATORY SYSTEMAir 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 relaxesand the change of pressure in the lungs compared to that of the outside, forcesair in and the lungs inflate. As heart beat, the respiration rate is faster thanin humans.

DIGESTIONINGESTIONThe dog needs to drink huge amounts of water for its body needs since a lot ofit is lost in excretion, urine, and the evaporation of water in the respiratorycanals. The dog drinks by moving its tongue back and forth and in form of aspoon. Like that it impulses the water into the mouth. The dog keeps the bigchunks of food still with its anterior paws which serve as “hands”. To eatsolid food, the dog moves its head into the food source, penetrating the foodin its mouth.

The teeth perform an indispensable job in mechanical digestioneventhough it is not very effective in the dog since the mandible does not movelaterally. The secretion of saliva can be produced by the taste or smellstimulus or when the dog perceive that food is present.GASTRIC DIGESTIONThe dogs stomach only contracts when food is present to mix the foodintensively. The daily production of gastric juice is between 2 and 3 liters.This mixture of hydrochloric acid and enzymes breakdown proteins and separatethe conjunctive tissue of meat. The production of gastric juice happens whenfood is ingested or when its eating time in the dogs schedule.

INTESTINAL DIGESTIONThe chime, the product from the stomach, passes to the small intestine. Thepancreatic juice in the intestine contains enzymes that attack fats, proteins,and starch. The volume of the bile from the liver secreted is of 25milliters perkilogram of the dogs weight each day. Bile helps to set favorable conditionsfor the pancreatic juice to work and it eliminates different wastes.

The gastricjuice finish the braking down of food. The products are then absorbed into theblood 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, digestionof maternal milk is restricted to the stomach. A special enzyme which finishesafter lactancy is present for the breakdown of milk.EXCRETIONThe wastes pass through the large intestine where the feces are produced.

Thenthese feces go through the rectum and then to the anus where they finally leavethe body.REPRODUCTIONThe male reproductory system as well as the female one is controlled by thehormones coming from the hypofisis and the nerve signals coming from thehypothalamus.THE MALE DOGThe reproduction organs of the dog function yearlong. One millimeter of spermcontains 100,000 to 200,000 and the volume and concentration of these lower ifthe dog copulates too much in a row. The testosterone, the sex hormone of themale dog, is vital for the production of sperm cells, the definition ofsecondary sex characteristics (bigger size and weight, and the bark is of alower pitch), and sexual behavior.THE FEMALE DOGThe reproduction system of the female dog is much more complex than that of amale dog. The female dog has estruation each six months more or less.

There arefour periods in the sexual cycle: the proestruation, the menstruation, theposestruation, and the anaestruation. The anaestruation is the period in whichthe dog is not ready for reproduction. In the proestruation, which lasts for 9days, the follicles grow in the ovaries. The dogs vagina swells and it spills amucus type substance, later blood. The estruation comes next and it longs for 4or 8 days. There is no more blood coming from the vagina but the dog is verynervous.

Ovulation occurs starts 3 to 5 days after the estruation starts. Itlasts 12 to 72 hours. The posestruation occurs if the dog is not pregnant and itlasts for 2 months. The walls of the uterus widen because of the progesteronesecreted in the ovary. The anestro lasts 3 months and a half and it is theresting of the female reproductive system.MATING AND PREGNANCYCopulation permits the contact of eggs and sperm cells to form zygotes.

Thepenis of the dog gets erect by the filling of erectal tissue with blood and thepenile bone. Then it is introduced into the relaxed and lubricated vagina of thedog. Then the penis of the dog expands and the dogs vagina muscles contracttrapping the penis in the vagina for a long time. The vagina then produces threeejaculations 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 ofoffspring production. If the dog gets fertilized then it takes 2 months for theparturition of the puppies. In the parturition, the female dog expels the puppyafter it releases the amniotic liquid and the fetal sacs.

The female cleans thepuppy with its tongue to familiarize it with its mother and motivate itsphysiological functions and then it licks its vagina carefully. After. Theplacenta is released and it is eaten by the mother. The period between puppy isbetween half and one hour. The puppies sucking of the mothers breast isessential for the further production of milk. The puppies bumps, with theirheads, on their mothers breasts is important for the production of hypofisiaryhormones in the dog.

THERMO-REGULATIONThe dog is a ectothermic animal and its body temperature is of 38,5C. Thetemperature regulators in young puppies is still imperfect so it needs the heatof the mother or other siblings. The puppy regulates its temperature but it ishigher than that of an adult dog. When temperatures are low the dog uses twodifferent systems to prevent heat loss: lower the loss of heat or producing moreheat.

The dog can lower the loss of heat by constricting the blood vessels ofperipheral regions (extremities, ears, skin). This lowers the amount of heatexposed to the environment. The fur also isolate the body from cold. Littlemuscles in the bases of the hairs make hairs stiffer, increasing the warm airlayer between the fur and the skin. The dog also arcs its body or goes nearother dogs to prevent heat loss. If this is not enough, the dog uses more energyto keep the body temperature stable. The metabolism works more intensely(specially in the liver) and fat and other energy sources are used.

The contrarysituation is also possible, too much heat. The dog uses the blood vessels torelease extra heat. It dilates them in the peripheral regions to release theextra energy to the surroundings. When heat is too much the dog seeks cool andhumid places to rest and release their heat.

In other mammals evaporation ofsweat coming from sweat glands alleviate the heat but the sweat glands in dogsare few and located in the feet cushions that makes them quite inefficient. Ascompensation for the scarce sweat released, the dog has a cooling system basedin the mouth. The water of the mouth cavity, bronchi, and trachea evaporateswith an intense respiratory rate. This cools the body of the dog but waterlosses are huge.

SENSE ORGANSThe smell is the most developed sense in the dog. A dog is capable of smelling adrop of acetic acid which has been diluted in a thousand liters of water. A dropof this solution is diluted in a thousand liters and the dog is still capable ofdetecting the acetic acid. The olfactory capability of dogs depend on the typeof dog, the race. As comparison to the human smell, an average dog has 147million smelling units the human only has 500,000.

The nose and the receptorsfunction as the ones of other mammals such as humans. The ear is also quitedeveloped in dogs. Dogs can hear very high pitched sounds such as ultrasonic.The auditive range of dogs is between 20Hz and 60,000Hz. The humans is from16Hz to 20,000Hz.

The functioning of the ear is the same as in a human. Thevision capability of the dog is not comparable to that of a human. They canperceive 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 specialcoating in the eye globe that permits the dog to see more light when it isdarker.LOCOMOTION(Look at the diagram to see how dogs move) Locomotion in dogs are the same asmost complex animals.

Flexor and extensor muscles work in pairs to move thestructures.BEHAVIORTERRITORIALITYThe male dog marks its “hunting” territory by odor signals produced by the analglands. The smell also attracts females into the territory.

When dogs, male andfemale, urinate at a certain place, that means that that is a common territory.The dog defends its territory instinctively when an intruder that is not acompanion appears. This defense instinct makes it have a guardian quality.THE CANINE HIERARCHYDogs that live in groups of dogs have hierarchies, inherited from their wildancestors. There are two types of dogs: dominant and submissive. This hierarchynot 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 instinctthat even exist in dogs living with owners in cities. In the relation with thehuman owner, the owner is always dominant except in cases where the dog hasmental disorders.SEXUAL BEHAVIORDogs are polygamists, they dont have a definite couple. When a female dog is inheat, it is nervous and seeks desperately for a male.

It releases ferormones inits urine that a male can smell at kilometers of distance. When they meet, thefemale exposes its vulva to the male. The sexual act goes after a series ofritual games and a profound smell familiarization. Then comes the copulation. Ifvarious dogs follow a female, disputes settle the hierarchy and the mostdominant one gets to reproduce.SEXUAL PROBLEMS OF DOGSFemale and male dogs may feel frustrated when they cant find a mating partner.Dogs can get depressed and they may tend to escape from their home.

Male dogsrelieve themselves by masturbating with an object. Female dogs may get verynervous and develop a hysterical pregnancy in which the dog produces milk as anexpression of its needs to have puppies.MATERNAL INSTINCTDays before giving birth, a dog looks for a safe, warm, and comfortable place toplace her dogs to be born, a “nest”.

The dog looks for its puppies but thosewho are deformed are killed by the mother herself (natural selection). A mothercuts the umbilical cord and licks its new born puppies to stimulatephysiological functions. If a mother does not do this, then she lacks maternalinstinct. A mother is aggresive if she sees that something(an intruder) ismenacing its puppies. If the person is familiar, then she is pleased to havethem near its puppies. Very few male dogs care for puppies but some do.THE DOGS LANGUAGEOLFACTORY COMMUNICATIONThe dog uses its urine that contains glandular secretions as well as urine.

Adog uses this to transmit messages to others and to mark its territory. Toidentify themselves, dogs smell each other profoundly especially the snout, thegenitals, and the anus. In sexual reproduction smell also plays an importantrole as I explained above.

The dog also can identify a prey by its smell.THE VOICEDogs use to bark to advert others of danger. A howl in the middle of the nightis a concentration call. When a dog is in heat a male dog can howl for hours andhours in desperation. The female responds with the same howl.

Two dogs that mayencounter an bark are just imposing themselves. This makes them have moreconfidence. The nature of dog sounds can be described as follows: a hoarse andcut bark expresses a menace (a dare to another animal or an advice to anintruder so that it moves out of the territory), a happy bark ( coming to itsowner or before going for a walk), a special bark to indicate a prey, etc. Thenthere are the obvious sounds: cry, lament, howl, screams, and grunts.THE EYESThe look of a dog can tell a lot.

A fixed look means fear or malevolence. Thelook of a dog to sheep or cows can control them and place them in order.ATTITUDES AND MIMICGestures of a dog to show happiness are the constant movement of the tail. Atail between the legs means fear. A dog in an aggressive posture shapes andmoves its body to make it look bigger: it elongates, its hair gets straight up,etc. To exhibit submission a dog often lies itself on the floor and with itstail between its legs it shows its genitals. When a dog tries to play withanother it lies in a sphinx position, or it “dances” around the other dog, or itgently bites the others tail, etc.

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