The dog’s anatomy decrypted: skeleton, coat, digestive, respiratory, nervous, cardiovascular …
The skeleton of the dog:
The skeleton of the dog is the frame of the body, where the muscles are inserted by their extensions: the tendons. The skeleton protects the brain and spinal cord as well as the lungs through the ribcage. The skull houses the brain, the sense organs, the pituitary gland, a true conductor of the endocrine system.
The vertebral column includes cervical vertebrae, thoracic vertebrae, lumbar vertebrae, sacral and coccygeal. The thirteen pairs of ribs fit on the thoracic vertebrae at the top and on the sternum at their base, except the last pair, called “floating ribs,” which remains free in the soft tissue.
The forelimb includes the scapula, humerus, radius ulna, carpus, metacarpal and phalanges. The pelvis, welded to the sacred vertebrae, begins the hind limb. The femur is prolonged by the tibia and the fibula, separated from the femur by the complex articulation of the knee, formed by the patella and the menisci. The leg ends with tarsus, metatarsal and phalanx. In the male dog, there is an additional bone: the penile bone, located in the penis.
The dogs feet:
The dog’s feet indicate the disposition of the limbs relative to imaginary vertical lines. For the forelimb, the vertical part of the tip of the shoulder, and for the hind limb of the tip of the buttock.
During the exhibition, the judge examines and notes the plumbs, front, side and back. In profile, if the vertical passes behind the member, it is said that the dog is encamped; if the vertical passes on the contrary in front of the member, it is said that the dog is under him.
Seen from the front or the back, if the limbs are deflected inside the verticals, the dog is said to be tight from front to back depending on whether it is the forelimb or the hind limb. A dog is said to be awkward if his feet are deflected inside, and panic if his feet are deflected to the outside.
The skin of the dog has a role of protection against temperature variations, against loss of water, against trauma and microbes … The skin contains many nerves that inform the brain by touch, but the tactile sense is much less developed in dogs than in humans. The skin is formed by the hypodermis, the dermis and the epidermis:
The hypodermis is the deepest layer of the skin. It is a tissue very rich in fat which gives the skin of the dog a great flexibility. Its thickness is not identical to all parts of the body. The hypodermis is very thick at the withers, for example, a region that the veterinarian often chooses for bites. It is in the hypodermum that excess fat is stored in obese dogs.
The dermis is located above the hypodermis. It is a layer of connective tissue that protects the body from blows thanks to its elasticity.
The epidermis is the outer layer of the skin. The cells in contact with the air are dead cells which desquamate and are renewed as and when their desquamation. Dandruff is caused by too much peeling.
Dog hair originates in the dermis. The size and consistency of the dog’s hair are different depending on the location of the body where they are implanted. Each hair is appended to a sebaceous gland that secretes sebum, a fatty substance that protects the coat. The hair is upright under the action of a tiny muscle, for example if the dog is aggressive, and inflates his fur to grow.
To cool the body, the man sweats, and the dog gasps. In fact the dog also sweats, but only by the foot pads and truffle where are located some sweat glands, or glands of sweat.
My dog loses his hair
Your dog inevitably loses hair during the seasonal moult (spring and fall) to replace part of his coat. It goes without saying that long-haired dogs lose more hair than dogs with short fur. The bitch in the process of birth or having just given birth also tends to lose more hair.
It is also possible that your dog loses his hair because of health disorders. Several diseases of the dog’s skin can cause hair loss, such as the ringworm (a mushroom that feeds on hair keratin), which is transmitted to humans and other animals. the demodectic mange , the dog mange or the dermatitis are other skin diseases that can cause the dog’s hair loss.
Hormonal diseases such as the dog ‘s diabetes mellitus , hypercorticism , hypothyroidism or hyperoestrogenism can also cause the dog to lose hair. Indeed, these hormones have the function of regulating hair growth.
Dogs can suffer from hair loss due to poor nutrition. We note the lack of protein, fatty acids or vitamin A as responsible.
Also pay attention to the treatments you give to your dog, it may be that his skin does not tolerate them. It also happens that the fall of the hair is due to an allergy of the dog.
The digestive system of the dog:
The digestive system of the dog includes the various organs involved in digestion, from the mouth to the anus, as well as the digestive glands, such as the liver and pancreas.
The food is ground in the mouth by the teeth, and soaked with saliva before being swallowed. The dog quickly swallows large enough pieces without chewing a lot.
The salivary glands, numerous, secrete the saliva that acts by moistening and lubricating the food.
The enzymes contained in saliva begin the phenomenon of digestion of certain constituents of food. The bolus then passes into the pharynx, the crossroads of the respiratory and digestive tracts, then into the esophagus to the stomach.
The musculature of the esophagus allows food to grow in its light, but it has no role in digestion.
The stomach of the dog is quite small, its capacity is of the order of one to two liters. But the stomach is a very dilatable organ. The dog can swallow large amounts of food, his stomach will expand and his belly will swell.
The glands of the stomach secrete extremely potent enzymes, as well as acids capable of digesting what the dog has swallowed. The musculature of the stomach helps digestion and the progression of food in the digestive tract to the small intestine.
It measures about six times the length of the dog, more than three meters … It is in the small intestine that the bile secreted by the liver and pancreatic juices is poured.
Throughout its length, the small intestine is dotted with glands favoring digestion.
Digestion ends in the large intestine, where faeces are formed. In the large intestine are also synthesized many vitamins essential to the body.
The rectum ends the digestive tract. In this portion, the feces are stored until expelled.
Two glands located on either side of the rectum, the anal glands, secrete a fatty and smelly product that serves to lubricate the passage of feces. The dog’s liver is composed of four liver lobes. The functions of the liver are numerous and varied: synthesis of lipids, albumins, synthesis of urea, uric acid, synthesis of agents of blood coagulation. The liver serves as a reservoir for blood and vitamins; it is also the organ that destroys the toxins.
The liver cells secrete the bile that is stored in the gallbladder, before spilling into the small intestine. Bile is mainly used to digest fats.
The pancreas secretes pancreatic juice that allows the breakdown of food thanks to the many enzymes it contains.
The pancreas also secretes insulin and glucagon, hormones regulating blood sugar levels.
The cardio-vascular apparatus of the dog:
The heart of the dog works like a pump that distributes blood throughout the body, through the arteries and veins. The heart includes two atria and two ventricles. The left heart and the right heart do not communicate, except in certain pathological cases.
Oxygen-enriched blood gains, by the arterial way, the organs of the body. Oxygen is used by cells of all organs as a source of energy. The blood is depleted of oxygen and enriched with carbon dioxide. Through the vein, the blood returns to the lungs to eliminate carbon dioxide and replenish oxygen, and so on every second of life, from birth to death.
What a wonderful machine that this heart beats regularly by adapting to the needs of the body throughout the dog’s life! When the dog makes an effort, the oxygen needs of the muscles increase, and the heart adapts by increasing the heart rate. At rest, the needs decrease, and the heart slows down thanks to a complex system of regulation of the heart beats.
Heart rate also varies with the dog’s age, physiological state and size. Most small dogs have an above-average heart rate. Birth abnormalities exist in puppies. They will be detected during the first visit to the veterinarian, for example at the time of the first vaccination.
To examine the heart, the veterinarian uses a stethoscope, to detect an abnormal sound, also called heart murmur. Radiography, ultrasound and electrocardiogram are used to clarify the diagnosis.
The mouth and teeth in dogs:
The mouth of the dog is lined by the oral mucosa. Ten salivary glands flow through their excretory ducts: two protein glands, two maxillary glands, two submaxillary glands, two sublingual glands, and two molar glands. Saliva contains many enzymes that start digestion. The teeth are implanted deep in the jaw.
In dogs, there are thirty-two milk teeth and forty-two adult teeth. The baby teeth appear first and then fall and are replaced by adult teeth. The examination of the dentition determines the age of the dog, because the teeth wear out and their degree of wear is proportional to their age, except in some special cases, such as dogs that eat pebbles, which causes premature wear.
Period of eruption of the baby teeth:
– at birth, the puppy has no teeth
– from the 15th to the 21st day: appearance of the incisors and upper canines
– from the 21st to the 30th day: appearance of the incisors and lower canines
– from the 3rd to the 5th week: appearance molars of milk
Eruption period of adult teeth:
– at 4 months: replacement of the milk tongs
– at 4 or 5 months: replacement of the milk terraces
– at 5 months: replacement of the corners and the canines of milk
Period of wear and leveling of adult teeth:
– at 15 months: the lower forceps are started
– at 18 months: the lower forceps are leveled, the lower half
– opened – from 2 to 3 years: the lower terraces are leveled, the upper clamps start
– from 3 years to 4 years old: upper claws level
– 4 years to 5 years old: upper terraces level and teeth begin to turn yellow
– after 6 years, it is difficult to estimate the age of the dog by examining only his teeth
When the lower jaw and the upper jaw are offset relative to each other, the dog is said to be prognathic. Prognathism can be superior or inferior. This defect causes the non-confirmation of the dog.
The urinary and genital system of the dog:
The urinary and genital tract of dogs are essential organs for the proper functioning of the body of dogs. If the urinary tract allows the evacuation of waste and toxins, the genital tract , in turn, provide reproductive function. Anatomy of these two anatomically speaking close zones but which fulfill very different roles.
The urinary system of the dog
The urinary system of the dog is formed by the kidneys and the urinary tract: ureter, bladder and urethra . By working, the body creates waste that is eliminated in the urine by the kidneys. The kidneys also allow, through a control system , to maintain the amount of water present in the body constant, triggering a set of mechanisms to remove excess water, or to reduce losses, in case of lack.
The kidneys are located in the abdominal cavity , under the lumbar vault. The right kidney is placed a little in front of the left kidney. Urine is collected in the pelvis and reaches the bladder through the ureter . The urine is stored in the bladder, which must be able to distend reasonably, until the urine is expelled through the urethra. The mechanism of urination is controlled by a complex nervous system.
The reproductive system of the male dog
The testicles are the male sex glands. It is in the testicles that the spermatozoa are formed . The testes secrete the male hormone called testosterone, as in humans.
The testicles are located outside the abdominal cavity so that their temperature remains lower than that of the body. A dog with testicles in the abdomen (ectopic testes) is sterile because sperm can not be formed.
Spermatozoa are collected in the epididymis and follow the vas deferens to the urethra. The vas deferens then opens on the urethra at the height of the prostate. The prostate secretes a liquid that comes to complete the sperm.
The penis , terminated by the glans, is protected by a fold of skin: the sheath. It is formed by the cavernous body , which swells with blood during erection, and by the penile bone.
A bulge , specific to the canine species, located on the penis also swells strongly at the time of coitus , which prevents the retraction of the penis out of the vagina. Coitus lasts fifteen to thirty minutes or more, and allows sperm to flow into the female genital tract .
The cryptorchidism of the dog
During the development of the fetus, the testicles migrate from their intra-abdominal position to the bursa, by the inguinal path. Sometimes the testicles are not in place in the purses. They were stopped in their migration. They can be found either in the abdomen or in the inguinal tract.
If both testicles are absent, the dog is said to be cryptorchid . If only one of the testicles is out of place in the purses, the dog is said to be monorchid . Cryptorchid dogs are sterile , monorchid dogs are fertile .
If the abnormality is detected early enough, when the puppy is still very young, medical treatment can sometimes correct the position of the sex glands. When the testes are not in place, it is advisable to have them removed because the dog is at risk of developing testicular tumors .
Good to know : Cryptorchid or monorchid dogs are not allowed for the confirmation test and are therefore excluded from breeding (for monorchid dogs).
The genitals of the bitch
The ovaries are the female genital glands. They are located in the abdomen at the height of the third and fourth lumbar vertebrae. Eggs, sexual cells, form in the ovaries.
After ovulation , the ovules reach the uterus by borrowing the oviducts, rather fine channels which, by their contractions, guide the eggs into the uterus. The uterus (or matrix) is formed by an endothelium composed of a muscularis and a serosa. It is in the endothelium that the egg will be implanted. Note: the muscularis can relax enormously.
The volume of a gestating uterus is multiplied by one hundred times the volume of the non-pregnant uterus. The smooth muscles of the womb help expel puppies at the time of delivery, thanks to very strong contractions . The serosa, an extension of the peritoneum, surrounds the muscular part of the uterus. The uterus is composed of two uterine horns and a body terminated by the cervix, and extended by the vagina .
The vagina of the bitch, located in the pelvic cavity, is inclined at 45 °. He completes the genital tract of the female. In the bitch there are five pairs of breasts : one pair of inguinal breasts, two pairs of abdominal breasts, and two pairs of thoracic breasts.
Puppies often compete for the inguinal teats, where the highest milk production takes place. The milk flows through five to eight holes pierced in each nipple.
The endocrine system of the dog:
The endocrine system of the dog is extremely complex. In human medicine, this science is exercised by specialists called endocrinologists. Here we will just give some information about the main glands of the endocrine system.
The endocrine glands do not have an excretory duct. Their secretions flow directly into the blood, to act on receptors of the body. They are vectors of internal information. The exocrine glands discharge their secretions into the external environment via an excretory canal. For example, the salivary glands are exocrine glands. Hormones activate the natural chemical reactions of the body. They help maintain the internal environment stable.
The pituitary, the size of a pea, is located under the encephalon. It is controlled by the hypothalamus, the pituitary is the true conductor of the entire endocrine system: it controls the secretions of all endocrine glands. Two glands located behind the larynx form the thyroid glands.
The thyroid glands have a role in the metabolism of water. The parathyroids, four in number, appended to the thyroid, regulate the calcium level and the metabolism of the bones. The adrenals are located in front of the kidneys. They secrete adrenaline and regulate the metabolism of carbohydrates and proteins. The pancreas includes an exocrine part, and an endocrine part. The endocrine pancreas secretes insulin, a regulating hormone for sugar in the blood.
Pancreatic tumors can cause hyperglycemia, increased blood sugar levels. The testes and ovaries secrete sex hormones whose roles are multiple: libido, secondary sexual characteristics, maintenance of pregnancy …
The dogs breathing apparatus:
The dog’s breathing apparatus begins with the nose, which is also the organ of olfaction, a very developed and vital sense in dogs. The air then passes into the sinuses, covered by a mucous membrane that protects the posterior airways, and which also plays an important role in the olfaction.
The numerous convolutions of the sinuses make it possible to increase the mucosal-air contact surface, and thus to warm the air and to multiply the olfactory capacities of the dog. The larynx, where the vocal cords fit, connects with the trachea.
The trachea, kept open by cartilaginous rings, extends from the larynx to the lungs. Both lungs are enveloped in the pleura. The trachea branched into many smaller and smaller bronchi forming the bronchial tree. To examine the respirator, the veterinarian uses the stethoscope and x-ray.
He may also perform other examinations after removal from the respiratory tract followed by laboratory tests. Recall that canines, and therefore the dog, decrease the temperature of their body, not by sweating, but by polypnea (acceleration of the respiratory rate).
To cool down, the dog is panting: this increases the flow of air in his airways and cools his body in this way.
The nervous system of the dog:
The nervous system of the dog is the center of control of the functioning of the body. Information goes back to him, and orders emanate from it and follow the nervous pathways to the organs, and to the cell. The nervous system is divided into two parts: the central nervous system, and the vegetative nervous system.
The brain, spinal cord and nerves form the central nervous system. The sensory nerves transmit information to the brain about sensations: hot and cold, pain, smell, and so on. This information is analyzed by the brain, which will give the order to act. The descending information will follow the path of the motor nerves.
In fact, as you can imagine, this phenomenon is extremely complex, and involves a large number of chain reactions. If we add that the functioning of the nervous system interwoven intimately with the precise workings of the other organs, we can have an idea of the multiplicity of the channels of transmission of information in the body.
The vegetative nervous system regulates vegetative life independent of consciousness: breathing, heart beat, digestion …
The nose and the olfaction in dogs:
Olfaction is an extremely developed sense in dogs. The man has understood for a long time since he uses this gift in many activities: hunting, search for missing persons, search for explosives, drugs, etc. If the world of men is above all a world of images, the world of dogs is above all a world of smells.
In the nasal fossae, there are volutes covered by the olfactory mucosa. The greater the area of contact with the air, the better the dog’s flair skills. Long-nosed dogs, like German Shepherds, have more flair than our pet dog friends. The information captured by the olfactory mucosa is transmitted to the brain by the olfactory nerve.
The dog distinguishes odors much better than man , especially the volatile fatty acids, released by the animal fats but also by the secretions of sweat glands (the sweat glands). That’s why it’s often said that dogs smell people who are afraid. The whole social life of the dog is based on smells.
From his birth, it is thanks to the smells that he recognizes his mother and that he finds the nurse breast. Males are able to detect a female in heat several kilometers away.
The eye and the vision in dogs:
Do dogs see the world in the same way as their master? We can ask ourselves the question. In fact, the dog ‘s eye is not very different from the human eye from a constitution point of view. For what he perceives, however, it’s different …
Anatomy of the dog’s eyes
The eyes are protected by the lower and upper eyelids.
The dog also has a third eyelid located at the inner corner of the eye and that is not seen normally.
The eyeball , on its non-transparent part, and the eyelids are lined by the conjunctiva .
The lacrimal glands are located above the eye. They secrete tears that protect the eye against aggression and prevent drying out of the cornea.The dog often encounters pathologies related to excess or lack of tears .
The cornea must remain transparent to allow light to pass. When injured, blood vessels are invaded to promote healing. These ships then disappear.
Finally, the retina is the light-sensitive area: it transmits the light information to the brain via the optic nerve .
The view of the dog
The lens works like a lens , which tends or contracts to focus the light on the retina.
The view of the dog is not very precise . It is a meaning that is not well developed at home, unlike humans. The histological analysis of the dog retina cuts suggests that he can not quite distinguish the colors , even if he does not see them in black and white, as was supposed at one time.
The dog is certainly more sensitive to certain colors than others but his vision of colors is anyway very far from that of the man.
On the other hand, we know that dogs very clearly distinguish movements , and are thus embarrassed if their preys stop.
Ear and hearing in dogs:
Dogs have a hearing very different from ours. Extremely fine, it is twice as developed as that of man. How is it possible ? Are the dogs’ ears similar to ours?
The dog’s ear
To better understand how the dog hears, it’s interesting to see how his ear is structured.
The dog ‘s ear is divided into three parts: the outer ear, the middle ear and the inner ear.
– The outer ear is formed by the deep external auditory canal and the auricle, which is very mobile thanks to the many muscles implanted there. The pavilion can move in all directions of space to capture the least noise. The external auditory canal ends with the eardrum.
– The middle ear contains three small bones – the hammer, the anvil and the stirrup – which transmit the sounds perceived by the eardrum to the auditory cells. The middle ear communicates with the pharynx by the Eustachian tubes.
– The inner ear is a very complex organ that contains both the auditory cells, in relation to the acoustic nerve, and an organ of balance that informs the brain on the position of the body in space. Injury of the inner ear will cause balance disturbances.
The dog’s hearing
The dog’s hearing is finely developed . He can hear both the low chirping of a chick several kilometers away and the lawn mower in the neighbor’s garden.
This is explained by the fact that dogs perceive ultrasound (frequency higher than 20 000 Hz) and infrasound (frequency less than 20 Hz), sound frequencies that range up to 50 000 Hz on average. By way of comparison, human hearing captures between 16 and 20,000 hertz.
It is especially in the inner ear that is the difference with the man. The cochlea, located in the temporal bone 1 and representing the “auditory” part of the inner ear , is provided with many sensory ciliated cells called the organs of Corti . The more there is, the more the ear is able to detect high frequencies . The sound waves from the middle ear then deform the eyelashes under the mechanical action of the liquid inside the cochlea, a process that captures the high frequencies.
On the other hand, the dog has many hair cells at the entrance of the cochlea, near the oval window , one of the passages between the middle ear and the inner ear . The oval window of the dog is 20 times smaller than the tympanum, housed in the middle ear and allows to perceive the ultrasound .
Finally, the difference with the hearing of the man is a physiological peculiarity : the ears of the dog are generally larger (proportionally to the rest of the body) and more mobile than those of the human being, because of their cartilage . The fact of being able to move one’s ears allows the ear to better perceive the sound and consequently, allows the pavilion to fulfill its role of sound box.
The sixth sense in dogs:
We have all heard of a dog that has traveled several hundred kilometers to find his masters. Highly developed sense of smell, remembrance of smells, telepathy, sixth sense , no serious scientific explanation has yet been able to lift the veil on these phenomena.
Dogs perceive natural disasters before humans. They feel the danger. They know if their master has problems. Most dog owners have developed with their animals a complicity in everyday life, so much so that speech becomes useless.
Dogs rub shoulders with us every day but like everyone else, they keep their secrets and mysteries.