The internal structure of the frog. Features of the structure of the frog

A frog is a typical representative of amphibians. Using the example of this animal, one can study the characteristics of the whole class. This article describes in detail the internal structure of the frog.

Covers of the body

The lake frog lives in water bodies and on their shores. It has a simple external structure - a flat wide head, smoothly turning into a short trunk, a reduced tail, short front legs with four fingers and elongated hind legs - with five. Will help understand the internal structure of the frog pattern, showing the skeleton and the basic system of organs.

First, we study the skin of the animal. The body of the frog is covered with smooth naked skin with a large number of multicellular glands secreting mucus. This secret lubricates the skin, helping to conserve water, promoting gas exchange. In addition, it protects against harmful microorganisms.

The thin and elastic skin of the frog not only protects and perceives external stimuli, but also plays an important role in gas exchange. In addition, the frog absorbs water exclusively through the skin. That's why she needs most of the time in dampness or water.

Skeleton

The structure of the frog skeleton has peculiarities in connection with adaptation to hocks. It consists of a skull, a spine, belts and a skeleton of extremities. Skull flattened, wide. In mature individuals, it retains a large amount of cartilaginous tissue, which makes relatives of frogs with brushhead fishes.

The short spine is represented by four divisions: trunk, sacral, cervical and caudal. The cervical region consists of only one ring-shaped vertebra, but due to its mobility the frog can tilt the head.

The trunk section includes seven vertebrae. There are no ribs in the animal. The sacral section is also represented by a single vertebra, to which the pelvic bones are attached. The last, caudal, section is represented by a long bone, a urostyle, which is formed from 12 fused vertebrae.

The structure of the frog skeleton is interesting due to the features of the formation of the limbs, the belts of which connect the skeletons of the limbs with the spine. The forelimb belt includes the sternum, two shoulder blades, two crow's bones and two clavicles, the foreleg itself consists of the shoulder, forearm and hand and four fingers (the fifth finger is in embryo).

The hindquarters of the hind limbs are more massive than the shoulder one due to the heavy load. It is represented by the fused bones of the pelvis. The skeleton of the hind legs includes a thigh, a shin and a foot with five fingers. The length of the hind legs is two to three times larger than the forelegs.

Musculature

The muscles of the frog can be divided into segmented muscles of the trunk and extremities, part of the muscles of the trunk have a metameric structure (akin to the musculature of fish). Musculature of hind limbs and jaws is especially well developed.

Digestive system

Features of the structure of the frog are clearly visible on the example of the structure of its digestive system. All internal organs of the amphibian are in a coelomic cavity. This is a kind of pouch whose walls consist of epithelial cells. There is a small amount of liquid inside the cavity. Most of the bag is occupied by the digestive system.

The digestive system begins with the oropharyngeal cavity. On its bottom is attached the language that the frog uses to catch insects. Thanks to its unusual structure, it is able to be ejected from the mouth at high speed and to stick a victim to it.

On the palatines, as well as on the lower and upper jaw of the amphibian, there are small conical teeth. They serve not for chewing, but primarily for keeping the prey in the mouth. This is another similarity of the amphibian with the fish. The secret secreted by the salivary glands moistens the oropharyngeal cavity and food. This makes it easier to swallow. There are no digestive enzymes in the saliva of the frog.

The digestive tract of the frog begins with a pharynx. Then follows the esophagus, and then - the stomach. The stomach is located duodenum, the rest of the intestine is laid in the form of loops. Ends the intestines with cloaca. Frogs also have digestive glands - liver and pancreas.

Caught with the help of tongue extraction is in the oropharynx, and then through the pharynx gets through the esophagus into the stomach. Cells located on the walls of the stomach secrete hydrochloric acid and pepsin, which promote digestion of food. Next, the semi-digested mass follows the duodenum, which also pours out the secrets of the pancreas and discharges the bile duct of the liver.

Gradually, the duodenum passes into the small intestine, where all useful substances are absorbed. Remains of food that is not digested, fall into the last section of the intestine - a short and wide rectum, ending in a cloaca.

The internal structure of the frog and its larvae is different. Adult individuals are predators and eat mainly insects, but tadpoles are the most real herbivores. On their jaws there are horny plates, with the help of which the larvae scrape off small algae together with the single-celled organisms living in them.

Respiratory system

Interesting features of the internal structure of the frog also affect breathing. The fact is that, along with the lungs, the amphibian skin filled with capillaries plays a huge role in the gas exchange process. Lungs are thin-walled paired bags with a cellular internal surface and a branched network of blood vessels.

How does a frog breathe? Amphibia uses valves that can open and close the nostrils, and the movements of the bottom of the oropharynx. In order to inhale, the nostrils open, and the bottom of the oropharyngeal cavity descends, and the air is in the mouth of the frog. To make it pass into the lungs, the nostrils are closed, and the bottom of the oropharynx rises. Exhalation is due to the loss of lung walls and movements of the abdominal muscles.

In males, the laryngeal fissure is surrounded by special arytenoid cartilages, to which vocal cords are stretched. High volume of sound is provided by voice bags, which are formed by the mucous membrane of the oropharynx.

Excretory system

The internal structure of the frog, or rather, its excretory system, is also very interesting, since the products of the life of the amphibian can be excreted through the lungs and skin. But most of them are allocated by the kidneys, which are located near the sacral vertebra. Kidneys themselves are oblong bodies, adjacent to the back. In these organs there are special glomeruli capable of filtering out the products of decay from the blood.

Urine in the ureter is excreted into the bladder, where it accumulates. After filling the bladder, the muscles in the abdominal surface of the cloaca contract and the liquid is ejected through the cloaca to the outside.

Circulatory system

The internal structure of the frog is more complex than that of fish. The heart of an adult frog is three-chambered, consisting of a ventricle and two atria. Because of a single ventricle, the arterial and venous blood is partially mixed, the two circles of blood circulation are not completely separated. The arterial cone, which has a longitudinal spiral valve, departs from the ventricle and distributes mixed and arterial blood into different vessels.

In the right atrium, mixed blood is collected: the venous enters from the internal organs, and the arterial blood comes from the skin. Arterial blood enters the left atrium from the lungs.

Atrial contraction is simultaneous, and the blood from both falls into a single ventricle. Due to the structure of the longitudinal valve arterial blood enters the organs of the head and the brain, mixed - to the organs and parts of the body, and the venous blood - to the skin and lungs. It may be difficult for schoolchildren to understand the inner structure of a frog. Scheme of the circulatory system of the amphibian will help to visualize how blood circulation works.

The circulatory system of tadpoles has only one circle of circulation, one atrium and one ventricle, as in fish.

The structure of the frog and human blood is different. Erythrocytes of frogs have a nucleus, an oval shape, and in humans - a biconcave form, the nucleus is absent.

Endocrine system

The endocrine system of the frog includes the thyroid, the sex and pancreas, the adrenal glands and the pituitary gland. The thyroid gland produces hormones necessary for the completion of metamorphosis and maintenance of metabolism, the sex glands are responsible for reproduction. The pancreas is involved in the digestion of food, the adrenal glands help regulate metabolism. The pituitary gland produces a number of hormones that affect the development, growth and coloration of the animal.

Nervous system

The frog nervous system is characterized by a low degree of development, it is similar in characteristics to the nervous system of fish, but has more progressive features. The brain is divided into 5 divisions: middle, intermediate, anterior, oblong brain and cerebellum. The forebrain is well developed and is divided into two hemispheres, each of which has a lateral ventricle - a special cavity.

In connection with the monotonous movements and in general a sedentary way of life, the cerebellum is small in size. The oblong brain is larger. Ten of the nerves come out of the frog's brain.

Sense organs

Significant changes in the sense organs of amphibians are associated with the release from the aquatic environment on land. They are already more complicated than fish, because they should help orient themselves in water and on land. The tadpoles develop lateral line organs.

Painful, tactile and temperature receptors are hidden in the epidermis layer. Papillae in the tongue, palate and jaws function as organs of taste. The organs of smell consist of paired olfactory sacs, which are opened both by external and internal nostrils, into the environment and the oropharyngeal cavity, respectively. In the water, the nostrils are closed, the sense of smell does not work.

As the ear, the middle ear is developed, in which there is an apparatus that amplifies the sound vibrations due to the eardrum.

The structure of the frog's eye is complex, because it needs to be seen both under water and on land. Protect the eyes of adults with mobile eyelids and a blinking membrane. Tadpoles do not have eyelids. The cornea of the frog's eye is convex, the lens is biconvex. Amphibians see far enough and have color vision.