The placental barrier refers to the selective properties of the placenta, as a result of which some substances penetrate from the mother’s blood into the blood of the fetus, while others are retained or enter the fetal body after appropriate biochemical processing.
The barrier separating maternal and fetal blood in the intervillous space consists of the trophoblast epithelium, or syncytium, covering the villi, connective tissue villi and the endothelium of their capillaries.
The barrier function of the placenta can only be performed under physiological conditions. Permeability of the placental barrier to harmful substances and microbes increases with pathological changes placenta resulting from damage to the villi by microbes and their toxins. Placental permeability may also increase due to thinning of the syncytium with increasing gestational age.
The exchange of gases (oxygen, etc.), as well as true solutions through the placental membrane, occurs according to the laws of osmosis and diffusion. This is facilitated by the difference in partial pressure in the blood of the mother and fetus. Proteins, fats, carbohydrates and other substances penetrate the placental barrier in the form of simple compounds formed under the influence of the enzymatic function of the placenta.
Different concentrations of potassium, sodium, phosphorus and other substances are created in the blood of the mother and fetus. Mother's blood, compared to fetal blood, is richer in proteins, neutral fats and glucose.
The fetal blood contains more protein-free nitrogen, free amino acids, potassium, calcium, inorganic phosphorus and other substances.
The placental barrier only partially protects the fetus from the penetration of harmful substances. Drugs, alcohol, nicotine, potassium cyanide, sulfonamides, quinine, mercury, arsenic, potassium iodide, antibiotics (penicillin and streptomycin), vitamins and hormones can pass through the placenta.
On the penetration of substances from maternal blood into fetal blood great influence influences the size of the molecules. At physiological pregnancy substances with a molecular weight below 350 can penetrate through the placental barrier into the fetal blood. In case of pregnancy pathology (toxicosis, ionizing radiation, etc.), as a result of dysfunction of the placental barrier, high-molecular substances (antigens, antibodies, viruses, toxins, etc.) can penetrate into the fetal blood. bacteria, protozoa and helminths).
The human placenta consists of maternal and fetal tissue. The mother's blood vessels flow into the intervillous space, into which the outgrowths of the chorion penetrate. In the latter, in loose tissue, there are fetal vessels.
On the surface washed by maternal blood there is syncytial tissue, the so-called trophoblastic membrane. The exchange of substances between the blood of the mother and the fetus is thus carried out through the following structures: the trophoblastic membrane, the loose tissue of the stroma of the chorion outgrowths, the endothelium of the chorion capillaries. During fetal development, the thickness of these layers is not the same and at the end of pregnancy is only a few microns. The contact area between the surface of the choroidal processes and the mother’s blood is also not constant and in the prenatal period is about 14 m2. IN early periods During pregnancy, the thickness of the barrier is significantly larger, and the surface area is smaller. In this regard, the permeability of the placental barrier for xenobiotics in different terms gestation is not the same. In general, in humans, it constantly increases until the 8th month of pregnancy, and then decreases again. The consequences for the fetus of the penetration of xenobiotics through the placenta are determined by the ratio of the power of toxicant flow through the placental barrier on the one hand, the size of the developing fetus and the state of the dividing and differentiating cells of its tissues, on the other.
Pedigree breeding of dogs Sotskaya Maria Nikolaevna
Placental barrier
Between the mother’s body and the fetus there is a so-called placental barrier. Its functions are aimed at protecting the internal environment of the fetus from the penetration of substances circulating in the mother’s blood that do not have energetic and plastic significance for the fetus and possible immunological aggression of the maternal body, as well as protecting the internal environment of the mother from the penetration of substances that disrupt her homeostasis from the blood fetus
The placental barrier consists of the trophoblast epithelium, syncytium covering the chorionic villi of the placenta, connective tissue of the villi and the endothelium of their capillaries. In the terminal villi, numerous capillaries are located immediately below the syncytium and placental barrier, and consist of two single-cell membranes. It has been established that substances with low molecular weight can mainly enter the blood of the fetus from the mother’s body. There is evidence of the passage of high-molecular substances, antigens, bacteria, viruses, and helminths through the placental barrier. The penetration of high-molecular substances, antigens, and bacteria is observed during the pathology of pregnancy, when the function of the placental barrier is disrupted.
In case of pregnancy pathology, many medicinal substances, as well as products of impaired metabolism penetrate into the blood of the fetus and have a damaging effect on it.
A fracture of the talus is observed in only 0.5% of cases, but all experts classify it as the most dangerous injuries, leading to severe consequences. This is explained by the fact that it is this bone that articulates with the articular surfaces of other bones of the foot and plays an important role in the biomechanics of the talocalcaneal, talonavicular and ankle joints. In addition, it bears the load of the entire body and has a relatively low blood supply, which leads to its slow healing, and in severe cases can cause necrosis of its fragment.
In this article we will introduce you to the causes, varieties, main manifestations and methods of first aid, diagnosis and treatment for fractures of the talus. Having received this knowledge, you will be able to properly provide first aid the victim and ask the doctor all the questions you have about the upcoming treatment.
The talus is small and is located between the calcaneus, fibula and tibia. Not a single muscle is attached to it.
The following parts are distinguished in the talus:
According to statistics, fracture of the body and neck of the bone occurs more often, and in more rare cases - posterior process(more often among football players). Lateral process fractures commonly occur in skateboarders.
The head of the talus connects to the scaphoid bone, its body is forked by the fibula and tibia, and the bottom is in contact with calcaneus. On its posterior process there are two tubercles - medial and lateral. Between them there is a tendon.
Blood enters the talus through the dorsalis pedis, posterior tibial and peroneal arteries.
The talus forms the lower part ankle joint and, unlike other bones of the human skeleton, it is most covered with articular cartilage tissue.
In most cases, a fracture of the talus occurs during sports or during road traffic accidents. Other causes of her injury may include the following factors:
When falling from a height onto your heels, the talus bone is pinched between the calcaneus and tibia. This mechanism of injury results in a compression (or comminuted) fracture.
Severe hyperextension of the foot causes a bone fracture in the neck area. Excessive flexion of the leg at the ankle provokes a fracture of the posterior process. If dorsiflexion is accompanied by a twist of the leg, a fracture of the outer process of the talus occurs.
There are two main mechanisms of such injuries:
The most commonly used classification of talus fractures is:
Like all fractures, a talus fracture can be open or closed.
A fracture of the talus is accompanied by the following symptoms typical of many fractures:
The nature of the manifestations of a fracture of the talus largely depends on the location of its fracture:
Fractures of the neck of the talus in 64% of cases are combined with the medial and other ankle bones or are accompanied by a rupture of the tibiofibular syndesmosis.
A fracture of the talus can lead to the following complications:
In severe cases, such injuries can cause loss of ability to work and disability.
The following factors can influence the development of complications after a fracture of the talus:
To relieve pain, the victim should be given an analgesic in tablet form or given an injection. In case of injuries in the ankle area, it is impossible to determine which bone is broken outside of a hospital setting. This is explained by the nonspecificity of the manifestations of a fracture of the talus. Urgent Care turns out in the same way as with fractures of other bones of this joint:
Remember that failure to promptly consult a doctor for fractures of the talus can lead to its necrosis. In such cases, the patient will need more long-term treatment and rehabilitation.
If signs of a fracture of the talus appear - pain, swelling in the ankle area, deformities - you should immediately consult an orthopedist. To confirm the diagnosis, the doctor will prescribe x-rays in different projections and, if necessary, CT or MRI.
To accurately confirm the diagnosis of a fracture of the talus, radiography is performed in lateral, direct and oblique projections. If necessary, photographs are taken in the Canale and Broden projections. The data obtained allows the specialist to obtain the most full picture injuries and create an effective treatment plan.
If there are questionable results or suspicion of an articular fracture, a CT scan may be recommended to the victim. MRI is performed to detect osteochondral injury to the dome of the foot or avascular necrosis.
Treatment tactics for a fracture of the talus depend on the nature of the fracture. The following techniques can be used for bone fusion:
For simple fractures, the patient is given an immobilizing plaster or polymer bandage in the form of a boot. A metal instep support is inserted into its sole. After applying an immobilizing bandage, the patient is recommended to have an elevated position of the leg, which prevents the development of excessive swelling, and to take painkillers.
The duration of immobilization is individual and depends on many factors - age, complexity of the fracture, the presence of diseases that impede bone healing. Typically, for simple fractures of the talus, a cast is applied for 6 weeks. After it is removed and control images are taken to confirm the fusion of the bone, the patient is allowed a dosed load on the foot by the doctor. Upon completion of a rehabilitation program that includes massage, physiotherapy and therapeutic exercises, all functions of the joint are usually fully restored after 3 months.
If there are displacements, closed reduction must be performed to compare the fragments before applying an immobilizing bandage. This procedure is accompanied severe pain and is carried out only after pain relief - intraosseous anesthesia.
The patient is placed on his stomach, and the orthopedist bends the leg in knee joint. After this, the doctor performs traction by the heel and bends the foot in parallel (with the other hand). When the required result is obtained - comparison of fragments - an immobilizing bandage is applied like a boot. The patient is prescribed painkillers.
After 7 weeks plaster cast remove and apply a new one, but with the foot bent at an angle of 90º. Immobilization lasts up to 4 months from the date of injury. After removing the immobilizing bandage and taking control photographs, the patient is allowed dosed loads on the limb and a rehabilitation program is drawn up.
Indications for performing open reduction – osteosynthesis – for fractures of the talus may be the following cases:
Surgical treatment of talus fractures should be carried out as soon as possible. early dates– in the first 8 hours after injury. Sometimes urgent interventions are performed.
The following surgical techniques can be used for open reduction of the talus:
After completion surgical intervention an immobilizing bandage is applied. Immobilization of the limb is not carried out only after compression-distraction osteosynthesis, since the rod apparatus is capable of fixing the leg in the required position.
IN postoperative period the patient is prescribed painkillers and antibiotic therapy for prevention purulent complications. When using a pin device, the sites where the pins are inserted are treated daily with antiseptic solutions.
After 7 days of limb immobilization, the patient is allowed early and strictly dosed movements in the joint. More full load on an injured leg is allowed after 3 months.
Experts attach great importance during the rehabilitation period after a fracture of the talus physical therapy. The recovery time of the talus and surrounding vessels depends on the age of the patient, the complexity of the injury and the presence of diseases that interfere with bone fusion. That is why the possibility and timing of the start of rehabilitation are prescribed by a doctor, who is guided by the data of X-ray images. For each patient, an individual program is drawn up to restore the functions of the ankle and toe joints.
