Situational task № 1. The diameter of the precapillaries is no more than 4-5 microns, and the diameter of erythrocytes is 6-7 microns, despite this, the erythrocytes pass through the capillaries. Explain the mechanisms of RBC passing through the capillaries. Situational task № 2. In a rabbit, the nerve that innervates the right ear was transected and the upper right cervical sympathetic node was removed. Ear skin temperature was measured shortly after the operation. It turned out that the temperature of the ear skin on the denervation side is 1.5 °C higher than on the opposite intact side. How to explain the increase in ear skin temperature after denervation? Situational task № 3. Patient A., 14 years old, surgical treatment of a bruised wound of the left thigh was done. 6 hours after the wound treatment, unpleasant sensations of numbness and coldness of the extremity appeared. Then the pain was appeared, the intensity of which has been increasing. The skin on the leg became pale. The pulsation on the popliteal artery of the leg and foot was no longer detected. What form of peripheral circulation disorder has developed in the patient? What was its possible cause? What are the mechanisms of development of the above symptoms?

Task 1: The mechanism of RBC passing through capillaries despite their larger size compared to the diameter of the precapillaries is due to the deformability of red blood cells. Erythrocytes are able to change their shape and squeeze through narrow capillaries by deforming their structure. This ability is facilitated by the presence of a flexible cell membrane and the absence of a cell nucleus, allowing the red blood cells to easily change shape and pass through capillaries.

Task 2: The increase in ear skin temperature after denervation can be explained by the loss of sympathetic vasoconstrictor tone. Normally, sympathetic nerves innervate blood vessels in the skin, causing vasoconstriction and regulating blood flow to maintain temperature. When the sympathetic nerves are transected and the sympathetic node is removed, there is a loss of vasoconstrictor tone leading to vasodilation and increased blood flow to the denervated ear skin, resulting in the observed increase in temperature.

Task 3: The patient has likely developed acute arterial occlusion, specifically acute arterial embolism, in the affected leg. The possible cause could be a blood clot or embolus blocking the popliteal artery, leading to a sudden decrease in blood flow to the leg and foot. The symptoms of numbness, coldness, increasing pain, skin paleness, and loss of pulsation are all indicative of ischemia and lack of blood supply to the extremity. The mechanisms of development of these symptoms include tissue hypoxia, accumulation of metabolic waste products, and nerve irritation due to ischemia, leading to the reported symptoms. Immediate medical intervention is necessary to restore blood flow and prevent tissue damage.

Task 1: The rabbit that died from strychnine poisoning is likely the one that was injected with strychnine into the area of inflammation. Inflammatory reactions can increase the absorption and distribution of drugs in the body due to increased blood flow and vascular permeability in the inflamed area. Therefore, injecting strychnine into the inflamed area would lead to a higher systemic absorption of the toxin, resulting in a higher concentration of strychnine in the bloodstream and a higher likelihood of toxicity and death.

Task 2: The negative effect of the heating pad on the bruised knee joint can be explained by the exacerbation of inflammation. Heat application can increase blood flow, leading to increased vascular permeability and the release of inflammatory mediators, causing swelling, redness, and pain. In the case of a bruised knee joint, the heat may have exacerbated the inflammatory response, leading to a worsening of symptoms and delayed healing.

Task 3: Venous hyperemia during inflammation is a result of increased blood flow to the affected area due to vasodilation of the local blood vessels. This increased blood flow helps to deliver immune cells, antibodies, and nutrients to the site of infection or injury, aiding in the clearance of pathogens and promoting tissue repair. However, prolonged venous hyperemia can lead to tissue hypoxia due to impaired oxygen delivery and accumulation of metabolic byproducts, which can contribute to tissue degeneration and atrophy. Despite these potential negative effects, venous hyperemia is a crucial component of the inflammatory response as it helps to mobilize the body's immune defenses and facilitate the healing process.