Answer:
C) Release of von Willebrand factor (vWF) from the endothelium, not the epithelium.
Explanation:
Hemostasis is the physiological process of reparation and maintenance of a blood vessel to stop excess loss of blood in case of vascular injury. This process occurs in four stages:
- Vascular Injury i.e. a breach in the endothelial barrier. This results in the dislodge of endothelial cells, exposing the collagen fibers underneath.
- Vascular constriction or vasoconstriction is the constriction of the blood vessels to prevent excessive blood loss.
- Platelet plug formation involves the aggregation and adhesion of platelets to the endothelium.
- Coagulation
Platelet plug formation occurs by the adhesion of circulating platelets to the collagen fibers that have been exposed by dislodging of the endothelial cells. The endothelium, as well as the platelets release a ligand known as the von Willebrand factor (vWF). This molecule acts as a relay or bridge between the integrin receptors on the platelets and the exposed collagen fibers.
Platelets also release chemicals to attract more platelets to the wound site, resulting in more vWF release. This results in more and more platelets adhering to the endothelium, leading to platelet plug formation.
Hibernation helps animals survive the changing seasons. Foods that bears eat, such as berries and flowers, are much less available during cold winter months. When they hibernate, bears enter a deep sleep. ... While they sleep, the bears can survive because their bodies live off of their stored fat or food.
During hibernation, the animal’s body temperature, heart rate and breathing rate all drop to significantly lower levels. Animals do this to survive the winter because the weather is cold and food is scarce. It is advantageous because these animals can quite literally shut themselves off for weeks at a time rather than try and survive through harsh weather conditions.
While many people think bears are hibernators, they actually participate in a similar, though not exact, practice. Instead of hibernating, bears fall into a deep sleep called torpor. During torpor, heart rate and breathing rate decreases, body temperature reduces slightly and bears do not eat or release bodily waste. Bears can sleep more than 100 days without eating, drinking, or passing waste!
Bears sleep in dens that they make themselves, as well as in hollow trees, caves and dens built by other bears. A den can be built in 3–7 days, however, the timing of den building varies from bear to bear. While some bears build their dens months before hibernation season, others choose to excavate their dens.
These animals can dramatically drop their body temperature to below freezing—salty body fluids work to prevent tissue crystallization in particularly cold temperatures.
So really, animals that are true hibernators don’t actually sleep through the entire winter.
The urea produced by their fat metabolism is broken down and the nitrogen is re-used by the bear to rebuild protein.
