Human fear responses to certain stimuli, such as darkness, heights, deep water, and blood, can often arise despite the absence of direct negative experiences. This phenomenon is rooted in evolutionary psychology, which posits that humans have developed a predisposition to fear stimuli that historically posed significant survival threats. This predisposition, known as preparedness, suggests that early humans who developed a fear of potentially dangerous entities, such as venomous snakes and...

Bones are dynamic organs that require a rich supply of oxygen and nutrients. Around 5% to 10% of the cardiac output supplies blood to the bones. A typical long bone has three main sources: the nutrient artery, the metaphyseal and epiphyseal arteries, and the periosteal arteries.
Nutrient Artery
The nutrient artery is the main blood vessel that enters the diaphysis via the nutrient foramen. While most long bones have only one nutrient foramen, large bones, such as the femur, may have two. This...