The 'Hormone Neurotensin' is a peptide found in the central nervous system and the gastrointestinal tract. In the gut, its primary functions include: MCQ with Answer and Explanation

Explanation:
Smooth muscle is non-striated, involuntary, and forms the muscular layer of the digestive tract (esophagus, stomach, intestines), responsible for peristalsis. Skeletal muscle is voluntary and striated, cardiac is heart-specific.

Explanation:
The Blood-Brain Barrier (BBB) is formed by tight junctions between endothelial cells in brain capillaries, making it highly selective. It allows the free diffusion of small, lipid-soluble molecules and essential gases. Therefore, oxygen, carbon dioxide, and lipid-soluble substances (like alcohol, nicotine, and some anesthetics) easily cross. Glucose, a water-soluble molecule essential for brain energy, crosses via specific carrier-mediated transport (GLUT1 transporters). Large proteins, peptides, most water-soluble drugs, and pathogens like bacteria and viruses are generally blocked from entering the brain parenchyma.

Explanation:
Urobilin (urochrome) is a breakdown product of bilirubin, giving urine its characteristic yellow color. Bilirubin is in bile, hemoglobin in red blood cells, melanin in skin. Dark yellow urine indicates concentrated urine due to dehydration.