Keratin is an intracellular fibrous protein that gives hair, nails, and skin their hardness and water-resistant properties. The cells in all of the layers except the stratum basale are called keratinocytes. Note the significant difference in the thickness of the epithelial layer of the thick skin. These slides show cross-sections of the epidermis and dermis of (a) thin and (b) thick skin. "Thick skin" is found only on the palms of the hands and the soles of the feet. It is made of four or five layers of epithelial cells, depending on its location in the body. The deeper layer of skin is well vascularized (has numerous blood vessels). Gynecomastia is primarily due to an imbalance between estrogen and testosterone levels, specifically a change in the ratio of estrogen to testosterone. It causes ductal tissue, connective tissue and fat to enlarge, leading to the appearance of female-like breasts. This study was conducted in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of the University Hospital of Padova (approval no. AOP2648) for studies involving human tissues. These continuous hormonal fluctuations in the female population have more clinical relevance, leading to cyclic modulation of fascial tension in response to periodic hormone variations. Unlike women, who experience marked fluctuations in sex hormone levels during the menstrual cycle, pregnancy, and menopause, men typically maintain more stable androgen levels throughout adulthood, with a gradual decline during aging. Physiological levels of testosterone attenuate profibrotic activity in cardiac fibroblasts by enhancing nitric oxide (NO) production . The inhibition of MMP-2 activity by testosterone contributes to the attenuation of ECM remodeling, which is crucial for maintaining tissue integrity and preventing fibrosis . Collagen I expression decreased from 6% in the follicular phase to 1.9% in the periovulatory phase, whereas collagen III and fibrillin levels increased, reflecting a shift towards a more elastic ECM composition during ovulation .
