HUMAN MEDICAL BIOLOGY, ANATOMY, PHYSIOLOGY AND PATHOLOGY - Y.I. Fedoniuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

CHAPTER 3. ANATOMICAL AND PHYSIOLOGICAL ASPECTS OF BODY FUNCTION SELF-REGULATION

GENERAL ISSUES IN THE ANATOMY AND PHYSIOLOGY OF SENSORY SYSTEMS

SKIN (THE ORGAN OF TOUCH, TEMPERATURE, AND PAIN SENSATION)

2. SKIN APPENDAGES

Skin Appendages include Hair, Nails, Sebaceous Glands, Sweat Glands, and Mammary Glands.

Hair is an epidermal derivative. It consists of a shaft, which projects above the skin surface, and a ROOT. The root terminates in an expansion called the hair bulb, which is responsible for hair growth. The root is embedded in the dermis within a Connective Tissue follicle into which the duct of a sebaceous gland opens. Hair color depends on the presence of pigment. When pigment disappears and air accumulates within the hair shaft, it turns gray.

Nails are horny plates resting upon a connective tissue nail bed. A nail comprises a root located in the nail groove, a body, and a free edge that extends beyond the nail bed.

Sebaceous glands are located between the two layers of the dermis. Their ducts open into the hair follicle. In areas devoid of hair (such as the transitional zone of the Lips and the glans Penis), sebaceous gland ducts open directly onto the skin surface. Sebaceous glands are absent on the palms and soles. Sebum lubricates the skin and hair, protecting them against excessive moisture and microorganisms.

Sweat glands are situated in the Deep Layer of the dermis. Their ducts open onto the skin surface. Along with Water, sweat glands excrete Metabolic waste products, such as urea, certain salts, and uric acid. They are particularly abundant in the axillary and inguinal regions.

The mammary gland (mamma) is a paired organ that embryologically represents a modified sweat gland, located at the level of the III to VI Ribs on the fascia overlying the pectoralis major Muscle. In childhood, the mammary gland is underdeveloped, and in males, it remains in this state throughout life. In females, its intensive development begins during Puberty, driven by the hormonal function of the Ovaries. During the Climacteric period (ages 45–55), as ovarian hormonal activity declines, the glandular tissue of the breast is replaced by adipose tissue. During reproductive maturity, the female mammary gland consists of 15–20 lobes resembling small glands that radiate outward from the nipple, which is situated on the anterior surface of the gland slightly below its center. Connective and adipose Tissues are interspersed between these small glandular units. The gland ducts open at the apex of the nipple, forming dilations known as lactiferous sinuses. The mammary gland achieves its full development during Pregnancy. The skin of the nipple and the surrounding pigmented area (areola) contains a considerable number of Blood Vessels, nerve endings, and smooth muscle Cells. Pituitary, ovarian, and other endocrine Hormones, as well as neural reflex mechanisms, play a major role in regulating Mammary Gland Function.