서면피부과 Your skin’s inner layer, Dermis, contains blood vessels, oil and sweat glands, hair follicles and nerves. It offers support and elasticity.
It also houses touch receptors (meissner corpuscles) and naked nerve endings. The latter extend into epidermis in ridges called papillae and give the skin an undulating appearance. It is thin in the papillary dermis and thicker in the reticular dermis.
Connective tissue is one of the four primary types of tissues found in the human body, along with epithelial, muscle and nervous tissues. It serves to connect different parts of the body together and hold other tissues in place. It also serves to separate organs from each other and encase them in a protective sac, as is the case with the three meninges that envelop the brain and spinal cord.
It is important to note that connective tissue can take on very varying forms. The most basic form is loose ordinary connective tissue, also known as areolar connective tissue. This type of connective tissue has a sampling of all the typical connective tissue cells and fibers, but in moderate proportions.
Loose connective tissue is differentiated from dense connective tissue by the structure of the fiber bundles. Dense connective tissue can be regular (with neatly arranged bundles of collagen fibers) or irregular (with multidirectional fibers such as that in tendons and ligaments). There is also elastic connective tissue, which is dominated by wavy elastic fibers, and is seen in the walls of large blood vessels, yellow ligaments and the lungs.
Blood vessels flow blood throughout the body, carrying oxygen and nutrients to tissues that need them, and delivering waste products back to the blood for transport to the kidneys. Larger blood vessels, including arteries and veins, have thick muscular walls that adjust to maintain their pressure and control blood flow. The walls of smaller blood vessels, including capillaries, are much thinner and less muscular.
The blood vessel walls are made of several layers, called tunics, named after garments first worn by ancient Romans. The inner layer, the tunica intima, consists of a thin layer of simple squamous epithelium glued to a basement membrane with polysaccharide molecules.
The middle layer, the tunica media, is a thick area of areolar connective tissue with bands of smooth muscle cells that contract to regulate blood flow. The outer layer, the tunica externa, is a substantial sheath of connective tissue with groups of elastic fibers that help hold the vessel in position. The walls of the smallest blood vessels, capillaries, are leaky, allowing materials to pass from the blood into body tissues and vice versa.
A tiny, oily gland found everywhere on the skin except the palms of hands and soles of feet, the sebaceous gland secretes a thick liquid called sebum that keeps the skin lubricated. Sebum is made by a glandular cell (sebocyte) in the dermis, and it also contains a waxy substance called triglyceride.
Each pore on the skin is connected to a hair follicle, which contains both a hair and an oil gland (sebaceous gland). Together, these structures form what is called a pilosebaceous unit. Each hair follicle also has an exit canal. The sebaceous gland and the hair follicle are connected by a short duct, which is sometimes visible as a small bump on the skin surface. The ducts empty sebum into the hair follicle, where it is picked up by the hair and carried to the scalp or other parts of the body.
The c-myc gene controls the development of both the epidermis and sebaceous glands, and the hedgehog pathway controls the differentiation of sebocytes. The prescription drug isotretinoin decreases the output of sebum by inhibiting c-myc expression. It also increases the effectiveness of topical treatments for acne.
Hair follicles are tube-shaped structures that hold and grow your hair. They’re located in the top layers of your skin, the epidermis and dermis. The four key components of a hair follicle are the papilla, germinal matrix, hair bulb and internal root sheath.
The papilla is at the base of the hair follicle and consists of connective tissue that holds blood vessels that nourish growing hairs. The follicle has a “stocking” that surrounds the papilla and the germinal matrix. The follicle has a cup in which the hair grows known as the infundibulum. The follicle also has arrector pili muscles and sebaceous glands.
The papilla has large nerve fibers that are innervated by autonomic nervous fibers. These fibers are primarily sympathetic cholinergic. They send visual and pheromonal signals that cause your skin to blush or emit body odor when stimulated. In addition, they regulate blood flow into the epidermis to conserve or dissipate heat.
Nerves connect the skin to other tissues and organs. They also carry sensory and motor information throughout the body in the form of electrical impulses. They’re classified as either afferent, which send signals from the peripheral nervous system to the central nervous system or efferent, which transmits signals from the central nervous system to muscles and glands.
There are hundreds of peripheral nerves in the body. Each one has a sleeve of fatty tissue, called the perineurium, around it. Then, each nerve is divided into bundles of axons, which are bundled together and wrapped in a layer of connective tissue, called the epineurium.
Each axon is coated by cells called Schwann cells. These cells wrap each axon in a fatty substance, called myelin, which helps the axons conduct electrical impulses faster.
Each spinal nerve is associated with a dermatome, which is a specific area of the body served by that particular nerve. A single spinal nerve may divide into anywhere from 2 to 30 peripheral nerves. Sensory nerves relay messages from the skin and internal organs back to the brain and spinal cord, while motor nerves help control involuntary or partially voluntary movements.