Organs Skin (Cross Section)

Stratum Corneum

This is the outermost layer of the epidermis, consisting of dead cells (corneocytes). This layer is composed of 15–20 layers of flattened cells with no nuclei and cell organelles. Their cytoplasm shows filamentous keratin. These corneocytes are embedded in a lipid matrix composed of ceramides, cholesterol, and fatty acids. The stratum corneum functions to form a barrier to protect underlying tissue from infection, dehydration, chemicals and mechanical stress. Desquamation, the process of cell shedding from the surface of the stratum corneum, balances proliferating keratinocytes that form in the stratum basale. These cells migrate through the epidermis towards the surface in a journey that takes approximately fourteen days.

Stratum Granulosum

This is a thin layer of cells in the epidermis. Keratinocytes migrating from the underlying stratum spinosum become known as granular cells in this layer. These cells contain keratohyalin granules, which are filled with histidine- and cysteine-rich proteins that appear to bind the keratin filaments together. Therefore, the main function of keratohyalin granules is to bind intermediate keratin filaments together. At the transition between this layer and the stratum corneum, cells secrete lamellar bodies (containing lipids and proteins) into the extracellular space. This results in the formation of the hydrophobic lipid envelope responsible for the skin’s barrier properties. Concomitantly, cells lose their nuclei and organelles causing the granular cells to become non-viable corneocytes in the stratum corneum.

Stratum Spinosum

The stratum spinosum (or spinous layer/prickle cell layer) is a layer of the epidermis found between the stratum granulosum and stratum basale. Their spiny (Latin, spinosum) appearance is due to shrinking of the microfilaments between desmosomes that occurs when stained with H&E. Keratinization begins in the stratum spinosum. This layer is composed of polyhedral keratinocytes. They have large pale-staining nuclei as they are active in synthesizing fibrilar proteins, known as cytokeratin, which build up within the cells aggregating together forming tonofibrils. The tonofibrils go on to form the desmosomes, which allow for strong connections to form between adjacent keratinocytes.

Blood Capillary

The blood capillaries are where the important functions of the circulation take place: the exchange of material between circulation and cells. Capillaries are the smallest of the body’s blood vessels. They are only one cell thick, and they are the sites of the transfer of oxygen and other nutrients from the bloodstream to other tissues in the body, they also collect carbon dioxide waste materials and fluids for return to the veins. They connect the tiny muscular branches of arteries, called arterioles, with tiny veins (called venules). Ultimately, the capillary is the site of internal or cellular respiration and is responsible for the utilization of oxygen by the tissue and the transporting of carbon dioxide as waste to the veins for elimination by the lungs. The arterial blood system branches extensively to deliver blood to over a billion capillaries in the body. The extensiveness of these branches is much more readily appreciated by knowing that the capillaries provide a total surface area of 1,000 square miles for exchanges of gases, waste, and nutrients between blood and tissue fluid. Oxygen rich blood flows from arterioles or small branches of the artery into the capillary bed and the pressure inside of the arteries is roughly fifty times that on the inside of the veins. It is this pressure difference that forces the blood into the capillary bed. Although the amount of blood flowing through a particular capillary bed is determined in part by a small circular muscle around the arteriole branches, the absence of smooth muscle and connective tissue layers permits a more rapid rate of transport between the blood and the tissue. Source

Sensory Nerve Fiber

The somatic nervous system includes the sensory and motor nerves that innervate the limbs and body wall. Sensory nerve fibers in the peripheral nerves are the peripheral axonal process of neurons in the dorsal root ganglion. The motor axons are the processes of anterior horn cells of the spinal cord. Source

Hair Follicle

The hair follicle is a dynamic organ found in mammalian skin. It resides in the dermal layer of the skin and is made up of 20 different cell types, each with distinct functions. The hair follicle regulates hair growth via a complex interaction between hormones, neuropeptides and immune cells. This complex interaction induces the hair follicle to produce different types of hair as seen on different parts of the body. For example, terminal hairs grow on the scalp and lanugo hairs are seen covering the bodies of fetuses in utero and in some new born babies. The process of hair growth occurs in distinct sequential stages. The first stage is called anagen and is the active growth phase, catagen is the resting stage, telogen is the regression of the hair follicle phase, exogen is the active shedding of hair phase and lastly kenogen is the phase between the empty hair follicle and the growth of new hair. The function of hair in humans has long been a subject of interest and continues to be an important topic in society, developmental biology and medicine. Of all mammals, humans have the longest growth phase of scalp hair compared to hair growth on other parts of the body. For centuries, humans have ascribed esthetics to scalp hair styling and dressing and it is often used to communicate social or cultural norms in societies. In addition to its role in defining human appearance, scalp hair also provides protection from UV sun rays and is an insulator against extremes of hot and cold temperatures. Differences in the shape of the scalp hair follicle determine the observed ethnic differences in scalp hair appearance, length and texture. There are many human diseases in which abnormalities in hair appearance, texture or growth are early signs of local disease of the hair follicle or systemic illness. Well known diseases of the hair follicle include alopecia or hair loss, hirsutism or excess hair growth and lupus erythematosus.

Arrector Pili Muscle

The arrector pili muscles are small muscles attached to hair follicles in mammals. Contraction of these muscles causes the hairs to stand on end, known colloquially as goose bumps. Each arrector pili is composed of a bundle of smooth muscle fibres which attach to several follicles (a follicular unit) and is innervated by the sympathetic branch of the autonomic nervous system. The contraction of the muscle is then involuntary–stresses such as cold, fear etc. may stimulate the sympathetic nervous system, and thus cause contraction. Contraction of the muscles has a number of different purposes. Its principal function in the majority of mammals is to provide insulation: air becomes trapped between the erect hairs, helping the animal retain heat. Erection of the porcupine’s long, thick hairs causes the animal to become more intimidating, scaring predators. Pressure exerted by the muscle may cause sebum to be forced along the hair follicle towards the surface, protecting the hair.

Hair Follicle Receptor

A hair plexus or root hair plexus is a special group of nerve fiber endings and serves as a very sensitive mechanoreceptor for touch sensation. Each hair plexus forms a network around a hair follicle and is a receptor, which means it sends and receives nerve impulses to and from the brain when the hair moves. Endings of sensory nerve fibers which form a plexus around a hair follicle in hairy skin. They are mechanoreceptors conveying touch sensation. Specifically, crude touch and pressure sensation conveyed through the anterior spinothalamic tract. The plexus acts as a receptor.

Hair Root

The part of a hair that is embedded in the hair follicle, its lower succulent extremity capping the dermal papilla pili in the deep bulbous portion of the follicle. Source

Hair Shaft

The part of the hair seen above the skin is called the hair shaft. The hair shaft is made up of dead cells that have turned into keratin and binding material, together with small amounts of water. This structure explains why we do not feel any pain whilst our hair is being cut. The hair shaft is formed of three layers: The medulla – the deepest layer of the hair shaft, only seen in large and thick hairs. The cortex – the middle layer of the hair shaft which provides the strength, colour and texture of a hair fibre. The cuticle – the outer layer of the hair shaft is thin and colourless. It serves as protection to the cortex.

Sweat Gland Pore

In terms of structure sweat glands can be divided into three distinct regions: 1) the coiled secretory portion that lies in the deeper layer of the skin or dermis, 2) the duct or hollow tube that passes through the dermis and to the outermost layer of the skin called the epidermis and, 3) the final portion of the duct which spirals its way through the epidermis giving rise to the surface pore, also called the acrosyringium. Each one of these portions or segments of the sweat gland have a specific function: 1) as its name implies, the secretory segment is responsible for the production of sweat – without the hard work of these little sweat gland components, we would all be in serious trouble: our bodies would heat up (hyperthermia) and damage to our vital organs would result. 2) during its passage through ductal portion of the gland, sweat is desalinated by cells that line the duct. In other words, salty elements such as sodium and chloride are reabsorbed to render a significantly less salty or hypotonic solution 3) the acrosyringium is the least active part of the sweat gland – it serves as a conduit for perspiration’s final journey to the surface of the skin. Source

Dermal Papilla

The dermal papilla is a structural formation located in the uppermost layer of the dermis. It can be found throughout the body, and its primary purpose to hook up the epidermis (the outermost layer of skin) to a blood supply. In terms of hair anatomy, dermal papilla in the scalp provides oxygen and nutrients to the hair follicle itself so that healthy new hairs may grow. The dermal papilla provides nutrition by extending from the dermis into the hair bulb. The hair bulb is a formation at the bottom of the hair follicle itself, and it is the structure responsible for sprouting the hair shaft up the follicle, past the scalp. Once the dermal papilla connects to the hair bulb, the hair may receive oxygen from the blood supply and continue its three phases of growth (anagen, catagen, and telogen). If the DP fails to reach the hair bulb, however, the phases are interrupted, and new hairs will not be able to grow. This only has to happen as little as one time before the hair follicle is rendered permanently useless. ATP is the bioorganic process in which oxygen is converted from the bloodstream into usable energy. Almost every area of the body utilizes ATP, even the hair. ATP is what gives hair the energy to grow. One of the major hurdles of hair transplantation is keeping the hair graft alive outside of the body, where it is unable to receive nutrition from the DP (Dermal Papilla). Source

Dermis

Is the lower or inner layer of the two main layers of cells that make up the skin. The dermis contains blood vessels, lymph vessels, hair follicles, and glands that produce sweat, which helps regulate body temperature, and sebum, an oily substance that helps keep the skin from drying out. Sweat and sebum reach the skin’s surface through tiny openings in the skin that act as pores. Source

Eccrine Sweat Gland

Eccrine sweat glands are smaller sweat glands. They are coiled tubular glands that discharge their secretions directly onto the surface of the skin. The most numerous types of sweat glands in our skin, found almost everywhere on the body, are called eccrine glands. These are the true sweat glands in the sense of helping to regulate body temperature. In other words, sweating causes the loss of body heat and thus cools us down on a hot day or when performing strenuous exercise. This is because as the water in sweat evaporates, it takes body heat with it. Source

Sebaceous Oil Gland

The fatty sebaceous gland is to lubricate the skin. This prevents the loss of moisture. In turn, the skin remains moisturized and flexible. Without sebum the skin would dry and lacerate easily. Dry patches are more prone to infection, as pathogens are able to penetrate through broken skin. This proves the importance of sebum in keeping the skin intact. Source

Vein

When blood has been pumped by the heart to various parts of the body, it must return back to the heart. The veins serve the purpose of delivering the blood back to the right atrium (chamber) of our heart. In the heart, blood will collect more oxygen and prepare to be pumped back out through arteries. This is a cycle that continues as long as a person is living. The largest vein in the body is called the vena cava, which is Latin for ‘hollow vein.’ There are two sections of the vena cava, one below the heart and one above it. The section above the heart is called the superior vena cava, and it returns blood from the head, neck, chest, and upper limbs back to the heart. You can remember this term by associating the word ‘superior’ with ‘above.’ The lower section is called the inferior vena cava, and it returns blood from all other parts of the body back to the heart. Similar to the aforementioned example, ‘inferior’ can be associated with ‘below.’ As we get farther away from the heart and toward extremities, veins branch out and get smaller and smaller. The smallest veins are called venules. Source

Artery

An artery is a vessel that carries blood away from the heart and toward other tissues and organs. Arteries are part of the circulatory system, which delivers oxygen and nutrients to every cell in the body. Source

Fat Tissue

Adipose tissue, or fat, is an anatomical term for loose connective tissue composed of adipocytes. Its main role is to store energy in the form of fat, although it also cushions and insulates the body. Adipose tissue is primarily located beneath the skin, but is also found around internal organs. The integumentary system comprises the skin and its appendages acting to protect the body from various kinds of damage, such as loss of water or abrasion from outside. The integumentary system includes hair and nails. In the integumentary system, which includes the skin, it accumulates in the deepest level, the subcutaneous layer, providing insulation from heat and cold. Source

Papilla Of Hair

Pacinian Corpuscle

Touch receptors known as Pacinian corpuscles occur under the skin, being abundant particularly around muscles and joints. Local pressure exerted at the surface or within the body causes deformation of parts of the corpuscle, a shift of chemical ions (sodium or potassium), and the appearance of a receptor potential at the nerve ending. This receptor potential, on reaching sufficient strength, acts to generate a nerve impulse within the Corpuscle (nerve endings in the skin responsible for sensitivity to vibration and pressure). Skin contains many sensory receptors. Pacinian corpuscles are the most obvious as they form large under the microscope. The outer layers are composed of flattened cells, collagen fibers and a lymph-like fluid. Pacinian corpuscles are sensitive to mechanical and vibratory pressure. Sou rce