EXCRETORY SYSTEM

By : Devi Putri T Ditya Anif H

Dodgalih Nur MKafinda Putra

Mudzaffar Khalid

Skin 1. Structure and Function of Skin Human skin is composed of two

main parts, namely epidermis and dermis (corium).

Epidermis The epidermis is composed of the outermost

layers of the skin. It forms a protective barrier over the body's surface, responsible for keeping water in the body and preventing pathogens from entering, and is a stratified squamous epithelium, composed of proliferating basal and differentiated suprabasal keratinocytes. The epidermis also helps the skin regulate body temperature.

The epidermis can be further subdivided into the following strata or layers (beginning with the outermost layer):

Stratum corneum Stratum lucidum (only in palms and

soles. Stratum granulosum Stratum spinosum Stratum germinativum (also called the

stratum basale)

Stratum corneum

The stratum corneum (Latin for horned layer) is the outermost layer of the epidermis, consisting of dead cells (corneocytes) that lack nuclei and organelles. The purpose of the stratum corneum is 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.

Back

Stratum lucidumThe stratum lucidum (Latin for "clear layer") is athin, clear layer of dead skin cells in the epidermisnamed for its translucent appearance under amicroscope. It is found only in areas of thick skin,

most noticeably on the palms of the hands and the soles of the feet. Located between the stratum granulosum and stratum corneum layers, it is composed of three to five layers of dead, flattened keratinocytes. The keratinocytes of the stratum lucidum do not feature distinct boundaries and are filled with eleidin, an intermediate form of keratin.

Back

Stratum granulosum

The stratum granulosum (granular or malphigian layer) 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, protein structures that promote hydration and crosslinking of keratin.

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.

Back

Stratum spinosum

The stratum spinosum (or spinous layer) is a layer of theepidermis found between the stratum granulosum and

stratum basale. This layer is also referred to as the "spinous" or "prickle-cell" layer. This appearance is due to desmosomal connections of adjacent cells. 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 allowing strong connections to form between adjacent keratinocytes.

Back

Stratum germinativumThe stratum basale (basal layer, sometimes referred

to as stratum germinativum) known as Malphigian layer is the deepest layer of the five layers of the epidermis, which is the outer covering of skin in mammals. The stratum basale is a continuous layer of cells. It is often described as one cell thick, though it may in fact be two to three cells thick in glabrous (hairless) skin and hyperproliferative epidermis (from a skin disease). The stratum basale is primarily made up of basal keratinocyte cells, which can be considered the stem cells of the epidermis. They divide to form the keratinocytes of the stratum spinosum, which migrate superficially.Other types of cells found within the stratum basale are melanocytes (pigment-producing cells), Langerhans cells (immune cells), and Merkel cells (touch receptors).

Back

DermisThe dermis is the layer of skin beneath the epidermis

that consists of connective tissue and cushions the body from stress and strain. The dermis provides tensile strength and elasticity to the skin through an extracellular matrix composed of collagen fibrils, microfibrils, and elastic fibers, embedded in proteoglycans.

It harbors many Mechanoreceptors (nerve endings) that provide the sense of touch and heat. It also contains the hair follicles, glandula sudorifera (sweat glands), sebaceous glands (lipid glands), apocrine glands, lymphatic vessels and blood vessels. The blood vessels in the dermis provide nourishment and waste removal from its own cells as well as for the epidermis.

The dermis is tightly connected to the epidermis through a basement membrane and is structurally divided into two areas: a superficial area adjacent to the epidermis, called the papillary region, and a deep thicker area known as the reticular region.

Functions Protection: an anatomical barrier from pathogens and damage

between the internal and external environment in bodily defense; Langerhans cells in the skin are part of the adaptive immune system.

Sensation: contains a variety of nerve endings that jump to heat and cold, touch, pressure, vibration, and tissue injury (see somatosensory system and haptic perception).

Heat regulation: increase perfusion and heatloss, while constricted vessels greatly reduce cutaneous blood flow and conserve heat. Erector pili muscles are significant in animals.

Control of evaporation: the skin provides a relatively dry and semi-impermeable barrier to fluid loss.

Storage and synthesis: acts as a storage center for lipids and water Absorption: oxygen, nitrogen and carbon dioxide can diffuse into the

epidermis in small amounts; some animals use their skin as their sole respiration organ (in humans, the cells comprising the outermost 0.25–0.40 mm of the skin are "almost exclusively supplied by external oxygen", although the "contribution to total respiration is negligible").

Water resistance: The skin acts as a water resistant barrier so essential nutrients aren't washed out of the body.

2. Process (Mechanism) Sweat consists of water vapor. The

excretion of sweat from the skin in the form of water vapor is called perspiration. The components of sweat are water, salt solutes and urea.

Sweat s secreted by the sweat glands whose activity is regulated by temperature controlling center of center nerve system (brain cells) in hypotalamus. The sweat glands absorb water and mineral salt from blood, which are then excreted through skin in the form of sweat.

3. Skin Disorders PsoriasisPsoriasis is a skin disorder that affects at leastone out of every fiftypersons in the United States with both sexes andall age groups involved. The exact cause ofpsoriasis is unknown. Psoriasis is neitherinfectious nor contagious. Psoriasis is more likelyto occur in persons whose family members alsohave this condition; thus part of the cause iscertainly hereditary.

EczemaEczema is one of the most common skin conditions,

affecting people of all ages and both sexes. The terms eczema and dermatitis are often used by doctors to describe the same set of symptoms; irritated, red and itchy inflamed skin.

Tinea versicolorTinea versicolor is a mild, chronic fungal infection of

the outside layer of the skin (stratum corneum) and is usually asymptomatic. Some patients do complain of itching, but this is usually mild and resolves as the rash is treated. The lesions have often a geographic like configuration with a somewhat branny appearance and appear as a discolored area of the body. On untanned skin the rash is pink to brown.