The Integumente are an integral part of the plant seeds of seed plants. There are Hüllschichten which encircle the Nucellus. After fertilization, the Integumente to Testa.
They leave a small opening, the Mikropyle freely through which the scar on the subject with the pollen in the pollen tube fertilization hindurchwächst.
Showing posts with label integumentary. Show all posts
Showing posts with label integumentary. Show all posts
EPIDERMIS
The epidermis contains 2 major and 2 minor cell populations specialized for specific functions. Major populations include the keratinocytes and melanocytes. Minor populations include Langerhans' and Merkel's cells.
A. Keratinizing System: The keratinocytes make up most of the epidermis. They participate in the continuous turnover (renewal) of the skin surface by passing through 4 overlapping processes: cell renewal, or mitosis; differentiation, or keratinization; cell death; and exfoliation (the sloughing of dead cells from the skin surface). The entire process takes 15-30 days and occurs in waves. A cell layer produced by a mitotic wave in the basal layer undergoes keratinization in synchrony. Each wave pushes the cell layers produced in earlier waves toward the surface. The layers from several waves, each at a different depth and step in the process, give a stratified appearance to vertical sections of the epidermis. The 5 layers of the epidermis are distinguished by the shape, staining properties, contents, and orientation of the keratinocytes they contain.
A. Keratinizing System: The keratinocytes make up most of the epidermis. They participate in the continuous turnover (renewal) of the skin surface by passing through 4 overlapping processes: cell renewal, or mitosis; differentiation, or keratinization; cell death; and exfoliation (the sloughing of dead cells from the skin surface). The entire process takes 15-30 days and occurs in waves. A cell layer produced by a mitotic wave in the basal layer undergoes keratinization in synchrony. Each wave pushes the cell layers produced in earlier waves toward the surface. The layers from several waves, each at a different depth and step in the process, give a stratified appearance to vertical sections of the epidermis. The 5 layers of the epidermis are distinguished by the shape, staining properties, contents, and orientation of the keratinocytes they contain.
GENERAL FEATURES OF THE SKIN
A. General Functions: The skin is the largest and heaviest organ. It protects against microorganisms, toxic substances, dehydration, ultraviolet radiation, impact, and friction. It also acts as a sensory receptor and has a role in excretion, vitamin D metabolism, and regulation of blood pressure and body temperature.
B. General Organization: Human skin (the integument) is of 2 types. Thick skin, restricted to the palms of the hands and soles of the feet, lacks hairs and has abundant sweat glands. Thin skin, which has hairs, covers the rest of the body. Thick or thin, the skin consists of 2 distinct but tightly attached layers, the epidermis and dermis, which are underlain by the hypodermis.
1. Epidermis. This outer (superficial) layer of skin, composed of keratinized stratified squamous epithelium, derives from embryonic surface ectoderm. It is avascular, receiving nourishment from vessels in the underlying dermis. Its only innervation is by unencapsulated (free) nerve endings. The epidermal layer is further divided into 5 stratea; these layers, in order from superficial to deep, are the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. The thickness of these layers differs in thick and thin skin.
2. Dermis, This inner (deeper) layer is a vascular connective tissue of mesodermal origin. It can be further divided into a superficial papillary layer and a deeper reticular layer. The papillary layer contains extensive capillary networks, which nourish the epidermis. The reticular layer contains many arteriovenous anastomoses that help regulate blood pressure and body temperature. It is richly supplied with free nerve endings, a variety of encapsulated sensory receptors, and autonomic fibers that control the vascular smooth muscle. Even in thick skin, the dermis is much thicker than the overlying epidermis.
3. Hypodermis, Although not a part of the skin, this layer of mesoderm-derived loose connective and adipose tissue underlying the dermis flexibly binds the skin to deeper structures. Its thickness varies, depending on nutritional status, level of activity, body region, and gender. The hypodermis is also called the subcutaneous fascia and, where thick enough, the panniculus adiposus
Structures Associated With the Skin: Glands (sebaceous and sweat), hairs, and nails arise from epidermal downgrowths into the dermis during embryonic development. These structures, which are mainly of epithelial origin, require epitheliomesenchymal interactions between the epidermis and dermis for their formation and maintenance
B. General Organization: Human skin (the integument) is of 2 types. Thick skin, restricted to the palms of the hands and soles of the feet, lacks hairs and has abundant sweat glands. Thin skin, which has hairs, covers the rest of the body. Thick or thin, the skin consists of 2 distinct but tightly attached layers, the epidermis and dermis, which are underlain by the hypodermis.
1. Epidermis. This outer (superficial) layer of skin, composed of keratinized stratified squamous epithelium, derives from embryonic surface ectoderm. It is avascular, receiving nourishment from vessels in the underlying dermis. Its only innervation is by unencapsulated (free) nerve endings. The epidermal layer is further divided into 5 stratea; these layers, in order from superficial to deep, are the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. The thickness of these layers differs in thick and thin skin.
2. Dermis, This inner (deeper) layer is a vascular connective tissue of mesodermal origin. It can be further divided into a superficial papillary layer and a deeper reticular layer. The papillary layer contains extensive capillary networks, which nourish the epidermis. The reticular layer contains many arteriovenous anastomoses that help regulate blood pressure and body temperature. It is richly supplied with free nerve endings, a variety of encapsulated sensory receptors, and autonomic fibers that control the vascular smooth muscle. Even in thick skin, the dermis is much thicker than the overlying epidermis.
3. Hypodermis, Although not a part of the skin, this layer of mesoderm-derived loose connective and adipose tissue underlying the dermis flexibly binds the skin to deeper structures. Its thickness varies, depending on nutritional status, level of activity, body region, and gender. The hypodermis is also called the subcutaneous fascia and, where thick enough, the panniculus adiposus
Structures Associated With the Skin: Glands (sebaceous and sweat), hairs, and nails arise from epidermal downgrowths into the dermis during embryonic development. These structures, which are mainly of epithelial origin, require epitheliomesenchymal interactions between the epidermis and dermis for their formation and maintenance
Subscribe to:
Posts (Atom)