In biology, the term “integument” refers to a network of properties that make up an organism’s covering. The integument defines the boundaries of the organism’s body, insulating it from its surroundings and shielding it from outside elements. It communicates with the outside world, allowing an organism to survive in a particular environment.
The integument is “a substance or coating that covers or includes the parts of the organism.” This can be a membrane, cuticle, or skin that covers a layer on the organism or a particular part. The integument, for example, is any secretion made by an organism to cover itself or the cell membrane in unicellular organisms like bacteria or protozoans.
In contrast, the integument in vertebrates is made up of different derived components, including hair, feathers, and scales.
Table of Contents
- Integument – Meaning and Definition
- Human Integumentary System
- Functions of Integument
- Frequently Asked Questions (FAQs)
Integument – Meaning and Definition
Integument comes from the Latin word “integumentum,” which means a covering. Integumentary is the adjective form of integument. Below are definitions of the term integument according to anatomy and botany:
In anatomy, the largest organ in humans and vertebrates is the integument. It carries out a variety of essential tasks, such as insulation, thermoregulation, secretion, sensation, and protection against viruses, chemicals, and abrasive damage.
In botany, the ovule’s integuments are its outer layer(s), and when the ovule matures after fertilisation, they turn into the seed coat. Angiosperms typically have two layers of integument, whereas gymnosperms often have one.
Components
The cell membrane and any covering it secretes constitute unicellular organisms’ integuments. The exterior cell wall of almost all bacteria helps to protect them by keeping the cells rigid and in shape. However, multicellular invertebrates only have one outer layer of epithelial cells. These cells can create a wide range of surface coverings, from the mucous coat of cnidarians (sea anemones, polyps, and jellyfish) to the hard cuticle of insects.
In terms of composition and extent, the noncellular coatings of invertebrate integuments are incredibly diverse and comprise many taxonomic groups. However, in arthropods such as insects, crustaceans, and spiders, a multilayered and hardened integument creates an exoskeleton to which muscles are linked. These rigid structures may serve only as protective armour for these creatures.
Human Integumentary System
The integumentary system is the group of organs that composes the body’s outer layer and protects it against several dangers such as infection, abrasion, desiccation, chemical attack, and radiation injury. In humans, the integumentary system includes the skin, a thickened, keratinised epithelium consisting of several cell layers and is largely water-resistant.
In addition to the skin, the integumentary system also consists of the hair and nails, which are skin-derived organs. They protect the body from danger, detect its surroundings, and support its homeostasis.
The Skin
The largest and heaviest organ of the body is the skin. It has numerous layers, each with a different function, and covers the entire body surface. There are three primary layers in it:
- Epidermis: The epidermis is the skin’s outermost layer. It is thin and continuously sheds dead skin cells.
- Dermis: The middle layer of the skin is the dermis. It has sweat glands, blood vessels, nerves, and hair follicles.
- Subcutaneous Layer: The innermost layer of skin is the subcutaneous layer. It comprises connective tissue and fat that connects the skin to the muscles beneath it. It provides insulation and cushion.
The skin serves as a physical barrier and the first line of defence against illnesses brought on by microorganisms. It also contains components of the innate and adaptive immune systems. Its main functions are to control body temperature, remove waste, and protect the body from disease and injuries.
Glands
Cells that function as a unit to discharge a substance such as sweat or oil are called glands.
The body has two different types of glands. Since the endocrine glands lack a duct system, they immediately release their substances into the blood. In contrast, the skin is hosted by various exocrine glands with ducts that enable them to discharge chemicals onto the epithelial surface. Some of these exocrine glands are:
- Apocrine Sweat Glands: Odorous perspiration is produced by these glands. Large, branching glands often develop in the genital region and armpits. They do not play a significant role in cooling.
- Eccrine Sweat Glands: Its function is to cool the body and excrete waste by water secretion. These primary, coiling, tube-like glands are found all over the body. They produce clear, little-to-no oily, and odourless perspiration.
- Sebaceous Glands: These glands release sebum, an oily material that hydrates and protects the skin.
- Ciliary Glands: They are modified apocrine sweat glands that are found in the eyelids. They lubricate the eye and keep it clean.
- Ceruminous Glands: These ear canal glands are also modified apocrine glands responsible for producing ear wax. The ear is protected from water and unwanted objects by ear wax, a sticky material.
- Mammary Glands: The front of the chest wall includes two mammary glands. The glands produce milk to nourish newborns in individuals assigned female at birth.
Hair
The epidermis produces thin thread-like structures called hair. They are generally pigmented, which gives them their colour and are made of a protein called keratin.
Except for the palms of the hands and the soles of the feet, the entire body is covered in hair. Hairs provide defence against UV rays, wounds, and extreme temperatures. They also contribute to the sensation since they have nerve endings that can feel temperature, pressure, and touch.
Nails
The upper surface of the fingers and toes are protected by hard, bony structures called nails. They develop from the base of the nail bed and are made of a protein called keratin.
Nails promote fine motor functions like picking up small things and protect the finger tips from harm.
Integuments in Invertebrates
Cnidarians
The epidermis in cnidarians provides all the essential components of an integument. It may also contain pigment cells, gland cells, stinging cells, sensory cells with projecting hairs, and epithelial cells, some of which may be contractile.
Protozoans
Protozoan-secreted coats range in hardness from soft forms like that of Amoeba, to forms with a cuticle that can be made of cellulose or protein like that of Monocystis (plantlike flagellates).
Flukes and Roundworms
The parasitic flukes have a relatively thick integument covered in sensory papillae, microvilli, an apical membrane thrown into pits and ridges, and many spines. Roundworms have an epicuticle that is thick and flexible and has three easily recognisable zones.
Arthropods
Arthropods have the most complex exoskeleton structures (insects and crustaceans). Chitin creates a flexible yet robust cuticle in the integument of caterpillars.
Functions of Integument
Integument serves as an intermediary between the organism and environment that it belongs to. The integument serves essential functions like:
- Offers physical protection against bacteria and pathogens.
- Absorbs physical impact and helps heal cuts, abrasions, and other wounds.
- Protects our body from infection and cushions it.
- Protects us from sunburn and ultraviolet (UV) rays from the sun.
- Secretes sebum, perspiration, and other bodily waste.
- Keeps us cool by controlling our body’s temperature.
- Helps us sense cold, heat, and other feelings.
- Synthesises vitamin D.
The skin, glands, hair, and nails comprise the integumentary system. It collaborates with other biological systems to protect the body from injury and maintain homeostasis.
The integumentary system can be impacted by several disorders, including ringworm, psoriasis, skin cancer, athlete’s foot, cold sores, and skin cancer.
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