Integumentary System Flashcards
Functions of the Integumentary system
- Protection against external agents ultraviolet rays, and water loss (desiccation)
- Regulate temperature and ions-water balance
- Calcium homeostasis because of vitamin D synthesis in the sebaceous gland
- Sensory appreciation;
5.fat storage. –> in hypodermis ( not apart of skin technically)
Clinical examination of the skin reveals…
Clinical examination of the skin reveals ectoparasites and internal disease processes resulting from endocrine and nutritional disorders.
General Organization of the skin
Made of two components: epidermis and dermis.
Beneath the dermis lies hypodermis (subcutaneous tissue, site for sc injections) that contains loose CT filled with fat and is not considered part of the skin.
Epidermis
Thickness varies from among areas of the body; generally, thin in hairy skin.
The 5 layers of epidermis from inner to outer
- Stratum (S) basale (germinativum)
- S spinosum (basale and spinosum combined termed the malpighian layer)
- S granulosum
- S lucidum,
- S corneum
Mitotic Cells
Mitotic cells are limited in the Basale and Spinosum layers, continuously divide, and replace cells in other layers, which are then shed as horny cells from the surface of the S corneum.
Tonofilaments
Cells in the S spinosum have thick keratin bundles called tonofilaments, which terminate at desmosomes
(note, thick skin has a thicker S spinosum and more abundant tonofilaments and desmosomes, which protect against friction and pressure).
Keratohyalin granules
Cells in the S granulosum contain non-membrane bound, basophilic, keratohyalin granules that become a part of the keratin; and membrane-bound lamellar granules, whose content is released in the intercellular space where it serves as a seal between skin cells.
What epidermis layer is absent in thin skin
Stratum Lucidum
Keratin
Is a filamentous protein, which is present in all epithelial cells, but is more abundant in skin cells (keratinocytes).
Epidermal Cell types
Keratinocytes
Melanocytes
Langerhans Cells
Merkel’s Cells
Keratinocytes
Synthesize soft keratin and are continuously replaced by mitotic cells in the malpighian layer.
Protect from invading organism and dehydration
Melanocytes
- Neural crest cells in origin
- Found in the malpighian layer and hair follicles
- Posses dendritic like processes, which insinuate between keratinocytes
- protection from UV light
The process of melanin synthesis.
Melanocytes synthesize melanin (only melanocytes can synthesize melanin because they contain tyrosinase enzyme that is essential for converting tyrosine amino acid, after a series of reactions [dopa, dopaquinone] into melanin).
- After synthesis, melanin granules are transferred into keratinocytes in the malpighian layer.
(Note, keratinocytes do not synthesize melanin, but they contain melanin)
How does the process of melanin synthesis differ among races.
Numbers of melanocytes do not differ among races,
what differs is the ability of melanocytes to synthesize melanin and transfer melanin into keratinocytes
Albinism
Albinos lack tyrosinase enzyme and thus their melanocytes cannot synthesize melanin and melanin protects against ultraviolet rays (that is why albinos are more prone to skin cancers)
Melanoma
Melanoma are malignant growth of melanocytes.
Langerhans Cells
Macrophages
Antigen-presenting cells, originate from monocytes, present antigens to T lymphocytes and thus play a role in the immunological skin reactions.
Merkel’s Cells
Sensory mechanoreceptors, present in the thick skin, and are richly innervated by free nerve endings.
Dermis
An important part of our daily-use leather goods; contains two layers:
1. Papillary layer
2. Reticular layer
Papillary Layer
Papillary layer is composed of loose CT, contains all CT cell types and abundant blood supply, and constitutes major part of the dermal papilla.
Reticular Layer
Reticular layer is composed of dense irregular CT, more fibers (mainly type I collagen, also a network of elastic) and fewer cells than the papillary layer; contains smooth muscle (arrector pilorum), nerve fibers (vasomotor, pilomotor, sudomotor), and receptors (touch, heat, cold, pressure).
Hypodermis
Subcutaneous tissue
Consists of loose CT that contains large blood vessels, nerves, skin glands, and is filled with fat cells, especially in thick skin (foot pad). Note, it corresponds to the superficial fascia filled with formaldehyde in the embalmed animals, not a part of the skin, site for sc injections.
Integumentary Blood Supply
Deep or subcutaneous plexus
Deep or subcutaneous plexus
Present in the hypodermis, formed by large blood vessels.
Middle of cutaneous plexus
Associated with hairs and glands of the dermis.
Superficial or subpapillary plexus
Supplies papillary layer and epidermis.
Superficial arteriovenous anastomoses
Thermoregulatory structures, present in the papillary layer of the pig and man but are absent in other domestic species.
This explains why pig’s skin is a good model to study skin diseases in human.
Skin Glands
Sebaceous and sweat
Sebaceous
- Scattered all over the body, except in the foot pad
- Associated with hair follicle, except in the lip, penis and vulva
- Cells are aggregated to form alveoli with no apparent lumen, cells near the base divide and cells near the apex die and release their entire contents (holocrine secretion);
- The secretion (sebum) lubricates hair shaft, protects skin from drying, diminishes water loss, and contains precursor to vitamin D.
- Examples: infraorbital, inguinal, and interdigital regions of sheep; the base of the horn of goats; anal sacs of cats; the prepuce and circumanal region of dogs.
Sweat
Present in the lower dermis or hypodermis.
Two types:
Eccrine (merocrine)
Apocrine
Eccrine (merocrine)
Develop independently from hair follicles and thus open via a long duct directly on the skin surface, secretory cells are cuboidal to columnar that surround a narrow lumen; active throughout life; secretion is watery and functions in heat and ion regulation.
Apocrine
Apocrine: associated with hair follicles and thus they open into hair follicles above the opening of the sebaceous gland; low cuboidal cells with or without apical protrusions surrounding a wide lumen; secretion is viscous, seasonal, and becoming active with puberty. Myoepithelial cells surround secretory cells of sweat glands.
Species Variation
Sweat glands are absent in rats, rabbits, and birds; are poorly developed in dogs and pigs (hence of little use in thermoregulation).
Species Variation Apocrine
Distributed throughout the skin in most domestic species; they secrete profusely in the horse, while the secretion is scant in most other species; least active in goats and cats.
Function: is to produce a viscous secretion that serves as a sex attractant in some species and to regulate temperature, especially in the horse and cattle.
Species Variation Merocrine
Present in the foot pads of dogs and cats, the frog of horse hoofs, the planum nostrale and carpal glands of pigs, and the planum nasolabial of the cattle.
What controls sweating in all domestic species except for horse
Sweating is under the control of sympathetic cholinergic nerve fibers in all domestic species
What controls sweating for horses
Sweating is under the control of sympathetic adrenergic fibers.
Hair
Thread-like epidermal structures distributed evenly in the horse and cow, arranged into groups forming hair beds in the pig, dog, and cat; each hair bed contains two to four clusters of hair follicles and has one principal (guard) hair and three to nine auxiliary (wool) surrounding hairs.
Hair growth and replacement
Hair is formed by germinal matrix covering the dermal papilla, growth is cyclic: anagen (active growth), catagen (involution), telogen (resting). Hair color is created by melanocytes present in the germinal matrix covering the dermal papilla.
Complete Hair consists of
Hair shaft
Hair root
Hair follicle
Hair bulb
Dermal Papilla
Arector pili
Hair Shaft
Free threadlike part above the skin and consists of medulla, cortex and cuticle
Hair Root
Portion of hair beneath the skin
Hair follicle
A sheath covering the root consists of following parts: CT sheath, glassy membrane, external root sheath (continuation of stratum germinativum), and internal root sheath (composed of Henle’s layer, Huxley’s layer with trichohyalin granules, and cuticle).
Hair Bulb
The hair bulb is the terminal expanded part of the hair follicle in which hair is rooted. It is indented by a dermal papilla, which contains blood vessels that are necessary for sustaining and growth of the hair.
Arector Pili
Arrector pili is a bundle of smooth muscle attached at an angle to the CT sheath of the hair follicle and thus its contraction in response to cold or fear or anger is responsible for hair elevation.
Types of hairs
Cover hairs: most common as described above; wool hairs: form the fleece of sheep and goat; tactile hairs: thick and long, contains blood sinus between outer and inner layers of CT sheath, is highly innervated, examples include whiskers in carnivores.
Hair growth and replacement
Hair is formed by germinal matrix covering the dermal papilla, growth is cyclic: anagen (active growth), catagen (involution), telogen (resting).
Hair color is created by melanocytes present in the germinal matrix covering the dermal papilla.
