Overview
The skin (cutis) covers the whole body surface and is continuous with the mucous membranes at the natural openings. It works as a physical, chemical and microbiological barrier, takes part in thermoregulation and in the perception of touch, temperature, pain and itch, and stores water, electrolytes and fat. In the cat it is thin, elastic and very loosely attached to the underlying tissue, especially over the dorsal neck (the "scruff").
Layers
- Epidermis: keratinised stratified squamous epithelium without blood vessels. In the haired skin of the cat it is thin; it becomes much thicker on the pads and the nasal planum.
- Dermis: connective tissue with collagen and elastic fibres; it holds vessels, nerves, hair follicles, arrector pili muscles and glands.
- Hypodermis (tela subcutanea): loose connective tissue with fat, which lets the cat's skin slide widely.
Hair and glands
- Compound hair follicles: one primary hair surrounded by several secondary hairs leave through the same opening. Grooming with the tongue, which is covered in horny papillae, removes dead hair.
- Vibrissae (pili tactiles): long tactile hairs with a venous sinus around the follicle and a rich nerve supply. On the face: muzzle (whiskers), supraorbital, genal and mandibular. On the thoracic limb, the carpal vibrissae on the palmar side of the carpus.
- Sebaceous glands: open into the follicles. They are well developed on the chin and lips, the eyelids and the dorsal tail base (tail gland or supracaudal organ); their secretion is used for scent marking when the cat rubs.
- Sweat glands: apocrine in all haired skin; eccrine only in the pads, which sweat with heat and stress. The cat does not lose heat by sweating; panting is a warning sign.
- Others: cats lack the circumanal (hepatoid) glands of the dog. The anal sacs open on each side of the anus. Females have four pairs of mammary glands.
Specialised regions
- Nasal planum: hairless and heavily keratinised.
- Pads (tori): digital pads, one metacarpal or metatarsal pad and, on the thoracic limb, a carpal pad.
Clinical relevance
- Injection-site sarcoma: aggressive mesenchymal tumour arising where vaccines or other injectable drugs were given. Vaccination in the distal limbs or tail rather than the interscapular region is recommended, and any mass that persists for more than three months, is larger than 2 cm or is still growing one month after injection should be biopsied (3-2-1 rule).
- Dermatophytosis: infection by Microsporum canis, common in kittens and long-haired cats (Persians); it is a zoonosis.
- Eosinophilic granuloma complex: indolent ulcer of the upper lip, eosinophilic plaque and eosinophilic granuloma, often with an allergic basis.
- Others: chin acne, tail gland hyperplasia ("stud tail") in intact males, squamous cell carcinoma on the ears, eyelids and nasal planum of white cats exposed to sun, and mammary tumours, most of which are malignant.
- Routes of administration: subcutaneous injections are given into the loose skin; the site of each vaccine should be recorded.