Integument & Special Senses PDF

# Integument The integument is the outer covering of the body. It consists of the skin and its glands, hair, footpads, and claws. ## Skin The skin is the external surface of the body. It serves as a complete barrier against the external environment. ### Composed of Three Layers: * **Epidermis*...

# Integument The integument is the outer covering of the body. It consists of the skin and its glands, hair, footpads, and claws. ## Skin The skin is the external surface of the body. It serves as a complete barrier against the external environment. ### Composed of Three Layers: * **Epidermis** * **Dermis** * **Hypodermis** (subcutaneous layer) ### Functions * **Protection**: Protects the body from external environment and pathogens. * **Sensory**: Detects touch, temperature, and pain. * **Secretion/Excretion**: Secretes sweat and sebacceous fluids. * **Production**: Produces Vitamin D. * **Storage**: The hypodermis stores fat. * **Pigmentation**: Produces melanin, which protects the skin from UV light. ## Footpads The epidermis of the footpads is thickened and hairless. Adipose tissue in the dermis forms the digital cushion. Dogs have an epithelial layer that is arranged in conical papillae, giving a rough feel. Cats have a much smoother epithelial surface. ## Nose/Rhinarium The nose is hairless and contains keratin to give additional toughness. It is heavily pigmented for UV protection. ## Claws Claws are composed of: * **Unguicular Crest**: The claw covering the unguicular process. * **Unguicular Process**: The base of the claw. * **Extensor Tendons**: Extend the claw. * **Middle Phalanx**: The middle bone of the digit. * **Tendon of Deep Digital Flexor**: Flexes the middle phalanx. * **Flexor Tubercle**: A small bump on the middle phalanx. * **Distal Phalanx**: The tip of the claw. * **Digital Pad**: The pad below the claw. ## Hair Hair is composed of: * **Hair Follicle**: The structure that holds the hair root. * **Hair Bulb**: The base of the hair follicle. * **Hair Root**: The portion of the hair that anchors the hair to the skin. * **Hair Shaft**: The visible portion of the hair. * **Arrector Pili Muscle**: A small muscle that contracts to raise hair. * **Pore of Sweat Gland Duct**: The opening of the sweat gland. * **Sebaceous Gland**: Secretes an oily substance that lubricates the hair and skin. * **Eccrine Sweat Gland**: Secretes sweat. * **Pacinian Corpuscle**: A sensory receptor that detects pressure and vibrations. ## Dermis The dermis is the middle layer of the skin. It is composed of dense connective tissue that is vascular. It contains nerve fibers, nerve endings, and elastic fibers, along with hair follicles and sweat and sebaceous glands. ## Hypodermis The hypodermis is the deepest later of the skin. It is a subcutaneous (s/c) layer composed of loose connective tissue and fat. # Functions of the Integument ## Protection The integument protects the body from the external environment and prevents entry from pathogens. ## Maintenance of Homeostasis The integument helps to maintain homeostasis through: * Conserving water * Maintaining body temperature. ## Excretion The integument excretes materials through the sebaceous glands and sweat glands ## Synthesis of Vitamin D The integument synthesizes Vitamin D3 from UV light. The liver converts Vitamin D3 into a compound used to synthesize calcitriol. Calcitriol is a hormone that regulates absorption of calcium and phosphorus from the intestines. ## Storage The integument stores fat for energy reserves. ## Sensation Sensory receptors within the dermis detect chemical, mechanical, and thermal stimuli, protecting the animal from injury and damage. ## Pigmentation Melanocytes (junction of dermis and epidermis) produce melanin, which protects the animal from UV light. # Epidermis The epidermis is the superficial, avascular layer of the skin. ## Stratified Squamous Epithelium The epidermis is composed of stratified squamous epithelium. The epidermis consists of five layers: * **Stratum Corneum**: The outermost layer of keratinized cells that are constantly being sloughed off. Keratinization is complete in this layer. * **Stratum Lucidum**: A thin layer of cells that have lost their nuclei. This layer is only present in thick skin, such as on the palms of the hands and soles of the feet. * **Stratum Granulosum**: A layer of cells that contain granules of keratohyalin. This layer is responsible for synthesizing keratin. * **Stratum Germinativum**: The deepest layer of the epidermis, also known as the basal layer. This layer contains stem cells that continuously divide to produce new epidermal cells. * **Stratum Spinosum**: A thick layer of cells that are connected by desmosomes. This layer also contains keratinocytes. # Special Senses ## Eye The eye is a specialized sense organ that detects light. It consists of three layers: * **Sclera**: The tough outer layer of the eye that maintains the shape of the eye. * **Uvea**: The middle layer, also known as the vascular layer. It consists of the choroid, ciliary body, and iris. * **Retina**: The innermost layer of the eye that contains photoreceptor cells that convert light into nerve impulses. ### Eye Position The eye position in animals is dependent on their environment. * **Predators**: Cats and dogs have a front-facing eye position that allows them to accurately judge distances. * **Prey**: Rabbits and Guinea pigs have side-facing eye positions. ### Vitreous Humor The vitreous humor is a jelly-like substance that fills the space between the lens and the cornea, maintaining the shape of the eye and providing nutrients. ### Aqueous Humor The aqueous humor is a watery fluid that fills the space between the cornea and the iris. It provides nutrients and helps to maintain the shape of the eye. ### Forea The fovea is a depression in the retina where the field of vision is focused and becomes concentrated. ### Vitreous Body The vitreous body contains vitreous humor. This humor makes up 80% of the volume of the eye. ### Lacrimal Gland The lacrimal gland produces tears, which spread across the eye via blinking. Tears drain through the punctum lacrimale and into the nasal cavity. ## The Eye Diagram The eye is composed of the following structures: * **Posterior Chamber**: The space between the lens and the cornea. * **Anterior Chamber**: The space between the cornea and the iris. * **Vitreous Humor**: A jelly-like substance that fills the space behind the lens. * **Choroid**: The pigmented layer that contains blood vessels and supplies the internal structures. * **Sclera**: The protective outer layer that maintains the shape of the eye. * **Pupil**: The opening in the iris that allows light to enter the eye. * **Lens**: A transparent structure that focuses light onto the retina. * **Cornea**: The clear front portion of the eye that helps to focus light. * **Iris**: The colored part of the eye that controls the amount of light entering the eye. * **Ciliary Muscle**: A muscle that controls the thickness and shape of the lens. * **Suspensory Ligaments**: Ligaments that support the lens. * **Conjunctiva**: A thin membrane that covers the front of the eye and helps to lubricate and protect the eye. * **Retina**: The innermost layer of the eye that contains photoreceptor cells that convert light into nerve impulses. * **Optic Nerve**: The nerve that carries nerve impulses from the retina to the brain. ## Eyeball The eyeball is composed of three layers: * **Sclera**: The tough, fibrous outer layer that maintains the shape of the eye. * **Uvea**: The middle vascular layer that supplies nutrients. * **Retina**: The innermost layer containing photoreceptor cells. ### Cornea The cornea is the transparent, anterior part of the eye. It has a poor blood supply but is well supplied with nerve fibers. The cornea is the first part of the eye to be hit by light, focusing light on to the retina. ### Choroid The choroid is the darkly pigmented, vascular layer of the eye that lies adjacent to the retina. It contains blood vessels that supply the internal structures and prevent light from escaping. ### Tapetum Lucidum The tapetum lucidum is a triangular area of yellow-green iridescent light-reflecting cells in the choroid. This structure reflects light back to the photoreceptor cells, improving night vision – hence the "eye shine" when headlights are pointed at animals. ### Ciliary Body The ciliary body is a smooth muscle, a continuation of the ciliary body, that controls the thickness and shape of the lens by adjusting tension on the suspensory ligaments. ### Suspensory Ligaments The suspensory ligaments are radial and circular muscle fibers that surround the lens. They support the lens and help to focus light. ### Iris The iris is the colored part of the eye that controls the amount of light entering the eye by regulating the size of the pupil. The pupil appears black because the choroid is opaque and darker than the iris. The pigmented cells in the iris give the eye its color, and the nerve supply is via the oculomotor nerve. ## Retina The retina is the innermost layer of the eye containing photoreceptor cells that detect light. It is closest to the choroid and has an agumented layer that prevents light leaking into the eyeball. ### Photoreceptor Cells The photoreceptor cells are responsible for detecting light. * **Rods**: Rods detect black and white and are used for night vision - responsible for 95% of our vision. * **Cones**: Cones detect color and are used for daytime vision. They are responsible for 5% of our vision. ### Bipolar Neurons Bipolar neurons transmit information from the rods and cones to the next layer, the ganglion cells. ### Ganglion Cells Ganglion cells are the nerve cells in the retina whose axons travel along the retina to the optic disc. The optic disc marks the location where the optic nerve leaves the eye and contains no rods and cones, creating a “blind spot." ## Formation of an Image The formation of an image can be considered as a four-step process: 1. **Light Rays**: Light rays from an object pass: * **Through the Cornea and Pupil**: The cornea bends the light rays, and the pupil controls the amount of light entering the eye. * **Through the Lens**: The lens focuses the light rays on to the retina. The curvature of the lens is adjusted by the ciliary muscle. * **Through the Retina**: The photoreceptor cells on the retina detect the light rays. Some light is reflected back by the tapetum lucidum to stimulate more photoreceptor cells. 2. **Nerve Impulses**: The light rays are converted into nerve impulses that travel along the optic nerve to the brain. 3. **Optic Chiasma**: Some of the nerve impulses cross to the opposite side of the brain at the optic chiasma, so that each cerebral hemisphere receives information from both eyes. 4. **Visual Cortex**: The nerve signals are then carried to the visual cortex of the cerebral hemispheres where they are interpreted as an image. * The image formed on the retina is an inverted and smaller image of the original object, but the brain automatically inverts it. * Predators have a narrow field of view and a wide area of binocular vision. * Prey have a wide field of view and a narrow area of binocular vision. # Ear The ear is the organ of hearing and balance. It is divided into three parts: * **External Ear**: The outer ear consists of the pinna/auricle, the external acoustic meatus (EAM), and ceruminous glands. * **Middle Ear**: The middle ear consists of the tympanic membrane, the tympanic cavity, and the auditory ossicles. * **Inner Ear**: The inner ear consists of the cochlea, the vestibule, and the semicircular canals. ## External Ear The external ear consists of: * **Pinna/Auricle**: The external part of the ear. It directs soundwaves towards the EAM. * **External Acoustic Meatus (EAM)**: The canal leading to the eardrum. * **Ceruminous Glands**: Secretes earwax which traps foreign materials. ## Middle Ear The middle ear consists of: * **Tympanic Membrane**: The eardrum, which separates the external ear from the middle ear. It vibrates in response to soundwaves and transmits these vibrations to the auditory ossicles. * **Tympanic Cavity**: The air-filled space behind the eardrum that contains the auditory ossicles. * **Auditory Ossicles**: Three small bones (malleus, incus, and stapes) in the tympanic cavity, connected by synovial joints to transfer vibrations from the eardrum to the inner ear. ## Inner Ear The inner ear lies within the petrous temporal bone. It contains the cochlea, the vestibule, and the semicircular canals. ### Cochlea The cochlea is a snail-shaped structure that is filled with a fluid called endolymph. ### Vestibule The vestibule is a structure containing two sac-like structures called: * **Utricle**: The central part of the vestibule. * **Saccule**: A smaller, spherical sac lying beneath the utricle. ### Semicircular Canals The semicircular canals are three canals filled with a fluid called endolymph, connected to the vestibule by the ampulla. Ampullae contain sense organs – “crista” – that sense motion. ### Membranous Labyrinth The membranous labyrinth is a network of interconnected tubes filled with endolymph. It contains all parts of the inner ear: the cochlea, the vestibule, and the semicircular canals. # Vestibulocochlear Nerve (Auditory Nerve) The vestibulocochlear nerve is a cranial nerve that carries information from the inner ear to the brain. It is made up of two branches: * **Cochlear branch**: Carries sensory information about sound from the cochlea. * **Vestibular branch**: Carries sensory information about balance from the vestibule and semicircular canals. # Taste (Gustation) Taste buds are the primary organs for flavor. They are located on the tongue, soft palate, and epiglottis. Chemicals dissolve in saliva and stimulate the taste buds. Sensory signals travel via the glossopharyngeal nerves and the vagus nerve. # Touch Touch receptors are found in the skin. There are different types of touch receptors, each designed to detect a specific type of stimulation: * **Pain receptors**: Free nerve endings in the epidermis detect pain stimuli. * **Heat/cold receptors**: Encapsulated in the dermis, they are bulbous corpuscles that detect heat (bulbs are “hot”) and cold. * **Pressure receptors**: Lamellar corpuscles that detect pressure. * **Touch receptors**: Meniscoid corpuscles, found in the dermis and epidermis. # Smell (Olfaction) Smell is detected by numerous olfactory nerves that pass through tiny holes in the ethmoid bone. These nerves are directly connected to the olfactory lobe in the brain. Molecules dissolved in mucus lining the nasal passage stimulate the olfactory nerve endings. ## Vomeronasal Organ (Jacobson’s Organ) The vomeronasal organ is also known as Jacobson’s organ. It is associated with the Flehmen response in dogs, and it's involved in detecting pheromones. ## Dogs Dogs have tightly coiled nasal conchae, which increases the surface area of the nasal cavity, heightening their sense of smell.