The Integumentary System, Anatomical Terms, and Other Random Stuff

VTMD 206

Integument

• A physical barrier between your insides and the outside world

• A shield against impact, abrasion, water gain/loss, heat gain/loss, radiation, invasion by pathogens/parasites/predators, etc.

Elements include:

• Skin

• Hair

• Skin glands

• Nails

• Claws

• Hooves

• Horns

• Feathers

• Blood vessels in the skin

• Nerves in the skin

Protection, Thermoregulation, Hydration, Sensory Organ, Communication

Functions of the Integument (5)

Epidermis

External Layer of Skin

• Keratinized

  • Forms a resistant layer

• Limited physical strength

  • Can be scratched off

• Resistant to friction

  • Thick in areas of the body where there is a lot of friction

• Inhibits diffusion

  • Impermeable barrier to environment, therefore helps to sustain homeostasis

• Sustains homeostasis

• No blood supply

• Innervated (but poorly)

• : The outermost layer of the skin provides protection against environmental
  factors, such as pathogens, UV radiation, and chemicals. It also supplies hair follicles,
  and sweat glands.

Dermis

Inner Layer of the Skin

• Strong

• Collagen rich

  • Forms a matrix, adds to strength

• Vascular

• Well innervated

• Cannot maintain homeostasis

• Structure that supports, nourishes, and, to some degree, regulates the epidermis and appendages

• Contains blood vessels responsible for thermoregulation, nerve plexuses for cutaneous sensation (incl. T), and myelinated and unmyelinated nerves

• Motor nerves in the ____ innervate blood vessels and arrector pili muscles

  • Except horses, epitrichial glands not innervated

• Sensory nerves are distributed in the dermis, hair follicles, and specialized tactile structures. These nerves allow the skin to respond to the sensations of touch, pain, itch, heat, and cold

• Located beneath the epidermis, the dermis contains blood vessels, nerve
  endings. It plays a crucial role in regulating body temperature and providing structural
  support to the skin

Subcutis (subcutaneous layer/hypodermis/superficial fascia)

Layer Below the Dermis

NOT part of the integument

• Layer of loose connective tissue underneath the dermis that allows it to move overtop of underlying tissues

• Sometimes thin muscle inside this layer

  • Ex. Cutaneous trunci muscle - role in skin twitching

• This layer lies beneath the dermis and
  consists of fat and connective tissue. It acts as insulation and energy storage, helping to
  regulate body temperature and providing cushioning

Transverse Plane

Plane of the Body

• divides the body into cranial and caudal portions / Divides the body into surfaces at right angles (90 degrees) to the long axis

Dorsal (frontal) Plane

Plane of the Body

• divides the body into dorsal and ventral portions / Divides the body into surfaces parallel to the ground

Median Plane

Plane of the Body

• divides the body down the center into symmetrical halves / Divides the animal's body into left and right halves. A median plane runs through the midline

Sagittal Plane

Plane of the Body

• divides the body into left and right portions, parallel to median plane / Divides the body into surfaces parallel to the median plane

Cranial

Directional Term

Towards the head / Refers to the direction towards the head of the animal. For example, the shoulder is cranial to the hip

Caudal

Directional Term

Towards the tail / Indicates the direction towards the tail or posterior end. The tail is caudal to the head

Rostral

Directional Term

Indicates the direction towards the nose of the animal when referring to the head. The eyes are cranial to the ear

Dorsal

Directional Term

towards back/upper surface / Pertains to the back of the animal, or the front part of the limb. The spine is located dorsal to the abdomen

Ventral

Directional Term

towards the belly/underside / Relates to the belly of the animal. The abdomen is the ventral to the spine

Medial

Directional Term

towards the middle of the body/towards the midline / Describes a structure closer to the midline of the animal's body. The heart is medial to the rib cage.

Lateral

Directional Term

towards the side of the body/away from the midline / Signifies a structure farther away from the midline, such as the limbs being lateral to the body

Plantar

Directional Term

ventral/bottom/underside surface of hind limb / Structures toward the rear of the distal (below tarsus) hindlimb/hind paw/hind hoof.

Palmar

Directional Term

ventral/bottom/underside surface of front front limb / Structures toward the rear of the distal (below carpus) forelimb/fore paw/front hoof

Proximal

Directional Term

loser to the body's core or point of attachment

Distal

Directional Term

Farther away from the body's core or point of attachment

Coronet (coronary band)

Part of the Hoof

• the top border of a horse's hoof where the hoof wall meets the skin.

• region of the hoof below the periople

  • Sometimes identified as a slight swelling

Periople

Part of the Hoof

• a thin, protective band of tissue around the lower part of the hoof wall, helping to maintain moisture and prevent drying

• Rubbery/supple keratinized material

  • Part of the epidermis, but before the full keratinization

  • Can identify as the first bit of tissue without hair

Sole

Part of the Hoof

• the flat, concave part of the hoof's underside, between the hoof wall and the frog. It offers support and protection to internal structures

Frog

Part of the Hoof

• a triangular, pliable structure on the underside of the hoof near the back

• It aids in shock absorption, weight distribution, and provides traction

Heel

Part of the Hoof

• Refers to the rear portion of the underside of the hoof

Bulbs

Part of the Hoof

• Part of the heel

• Fleshy structures at the back that protect and assist in shock absorption

White Line

Part of the Hoof

• A thin layer connecting the inner hoof wall to the sole

• Separation between the laminar dermis and the start of the sole dermis with finger-like projections

Digital cushion

Part of the Hoof

• A wedge-shaped, shock absorbing pad within the hoof composed of connective tissue and fat

Perioplic dermis

Part of the Hoof

• the dermis beneath the periople at the hoof margin that produces a thin, glossy protective horn layer to regulate moisture and prevent hoof wall dehydration

• has finger like projections

Coronary dermis

Part of the Hoof

• the highly vascularized dermis of the coronary band containing papillae that produce the dense tubular horn forming the bulk and strength of the hoof wall

• has finger like projections

  • Finger like projections produce tubular horn that grows down the hoof wall

  • The space in between is the intertubular horn

• Much longer in ruminants

Laminar dermis

Part of the Hoof

• the dermis lining the hoof wall that forms interdigitating primary and secondary laminae with the epidermis, anchoring the hoof capsule to the distal phalanx and supporting weight

• No finger-like projections

• Subcutaneous tissues stop at _______ _______ and _______ ________ lays directly on the periosteum (bone) to provide a strong attachment

Terminal papillae at distal ends of laminae

Part of the Hoof

• small papillae at the junction where laminae end distally, producing horn to bridge the hoof wall and sole, contributing to the white line

Sole Dermis

Part of the Hoof

• the dermis underlying the sole, with papillae that generate softer, more porous horn providing protection to the distal phalanx and aiding shock absorption

• Finger-like projections produce tubular horn

Dermis of the bulb

Part of the Hoof

• the dermis at the heel bulbs that produces elastic, resilient horn blending with the frog and wall, essential for cushioning and expansion of the hoof during weight-bearing

Hoof Wall

Part of the Hoof

• straight down section of the hoof

  • External pigmented layer

  • Internal non-pigmented layer beneath

  • Epidermis is not very productive, produces just enough keratinized material to allow to grow down

• Lies on top of laminar dermis

Terminal Horn

Part of the Hoof

• where dermis turns at a sharp angle

  • Changes from lamina back to finger-like projections

  • Now softer keratinized material as compared to hoof wall

Space

The structure of the epidermis can distribute force in _____

• Ex. Surface area for which claw sheath is attached to animal is very large (spreads out force), but part that interacts with prey is very small (concentrates force)

• Ex. Turtle shell has a wide surface area to distribute force to resist it more effectively

Time

The structure of the epidermis can distribute force in _____

• Ex. Swinging a hard claw / beak / thagomizer builds momentum over, and concentrates force on impact

  • Concentrating strength through biomomentum over time

• Soft padding, flexible connective tissue, tissue that water can squeeze out of, etc can spread impacts back out over time

  • If on receiving end of the impact, want to have a compliant/soft surface to spread out impact over time

  • Ex. lion’s mane, contact begins at fluffy dead man which disperses forces over time

Free Nerve Endings

Type of Sensory Nerve Ending in the Integument

Free Nerve Endings

Type of Sensory Nerve Ending in the Integument

• React to touch, heat, damage, injury (including to surrounding tissue, by reacting to products released by injured cells)

• May have some small associated structures around them (named before microscope resolution was high enough to see them)

  • Basically ____, but may have a little over them

  • Because so little around them, very sensitive

  • Tells you right away when somethings is wrong

Mechanoreceptors

Type of Sensory Nerve Ending in the Integument

• Encapsulated nerve endings are more selective, focus on different mechanical signals (varying in both field sizes and rates of change)

• A variety of sensory neurons are associated with hair follicles, with the long lever arm of the hair these provide sensitive “remote” touch detection

  • More shielding around them which allows them to be more selective about what they respond to 

  • Response times vary

  • Hairs provide “remote” detection, can respond to things before they even touch you

Homeostasis

The tendency to resist change in order to maintain a stable relatively constant internal environment

• A change in the internal or external environment is called a stimulus and is detected by a receptor, the response of the system is to adjust the activities of the system so the value moves back toward the set point

• Stimulus → Receptor → Control Center → Effector

• Involves negative feedback loops - counteract changes of properties from target values (set points) 

  • Oppose a stimulus

  • Ex. temperature is detected by sensors (nerve cells) and relay info to temp-regulatory center/control center (brain), info is them processed and effectors (sweat glands are activated)

  • ______ circuits generally involve 2 negative feedback loops

    • One if parameter is above set point

    • And one if parameter is below set point

• And positive feedback loops - move the system away from its starting state/amplify initiating stimuli

  • Usually found in processes that need to be pushed to completion when the status quo needs to be maintained

Stimulus → sensor → control center → effector

How negative feedback loops work to return body to homestasis

Epithelial tissue

Type of Tissue

• Tightly packed sheets of cells that cover the outside of the body and line body cavities

• Apical (faces inside) and basal (faces outside) sides

• Tightly packed to act as a barrier

• Often joined by specialized junctions

Connective tissue

Type of Tissue

• Cells suspended in extracellular matrix

• Supports other tissues

• Ex. adipose, bone, cartilage, blood

BT rises → receptors detect → hypothalamus → sweat glands activate, vasodilation occurs, etc

Describe negative feedback loop to return body to homeostasis when body temperature RISES

BT falls → receptors detect → hypothalamus → piloerection, vasoconstriction, shivering, etc.

Describe negative feedback loop to return body to homeostasis when body temperature FALLS

Countercurrent heat exchange

• an arrangement of blood vessels in which heat flows from warmer to cooler blood, usually reducing heat loss

Nonshivering thermogenesis

•  provides another mechanism for heat production. This mechanism depends on specialized fat tissue known as brown fat, or brown adipose tissue. Some mammals, especially hibernators and baby animals, have lots of brown fat. Brown fat contains many mitochondria with special proteins that let them release energy from fuel molecules directly as heat instead of channeling it into formation of the energy carrier ATP

Endotherms

• those that maintain constant BT regardless of environment 

• can alter metabolic heat production to maintain body temperature using both shivering and non-shivering thermogenesis

Ectotherms

• Those whose BT matches environment and must therefore change environments to alter BT 

• Many animals regulate their body temperature through behavior, such as seeking sun or shade or huddling together for warmth

Hypothalamus

Temperature control center in the brain

Vasodilation

Opening up of blood vessels to the skin by relaxation of smooth muscles brings more blood and heat to the body surface facilitating radiation and evaporation of heat, cooling the body

Vasoconstriction

narrowing of blood vessels to the skin by contraction of smooth muscles which reduces blood flow in peripheral blood vessels, forcing blood towards the core and vital organs, conserving heat

Piloerection

• Arrector pili muscles can contract causing hairs to stand up increasing the insulating effect of the hair

Appendageal system

• Grows out of the epidermis and consist of hair follicles, sebaceous and sweat glands, and specialized structures

• Primary function of hair is to provide a mechanical barrier to protect the host from UV damage, and to facilitate thermoregulation

• Trap hair between secondary hairs to conserve warmth

• Shorter, thicker hair, with few secondary hairs can facilitate cooling as air can move more easily through it

• Sebaceous glands secrete sebum into the hair follicles and onto the epidermal surface - can also be used for scent marking

• Epithrichial and atrichial sweat glands are part of the thermoregulatory system

Epidermis, Dermis, Hypodermis

Name the three distinct (micro)anatomic layers of the skin

Stratified squamous epithelium

What type of epithelium makes up the epidermis?

Basal layer (stratum basale)

Deepest layer of the epidermis

• Single layer of cells

• First layer of cells above the dermoepidermal junction

• Cells are very plump/alive and healthy

Cornified/horny layer (stratum corneum)

Top layer of the epidermis

• Layer on the surface

• As cells move towards the surface, they become flatter, lose nuclei, die, become more keratinized

Keratinocytes

Cell of the Epidermis

• Make up around 90% of epidermal cells

• Differentiation of these cells is a form of cell death, they are born at the dermal-epidermal junction and are dead by the time they reach the surface

Melanocytes

Cell of the Epidermis

• Make skin pigment

• Are scattered among the basal cells of the stratum basale

• From the cell body numerous slender processes extend between cells of the stratum spinosum. Melanin granules are synthesized in the cell body and transported to the tips of these cytoplasmic processes, where they are “donated” to adjacent keratinocytes, conferring colour to skin and fur and protecting against solar radiation

• The rounded cell bodies of ________ are interspersed among basal keratinocytes at a ratio between approximately 1:4 and 1:10

• Are identified among basal cells in routine skin sections by their elongated nuclei and clear cytoplasm.

Langerhans Cells

Cell of the Epidermis

• Immune cells responsible for antigen presentation

• antigen-presenting cells that encounter and present antigens arriving through the skin to immune cells of the dermis

• They are derived from bone marrow

• Not readily seen in routine histologic sections

Merkel cells

Cell of the Epidermis

• Pressure reception

• Sensory cell

Sebaceous glands

Appendages associates with hair follicles

• Accumulate dead cells full of fat that goes on hair and keeps it waterproof

• Secrete sebum into the hair follicles and onto the epidermal surface - can also be used for scent marking

• Secrete an oily substance that coats hair and skin 

• Are small lobules of lipid -laden cells whose secretion drains via a short duct either into hair follicles or directly onto the skin surface. Those opening into hair follicles are typically found in the triangle formed by the skin surface, the follicle, and the arrector pili muscle. They are composed of a layer of basal (stem) cells that divide and give rise to finely vacuolated secretory cells that synthesize lipid. The innermost, mature secretory cells undergo programmed cell death, and the dead cells and secretion are discharged from the gland as sebum. Sebum keeps skin soft and pliable and gives hair a glossy sheen

• Are found in all areas except the footpads and nasal planum. Certain areas are particularly rich in _________, particularly the mucocutaneous junctions, the interdigital spaces, the dorsal neck, the rump, the chin (of cats), and the tail head (of dogs). These latter two sites are so rich in sebaceous glands that they have been designated the submental organ and supracaudal organ, respectively

Sweat glands

Appendages associates with hair follicles

• deeper in the dermis, open into the follicle itself (small animals - less effective) or directly onto the skin surface (humans, horses)

• Are found over the entire body of most domestic species and produce a watery secretion that cools the body by evaporation. This secretion is abundant in horses only, and is scant in most other species, in which it may serve as a means of communication rather than thermoregulation

• Are coiled tubular structures lying in the dermis below sebaceous glands and opening via ducts either into the follicle or directly onto the skin surface

• They are lined by cuboidal or columnar epithelial cells and surrounded by a thin layer of contractile cells, the myoepithelial cell layer

Arrector pili mucscle

• Connects the base of the hair follicle to the dermoepidermal junction, causes hair to stand up

Desquamination (sloughing off of skin cells)

Cells of the epidermis replicate continually yet the epidermis stays the same thickness. How is this achieved? 

Circumanal glands

Hundreds of little sebaceous gland openings around the anus

Anal sacs

Under the skin (one on each side) that secrete into the last part of the rectum

Primary/Guard Hairs

Type of Hair

• Larger and stiffer

• Form an outer protective layer 

• Larger diameter

• Rooted more deeply in the dermis or subcutis

• Associated with sebaceous and apocrine sweat glands and an arrector pili muscle

• Top coat

• Straight, stiff, long

• From primary follicles

• Associated with skin glands

• Erector pili muscle attached to each follicle

• Seasonal shedding

• the longer and
  coarser hairs that extend beyond the layer of wool hairs. The main function of guard hairs
  is to protect the underlying layers of fur and the skin. They serve as a barrier against
  environmental factors such as moisture, UV radiation, and physical abrasion. often have specialized adaptations, such as waterproofing or coloration for camouflage,
  depending on the animal species

Secondary/wool hairs

Type of Hair

• Undercoat

• Finer and denser

• Provides insulation and warmth

• Follicles are smaller in diameter

• More superficially rooted

• May be accompanied by a sebaceous gland, but lack a sweat gland and arrector pili muscle

• Undercoat

• Fine, wavy, short, densely packed

• From secondary follicles

• Generally not associated with skin glands

• Generally not shed

• typically
  soft, fine, and densely packed hairs found close to the skin of certain mammals. The
  primary function of wool hairs is to provide insulation and maintain body temperature.
  They trap a layer of air close to the skin, which acts as an effective insulator, helping to
  keep the animal warm in cold environments

Tactile hairs

Type of Hair

• Used for sensation

• Long strong hairs

• Held in follicles deeply embedded into the tissue even into subcutis

• Specialized follicle - when moved causes fluid movement

• also known as vibrissae or whiskers, are
  specialized sensory hairs found on the faces and other parts of many mammal

Simple Follicles

Type of Hair Follicle

• Individual hair follicles from which a single hair shaft emerges through one skin opening

• Typical in omnivores and herbivores (horses, cattle, pigs, rodents)

• Each follicle is distributed separately throughout the dermis resulting in a uniform coat texture

• Associated with primary (guard) hairs and are often accompanied by sebaceous and sweat glands, as well as an arrector pili muscle that allows the hair to stand up

Nails

composed of tightly packed keratinized cells and are found on the tips of
phalanges. They provide protection and can be used for defense

Comb

• a fleshy, crest-like structure located on the top of a chicken's head

• It is typically red and can come in various shapes and sizes depending on the chicken's breed

• Contains a network of blood vessels that helps with thermoregulation

Wattles

• fleshy, hanging lobes of skin that dangle beneath a chicken's beak
  and on either side of the head.

• Can vary in size and color among chicken breeds.

• Play a role in thermoregulation, but they can also be involved in social interactions and mating displays.

Pterylosis

• a term used to describe specific regions on a bird's body that are related to the distribution of feathers. These terms help describe the feather tracts on a bird's body

Pterylae

• the areas on a bird's body where feathers are densely
  concentrated

• These regions are sometimes referred to as "feather tracts".

• Feathers in _____ are organized in rows or patches

Apterylae

• The areas on a bird's body where feathers are absent or sparsely
  distributed

• These regions are sometimes called "featherless tracts" or "naked
  tracts."

Compound follicles

Type of Hair Follicle

• Clusters of several hair follicles grouped together, with multiple hair shafts through a single opening

• Commonly found in carnivores (dogs, cats)

• Central primary hair is surrounded by several smaller secondary hairs all sharing the same follicular orifice

• Allow for a dense undercoat and contribute to the plush texture seen in many dog and cat breeds

Anagen, catagen, telogen, exogen, kenogen

Phases of the hair cycle

Anagen

Phase of the Hair Cycle

• Growth phase

• Active growth phase

• Hair follicle is fully functional, hair bulb rapidly divides to produce new hair shaft

• Length of the phase determined by how long the hair grows before stopping

• A predominance of follicles in _____ is associated with active hair growth and a thick, healthy coat

• In some breeds, such as poodles, most follicles remain in _____, resulting in continuous hair growth and less shedding

Catagen

Phase of the Hair Cycle

• Transitional phase

• Short transitional phase that marks the end of active hair growth

• Hair follicle undergoes regression and the lower part of the follicle shrinks and detaches from the blood supply

Telogen

Phase of the Hair Cycle

• Resting phase

• Hair follicle is inactive and the mature hair (club hair) remains anchored in the follicle, but is no longer growing

• Can last for varying lengths of time based on species, breed, and body region

• Many seasonal shedders have a high percentage of follicles in telogen before shedding begins

Exogen

Phase of the Hair Cycle

• Shedding phase

• Mature hair is released and shed from follicle

• Allows a new hair to grow from follicle to restart the cycle

• Often overlaps with late telogen and early anagen

Kenogen

Phase of the Hair Cycle

• Empty follicle phase

• Hair follicle is empty, no hair shaft present

• Not experienced by all follicle and duration varies

Compounded

Dogs and cats have _____ follicles

Simple

Horses and cattle have _____ follicles

Hair

• Originates from follicles

• Products of the epidermis, but find their way into the dermis and even into the subcutaneous tissues

Footpads

• Naked, densely cornified epidermis

• Dermis unremarkable (same as elsewhere)

• Thick subcutis

• Contain sweat glands

Antlers

• NOT part of the integument

• Generally only had by malez of the species

• Made of bone, so part of skeleton not integument

• Is covered in velvet that is part of the integument

• Shed and regrown every year

Horns

• Part of the integument

• Typically present on both male and female of the species

• Sometimes polled – born naturally without horns (selected for)

Carpal glands

Gland on the carpus of pigs

Interdigital gland and inguinal gland

Specific glands of sheep

Uropygeal gland

One of the 3 Glands of Birds

• On top of base of tail, spread secretions while preening (especially for waterproofing)

Oral gland

One of the 3 Glands of Birds

• Near ear

Oral gland

One of the 3 Glands of Birds

• Near vent underneath tail

Contour feather

Classification of Feather

• Give the bird shape

• Designed to shed water

• Repel the environment

• Have segments that allow to bind together - allows feathers to be light and sturdy

Down feather

Classification of Feather

• Soft fluffy plumage beneath contour feathers that serve primarily for insulation

• Designed to trap air and take up space