Form and Function Exam 4

Functions of the Integumentary System

Skin

The body’s continuous outer covering; a layered structure that prevents water loss and blocks physical and biological threats

Epidermis

The outer epithelial layer forms a keratinized barrier

Dermis

Connective tissue layer containing blood vessels, nerves, hair follicles, and glands

Hypodermis

Attaches skin to underlying tissue, contains fat that cushions and insulates

Stratum

A distinct layer of tissue

Stratum corneum

Outermost & thickest layer; many layers of dead, keratin-filled corneocytes

Stratum lucidum

Only in thick highly keratinized skin, a layer of flattened dead cells

Stratum granulosum

Keratinization begins; cells become increasingly flattened; lipid release for water-resistance

Stratum spinosum

Keratinocytes connected by desmosomes; mechanical strength

Stratum basale

Deepest epidermal layer (basement membrane); mitotically active to replace epidermal cells; contains melanocytes

Keratinization

The process of turning living epidermal cells into the tough, dead, keratin-filled cells that form the protective outer layer

Keratinocytes

Mitotically active cells; produce keratin proteins

Corneocytes

Dead cells in stratum lucidum & corneum

Extracellular lipids

Water resistance

Papillary Dermis

• Thin superficial portion of the dermis, immediately beneath the epidermis.

• Loose connective tissue - forms dermal papillae

• Houses small capillaries (heat exchange), sensory nerves, & immune cells

Reticular Dermis

• Dense irregular connective tissue

• Collagen fibers - Tensile strength

• Elastic fibers - Stretch/Recoil

• Houses hair follicles, sweat glands, sebaceous glands, arrector pili muscle, larger blood and lymphatic vessels, and sensory nerves

Hair

Keratinized structure produced by epidermal cells within a hair follicle

Hair Shaft

Portion above the skin; dead keratinized cells

Hair Root

Below the skin surface; located within the follicle

Hair Bulb

Enlarged base of root; surrounds the dermal papilla

Hair Matrix

Rapidly dividing cells around the papilla; move upward & keratinize.

Contains melanocytes; pigment determines hair color

Dermal Papilla

Connective tissues & capillaries; supplies nutrients to growing hair

Primary Hair Follicles

• Larger follicles that develop first during fetal development

• Coarser, longer hairs of the coat- the most visible outer layer

• Guard hairs

Secondary Hair Follicles

• Develop later- smaller and more numerous

• Produce finer hair fibers

• Excellent for insulation- undercoat

Tactile Hairs

• Specialized sensory hairs (whiskers)

• Common around the muzzle, lips, eyes, and face

• Movement of hair - signals to the Central Nervous System (CNS)

Wool

• Specialized type of hair

• Primary follicles = Coarse Wool

• Increased number of Secondary follicles = Fine Wool

Crimp

• Different sides of the hair fiber didn’t keratinize identically

• Fiber bends as it grows

• Creates loft and traps air = insulation

Contour Feathers

Outer body covering; provides protection and body shape

Flight Feathers

Large feathers of wings and tail

Down Feathers

Fluffy; traps air for insulation

Vane

Forms that flat surface for flight, insulation, and protection

Rachis

Central shaft that supports the feather

Calamus

Hollow base anchored in the skin (feather follicle)

Barb

Branching structures that extend from the rachis

Barbule

Smaller branches from barbs that interlock with adjacent barbules

Hooklet

Tiny hooks that ‘zip’ barbules together to form a continuous vane surface

Claws

Hard outer covering of the distal phalanx, a modification of the human nail. Provides traction and a tool for defense

Nail Matrix

Continually grows and produces a new claw

Quick (nail bed)

Very sensitive, living tissue with blood vessels and nerves

Hooves

Horny outer covering of a distal phalanx that supports body weight and allows for locomotion.

Ungulates

Hooved animals

Cloven Footed

2 digits per foot (pigs, cows, sheep, and goats)

Outer Epidermal layer

No sensation, hardened to support movement

Inner dermal layer (Corium)

Blood transport in the leg. Vasculature with nerve endings

Coronary Band

Growth region that produces much of the hoof wall

Hoof Wall

Hard, keratinized outer covering

Toe

Most cranial portion of the hoof/claw

Sole

Keratinized ground-facing surface

Heel

Caudal portion; softer, more elastic than wall

White Line

Point where the hoof wall is connected to the sole. This is a common area for abscesses or damage

Digital Cushion

Pad of fatty tissue that is located directly above the sole as a shock absorber, protecting the corium

Laminae

Tissue that attaches P3 to the hoof capsule/wall

Sensitive Laminae

Living, vascular and innervated tissue

Insensitive Laminae

Keratinized epidermal laminae that interlock with sensitive laminae

Dewclaws

Remnants of digits, serving little to no function and common in dogs, cattle, pigs, and sheep/goats

Horns

Outer keratin layer with living tissue within it, derived from frontal bones; growing continuously throughout an animal’s life

Molting

• Old feather loosens and is shed

• New feather develops in the same follicle

• New feather pushes up, replacing the old

• Cycle repeats

Tattoos

Tattoo ink must penetrate into the Dermis to be permanent

Arrector Pili Muscle

Smooth muscle near the base of the hair follicle; its contraction causes hair to “stand on end” (goosebumps) for heat retention, sympathetic nervous system, or to make the animal appear larger

Layers of barrier defense

• Physical: skin, hair, mucosal barriers, mucus, cilia, and mechanical flushing

• Chemical: sebum, sweat, lysozyme, stomach acid, Antimicrobial peptides, and local pH

• Biological: Resident microbiota; that compete with pathogens for space & nutrients

Mechanical Flushing

Tears, saliva, and urine wash microorganisms away

Specialized hair that helps protect body openings

• Nasal Hairs

• Eyelashes

• Ear canal hairs

Sebaceous Glands

Creates sebum (chemical) barrier that lubricates and waterproofs skin/hair, inhibiting microbial growth

Sweat Glands

Located within the dermis, it produces sweat onto skin surfaces for thermoregulation

Types of Glandular Secretion

• Holocrine: Entire cell breaks down

• Eccrine: Exocytosis; cell remains intact

• Apocrine: Apical portion pinches off

Specialized sebaceous glands

• Sheep- Lanolin

• Pigs- carpal glands

• Goats- horn glands

Sheep- sebaceous gland

Infraorbital, Interdigital, and Inguinal pouches, which secrete lanolin- a fatty yellow substance that covers and sticks when dry. Thought to be marking glands

Pig-Carpal glands

Exocrine scent organ: in the inner lower part of the front legs, near the carpus that secretes pheromones. This is more developed in boars and cycling females

Goats- horn glands

Caudal to the base of the horn; secretions increase during mating

Horses- Sweat glands

Sweat glands are located over the entire body; producing protein-rich sweat containing latherin

Porcine- sweat glands

Limited sweat glands, rely on wallowing, shade, and cooler surfaces to help regulate body temperature

Dogs-sweat gland

Body sweat glands produce scent, not sweat. Dogs cool themselves by panting.

Skin barriers

Surface cells: Dead, keratinized corneocytes

Thickness: Many layers

Moisture: Dry

Main Job: Protection

Primary defenses: Keratin, lipids, shedding of cells

Mucosal barriers

Surface cells: Living epithelial cells

Thickness: Single layer + basement membrane

Moisture: Must stay moist to function

Main Job: Exchange, absorb, secrete, gas exchange

Primary defenses: Mucus, tight junctions, flushing, microbiota

Mucosal surface

• Upper respiratory tract

• Mouth & Esophagus

• Lungs (alveoli)

• GI Tract

• Urinary bladder

• Female reproductive tract

• Eyes/ conjunctiva

Mucus

Traps pathogens and protects epithelial cells from low pH (stomach)

Ciliated cells

Move mucus and trapped material toward removal-conducting pathways. Common in URT and SI

Biofilm formation

Antimicrobial peptides, which prevent bacterial attachment, are surrounded by a self-produced extracellular protective matrix

Low pH

Inhibits the growth or survival of many pathogens

Tears

Lacrimal ducts; wash eye surface

Saliva

Salivary glands, wash microbes/debris from the oral cavity

Urine

Flushes urethra

Lysozyme

Antimicrobial enzyme found in body fluids: tears,saliva, milk, egg whites and mucus. Breaks bonds within peptidoglycan chain

Microbial Competition

The resident microbiota occupy attachment sites, use available nutrients and provide colonization resistance

Antimicrobial peptides

• Found on skin and mucosal surfaces

• Defensins: Damage microbial membranes

• Cathelicidins: Disrupt microbial membranes, recruit immune cells, and support wound healing

Layers of the Immune System

• Physical & Chemical Barriers

• Innate Immune System

• Adaptive Immune System

Innate Immunity

Immediate non-specific defense against pathogens and tissue damage by recognizing common patterns associated with pathogens or tissue damage

Recognize the problem (Step 1)

Detect pathogens or damaged cells

Initiate Inflammation

Sound the alarm and recruit help

Universal Defense System

Contain and destroy the threat

Report back to base

Communicate with the adaptive immune system

Pathogen Associated Molecular Patterns (PAMPs)

Common molecular features found on or inside pathogens (bacteria, viral RNA)

Damage Associated Molecular Patterns (DAMPs)

Molecules released/exposed by damaged or dying host cells (ATP, DNA, intracellular proteins)

Pattern Recognition Receptors (PRRs)

On or within innate immune cells that bind to PAMPs and DAMPs

Macrophages

Tissue resident phagocytes that release cytokines to recruit more cells; recognize PAMPs/DAMPs

Mast Cells

Tissue resident that releases histamine and inflammatory mediators

Dendritic Cells

Capture and process antigen; carries toward adaptive immune system

Blood Smears

Circulating leukocytes

Tissue Histology

Immune cells in tissue