Integuments - Week 2 Dr. Ira Mandle structure of farm animals PDF

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Very good notes for the course. Every blank is filled and these will get you an A. Notes cover the reproductive system, respiratory system, cardiovascular system, urinary system....

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Integuments – Week 2  

One of the largest and most extensive organ system in the body. o Covers the entire animal Includes: o Skin or hide o Sweat and oil glands, mammary glands o Hair (wool, fur, feathers) o Nails (hooves, claws, foot pads) o Horns

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All of these are components considered modification of the surface epithelium which are sheets of cells covering the external surface of the body. Function of integuments:  Protects against microbes, insects, external parasites, environmental, chemical, UV radiation, physical abrasion o Skin surface deals with on a day to day basis: constant rubbing, scratching, direct contact with physical environment which gets worse is animal is fleeing from predator or producer o Grazing animals are completely exposed to the sun (darker hair coat animals warmer vs. lighter hair coats in the summer). o AW issue if grazing animals don’t have access to shade? o Animals housed outside during the winter: different breeds hair coats get thicker. Farm animal species ration or diet formulation programs take this info into account to calculate nutrient requirements. o Different breeds have different back fat thickness (which impacts how well animal do outdoors). o Preventing dehydration o Body temperature regulation: Perspiration (sweating), hair coat, and cutaneous blood flow (blood flow to the skin). Cutaneous: means of the skin. o Detecting sensory information (touch and pressure) and relaying it to the CNS.  Think about animal swatting flies and whiskers o Excretion of organic wastes and excess salts and water. (sweat). o Synthesis of vitamin D. o Protection (nails, horns, and claws). o Food gathering (claws important for birds as forelimbs replaced by wings). Characteristics of skin:  Covers the external surface of the animal  Has the ability to regenerate and heal o Human epidermis replaces every 4 to 7 weeks o 25 to 50 days is the range across species

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Species difference in skin thickness and how loosely (firmly) skin attaches to underlying body structure. o Loose attachment enables movement with out tearing Thickest in areas where greatest exposure to environment (back, between shoulder blades, pads of paws) Thinnest where animal is best protected (groin, around the eye).

Layers of the skin    

Epidermis (outer layer) Dermis (makes up most of the integument), (blood vessels are located here). Hypodermis (blood vessels are located here) o Subcutaneous fat or back fat is located in this layer. Subcutaneous: under skin. Structures and functions for each layer will differ for the most part. (Some similarities).

Epidermis:  

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Layers of flat cells: stratified squamous epithelium (flat hexagonal cells) Avascular and generally free of nerve endings o How does it get Nutrients?  Via simple diffusion from the underlying skin layer (from capillaries located in the dermis). Made up of 3 to 5 histological layers Basal layer of epidermis (basement membrane) adjacent to dermis, where keratinocytes dividing to produce daughter cells o Made up of keratinocytes (these cells make up 90% of the cells in the epidermis) which divide via mitosis to form daughter cells that push older cells towards the skin surface. o As cells migrate towards surface, they lose access to nutrients as they are too far away from the dermal capillaries (no blood vessels in epidermis); cells flatten, die, and undergo changes including loss of nuclei, cytosol and organelles which are replaced by the fibrous proteins, keratin and water proofing granules made up of glycolipids.  This provides the skin with the ability to prevent water loss

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To make room for keratin, the cells must dump their vital nuclei and organelles

o In this cell conversion process, superficial cells harden and dry out via the processes of keratinization and cornification  Keratinization: Getting the fibrous protein, keratin into the epithelium  Cornification: (conversion of superficial cells in the epidermis to stratified squamous epithelium along with hardening and release of glycolipids).  Glycolipids released to waterproof skin and to slow water loss from epidermis o Function of keratin  Keratinization and cornification make the skin tough and resistant to drying  Want to keep water in and keeping microbes, insects, debris, heat out from the body. Protects from invasion from substances and organisms. o Shedding of epidermal cells (millions per day)  Turnover of epidermal cells; exfoliation o Keratin is a fibrous protein with poor essential amino acid balance. Epidermis: other cell type (keratinocytes make up 90% of the epidermis but there are others). o Desmosomes: anchors and connects keratinocytes to form a more protective barrier o Melanocytes: produce pigments, melanin which protects against UV radiation o Merkel cells at the epidermal/dermal junction: act as sensory receptors to light touch. (Epidermis generally is free of nerve endings). o Langerhans’s cells: phagocytise foreign debris or microorganisms  Immune cell type: macrophage; engulf microbes  These are cells involved with development of an itch or rash; respond to phagocytizing invaders; Langerhans’s cells engulf microbes so that they can be handled by the immune system

Dermis, also called the corium  make up most of the integument/skin   

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Location: between epi and hypodermis How is the dermis separated from epidermis? o Basement membrane of the epidermis What is the relationship between epidermis and dermis? o Epidermis has folds which project downwards into the dermis o Dermis has dermal papillae which project downwards into the epidermis in an arrangement where the dermal papillae interdigitate with the epidermal projections to “cement” the two layers Makes up 80% of total mass of the skin, the dermis makes up most of the integument

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This layer makes up the animal hide (used to make leather) Numerous cell types and structures o Fibroblasts: for synthesizing connective tissue proteins o Macrophages: for the immune system o Nerve endings o Adipocytes o Hair follicles o Smooth muscle o Sweat and sebaceous glands o Blood vessels (arteries, veins, capillaries) and lymphatic vessels (latter for the immune system).

Function of the dermis: 

Provides structural strength and flexibility of skin o Due to the presence of fibroelastic connective tissue  High amounts of collagen, elastin, reticular fibers (connective tissue proteins) produced by fibroblasts. Responsible for strength and flexibility of the skin.  Elastin fibers are responsible for:  Ability to stretch the skin  The long wearing attributes of leather  Reticular fibers join connective tissues to other tissues o Presence of blood vessels:  Provides nutrients to the epidermis  Waste removal and temperature regulation o Sensory receptors (Meissner’s corpuscles), (light touch, pain, moisture, temperature change)  Sends information to the CNS which will process info and tell body how to respond o Classification of the dermis versus epidermis  Epidermis is considered cellular in nature since this layer is mostly composed of keratinocytes  Dermis is considered fibrous in nature due to the large amount of fibroelastic connective tissues. (Collagen, elastin, reticular fibers).

Hypodermis    

Location: underneath dermis  will find adipose tissue and blood vessels Also known as the subcutaneous fat layer Made up of areolar connective tissue (CT) (loose CT which binds to cells) and adipose tissue, blood vessels, lymphatic vessels, and nerves Areolar CT made up of fibroblasts, collagen, elastin, and reticular fibers described for dermis

o Areolar CT allows skin to move over underlying muscles and bone with out tearing  Ensures flexibility o Areolar CT cushions and protects skin and underlying muscles and organs o Adipose tissues acts as shock absorber and for thermoinsulation, source of energy for animals

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Site of Pacinian corpuscles: touch receptors that respond to heavy pressure and vibrations o All layers of the integument will have receptors that respond to touch; these receptors will get stimulated and then send info to the CNS; body told how to responds See large amounts of blood vessels in hypodermis: Why? o Associated with adipose tissue for depositing more triglycerides into adipose tissue depots in the hypodermis when energy intakes exceed energy requirements (fat deposition in the body) o Associated with adipose tissue for mobilizing adipose tissue when energy intakes to not meet energy requirements; important for lactation: sows, cows, ewes will mobilize this fat to supply energy to meet demands for milk production Sweat Glands 

Two types of sweat glands: eccrine + apocrine o Both located in the dermis or hypodermis; found all over the body (numerous in farm animals) o Farm animals generally only have apocrine sweat glands that open into hair follicles  Eccrine sweat glands in primates secrete mixture of water, salts, lactic acids with primary function to cool the body  Not many farm animals sweat  Dogs?  Eccrine glands found on foot pads so not effective for cooling  They cool themselves primarily by panting, chickens do this too

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Apocrine glands and sebaceous glands open into hair follicles Eccrine glands connect to the skin surface by a long duct

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Cooling for humans: Function of the eccrine sweat glands in humans For many animals, apocrine glands produce a secretion containing water, fatty acids, and proteins which combined with sebaceous gland secretions are responsible for characteristic odors or horses, cattle and dogs Apocrine glands: o Species differences for role of apocrine secretion in heat loss (for cooling)  Horses (only farm animal) producing large amounts of sweat  Cattle differences: Bos taurus vs bos indicus  Bos indicus (Zebu/Brahman): much larger number of sweat glands. Have large floppy dew lap and large hump.  Cattle and sheep will generally pant  Pigs don’t do either  will role in mud or water o Skin importance:  Temperature regulation in farm animals  Changes in blood flow thru skin capillaries alters amount of warm blood near body surface which affects thermoregulation o Increases the amount of blood near the body surface enables animal to dissipate heat to help cool themselves  Blood vessels increase in size (vasodilation) to increase blood flow to the surface of the skin.

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Sebaceous or oil glands: open up onto hair follicle.  Oil glands are found all over the body of the dermis o These glands release secretion (sebum) onto hair follicles or on to skin surface o Oil glands degrade epithelial cells to produce lipid (fat)-based sebum (glycerides and fatty acids)  Sebum similar to lanolin which is the product of sebaceous glands in sheep  Sebum functions to  Keep hair follicles from becoming brittle (traps moisture to prevent excessive drying) body’s way to protect the hair  Prevents excess evaporation of moisture from skin (keeps skin from drying out).  Keeps skin soft (natural skin cream)  Has bacteriostatic and antifungal properties o Specialized oil glands used to mark territories and attract mates in some species  Combine with apocrine gland secretions Hair or Pili: (layers of dead keratinized cells)  Numerous functions

o Insulatory (helps maintain body temperature) by trapping air (important for animals housed outside during the winter) o Absorbs light to help warm animals (dark coloured hair coats)  Dark coloured hair is not advantageous in the summer o Protection via camouflage but also as a layer between environment and skin/hide o Sensory reception (whiskers) o Areas on body where hair is not present: hooves, lips, paw pads, horns, nipples, nasal regions o Hair follicle is an invaginating (infolding or pocket) of the epidermis which serves to anchor the hair. Hair:  Hair production dependent on number and and size of hair follicles on the skin o Hair follicle is an invagination (infolding) of the epidermis which can extend from the skin surface to as the dermis (hypodermis)  Hair follicles serves to anchor the hair o Hair production occurs at the base of follicle  Mound of dermal cells (papilla) covered by rapidly dividing epithelial cells called matrix  Daughter cells get pushed away from papilla and die from lack of nutrients; these cells become keratinized  Similar process to keratinization of epithelial cells  Keratin in hair, harder and more durable than keratin in epidermis  Hair can be referred to as layers of dead skin Types of hair  Guard or primary hairs that form smooth outer coat o Protect against abrasion and moisture  Wool hairs that form undercoat (soft and curly) o Wool sheep lack guard hairs so wool hairs are long fine hairs  Innervated tactile hairs that serve as organs of touch (whiskers found around mouth or muzzle; used as probes and to feel)  Hair colour results of melanin production: quantity and quality, distribution, and turnover  No hair in birds; have feathers which function to protect against the element, enable flying, maintaining body temperature, protection from predators, sexual attraction. o As domestic poultry get older, they need lower barn temperatures (less supplemental heat) due to feather development and the Insulatory function of feathers. o As domestic poultry are susceptible to heat stress  Hair and feathers made up primarily of protein o Both have a poor essential amino acid composition- the same is true for keratin found in the epidermis – Why do you think this has occurred with a poor essential

AA composition? Because you will see turn over of these proteins, no sense in have a major loss of these amino acids.

Hooves and horns  Comparison between the bones of the human hand and the animal  No carpal bones on the hoof , but the cannon bone shown in the figure is the metacarpus which is then attached to the phalanges (phalanxes).  The fingers are divided into different phalanges; we see a similar arrangement in farm animals with each of the phalanges referred to as a phalanx.

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Proximal phalanges: first phalanx Intermediate phalange: second phalanx Distal phalanges: distal phalanx The canon bone is the metacarpal (metatarsal) which is located proximal to the phalanges Both at made up of modified epidermis Most farm animals have hooves o Known as ungulates as have a well developed hoof associated with the distal phalanx (digit) o Ungulates means hoofed animal; ungulates use tips of their toes to sustain entire body weight when moving o Hoof also known as an ungula or claw o Horses are odd toed ungulates  Supporting all their body weight on one toe o Pigs/cattle/sheep/goats are even toed ungulates  Supporting all their body weight on two toes  In the human hand, there is a metacarpal bone associated with each finger  In cattle, they are walking on 2 toes and the metacarpal bone have fused to form the canon bone. We see the same on the hind limb with the metatarsal.  Bovine metacarpal (metatarsal) is the same as the canon bone which is the same as the shank.

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No thumb in farm animals The index finger and dewclaws (non-weight bearing) which have regressed over evolution Ruminants walk on 2 digits while horses walk on one digit (the middle finger of the human hand) Hoof is an extension of skin from the lower limbs, known as hard, often pigmented outer covering of the distal digit (phalanx) Hoof, ungula, or claw (all these terms refer to the hoof that is going to cover the distal digit (phalanx) of the forelimb of hindlimb

Outer layer is cornified layer derived from epidermis o Avascular and insensitive to pain Both claws and hooves rest on underlying sensitive tissue called the corium Underneath outer layer is the inner vascularized dermis or corium which has blood vessels to supply nutrients and is innervated (can sense pain) Why do horses wear shoes?  Increase integrity of hoof wall  Increase traction  Strengthens the foot  Prevents expansion of the hoof when the animal carried weight  Provides a protective barrier between the hoof and ground

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Formed over corneal (horn) process of the frontal bones on the skull on cattle, sheep, goats In adults, horns are hollow and communicate directly with the frontal sinus. Horn core (germinal center, bud, or button) found on frontal bone o Core covered by dermis (also called corium) and acts as the site for growth  Horn elongates from the base  Horn cells considered epidermal cells Horn made up of dense keratin similar to hoof wall and hair

Horn Growth is influenced by:

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 Nutrition  Sex: females have smaller horns or no horns  Genetics: polled cattle (lack horns naturally) DEHORNING: Destroy corium where horn buds found o Surgical removal of horn button o Destruction of horn button using hot iron or caustic paste (cauterization). Horns are not the same as antlers which are found mostly on males, dermal in origin, grow and shed annually, emerge as bony protuberances from skull...