Histology

• Medium arteries have three layers: Tunica Adventitia (outer) which is a connective tissue blended to its surrounding, Tunica Media (middle) which is smooth muscle that is circularly arranged and contains elastic and collagenous fibers, and Tunica Intima (endothelium & inner layer) which is lined by simple squamous epithelium, has a small amount of connective tissue, and has an internal elastic membrane.
• Arteries tend to be more round in cross-section, have an internal elastic membrane, thicker tunica media/smooth muscle layer, and are a perfect example of a highly vascularized organ with a network of arteries and veins present.
• Glucagon, a hormone produced by alpha cells, originates from the liver and helps glucose levels rise back up.
• The wattle is a perfect example of a highly vascularized organ with a network of arteries and veins present.
• Veins do not have an elastic membrane, have purkenje cells (x.s / L.s) present, and have a thick tunica adventitia instead of tunica media.
• Insulin, a hormone produced by beta cells, originates from the liver, skeletal muscle, and adipose tissue and regulates glucose metabolism.
• Medium arteries, which are typical cardiovascular conduits, have connective tissue in them, tunica intima and tunica media, for the purpose of support.
• Veins tend to be larger in diameter and have a collapsed irregular lumen because they don't have much connective tissue layers in their tunica media.
• Epidermis consists of four layers: Stratum basale (inner), Stratum intermedium (spinosum), Stratum transitivum, and Stratum corneum (outer).
• Feather is composed mainly of keratin, located in a follicle and extends from the epidermis to the dermis.
• Dermis or corium is poorly defined dermal papillae and an extensive lymphoid tissue divided into layers: Stratum superficial, Stratum profundum, Stratum compactum, and Stratum laxum.
• Adnexa A includes feather, which originates from the epidermis.
• Avian skins present feathers.
• Skin (Integument) is devoid or lack of glands expect for the uropygial or preen gland and is considered as an organ of lipogenesis.
• Feather remains in the follicle until it is plucked or molted.
• Highly keratinized areas of epidermis present tubular and inter tubular horns without hairs.
• Feather follicle does not extend over a dermal papilla, thus a remnant of the vascular connective tissue of dermal papilla extends to the core of the feather as feather pulp.
• Hypodermis (Subcutis) is similar to that in mammals except that it has an extensive lymphatic tissue.
• Avian integument consists of the skin (integument), Hypodermis (subcutis), Adnexa (feather, feather follicle, uropygial gland), and Special epidermal structures (comb, wattle, beak, spur, claw, and toe pad).
• Epidermis is thin, loose, dry and thicker in unfeathered than in feathered skin.
• Lipogenesis is where fatty tissues are formed.
• There are three types of feathers: Flight feather, Down feather, and Filoplume.
• Foliate papillae are located in the caudal part of the dorsum and are leaflike as in leaves of a book, with a series of three or more oval, flat-topped mucosal folds separated by grooves or furrows.
• Scattered along the lateral walls of the fungiform, foliate and circumvallate papillae are light-stained, barrel-shaped structures with a small opening called taste pure.
• The taste bud is composed of supporting or sustentacular cells (Type I cells) located in the periphery of the taste bud, gustatory cells (Type II cells) which are bipolar neurons specialized to receive stimuli for the sense of taste, and basal cells which protect the gustatory cells.
• Brachydont or simple teeth are present in carnivores and humans and stop growing after eruption.
• Vallate or circumvallate papillae are the largest and the least numerous type, visible with the naked eye, arranged in a V line in the caudal part of the tongue, completely embedded in the tongue and anchored at the bottom by a short broad stalk, surrounded by a deep "moat" into which the lingual (von Ebner's) salivary glands secrete, and on dorsal view is doughnut-shaped with a central round prominence separated by a narrow trench ("moat").
• Teeth are used by mammals in procuring, cutting and chewing food and as weapons of offense and defense, are mineralized structures embedded in the alveolar sockets of the lower (mandible) and upper (maxilla) jaws, and there are two types of teeth according to the manner and rate of growth and the arrangement of the different layers of the tooth wall: Brachydont and Hypodont teeth.
• Transitional Epithelium is water impermeable due to large numbers of zonula occludens between cells, protecting the urinary tract from damage caused by hypertonic urine and preventing dilution of the urine by osmosis.
• Non-keratinized/non-cornified epithelium is a superficial layer that is not covered by keratin or cornified material and lines the inner surfaces of the body that are exposed to considerable wear and tear such as the vagina, conjunctiva, esophagus, and urethra.
• Stratified Cuboidal Epithelium consists of two or more layers, with the basal layer resting on a basement membrane, and two layers: Basal Cuboidal and Superficial Cuboidal.
• Glandular Epithelia/Epithelial Glands are derived from surface epithelium and are highly specialized to perform secretory function.
• Transitional Epithelium refers to the changing shape of superficial cells of the epithelium, depending on the state of contraction or distention of the organ.
• Glandular Epithelia/Epithelial Glands are classified according to its morphology, with Endocrine Glands having no ducts, secreting hormones, transported by blood and lymph to the site of utilization, and Exocrine glands having secretions released into an external or internal surface, provided with ducts, arranged into a secretory unit with lumen and enclosed by a basement membrane.
• In the collapsed state of Transitional Epithelium, the basal layer of cuboidal or columnar cell, two to four Middle layers of polyhedral cells, and two to three superficial layers of balloon shaped cells with convex free surfaces are present.
• Connective Tissues do not contain a stratum corneum in nonkeratinized stratified squamous epithelium found on moist surfaces.
• Stratified Columnar Epithelium is tall, prismatic cell that does not extend to the basement membrane, with two or more cell layers, and two layers: Basal Cuboidal and Superficial Columnar.
• All epithelial cells, when viewed from the top, are polygonal in shape.
• In the distended state of Transitional Epithelium, the basal cuboidal layer, one to two Middle layers of polyhedral cells, and one to two superficial layers of squamous cells are present.
• The Thymus is relatively largest (in relation to body weight) very early in life, and actually continues to grow in absolute size for a while after birth.