Avian Anatomy: Integument and Feather Types

Avian Anatomy Learning Objectives

• Grasp anatomical adaptations unique to birds including, integument, cardiorespiratory, gastrointestinal, musculoskeletal, urogenital and immune systems
• Understand clinical applications of avian anatomy
• Discuss illnesses unique to birds, related to anatomical adaptations
• Understand the anatomical position of the avian skeleton
• Identify relevant soft-tissue external structures assessed during physical examinations
• Know difference between feather types
• Identify soft-tissue organs of respiratory, gastrointestinal, immune, and urogenital tracts

Integument

• Components include skin, feathers, and ornamentation
• Skin is thin
• Birds lack sweat glands
• Feathers grow in tracts
• Feet and legs have scales
• Beak derives from skin
• The uropygial gland at tail base enables waterproofing
• Patagium is a triangular area between shoulder, elbow, and wrist joints, increasing wing surface and aiding flight aerodynamics

Feather Types

• Pteryla are tracts in skin where feathers grow
• Apteria are featherless skin between pterylae
• Contour feathers are externally visible with an alula, primary, axillary, and secondary
• Down feathers lack barbules, conserve heat under contour feathers, and abound in waterfowl

Ornamental Features

• Ornamental outgrowths include a thick, vascular dermis, and are easily injured
• Examples include comb, wattle, and snood
• Most birds lack ear lobes

Musculoskeletal

• Avian skeleton is adapted for flight
• Bones are light, compact, and strong with a high calcium phosphate content
• Characterized by a prominent sternum, open ventral pelvis, a forelimb forming a wing, and fused vertebrae
• The pneumatic humerus bones are hollow
• Thin cortex
• Trabeculae give strength

Notarium, Keel and Sternum, Synsacrum, Pygostyle

• Notarium: fusion along dorsal spinous processes of most thoracic vertebrae
• The keel and sternum support internal organs, enable respiration, aid body condition, and allow positioning for radiography
• Synsacrum: fusion of last 2 or 3 thoracic, all lumbar and sacral, and first few caudal vertebrae
• Pygostyle: fusion of most caudal 3-4 vertebrae

Avian Skull

• The lower jaw articulates with upper jaw through a quadrate bone
• Upper jaw is movable relative to cranium
• Large orbits are separated by interorbital septum
• Features a single occipital condyle

Thoracic Limb

• Birds have a well-developed clavicle creating strong pectoral girdle
• The furcula forms the wishbone
• The fused clavicles unite to form the furcula
• Coracoid bone: extends from humerus to the keel
• Acts as a brace during wing strokes
• The ulna is larger than the radius
• Birds have two carpal bones (radial and ulnar carpal bones)
• 3 Metacarpals

Pelvic Limb

• The role is of sole locomotion limb
• Hip bones consist of the ilium, ischium, and pubis
• Fused dorsally with the synsacrum
• Femur: resembles a mammalian bone
• Use for sampling bone marrow
• Tibia: fused distally with proximal row of tarsal bones forming the tibiotarsus
• Distal tarsal bones are fused with metatarsal bone as tarsometatarsus

Musculoskeletal Wing

• The triceps muscle extends the elbow joint
• The biceps brachii flexes the elbow joint
• The brachial vein, patagium, and extensor carpi radialis
• The carpal joint and flexor carpi ulnaris
• The cutaneous ulnar (wing) vein

Pectoralis and Supracoracoideus

• The pectoralis muscle is superficial
• Its contraction produces the downstroke
• The supracoracoideus muscle is smaller and used during take-off
• Both keel originates
• Both insert on the humerus
• Opposing actions occur

Cardiorespiratory System

• Larynx is not involved in vocalization
• Has a laryngeal mound as landmark for endotracheal intubation
• Lacks an epiglottis
• The trachea is located on right side of neck
• Has complete cartilaginous rings
• Ends at the syrinx bifurcation

Syrinx

• Is a vocal apparatus at the tracheal bifurcation
• Special organ enables songbirds vocal gymnastics
• Creates two unrelated pitches at once
• The lungs have constant volume unlike mammals
• The lungs are closely associated with the ventral aspect of ribs
• Air sacs are external to the lung
• Clavicular, cervical (singular); cranial thoracic, caudal thoracic, abdominal (paired)

Heart

• Heart structure is much like mammals
• Not covered by the lungs
• Apex covered by the liver

Gastrointestinal Tract

• Consists of the esophagus, crop, proventriculus, ventriculus, paired ceca, ileum, jejunum, colon/rectum, duodenal loop, meckel's diverticulum, cloaca, and vent

Choana

• Birds lack a soft palate
• Bone palate with longitudinal fissure- connects oral and nasal
• Lined with caudal papilla- moves caudally
• Salivary glands and taste buds are poorly developed
• Birds use dry food have more saliva

The Crop

• The crop is an out-pouching of the esophagus
• Cranial to the thoracic inlet on the right side in chickens
• Few bird species lack
• Temporary storage
• The proventriculus is the glandular stomach
• Secrete digestive enzymes
• The ventriculus is non-glandular and the muscular stomach
• Breaks up larger food

Small Intestine

• Duodenum form a tight loop
• Jejunum forms coils at the mesenteric
• Mekel's diverticulum the yolk stalk
• The Ileum is short and located between the ceca

Large intestine

• Large intestine is comprises the ceca and the colon
• The caeca have are particularly well developed in chicken
• Colon ( or rectum) is last segment of intestine to the cloaca
• Terms interchangeable

Cloaca

• Coprodeum- receives colon
• Urodeum-receives ureters
• Uroproctodeum the cloacal vent

Urinary System

• Kidneys and Ureters are present
• No pelvis; no urinary bladder

Male Genital System

• Males have paired testes
• Located inside the abdomen
• Lack a scrotum
• The deferent ducts connect to the cloaca and urine passes through the proctodeum

Egg Production

• Usually one oviduct, on left
• Infundibulum: 7 cm, has albumen
• Magnum: 30 cm, forms the egg
• Isthmus: 8 cm
• Shell gland develops the shell
• Seconds to pass through the Vagina

Immune System

• No palpable lymph nodes like mammals
• Thymus and Bursa regress early
• The thymus develops T cells
• The bursa develops B cells
• Spleen: at junction where gastric joins intestine