Avian Anatomy and Physiology Flashcards
What is the purpose of the digestive system?
To keep the host nourished and healthy
How is the avian digestive system different than mammals?
It is faster and more efficient?
Why are the two reasons the avian digestive system is faster and more efficient than other vertebrates?
1.) Birds cannot afford to store heavy food materials in their bodies for long periods of time since they need to minimize weight for flight
2.) Because of flight, because they’re small (lose heat more rapidly), and because they’re warm blooded, they use a lot of energy, so digestion needs to act quickly to supply this
How long does it take a shrike to digest a mouse and a robin to digest fruit?
Shrike -> 3 hours
Robin -> 30 minutes
What is the most common activity done by birds during the day?
Eating and foraging
When is most foraging done?
Mornings and evenings
What type of feeders are birds?
Opportunistic feeders
What is another name for the gastrointestinal tract?
The alimentary canal
What is the gastrointestinal tract and what does it span in birds?
The entirety through which food passes
Spans beak to cloaca
What is the difference between a bill and a beak?
A beak is a curved bill
What are the main functions of the bill/beak?
Grabbing, tearing, crushing, holding, and swallowing food
How does the avian jaw differ between mammals and avians?
The avian jaw is somewhat mobile, meaning it can extend upward
What allows for the different positions and mobility of the jaw?
Lateral and longitudinal dexterity
The beak is able to do what with a big meal?
Hold or receive it
What are examples of when form and function are important?
Structure, dietary preferences, adaptation, and environment
What is the avian mouth made of?
A hard palate divided by a long narrow slit that acts as an opening to the nasal passage
What is the long narrow slit in the avian mouth called?
Choanal slit
The choanal slit, coupled with what, makes it impossible for birds to do what?
The choanal slit and the absence of a soft palate make it impossible for birds to create a vacuum to draw food or water into their mouths
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They can’t use straws, so they need to draw water in by moving their head
What are characteristics of the avian tongue?
It is hard, short, narrow, and triangular
How does the number of taste buds in avians compare to mammals?
Avians have very few compared to mammals and they are situated mostly in the back of the mouth/throat for avians
What tastes can birds perceive?
Sweet, sour, and bitter
How do birds utilize flavor?
To learn which foods are more nutritious
In terms of food, what do birds prefer?
Texture over flavor
What do birds have on their tongue and palate and how do they use them?
A complex system of touch receptors that they use to make food-based decisions based on how something feels
What is the most under-developed sense in birds?
Smell
What is the esophagus?
A long, thin, tubular muscle that connects the mouth to the stomach
Why do most birds have well developed salivary glands?
To lubricate food entering the esophagus
What are under-developed or absent in aquatic birds?
Salivary glands
What is an enlargement of the esophagus that many birds have?
The crop
Where is the crop located?
Midpoint of the esophagus
What is the function of the crop?
It is a food and water storage organ
What type of mentality does the crop enable?
Dine and dash
What does the crop do besides storage?
Meters contents into the digestive tract
What type of digestion occurs in the crop?
A very small amount of salivary enzyme digestion
What is characteristic of a pendulus crop?
When it hangs and swings
If there is slow passage through the crop and food stays there longer than it should, what happens?
Micro-organisms begin to live there and create gas, which causes the crop to bloat
What do birds have a more efficient stomach than?
Reptilian ancestors
What type of stomach do birds have?
A complex two-part stomach
What are the two parts of the stomach?
Proventriculus and gizzard
What is characteristic of the proventriculus?
It is a soft-walled glandular tube
What do the epithelial mucosa in the proventriculus secrete?
HCl (lowers pH), digestive enzymes, and mucus
What does the proventriculus do?
Initiates the breakdown of food
What type of bird has a stomach with a pH below 0.1?
Carcass eaters, like vultures
What is another name for the gizzard?
Ventriculus
What is characteristic of the gizzard?
It is a hard/thick-walled organ that has a sand-paper like inner surface
What does the gizzard do?
Performs mastication (what chewing does)
Why do some birds swallow stones?
To help breakdown food in the stomach
What happens to the gizzard in birds that feed on easily digestible foods like fruits and berries?
It is reduced in size and function
When the gizzard is greatly reduced, what is the stomach almost completely comprised of?
Glandular proventriculus
Rank in decreasing order the diets that a chicken can be fed that would result in the greatest sized gizzard
Raw diet > pellet diet > mash diet
What happens in the small intestine?
Food is digested and absorbed
How does the small intestine vary among avians?
Varies in length and structure depending on preferred diet of the species
What type of birds have a shorter small intestine, and which type’s is larger?
Carnivorous birds have a shorter small intestine and omnivorous and herbivorous birds have a longer small intestine
How does the avian small intestine compare with the mammalian short intestine?
It is relatively featureless when compared to the mammalian SI consisting of the duodenum, jejunum, and ileum
What is the duodenum?
The intestinal loop around the pancreas
How are the liver and pancreas connected to the duodenum?
By ducts
How does the liver compare with mammals?
Liver is larger in birds
What does the liver do?
It stores fats and carbs and is the major site of protein synthesis
What receives the most nutrients from the small intestine before other body tissues?
Liver
What does the duodenum contribute?
Bile, pancreatic enzymes, and neutralization of gastric juices
What does bile do?
Emulsifies fats
What do pancreatic enzymes do?
Aide in digestion
What do the jejunum and ileum provide?
Peristalsis and absorption of nutrients
When nutrients are absorbed via the jejunum and ileum, where do they go?
They are absorbed into mesenteric veins and enter the portal hepatic system
What, specifically, is the jejunum?
The intestine located between the duodenum and Meckel’s diverticulum
What, specifically, is the ileum?
The intestine located between Meckel’s diverticulum and the ileocecal junction
What is Meckel’s diverticulum?
Vestigial remnant of the vitelline duct or yolk sac that is the junction between jejunum and ileum
What is the ileocecal junction?
Where the ileum and ceca meet
What are the ceca?
Two pouches located at the junction of the small and large intestine
What takes place at the ceca?
Water re-absorption and fermentation of remaining food materials
What does the ceca produce in chickens?
Several fatty acids and 8 B-vitamins
How do the ceca vary?
Vary in size and functionality depending on diet preference of bird species
Why is microflora present in the ceca?
Because of the presence of fiber and other undigested materials
Describe the GI tract of a red-tailed hawk and explain
Short small intestine with very small ceca
Short SI because carnivore, small ceca because not much fiber in carnivore diet)
Describe the GI tract of a hoatzin and explain
Large crop and foregut because herbivorous and a lot of fermentation ocurrs
Most birds have a very small large intestine, what bird has a long intestine?
Ostrich
In species with a relatively small ceca, what can help compensate this?
An expanded foregut, like in hoatzins, a larger midgut, like in emus, or a longer colon, like in ostriches
What are two other names for the large intestine?
Colon and rectum
What has the large intestine been reduced to in most birds?
A short, featureless connection between the small intestine and the cloaca
What happens at the large intestine?
Water reabsorption
What is the function of the cloaca?
It’s the final holding site of waste products
What is the urinary waste of birds?
Urates, not urine
What are the roles of the respiratory system?
1.) Absorption of CO2
2.) Release of CO2
3.) Vocalization
4.) Temperature regulations
5.) Helps with rapid adjustments to acid/base balance
What is the second most efficient respiratory system in the animal kingdom (and what’s first)?
Avians have the second most efficient respiratory system in the animal kingdom, second only to insects
What is the most common cause of death in poultry flocks?
Respiratory disease
What is another name for the larynx?
Glottis
What is the larynx?
An opening to the trachea/windpipe
In terms of the respiratory system, what does the choanal slit/cleft do?
Allows for breathing through the nostrils when the beak is closed
What does the choanal slit connect?
Trachea to the sinuses and nares
How does the choanal slit relate to the immune system?
It’s where the first exposure of food and water to the immune system takes place
How do the glottis and choanal slit relate when the mouth is closed?
The glottis fits into the choanal slit
What is another name for the trachea?
Windpipe
What is the trachea?
A hollow tube that provides airflow to/from the lungs for respiration
How does the size of the avian trachea relate to the mammalian trachea?
It’s 2.7 times longer and 1.29 times wider than mammals of similar size
What is the syrinx?
The bifurcation of the trachea-where the trachea splits into two primary bronchi
What does the syrinx serve as?
The avian voice box
When do primary bronchi form?
At the bifurcation at the syrinx
What are the primary bronchi called when they enter the lungs?
Mesobronchi
What do the mesobronchi do?
When passing through the lungs, they branch into dorsobronchi
What does a breath of air do after passing through the dorsobronchi in the lungs?
It “turns around” and passes through the lungs again to leave the system
What do dorsobronchi do?
Branch into smaller parabronchi as the air leaves the system
What is the size of the parabronchi?
several mm long and 0.5-20 mm in diameter
What are the parabronchi analogous to?
Alveoli in mammalian lungs
What do the parabronchi walls have?
Hundreds of tiny, branching air capillaries that are surrounded by a network of blood capillaries
What is the site of gas exchange in the lungs?
The branching air capillaries surrounded by the network of blood capillaries in the parabronchi walls
What helps the trachea remain stiff?
Rings of cartilage along the walls
What allows for unique vibration/sound to be made?
The muscles on the sides of the cartilage rings that can distort the rings and allow for unique vibrations and thus sounds to be made
How does sound travel out of a bird?
It echoes up and out of the trachea
What is the avian breathing pattern?
A continuous flow of air that passes completely through the lung
What is a tidal breathing pattern and what animals employ this?
Mammalians have a tidal breathing pattern and they breathe in, the lungs expand, the breath doesn’t go any further, and then they breathe out
When air passes through an avian’s lung, what does it completely go into?
One of the 9 auxiliary air sacs
Why is the mammalian breathing pattern not as efficient as the avian breathing pattern?
Our lungs don’t ever completely deflate because that would cause them to collapse, however, that also means all of the old air cannot be expelled from the lungs
Why is the avian breathing pattern so efficient?
The air passes completely in and out of the lung, so there is no mixing between fresh and stale air. This means that the air entering the lung is very oxygen rich, which provides a higher concentration gradient between O2 in the lungs and CO2 in the blood, allowing for very easy gas exchange
What are the 9 avian air sacs?
1 interclavicular, 2 cervical, 2 anterior thoracic, 2 posterior thoracic, and 2 abdominal
What do the air sacs not do and what do they do instead?
They do not play a role in gas exchange, instead they serve to store the air
What do the air sacs allow?
A continuous stream of air to pass through the lungs
What are the air sacs connected to?
Pneumatic bones (i.e. skull, furcular, pelvis, lower back bones)
What two things do the air sacs create/promote in the bird’s body?
Heat exchange and buoyancy
Describe the route air takes through the lungs
It enters, goes through the mesobronchi and the dorsobronchi directly to a caudal air sac. It sits in that air sac momentarily, then takes an alternate route through the parabronchi, which is where gas exchange occurs, to a cranial air sac, where it momentarily sits again, then leaves the lungs
What happens to the breath on inhalation #1?
The breath travels through the lungs (no gas exchange) into the posterior, thoracic, and abdominal air sacs
What happens to the breath on exhalation #1?
The abdomen contracts, squeezing the air out of the air sacs and through the parabronchi, allowing for gas exchange.
Technically, air enters the lungs on this exhalation
What happens to the breath on inhalation #2?
Stale breath is pushed from the lungs into the anterior and interclavicular air sacs where it is held momentarily
(A second breath comes in here and starts at inhalation #1)
Technically the air leaves the lungs on this inhalation
What happens to the breath on exhalation #2?
The stale breath is pushed out of the anterior and interclavilcular air sacs, up the trachea, and out the nostrils
What does not happen to breaths in the lungs?
Fresh and stale breaths do not mix
What is the integumentary system?
The surface of the bird
What does the avian integumentary system consist of?
Skin, appendages (beaks and claws), and feathers
What are the functions of the integumentary system?
Protection, thermal regulation, sensation, pigmentation, and synthesis of Vitamin D
What are the three layers of the skin?
Epidermis, dermis, and hypodermis
What is the epidermis?
An epithelial cellular layer that is the outermost tissue layer that consists of three separate layers itself
What is the deepest layer of the epidermis?
A germanitive layer that is constantly proliferating cells
What happens in the middle layer of the epidermis?
Cells migrate up from the germanitive layer and transition from columnar to squamous
What happens at the most superficial layer of the epidermis?
The cells are completely flattened and full of keratin. The cells then flake off which contributes to dander and dust
What is the most protective layer of the skin?
The outermost layer of the epidermis
What is the dermis?
The middle tissue of the skin
What is the hypodermis?
The innermost tissue layer of the skin
What are the dermis and hypodermis made of?
They contain cells, but also contain a higher degree of collages and other connective tissue fibers as well as muscle
What are the five distinct areas where the skin is different?
1.) Lower legs and feet
2.) Footpad (plantar region)
3.) Comb and wattles
4.) Beaks and toenails
5.) Feathered areas
Describe the skin on the lower legs and feet of the bird and how did birds obtain this feature?
They are covered in highly keratinized scales that are attached to the epidermis. This trait is a carry-over from reptilian ancestors
What is the footpad?
The bottom of the foot, which is made of squishy and flexible skin
What does the footpad do and how is the skin on it described?
It helps withstand compressive and abrasive forces
What is a common concern relating the footpad skin?
Footpad dermatitis
What are the wattle and comb?
Red, fleshy structures on the head
What is characteristic of the wattle and comb and what is their function?
They are soft, fleshy, pigmented, and highly vascularized. They help with thermoregulation and mate attraction
What is the beak made of?
A bone that is covered by a closely attaches layer of highly flattened keratinized skin
What are the toenails/claws made of?
A claw root covered by columns of flattened keratinized cells
How do bills and beaks benefit each species of bird?
They are highly adapted and modified depending on the species and their environment and diet
What is a quintessential feature unique to birds and dinosaurs?
Feathers
What is characteristic of the skin of feathered areas and why?
It is usually thinner because the feathers provide protection
What varies among species in regards to feathers and why?
Feather number varies due to size of the bird and environment (aquatic, cold, etc.)
When does feather development begin?
In the embryo
What are the three steps of feather development?
1.) The feather papillae forms, creating a bump in the skin
2.) Folds/invaginations form a collar around the papillae
3.) The feather follicle is formed from the invaginations
What is the living portion of the feather called?
Pulp
What part of the feather is visible?
The dead, protein structure
What artery brings blood to the feather?
The axial artery
What does the feather muscle do?
Allows for movement and twisting, lifting, and raising of the feather
What is the word for the pattern and distribution of feathers?
Pterylosis
Where do feathers sprout from?
Feather tracts
How are feathers and feather tracts distributed across the skin?
Feather tracts are not uniformly distributed over the skin (exceptions being penguins, ostriches, and emus), but feathers are
What are areas with present feather tracts called?
Pterylae
What areas without feather tracts called?
Apteria
What is characteristic of distribution of pterylae and apteria?
Their distribution is characteristic of taxonomic groups
What is a bird patch?
Where a bird sheds or pulls out feathers to better distribute heat to its eggs
How are feathers designed?
They are designed perfectly for flight and thermal protection
How do the colors of feathers benefit the bird?
They help camouflage and help with mating displays
What are other roles of the feathers?
Feeling, hearing, digestion (can’t be digested, act like fiber), making/muffling sounds, transporting water, escaping predators, and tail feathers help with bracing and climbing
What are feathers composed of?
Beta-keratin
What are the parts of the feather?
Calamus, rachis, barbs, barbules, and hooklets/barbicels
What is the calamus?
The hollow barbless base of a feather
What is the rachis?
The stiff central shaft of the feather which barbs branch from
What are the barbs?
Main branches of the feather that stem off of the rachis
What are barbules?
Secondary branches off of barbs
What are hooklets/barbicles?
An interlocking microstructure between barbules
What does diversity in feathers and their function come from?
Modification in the branching structure
What are pennaceous feathers?
Feathers with a clean, interlocking structure
What are plumulaceous feathers?
Feathers that lock the interlocking structure and are flowier and softer
What are the 7 types of feathers?
Wing (remiges), down, tail (rectrices), contour, semiplume, filoplume, and bristle
How are wing feathers specialized for flight?
They are stiff an asymmetrical
What is the vane and afterfeather of the wing feather?
The vane has the pennaceous structure and the afterfeather has the plumulaceous structure
What is characteristic of the vane?
Both wind and waterproof
How are wing feathers typically arranged?
Usually have 10 primary and 10 secondary feathers
Where are flight feathers attached to the bird’s body?
Attached to the bone instead of the skin
What contributes to the aerodynamic qualities of the wing feather? What do they support and what do they accomplish?
Shape, overlapping, lamination, and durability
They support the airfoil structure of the wing to accomplish lift
Explain Bernoulli’s principle and the lift effect on the wing
The air molecules travelling over the wing need to travel a further distance than the air molecules travelling below the wing in the same amount of time. The air molecules flowing over the top don’t exert as much pressure as the air molecules on the bottom, so the air molecules on the bottom are able to hold the wing up due to the higher pressure
Describe the interlocking structure of the tail feathers
They have a similar interlocking structure to wing feathers (pennaceous at top and plumulaceous at bottom) but they are more symmetrical
What are the functions of the tail feathers?
They provide steering and balance during flight, brake for landing, balancing, and are sometimes ornamental to help with mate attraction
How are tail feathers typically arranged?
Six pairs
How are contour feathers arranged?
Cover the body to contribute to its streamline shape and to contribute to the wings’ airfoil structure
Overlap to help with insulation and protection
How can contour feather color differ?
They can be colorful to attract mates or drab to help with camouflage
What types of feathers are mixed among and beneath other feathers?
Semiplume and down feathers
What is different about the structure of semiplume feathers?
They have a central rachis, but no hooklets
What structure do semiplume feathers provide?
A fluffy, insulating structure
What is different about the structure of down feathers?
They have highly branched barbs, but have little to no central rachis and no hooklets
Where are down feathers located and what do they do?
They are located closest to the body and trap heat
What is the structure of filoplume feathers?
Have a very simple structure with very few barbs
What is the purpose of filoplume feathers?
Can be sensory or decorative
What is the structure of the bristle feathers?
They have the simplest structure with a stiff rachis and no barbs
Where are bristle feathers commonly found and what is their purpose?
They are common found on the head/face around the mouth and eyes and they help prevent dirt and dust from interfering with facial structures
What is preening?
A bird’s grooming process, which is when it conditions its feathers
How does a bird preen?
It collects “oil” from its preen gland using its beak or head and transfers that oil across its body to help condition and realign the feathers
What is the preen gland?
A two-lobed structure that is present in most birds
How does the preen gland vary?
It can vary in size, but is larger in aquatic birds
What do birds that lack a preen gland rely on?
“Powder-down” feathers and/or sebaceous skin secretions
What do the oily secretions from the preen gland include?
Waxes, triglycerides, and hydrocarbons
Where is the preen gland located?
Base of the tail above the last vertebrae
What are the four advantages to preening?
Weather/waterproofing, grooming, contains antibacterial and antifungal properties, and maintains appearance for mate attraction
How do gland secretions help with weather and waterproofing?
They coat and protect each feather and promote flexibility
What are the two advantages of the grooming action?
Aligns feathers to maintain an aerodynamic shape and removes dirt and parasites
How does grooming help with mate attraction?
Maintains appearance for mate attraction and in some species the secretion has a pheromone that helps attract mates
How does heart rate compare to body mass?
It is inversely proportional
How is the avian heart similar to the mammalian heart?
It is 4 chambered and has separate pulmonary and systemic circulation
What are the three differences between mammalian and avian hearts?
1.) Avians have a triangular heart
2.) Avians have two superior anterior veins that enter the right artium and one inferior vena cava that enters the right atrium (this part is like mammals)
3.) Avians’ aortic arch has a rightwards orientation vs. leftwards in mammals
In what way is the avian skeleton modified?
To meet the demands of flight
How is the avian skeleton divided and what is included in each division?
Axial and appendicular
Axial skeleton includes skull, vertebral column, ribs, and sternum
Appendicular skeleton includes wings, legs, pectoral girdle, and pelvic girdle
What are the main adaptations of the avian skeleton?
1.) It is rigid
2.) Mass has been reduced and redistributed vs. other species
3.) Limbs were adapted
How is rigidity achieved in the avian skeleton?
Through the fusion of bones into structures
What bones fuse to form the pelvic girdle?
Ilium, ischium, pubis, sacral, and some caudal vertebrae
How are the thoracic vertebrae laid out in avians and what does this cause?
There is some fusion, but they are tightly interlocked through uncinate processes, which are protrusions of the ribs that overlap with previous ribs, that prevent twisting and bending of the bird’s back, causing birds to be stiff-backed
Why are birds stiff-backed?
So they don’t have to waste energy engaging core muscles during flight
Why are the keel and sternum so large?
To allow for the attachment of huge breast muscles to help with flight
What is the coracoid and what is its function?
A bone with a high degree of fusion that helps support the tendons of the breast muscles
What is the furcular?
Fused clavicles known as the wishbone that helps the interclavicular air sac to expand and contract during flight
What do birds lack in their head and what replaces this function?
Birds lack teeth, but “chewing” is achieved by the light but strong beak and the gizzard
What vertebrae do birds not have?
Caudal/tailbone
What do birds have significantly less of in all of their bones?
Bone marrow
Birds’ bones are pneumatic, what does this mean?
They are lightweight but strong
Why are pneumatic bones strong?
They have trabeculae that span across them to form a scaffolding
What do birds still have in their bones and how is it different?
They still have medullary/spongy bones, but the calcium from them is constantly mobilized so eggs can be formed
What have birds lost most of the length of?
Their tail
What is the carpometacarpus?
The fusion of the avian hand
Why is the avian wrist/hand highly fused with only a few digits?
To provide attachment points for the primary wing feathers
What bones in the leg are fairly conventional?
The bones in the upper leg
How are the bones of the lower leg different and why are they different?
They are highly fused to aide in shock absorption of taking off, landing, and running
How do birds walk?
On their toes
What does digitigrade mean?
Something that walks on its toes
