Lecture 2 -- Anatomy and Physiology of Birds

What is the significance of a bird's beak/bill in relation to weight?

The presence of a bill/beak reduces weight.

Describe the anatomy of birds’ beak

A bony projection covered with soft tissue that contains blood vessels and nerves forms the base of the beak. The very end is covered with a keratinized sheath.

What is the keratinised sheath covering called?

Rhamphotheca

What is the upper beak called?

Rhinotheca

What is the lower beak called?

Gnathotheca

The structure of a bird’s tongue depends on what?

Depends on diet

E.g. Chicken have point sharp looking tongue; Parrot have flashy round tongue

How would we describe abnormalities such as scissor beak in birds?

Upper and lower portion of beak do not line up

How would we describe abnormalities such as parrot beak in birds?

Upper beak rests on or inside lower beak

How would we describe abnormalities such as simple overgrowth in birds?

Abnormally long beak

→ Usually upper beak (Upper beak seems to grow a little bit faster → Less likely to be worn down)

What can be a consequence of improper beak trimming in birds?

If trimmed too short, it can cause injury due to blood and nerve supply in the beak.

Identify the two structures shown in the picture.

1: Ceres

2: Nostril

What is cere? Where is the cere located in different types of birds?

• Waxy structure at base of beak

• In most species, nostrils are hosed within the cere = The nostrils are in caudal portion

• In owl, the nostrils are distal to the cere

How can the cere be used in sexing budgies?

Males have a blue cere, while females have a tan or pink cere.

Where is the oesophagus located in birds?

On the birds right side, just lateral to glottis

Describe the tube feeding techniques

Insert the tube from the left side of the bird’s mouth → Pass it gently across to the right-hand side, over the base of the tongue → Wait for the bird to swallow; this ensures the glottis closes → Once swallowed, the tube will be correctly positioned in the oesophagus.

What is the appropriate site in birds for swabbing to diagnose respiratory diseases?

Choana

Identify the two structures shown in the picture.

What is the choana, and what is its function?

• Opening on roof of oral cavity

• Connects the nostrils to the trachea → When the beak is close, the birds can breath through that

What condition can be indicated by blunting of choanal papillae?

• Nutritional deficiencies e.g. hypovitaminosis A

• Chronic respiratory disease.

P.S. Chonal papillae normally are small spiky projection which are located on the roof of the mouth 

What is the purpose of the crop in birds?

It acts as a temporary food storage sac before digestion.

Do all birds have a crop?

• No. Depending on diet. 

  • Green eaters and seed eaters have bigger crop 

  • Most carnivorous birds like hawks and eagles pass food directly to the stomach

What is crop milk, and which bird produces it?

• Fat-filled epithelial cells sloughed off and regurgiated to feed young

• Produced by pigeons

What are some potential problems that can occur with the crop?

• Sour crop 

  • Yeast infection/ overgrowth → Crop become thicken + Normal bacterial population is disrupted 

• Crop impaction

  • Failure of food to leave crop and enter proventriculus

  • Often caused by ingestion of stringy material e.g. grass/ disorders of motility

What are the two distinct areas of the bird's stomach?

• Proventriculus

• Ventriculus = Gizzard

What are the difference between proventriculus and ventriculus

• Proventriculus

  • Glandular stomach

  • Secretion of digestive enzyme = Enzymatic digestion of food

• Ventriculus

  • Muscular stomach

  • Contains particles of ingested grit 沙粒 to aid grinding of food material = Mechanical breakdown of food

What is a key function of the proventriculus?

Secretion of digestive enzymes and enzymatic digestion of food.

How does the anatomy of the small intestine differ in herbivores compared to carnivores?

Herbivores have a highly coiled small intestine, while carnivores have a shorter and simpler one.

Where is the pancreas located in birds?

Located between arms of the duodenal loop

Name the structure that is shown in the picture 

Mekels diverticulum 

What is Mekels diverticulum? Where is it located? 

• Remnant of yolk sac attachment 

• Located at the junction between jejunum and ileum 

What is the main function of the large intestine in birds?

Reabsorption of water and electrolytes.

What is the difference in the large intestine when comparing birds and mammals?

Relatively short

What is ceca?

• Out-pouching of large intestine

• Histologically similar to large and small intestine

• Contain lymphoid tissue

The size of the ceca varies between species. Which birds have larger ceca, and which have smaller ceca?

• Passeriformes have smaller ceca

• Galliforms have lave larger ceca

Variation in diet leads to variation in the gastrointestinal (GI) system. In terms of seed eaters, fruit eaters, and meat/fish eaters, what are the anatomical differences in their GI systems?

• Seed eater 

  • Well developed crop, proventriculus and gizzard (For grinding seed particles)

  • Long intestine 

  • Distinct caeca 

• Fruit eaters 

  • Shorter intestine 

  • Caeca less distinct 

• Meat/ Fish eaters 

  • Caeca and gizzard rudimentary 

  • Well developed pancreas and proventriculus (For enzymatic digestion of protein that they are taken in their diet)

What is the cloaca?

The terminal portion of the reproductive, urinary, and gastrointestinal tracts

There are three regions of the cloaca. What are they, and what does each region receive?

• Coprodeum 

  • Receives faeces and digestive waste from intestine

• Urodeum

  • Receives ureters and products of reproductive tract

• Proctodeum

  • Houses bursa of Fabricius (part of the lymphatic system) on dorsal midline

Since the waste from the gastrointestinal and renal systems, as well as products from the reproductive tract, are all collected, through what single opening do they exit?

Vent = External opening 

What adaptations do birds have to prevent contamination between the reproductive, gastrointestinal, and renal systems?

Tissue outpouchings between cloacal compartments act as barriers, preventing contamination between the digestive

E.g. When a bird lays an egg, outpouching closes off one compartment from the next → Ensure feces do not contaminate the egg as it passes through

Do birds have gall bladder?

Yes

How many lobes does a bird’s liver have, and where is it located?

• Two (Right larger than left)

• Located caudal to heart and close to proventriculus and spleen

What enzymes do birds’ pancreas secrete?

Exocrine: Amylases, proteases and lipases

Endocrine: Insulin, glucagons, somatostatin (= growth hormone–inhibiting hormone)

What is the avian kidney's unique feature regarding urine transport?

There is no urinary bladder; urine is transported directly to the cloaca via ureters.

How many lobes are there in each kidney of a bird? What are they?

• 3 lobes

• Cranial, Middle and Caudal

Do birds have a urinary bladder?

No

Since birds have no urinary bladder, how does urine pass out of the body?

Urine transported directly from the kidneys to cloaca via ureters

What types of nephrons do birds have?

• Have both reptilian and mammalian type nephrons

• Can switch between depending on the need for water conservation

Birds generally lose quite a lot of water through the kidneys. What mechanisms do they have to prevent excessive water loss?

They are able to retrograde flow into colon from cloaca → Allow more water reabsorption in the colon 

What is the end product of metabolism in birds? Where is it formed? How is uric acid excreted in birds?

• Uric acid

• Formed in the liver

• Excreted via glomerular filtration and tubular secretion as white “precipitate” within urine

What indicates healthy droppings in birds? What causes that appearance?

• Urine, uric acid and faeces come out at the same time

• Urate (Salt form of uric acid) appear white + Faeces appears green + Clean watery urine = White, green appearance

What special feature in male avian’s reproductive system compared to mammals

• Short epididymis = Not much capacity for sperm storage

• Ductus deferences is the main storage site for sperm

• Paired testes located within the abdominal cavity

• Accessory sex gland absent

Where is the paired testes located in avians?

• Within the abdomen
  !! At cranial lobe of kidneys !!

Different from mammals, bird testes are functional even at high body temperatures (40–41°C). However, when does the majority of spermatogenesis take place?

Takes place during the night when temperatures lower

Since birds have little capacity for sperm storage, what are their adaptations?

Testes enlarge during breeding season → Increase the output of sperm without having to store it for long period of time 

What is phallus?

Unlike most mammals, most birds lack a penis, but in species that do have one = Phallus

What species of bird have phallus?

• Duck, geese and ratites

• Phallus acts as intromittant organ - analogous to the penis

In chickens, passerines, and other fowl, the phallus is a non-intromittent organ. How do they achieve fertilization?

• Phallus exists in chickens, passerines, and some other fowl but it is non-intromittent

→ During mating, the male’s phallus touches the female’s cloaca = Sperm is transferred externally from the male to the female

Psittacines do not have a phallus. How do they achieve fertilization?

Fertilisation occurs by eversion of the cloaca containing papillae

Where is the ovary located in birds?

Located cranial to kidney, tightly attached to dorsal body wall and adhered to caudal vena cava 

How does the avian ovary differ from the ovaries of other species?

1. Right ovary and oviduct regress = Only left ovary and oviduct fully developed and functional

2. Mature ovary contains a bunch of follicle

3. Those follicles develop in sequential order

What are the common eggy issues in aivans

• Follicular stasis

  • Inappropriate maturation of follicle within the ovary without ovulation

• Excessive egg production

  • Eggs are produced without mate or season due to overactive reproductive tract

• Egg binding

  • Egg takes longer than normal to pass out of reproductive tract = Dystocia

Occurrence of ovulation depends on species. How do hens differ from pet birds in terms of ovulation?

• Hens are continual layers

  • Next follicle ovulated ~30mins after laying

• Pet birds are usually determinate layers

  • Produce a clutch of egg → Egg laying then ceases for a period

Why should we not remove eggs from some pet birds, e.g., cockatiels?

• They are indeterminate layers 

  • Produce clutches but also have the ability to replace a lost egg → They may keep producing egg if we remove an egg from the clutches → Might leak all the calcium from their bone

What are the five functional regions of the female bird's reproductive tract? What happened in those regions?

• Infundibulum

  • Receives ovulated folllicle 

  • Fertilisation take place 

  • Site of formation of chalazae = Albuminous cords, which hold yolk in central position within the egg (White bit beside the yolk)

• Magnum

  • Egg white (albumin) develops around yolk

• Isthmus

  • Shell membrane (Thee peely bit on the egg shell) produced, which help hold everything together 

• Uterus (shell gland)

  • Calcification of shell

• Vagina.

  • Adds egg cuticle (Semi permeable layer coating on the egg) → Protect the egg by stopping the bacteria entering the eggs but allow the egg to breathe

  • Site of sperm storage

P.S. Yolk = Ovulated follicle 

Why should we not wash bird eggs?

Might take away the protective coating

What cardiovascular feature in birds differs compared to mammals of similar body mass? Why?

• Higher cardiac output + cardiac size (heart size inversely proportional to body mass) as flight is metabolically demanding → Cardiovascular system have to be capable of sustaining prolonged muscular activity

• Higher blood pressure

• Faster heart rate (Up to 800 bpm)

How many chambers does the avian heart have?

Four

Why do birds have nucleated red blood cells?

Birds evolved in a period where the earth’s oxygen levels were higher 

What do we have to be aware of when giving medication to birds?

• Renal portal system (Blood drained from the hindlimb goes straight to the kidney’s through capillary bed rather than circulation first) 

What is the vocal organ of bird? Where is it located? What is the function of the syrinx in birds?

• Syrinx

• Loacted at the base of trachea, beofre the primary bronchi branches off

• Function: Vibrate when air pass over it → Allows range of vocal sounds

What is unique about the avian respiratory system compared to mammals?

• No diaphragm 

• Fixed lungs (Do not expand) 

  • Thoracic and abdominal muscle expand coelomic cavity (Not the abdominal cavity and thoracic cavity)

• Absence of alveoli (Have parabronchi instead)

What are parabronchi, and what is their function?

• System of narrow tubes which allow air flow in one direction only

What do birds have for gas exchange?

• Lungs (Capillaries surround the parabronchi)

What are the air sacs in birds?

• Muco-serous extension of secondary bronchi

Into what structures can some bird air sacs extend?

• Some extend into hollow pneumatic bones

Which bones in birds are pneumatic bones?

• Skull 

• Humerus

• Clavicle 

• Keel 

• Pelvic girdle 

• Lumbar vertebrae

• Sacral vertebrae

Label the structure of birds’ respiratory system 

How many air sacs do most birds have? What is the function of the air sacs in birds?

• Nine 

  • One intercalvicular air sac (Sitting between the clavicles) 

  • Two cervical air sacs (At the base of the neck)

  • Two anterior thoracic air sacs 

  • Two posterior thoracic air sacs

  • Two abdominal sacs 

• Function: Act as “bellows” 風箱“ to push air through lungs

(They do not perform gas exchange themselves but move air through the lungs)

What is the structural characteristic of bird air sacs?

• Thin walled with poor blood supply

What types of infections are bird air sacs particularly vulnerable to? Give one example

• Susceptible to bacterial/fungal infection

• Example: Air sacculitis = Inflammation of the air sacs secondary to bacterial infection

What can trauma e.g. fracture of bone to air sacs result in?

 Development of sub-cutaneous emphysema 

Describe the pathway of air through respiratory system of avian, for nares to the site of gas exchange

• Air drawn in through nares → Travels through conchae (rostral, middle and caudal) and paranasal sinuses → Oral cavity (Communicate with nasal cavity through conanal slit) → Trachea → Bifurcates into left and right primary bronchi → Subdivide into secondary bronchi → Air sac → Parabronchi → Atria (Small side chambers, along the parabronchi) which contain air capillaries, where gas exchange occurs

How does air flow through the avian respiratory system?

Birds breathe using a “one way system” = Move air in a single direction through their lungs during both inhalation and exhalation

What happens during inspiration in the bird respiratory system?

• Air flows down the trachea, along bronchi, then into the posterior air sacs (posterior thoracic and abdominal), while air already in the lungs moves into the anterior air sacs (anterior thoracic, interclavicular, and cervical)

What happens during expiration in the bird respiratory system?

Air from the posterior air sacs flows through the parabronchi (where gas exchange occurs), and air in the anterior air sacs is expelled through the trachea.

Do birds have lymph nodes?

• No

• But they have lymphatic tissue distribute throughout the body instead 

Where are immune cells produced in birds during embryonic development?

In the embryonic liver, yolk sac and bone marrow

In birds, where do B cells mature?

Bursa of Fabricius.

Where is the Bursa of Fabricius located in birds?

Dorsal to the cloaca.

Where do T cells mature in birds?

Thymus 

Where is the thymus located in birds?

In the neck region

The thymus and Bursa of Fabricius become smaller and rudimentary in adult birds. Which structures then play a role in avian immunity?

Bone marrow

→ It is a primary lymphatic organ that eventually takes over immune cell production as other organs regress

What can result from early destruction of the thymus or bursa (due to experiment or viral disease)?

Impaired immune function and failure to respond to vaccination

What are the secondary lymphatic tissues in birds?

• Gut-associated lymphatic tissues, including caecal tonsils

• Respiratory associated lymphatic tissues

• Conjunctiva associated lymphatic tissues

• Spleen

• Harderian gland (Located close to the eyes)