Compared to other domesticated animals like cows and goats, chickens are merely little creatures on two feet covered with a curious load of feathers.
But their small size shouldn’t fool you—studying chicken anatomy can be daunting. This article presents a high-level overview of chicken anatomy and physiology.
Table of Contents
Parts of a Chicken You Need to Know
You can look at the many parts of a chicken in different ways to make it easier to group them based on their location or purpose.
Below are some easy ways to explore the anatomy of a chicken.
External Parts of a Chicken
From the head to the footpad, a chicken has many external parts, including:
- The head: The eyes, eye ring, ear opening, ear lobe, beak, and comb are all located on the head. The wattles hang downward from the throat. Chickens do not have teeth or external ears.
- The neck
- The central body: You can look at the body between the head and legs as the main body of a chicken. It houses the breast, feathers, wings, and back.
- The legs: A chicken’s leg comprises the thigh (the upper part of the leg next to the bird’s main body), drumstick (lower leg), hock (joint connecting the thigh to the shank), toes, claws, spur, toenails, and the shank.
The toes, which are used for walking and standing, are usually three and point forward. Some chickens have a fourth toe pointing backward, sometimes called the claw. Chicken breeds with five toes per foot are very rare.
The toes and shanks of some chicken breeds are covered with feathers.
- Feathers: Some critical uses of feathers in chickens include camouflage, providing warmth when it’s cold, aestheticism/decoration, courtship, and cooling chickens when it’s too hot.
The different types of feathers include the hackle, saddle feathers, sickle feathers, flight feathers (in the wings), primary feathers, and secondary feathers. The latter two are separated by the axial feather.
- The skin: As with most other animals, including humans, the skin is the biggest part of a chicken’s body.
Together with the feathers, the skin protects and insulates chickens from external elements. It is the bird’s sensory monitor for pleasure, heat, pain, and cold. It also has special compounds that synthesize vitamin D from sunlight.
Types of Chicken Skin
The skin of a bird can be classified into different types based on the function each type is modified for:
- Feathered skin: This is the largest chicken skin type. The feathers grow outward from the follicles off of the skin.
- Footpad: This is the thick, tough, but flexible base of the foot or the underside of the toes.
- The earlobe: This is a specialized chicken skin found on the side of the head below the ear. Its color may be white or red, depending on the breed.
- Wattles and combs: When a chicken begins to mature, it produces sex hormones that cause the formation of secondary sexual appendages called wattles and combs.
- Scaled skin: The legs and feet are covered in scaled skin that provides optimum protection.
- Toenails and beak: These are special skin types made of hardened keratin. The hard beak is used to take in food and as a weapon against external threats. The toenails are for ransacking the ground for food items like insects and seeds.
Internal Parts of a Chicken
The internal parts of a chicken include:
- Larynx, trachea, and lungs
- Heart
- Brain
- Esophagus, crop, proventriculus, kidney, ceca, gall bladder, spleen, liver, gizzard, pancreas, small intestine, and large intestine
- Ovary and oviduct
- The bones: Chicken bones are mainly made of tightly bound collagen fibers and phosphorus and calcium.
About 80% of a bird’s phosphorus and 99% calcium are stored in the bones and are converted into usable states by vitamin D. The egg shell becomes weak or non-existent if the chicken has a calcium deficiency.
Types of Bones in Chickens
Chicken bones are grouped into two types:
- Medullary bones: Calcium is stored in these bones, whose centers contain the bone marrow for making blood cells. The legs, ribs, and shoulder blades are medullary bones.
- Pneumatic bones: Examples of these bones include the skull, collar bones, humerus (or arm bone), and the pelvis. The bones are hollow and connect to the chicken’s respiratory system through air sacs.
The largest bone in a chicken is the sternum, covering half of the body cavity. It is the part onto which the wings attach with the help of strong muscles.
The internal body parts of chickens can be classified according to their functions as a group. This gives rise to digestive, respiratory, muscular, skeletal, and reproductive systems.
The Digestive System of Chickens
A bird’s digestive system comprises the esophagus, crop, proventriculus, gall bladder, spleen, liver, gizzard, pancreas, small intestine, large intestine, ceca, and kidney.
The esophagus or gullet guides food from the chicken’s mouth to the stomach.
The small pouch in the esophagus called the crop acts as a temporary food store before the food reaches the stomach. It enables the chicken to take in as much food as possible without stopping to digest it first.
Another part of the esophagus is the avian gizzard that grinds up ingested food with the help of grit before releasing the food into the stomach.
A bird’s spleen filters the blood and produces antibodies to fight pathogens and ensure optimal chicken health.
Actual digestion begins in the proventriculus, also called the true stomach. Digestion happens here through hydrochloric acid and digestive enzymes like pepsin.
The avian pancreas produces pancreatic juice, which comprises digestive enzymes. It also produces hormones glucagon and insulin that are used to metabolize carbohydrates.
The ceca (singular cecum) reabsorb some of the water still held in the digested food. They also ferment coarse food particles that may still be in the digested material.
Chickens use the bile produced by the liver to solubilize and absorb dietary fats and excrete some wastes.
A chicken’s gall bladder stores and concentrates the bile juice produced by the hepatocytes. The bile juice has electrolytes, cholesterol, bile salts, biliverdin pigment, and phospholipids.
The Reproductive System of Chickens
The female chicken reproductive system is different from the male one since roosters and hens play different reproductive duties. The organs of egg-laying hens are delicate because a lot of energy is required to lay eggs, and the whole process eventually wears them down.
A rooster’s reproductive organs are all located inside the body cavity for optimum protection. Birds are delicate little creatures. The organs must be protected for posterity!
The male reproductive system comprises two ever-functional testes and avian sperm ducts. During mating, which takes only a few seconds, the rooster mounts the hen, and the cloacas of the two touch, allowing the transfer of sperm to the hen.
The reproductive system of a female chicken supports mating, fertilization, and egg production. It comprises one functional ovary, the oviduct, a predetermined number of eggs, and the cloaca.
Laying hens may decide to fertilize the eggs or not by deciding to keep the sperm in the oviduct or expel it if she doesn’t like the rooster enough!
The accepted sperm stays viable for about 30 days in the oviduct and may be used to fertilize one or several eggs, which the hen lays and later sits on if she finally decides to go broody. It’s interesting how much the tiny brain of a hen can do!
Fertilized chicken eggs are nutritious enough to support the life of the developing chick before hatching during natural or artificial incubation.
The Respiratory System of Chickens
The avian respiratory system comprises the nostril, trachea, larynx, and two symmetrical lungs.
The Skeletal System of Chickens
Birds can stand up and walk voluntarily with the help of the skeletal muscle, which also protects all internal organs and tissues.
The skeletal muscle defines the chicken’s shape and forms the poultry meat we love to bits.
The Muscular System of Chickens
The cardiac muscle and smooth muscle form the muscular system of a chicken.
The autonomic nervous system controls the smooth muscle found in blood vessels, intestines, gizzards, and organs.
Why It’s Important to Know the Anatomy of Chickens
You’ll want to understand the anatomy and physiology of chickens to enable you to correctly interpret and correct any problems that may arise in your backyard chickens.
For example, knowing the parts and functionality of the digestive tract helps you understand what your chickens need in their diet. You can then provide them things like sand or calcium carbonate, especially if your birds rarely leave their chicken coops to forage outside.
Conclusion
And it’s a wrap with the high-level overview of chicken anatomy and physiology to help you understand your chickens better. We hope you found this an interesting read!