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Hamburger–Hamilton Stages
In developmental biology, the Hamburger–Hamilton stages (HH) are a series of 46 chronological stages in chicken, chick development, starting from laying of the egg and ending with a newly hatched chick. It is named for its creators, Viktor Hamburger and Howard L. Hamilton. Chicken embryos are a useful model organism in experimental embryology for a number of reasons. Their domestication as poultry makes them more readily available than other vertebrates (such as mice), and being oviparous, the embryos are easily accessible. However, the rate of development can be affected by a range of factors; including the specific breed, the temperature of incubation, the delay between laying and incubation, and the time of year, raising the need to create a standardised system based on morphology (biology), morphology rather than chronological age. There had been a previous attempt to create a morphological system for staging chick development by the German embryologists Keibel and Abraham i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Developmental Biology
Developmental biology is the study of the process by which animals and plants grow and develop. Developmental biology also encompasses the biology of regeneration, asexual reproduction, metamorphosis, and the growth and differentiation of stem cells in the adult organism. Perspectives The main processes involved in the embryonic development of animals are: tissue patterning (via regional specification and patterned cell differentiation); tissue growth; and tissue morphogenesis. * Regional specification refers to the processes that create the spatial patterns in a ball or sheet of initially similar cells. This generally involves the action of cytoplasmic determinants, located within parts of the fertilized egg, and of inductive signals emitted from signaling centers in the embryo. The early stages of regional specification do not generate functional differentiated cells, but cell populations committed to developing to a specific region or part of the organism. These a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neural Folds
The neural fold is a structure that arises during neurulation in the embryonic development of both birds and mammals among other organisms. This structure is associated with primary neurulation, meaning that it forms by the coming together of tissue layers, rather than a clustering, and subsequent hollowing out, of individual cells (known as secondary neurulation). In humans, the neural folds are responsible for the formation of the anterior end of the neural tube. The neural folds are derived from the neural plate, a preliminary structure consisting of elongated ectoderm cells. The folds give rise to neural crest cells, as well as bringing about the formation of the neural tube. Development In the embryo, the formation of the neural folds originates from the area where the neural plate and the surrounding ectoderm converge. This region of the embryo is formed after gastrulation, and consists of epithelial tissue. Here, the epithelial cells elongate by means of microt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beak
The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for food, courtship, and feeding young. The terms ''beak'' and ''rostrum'' are also used to refer to a similar mouth part in some ornithischians, pterosaurs, cetaceans, dicynodonts, anuran tadpoles, monotremes (i.e. echidnas and platypuses, which have a beak-like structure), sirens, pufferfish, billfishes and cephalopods. Although beaks vary significantly in size, shape, color and texture, they share a similar underlying structure. Two bony projections – the upper and lower mandibles – are covered with a thin keratinized layer of epidermis known as the rhamphotheca. In most species, two holes called ''nares'' lead to the respiratory system. Etymology Although the word "beak" was, in the past, generally restricted to the sharpened b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feather
Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and a premier example of a complex evolutionary novelty. They are among the characteristics that distinguish the extant birds from other living groups. Although feathers cover most of the bird's body, they arise only from certain well-defined tracts on the skin. They aid in flight, thermal insulation, and waterproofing. In addition, coloration helps in communication and protection. Plumology (or plumage science) is the name for the science that is associated with the study of feathers. Feathers have a number of utilitarian, cultural, and religious uses. Feathers are both soft and excellent at trapping heat; thus, they are sometimes used in high-class bedding, especially pillows, blankets, and mattresses. They are also used as filling for winter ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eyelids
An eyelid is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. The human eyelid features a row of eyelashes along the eyelid margin, which serve to heighten the protection of the eye from dust and foreign debris, as well as from perspiration. "Palpebral" (and "blepharal") means relating to the eyelids. Its key function is to regularly spread the tears and other secretions on the eye surface to keep it moist, since the cornea must be continuously moist. They keep the eyes from drying out when asleep. Moreover, the blink reflex protects the eye from foreign bodies. The appearance of the human upper eyelid often varies between different populations. The prevalence of an epicanthic fold covering the inner corner of the eye account for the majority of East Asian and Southeast Asian populations, and is also found i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Joints
A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw-Hill Connect. Webp.274/ref> They are constructed to allow for different degrees and types of movement. Some joints, such as the knee, elbow, and shoulder, are self-lubricating, almost frictionless, and are able to withstand compression and maintain heavy loads while still executing smooth and precise movements. Other joints such as sutures between the bones of the skull permit very little movement (only during birth) in order to protect the brain and the sense organs. The connection between a tooth and the jawbone is also called a joint, and is described as a fibrous joint known as a gomphosis. Joints are classified both structurally and functionally. Classification The number of joints depends on if sesamoids are included, age of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Limb Bud
The limb bud is a structure formed early in vertebrate limb development. As a result of interactions between the ectoderm and underlying mesoderm, formation occurs roughly around the fourth week of development. In the development of the human embryo the upper limb bud appears in the third week and the lower limb bud appears four days later. The limb bud consists of undifferentiated mesoderm cells that are sheathed in ectoderm. As a result of cell signaling interactions between the ectoderm and underlying mesoderm cells, formation of the developing limb bud occurs as mesenchymal cells from the lateral plate mesoderm and somites begin to proliferate to the point where they create a bulge under the ectodermal cells above. The mesoderm cells in the limb bud that come from the lateral plate mesoderm will eventually differentiate into the developing limb’s connective tissues, such as cartilage, bone, and tendon. Moreover, the mesoderm cells that come from the somites will eventua ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Limb (anatomy)
A limb (from the Old English ''lim'', meaning "body part") or leg is a jointed, muscled appendage that tetrapod vertebrates use for weight-bearing and terrestrial locomotion such as walking, running and jumping, for paddle-swimming, or for grasping and climbing. The distalmost portion of a limb is known as its extremity. The limbs' bony endoskeleton, known as the appendicular skeleton, is homologous among all tetrapods. All tetrapods have four limbs that are organized into two bilaterally symmetrical pairs, with one pair at each end of the torso. The cranial pair are known as the forelimbs or ''front legs'', and the caudal pair the hindlimbs or ''back legs''. In animals with more upright posture (mainly hominid primates, particularly humans), the forelimbs and hindlimbs are often called upper and lower limbs, respectively. The fore-/upper limbs are connected to the thoracic cage via the shoulder girdles, and the hind-/lower limbs are connected to the pelvis v ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Larynx
The larynx (), commonly called the voice box, is an organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal inlet is about 4–5 centimeters in diameter. The larynx houses the vocal cords, and manipulates pitch and volume, which is essential for phonation. It is situated just below where the tract of the pharynx splits into the trachea and the esophagus. The word ʻlarynxʼ (plural ʻlaryngesʼ) comes from the Ancient Greek word ''lárunx'' ʻlarynx, gullet, throat.ʼ Structure The triangle-shaped larynx consists largely of cartilages that are attached to one another, and to surrounding structures, by muscles or by fibrous and elastic tissue components. The larynx is lined by a ciliated columnar epithelium except for the vocal folds. The cavity of the larynx extends from its triangle-shaped inlet, to the epiglottis, and to the circular outlet at the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pharynx
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its structure varies across species. The pharynx carries food and air to the esophagus and larynx respectively. The flap of cartilage called the epiglottis stops food from entering the larynx. In humans, the pharynx is part of the digestive system and the conducting zone of the respiratory system. (The conducting zone—which also includes the nostrils of the nose, the larynx, trachea, bronchi, and bronchioles—filters, warms and moistens air and conducts it into the lungs). The human pharynx is conventionally divided into three sections: the nasopharynx, oropharynx, and laryngopharynx. It is also important in vocalization. In humans, two sets of pharyngeal muscles form the pharynx and determine the shape of its lumen. They are arranged ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Branchial Arches
Branchial arches, or gill arches, are a series of bony "loops" present in fish, which support the Fish gill, gills. As gills are the primitive condition of vertebrates, all vertebrate embryos develop pharyngeal arches, though the eventual fate of these arches varies between taxon, taxa. In gnathostomata, jawed fish, the first arch develops into the jaws, the second into the hyomandibular complex, with the posterior arches supporting gills. In amphibians and reptiles, many elements are lost including the gill arches, resulting in only the oral jaws and a Hyoid bone, hyoid apparatus remaining. In mammals and birds, the hyoid is still more simplified. All Basal (phylogenetics), basal vertebrates breathe with gills. The gills are carried right behind the head, bordering the posterior margins of a series of openings from the esophagus to the exterior. Each gill is supported by a Cartilage, cartilaginous or Bone, bony gill arch. Bony fish have four pairs of arches, chondrichthyes, c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paraxial Mesoderm
Paraxial mesoderm, also known as presomitic or somitic mesoderm is the area of mesoderm in the neurulating embryo that flanks and forms simultaneously with the neural tube. The cells of this region give rise to somites, blocks of tissue running along both sides of the neural tube, which form muscle and the tissues of the back, including connective tissue and the dermis. Formation and somitogenesis The paraxial and other regions of the mesoderm are thought to be specified by bone morphogenetic proteins, or BMPs, along an axis spanning from the center to the sides of the body. Members of the FGF family also play an important role, as does the WNT pathway. In particular, Noggin, a downstream target of the Wnt pathway, antagonizes BMP signaling, forming boundaries where antagonists meet and limiting this signaling to a particular region of the mesoderm. Together, these pathways provide the initial specification of the paraxial mesoderm and maintain this identity. This specificat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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