Hamburger-Hamilton stages
Encyclopedia
In developmental biology
, the Hamburger-Hamilton stages (HH) are a series of 46 chronological stages in 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
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 in 1900, but this system lacked detail and was not widely used, with most researchers relying on somite
number or age to identify the stage of development. Hamburger and Hamilton aimed to provide a detailed description of developmental events, modelled on an earlier system for Axolotl
by Harrison.
The Hamburger-Hamilton system provides advantages over the Carnegie system
in that it allows the developing chick to be accurately staged both at embryonic
and fetal
stages, and is used universally in chick embryology.
landmarks. Although most organ systems have a stereotypical appearance at each stage, there are a few which particularly lend themselves to use in staging chick development.
Developmental biology
Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...
, the Hamburger-Hamilton stages (HH) are a series of 46 chronological stages in chick
Chicken
The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...
development, starting from laying of the egg
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
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
Model organism
A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...
in experimental embryology
Embryology
Embryology is a science which is about the development of an embryo from the fertilization of the ovum to the fetus stage...
for a number of reasons. Their domestication
Domestication
Domestication or taming is the process whereby a population of animals or plants, through a process of selection, becomes accustomed to human provision and control. In the Convention on Biological Diversity a domesticated species is defined as a 'species in which the evolutionary process has been...
as poultry
Poultry
Poultry are domesticated birds kept by humans for the purpose of producing eggs, meat, and/or feathers. These most typically are members of the superorder Galloanserae , especially the order Galliformes and the family Anatidae , commonly known as "waterfowl"...
makes them more readily available than other vertebrates (such as mice
MICE
-Fiction:*Mice , alien species in The Hitchhiker's Guide to the Galaxy*The Mice -Acronyms:* "Meetings, Incentives, Conferencing, Exhibitions", facilities terminology for events...
), 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
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
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 in 1900, but this system lacked detail and was not widely used, with most researchers relying on somite
Somite
A somite is a division of the body of an animal. In vertebrates this is mainly discernible in the embryo stage; in arthropods it is a characteristic of a hypothetical ancestor.- In vertebrates :...
number or age to identify the stage of development. Hamburger and Hamilton aimed to provide a detailed description of developmental events, modelled on an earlier system for Axolotl
Axolotl
The axolotl , Ambystoma mexicanum, is a neotenic salamander, closely related to the Tiger Salamander. Larvae of this species fail to undergo metamorphosis, so the adults remain aquatic and gilled. It is also called ajolote...
by Harrison.
The Hamburger-Hamilton system provides advantages over the Carnegie system
Carnegie stages
In embryology, Carnegie stages are a standardized system of 23 stages used to provide a unified developmental chronology of the vertebrate embryo....
in that it allows the developing chick to be accurately staged both at embryonic
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
and fetal
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
stages, and is used universally in chick embryology.
Stages of Development
Chick embryos can be "staged" according to the different morphologicalMorphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
landmarks. Although most organ systems have a stereotypical appearance at each stage, there are a few which particularly lend themselves to use in staging chick development.
- In the very early embryo, the primitive streakPrimitive streakThe primitive streak is a structure that forms during the early stages of avian, reptilian and mammalian embryonic development.-Introduction:...
is the only visible landmark, and its shape and size is used to stage HH1-6 embryos. - The nervous systemNervous systemThe nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
is formed by a process of neurulationNeurulationNeurulation is the stage of organogenesis in vertebrate embryos, during which the neural tube is transformed into the primitive structures that will later develop into the central nervous system....
. Stages 5–8 may be defined by the formation of a head fold, the neural foldsNeural foldsIn front of the primitive streak two longitudinal ridges, caused by a folding up of the ectoderm, make their appearance, one on either side of the middle line...
, and their fusion to form the neural tubeNeural tubeIn the developing vertebrate, the neural tube is the embryo's precursor to the central nervous system, which comprises the brain and spinal cord...
. The expansion of anterior neural tube to form the brainBrainThe brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
may also be used to identify later stages. - SomitogenesisSomiteA somite is a division of the body of an animal. In vertebrates this is mainly discernible in the embryo stage; in arthropods it is a characteristic of a hypothetical ancestor.- In vertebrates :...
- the progressive segmentation of the paraxial mesodermMesodermIn all bilaterian animals, the mesoderm is one of the three primary germ cell layers in the very early embryo. The other two layers are the ectoderm and endoderm , with the mesoderm as the middle layer between them.The mesoderm forms mesenchyme , mesothelium, non-epithelial blood corpuscles and...
- provides a convenient method for staging embryos between stage 6 and 14. Somites form with surprising regularity every 90 minutes. Stage 10 embryos have 10 somites, and as a rule of thumb, the embryo gains 3 somites during each stage (i.e. Stage 11 embryos have 13 somites, Stage 12 embryos have 16, etc.). The authors note, however, that beyond 22 somites (HH14) it is better to rely on other markers. - Formation of the Branchial arches; which will give rise to the structures of the jawJawThe jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...
, pharynxPharynxThe human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
and larynxLarynxThe larynx , commonly called the voice box, is an organ in the neck of amphibians, reptiles and mammals involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume...
; begins at HH14 and is used as a marker throughout development. - The morphology of the limbsLimb (anatomy)A limb is a jointed, or prehensile , appendage of the human or other animal body....
, starting with the appearance of wing budLimb budIn embryology, the limb bud is a structure formed by the developing limb, derived from lateral plate mesoderm. It is intimately related with the apical ectodermal ridge, which secretes factors inducing the initial differentiation of the limb bud...
at stage 16, is a useful landmark for staging chick embryos and fetuses until hatching. Between stages 15 and 35, the appearance of specific structures within the limbs (such as joints and digits); at later stages the length of the toes are used. - The formation and development of the eyelids, primordial featherFeatherFeathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
s and beakBeakThe beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...
are used in a similar way to stage later development.