ZOOHCC - 601: Developmental Biology (Theory)
Unit 1: Introduction
Basic concept of developmental biology
Developmental biology is a branch of biology that studies how multicellular organisms develop from a single cell, and how their organs and tissues are formed and organized. It encompasses the processes of growth, differentiation, and morphogenesis, as well as the underlying genetic, molecular, and cellular mechanisms that control these processes.Some of the basic concepts of developmental biology include:
Cell differentiation: The process by which a relatively unspecialized cell becomes a specialized cell with a particular function, such as a muscle cell or a nerve cell. Morphogenesis: The process by which cells organize themselves into tissues and organs, and how these structures take shape. Cell signaling: The process by which cells communicate with each other to coordinate their activities, such as signaling molecules that regulate cell differentiation and morphogenesis. Gene regulation: The process by which genes are turned on or off to control the expression of specific proteins, which in turn regulate cell behavior and development. Stem cells: Cells that have the potential to develop into many different cell types, and play a key role in development and tissue repair. Evolutionary developmental biology: The study of how developmental processes have evolved over time, and how changes in these processes have contributed to the diversity of life on Earth.Basic concepts of Phases of development
In developmental biology, the phases of development refer to the sequential changes that occur in an organism as it grows and develops from a single cell to a complex organism with specialized tissues and organs. The key phases of development in developmental biology are:
Fertilization:
This is the initial phase of development, which begins with the fusion of a sperm and egg cell, resulting in the formation of a zygote.
Fertilization is the process by which a sperm cell fuses with an egg cell to form a zygote, which will develop into an embryo. The events that occur during fertilization are:
Sperm activation:
The sperm undergoes a process called capacitation, in which the membrane surrounding the sperm head becomes more permeable to allow the sperm to penetrate the egg.
Penetration of the egg:
The sperm moves through the female reproductive tract and reaches the egg in the fallopian tube. The sperm then releases enzymes that break down the protective layer surrounding the egg, allowing the sperm to penetrate the egg membrane.
Fusion of egg and sperm:
Once the sperm penetrates the egg, the nuclei of the egg and sperm fuse, resulting in the formation of a zygote.
Activation of the egg:
The fusion of the egg and sperm triggers a series of biochemical reactions that prepare the egg for its first cell division.
Formation of the fertilization membrane:
After fertilization, the egg membrane becomes impenetrable to prevent the entry of additional sperm.
Formation of the zygote:
The zygote undergoes rapid cell division and travels down the fallopian tube towards the uterus, where it will implant in the uterine wall and continue to develop into an embryo.
Cleavage:
During this phase, the zygote undergoes rapid cell division, resulting in the formation of a multicellular embryo.
Cleavage is the process of rapid cell division that occurs after fertilization, which results in the formation of a multicellular embryo. During cleavage, the zygote divides into smaller cells called blastomeres, which are similar in size and shape. The events that occur during cleavage are:
Zygote division:
The zygote undergoes a series of cell divisions without any significant growth, resulting in the formation of two, then four, then eight cells, and so on.
Blastomere size:
The size of the blastomeres decreases with each division as the total volume of the zygote remains the same.
Formation of the morula:
After several rounds of cell division, the embryo forms a solid ball of cells called the morula.
Blastulation:
The morula continues to divide, and a fluid-filled cavity forms inside, resulting in the formation of a hollow ball of cells called the blastula.
Cell differentiation:
During cleavage, the blastomeres become more specialized as they differentiate into two cell populations - the inner cell mass (ICM) and the outer layer of cells called the trophoblast. The ICM will give rise to the embryo, while the trophoblast will form the placenta and other supporting tissues.
Blastulation:
The morula develops into a hollow ball of cells called a blastula, with an inner cell mass and an outer layer of cells called the trophoblast.
During blastulation, the morula, which is a solid ball of cells, transforms into a hollow ball of cells called the blastula. Blastulation occurs during early embryonic development, following the cleavage stage, and is a critical step in the formation of a multicellular embryo. The events that occur during blastulation ar
Fluid accumulation:
As the blastomeres continue to divide, a fluid-filled cavity called the blastocoel forms inside the morula, creating a hollow ball of cells.
Formation of the blastula:
The embryo, now in the blastula stage, consists of a single layer of cells called the blastoderm, which surrounds the blastocoel.
Differentiation of the blastoderm:
The blastoderm differentiates into two distinct cell populations: the inner cell mass (ICM) and the outer layer of cells called the trophoblast.
Inner cell mass:
The ICM is a cluster of cells located at one end of the blastula. These cells will differentiate into the three primary germ layers during gastrulation, giving rise to all the tissues and organs of the body.
Trophoblast:
The trophoblast is the outermost layer of cells, which will give rise to the placenta and other supporting structures.
Gastrulation:
In this phase, the cells of the embryo start to differentiate into three germ layers - ectoderm, mesoderm, and endoderm - which will give rise to the different tissues and organs of the organism.
Gastrulation is the process by which the blastula, a hollow ball of cells formed during cleavage, transforms into a three-layered structure called the gastrula. During gastrulation, cells of the blastula move and rearrange themselves to form three primary germ layers - the ectoderm, mesoderm, and endoderm - which will give rise to the various tissues and organs of the body. The events that occur during gastrulation are:
Invagination:
A group of cells on one side of the blastula folds inward to form a depression called the blastopore.
Formation of the germ layers:
The cells around the blastopore move and differentiate into three germ layers: the ectoderm, mesoderm, and endoderm.
Ectoderm:
The outermost germ layer becomes the ectoderm, which gives rise to the skin, hair, nails, nervous system, and other structures.
Mesoderm:
The middle germ layer becomes the mesoderm, which gives rise to the muscles, bones, blood vessels, heart, kidneys, and other structures.
Endoderm:
The innermost germ layer becomes the endoderm, which gives rise to the lining of the digestive tract, respiratory tract, liver, and pancreas
Formation of the notochord:
A rod-shaped structure called the notochord forms along the dorsal (back) side of the embryo, which signals the beginning of neurulation.
Neurulation:
The ectoderm forms a neural plate that folds to form the neural tube, which gives rise to the brain and spinal cord.
Neurulation is the process by which the neural plate, a specialized region of ectodermal cells, folds and fuses to form the neural tube, which will give rise to the brain and spinal cord. Neurulation occurs during embryonic development, following gastrulation, and is a critical step in the formation of the nervous system. The events that occur during neurulation are:
Formation of the neural plate:
During early development, the ectoderm thickens along the dorsal (back) side of the embryo, forming a flat, elongated structure called the neural plate.
Neural plate folding:
The neural plate folds inward, forming a neural groove along its midline.
Neural tube formation:
The neural folds approach and fuse together, forming the neural tube, a hollow structure that will develop into the brain and spinal cord.
Neural crest formation:
During neural tube formation, a group of cells called the neural crest separates from the neural tube and migrates to other regions of the embryo, where they will give rise to a variety of different cell types, including some of the peripheral nervous system, cranial cartilage, and pigment cells.
Differentiation of the neural tube: The neural tube differentiates into three primary regions: the forebrain, midbrain, and hindbrain, each of which will give rise to specific structures and functions of the brain and spinal cord.
Organogenesis:
This phase involves the formation of specialized organs and structures from the germ layers. For example, the neural tube forms from the ectoderm and gives rise to the brain and spinal cord, while the mesoderm gives rise to the heart, bones, and muscles.
Organogenesis is the process by which the three germ layers formed during gastrulation give rise to the various organs and organ systems of the body. Organogenesis occurs during embryonic development and is a critical step in the formation of a fully functional organism. The events that occur during organogenesis are:
Germ layer differentiation:
The three primary germ layers (ectoderm, mesoderm, and endoderm) differentiate into specific cell types and begin to form various organs and organ systems.
Ectodermal development:
The ectoderm gives rise to the skin, hair, nails, nervous system, and other structures.
Mesodermal development:
The mesoderm gives rise to the muscles, bones, blood vessels, heart, kidneys, and other structures.
Endodermal development:
The endoderm gives rise to the lining of the digestive tract, respiratory tract, liver, and pancreas.
Formation of organ systems:
The different organs formed from the three germ layers interact to form various organ systems, including the circulatory, respiratory, digestive, and nervous systems.
Tissue differentiation:
The cells within each organ differentiate into specific cell types, such as neurons, muscle cells, and blood cells, which are essential for the proper functioning of the organ.
Maturation of organs:
As the organs mature, they acquire their final size, shape, and function.
Growth and maturation:
During this phase, the organism continues to grow and mature, with organs and tissues becoming more specialized and functional.
Aging and senescence:
This final phase of development involves the gradual decline of the organism's functions and eventual death.
