development I and II

Question 1

what is development?

Answer 1

all changes that occur during a life cycle, embryonic, after birth/hatching

Question 2

what are model organisms?

Answer 2

they are species specifically chosen for research because they can easily be studied

Question 3

what is fertilization?

Answer 3

sperm (usually flagellated, motile) + ovum (large, nonmotile = zygote

Question 4

what are the consequences of fertilization?

Answer 4

restores the 2n (diploid), often determines sex, activates egg and stimulates reactions promoting development

Question 5

what are the major steps in fertilization?

Answer 5

the sperm dissolves the protective layers around the egg and binds to surface receptors to ensure compatibility between the sperm and egg of the same species. at the same time to egg undergoes changes to its surface to prevent polyspermy.

Question 6

what surrounds the egg?

Answer 6

the egg has a plasma membrane and one or more coverings that aid in fertilization. these coverings act as barriers to interspecific fertilization, which is particularly important for species that undergo external fertilization. in mammals, the egg is surrounded by coverings both internally and externally, and fertilization typically occurs internally.

Question 7

what is the acrosomal reaction?

Answer 7

this is a process in fertilization where the sperm penetrates the protective layers of the egg. the sperm pushes through follicle cells and binds to receptor in zona pellucinda (ZP3), the acrosome (strucutre at the tip of sperm) busts and releases enzymes, helps the sperm through the zona pellucinda, this penetration, known as plasmogamy, leads to the cortical reaction

Question 8

what is the cortical reaction?

Answer 8

follows the acrosomal reaction in the fertilization process, Ca2+ is released in the egg from smooth ER, a wave of Ca2+ spreads through the egg, cortical granules fuse with plasma membrane, enymes are released and trigger a slow block

Question 9

what is a slow block in mammals?

Answer 9

• an enzyme catalyzes changes in the zona pellucida -> hardens + alters sperm receptors
• blocks polyspermy from occurring.

Question 10

what is the activation of the egg?

Answer 10

• follows cortical reaction
• triggered by the increase in calcium ions (Ca2+) in the cytoplasm
• leads to increased respiration, activation of maternal enzymes and proteins, and increased protein synthesis using the mRNA already present in the egg.
• nuclear fusion also occurs, the secondary oocyte that was arrested at metaphase II resumes the process and meiosis is completed (fertilization triggered this)

Question 11

what is nuclear fusion and what is the result?

Answer 11

microtubules guide the sperm nucleus to the egg. in humans, several hours after the sperm enters the egg, this process results in the formation of a zygote, which is diploid and totipotent, meaning it has the potential to give rise to all cell types.

Question 12

when does fertilization end?

Answer 12

when the zygote undergoes its first division, for mammals that is about 12-26 hours in

Question 13

what is cleavage?

Answer 13

the second step of embryonic development where the zygote becomes a multicellular embryo, there are rapid divisions with no cell growth

Question 14

what does yolk do to the pattern of division?

Answer 14

yolk is a mixture of proteins, phospholipids, and fats that serves as food for the developing embryo. the amount and distribution of yolk vary between animal groups and depend on the needs of the embryo. Embryos with little yolk develop faster and exhibit equal cleavage, while those with lots of yolk develop more slowly and show unequal cleavage.

Question 15

what are the stages of cleavage?

Answer 15

zygote (1 cell) -> embryo (2+ cells) -> blastula: a hollow embryo (with blastocoel) at least 128 blastomeres

Question 16

what are the patterns of cleavage?

Answer 16

equal holoblastic, unequal holoblastic, and mesoblastic

Question 17

what is equal holoblastic?

Answer 17

a pattern of cleavage where complete division occurs and the cells are equal sizes. there is a central blastocoel. EX: echnioderms, mammals, and annelids

Question 18

what is unequal holoblastic?

Answer 18

asymmetric cleavage caused by the yolk distribution, the yolk slows down cytokinesis, this includes amphibians

Question 19

what is meroblastic?

Answer 19

where only regions without yolk divide completely
examples: birds, reptiles, many fishes, insects

Question 20

what occurs after cleavage?

Answer 20

After the normal cell cycle resumes and cell division slows, morphogenesis, a cellular and tissue-based process by which the animal body begins to take shape, occurs during the next two stages of development: gastrulation and organogenesis.

Question 21

what is gastrulation?

Answer 21

a morphological process by which hollow blastula becomes layered embryo (gastrula) with the three embryonic germ layers, ectoderm (outside), endoderm, and mesoderm

Question 22

how does gastrulation in sea urchins work?

Answer 22

During gastrulation, various processes occur:
1. Cells at the vegetal pole (bottom) migrate into the blastocoel and later secrete calcium carbonate to form a simple skeleton.
2. The vegetal plate forms, and its cells flatten and fold inwards, creating the archenteron.
3. Cells at the tip of the archenteron extend to the opposite wall and make contact, eventually fusing the archenteron with the blastocoel wall to form the digestive tube.
4. This process results in the formation of three germ layers: the ectoderm, endoderm, and mesoderm, which give rise to structures like the mouth, anus, and cilia

Question 23

how does gastrulation in birds work?

Answer 23

In vertebrates, the process of germ layer formation is significantly different from that in echinoderms due to the presence of a large amount of yolk, which complicates the typical process. Vertebrate embryos undergo meroblastic cleavage, resulting in two primary layers: the upper epiblast (from which the embryo derives) and the lower hypoblast, both situated on top of the yolk mass.During a process called involution, epiblast cells migrate towards the midline. Some remain on the surface, contributing to the formation of the ectoderm. Others move inwards towards the yolk, then laterally, giving rise to the mesoderm. Alternatively, some cells move downward, displacing the hypoblast and forming the endoderm. Additionally, a primitive streak, known as the blastopore, forms during this process. Hypoblast cells play a role in forming a sac around the yolk and serve as a connection between the yolk and the embryo but do not directly contribute to the embryo itself.

Question 24

how does gastrulation occur in humans?

Answer 24

After cleavage, the blastocyst forms, which is the mammalian version of the blastula. It reaches the uterus about six days after fertilization and consists of approximately 100 cells surrounding a central cavity. The blastocyst has two main parts: the trophoblast, an outer single layer of cells, and the inner cell mass, a cluster of cells that becomes the embryo and is the source of the embryonic cell line. During implantation, the trophoblast contacts the uterine lining, secretes enzymes, and erodes an area of the endometrium. The embryo then penetrates this area, thickens, and extends projections into the endometrium. Gastrulation, which takes about one week and occurs during the 2nd-3rd week of pregnancy, is when the inner cell mass forms a flat disk with two layers. Some epiblast cells remain in place, forming the ectoderm. Others migrate in between the layers to become the mesoderm, and some migrate and mix with the hypoblast to become the endoderm. The human gastrula also develops extraembryonic membranes: the chorion, amnion, yolk sac, and allantois. These membranes hold liquid, form blood vessels, and facilitate gas exchange and the disposal of waste products.

Question 25

what is organogenesis?

Answer 25

the process of organ formation, when the embryo begins to increase in size, the nervous system is the first to develop in most vertebrates

Question 26

what is nuerlation?

Answer 26

during the formation of the nervous system, cells in the dorsal mesoderm develop into the notochord. the notochord then induces the overlying ectoderm to thicken, forming the neural plate. this process, known as induction, is where cells stimulate or influence the differentiation of neighboring cells.

Question 27

what is the neural plate?

Answer 27

an embryonic region, it rolls up and becomes the neural tube (why the nerve chord is hollow), develops int the CNS, anterior portion is the brain while the remainder is the spinal cord, some common developmental problems include folic acid deficiency

Question 28

how do cells migrate in organogenesis?

Answer 28

The formation of the nervous system includes both local and long-range cellular interactions and migration. Cells from the neural crest contribute to the development of various structures, such as parts of nerves, teeth, the skull, and bones. Somites, which are blocks of mesoderm cells located alongside the notochord, give rise to segmented or serially repeated structures like ribs, vertebrae, and the muscles associated with them.

Question 29

what occurs during the 1st trimester of human development?

Answer 29

The most significant changes occur for both the mother and the embryo during pregnancy. After implantation, the embryo secretes human chorionic gonadotropin (hCG), which acts like luteinizing hormone (LH) to maintain progesterone and estrogen levels from the corpus luteum during the first trimester, typically the first 2-4 weeks. During this time, the embryo receives nutrients directly from the endometrium. as the pregnancy progresses, the trophoblast (the outer layer of the blastocyst) mixes with the endometrium and develops into the placenta.

Question 30

what is the placenta?

Answer 30

an organ of exchange between the mother and embryo, provides nutrients and oxygen, removes waste excreted by mother, and the umbilical cord connects the embryo to the placenta

Question 31

how do twins happen?

Answer 31

identical twins share a placenta while fraternal twins have separate placentas. the inner cell mass can split during 1st month -> 2 groups of cells -> identical

Question 32

what happens during labor?

Answer 32

Around 266 days, or 38 weeks, or approximately 9 months into pregnancy, labor begins. Labor is characterized by uterine contractions that push the fetus and placenta out of the body. The process is regulated by various factors, including prostaglandins, the hormone estriol, and oxytocin.

Question 33

how does positive feedback during labor work?

Answer 33

image