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Bio Chapter 3

Terms in this set (27)

where does fertilization occur

how does the sperm penetrate the egg

what happens after the sperm penetrates
ampulla (widest part of the fallopian tube), rmr secondary oocyte is released in fallopian tube during ovulation from follicle


it releases acrosomal enzymes that allow it to penetrate the 2 layers around the oocyte and bind


it forms an acrosomal apparatus, a tube structure that extends to and penetrates the cell membrane of the secondary oocyte

then there is a cortical reaction (release of calcium ions)
what is the purpose of the cortical reaction
calcium ions depolarize the cell membrane of the ovum so this can prevent fertilization of the ovum by multiple sperm cells and can increase the metabolic rate of the newly formed dip zygote

depolarized membrane is called fertilization membrane
what are 2 ways twinning can occur
dizygotic (fraternal) twins form when 2 eggs are ovulated and fertilized by 2 diff sperm (these twins are just as genetically similar as siblings)

monozygotic (paternal) twins form when a zygote splits into 2 (genetically the same because the genome splits)
fertilization

what is the process of cleavage

what is the benefit of this process?
the zygote needs to move to uterus to implantation on the endometrium

while it does it this it undergoes rapid mitotic cell division (this is cleavage)

first cleavage creates an embryo

after several rounds of mitosis the embryo total size remains unchanged (because it is just dividing into smaller subunits but still all intact)


by dividing into smaller cells the cell will increase 2 ratios: the nuclear to cytoplasmic (NC) ratio and the surface area to volume ratio

this means there is an increased area for gas and nutrient exchange relative to the overall volume
what is indeterminate cleavage

what is determinate cleavage
results in cells that can still develop into complete organisms

results in cells with fates already determined meaning these cells are committed to differentiating into a certain type of cell
what is a morula

describe the process of blastulation
after several divisions, the embryo becomes a solid mass of cells which is a morula

morula undergoes blastulation to form a blastula which is a hollow ball of cells with a fluid-filled cavity called a blastocoel (in mammals we call a blastula a blastocyte)

blastula has an inner cell mass and an outer layer of trophoblast cells
implantation

explain how the trophoblast cells work to carry out the process of implantation

explain the structure of the umbilical cord
blastula moves through fallopian tubes into the uterus and implants itself into the endometrium

the trophoblastic cells give rise to the chorion (extraembryonic membrane that will develop into placenta)

trophoblast form chorionic villi that are microscopic fingerlike projections that penetrate the endometrium

chorionic villi develop into placenta that help with the maternal-fetal gas exchange


embryo to connected to the placenta by the umbilical cord

umbilical cord has 2 arteries and one vein (vein carries oxygenated and rich with nutrients blood from the placenta to the embryo and arteries carry deoxygenated blood and waste away)
what is the yolk sac

what is the allantois

what is the amnion
supports embryo until placenta is functional

extraembryonic membrane involved in early fluid exchange b/t embryo and yolk sac

extraembryonic membrane that surrounds the allantois and is fluid that acts as a shocker absorber to lessen the impact of maternal motion during embryo development
gastrulation

describe the process of gastrulation

what is the archenteron and blastopore
this is after implantation and it generates 3 distinct cell layers

this is the invagination of the blastula and cells continue to move towards the invagination which results in an elimination of the blastocoel

once the 2 membranes merge, it creates a tube through the middle

this creates the gastrula


membrane invagination into the blastocoel is called the archenteron

opening of archenteron is called the blastopore
what are primary germ layers

what is the ectoderm

what is the mesoderm

what is the endoderm
cells migrate into what remains of the blastocoel which creates 3 layers of cels called primary germ layers

outermost layer, gives rise to integument like the epidermis, hair, nails and the epitheia of the nose, mount and lower anal canal, also the lens of the eye, nervous system and inner ear are derived from ectoderm

middle layer, develops into musculoskeletal, circulatory and most fo the excretory systems

innermost layer, forms the epithelial linings of the digestive, respiratory, and bladder tract
differentiation

how are cells with the same genes able to develop into distinct cells with specialized functions?
mostly by selective transcription of the genome, only genes needed by cell type are transcribed

also the process of induction which is where one group of cells can influence nearby cells with the help of inducers
Neurulation (development of the nervous system)

nervous system is derived from ectoderm

so how does this happen?
begins after the 3 germ layers are formed

a rod of the mesodermal cells called notochord forms along the long axis of the organism like a primitive spine

notochord induces a group of overlying ectodermal cells to slide inwards to form neural folds that surround a neural groove

neural folds grow toward one another until they fuse into a neural tube which gives rise to the central nervous system

at the tip of each neural fold are neural crest cells

these cell migrate outwards to form the peripheral nervous system

finally ectodermal cells will migrate over the neural tube and crest to cover the rudimentary nervous system
problems in early development

why is this a sensitive time

what are teratogens?
the germ layers are forming and organogenesis begins (organ formation)


substances that interfere with development and can cause detects or death of developing embryo
cell specialization

cells in tissues that create organs must be organized so the organs can function properly

what are the 3 steps of cell specialization

describe the process of specification and determination
specification, determination and differentiation


specification is when cell is REVERSIBLY designated as a specific cell type

determination is the commitment of a cell to a particular function in the future, it is now irreversibly committed

before determination it could have been any cell type even if it had gone through specification

there are multiple ways determination can occur...

one way is when the mRNA and protein of a parent cell is distributed and a specific mRNA and protein mlc are present in a DC (this results in determination)

also can occur due to secretion of specific mlcs from nearby cells, these mlcs are called morphogens and they cause neighboring cells to follow a particular developmental pathway
cell specialization

describe the process of differentiation (this involves potency)
in determination, the cell is committed but has not created the what is needed to carry out the functions of that cell type, this is goal of differentiation

now the cell undergoes changes in structure, biochem and function to develop into determined cell type

the tissues a particular stem cell can differentiate into are determined by its potency

cells with the greatest potency are called totipotent and these can differentiate into any cell type

after a few more divisions these totipotent cells start to differentiate into the 3 germ cell layers and are now called pluripotent

pluripotent can differentiate into any cell type but not those found in placenta structure

cells that continue to be more specialized are said to be multi-potent and these are differentiate into multiple types of cells within a particular group
cell-cell communication can occur in 4 different ways

what are they?
autocrine signals act on the same cell that secreted the signal

paracrine signals act on cells in the local area

juxtacrine signals do not usually involve diffusion but involve a cell directly stimulating receptors of an adjacent cell

endocrine signals involve secreted hormones that ravel through the bloodstream to a distant target tissue
what are growth factors and what is their function
inducers are often growth factors

these promote differentiation and mitosis in certain tissues

function on specific cells or in certain areas
Why is cell migration important?

explain how cell death works (apoptosis and necrosis)
cells need to disconnect from adjacent structures and migrate to their correct location

for example the anterior pituitary gland originates from a segment of the oral ectoderm and must migrate from the top of the mouth to its final location just below the hypothalamus


during apoptosis the cell undergoes changes in morphology and divides into many self-contained protrusions called apoptotic blebs that can be broke into apoptotic bodies and digested by other cells

necrosis is cell death where the cell dies as a result of injury, internal substances can be leaked which causes irritation of nearby tissues or even an immune response
cell regeneration

what is regenerative capacity, complete regeneration and incomplete regeneration?

how much regenerative capacity do humans have?
regenerative capacity is the ability of an organisms to regrow certain parts of the body

species that undergo complete regeneration typically retain extensive clusters of stem cells within their bodie

incomplete regeneration implies the newly formed tissue are not identical in structure of function to the tissue that has been injured or lost


humans have incomplete regeneration like when we are injured but regenerative capacity varies by tissue type

liver tissue has high RC and therefore living donors can donate up to 50% of their liver tissue because their own livers will regenerate the missing portion

the heart has little RC and kidneys have moderate RC
senescence and aging

what is senescence

how is senescence seen in the body
senescence is biological aging where our mlc and cellular structure change and this disrupt metabolism and eventually the organism dies

senescence for cells is the failure of cells to divide which may be due to shortening telomeres (these reduce lost of genetic material from the ends of chromo)

senescence at an organismal level means the bodies ability to response to a changing environment reduces
placenta is the organ where nutrients, gas and waste exchange occurs

what process helps with this?

what helps enhance the transfer of O from maternal to fetal circulation?
diffusion moves these products

diffusion needs a gradient which means there is a higher partial pressure of O in maternal blood than fetal blood


fetal blood cells contain fetal hemoglobin (HbF) which has a greater affinity for O than maternal hemoglobin

also helps with the movement of O into fetal circulatory system
what is the function of the placenta barrier

why is the placenta considered an endocrine organ also
immunity

the fetus is immunlogically naive as it has not been exposed to pathogens

so antibodies cross the placenta membrane to provide protection incase of any exposure in utero


because it produces progesterone, estrogen and hCG (all needed to maintain preg)
umbilical information will be on MCAT

what do the umbilical arteries do

what do the umbilical veins do
other arteries carry blood away from the heart but UA carry blood from fetus to placenta

other veins carry blood towards the heart, but UV carry blood to the fetus from the placenta

rmr oxygenation occurs in the placenta and not the fetal lungs so UA carry deoxy blood and the UV carry oxygenated blood
what are 4 keys differences b/t fetus and adult circulation
lungs and liver both do not serve significant functions prior to birth

gas exchange does not occur at the lungs rather at the placenta

detoxification and metabolism are primarily controlled by the mother's liver and nutrient and waste exchange occur at the placenta as well

so fetus does not depend on its own lungs and liver as these are underdeveloped organs and sensitive to the high blood pressure and the fetus develops 3 shunts to direct blood away from these organs
what are the 3 stunts developed by a fetus to direct blood away from lungs and liver
first shunt is called foramen ovale which is a one way valve that connects to the right atrium to the left atrium

this allows blood to enter the right atrium from the inferior vena cava to flow into the left atrium instead of the right ventricle and thereby be umped through the aorta into system circulation


second shunt is called ductus arteriosus which shunts leftover blood from the pulmonary artery to the aorta and the pressure difference b/t the right and left side of the hear pushes blood through this opening and into systemic circulation


third shunt is called the ductus venosus which shunts blood returning from the placenta via umbilical cord into the inferior vena cava so it bypasses the liver
what are the key developments in the first, second and third trimester
major organs begin to develop during first few weeks, heart beats at 22 days and then eyes, gonads, limbs and liver start to form

by five weeks the embryo is 10 mm and by week 6 it has grown 15 mm

the cartilaginous skeleton begins to harden into bone by week 7

by end of week 8 most organs have formed and brain is fairly developed and now the embryo is called a fetus

by end of 3rd month fetus is 9 cm long


second trimester the fetus undergoes a lot of growth and moves within amniotic fluid, face starts to look human, fingers and toes elongate

by end of 6th month fetus is 30 to 36 cm


7th and 8th month have rapid growth and brain development, antibodies are transferred by highly selective active transport from mom to fetus for protection from pathogens once baby is born

growth rate slows and fetus is less active as it has less room to move around
birth

how is vaginal childbirth or parturition accomplished
by rhythmic contractions of uterine smooth muscle, coordinated by prostaglandins and the peptide hormone oxytocin

first the cervix thins out and the amniotic sac ruptures (water breaking)

then strong uterine contractions result in birth of fetus

then placenta and umbilical cord are expelled (afterbirth)
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