MCAT Biology Chapter 3

Fertilization occurs in

Ampulla

Ampulla

Widest part of fallopian tubes

Acrosomal apparatus forms when

Sperm contacts secondary oocytes cell membrane after penetrating zona pallucida and corona radiata

Acrosomal apparatus

Tube from sperm to secondary oocyte to inject pronucleus

Cortical reaction

Sperm releases Ca²⁺ ions depolarize ovum membrane

Cortical reaction purpose

Prevents fertilization from multiple sperm and to increase metabolism of zygore

Fertilization membrane

Depolarized, impermeable zygote membrane after cortical reaction

Twin mechanisms

Dizygotic, monozygotic

Dizygotic/fraternal twins

Fertilization of 2 seperate ovum, with seperate placentas, chrion, and amnion

Monozygotic/identical twins

Single zygotes spilts into two zygotes

Types of monozygotic twins

Conjoined, monochorionic/monoamniotic, monochorionic/diamniotic, dichorionic/diamniotic

Monozygotic twin type is determined by

When the zygote seperation ocurred

After fertlization, zygote must ____ in time

Impant in the endometrium

First cleavage

Zygote creates an embryo as it travels to be implanted

Indeterminate cleavage

Makes cells that can develop into organsims

Monozygotic twins result from ____ cleavage

Indeterminate

Determinate cleavage

Makes cells that will differentiate

Morula

When the embryo is a solid mass of cell

Morula undergoes ___ to become a _____

Blastulation; blastula

Blastocoel

Fluid filled cavity in blastula

Blastocyst is a ____ ______ and contains the ____ and _______ ____ _____

Mammalian blastula; trophoblasts; inner cell mass

Trophoblast cells

Surrond blastocoel, forms chorion, placenta to get maternal blood to embryo

Inner cell mass

Forms the organism

Yolk sac

Supports embryo till placenta forms

Chorionic villi

Formed by trophoblasts

Penetrates endometrium

Develops into placenta for gas exchange

Chorion

Membrane outside embryo that develops into placenta, forsm from trophoblasts

Umbilical cord

Connects embryo to placenta, with 2 arteries and one vein

Formed from allantois and yolk sac

Amnion

Thin, strong membrane around allantois for shock absorption

Allantois

For early fluid exchange between embryo and yolk sac

Gastrulation

Formation of three cell layers

Occurs after

Gastrula

2 membranes merge to form a tube

Archenteron

Membrane invagination into blastocoel, develops into the gut

Blastopore

Opening of archenteron

Deutersomes

Blastopore develops into anus

Protosomes

Blastopore develops into mouth

Primary germ layers

Ectoderm, mesoderm, endoderm

Primary germ layers are established by

Cells migrating into blastocoel

Ectoderm

Outermost layer, forms integument, nervous system, adrenal medulla

Mesoderm

Develops into musculoskeletal, circulatory, excretory system

Forms gonads, muscular, connective tissue for respiratory, degestive system, adrenal cortex

Endoderm

Forms epithelial cells of digestive and respiraotry tracts, pancreas, thyroid, bladder, lower urinary tracts, part of liver

Differentiation occurs primarily through ____ _____

Selective transcription

Induction

Ability of cells to influence nearby cells

Used in selective transcription, guiding neuronal axons, making sure organ cells work together

Inducers diffuse from _____ to ______ _____ to mediate _____

Organizing; responsive cells; induction

Neurulation

Development of nervous system from ectoderm

Notochord

Rod of mesodermal cells, forms primitive spine

____ induces ectodermal cells to slide inward and form _____ ____ surrounding a _____ _____ to form a _______ _____

Notochord; neural folds; neural groove; neural tube

Neural crest cells

At the tip of neural folds, form PNS

Neural tubes form the _____

CNS

Ectodermal cells migrate over ______ to cover ______

Neural tube, crests; rudimentary nervous system

Teratogens

Substance interfering with embryonic development, specifically organogenesis

Teratogen effects depend on

Genetics, and its type

Maternal health issues that can influence development

Hyperglycemia, folic acid deficiency

Folic acid deficiency can cause

Spina bifida, anencephaly

Cell specialization stages

Specification, determination, differentiation

Specification

Cell is designated its cell type, reversible

Determination

Cell is committed to its cell type, irreversible

Determination can occur through

Presence of specific mRNA, proteins

Morphogens secreted from cells to influence neighboring cells

Differentiating

Changing the structure, function, biochemistry of a cell to match its cell type

Stem cell

Cells that haven’t differentiated

Exist in embryonic and adult tissue

Differentiate based on its potency

Totipotent

Embryonic, can differentiate into any cell type fetal or placental

After the ___ cell stage, morula begins to divide into _____ and ____

16; inner cell mass; trophoblast

Pluripotent

Cells after the germ layers differentiate

Can develop into any type of cell except placental

Multipotent

Can differentiate into different cell types within a group

Stem cell issues

Ethical, may reject, could become cancerous

Responder

Cell that is induced

Must be competent, able to respond to inducer

Autocrine

Signal acts in same cell as released the signal

Paracrine

Signals acts on nearby cells

Juxtacrine

Signal acts on cells directly next to it

Endocrine

Hormone travels through the blood stream to act on target tissue

Growth factors

Inducers, peptides that promote differentiation and mitosis

Reciprocal development

2-way induction

Signaling gradients

Closer to the signals origin has a higher exposure

Unique combination of gradients creates different cell types

During apoptosis the cell divides into _____ ____ and then broken apart into _____ _____ to be _____

Apoptotic blebs; apoptotic bodies; digested

Necrosis

Cell death due to injury, different from apoptosis

Internal substances may leak

Blebs prevent the release of

Harmful susbtances into extracellular environment

Complete regeneration

Tissue can be replaced identically by stem cells

Incomplete regeneration

Tissue can be replaced, but not identical in structure, function

More common in humans

Senescence

Biological aging, typicaly after 50 cell divisions

Telomeres

Ends of chromosomes to knot off DNA, shorten with each replication

Telomerase

Extends telomeres, prevents senescence

Maternal and fetal blood cannot ____, transfer nutrients through _____

Mix; diffusion

Placenta fucntions as a

Endrocrine organ, protection from pathogens, site of oxygenation

Fetal hemoglobin has a _____ affinity for ____ than maternal hemoglobin

Higher; oxygen

Fetal circulation

Lungs and liver are not significant, blood is shunted away

Gas, waste, nutrient exchange in the placenta

Maternal liver does detox and metabolism

Umbilical arteries

Carry fetal blood away from fetus to placenta

Umbilical veins

Carries blood from placenta to fetus

Foramen ovale

Connects RA to LA to bypass lungs

Ductus arteriosus

Shunts blood from PA to aorta

The shunts in the fetal heart work due to

Pressure differential between right and left sides of the heart

Ductus venosus

Shunts blood from the umbilical vein into inferior vena cava

First trimester

Forms fetus, organs and brain have formed, bones begin to harden

Second trimester

Fetus begins to move, face develops

Third trimester

Brain develops, antibodies are transferred in to build immunity

Parturition

Vaginal childbirth

Uterine contractions are coordinated by

Prostaglandins and oxytocin

Stages of childbirth

Cervix effacement and water breaks, uterine contracts to give birth, placenta is expelled in afterbirth