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What are the 5 stages of pre-embryonic development?
Fertilization, cleavage, blastocyst stage, implantation, gastrulation
What happens in fertilization?
the paternal and maternal chromosomes fuse to form a zygote, moves down the uterine tube and goes through rounds of mitosis and cytokinesis, implants in uterine tube
What happens in cleavage?
period of rapid mitotic cell division, blastomeres are produced, relative size the same, daughter cells become smaller, solid mass of cells called a morula is made
What happens in the blastocyst stage?
morula with 32 cells has entered the uterus, blastomeres inside secrete enzymes that break down the zona pellucida, morula now becomes a blastocyst at the end of day 4, mitotic divisions continue, differentiates into trophoblast and inner cell mass
What happens in implantation?
Trophoblast cells secrete enzymes that break down the zona pellucida & allow blastocyst to hatch, blastocyst then floats free in uterine cavity until day 6, trophoblast cells adhere to the endometrium and embeds in uterine wall, trophoblast cells proliferate and form 2 layers, hCG begins to be secreted by trophoblast cells, inner cell mass undergoes change and becomes bilaminar embryonic disc
What two distinct layers are formed when trophoblast cells proliferate?
Cellular (inner) and syncytial (outer) trophoblast
What makes up the bilaminar embryonic disc?
hypoblast (deeper layer) and epiblast (superficial layer)
What day is implantation complete?
day 11
When implantation is complete, what two structures form?
amniotic sac and yolk sac
What happens in gastrulation?
changes begin and primary germ layers form, bilaminar disc elongates and broadens at anterior end and a primitive streak appears on dorsal surface, third germ cell layer develops and the bilaminar embryonic disc transforms into a three-layered embryo
What are the three layers in the three-layered embryo?
endoderm, ectoderm, mesoderm
What is a blastomere?
identical cells formed by cleavage divisions
What does a blastomere do?
secrete enzymes that break down the zona pellucida and allows the blastocyst to hatch
What is a blastocyst?
a hollow ball of cells with a cluster of cells inside known as the inner cell mass
What is a morula?
solid ball of blastomeres surrounded by zona pellucida
What are the two distinct cellular components of a blastocyst?
Trophoblast and inner cell mass
What is the function of the trophoblast?
Adheres to, digests, and implants in the endometrium, protects the conceptus from attack by the mother's immune cells
What role does the hCG play in sustaining pregnancy?
Maintains hormone production by the corpus luteum, preventing menses, helps prevent the mother's immune system from rejecting the implanted embryo
How has knowledge of the hCG hormone become clinicaly and commercially useful?
hCG in a women's blood or urine is what is detected in pregnancy tests
From what embryonic structure does the bilaminar embryonic disk originate?
Inner cell mass
What are the three primary germ layers?
endoderm, mesoderm, ectoderm
What is the endoderm?
the internal germ layer that lines the digestive, respiratory and urogenital systems and the glands associated with these systems
Which germ layer enters the primitive streak?
Endoderm
What is the mesoderm?
the middle layer between ectoderm and endoderm
What two structures are in the mesoderm?
mesenchyme and notochord
What is the notochord?
a flexible rod that provides stable support for embryo
What is the ectoderm?
outer layer at dorsal side of embryonic disc
Examples of ectoderm
structures of the nervous system and the skin epidermis
The endoderm, mesoderm, and ectoderm are all considered....
epithelia
What are the four extraembryonic membranes?
amnion, chorion, yolk sac, and allantois
What is the amnion?
a thin but tough sac of membrane that covers an embryo, surrounds the amniotic cavity
What does the amnion do?
Provides a buoyant environment that protects the developing embryo against physical trauma and helps maintain a constant temperature
Amnion is also called?
bag of waters
What is the yolk sac?
endoderm-lined membrane that receives nourishment from the endometrium, forms part of the gut
All the body organs derive from the primary germ layers. True or False?
True
The yolk sac is the source of the....
earliest blood cells
What is the allantois?
membrane sac that stores waste and is the site for gas exchange, delivers oxygen to embryo, structural base for the umbilical cord that links embryo to the placenta
What is the chorion?
outer membrane that surrounds the amnion and the embryo, develops fingerlike chorionic villi, formed by the trophoblast and the extraembryonic mesoderm
What is the function of the chorion?
helps in the exchange of nutrients, gases, and wastes between the embryo and the mother's body, protects and nurtures the embryo
What is a tissue?
groups of similar cells which are specialized to perform a specific function
What are the 4 basic types of tissue?
epithelial, connective, muscle, nervous
What does epithelial tissue do?
form boundaries between different environments, lines body cavities, forms glands, covers exposed body surfaces, forms boundaries between different environments
Example of epithelial tissue
lining of digestive tract and other hollow organs
What does connective tissue do?
supports, protects, binds other tissues together, fills internal spaces
Connective tissue is a ________________ support to organs
structural
Examples of structures that have/are connective tissue
Bones, tendons, fat
What does muscle do?
contracts to cause movement, generates heat used to maintain core body temperature
Examples of muscles
skeletal, cardiac, smooth
What does nervous tissue do?
carries information from one part of the body to another through electrical impulses (internal communication)
Examples of nervous tissue
brain, spinal cord, nerves
What 3 general features tend to anchor cells together and stabilize tissues?
glycoproteins on cell surface, basement membrane, intercellular junctions
Glycoproteins on cell surface help anchor cells to....
one another
Basement membrane helps anchor cells to...
connective tissue
Intercellular junctions are ______________________ in the membrane
specializations
Name the 5 common types of cellular junctions
tight junctions, adherens junctions, desmosomes, hemidesmosomes, gap junctions
Describe tight junctions
the fusion of transmembrane proteins of adjacent cells in the intercellular space that circle the entire cell
What do tight junctions do?
helps cells adhere to all surrounding cell, prevents leakage of extracellular fluid, doesn't allow any space between adjacent cells
What are adherens junctions?
a dense protein layer of proteins on the inside of the plasma membrane that attaches both to membrane proteins and to cytoskeletal proteins
Which junction has a long, extended plaque?
adherens junction
In adherens junctions...
cadherins attach intracellularly to a plaque and extends through the plasma membrane and attach to cadherins from an adjacent cell
In adherens junctions, there are _______________ _______ that hold cells together so ET can be a strong membrane barrier
adhesion belts
What are desmosomes?
button shape plaque under plasma membrane with intermediate filaments extending through cytoplasm and attaching to desmosome on opposite side of cell
Desmosomes have...
cadherins
Desmosomes resist pulling of tissue which creates internal _______________ in tissue
strength
Desmosomes are common in ____________ & ____________ muscle and _______________
cardiac; smooth; skin
Hemidesmosomes are common in what tissue?
epithelial
The plaque of hemidesmosomes have...
transmembrane integrin proteins inserted, integrins attaching to laminins on outside of cell, and intermediate filaments
What do integrins do in hemidesmosomes?
anchor to plaque and extend through the membrane nd anchor proteins in basement membrane
What do intermediate filaments provide?
strength and stability to tissue
What are gap junctions?
communicating junctions where adjacent cells are close together
Gap junctions contain ___________ in the plasma membrane which form hollow cylinders called _________________
connexins; connexons
What do gap junctions do?
allow passage of chemical substances like solutes between cells, allow ion flow to synchronize activity in cells
What are the two major categories of epithelial tissue?
covering and lining epithelium, glandular epithelium
What are some special characteristics of ET that distinguish it from other tissues?
high degree of cellularity, specialized cellular/lateral contacts, polarity, avascularity, presence of a basement membrane, has a nerve supply, high regenerative capability
What type of specialized lateral contacts are common in epithelium?
hemidesmosomes
What is meant when we describe epithelial tissue as demonstrating polarity?
Cells near apical surface are different than the ones nearer the basal surface
What is the function of the basement membrane?
Anchors and supports ET sheets, helps it resists stretching and tearing, defines epithelial boundary
What are the 2 layers of the basement membrane?
basal lamina and reticular lamina
What is the basal lamina?
a thin superficial layer secreted by the ET cells
What does the basal lamina do?
acts as selective filter between the blood and the ET, acts as scaffolding which epithelial cells can migrate to repair a wound
What is the reticular lamina?
a deeper layer made up of collagen fibers produced by the underlying CT
What does the reticular lamina do?
anchor the basal lamina to underlying CT and provides mechanical strength
Which layer of the basement membrane is produced by epithelial cells?
basal lamina
Which layer of the basement membrane is produced by fibroblasts in the CT?
reticular lamina
What are the general functions of covering and lining epithelium?
protection, absorption and secretion, filtration and excretion, surface transport, sensory functions
What are the primary functions of simple epithelium?
filtration and rapid diffusion
What are the primary functions of stratified epithelium?
protects underlying tissues in areas subjected to abrasion
What is a gland?
one or more ET cells specialized to produce and secrete a product called secretion
What are endocrine glands?
ductless glands that secrete hormones directly into the interstitial fluid surrounding the secreting cell which then enter the blood
What are exocrine glands?
glands that form a duct which transports secretions to the epithelial surface
Exocrine glands may be ______________ or __________________
unicellular; multicellular
Unicellular glands secrete onto the
epithelial surface
Multicellular glands secrete product into a...
duct that opens on an epithelial surface
What are the body's only unicellular exocrine glands?
mucous cells and goblet cells
Mucous and goblet cells are found in...
epithelial linings of intestinal and respiratory tracts
Mucous and goblet cells produce...
mucin
What are the two basic structural components of multicellular exocrine glands?
epithelium-derived duct and secretory unit (acinus)
What is the difference between simple and compound exocrine glands?
Simple exocrine glands have an unbranched duct whereas compound exocrine glands have branched ducts
Tubular secretory portions of multicellular exocrine glands have...
secretory cells that form tubes
Alveolar secretory portions of multicellular exocrine glands have...
secretory cells that form small, flask-like sacs
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