Tissues Flashcards
What is a zygote?
fusion of a sperm and ovum
What is a blastomere?
identical cells formed by cleavage divisions
What is a morula?
solid mass of blastomeres surrounded by zona pellucida, usually reaches uterus 4 days after fertilization
When does the morula reach uterus?
4 days after fertilization
What is a blastocyst?
hollow ball that forms when the morula contains exactly 32 cells
When is the blastocyst composed of hundreds of cells?
By the end of the 5th day
What are the two type of cell types in the blastocyst stage?
Trophoblast and inner cell mass
What is a microvilli?
fingerlike extensions of the plasma membrane that increase the exposed surface area.
What are cilia?
tiny hairlike projections that propel substances along their free surface
What are basal lamina?
noncellular adhesive, thin supporting sheet that is adjacent to basal surface of epithelium and consists of glycoproteins secreted by epithelial cells * selective filter and scaffolding that epithelial cells migrate along to repair a wound
What is the reticular lamina?
layer of extracellular material containing network of collagen protein
What is a trophoblast?
single layer of flattened cells
What is an inner cell mass?
small cluster of 20-30 cells
What are the 4 stages of formation of primary germ layer?
cleavage, blastocyst, implantation and gastrulation
When does a blastomere form a solid mass called morula that forms a hollow ball called blastocyst?
when there are exactly 32 cells
What happens during implantation?
Trophoblast cells secrete enzymes, which break down the zona pellucida and allow blastocyst to “hatch” at approx. day7. Blastocyst floats in uterine cavity until day 7-8, when it adheres to endometrium (lining of uterus) and embeds in uterine wall
What is timeline of events for formation of germ layer?
Day 4: ovum in upper uterine tube
Day 7: blastocyst hatches
Day7-8: floats in cavity
and then adheres to uterine wall
What are the stages by day?
Day 4: blastomere -> morula
Day 7: blastocyst
Day 7-8: blastocyst
What are the two trophoblast layers?
cellular trophoblast and syncytiotrophoblast(inner and outer layer, respectively)
How long does implantation take?
one week and finishes by day 14
What is hCG?
Human chorionic gonadotropin, which is secreted by trophoblast cells during implantation and later secreted by chorion. where placenta ultimately takes over endocrine function
HELPS MAINTAIN UTERINE LINING
what happens to inner cell mass during implantation?
becomes bilaminar embryonic disc to develop into embryo proper and separation in epiblast becomes amniotic cavity
What happens during gastrulation?
after amnion forms, embryonic disc elongates and primitive streak appears on dorsal surface and bilaminar embryonic disc transforms into three-layered embryo
What are the three primary germ layers?
endoderm, ectoderm and mesoderm
Endoderm, ectoderm and mesoderm is common where?
epithelia (endoderm) Nervous system(ectoderm) Everywhere else (mesoderm)
What is histology?
study of tissues
What are the four types of tissues and their functions?
Epithelial (lining for digestive tract, respiratory system, urogenital system, glands in these systems)
Connective (provides structural support)
Muscle (able to perform contraction and cause movement to occur)
Nervous (electrical impulses)
3 GENERAL FEATURES THAT HELP TO ANCHOR CELLS AND STABILIZE TISSUES
Glycoproteins on cell surface
Basement membranes
intercellular junctions
What are the types of junctions?
Tight, adherens, desmosomes, hemidesmosomes and gap
what are the functions of tight junctions?
result from fusing together of transmembrane proteins of adjacent cells; tight to eliminate space to make materials impermeable to movement in cell layer
what are functions of adherens junctions?
dense protein layer at inner surface of plasma membrane
(a plaque) attaches to membrane proteins and cytoskeletal proteins
Transmembrane glycoproteins, called cadherins, attach intracellularly to a plaque - extend through plasma membrane and attach intracellularly to a plaque - extend through plasma membrane and attach to cadherins from an adjacent cell
Cadherins are one type of cellular adhesion molecule (CAM)
Adhesion belts (areas of extensive adherens junctions) are often present in epithelial tissues
Most common in epithelial tissues
Identify the stages of pre-embryonic development, beginning at fertilization at gastrulation. Describe the main event(s) of each stage.
Cleavage: zygote begins to divide 24 hrs after fertilization and continues with the more rapid mitotic divisions of cleavage as it travels down the uterine tube. Period of fairly rapid mitotic divisions of zygote without intervening growth.
36 hrs after fert., first cleavage division created two identical cells called blastomeres
72 hrs post fert., morula forms: loose collection of cells that form a berry-shaped cluster of 16+ cells and travels toward uterus
Blastocyst Formation: fluid-filled hollow sphere composed of single layer of large, flattened cells called trophoblast cells and inner cell mass
Day 4/5 post fert., 100-cell embryo floats in uterus
Zona pellucida breaks down and blastocyst hatches from it
Trophoblast cells: single layer of flattened cells
Inner cell mass: small cluster of 20-30 rounded cells clinging to inside of blastocyst
Creates placenta to protect against mother’s cells from attack
Describe the histological differences between a morula and a blastocyst.
A morula is a loose collection of cells that from a berry-shaped cluster of 16 or more cells and the blastocyst contains both trophoblast cells and a small cluster of 20-30 rounded cells called the inner cell mass surrounded by the zona pellucida
What are the two distinct cellular components of a blastocyst?
Trophoblast: single layer of flattened cells
Inner cell mass: small cluster of 20-30 rounded cells clinging to inside of blastocyst
What is the function of a trophoblast?
Adheres to endometrium (lining of the uterus) and embeds in uterine wall to proliferate and form two distinct layers
What role does human chorionic gonadotropin (hCG) play in sustaining pregnancy? How has knowledge of this hormone become clinically and commercially useful?
The trophoblast cells secrete hCG to maintain the viability of the corpus luteum. It bypasses hypothalamic-pituitary-ovarian controls at this critical time and prompts the corpus luteum to continue secreting progesterone and estrogens. It also has protease activity and is an autocrine growth factor that promotes placental development.
From what embryonic structure does the bilaminar embryonic disk originate?
develops into the embryo proper from inner cell mass
Identify the three primary germ layers and describe which tissues ultimately derive from each.
Endoderm -> the epithelial linings of the digestive, respiratory and urogenital systems, and the glands associated with these systems
Ectoderm -> the structures of the nervous system and the skin epidermis
Mesoderm -> virtually everything else
Identify the four extraembryonic membranes and describe the function of each.
mucous membranes – line cavities which open to the outside of the body (e.g., respiratory & digestive tracts)
composed of epithelium (may be simple or stratified) over a thicker layer of loose CT (called the lamina propria)
serous membranes –
moist membranes that line body cavities that do not open to the outside, and that cover organs in that cavity
composed of simple squamous ET which lies on top of subserous fascia
serous membranes consist of 2 layers:
parietal layer lines body cavity
parietal layer reflects back over the organs in the cavity to form the visceral layer
serous fluid is secreted into the potential space between the visceral & parietal layers
cutaneous membrane –usually referred to as “the skin”
synovial membranes –line joint cavities of freely moveable (synovial) joints
What is a tissue?
A tissue is a group of cells that are similar in structure and perform a common or related function. Four primary tissue types interweave to make the body: epithelial, connective, muscle and nervous
Identify and describe the general function of each of the four basic tissue types.
Epithelial tissue covers
Connective tissue supports
Muscle produces movement
Nervous tissue controls