Embryology and Fetal Development Flashcards
What happens in the embryonic period of development?
First 8 weeks- cells divide, tissues and organs form, structures the support and nourish the developing embryo form
What happens in the fetal period of development?
8 weeks to birth- body grows rapidly and organ begin to function and coordinate to form organ systems
How many chromosomes are in a human zygote? Where do they originate from?
A human zygote has 46 chromosomes. 23 from the sperm and 23 form the egg. They pair up at fertilization (23 pairs=46) *Male determines sex of zygote
Why does an egg have to be fertilized within 12-24 hours?
The egg loses its capacity to develop further after 24 hours. It starts to degenerate after 24 hours.
Why do only a few sperm arrive in the oviduct where the egg is?
The vagina is acidic (where many sperm are killed, only one oviduct has the egg (only one ovary releases an egg each month) and many sperm travel up the wrong oviduct.
What is the chromosome layout for boys and girls?
44 + XX=girl, 44+XY= boy
Why doesn’t the first sperm that reaches the egg enter and join with it?
It takes the action of many sperm and the enzyme in their acrosomes to break through the jelly coat of an egg. The first sperm that arrives needs the help of many other to get through this barrier, and a sperm arriving later will get in first
Define fertilization?
When the sperm and egg nucleus fuse
Define cleavage, where does it occur?
Cell division without enlargement of the cell. It occurs in the Fallopian Tubes (oviduct)
Flow chart from zygote to blastocyst
Zygote-> 2 cells-> 4 cells-> 8 cells-> 16 cells (morula)-> blastocyst (fluid filled space)
Name and describe the layers of a blastocyst
Out Cell Mass: trophoblast (becomes chorion, secretes hCG-> maintains Corpus Luteum)
Inner Cell Mass: fluid filled space turns into embryo
Flow Chart from ovulation to implantation.
Ovulation-> fertilization-> cleavage-> morula-> early blastocyst-> implantation
Flow Chart about an egg from ovary to outer cell mass of a zygote
Ovary-> fimbriae-> ovum-> fertilization with sperm-> zygote-> 2 cell stage-> 4 cell stage-> 8 cell stage-> 16 cell stage (morula)-> inner cell mass-> outer cell mass.
What is the process of cleavage?
Cell division (mitosis) that increases the number of cells in the embryo but doesn’t increase the size of the embryo
What group of cells does the embryo develop from?
Inner cell mass (embryoblast)
What is implantation?
When the blastocyst buries itself into the endometrium. The trophoblasts (outer cell mass) secretes enzymes to digest parts of the endometrium and the blastocyst sinks into the lining of the uterus. The endometrium now supplies the embryo w/ enough nutrients.
What is hCG and how long is it secreted for?
It is a hormone by the trophoblasts for the first trimester of pregnancy. It has the same action of LH- it maintains the CL thus the Cl will not degenerate but will continue to produce progesterone and estrogen to maintain the endometrium lining.
What is the amniotic cavity?
When a space begins to form between the inner cell mass and the trophoblast
What happens as the amniotic cavity forms?
The inner cell mass flattens into a disk shape. The disk consists of 2 layers then develops a 3rd.The outer ectoderm, inner endoderm, and the the mesoderm in between the two. This forms the body of the embryo
What is the process called forming the three layers? What is the names of these three layers? Identify the name if the developing embryo at this time?
Gastrulation. Primary Germ Layer. Gastrula
Define morphogenesis
The series of events that form distinct structures of a developing organism, gastrulation marks the beginning of this process and how the human body takes shape
Define differentiation (specialization)
Cellular process that enables a cell to develop a particular shape and to preform specific functions. Once you are a blastocyst, cells begin to take their set functions and are called “specialized cells”
How are the development of primary germ layers related to differentiation?
The development of the three germ layers (gastrulation) is the START of differentiation. All body cells originate from three layers.
Identify 3 structures that form the: Ectoderm
Skin, hair, nails, brain, NS, eyes, pituitary gland, adrenal medulla (Outer Layer)
Identify 3 structures that form the: Endoderm
Lining of respiratory/ digestive tract, gall bladder, pancreas, (Inner Layer)
Identify 3 structures that form the: Mesoderm
Muscles, heart, spleen, internal reproductive organs, adrenal cortex, kidneys (Middle Layer)
What is the first system to develop? What is the first system to be completed?
Nervous system and Circulatory System
Identify 3 events that occur during the third week?
Neurulation: the neural plate, followed by its development into the neural tube.
Skeleton Formation: notochord forms from the mesoderm
Heart Formation: heart is beating by day 18-21
Identify 3 events that occur during the fourth week?
Blood cells form, lungs and kidneys take shape, limb buds form, head w/ eyes, ears and nose visable
Identify 3 events that occur between the fifth and eighth week?
Week 5: eyes open, brain differeciate
Week 6: limbs lengthen and flex, glands make hormones to develop external genitals
Week 7-8: Organs are formed, NS coordinates activity, cartilage in skeleton forms
Description and function/fate of: Chorion
Outer most layer- secrets hCG, becomes the placenta and makes chorionic villi to increase surface are for exchanges of gases/nutrients
Description and function/fate of: Amnion
Transparent sac that encloses embryo, it is a shock absorber, and controls the temperature of embryo surroundings, stops pathogens from entering
Description and function/fate of: Allantois
Sausage shaped, becomes the umbilical cord. Its function is to break up and form the bladder
Description and function/fate of: Yolk Sac
Small sac suspended from abdominal are of embryo. It forms the digestive tract, makes red blood cell until liver takes over, forms future egg and sperm cells. IT IS NOT A SOURCE OF NUTRIENTS
What is the function of the placenta and umbilical cord?
Placenta: the site of exchange of materials between fetus and mom (using diffusion)
Umbilical Cord: to transport materials to and from the placenta
Flow Chart between mom and baby
Placenta-> diffusion-> site of exchange between fetus and umbilical cord-> transports materials between placenta and mom
What substances pass from the mother to the fetus?
Oxygen, nutrients (glucose, amino acids, fatty acids, vitamins, minerals), hormones (hCG, progesterone, estrogen), antibodies (immunity).
What substances pass from fetus to mother?
Carbon dioxide, (wastes, urea, ammonia, creatine), hormones (hCG)
What is the role of the umbilical cord?
Contains a vein to bring oxygen rich blood to the fetus. Contains 2 arteries which take oxygen poor blood to the placenta from the fetus.
Name 3 things that occur in the first trimester
Nervous system starts to develop, blood cells and major blood vessels start to form, external reproductive organs are distinguishable (12th week)
Name 3 things that occur in the second trimester
Heartbeat is heard, mother begins to feel movement, fetus becomes covered in lanugo (oily substance)
Name 3 things that occur in the third trimester
Layers of fat develop underneath the skin, digestive and respiratory systems are last to develop, fetal brain cells form rapidly to make connections
What is a teratogen?
It is any agent that causes a structural abnormality due to exposure during pregnancy (affects the normal development of the embryo/fetus)
Where are the hormones that maintain a pregnancy for the remaining trimesters?
Progesterone and estrogen are secreted by the placenta
What two hormones are involved in lactation?
Prolactin and oxytocin
Hormone site of production, storage, target tissues and mode of action: Oxytocin
Hypothalamus, posterior pituitary. Targets the uterus to stimulate uterine muscle contractions and stimulates prostaglandins and mammary gland cause milk release
Hormone site of production, storage, target tissues and mode of action: Prolactin
Anterior pituitary. Targets the mammary glands (breasts). Stimulates production of milk
What 2 hormones are involver in labour?
Oxytocin and prostaglandins (PG’s)
What is the role of prostaglandins in labour?
They are secreted by the placenta, directly stimulate uterine muscle to contract and expel the fetus
Why doesn’t breast milk production occur during pregnancy?
Prolactin is not secreted during pregnancy due to high levels of P & E that inhibit it. Once parturition occurs, P & E levels drop, prolactin levels rise and milk production occurs
