Chapter 17 - Development Of A Human Embryo Flashcards
What does a zygote develop into?
An embryo
What happens to a zygote after fertilisation?
It begins to travel down the uterine tube and divide by mitosis
What is a blastocyst?
A hollow ball of cells that surround a cavity filled with fluid that forms during the early stages of embryonic development
When does a blastocyst develop?
About six days after fertilisation
What are the primary germ layers?
- endoderm
- mesoderm
- ectoderm
What are the first two months of pregnancy referred to as?
The embryonic period
What structures does the endoderm form?
- epithelium of alimentary canal and its glands
- epithelium of the urinary bladder, urethra and gall bladder
- epithelium of pharynx, larynx, auditory canal, trachea, bronchi and lungs
- epithelium of tonsils, thyroid, parathyroid and thymus gland
- epithelium of vagina and associated glands
What structures does the mesoderm form?
- skeletal, smooth and cardiac muscles
- cartilage, bone, blood and other connective tissue
- lymphoid tissue
- endothelium or the body cavity and joint cavities
- epithelium of the kidneys and ureters
- epithelium of the ovaries, testes and reproductive tracts
- epithelium of the adrenal cortex
- dermis of skin
What structures does the ectoderm form?
- epidermis of skin
- hair, nails, glands of skin
- lens, cornea and muscles of the eye
- receptor cells of the sense organs
- epithelium of the mouth, nostrils, sinuses, glands of mouth and anal canal
- enamel of teeth
- entire nervous system
- anterooms love of pituitary gland
- adrenal medulla
What is the placenta?
The organ the supplies nutrients and removes wastes from the foetus, serves as an endocrine organ, producing hormones necessary to maintain pregnancy
Functions of the Placenta: Endocrine
- secretes a number of hormones necessary for maintaining the pregnancy
Function of the Placenta: Excretory
- transport nitrogenous wastes such as urea, uric acid, ammonia and creatinine from the foetal blood to the mothers blood for excretion by the mother’s kidneys
Function of the Placenta: Immune
- transports antibodies from the mother into the foetal blood supply so that the foetus has immunity to some infectious diseases
Function of the Placenta: Nutritional
- transports nutrients such as glucose, amino acids, fatty acids, vitamins and minerals from the mothers blood to the foetal blood
- stores some essential nutrients early in pregnancy and releases them later when demand is greater
Function of the Placenta: Respiratory
- transports oxygen from the mother to the foetus, and carbon dioxide from the foetus to the mother
What are the roles of the Placenta?
- endocrine
- excretory
- immune
- nutritional
- respiratory
(Every evening I need rest)
When has the Placenta fully formed?
By the end of the third month
What are embryonic membranes?
Four membranes that lie outside the embryo and serve to protect and nourish as it develops
What is the amnion?
The first embryonic membrane to develop
What happens to amnion 8 days after fertilisation?
It surrounds the embryo, inclosing a cavity into which it secrete amniotic fluid
What does amniotic fluid do?
- protects the embryo from physical injury by acting as a shock absorber
- maintains a constant temperature
- allows the embryo and later, foetus to move freely
What happens to the amnion before childbirth?
It ruptures releasing the amniotic fluid, referred to as breaking of the waters
What do the additional two embryonic membranes do?
Become parts of the umbilical cord
What is the second embryonic membranes?
Chorion
What is the chorion formed from?
The outer layers of the blastocyst and a layer of mesodermal cells
How long is an embryo after 1 month?
Just under 4mm long
What occurs during the fifth week of pregnancy?
The arm and leg buds start to appear (arm buds slightly more advanced)
What has occurred by the 8th week of pregnancy?
- embryo has a recognisably human form
- all organs are present (not all fully functional)
- 3cm in length and 1 g
- sex is evident as external sexual organs are formed
What is the function of the chorion?
Becomes the main part of the foetal portion of the Placenta
What is on one side of a blastocyst?
A group of about 30 cells called the inner cell mass
What is implantation?
The process by which the blastocyst sinks/implants into the endometrium
When does implantation occur?
2-3 days after the blastocyst has arrived in the uterus
8-9 days after fertilisation
What does the umbilical chord do?
Carries blood from the foetus and mother
What are primary germ layers?
Embryonic tissues that will differentiate into all the tissues and organs of the body
What is a zygote?
A SINGLE CELL that results from the fertilisation of an egg by a sperm
What is the inner cell mass?
The group of cells in the blastocyst that develop into the embryo
What are stem cells?
Cells that have the ability to specialise into different types of body cells
What is proliferation?
The process by which cells replicate themselves
What is a tissue?
A group of cells that are similar in structure and function
What is differentiation?
The process by which unspecialised cells develop special characteristics, to suit particular functions
What are the three sources of stem cells?
- Umbilical corps and placental stem cells
- Embryonic stem cells
- Adult stem cells
Totipotent stem cells
- can give rise to all the cell types that make up the human body and all the cells that surround the developing embryo (including the Placenta)
Pluripotent stem cells
- can give rise to all the cell types that make up the body but not all the cell types that make up the embryonic membranes
Multipotent stem cells
- can develop into more than one of the cells types that make up the body but not all cell types
What are the three types of stem cells?
- totipotent
- pluripotent
- multipotent
