Reproduction Flashcards
Erection
penis becomes enlarged and firm
Sexual excitation initiates blood flow
ejaculation
Rhythmic contraction of epididymus, vas deferens, seminal vesicle, prostate gland
propels contents of the ducts and glands into the urethra and then out the body
Semen
provide nourishment
Neutralises acidic nature of urethra and female vagina, protecting sperm.
insemination
Sperm travel through cervix and body of uterus into uterine tubes
quickly reach upper portions of uterine tubes, often a few minutes
Along wt swimming, contractions in uterus walls and uterus tubes help sperm reach egg faster
sperm mortality
Death rate of sperm is high
only few 1000s reach uterine tube
Ova
Has two layers around it: corona radiata and zona pellucida
corona radiata
Follicle cells held together by cementing materials that contain acid
outer layer
Zona pelucida
glycoprotein matrix surrounding the plasma membrane of oocyte
Inner layer
Acro some (fertilisation)
acrosome of sperm head uses enzymes to break down acid in cementing material holding cells of corona radiata together.
1 acrosome’s enzymes are inefficient therefore 1000s of sperm needed to loosen layer to allow 1 sperm to reach egg.
Once sperm through corona radiata
encounters zona pellucida and initiates acrosomal reaction.
Release of digestive enzyme from acrosome, breaking down glycoprotein matrix of zona pellucida, giving access to plasma membrane of Oocyte, preventing entrance of any more sperm. This ensure only one haploid cell joins wt Oocyte.
once sperm entered oocyte
Tail is absorbed, head begins to move through cytoplasm to form male pronucleus, the haploid nucleus of sperm.
entrance of sperm stimulates secondary Oocyte to complete 2nd meiotic division.
Nucleus of Oocyte develops into female pronucleus, haploid nucleus of Oocyte, fuses with male pronucleus, forming single diploid nucleus.
Oocyte is now referred to as zygote.
Blastocyst formation (after fertilisation)
zygote travels down uterine tube and begins to divide by mitosis
Blastocyst
6 days after fertilisation, zygote has reached uterus and developed into blastocyst.
Hollow ball of cells that surround a cavity filled wt fluid
at one side is inner membrane (group of 30 cells), embryoblast. Inner cell mass composed of stem cells, differentiation develops embryo.
Implantation
blastocyst remains free within cavity pf uterus for 2-3 days then sinks into soft endometrium, to become firmly attached to wall of uterus.
Enables the blastocyst to gain nourishment for growth and development by absorbing nutrients from glands and blood vessels of uterine lining
hormone production
Blastocyst development depends on endometrium being maintained.
high levels of oestrogen and progesterone stop break down of endometrium, ceases menstrual cycle.
Corpus luteum secretes hormones until placenta is able to produce them, usually after 8-12 weeks.
1st 2 months referred as embryonic period, after 2 months embryo reffered to as foetus
Cell differentiation
cells making up inner cell mass of blastocyst are stem cells.
Genes and chemicals and contact wt other cells causes differentiation
totipotent stem cell
Has potential to create any type of cell necessary for embryonic development
pluripotent stem cells
Cells of inner cell mass
able to give to many, but not all, cell types necessary for foetal development
Multipotent stem cells
pluripotent that has undergone further specialisation
Give rise to cells that have particular function
primary germ layer
3rd week of development
Inner cell was undergoes changes as cells change to multipotent
resutlts in formation of 3 primary germ layers: Ectoderm, Mesoderm, Endoderm
Ectoderm
outermost germ layer
Form outer parts of body
(Eg. Skin, hair, mammary gland, nervous system)
Mesoderm
middle germ layer
Allows formation of stomach and intestines
(eg. Skeleton, muscles, connective tissue, heart, blood)
Endoderm
Innermost germ layer
(eg. Lining of digestive system, lungs, thyroid)
Embryonic membranes
4 embryonic membranes form: amnion, chorion, Yolk sac and Allantois
Lie outside embryo and serve to protect and nourish it as it develops
Amnion
First membrane to develop
8th day it surrounds embryo, enclosing cavity within which it secretes amniotic fluid, fluid is shock absorber, protecting baby, and helps maintain constant temp, and allowing foetus to move freely
Expands during growth, usually bursting at childbirth