Reproductive system 2 Flashcards
What are the 3 significant stages of the menstrual cycle that we observe
Menses (5 days)
Proliferative stage
Secretory stage
What is the purpose of the menstrual cycle
Prepares the body for pregnancy
Describe what occurs during menses
Removal of superficial layer of endometrium
Day 1 of cycle - first full day of bleeding
Describe what happens during the proliferative stage (~10 days I think)
Here, there is a sustained increase in estrogen, which stimulates GnRH secretion by the hypothalamus
GnRH triggers LH and FSH secretion from anterior pituitary
FSH stimulates estrogen production by developing follicles, resulting in positive feedback
A large increase in LH triggers ovulation (approx day 14), which involves ovary releasing an egg.
Describe what happens during the secretory stage (Day 14 - day 28 ; i think)
Because ovulation had already occurred, the corpus luteum remaining secretes progesterone and small amounts of estrogen bit not as much as the middle of the menstrual cycle (net decrease in estrogen)
The progesterone thickens the endometrium and causes fluid secretion (nutrients for embryo), which assists sperm when travelling through vagina
progesterone and estrogen inhibit hypothalamus and anterior pituitary and hence LH and FSH decline after ovullation, whilst progesterone reaches its peak, and estrogen also decreases
What happens 7-8 days after ovulation
Fertilisation has either occurred or not.
if fertilisation occurs, endometrium becomes fully developed, and Human chorionic gonadotropin (HCG) production by trophoblasts during implantation of embryo maintains corpus luteum, and prevents further release of LH and FSH by the hypothalamus
If fertilisation doesn’t occur, the endometrium is sloughed (shed or removed), the corpus luteum degenerates, ultimately reducing progesterone and increasing FSH for the next cycle
What is the function of GnRH
Causes pituitary gland in brain to make and secrete hormones luteinizing hormone (LH) and follicle stimulating hormone)
What is the function of LH
Triggers ovulation, forms the corpus luteum, supports early pregnancy.
What is the function of FSH
FSH’s main function is to help regulate the menstrual cycle. Specifically, FSH stimulates follicles on the ovary to grow and prepare the eggs for ovulation. As the follicles increase in size, they begin to release estrogen and a low level of progesterone into your blood.
What is the function of estrogen
Helps regulate the menstrual cycle
It can help inhibit hypothalamus release of GnRH and thus LH and FSH
What is the function of progesterone
The main function of progesterone is to prepare the endometrium (lining of your uterus) for a fertilized egg to implant and grow. If a pregnancy doesn’t occur, the endometrium sheds during your menstrual period. If conception occurs, progesterone increases to support the pregnancy.
It can help inhibit hypothalamus release of GnRH and thus LH and FSH
Basically supports pregnancy
What is the function of the endometrium
The physiological functions of the uterine endometrium (uterine lining) are preparation for implantation, maintenance of pregnancy if implantation occurs, and menstruation in the absence of pregnancy.
What are the 7 stages to forming a baby
1) Fertilisation (Day 0)
2) Cleavage (Day 1-6)
3) Implantation (Day 7 - 10)
4) Gastrulation (Day ~12)
5) Neurulation (Day ~18)
6) Organogenesis (Begins ~3 to 8 weeks and continues until birth)
7) Parturition
What is a zygote
Formed when the pronuclei of sperm and egg fuse
What happens during fertilisation
The body must prevent polyspermy from occurring in this stage (i.e. more than one sperm penetrating the oocyte)
What are the two mechanisms preventing polyspermy
Fast block (Na+)
Slow block (Ca2+)
Explain the process of fast block to polyspermy
In this phase, Na+ diffuses into oocyte from extracellular space, and this depolarises the cell. For reasons unknown, sperm can bind to, but wont enter a depolarised egg. Essentially forms an electrical barrier. This doesn’t last long
Explain the process of slow block to polyspermy
This is where Ca2+ is released by the ER, initating cell division (complete meiosis) and triggering a cortical reaction.
With Ca2+, it releases cortical granules, which assist in forming a fertilisation membrane. (Cortical granules fuse with egg plasma membrane, making the layer impenetrable - the fertilisation membrane)
What happens during the cleavage stage
Involves mitotic division as embryo migrates down oviduct to uterus. ENds up forming a “morula” which is a cluster of cells formed by cell division
Blastocyst forms from the morula after around 6 days. This contains rapidly dividing cells
What does the blastocyst consist of
Rapidly dividing cells
Trophoblast (provides nutrients to embryo)
Inner cell mass (which are cells that will become the embryo)
Blastocele (which is the liquid surrounding inner cell mass, and permits cell migration during gastrulation)
What happens during the implantation stage
This is where the blastocyst burrows into the uterine wall. The process produces human chorionic gonadotropin (HCG). This stimulates the corpus luteum to produce progesterone to maintain the pregnancy.
What happens during the gastrulation stage
It is the process where an embryo transforms from a one dimensional layer of epithelial cells, and reorganise into a multilayered, multidimensional structure called the gastrula. It contains the ectoderm, mesoderm and endotherm germ cell layers which will then develop into other systems.
Where is the ectoderm and what does it differentiate into
It is on the outside, and forms the skin and nervous system
Where is the mesoderm and what does it differentiate into
It is in the middle and forms the organs, muscle and bone
