Reproductive system 2

Question 1

What are the 3 significant stages of the menstrual cycle that we observe

Answer 1

Menses (5 days)

Proliferative stage

Secretory stage

Question 2

What is the purpose of the menstrual cycle

Answer 2

Prepares the body for pregnancy

Question 3

Describe what occurs during menses

Answer 3

Removal of superficial layer of endometrium

Day 1 of cycle - first full day of bleeding

Question 4

Describe what happens during the proliferative stage (~10 days I think)

Answer 4

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.

Question 5

Describe what happens during the secretory stage (Day 14 - day 28 ; i think)

Answer 5

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

Question 6

What happens 7-8 days after ovulation

Answer 6

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

Question 7

What is the function of GnRH

Answer 7

Causes pituitary gland in brain to make and secrete hormones luteinizing hormone (LH) and follicle stimulating hormone)

Question 8

What is the function of LH

Answer 8

Triggers ovulation, forms the corpus luteum, supports early pregnancy.

Question 9

What is the function of FSH

Answer 9

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.

Question 10

What is the function of estrogen

Answer 10

Helps regulate the menstrual cycle

It can help inhibit hypothalamus release of GnRH and thus LH and FSH

Question 11

What is the function of progesterone

Answer 11

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

Question 12

What is the function of the endometrium

Answer 12

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.

Question 13

What are the 7 stages to forming a baby

Answer 13

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

Question 14

What is a zygote

Answer 14

Formed when the pronuclei of sperm and egg fuse

Question 15

What happens during fertilisation

Answer 15

The body must prevent polyspermy from occurring in this stage (i.e. more than one sperm penetrating the oocyte)

Question 16

What are the two mechanisms preventing polyspermy

Answer 16

Fast block (Na+)

Slow block (Ca2+)

Question 17

Explain the process of fast block to polyspermy

Answer 17

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

Question 18

Explain the process of slow block to polyspermy

Answer 18

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)

Question 19

What happens during the cleavage stage

Answer 19

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

Question 20

What does the blastocyst consist of

Answer 20

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)

Question 21

What happens during the implantation stage

Answer 21

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.

Question 22

What happens during the gastrulation stage

Answer 22

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.

Question 23

Where is the ectoderm and what does it differentiate into

Answer 23

It is on the outside, and forms the skin and nervous system

Question 24

Where is the mesoderm and what does it differentiate into

Answer 24

It is in the middle and forms the organs, muscle and bone

Question 25

Where is the endoderm and what does it differentiate into

Answer 25

It is at the bottom/inside/closest to endometrium, and forms the digestive system

Question 26

What is the primitive streak

Answer 26

The beginning of gastrulation is marked by the appearance of the primitive streak, a groove in the caudal end of the epiblast layer. Thus, the formation of the primitive streak firmly establishes the cranial/caudal axis. The primitive streak initially forms via a thickening of cells near the connecting stalk.

Question 27

What is an epiblast

Answer 27

The epiblast is the pluripotent primary lineage that will form the definitive germ layers in a complex process of differentiation and morphogenetic movements called gastrulation.

Question 28

What happens during the neurulation stage

Answer 28

During primary neurulation, the original ectoderm is divided into three sets of cells: the internally positioned neural tube, which will form the brain and spinal cord, the externally positioned epidermis of the skin, and the neural crest cells.

Folding of neural tube determines position of grey matter and white matter in the CNS

Question 29

What is gray matter

Answer 29

Unmyelinated neurons and cell bodies

Question 30

What is white matter

Answer 30

Myelinated neurons

Question 31

Does spinal cord have white or grey matter on inside or outside

Answer 31

White matter outside

grey matter inside

Question 32

Does brain have white or grey matter on inside or outside

Answer 32

Grey matter outside and white matter inside

Question 33

What is organogenesis

Answer 33

Organogenesis is the process of formation of organs from three germ layers.

For example, brains begin developing in week 3 through neurulation, heart begins developing in week 3, the four chambers formed in week 7 and kidneys begin developing in week 9

Question 34

What is parturition

Answer 34

It is the process of expelling the fully formed baby from uterus after gestation period of 280 days

Here, the stress on baby head releases hormone from fetal hypothalamus of the baby, causing ACTH from fetal pituitary. This then stimulates adrenal cortical steroid

This in turn activates progesterone synthesis levels to turn off, and increase estrogen and prostaglandin synthesis in the mothers womb,which contribute to uterine smooth muslce contractions. The uterine stretch further stimulates sensory neurons which cause a release in oxytocin further causing uterine contractions

Question 35

What is the gestation period

Answer 35

Describes the 3 trimesters of pregnancy and lasts 280 days.

1st trimester: doesnt show on belly as cells are just begining to undergo differentiation

2nd trimester: Belly will start to expand as fetal features get bigger

3rd trimester; fully developed baby