Reproduction And Development Flashcards
With exception to which hormones, all reproductive hormones are _ hormones released from the testes, ovaries, and placenta
Except for FSH, LH, HCG, and inhibin which are peptide hormones
All other reproductive hormones are steroid hormones
Gonads
Organs involved in the production of gametes
Male Gonads
Testes
Involved in the production of gametes, or spermatocytes
Seminiferous tubules
Organ in which the production of sperm occurs
Set of long twisted tubes in the testes that are lined by Sertoli cells and spermatogonia
Spermatogonia
Located in the seminiferous tubules and arise from epithelial tissue to become spermatocytes, spermatids, and spermatozoa
Sertoli Cells
Surround and nurture the spermatocyte and spermatids
Stimulated by follicle-stimulating hormone (FSH)
Secrete inhibin, a glycoprotein hormone that acts on pituitary gland and inhibits FSH secretion
Leydig Cells
Cells located in the interstitium between the seminiferous tubules
Release testosterone when stimulated by luteinizing hormone
Primary androgen
AKA male sex hormone
Testosterone
Stimulates the germ cells to differentiate into sperm
Responsible for development of secondary sex characteristics
Helps to initiate growth spurt and stimulates closure of epiphyses of long bones (ends growth in height)
Secondary Male Sex Characteristics
Pubic hair, enlargement of the larynx, growth of the penis and seminal vesicles
What is Spermatogonium and how does it mature?
Sperm stem cell before it undergoes meiosis
After entering meiosis, becomes spermatocyte
At end of meiosis, becomes spermatid
Spermatid loses cytoplasm and forms the head, mid-piece, and tail to become a spermatozoon (sperm)
Spermatozoon
AKA sperm
Matured male gamete with a head, mid-piece, and tail
Head: composed of nuclear material and an acrosome (contains lysosome-like enzymes for penetrating the egg during fertilization)
Midpiece: Contains many mitochondria to provide energy for movement of tail
Only nuclear portion of sperm enters the egg
Where does the spermatozoon mature?
Exits the seminiferous tubules and is carried to epididymis to mature
After ejaculation, spermatozoa are propelled through the vas deferens into the urethra and out of the penis
Semen
Complete mixture of spermatozoa and fluid that leaves the penis upon ejaculation
Composed of fluid from the seminal vesicles, prostate, and bulbourethral glands (Cowper’s glands)
Capacitation
Process that occurs in the vagina in which spermatozoa become activated for fertilization
When does the ovarian cycle begin?
Start of oogenesis begins at birth where all of the eggs are arrested as primary oocytes in prophase I of meiosis at birth
When does the ovarian cycle begin?
At puberty
Follicle stimulating hormone stimulates the growth of granulosa cells around the primary oocyte
Granulosa cells secrete a viscous substance around the egg called the zona pellucida and egg becomes primary follicle
How does the primary follicle become the secondary follicle?
Theca cells in the primary oocyte differentiate from the interstitial tissue and grow around the follicle to form a secondary follicle
Upon stimulation by luteinizing hormone, theca cells secrete androgen, which is converted to estradiol (type of estrogen) by granulosa cells in presence of FSH and secreted into the blood
Luteal Surge
Just before ovulation, estradiol level rises rapidly and causes a dramatic increase in luteinizing hormone secretion
Results from positive feedback from rising estrogen which increases LH levels, which increases estrogen
Causes ovulation, bursting of follicle, and release of the egg (secondary oocyte) into body cavity
What happens when the egg is released from the ovary?
Egg is swept into the fallopian (uterine) tube by the fimbriae
Remaining portion of the follicle is left behind to become the corpus luteum
Corpus luteum secretes estradiol and progesterone through pregnancy, or 2 weeks after if not pregnant until it degrades into the corpus albicans
What are the stages of oocyte development and ovulation?
- Primary oocyte within follicle
- Follicle is growing and consists of oocyte and zona pellucida surrounded by granulosa cells surrounded by theca cells
- Follicle grows into secondary (Graafian) follicle
- Ovulation: follicle ruptures, releases secondary oocyte, secondary oocyte with corona radiata
- Corpus luteum develops from remnants of follicles
- Corpus luteum degenerates to corpus albicans if no fertilization of egg
Ovarian Cycle
- Follicular Phase: Begins with development of follicle and ends with ovulation
Includes Menstruation and Proliferation phase - Luteal Phase: Begins with ovulation and ends with degeneration of corpus luteum into corpus albicans
Includes Secretory Phase
When does the uterine cycle begin?
Day 0, also the first day of menstruation and the first day of the follicular phase
When does menstruation stop?
As the follicle matures and begins to release more estradiol
Proliferation phase then begins
Proliferation Phase
Phase after menstruation in which the uterine wall is rebuilt (building phase)
Lasts until ovulation
What happens after ovulation?
Corpus luteum begins to secrete progesterone, acts as maintennace hormone for uterus
Corpus luteum will degrade if no pregnancy into corpus albicans, no longer able to secrete progesterone to maintain uterine wall
Uterine wall sloughing off begins menstruation
What hormones are involved in the ovarian cycle and how do they vary?
FSH is high at beginning of menstruation, slowly drops, and surges just before ovulation. FSH drops to low again, and starts to rise for start of menstruation
LH is low at beginning of menstruation, surges just before ovulation and then drops to very low.
Estrogen is low during menstruation, surges at end of proliferation, drops at ovulation, and rises during secretory phase
Progesterone is low during menstruation, and slowly rises once ovulation starts, dropping near end of secretory phase
What happens as sperm makes contact with egg?
Enzymes digest a path for sperm through granulosa cells and zona pellucida
Cell membranes of sperm head and oocyte fuse upon contact, sperm nucleus enters cytoplasm of oocyte causing the cortical reaction
What is the cortical reaction?
Cortical reaction happens when sperm enters cytoplasm of oocyte and prevents other sperm from fertilizing the same egg
Second meiotic division of oocyte occurs and oocyte becomes ovum, releases second polar body
When does fertilization occur?
When the nuclei of the ovum and sperm fuse to form the zygote
Embryonic Cleavage
The stage that occurs after fertilization which involves repeated divisions of the zygote through the 2-cell, 4-cell, and 8-cell stage
Occurs while the zygote is in the fallopian tube
Zygote becomes morula when reaches 16 cells
Do the cells grow in size during cleavage?
Embryo does not grow during cleavage.
First 8 cells are equivalent in size and shape
Totipotent- potential to express any of their genes
Blastocyst
Mostly hollow ball filled with fluid, small cell mass on one side
Formed after cells of morula continue to divide for four days
Blastocyst implants in the uterine wall and fuses with uterine tissue to form placenta
Implantation
Process that occurs about seven days after fertilization
Outer cells of blastocyst implants in uterine wall and fuse with uterine tissue to form placenta
Small mass of cells on inside of blastocyst become embryo, made up of stem cells which are pluripotent- can develop into most types of cells in human body
Marks the beginning of the pregnancy
What occurs after implantation?
Placenta begins secreting the peptide hormone human chorionic gonadotropin (HCG)
Prevents degeneration of corpus luteum and maintains secretion of estrogen and progesterone
HCG first sign of pregnancy
When does the placenta reach full development?
End of first trimester
Begins to secrete own estrogen and progesterone, lowers secretion of HCG
When do cells begin to differentiate?
At end of 8-cell stage due to cell-to-cell communication
Blastocyst: inner cells become embryo, outer cells become placenta
Determination
Cell becomes committed to a specialized developmental path
Cells undergo determination such that they will give rise to a particular tissue early on
Cell Differentiation
Specialization that occurs at the end of development
Forms a specific type of specialized tissue cell
Fate of a cell is determined early on, but does not differentiate into specialized tissue cell until later
Involves complex series of intercellular interactions
Example of gene regulation in development
How do differentiated cells express different cell functions?
Cell still contains entire genomes, but parts of genome that are not required for specialized function of cell are note expressed
Due to epigenetic regulatory factors such as signals from other cells
Multipotent Stem Cells
Non terminally differentiated cells such as skin, liver, and blood cells that can regenerate these systems as needed
These types of tissues are susceptible to injury
Gastrulation
A process in embryonic development in which the gastrula is formed
Occurs in third week after fertilization
First cell movements occur as cells begin to slowly move about the embryo
Primitive streak is formed-mesoderm destined cells
Three primary germ layers are formed: (1) ectoderm, (2) mesoderm, (3) endoderm
What’s the difference between totipotent, pluripotent, and multipotent stem cells?
Totipotent: Can become any cell, placenta or embryo
Pluripotent: Can become any one of the initial three germ layers, part of embryo
Multipotent: Can replace cells of a particular lineage, such as skin, liver, and blood
What is the fate of the cells in the ectoderm?
Epidermis of skin, nervous system, sensory organs
What is the fate of the mesoderm?
Skeleton, muscles, blood vessels, heart, blood, gonads, kidneys, dermis of skin
What is the fate of the cells in the endoderm?
Lining of digestive and respiratory tracts, liver, pancreas, thymus, thyroid
Neurulation
Process in the third week of embryonic development, in which the gastrula develops into a neurula
Notochord (mesoderm) causes overlying ectoderm to thicken and form neural plate
Notochord degenerates, and neural tube forms from neural plate to become spinal cord, brain, and most of nervous system
Neural Crest
Cells of the ectoderm that are close to the neural tube
Function mostly as accessory cells to nervous system (Schwann cells), second order neurons of autonomic nervous system, and parts of endocrine system (adrenal medulla, C cells of thyroid)
Neural crest cells undergo cell migration to travel to various locations in body
How is apoptosis essential for embryonic development?
Aids development of nervous system
Aids operation of immune system
Causes destruction of tissue between fingers and toes to create hands and feet in humans
Damaged cells undergo apoptosis as well
How is apoptosis regulated?
Regulated by protein activity, as opposed to regulation at level of transcription of translation
Proteins are present but inactive in healthy normal cell
Cell Induction
One cell type affects the direction of differentiation of another cell type
Senescence
Process by which cells stop proliferating in response to environmental stressors and are ultimately cleared away by immune cells
Developmental process that allows shaping of tissues
Occurs in embryonic development and aging
Prenatal Development
Occurs before birth, and begins w/ development of embryo
Cleavage, blastula formation, gastrulation, neurulation, process of organ formation begins
9th week: major organs develop in final locations, considered a fetus
2nd trimester: not capable of independent survival
3rd trimester: growth in brain, not yet developed by parturition (birth) because too large
Motor Development
Takes infant from earliest stage (immobility) to independent walking
Basic milestones of progress the same
Cephalocaudal pattern: development head to toe
Proximodistal pattern: Midline to periphery
Progress starts with head, moves to trunk, moves down and out with limb movement
Lifting of head > lifting of chest > sit with support > sit without support > walking with support > standing independently > walking independently
Puberty
Biological Changes that lead to sexual maturity
Adolescent development includes psychosocial processes that accompany puberty
Sexual maturation occurs in context of primary sex characteristics and secondary sex characteristics
Reproductive hormones influence behavior
Adolescence
Socially designated period of rapid psychological and social change that is intertwined with pubertal development
Involves rapid physical growth and sexual maturation
