Bio 226: Reproductive system

Describe the process of spermatogenesis within sustentacular cells:

occurs in the seminiferous tubules of the testis

• spermatogonia (stem cells): diploid cells divide by mitosis

• primary spermatocytes: cells enter meiosis 1

• secondary spermatocytes: meiosis 2 (produces haploid)

• spermatids: haploid, immature sperm

• sperm cells: fully developed and released into the lumen

Sustentacular cells: act as nurse cells to help regulate every stage of development

What is the role of the epididymis?

Sperm storage and become capable of fertilization, also helps to transport to the vas deferens

What is the role of the vas deferens?

transport of sperm during ejaculation

What is the role of the seminal vesicles?

produces 60-70% of semen volume and mixes with sperm

• rich in fructose for energy source for movement to egg

• slightly alkaline, helps to neutralize the acidic environment of the vagina

What is the role of the prostate gland?

adds fluid to semen (contributes 20-30%)

• activates, protects and enzyme rich fluid

What is the role of the bulbourethral glands?

The glands that prepare the urethra for the passage of semen

• helps in lubrication (pre-cum)

What are the components of semen? What are their functions?

1. sperm cells: carry actual reproductive cells that carry DNA

2. fluid from seminal vesicles (60-70%): energy source

3. prostate gland: activate sperm motility

4. bulbourethral glands: pre cum

In men, what is the role and regulation of gonadotropic releasing hormone?

key hormone that controls the male reproductive system by signaling the pituitary to release other hormones

• signals the FSH and LH

Controlled by negative feedback

In men, what is the role and regulation of follicle stimulating hormone?

controls sperm production: acts on the seminiferous tubules

regulated by GnRH and negative feedback by inhibin

In men, what is the role and regulation of interstitial cell stimulating hormone?

controls testosterone production

• supports spermatogenesis

Regulated by GnRH: negative feedback loop

In men, what is the role and regulation of inhibin?

produced in the testes that helps to regulate sperm production by controlling FSH levels

• inhibits the secretion of FSH→ slows sperm production

In men, what is the role and regulation of testosterone?

• develops male reproductive organs

• supports sperm growth

• secondary sex characteristics

• sex drive

• Controlled by LH

Describe the sex-determining region of the Y chromosome:

codes for a transcription factor (allows gene to be expressed for male development)

• if gene is damaged=intersex

• if receptors aren’t sensitive=don’t physically develop into a man

Describe the process of oogenesis:

process of forming a mature egg

• primary oocytes begin meiosis but don’t continue past prophase, each surrounded by follicle cells→ primordial cells

• a few primordial follicles begin to develop during menstrual cycle but only one stays

• meiosis l: haploid, produce 1st polar body

• meiosis ll: stops in metaphase ll

• ovulation: secondary oocyte is released from the ovary and travels into the fallopian tube

If fertilization occurs: completes meiosis ll and produced second polar body (mature egg/zygote)

if fertilization does not occur: oocyte degenerates and meiosis ll is not completed

Describe follicle maturation:

1. follicle(ball of cells surrounding oocyte)

2. primordial follicle

3. primary follicle

4. antral follicle

5. mature antral follicle

6. ovulation

What is the uterine tube and what is its function?

tubes that connect the ovaries to the uterus

• capture ovulated egg

• site of fertilization

• transport of the zygote

What is the uterus and what is its function?

hollow, muscular organ between the uterine tubes and the vagina

• site of implantation (where pregnancy begins)

• support and nourishment of the embryo/fetus

• menstrual cycle regulation

What is the cervix and what is its function?

narrow, lower part of the uterus that connects it to the vagina

• protection of the uterus

• sperm transport

• closed during pregnancy, opens during birth

what is the vagina and what is its function?

muscular, elastic tube that connects the cervix to the outside of the body

• receives sperm

• passageway for the delivery of the body

• exit of menstrual flow

• protection

In women, describe the role and regulation of gonadotropin releasing hormone?

Key hormone produced by the hypothalamus that controls the entire ovarian cycle

• stimulates FSH and LH

Regulated by estrogen and progesterone

In women, describe the role and regulation of follicle stimulating hormone?

controls early ovarian follicle development and helps regulate the menstrual cycle

• supports estrogen production

• selects the dominant follicle

Regulated by GnRH, negative feedback from estrogen or inhibin

In women, describe the role and regulation of luteinizing hormone?

controls ovulation and supports hormone production after ovulation

• triggers ovulation: causes follicle to rupture and release 2nd oocyte

• forms the corpus luteum

• stimulates progesterone

Regulated by GnRH, negative and positive feedback

In women, describe the role and regulation of estrogens?

regulates the female reproductive system and menstrual cycle

• develops secondary sex characteristics

Controlled by FSH, GnRH, negative and positive feedback

In women, describe the role and regulation of progesterone?

prepares and maintain the uterus for pregnancy and helps to regulate the menstrual cycle

• maintains uterine lining

• prevents new ovulation

• supports early pregnancy

• thickens cervical mucus

Regulated by LH, negative feedback, and corpus leuteum

In women, describe the role and regulation of inhibin?

helps to control the menstrual cycle by regulating FSH levels

In women, describe the role and regulation of androgens?

mainly the building blocks for estrogen

Describe the evens of the follicular and luteal phases of the ovary:

Follicular: day 1 of menstruation

• Several follicles in the ovary grow

• only 1 becomes dominant and others degenerate

• produce estrogen: rebuilds the uterine lining

Luteal: after ovulation

• when follicle ruptures it becomes the corpus luteum

• secretes progesterone: prepares uterus for implantation

Describe the menstrual, proliferative, and secretory phase of the endometrium:

• menstrual: lining is shed (because decreased progesterone and estrogen)

• proliferative: rebuilding and thickens the endometrium

• secretory phase: fully developed and ready for implantation

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Compare what happens to hormones and ovarian events when fertilization occurs vs when it doesn’t

Fertilization occurs:

• progesterone levels remain elevated

• embryo produces hCG

• corpus luteum is maintained (1st trimester nutrients until placenta is created)

Fertilization does not occur:

• corpus luteum degenerates

• progesterone and estrogen levels drop

• uterine lining sheds (menstruation)- cycle restarts

What happens to the secondary oocyte and remnant of the antral follicle following ovulation

secondary oocyte: released into the uterine tubes but stopped in metaphase ll of meiosis

• fertilization: sperm enters and meiosis ll is completed to form a mature ovum, second polar body and becomes zygote

• no fertilization: degenerated within 24 hrs

antral follicle: ruptured follicle transforms into the corpus luteum

• fertilization: corpus luteum maintains, progesterone stays high

• no fertilization: corpus luteum degenerates and triggers period

describe the process of fertilization and implantation:

Fertilization:

• sperm reaches the oocyte

• penetrates the outer cells (zona pellucida and other glycoproteins)

• sperm and oocyte membranes fuse

• complete meiosis ll

• form zygote → morula (extra cells)→ blastocyte (hollow)

Implantation: blastocyte embeds into the uterine lining

• blastocyte arrives uterus

• attaches to the endometrium

• trophoblast cells invade the endometrium (begin to form placenta)

• secrete hCG

Define zygote:

the first cell formed when a sperm cell fertilizes an egg

Define morula:

solid ball of cells formed after a zygote undergoes several rounds of cell division

Define blastocyst:

hollow ball of cells with a fluid-cavity that develops 5-6 days after fertilization

• stage that implants into the uterine wall, allows pregnancy to begin

Define embryo:

early stage of human development that occurs after implantation

• called this for the first 8 weeks

• when major organs and body structures start to form

Define fetus:

later stage of human development after the embryo

• from about week 9 after fertilization until birth

• major organs grow and mature

What is the role of the extra-embryo structures that develop from the trophoblast?

support, protect, and nourish the developing embryo

• forms a large part of the placenta make sure the embryo gets food, oxygen, protection, and hormonal support

Explain how the exchange of nutrients and wastes cross the placental membrane:

diffusion: gases and small molecules

facilitated diffusion: like glucose

active transport: amino acids, Ca2+, and iron

*placenta acts as a selective filter

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Describe fetal circulation vs circulation after the child is born:

• gas exchange at placenta, not at lungs

• 3 mechanisms to shunt the blood in the heart

  • Ductus venosus: bypasses liver and other capillary exchange

  • foramen ovale: right artium→ left atrium

  • ductus arteriosus: bypasses the lungs (connects pulmonary artery→ aorta)

What are the hormonal changes that occur during pregnancy"?

hCG: produced early by trophoblasts in the placenta, secretes estrogens and progesterone

*after 1st trimester, placental hormones takes over

progesterone: maintains uterine lining, prevents contractions (oxytocin), fetal development

estrogen: uterine growth, blood flow to uterus, mammary glands

relaxin: relaxes pelvic floor

Aldosterone: women need more water and salt for larger mass

parathyroid hormone: raises blood calcium to make babies skeletal system

Describe the birth process:

1. uterine contractions

2. cervix dilates

3. water breaks

4. deliver baby

5. deliver placenta

*positive feedback loop

What is the role of progesterone and oxytocin during the birthing process?

Progesterone: keeps uterus calm but inhibiting uterine contractions, maintains uterine lining, decreases towards the end of pregnancy

oxytocin: stimulates uterine contractions, push baby down, stronger contractions, delivery

How does the birthing process use positive feedback?

cycle keeps amplifying itself until baby is delivered

• babies head pushes against the cervix

• stretching stimulates release of oxytocin

• oxytocin causes stronger contractions

• pushes babies head harder against the cervix

• more stretching

• more oxytocin

Describe the structure of mammary glands:

produce and secrete milk for babies

• alveoli: milk producing units (push milk out)

• ducts: carry milk

• nipple: releases the milk

exocrine glands

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What is the role of lactogen in mammary glands in milk production?

stimulates growth of mammary glands and prepares the breast for lactation

*no milk actually being made

What is the role of prolactin in mammary glands in milk production?

stimulates the alveolar cells to produce milk

What is the role of oxytocin in mammary glands in milk production?

responsible for the milk ejection

Why is milk secretion a neuroendocrine reflex?

it involves both nervous system and endocrine systems

• neuro: detects suckling and sends signal to brain

• endocrine: releases oxytocin in the blood to act on the breast