Unit 4: Reproductive Systems, Human Variation, Fertilization

BIOL 1003

sex determination (environment)

some aspect of the environment influences which traits develop

sex determination (genetic)

chromosomes determine sex

testis (sperm production)

• house seminiferous tubules (where sperm are made)

• specialized cells (Leydig cells) produce testosterone

scrotum (sperm production)

• pouch of skin that holds the testes

• expands/contracts to regulate temperature

seminiferous tubules (sperm production)

structures within the testes that are the actual sites of sperm production

epididymis (sperm production)

• rubbery device which sits astride the testes

• sperm mature and are stored prior to ejaculation

seminal vesicles (semen production)

• produce alkaline fluid that can neutralize acidity of the vagina

• fluid contains fructose and nutrients to provide energy for the sperm

bulbourethral (cowper’s) glands (semen production)

• provide a mucus-rich alkaline fluid that lubricates and neutralizes the inside of the urethra (leftover urine) for easier passage of sperm

prostate gland (semen production)

• organ which wraps around urethra and provides muscular contractions to propel semen during ejaculation

• block urine flow from bladder during ejaculation

• provides enzymes and zinc that aid in sperm mobility

vas (ductus) deferens (transport)

muscles that line the vas deferens contract to propel semen during ejaculation

ejaculatory ducts (transport)

ducts formed by the joining of vas deferens with the duct from the seminal vesicle, empties into urethra

penis (transport)

• the organ encircles the urethra as the urethra exists the abdomen

• changes from flaccid to effect

urethra (transport)

the tube that runs from the bladder through the penis through which urine and semen exit the body

order sperm travels…

1. seminiferous tubules

2. epididymis

3. vas deferens

4. ejaculatory duct (then)

5. urethra

6. penis

1. diploid, 4 un-replicated

~S phase

2. diploid, 4 replicated

~Meiosis 1

3. haploid, 2 replicated

~Meiosis 2

4. haploid, 2 un-replicated

~Maturation

5. haploid, 2 un-replicated

all human fetuses start with the same beginning reproductive organs…

• gonad (testes or ovaries)

• tubes (female duct or male duct)

• urogenital sinus

what develops male reproductive structures?

SRY gene present on the Y chromosome

• Sertoli cells lead female structures to degrade

• Leydig cells migrate into the gonad and produce testosterone → further development of male structures

negative feedback

the effect of an action decreases the subsequent action

hypothalamus - male

secretes GnRH

pituitary - male

responds to GnRH by releasing LH and FSH

Luteinizing Hormone (LH) - male

targets Leydig cells (in seminiferous tubules) to secrete testosterone

Follicle Stimulating Hormone (FSH) - male

targets Sertoli cells (in seminiferous tubules) to stimulate spermatogenesis

testosterone - male

• inhibits hypothalamus

• inhibits secretion of GnRH

• makes pituitary less responsive to GnRH

ovary (egg production)

• site of egg production

• if fertilized…site is corpus luteum

• produces hormones (estrogen, progesterone, and testosterone)

corpus luteum (egg production)

• sit of egg maturation within the ovary

• after ovulation, produces progesterone to maintain a possible pregnancy

uterus (egg production)

• muscle-lined, triangular organ where fertilized egg implants and develops

• organ develops a thick blood lining and sheds on a monthly cycle

vagina (transport)

• expandable structure that serves as the opening of the female reproductive tract

• point of sperm entry and exit of unfertilized eggs, menstrual discharge, and babies

cervix (transport)

• the opening between the vagina and uterus

• size of opening varies

oviducts (fallopian tubes)

• ducts transport mature eggs from the ovary toward the uterus

• place of fertilization

vulva

• exterior parts surrounding the vagina

• labia majora, labia minora, clitoris, urethra

clitoris

a sensitive nerve-rich organ

A = mitosis

B = meiosis 1

C = meiosis 2

D = before birth

positive feedback

the effect of an action increases the subsequent action

hypothalamus - female

secretes GnRH

pituitary - female

responds to GnRH by releasing LH and FSH

Luteinizing Hormone (LH) - female

• targets follicle cells and corpus luteum

• stimulates follicle cells to produce estrogen (1-12)

• stimulates follicle growth and ovulation (12-14)

• stimulates corpus luteum to secrete progesterone & estrogen (15-28)

Follicle Stimulating Hormone (FSH) - female

• targets follicle cells

• stimulates follicles to produce estrogen and grow (oogenesis), ovulation

Follicular Phase (1-12)

• negative feedback : high E = low GnRH

  - low GnRH → low LH + FSH → low estrogen

• low estrogen leads to endometrium shedding

• follicle cells begin growing

Ovulation (12-14)

• menstruation complete → endometrium thickens

• follicles mature in ovary

• positive feedback : high E = high GnRH

    - high GnRH → high LH + FSH → high estrogen + progesterone → ovulation

• rupture releases an oocyte → oocyte travels into oviducts and completes meiosis 

Luteal Phase (15-28)

• negative feedback : high E + P = low GnRH

    - low GnRH → low LH + FSH → estrogen + progesterone begin to fall at end of phase

if oocyte not fertilized…

• corpus luteum degrades → drop of progesterone → triggers menstruation and follicular phase

if oocyte fertilized…

• oocyte completes meiosis 2, forming a zygote and polar body

• zygote travels through oviduct, completes several cell divisions (blastocyst)

• blastocyst implants uterine lining → produces HGG → signals corpus luteum to produce progesterone

• high progesterone → inhibits shedding of uterine lining so pregnancy is maintained

all internal structures begin with…

• 2 biopotential gonads

• 2 sets of ducts (mullerian or wolfifan)

a fetus will develop female structures unless…

the SRY gene is present (typically on Y chromosome)

• SRY translated and transcribed into TDF protein

TDF (testes-determining factor)

• prevents transcription of ovary-promoting genes

• turns ON transcription of testes-promoting genes

  • Sertoli cells secrete a hormone causing degradation of female structures

  • Leydig cells secrete testosterone which promote male structures development

intersex

having characteristics that don’t fit binary notion (male or female) reproductive systems

*1-2 people per 100 people

gender identity

an internal sense of being male, female, neither, or some combination of both.

cisgender

people whose gender matches the sex they were assigned at birth

transgender

people whose gender does not match the sex they were assigned at birth

nonbinary

a person whose gender identity is a combination of or goes beyond the gender binary of woman and man

gender dysphoria

a feeling of distress that can happen when a person's gender identity differs from their sex assigned at birth or from their sex-related physical characteristics