Lecture 4. Gonads, Gonadotrophins, and Gametogensis

Gonads

ovaries and testes

two jobs of gonads

produce sex hormones and produce gametes

sex hormones

hormones that regulate the development and functioning of reproductive organs and that stimulate the development of male and female sexual characteristics

testosterone

sex hormone in males

estrogen and progesterone

sex hormones in females

gametes

sex cells; sperm in makes and oocytes in females

Hormones

Chemical messengers

Paracrine hormones

Travel short distances directly to nearby cells or target organ, does not travel through the blood stream

Endocrine Hormones

Travel via the bloodstream from the gland that produces it to the organ on which it will act (target organ)

receptors

parts of the cell membrane that receive the signal/ hormone

receptor specificity

allows each receptor to respond to particular stimuli/hormone

free hormone

not bound to binding protein

travel freely in the bloodstream and free/active to bind to receptors 

bound hormone

hormone "bound" to a carrier protein (like a chaperone)

Sex hormone Binding Globulin (SHBG)

A protein that binds with the sex hormones testosterone and estrogen, hormones are inactive when bound to SHBG

Hypothalamus

Part of brain that monitors levels of sex hormones; if more needed, secretes gonadotropin-releasing hormone (GnRH)

Gonadotropin-releasing hormone (GnRH)

Paracrine hormone made by hypothalamus and sent to pituitary that says that more sex hormone is needed

Pituitary Gland

Gland next to brain, when receives GnRH from hypothalamus, will produce two endocrine hormones, LH and FSH, that travel via bloodstream to the gonads

LH and FHS

Two hormones secreted by the pituitary gland out into the bloodstream to tell the gonads to get to work; endocrine hormones.

They are also called gonadotropins.

Gonadotrophins

Gonado = gonads
Tropin = moving toward
ex: LH and FSH

LH

tells gonads to make more sex hormones (estrogen or testosterone)

FSH

tells the gonads to make gametes (sperm or ova)

Negative Feedback System

A reaction that causes a decrease in function in response to some kind of stimulus (like testosterone or estrogen levels), functions like a thermostat to keep things stable.

Puberty

the period of sexual maturation, during which a person becomes capable of reproducing

hypothalamus becomes less and less sensitive to negative feedback, allowing hormone levels to increase significantly

Physical changes during puberty

primary sex characteristics, secondary sex characteristics, and height

Nutrition, pesticides, and plastics may all be potential causes of the onset puberty in girls coming _______________.

earlier

Xenoestrogens

foreign chemicals that bind to estrogen receptors and induce estrogen-like effects

Persistent organic polluntants

synthetic chemicals that persist in the environment and do not degrade easily

Endocrine disrupting chemicals

chemicals that disrupt the hormone system by acting like hormones

Atrazine

a xenoestrogen that is the most commonly used weedkiller in the U.S.

BPA (Bisphenol-A)

plastic additive that is a xenoestrogen

Phthalates

xenoestorgen and plasticizer, found in flexible PVC and other plastics 

Gamete

Sex cell (sperm or ovum) that contains some of the genetic information from the parent and is necessary for sexual reproduction

Haploid

having only one complete set of chromosomes, only 23 chromosomes

Mitosis

cell doubles itself to produce another, identical cell

Meiosis

cell goes through a process to create 4 cells, each of which are haploid, and are different from each other

The four basic steps of Meiosis are:

1. Duplication
2. Crossover
3. First Division
4. Second Division

Duplication

the first step in meiosis where exact replicas of each chromosome are created

Crossover

the second step in meiosis where the doubles of each chromosome exchange some genes

First division

the third step in meiosis in which the duplicated and crossedover-ed chromosomes separate from each other

Second division

the fourth step in meiosis in which the chromosomes have to separate from their duplicates

What is the end result of meiosis?

4 haploid cells