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Reproductive system. Hormonal Regulation of Reproduction. Hypothalamus : pulse generator Gonadotropin releasing hormone ( GnRH ) Anterior pituitary Luteinizing hormone (LH) Follicle stimulating hormone (FSH) Gonads produce steroid and peptide hormones

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Hormonal regulation of reproduction
Hormonal Regulation of Reproduction

  • Hypothalamus: pulse generator

    • Gonadotropin releasing hormone (GnRH)

  • Anterior pituitary

    • Luteinizing hormone (LH)

    • Follicle stimulating hormone (FSH)

  • Gonads produce steroid and peptide hormones

    • Gonads are the main source of sex steroids

    • Peptide hormones: inhibin and activin


Feedback loops control gonadotropin release
Feedback Loops Control Gonadotropin Release

Internal andenvironmentalstimuli

CNS

GnRH

Hypothalamus

Short-loop negative feedback

KEY

Stimulus

Anteriorpituitary

Integrating center

Efferent pathway

Effector

Long-loop feedbackmay be negativeor positive

Tissue response

LH

FSH

Gonads(ovaries or testes)

Females only

Endocrinecells

Gameteproduction

Steroid andpeptide hormones


Synthesis pathways for steroid hormones
Synthesis Pathways for Steroid Hormones

Cholesterol

Progesterone

Dihydro-testosterone(DHT)

Testosterone

aromatase

Corticosterone

Cortisol

Estradiol

Aldosterone

Intermediate steps



Testes protection - Testicular Thermoregulation

  • Sperms are not produced at core body temperature

  • In the scrotum, the testes are kept 2-3°C cooler than in the pelvic cavity. This is essential for sperm production.

  • Cooling mechanisms

    • The cremaster muscle contains strips of the internal abdominal oblique muscle around the spermatic cord.

      • It can elevate or lower the testes.

    • The dartos muscle is a subcutaneous layer of smooth muscle that wrinkles skin reducing surface area of scrotum. Can lifts testis upwards

    • The pampiniform plexus is an extensive network of veins that surround the testicular artery in the spermatic cord, keeping the testes cooler countercurrent heat exchange that cools arterial blood entering testis


Cells in the testes 3 types
Cells in the testes – 3 types

  • 2 populations found in the Seminiferous tubule

    • Germinal epithelium – lines the lumen of the tubules

      • consisting of several layers of germ cells in the process of becoming sperm

    • Sustentacular (Sertoli) cells.

  • Between the seminiferous tubules are clusters of interstitial (Leydig) cells, the source of testosterone (will be discussed later with hormonal control).


The functions of sertoli cells and btb
The functions of Sertoli cells and BTB

  • Sertoli cells protect the germ cells and promote their development. Tight junctions between adjacent sustentacular cells form a blood-testis barrier (BTB)

    • The fluid inside the tubules contains high levels of androgens, potassium and amino acids

    • The BTB prevents the immune system from attacking the developing spermatozoa (contain specific Ag that are not found on any other cell)

  • Sertoli cell supply nutrients to the developing sperms

  • Phagocytize cytoplasm shed by spermatids

  • Secrete inhibin- negative feedback loop for FSH

  • Secrete androgen-binding-protein (ABP) – binds testosterone inside tubules to maintain high levels


Spermatogenesis
Spermatogenesis

  • Cells making up the walls of seminiferous tubules are in various stages of cell division

  • These spermatogenic cells give rise to sperms in a series of events

    • Mitosis of spermatogonia, forming spermatocytes

    • Meiosis forms spermatids from spermatocytes

    • Spermiogenesis – spermatids to sperm


Ovulation with fertilization is followed by final step of meiosis
Ovulation with Fertilization Is Followed by Final Step of Meiosis

FEMALE

STAGE OF CELL DIVISION

MALE

Spermatogonium

1

MITOSIS

Oögonium

Germ cell proliferation

46 chromosomesper cell (only twoshown here)

Embryo

Embryo

46(diploid)

Oögonia

Spermatogonia

MEIOSIS

2

DNA replicatesbut no cell division.

Primaryoocyte

Primaryspermatocyte

Sisterchromatids

Sisterchromatids

46 chromosomes,duplicated

3

First meioticdivision

First

polarbody

Secondaryoocyte(egg)

Reproductive adult

Secondaryspermatocytes

Primary gamete dividesinto two secondary gametes.

23 chromosomes,duplicated

(may notoccur)

Reproductive adult

4

Second meioticdivision

Spermatids

Disintegrates

Egg releasedfrom ovary atovulation.

Secondary gamete divides.

develop into

23 chromosomes(haploid)

Sperm

FERTILIZATION

6

One primary oocyteyields 1 egg.

One primary spermatocyteyields 4 sperm.

5

Secondpolar bodydisintegrates.

Unfertilized eggpasses out of body.

Zygote

Figure 26-5, steps 1–6


Spermiogenesis: Spermatids to Sperm Meiosis

  • Spermiogenesis – spermatids lose excess cytoplasm and form a tail, becoming sperm

spermiogenesis

spermatogenesis

http://distance.stcc.edu/AandP/AP/AP2pages/reprod/spermato.htm


Mitosis of spermatogonia
Mitosis of Spermatogonia Meiosis

  • Spermatogonia – outermost cells in contact with the epithelial basal lamina

  • Spermatogenesis begins at puberty as each mitotic division of spermatogonia results in type A or type B daughter cells

  • Type A cells remain at the basement membrane and maintain the germ line

  • Type B cells move toward the lumen and become primary spermatocytes


Spermatogenesis Meiosis

Spermatogonium (2n)

differentiation

Primary spermatocyte (2n)

Primary spermatocyte

Division – 1st meiosis

secondary spermatocyte (n)

2nd meiosis

Spermatid (n)


Sper Meiosis miogenesis

spermatozoa


Hormonal regulation of testicular function
Hormonal Regulation of Testicular Function Meiosis

  • The hypothalamus releases gonadotropin-releasing hormone (GnRH)

  • GnRH stimulates the anterior pituitary to secrete FSH and LH

    • FSH causes sustentacular cells to release androgen-binding protein (ABP)

    • LH stimulates interstitial cells to release testosterone

  • ABP binding of testosterone enhances spermatogenesis


Testosterone inhibits the hypothalamus and anterior pituitary
Testosterone Inhibits the Hypothalamus and Anterior Pituitary

GnRH

Hypothalamus

Anteriorpituitary

FSH

LH

Leydigcells

Spermatogonium

Inhibin

Testosterone (T)

Spermatocyte

Testes

Sertolicell

Secondmessenger

To bodyfor secondaryeffects

Cellproducts

Sertolicell

Androgen-bindingprotein (ABP)

ABP

T

Figure 26-11 (9 of 9)


Testosterone
Testosterone Pituitary

  • The principal androgen (male sex hormone) is testosterone.

  • This steroid is manufactured by the interstitial (Leydig) cells of the testes.

  • Secretion of testosterone increases sharply at puberty and is responsible for the development of the secondary sexual characteristics of men.

  • Testosterone is also essential for the production of sperm.




Ovaries
Ovaries Characteristics

  • Ovaries contain the ovarian follicles

  • Each follicle consists of an immature egg (oocyte)

  • Cells around the oocyte are called:

    • Follicle cells (one cell layer thick)

    • Granulosa and theca cells (when more than one layer is present)

  • The follicles and the oocytes are going through cyclic development – ovarian cycle


The ovarian cycle
The ovarian cycle Characteristics

  • Combination of follicles and oocyte development

  • Divided to 2 major periods (phases)

    • Follicular phase – period of follicle growth (days 1–14)

    • Luteal phase – period of corpus luteum activity (days 14–28)

  • The 2 phases are “separated” by Ovulation (release of the secondary oocyte from a tertiary follicle)


Luteal phase Characteristics

Follicular phase

ovulation

http://biology.clc.uc.edu/courses/bio105/sexual.htm


Follicular development folliculogenesis
Follicular development - Characteristics Folliculogenesis

  • The folliculogenesis occurs during follicular phase

  • Primordial Follicle –flattened granulosa cell layer, basement membrane, oocyte

  • Primary Follicle – growth of oocyte, zonapellucida formation, cuboidal granulosa cells

  • Secondary Follicle – add layers of granulosa cells, formation of theca cells


Folliculogenesis
Folliculogenesis Characteristics

  • Early Tertiary Follicle – antrum formation, zona pellucida thickens, theca interna and theca externa form, basement membrane is still present between theca and granulosa cells, blood vessels are in the theca cell layer but not in follicle

  • Tertiary/pre-ovulatory/Graffian – full size follicle ready to ovulate; oocyte surrounded by corona radiata (granulosa cells) and attached to follicular wall by the comulus oophorus


Follicular phase
Follicular Phase Characteristics

  • A few follicles begin to develop from primordial follicle

  • Oocyte grows, granulosa cells proliferate

  • Zona pellucida and antrum form


Follicular phase1
Follicular Phase Characteristics

  • Dominant follicle continues development, rest regress

  • Corona radiata develops

  • Graafian follicle = mature follicle

  • Ovulation


Photomicrograph of an early tertiary follicle Characteristics

http://www.endotext.org/female/female1/femaleframe1.htm


Luteal phase
Luteal Phase Characteristics

  • After ovulation, the ruptured follicle collapses, granulosa cells enlarge, and along with internal thecal cells, form the corpus luteum

  • The corpus luteum secretes progesterone and estrogen

  • If pregnancy does not occur, the corpus luteum degenerates in 10 days, leaving a scar (corpus albicans)

  • If pregnancy does occur, the corpus luteum produces hormones until the placenta takes over that role (at about 3 months)


Luteal phase1
Luteal Phase Characteristics

  • Ruptured follicle  gland = corpus luteum

  • Corpus luteum secretes mostly progesterone

  • Corpus luteum reaches max activity 10 days, then degenerates


Corpus luteum
Corpus Characteristics luteum

  • The fate of the corpus luteum depends on fertilization:

    • If pregnancy does not occur, the corpus luteum degenerates in 10 days, leaving a scar (corpus albicans)

    • If pregnancy occurs, the corpus luteum produces hormones until the placenta takes over that role (at about 3 months)


The ovarian cycle1
The Ovarian Cycle Characteristics


Oogenesis oocyte development
Oogenesis – oocyte development Characteristics

FEMALE

STAGE OF CELL DIVISION

MALE

Spermatogonium

1

MITOSIS

Oögonium

Germ cell proliferation

46 chromosomesper cell (only twoshown here)

Embryo

Embryo

46(diploid)

Oögonia

Spermatogonia

MEIOSIS

2

DNA replicatesbut no cell division.

Primaryoocyte

Primaryspermatocyte

Sisterchromatids

Sisterchromatids

46 chromosomes,duplicated

3

First meioticdivision

First

polarbody

Secondaryoocyte(egg)

Reproductive adult

Secondaryspermatocytes

Primary gamete dividesinto two secondary gametes.

23 chromosomes,duplicated

(may notoccur)

Reproductive adult

4

Second meioticdivision

Spermatids

Disintegrates

Egg releasedfrom ovary atovulation.

Secondary gamete divides.

develop into

23 chromosomes(haploid)

Sperm

FERTILIZATION

6

One primary oocyteyields 1 egg.

One primary spermatocyteyields 4 sperm.

5

Secondpolar bodydisintegrates.

Unfertilized eggpasses out of body.

Zygote


Oogenesis
Oogenesis Characteristics

  • Ovum production

  • Occurs monthly in ovarian follicles

  • Part of ovarian cycle

  • Happens during the Follicular phase (preovulatory)


Oogenesis1
Oogenesis Characteristics

  • Production of female sex cells by meiosis

  • In the fetal period, oogonia (2n ovarian stem cells) multiply by mitosis and store nutrients

  • Primordial follicles appear as oogonia are transformed into primary oocytes

  • Primary oocytes begin meiosis but stall in prophase I


Oogenesis puberty
Oogenesis: Puberty Characteristics

  • At puberty, one activated primary oocyte produces two haploid cells

    • The first polar body

    • The secondary oocyte

  • The secondary oocyte arrests in metaphase II and is ovulated

  • If fertilized, the second oocyte completes meiosis II, yielding:

    • One large ovum (the functional gamete)

    • A tiny second polar body


Oogenesis2
Oogenesis Characteristics


Oogonia Characteristics (multiple by mitosis until 5th month of fetal development)

Arrested development (until shortly before birth)

Primary oocytes (arrest in prophase I)

___________________________________________________________

Puberty

Oocyte in Graafian follicle – complete meiosis I

Secondary oocyte first polar body

Arrested in metaphase II

If fertilization occur

Complete meiosis II

Ovum second polar body


Actions of estrogens from growing follicle
Actions of Characteristics Estrogens from growing follicle


Actions of progesterone from the corpus luteum
Actions of Characteristics Progesterone from the Corpus luteum


Uterine cycle
Uterine cycle Characteristics

  • Repeating series of changes in the endometrium

  • Menses

    • Degeneration of the endometrium

    • Menstruation

  • Proliferative phase

    • Restoration of the endometrium

  • Secretory phase

    • Endometrial glands enlarge and accelerate their rates of secretion


Beginning of new cycle menstrual phase of the uterus
Beginning of new cycle - Menstrual Phase of the Uterus Characteristics

  • If fertilization does not occur, the corpus luteum degenerates and estrogen and progesterone levels decrease.

  • The lack of estrogen and progesterone leads to the collapse of the endometrium, which in turn leads to menstruation.


Menstrual and prolifarative phases corresponds follicular phase of ovary
Menstrual and prolifarative phases (corresponds Follicular Phase of Ovary)

  • FSH and LH increase during follicular phase because progesterone concentration is low and therefore negative feedback on these pituitary hormones is low.

  • FSH and LH stimulate primary follicles (containing primary oocytes) to grow and stimulate their theca cells to produce estrogen.

  • Estrogen leads to a thickening of the endometrium.


Menstrual and prolifarative phases corresponds follicular phase of ovary1
Menstrual and prolifarative phases (corresponds Follicular Phase of Ovary)

  • The one dominant follicle (Graafian follicle) survives because

    • it is hyperresponsive to FSH and can maintain itself even under low FSH

    • it also becomes sensitive to LH.

  • LH surge appears because increased estrogen exerts a positive feedback effect on the LH releasing mechanism of pituitary.

  • LH surge leads to release of the primary oocyte (ovulation)


Secretory phase of the uterus corresponding to luteal phase of ovary
Secretory Phase of the Uterus (corresponding to Luteal Phase of Ovary )

  • The now empty follicle, corpus luteum, starts secreting progesterone that exert a negative feedback on secretion from LH and FSH, preventing new follicles from maturing.

  • Progesterone converts the endometrium into a secretory tissue full of glycogen and blood vessels, ready to receive a fertilized egg.


The uterine cycle
The Uterine Cycle of Ovary )

Figure 26-13 (2 of 2)


Corpus luteum degenerates and ceases hormone production
Corpus of Ovary )Luteum Degenerates and Ceases Hormone Production

Phases of theOvarian Cycle

Luteal Phase

Ovulation

Follicular Phase

LH

Gonadotrophichormonelevels

FSH

Ovariancycle

Corpusluteumformation

Maturecorpusluteum

Primaryfollicle

Corpusalbicans

Ovulation

Theca

Antrum

Progesterone

Ovarianhormonelevels

Estrogen

Inhibin

Uterinecycle

PROLIFERATIVEPHASE

Phases of theUterine Cycle

MENSES

SECRETORY PHASE

36.7

Basal bodytemperature

(–C)

36.4

Figure 26-13 (4 of 4)

DAYS

28/0

7

14

21

28/0


Hormonal control of the menstrual cycle follicular phase
Hormonal Control of the Menstrual Cycle: Follicular Phase of Ovary )

LH

FSH

Ovum

Follicle

Corpus luteum

Estrogen

Inhibin

Progesterone

GnRH

Hypothalamus

Pituitary

FSH

LH

Follicle

Granulosacells

Thecalcells

Androgens

Estrogens

(a) Early to mid-follicular phase

Figure 26-14 (1 of 4)


Hormonal control of the menstrual cycle late luteal phase
Hormonal Control of the Menstrual Cycle: Late Luteal Phase of Ovary )

LH

FSH

Ovum

Follicle

Corpus luteum

Estrogen

Inhibin

Progesterone

GnRH

GnRH

GnRH

GnRH

Hypothalamus

Pituitary

Tonic secretionresumes

FSH

LH

FSH

LH

FSH

LH

FSH

LH

Corpus luteum(from ovulatedfollicle)

Corpusluteumdies

Follicle

New folliclesbegin todevelop

Follicle

Thecalcells

Granulosacells

secretes

Granulosacells

Thecalcells

Estrogen

Androgens

Inhibin

Estrogen andprogesterone

Progesterone

Androgens

Inhibin

High estrogenoutput

Small amount ofprogesterone

Estrogens

(a) Early to mid-follicular phase

(b) Late follicular phase and ovulation

(c) Early to mid-luteal phase

(d) Late luteal phase

Figure 26-14 (4 of 4)


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