Reproductive system

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

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 Gonads are the main source of sex steroids Peptide hormones: inhibin and activin


Feedback Loops Control Gonadotropin ReleaseInternal and

environmentalstimuli

CNS

Hypothalamus

Anteriorpituitary

Steroid andpeptide hormones

Gameteproduction

GnRHShort-loop negative feedback

Long-loop feedbackmay be negative

or positive

Stimulus

Integrating center

Efferent pathway

Effector

Tissue responseLH

Endocrinecells

FSH

Gonads(ovaries or testes)

KEY

Females only


Synthesis Pathways for Steroid HormonesCholesterol

Progesterone

TestosteroneDihydro-

testosterone(DHT)

aromatase

EstradiolCorticosterone Cortisol

Aldosterone Intermediate steps


Male Reproductive System

Figure 27.1


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 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 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

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


MALEFEMALE

Spermatids

develop into

MITOSISSTAGE OF CELL DIVISION

46(diploid)

Sisterchromatids

Sisterchromatids

MEIOSIS

Second meioticdivision

Secondary gamete divides.23 chromosomes

(haploid)

First meioticdivision

Primary gamete dividesinto two secondary gametes.

23 chromosomes,duplicated

Spermatogonia

Oögonium

Secondaryoocyte(egg)

Disintegrates

Secondpolar body

disintegrates.

Zygote

Sperm

Oögonia

Secondaryspermatocytes

(may notoccur)

Egg releasedfrom ovary at

ovulation.

Primaryspermatocyte

Spermatogonium

One primary spermatocyteyields 4 sperm.

One primary oocyteyields 1 egg.

Primaryoocyte

FERTILIZATION

Unfertilized eggpasses out of body.

Firstpolarbody

Germ cell proliferation

46 chromosomesper cell (only two

shown here)

DNA replicatesbut no cell division.46 chromosomes,

duplicated

Em

bryo

Em

bryoR

epro

duct

ive

adul

tR

eproductive adult

1

2

3

4

5

6

Figure 26-5, steps 1–6

Ovulation with Fertilization Is Followed by Final Step of Meiosis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings http://distance.stcc.edu/AandP/AP/AP2pages/reprod/spermato.htm

spermatogenesis

spermiogenesis

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

Spermiogenesis: Spermatids to Sperm


Mitosis of Spermatogonia 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


SpermatogenesisSpermatogonium (2n)

Primary spermatocyte (2n)

Primary spermatocyteDivision – 1st meiosis

secondary spermatocyte (n)

Spermatid (n)

differentiation

2nd meiosis


Spermiogenesis

spermatozoa


Hormonal Regulation of Testicular Function 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


LH

GnRHHypothalamus

Anteriorpituitary

Inhibin

Testes

Leydigcells

Testosterone (T)

To bodyfor secondary

effects

FSH

Sertolicell

Cellproducts

Secondmessenger

Sertolicell

ABP TAndrogen-binding

protein (ABP)

Spermatogonium

Spermatocyte

Figure 26-11 (9 of 9)

Testosterone Inhibits the Hypothalamus and Anterior Pituitary


Testosterone

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.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Table 22.2

Effects of Androgens gonads and Secondary Sex Characteristics


Accessory Glands Contribute to Semen


Ovaries 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


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)

The ovarian cycle


Follicular phase Luteal phaseovulation

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


Follicular development - Folliculogenesis The folliculogenesis occurs during follicular phase Primordial Follicle –flattened granulosa cell layer,

basement membrane, oocyte Primary Follicle – growth of oocyte, zona pellucida

formation, cuboidal granulosa cells Secondary Follicle – add layers of granulosa cells,

formation of theca cells


Folliculogenesis 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

A few follicles begin to develop from primordial follicle

Oocyte grows, granulosa cells proliferate

Zona pellucida and antrum form


Follicular Phase

Dominant follicle continues development, rest regress

Corona radiata develops Graafian follicle = mature follicle Ovulation







Photomicrograph of an early tertiary follicle

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



Luteal Phase 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 Phase Ruptured follicle gland = corpus luteum Corpus luteum secretes mostly progesterone Corpus luteum reaches max activity 10 days, then

degenerates


Corpus 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 Cycle


MALEFEMALE

Spermatids

develop into

MITOSISSTAGE OF CELL DIVISION

46(diploid)

Sisterchromatids

Sisterchromatids

MEIOSIS

Second meioticdivision

Secondary gamete divides.23 chromosomes

(haploid)

First meioticdivision

Primary gamete dividesinto two secondary gametes.

23 chromosomes,duplicated

Spermatogonia

Oögonium

Secondaryoocyte(egg)

Disintegrates

Secondpolar body

disintegrates.

Zygote

Sperm

Oögonia

Secondaryspermatocytes

(may notoccur)

Egg releasedfrom ovary at

ovulation.

Primaryspermatocyte

Spermatogonium

One primary spermatocyteyields 4 sperm.

One primary oocyteyields 1 egg.

Primaryoocyte

FERTILIZATION

Unfertilized eggpasses out of body.

Firstpolarbody

Germ cell proliferation

46 chromosomesper cell (only two

shown here)

DNA replicatesbut no cell division.46 chromosomes,

duplicated

Em

bryo

Em

bryoR

epro

duct

ive

adul

tR

eproductive adult

1

2

3

4

5

6

Oogenesis – oocyte development


Ovum production Occurs monthly in ovarian follicles Part of ovarian cycle Happens during the Follicular phase (preovulatory)

Oogenesis


Oogenesis 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 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


Oogenesis


Oogonia (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 bodyArrested in metaphase II

If fertilization occur

Complete meiosis II

Ovum second polar body


Actions of Estrogens from growing follicle


Actions of Progesterone from the Corpus luteum




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

Uterine cycle


Beginning of new cycle - Menstrual Phase of the Uterus

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)

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.


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)

Menstrual and prolifarative phases (corresponds Follicular 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.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 26-13 (2 of 2)

The Uterine Cycle

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsDAYS

36.4

36.7

7 14 21 28/028/0

Follicular Phase Ovulation Luteal Phase

Phases of theUterine Cycle

Phases of theOvarian Cycle

Basal bodytemperature

(–C)

Uterinecycle

Ovarianhormone

levels

Ovariancycle

Gonadotrophichormone

levels

Primaryfollicle Theca Ovulation

Corpusluteum

formation

Maturecorpusluteum

Corpusalbicans

Progesterone

MENSES PROLIFERATIVEPHASE

SECRETORY PHASE

InhibinEstrogen

Antrum

LH

FSH

Figure 26-13 (4 of 4)

Corpus Luteum Degenerates and Ceases Hormone Production


LHFSH

GnRH

Androgens

Estrogens

(a) Early to mid-follicular phase

Follicle

Granulosacells

Thecalcells

Corpus luteum

Progesterone

Ovum

LHFSH

FollicleEstrogen

Inhibin

Pituitary Hypothalamus

Figure 26-14 (1 of 4)

Hormonal Control of the Menstrual Cycle: Follicular Phase


LHFSH

GnRH

Androgens

Estrogens

(a) Early to mid-follicular phase

Follicle

Granulosacells

Thecalcells

(b) Late follicular phase and ovulation (d) Late luteal phase

FSH LH

New folliclesbegin todevelop

Corpusluteum

dies

Tonic secretionresumes

Corpus luteum

Progesterone

Ovum

LHFSH

Follicle

Estrogen andprogesterone

FSH LH

Corpus luteum(from ovulated

follicle)

EstrogenProgesterone

Inhibin

GnRHGnRH

secretes

(c) Early to mid-luteal phase

Estrogen

Inhibin

Follicle

Granulosacells

Thecalcells

Inhibin

High estrogenoutput

Small amount ofprogesterone

Androgens

LHFSH

GnRH

Pituitary Hypothalamus

Figure 26-14 (4 of 4)

Hormonal Control of the Menstrual Cycle: Late Luteal Phase


Menstrual phase Proliferetive phase

Secretory phase

Follicular/preovulatory phase Luteal/postovulatory phase

Days 1-5 6-14 15-28

Hormones All low High estrogen; low progesterone

High progesterone; low estradiol

Endometrium

Necrotic tissue falls away from the uterine wall

Repaired and become thicker

Very well vascularized. Thick

Glands Not developed. Simple Gland proliferate Glands increase in size and secrete nutritional substances

Follicles Primordial follicles develop into primary and then secondary follicles

One follicle continue to grow into Graafian follicle and ovulate by the end of this phase

No follicular development. Corpus luteum is present

Oocyte/s First meiosis; arrested in prophase I First meiosis completed; secondary oocyte arrested in metaphase II ovulates

If fertilization occur second meiosis is completed

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Reproductive system

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