1 9.3 - Human Reproductive System (male). At the end of this lesson, student should be able to :...

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9.3 - Human Reproductive

System (male)

• At the end of this lesson, student should be able to :

a) Describe the structure of spermatozoa.b) Explain the role of hormones in

spermatogenesis.c) Describe & explain the stages of

spermatogenesis.

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Learning outcomes

Describe the developmental process & maturation of a male gamete in

mammals. (PSPM 05/06)

Describe the sequence of events in spermatogenesis. (PSPM 09/10)

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9.3 : Human reproductive system (a) Describe the structure of spermatozoa.

Structure of sperm/spermatozoa

a) Headb) Neckc) Middle pieced) Acrosomee) Mitochondriaf) Nucleus g) Tail

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9.3 : Human reproductive system (a) Describe the structure of spermatozoa.

• Head containing the haploid nucleus is tipped with a special vesicle, the acrosome.

• Acrosome contains hydrolytic enzyme that help the sperm penetrate the egg.

• Behind the head, the sperm contains large number of mitochondria provide ATP for movement of the tail.

• At puberty, the hypothalamus secretes Gonadotropin Releasing Hormone (GnRH).

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9.3 Human reproductive system (b) Explain the roles of hormones in spermatogenesis

Role of hormones in spermatogenesis

• GnRH stimulates the anterior pituitary gland to secrete two gonadotropic hormones: Follicle Stimulating Hormone (FSH) & Luteinising Hormone (LH).

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• Although these hormones are named for their action in the female, they are also involved in regulating male reproductive function.

• In males, FSH acts on Sertoli cells, which nourish

developing sperms, thus stimulate/assist spermatogenesis.

LH stimulates the Leydig cells (interstitial cells) in the testis to secrete testosterone, thus promote spermatogenesis in seminiferous tubules. 9


• The principle of negative feedback inhibition applies to the control sex hormone production in males.

• GnRH stimulates the anterior pituitary gland to secrete two gonadotropic hormones: Follicle Stimulating Hormone (FSH) & Luteinising Hormone (LH).

• FSH causes the Sertoli cells to release a peptide hormone called inhibin that specifically inhibits FSH secretion.

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• Similarly, LH stimulates testosterone secretion, and testosterone feeds back to inhibit the release of LH by :

directly at the anterior pituitary

indirectly by reducing GnRH secretion by the hypothalamus

• These negative – feedback circuits maintain the hormones production at optimum level.

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Feedback mechanism & hormonal interactions in spermatogenesis

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Type of hormone & its function in spermatogenesis

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• Spermatogenesis is the production of sperm (spermatozoa).

• It happens in the seminiferous tubules of testis, beginning during puberty when a boy is between about 11 & 15 years old, and continuing throughout the rest of life.

• About 100 to 200 million sperm are made each day & low temperature is required for normal sperm development (340C). 14

9.3 Human reproductive system (c ) Describe and explain the stages of spermatogenesis

Spermatogenesis

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Structure of testis & it cross section

• Spermatogenesis differs from oogenesis in three ways :

All four products of meiosis develop into sperm while only one of the four becomes an egg.

Spermatogenesis occurs throughout adolescence & adulthood.

Sperm are produced continuously without the prolonged interruptions in oogenesis.

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• Immature sperms are produced in the seminiferous tubules (in testis).

• Then develop into mature sperm in the epididymis.

• Mature sperm are stored in the vas deferens, a long tube that extends from the epididymis.

• The whole process, from epithelial cell (primordial germ cells) to sperm, takes around 64 days.

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Human testis

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Stages of Spermatogenesis

• Germinal epithelium cells/ primordial germ cell in testis divide & differentiate into stem cells that divide mitotically to form spermatogonia (2n).

• Spermatogonia are diploid cells, and they divide by mitosis to produce more spermatogonia.

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• Some of spermatogonia stay near the edge of the tubule & form more spermatogonia (2n).

• Some move towards the middle of the tubule & grow larger (cells with more cytoplasm), forming cells called primary spermatocytes (2n).

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• Each primary spermatocytes (2n) then begins to divide by meiosis (meiosis I).

• To form two secondary spermatocytes (n)

• Two or three days later, each secondary spermatocytes (n) undergoes the second meiotic division, producing haploid spermatids (n).

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• Over the next few weeks, each spermatid gradually develops into a spermatozoa.

• Spermatids obtain the nutrient from the Sertoli cells & undergo cell differentiation (formation of structures like flagella and acrosome) & finally develops as mature sperm (spermatozoa).

Spermatids develops as mature sperm (spermatozoa)

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Spermatogenesis process

• As stages take place, the cells get closer & closer to the lumen in the middle of the tubule.

• They are nourished by very large, non-dividing cells called Sertoli cells or nurse cells.

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Lumen of seminiferous

tubule

• Sperms become detach from the Sertoli cells & release into the lumen.

• Fully formed sperm move from the lumen of the seminiferous tubules to the epididymis, carried in fluid secreted by the Sertoli cells.

• At this stage they do not swim until they are ejaculated.

• Once released, a healthy sperm can swim up to 4 mm per minute.

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Spermatogenesis in theseminiferous tubules

Mature sperm cells

Spermatogonium

Sertolicells

Primaryspermatocyte

100 µm

Sertolicells

Wall of theseminiferous tubule

Spermatogonium

Primaryspermatocyte

Secondaryspermatocyte

Spermatid

Maturespermcells

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9.3 - Human Reproductive

System (female)

At the end of this lesson, students should be able to:

d. Describe the structure of the secondary oocyte.e. Describe and explain the stages of oogenesis.f. Describe female reproductive cycle (ovarian &

uterine/menstrual cycle).g. Explain the role of hormones in both cycles.

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Learning outcomes

Describe the process of the production of ovum from mature

ovary in human. (PSPM 04/05)

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• Female gonads : Ovaries

• Functions:

1. Produce female gametes (egg/ovum).

2. Produce female sex hormones (estrogen & progesterone).

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Female Reproductive System

9.3 Human reproductive system (d) Describe the structure of the secondary oocyte.

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Funnel of oviduct

/Uterine lining

/muscular wall


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• It locate in the abdominal cavity.

• It flanking & attached by mesentery to, the uterus.

• Each ovary is enclosed in a tough protective capsule & contains follicles.

• Each follicle consists of an oocyte.

• Oocyte is a partially developed egg, surrounded by a group of support cells.

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• The surrounding cells (follicle cells) nourish & protect the oocyte during oogenesis.

• During a typical 4-week menstrual cycle, one follicle matures & expels its secondary oocyte (egg), a process called ovulation.

• Prior to ovulation, cells of the follicle produce the primary female sex hormone, estradiol, a type of estrogen.

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• After ovulation, the remaining follicular tissue grows within the ovary, called corpus luteum.

• The corpus luteum secretes additional estradiol, as well as progesterone, a hormone that helps maintain the uterine lining during pregnancy.

• If the egg cell is not fertilized, the corpus luteum degenerates, and a new follicle matures during the next menstrual cycle.

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• Oviduct, or Fallopian tube, extends from the uterus toward each ovary.

• At ovulation, the egg released into the abdominal cavity near the funnel-like opening of the oviduct.

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• Together with wavelike contractions of the oviduct, the cilia convey the egg down the oviduct to the uterus (womb).

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Sperm cell. Coloured scanning electron micrograph (SEM) of a sperm cell in a fallopian tube. Magnification: x400 - Stock Photo

• The uterus is a thick, muscular organ that can expand during pregnancy.

• The inner lining of the uterus, the endometrium, is richly supplied with blood vessels.

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• The neck of the uterus, the cervix, opens into the vagina.

• The vagina is a muscular but elastic chamber that is the site for insertion of the penis & deposition of sperm during copulation.

• It also serves as the birth canal through which a baby is born.

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Female reproductive organOVARY One of a pair of primary reproduction organ in which

oocytes (immature egg) form & mature, produces hormones (estrogen & progesterone) which stimulate maturation of oocytes, formation of corpus luteum & preparation of the uterine lining for pregnancy.

OVIDUCT (FALLOPIAN

TUBE)

One of a pair of ciliated channels through which oocytes are conducted from an ovary to uterus, usual site of fertilization.

UTERUS Chamber in which embryo develops.

CERVIX Secrete mucus that help sperm move into uterus & that bars many bacteria.

VAGINA Organ of sexual intercourse, also serves as birth canal. 48

• Oogenesis refers to production of egg cell/ ovum, that occurs in ovaries of female.

• It begins before birth, but complete its final development after fertilization.

• Oogenesis begins in the female embryo with the production of oogonia from primordial germ cells.

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9.3 Human reproductive system (e) Describe and explain the stages of oogenesis

Oogenesis

• About 5 to 6 weeks after zygote has been formed, primordial germ cells of embryo’s developing ovaries divide by mitosis rapidly to produce diploid oogonia.

• By the time the embryo is 24 weeks old, she has millions of oogonia in her ovaries. 50


In embryonic stage…

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• The oogonia will undergo mitosis & become primary oocytes.

• Follicle cells of ovary surround the primary oocytes known as primordial follicles.

• The primary oocytes begin the first stage of meiosis but do not complete it, remaining in prophase I.

• At birth a female has about 2 million primary oocytes (surrounded by follicle) in the ovarian cortex.

• By the time she reaches puberty, she has about 400,000 of them in the ovaries.

• At this time, a few follicles are activated each month.

• However, usually only one follicle is selected to mature each month, with its primary oocyte completing meiosis I & the others will disintegrate.

• This give only about 500 follicles fully mature between puberty & menopause.

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Start during puberty..

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• The primary oocyte completes the first meiotic division & yield two haploid cells of different size.

The smaller one - a first polar body.

The larger, haploid cell - a secondary oocyte.

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• The first polar body play no role in fertilization & development.

• The first polar body may or may not divide. It may undergo meiosis II & produce two smaller polar bodies or it may be degenerate.

• The secondary oocyte continues the second division of meiosis but stops in metaphase II.

• The secondary oocyte is released at ovulation.

Fertilization…

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• If a sperm does penetrate the secondary oocyte, it will quickly complete meiosis II producing ovum & second polar body.

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• If secondary oocyte is not fertilised, it simply dies & degenerate.

• Thus, the functional product of complete oogenesis is a single mature egg already containing a sperm head fertilized egg.

• Fertilization is defined strictly as the fusion of the haploid nuclei of sperm & secondary oocyte.

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• As the primary oocyte begins to enter prophase I of meiosis, some of the surrounding cells in the ovary form a layer around it, producing a primordial follicle.

• Some of the follicles develop into primary follicles.

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Development of Follicle

• Primary follicle - several layer of cells called granulosa cells, surround & nourish the primary oocyte.

• At puberty, hormones (FSH & LH) are produced which FSH stimulate the primary follicles to develop into secondary follicles (growing follicles).

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• One of these secondary follicles begins to grow more rapidly to form a fully developed Graafian follicle (vesicular follicle/mature follicle).

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Oogenesis and

development of follicle

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Oogenesis and

development of follicle

• Other cells from the ovary (thecal cells) form more layers around each follicle, forming a theca.

• The granulosa cells secrete a protective layer of glycoprotein which forms the zona pellucida around the secondary oocyte.

• About 8-10 hours before being released from the ovary, primary oocyte (2n) complete the meiosis I & produce secondary oocyte (n) & first polar body in the Graafian follicle.

Source of picture: http://legacy.owensboro.kctcs.edu/

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Zona pellucida

Granulosa cells

Secondaryoocyte

Area filled by thecal cells

Fluid-filled space

Graffian Follicle

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• During ovulation, the Graafian follicle then ruptures, shedding the secondary oocyte which is still surrounded by granulosa cells from the ovary.

• Ovulation process triggers by the high LH level.

• The ruptured follicle left behind after ovulation develops into corpus luteum.


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Ovulation takes place in the tissues

of the ovary.

The yellow blob is a protruding egg cell,

surrounded by supportive cumulus

cells. The reddish part is the follicle

(S), & the pale pink tissue is part of the

ovary (F).

S

F

Ovulation. An egg cell (or secondary oocyte) is released from a follicle at the surface of the ovary. The orangish mass below the ejected egg

cell is part of a mammalian ovary

Egg cell

Ovary

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Primary oocyte

(2n)

Primary oocyte (2n) complete meiosis I and produce secondary oocyte (n) and first polar body, just before ovulation occurs

/Graafian follicle/ Vesicular follicle

/Secondary

follicle

Source of picture: Campbell, 8th edition, page 1009

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• If the released secondary oocyte is not fertilised & does not complete oogenesis, the corpus luteum degenerates.

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• If fertilization occurs, corpus luteum secretes estrogen & progesterone, a hormone that helps maintain the uterine lining during pregnancy (until the placenta take this task).

• Cytoplasm - containing granules of fat & cortical granules.• Nucleus - a large haploid nucleus (pro-nucleus)• Plasma membrane - surrounds the cytoplasm of the

secondary oocyte.• Granulosa cell - layer of follicle cells.• Antrum - fluid-filled space; secreted by granulosa cells.• Zona pellucida - secrete by granulosa cells, function in

mediates sperm-egg recognition during fertilization.• Corona radiata - layer of follicle cells called granulosa cell

which protects & nourish the secondary oocyte.74


Structure of the secondary oocyte

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Secondary oocyte before ovulation

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Secondary oocyte after ovulation

Describe the process of the production of ovum

from mature ovary in human (PSPM 04/05)

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Female reproductive cycle1. Ovarian cycle

2. Menstrual / uterine cycle

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• At puberty, human females produce gametes in cycles.

• Ovulation only occurs after the endometrium (uterus lining) has started to thicken & develop a rich blood cell.

• Preparing the uterus for the possible implantation of embryo.

• If pregnancy does not occur, the uterine lining is sloughed off & another cycle begins.

9.3 Human reproductive system (f) Describe the female reproductive cycle (ovarian & uterine/menstrual cycle).

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• The cyclic shedding of the endometrium from the uterus, which occurs in a flow through the cervix & vagina, is called menstruation.

• There are two closely linked reproductive cycles in human females (menstrual cycle/ uterine cycle & ovarian cycle).

• Hormone activity links the two cycles, synchronizing ovarian follicle growth & ovulation with the preparation of uterine lining that can support embryonic development.


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1. Gonadotropin releasing hormone (GnRH) secreted by the hypothalamus.

2. Follicle-stimulating hormone (FSH) secreted by the anterior pituitary gland.

3. Luteinizing hormone (LH) secreted by the anterior pituitary gland.

4. Estrogens secreted by the ovaries.

5. Progesterone secreted by the ovaries.


Hormonal coordination of the menstrual & ovarian cycles

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Roles of Hormone

• Ovarian cycle is refer to sequence of changes in ovary.

• Ovarian cycle consist of two phase,

1. Follicular phase 2. Luteal phase

• Between these two phase is ovulation process.


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1. Ovarian Cycle

• During follicular phase, FSH stimulate development of primary follicle to form Graafian follicle.

• In ovulation, Graafian follicle rupture, releasing secondary oocyte.

• In luteal phase, the ruptured Graafian follicle develops into corpus luteum.


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i) Follicular phase (follicles develop & oocytes mature)

• ~ 14 days (starts from 1st day of menstruation).

• During the first 5th days of follicular phase, hypothalamus will release the GnRH, which stimulate the anterior pituitary gland to release FSH & LH.

9.3 Human reproductive system (g) Explain the role of hormones in both cycle.

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• FSH, aided by LH, stimulates the development of primary follicle to become Graafian/ matured follicle.

• Several follicles begin to grow each cycle, but usually only one follicle become secondary oocyte, others disintegrate.

• The developing/ growing follicle secrete estrogen (estradiol).

• There is a slow rise in estrogen secreted during most of the follicular phase.

• The low levels of estrogen inhibit secretion of the pituitary hormones, keeping the levels of FSH & LH relatively low.


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• When estrogen secretion by the growing follicle begins to rise steeply, the FSH & LH levels increase markedly.

• A high concentration of estrogen stimulate GnRH secretion by acting on the hypothalamus.


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• GnRH stimulate the anterior pituitary gland to secrete high level of to FSH & LH.

• The effect is greater for LH.

• The high level of estrogen increases the GnRH sensitivity of LH-releasing cells in the pituitary.

• Follicles also respond more strongly to LH because more of their cells have receptors for this hormone.

• The concentration of LH and FSH at peak at about the 12th day of the cycle


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• The result is final maturation of the follicle, induced by high LH levels.

• The follicular phase ends at ovulation, about a day after the LH surge.


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ii) Ovulation

• In response to the peak in /high LH levels.

• Graafian follicle & adjacent wall of the ovary rupture, releasing the secondary oocyte.

• Occurs 14 days after the start of menstruation.


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iii. Luteal phase (formation & degeneration of corpus luteum)

• Following ovulation, high LH stimulates formation of corpus luteum, from follicular tissue left behind in ovary.

• Under continued influence of LH, the corpus luteum secretes estrogens & large amount of progesterone.Estrogens stimulate

continued development of endometrium.

Progesterone stimulates maintenance of the endometrium


• Increasing levels of both estrogens & progesterone exerts a negative feedback on the hypothalamus & pituitary, reducing the secretion of LH & FSH to very low levels.


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• If the secondary oocyte is not fertilized near the end of the luteal phase, corpus luteum disintegrates/degenerate causing decline of estrogen & progesterone levels.


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• This enables the pituitary begins to secrete enough FSH & LH, to stimulate the growth of new follicles in the ovary (initiating next ovarian cycle)


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• If secondary oocyte get fertilized by sperm, corpus luteum remain & produce estrogen and progesterone, until placenta form.

• If pregnancy occurs. Corpus luteum secretes sufficient progesterone to maintain the uterine lining & sustain the developing embryo.


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• Averages 28 days

• Uterine cycle refers to the a sequence of changes that occur in the lining of the uterus (endometrium) of a non-pregnant female.

• The first day of menstruation (the initial discharge of blood and uterine lining) is designated as Day 1 of the cycle.


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2. Uterine (Menstrual Cycle)

• Involve 3 phasei. Menstrual flow phaseii. Proliferative phaseiii. Secretory phase


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i. MENSTRUAL FLOW PHASE (1-5 DAYS)

• Menstruation occurs if fertilization does not occur & corpus luteum disintegrate.

• The endometrium disintegrates & uterus contracts.


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• Small blood vessels in the endometrium constrict, releasing blood that is shed along with endometrial tissue & fluid bleeding / menstruation.

• Due to low levels of progesterone (function in stimulates maintenance of the endometrium wall.


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ii. PROLIFERATIVE PHASE (1-2 WEEKS) ~ FOLLICULAR

PHASE EVENTS• Endometrium that already

shed in menstrual flow phase will be repaired & thickening.• Stimulated by estrogen that

secreted from growing follicle in ovary.


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iii. SECRETORY PHASE (ABOUT 2 WEEKS) ~ LUTEAL PHASE EVENTS

• The endometrial continues to thicken, preparation for any implantation of fertilized egg.

• Its arteries enlarge & endometrial glands grow to secrete nutrient fluid rich in glycogen.

• Both requires estrogen & progesterone that secreted from corpus luteum in ovary.


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• If no implantation of the fertilized egg at the end of secretory phase, endometrium sheds again & new menstrual cycle begins.


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Describe the hormonal control during ovarian cycle.

(PSPM 07/08)

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The Uterine Cycle vs. Ovarian cycle• Hormones coordinate the uterine cycle with the

ovarian cycle by :

Thickening of the endometrium during the proliferative phase coordinates with the follicular phase.

Secretion of nutrients during the secretory phase coordinates with the luteal phase.

Shedding of the endometrium during the menstrual flow phase coordinates with the growth of new ovarian follicles.


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· The rate of secretion of estrogens by the growing follicle rises steeply.

· Stimulates the secretion the GnRH.

· Stimulates the secretion of FSH & LH.

· LH secretion is especially high.


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· LH induces the final maturation of the follicle & ovulation.

· The follicular phase of the ovarian cycle is coordinated with the proliferative phase of the menstrual cycle.


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· Secretion of estrogens during the follicular phase stimulates endometrial thickening.

· Following ovulation, LH stimulates the formation of the corpus luteum.


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· Luteal phase of the ovarian cycle.

· LH stimulates the corpus luteum to secrete estrogens & progesterone.

· High levels of estrogens & progesterone inhibit FSH & LH secretion.


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· Near the end of the luteal phase the corpus luteum disintegrates.

· Concentrations of estrogens & progesterone decline abruptly.

· FSH secretion increases & initiates a new follicular phase// stimulate development of follicles.

· The luteal phase of the ovarian cycle is coordinated with the secretory phase of the menstrual cycle.

· The estrogens & progesterone of the luteal phase stimulate development & maintenance of the endometrium.


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· With the disintegration of the corpus luteum estrogens & progesterone levels decline.

· Menstruation occurs & a new menstrual cycle begins.


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· Menopause: cessation (stop) of ovarian & menstrual cycles.

· After about 500 cycles

· Usually occurs between ages 46 & 54.

· Due to ovaries decreased responsiveness to gonadotropins.


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1 9.3 - Human Reproductive System (male). At the end of this lesson, student should be able to :...

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