Human Reproduction Notes

In this article we will discuss about Human Reproduction Notes:- Male Reproductive System, Female Reproductive System, Gametogenesis, Menstrual Cycle, Fertilization and Embryonic d Implantation, Pregnancy and Development, Parturition and Lactation

Reproduction is ability to produce individuals of same species
Humans are sexually reproducing and viviparous
Sexual reproduction generally involves 2 parents
Reproductive events in humans
- Gametogenesis
- Insemination
- Fertilisation
- Implantation
- Gestation
- Parturition

Adolescence

Time of life when a child reaches reproductive maturity
Number of changes occurring in the body
Process of these changes is known as puberty

Reproductive system in human

Mammalian reproductive system consists of

I) Primary sex organs

Present at birth
Also called gonads
Testes in male and ovaries in female

II) Secondary sex organs

Develop during puberty
Prostate, seminal vesicles and penis in male
Uterus, fallopian tubes and vagina in female

III) External sex characters

Distinguish two sexes of a species in appearance
Low pitch voice, beard and narrow hips in male
High pitch voice, smooth face and broad hips in female

Male reproductive system

Male reproductive system includes a pair of testes, along with accessory ducts, glands and external genitalia
Male reproductive system performs two major functions
Spermatogenesis is formation of sperms
Transfer of sperm to female reproductive tract

Gonads (testes)

Located in extra abdominal region
Testis consists of two flat, oval bodies, one on each side
Both testes are located in small bag like structure is called scrotum or scrotal sac
Testis is attached to the scrotum by a band of connective tissue known as gubernaculum
Temperature of scrotum is 2°C below the body temperature, which is essential for the formation of sperms
Failure of testis to descend in scrotum from abdominal cavity is called cryptorchidism

Internal structure of testes

Testis is covered by three layers
- Outer most is tunica vaginalis
- Middle layer is tunica albuginea
- Inner most is tunica vasculosa
Lobules present in testes are called testicular lobules
There are about 250 testicular lobules in each testis
Each lobule filled with 1 to 3 highly coiled seminiferous tubules
Spermatogenesis occur in seminiferous tubules
Seminiferous tubules have 2 types of cells
- Male germ cells (Spermatogonia) undergoes spermatogenesis to form sperms
- Sertoli cell (subtentacular cells) provide norishment to germ cell and sperms
Between the seminiferous tubules, groups of polyhedral cells are found which are called interstitial cells or Leydig cells
Leydig cells secrete testosterone

Male sex accessory ducts

Rete testes

Located inside the testis
Carries sperm from seminiferous tubules

Vasa efferentia

Connecting link between rete testes and epididymis

Epididymis

In man it is 6m in length
Epididymis is divided into three parts
- Upper part: head or caput epididymis (highly coiled)
- Middle part: body or corpus epididymis
- Lower part: tail or cauda epididymis
Testis and epididymis together are called testicle
Epididymis function is storage, nutrition and physiological maturation of sperms
Sperms concentrated and stored in the cauda region until ejaculation

Vas deferens

Tube like structure emerging from tail part of epididymus
Opens to ejaculatory ducts

Ejaculatory ducts

Ejaculatory ducts formed by union of vas deferens and duct of seminal vesicle
Ejaculatory ducts opens into urethra

Urethra

Urethra is common passage for urine and sperms
Originated from urinary bladder
Open to the exterior through urethral meatus

Male reproductive glands

Male glands collectively secrete seminal plasma
Semen = seminal plasma + sperms

Seminal vesicle

Also called uterus masculina
It is elongated sac like structure between urinary bladder and rectum
Secretes seminal fluid
Seminal fluid is transparent jelly like substance, makes 50-65% of semen.
Its slightly alkaline (ph 7.3)
Fructose, ascorbic acid, prostaglandins, bicarbonate
Fructose is activate sperms

Prostrate gland

Large gland which lies at the base of the bladder
It secretes alkaline prostate fluid it is milky, thick and sticky
It makes about 20-30% part of semen
Prostate, spermine, citric acid, cholesterol,phospholipids, zinc acid, phosphatease and clotting enzymes

Bulbourethral glands

Also called cowpers glands
Pair of glands found in lateral side of urethra
It secrets transparent slimy, jelly like mucus
It is slightly alkaline
Destroys acidity of urethra and cleans it for sperm movement
It’s also helps in lubrication of penis

External genitalia

Penis

Penis is male copulatory organ
Urethra starts at the urinary bladder, pass through the penis and open outside by urethral meatus
Terminal part of penis is bulging is called glans penis
Glans penis is covered by movable skin called as prepuce or foreskin
Inside the prepuce, there are modified oil glands called glands of tyson
Penis made up of some special type of tissue that helps in erection
Composed of three longitudinal cylindrical masses of tissues: corpora cavernosa and corpus spongiosum
External opening of penis is called penile or urethral meatus

FEMALE REPRODUCTIVE SYSTEM

Female reproductive system consists of pair of ovaries, along with accessory ducts, glands and external genitalia.
Function of female reproductive system
- Oogenesis is formation of egg
- Allow the entry of sperms
- Site for fertilisation

FEMALE REPRODUCTIVE SYSTEM
Gonads	Pair of ovaries
Accessory Ducts	Pair of oviduct, Uterus and vagina
External genitalia	Mons pubis, Labia majora, Labia minora, Hymen and Clitoris
Glands	Bartholin gland, Skene gland and mammary glands

OVARIES

Ovaries are primary sex organ in female
Located one on each side of lower abdomen
Ovary connected to pelvic wall and uterus by ligaments
Ovary length is 2 to 4 cm
Function of ovary
- Oogenesis
- Secretion of hormones (Estrogen, Androgen, Progesteron and inhibin)

Ligament of ovary

Ovarian ligament is fibrous ligament that connects ovary to side of the uterus
Broad ligament helps to support the uterus and maintain its position in the pelvic cavity
Mesovarium is the portion of the broad ligament. it suspends the ovaries

Internal structure of ovary

Ovary is covered by layer of cubical epithelium called germinal epithelium
Beneath this epithelium, tunica albuginea is present
Inner region of ovary is called stroma, its divided into 2 zones

Cortex: Peripheral, dense and contain ovarian follicles
Medulla: Inner, abundant blood vessels and nerve fibres

Follicular cells
- They are supporting cells
- Surrounded the oocyte within the follicle
- Follicular cells produces hormones
- Maturation of follicle is called folliculogenesis

Folliculogenesis

Primodial follicles

Developed in fetal stage
Composed of primary oocyte surrounded by squamous epithelium

Primary follicles

Developed after puberty
Composed of primary oocyte surrounded by cuboidal epithelium

Secondary follicles

Composed of primary oocyte surrounded by many layer of follicular cells known as granulosa cells

Graafian follicles

Composed of secondary oocyte surrounded by many layer of follicular cells
Following layers of cells are observed from the oocyte
- Corona radiata: Immediately around the zona pellucida
- Corona radiata: Cluster of cell surround the oocyte
- Granulosum: present just after the cumulus cells. its secrete liquor fluid of the antrum
- Teca interna: Spindle shaped cells around the granulosa cells
- Teca externa: Outer most layer of loose connective tissue

Ovalation

Release of mature oocyte from the ovary to the fallopian tube is called ovulation

Process of ovulation

Mature follicle protrudes from the ovary. this condition is called stigma
Increase secretion of liquor folliculi
Folicular wall become thin and rupture
Relase of oocytes

Empty ovarian follicles

Corpus hemorrhagicum

During ovulation blood vessels ruptured which cause bleeding inside the follicle
The follicle looks like red mass, hence known as corpus hemorrhagicum

Corpus luteum

The granulosa cell and theca interna cell enlarge and hypertrophied
Accumulate yellow pigment (lutein)
The mass now become yellow. This mass is called corpus luteum

Corpus albicans

After the regression of corpus luteum the mass is replaced by white tissue

ACCESSORY DUCTS AND UTERUS

FALLOPIAN TUBES

Also known as Oviducts or uterine tube
Fallopian Tube carry eggs from the ovaries to uterus
Oviduct is differentiated into three parts

Infundibulum

Funnel shaped end of fallopian tube is called infundibulum
Fimbriae, found on the lateral end of each tube, are fringe like protrusions
It helps in collection of ovum after ovulation

Ampulla

Infundibulum leads to ampulla
Ampulla is the wider and longest part of oviduct
Fertilization of ovum takes place

Isthmus

It is last part of the oviduct
Isthmus opens to uterus

UTERUS OR WOMB

Uterus look like unverted pear shaped
Located in the pelvic region between urinary bladder and rectum
It is attached to pelvic wall by ligaments
Major portion of uterus is the body
Rounded region above to body is fundus
Uterus opens into vagina through a narrow cervix. Its cavity is termed as cervical canal
Birth canal = Cervical canal + Vagina
Uterus is the site for implantation

Uterus wall layers

Uterus walls is composed of three layers

Perimetrium

External thin layer
Made up of loose connective tissue

Myometrium

Midlle thick layer of smooth muscles
Myometrium exhibits strong contraction during delivery

Endometrium

Inner glandular layer
Endometrium is composed of two layers: basilar and functional
Basilar layer is permanent, vascular and very thin
Functional layer of endometrium is regenerated and lost during each menstrual cycle

VAGINA

Vagina is muscular tube about 810cm long
Vagina is female copulatory organ
The vagina receives sperm from the male penis during sexual intercourse
Opening of the vagina in young females is partially closed by thin membrane called hymen
During reproductive life the vagina contains Lactobacillus acidophilus
These bacteria produce lactic acid from glycogen. it keeps vaginal pH between 4.9 to 3.5
This acidity helps to prevent vaginal infections

EXTERNAL GENITALIA

Accessory structure of female reproductive system that are external to the vagina
Vulva includes the mons pubis, clitoris, labia majora, labia minora and Bartholin’s gland
Mons pubis: Its fatty tissue cushion which is covered by skin and public hair
There are 2 pairs of lips like tissue around vagina
- Labia majora: Outer fleshy folds surrounding the vagina
- Labia minora: Inner fleshy folds located under labia majora
Clitoris: Small finger-like structure located at the upper meeting point of two labia minora

FEMALE ACCESSORY GLANDS

Bartholins gland

Pair of glands situated on each side of vaginal opening
Secretion of Bartholin’s gland help in lubrication during copulation

Skene’s glands

Pair of glands situated around the lower end of the urethra
They secrete a lubricating fluid

Mammary gland

Mammary Gland are found in all female mammals
Mammary Gland functional only in females
Overgrowth of breast in male is called Gynaecomastia
Externally, each breast has raised nipple, which is surrounded by a circular pigmented area called areola
Mammary glands composed of glandular tissue and fats
Mammary gland function is regulated by hormones
- Estrogen – Stimulate the development of glandular tissue
- Progesterone – Stimulate the development of the duct system
- Prolactin – Stimulate the production of milk

Internal structure of mammary gland

Adult female breast contains 15 to 20 lobules of glandular tissue
Each lobule divided into numerous alveoli
Alveoli is group of cells having lumen within
Alveoli secrete milk, its stored in the cavities of alveoli
Alveoli open in mammary tubules which join to form mammary duct
Several mammary ducts join to form ampulla
Mammary ampulla continues as lactiferous duct and open at surface of nipple

GAMETOGENESIS

Gametogenesis is the process of gamete formation
Gametes are formed from germ cells of gonads
There are two types of gametogenesis
1. Spermatogenesis
2. Oogenesis

SPERMATOGENESIS

Spermatogenesis is the process of producing sperms
Occurs in seminiferous tubules at the time of puberty and continues throughout life
Hormones regulates spermatogenesis
- Gonadotropin releasing hormone (gnRH): secrete from hypothalamus at puberty
- Luteining hormone (LH): stimulate leydig cells and synthesis testosteron
- Follicle stimulating hormone (FSH): stimulate sertoli cells
Stages of spermatogenesis
- Formation of spermatids: germ cell produce spermatids
- Spermiogenesis: spermatids transform into sperm

Stages of spermatogenesis

I) Formation of spermatids

Spermatid formation occurs by 3 phases

Multiplication

Spermatogonia present inside the wall of seminiferous tubules
Spermatogonium divide mitotically to increase in number

Growth

Some spermatogonia stop dividing
Some spermatogonia actively grows into primary spermatocyte
That growing cells obtain nourishment from sertoli cells

Maturation

Primary spermatocyte complete meiosis i to produce 2 cells called secondary spermatocytes
Both secondary spermatocytes undergo meiosis ii to produce 2 spermatids each

II) Spermiogenesis

Spermatids are non motile
Each spermatid is transformed into sperms
Spermatids head remain attach to sertoli cells, tail hanging in lumen of seminiferous tubules
Sperms are finally released from seminiferous tubules by the process called spermiation

Changes during spermiogenesis

Condensation of nucleus
Spermatid length increases
Centrioles rearranged
Golgi body breakdown to form acrosome
Mitochondria coiled

Structure of sperm

Human sperm was first seen by hamm and leeuwenhoek
Human sperms move at speed of 3mm/min through female genital tract
The spermatozoa has four parts: head, neck, middle piece and tail

Head

The head contains two main parts
Nucleus: elongated
Acrosome: bag like structure filled with lytic enzymes called sperm lysin

Neck

Neck is very short containing proximal and distal centriole
Two centrioles arranged one after the other behind the nucleus

Middle piece

Middle piece contains spiral rows of mitochondria
Provide energy and strength to the sperm for locomotion

Tail

Vibrating posterior portion of sperm which helps in swimming
Tail is made up of axial filament and small amount of cytoplasm

OOGENESIS

It is type of gametogenesis in females
Oogenesis is the discontinuous process
This process begins before birth, stops in mid and resumes after puberty
Hormones regulates oogenesis
- Luteinzing hormone (LH): stimulate the ovulation and maintaining corpus luteum
- Follicle stimulating hormone (FSH): stimulate the follicular cells for maturation
Oogenesis occurs through the following phases
- Multiplication phase
- Growth phase
- Maturation phase

Phases of oogenesis

I) Multiplication phase

In this stage germs cells repeatedly divide by mitosis
Result of mitosis produce large number of egg mother cells or oogonia
This happens 3 to 8 months of gestation in embryo
Millions of oogonia formed within ovaries
This process completes in embryo stage

II) Growth phase

Growth phase is longest phase in oogenesis
In this process oogonia grow in size and form primary oocytes
During growth phase size of cells increases many times
Primary oocytes enter into meiosis i and get temporarily arrested at prophase i diplotene stage
Primary oocytes then get surrounded by layer of granulosa cells to form primodial follicles

III) Maturation phase

In this stage primary oocytes under go meiosis i to produce two haploid cells
Larger one called secondary oocyte and smaller one called polar bodies
Secondary oocyte proceeds meiosis ii, only up to metaphase ii and division is arrested at this stage
Then secondary oocyte is shed from the graffian follicle and ovary
Secondary oocyte goes inside the fallopian tube and wait for sperm
If the secondary oocytes doesn’t receive sperm, it disintegrates and shed off in menstrum
If sperm meet the secondary oocytes fertilisation gets started
Meiosis ii restart and completion with help of spermatozoa
End of meiosis ii two unequal cells formed, large cell is ovum and small cell is polar body

Structure of human egg

Human egg is largest cell in the body
Human egg also known as mature ovum or secondary oocyte
Mature ovum covered with 3 distinct membranes in human
- Corona radiata: made up of follicular cell
- Zona pellucida: thick non cellular membrane and developed from follicular cells
- Vitelline membrane: forming surface of cytoplasm
Cytoplasm have 2 zones
- Exoplasm: peripheral and less dense
- Ooplasm: inner and contain nucleus, organelles, yolk

CLASSIFICATION OF EGGS

I) On the basis of amount of yolk

Microlecithal egg

The amount of yolk is much less than the amount of cytoplasm
Examples: mammalian eggs

Mesolecithal eggs

The amount of yolk is moderate
Examples: eggs of amphibia

Macrolecithal eggs

Eggs are with large amount of yolk
Examples: insects egg and birds

II) On the basis of distribution of yolk

Isolecithal eggs

Yolk is evenly distributed in these eggs
Example: mammalian eggs

Telolecithal eggs

Yolk is concentrated in one part of the egg
Example: eggs of amphibia

Centrolecithal eggs

Yolk is located in the centre and surrounded by cytoplasm
Example: insects egg

III) On the basis of shell

Cleidoic eggs

Eggs surrounded by hard shell
These eggs have more amount of yolk
Example: birds and reptiles eggs

Non cleidoic eggs

Eggs are not surrounded by hard shell
Examples: mammals and amphibians

MENSTRUAL CYCLE

Process of bleeding through vagina due to breakage of endometrium is called menstruation
In this cycle female body prepares itself for pregnancy
If pregnancy does not occur then the body aborts all preparation
In healthy female menstruation occurs at average interval of about 28 days
Menarche: first menstruation that begins at puberty
Menopause: menstrual cycle stop at about 50 years of age
Menstrual cycle has four main phases
1. Menstruation phase
2. Follicular phase
3. Ovulatory phase
4. Luteal phase

Phases of menstrual cycle

I) Menstruation phase

Days 15 of the cycle are known as menstrual phase
During menstrual phase, the layer of endometrium gets shed off
Due to breakdown of endometrial lining of uterus, bleeding continues upto 4-5 days
Blood clotting doesn’t occur due to presence of fibrinolytic enzymes
In every cycle 40-80 ml blood loss

Hormonal change

Progesterone are low
FSH increase due to negative feedback of low level of progesterone

II) Follicular phase

Uterine bleeding is stopped
Follicle grows, matures and secretes estrogen during this phase
Endometrium line start to repair

Hormonal change

High estrogen is stimulate pituitary gland for decrease FSH and increase LH secretion
This abrupt rise in LH concentration in blood is called LH surge

III) Ovulatory phase

Occurs around 14th day
Rupture of graafian follicle and release of an ovum

Hormonal change

Fall in FSH level and arise in LH
Increased concentration of LH causes the graafian follicle to rupture

IV) Luteal phase

The ruptured graafian follicle transforms into corpus luteum
Corpus luteum secretes progesterone and some estrogens
It fertilization occurs
Corpus luteum persists
If fertilization does not take place
Corpus luteum remains functional for 10 days
After 10 days, begins to degenerate into a corpus albicans
This causes disintegration of the endometrium leading to menstruation

Hormonal change

If ovum is not fertilized, the higher level of progesterone inhibits the production of LH
Withdrawal of LH causes regression of corpus luteum and fall in progesterone level

FERTILIZATION

Process of fusion of male and female gamtes to form zygote is called fertilization
Fertilization normally occurs in ampulla region
Fertilization only occur if ovum and sperm are transported at the same time in ampulla
Fertilization involves the following steps
- Entry of sperm
- Fertilizin and antifertilizin reaction
- Release of sperm lysin
- Fertilization cone
- Completion of meiosis ii
- Cortical reaction
- Fusion of gametes

Entry of sperm

In male single ejaculation contain 3ml of semen, its deposited in vagina
Nearly 100+ sperms reach fallopian tube
Capacitation is the preparation of sperm to fertilize the ovum
Removal of sterol and glycoprotein and ca2+ ions taken

Fertilizin and antifertilizin reaction

Fertilizin is a protein secreted from egg cytoplasm
Antifertilizin is a protein present in plasma membrane of the sperm
Fertilizin acts as receptor for antifertilizin
Reaction between fertilizin and antifertilizin makes the sperm more capable of fertilizing the egg of same species

Release of sperm lysin

Corona digestive enzyme: digest the cells of corona radiata
Acrosin: digest zona pellucida

Fertilization cone

Acrosome of sperm touches surface of egg, the cytoplasm of egg bulges forward forming receptive cone or fertilization cone
Receptive cone is the region where sperms enters the egg

Completion of meiosis ii

Metaphase factors are deactivated
Anaphase promoting factors are activated
Secondary oocyte undergoes meiosis ii, resulting in formation of ovum and second polar body

Cortical reaction

Entry of other sperm is prevented by development of fertilization membrane
Massive exocytosis of cortical granules to diffuse and alter the structure of zona pellucida.
In human both head and tail of sperm enter the cytoplasm of oocyte

Fusion of gametes

Nucleus of sperm absorb water from egg cytoplasm and becomes enlarged
Enlarged male nucleus is called male pronucleus
Nuclei of both gametes fuse to form zygote
Fusion of gametic pronuclei is called karyogamy
Mixing of two sets of chromosomes of two gametes is called amphimixis

Significance of fertilization

Help to restore the total number of chromosomes in the organism
Fertilization combines the characters of two parents. This brings genetic variations
It determines the sex of the embryo in human

MORULA FORMATION

After fertilization, the zygote continue to divide by rapid mitotic cell division called cleavage
Cleavage in fertilized egg starts in fallopian tube after fertilization
The large zygote divide into many smaller daughter cells called blastomeres
After 4-5 cleavages approximately 16-32 cells formed
There is no growth phase between cleavages
This solid ball of cells called morula

Cleavage

Cleavage also known as cellulation and segmentation
The term was given by von baer
After fertilization, zygote continue to divide by rapid mitotic cell division called cleavage

Types of cleavage

Determinate cleavage: fate of the cells being set early in the embryo development
Indeterminate: each cell has the potential of developing into a complete organism

Stages of morula formation

Zygote to 2 cell stage

Occurs 24-30 hours after fertilization
Unicellular zygote changes into two blastomeres
Occurs in the upper portion of fallopian tube

2 cell stage to 4 cell stage

Occurs after 1st cleavage
Larger cell divide and form 3 cell stage
Then later smaller cell also divide and form 4 cell stage

4 cell stage to 8 cell stage

3rd cleavage occurs
Cleaved cells pushed from fallopian tube towards uterus

8 cell stage to morula

At the end of 4th cleavage of fertilization
The solid ball of 16-32 cells formed
This solid ball like structure is called morula
No change in overall size from zygote to morula

BLASTULATION

Blastula formation is called blastulation
Morula changes to blastula due to rearrangement of blastomeres
Blastula is typically a hollow, multicellular ball like cells produced at the end of cleavage
Fluid filled cavity of blastula is called blastocoel
Blastocyst is formed, zona pellucida becomes thinner and finally disappears
By this time the developing embryo reaches the uterus and implants into the uterine wall

Structure of blastocyst

Blastocyst has 3 parts: trophoblast, inner cell mass and blastocoel

Trophoblast

Single outer layer of large flat cells
Helps in absorbing nutrition fro the embryo
Later form into chorion, amnion and part of placenta

Embryoblast

Inner cells mass forms the body of embryo
Embryo develops from embryoblast
Thin layer of trophoblast that overlies the embryoblast

Blastocoel

Fluid filled cavity which helps in rapid expansion of blastocyst

IMPLANTATION

Attachment of the blastocyst to the uterine wall
Implantation takes place about seven days after fertilisation
Zona pellucida help to prevent the implantation of blastocyst at an abnormal site
Upon implantation, the endometrium undergoes changes referred to as the decidual cell reaction
Blastocyst attaches itself by embryonic pole, close to the endometrium
Increases the permeability of blood vessels and wall of endometrium
Trophoblast cells of blastocyst have power to stick to the uterine wall
Endometrium get disturbed by finger like structure is called chorionic villi
Chorionic villi penetrate by lytic or mechanical way
By the end of 10th day, whole embryo is deeply embedded into the endometrium, completing implantation process

GASTRULATION

Process of single layered blastula is transformed into gastrula
Gastrula covered with three layers called germ layers
Germ layers are give rise to specific parts of the organism

Ectoderm

Outermost layer of developing embryo
Give rise to integumentary system (the outer skin, nails and hair) as well as the nervous system (central and peripheral system)

Endoderm

Innermost layer of developing embryo
Gives rise to epithelial layer of the digestive tract, lungs, pancreas, bladder, liver as well as the thyroid gland, parathyroid gland and thymus

Mesoderm

Middle layer of developing embryo
Give rise to musculoskeletal system (bone, cartilage, skeletal muscle, cardiac muscle, smooth muscle), cardiovascular system (the heart and blood vessels), excretory system (kidneys) and reproductive system (gonads)

Formation of layers by gastrulation

Formation of endoderm

Blastocyst grows in size by obtaining nutrition from the uterus
Some cells separate from embryonic knob to form endoderm in blastocoel
Remaining inner cell mass forms embryonic disc

Formation of mesoderm

Mesoderm is formed from the caudal margin of the embryonic disc.
Prior to this the existing cells undergo rapid division and a mass of cells detach from the embryonic disc to form mesoderm.

Formation of ectoderm

After the separation of mesoderm, the remaining cells of the embryonic disc form the ectoderm layer
In this manner the three germ layers such as ectoderm, mesoderm and endoderm are formed.

PLACENTA

Placenta is structural and functional connection between foetus and maternal tissue
Placenta is found in all viviparous animals
Placenta is formed of tissues from mother and foetus. So called as fetomaternal organ
Chorionic villi and uterine tissue become interdigitated with each other

Placenta has two components

Fetal part – develops from chorion
Maternal part – develops from functional layer of decidua basalis

Umbilical cord

Umbilical cord connecting the foetus with the placenta
Umbilical cord contain two umbilical arteries and one vein
Blood vessels in umbilical cord are surrounded by wharton’s jelly
Placenta and umbilical cord are transport system for substances between mother and fetus

Functions of placenta

Exchange of materials between foetal and maternal blood
Placenta also serves as a repiratory medium for exchange of o2 and co2
The nitrogenous and metabolic waste from foetus are released into blood of mather
It also produces hormones
- Human chorionic gonadotropin (HCG)
- Human placental lactogen (HPL)
- Progestogens and estrogens
Provides passive immunity antibodies
Harmful drugs and chemicals cross placenta and cause foetal deformity
Some viruses may cross the placenta and cause infection to foetus

EXTRA EMBRYONIC MEMBRANES

Central part of blastula gives rise to embryo
Peripheral portion of blastula does not take part in embryo formation
The peripheral part is known as extra embryonic region or trophoblasts
This extra embryonic region takes part in formation of certain membranes called extra embryonic membranes
Extra embryonic membranes are four types: chorion, amnion, yolk sac and allantois
On the basis of amnion two groups of vertebrates are categorised
- Amniota – this group of animals have amnion in the embryos. E.g. reptilia, aves and mammalia
- Anamniota – this group of animals devoid of amnions in their embryos. E.g. cyclostomata, pisces and amphibia

Four types of extra embryonic membranes

Chorion

Chorion is the outer foetal membrane
Chorion is the name given to trophoblast after formation of embryo
Chorion helps in gaseous exchange
Acts as extra embryonic lungs in reptiles, birds and prototherians

Amnion

A thin protective membrane that surrounds the embryo
Amniotic cavity filled with fluid called amniotic fluid
Fetal cells are present in amniotic fluid
Embryo in this stage is called as foetus remains hanging in amniotic fluid
Amnion well developed in amniote (mammals, birds, reptiles)

Yolk sac

Initially the size of yolk sac is larger as compared to that of embryo
Behaves like extraembryonic gut
In human it is vestigial and after 8 weeks size reduced
Well developed in bird and reptiles

Allantois

Allantois is a hollow sac like structure
In human allantois does not function
Allantois works well in reptiles, birds and prototherians
Acts as extra embryonic kidney
Allanotis stores nitrogenous wastes

PARTURITION

Parturition means birth of the baby
The average duration of human pregnancy is about 9 months called as the gestation period
During parturition, uterus contracts to push the fetus towards cervix
This contraction continues until the fetus comes down the birth canal
After parturition, uterus releases the placenta and it passes out immediately after the fetus is born

Mechanism of parturition

Fully developed foetus and the placenta gives signals for parturition
Initiation of mild uterine contractions called foetal ejection reflex
Due to mild uterine contractions, the oxytocin release from pituitary
Oxytocin causes stronger uterine contractions
Due to these stronger contractions, the foetus starts moving towards the vagina
The labour pain during child birth is due to this hormone.
After parturition oxytocin stimulates milk ejection
Relaxin hormone is secreted by placenta and ovary.
This hormone relaxes the pubic symphysis

Three stages of parturition

Dilation stage

Cervix and vagina gets dilated
Uterine contractions begin from top, forcing the baby towards the cervix
Oxytocin induced uterine contractions
As the baby is pushed down in the uterus, its head comes to lie against cervix
It ends in rupturing of amniotic membrane of foetus

Expulsion stage

This stage starts at full dilation and continues until birth
The foetus passes out through cervix and vagina with head in forward direction
This stage ends with the childbirth and the umbilical cord is clamped

Placental stage

After the delivery of the baby the placenta separates from the uterus and is expelled out

LACTATION

Lactation is process of milk secretion from the mammary glands after childbirth
Mother milk provides nutrition and immunity to the young one
The secretion of milk from alveoli of mammary glands starts from end of pregnancy period
The ejection of milk starts after child birth
Lactation is complex neuro endocrine process
Lactation is divided into four phases
- Preparation of breasts
- Secretion of milk
- Ejection of milk
- Maintenance of lactation

Stages of lactation

Mammogenesis

Mammary gland growth occurs
The size and weight of breast increases
Generally, a female is ready to produce milk during the fifth or sixth month of her pregnancy
Progesterone influences growth in size of alveoli and lobes
Estrogen stimulates the milk duct system to grow and differentiate

Lactogenesis

Alveoli of mammary glands secrete milk
Prolactin secretion is stimulated when estrogen and progesterone levels are low
Placenta is responsible for progesterone production. After parturition, placenta loss so progesterone decreases suddenly
Low level progesterone stimulates anterior lobe of pituitary to secrete prolactin
Now, prolactin stimulates milk secretion

Galactokinesis

Ejection of milk from the alveoli of the mammary glands
Milk ejection is under the control of oxytocin
Oxytocin is released from posterior pituitary gland during nipple stimulation or sensory stimulation
Oxytocin causes ejection of milk from alveoli by contraction of muscles around mammary gland

Galactopoiesis

Galactopoiesis is the maintenance of lactation once lactation has been established

DISORDERS OF REPRODUCTIVE SYSTEM

Oligospermia

Oligospermia is a male fertility issue characterized by a low sperm count
World health organization (who) classifies sperm counts
- Mild oligospermia is 10 to 15 million sperm/ml
- Moderate oligospermia is considered 5 to 10 million sperm/ml
- Severe oligospermia is diagnosed when sperm counts fall between 0 and 5 million sperm/ml

Azoospermia

Azoospermia means there’s no sperm in a man’s ejaculate
Its causes include a blockage along the reproductive tract, hormonal problems, ejaculation problems or issues with testicular structure or function
Many causes are treatable and fertility can be restored

Cryptorchidism

Cryptorchidism is the absence of one or both testes from the scrotum
It is the most common birth defect of the male genital tract

Gynecomastia

Gynecomastia is enlargement of breast size in males
Its happen due to reduced male hormones (testosterone) or increased female hormones (oestrogen)

Hysterectomy

Hysterectomy is an operation to remove the uterus
This surgery may be done for different reasons
Once you’ve had a hysterectomy, you’ll stop having menstrual periods

Oophorectomy

Oophorectomy is surgical procedure to remove one or both of ovaries
When you have one ovary removed, it’s called unilateral oophorectomy. Removal of both ovaries is called bilateral

Ectopic pregnancy

Ectopic pregnancy occurs when a fertilized egg implants and grows outside the uterus
Ectopic pregnancy most often occurs in a fallopian tube

Teratogens

Some substance that can disturb the development of an embryo or fetus
Teratogens may cause a birth defect in the child

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Human Reproduction Notes | Class 12 & NEET Free Notes