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REPRODUCTION IN LOWER AND HIGHER ANIMALS - Coggle Diagram
REPRODUCTION IN LOWER AND HIGHER ANIMALS
sexual reproduction(amphimixis)
production of offspring by formation and fusion of gametes
2 main phases of life in sexually reproducing animals
1.
juvenile
-physical growth phase from birth
2.
reproductive maturity phase
-attained after physical growth is almost over and involve growth and activity of sex organs.animals can reproduce sexually
events after sexual maturity;
1.pre fertilization-gametogenesis and gamete transfer
2.fertilization-fusion of male and female gamete
post fertilisation-formation of zygote and embryogenesis
Human reproduction
sperm and eggs are produced by
primary sex organs-
testis in male and ovary in female
secondary sexual character
-male and female can be differentiated by certain specific features(ssc),organs other than ovary and testis-secondary sex organs
Male reproductive system
testis
pair of testes,mesodermal in origin formed in lower abdominal cavity
located in pouch-scrotum
during early foetal stage they develop in abdominal cavity and later descend in scrotal sac through passage-inguinal canal
each testis-4-5cm long,2-3cm wide and 3cm thick
various stages of spermatogenesis are seen in seminiferous tubule;
innermost-spermatogonia cell(2n),primary spermatocyte(2n),secondary spermatocyte(n),spermatids(n) and sperms(n)
leydig or interstitial cells lie in betn seminiferous tubules,secrete male hormone-testosterone
Histology;
outermost incomplete peritoneal covering tunica vaginalis
below it externally covered collagenous connective tissue layer tunica albuginea
inner to it is tunica vasculosa(thin membranous vascular layer)
fibres from each tunica albuginea divide each testis into 200-300 testicular lobules,each with 1-4 highly coiled seminiferous tubules
each seminiferous tubule is internally lined by cuboidal germinal epithelial cells(spermatogonia) and few pyramidal cells-sertoli cells(provide nutrition to sperms)
germinal epithelial cell undergo gametogenesis to form spermatozoa
accessory ducts
all seminiferous tubules at the posterior surface form a network of tubules-
rete testis
12-20 fine tubules arising from rete testis-
vasa efferentia
; carry sperms from testis and open into
epididymis
its a long highly coiled tube differentiated to upper caput,middle corpus and lower cauda epididymis,it stores sperms and here sperms undergo maturation
then it leads to
vas deference
which travels upto abdominal cavity,loops over ureter then joins seminal vesicles to form
ejaculatory duct
the ejaculatory duct passes through prostate gland and opens into urethra
urethra is the common passage for semen and urine so called-urinogenital duct
in males urethra is long and extends through penis ,it opens to outside by an opening-urethral orifice
glands
seminal vesicles
pair of glands at posterior side of urinary bladder
secretes alkaline seminal fluids which contribute 60% total vol of semen;
-fructose=provide energy for sperm movement
-fibrinogen=coagulates semen into bolus for quick propulsion into vagina
-prostaglandins=stimulates reverse peristalsis in vagina and uterus aiding fast movement of sperms towards egg in female body
prostate glands
large and single gland having 20-30 lobes,located underneath bladder and surrounds urethra
releases milky white and slightly acidic prostatic fluid into urethra
forms 30%of total vol of semen,contains citric acid,acid phosphatase and other enzymes
acid phosphatase protect sperm from acidic environment of vagina
cowpers gland/bulbourethral gland
small pea sized paired gland at either side of urethra
secrete alkaline viscous mucous like fluid which acts as lubricant during copulation
semen
viscous alkaline fluid ejaculated by male reproductive system
at 1 ejaculation 2.5-4ml of semen is given out containing 400 million sperms
contains secretions of epididymis and accessory glands
external genitalia
penis
male copulatory organ
cylindrical,muscular,3 bundles of erectile tissues
pair of postero-lateral tissue-copora cavernosa and corpus spongiousm
swollen tip of penis-glans penis,covered by loose fold of skin -foreskin/prepuce
scrotum
loose pouch of pigmented skin lying behind penis
divided into right and left scrotal sac by a septum of tunica dartos made of smooth muscle fibres
foetal testes r guided and stored in scrotum sac by short fibro muscular band-gubernaculum
testes remain suspended in scrotum by spermatic chord
failure of testes to descend in scrotum-cryptochidism,result sterility
cremaster and dartos muscles of scrotum help drawing testes close or away from body,this help to maintain temp of testes 2-3 degree lower than body for spermatogenesis
Female reproductive system
ovary
primary female sex organ
function:production of eggs/ovum and female reproductive hormone
solid,oval,almond shape 3 by 1.5 by 1cm
in upper lateral part of pelvis near kidneys
held in position by ligaments by attaching it to uterus and abdominal wall
ovarian ligament attaches ovary to uterus
produces 5 hormones;estrogen,progesteron,relaxin,activin,inhibin
Histology
maturation of primordial follicle to primary ;each has multilayered cuboidal follicles and stroma cells add theca to follicle,then it becomes secondary follicles
then there is growth of oocyte and granulose cells increase in no. and produce estogen
secondary follicle grows to graafian follicle by addition of more follicle cells,in this process they move towards surface of ovary
graafian follicle presses towards thin wall of ovary and creates blistered like appearence
egg is released from the follicle during ovulation and remaining part of follicle changes to temporary endocrine gland-corpus luteum
no fertilization-corpus luteum degenrate into white scar-corpus albicans
Structure of graafian follicle
mature ovarian follicle
eccentric secondary oocyte is surrounded by non-cellular layer zona pellucida secreted by vitelline membrane of oocyte
outermost protective fibrous cover=theca externa,inner to it=thec interna-produces estrogen
inner to theca interna follicular cells form membrana granulosa,from it cells differentiate into discus proligerus and corona radiata
cumulus oophorus -oocyte and surrounding granulosa cells
antrum(fluid(liquor folliculi) filled cavity) betn oocyte and membrana granulosa
oviduct
pair of muscular ducts lying horizontally over peritoneal cavity
its proximal part lies close to ovary and opens into uterus
internally lined by ciliated epithelium
divided into 3 parts;
1.infundibulum
-proximal funnel like part with opening -ostium,surrounded by fingers-fimbriae,cilia and fimbriae helps to drive ovulated egg to ostium
2.ampula
-middle long straight part of oviduct,fertilisation of ovum occurs here
3.isthmus/cornua
-distal narrow part of duct opening into uterus
uterus
hollow muscular pear shaped above and behind bladder
7.5-5-2.5cm
3 regions;
1.fundus-upper dome shaped part,here is implantation of embryo
2.body-broad part which gradually tapers downwards
3.cervix-narrow neck(2.5cm) extends into vagina,passage has 2 openings;internal os towards body and external os towards vagina
3 layers of uterine wall;outermost
perimetrium
,middle thick muscular
myometrium
made of thick smooth muscles,vigourous contraction of these muscles cause labor pain during parturation,innermost layer
endometrium
made of stratified epithelium,richly supplied by blood vessels and uterine glands and provides nourishment to developing foetus
vagina
tubular,female copulatory organ,7-9cm long
lies betn cervix and vestibula
vaginal wall=inner mucosa lining,middle muscular layer and outer adventitia layer
mucosal epithelium is stratified,non-keratinised and store glycogen
no glands but vagina receive cervical secretions of mucous
opening of vagina into vestibula-vaginal orifice
opening is partially covered by fold of mucous membrane-hymen
vagina acts as passage for menstruation and birth canal during parturation
external genitalia
parts external to vagina r collectively called-vulva/pudendum,includes;
1.
vestibule
-median vertical depression enclosing urethral and vaginal opening
2.
labia minora
-another pair of thin folds interior to labia majora,they merge posteriorly to form fore chette and anteriorly converge into a hood like covering on clitoris
3.
clitoris
-small conical and sensitive projection lying at anterior end of labia minora,has erectile pair of tissues-copora cavernosa and is similar to penis
4.
labia majora
-pair of fleshy folds of skin forming boundry of vulva,similar to scrotum.they surround and protect other parts of genitalia and enclose vaginal and urethral openings in vestibule
5.
mons pubis
-fleshy elevation above labia majora it and outer part of labia majora have pubic hair
accessory glands/vestibular glands/bartholin glands
pair of glands similar to cowper glands of male,open into vestibule and release lubricating fluid
mammary glands
development occurs at puberty due to estrogen,progesteron
lactotrophic hormone or prolactin help in development of lactiferous tubules in pregnancy
modified sweat glands
pair of round structures in subcutaneous tissue of anterior thorax in pectoral region(from 2nd to 6th rib)
each mammary gland contains fatty connective tissues and many lactiferous ducts
glandular tissues in each breast divided into 15-20 mammary lobes each with alveolar glands and lactiferous ducts
each alveolar gland secretes milk which is stored in lumen of alveoli
alveoli opens to mammary tubules which join together to form mammary duct
many mammary ducts join to form ampula which is connected to lactiferous duct
which converge towards nipples,they are surrounded by dark brown circular area of skin-areola
puberty
reproductive system becomes functional
sex organs produce gametes and sex hormones
male
12-15yrs
secondary sexual character appear under influence of testesterone and remain functional throughout life
female
onset of menstrual cycle(menarche) at 10-14yrs
cycles are till menopause(45-50yrs)
menarche-menopause=reproductive age of female
menstrual cycles,menarche n menopause controlled by-gonadotropic hormones
menstrual cycle
4 phases
menstrual phase
ovulated egg is not fertilised and is therefore shed out along with menstrum
beginning of each cyle-first day-menses or loss of blood(45-100ml) for 5 days approx
endometrium of uterus breaks down under effect of prostaglandins released due to decreased level of progesterone and estrogen
due to thi,blood,tissue fluid,mucucs,endometrial lining and unfertilized oocyte discharged from vagina
in this endometrium lining becomes 1mm thin
here blood does not clot-fibrinolysin
proliferative phase
from end of menstruation-ovulation
5th-13th day of menstrual cycle
few secondary follicles proceed to develop but only 1 develops into graafian follicle,other degenerate-atresia
developing secondary follicle secretes estrogen
stimulation for proliferation of new follicles influenced by GnRH which stimulates release of FSH
endometrium begin to regenerate-increase in quantity of estrogen
regeneration also involves formation of endothelial cells,endometrial or uterine gland and network of blood vessels
thickness of endometrium reaches 3-5mm
ovulatory phase
shortest phase of menstrual cycle
maturation of graafian follicle and release of ovum into pelvic cavity,14th day
rapid secretion of LH by +ve feedback mechanism causes ruptrue
ovulation may occur with mild /severe pain in lower abdomen
secretory/luteal phase
from ovulation-next menses(15th to 28th day)
release of secondary oocyte and remaining part of graafian follicle turns into corpus luteum under effect of LH
it secretes progesterone and estrogen
if egg not fertilised in 24hhrs,corpus luteum remains for 2 week and then degenerate to white scar corpus albicans
corpus luteum release progesterone and small amount of estrogen and inhibin,under their effect endometrial glands grow,become coiled and start uterine secretions
endometrium thickens(8-10mm)
inhibin stops secretion of FSH
these changes r needed for fertilization and implantation
if egg is fertilised and embryo is implanted,hCG is secreted to extend life of corpus lutuem and stimulate its secretory activity
pregnancy is indicated by presence of hCG in maternal blood or urine
gametogenesis
process of formation of gamete in sexually reproducing animals
SPERMATOGENESIS
process of formation of male gamete-sperm/spermatozoa from germinal epithelium of testis
at onset of puberty,hypathalamus begin secretions of gonadotropin releasing hormone(GnRH),it initiates increase in secretion of FSH(follicle releasing hormone)which induces spermatogenesis
cells of germinal epithelium undergo spermatogenesis to produce sperms
spermatogenesis in 3 phases;
1.multiplication phase
-primordial germ cells(2n) of seminiferous tubule undergo repeated mitosis to form large no. of spermatogonia(2n),each spermatogonium is diploid i.e 46 chromosomes
2.growth phase
-some of spermatogonia stop dividing and grow in size due to accumlation of food to develop into primary spermatocytes(2n)
3.maturation phase
-involves meiotic/reductional division,spermatocytes undergo meiosis 1 leadind to formation of 2 haploid cells-secondary spermatocytes(n)-meiosis 2-4 haploid spermatids(non-motile and non-functional)-spermiogenesis-functional spermatozoa.during this processs of change,spermatids remain held to each other and to sertoli cells by cytoplasmic bridges.sperm heads remain attached to sertoli cells and their tail hanging in lumen of seminiferous tubule .during spermiogenesis,length of spermatids increase,centrioles rearranged as primary and distal centrioles.mitochondria becomes rapidly coiled and acrosome is formed from golgli complex
STRUCTURE OF SPERM
head
-oval shape,contains haploid nucleus,above nucleus
cap-like structure-acrosome,formed from golgi body,contains hydrolytic enzymes;hyaluronidase and proteolytic enzymes like zona lysins and corona penetrating enzymes
neck
-very short region,having 2 centrioles-proximal centriole and distal centriole
middle piece
-axial filament surrounded by 10-14 spiral turns of mitochondria,produces energy necessary for movement of sperm
tail
-long,slender,tapering part containing cytoplasm,fine thread-axial filament,it arises from distal centriole and travels throughout length of tail,partly surrounded by plasma membrane(main piece)and part without plasma membrane-end piece
OOGENESIS
formation of haploid female gamete(ova) from diploid germinal epithelium
involves mitosis and meiosis
3 stages
1.multiplication phase
-primary germinal cells of ovary undergo repeated mitotic division to form millions of gamete mother cells or oogonial cells(2n).this process is completed in embryonal stage of human females
2.growth phase
-some of oogonia stop dividing and grow in size to form primary oocytes(2n),cellular organelles increase in no.
3.maturation phase
-oogenesis tales place in ovaries,b4 birth of female baby.primary oocytes undergo meiosis1 and meiosis2.diploid primary oocyte undergo meiosis1 and form 2 haploid daughter cells,due to unequal division of cytoplasm,out of 2 one is large(secondary oocyte(n)) and other is small cell(1st polar body(n)),secondary oocyte(n) proceed with meiosis2 only upto metaphase 2,its division is further stopped,secondary oocyte is further shed from graafian follicle and ovary.restart and completion of meiosis2 happen after entry of sperm.this last phase is completed in ampulla of fallopian tube during fertilization.in this division also 2 unequal daughter cells (large-ovum (n)and small-2nd polar body(n))are formed,ovum so formed functions as female gamete and is ready for fertilization
STRUCTURE OF SECONDARY OOCYTE
unfertilised egg released from ovary-secondary oocyte is non-cleiodoic and microlecithal.size-0.1mm,non-motie,round and haploid female gamete,nucleus of egg-germinal vesicle,typical nucleus is formed at the time of fertilization,cytoplasm of egg devoid of centriole=ooplasm.
egg is surrounded by various coverings-egg membrane-vitellline membrane-secretes glycoproteinous membrane-zona pellucida on its outside,outside zona pellucida -radially elongted cells-corona radiata,these cells are derived from innermost layer of granulosa cells,they r strongly held to zona pellucida and each other by hyaluronic acid
betn vitelline membrane and zona pellucida-fluid filled perivitelline space,contains first polar body
egg shows polarity,side having germinal vesicle and first polar body-animal pole and opposite side-vegetal pole
fertilization
fusion of haploid male and female gamete to form diploid zygote
movement of sperm towards egg