reproduction - March 5th & 7th Flashcards
What are the four phases of Gametogenesis?
- Extraembryonic primordial germ cells (PGCs) and their migration to the gonads
- Increase in # of PGCs by mitosis
- Decrease in chromosomal material by meiosis
- Structural and function maturation of gametes (oogenesis and spermatogenesis)
What are Primordial Germ Cells (PGCs)?
- Earliest recognizable precursors of gametes
- originate outside of the gonads in the hindgut
- migrate into gonads during early embryonic development
What is the function of spermatogenesis?
spermatozoa produced from male PGCs by meiosis and mitosis
Where does spermatogenesis occur?
in the testes
how many gametes are produced per cycle of spermatogenesis?
4
What are the intitial cells of spermatogenesis called?
spermatogonia
What are the cells called after mitosis of spermatogonia in spermatogenesis?
primary spermatocytes
Are spermatogonia haploid or diploid?
diploid
Spermatogonia give rise to two daughter cells, what happens to them?
- one daughter cell remains at the basement membrane as a stem cell
- second daughter cell (primary spermatocyte) moves toward the tubule lumen for further division
Describe the steps of spermatogenesis
- 1st meiosis: DNA duplicates and daughter cell (primary spermatocyte) splits into 2 new, haploid daughter cells (secondary spermatocytes)
- 2nd meiosis: sister chromatids in secondary spermatocytes are split into 4 daughter cells (spermatids)
Primary spermatocyte undergoes 2 meiotic divisions to form 4 haploid spermatids
What is Spermatocytogenesis?
- from spermatogonium to primary and then secondary spermatocyte
- Phase 1: spermatogonial phase (type A dark (Ad) spermatogonia are stem cells of the seminiferous epithelium ; Type A pale (Ap) spermatogonia are committed to differentiation ; Type B spermatogonia are differentiated from Type A)
- Phase 2: Each primary diploid spermatocyte duplicates its DNA and divides into two haploid, secondary spermatocytes by meiosis 1
What is Spermatidogenesis?
From secondary (haploid) spermatocyte to spermatid (haploid)
brevity of this stage meawns that secondary spermatocytes are rarely seen in histological studies
What is Spermiogenesis?
from spermatid to mature, immotile spermatozoon
- spermatids form tail by growing microtubules (axoneme) on one of the centrioles (basal body)
- Anterior part of tail (midpiece) thickens due to mitochondrial arrangement (energy supply)
- DNA undergoes condensation
- Tightly-packed chromatin transcriptionally inactive
- Golgi apparatus surrounds condensed nucleus forming the acrosome
- Testosterone removes remaining extra cytoplasm and organelles (residual bodies phagocytosed by Sertoli cells)
What is Spermiation?
from mature, immotile spermatozoon to mature, motile spermatozoon
- release of mature spermatozoa from Sertoli cells into the lumen of the seminiferous tubule
- mature immotile spermatozoa transported to the epidiymis in testicular fluid secreted by Sertoli cells with the aid of peristaltic contractions
What do the Sertoli Cells do?
- maintain environment and protect spermatids from immune system (blood-testis barrier & FAS-ligand that triggers apoptosis of T-cells thus preventing immune attack on developing sperm
- phagocytose residual cytoplasm
- secrete: supporting testicular fluid, sibstances that initiate meiosis, ABP (concentrates testosterone close to developing gametes), hormones affecting pituitary gland in control of spermatogenesis
Describe the steps of sperm transport in the male reproductive tract
- non-motile infertile spermatozoa passively transported via testicular fluid from seminiferous tubules to caput of epididymis
- 4-12 days in epididymal duct where biochemical maturation takes place
- upon ejaculation, spermatozoa pass through ductus deferns and mix with secretions from the seminal vesicles
Describe the steps of sperm transport in the female reproductive tract
- sperm deposited in upper vagina (rapid elevation of pH)
- passage through cervix
- passage through uterus
- entry into uterine tubes
- passage up uterine tube by flagellar movement and contractions of tube
composition and buffering capability of seminal fluid protect spermatozoa from acidity of upper vagina. Buffering only lasts a few minutes which is enough for sperm to approach the cervix at the optimal pH for sperm motility
Massive numbers of spermatozoa get trapped in ________ in the female reproductive tract
mucosal folds of cervical crypts
slow release of spermatozoa through cervial mucus ensures what?
continued availability of spermatozoa to enter oviduct for fertilization
The ovum secretes ____ that helps sperm transport
chemoattractant
The oviduct has a unique function of conveying spermatozoa and eggs in the ____ directions almost _______
opposite ; simultaneously
The frequency and amplitude of oviductal contractions are regulated by:
- ovarian hormones
- components of seminal plasma
- prostaglandins
Sperm have a ____ lifespan after ejaculation
limited
While migrating in the genital tract, sperm are rapidly seperated from ____ and resuspended in _____
seminal plasma ; female gential fluid
most sperm are eliminated at ____ and ______
cervix ; uterotubal junction
What is capacitation?
- process of physiological changes occurring in mammalian spermatozoa during passage through female reproductive tract that enables them to penetrate ovum membrane
- alteration of glycoprotein surface of spermatozoa under influence of female tissue secretions within the reproductive tract
The ____ of the oocyte facilitates sperm binding and serves as a protective membrane
zona pellucida
the ____ of an oocyte delivers protein (support)
corona radiata
fertilization usually occurs in the ____ area of the uterine tube
ampullary
____ emanating from the acrosome of sperm head may play a role in penetration
hyaluronidase
The zona pellucida allows only sperm of the same ____ to enter the ovum
species
Sperm ____ plays a major role in penetration of corona radiata
motility
Which layer surrounding an oocyte prevents the premature implantation of an embryo?
zona pellucida
what is the acrosomal reaction?
- orderly fusion of the spermatozoa plasma membrane and outer acrosomal membrane
- release of acrosomal enzymes allows spermatozoon to digest its way through the zona pellucida
- acrosomal reaction releases hyaluronidase and acrosin
What are the mechanisms that prevent polyspermy?
- Fast Block: rapid depolarization of ovum’s plasma membrane, occuring 2-3s after fusion
- Slow Block: cortical reaction; calcium wave from site of sperm-ovum fusion, cortical granules fuse with plasma membrane and release hydrolytic enzymes and polysaccharides into perivitelline space, content of cortical granules hydrolyzes sperm receptors in the zona
What is oligospermia
- <20M sperm/mL
- Decreased Fertility
Spermatozoa can survive for ____ after ejaculation
~80 hrs.
Female ____ helps maintain metabolic requirements of spermatozoa
cervical mucus
What is artificial insemination
sperm washed and injected into uterus
What is in-vitro fertilization
oocytes harvested and fertilized in a lab and then re-implanted into uterus
an erection is a largely ____ event
hemodynamic
What happens during an erection?
- parasympathetic nerve-induces vasodilation of arterioles through relaxation of smooth muscle
- allows blood to flow into corpus cavernosum
- veins contract (less blood outflow)
- increased intracavernosal pressure results in erection
Which neurotransmitter mediates erections?
nitric oxide (NO)
What is the role of NO in erection?
- acts on vascular smooth muscle cell, activating guanylate cyclase which catalyzes conversion of GTP to cGMP
- cGMP causes Ca2+ channels in vascular smooth muscle cell to close (cytoplasmic Ca2+ conc. decreases)
- vascular sooth muscle cell relaxes resulting in vasodilation of penis and engorgement of erectile tissue
What was the Sildenafil (Viagra) initially supposed to treat?
angina (chest pain)
Viagara inhibits ____ that catalyzes ____ resulting in _____
phosphodiesterase (PDE) ; breakdown of cGMP, increase of cGMP availability promoting erection
Each mammary gland contains _______
7-10 lobes
Lobes in mammary glands are further subdivided into ______
lobules
Lobules in mammary glands contain ____ which secrete milk into ______
alveoli ; secondary tubules
Describe the movement of mil in the mammary glands starting from the secondary tubules
secondary tubules -> mammary ducts -> lactiferous duct -> nipple
The ____ secretes ____ and ____ which stimulates growth and decelopment of mammary glands and ducts
placenta ; estrogen ; progesterone
After birth, estrogen secretion ____ and prolactin secretion ______
decreases ; increases
milk production is under the control of the hormone ____ from the ______
prolactin ; anterior pituitary
Milk release is under control of the hormone ____ from the _____
oxytocin ; posterior pituitary
Prolactin release is stimulated by:
suckling stimulus
oxytocin release is stimulated by;
suckling stimulus, visual/auditory cues, thought of child
The ____ gene is a sex determining gene (thought to be important for male determination) located on the ____ chromosome
SRY ; Y
In the presence of SRY embryonic gonads become ____, in the absence of SRY, embryonic gonads become ____
testes ; ovaries
In the presence of testosterone ____ is made from Sertoli cells which maintains the ____ and degenerates the ____ in a ten week old fetus
Mullerian inhibition factor; woffian duct; mullerian duct
In the absence of testosterone there is no ____ the ____ degenerates and the ____ is maintained in a 10 week old fetus
Mullerian inhibition factor; Wolffian duct; Mullerian duct
The Wolffian duct becomes:
- seminal vesicle
- vas deferens
- epididymis
The Mullerian duct becomes:
- fallopian tube
- uterus
- vagina
How do the external genetalia of males and females compare during the first 6 weeks of development?
essentially identical; urogential sinus, genital tubercle, urethral folds, labioscrotal swellings
in females the labioscrotal swellings form the ____, in males they form the ____
labia majora ; scrotum
in females the genital tubercle forms the ____, in males it forms the ____
clitoris ; penis
How can an XX male occur?
They inherit the SRY gene on an X chromosome that’s been recombined with Y
How can an XY female occur?
They don’t inherit the SRY gene on the Y chromosome because it’s been recombined with the uninherited X chromosome from the father
Testes determination requires ____ receptor family
insulin
what is true hermaphroditism?
intersex condition where individuals have both ovary and testis tissue
What is pseudohermaphroditism?
individual has external genitalia of one sex and internal sex organs of the other sex
Puberty has earlier and more obvious signs in:
females
during puberty there is coupling of interactions between the ____ and _____
nervous system ; gonadal steroid hormones
At birth FSH and LH levels are ____ and remain this way until the first six months of postnatal life. The levels then____ until puberty.
high ; decline
puberty is triggered by ____ secretion of the hormone _____
pulsatile ; LH
____ stimulates the release of LH
GnRH
LH results in increased _____
sex hormones, estradiol in females, testosterone in males
Increased sex hormone secretion results in the development of ________ characteristics
secondary sex
What happens in children with a GnRH deficiency?
They fail to sexually mature
What is precocious puberty?
very early onset of puberty
