Sex determination and reproductive systems - Reproduction 1 Flashcards
Learning objectives:
* Understand the key processes in regulating sex determination
* Understand the anatomy and function of the male reproductive system
* Describe the roles of the sertoli and leydig cells and their hormonal control
* Have an understanding of the hormonal regulation of the male reproductive system
* Spermatogenesis vs Oogenesis
What are the 3 levels of biological differences between males and females?
- Genetic
- Gonadal
- Phenotypic
What is the genetic level of biological difference between males and females?
What does it drive?
Depends on combination of sex chromosomes at the time of conception: XX-Female and XY-Male
Genetic drives gonadal
What is the gonadal level of biological difference between males and females?
What does it drive?
Gonadal is whether the testes or varies develop
Presence/absence of Y chromosome determines gonadal differentiation
Gonadal then leaves to phenotypic difference
What is the genetic level of biological difference between males and females?
Phenotypic refers to the apparent anatomic sex of individual
Determined by gonadal sex
See slide 5
If an ovum with X sex chromosome is fertilised by sperm with Y sex chromosome what happens?
- X ovum fertilised with Y sperm causes an embryo with XY sex chromosome to form.
- Leads to male genetic sex and then sex-determining regions of the Y chromosome (SRY) codes for the production of testis-determining factor (TDF)
- TDF directs differentiation of gonads into testes and testes are the gonadal sex of the male
See slide 5
What happens when an ovum with X sex chromosome is fertilised by sperm with X sex chromosome?
- An embryo is then formed with XX sex chromosome.
- The genetic sex is then female.
- Since there is no Y chromosome there is no SRY and therefore no TDF
- With no TDF, the undifferentiated gonads develop into ovaries
- Ovaries are the gonadal sex of the female
Slide 6 see
1. Wolffian duct differentiate into?
2. Mullerian ducts differentiate into?
- Male reproductive tract
- Female reproductive tract
Slide 7 see diagram
Testes secrete what?
Testosterone and Mullerian inhibiting factor
Mullerian inhibiting factor causes what?
Degeneration of Mullerian ducts
Testosterone is converted to?
Dihydrotestosterone
Dihydrotestosterone promotes the development of what?
Promotes development of undifferentiated external genitalia along the male lines such as the penis and scrotum
Leading to phenotypic sex of the male
What does testosterone transform Wolffian ducts into?
Into male reproductive tract for example ductus, deferenes, ejaculatory duct, seminal vesicles and epidiymis, etc
The phenotypic sex of the male
What is released or not released in the case of the ovaries?
No testosterone or Mullerian-inhibiting factor is secreted
The absence of testosterone leads to what?
Degeneration of the Wolffian ducts and the development of undifferentiated external genitalia along female lines such as the labia and clitoris
Leading to the phenotypic sex of the female
Absence of Mullerian inhibiting factor causes the development fo what?
Development of Mullerian ducts into female reproductive tract such as the uterus, oviducts, etc
Leading to the phenotypic sex of the female
What is the anatomy of the reproductive systems?
Gonads, reproductive tract and accessory sex glands
What are the gonads?
Primary reproductive organs: testes and ovaries
What is the functions of the mature gonads?
- Gametogenesis: spermatozoa; ova
- Secreting sex hormones
– Testosterone in males
– Oestrogen and progesterone in females
Although males have more androgens and females have more oestrogens
and progesterone, are all these hormones found in both sexes?
Yes
Hypothalamic-pituitary Goanadal axis
See slide 9
Gonadotropin-releasing hormone (GnRh) is
1. Released from where?
2. Acts on what?
3. To do what?
- GnRH released from the hypothalamus
- Acts on the anterior pituitary gonadotrophs 3. To release follicle stimulating hormone (FSH) & Luteinising hormone (LH)
FSH and LH act on what?
They stimulate the release of?
FSH & LH act on the gonads stimulating testosterone and oestrogen release
Feedback regulation can be +/-?
Either or
Feedback regulation by gonadal products such as steroids and peptides takes place at what level?
Level of both hypothalamus and pituitary
See slide 10 on Anterior pituitary gland
(endocrine lectures as well)
See slide 11 HPG axis has both positive+feedback mechanisms
1. A day after menstruation what secretion begins?
2. During the first 11-12 days of follicle growth, what happens to the rate of secretion of FSH and LH?
3. Why does this happen?
- FSH+LH which causes growth of the follicle
- They decrease slightly
- Due to the negative feedback effect of estrogen on the ATP
See slide 11 HPG axis has both positive+feedback mechanisms
1. What happens about day 12 of the monthly cycle?
2. High levels of estrogens causes what feedback?
3. This leads to?
- The high secretion of FSH & LH start to increase
- Due to high level of estrogens causing positive feedback
- Leads to pre-ovulatory LH surge & FSH
surge
See slide 11 HPG axis has both positive+feedback mechanisms
1. Between ovulation and the beginning of menstruation what does the corpus luteum do?
2. What is effect of estrogen is increased when progesterone is available?
3. What effect foes this have on AP and hypothalamus and to do what?
4. Hormone inhibin is secreted by?
5. What does it inhibit the secretion of?
- Corpus luteum secretes large quantities of progesterone & estrogen & inhibin.
- The inhibitory effect of estrogen is
increased when progesterone is available. - This inhibitory effects more on the AP directly & to lesser extent on the hypothalamus to inhibit the secretion of GnRH. 4. The hormone inhibin secreted by the granulosa cells of the ovarian corpus luteum
- It inhibits the secretion of FSH & to lesser extent LH
See slide 12
Positive and negative feedback loops of the HPG axis
Demonstrate highly precise temporal control over the concentration of gonadal and steroid hormone that occurs across the menstrual cycle in women
What are the testes?
Sperm producing organs
The male gonads
Where are testes suspended from?
Outside abdominal tract (temp)
Accessory male reproductive sex organs?
Seminal vesicles, prostate gland, bulbourethral
glands
Secretions conducive to sperm viability
Slide 14 see diagram
Explain the hypothalamic-pituitary gonadal axis pathway involving FSH and LSH
Hypothalamus releases GnRh into anterior pituitary which stimulates FSH to be released which acts on Sertoli cells and releases Androgen binding protein to cause spermatogenesis
Hypothalamus releases GnRh into anterior pituitary which releases LH causing Leydig (Interstitial cells) releasing testosterone which work in conjunction with sertoli cells to cause spermatogenesis
Slide 15 see
FSH is necessary for initiation of?
Spermatogenesis
Testosterone acts as autocrine/paracrine?
It works with FSH to stimulate?
Paracrine
Spermatogenesis
How many compartments of the testes?
250-200
What part of testes produces sperm?
Seminiferous tubules
Leydig cells are interstitial cells which make and secrete?
Testosterone
Sertoli cells are epithelial cells that are contained within? and support the development of?
Contained within seminiferous tubules and support sperm development
What other androgens other than testosterone do Leydig cells make and secrete?
Androstenedione and Dehydroepiandrosterone
LH secretion supports what activity and through what interaction? With stimulation of what sequence?
LH secretion supports steroidogenic enzyme
activity in the testis through interaction with LH receptors and stimulation of the
adenylate cyclase/protein kinase sequence
Sertoli cells - what is their association with the blood-testes barrier?
They make it
Sertoli cells regulate spermatogenesis and spermiogenesis by secretion of which factors?
They secrete androgen-binding protein and Inhibin
Androgen binding protein maintains what?
Steady concentration of androgens for sperm development
What effect does Inhibin have on FSH?
Negative feedback on FSH
Sertoli cells nurture sperm and control their development - through what kind of function is this?
Phagocytic function
Sertoli cells secrete what for sperm transport?
Luminal fluid
Sertoli cells act as target for what hormones?
FSH and testosterone
Slide 19
Male reproductive system - what are the 3 of the sex accessory glands?
Bulbourethral gland, seminal vesicle and prostate gland
Prostate gland secretes what to do what?
Secrete alkaline fluid to neutralise acidic vaginal secretions
Seminal vesicle releases?
Fructose, PGs and clotting precursors
Bulbourethral gland secretes?
Mucus for lubrication
3 Major steps of spermatogenesis?
- Mitotic proliferation
- Meiosis
- Packaging (of cell elements, spermiogenesis)
Spermatogenesis results in?
Many highly specialised mobile sperm called spermatozoa
Undifferentiated diploid primordial germ cells
(spermatogonia) are converted into?
Haploid spermatozoa (sperm)
See slide 21 - Spermatogenesis
1. Mitotic proliferation takes place where?
2. What about Meiosis?
3. And Packing (spermiogenesis)?
- Basal
- Adluminal
- Lumen
Spermiogenesis - spermatids are transformed into?
Spermatazoa
What does the head of a spermatozoa consist of?
Consists primarily of the nucleus (contains DNA - haploid)
What is acrosome within spermatozoa?
–Enzyme-filled vesicle that caps tip of the head
–Used to penetrate ovum
–Formed by endoplasmic reticulum and Golgi complex before these organelles are discarded
Midpiece is what area of spermatozoa?
Area where mitochondria are concentrated
Tail of spermatozoa provides and contains?
Provides mobility for spermatozoon – contains contractile filaments
Spermatozoa are released into lumen of seminiferous tubules which mature for how many days?
Can they move?
Spermatozoa released into lumen of seminiferous tubules are immotile
Its for 20 days
During sperm maturation
Autosomal recessive genetic syndrome what is it?
Impairment in expression of 5-Alpha-reductase and can lead to somebody with a XY genotype developing a sexually ambiguous set of genitalia with feminine characteristics although not completing being female due to the inability to convert testosterone into dihydrotestosterone
Slide 24 slide
Path of sperm
Number and location of testis?
Pair located in the scrotum, a skin covered sac suspended within the angle between the legs
Functions of testis?
Make sperm and secrete testosterone
Sex steroid hormones made at the end of the HPG axis have what feedback and on what?
Negative feedback
On the hypothalamus and anterior pituitary
Epididymis and Ductus Deferens number and location?
Pair
1 epididymis is attached to the rear or each testis
1 ductus deferens travels from each epididymus up out of the scrotal sac through the inguinal canal and empties into the urethra at the neck of the bladder
Functions of Epididymis and Ductus D
Serves as the sperm’s exit route from the testis
Serves as the site for maturation of the sperm for motility and fertility
Concentrates and stores the sperm
Paracrine signalling means?
Doesn’t enter vasculature, acts on receptors in nearby tissue
Testosterone is also responsible by endocrine signalling for the maintenance of accessory reproductive organs and secondary sex characteristics - effect on?
1. Sex drive?
2. Protein synthesis in skeletal muscle?
2. Bone growth in adolescence?
- Increases
- Increases
- Increases
Number and location of seminal vesicle?
Pair
Both empty into the last portion of the ductus deferens one on each side
60% volume is semen
Functions of seminal vesicle?
Supply fructose to nourish the ejaculated sperm
Secrete prostaglandins that stimulate motility to help transport the sperm within the male and female
They provide the bulk of the semen and precursors for the clotting of semen
Prostate gland - number and location?
Single
Completely surrounds the urethra at the neck of the bladder
Functions of prostate gland?
Secrets an alkaline fluid that neutralises the acidic vaginal secretions
Triggers clotting of the semen to keep the sperm in the vagina during penis withdrawal
Bulbourethral gland - number and location?
Pair
Both empty into the urethra - 1 on each side just before the urethra enters the penis
Functions of Bulbourethral gland?
Secrete mucus for lubrication
See slide 26
Events leading to erection
Either Mechanical stimulation of receptors in penis or activity in descending pathways from brain into spinal cord causes -
1. Effect on sympathetic / parasympathetic neurons to penis?
2. Nerves at sympathetic / parasympathetic?
- Decreases activity in sympathetic and increased in parasympathetic
- Sympathetic neurons at the lumbar pudenal nerve and Sacral cavernous nerve at parasympathetic neurons
What is Viagra/Sildenadil?
How does it work?
Phosphodiesterase inhibitor blocks the degradation of cGMP
cGMP – Smooth muscle relaxation
Arterial dilation in penis
Increased blood flow to penis
What causes ejaculation?
Increased sympathetic nerve activity triggers contraction of epididymis, vas deferens and ejaculatory ducts
See slide 26
Events leading to erection
Increases parasympathetic neurons to penis causes what effect
1. On arteries to make?
2. Smooth muscle?
3. Blood flow?
4. Blood volume and blood pressure in erectile tissue causes what and how does it stop an erection?
5. What kind of feedback?
1 Arteries supplying blood to erectile tissues, makes NO
2. NO causes smooth muscle to relax
3. Causes increased blood flow
4. Blood volume and blood pressure in erectile tissue increases causes an erection
Causes compression of veins draining erectile tissue and decreasing the outflow of blood when stopping the erecetion
5. Positive
Nitric oxide role in erections?
NO nitric oxide production by epithelial cells of blood vessels - smooth muscles of the penile arteries to relax and fill with blood,
resulting in an erection.
Semen normal ejaculate has how much and what speed and pH?
Semen: normal ejaculate ~3.5mls fluid, containing 120.106 sperm/ml, @ a pH of 7.5
Once ejaculated sperm survive @ body temp for how long?
24-48 hours
What is VIP in determining fertility?
The number, motility and morphology of sperm
What sperm count is indicative of infertility?
A sperm count < 20.106/m
What prevents voiding of bladder and release of urine during ejaculation?
Closure of urethral sphincter at base of bladder
Female reproductive is separated into internal and external parts
1. Internal is ?
2. External is ?
- Ovaries, Fallopian tubes, uterus and upper portion of vagina
- (Vulva) - Lower portion of vagina, labia minora and majora, clitoris, vestibular glands and mons pubis
- Ovaries what is here?
- What happens at fallopian tubes?
- Uterus is for?
- Upper portion of vagina is for?
- Ovaries – Germ cells and hormones
- Fallopian tubes – Conception and zygote transport
- Uterus – Incubation and parturition
- Upper portion of vagina - (copulation and parturition)
- Lower portion of vagina is for?
- What about the Labia minora+majora, the clitoris?
- What happens at vestibular glands?
- Function of mons pubis?
- Lower portion of vagina - copulation and parturition
- Labia minora and majora, clitoris -copulation
- Vestibular glands - secretions
- Mons pubis - protect pubic bone
Reproductive system of female has cyclic changes in activity due to the?
Menstrual cycle
There is restricted periods of fertility - when can it occur?
During ovulation
There is a limited gamete production when is this etablished?
Pool established at birth
See slide 31 diagram
Mitotic division then meiotic
Primary female reproductive organs the ovaries make and secrete?
Make ova for oogenesis and secrete female sex hormones
Oestrogen is essential for?
It establishes?
Role with sperm?
Contributes to?
» Essential for ova maturation and release
» Establishment of female secondary sexual
characteristics
» Essential for transport of sperm in oviduct
» Contributes to breast development in anticipation of lactation
Progesterone is important in making ?
Progesterone is referred to as the what hormone?
Contributes to ability of?
» Important in preparing suitable environment for nourishing a developing embryo/fetus
» Pregnancy
» Contributes to ability of breasts to produce milk
Spermatogenesis vs Oogenesis
1. Takes how long?
2. Unlimited life?
3. Primary oocyte/spermatocyte yields?
4. Spermatozoa vs ovum?
- S- Accomplished within two months and O - Take anywhere from 12 to 50 years to complete on cyclic basis from onset of puberty until menopause
- S - Postpubertal male can produce several hundred million sperm each day whereas O- Female born with limited, largely nonrenewable supply of germ cells
- S - Each primary spermatocyte yields four
equally viable spermatozoa whereas O -Each primary oocyte yields only one cytoplasm-rich ovum and three cytoplasmpoor polar bodies that disintegrate - S- Spermatozoa= motile nucleus whereas O -Ovum= immobile with complex cytoplasm
There is identical steps of chromosome replication and division during gamete production in both sexed however what 2 key things are different?
Timing and end result are very different
