Reproductive Physiology

Question 1

Recall the component parts of the male reproductive system, draw diagrams to illustrate the main cellular components, including testis and seminiferous tubules, and explain the significance of the Sertoli and Leydig cells for spermatogenesis and hormone production.

Answer 1

Human Male Anatomy

• Testis – contain seminiferous tubules (to produce sperm) and Leydig cells which produce testosterone.
• Epididymis – one within each scrotal sac. Sperm are stored in these and at ejaculation, sperm pass through the vas deferens (contractile) and are mixed with fluid from the seminal vesicles. The fluid then leaves the duct and passes into the urethra to mix with prostate secretions.
• Urethra : both used for urination and ejaculation

Question 2

Overview the male reproductive system

Answer 2

Regualatory hormones

• Gonadotrophin releasing hormone (GnRH)
  
  • Hypothalamus
• Luteinising hormone (LH)
  
  • Anterior pituitary
• Follicle stimulating hormone (FSH)
  
  • Anterior pituitary
• Testosterone (T)
  
  • Testis

Their only target are in the testis receptors and it’s there that these hormones exerts its functions

Leidig cells make testosterone which help produce sperm as they enter the seminiferous tubules- they produce Antigen binding protein which binds testosterone and regulates the funciton of sertoli cells

Sertoli cells will release inhibin - which will decrease the release of LH and FSH - negative feedback

Male Regulatory Systems

• Leydig cells – testosterone – LH stimulated.
• Sertoli cells – Inhibin – FSH stimulated.

Question 3

Spermatogenesis

Answer 3

The whole process of meiosis and mitosis occurs in the seminiferous tubules - resulting in a haploid cell (spermatogenesis)

Spermatogenesis

1. Germ cells 44+XY (diploid).
   * Mitotic division.
2. Primary spermatocyte 44+XY (diploid).
   * 1st meiotic division.
3. Secondary spermatocyte 22+X, 22+Y (haploid).
   * 2nd meiotic division.
4. Spermatids 22+X, 22+Y (haploid).
5. Spermatozoa 22+X, 22+Y (haploid).

200m sperm/day, starts at puberty.

Male reproductuve function:

• Starts at puberty
• Functions continually
• Normally continues throughout the rest of life
• Sperm quantity and quality generally decreases with increasing age
• LH stimulates testosterone production
• FSH and testosterone sustain Sertoli cell function
• Sertoli cells support spermatogenesis

Question 4

Recall the component parts of the female reproductive system

Answer 4

Human Female Reproductive System

• Starts at puberty
• Functions cyclically
• Normally operates until ~45 years of age
• Egg quality generally decreases with increasing age
• FSH stimulates (some) development of ovarian follicles & 17b-estradiol synthesis
• LH stimulates progesterone production
• The steroids regulate uterine endometrium

Anterior pituitary: LH, FSH
Ovaries: oestrogen and progesterone

progesterone and oestrogen feedback onto the hipothalamus and the pituitary

Question 5

draw diagrams of the ovary to illustrate the main stages in the maturation of an oocyte,

Answer 5

Human Female Anatomy

The ovary – produce the gametes and steroids (oestrogens and progesterone’s).

The fallopian tubes – oviduct – sustains oocyte or conceptus:

Isthmus, ampulla (fertilisation), infindubulum, fimbriae

Uterus – conceptus implants here.

Question 6

explain the significance of the granulosa and thecal cells for sex steroid hormone production.

Answer 6

Female Ovary

• Many follicles do not develop all the way to ovulation; many undergo atresia.
• Thecal cells – oestrogen and androgens – LH.
• Granulosa cells – androgens à oestradiol (produce progesterone in the second-half of the cycle) – FSH.

Progestogens – maintain endometrium.

Oestrogens – stimulate proliferation of the endometrium.

Question 7

Define the key stages of the menstrual cycle.

Answer 7

Changes in the female in the HPO axis (ovarian cycles)

We start from gnth which stimulates LH and FSH which stimulates release of estradiol from the ovaries which triggers negative feedback and decreases the hypothalamic gnrh secretion

Mid cycle

Hypothalamus and AP are sensitised to estradiol and estradiol secretion stimulates estradiol production

Luteal Phase

Menstrual Cycle

• Composed of the endometrial & ovarian cycles.
• Endometrial – menstrual, repair and proliferative, secretory phases.
• Ovarian – follicular, luteal phase.

1. FSH & LH stimulate the follicular phase which results in oestradiol production à stimulates the endometrial proliferation.
2. Oestradiol (E2) production continues at a greater pace and –ve feedback switches to +ve and ovulation occurs.
3. Corpus luteum produces progesterone and E2 and the endometrium enters the secretory phase.
4. Steroid progesterone secreted from ovaries again induces negative feedback

Time frame

• Menstrual cycles last ~28 days (21-35 days).
  
  • In younger people, it may be longer.
  • Older people, shorter OR longer.
• Note the change of –ve to +ve feedback of E2.

This variability of the time frame of mestrual cycle - makes it uncertain when fertilization occurs and ovulation and hence pregnancy

Question 8

Draw a diagram to illustrate fluctuations in hormonal levels during the menstrual cycle, including oestradiol, progesterone, LH and FSH, and recall homeostatic mechanisms within the hypothalamo-pituitary-gonadal axis.

Answer 8

Menstrual Cycle

Note basal body temperature raises around ovulation.

1. Gradual rise of oestradiol by developing follicle (FSH).
2. Follicles grow and –ve feedback on LH and FSH.
3. Dominant follicle selected and produces lots of E2 à –ve feedback switch to +ve feedback à LH surge.
4. Ovulation.
5. Corpus luteum produces E2 and progesterone à -ve feedback on LH and FSH.
6. No fertilisation à E2 and progesterone fall and endometrium enters secretory phase.

Question 9

Define the key phases of the endometrial cycle and how they are linked to the menstrual cycle.

Answer 9

Endometrium:

• Oestrogen dominates the proliferative or follicular phase.
• Progesterone dominates the secretory or luteal phase.
• Terminology used depends upon what is being described:
• Endometrium/Uterine – proliferative/secretory.
• Ovarian – follicular/luteal.

Thinnest – 2-4mm.

Thickest – 7-16mm.

Menstrual cycle: There is thickening of the uterus induced by increasing progesterone levels

And when progesterone falls, there is a signal for shedding the endometrium

Oestrogen - shedding

PRogesteron - build up

Question 10

Define the process of gametogenesis in human tests and females.

Answer 10

Folliculogenesis (INSIDE THE OVUM).

Oogonia 44+XX (diploid).

• Mitotic division.

Primary oocytes 44+XX (diploid).

• 1st meiotic division.

Secondary oocyte (+polar body) 22+X, 22+X (haploid).

• 2nd meiotic division.

Ovum (+ polar body) 22+X, 22+X (haploid).

• Ovulation = release of mature oocyte (egg) from the ovary
• Oocyte is 2n at this stage, in meiotic arrest (metaphase II)
• Enters the Fallopian tube
• Needs to be fertilised within 24 hours, as it degenerates after this

Note – 1st meiotic division is linked to the LH surge, meiosis 2 follows immediately after this BUT pauses in metaphase 2 (as shown).

Note – the second polar body is generated after the 2nd meiotic division which occurs in the fertilised cell.

Important Points:

• Time taken for primordial follicle à secondary oocyte is MORE than one month.
  
  • The human ovary contains multiple follicles at ALL stages of development with one dominant (Graafian) follicle at any one time.
  • The ovaries alternate the release as well (so each one releases one follicle each ~56 days).
• Human ovaries contain 2m primordial follicles at birth -> only 400 released at ovulation in a lifetime.
• During meiosis, both the 1st and 2nd divisions are paused during follicular development.
  
  • Meiosis 1 starts during embryonic development, but halts at diplotene stage of prophase 1 (primary follicle) which is arrested until puberty (meiosis then resumes and 2nd follicles develop).
  • 2nd follicles then undergo a second arrest.

Key points:

• Ovaries – contain ~6m primordial follicles at ~20w development -> ~1m at delivery of infant.
  
  • 400 released over a lifetime.
• Testes – produce 100m sperm/day from puberty onwards.

Formation of follicle gradually getting more mature - selected for final growth only later

Question 11

Recognise the mechanisms of fertilisation

Answer 11

Fertilisation

1. Deposition of sperm near the cervix.
   
   • Cervical mucous is hostile to sperm which forms a physical barrier.
   • Cervical mucous changes at mid-cycle to permit sperm to enter the uterus.
2. Passage of sperm through uterus and then fallopian tubes.
3. Sperm (swims) moves to fallopian tube ampulla.
   
   • 2mm/min, 12cm/hour.
   • Survival of the fittest.
   • Capacitation takes place (within the uterus) which matures the spermatozoa.
4. Egg meets sperm fusion of egg with sperm (24 hours post ovulation).
   
   • Acrosome reaction – penetration of zona pellucida (& Coronal cells).
   • Calcium flux.
   • Resumption of meiosis, release of 2nd polar body.
   • Alignment of maternal and paternal chromosomes to generate zygote.
5. Change in Zona Pellucida to stop additional sperm fusing.
6. Initiation of mitotic divisions in embryo by the joining of male and female pronuclei

After fertilisation

• Meiotic arrest is removed and meiosis continues
• Last step of female reproduction
• Meosis of maternal chromosomes resumes, forming female pronucleus (23 chromatids), and 2nd polar body.
• Sperm chromosomes decondense to form male pronucleus (23 chromatids).
• Chromatids in both pronuclei are duplicated
• They align on the mitotic spindle, and are separated into 2 identical ‘daughter’ cells (1st cleavage division of the embryo).

Capacitation - sperm is faster and goes through capacitation

Acrosome reaction - sperm digests zona pellicida to allow

Answer 12

cyclicAMP is increased by Viagra/.?