Reproductive physiology Flashcards
Distinguish between biological sex, sexual reproduction and sexual intercourse
Biological sex: depends on chromosomes and which gametes are produced
Sexual reproduction: produces offspring that are genetically different from the parents
Sexual intercourse: procreative activity to allow for sexual reproduction and bonding
What is the urethra an opening for in males
Ejaculatory duct and urine from the bladder
Urogenital system
Summarise 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.
What is the key aim of the male reproductive system
The human male reproductive system is (if compared to the female system) relatively simple. The two main functions are the provision of androgens (primarily testosterone) to initiate and sustain the necessary male phenotype, and the production of mature sperm.
Summarise the regulatory hormones in the male reproductive system
Gonadotrophin releasing hormone (GnRH) Hypothalamus Luteinising hormone (LH) Anterior pituitary Follicle stimulating hormone (FSH) Anterior pituitary Testosterone (T) Testis
Describe the male HPG axis
GnRH released in pulses each hour from hypothalamus
GnRH causes pulsatile LH/FSH release from the APG
LH stimulates Leydig cells (only cells to express LH receptors) to produce testosterone
FSH stimulates Sertoli cells to support spermatogenesis, also requires testosterone
Describe the role of the Sertoli cells and Leydig cells in the male reproductive system
Sertoli cells: form the seminiferous tubules, containing FSH/androgen receptors; act as primary control of spermatogenesis - in response to FSH will produce INHIBIN and androgen binding protein to support spermatogenesis (carries the testosterone in the seminiferous fluid)
Leydig cells: lie outside tubules, with LH receptors, responding by stimulation by producing testosterone - assists spermatogenesis
When are the germ cells activated in males
During puberty
Not all cells enter the cyclic development phase, some germ cells return to their quiescent state until they are stimulated to develop.
Outline the process of spermatogenesis
Spermatogonia outside of seminiferous tubules divide by mitosis, with one cell remaining a spermatogonia and the other forming a 1o spermatocyte (2n)
The 1o spermatocytes then undergo meiotic division to produce haploid 2o spermatocytes, containing either 22X or 22Y chromosomes. At this stage, they pass between the Sertoli cells forming the seminiferous tubules.
The 2o spermatocytes (n) undergo meiosis 2 to produce four spermatids (n) which enter luminal compartments for nutrition - Sertoli cell secretions give spermatids their rudimentary tails.
Spermatids differentiate to spermatozoa in spermiogenesis
Spermatozoa travel to epididymis for flagella development and mitochondrial gain
What is the role of the different meiotic divisions in spermatogenesis
The 1o spermatocyte (2n) undergoes meiosis 1 to produce two 2o spermatocytes (n)
The 2o spermatocytes (n) undergo meiosis 2 to produce four spermatids (n) which enter luminal compartments for nutrition
Summarise male reproductive 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
Generally, why is sperm quality quite low
200m sperm/day, starts at puberty.
So it’s a really rapid process, and therefore error prone
Only 4% of the sperm sample will be able to fertilise the egg
But this is still a high number of viable sperm, giving the shear quantity of sperm in the ejaculate.
Summarise the 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 & 17β-estradiol synthesis
LH stimulates progesterone production
The steroids regulate uterine endometrium
What is the key consequence of egg quality decreasing with increasing age
Held in meiotic arrest until stimulated.
More chance of abnormalities in fetus.
Describe the role of the ovaries
The ovary Parallel functions to the testes, in that they produces the gametes (oocytes) and the steroids needed for female reproductive function (progesterone and estrogens).
Describe the role of the Fallopian tube and uterus
The Fallopian tube (oviduct) through which the oocyte reaches the uterus. Provides an appropriate environment to sustain either an oocyte or a conceptus (fertilised oocyte).
The uterus, in which the conceptus normally implants and is supported throughout pregnancy.
Describe the changes in the female HPO cycle throughout the menstrual cycle
Folicular phase- mainly Oestradiol released from the ovary- this has negative feedback on the axis
Midycle- mainly Oestradiol released from the ovary- this now has positive feedback on the axis- generates the rapid peak of LH and FSH needed for ovulation.
Luteal phase- mainly progesterone released from the ovaries- negative feedback on the axis
Summarise female sex hormone production
Ovum surrounded by granulosum cells, then by thecal cells with LH receptors, to allow LH to simulate steroidogenesis to androgen stage (lack aromatase)
Androgens diffuse into granulosa cells containing FSH receptors (only tissue in body that expresses) and aromatase, and when FSH binds, aromatase activated to convert androgens to oestradiol
When corpus luteum stage, androgens produced and transformed to oestradiol and progesterone
What are the gonadotrophin-independent stages of egg development
Primordial follicle pool
Primary follicles
Preantral follicle
What are the gonadotrophin-dependent stages of egg development
small antral follicle
large antral follicle
preovulatory follicle.
All, except the preovulatory follicle can undergo atresia.
Differentiate between the granulosa cells and the thecae cells
The thecal cells of the developing follicles are responsible for the production of estrogens, and the granulosa-luteal cells produce estrogens and progesterone during the second half of the ovarian cycle.
§ 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.
Describe the length of the human menstrual cycle
The human menstrual cycle lasts approximately 28 days, but this varies substantially between human females, and also in individuals. Most sources suggest a normal range between 21 – 35 days in adult females, but in younger teenagers (i.e shortly after menarche), the length may be up to 45 days. At the other end of the reproductive spectrum, when a woman is approaching the menopause, her menstrual cycle is likely to become irregular in length; shorter or longer, or perhaps skip a month or two before resuming.
