Puberty, menstrual cycle and menopause/ later life Flashcards
When do boys start puberty?
age 10-14- lasts an avg of 3 yrs
When do girls start puberty?
age 9-13- lasts an avg of 2.5 yrs
What is the first sign of puberty in boys and in girls?
Boys= pubic hair growth and testis descent/ enlargement Girls= pubic hair growth and breast bud development (thelarche)
What is the crucial weight for girls to start puberty?
47kg
How can you asses what stage of puberty someone is at?
The tanner scale
What drives pubic hair growth in men and women?
Testosterone- however in women it is lower and suppressed by carrier proteins which inactivate it
What causes earlier epiphyseal fusion in girls?
Oestrogen- this is why they end up being smaller
What effect will precious puberty have on height?
your growth plates will fuse earlier so youll be shorter
What can cause precious puberty?
Adrenal, pituitary or testicualr tumours, brain or spinal injuries, hypothyroidism, obesity and meninigits
However, 90% of the time in females it is idiopathic
What triggers the start of puberty? (common to both M and F)
Gradual increases in gonadotrophin releasing hormone (GnRH) from the hypothalamus- leptin and photoperiod have been shown to increase this release. The GnRH is released in a pulsatile fashion to the ant pituitary which releases FSH and LH in response. This will cause testosterone and oestrogen release (in boys too- as the testosterone is converted to oestoradiol), this will have a positive feedback on growth hormone release, which causes the growth spurt.
Why might leptin be important in stimulating GnRH release?
It is released from adipose tissue, and so may be indicating to the body that it has enough fat/ energy stores for puberty to start.
How does the time of day affect GnRH release?
GnRH release increases at night
What happens in males when FSH and LH release increases at the start of puberty?
LH stimulates leydig cells to produce testosterone.
Sertoli cells will react to FSH by increasing sperm production, they also produce inhibin which starts to regulate the LH and FSH production.
What affect does the rise in FSH and LH at the start of puberty have on female hormones?
FSH causes granulosa cells of follicles to release oestrogen and inhibin and start follicular development for the menstrual cycle to start.
LH acts on theca interna cells to release androgens such as progesterone which also drive puberty and development.
What is the most common cause of delayed puberty?
Constitutional delay- they just have low GnRH, FSH and LH
What 3 processes cause genetic variation of gametes?
- crossing over: homologous chromosones exchange regions of DNA in prophase 1
- independant assortment: random alignment of homologous chromosomes in metaphase 1
- random segregation: random distribution of alleles among the 4 gametes
Where does spermatogenesis occur?
Within gaps in between sertoli cells within seminiferous tubules. The sertoli cells provide nutrients for sperm growth and development from spermatogonium and also form tight junctions to form a barrier from the blood.
What is the difference between spermatogenesis and spermiogenesis?
spermatogenesis is the whole process from permatogonium to spermatozoa, spermiogenesis is just the maturation from spermatid to spermatozoa.
Where do spermatogonium come from?
Primordial germ cells of the yolk sac
How much fluid is produced in each ejaculate? What is the normal sperm count?
2-4 ml// 20- 200 million per ml
Describe the process of spermatogenesis?
- From puberty, Ap spermatogonium in the basal membrane start to divide by mitosis but produce a primary spermatocyte and another spermatogonium
- Ad spermatogonium dont divide, but act like a reserve
- The primary spermatocyte divide by meiosis into secondary spermatocytes and then again into spermatids
- Spermatids are released into the seminiferous tubules
- They remodel as they pass through the seminiferous duct and rete testis until they get to the epididermis, they’re non motile at this stage and are moved by peristalsis
What is a spermatogenic cycle and how long is it?
The time taken for one group of cells along the seminiferous tubule to get back to the same stage of spermatogenesis- takes approx 16 days. This is because differnt parts of the seminiferous tubule are at differnt stages to ensure constant production of sperm
What is a spermatic wave?
The distance between the two regions of the seminiferous tubule that are in the same stage of the spermatic cycle
What triggers capacitation?
Progesterone and other hormones from the ovum and vagina
What occurs during capacitation?
G proteins in the sperm become activated which causes the sperm to loose its glycoprotein and cholesterol membrane on the head of the sperm
Describe the process of oogenesis before puberty
- primordial germ cells from the yolk sac colonise the gonadal cortex and differentiate into oogonia
- they proliferate rapidly by mitosis
- By the end of the 3rd month gestation they’re arranged in clusters with flat epithelial cells around them
- some differentiate to create a primary oocyte
- many oogonia and primary oocytes degenerate because theyre not perfectly formed
- The primary oocytes are stuck in meiosis 1
What is the primordial follicle made up of?
the oocyte and the follicular cells (the flat epithelial cells around it)
Describe the completion of oogenesis after puberty (4 stages)
- preantral stage- follicular cells become cuboidal and differentiate into granulosa cells, these secerete glycoprotein onto the ovum to form the zona pellucida
- antral stage- air filled spaces form between granulosa cells which come together to make one large space called the antrum. The outer layer of granulosa cells differentiates into the theca externa and theca interna
- preovulatory stage: surge in LH induced the preovulatory stage, this is where meiosis 1 completes to form the polar body and secondary oocyte
- the secondary oocyte starts meiosis 2 but arrests in metaphase
What effect do LH and FSH surges have on the follicle before ovulation?
Rapid proliferation to from the graafrian follicle. LH increases collagenase activity and prostaglandins cause local muscle contraction, these help the oocyte break free of the ovary walls
Describes what happens to the follicle after ovulation? State what happens if fertilisation does and does not take place
The remaining granulosa and theca cells become vascularised. They then develop a yellow pigment and become lutein cells which secrete oestrogen and progesterone. If HcG is released form an embryo, the corpus luteum continues to grow and form the corpus luteum graviditatis which continues to secrete progesterone until the placenta takes over. If no fertilisation, it degenerates and forms a fibrotic scarcaled corpus albicans