reproductive system๐๐ธ lecture 1 Flashcards
Reproduction is the processโฆ
which new individuals of a species are produced and the genetic material is passed on from generation to generation
Reproductive processes are mediated by
a hierarchical arrangement of endocrine glands ultimately under the control of the central nervous system, but with complex regulatory mechanisms operating between the various levels of the hierarchy.
Hypothalamus main function is to
act as a homeostatic regulator for reproduction, stress, body temperature, hunger, thirst, and sleep.
The hypothalamus is a
neuroendocrine organ, as it processes both neural and hormonal information.
Posterior pituitary
hormones are released from the posterior pituitary.
Neurosecretory neurones are aggregatedโฆ
into nuclei
Neurosecretory cells possess long axon tracts which pass into the
posterior pituitary
The neurosecretory peptide hormones are synthesised where ?
in the hypothalamus
travel bound to carrier proteins down to the axon terminals and stored in
secretory vesicles
Nerve impulses travel along the axon to trigger exocytosis of the secretory vesicles which releases
peptide hormones.
The two neurosecretory peptide hormones are
oxytocin and antidiuretic hormone (ADH or vasopressin).
neurosecretory peptide hormones are synthesised in the hypothalamus and transported to..
posterior pituitary, where they are stored and released
Oxytocin
has major efects on smooth muscle contraction, causing milk ejection and contraction of uterus during childbirth. Secretion is stimulated in response to stimulation of nipples or uterine distension. Oxytocin is used to induce labour.
Anterior pituitary
Neurosecretory neurones synthesise releasing and inhibiting hormones in their cell body into vesicles, which travel to the axonal terminus
In response to nerve impulses, these neurosecretory peptide hormones are secreted into
linking hypophyseal portal vessels, a vascular arrangement in which blood lows from one capilliary bed to another without going through the heart in its journey.
Gonadotrophs
anterior pituitary secretory cells arranged in clumps at the termini of the portal blood vessel.
Inhibiting hormones act on
Gonadotrophs (producing the two gonadotrophins;
Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH)).
Gonadotrophin releasing hormone (GnRH)
Site of secretion , Chemical class
Hypothalamus
Water Soluble
Peptides and proteins
Follicle-stimulating hormone
Site of secretion , Chemical class
Anterior pituitary
Water Soluble
Peptides and proteins
Luteinising hormone
Site of secretion , Chemical class
Anterior pituitary
Water Soluble
Peptides and proteins
Oxytocin
Site of secretion , Chemical class
Posterior pituitary
Water Soluble
Peptides and proteins
Androgens
Site of secretion , Chemical class
Testes
Lipid Soluble Steroid hormones
Oestrogens
Site of secretion , Chemical class
Ovary
Lipid Soluble Steroid hormones
Progestagens
Site of secretion , Chemical class
Ovary
Lipid Soluble Steroid hormones
Features of hormone regulation
Homeostatic mechanisms involving negative and positive feedback loops regulate hormone levels
Negative feedback
control is one of the most important mechanisms. This often involves signalling between the hypothalamus, the pituitary and the target organ.
Pulsatile release
Hypothalamic secretions are released in discrete bursts, separated by periods of little or no secretion. Seen as a pulsatile release of pituitary hormones. This prevents receptor desensitisation and down-regulation.
Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH)
Bind to receptors in the ovary and testis. Promote the synthesis of sex steroid hormones and gametogenesis.
Androgens
Testosterone is the main secretory product of the testis, and associated with the development and maintenance of male characteristics and fertility.
Testosterone 5ฮฑ Dihydrotestosterone
Some key properties
- Male sex development
- Spermatogenesis
- Sexual behaviour
- Muscle development
Oestrogens Main role
is in development and maintenance of female characteristics and fertility.
The main site of oestrogen production is the granulosa cells of the growing follicle.
Oestradiol
Oestrone
Oestriol
Some key properties
- Female sex development
- Growth of the endometrium
- Regulation of the menstrual cycle
- Bone growth
Progesterone is the major
steroidal hormone of the corpus luteum and of the placenta. Associated with the preparations for pregnancy and its maintenance.
Sex determination
Commitment of the bipotential gonad to a testis or an ovary.
The Sex-determining Region on the Y chromosome (known as the SRY gene) provides
the pathway for testes to develop.
The presence of a testis determines the sexual fate of the embryo, against the basic feminine trend. In the absence of SRY, the embryo develops into a female.
Sex diferentiation
The phenotypic development of genital structures due to the action of hormones produced following gonadal development.
Male diferentiation The internal genitalia
Mรผllerian duct regression occurs under the control of
Anti-mรผllerian hormone (AMH)
Male diferentiation The internal genitalia
Testosterone secreted by the testis actively maintain
Wolffian ducts.
Male diferentiation The internal genitalia
The Wolan ducts develop into
epididymis, vas deferens and seminal vesicles.
The internal genitalia
The testis descends from its internal position to the scrotum, usually after
7th month.
The internal genitalia Female diferentiation
The Wolan ducts
begin to regress slowly from about 10 weeks.
Female diferentiation of the genital tract lags behind male organogenesis
Female diferentiation The internal genitalia
The Mรผllerian ducts develop
fallopian tubes, uterus, cervix, and upper vagina.
The external genitalia
The male and female external genitalia develop from a single bipotential precursor.
The external genitalia
Male diferentiation
How is the shaft of the penis formed
Fusion of the urethral folds enclosing the urethral tub
The external genitalia
Male diferentiation
How is the scrotum formed
Labioscrotal swellings fuse in the midline
The external genitalia
Male diferentiation
Hope is the glans penis formed
The genital tubercle (glans area) expands
The external genitalia Female diferentiation
How is the labia minora and majora formed
The urethral folds and labioscrotal swellings remain separate
The genital tubercle (glans area) forms
the clitoris
Puberty
Puberty is the physical, emotional, and sexual transition from childhood to adulthood.
reawakeningโ of the reproductive endocrine systems, which leads to full
secondary sexual maturation with capacity for reproduction
gonadotrophins are very low during childhood until
initiation of events leading to puberty.
Endocrine changes during puberty
irst endocrine sign of puberty
An increase in plasma LH levels
and is the result of an increase in GnRH release.
Gonadotrophin secretion (both LH and FSH) occurs in early puberty at
night during sleep.
In late puberty, daytime
LH pulses also increase.
Sex steroids rise in response to
increase in plasma LH.
Secondary sexual characteristics
Characteristics develop at diferent chronological ages in different individuals the sequence in which the changes occur are quite characteristic for each sex staging criteria (Tanner stage) allows abnormalities to be detected, and comparisons made between individuals.
Menopause
The menopause is the consequence of the ovaries running out of follicles, and occurs between 50 and 52 years of age.
Menopause
Postmenopausal oestrogen production
one year after the menopause the ovary has essentially ceased producing hormones (ovarian senescence). Oestrogen production reduces to less than one- tenth of previous.
Menopause
Oestrogen (oestrone) arises mainly from
production in the stromal cells of adipose tissue. Oestrone is a weak oestrogen.
Menopause Symptoms
Vasomotor
hot lushes night sweats
Menopause Symptoms
Genitourinary symptoms
atrophic changes vaginal dryness
Menopause Symptoms
Bone metabolism
osteoporosis
Menopause Symptoms
Behavioural/Psychological changes
depression, tension, anxiety, mental confusion loss of libido
Most of these symptoms of the menopause may be prevented or arrested by
oestrogen treatment (known as menopausal hormone therapy). However higher risk of cancers
GnRH only has a
Positive effect
5 alpha dihydeotestostrone
More patient has a more direct effect on target tissue
Oestradiol is produced
From puberty to menopause
By grandulosa cells and granule follicles
Oestrone
. Main one in men
Produced in fat tissue
Important after menopause
Oestriol
Weaker
Important during pregnancy
Progesterone
Only in women for pregnancy regulation/ maintains lining of uterus
. Seen after mensuration
How many chromosomes
46
How many autosomes
22 pairs of autosomes
Why do males develop earlier
Due to driving hormones
Mรผllerian duct regression due to
Secretions from the sitloe cells
Wolffian duct driven by
Secretions from the laydig cells e.g testosterone
Androgen insensitivity syndrome
. Person is Xy
. Has has testes, but the genital ducts and/or external genitals are female.
. This person has a mutation in their androgen receptor gene which prevents androgen function
. In the absence of androgen action, the external genitalia will appear female.
Breast development
Time and age
What leads to it
.First physical sign of secondary sexual maturation at age ~10-11
.Oestrogen secretion leads to the appearance of a breast bud, followed by formation of a breast mound
.Ovulation, with subsequent progesterone secretion, leads to full breast development
Sexual hair development
Age and time
What causes it
Usually within 6 months of the appearance of the breast bud at age ~10-12
Due to exposure of hair follicles to androgens
Axillary hair follows ~1 year after pubic hair
Growth spurt
Stimulated
Ages f and m
Growth is stimulated by steroid hormones (oestrogen and androgen), with epiphyseal closure (bony ends) by oestrogen.
Occurs in girls age ~11-12, and boys age ~13-15
Menarche
Age and time
Menarche occurs at an average age of 12-13 years.
The first ovulation does not take place until 6-9 months after menarche, because the positive feedback mechanisms of oestrogen have not developed.
Regular ovulatory cycles are established โฆ
1-2 years after menarche.
Testicular and penile enlargement
Are
First signs of secondary sexual development is enlargement of the testicles
What causes Testicular and penile enlargement
Leydig cells enlarge and secrete testosterone, giving rise to increased testicular size.
Elongation and enlargement of the penis begins within year of testicular enlargement.
Physical changes in boys
Sexual hair growth
Time
Pubic hair appears about 6 months after the beginning of testicular enlargement
Physical changes in boys
Sexual hair growth Axillary hair begins
18 months later, and facial hair later
Physical changes in boys
Spermache
Motile sperm is seen in urine at ~13-14 years
First ejaculation occurs soon after
Physical changes in males and females
Body shape in males and females is determined by the differential affects of androgen and oestrogen
The timing of puberty
Girls
And what weight must be attained before the activation of the hypothalamo-pituitary-gonadal axis can occur.
The age at which girls first menstruate shows a clear trend towards earlier menarche in girls.
Mean weight of girls at the beginning of menarche is ~47 kg.
Precocious puberty
The appearance of the physical & hormonal signs of puberty before: ages m and f
7 yrs in girls 9 yrs in boys
Precocious puberty
Usually a GnRH dependent problem, often extreme cases are due to a hypothalamic tumour
Delayed puberty
The lack of appearance of the physical and hormonal signs of puberty
Delayed puberty
Ages and cause
~13 years in girls ~14 years in boys
Occurs when the gonadotrophin signals from the pituitary are inadequate for sex steroid hormone secretion.
Menopause
Age and cause
Definition
The menopause is the ovaries running out of follicles,
50 and 52 years of age
Last natural menstrual bleeding signifies the end of her reproductive life and is referred to as the menopause
Postmenopausal oestrogen production
one year after essentially ceased producing hormones
Oestrogen production reduces to less than one-tenth of previous
Oestrogen (oestrone) arises mainly from production in the stromal cells of adipose tissue.
