Reproductive system 2 Flashcards
The Endocrine System hormones
- Collection of glands located throughout the body that manufacture and secrete hormones to regulate physiological function
- Produced by ductless glands within the endocrine system
Major endocrine gland
- Adrenal glands
- Hypothalamus
- Ovaries and testes
- Pancreas
- Thyroid and parathyroid
- Pineal gland
- Pituitary gland
- Thymus gland
Classes of hormones
Hormones derived from amino acids
- Dopamine, epinephrine that have a tyrosine precoursor
Classes of hormones
Proteins and peptides
Insulin and growth hormone are examples of protien hormones
Classes of hormones
Hormones derived from lipids
- Prostaglandins are derived from phospholipids
- Steroids derived from cholesterol
- Most RH steroids but stimulated by other classes
Reproductive hormones
Synthesised and secreted Increasing at puberty and normally decreasing in old age
Cholesterol acts as a precoursor for
- Steroid hormones
- Adrenal steroids
- Glucocorticoids
- Mineralcorticoids
Structure of cholesterol
- 4 cycloalkane rings
- Large hydrocarbon chain
- Essential component of cellular membrane
- From diet
Reproductive hormones
- Sex steroids or steroid hormones
- Produced mainly by the gonads (ovaries and testes)
- Some production by placenta, adrenal glands
Classes of Reporductive hormone
- Oestrogens
- Androgens
- Progestogens
- These bind with the respective receptors
Oestrogens
- Oestradiol
- Oestrone
- Oestriol
Androgens
- Testosterone
- 5a-dihydrotestosterone
- Androstenedione
- Dehydroepiandrosterone
Major functions of
reproductive hormones
- Binds to the complementory receptor on target tissue
Primary role of reproductive organs
Maturation of reproductive organs, fertility and pregnancy
Secondary role of reproductive hormones
- Development of physical characteristics
Testes anatomy where is hormone produced?
- Testosterone is produced in Leydig cells
Ovarian anatomy steroid hormone
production
- Ovarian granulosa cells produce oestrogen
Where are androgens produced
Ovarian theca cells
Where is progesterone produced
- placenta - placental syncytiotrophoblasts
- Eventually takes over from corpus luteum
Generic mechanism of action
- Hormones enter cells
- Hormones bind to intracellular receptor
- Conformation change and translocation
- DNA binding
- Gene expression
Regulation of gonadal steroidogenesis
- Regulation via the HPG axis hypothalamus, pituitary and gonad
Hypothalamus
- Small structure at base of forebrain
- Hypothalamus releases GnRH
- Released into blood
- Reach pituitary
Pituitary
- Pea-sized gland located at the base of the
skull ventral to the hypothalamus - Posterior and anterior lobes
- Anterior pituitary contains specialised cells
- GnRH stimulates gonadotropes to
- Produce gonadotrophins
What produces gonadotrophins
- glycoproteins
- FSH (follicular stimulating hormone)
- LH (Lutenising hormone)
- hCG
LH main functions
- In females acts on ovarian follicle inducing ovulation
- Acts on testes producing testosterone
FSH main functions
- In females promotes ovarian follicle development
& oestrogen production - In males it stimulates spermatogenesis in testes
HPG axis (LH)
- Hypothalamus stimulates the GnRH and the fast GnRH pulse causes LH synthesis and secreation
- LH stimulates the steroidogenesis and reproductive hormone synthesis
- Physological effects
HPG axis (FSH)
- Hypothalamus stimulates the GnRH and the slow GnRH pulse causes FSH synthesis and secreation
- FSH stimulates the steroidogenesis and reproductive hormone synthesis
- Physological effects
Negative feedback
Decreases level of signal and maintains homeostasis
Direct negative feedback
- Steroid hormones testosterone/oestrogen decrease secretion of gonadotrophins
Indirect negative feedback
- Steroid hormones inhibit their own production indirectly by inhibiting hypothalamus GnRH
- Decreased pituitary gonadotrophin secretion
- Reduced steroid hormone production
Negative regulation of steroidogenesis
by inhibin
- Protein hormone and in females, released by granulosa cells in response to FSH
- In males, produced by Sertoli cells in response to androgens
- Negative regulator of FSH
Positive feedback
- Leads to an increase in hormone level
- Occurs within follicular phase of uterine cycle
- Oestrogen-induced LH to trigger ovulation
