HPG Axis Flashcards
What does successful reproduction require?
- Fertilisation
- Support of conceptus, embryo, and fetus
- Birth at the right time
- Support of the neonate
What is crucial to all the steps of successful reproduction?
Hormones of the hypothalmic-pituitary-gonadal (HPG) axis
What does the output of the hypothalamus-pituitary unit regulate the function of?
- Thyroid
- Adrenals
- Reproductive glands
What does the hypothalamic-pituitary unit control?
- Somatic growth
- Lactation
- Milk secretion
- Water metabolism
What does the hypothalamus always produce, regarding hormone cascades?
A releasing hormone that is specific to the hormone cascade that it follows
What are the common features of the releasing hormones produced by the hypothalamus?
- Secretion in pulses tied to internal biological clock
- Act on specific membrane receptors
- Transduce signals via second messengers
- Stimulate release of one or more pituitary hormones
- Stimulate synthesis of pituitary hormones
- Stimulates hyperplasia and hypertrophy of target cells
- Regulates its own receptor
Does the hypothalamus produce any hormones other than releasing hormones?
No
Give 7 hypothalamic releasing hormones
- Corticotrophin releasing hormone
- Thyrotropin releasing hormone
- Growth hormonne releasing hormone
- Somatostatin
- Gonadotropin releasing hormone
- Prolactin releasing hormone
- Prolactin inhibiting hormone
What is the effect of corticotrophin releasing hormone on the pituitary?
Stimulates ACTH release
What is the effect of thyrotropin releasing hormone on the pituitary?
Stimulates TSH and prolactin secretion
What is the effect of growth hormone releasing hormone on the pituitary?
Stimulates GH secretion
What is the effect of somatostatin on the anterior pitutiary?
Inhibits GH (and other hormone) secretion
What is the effect of gonadotrophin releasing hormone (GnRH) on the pituitary?
Stimulates LH and FSH secretion
What is the effect of prolactin releasing hormone on the pituitary?
Stimulates PRL secretion
What is the effect of prolactin inhibiting hormone on the pituitary?
Inhibits PRL secretion
What is the pituitary gland also known as?
Hypophysis
Where does the pituitary gland lie?
In depression of base of skull known as pituitary fossa, or sella turcica
What does the pituitary gland resemble in terms of size and shape?
A bean
What seperates the anterior and posterior pituitary?
Lumen of Rathke’s pouch
What is the anterior pituitary also known as?
Adrenohypophysis
Is the adrenohypophysis made of nervous tissue?
No
How is the adrenohypophysis connected to the hypothalamus?
By the superior hypophyseal artery
What is the anterior pituitary made up of?
Collection of hormone producing glandular cells
What are the hormone producing cells of the anteiror pituitary under the control of?
The hypothalamus
How does the hypothalamus control the hormones produced by the anterior pituitary?
The hypothalamus tells the pituitary which hormone is needed with specific releasing hormone
What are the cell types of the anterior pituitary?
- Thyrotrophic cells
- Mammotrophic cells
- Corticotrohic cells
- Somatotrophic cells
- Gonadotrophic cells
- Pars intermedia cells
What hormone do thyrotrophic cells produce?
Thyroid stimulating hormone
What does thyroid stimulating hormone act on?
The thyroid gland
What hormone do mammotrophic cells produce?
Prolactin
What does prolactin act on?
- Mammary glands
- Testes
What hormone do corticotrophic cells produce?
ACTH
What does ACTH act on?
Adrenal cortex
What hormone do somatotrophic cells produce?
Growth hormone
What does growth hormone act on?
All body tissues, especially;
- Bone
- Muscle
- Connective tissue
What % of AP cells are gonadotrophic cells?
5-10%
What hormones do gonadotrophic cells produce?
- FSH
- LH
What do FSH and LH act on?
Gonads- testes and ovaries
What hormone do the pars intermedia cells produce?
Melanocyte-stimulating hormone (MSH)