Session 2 Flashcards
What are the 2 glands that make the Pituitary gland?
Anterior
Posterior
What does the Anterior Pituitary gland arise from?
Rathke’s pouch in the roof of the mouth and then migrates.
It is NOT nervous tissue
What does the Posterior Pituitary gland arise from?
Nervous tissue. It is a neurosecretory gland
What does the Anterior Pituitary gland secrete?
Mainly trophic hormones.
Glycoprotein hormones - FSH, LH, TSH
Polypeptide hormones - GH, ACTH, Prolactin
What cells secrete FSH & LH?
Gonadotrophs
What cells secrete TSH?
Thyrotrophs
What cells secrete GH?
Somatotrophs
What cells secrete ACTH?
Corticotrophs
What cells secrete Prolactin?
Lactotrophs
What does the Posterior Pituitary gland secrete?
ADH
Oxytocin
What controls Anterior Pituitary gland secrete?
Hypothalamus via Releasing hormones
How do Releasing hormones travel to the Anterior Pituitary gland?
Hypophyseal portal circulation (Released from Median eminence –> Anterior Pituitary)
What hormone does the Hypothalamus use to control FSH & LH?
Gonadotrophin releasing hormone (GnRH)
Release is pulsatile (Around once per hour)
What is the effect of GnRH?
Stimulates the Gonadotrophs to secrete FSH & LH.
Response is variable
What is the primary tissue that FSH & LH act on?
Gonads
What does the action of FSH & LH on Gonads cause?
Stimulates the secretion of gonadal steroids that will go on to control other reproductive processes.
What acts as negative feedback on the Hypothalamic-Pituitary-Gonadal axis?
FSH & LH
What is GnRH secretion controlled by?
Neurones that are influenced by;
- Other neurones in the brain (Allows influence of environmental factors)
- Feedback from the gonads
What causes an increase in Inhibin secretion?
Increased Spermatogenesis
Where does Inhibit act?
On the Anterior Pituitary gland
What is the effect of increased Inhibin?
Decrease in FSH secretion, therefore Sertoli cells are stimulated less
How does the Testosterone level vary?
Long term it is constant, but in the short term it varies via a Circadian rhythm
- Peaks in the morning
- Lowest levels in the evening
How can Testosterone be influenced by the environment?
Different stimuli can cause an increase in Testosterone levels
In males, how does Testosterone effect FSH & LH?
It causes the levels to decrease
In females, how does Oestrogen effect FSH & LH?
Normal levels = Decrased FSH & LH
High levels = Increased FSH & LH
In males, how does Testosterone effect GnRH?
Decreases its secretion
In females, how does Oestrogen effect GnRH?
Normal levels = Decreased GnRH
High levels = Increased GnRH
How does the LH surge occur?
Oestrogen levels are above a threshold point which causes GnRH to be high. This causes lots of GnRH to be secreted in a positive feedback loop
How does Progesterone change the effects of Oestrogen?
When Progesterone is high, the inhibitory effects of Oestrogen are increased. It also prevents positive feedback of the high levels of Oestrogen resulting in no LH surge
What produces Inhibin?
The gametes, therefore the more gametes there are the more Inhibin
Inhibition from the gonads selectively suppresses which hormone?
FSH
No effect on LH
How are the Testosterone levels maintained?
Negative feedback control
How does the negative feedback control effect Testosterone levels?
FSH binds to Sertoli cells (Testicular cells) which are the supporting cells of Spermatogenesis (Which would cause more gametes to form so more Inhibin)
What does LH bind to?
Leydig cells (Testicular cells)
What do Leydig cells secrete?
Testosterone
What does LH promote the secretion of?
Testosterone
What does Testosterone inhibit?
GnRH
