Hypothalamic-Pituitary Relationships

Question 1

What is the hypophysial stalk?

Answer 1

Physical connections between the hypothalamus and pituitary gland

Question 2

What occurs with injury to the hypophysial stalk?

Answer 2

Oxytocin and vasopressin can still be released

Damage would prevent the release of hormones to the pituitary from the hypothalamus

Question 3

Due to anatomical location tumors in the pituitary expand and put pressure on what?

Answer 3

The optic nerves

Visual problems and dizziness are often associated with pituitary tumors

Question 4

The connection between the hypothalamus and posterior pituitary is what?

Answer 4

A neural signal

Question 5

Describe the posterior pituitary

Answer 5

Derived from neural tissue
It is a collection of axons and nerve terminals whose cell bodies are located in the hypothalamus (includes the supraoptic nucleus and pareventricular nucleus)

Question 6

What hormones are secreted by the posterior pituitary gland?

Answer 6

ADH (vasopressin) and oxytocin (neuropeptides)

Produced by cell bodies in the hypothalamus but released from the pituitary

Question 7

What connects the anterior pituitary gland to the hypothalamus?

Answer 7

The hypothalamic-hypophysial portal blood vessels
Hormones move through the portal system to the anterior pit in high concentrations allowing for rapid response by the pituitary through the release of their own tropic hormones

Question 8

What are the different hormone families?

Answer 8

ACTH family
TSH, FSH and LH family
GH and prolactin fam

Question 9

What is the ACTH family?

Answer 9

Corticotrophs that secrete ACTH

Question 10

What is the TSH, FSH and LH family?

Answer 10

Composed of two subunits: have the same alpha subunit in structure but differ in beta subunits
Thyrotrophs: secrete TSH
Gonadotrophs: secrete FSH and LH

Question 11

What is the GH and prolactin family?

Answer 11

Somatotrophs: secrete GH
Lactotrophs: secrete prolactin
Very similar to each other in aa sequence

Question 12

What is a primary endocrine disorder?

Answer 12

Associated with altered hormone levels due to defects in the peripheral endocrine gland (ex. Thyroid gland)

Question 13

What is a secondary endocrine disorder?

Answer 13

Associated with altered level of hormones due to defects in the pituitary gland

Question 14

What is a tertiary endocrine disorder?

Answer 14

Associated with altered levels of hormone due to defects in the hypothalamus

Question 15

Describe the secretion of GnRH

Answer 15

Released from the hypothalamus in a pulsatile fashion which is necessary for the normal function of the gonadotropins and secretion of LH and FSH
Acts on gonadtrop cells in the ant pituitary

Question 16

What is the role of LH and FSH in the testes?

Answer 16

LH stimulates Leydig cells for production of testosterone in testes
FSH acts on Sertoli cells and stimulates them to be responsive to androgens which aids in spermatogenesis

Question 17

Describe the negative feedback that can occur from the testes

Answer 17

Sertoli cells secrete inhibin which inhibits LH and FSH from the ant pituitary
Testosterone has a negative feedback at the hypothalamus and ant pituitary decreasing LH (ant pituitary) or GnRH release (hypothalamus)

Question 18

What is the role of LH and FSH in the ovaries?

Answer 18

LH acts on theca cells to produce androgens which are converted into estrogen in granulosa cells
FSH acts on granulosa cells to induce synthesis of estrogens which allow for follicle development

Question 19

Describe the negative feedback that can occur from the ovaries

Answer 19

Granulosa cells produce inhibin to regulate FSH levels from the ant pituitary
Progestins and estrogens can have negative feedback at the level of GnRH, FSH, and LH secretion
Mid cycle estrogen becomes a positive influence on hormone secretion

Question 20

What is acromegaly?

Answer 20

Rare disorder characterized by excess growth of ST, cartilage and bones in the face, hands and feet
Produces large thickened fingers/toes; hats, rights and shoes will feel too tight; gradual change in facial features
Due to excessive GH which can also decrease sensitivity of peripheral tissues to insulin and leads to an increase in blood glucose and produces compensatory hyperinsulinemia

Question 21

Describe the fluctuation of GH throughout the day

Answer 21

GH secretion fluctuates throughout the day with the highest secretion occurring during sleep
Sleep disturbances disturb GH secretion
Peaks with exercise (or even stress)

Question 22

Describe GH secretion throughout life

Answer 22

GH is secreted throughout life with a large spike during puberty and a decline shortly after
Stays constant throughout adult life and decreases in senescence

Question 23

What factors will stimulate release of GH?

Answer 23

Fasting/hunger/starvation, hypoglycemia, hormones of puberty, exercise, sleep and stress

Question 24

What are the direct actions of GH?

Answer 24

Stimulate response in bone and muscle, growth of cells (hypertrophy), increase in cell numbers (hyperplasia), increased cell metabolism (increase in glycogen and fat breakdown which allows for increased energy and protein synthesis)

Question 25

What are the indirect actions of GH?

Answer 25

Produces IGF-1 which effects almost every cell type in the body to cause proliferation and growth (hypertrophy and hyperplasia), and increase metabolic function of cells

Question 26

Gigantism occurs due to what?

Answer 26

Excess GH before closure of the bone epiphyses due to IGF1 stimulated long bone growth

Question 27

Acromegaly occurs with excess GH after what?

Answer 27

Closure of the bone epiphyses due to promotion of growth of deep organs and cartilaginous tissue

Question 28

Describe GH insensitive (a primary endocrine disorder)

Answer 28

Liver is not responsive to GH and an increase in GH levels occur Prevents the production of IGF-1 which means it loses its negative feedback on GH Feedback lost means hormone levels are not regulated High GH, low IGF-1

Question 29

What will be seen with a secondary deficiency in GH?

Answer 29

GH is not being produced or released from pituitary gland | Results in decreased levels of IGF as well

Question 30

What will occur with a tertiary deficiency of GH?

Answer 30

GHRH is not being produced or released | Results in decreased levels of IGF as well

Question 31

Describe the effects of GH during the fed state

Answer 31

Fed state = increased carb intake meaning increased blood sugar and adequate insulin + increased protein intake meaning adequate aa availability —> Liver will produce IGF-1 —> mitogenesis, lipolysis and cell differentiation

Question 32

Describe the effects of GH during unfavorable growth conditions

Answer 32

Unfavorable conditions = increased carb intake but decreased protein intake —> GH is inhibited and liver will not produce IGF-1 —> lipogenesis and carb storage —> weight gain

Question 33

Describe the effects of GH in a fasted state

Answer 33

Decreased carb and protein intake —> peripheral metabolism shifts to lipid as energy source —> GH levels increase and liver will produce IGF-1 —> lipolysis, ketogenic metabolism and diabetogenic GH promotes lipolysis but can also promote insulin insensitivity GH raises blood glucose by decreasing peripheral glucose uptake and stimulating hepatic gluconeogenesis

Question 34

What is the diabetogenic effect of GH?

Answer 34

Increase in blood glucose concentration which causes insulin resistance Decreased glucose uptake and utilization by target tissues Increased lipolysis in adipose tissue Results in increased insulin levels

Question 35

What are some metabolic functions of GH?

Answer 35

Increased protein synthesis and organ growth through increased uptake of amino acids which stimulates synthesis of DNA, RNA and protein (mediated by somatomedins) Increases metabolism of cartilage forming cells and chondrocyte proliferation (linear growth)

Question 36

IGF-1 can have a positive feedback effect on what?

Answer 36

GHIH | But negative on GH

Question 37

Describe the secretion of prolactin

Answer 37

Secreted by lactotrophs Production and secretion highly associated with pregnancy Secretion is pulsatile and is under tonic inhibition by dopamine

Question 38

What is the function of prolactin?

Answer 38

Mammary gland growth and stimulates/maintains production of milk in pregnancy and lactation

Question 39

What negative feedback effects can prolactin have?

Answer 39

Can have negative feedback effects on GnRH in the hypothalamus Can cause lactational amenorrhea meaning women who are lactating have abnormal/absent menstrual cycles and it causes a decreased production of LH and FSH altering the follicle cycle

Question 40

How is oxytocin produced?

Answer 40

Produced as prepro-oxytocin in hypothalamus —> will be cleaved and packed into vesicles —> pro-oxyphysin —> travels down neuronal axon and becomes modified —> mature oxytocin by the time it reaches the pituitary Stored in vesicles until it is reached

Question 41

What are the two major functions of oxytocin?

Answer 41

Milk ejection and uterine contraction

Question 42

Describe the effects oxytocin has on milk ejection

Answer 42

Milk let down: stimulates contraction of myoepithelial cells lining milk ducts Major stimulus: suckling but also sight, sound or smell of an infant

Question 43

Describe the effects of oxytocin on uterine contraction

Answer 43

Stimulated by dilation of the cervix or orgasm | Creates positive feedback loop