HUBS 191 Lecture 26

Question 1

where is the pituitary gland located

Answer 1

in the fossa of the sella turcica of the sphenoid bone and the base of the brain

Question 2

what controls the pituitary glands function

Answer 2

the hypothalamus

Question 3

what is the anterior pituitary

Answer 3

the anterior lobe of the pituitary is derived from epithelial tissue (therefore is secretes hormones) and accounts for around 75% of the pituitary gland

Question 4

what are the 2 parts of the anterior pituitary gland

Answer 4

pars distils (the larger part)
pars tuberalis which wraps around the infundibulum superiorly

Question 5

what type of tissue is the posterior pituitary composed of

Answer 5

neuroectoderm (neural tissue) mostly composed of supportive glial-type cells called pituicytes

Question 6

what are the 2 parts of the posterior pituitary

Answer 6

pars nervosa (large bulbar portion)
infundibulum (connecting with the hypothalamus of the brain)

Question 7

what is the pars intermedius

Answer 7

the intermediate lobe of the pituitary that lies between the anterior and posterior lobes that may produce melanocyte stimulating hormone but is mostly inactive in adult life

Question 8

different groups of neurons in the hypothalamus can…

Answer 8

1. control secretion of anterior pituitary via releasing hormones (RH) and release inhibiting hormones (RIH)
2. synthesize hormones secreted by the posterior pituitary (transported along axon terminals)
3. directly control secretion of cells in the adrenal medulla (part of the SNS)

Question 9

releasing hormones and/or release inhibiting hormones are secreted from hypothalamus neurons in the region of _____________ at the base of the hypothalamus

Answer 9

median eminence

Question 10

in the hypothalamic - hypophyseal portal system RH/RIH diffuse into the ___________ which is supplied by the _______

Answer 10

first capillary network - superior hypophyseal artery (branch of internal cartoid)

Question 11

in the hypothalamic - hypophyseal portal system _______ carry the RH/RIH to the second capillary network in the _____ pituitary

Answer 11

portal veins - anterior

Question 12

in the hypothalamic-hypophyseal portal system RH/RIH diffuse out of the second capillary ____ and stimulate or inhibit secretion of hormones from _____pituitary cells

Answer 12

plexus/network - anterior

Question 13

blood containing anterior pituitary hormones then drain into _______________ to enter systemic circulation

Answer 13

anterior hypophyseal veins

Question 14

what are the supraoptic nuclei (SON) and paraventricular nuclei (PVN)

Answer 14

neurosecretory cells in the hypothalamus that produce hormones ADH and oxytocin

Question 15

how are ADH and oxytocin transported from the SON/PVN

Answer 15

they are packed into secretory vesicles and transported along axons to terminals in the posterior pituitary where they are stored

Question 16

when are ADH and oxytocin released from the posterior pituitary

Answer 16

they are released via exocytosis when action potentials arrive at the terminal and diffuse into the capillary plexus of the posterior pituitary

Question 17

what is the capillary plexus of the posterior pituitary supplied and drained by

Answer 17

supplied by the interior hypophyseal arteries
drained by the posterior hypophyseal veins

Question 18

what is oxytocin, where is it synthesised and stored

Answer 18

a peptide hormone synthesised mostly in the PVN and stored in nerve terminals in the posterior pituitary

Question 19

what are the stimuli for release of oxytocin

Answer 19

stretching of the cervix of the uterus during childbirth
infant suckling during breastfeeding

Question 20

what is antidiuretic hormone (ADH), where is it synthesised and stored

Answer 20

a peptide hormone (2 amino acids different from oxytocin), synthesised mostly in neurons of SON and stored in the posterior pituitary

Question 21

what is ADH secreted in response to

Answer 21

an increase in ECF osmolarity

Question 22

how does ADH function in the body

Answer 22

in increase in ECF osmolarity is detected by osmoreceptors (neurons) in the hypothalamus that signal neurosecretory cells triggering APs and release of ADH from terminals in the posterior pituitary. ADH diffuses into the capillary plexus and travels in blood and kidney. binds to receptors on collecting duct cells in kidney and increases water reabsorption

Question 23

what will a decreased ECF osmolarity mean for the secretion of ADH

Answer 23

it will cause a reduction in ADH secretion

Question 24

at high doses what does ADH do

Answer 24

constrict arterioles in the body and increase arterial pressure - hence the alternative name, vasopressin

Question 25

what are the two types of diabetes insipidus

Answer 25

neurogenic and nephrogenic

Question 26

what is the difference between neurogenic and nephrogenic diabetes insipidus

Answer 26

neurogenic is an insufficient ADH secretion which may occur following trauma or injury nephrogenic is when the kidneys don't respond to ADH this is a genetic disease but can also be medication induced

Question 27

what does neurogenic diabetes insipidus cause

Answer 27

large volumes of dilute urine due to reduced water reabsorption by collecting ducts of nephrons in the kidney which leads to dehydration

Question 28

what is syndrome of inappropriate ADH secretion (SIADH)

Answer 28

some medication and drugs such as MDMA can cause/trigger inappropriate release of ADH, coupled with hyperthermia and drinking lots of water this can lead to over hydration

Question 29

in SIADH what can over hydration lead to

Answer 29

hemodilution results in low ECF sodium (HYPOnatremia). water moves along it's osmotic gradient and into cells. brain swelling (cerebral oedema) can result in reduced levels of consciousness, seizures, coma and death in some cases

Question 30

what type of hormone is growth hormone, where is it produced and what causes it's release

Answer 30

a protein hormone produced and secreted by somatotrophs of the anterior pituitary in response to GHRH

Question 31

what does hGH promote

Answer 31

increase size of cells, number of cells (particularly muscle, bone and cartilage).

Question 32

what does hGH do during childhood and adulthood

Answer 32

in childhood it increase growth rate of the skeleton and muscles - in adulthood it helps maintain mass of muscle and bones and promotes healing of injuries and tissue repair.

Question 33

can hGH be produce recombinantly

Answer 33

yes - it can be produced to treat GH deficiency or in sports doping

Question 34

how does hGH exerts it effects

Answer 34

hGH causes liver (and to a lesser extent some other tissues) to form proteins called somatomedins (also known as insulin like growth factors) which mediate growth hormone effects

Question 35

what is the most important somatomedin/insulin like growth factor (IGF)

Answer 35

somatomedin C also known as insulin like growth factor 1 (IGF-1). most (not all) of the growth effects of GH are thought to result from IGF-1 rather than the direct action of GH itself

Question 36

what are the metabolic effects of GH

Answer 36

promotes growth and protein synthesis when nutrition state is favourable switches cell metabolism toward use of lipid as an energy source GH attenuates (weakens) some of insulins actions

Question 37

how does GH promote growth and protein synthesis

Answer 37

it increases amino acid transport and promotes protein synthesis increases cartilage, muscle and bone growth increases cells size and number in many other tissues

Question 38

how does GH switch cell metabolism towards the use of lipid as an energy source

Answer 38

it increases mobilisation of fatty acids from adipose tissue (fasted state) increase use of fatty acids an energy for cells glucose in blood available for cells that are more dependent on it as an energy source

Question 39

how to GH attenuate (weaken) some of insulins actions

Answer 39

less glucose taken up from blood by muscle and adipose tissue increased glucose released into blood by liver

Question 40

how is GH secretion regulated

Answer 40

it is secreted in a pulsate manner with bursts every few hours. dual control via releasing and inhibiting hormones

Question 41

GHRH stimulates GH release I response to factors such as:

Answer 41

deep sleep, low blood glucose, strenuous exercise, fasting or starvation, trauma or stress, testosterone/estrogen

Question 42

GHIH (somatostatin) reduces GH secretion in response to factors such as:

Answer 42

increase blood glucose, increased fatty acids in blood, increase somatomedins in blood, aging

Question 43

lack of GH during childhood can cause - and how is this cured

Answer 43

dwarfism - this may be cured by administration of GH deficiency and Tx if commenced early enough

Question 44

what does excess GH prior to the closure of epiphyseal plates lead to

Answer 44

giantism

Question 45

what does excess GH secretion after epiphyseal plates fuse lead to

Answer 45

acromegaly