The Hypothalamus-pituitary Axis Flashcards
1
Q
What is endocrine secretion?
A
Some hormones diffuse directly into capillaries to act on distant target organs
2
Q
What is paracrine secretion?
A
Others are secreted and act more locally
3
Q
What is autocrine secretion?
A
Glands which act on themselves
4
Q
What capillaries surround endocrine glands?
A
Fenestrated capillaries
5
Q
What are the major endocrine organs?
A
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid gland
Thymus gland
Adrenal glands
Pancreas
Ovary
Testis
6
Q
What are the three factors which control hormone release for the endocrine glands?
A
Humoral
Neural
Hormonal
7
Q
Example of humoral control?
A
Calcium control of secretion of parathyroid
8
Q
Example of neural control?
A
SNS fibres controlling release of adrenal medulla to secrete catecholamines
9
Q
Example of hormonal control?
A
Hypothalamus releases hormone which causes stimulation of anterior pituitary gland
10
Q
What are the main hormones in the adrenal cortex/medulla?
A
Glucocorticoids
Mineralocorticoids
Catecholamines
11
Q
What are the main hormones in the thyroid?
A
Thyroid hormone
Calcitonin
12
Q
What are the main hormones in the parathyroids?
A
PTH
13
Q
What are the main hormones in the pancreas?
A
Insulin
Glucagon
Pancreatic polypeptide
Somatostatin
14
Q
What are the main hormones in the GI tract?
A
CCk, GIp, GLP1&2, glucentin, gastrin
15
Q
What are the main hormones in pineal?
A
Melatonin
16
Q
What are the main hormones in the thymus
A
Thymopoietin
17
Q
What are the main hormones in the gonads?
A
Sex steroids
Inhibins
Activins
18
Q
What are the main hormones in the heart?
A
Natriuretic peptides
ANP
BNP
19
Q
What are the main hormones in the liver?
A
Insulin-like growth factors
Leptin
Angiotensin
20
Q
What are the main hormones in the kidney?
A
Erythropoietin
Renin
21
Q
What are the main hormones in the adipose tissue?
A
Leptin
22
Q
What is the pituitary gland enclosed in?
A
Bony sella turcica of the sphenoid
23
Q
What is the pituitary gland related to?
A
Cavernous sinus
24
Q
Where does the pituitary gland lie?
A
Immediately posterior to the optic chiasma and sphenoid sinus
25
What are the two lobes of the pituitary gland?
Anterior and posterior
26
What are the three parts of the anterior pituitary?
Pars anterior
Pars tuberalis
Pars intermedia
27
What s the derivative of paris intermedia?
Rathke's pouch
28
What is contained in pars intermedia?
May contain colloid-filled, epithelial lined follicles
Numerous basophilic cells
29
Where does the anterior pituitary grow?
Up-growth of epithelium from the oral cavity (rathke's pouch)
30
Where does the posterior pituitary grow?
Down-growth from the infundibulum in the brain
31
What occurs in week 8 of pituitary growth?
Rathke's pouch loses contact with the oral cavity
32
What can occur in Rathke's pouch?
Craniopharyngioma slow growing tumours may develop along the track of Rathke's pouch
33
What are the two stains in the anterior pituitary gland?
Chromophils- take up the stain; acidophils and basophils
Chromophobes- do no take stain
34
What connects the hypothalamus to the pituitary gland?
Pituitary stalk
35
What are the nuclei of the hypothalamus?
Preoptic nuclei
Suprachiasmatic nuclei
Paraventricular nuclei
Dorsomedial nucleus
Posterior nucleus
Ventromedial nucleus
Supraoptic nucleus
Arcuate nucleus
Infundibular nucleus
36
What runs in the pituitary stalk?
Hypothalamo-hypophyseal tract
Primary plexus of hypophyseal portal system
37
What converges on the hypothalamo-hypophyseal tract?
Axons from the hypothalamus nuclei to the posterior pituitary
38
What artery supplies the posterior pituitary capillary bed?
Inferior hypophyseal artery
39
What are herring bodies?
Herring bodies or neurosecretory bodies are structures found in the posterior pituitary. They represent the terminal end of the axons from the hypothalamus, and hormones are temporarily stored in these locations
40
What artery feeds the pituitary stalk and base of hypothalamus capillary bed?
Superior hypophyseal artery
41
What is the median eminence?
The median eminence is the structure at the base of The hypothalamus where hypothalamic-releasing and –inhibiting hormones converge onto the portal capillary system that vascularizes the anterior pituitary gland
42
What connects the anterior pituitary to the median emminence?
Long and short portal veins
43
What are the cells called in the AP?
Trophic cells
44
What are the neurohormones that control secretions from the anterior pituitary?
Thyrotropin releasing hormone
Corticotropin releasing hormones
Growth hormone-releasing hormone
Somatostatin/ growth hormone releasing hormone
Gonadotropin-releasing hormone
Prolactin releasing factor
Prolactin release inhibiting factor
45
What are the neurohormones that control secretions from the posterior pituitary?
Vasopressin/ ADH
Oxytocin
46
Function of trophic hormones?
Primary actions on other endocrine glands
47
What ar ethe trophic hormones of the AP?
TSH
ACTH
LH and FSH
48
What hormones released from AP target peripheral cells?
GH
PL
MSH
49
What types of cells is TSH?
basophils
50
What types of cells is ACTH?
basophils
51
What type of cells is LH naf FSH?
basophils
52
What type of cells are GH?
Acidophils
53
What type of cells are PL?
Acidophils
54
What type of cells are mSH?
basophils
55
Describe the pathway of growth hormone release and inhibition from the pituitary gland?
Neurosecretory cells in the arcuate nucleus secrete growth hormone-releasing hormone GNRH that reaches the somatotrophs ia the hypophyseal portal blood supply
Cells in the periventricular region release somatostatin, a hormone that is a potent inhibitor of growth hormone GH secretion, into the portal blood supply
GNRH causes somatotrophs to synthesize and release GH
Somatostatin inhibits the release of GH by somatotrophs
56
Describe the mechanism of GHRH?
GHRh binds to receptor
This activates stimulating G-protein which dissociatives and the alpha subunit and goes on to stimulate adenylate cyclase
Adenylate cyclase forms cAMP to form PKA which activates calcium channel to cause depolarisation
This depolarisation causes exocytosis of GH
57
Describe mechanism of somatostatin?
Binds to receptor
Inhibiting G-protein , stops production of cAMP and therefore depolarisation
58
Describe the feedback inhibition of GH release?
GH stimulates secretion of IGF-1 from peripheral target tissue
IGF-1 then directly inhibits GH release by suppressing the somatotrophs
IGF-1 indirectly inhibits GH releas eby suppressing GNRH release from arcuate nucleus in the hypothalamus
IGF-1 indirectly inhibits GH release by increasing secretion of somatostatin from nucleus in the periventricular region
GH inhibits its own secretion via short loop feedback on somatotrophs
59
What rhythm of release does GH follow?
Circadian
Growth hormone at highest during sleep
60
What are the direct effects of GH?
Produce insulin-like growth factors from the liver
Anti-insulin actions
61
What are the indirect IGF effects from GH?
Increased cartilage formation and bone growth
Increased general protein synthesis and cell growth/division
62
What are the direct anti-insulin effects from GH?
Increased lipolysis in adipose tissue
Increased blood glucose
Both due to decreased glucose uptake in muscle and adipose tissue
63
Whata re the physiological consequences of GH release?
Increase linear growth and lean body mass
Vital importance for normal post-natal development and rapid growth through puberty maintenance of protein synthesis and tissue functions in adults
64
What are the pathologies associated with GH deficiency?
Dwarfism in children
65
What are the pathologies associated with GH excess before puberty?
Gigantism- due to excess stimulation of epiphyseal plates
66
What are the pathologies associated with GH excess after puberty?
Periosteal bone growth causing enlarge hand, jaw and foot size
Soft tissue growth leading to enlargement of the tongue and coarsening of facial features
Insulin resistance and glucose intolerance
67
What do you treat GH excess with after puberty?
Long-acting somatostatin
68
Physical signs of gigantism?
Gradual enlargement of the hands and feet
Rapid growth
Swelling of soft tissue
Skin tags
Muscle weakness and fatigue
Skin changes
Hirsutism
Coarsening of facial features
69
Other symptoms of gigantism?
Arthralgia
Amenorrhea
Hyperhidrosis
Sleep apnea
Headaches
Paresthesia
Loss of libido
Hypertension
Thyroid disorders
Visual field defects
70
What is the axis to form oestrogen and testosterone?
GNRH from hypothalamus
FSH and LH from anterior pituitary
Acts on gonads and form hormones
71
Axis of thyroxine and triiodothyronine?
TRH from hypothalamus
TSH from anterior pituitary
Thyroid
72
Axis of breast milk production and developent?
TRH from hypothalamus
Prolactin from AP
Breasts
73
Axis of cortisol?
CRH from hypothalamus
ACTH from AP
Adrenal cortex- cortisol
74
What hormones are released from the PP?
Arginine vasopressin or ADH
Oxytocin
75
Action of ADH?
Antidiuretic hormone stimulates water reabsorption by stimulating insertion of "water channels" or aquaporins into the membranes of kidney tubules. These channels transport solute-free water through tubular cells and back into blood, leading to a decrease in plasma osmolarity and an increase osmolarity of urine
76
Action of oxytocin?
The two main actions of oxytocin in the body are contraction of the womb (uterus) during childbirth and lactation. Oxytocin stimulates the uterine muscles to contract and also increases production of prostaglandins, which increase the contractions further
77
What signals for ADH release?
INcreased blood osmolality
Decreased blood volume
RAAS system producing angiotensin II
78
Where are osmoreceptors?
Brain
79
Where are volume receptors?
Carotid
Aorta
Left atrium
80
Where is ADH produced?
Synthesized in neurosecretory cells within the supraoptic nucleus and paraventricular nucleus
81
Where is oxytocin produced?
Hypothalamic neurons in the paraventricular and supraoptic nuclei
82
Describe the structure of oxytocin in the PP?
Bound to glycoproteins it is carried in the axons to the PP where it is stored in vesicles in th eexpandaded ends of the axons (herring bodies)
83
What is the hypothalamic control of milk production and ejection?
Stimulus from suckling travels from breast through the spinal cord to the hypothalamus
Neurons from the spinal cord inhibit dopamine release from the arcuate nucleus. The decreased level of DP removes the inhibition that DA normally produces on lactotrophs in the AP, leading to prolactin release. Prolactin stimulates milk production in the breast
Neurons from the spinal cord also stimulate the production and release of oxytocin from the paraventricular and supraoptic nuclei. Oxytocin is released in the PP and into the systemic blood, where it then makes its way to the breast and myoepithelial cells
Neurons from the spinal cord inhibit neurons in the arcuate nucleus and preoptic area of the hypothalamus, causing a fall in GNRH production. The reduced stimulation of gonadotrophs inhibits the ovarian cycle
84
Where is the pineal gland?
Lies in the midline in the posterior part of the roof of the 3rd ventricle
85
What are the connections from the pineal gland?
Pinealocytes have neural connection with the hypothalamus
86
What is the function of the pineal gland?
In darkness secretes melatonin from tryptophan
Regulates circadian rhythms
Regulates reproductive processes including the onset of puberty
Effects on aging and regulation of the immune system
87
How does pineal gland come up in x-ray?
Over time it accumulates calcium phosphate which is visible in the mid line on x-rays and other scans
