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Endocrinology > Introduction to the Hypothalamic-Pituitary Axis - Lecture 3 > Flashcards

Introduction to the Hypothalamic-Pituitary Axis - Lecture 3 Flashcards

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1
Q

Describe the size and shape of the Pituitary gland and its location

A

It is shaped and sized like a lima bean and it sits in a protected pocket of bone connected to the brain by a thin stalk. The bone is part of the Sphenoid.

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2
Q

How many glands make up the Pituitary gland?

A

The Pituitary gland consists of two glands, the Anterior Pituitary and Posterior Pituitary.

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3
Q

What is the name of the stalk that connects the Pituitary gland to the brain?

A

Infundibulum

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4
Q

Describe the Anterior and Posterior Pituitary gland and its tissue types.

A
  • The Anterior Pituitary gland is a true endocrine gland of epithelial origin. Derived from embryonic tissue that formed the roof of the mouth.
  • The Posterior Pituitary gland is an extension of neural tissue of the brain, basically and extension of the brain.
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5
Q

Name the two hormones found in the POSTERIOR PITUITARY and describe what kind of hormones they are.

A

OXYTOCIN - controls ejaculation of milk in breast-feeding & contractions of the uterus during labour

VASOPRESSIN (antidiuretic hormone, ADH) - acts on Kidneys to regulate water balance in the body
Both of these hormones are neurohormones.

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6
Q

Where are Oxytocin and vasopressin found?

A

In the PARAVENTRICULAR and SUPRAOPTIC NUCLEI. These are located in the Hypothalamus gland and each hormone is made in a cell body of a neuron.

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7
Q

Does the POSTERIOR pituitary gland make hormones?

A

NO, it does not, only the Anterior Pituitary does.

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8
Q

Describe the pathway of Oxytocin and Vasopressin.

A

the hormones are made and packaged in the cell body of a neuron in the Hypothalamus

the hormones are transported down the nerve cell axons via secretory vesicles to the POSTERIOR pituitary gland

the hormones are stored in the POSTERIOR pituitary gland until they are released into the circulation via exocytosis in response to membrane depolarisation.

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9
Q

Which organs do Oxytocin and Vasopressin act on?

A

VASOPRESSIN acts on the Kidneys to regulate water balance in the body (water reabsorption in the body).

OXYTOCIN controls the ejection of milk during breast feeding and contractions of the uterus during labour and delivery.
Oxytocin may play a role in social, sexual and maternal behaviour too.

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10
Q

Is the POSTERIOR pituitary gland and actual gland?

A

No it is not. It does not synthesise and secrete hormones

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11
Q

Is the ANTERIOR pituitary gland an actual gland?

A

Yes it is, it does synthesise and secrete hormones.

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12
Q

How many physiologically significant hormones does the anterior pituitary gland secrete?

A

6

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13
Q

Name the 6 hormones of the ANTERIOR pituitary gland

A
  1. Prolactin (PRL)
  2. Thyroid stimulating hormone (TSH)
  3. Adrenocorticotrophic hormone (ACTH)
  4. Growth hormone (GH)
  5. Follicle stimulating hormone (FSH)
  6. Luteinizing hormone (LH)
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14
Q

The secretion of all the ANTERIOR pituitary hormones is controlled by what?

A

Hypothalamic neurohormones (hormones from the Hypothalamus)

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15
Q

What is the Portal System?

A

It is a series/system of blood vessels which connects the Hypothalamus with the Anterior pituitary

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16
Q

What is the function of the Portal System?

A

It is to QUICKLY transport and exchange hormones between the Hypothalamus and the Anterior pituitary glands

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17
Q

What are tropic hormones?

A

They are hormones that control the secretion of other hormones, they have other hormones as their target. Their names usually end in ‘tropin’.

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18
Q

What are the target organs of the 6 Anterior pituitary gland?

A
  1. Prolactin (PRL) - Mammary glands
  2. Thyroid stimulating hormone (TSH) - Thyroid gland
  3. Adrenocorticotrophic hormone (ACTH) - Adrenal cortex
  4. Growth hormone (GH) - musculoskeletal system
  5. Follicle stimulating hormone (FSH) - ovaries
  6. Luteinising hormone (LH)
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19
Q

How do the hormones in the Hypothalamus work with the hormones of the Anterior pituitary gland?

A

The neurons in the Hypothalamus secrete RELEASING and INHIBITING hormones into the Portal System

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20
Q

Besides connecting the Hypothalamus and Anterior pituitary, what important reason is the Portal system there for?

A

To avoid dilution of the releasing and inhibiting hormones. They are not secreted into a large area of the blood stream, rather into the small Portal System. This way a small amount of hormone remains concentrated in a tiny volume of portal blood and goes directly to its target. And in this way only a small amount of hormone needs to be made and secreted.

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21
Q

What is the Posterior Pituitary gland?

A

It is an extension of the brain that secretes neurohormones which are made in the Hypothalamus.

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22
Q

What connects the Hypothalamus and the Anterior Pituitary gland?

A

The Hypophyseal Portal System.

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23
Q

What does the Hypothalamus do for the Anterior Pituitary gland?

A

The Hypothalamus secretes different tropic hormones that control the synthesis/release of hormones from the Anterior Pituitary.

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24
Q

List the Hypothalamic, Pituitary hormones and the endocrine targets they act on.

A

Dopamine - inhibiting hormone –> Prolactin –> Breasts

TRH Thyrotropin - releasing hormone –> TSH Thyroid stimulating hormone –> Thyroid gland

CRH Corticotropin - releasing hormone –> ACTH Adrenocorticotropic hormone –> Adrenal Cortex

GHRH (dominant) –> Growth hormone –> Liver

SS Somatostatin (also called Growth Inhibiting hormone GHIH) –> Growth hormone –> LIver

GnRH Gonadotropin - releasing hormone –> FHS & LH –> Endocrine cells of the Gonads

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25
Regarding GH (Growth hormone), how long is the amino acid chain?
191 Amino acid peptide chain
26
What does GH use to travel through the plasma?
A GH binding protein
27
What is GH important for?
For normal growth
28
Do plasma levels of GH decline and if so when?
They do decline soon after attainment of full adult size
29
Is GH a peptide or steroid hormone?
A PEPTIDE hormone
30
Where is GH made and released from?
The Anterior Pituitary gland
31
Which of the two inhibits the release of GH, Somatostatin or GHRH?
Somatostatin (SS)
32
Describe the Negative Feedback of GH.
GH (and IGF's) inhibit GHRH release and stimulates Somatostatin release. And IGF’s inhibit GH release.
33
What parts of the body does GH act on?
Liver, skeletal muscle, other tissues
34
What type of growth do IGF's stimulate?
Bone growth and cartilage growth
35
For what time period is GH essential for?
Childhood and adolescence
36
Regarding stimulating long bone growth, what time period does GH do this?
Prior to the epiphyseal closure.
37
In childhood, what does GH deficiency lead to?
Dwarfism
38
What are the causes of GH deficiency?
Genetic | Damage to Pituitary gland
39
What is used to treat GH deficiency?
Recombinant Human Growth Hormone replacement therapy to replace the normal hormone. Results are not that great.
40
What is the result in GH excess in childhood?
Gigantism. There is no epiphyseal closure so the long bone just keeps growing.
41
Is Gigantism common?
It is rare, approximately 3 cases in a million
42
What causes Gigantism in children?
Pituitary adenoma, which is a tumour on the Pituitary gland
43
Does GH excess affect children or adults?
It affects both
44
What results from an excess of GH in adults?
Acromegaly, which means large extremities. Adults display lengthening of the jaw, growth of the hands and feet and a coarsening of the features.
45
What is the treatment for GH excess?
Somatostatin analogues Dopamine agonist Growth Hormone receptor antagonists Surgery
46
What results from an excess of GH in children?
Gigantism
47
Where is 99% of calcium in the body found?
In the bones
48
What is required to maintain Calcium balance?
Dietary intake should equal Ca2+ loss in the urine and faeces.
49
Where do we get our extracellular fluid calcium from?
1. from diet 2. from Kidney reabsorption 3. and bone - breakdown of bone
50
What are the 3 key hormones that regulate calcium homeostasis?
1. Parathyroid hormone PTH (from Parathyroid gland) 2. Calcitriol (synthesised in Kidney) - Vitamin D 3. Calcitonin (synthesised in Thyroid gland)
51
Where is Parathyroid hormone PTH synthesised and released from?
From the Parathyroid glands.
52
What regulates the release of Parathyroid hormone?
The Plasma calcium concentration
53
What stimulates the release of PTH?
The decrease in Calcium
54
What is the name of the receptor that INHIBITS the release of PTH?
CaSR - calcium sensing receptor
55
What percentage of body calcium is stored in bone?
99%
56
Is the body's 1% calcium found outside of the bones important? Explain the yes or no.
The 1% calcium outside of the bones is critical to physiological functioning in the body.
57
What are the actions of the Parathyroid hormone (PTH)?
1. It increases plasma calcium by increased bone resorption by increase renal calcium reabsorption by increasing calcium absorption from the intestine 2. Increases Calcitriol release (Vitamin D)
58
What is Calcitriol and and what is it formed from?
Calcitriol is Vitamin D3 and it is formed from Vitamin D
59
Where is Calcitriol produced?
Made in the Kidneys
60
What stimulates the synthesis of Calcitriol?
The Parathyroid hormone (PTH)
61
Besides the Parathyroid hormone (PTH), is there any other hormone that stimulates the release of Calcitriol?
Prolactin (from the Anterior Pituitary gland) also increases the release of Calcitriol.
62
What is the function of Calcitriol?
The function of Calcitriol is similar to that of PTH, it increases intestinal calcium reabsorption.
63
What is Calcitonin?
It is a hormone which is made in the Thyroid gland.
64
What releases Calcitonin?
INCREASED plasma calcium levels releases Calcitonin. This hormones helps to regulate Calcium homeostasis.
65
Is Parathyroid hormone a peptide or steroid hormone?
A peptide hormone
66
What is the main function of Parathyroid hormone?
To INCREASE plasma Ca2+ concentrations
67
What stimulates the release of Parathyroid hormone?
The decrease of plasma Ca2+ levels
68
What is the plasma Ca2+ levels monitored by?
A Ca2+ sensing receptor located on the cell membrane (CaSR)
69
What type of a receptor is a CaSR?
A GPCR - G-Protein Coupled Receptor
70
Which organs does PTH act on to INCREASE levels of plasma Ca2+?
Bone, Kidneys and Intestine ---> to increase plasma Ca2+ levels
71
Is the Anterior Pituitary gland connected to the brain?
No it is not.
72
Is the Posterior Pituitary gland connected to the brain?
Yes it is by the Infundibulum.
73
Where are Oxytocin and Vasopressin made?
In neural cell bodies located in the hypothalamic paraventricular nucleus - which is a nucleus located in the Hypothalamus
74
Explain how Oxytocin and Vasopressin are synthesised and transported?
They are made in the cell bodies of neurons which sit inside the Infundibulum. They travel down their vesicles through the axons At the terminals they are released into capillaries that are located in the Anterior Pituitary gland. They then go off into blood into the systemic circulation.
75
What is Vasopressin?
It is an anti-diuretic hormone ADH
76
Which glands/organs does Oxytocin act on?
Mammary glands to secret milk in mothers. Uterine muscles for contraction during labour.
77
Which glands/organs does Vasopressin act on?
The Kidney's. It acts on receptors found in Kidney's for water retention in the Kidney's.
78
Explain how the Portal system is used to move hormones from the Hypothalamus to the systemic circulation.
There are neural cell bodies in the Hypothalamus. They are there because hormones are produced there. The hormones are then released into the capillary bed of the Median Eminence which is part of the first series of capillaries. The hormones then make their way down to the Anterior Pituitary by passing through the Portal blood Vessels which lie between the median eminence and the 2nd series of capillaries which are found in the Anterior Pituitary. The Hormones then act upon the cells that contain the receptors for those particular hormones. When those cells are activated they produce another hormone. That hormone then goes off into the systemic circulation on to its target.
79
What does the Portal system consist of?
Two sets of capillaries and a portal vessel (blood vessels).
80
What are the Hypothalamic releasing factors responsible for?
They influence the release or inhibition of Anterior Pituitary hormones.
81
Of the 6 Anterior Pituitary hormones, which 2 have both releasing and inhibiting factors?
Prolactin - Dopamine inhibits and Oxytocin is thought to release it. Growth Hormone - GHRH releases and Somatostatin (SS) inhibits.
82
Which Hypothalamic hormone stimulates the release of TSH Thyroid stimulating hormone.
TRH - Thyroid releasing hormone from the Hypothalamus
83
Which Hypothalamic hormone stimulates the release of GH?
GHRH - Growth Hormone Release Hormone from the Hypothalamus.
84
Which Hypothalamic hormone stimulates the release of FSH and LH?
GnRH - Gonadotropin Releasing Hormone.
85
Which Hypothalamic hormone stimulates the release of ACTH - Adrenocorticotropin hormone?
CRH - Corticotropin Releasing Hormone.
86
Summarise in 3 steps what the releasing factors produced in the Hypothalamus do.
The releasing factors are produced firstly in the Hypothalamus. Those factors influence specific cells in the Anterior Pituitary to release their specific hormones. Then those hormones act either on glands or target tissue.
87
Which organs does GH act on?
Muscular skeletal, bones and the LIVER.
88
In Hormonal Feedback Loops, which glands can Hormone Y INHIBIT (hormone Y is the hormone produced by the target organ/gland)?
1. It can inhibit Hormone X which is the Anterior Pituitary hormone. 2. It can inhibit the neurohormone produced in the Hypothalamus.
89
In Hormonal Feedback Loops, which hormones can Hormone X INHIBIT?
Hormone X which is the Anterior Pituitary hormone, can inhibit the neurohormone in the Hypothalamus.
90
Regarding Hormonal Feedback Loops, which hormone can ACTH INHIBIT?
Adrenocorticotropic hormone ACTH from the Anterior Pituitary can INHIBIT Corticotropin Releasing Hormone CRH.
91
How does GH travel in the plasma?
It travels through the plasma bound to a GH binding protein.
92
Is GH released in childhood or adulthood?
It is released in both. It is released mainly in children and slows down once we reach our full size. It is continued to be released however throughout adulthood.
93
Where is GH released from?
The Anterior Pituitary.
94
Does GH have inhibiting or releasing factors?
It has BOTH
95
Regarding negative feedback loops, what inhibits GHRH release and what does it stimulate release of?
GH and IGF's INHIBIT the release of GHRS and STIMULATES Somatostatin release. Basically, we already have enough GH so we don't want anymore so we inhibit GHRH and we encourage Somatostatin which inhibits the release of more GH.
96
Does stress and exercise increase or decrease GH secretion?
It INCREASES it.
97
Do Somatostatin and GHRH act in synergism or antagonistically?
ANTAGONISTICALLY
98
What INHIBITS GHRH?
Both GH and IGF's
99
What do GH and IGF's do?
Act on bone and soft tissue growth.
100
What do IGF's act on?
On bone and cartilage growth.
101
When GH acts on the Liver, what does it do this for?
To induce IGF's
102
What does GH act on?
Cartilage growth Increase Blood Glucose Bone and tissue growth Also acts on the Liver to induce IGF's
103
What do IGF's act on?
Cartilage growth Increase Blood Glucose Bone and tissue growth Influences cartilage production
104
Does GH influence cartilage production?
Not directly, but it influences it through IGF's.
105
What is GH essential for?
Normal growth.
106
What does GH stimulate in childhood and adolescence?
Long bone growth
107
Where does bone growth occur in the bone?
Epiphyseal Plate. Once it closes up, the long bone does not get any longer.
108
What happens if you don't have enough GH?
Dwarfism
109
What results from an excess of GH in Adults?
Acromegaly. Bones of fingers, extremities, the jaw continues to grow. Tumours are responsible for this.
110
What are the treatments for Acromegaly?
Somatostatin analogues. Somatostatin is an inhibitor of GH release.
111
Does GH travel alone in the plasma?
It can but it also travels bound with plasma protein. Remember that protein does not filter easily in the Kidney's.
112
Which compartment has a higher concentration of Calcium, intracellular or extracellular?
Extracellular
113
Why is FREE calcium low inside the cell?
The calcium is actually there, stored inside organelles, however it is not available, even though it is there.
114
What happens because of the fact that free calcium is low in the cytoplasm?
This allows Calcium to travel down its concentration gradient which is into the cell.
115
Which 2 hormone stimulate the release of Calcitriol?
The Parathyroid hormone and Prolactin (A. Pituitary)
116
Which of the 2 calcium releasing hormones are the most important out of the 3?
Parathyroid hormone | Calcitriol
117
What is the receptor that Calcium uses?
CaSR - Calcium Sensing Receptor
118
What type of receptor is a CaSR?
A GRCR - G Protein Coupled Receptor
119
What happens when plasma calcium levels decrease?
Parathyroid hormone is released
120
Where are CaSR located?
On the cells of the Parathyroid gland
121
What happens to the CaSR receptors when the plasma calcium concentration is INCREASED?
The CaSR receptor is activated and this INHIBITS the release of Parathyroid hormone. So basically Calcium activates this receptor which reduces the release of more Calcium via the Parathyroid hormone.
122
What results in the CaSR not being activated?
LOW calcium concentrations in the blood.
123
What is the job of Parathyroid hormone?
To INCREASE plasma Calcium levels in the extracellular fluid.
124
How does the Parathyroid gland facilitate plasma calcium INCREASE?
It does it two ways DIRECTLY. It does it one way INDIRECTLY. Directly - increases bone resorption increases calcium reabsorption in Kidney Indirectly - induces the RELEASE of Calcitriol in the Kidney --> which then goes on and absorbs calcium from the GIT after we eat.
125
What is resorption of bone mean.
It is the regulated breakdown of bone to increase plasma calcium levels. The Parathyroid hormone INDUCES this action.
126
In essence, what is Calcitriol and where is it synthesised?
It is Vitamin D3 and it is make by the Kidneys.
127
What is Calcitriol's job?
To increase plasma calcium in the body. Similar to the Parathyroid hormones job.
128
How does Calcitriol absorb calcium in the body? List the direct and indirect ways.
DIRECTLY - it INCREASES the calcium absorbed from the GIT. INDIRECTLY - evidence suggests it does this the same as the Parathyroid hormone. 1. increases bone resorption 2. increases renal calcium absorption
129
What is Calcitriol's MAIN job?
To INCREASE calcium intake from the GIT

Endocrinology (5 decks)

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