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A Physiology > 7.1. The hypothalamus-pituitary gland system. Growth hormone and somatomedins. > Flashcards

7.1. The hypothalamus-pituitary gland system. Growth hormone and somatomedins. Flashcards

1
Q

I. PITUITARY GLAND
1. What are the features and position of pituitary gland?

A
  • Master gland in endocrinology -> produces many hormones and controls the function of the periphery endocrine glands
  • Located in the base of the skull (sella turcica)
  • The pituitary is connected to the hypothalamus via the pituitary stalk (close to optic chiasm)
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2
Q

I. PITUITARY GLAND
2. What is the position of pituitary gland?

A

Located in the base of the skull (sella turcica)

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3
Q

I. Basics
3. What is the Approximal weight of pituitary gland?

A

0,6g in the adult

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4
Q

I. Basics
4. What are the characteristics of Posterior lobe of pituitary (neurohypophysis)?

A
  • Contain axon terminals
  • The paraventricular + supraoptic nuclei in the HT contain
    magnocellular secretory neurons
  • These neurons send their axons to the posterior lobe
    through the pituitary stalk
  • These neurons will produce peptide hormones (ADH + oxytocin), which can be released from the axon terminals into the blood circulation -> neurocrine secretion
    => When there is an AP on the neuron, it will run along the fiber and this will be the stimulus which releases the hormone in the circulation (controlled by CNS)
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5
Q

I. Basics
5. Which are the nuclei contained in neurohypophysis?

A
  • The paraventricular + supraoptic nuclei in the HT contain magnocellular secretory neurons
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6
Q

I. Basics
6. What are the 2 hormones produced by neurohypophysis?

A
  1. Vasopressin (ADH/AVP)
  2. Oxytocin
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7
Q

I. Basics
7. What are the characteristics of vasopressin (neurohypophysis)?

A
  • Role in kidney (absorption in collecting duct)
  • Regulates water balance of the body
  • If ↑concentration in the circulation = vasoconstriction
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8
Q

I. Basics
8. What are the characteristics of oxytocin (neurohypophysis)?

A
  • Stimulates the contraction of the pregnant uterus (contributes to delivery of baby)
  • [oxytocin]↑ -> uterine contraction↑ -> cervix stretch↑ (aids in delivery)
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9
Q

I. PITUITARY GLAND - Anterior lobe of pituitary (adenohypophysis)
9A. What are the characteristics of adenohypophysis?

A
  • Derivative of Rathke’s pouch
  • Highly vascular glands
  • Parvocellular nuclei of the HT produces a variety of hormones
  • Hormone producing cells = acidophilic, basophilic,
    chromophobic cells
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10
Q

I. PITUITARY GLAND - Anterior lobe of pituitary (adenohypophysis)
9B. What are the hormone producing cells of adenohypophysis?

A
  • Hormone producing cells = acidophilic, basophilic,
    chromophobic cells
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11
Q

I. PITUITARY GLAND - Anterior lobe of pituitary (adenohypophysis)
9C. What are the nuclei included in adenohypophysis?

A
  • Parvocellular nuclei of the HT produces a variety of hormones
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12
Q

I. PITUITARY GLAND
10A. What are the 3 hormone families of the pituitary?

A
  1. Growth hormone / prolactin family
  2. Glycoprotein family
  3. Pro-opio-melano-cortin (POMC) family
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13
Q

I. PITUITARY GLAND
10B1. What are the 3 hormones of Growth hormone / prolactin family? Which cells produce them?

A
  1. Growth hormone (GH)
  2. prolactin (PRL)
  3. human chorionic somatomammotropin (hCS)
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14
Q

I. PITUITARY GLAND
10B2. What are the characteristics of growth hormone (GH)?

A

Somatotropic cell -> growth hormone (GH)
- Placenta secretes placental GH, which may suppress GH secretion of the maternal pituitary gland (negative feedback)

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15
Q

I. PITUITARY GLAND
10B3. What are the characteristics of prolactin (PRL)?

A

Mammotropic (lactotrope) cell -> prolactin (PRL)
- Milk production (breast feeding)
- Growth and development of breast
- Most frequent hormone producing pituitary tumor: prolactinoma
+) Causes overproduction of prolactin
+) Gynecomastia: enlargement of breast tissue in males
+) Galactorrhea: spontaneous milk leakage in females

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16
Q

I. PITUITARY GLAND
10B4. What are the characteristics of human chorionic somatomammotropin (hCS)?

A

Placenta secretes human chorionic somatomammotropin (hCS)
- Hormone of highest secreted amount in the human body
- May contribute to ↑ in [glucose] + [AA], but normal pregnancy in its absence

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17
Q

I. PITUITARY GLAND
10C1. What are the main features of hormones in Glycoprotein family?

A

Hormones in this family are composed of 2 subunits:
- α-subunit: identical in every hormone
- β-subunit: is different in every hormone (provides specificity)

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18
Q

I. PITUITARY GLAND
10C2. What are the 3 main hormones of glycoprotein family?

A
  1. thyroid stimulating hormone (TSH)
  2. Follicle stimulating hormone (FSH)
  3. Luteinizing hormone (LH)
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19
Q

I. PITUITARY GLAND
10C3. Which cell produces thyroid stimulating hormone (TSH)?

A

Thyrotropic cell

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20
Q

I. PITUITARY GLAND
10C4. Which hormones are produced by gonadotropic cell? What are the characteristics of these hormones?

A
  • Follicle stimulating hormone (FSH):
    +) Ovary (granulosa cells): stimulates development of follicles
    +) Testis (Sertoli cells): regulates spermatogenesis
  • Luteinizing hormone (LH):
    +) Ovary (theca cells)
    +) Testis (Leydig cells)
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21
Q

I. PITUITARY GLAND
10D1. What are the characteristics of hormones Pro-opio-melano-cortin (POMC) family?

A
  • POMC a precursor polypeptide (prohormone) with 241 AA residues
  • POMC is cleaved at different sites to give rise to multiple peptide hormones

POMC: -pro = has to be cleaved, -opio (β-endorphin) = opiate, -melano (α-MSH) = melanocyte-stimulating hormone, -cortin (ACTH) = cortex of adrenal gland / adrenocorticotropic hormone

22
Q

I. PITUITARY GLAND
10D2. What are the 2 main hormones of Pro-opio-melano-cortin (POMC) family?

A
  1. adrenocorticotropic hormone (ACTH)
  2. α-melanocyte stimulating hormone (α-MSH)
23
Q

I. PITUITARY GLAND
10D3. What are the characteristics of adrenocorticotropic hormone (ACTH)?

A

Corticotropic cell -> adrenocorticotropic hormone (ACTH)
- Major effect is on the adrenal cortex, especially the fasciculate layer
- Fasciculate layer produces glucocorticoids (most important: cortisol)
- β-endorphin: neurotransmitter + hormone associated with hunger, sexual behavior etc.

24
Q

I. PITUITARY GLAND
10D4. What are the characteristics of α-melanocyte stimulating hormone (α-MSH)?

A
  • responsible for pigmentation of the skin + production/release of melanin in hair
  • equivalent to the first 13 AAs of the ACTH -> related closely
  • serious ACTH overproduction -> skin pigmentation (Addison’s disease) LIFE THREATHENING!
    => Destruction of the adrenal gland -> no cortisol produced = ↑ACTH (person cannot survive)
25
Q

I. PITUITARY GLAND - Regulation of pituitary hormone secretion
11A. What are the 2 most important regulators of pituitary hormone secretion?

A
  1. Hypothalamus
  2. Negative feedback from the periphery
26
Q

I. PITUITARY GLAND - Regulation of pituitary hormone secretion
11B. Why is hypothalamus the most important regulators of pituitary hormone secretion?

A
  1. Releasing hormones (RH)
  2. Release-inhibiting hormones (RIH) (through the special portal circulation of the pituitary)
27
Q

I. PITUITARY GLAND - Regulation of pituitary hormone secretion
11C. Why is Negative feedback from the periphery the most important regulators of pituitary hormone secretion?

A

By a hormone produced in the target glands (tissues)

28
Q

I. PITUITARY GLAND
12. How is portal circulation of the pituitary occur?

A
  • The HT contains cell bodies of neurons which produce RH + RIH
  • These cell bodies send their axons to the median eminence, where we have a capillary bed
  • Here, the neurons secrete their products into the circulation
  • There is a 2nd capillarization in the adenohypophysis -> connected in series -> portal circulation
29
Q

I. PITUITARY GLAND - Hormones from the HT affecting the adenohypophysis
13A. What are the hormones from the HT that affect the adenohypophysis?

A
  1. Growth hormone releasing hormone (GHRH)
  2. Somatostatin (SST)
  3. Thyrotropin releasing hormone (TRH)
  4. Gonadotropin releasing hormone (GnRH)
  5. Corticotropin releasing hormone (CRH)
  6. Dopamine
30
Q

I. PITUITARY GLAND - Hormones from the HT affecting the adenohypophysis
13B. How is Growth hormone releasing hormone (GHRH) affecting the adenohypophysis?

A

Growth hormone releasing hormone (GHRH) uses a Gs GPCR to stimulate release of growth hormone (GH).
- Somatostatin (SST) uses a Gi GPCR to decrease the production of GH

31
Q

I. PITUITARY GLAND - Hormones from the HT affecting the adenohypophysis
13C. How is Somatostatin (SST) affecting the adenohypophysis?

A

Somatostatin (SST) uses a Gi GPCR to decrease the production of GH

32
Q

I. PITUITARY GLAND - Hormones from the HT affecting the adenohypophysis
13D. How is Thyrotropin releasing hormone (TRH) affecting the adenohypophysis?

A

Thyrotropin releasing hormone (TRH) uses a Gq receptor to activate thyroid stimulating hormone (TSH).

33
Q

I. PITUITARY GLAND - Hormones from the HT affecting the adenohypophysis
13E. How is Gonadotropin releasing hormone (GnRH) affecting the adenohypophysis?

A

Gonadotropin releasing hormone (GnRH) mostly uses a Gq receptor (and less-so a Gi) to stimulate the release of luteinizing hormone (LH) and follicle stimulating hormone (FSH)
- After puberty, this release must be pulsatile to function correctly without desensitization

34
Q

I. PITUITARY GLAND - Hormones from the HT affecting the adenohypophysis
13F. How is Corticotropin releasing hormone (CRH) affecting the adenohypophysis?

A

Corticotropin releasing hormone (CRH) uses a Gs receptor to stimulate adrenocorticotropic hormone (ACTH), which is the major stimulator for cortisol production in the adrenal gland,

35
Q

I. PITUITARY GLAND - Hormones from the HT affecting the adenohypophysis
13G. How is Dopamine affecting the adenohypophysis?

A

Dopamine inhibits the anterior lobe secretion of prolactin.
- Prolactin is normally secreted constitutively from the anterior lobe (does not require any stimulus), but then prolactin is downregulated by dopamine via a D2 (Gi) receptor -> TRH, VIP and a newborn baby suckling all stimulate the release of prolactin.

36
Q

II. HYPOTHALAMUS-PITUITARY GLAND SYSTEM - Growth hormone (GH)
1A. How is the regulation of GH occur?

A
  • GH has a pulsatile secretion pattern about every 2 hours and has its highest concentration during sleep (lowest during day). GH is also more heavily secreted in
    childhood/puberty
  • GH is secreted in response to: GHRH, hypoglycemia (↓[glucose]), fasting (ghrelin), sleep, stress, physical exercise, basic amino acids and α2 adrenergic agonist
    (clonidine)
  • Secretion of GH is inhibited by: somatostatin, hyperglycemia (↑[glucose]), increased
    [FFA] in blood
37
Q

II. HYPOTHALAMUS-PITUITARY GLAND SYSTEM - Growth hormone (GH)
1B. GH is secreted in response to ….

A
  • GH is secreted in response to: GHRH, hypoglycemia (↓[glucose]), fasting (ghrelin), sleep, stress, physical exercise, basic amino acids and α2 adrenergic agonist
    (clonidine)
38
Q

II. HYPOTHALAMUS-PITUITARY GLAND SYSTEM - Growth hormone (GH)
1C. Secretion of GH is inhibited by ….

A

Secretion of GH is inhibited by: somatostatin, hyperglycemia (↑[glucose]), increased [FFA] in blood

39
Q

II. HYPOTHALAMUS-PITUITARY GLAND SYSTEM - Growth hormone (GH)
2. The negative feedback control of GH is due to… (3 REASONS)

A
  1. GHRH inhibiting its own secretion from the hypothalamus
  2. The somatomedin IGF-1 (insulin-like growth factor 1, produced in the liver as a result of GH) that comes back to inhibit the release of GH from the adenohypophysis
  3. GH and IGF-1 activating the release of somatostatin, thus, inhibiting GH from being released
40
Q

II. HYPOTHALAMUS-PITUITARY GLAND SYSTEM - Growth hormone (GH)
3. How does GH receptor (cytokine receptor) signaling occur?

A
  • When GH binds to a receptor, it activates the JAK2 kinase and/or Grb2-SOS-Ras ( -> causes MAP kinase cascade -> gene expression)
  • JAK2 pathway is more important, and these are cytokine signaling pathways using the tyrosine kinase mechanism
  • When the JAK2 is activated, the major substrate to be phosphorylated is STAT5, which then dimerize, translocates to the nucleus, and this causes increased gene expression of certain genes (production of somatomedins such as IGF-1 and IGF-2, GH etc.)
41
Q

II. HYPOTHALAMUS-PITUITARY GLAND SYSTEM - Growth hormone (GH)
4A. What are the 2 main effects of GH

A
  1. Acute (metabolic)
  2. Chronic – GH
42
Q

II. HYPOTHALAMUS-PITUITARY GLAND SYSTEM - Growth hormone (GH)
4B. What does Acute (metabolic) – GH do?

A

Acute (metabolic) – GH will directly cause an increase of:
- ↑glucagon secretion and ↓glucose tissue uptake -> ↑[glucose]plasma
- Lipolysis (by targeting adipocytes) -> ↑[FFA]plasma
- Amino acid uptake of tissues↑, protein synthesis↑

43
Q

II. HYPOTHALAMUS-PITUITARY GLAND SYSTEM - Growth hormone (GH)
4C. What does Chronic – GH do?

A

Chronic – GH indirectly causes growth (through somatomedins) via:
- Bone length growth (diameter, calcification↑)
- Chondrocyte differentiation↑
- Collagen synthesis↑
- Mucopolysaccharide synthesis↑
- Growth of organs↑

44
Q

II. HYPOTHALAMUS-PITUITARY GLAND SYSTEM - Growth hormone (GH)
5. What are other things the growth require except GH?

A
45
Q

II. HYPOTHALAMUS-PITUITARY GLAND SYSTEM - Growth hormone (GH)
6. What happen if there is GH deficiency in childhood?

A

GH deficiency in childhood
=> pituitary dwarfism (nanosomia)
- Average height >120cm
- All the physical parts of the body develop inappropriate portion to one another
- Maybe: child-like facial features (e.g. small chin)

46
Q

II. HYPOTHALAMUS-PITUITARY GLAND SYSTEM - Growth hormone (GH)
7. What happen if there is GH overproduction in childhood?

A

GH overproduction in childhood => gigantism:
- GH-producing pituitary adenoma (benign tumor)
- Rapid growth (before closure of the epiphyseal plates)
- Average height < 220-230cm
- Large organs, high performance
- Bitemporal hemianopia may occur (loss of vision in outer half of both visual field) -> compression of optic chiasm by tumors
=> Without treatment: low life expectancy

47
Q

II. HYPOTHALAMUS-PITUITARY GLAND SYSTEM - Growth hormone (GH)
8. What happen if there is GH overproduction in adult?

A
  • GH overproduction in adulthood -> acromegaly
  • Exaggerated GH effect after closure of the epiphyseal plates
  • ‘’endings’’ grow:
    +) ‘’coarse’’ features (chin, nose, pronounced brow protrusion)
    +) Fingers, foot grow + thicken (larger shoes needed, ring does not fit)
    +) Mandible grows, but teeth do not = teeth gapping
    +) Macroglossia
  • Organs enlarge:
    +) Heart (cardiac failure at the age of 50-60)
    +) Liver
    +) Kidney (large nephron, GFR↑, glucose reabsorption↑)
  • Metabolic disturbances: glucose tolerance↓, diabetes mellitus
  • Without treatment: low life expectancy
48
Q

II. HYPOTHALAMUS-PITUITARY GLAND SYSTEM - Somatomedins
9. What are the main features of Somatomedins?

A
  • Somatomedins are a group of hormones that are stimulated by GH and (mostly) promote cell growth and division.
  • These are local growth factors and are responsible for indirect effects of GH
  • Produced by the target tissue
49
Q

II. HYPOTHALAMUS-PITUITARY GLAND SYSTEM - Somatomedins
10. Explain a special case in liver related to Somatomedins

A
  • A special case in the liver: GH -> IGF-1 enters circulation (hormone)
    +) Negative feedback: [somatostatin]↑ = inhibits GH release
    +) Has a binding protein in blood plasma
    +) GH -> IGF-1 (also known as somatomedin C) -> growth
50
Q

II. HYPOTHALAMUS-PITUITARY GLAND SYSTEM
11. Explain the Relation of acute and chronic effects of GH

A
  • GH and somatomedins have a complicated relationship with fasting, which stimulates GH and at the same time inhibits production of somatomedins.
  • This means that even though growing children who are not eating enough food may have higher amounts of GH, they still have lower amounts of somatomedins -> means that they will not grow as much as if they were well-fed.
51
Q

II. HYPOTHALAMUS-PITUITARY GLAND SYSTEM
12. Make a schematic diagram explain major pathways of growth regulation by the GH system

A

A Physiology (88 decks)

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