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MEH > Lecture 15 > Flashcards

Lecture 15 Flashcards

1
Q

What is the hypothalamic pituitary axis?

A

Link between endocrine and nervous system.

-hypothalamus and pituitary gland form a functional unit

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2
Q

Where is the hypothalamus found?

A

Area of brain situated beneath the thalamus

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3
Q

Where is the pituitary gland found?

A

Sits beneath hypothalamus, in socket of bone called the sella turcica

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4
Q

What are some processes which the hypothalamus and pituitary gland modulate?

A
  • body growth
  • reproduction (LH and FSH)
  • adrenal gland function
  • water homeostasis
  • milk secretion/ lactation (prolactin/oxytocin)
  • thyroid gland function
  • puberty
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5
Q

What are the two parts of the pituitary gland?

A

Anterior and posterior pituitary gland

Posterior is not a gland because it doesn’t make its own hormones-they are produced in hypothalamus

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6
Q

What connects the hypothalamus and posterior pituitary?

A

Infundibulum (pituitary stalk)

-hypothalamus drops down through infundibulum to form posterior pituitary

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7
Q

What are the embryological origins of the parts of the pituitary glands?

A

Anterior: evagination of oral ectoderm (Rathke’s pouch)
-from the primative gut tissue
Posterior: originates from the neuroectoderm
-primitive brain tissue

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8
Q

What is the neurocrine function of the posterior pituitary?

A

Nuclei in hypothalamus (collection of cell bodies with similar function)
-paraventricular nucleus
-supraoptic nucleus
Hormones synthesised in hypothalamus and transported down nerve cells to posterior pituitary gland (neurocrine signalling)
-stored and released from posterior pituitary gland into circulation to act on distant targets

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9
Q

What hormones are made in hypothalamus and enter the posterior pituitary gland?

A

Oxytocin

ADH

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10
Q

What is the anterior pituitary function?

A
  • control and release of hormones from pituitary (inhibiting/releasing hormones) via hypothalamus
  • hormones synthesised in hypothalamus transported down axons and stored in the MEDIAN EMINENCE
  • hormones then released into blood supply: HYPOPHYSEAL PORTAL SYSTEM
  • travel down blood supply into anterior pituitary
  • hypothalamic hormones stimulate/inhibit target endocrine cells in anterior pituitary
  • theses secrete hormones into circulation to act on distant targets
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11
Q

What other functions other than endocrine does the anterior pituitary carry out?

A

-autocrine
-paracrine
Anterior pituitary hormones effect neighbouring cells

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12
Q

Function of oxytocin?

A
  • milk let down reflex

- uterus contractions during birth (Ferguson Reflex)

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13
Q

What is ADH also known as?

A

Vasopressin

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14
Q

Function of ADH?

A

Number of aquaporin channels increase: reabsorb more water- conserve water
Regulation of water volume

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15
Q

What are the tropic hormones of hypothalamus?

A
  1. TRH (thyrotropin releasing hormone)
  2. PIH (prolactin release-inhibiting hormone: dopamine)
  3. CRH (Corticotropin releasing hormone)
  4. GnRH (gonadotropin releasing hormone)
  5. GHRH (growth hormone releasing hormone)
  6. GHIH (growth hormone-inhibiting hormone) (stomatostatin)
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16
Q

What are the hormones released from hypothalamus to anterior pituitary called tropic hormones?

A

They affect release of another hormone

have direct effect on release of anterior pituitary hormones

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17
Q

What is PIH also known as?

A

Dopamine (neurotransmitter)

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18
Q

What is GHIH also known as?

A

Somatostatin

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19
Q

What are the hormones produced by the anterior pituitary?

A
  • TSH (thyroid stimulating hormone > secretion of thyroid hormone from thyroid gland)
  • ACTH (adrenocorticotropic hormone > secretion of hormones from adrenal cortex)
  • LH (luteinising hormone > ovulation and secretion of sex hormones)
  • FSH (follicle stimulating hormone > development of eggs and sperm)
  • PRL (prolactin > mammary gland development and milk secretion)
  • GH (growth hormone > growth and energy metabolism. STIMULATES IGF’s)
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20
Q

Give an example of the negative feedback in the hypothalamic pituitary axis:

A 
ADRENAL AXIS 
Stress/pain/hypoglycaemia/low BP
-hypothalamus stimulates release of CRH
-CRH affects the anterior pituitary
-anterior pituitary releases ACTH
-ACTH acts on the adrenal cortex causing it to release cortisol 
-cortisol affects many tissue types
  • ACTH can feedback to the hypothalamus
  • cortisol feedbacks to anterior pituitary or hypothalamus
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21
Q

What factors influence growth?

A
  • genetics
  • environment
  • nutrition
  • hormones (especially growth hormone: particularly in children)
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22
Q

What is an increase in cell number?

A

Hyperplasia

Growth

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23
Q

What is an increase in cell size called?

A

Hypertrophy

Growth: in growth of muscle

24
Q

What is atrophy?

A

-decrease in cell size
-decrease in cell number
(Getting smaller)

25
Q

Difference between apoptosis and necrosis?

A

Necrosis is cell death by damage whereas apoptosis is programmed cell death

26
Q

What type of hormone is growth hormone?

A

Peptide hormone

-has a signal peptide which needs to be cleaved before proper folding

27
Q

Where is growth hormone produced?

A

Anterior pituitary

Stimulated by GHRH, inhibited by somatostatin-GHIH

28
Q

How are growth-promoting effects exerted?

A

Indirectly via insulin-like growth factors

29
Q

Why is GH essential for normal growth?

A
  • GH stimulates long bone growth prior to epiphyseal closure (children)
  • IGF’s stimulates bone growth and cartilage growth
  • GH and IGF’s maintain muscle and bone mass in adults an promote healing/tissue repair, and modulating metabolism and body composition
30
Q

What regulates secretion of GH?

A

Via hypothalamus

GHRH: increases GH secretion and somatostatin: decreases GH secretion

31
Q

When do you get a surge of GH secretion?

A
  • after onset of deep sleep
  • stress
  • exercise
  • decrease in glucose/fatty acids
  • fasting
32
Q

What is the short/long loop negative feedback in GH secretion?

A

Long loop (mediated by IGF’s)

  • inhibit release of GHRH from hypothalamus
  • stimulate release of somatostatin from hypothalamus
  • inhibit release of GH from anterior pituitary

Short loop
-GH itself stimulating release of somatostatin.

33
Q

What happens in growth hormone deficiency?

A

Childhood: pituitary dwarfism (proportionate type of dwarfism)

  • due to complete or partial deficiency
  • growth rate slower than expected
  • delayed/no sexual development during teenage years
34
Q

How do you treat GH deficiency?

A

GH therapy

35
Q

What does GH excess cause?

A

Gigantism in childhood

  • very tall
  • rare
  • caused by pituitary adenoma

Acromegaly

  • pituitary adenoma develops in adults
  • large hands/feet/lower jaw
36
Q

How does GH exert its effects on cells?

A

-GH binds to tyrosine kinase receptors causing change of shape and it autophophorylates itself
-these activate Janus kinases (intracellular:JAKs)
-activating many signalling pathways
= transcription factor activator and IGF production

37
Q

What are the 2 types of IGF’s?

A

IGF1 (main GF in adults)

IGF2 (involved in fetal growth)

38
Q

What do IGF’s modulate?

A
  • hypertrophy
  • hyperplasia
  • protein synthesis increase
  • increase rate of lipolysis in adipose tissue
39
Q

What is the action of dopamine?

A

Inhibits release of prolactin

40
Q

Difference between tropic and trophic hormones:

A

Trophic: affect growth
Tropic: affect release of another hormone
A hormone can be both of these

41
Q

What does TRH from hypothalamus cause?

A

Secretion of TSH which acts on the thyroid gland stimualting it to produce thyroid hormone T3 and T4, which affect metabolic rate

42
Q

What does CRH from hypothalamus cause?

A

Secretion of ACTH which acts on the arenal gland stimulating it to produce cortisol, which responds to stress via metabolic actions

43
Q

What does PIH (dopamine) from hypothalamus cause?

A

Inhibits secretion of prolactin which acts upon the mammary glands to encourage breast growth and milk secretion

44
Q

What does GHRH and GHIH from hypothalamus cause?

A

GHRH:
-secretion of growth hormone which acts upon the liver to stimulate it to produce IGF’s which enhance growth/act on many other tissues to enhance growth
GHIH:
-inhibits secretion of growth hormone and therefore all of the above

45
Q

What does GnRH from hypothalamus cause?

A

Secretio of LH/FSH
LH: acts upon ovaries in woman and testes in male, stimulating release of sex hormones
FSH: acts upon ovaries in woman and testes in male, stimulating gamete production

46
Q

What is an IGF and what are they also called?

A

Insulin-like growth factor

-somatomedins

47
Q

Which organs respond to GH?

A

Liver and skeletal muscle

  • produce and secrete IGF’s
  • growth promoting effects are usually exerted indirectly via IGF’s
48
Q

When do you get a decrease in production of GH?

A
  • during REM sleep (light sleep)
  • increase in glucose or fatty acids
  • obesity
49
Q

Why could you develop pituitary dwarfism?

A

During traumatic birth

-skull becomes crushed

50
Q

How do IGF’s act?

A

Through IGF receptors (different from GH receptors)

51
Q

What types of actions other than endocrine can IGF’s exhibit?

A
  • paracrine

- autocrine

52
Q

What other hormones also influence growth?

A
  • insulin (enhances somatic growth, interacts with IGF receptors)
  • thyroid hormones (promote CNS development and enhance GH secretion)
  • androgens (accelerate pubertal growth spurt, increase muscle mass, promote closure of epiphyseal plates)
  • estrogens (decrease somatic growth, promote closure of epiphyseal plates)
  • glucocorticoids (inhibit somatic growth: normal cells)
53
Q

What can act/bind to IGF receptors?

A 
IGF 1 (can act on all 4 receptors)
IGF 2 (only act on IGF1/2 receptors)
Insulin (can also act on insulin/hybrid/IGF1 receptors, NOT IGF2)
54
Q

Does IGF2 receptor have tyrosine kinase activity?

A

No

55
Q

What does dopamine decrease and why?

A

GH/GnRH/LH/FSH

Through dopamine D2 GPCR’s (Gi)

MEH (22 decks)

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