Endocrine Physiology Flashcards

1
Q

Describe the Posterior Pituitary (derivative, composition, and AKA)

A
  • Derived embryonically from an outgrowth of the brain
  • Composed of nervous tissue
  • Also called the neurohypophysis
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2
Q

Describe the Anterior Pituitary (derivative, composition, and AKA)

A
  • Derived embryonically from an outpouching that buds off from the roof of the mouth
  • Composed of glandular tissue
  • Also called the adenohypophysis
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3
Q

Describe the hormones released from the Posterior vs. Anterior Pituitary

A

Posterior:

  • Oxytocin –> Uterine muscles + mammary glands
  • ADH –> Kidney tubes

Anterior:

  • TSH
  • ACTH
  • FSH + LH
  • GH
  • PRL
  • Endorphins
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4
Q

Describe the Posterior Pituitary

A
  • Neuroendocrine system
  • Composed of neurosecretory cells whose cell bodies lie in the hypothalamus.
  • Infundibular stalk arises out of the median eminence
  • Connects the hypothalamus and posterior pituitary.
  • Axons from the hypothalamus terminate on capillaries in the posterior pituitary.
  • Functionally, the posterior pituitary is an extension of hypothalamus
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5
Q

Describe the Anterior Pituitary

A

Unlike the posterior pituitary, which releases hormones synthesized by the hypothalamus, the anterior pituitary synthesizes its own hormones.
The portal system carries neurohormones from the hypothalamus to anterior pituitary to control its secretions.

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6
Q

What are the Anterior Pituitary Cell Types

A
  • GH secreted by somatotrophs
  • PRL secreted by lactotrophs
  • ACTH secreted by corticotrophs
  • TSH secreted by thyrotrophs
  • LH, FSH secreted by gonadotrophs
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7
Q

Anterior Pituitary Hormones

A

TSH, ACTH, FSH and LH are all tropic hormones:

  • they regulate the secretion of another specific endocrine gland
  • FSH and LH are referred to as gonadotropins - they control secretions of the sex glands

An anterior pituitary hormone may be regulated by a stimulatory and an inhibitory hypothalamic hormone (ex. GH, TSH, PRL)

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8
Q

Effects of Anterior Pituitary Hormones

A
  • Usually, the effect of the stimulatory hormone predominates.
  • Except, PRL (effect of Dopamine&raquo_space;> TRH)
  • So, if pituitary is separated from hypothalamus, PRL levels increase, while all others decrease
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9
Q

What happens when one gets a Pituitary Adenoma (noncancerous tumors that occur in the pituitary gland)?

A

Prolactin-secreting pituitary adenomas are the most common type!… Secrete more PRL

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10
Q

What is the primary function of PRL?

A

-Major hormone responsible for milk production

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11
Q

Where is PRL synthesized/secreted?

A

-Synthesized/secreted by lactotrophs in pituitary

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12
Q

What controls the release of PRL?

A

Release is controlled by two hormones:
Dopamine (inhibitory)
Thyroid releasing hormone (stimulating)

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13
Q

What is the Function of PRL?

A
  • Growth of breasts
  • Lactogenesis: synthesis of enzymes involved in milk production
  • Inhibition of ovulation: inhibits GnRH release and thus, LH release
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14
Q

What are the Clinical Features of Prolactinoma in young menstruating women and men/postmenopausal women?

A

1) Young menstruating women
- Irregular menses (amenorrhea, oligomenorrhea, delayed menarche)
- Infertility
- Galactorrhea (30-80% of women)
- Hirsutism
- Typically microadenomas

2) Men and postmenopausal women
- Decreased libido (80%)
- Impotence (full or partial)
- Hypogonadism
- Galactorrhea (20-30%)
- Visual field abnormalities
- Extraoccular muscle palsies
- Headaches
- Typically macroadenomas

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15
Q

What are the Clinical Features of Prolactin-Secreting Pituitary Adenomas?

A

1) Prolactin microadenoma
- Usually less than 1 cm in diameter
- Only presenting symptoms may be amenorrhea-galactorrhea syndrome

2) Larger pituitary adenomas
- May have intracranial symptoms: bitemporal hemianopia, retro-orbital headaches
- May also have pituitary failure with thyroid, gonadal, and adrenal insufficiency

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16
Q

Describe Growth Hormone (GH)

A
  • Single most important hormone for normal growth to adult stature.
  • Secreted throughout life.
  • Has profound effects on protein, carbohydrate, and fat metabolism.
  • Many effects of GH are mediated through insulin-like growth factors (IGFs).
17
Q

Discuss Growth Hormone Secretory Rates

A
  • Vary over a lifetime
  • Secretion rate increases steadily from birth into early childhood
  • Remains relatively stable in childhood
  • Atpuberty, there is an enormous secretory burst, induced in females by estrogen and in males by testosterone. responsible for thegrowth spurtof puberty
  • After puberty, the rate of growth hormone secretion declines to a stable level.
  • In senescence, growth hormone secretory rates and pulsatility decline to their lowest levels.
18
Q

Discuss Regulation of GH Secretion

A

Controlled by two pathways from the hypothalamus

1) stimulatory (GHRH)
2) inhibitory (somatostatin, also known as somatotropin release–inhibiting factor [SRIF]).
- Liver is a major target organ of GH –> Principal site of IGF production
- Additional IGF is generated within other target tissues as well

19
Q

Describe the effect that GHRH has on GH and when the most GH is present.

A
  • GHRH causes peak GH within 30 minutes followed by sustained increase for 1-2 hrs.
  • Largest secretory burst occurs within 1 hour of falling asleep.
20
Q

What are the General Actions of GH

A

Overall, growth-promoting effects in virtually every organ.

1) Anabolic; increases in…
- DNA, RNA, Protein synthesis
- Cellular hypertrophy & hyperplasia
- “Protein Sparing” (body uses glucose and fat first for energy, conserving protein)

2) Catabolic; Induction of Insulin Resistance
- Decreased glucose uptake and utilization by target tissues
- increased plasma glucose
- increased lipolysis and plasma free fatty acids
- Increased insulin levels

21
Q

Describe impact of Growth Hormone or IGF-1 Deficiency and its causes

A

Growth Hormone or IGF-1 Deficiency during…

  • Prepuberty: Dwarfism - failure to grow, short stature, mild obesity, and delayed puberty
  • Postpuberty: Not a major problem

Causes:
Defect anywhere in hypothalamic-pituitary axis
Failure to generate somatomedins
Deficient GH or somatomedin receptors

22
Q

Describe impact of Hypersecretion of Growth Hormone and its causes

A

Hypersecretion of Growth Hormone during…

-Prepuberty: Gigantism - increased linear growth due to intense hormonal stimulation at the epiphyseal plates.
Postpuberty: Acromegaly - increased periosteal bone growth, increased organ size, increased hand and foot size, enlargement of the tongue, coarsening of facial features, insulin resistance, and glucose intolerance

Cause: most often due to a GH–secreting pituitary adenoma

23
Q

Describe Thyroid Hormones secretion and effects

A
  • Synthesized and secreted by epithelial cells of the thyroid gland.
  • They have effects on virtually every organ system in the body including those involved in normal growth and development.
  • Essential for normal growth and maturation
  • Iodide (I-) must be adequately supplied in the diet to make thyroid hormones
24
Q

What are the different types of secreted Thyroid hormones?

A

Two active thyroid hormones secreted:

  • triiodothyronine (T3): most active
  • thyroxine (T4): secreted in higher amounts (T4 can be converted to T3)
25
Q

Describe the Functional unit = Follicle in the thyroid

A
  • Colloid: Lumen of follicle; filled with thyroglobulin which binds thyroid hormones
  • Follicular cell: Synthesize and secrete thyroid hormones
  • Extra follicular cell: Synthesize and secrete calcitonin (lowers blood calcium)
26
Q

Steps in thyroid synthesis 1

A

See picture

27
Q

Steps in thyroid synthesis 2

A

See picture

28
Q

Describe the Thyroid Hormone HPT Axis- Feedback Loops

A

The hypothalamus releases Thyrotropin-releasing hormone (TRH) –> Causes the anterior pituitary to release Thyroid-stimulating hormone (TSH) –> Which leads to production of T3 and T4 in the Thyroid –> Which then inhibits the anterior pituitary glad from releasing TSH

29
Q

Describe the actions of Thyroid hormones

A

1) Basal metabolic rate (BMR)
- Increase NaK ATPase activity
- Increased oxygen consumptionand a resulting increase inBMRandbody temperature.

2) Metabolism
- Increase glucose absorption from the gastrointestinal tract
- Potentiates gluconeogenesis, lipolysis, and proteolysis

3) Cardiovascular and respiratory
- High demand for O2; increased CO, increased HR and SV, contractility
- Upregulate cardiacβ1-adrenergic receptors

4) Growth
- required for growth to adult stature; acts synergistically with GH for ossification and fusion of bone plates

5) CNS
- In theperinatal period, thyroid hormone is essential for normal maturation of the CNS

30
Q

Describe the Adrenal Glands and what hormones they produce

A

Medulla: 20% of the tissue
Cortex: 80% of the tissue

Hormones produced:

1) Catecholamines
2) Mineralocorticoids (aldosterone)
3) Glucocorticoids (cortisol)
4) Androgens (DHEA)

31
Q

Describe the hormones made in the Adrenal Medulla

A

Catecholamines (Epinephrin and Norepinephrine)

  • Secretes primarily epinephrine, some norepinephrine
  • Have the same effects on target organs as direct stimulation by sympathetic nerves
  • Longer lasting

Rapidly increases in response to:

  • Exercise
  • Emergencies
  • Exposure to cold