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Physiology for Anaesthetists > Endocrine - Hypothalamus and pituitary > Flashcards

Endocrine - Hypothalamus and pituitary Flashcards

1
Q

Define a hormone

A

Substance released by a cell, gland or organ in one part of the body that exerts its effects on tissues elsewhere in the body

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2
Q

How are hormones classified

A

PEPTIDE HORMONES

  1. Short chain
    - -> TRH
    - -> ADH
    - -> ACTH
    - -> Insulin
  2. Longer chain
    - -> GH
    - -> PRL
  3. Glycopeptides (peptide chain plus CHO attached)
    - -> LH
    - -> FSH
    - -> TSH

LIPID and PHOSPHOLIPID DERIVED HORMONES

  1. Steroid hormones
    - -> Cortisol
    - -> Aldosterone
    - -> Testosterone
    - -> Oestrogen
  2. Eicosanoids
    - -> Prostaglandins
    - -> Thromboxanes
    - -> Leukotrienes

MONOAMINE DERIVATIVES

  1. Catecholamines
  2. Serotonin
  3. Thyroxine
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3
Q

How do peptide hormones bring about their effects at target tissues

A

Stored as granules
Released by exocytosis
Bind to CELL SURFACE RECEPTORS

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4
Q

From which substance are the steroid hormones derived

from which substance are eicosanoids derived

A

Steroids –> from cholesterol

Eicosanoids –> Phospholipid bilayer of cell membranes

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5
Q

Are the steroid hormones synthesized and stored?

A

No. They are synthesized as required and immediately released into circulation

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6
Q

What are the mechanisms of action of steroid hormones and eicosanoids

A

Steroids
–> High lipid soulbility –> cross cell membrane and bind to cytosolic receptors –> steroid receptor complex enters the cell nucleus to influence gene transcription.

Eicosanoids
–> complex mechanisms of action with a wide range of functions throughout the body

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7
Q

Describe the mode of action of the monoamine-derived hormones

A

Catecholamines and serotonin

  • -> Stored as granules prior to release
  • -> Cell membrane receptors

Thyroxin

  • -> Incorporated into thyroglobulin
  • -> Binds to receptors at the cell nucleus
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8
Q

Summarise the functions of the hypothalamus

A
  1. Autonomic nervous system (e.g. limbic system –> fear –> hypothalamus –> SNS response)
  2. Thermoregulation
  3. Hunger
  4. Water regulation
  5. Sleep-wake cycles (circadian rhythms)
  6. Control of Pituitary
  7. Behaviour (punishment & reward)
  8. Regulation sexual function
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9
Q

How is thermoregulation regulated by the hypothalamus

A

It integrates signals from the peripheral and central (hypothalamic) thermoreceptors. and controls the balance of activities between the two hypothalamic centers: heat loss and heat gain center

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10
Q

How does the hypothalamus regulate hunger

A

Controlled by the relative activities of the feeding and satiety centres in the hypothalamus. These centers are influenced by glucose, GIT hormones (CCK and glucagon) and adipose hormones (Leptin)

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11
Q

how does the hypothalamus regulate water

A
  1. Thirst center
  2. Osmoreceptors in the hypothalamus control renal water excretion in conjunction with ADH secretion by the pituitary gland
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12
Q

How does the hypothalamus control sleep wake cycles

A

Stimulate anterior hypothalamus –> sleep
Stimulate posterior hypothalamus –> wakefulness
Circadian rhythms originate here

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13
Q

How does the hypothalamus control pituitary function

A

Anterior lobe is controlled by secretion of hypothalamic hormones into the long portal vein

Posterior lobe is controlled by direct neural connections from the hypothalamus

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14
Q

Describe the anatomy of the pituitary/hypothalamus

A

Pituitary is a pea sized gland located in the sella turcica, a depression in the sphenoid gland at the base of the skull. It is situated directly below th hypothalamus and is connected to the hypothalamus by the pituitary stalk

The diaphragma sella is a fold of the dura mater which covers the pituitary superiorly. A gap allows the pituitary stalk to pass through

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15
Q

What important structures lie adjacent to the pituitary

A

Superior: pituitary stalk and hypothalamus

Laterally: Cavernous sinus

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16
Q

What important structures lie within the cavernous sinus

A

3, 4, 5(1), 5(2), 6 and the internal carotid artery

17
Q

Describe the anatomy of the pituitary

A

Larger lobe = anterior
Smaller lobe = posterior
Separated by pars intermedia

18
Q

Describe the blood supply to the pituitary gland

A

ANTERIOR LOBE
Superior hypophyseal artery (branch of internal carotid artery)

Long portal veins
–> connect hypothalamic capillary network to anterior pituitary capillary network

Short portal veins
–> connect posterior pituitary lobe capillary network to anterior lobe capillary network

POSTERIOR LOBE
Inferior hypophyseal artery (branch of internal carotid)

VENOUS BLOOD FROM BOTH DRAINS INTO THE CAVERNOUS SINUS

19
Q

List the hormones secreted by the hypothalamus

A
  1. TRH (secretion of TSH)
  2. GnRh (secretion of FSH/LH)
  3. CRH (secretion ACTH)
  4. GHRH (Secretion GH)
  5. Somatostatin (Inhibits GH release. Slight inhibition TSH)
  6. Dopamine (Inhibits PRL release)
20
Q

List the hormones secreted by the pituiatry

A 
ANTERIOR LOBE
Stimulating hormones
1. TSH
2. FSH
3. LH
4. ACTH

Directly acting hormones

  1. PRL
  2. GH

POSTERIOR LOBE

  1. ADH
  2. Oxytocin
21
Q

What is meant by the term ‘hypothalmic-pituitary axis’

A

Two negative feedback loops
1. Short loops –> anterior pituitary lobe hormones inhibit hypothalamus

  1. Long loops –> peripheral endocrine glands secrete hormones in response to hormones secreted by anterior pituitary. These peripheral hormones inhibit the hypothalamus
22
Q

What is the function of TSH

A

Stimulate synthesis and release of T3 (and T4) from the thyroid gland

23
Q

What is the function of LH in males and females

A

FEMALES
Rapid increase LH –> ovulation in females

Following ovulation, LH promotes the development of the corpus luteum

MALES
LH stimulates the secretion of testosterone by Leydig cells

24
Q

What is the function of FSH in males and females

A

FEMALES

  1. Promotes oestrogen synthesis
  2. Promotes development of ovarian follicles

MALEs
1. FSH aids sperm maturation

25
Q

What is the function of ACTH

A

Cortisol release from the zona fasiculata

26
Q

What causes skin hyperpigmentation in Addison’s disease

A

Excessive ACTH is degraded to produce alpha-MSH (alpha - melanocyte stimulating hormone)

27
Q

What is the function of GH

A

DIRECT EFFECTS
–> Stimulates lipolysis through its action on adipose cell GH receptors –> increasing circulating ffas

INDIRECT EFFECTS
–> Stimulates liver secretion of IGF-1 (insulin-like growth factor 1) –> promotes cell growth and development.

28
Q

Describe the release and inhibition of GH

A

Pulsatile release from anterior pituitary –> particularly at night.

GHRH –> stimulates GH secretion
Somatostatin –> inhibits GH secretion

IGF-1 –> inhibits GH release

Most of the time GH levels are low
Increased levels during physiological stress, hypoglycaemia and exercise

29
Q

What is the function of prolactin

A

Promotes breast development during pregnancy

Promotes milk production following delivery

30
Q

How does PRL secretion differ from other pituitary hormones

A

There is no releasing hormone for PRL

Hypothalamus controls PRL secretion through tonic dopamine release –> inhibits PRL release

Stimulation of PRL release

  1. Suckling
  2. Sex
  3. Stress response
  4. Epileptic seizure
31
Q

What is the seventh hormone secreted by the pars intermedia of the hypothalamus and when does the secretion of this hormone become clinically apparent

A

alpha-MSH (melanocyte stimulating hormone)

This is responsible for the skin pigmentation during pregnancy

32
Q

Name the hormones secreted by the posterior lobe of the pituitary and state where these hormones are synthesized. How are these hormones released into circulation

A

ADH and Oxytocin
These are synthesized in the hypothalamus, packaged into tiny vesicles and transported to the posterior lobe through nerve axons and then stored in granules within the nerve terminals. Action potential from the hypothalamus cause release of the granules into systemic circulation.

33
Q

What are the physiological effects of ADH

A
  1. Insertion of aquaporins and urea transporters (UT-A1) into the cell membrane of collecting ducts –> increased water absorption.
  2. Vasoconstriction
    - -> at normal concentrations –> minimal contribution of ADH to arterial tone
    - -> At high concentrations –> pwerful vasoconstrictor
34
Q

What stimulates and inhibits ADH secretion

A

Stimulates

  1. Increased plasma osmolarity
  2. Decreased blood pressure (lesser extent)

Inhibits
1. Alcohol (leading to diuresis)

35
Q

What are the effects of oxytocin

A
  1. Contraction of uterine smooth muscle during labour
  2. Let-down reflex in lactation (milk into duct system)
  3. Psychological ‘cuddle hormone’
36
Q

What stimulates oxytocin release

A
  1. Stretching of the cervix by the fetal head

2. Suckling –> myoepithelial cells contract –> allowing newly formed milk into the duct system

37
Q

What are the four ways that a benign tumour of the anterior lobe of the pituitary can present

A
  1. Hormone hypersecretion (e.g. galactorrhoea with excessive PRL)
  2. Hormone hyposecretion (e.g. hypothyroidism / adrenocortical insufficiency / infertility)
  3. Mass effect
    E.g. 1. optic chiasm –> bitemporal hemianopia)
    E.g. 2. Cranial nerve palsy
    E.g. 3. 3rd ventricle obstruction –> hydrocephalus
  4. Incidental finding (CT/MRI for another reason)
38
Q

Describe the anaesthetic concerns with regard to pituitary debulking surgery

A

Most commonly excised via the trans-sphenoidal approach

  1. Shared airway
  2. Minimal haemodynamic instability and a smooth extubation

Physiology for Anaesthetists (61 decks)

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