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PHYSIOLOGY IV > LECTURE 2 (Hypothalamus & Pituitary) > Flashcards

LECTURE 2 (Hypothalamus & Pituitary) Flashcards

(41 cards)

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1
Q

Describe the pituitary gland/Hypophysis anatomy

A
  • It lies in the Sella turcica (a bony cavity at the base of the brain) and is connected to the hypothalamus via the PITUITARY/HYPOPHYSIAL STALK
  • Divided into anterior pituitary (Adenohypophysis) and posterior pituitary (Neurohypophysis)
  • Between anterior + posterior is an avascular zone called the “pars intermedia”
  • Embriologically from two different sources = anterior pituitary from RATHKE’S POUCH (embryonic invagination of pharyngeal epithelium) & posterior pituitary from a neural tissue outgrowth from hypothalamus
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2
Q

What do the origin of both the anterior and posterior pituitary tell us?

A
  • Anterior = explains epithelium nature of cells
  • Posterior = explains the presence of large numbers of glial-type cells
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3
Q

Which hormones are secreted by the Anterior pituitary?

A
  • Growth hormone (promotes growth of entire body by affecting protein formation and cell multiplication and differentiation)
  • Adrenocorticotropin (controls secretion of adrenocortical hormones which affect glucose, protein and fat metabolism)
  • Thyroid-stimulating hormone/Thyrotropin
  • Prolactin (promotes mammary gland development and milk production)
  • FSH and LH
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4
Q

Which hormones are secreted by the posterior pituitary gland?

A
  • Antidiuretic hormone/Vasopressin (controls rate of water excretion into the urine, controlling the concentration of water in the body fluids)
  • Oxytocin (helps express milk from breast glands + delivery of baby)
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5
Q

What are the 5 different cell types of the anterior pituitary gland?

A
  • Somatotropes
    [release GROWTH HORMONE/somatotropin]
  • Corticotropes
    [release ACTH/corticotropin]
  • Thyrotropes
    [release TSH/thyrotropin]
  • Gonadotropes
    [release Follicle-stimulating hormone/Luteinising hormone]
  • Lactotropes/Mammotropes
    [release Prolactin]
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6
Q

What is the physiological action of Growth hormone/Somatotropin?

A
  • Stimulates body growth
  • Stimulates secretion of IGF-1
  • Stimulates lipolysis
  • Inhibits actions of insulin on carbohydrate and lipid metabolism
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7
Q

What does ACTH/Corticotropin do?

A
  • Stimulates production of glucocorticoids and androgens by adrenal cortex
  • Maintains size of zona fasciculate and zona reticular of cortex
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8
Q

What does TSH/Thyrotropin do?

A
  • Stimulates production of thyroid hormones by thyroid follicular cells
  • Maintains size of follicular cells
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9
Q

What do FSH and LH do?

A
  • Stimulates development of ovarian follicles
  • Regulates spermatogenesis in testis
  • Causes ovulation and formation of corpus luteum in the ovary
  • Stimulates production of oestrogen and progesterone by the ovary
  • Stimulates testosterone production by the testis
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10
Q

What does Prolactin do?

A

Stimulates milk secretion and production

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11
Q

Somatotropes stain strongly with acid dyes and are therefore called _____________

A

Acidophils

Explanation: Thus, Pituitary tumours that secrete large quantities of human growth hormone are called acidophilic tumours

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12
Q

Where are the cell bodies that secrete the posterior pituitary hormones?

A

Large neurons called “magnocellular neurons” located in the SUPRAOPTIC and PARAVENTRICULAR NUCLEI of the hypothalamus

TRANSPORT: the hormones are then transported in the AXOPLASM of the neurons’ nerve fibers passing from the hypothalamus to the posterior pituitary gland

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13
Q

What happens when the pituitary gland is removed from its normal position beneath the hypothalamus and moved to somewhere else in the body?

A

Its rates of secretion of the different hormones fall to very low levels

Explanation: Almost all secretion by the pituitary is controlled by either hormonal or nervous signals from the hypothalamus

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14
Q

What controls the anterior and posterior pituitary gland?

A

Anterior = Hormones called HYPOTHALMIC RELEASING/INHIBITORY HORMONES secreted within the hypothalamus and transported through HYPOTHALMIC-HYPOPHYSIAL PORTAL VESSELS which act on glandular cells to control secretion

Posterior = Nerve signals from the hypothalamus and terminate in the posterior pituitary

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15
Q

Describe the transport of hypothalamic hormones to the anterior pituitary gland

A

Special neurons in the hypothalamus synthesise and secrete hypothalamic releasing and inhibitory hormones -> neurons originate in various parts of hypothalamus and send their nerve fibers to the MEDIAN EMINENCE and TUBER CINEREUM (extension of hypothalamic tissue into the pituitary stalk) -> hormones absorbed in hypothalamic-hypophysial portal system + carries to anterior pituitary gland sinuses

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16
Q

Which hormones are released by the hypothalamus to act on the anterior pituitary gland?

A
  • Thyrotropin-releasing hormone (TRH)
    [causes release of thyroid-stimulating hormone]
  • Corticotropin-releasing hormone (CRH)
    [causes release of adrenocorticotropin]
  • Growth hormone-releasing hormone (GHRH)
    [causes release of growth hormone and growth hormone inhibitory hormone/somatostatin]
  • Gonadotropin-releasing hormone (GnRH)
    [causes release of LH and FSH]
  • Prolactin inhibitory hormone
    [causes inhibition of prolactin secretion]
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17
Q

What are the different effects of Growth hormone?

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A
  • Increased rate of protein synthesis in most cells of the body
  • Increased mobilisation of fatty acids from adipose tissue (increased free fatty acids in blood and use for energy)
  • Decreased rate of glucose utilisation throughout the body
  • Increases size of cells and increased mitosis
18
Q

How does Growth hormone promote protein synthesis?

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A
  • Enhances transport of most amino acids through the cell membranes to the interior of cells
  • Increased of RNA translation for protein synthesis
  • Increased nuclear transcription of DNA to RNA
  • Decrease in breakdown of cell protein
19
Q

How does Growth hormone enhance fat utilisation?

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A

GH causes the release of fatty acids from adipose tissue -> increases the concentration of fatty acids in the body fluids -> GH enhances conversion of fatty acids to acetyl-coenzyme A (acetyl-CoA) and its subsequent utilisation of energy

PROBLEMS: excessive GH -> fat mobilisation from adipose tissue is so large that ACETOACETIC ACID are formed by the liver and released into body fluids causing KETOSIS and FATTY LIVER

20
Q

How does Growth hormone decrease carbohydrate utilisation?

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A
  • Decreased glucose uptake in tissues such as skeletal muscle and fat
  • Increased glucose production by the liver
  • Increased insulin secretion
21
Q

Why are the growth hormone’s effects called “diabetogenic”?

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A

Weakenes insulin’s actions to stimulate uptake + utilisation of glucose in skeletal muscle and adipose tissue + inhibit gluconeogenesis -> increased blood glucose concentration and compensatory increase in insulin secretion

22
Q

What is necessary for the Growth-promoting action of growth hormone?

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A
  • Insulin activity
  • Carbohydrates in diet

Explanation: Carbohydrates and insulin provide energy needed for metabolism of growth and insulin for transport of amino acids into cells

23
Q

How does growth hormone stimulate cartilage and bone growth?

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A
  • Increased deposition of protein by the chondrocytic and osteogenic cells that cause bone growth
  • Increased rate of production of these cells
  • A specific effect of converting chondrocytes into osteogenic cells -> deposition of new bone
24
Q

What are Somatomedins?

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A

Growth hormone causes the liver to form small proteins called “Somatomedins” that increase all aspects of bone growth.

They are also called “Insulin-like growth factors” since their effect on growth is similar to insulin.

ADDITION: They bind strongly to plasma proteins so have a prolonged duration (20 hours) compared to GH (20 minutes)

25
What factors stimulate secretion of Growth hormone?
- Starvation (especially with severe protein deficiency) - Hypoglycaemia/low concentration of fatty acids in blood - Exercise - Excitement - Trauma - Ghrelin (hormone secreted by stomach before meals)
26
Describe the secretion and action of Growth hormone from the hypothalamus to the anterior pituitary
VENTROMEDIAL NUCLEUS causes secretion of GROWTH-HORMONE RELEASING HORMONE & SOMATOSTATIN (same area which is sensitive to blood glucose conc) -> GHRH attaches to cell membrane receptors of growth hormone cells on pituitary -> receptors activate ADENYLYL CYCLASE causing an increase in intracellular level of cAMP SHORT TERM EFFECTS: increase Ca2+ transport into cells -> causes fusion of GH secretory vesicles with cell membrane + release of hormone into blood LONG TERM EFFECTS: increase transcription in nucleus -> stimulate synthesis of new growth hormone
27
What is Panhypopituitarism?
Decreased secretion of all the anterior pituitary hormones Explanation: May be congenital (present from birth) or occur suddenly or slowly during life (primarily due to pituitary tumour which destroys pituitary gland)
28
What is Dwarfism growth like?
All the physical parts of the body develop in appropriate proportion to one another but the rate of development is greatly decreased Most dwarfs never secrete enough gonadotropic hormones so cannot reproduce but 1/3 of dwarfs can
29
What are the common abnormalities that cause Panhypopituitarism in adults?
- Craniopharyngiomas/Chromophobe tumours = may compress the pituitary gland until the functioning anterior pituitary cells are totally or almost destroyed - Thrombosis of pituitary blood vessels = usually occurs when a new mother develops circulatory shock after birth
30
What are the effects of Adult Panhypopituitarism?
- Hypothyroidism - Depressed production of glucocorticoids by adrenal glands - Suppressed secretion of Gonadotropic hormones (sexual functions are lost)
31
How does Gigantism occur?
The acidophilic, growth-hormone producing cells of the anterior pituitary become excessively active (producing tumours) -> lots of growth hormone before adolescence (before epiphyses have fused) -> gigantism
32
What condition do giants usually have?
Hyperglycaemia/Diabetes mellitus Explanation: Beta cells of the islets of langerhans in the pancreas are prone to degenerate because they become overactive
33
How does Acromegaly occur?
If an acidophilic tumour occurs after adolescent, the person cannot grow taller but bones can become thicker + soft tissues can continue to grow MANIFESTATIONS: - Lower jaw protrudes forward - Forehead slants forward due to excess development of supraorbital ridges - Nose increases as twice normal size - Large hands, fingers and feet - Hunched back/Kyphosis - Soft tissue organs (tongue, liver, kidneys) become enlarged
34
What are the pros and cons of growth hormone therapy in older people?
PROS - Increased protein deposition in the body, especially in muscles - Decreased fat deposits - Feeling of increased energy CONS - Insulin resistance/diabetes - Edema - Carpal tunnel syndrome - Arthralgias (joint pain)
35
Where are ADH and Oxytocin formed?
Oxytocin = paraventricular nuclei ADH = supraoptic nuclei BOTH in the hypothalamus
36
Describe the posterior pituitary gland/neurohypophysis
- Composed of PITUICYTES (do not secrete hormones, just support terminal nerve fibers and endings from nerve tracts that originate in supraoptic and paraventricular nuclei of hypothalamus) - Hormones initially synthesised in the cell bodies of the supraoptic and paraventricular nuclei are transported with "carrier" proteins called NEUROPHYSINS down to nerve endings in posterior pituitary gland
37
How does Antidiuretic hormone work?
In absence, collecting tubules and ducts become almost impermeable to water, preventing significant reabsorption of water -> extreme dilution of urine. In presence, permeability of collecting ducts and tubules to water increases allowing reabsorption, conserves water I the body and produces very concentrated urine. MOA: ADH combines with membrane receptors that activate adenylyl cyclase and cause formation of cAP inside tubular cell cytoplasm -> phosphorylation of elements in special vesicles -> vesicles insert into apical cell membranes providing areas of high water permeability
38
Describe the regulation of ADH production
When extracellular fluid becomes too concentrated, fluid is pulled by osmosis out of the osmoreceptor cell -> decreases in size -> initiates appropriate nerve signals in hypothalamus to cause additional ADH secretion OPPOSITE WHEN EXTRACELLULAR FLUID BECOMES TOO DILUTE
39
Why is ADH also called "Vasopressin"
Since higher concentrations of ADH have an effect of constricting arterioles throughout the body and increasing arterial pressure
40
Describe how Oxytocin aids in milk ejection by the breasts
Suckling on breasts stimulates signals to be transmitted through sensory nerves to oxytocin neurons in paraventricular and supraoptic nuclei in hypothalamus -> causes release of oxytocin by posterior pituitary -> oxytocin carried to breasts where is causes contraction of MYOEPITHELIAL CELLS that lie outside of and form a lattice work surrounding the alveoli of the mammary glands
41
What is the main hormone produced by the Anterior pituitary gland?
Growth hormone

PHYSIOLOGY IV (14 decks)

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