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PHYG 216 > Module 1 Section 2 (Hypothalamic-Pituitary Axis) > Flashcards

Module 1 Section 2 (Hypothalamic-Pituitary Axis) Flashcards

1
Q

Describe the structure and function of the hypothalamic-pituitary axis.

A

Both the anterior and posterior lobes of the pituitary gland release hormones that regulate the functions of other endocrine glands or organs.

The hypothalamus controls this hormone release, but does so in a different manner for each lobe.

Posterior Pituitary Lobe

  • The hypothalamus is connected to the posterior pituitary by a neural pathways.
  • Within the hypothalamus there are 2 well-defined clusters of neurons, called the supraopticnucleus and the paraventricular nucleus. Axons from these nuclei project down the pituitary stalk and terminate on blood vessels in the posterior pituitary.

Anterior Pituitary Lobe

  • The hypothalamus is connected to the anterior pituitary by a unique vascular link: the hypothalamic-hypophyseal portal system.
  • The hypothalamus secretes hormones into this portal system and they are carried directly to the anterior pituitary where they either inhibit or promote the release of anterior pituitary hormones
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2
Q

Differentiate between the hormones of the anterior and posterior pituitary.

A

Posterior pituitary gland
- Vasopressin
• Also called antidiuretic hormone (ADH)
• 2 major actions: 1) enhancing the
retention of water by the kidneys; and 2) causes contraction of arteriolar smooth muscle.
- Oxytocin
• 2 major roles: 1) stimulating contraction of uterine smooth muscle cells during
childbirth; and 2) promoting milk ejection during breastfeeding.

Anterior pituitary gland
- All are peptide hormones
- Most are tropic hormones (once released, these hormones stimulate other endocrine glands to release their hormones)
- Thyroid-Stimulating Hormone (TSH or Thyrotropin)
• Stimulates the release of thyroid hormones from the thyroid gland.
- Luteinizing Hormone (LH)
• In females LH, is responsible ovulation and formation of the corpus luteum. It also stimulates the
secretion of estrogen and progesterone from the ovaries.
• In males, LH stimulates the release of
testosterone from the interstitial cells of Leydig.
- Prolactin (PRL)
• This is the only anterior pituitary hormone that is not tropic. In females it enhances breast
development and milk production.
• Although present in males, its physiological purpose is not clear.
- Follicle-Stimulating Hormone (FSH)
• In females, FSH stimulates the growth and development of ovarian follicles and promotes secretion of
estrogen by the ovaries.
• In males, FSH is required for sperm production.
- Growth Hormone (GH or Somatotropin)
• This is the primary hormone responsible for regulating overall body growth and is also involved in
metabolism.
- Adrenocorticotropic Hormone (ACTH or Adrenocorticotropin)
• Stimulates secretion of cortisol by the adrenal cortex.

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3
Q

Describe the importance of the hypothalamic-hypophyseal portal system.

A

It’s a vascular link b/w the hypothalamus and the anterior pituitary.

The steps:
1) Hypophysiotropic hormones (releasing & inhibiting hormones) are produced by neurosecretory neurons in the hypothalamus which enters the hypothalamic capillaries.

2) These hypothalamic capillaries rejoin to form this portal system which acts as a vascular link to the anterior pituitary.
3) The portal system branches into the capillaries of the anterior pituitary.
4) The hormones (which leaves the blood across the anterior pituitary capillaries) control the release of anterior pituitary hormones.
5) When stimulated by the hypothalamic releasing hormone, the anterior pituitary secretes a hormone into these capillaries.
6) The anterior pituitary capillaries rejoin to form a vein, through which the anterior pituitary hormones leave the ultimate discribition throughout the body by the systemic circulation.

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4
Q

Discuss the difference between nervous and endocrine control under each category

Response time

  • Nervous control:
  • Endocrine control:

Duration of effects:

  • Nervous control:
  • Endocrine control:

Number of targets

  • Nervous control:
  • Endocrine control:
A

Response time

  • Nervous control: rapid response (miliseconds)
  • Endocrine control: slow response (mins-hrs)

Duration of effects:

  • Nervous control: brief in duration (ends when stimulus stops)
  • Endocrine control: long in duration (effects persist after stimulus stops)

Number of targets

  • Nervous control: hard-wired to one specific target (muscle or gland)
  • Endocrine control: many different targets in the body (blood circulates)
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5
Q

What is the pituitary gland and where is it located?

A

The pituitary gland is a very small gland located in a bony cavity at the base of the skull.

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6
Q

The pituitary gland is divided

into two anatomically and functionally distinct lobes. What are they?

A

Posterior Pituitary Gland
- The posterior pituitary gland is comprised of neural-like tissues and is sometimes called the
neurohypophysis.

Anterior Pituitary Gland
- The anterior pituitary gland is comprised of glandular epithelial tissues and is also called the
adenohypophysis.

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7
Q

What does the hypothalamus do?

A

The hypothalamus controls this hormone release, but does so in a different manner for each lobe.

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8
Q

How does the hypothalamus stimulate hormone release in each lobe of the pituitary gland?

A

Posterior pituitary lobe

  • A neural pathway connects the hypothalamus and this lobe
  • There are 2 clusters of neurons, the supraoptic nucleus and th paraventricular nucleus, within the hypothalamus.
  • Axons from the nuclei go down the pituitary stalk (narrow region that connects the hypothalamus and the pituitary) and stop on blood vessels of this lobe.

Anterior pituitary lobe

  • The hypothalamus and this lobe are connected by a vascular link: the hypothalamic-hypophyseal portal system
  • The hypothalamus secretes hormones into this portal which is they carried directly to the lobe where they either inhibit or promote the release of anterior pituitary hormones.
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9
Q

Define the hypothalamic-hypophyseal portal system

A

Arteries and capillaries that carry blood and regulatory
hormones (called releasing hormones) from the hypothalamus to the adenohypophysis (or anterior
pituitary), where the target cells of the releasing hormones are located.

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10
Q

Where are the hormones of the posterior pituitary gland synthesized? What happens after? When are they released?

A

They are synthesized in the neuron bodies located within the hypothalamus.

After, they are packaged into vesicles which are transported down the axons to the nerve endings in the posterior pituitary.

When a stimulus reaches the hypothalamus, these neurons then transmit an action potential that then causes the release of these hormone-containing vesicles into the blood.

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11
Q

Match the hormone with the function and state whether they are an anterior or posterior hormone:

  • FSH
  • GH
  • Vasopressin
  • Oxytocin
  • TSH
  • PRL
  • ACTH
  • LH

1) Uterine contraction during birth and milk ejection during
breastfeeding
- Hormone:
- Anterior or posterior:

2) Regulation of body growth and metabolism
- Hormone:
- Anterior or posterior:

3) Growth and development of ovarian follicles, sperm
production
- Hormone:
- Anterior or posterior:

4) Water retention by kidneys and arteriolar smooth muscle
contraction
- Hormone:
- Anterior or posterior:

5) Cortisol secretion by adrenal cortex
- Hormone:
- Anterior or posterior:

6) Breast development and milk production
- Hormone:
- Anterior or posterior:

7) Release of hormones from the thyroid gland
- Hormone:
- Anterior or posterior:

8) Ovulation and corpus luteum formation
- Hormone:
- Anterior or posterior:

A

1) Uterine contraction during birth and milk ejection during
breastfeeding
- Hormone: oxytocin
- Anterior or posterior: posterior

2) Regulation of body growth and metabolism
- Hormone: GH (growth hormone)
- Anterior or posterior: anterior

3) Growth and development of ovarian follicles, sperm
production
- Hormone: FSH (Follicle-Stimulating Hormone)
- Anterior or posterior: anterior

4) Water retention by kidneys and arteriolar smooth muscle
contraction
- Hormone: Vasopressin
- Anterior or posterior: posterior

5) Cortisol secretion by adrenal cortex
- Hormone: ACTH (Adrenocorticotropic Hormone)
- Anterior or posterior: anterior

6) Breast development and milk production
- Hormone: PRL (Prolactin)
- Anterior or posterior: anterior

7) Release of hormones from the thyroid gland
- Hormone: TSH ( Thyroid-Stimulating Hormone)
- Anterior or posterior: anterior

8) Ovulation and corpus luteum formation
- Hormone: LH (Luteinizing Hormone)
- Anterior or posterior: anterior

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12
Q

How is hormone secretion of the anterior pituitary regulated?

A

Release of these hormones is mainly controlled by hormones produced in the hypothalamus.

Neurosecretory neurons in the hypothalamus produce several releasing and inhibiting hormones.
- Upon stimulation, these hormones are released into the hypothalamic-hypophyseal portal system where they travel to the anterior pituitary to influence the release of its hormones.

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13
Q

What are the hypothalamic hormones and which anterior pituitary hormones do they influence?

A
  • Growth Hormone Inhibiting Hormone (GHIH): inhibits the release of growth hormone and TSH.
  • Prolactin-Inhibiting Hormone (PIH): inhibits the release of prolactin.
  • Prolactin-Releasing Hormone (PRH): stimulates the release of prolactin.
  • Thyrotropin-Releasing Hormone: (TRH): stimulates the release of TSH and prolactin.
  • Growth Hormone Releasing Hormone (GNRH): stimulates the release of growth hormone.
  • Gonadotropin-Releasing Hormone (GnRH): stimulates the release of FSH and LH.
  • Corticotropin-Releasing Hormone (CRH): stimulates the release of ACTH (corticotropin).
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14
Q

Discuss the regulation of hypothalamic hormones.

A

The hypothalamic neurons that secrete these hormones receive lots of inputs that include both neuronal and hormonal and includes both inhibitory and stimulatory inputs.

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15
Q

Some sections of the hypothalamus do not have a blood-brain barrier. What occurs as a result of this?

A

B/c of it, the hypothalamus can sample or monitor the blood and respond to circulating chemicals or even changes
of plasma composition such as osmolarity.

The hypothalamus also receives extensive input from other
brain areas.
- Ex: the connection between the hypothalamus and brain areas
involved in stress and emotion, both of which can lead to hypothalamic hormonal release.

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16
Q

Define the brain-blood barrier.

A

A highly-selective semi-permeable membrane surrounding the brain and spinal
cord that separates the circulating blood from the central nervous system.

17
Q

True or false: Stress is an important factor in the regulation of the release of hypothalamic releasing and inhibiting
hormones.

A

True

18
Q

Discuss the general chain of command for the hypothalamic hormones.

A

3-hormone hierarchic chain of command: hypothalamic hormone is released into the portal system then goes to the pituitary gland to regulate the output of a tropic hormone which is then transported by the systemic circulation to its target endocrine gland, where it regulates secretion of the 3rd hormone, producing its physiological effect

19
Q

Understand negative feedback as it applies to hormones of the hypothalamic-pituitary axis.

A

The hormone ultimately secreted by the target gland acts in a negative-feedback fashion to reduce
secretion of the regulatory hormones higher in the chain of command.

20
Q

Discuss the negative feedback for stress.

A

Stress —(+)—> hypothalamus ——> increases corticotropin-releasing hormone —(+)—> anterior pituitary ——> increases adrenocorticotropic hormone —(+)—> adrenal cortex ——> increases cortisol —(+)—> most cells ——> metabolic changes that help resist stress.

In short, stress stimulates the hypothalamus to release CRH, which causes the release of ACTH from the anterior pituitary. This hormone then causes the release of cortisol from the adrenal cortex. The released cortisol has a negative feedback effect on both the hypothalamus and the anterior pituitary.

21
Q

In response to stress, the hypothalamus increases its secretion of ___

a) epinephrine
b) Corticotropin-releasing hormone
c) Oxytocin
d) Vasopressin

A

b) Corticotropin-releasing hormone

22
Q

Corticotropin-releasing hormone then
stimulates the ____ pituitary to release _____.
a) Anterior, Adrenocorticotropic Hormone
b) Posterior, Cortisol
c) Anterior, Corticotropin-releasing hormone
d) Posterior, Corticotropin-releasing hormone

A

a) Anterior, Adrenocorticotropic Hormone

23
Q 
ACTH then acts on the adrenal \_\_\_\_\_\_ to
release \_\_\_\_\_\_\_\_.
a) Cortex, Corticotropin-releasing Hormone
b) Gland, Cortisol
c) Cortex, Cortisol
d) Medulla, Cortisol
A

c) Cortex, Cortisol

24
Q 
ACTH then acts on the adrenal \_\_\_\_\_\_ to
release \_\_\_\_\_\_\_\_.
a) Cortex, Corticotropin-releasing Hormone
b) Gland, Cortisol
c) Cortex, Cortisol
d) Medulla, Cortisol
A

c) Cortex, Cortisol

25
Q

Cortisol then acts in a negative feedback
fashion to reduce the secretion of regulatory
hormones from the ________ and _____________.
a) Hypothalamus, Posterior Pituitary
b) Hypothalamus, Anterior Pituitary
c) Adrenal Cortex, Anterior Pituitary
d) Anterior Pituitary, Posterior Pituitary

A

b) Hypothalamus, Anterior Pituitary

26
Q

Describe the chain of command for stress.

A

Stress —(+)—> hypothalamus ——> increases corticotropin-releasing hormone —(+)—> anterior pituitary ——> increases adrenocorticotropic hormone —(+)—> adrenal cortex ——> increases cortisol —(+)—> most cells ——> metabolic changes that help resist stress.

In short, stress stimulates the hypothalamus to release CRH, which causes the release of ACTH from the anterior pituitary. This hormone then causes the release of cortisol from the adrenal cortex. The released cortisol has a negative feedback effect on both the hypothalamus and the anterior pituitary

27
Q

Match the hormones to their function:

  • Prolactin-Releasing Hormone (PRH)
  • Growth Hormone Releasing Hormone (GHRH)
  • Prolactin-Inhibiting Hormone (PIH)
  • Corticotropin-Releasing Hormone (CRH)
  • Gonadotropin-Releasing Hormone (GnRH)
  • Thyrotropin-Releasing Hormone (TRH)
  • Growth Hormone Inhibiting Hormone (GHIH)

1) Stimulates the release of ACTH (corticotropin)
2) Stimulates the release of TSH and prolactin
3) Inhibits the release of prolactin
4) Stimulates the release of FSH and LH
5) Inhibits the release of growth hormone and TSH
6) Stimulates the release of growth hormone
7) Stimulates the release of prolactin

A

1) Stimulates the release of ACTH (corticotropin)
- Corticotropin-Releasing Hormone (CRH)

2) Stimulates the release of TSH and prolactin
- Thyrotropin-Releasing Hormone (TRH)

3) Inhibits the release of prolactin
- Prolactin-Inhibiting Hormone (PIH)

4) Stimulates the release of FSH and LH
- Gonadotropin-Releasing Hormone (GnRH)

5) Inhibits the release of growth hormone and TSH
- Growth Hormone Inhibiting Hormone (GHIH)

6) Stimulates the release of growth hormone
- Growth Hormone Releasing Hormone (GHRH)

7) Stimulates the release of prolactin
- Prolactin-Releasing Hormone (PRH)

PHYG 216 (28 decks)

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