Neuroendocrine

Question 1

What are the three main components of the neuroendocrine system, and how do they interact?

Answer 1

Brain (Hypothalamus): Signals the pituitary gland.
Pituitary Gland: Signals target glands.
Target Glands: Release hormones that act on tissues.

Question 2

What are the three patterns of brain signaling in the neuroendocrine system?

Answer 2

Circadian, pulsatile, and reactive.

Question 3

What is the role of the hypothalamus in neuroendocrine regulation?

Answer 3

The hypothalamus is the primary structure for transmitting signals from the central nervous system to the endocrine system through releasing hormones.

Question 4

What is the function of the pituitary gland?

Answer 4

The pituitary gland is the ‘master gland’ that triggers endocrine responses through stimulating hormones.

Question 5

What is the role of target glands in the neuroendocrine system?

Answer 5

Target glands release hormones that act on various body tissues.

Question 6

What and where is the hypothalamus?

Answer 6

The hypothalamus is a group of nuclei located in the diencephalon.

Question 7

Describe the boundaries of the hypothalamus.

Answer 7

Rostral: Lamina terminalis
Dorsal: Hypothalamic sulcus
Lateral: Substantia innominata and internal capsule
Medial: Inferior portion of the third ventricle
Caudal: Merges into the midbrain tegmentum and periaqueductal gray.

Question 8

Who established the criteria for a releasing factor, and what year?

Answer 8

Geoffrey Harris in 1955.

Question 9

What are the criteria for a substance to be considered a releasing factor for adenohypophysial hormones?

Answer 9

The substance must be present in higher concentrations in hypophyseal portal vessels than in systemic blood vessels.
The substance’s concentration in hypophyseal portal vessels should vary based on the electrical or reflexive actions of hypothalamic nerves.
Activity in the adenohypophysis (anterior pituitary) must be correlated with the substance’s varying concentrations in hypophyseal portal vessels.
Cells in the adenohypophysis must be responsive to the substance (releasing hormone).

Question 10

How are cells that respond to hypothalamic releasing hormones organized in the pituitary gland?

Answer 10

These cells are mixed in proportions throughout the pituitary gland.

Question 11

Name the three mechanisms of hormone action.

Answer 11

Classical genomic interaction
Non-classical genomic interaction
Non-classical non-genomic pathways.

Question 12

What determines the specific effects a hormone has on a cell?

Answer 12

Receptor type on the cell
Characteristics of the receiving neuron.

Question 13

What is the main function of the HPA axis?

Answer 13

The HPA axis is primarily involved in the body’s response to stress and arousal.

Question 14

What are the key steps in the HPA axis pathway?

Answer 14

Hypothalamus (PVN): Releases corticotropin-releasing hormone (CRH) in response to stress or arousal.
Anterior Pituitary: CRH stimulates the release of adrenocorticotropic hormone (ACTH).
Adrenal Cortex: ACTH acts on the adrenal cortex to release cortisol (humans) or corticosterone (rodents).

Question 15

What are the two main types of receptors for glucocorticoids, and how do they differ?

Answer 15

Mineralocorticoid receptors (MR): High affinity, primarily bound during the circadian cycle.
Glucocorticoid receptors (GR): Low affinity, become occupied during periods of arousal or stress.

Question 16

How does negative feedback regulate the HPA axis?

Answer 16

Cortisol (or corticosterone) inhibits the release of CRH from the hypothalamus and ACTH from the anterior pituitary.

Question 17

What happens to the HPA axis during chronic stress?

Answer 17

Chronic stress can disrupt the normal circadian rhythm of cortisol release.
This dysregulation can negatively impact cognitive function, particularly learning and memory.

Question 18

What other factors can influence the activity of the HPA axis?

Answer 18

Inhibitory: GABA, somatostatin, endocannabinoids
Stimulatory: Low cortisol levels, catecholamines, glutamate
Feeding signals.

Question 19

What is a significant implication of HPA axis dysregulation?

Answer 19

HPA axis dysregulation is implicated in conditions like depression.

Question 20

How is the production of ACTH related to beta-endorphin?

Answer 20

ACTH is cleaved from a larger peptide called POMC. Beta-endorphin is a byproduct of this cleavage process.

Question 21

What is the significance of the co-release of ACTH and beta-endorphin?

Answer 21

It suggests a coordinated response to stress, where ACTH mobilizes the body and beta-endorphin inhibits pain.

Question 22

What is important to consider regarding the different layers of the adrenal cortex?

Answer 22

Each layer of the adrenal cortex contains different cell types that produce different steroids, including glucocorticoids, androgens, and mineralocorticoids.

Question 23

What is the main role of the HPT axis?

Answer 23

The HPT axis is crucial for regulating cellular metabolism.

Question 24

Outline the key steps in the HPT axis pathway.

Answer 24

Hypothalamus: Releases thyrotropin-releasing hormone (TRH).
Anterior Pituitary: TRH stimulates the release of thyroid-stimulating hormone (TSH).
Thyroid Gland: TSH acts on the thyroid gland to release thyroid hormones (T3 and T4).

Question 25

How does negative feedback regulate the HPT axis?

Answer 25

Thyroid hormones (T3 and T4) inhibit the release of TRH from the hypothalamus and TSH from the anterior pituitary.

Question 26

Explain how binding globulins influence HPT axis regulation.

Answer 26

Binding globulins, like albumin, bind to thyroid hormones, rendering them inactive. Dysregulation can occur if there are changes in the levels of these binding proteins, affecting the amount of free (active) hormone.

Question 27

List the factors that can influence HPT axis activity.

Answer 27

Temperature Physical activity Glucocorticoids (inhibitory) Metabolic signals.

Question 28

What is the primary function of the HPL axis?

Answer 28

This axis is involved in growth and metabolism, particularly through the release of insulin-like growth factor-1 (IGF-1).

Question 29

What are the main steps involved in the HPL axis pathway?

Answer 29

Hypothalamus: Releases growth hormone-releasing hormone (GHRH). Anterior Pituitary: GHRH stimulates the release of growth hormone (GH). Liver: GH acts on the liver to release insulin-like growth factor-1 (IGF-1).

Question 30

What is the negative feedback mechanism in the HPL axis?

Answer 30

IGF-1 inhibits the release of GHRH and GH. Additionally, somatostatin directly inhibits GH release.

Question 31

What contributes to the complexity of the HPL axis regulation?

Answer 31

The HPL axis is regulated by multiple signaling pathways and involves the interplay of both stimulatory (GHRH) and inhibitory (somatostatin) neurons.

Question 32

How is the HPL axis unique in its influence?

Answer 32

The HPL axis is particularly influenced by the actions of other hormones in the body.

Question 33

Describe the primary function of the Hypothalamic-Pituitary-Mammary axis.

Answer 33

This axis is primarily involved in milk production.

Question 34

What are the main components of the Hypothalamic-Pituitary-Mammary axis pathway?

Answer 34

Hypothalamus: Releases dopamine, which acts as a prolactin-inhibiting hormone. Anterior Pituitary: Dopamine inhibits the release of prolactin (PRL). Mammary Gland: PRL acts on the mammary gland to stimulate milk production.

Question 35

What are some possible dysregulation mechanisms in this axis?

Answer 35

While the sources don't specifically elaborate on dysregulation, potential mechanisms could include alterations in dopamine signaling or prolactin receptor sensitivity.

Question 36

How does this axis differ from typical hypothalamic-pituitary-target gland axes?

Answer 36

This axis deviates slightly from the typical pattern because milk itself is not a hormone that circulates in the bloodstream to act on distant tissues. Instead, it is produced and utilized locally within the mammary gland.

Question 37

What is the primary function of the HPG axis?

Answer 37

The HPG axis regulates reproductive function in both males and females.

Question 38

What are the main steps in the HPG axis?

Answer 38

Hypothalamus: Releases gonadotropin-releasing hormone (GnRH). Anterior Pituitary: GnRH stimulates the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Gonads: LH and FSH act on the gonads (testes in males and ovaries in females) to stimulate the release of gonadal steroids (estrogens, progestins, and androgens).

Question 39

Explain the negative feedback loop within the HPG axis.

Answer 39

Gonadal steroids inhibit the release of GnRH from the hypothalamus and LH and FSH from the anterior pituitary.

Question 40

What is a key factor influencing the HPG axis, particularly in females?

Answer 40

The menstrual cycle (or estrous cycle in other mammals) significantly influences the HPG axis in females due to cyclical fluctuations in hormone levels.

Question 41

How does the pattern of GnRH release affect LH and FSH secretion?

Answer 41

Pulsatile GnRH release: Essential for normal LH and FSH secretion. Continuous GnRH administration: Suppresses LH and FSH release. Faster GnRH pulse frequency: Favors LH release. Slower GnRH pulse frequency: Favors FSH release.

Question 42

Explain the concept of 'fluid targets' in the HPG axis.

Answer 42

The receptors for gonadal steroids in target tissues, like the brain and reproductive organs, can change in their expression levels throughout the reproductive cycle. This means that the responsiveness of these tissues to hormones fluctuates over time.

Question 43

How does estradiol influence brain connectivity?

Answer 43

Estradiol affects synaptic plasticity, particularly by influencing the density of dendritic spines, which are important for learning and memory. These changes are dynamic and fluctuate with the levels of estradiol across the cycle.

Question 44

What is the significance of the masculinization of the hypothalamus in the context of the HPG axis?

Answer 44

During development, exposure to androgens can masculinize the hypothalamus, making it less responsive to estradiol surges later in life. This is important because in females, the surge of estradiol before ovulation is crucial for triggering the release of GnRH, which in turn stimulates the LH surge necessary for ovulation. In males, the masculinized hypothalamus does not respond to estradiol in this way, preventing the positive feedback loop that leads to ovulation.

Question 45

What distinguishes the posterior pituitary from the anterior pituitary in terms of its connection to the hypothalamus?

Answer 45

The posterior pituitary receives direct neuronal connections from the hypothalamus, while the anterior pituitary is connected via the hypophyseal portal system.

Question 46

Which hormones are released from the posterior pituitary, and where are they produced?

Answer 46

Vasopressin: Produced in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus. Oxytocin: Also produced in the PVN and SON.

Question 47

What is a primary function of vasopressin, and how is it regulated?

Answer 47

Vasopressin is involved in fluid balance. Regulation involves signals from receptors in the bloodstream that are sensitive to changes in blood composition, such as baroreceptors that detect pressure changes and osmoreceptors that sense osmolarity.

Question 48

What are some potential ways dysregulation could occur in the posterior pituitary?

Answer 48

Although not specifically addressed in the sources, dysregulation could involve: Altered signaling from receptors that monitor blood composition. Changes in the release of vasopressin and oxytocin from the posterior pituitary. Changes in the sensitivity or function of vasopressin and oxytocin receptors in target tissues.

Question 49

Distinguish between sexual determination and sexual differentiation.

Answer 49

Sexual determination: The genetic determination of sex, based on the sex chromosomes (XX for female, XY for male). Sexual differentiation: The process by which the body develops male or female characteristics, driven by hormonal influences.

Question 50

What is the role of the SRY gene in sexual differentiation?

Answer 50

The SRY gene on the Y chromosome is responsible for masculinizing the gonads, leading to the development of testes.

Question 51

How do the testes contribute to masculinization?

Answer 51

Testes secrete anti-Müllerian hormone, which promotes the development of male external genitalia and suppresses the development of the female reproductive tract. Testes also produce testosterone, the primary androgen responsible for masculinizing other tissues in the body, including the brain.

Question 52

When do critical periods for sexual differentiation occur?

Answer 52

Rodents: Perinatal period (around the time of birth). Primates: Late second/early third trimester of gestation.

Question 53

What hormone do testes secrete, and what is its role?

Answer 53

Testes secrete anti-Müllerian hormone, which promotes the development of male external genitalia and suppresses the development of the female reproductive tract.

Question 54

What do testes produce that is responsible for masculinizing tissues?

Answer 54

Testes produce testosterone, the primary androgen responsible for masculinizing other tissues in the body, including the brain.

Question 55

When do critical periods for sexual differentiation occur in rodents?

Answer 55

Critical periods for sexual differentiation in rodents occur during the perinatal period (around the time of birth).

Question 56

When do critical periods for sexual differentiation occur in primates?

Answer 56

Critical periods for sexual differentiation in primates occur during the late second/early third trimester of gestation.

Question 57

What is the significance of the early androgen surge during critical periods?

Answer 57

This surge of testosterone masculinizes the brain, organizing neural circuits in a male-typical way.

Question 58

What evidence suggests that the SRY gene may affect the brain independent of hormones?

Answer 58

Studies have shown that blocking SRY expression in adult male rats can alter dopamine signaling in the brain and lead to motor impairments, even though the hormonal environment remains male-typical.

Question 59

What are the implications of the findings about the SRY gene's independent effects?

Answer 59

This suggests that sexual differentiation of the brain is not solely determined by hormones but also involves direct genetic influences from the sex chromosomes.