Endocrine System Lecture 3

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Questions and Answers

What is the primary origin of the anterior pituitary?

Neural tissue

Rathke's pouch (correct)

Hypothalamic tissue

Epithelial tissue of the brain

What type of tissue is the anterior pituitary composed of?

Epithelial tissue

Muscular tissue

Glandular tissue (correct)

Neural tissue

What is the function of the portal vein in the hypothalamo-hypophyseal portal circulation?

To connect the capillary beds in the hypothalamus and anterior pituitary (correct)

To regulate the sympathetic nervous system

To stimulate the release of prolactin hormone

To transport hormones from the anterior pituitary to the hypothalamus

How does the anterior pituitary receive hormonal input from the hypothalamus?

Through the portal blood system Signup and view all the answers

What is the primary function of prolactin hormone?

To stimulate milk synthesis in breasts Signup and view all the answers

What is the function of the portal blood system in the hypothalamic-pituitary axis?

To allow for blood to flow through two consecutive capillary beds before returning to the heart Signup and view all the answers

What is the role of dopamine in regulating prolactin hormone?

It inhibits the release of prolactin hormone Signup and view all the answers

What is the primary function of the anterior pituitary?

To synthesize and secrete hormones in response to neural input from the hypothalamus Signup and view all the answers

What stimulates the release of prolactin hormone?

Suckling and hearing infant cries Signup and view all the answers

What is TRUE about the hypothalamic-pituitary axis?

It involves the direct transportation of hormones from the hypothalamus to the pituitary through the portal blood system Signup and view all the answers

What is the function of the adrenal medulla?

To secrete catecholamines as part of the sympathetic nervous system Signup and view all the answers

What is the function of the adrenal cortex?

To secrete steroids, including corticosteroids and androgens Signup and view all the answers

What is the role of the hypothalamus in the hypothalamic-pituitary axis?

To regulate the release of hormones from the pituitary gland Signup and view all the answers

What is the role of the hypothalamic-pituitary axis in regulating the adrenal glands?

It regulates the release of steroids from the adrenal cortex Signup and view all the answers

What is the significance of the hypothalamic-pituitary axis?

It enables the regulation of hormone production and secretion by the pituitary gland Signup and view all the answers

What is the pathway by which the hypothalamic-pituitary axis regulates the release of prolactin hormone?

Hypothalamus → anterior pituitary → prolactin hormone Signup and view all the answers

What is the primary function of aldosterone?

Retention of Na+ and excretion of K+ Signup and view all the answers

Which hormone stimulates the synthesis and secretion of glucocorticoids?

Adrenocorticotropic Hormone (ACTH) Signup and view all the answers

What is the role of Corticotropin-Releasing Hormone (CRH) in the HPA axis?

Stimulation of anterior pituitary to synthesize and secrete ACTH Signup and view all the answers

What is the precursor molecule for corticosteroids?

Pregnenolone Signup and view all the answers

Which hormone is a weak androgen?

Dehydroepiandrosterone (DHEA) Signup and view all the answers

What is the primary function of glucocorticoids?

Influence on metabolism and stress response Signup and view all the answers

Which hormone is controlled by LH from the anterior pituitary?

Dehydroepiandrosterone (DHEA) Signup and view all the answers

What is the effect of glucocorticoids on the hypothalamus and pituitary?

Feedback to inhibit CRH and ACTH secretion Signup and view all the answers

What is the primary function of the autonomic nervous system?

To send motor output to internal organs Signup and view all the answers

What is the main effect of epinephrine and norepinephrine on the cardiovascular system?

Increased heart rate and cardiac output Signup and view all the answers

What is the role of the parasympathetic branch of the autonomic nervous system?

To promote the 'rest and digest' response Signup and view all the answers

What is the primary function of the hypothalamic-pituitary-thyroid axis?

To regulate thyroid hormone production Signup and view all the answers

What is the primary function of thyrotropin-releasing hormone (TRH)?

To bind to receptors on the anterior pituitary to stimulate TSH production Signup and view all the answers

What is the primary function of thyroid-stimulating hormone (TSH)?

To stimulate the growth of thyroid cells and the production of thyroid hormones Signup and view all the answers

What is the effect of epinephrine and norepinephrine on glucose metabolism?

Increased blood glucose levels Signup and view all the answers

What is the relationship between the sympathetic and parasympathetic branches of the autonomic nervous system?

They have opposite effects on the body, with the sympathetic branch stimulating the 'fight or flight' response and the parasympathetic branch promoting the 'rest and digest' response Signup and view all the answers

What is the primary function of triiodothyronine (T3) and tetraiodothyronine (T4) in the body?

To act on most cells of the body, altering gene expression Signup and view all the answers

What is the primary difference between T3 and T4?

T3 has higher bioactivity, while T4 is more abundant in circulation Signup and view all the answers

What is the effect of T3 and T4 on oxygen consumption in most tissues?

Increase oxygen consumption Signup and view all the answers

Which of the following is a common cause of hypothyroidism?

Iodine deficiency Signup and view all the answers

What is the effect of T3 and T4 on protein metabolism?

They affect protein, carbohydrate, and fat metabolism Signup and view all the answers

What is the role of T3 and T4 in children?

They are necessary for normal growth and development Signup and view all the answers

What is the characteristic of T3 and T4 in terms of their circulation in the bloodstream?

They are lipophilic and circulate bound to carrier proteins Signup and view all the answers

What is the effect of low thyroid hormone levels on the thyroid gland?

It leads to an increase in TSH secretion, potentially causing goiter Signup and view all the answers

Study Notes

The Anterior Pituitary

Develops from outpocketing of the roof of the mouth (Rathke's pouch; epithelial tissue)
Glandular tissue (non-neural) that receives little neural input
Synthesizes and secretes hormones in response to blood-borne hormones received from the hypothalamus
Receives direct blood circulation from the hypothalamus (portal system)

Portal Blood System

Hypothalamo-hypophyseal portal circulation connects capillary beds in the hypothalamus and anterior pituitary
Closed, direct, one-way circulation from the hypothalamus to the anterior pituitary
Materials can enter and exit the blood only at the capillary beds

Anterior Pituitary Function

Releases hormones in response to releasing hormones from the hypothalamus
Releasing hormones are synthesized in neurosecretory cells in the hypothalamus and transported to the anterior pituitary
Anterior pituitary cells release hormones in response to stimulating hormones, which then circulate throughout the body

Prolactin

Protein hormone from the anterior pituitary that stimulates milk synthesis in breasts
Has other functions, including:
- Parental behavior
- Osmoregulation
- Growth and development
- Stress response
Under mainly inhibitory hypothalamic control by dopamine (or prolactin inhibiting hormone, PIH)
Stimulated by suckling and hearing infant cries, which stimulates thyrotropin releasing hormone (TRH) and prolactin secretion

The Hypothalamic-Pituitary-Adrenal (HPA) Axis

Hypothalamic hormone: Corticotropin-releasing hormone (CRH) stimulates anterior pituitary to synthesize and secrete adrenocorticotropic hormone (ACTH)
Anterior pituitary hormone: ACTH stimulates adrenal cortex to synthesize and secrete glucocorticoids
Adrenocortical hormones: Glucocorticoids (cortisol, corticosterone) feed back to hypothalamus and pituitary to inhibit CRH and ACTH secretion

Adrenal Glands

Sit on top of kidneys like little party hats
Comprise two distinct organs: adrenal medulla (inner region) and adrenal cortex (outer region)
Adrenal medulla secretes catecholamines (epinephrine, norepinephrine) as part of the sympathetic nervous system
Adrenal cortex secretes steroids (corticosteroids and androgens)

Adrenal Cortex

Glandular tissue with three zones producing different steroid hormones
Aldosterone (mineralocorticoid) regulates mineral and water metabolism
Cortisol, corticosterone (glucocorticoids) regulate glucose metabolism, stress response, and other functions
Dehydroepiandrosterone (DHEA) (androgen) has a role in aging

Hypothalamic-Pituitary-Thyroid (HPT) Axis

Hypothalamic hormone: Thyrotropin-releasing hormone (TRH) stimulates anterior pituitary to synthesize and secrete thyroid-stimulating hormone (TSH)
Anterior pituitary hormone: TSH stimulates thyroid gland to synthesize and secrete thyroid hormones
Thyroid hormones: Triiodothyronine (T3), tetraiodothyronine (T4; thyroxine) regulate metabolism, growth, and development

Thyroid Hormones

Iodinated dimers of tyrosine
T4 is converted to T3 in target cells
Bind to nuclear receptors or membrane receptors to regulate gene expression and metabolism
Functions in adults:
- Increase oxygen consumption in most tissues
- Increase thermogenesis
- Affect protein, carbohydrate, and fat metabolism
- Permissive effects on reproduction
Functions in children:
- Necessary for normal growth and development (especially in the nervous system - synapses, myelin)

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Description

This lecture covers the anterior pituitary, prolactin, adrenal glands, and the hypothalamic-pituitary-thyroid axis. Learn how these systems interact and are controlled by the hypothalamus.