Yin Unit2-Neuroendocrinology

8/7/2019 Yin Unit2-Neuroendocrinology

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Prohormone biosynthesis

Receptor

Transportation

in blood

Effector

Response

Endocrine System

Hyperfunction

Endocrine System

Hypofunction

Endocrine gland

Target cell

Degradation

Excretion

Storage

Inputs

Degradation

Excretion

Hyperplasia

Tumor / CancerDestruction

Over stimulationOver inhibition

Secretion

Hormone processing

Review of Endocrine System

Antagonist Agonist

Inhibition Stimulation


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Know Major Hormone Signal

Transduction Pathwaysp 674


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Learning Objectives

By the end of this lecture you will learn about:

The basic neuroanatomy and function of the hypothalamus andpituitary the central endocrine organs.

The definition of neuroendocrinology.

The hypothalamic-pituitary anatomical & functional links. Understand posterior pituitary hormones and their functions.

Know all of the hypothalamic releasing/inhibiting hormones, theircorresponding pituitary hormones, and corresponding targethormones by abbreviation and by full name(s)!

Learn more about negative feedback.

Learn about biological rhythms controlled by hypothalamus andpineal hormones.


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I. Central Endocrine Organs

Brain (hypothalamus) Releasing/inhibiting hormones

Functions include reproduction, lactation, thyroid/metabolism,growth, stress

Anterior pituitary Has corresponding hormones to each hypothalamic hormone

Posterior pituitary Water balance, milk ejection

Pineal Biological rhythms


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What is Neuroendocrinology?

Link between nervous and endocrinesystems.

Primary driving force is typically the nervous

system; the endocrine system responds tonervous system signal; the endocrine systemfeedback to nervous system.

Often a single cell can have both neuronaland endocrine qualities.

Example: The hypothalamus.


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From AC Gore,

Fundamental Neuroscience

Vol 3, Ed. Squire et al, 2008

Overview of Hypothalams Neuroendocrine System

Pay a@enon to feedbackregulaon at

hypothalamus & pituitary


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Anatomical Relationship Between

Hypothalamus & Pituitary


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Hypothalamus

Anterior Pituitary

AKA: Portal Capillary Vasculature

Fig 188, p 676Fig 185, p 671

Hypothalamus

Posterior Pituitary


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Anterior Pituitary

Cells

Capillary

Secretory

vesicles incytoplasm

Posterior Pituitary

Neuroterminals

Nucleus

Extracellularspace

Secretory

vesicles innerve terminals

Electron microscopy (TEM) images of pituitary from a female rat


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II. Hypothalamus - Anterior Pituitary -Target System

Hypothalamic hormones involved in anterior pituitary

regulation are tropic hormones

Stimulate/inhibit hormone secretion of anotherendocrine gland (Anterior pituitary)

Stimulates and maintains the target function.

Most anterior pituitary hormones are tropic hormones

Stimulate/inhibit hormone secretion of another

endocrine gland (Target organ, e.g., thyroid gland,

testis).

Stimulates and maintains their target functions.Loss of secretion of a tropic hormone results in

hypotrophy/atrophy of the target.


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Vascular Link Between Hypothalamus &

Anterior PituitaryFig 18-8, p 676


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Hypothalamic Releasing & Inhibiting Hormones

Hormone Effect on Anterior Pituitary

Thyrotropin-Releasing

hormone (TRH)

Stimulates release of TSH

and prolactin

Corticotropin-Releasing

hormone (CRH)

Stimulates release of ACTH

Gonadotropin-releasinghormone (GnRH)

Stimulates release of FSHand LH

Growth-hormone releasing

hormone (GHRH)

Stimulates release of

growth hormone

Somatostatin (Growth-

hormone inhibiting hormone;

GHIH)

Inhibits release of growth

hormone and TSH

Prolactin-releasing hormone

(PRH)

Stimulates release of

prolactin

Dopamine (Prolactin-inhibiting

hormone; PIH)

Inhibits release of prolactin

Table 18-4, p 674

Secreon of each anterior

pituitary hormone is

smulated or inhibited by

one or more hypothalamic

hypophysiotropic hormones

Not identified yet


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Anterior Pituitary Synthesizes and Secrete 6

Different Protein (Peptide) HormonesTropic:

Thyroid-stimulating hormone(TSH): Stimulates secretion of thyroid hormone

Adrenocorticotropic homone (ACTH): Stimulates secretion of cortisol by adrenal cortex

Follicle-stimulating hormone (FSH): In females, stimulate growth and development of

ovarian follicles; promotes secretion of estrogen by ovaries. In males, required for

sperm production

Luteinizing hormone (LH): In females, responsible for ovulation and luteinization;

regulates ovarian secretion of female sex hormones. In males, stimulates

testosterone secretion.

Growth hormone (GH): Primary hormone responsible for regulating overall body growth;

involved in metabolism. Stimulates IGF-1 secretion.

Not Tropic:

Prolactin (PRL): Enhances breast development and milk production in female.


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Targets of Anterior Pituitary Hormones

Fig 18-6, p 673


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Links Between

Hypothalamic - Anterior Pituitary - Target HormonesGnRH

CRH

TRH

GHRH/ss

PIH (DA)

LH/FSH

ACTH

TSH

GH

PRL

Sex steroid hormonesCorsol (glucocorcoids)

Thyroid hormones

IGFI (also growth)

Milk synthesis


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III. Hypothalamus + Posterior Pituitary -

Target System

1. The paraventricular and supraoptic

nuclei both contain neurons that

produce vasopressin and oxytocin. The

hormone, either vasopressin or oxytocin

depending on the neuron, is synthesizedin the neuronal cell body in the

hypothalamus.

2. The hormone travels down the axon to

be stored in the neuronal terminals

within the posterior pituitary.

3. When the neuron is excited, the storedhormone is released from the terminals

into the systemic blood for distribution

throughout the body.

Fig 185, p 671


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Posterior Pituitary

Along with hypothalamus forms neuroendocrine

system

Does not synthesize any hormones Store and release two small peptide hormones

Vasopressin

Conserves water during urine formation

Oxytocin

Stimulates uterine contraction during childbirth and milk

ejection during breast-feeding


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Vasopressin (VP)

Also called ADH (anti-diuretic hormone) andarginine vasopressin (AVP).

Major function: Enhances water retention by the kidneys; it is

primary regulator of water balance in the body. Result is to cause changes in drinking and salt appetite.

Works together with CRH on stress response.

Arteriolar smooth muscle contraction (bloodpressure) - minor effect

Regulated by osmoreceptors in hypothalamus,that respond to a rise in plasma osmolarity (soluteconcentration).


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Vasopressin and Oxytocin

They are synthesized off of genes located head to head in

opposite orientations.

Each is nine amino acids (nonapeptide) and they are

structurally similar.

Both are in cells that are relative large (20-40 um), known as

magnocellular neurons*.

One type of OT receptor, on breast tissue, pituitary, brain,

uterus, arterioles.

Three types of AVP receptors, on kidney, pituitary, brain.

All receptors are G-protein coupled receptors.

*Contrast this with parvicellular (small) cells of hypothalamicreleasing/inhibiting neurons


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Pineal Gland

Tiny, pinecone-shaped structure

Located in center of brain

Secretes melatonin, a tryptophan metabolite Hormone of darkness

Secretion falls to low levels during light of day

Functions Helps keep bodys circadian rhythms in synchrony with light-dark

cycle

Promotes sleep

Influences reproductive activity, including onset of puberty

Acts as antioxidant to remove free radicals

Enhances immunity

Metatonin


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Circadian Rhythms

Suprachiasmatic nucleus (SCN) Part of hypothalamus

Bodys master biological clock

Self-induced cyclic variations in clock proteinconcentrations within SCN bring about cyclic changesin neural discharge from SCN

Cycle takes about a day

Drives bodys circadian (daily) rhythms

SCN must be set daily by external cues so bodys

biological rhythms are synchronized with activity levelsdriven by surrounding environment

Fundamental Neuroscience, Vol 2 (2002)


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Circadian Rhythms

Daily changes in light intensity

Major environmental cue used to adjust SCN

master clock

Photoreceptors in retina pick up light signalsand transmit them directly to SCN

SCN relays message regarding light status to

pineal gland


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Circadian (Diurnal) Rhythms of Hormones

From: Richter et al., Biological Research 37, 2004


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Examples of Other Circadian Rhythms in Humans

FundamentalNeuroscience,

Vol 2 (2002)

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Yin Unit2-Neuroendocrinology