hba homeostasis and the endocrine system 2

7/31/2019 HBA Homeostasis and the Endocrine System 2

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Homeostasis and theEndocrine System 2

Dr Terri Meehan-Andrews

School of Human BioscienceAS2 Room 3.07

Email: [email protected]


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Aims and Objectives

Text reference: Chapter 16. The Endocrine System. The Pituitary Gland

and Hypothalamus

Describe the structural and functional relationships

between the hypothalamus and a) the anterior and b) the

posterior pituitary gland

For thyroid hormone describe: actions, synthesis(briefly), hormonal stimulation of synthesis and secretion

and negative feedback control involving hypothalamic

and pituitary hormones


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Hypothalamus

Regulates a wide variety ofphysiological processes:

maintenance of bodytemperature,

water balance, sleeping

feeding

Via the autonomic nervous

system and the neuroendocrinesystem.

Its endocrine functions aremediated by the pituitary gland.

Figure 16.6


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Pituitary Gland Pituitary gland

two-lobed organ that secretes eight major hormones Connected to hypothalamus via infundibulum

Posterior pituitary (neural tissue) Receives, stores, and releases hormones from the hypothalamus

Anterior pituitary, made up of glandular tissue Synthesizes and secretes a number of hormones


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Posterior Pituitary

Neural tissue

Connection: hypothalamic hypophyseal tract

Two hormones are synthesized in the hypothalamus in cell bodies of

neurons

Oxytocin and antidiuretic hormone (ADH)

Hormones

travel down axons of tract into the posterior pituitary

stored in axon terminals

released into circulation when stimulated


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Hypothalamicneuronssynthesize oxytocinand ADH.

Oxytocin and ADH aretransported along thehypothalamic-hypophysealtract to the posteriorpituitary.

Oxytocin and ADH arestored in axon terminalsin the posterior pituitary.

Oxytocin and ADH arereleased into the blood

when hypothalamicneurons fire.

Paraventricularnucleus

Supraopticnucleus

Optic chiasma

Hypothalamus

Inferiorhypophyseal artery

Oxytocin

ADH

Infundibulum(connecting stalk)

Hypothalamic-hypophyseal

tract

Axonterminals

Posteriorlobe of

pituitary

1

2

3

4

Figure 16.5

Relationships of the Posterior pituitary glandand hypothalamus.


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Pituitary Pituitary

Oxytocin

Breast - hormonal trigger for milk ejection or

let down

Uterus - Strong stimulant of uterine

contraction

Anti diuretic hormone Stimulates the Kidney tubules to reabsorb

water (less urine formed)


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Anterior Pituitary

Glandular tissue Connection (vascular)hypophyseal portal

system

Manufactures, stores and secretes 6different hormones (all proteins)

Tropic hormones hormones that regulate

the secretion and growth of otherendocrine glands


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Anterior Pituitary

Stimulus

Hypothalamus (releasing hormone)

Hypophyseal portal system

Anterior pituitary tropic H (2)

Blood stream (circulation)

Endocrine organ

growth, hormone production and secretion


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When appropriately

stimulated,hypothalamic neuronssecrete releasing andinhibiting hormonesinto the primarycapillary plexus.

Hypothalamic hormonestravel through the portalveins to the anterior pituitarywhere they stimulate orinhibit release of hormonesfrom the anterior pituitary.

Anterior pituitaryhormones are secretedinto the secondarycapillary plexus.

Hypothalamus

Hypothalamic neuroncell bodies

Hypophysealportal system Primary capillary

plexus Hypophyseal

portal veins Secondary

capillaryplexus

Superiorhypophyseal artery

Anterior lobeof pituitary

TSH, FSH,LH, ACTH,

GH, PRL

1

2

3

Figure 16.5b

Relationships of the Anterior pituitary glandand hypothalamus.


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Anterior Pituitary

Six hormones

Growth hormone Stimulates growth and metabolism

Prolactin stimulates milk production by the breasts

The tropic hormones (stimulate the secretion of other hormones):

Thyroid-stimulating hormone (TSH)

thyroid hormone synthesis and secretion

Adrenocorticotropic hormone (ACTH)

release of glucocorticoids (cortisol) from the adrenal cortex

Gonadotrophins

Follicle-stimulating hormone (FSH) stimulates follicular

development

Luteinizing hormone (LH) stimulates testosterone

synthesis and production


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Hypothalamus is a key integration centre of the brainUnderstand all of the connections

Signals viathe nervous

system

Anterior Pituitary Posterior Pituitary


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Thyroid Gland The largest endocrine gland, located in the anterior neck, consists of two

lateral lobes connected by a median tissue mass called the isthmus

Composed of follicles that produce the glycoprotein thyroglobulin Colloid (thyroglobulin + iodine) fills the lumen of the follicles and is the

precursor of thyroid hormone

Other endocrine cells, the parafollicular cells, produce the hormonecalcitonin


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Thyroid Hormone

Thyroid hormonethe bodys major metabolic hormone Consists of two closely related iodine-containing compounds

T4 thyroxine; has two tyrosine molecules plus four boundiodine atoms

Converted to T3 at target tissue

T3 triiodothyronine; has two tyrosines with three boundiodine atoms

Biologically active form


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Thyroid Hormone

T4 and T3 are carried in plasma bound bind to

thyroxine-binding globulins (TBGs) produced by

the liver Protects from metabolism and excretion

Mechanisms of activity are similar to steroids

Revise signaling


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Thyroid Hormone

Glucose

oxidation

Metabolic rate

Heat production

Regulating tissuegrowth

CNS

Development

Mentalalertness

Reflexes

Stress

Thyroid produce and secretethyroid hormones

Hypothalamus

Negativefeedback loop

ThyroidReleasing hormone

Thyroid stimulatinghormone

T3 and T4

TemperatureMetabolic Rate


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Pathology

If levels of T3/T4 were low, what wouldhappen to the levels of TRH and TSH?Why?

What do you think would be symptoms forhypothryoidism (low T3/T4 levels)

hba homeostasis and the endocrine system 2

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