Chapter 75

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How do adrenal medullae and pituitary gland secrete their hormones?

In response to neural stimuli

What about growth hormone?

It is from anterior pituitary gland, causing growth in most parts of body

What about thyroxine?

It is from thyroid gland, increasing the rate of chemical reactions in almost all body's cells

What does adrenocrticotropic hormone sitmualte?

It is a hormone from anterior pituitary gland stimulating adrenal cortex

What effect do ovarian hormones have?

Effect on female sex organs and econdary sexual charaacteristics of female body

What is placenta?

It is an additional source of sex hormones

What happens without thyroxine and triiodothyronine from thyroid gland?

Almost all chemical reactions of body become sluggish, and person would become sluggish as well

What happens without insulin?

Body's cells could use little of the food carbohydrates for energy

Which are the general classes of hormones?

1) Proteins and polypeptides 2) Steroids 3) Derivatives of amino acid tyrosine

Which are the proteins and polypeptides hormones?

Insulin, glucagon, parathyroid hormone

What are steroids secreted by?

By adrenal cortex (cortisol and aldosterone), ovaries (estrogen and progesterone), testes (testosterone), and placenta (estrogen an dprogesterone)

What are derivatives of amino acid tyrosine secreted by?

By thyroid (thyroxine and triiodothyronine) and adrenal medullae (epinephrine and norepinephrine)

Where are polypeptide and protein hormones stored?

In secretory vesicles until needed

What are proteins?

Polypeptides with 100 or more amino acids (and fewer are peptides)

How are protein and peptide hormones are synthesized where?

On rough end of endoplasmic reticulum, synthesized first as larger proteins that are not biologically active (preprohormones) and are cleaved to form smaller prohormones in endoplasmic retiulum)

Where are prohormones transferred?

To Golgi apparatus for packaging into secretory vesicles

How is secretion of hormones done?

Vesicles are stored within cytoplasm, and are bound to cell membrane until secretion is needed, and are extruded into interstitial fluid or bloodstream by exocytosis

What is the stimulus for exocytosis?

Increased cytosolic calcium concentration

What does increased cyclic adenosine monophosphate (cAMP) lead to?

Subsequent activation of protein kinases that initiate secretion of hormone

What are the peptide hormones?

They are water soluble, allowing them to enter circulatory system easily, where they are carried to their target tissues

What is the chemical structure of steroid hormones?

It is similar to that of cholesterol, and are synthesized from cholesterol

What properties do steroid hormones have?

They are lipid soluble and consist of three cyclohexyl rings and one cyclopentyl ring combined into a single structure

What does happen because of the fact that steroid are highly lipid soluble?

Once they are synthesized, they can simply diffuse across cell membrane and enter interstitial fluid and then the blood

What are amine hormones derived from?

From tyrosine

Thyroid hormones are synthesized and stored in thyroid gland and incorporated into macromolecules of what?

Of the protein thyroglobulin

What happens after entering the blood?

Most of the thyroid hormones combine with plasma proteins, especially thyroxine-binding globulin, which slowly releases the hormones to the target tissues

Where are epinephrine and norepinephrine formed?

In adrenal medulla

Catecholamines are taken up into what?

Into preformed vesicels and stored until secreted

Catecholamines are released from adrenal medullary cells by what process?

By exocytosis

What happens once catecholamines enter circulation?

They can exist in plasma in free form or in conjugation with other substances

When does positive feedback occur?

When biological action of hormone causes additional secretion of hormone

Give an example of positive feedback?

Is the surge of luteinizing hormone (LH) that occurs as a result of stimulatory effect of estrogen on anterior pituitary before ovulation(the secreted LH acts on ovaries to stimulate additonal secretion of estrogen causing more secretion of LH)

What about cyclic variations occuring in hormone release (growth hormone)?

Secretion of growth hormone is markedly increased during early period of sleep but is reduced during later stages of sleep

What about water-soluble hormones (peptides and catecholamines)?

They are dissolved in plasma and transported from their sites of synthesis to target tissues, where they diffuse out of capillaries, and ultimately to target cells

What about steroid and thyroid hormones?

They circulate in blood while being bound to plasma proteins

Which factors can icnrease or decrease concentration of hormone in blood?

1) rate of hormone secretion into the blood 2) rate of removal of hormone from blood which is called metabolic clearance rate

How do we calculate the clearance rate?

1) rate of disappearance of hormone from plasma, 2)plasma concentration of hormone

What is the formula for metabolic clearance rate?

Metabolic clearance rate=Rate of disappearance of hormone from plasma/Concentration of hormone

How are hormones cleared from the plasma, what ways?

1) metabolic destruction by tissues 2) binding with tissues 3) excretion by liver into bile 4) excretion by kidneys into urine

What about the hormones that are bound to plasma proteins (clearance)?

Hormones that are bound to plasma proteins are cleared from blood at much slower rates and may remain in circulation for several hours or even days

What is the first step of a hormone's action?

It is to bind to specific receptors at target cell

What are hormone receptors?

They are large proteins, and each cell that is to be stimulated usually has some 2000 to 100 000 receptors , and each receptor is highly specific for a single hormone

What are the locations for the different types of hormone receptors?

1) In or on surface of cell membrane 2) in cell cytoplasm 3) in cell nucleus (for exmaple thos of thyroid hormones)

How are receptor proteins often inactivated or destroyed?

Down-regulation of receptors can happen due to 1) inactivation of receptor molecules 2) inactivation of intracellular protein ignaling molecules 3) temporary sequestration of receptor to inside of cell 4)destruction of receptors by lysosomes after internalzied 5)decreased production of receptors

What does up-regulation of receptors mean?

Stimulating hormone induces greater than normal formaiton of receptor or intracellular signaling moleculels by target cell or greater availability of receptor for interaction with the hormone

How does a hormone affect its target tissues?

By first forming a hormone-receptor complex, which alters the function of receptor, and the activated receptor initiates hormonal effects

Where do acetylcholien and norepinephrine combine with receptors?

In postsynaptic membrane, causing a change in structure of the receptor, (io channel-linked receptors)

Ion channel-linked receptors do what?

They open or close channels for sodium ions, others for potassium ions, others for calcium ions and so forth

What about G proteins?

Hormones activate receptors indirectly regulating the activity of target proteins by coupling with groups of cell membrane proteins called GTP binding proteins (G proteins)

What about the G protein-coupled receptors?

All have seven transmembrane segments that loop in and out of cell membrane