Exam 2 (Lecture 1) - Intro to Endocrine Physiology

Question 1

Explain Berthold’s experiment (observations/conclusion).

Answer 1

Took place in 1894 with chickens

Observation #1: Removal of testes (before puberty) leads to caponization (female-like) phenotype

Observation #2: Transplanted testes supported the development of male phenotype. This effect was not mediated by nerves, because he had cut the nerves before implantation

Conclusion: Postulated existence of a substance that travels through the bloodstream to target organs = (hormones); discovered presence of testosterone, even though it wasn’t known yet

Question 2

What do you need to be able to do in order to define what a hormone is?

Answer 2

Answer these 3 questions:

1) What is it?
2) What it its chemical nature?
3) What does it do at the target tissue?

Question 3

So…

What is it?

Answer 3

A signaling molecule released by a cell and conveyed by the blood stream, by neural axons, or by local diffusion to cells in target tissues.

Question 4

What is its chemical nature?

Answer 4

Protein, peptide, catecholamine, steroid or iodinated tyrosine derivative.

Question 5

What does it do at the target tissue?

Answer 5

Regulates existing metabolic pathways (through second messengers) OR

Regulates synthesis of enzymes and other proteins at the DNA level.

**In this way, it regulates the rates of specific reactions without itself contributing energy or initiating the process (ie hormones DO NOT start the process; they REGULATE it)

Question 6

Hormones

Answer 6

Products of cells (signaling molecules)

Question 7

Endocrine secretion

Answer 7

Hormone-releasing cells secrete hormones into the internal environment

Question 8

Endocrine cells

Answer 8

Cells that release hormones into the environment in which they live (interstitial fluid); can be found in endocrine glands or scattered throughout tissues

Question 9

Endocrine glands

Answer 9

Specialized glands made up of endocrine cells; hormones leave here and can diffuse into blood, for example, and travel to target tissues

Question 10

Endocrine system

Answer 10

The collection of endocrine glands and other endocrine cells

Question 11

Endocrinology

Answer 11

Sub-discipline of physiology that studies the endocrine system

Question 12

Exocrine glands

Answer 12

Release secretions outside the body; typically in ducts first and then out to the outside. (Example is acinar glands in pancreas (main part of pancreas) that dumps hormones into duodenum)

Question 13

What is the function of the endocrine system?

Answer 13

To regulate:

1) Metabolism
2) Fluid status
3) Growth
4) Sexual development
5) Reproduction

*The endocrine and nervous systems work together to maintain homeostasis

Question 14

What is an autocrine cell?

Answer 14

A cell that has receptors for the hormone it releases; hormone acts on the cell that released it

Question 15

What is a paracrine cell?

Answer 15

Hormone acts on adjacent cells without entering the blood stream (based on diffusion)

VERY common type

Question 16

What is an endocrine cell?

Answer 16

Before reaching the target cells, hormones first enter the blood stream (via exocytosis); then diffuse out of the blood to act on target cell(s)

Question 17

What is a neurocrine (neuroendocrine) cell?

Answer 17

Hormone secreted by neuron; interaction between neurons and endocrine cells

Question 18

What are the 5 categories of hormones?

Answer 18

1) Peptide, protein, and glycoprotein hormones

2) Catecholamine hormones

3) Thyroid hormones

4) Steroid hormones

5) Non-traditional hormones (cytokines, prostaglandins)

Question 19

What are characteristics of peptide and protein (and glycoprotein) hormones?

Answer 19

1) Synthesis: DNA –> mRNA –> preprohormone –> pro hormone –> hormone (ie larger molecule cleaved to smaller molecule)

2) Storage: in secretory granules (vesicles) originating from Golgi complex

3) Secretion: Exocytosis

*Water or lipid-soluble

Question 20

What are examples of peptide and protein hormones?

Answer 20

Peptides: vasopressin, oxytocin, glucagon

Proteins: insulin, growth hormones, prolactin

Question 21

What are characteristics of catecholamine hormones?

Answer 21

1) Synthesis: From amino acids and tyrosine

2) Storage: In secretory granules (vesicles)

3) Release: By exocytosis

*Soluble in water; determines how quickly it can diffuse (ie interstitial fluid is water-based so would diffuse well/quickly)

Question 22

What are examples of catecholamine hormones?

Answer 22

Epinephrine, norepinephrine, dopamine

Question 23

What are characteristics of thyroid hormones?

Answer 23

1) Synthesis: From tyrosine and iodide (most synthesis is extracellular)

2) Storage: Extracellularly in follicles of thyroid gland

3) Secretion: Retrieval from the follicle and enzymatic release from the storage protein

*Lipophilic (hydrophobic) - transported in plasma where they are bound to carrier proteins; they are charged and thus CANNOT cross membranes freely; their uptake is mediated by transporters

Question 24

What are examples of thyroid hormones?

Answer 24

Thyroxine (T4) and triiodothyronine (T3)

Question 25

What are characteristics of steroid hormones?

Answer 25

1) Synthesis: From cholesterol

2) Storage: Not stored in the gland of origin or elsewhere - the increase of secretion is achieved by mobilizing the synthesis from cholesterol

3) Release: Transported in plasma where they are bound to carrier proteins

*Lipophilic, but CAN cross cell membranes easily

Question 26

What mechanism controls hormone secretion?

Answer 26

Negative feedback.

It’s a closed loop; the outcome of the process has affect on the beginning (inhibition is the effect)

Common, stable, and CRITICAL for the maintenance of homeostasis

Question 27

Positive Feedback

Answer 27

Rare; controls surges of hormones

The outcome of the process has affect on the beginning to produce more of the same outcome (produce more hormone)

Rare, but sometimes necessary
Unstable
Used when a surge of hormone is required, such as luteinizing hormone surge before ovulation

Question 28

What happens to hormones after they are released to the extracellular fluid?

Answer 28

After release into the ECF, hormones circulate either free or bound to other plasma constituents

Eventually, hormones are taken up be cells and are metabolically degraded, excreted in urine, or excreted in bile

Question 29

What is the hormone half-life time?

Answer 29

The time during which the hormone loses 50% of its biological activity

t1/2 varies between hormones. Peptide/proteins range from minutes to tens of minutes; vitamin D is ~ 15 days