Biology chapter 5

Question 1

What are glands?

Answer 1

Organs in the endocrine system that secrete hormones.

Question 2

What are hormones?

Answer 2

Signaling molecules that are secreted directly into the bloodstream to distant target tissues.

Question 3

VIP NOTES:

Answer 3

At target tissues, hormones bind to receptors and then induces a change in gene expression or cellular functioning.

Not all hormones share the same structure and function.

Question 4

Hormones can be subdivided into categories based on different criteria. First, hormones can be classified by their chemical identifies. What are the three types of hormones based on chemical identifies?

Answer 4

1. peptides
2. steroids
3. Amino-acid derivatives

Question 5

What are peptide hormones (How are they made)? Derived from what?

Answer 5

Peptide hormones are made up of amino acids ranging from quite small (sush as anti-diuretic hormones, ADH) to relatively large (such as insulin).

Peptide hormones are all derived from larger precursor polypetides that are cleaved during post-translational modification.

These smaller units are then transported to the golgi-apparatus for further modifications that activate the hormones and direct them to the correct locations in the cell.

Such hormones are released by exocytosis after being packaged into vesicles.

Question 6

Since peptide hormones are charged and cannot pass through the plasma membrane, what must they do? (explain what is first messenger and second messenger?)

Answer 6

Because peptide hormones are charged and cannot pass through the plasma membrane, they must bind to an extra-cellular receptor.

Accordingly, the peptide hormone is considered the first messenger, as it binds to the receptor and triggers the transmission of a second signal, known as the second messenger.

NOTE: There are many different receptor subtypes, and the type of receptor determines what happens once the hormone has stimulated the receptor.

Question 7

Explain what is meant by signaling cascade and amplification? provide an example.

Answer 7

The connection between the hormone at the surface (binding to the receptor at the plasma membrane) and the effect brought about by the second messengers within the cell is known as the signaling cascade.

For example, one hormone molecule may bind to multiple receptors before it is degraded.
Also, each receptor may activate multiple enzymes, each of which will trigger the production of larger quantities of second messegners. Thus, each step can result in an increase in signal intensity.

Question 8

What are three common second messangers?

Answer 8

1. cAMP
2. IP3
3. Calcium

Question 9

Explain the full pathway of a hormone binding to a G-protein coupled receptor (GPCR)?

Answer 9

1. Hormone binding the GPCR and activating it
2. The GPCR then either activate or initiate an enzyme called adenylate cyclase, which then rise or lower the levels of cAMP (second messageners) accordingly. (it either activates or initiates based on the type of GPCR receptor).
3. in case of rising it, cAMP then bind to intracellular targets, such as protein kinase A, which phosphorylates transcription factors like cAMP response element-binding protein (CREB) to exert the hormone’s ultimate effect.

NOTE: protein kinase A can modify other enzymes as well as transciption factors, and therefore it can have a rapid or slow effect on the cell.

Question 10

Compare and contrast between peptide hormones and steroid hormones?

Answer 10

Peptide:
1. the effects of peptide hormones are usually rapid but short lived because these hormones act through second messenger cascades, which are transient. (it is quicker to turn them on and off, compared with steroid hormones, but their effects do not last without relatively constant stimulation)
2. Peptide hormones are generally water-soluble, and thus they can travel freely in the bloodstream and usually do not require carriers.

Steroids:
1. The effects of steroid hormones are slower but longer lived because steroid hormones participate in gene regulation, causing alterations in the amount of mRNA and protein present in a cell by direct action on DNA.
2. Steroid hormones are not water soluble, so they must be carried by proteins in the bloodstream to travel around the body.
– Some of these protein carriers are very specific and carry only one type of hormones (such as sex hormone-binding globulin), while others non-specific (such as albumin).

Question 11

What are steroid hormones (made of what and produced by what)? Derived from what and that helps them be able to do what?

Answer 11

Steroid hormones are derived from cholesterol and are produced primarily by the gonads and adrenal cortex.

Steroid hormones are derived from non-polar molecules, and that makes them easily able to cross the cell membrane. Hence, their receptors are usually intracellular (in the cytosol) or intranuclear (in the nucleus).

Question 12

Explain the pathway of a steroid hormone binding to its receptor?

Answer 12

Upon binding of the steroid hormone to its receptor (either in the cytosol or in the nucleus), it forms a steroid hormone-receptor complexes.
These complexes then undergo conformational changed. A common form of conformational change is dimerization, which is the pairing of two receptor-hormone complexes.
The receptor complex can then bind directly to DNA, resulting in either increased or decreased transcription of particular genes (depending on the identity of the hormone).

Question 13

What is meant by the levels of carrier proteins can change the levels of active hormone?

Answer 13

Hormones are generally inactive while being attached to a carrier protein and must dissociate from the carrier to function.
Therefore, levels of carrier proteins can change the levels of active hormone.
For example, some conditions increase the quantity of a protein that carries thyroid hormones (TBG). This causes the body to percieve a lower level of thyroid hormone because the increased quantity of TBG binds a larger proportion of the hormone and thus there is less free hormone available to the body/cells.

Question 14

Amino acid- derviate hormones are less common than peptide and steroid hormones but include some important ones. What are these hormones?

Answer 14

Epinephrine, norepinephrine, triiodothronine, and thyroxine.

Question 15

Describe these hormones are derived from what?

Answer 15

These hormones are derived from one or two amino acids, usually with a few additional modifications.

For example, thyroid hormones are made from tyrosine and modified by the addition of several iodine atoms.

Question 16

VIP NOTE:

Answer 16

The chemistry of this family of hormones is considered less predictable and is one of the few instances where overt memorization is the best strategy.

For example, the catecholamines (epinephrine and noepinephrine) bind to GPCR, while thyroid hormones bind intracelluarly.

Question 17

What are direct hormones? Give an example?

Answer 17

Hormones secreted and act directly on a target tissue.

For example, insulin released by the pancreas causes increased uptake of glucose by muscle tissues (IE: acts on muscle tissues).

Question 18

What are tropic hormones? Give an example? Where do they usually originate?

Answer 18

Other hormones, known as tropic hormones, require an intermediary to act.

For example, GnRH from the hypothalamus stimulates the release of LH and FSH. LH then acts on the gonads to stimulate testosterone production in males and estrogen production in females.
GnRH and LH do not cause direct changes in the physiology of muscle, bone, and hair follicles; rather, they stimulate the production of another hormone (testerone) by another endocrine gland (gonads) that acts on these target tissues.

Usually in the brain and anterior pituatary gland, allowing for the coordination of multiple processes within the body.

Question 19

List all the endocrine glands? What is each of these organs capable of doing?

Answer 19

1. Hypothalamus
2. Pituitary
3. Thyroid
4. Parathyroid
5. Adrenal
6. Pancreas
7. Gonads (testes and ovaries)
8. Pineal

Each of these organs are capable of synthesizing and secreting one or more hormones.

FURTHERMORE: there are collections of cells within organs (such as the kidneys, gastrointestinal glands, heart, and thymus) that serve important endocrine roles. The organs in this group are traditionally not called endocrine organs because hormone production is not their main function.

Question 20

What is the hypothalamus? Where is it located?

Answer 20

Hypothalamus: the bridge between the nervous and endocrine systems. By regulating the pituatary gland through tropic hormones, the hypothalamus is capable of having different organism-wide effects

Location: in the forebrain, directly above the pituatary gland and below the thalamus.

Question 21

Because the hypothalamus and pituatary gland are close to each other, the hypothalamus controls the pituatary through paracrine release of hormones into the portal system that directly connects the two organs.

The hypothalamus also recieve input from a wide variety of resources. List 3 of these input sources?

Answer 21

1. Part of the hypothalamus, called the suprachiasmatic nuclues, recieve some of the light input from the retinae and helps to control sleep-wake cycles.
2. Other parts of the hypothalamus respond to increases in blood osmolarity.
3. Other parts of the hypothalamus regulate appetite and satiety.

Question 22

The release of hormones by the hypothalamus is regulated by what type of feedback? Explain that feedback? What are the 2 benefits of this feedback?

Answer 22

The release of hormones by the hypothalamus is regulated by a negative feedback

Negative feedback: occurs when a hormone (or product) later in the pathway inhibits hormones (or enzymes) earlier in the pathway.

This type of feedback maintains homeostasis and conserve energy by restricting production of substances that are already present in sufficient amounts.

Question 23

VIP NOTE:

Answer 23

The hypothalamus and pituatary gland are inextricably linked. The pituitary gland has an anterior and posterior component, each with a unique interaction with the hypothalamus.

Question 24

What is another term for pituatary?

Answer 24

Hypophysis is an alternative term for the pituatary.

Question 25

What is the hypophyseal portal system?

Answer 25

The hypothalamus secretes tropic hormones into the hypophyseal portal system, which is a blood vessel system that directly connects the hypothalamus with the anterior pituatary.

Once hormones have been released from the hypothalamus into this portal bloodstream, they travel down the pituatary stalk and when they reach the anterior pituatary they bind to receptors that stimulate the release of other hormones (the hormones that the anterior pituatary release and work on the specific organ/cell in the body to explicit the orangism effect).

NOTE: Hormones released from the hypothalamus travel directly to the anterior pituatary and cannot be found in appreciable concentrations in the systemic circulation.

Question 26

List the 5 tropic hormones released by the hypothalamus and the corresponding anterior pituatary hormone released in turn?

Answer 26

1. Gonadotropin-releasing hormone (GnRH)–> Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH)
2. Growth hormone-releasing hormone (GHRH)–> Thyroid-stimulating hormone (TSH)
3. Thyroid-releasing hormone (TRH)–> Thyroid-stimulating hormone (TSH)
4. Corticotropin-releasing factor (CRF) –> Adrenocorticotropic hormone (ACTH).

The 5th is an exception to this pattern: prolactin-inhibiting factor (PIF), which is actually dopamine, is released by the hypothalamus and causes a decrease in prolactin secretion (so, no hormone released by the anterior pituatary).

Question 27

What does each of these tropic hormones do then? Give an example of how it implement the negative feedback effects?

Answer 27

Each of these tropic hormones then causes the release of another hormone from an endocrine gland that has a negative feedback effects.

For example, release of CRF from the hypothalamus will stimulate the anterior pituatary to secrete ACTH. ACTH will then cause the adrenal cortex to increase the level of cortisol being secreted into the blood. However, high levels of cortisol is detrimental. To prevent excess cortisol secretion, cortisol inhibits the hypothalamus and anterior pituatary from releasing CRF and ACTH, respectively. And this makes sense because CRF and ACTH have already accomplished their desired effect: getting more cortisol in the blood.

Question 28

What does this mean in terms of receptors in the hypothalamus and pituatary gland? WHat is meant by Axes?

Answer 28

It means that cortisol receptors must be present in these organs; otherwise they wouldn’t be able to recognize that cortisol levels had increased.

Three-organ systems like these are commonly referred to as axes; for example, there is the hypothalamic-pituatary-adrenal (HPA) axis, the hypothalamic-pituatary-ovarian (HPO) axis, and so on.

Question 29

How does the hypothalamus send its tropic hormones to the posterior pituartary?

Answer 29

The posterior pituatary does not recieve tropic hormones through the hypophyseal portal system. Rather, neurons in the hypothalamus send their axons down the pituatary stalk directly into the posterior pituatary, which can then release its hormones: oxytocin and antidiuretic hormone.

Question 30

What is the function of oxytocin hormone?

Answer 30

Stimulates uterine contractins during labor, as well as milk letdown during lactation.

There is evidence that oxytocin is also involved in bonding behavior.

Question 31

What is the function of anti-diuretic hormone (ADH)? What is another name for that hormone?

Answer 31

Another name: vasopressin.

Increases reabsorption of water in the collecting ducts of the kidneys as it is released in response of increased plasma osmolarity or increased concentration of solutes within the blood.

Question 32

What does the anterior pituatary synthesizes and secrete?

Answer 32

7 different hormones: 4 tropic and 3 direct

Question 33

As mentioned, tropic hormones work by causing the release of another hormone at the organ level. List the four tropic hormones released by anterior pituatary, mentioned stimulated by what tropic hormone from hypothalamus, and the endocrine organ on which they act on?

Answer 33

1) FHS and LH are stimulated by GnRH from the hypothalamus and both of these hormones act on the gonads (testes and ovaries)
2) ACTH is stimulated by CRF from the hypothalamus and it acts on the adrenal cortex (which then release cortisol)
3) TSH is simulated by TRH from the hypothalamus and acts on the thyroid gland.