Biology chapter 5 Flashcards
What are glands?
Organs in the endocrine system that secrete hormones.
What are hormones?
Signaling molecules that are secreted directly into the bloodstream to distant target tissues.
VIP NOTES:
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.
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?
- peptides
- steroids
- Amino-acid derivatives
What are peptide hormones (How are they made)? Derived from what?
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.
Since peptide hormones are charged and cannot pass through the plasma membrane, what must they do? (explain what is first messenger and second messenger?)
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.
Explain what is meant by signaling cascade and amplification? provide an example.
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.
What are three common second messangers?
- cAMP
- IP3
- Calcium
Explain the full pathway of a hormone binding to a G-protein coupled receptor (GPCR)?
- Hormone binding the GPCR and activating it
- 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).
- 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.
Compare and contrast between peptide hormones and steroid hormones?
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).
What are steroid hormones (made of what and produced by what)? Derived from what and that helps them be able to do what?
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).
Explain the pathway of a steroid hormone binding to its receptor?
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).
What is meant by the levels of carrier proteins can change the levels of active hormone?
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.
Amino acid- derviate hormones are less common than peptide and steroid hormones but include some important ones. What are these hormones?
Epinephrine, norepinephrine, triiodothronine, and thyroxine.
Describe these hormones are derived from what?
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.
VIP NOTE:
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.
What are direct hormones? Give an example?
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).
What are tropic hormones? Give an example? Where do they usually originate?
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.
List all the endocrine glands? What is each of these organs capable of doing?
- Hypothalamus
- Pituitary
- Thyroid
- Parathyroid
- Adrenal
- Pancreas
- Gonads (testes and ovaries)
- 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.
What is the hypothalamus? Where is it located?
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.
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?
- Part of the hypothalamus, called the suprachiasmatic nuclues, recieve some of the light input from the retinae and helps to control sleep-wake cycles.
- Other parts of the hypothalamus respond to increases in blood osmolarity.
- Other parts of the hypothalamus regulate appetite and satiety.
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?
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.
VIP NOTE:
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.
What is another term for pituatary?
Hypophysis is an alternative term for the pituatary.
