Chapter 10 Flashcards
Puberty brings about many changes in the human body.
- Both genders get a growth spurt during puberty, & the 2ndary sex characteristics begin to develop.
- Males= the growth of body and facial hair, deepening of the voice, & the development of the genitals.
- Females= the growth of body hair, the onset of their menstrual cycle, & the development of breasts & broader hips.
- All of these developments r timed & controlled by hormones
A hormone is
a chemical made by cells in one part of the body that regulate the processes of cells in another part of the body
- are prduced by the endocrine system
- act as chemical messengers, enabling 1 part of the body to give instructions to another part
- Some cells even self-regulate, producing chemicals to stimulate their own cellular processes
Local regulators are
chemicals like hormones but act on nearby cells, rather than cells some distance away.
Hormones r secreted by…
the cells, tissues, & organs that compose the endocrine system
The endocrine system does what?
Regulates & coordinates organ functions like growth, development, reproduction, behavior, energy metabolism, & water balance. (like the nervous system)
The nervous system & Endocrine system
- Both systems regulate & coordinate body functions.
- r structurally, chemically, & functionally related, but they control organ & tissue functions in diff ways
–> Nervous system: Sends fast electrical signals for rapid responses to the external environment.
–> Endocrine system: Uses slower, longer-acting hormonal responses to control organ and tissue functions. - Nervous system regulates the release of most hormones, ultimately controlling the endocrine system.
Endocrine glands are
ductless secretory organs that secrete their hormones
directly into the blood or extracellular fluid.
–> (In contrast, exocrine glands, like the sweat & salivary glands, release their secretions into ducts that lead outside the body or into the body cavities)
- Hormones circulate throughout the body in blood & other fluids.–> As a result, most body cells r constantly exposed to a wide variety of hormones but only target cells will respond to a specific hormone cuz only they have receptor proteins that recognize & bind to that type of hormone
- Hormones r cleared from the body at a steady
rate by enzymatic breakdown in their target cells, in the blood, or in organs such as the liver or kidneys. –> The breakdown products are reused or excreted
There are more than ____known hormones and local regulators in humans. How do they compare to hormones and regulators in other animals?
60
- Many r identical or very similar in structure & function to the hormones in other animals, tho many animals have hormones not found in humans.
Hormones are identified by their _____________________.
chemical structure
There are 2 main types of Hormones:
- protein hormones, which are water soluble,
- steroid hormones, which are lipid soluble.
- Most hormones fall into one of these two types
A protein hormone is
a hormone composed of chains of amino acids that is water soluble; usually acts on cell membrane receptors
- amino acid chains= 3 amino acids to more than 200
- released into the blood or extracellular fluid by the cells in the endocrine glands where they are made.
- usually hydrophilic: they have an affinity for water & diffuse well through the blood & intercellular fluids
- 1 group of protein hormones= the growth factors, regulates the division & differentiation of many types of cells in the body
A steroid hormone is
a hormone composed of cholesterol that is not very water soluble; usually passes through the cell membrane & acts on receptors inside the cell
- not very soluble in blood but they can pass easily through the lipid bilayer of cellular membranes
–> Combine with hydrophilic carrier proteins to form water-soluble complexes, enabling diffusion into blood & other fluids.
- When it contacts a cell, it is released from its carrier protein.
- passes through the plasma membrane of the target cell & then binds to internal receptors in the nucleus or cytosol.
- Steroid hormones include aldosterone, cortisol, & the sex hormones. –> all natural
Some steroid hormones have very similar structures but produce very diff effects. Give an example
- ex, testosterone & estradiol, 2 major sex hormones that r responsible for the development of male & female characteristics, respectively, differ only in the presence or absence of a single methyl group
Prohormones
- Many hormones r secreted in an inactive or less active form called prohormones
- Prohormones r converted to active forms by target cells or enzymes in blood or tissues.
- Protein hormones are commonly synthesized as prohormones, which r then converted to the active form in the source cell –> some cases, further conversion occurs once the hormone has been secreted
- Ex, Angiotensinogen, secreted by the liver, is an inactive precursor. –> Cleaved by enzyme to an inactive form of angiotensin, which is activated by angiotensin-converting enzyme (ACE) to regulate blood pressure by increasing it. –> ACE inhibitors r used to manage high blood pressure.
Hormones are usually secreted in relatively ________________, but a process of amplification magnifies their effect. Explain
small amounts
- Once a receptor cell activates a few proteins, these
proteins activate other proteins, each of which activates other proteins, and so on.
- This chain reaction amplifies the effect of the small amount of hormone initially received.
Pathways for Water-Soluble Hormones
- Hormones use 2 main mechanisms to control cellular activities.
- The 1st mechanism governs water-soluble protein hormones (protein hormones), which cannot easily cross membranes
- bind to receptor molecules in the cell membrane, causing the receptor molecule to change shape.
- This activates a signal, which passes into the cell
- This signal can lead to internal changes in the cell, such as releasing enzymes that modify proteins by adding or removing phosphate groups.
- The signal may act only in the cytosol or affect the nucleus, as with many protein hormones such as growth factors
- Ex of the surface receptor mechanism is the protein hormone glucagon. –> When glucagon binds to surface receptors on liver cells, it triggers a series of reactions.
–> These reactions lead to the addition of phosphate groups, which activate the enzyme that governs the breakdown of stored glycogen into glucose.
glucagon is
a hormone produced by alpha cells in the pancreas that raises the blood glucose level by promoting the breakdown of glycogen in the liver
Pathways for Lipid-Soluble Hormones
The 2nd main mechanism involves hormones binding to receptors inside a cell –> used by most steroid hormones
- Steroid hormones=lipid based= lipid soluble= they pass easily through the plasma membrane.
- attach to receptors in the cytosol or nucleus of a cell.
- The hormone-receptor complex then binds to a control sequence on a specific gene, turning the gene’s action on or off.
- Activation & deactivation of the gene changes the
amount of protein that it synthesizes, which changes the cellular activity
- Ex,steroid hormone aldosterone.
-Secreted by adrenal glands when bp is low. - Travels through membranes & binds to receptors in kidney, sweat gland, & colon cells.
- The receptor acts as a transcription factor, synthesizing proteins that increase sodium reabsorption.
- Increased sodium leads to water retention, raising blood pressure.
The two mechanisms used by hormones are not mutually exclusive. Explain.
A single target cell may have receptors for several hormones & respond differently to each hormone.
- Ex, the liver cells of vertebrates have receptors for the pancreatic hormones insulin & glucagon.
- Insulin increases the uptake of glucose & its conversion to glycogen, which decreases the blood glucose level.
- Glucagon stimulates the breakdown of glycogen into glucose, which increases the blood glucose level.
particular hormones can interact with diff types of receptors in or on a range of target cells. Elaborate
- Diff responses r then triggered in each target cell
cuz the receptors trigger diff signal pathways. - As well, the response to a hormone may differ among species.
- Ex, melatonin, a protein hormone derived from tryptophan, is important in regulating daily & annual cycles in most animals. –> But, it also plays a role in regulating the salt glands of marine birds.
In summary, the mechanisms by which hormones work have 4 major features:
1) Only the cells that contain surface or internal receptors for the hormones respond to the hormones.
2) Once bound to their receptors, hormones produce a response by turning cellular processes on or off. They do this by altering the proteins that r functioning in or produced by the cell
3) Hormones are effective in very small concentrations cuz of the amplification that occurs in both the surface and internal receptor mechanisms.
4) The response to a hormone differs among target organs and among species.
Hormones as Part of Feedback Mechanisms
- Most hormones r regulated by negative feedback mechanisms.
- In a -ve feedback mechanism, a chemical that is affected at the end of the action pathway of a hormone controls the further action of the hormone by inhibiting an earlier chemical reaction.
- A response in a feedback loop may be the production of a substance or a decrease in the production of a substance
- Ex, hypothalamus releases thyroid-releasing hormone (TRH), which initiates a pair of hormone releases by the pituitary and thyroid glands.
- As the concof the thyroid hormone in the blood increases, it inhibits an earlier step in the pathway, the secretion of thyroid-stimulating hormone (TSH) by the pituitary gland.
Regulation of Body Processes by Hormones
- Some glands make multiple hormones, & many body processes r influenced by multiple hormones simultaneously.
- Glucose, fatty acids, and ions (e.g., Ca²⁺, K⁺, Na⁺) levels r regulated by hormones from different glands.
- Functions such as metabolism, digestion, growth, sexual development, & stress responses rely on multiple hormones.
- many systems= negative feedback loops adjust the level of secretion of hormones that act in opposing ways.–>maintains homeostasis in the body.
–> Consider regulation of fuel molecules, like glucose, fatty acids, &amino acids, in the blood. Between meals, 5 diff hormone systems, involving the digestive
tract, pancreas, nervous system, & pituitary & adrenal glands, all act together in a coordinated fashion to keep the body’s fuel levels in balance.
Many other important hormones are secreted
by other organs, such as…
the heart, liver, kidneys, and intestines, & have diff primary functions.