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Do two hormones have the same effect on a cell if the second messenger is the same?

Do two hormones have the same effect on a cell if the second messenger is the same?


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There are so many hormones/cytokines/neurotransmitters and receptors, all of which act through about 4-5 second-messenger systems. So if one particular cell has receptors for say, two different hormones which act via the same second messenger, is there any way that the cell can distinguish the two stimuli? I'm guessing there must be some distinguish between the two, otherwise, wouldn't the effect of both the hormones be the same?

For example, in a hepatocyte, beta-adrenergic receptors and glucagon receptors both act via Gs-coupled receptors, downstream of which, cAMP is increased. Since the cAMP is the same, the changes it would make are also the same. So does it to the hepatocyte, make no difference if the first messenger was epinephrine or glucagon?

I'm assuming the receptors would make a difference, but aren't the coupled G-proteins (Gs) also the same? Is there a difference of amplitude?

Note: I understand that it is not necessary for the hormones to produce an exclusively different effect. I also understand that systemic effects can be different because of differential distribution of receptors. My question pertains to the effects on a single cell.


Secondary signaling molecules like cAMP, Calcium, and Ras-Raf are common in many pathways and I think its a way of integrating different signals.We cannot say that at a moment only one pathway operates in a cell or a single pathway will be enough for a process to happen.I think common second messengers is a resource and time-saving method adapted by our system to coordinate different response efficiently.https://www.nature.com/scitable/topicpage/cell-signaling-14047077

Then how a cell can identify which pathway and process should go on? I think that each time this second messenger will make a small change in choosing down stream effectors.Like Calcium binds to calmodulin which in turn choose next binding partner.Maybe the number of second messengers like concentration and affinity decide which downstream effector will be appropriate for the required stimuli.You can see in this link about how different secondary messengers make different results https://www.ncbi.nlm.nih.gov/books/NBK9870/

About GPCR, more than 800 GPCR are there and you can see from this link http://jcs.biologists.org/content/116/24/4867

So, Do two hormones have the same effect on a cell if the second messenger is the same? I think yes, see this table (https://www.ncbi.nlm.nih.gov/books/NBK21705/)

Here, from the table, you can see adrenaline and glucagon are having the same effect in the liver cell and both have cAMP as a second messenger.But in cardiac muscle and intestine, adrenaline is having a different function. So I think it depends on the cell also.


37.2: How Hormones Work

  • Contributed by OpenStax
  • General Biology at OpenStax CNX

Hormones mediate changes in target cells by binding to specific hormone receptors . In this way, even though hormones circulate throughout the body and come into contact with many different cell types, they only affect cells that possess the necessary receptors. Receptors for a specific hormone may be found on many different cells or may be limited to a small number of specialized cells. For example, thyroid hormones act on many different tissue types, stimulating metabolic activity throughout the body. Cells can have many receptors for the same hormone but often also possess receptors for different types of hormones. The number of receptors that respond to a hormone determines the cell&rsquos sensitivity to that hormone, and the resulting cellular response. Additionally, the number of receptors that respond to a hormone can change over time, resulting in increased or decreased cell sensitivity. In up-regulation , the number of receptors increases in response to rising hormone levels, making the cell more sensitive to the hormone and allowing for more cellular activity. When the number of receptors decreases in response to rising hormone levels, called down-regulation , cellular activity is reduced.

Receptor binding alters cellular activity and results in an increase or decrease in normal body processes. Depending on the location of the protein receptor on the target cell and the chemical structure of the hormone, hormones can mediate changes directly by binding to intracellular hormone receptors and modulating gene transcription, or indirectly by binding to cell surface receptors and stimulating signaling pathways.


Types of Hormones

The hormones of the human body can be structurally divided into three major groups: amino acid derivatives (amines), peptides, and steroids (Figure 17.2.1). These chemical groups affect a hormone’s distribution, the type of receptors it binds to, and other aspects of its function..

Figure 17.2.1: Amine, Peptide, Protein, and Steroid Hormone Structure


Do two hormones have the same effect on a cell if the second messenger is the same? - Biology

Cells in the adrenal medulla synthesize and secrete epinephrine and norepinephrine . The ratio of these two catecholamines differs considerably among species: in humans, cats and chickens, roughly 80, 60 and 30% of the catecholamine output is epinephrine. Following release into blood, these hormones bind adrenergic receptors on target cells, where they induce essentially the same effects as direct sympathetic nervous stimulation.

Synthesis and Secretion of Catecholamines

Synthesis of catecholamines begins with the amino acid tyrosine, which is taken up by chromaffin cells in the medulla and converted to norepinephrine and epinephrine through the following steps:

Norepinephine and epinephrine are stored in electron-dense granules which also contain ATP and several neuropeptides. Secretion of these hormones is stimulated by acetylcholine release from preganglionic sympathetic fibers innervating the medulla. Many types of "stresses" stimulate such secretion, including exercise, hypoglycemia and trauma. Following secretion into blood, the catecholamines bind loosely to and are carried in the circulation by albumin and perhaps other serum proteins.

Adrenergic Receptors and Mechanism of Action

The physiologic effects of epinephrine and norepinephrine are initiated by their binding to adrenergic receptors on the surface of target cells. These receptors are prototypical examples of seven-pass transmembrane proteins that are coupled to G proteins which stimulate or inhibit intracellular signalling pathways.

Complex physiologic responses result from adrenal medullary stimulation because there are multiple receptor types which are differentially expressed in different tissues and cells. The alpha and beta adrenergic receptors and their subtypes were originally defined by differential binding of various agonists and antagnonists and, more recently, by analysis of molecular clones.

Receptor Effectively Binds Effect of Ligand Binding
Alpha 1 Epinephrine, Norepinphrine Increased free calcium
Alpha 2 Epinephrine, Norepinphrine Decreased cyclic AMP
Beta 1 Epinephrine, Norepinphrine Increased cyclic AMP
Beta 2 Epinephrine Increased cyclic AMP

Physiologic Effects of Medullary Hormones

In general, circulating epinephrine and norepinephrine released from the adrenal medulla have the same effects on target organs as direct stimulation by sympathetic nerves , although their effect is longer lasting. Additionally, of course, circulating hormones can cause effects in cells and tissues that are not directly innervated. The physiologic consequences of medullary catecholamine release are justifiably framed as responses which aid in dealing with stress. These effects can be predicted to some degree by imagining what would be needed if, for example, you were trapped in Jurassic Park when the power went off. A listing of some major effects mediated by epinephrine and norepinephrine are:

  • Increased rate and force of contraction of the heart muscle: this is predominantly an effect of epinephrine acting through beta receptors.
  • Constriction of blood vessels: norepinephrine, in particular, causes widespread vasoconstriction, resulting in increased resistance and hence arterial blood pressure.
  • Dilation of bronchioles: assists in pulmonary ventilation.
  • Stimulation of lipolysis in fat cells: this provides fatty acids for energy production in many tissues and aids in conservation of dwindling reserves of blood glucose.
  • Increased metabolic rate: oxygen consumption and heat production increase throughout the body in response to epinephrine. Medullary hormones also promote breakdown of glycogen in skeletal muscle to provide glucose for energy production.
  • Dilation of the pupils: particularly important in situations where you are surrounded by velociraptors under conditions of low ambient light.
  • Inhibition of certain "non-essential" processes: an example is inhibition of gastrointestinal secretion and motor activity.

Common stimuli for secretion of adrenomedullary hormones include exercise, hypoglycemia, hemorrhage and emotional distress.

Functional Anatomy of the Adrenal Glands

Adrenal Steroids


Do two hormones have the same effect on a cell if the second messenger is the same? - Biology

#1) Hormones : are certain chemicals used as signals, secreted by cells inside the body (into the blood), for the purpose of stimulating or inhibiting certain other cells, often all over the body.

Note that adrenaline is used both as a neurotransmitter (locally)
AND as a hormone (all over the body)

Glands that secrete hormones are called " endocrine " glands " endocrinology " is the name of the science that studies them.

#2) Most hormones belong to 3 categories of chemicals:

steroids : of which examples include male and female sex hormones insect molting hormone cortisone

proteins/peptides : insulin, secretin, all the pituitary hormones

and amino acid derivatives : adrenaline, thyroxine

#3) Hormones are secreted (most often) by specific glands such as the adrenal gland the thyroid gland , gonads (in males, the gonads are testes (singular is "testis" )

#4) Hormones produce effects (often large effects) at very low concentrations because hormone molecules bind to (fit exactly into binding site) on receptor proteins .

Proteins can't diffuse through plasma membranes into cells, so receptors for protein hormones are always on the outer surface of the plasma membrane and when they bind, this causes some internal change.

But steroids can diffuse through plasma membrane so usually steroid receptors are inside cells (& inside nuclei) and in many cases steroid receptors are transcription factors bind to DNA at certain base sequences, control whether RNA copies of those genes are or are not transcribed.

#5) Many hormones produce effect by second messengers of which the classic example is cyclic AMP .

This is synthesized from ATP by adenyl cyclase enzyme .

The effects of those hormones can therefore be mimicked or amplified by (for example) dibutyryl cyclic AMP

Cyclic GMP is also used as a second messenger, and so are inositol phosphates and diacylglycerol but it is enough for you to learn cyclic AMP

#6) Stabilization of hormone concentrations and many variables by negative feed-back cycles : an example of " Homeostasis "
an example: FSH and LH stimulate gonads to secrete more steroid sex hormones
But secretion of LH and FSH by the pituitary become less in response to more steroid sex hormones.
This is analogous to a thermostat regulating temperature,
notice that heating a thermostat will cause the furnace to be turned down.
In such a cycle, an odd number of the effects need to be inhibitory

#7) By what methods have hormones been discovered, and their chemical nature identified.

a) Surgical removal of glands: produces what effect?
Which chemical extracts will compensate for this removal?

Bioassays : comparing effects of different fractions of extracts. The example of serotonin .

b) Diseases in which too much or too little of a given hormone.

#8) In contrast, knowledge about hormone receptors comes more and more from molecular genetic methods (DNA sequences, from which amino-acid sequences can then be deduced)

#9) Pheromones : Outside the body influence other individual animals,
almost always of the same species and usually of the opposite sex often for attraction for mating
These are what your dog is sniffing so vigorously when you go on walks.

Are there human pheromones? of which we are not consciously aware?

Observations on synchronization of menstrual cycles in women in dorms.
Read about this in the textbook

Perfumes are made partly from extracts of glands from civet cat glands, which make pheromones.

Questions that might be on an exam:

c) Are all steroids also hormones? Are any steroids hormones? What are two specific examples of hormones that are steroids?

d) What is an example of a hormone that can diffuse right through the plasma membranes of cells, into their cytoplasm?

e) Most hormones belong to which general categories of molecules? (name 2 such categories)

f) Some hormones also belong to what third category of molecules, besides steroids and chains of amino acids?

g) Endocrine glands secrete what?

h) What are 3 or 4 specific examples of endocrine glands?

i) Do gonads secrete certain hormones, in addition to producing sperm and egg cells? [hint: yes but what effects do these hormones produce?]

j) What do hormones bind to, in cells?

k) How is this binding related to the specificity of hormones, and their ability to produce large effects, often even at very, very low concentrations?

*l) The time needed to reverse a hormone's effect tends to be longer for those hormones whose receptors are either especially specific (much less affected by other chemicals with nearly the same structure as the hormone), or which act at unusually low concentrations: figure out the logical connection between these 3 properties: high specificity high sensitivity and slow reversibility. [Hint: it has to do with the tightness of the bonding between hormones and their receptor proteins.]

m) Which kinds of hormones can diffuse (somewhat) freely into cells, diffusing right through the plasma membrane and the nuclear membrane?

n) The receptors for which class of hormones are often transcription factors, which become able to bind specifically to DNA having certain base sequences, but only when also bound to their hormones?

o) Receptors for which kinds of hormones have to be located on the outer surface of the plasma membrane?

p) What is an example of a "second messenger" (for hormones)?

q) What is the raw material from which cells synthesize molecules of this second messenger? What sort of stimulus causes cells to synthesize molecules of a second messenger?

*r) By what simple chemical trick can molecules of this second messenger artificially be enabled to diffuse through plasma membranes, so that they can diffuse into cells from the outside?

s) "Homeostatic" regulation of hormone concentrations or other variables is the result of what kind of feedback cycles? Hint: What are the differences between negative feedback cycles versus positive feedback cycles? Further hint: the propagation of nerve action potentials results from a positive feedback cycle, in which a certain change stimulates more change in the same direction?

*t) Before puberty (the onset of sexual maturity in humans and other animals, the pituitary gland is more sensitive to inhibition by steroid sex hormones then puberty results indirectly from the pituitary becoming LESS sensitive to this inhibition. This results in secretion of more of two kinds of hormones. Figure out what sense this makes. How can less sensitivity to a hormone cause increases in hormone effects?

*u) The active ingredients in birth control pills are certain steroid hormones. How can these produce an inhibition of egg cells production? Wouldn't it make more sense of more of a hormone resulted in more egg cells being produced?

v) Explain how a bioassay is used to identify the chemical nature of a certain hormone, or other biologically important molecule.

w) If a molecule were analogous to a hormone, but were secreted to the outside of a given kind of animal, and produced its effects on other individual animals of the same species, then what would be a 10 letter word starting with P that is the name for any such molecule?

*x) Suppose such a chemical produced strong but unconscious psychological effects, then what nefarious uses might it have?

*y) Invent (in general terms) a bioassay by which the chemical nature of such an external signalling molecule might be discovered or confirmed?

**z) Would sensitivity to such a chemical count as "extra-sensory perception" (ESP) in your opinion?

**!) Could action potentials in certain nerves in one animal be sensed by another animal? How? Could the second animal deduce the meaning of those signals? Hint: if all kinds of nerves use the same kind of action potential, then why does that make ESP less likely? Conversely, invent how a nervous system might need to work in order to make ESP more possible. (So that the significance of nerve signals could be decoded at a distance? Or is that perhaps not the essence of ESP?)


Endocrine system 1: overview of the endocrine system and hormones

The endocrine system comprises glands and tissues that produce hormones for regulating and coordinating vital bodily functions. This article, the first in an eight-part series, is an overview of the system

Abstract

The endocrine system is made up of glands and tissues that produce and secrete hormones to regulate and coordinate vital bodily functions. This article – the first in an eight-part series on the anatomy and physiology of the endocrine system – explores the nature of endocrine glands and tissues, and the role of hormones as chemical signals that are carried in the blood. It also highlights the varying roles of hormones in regulating and coordinating physiological processes, as well as maintaining homoeostasis in the body.

Citation: Knight J (2021) Endocrine system I: overview of the endocrine system and hormones. Nursing Times [online] 117: 5, 38-42.

Author: John Knight is associate professor in biomedical science, College of Human and Health Sciences, Swansea University.

  • This article has been double-blind peer reviewed
  • Scroll down to read the article or download a print-friendly PDF here (if the PDF fails to fully download please try again using a different browser)
  • Assess your knowledge and gain CPD evidence by taking the Nursing Times Self-assessment test

Introduction

The endocrine system is a series of glands and tissues that produce and secrete hormones, which are used by the body to regulate and coordinate vital bodily functions, including growth and development, metabolism, sexual function and reproduction, sleep and mood. This article – the first in an eight-part series on the anatomy and physiology of the endocrine system – provides an overview of the system, focusing on endocrine glands and tissues, and the role of hormones as chemical signals that are bloodborne. It also explains the diverse roles of hormones in regulating and coordinating physiological processes, and maintaining homoeostatic balance in the body.

The endocrine system (Fig 1) is incredibly complex: it consists of dedicated, specialised endocrine glands – such as the thyroid, parathyroids and adrenal glands – together with tissues such as fat (adipose tissue) and bone that have a secondary endocrine function and also secrete a range of hormones. It has been suggested that the microbial biome (the diverse plethora of micro-organisms colonising the human body) also functions as a “virtual endocrine organ”, secreting a cocktail of chemical signals that further influences human physiology (O’Callaghan et al, 2016).

Endocrine and exocrine glands

By definition, all glandular tissues produce secretions. Most glandular structures are epithelial in origin, and many are folded and organised into recognisable glands with a central duct. Glands possessing a duct are exocrine glands (Fig 2) the duct acts as a conduit into which secretions are released before being carried away to their sites of action. Exocrine glands include many of the digestive glands in the gut, sweat glands in the skin and mucus-producing glands in the mucous membranes of the mouth and reproductive tracts.

In contrast, endocrine glands have no duct, but release their secretions, called hormones, directly into the blood (Fig 2). For this reason, most endocrine glands are highly vascularised, and many of their component cells are in direct contact with blood capillaries. This close association with blood vessels facilitates the direct release of hormones into the blood and allows the blood to be continuously monitored for physiological changes that can initiate hormone release. As an example of this, the insulin-producing cells of the pancreas will release insulin when they detect an increase in blood–glucose concentration after the consumption of carbohydrate-rich food.

The highly vascular nature of endocrine glands also allows for the delivery of signals (usually other hormones) from other glands to regulate release of their own hormones. For example, the thyroid gland releases hormones that regulate metabolism, such as thyroxine, in response to the thyroid-stimulating hormone, which is produced by the anterior pituitary gland.

The major endocrine glands

Fig 1 shows the position of the major endocrine glands in the body however, it is important to be aware that many other organs and tissues have a secondary endocrine function, including the heart, kidneys, bone and adipose tissues (Knight et al, 2020 Moser and van der Eerden, 2019).

The hypothalamus

The hypothalamus is a vital region of the brain, which plays an important role in:

  • Thermoregulation
  • Behavioural and emotional responses
  • Regulation of appetite
  • Coordination of the autonomic nervous system
  • Generating a range of hormones that regulate the activity of endocrine glands.

Indeed, the hypothalamus can be thought of as the key crossover point between the nervous system and the endocrine system.

The pituitary gland

The pituitary gland is a pea-sized structure, typically weighing around 500mg it is located at the base of the brain, just behind the nasal cavity, where it is protected by the sphenoid bone of the skull (Ganapathy and Tadi, 2020). It has two major regions:

  • The posterior (back portion) –essentially, an extension of the hypothalamus, the posterior of the pituitary gland stores and concentrates two neuropeptide hormones called anti-diuretic hormone (ADH) and oxytocin, which are produced by the neurons (nerve cells) of the hypothalamus. ADH helps regulate fluid balance and blood pressure, while oxytocin – among other things – initiates parturition (childbirth).
  • The anterior (front portion) – this develops from the epithelial tissues in the roof of the embryonic oral cavity, which bulges up into the skull, fusing with the posterior pituitary. It produces several key hormones such as somatotropin (growth hormone) and melanocyte-stimulating hormone, which helps to regulate skin pigmentation. The anterior pituitary also produces several stimulating hormones that control the release of hormones from other endocrine glands. As an example of this, adrenocorticotropic hormone regulates the release of the long-term stress hormone, cortisol, from the adrenal cortex.

As the pituitary gland regulates hormone release from other endocrine glands, it is often referred to as the ‘master’ gland. This is something of a misnomer as the release of stimulating hormones from the pituitary gland is, itself, under the control of hormones produced by the hypothalamus this will be explored in Part 2.

Thyroid gland and associated parathyroids

The thyroid is a bilobed (two-lobed) organ that resembles a bow tie in shape it typically weighs 25-30g and is located just below the larynx (Dorion, 2017). The thyroid itself has two major populations of endocrine cells:

  • Follicular cells – these produce the iodine-containing hormones triiodothyronine (T3) and tetraiodothyronine (T4, also known as thyroxine), which regulate the body’s metabolism
  • Parafollicular cells – these produce the hormone calcitonin, which helps to regulate blood–calcium concentration.

The parathyroid glands are found embedded in the posterior portion of the thyroid gland. Most people have four parathyroid glands (explored in Part 3) these produce parathyroid hormone, which works antagonistically to calcitonin during calcium homoeostasis.

Pancreas

The pancreas is a vital organ in both the digestive and the endocrine systems residing in the U-shaped loop of the duodenum, it is typically 14-23cm in length and weighs around 100g (Longnecker, 2021).

The endocrine portions of the pancreas are known as the islets of Langerhans, which are small islands of glandular tissue found throughout the structure of the pancreas. The pancreatic islets contain several types of endocrine cells, including:

These two hormones – glucagon and insulin – play a key role in regulating blood–glucose concentration, which will be discussed in the section on homoeostasis later in this article.

Adrenal glands

There are two adrenal glands – one above each kidney. They are roughly triangular in shape, around 3cm in width and each weighs 4-6g (Lack and Paal, 2020). Adrenal glands have two major regions:

  • Adrenal cortex (outer region) – this produces steroid hormones, including the long-term stress hormone cortisol, aldosterone (which regulates the levels of sodium and potassium in the blood) and a group of testosterone-like hormones called androgens
  • Adrenal medulla (inner region) – this produces adrenaline (epinephrine) and noradrenaline (norepinephrine). These ‘fight-or-flight’ hormones – that are usually produced when a person is under threat, afraid or excited – function primarily to activate the sympathetic branch of the autonomic nervous system and prepare the body for immediate action.

Ovaries and testes

The ovaries are the primary reproductive organs in females, responsible for producing ova. Mature ovaries are fairly irregular, lumpy and almond shaped, typically 3-5cm long and weigh 5-8g, although they tend to decrease in size in later life (Wallace and Kelsey, 2004). Ova develop in fluid-filled sacs called follicles as follicles enlarge, they release oestrogen, the female sex hormone that promotes the thickening of the uterine lining (endometrium).

Once a follicle ruptures and releases its mature ovum into the fallopian tube during ovulation, the remnants of the follicle collapse into a structure called the corpus luteum (yellow body). This produces the second major female sex hormone, progesterone, which prepares the endometrium for implantation of a fertilised ovum (zygote) and, subsequently, maintains the integrity of the endometrial lining, should implantation occur.

The testes (testicles) are the paired primary reproductive organs in males, responsible for producing spermatozoa. They are oval shaped and, in adult males, are typically 4.5-5.1cm long and weigh 15-19g (Silber, 2018). Each testis contains a specialised group of endocrine cells called interstitial cells, which produce the male sex hormone testosterone. This is an anabolic steroid produced in greater amounts during puberty, when it promotes muscle development, growth of facial and body hair, and expansion of the larynx, leading to a deepening of the voice.

“It has been suggested that the microbial biome (the diverse micro-organisms colonising the body) also functions as a virtual endocrine organ”

Hormones as chemical signals

Hormones are traditionally defined as chemical signals, transported to their target tissues in the blood today, however, that definition is often expanded to include all chemical messengers that bind to target cells with high affinity. So far, more than 100 hormones have been identified in the human body, and this rises to more than 200 if hormone-like substances are included (Silver and Kriegsfeld, 2001).

Hormones exert their physiological effects by binding to specific receptors associated with their target cells (Fig 3). Many drugs have been designed to target these receptor sites, either to mimic the actions of hormones (for example, in the case of a hormone deficiency such as hypothyroidism, which is treated with levothyroxine) or to act as competitive antagonists to physically block the receptor, preventing the natural hormone from binding and exerting its effect. Hormones can be broadly divided into three major classes:

Peptide hormones

These are the largest hormones, with relatively high molecular weights. They are proteinaceous chemical signals, comprising chains of amino acids of varying lengths. Examples include:

Some peptide hormones are initially produced as inactive forms called prohormones a good example is insulin, which is first synthesised as a much larger molecule, called proinsulin, and then cleaved into its active, shorter form before being released into the blood.

Peptide hormones tend to exert their effects by binding to receptors on the surface of the plasma membranes of target cells, as shown in Fig 3. This triggers a variety of transmembrane events, leading to the production of second messengers (such as cyclic adenosine monophosphate), which, subsequently, initiate the desired effect of the hormone in the target cell (Foster et al, 2019).

Steroid hormones

Steroid hormones are lipids (fats), mostly derived directly from cholesterol, which acts as a precursor molecule for steroid biosynthesis. Examples include:

As steroid hormones are lipids, they rapidly diffuse across the phospholipid bilayer of their target cell membranes (Fig 3) and exert their effects by binding to receptors in the cytoplasm or nucleus (Ozawa, 2006). Steroid hormones tend to precipitate their desired effects by modulating the activity of particular genes in cells.

Amino acid-derived hormones

These are synthesised from amino acids, so are small molecules with low molecular weights. Examples include:

  • Adrenaline (epinephrine), derived from tyrosine
  • Thyroid hormones thyroxine T4 and T3, derived from tyrosine
  • Melatonin (which helps to regulate sleep), derived from tryptophan (Kleine and Rossmanith, 2016).

Like peptide hormones, some amino acid-derived hormones, such as adrenaline, bind to receptors on the surface of target-cell plasma membranes. Others however, such as T3 from the thyroid, cross the plasma membranes of their target cells and bind to receptors inside the cell in a similar manner to steroid hormones.

Locally acting hormones: autocrine and paracrine

As well as the hormones secreted by the major endocrine glands, there are various locally acting hormone-like substances. These are usually released into the interstitial fluid (the thin film of tissue fluid surrounding most cells) and exert their effects in the local vicinity.

Autocoids are chemical signals released by a cell that exert their effects on that same cell paracrine signals act more widely, affecting neighbouring cells in the immediate vicinity (Alberts et al, 2015). These locally acting hormones – both autocrine and paracrine – are usually rapidly broken down before they can enter the wider circulation. Good examples are the eicosanoids, a large family of lipid-derived molecules, which include the prostaglandins, thromboxanes, leukotrienes and lipoxins (O’Donnell et al, 2009).

Prostaglandins and the fever response

Fever (pyrexia) is commonly associated with infection. When phagocytic leukocytes (white blood cells) such as monocytes enter sites of infection and begin to trap and kill pathogens, they release a cytokine (a signalling chemical that is produced by immune cells) called interleukin-1 (IL-1). IL-1 is a small peptide that circulates in the blood before binding to receptors on cells in the hypothalamus – the region of the brain containing the thermoregulatory centre that is responsible for controlling body temperature, which usually has a set point of around 37°C (Knight et al, 2020).

Once IL-1 has binded to its receptor, the enzyme cyclooxygenase (COX) is activated, leading to the production of the eicosanoid, prostaglandin E2 (PGE2) this locally acting signal shifts the set point of the hypothalamus upwards (typically to around 38°C-39°C), leading to fever (Eskilsson et al, 2017).

Fever is a useful response during infection as it can slow the replication of pathogens, while simultaneously speeding up and enhancing pathogen killing by leukocytes. However, fever also takes enzymes in the body cells outside of their normal optimal temperature of 37°C, slowing the biochemical reactions that are necessary for life. This can cause people to experience malaise and feel generally unwell until the infection is dealt with and the temperature can return to normal.

If fever becomes extremely high (≥40°C), there is an increased risk of febrile convulsions. Antipyretic drugs – which include many common non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin – may be given to reduce the fever. NSAIDs work, primarily, by inhibiting the activity of the enzyme COX, thereby preventing the production of PGE2 and shifting upwards the set point of the thermoregulatory centre.

If a patient’s fever needs to be reduced, it is common practice to combine the use of antipyretic drugs and interventions such as reducing bed linen – for example, air-circulating or water-circulating blankets or hydrogel-coated water-circulating pads can also be used. There is no evidence that fans help with temperature regulation and should be avoided as they can increase the risk of shivering (Doyle and Schortgen, 2016).

The endocrine system and homoeostasis

An average adult human with a weight of 70kg is thought to comprise around 30-40 trillion cells (Sender et al, 2016). For each cell to function effectively, it must be maintained at the correct temperature and pH, and provided with a steady stream of nutrients and oxygen. At the same time, the local environment of each cell needs any waste metabolites, such as carbon dioxide and urea, to be efficiently removed.

Homoeostasis can be broadly defined as the ability to maintain a relatively stable internal environment it is essential to good health and survival (Modell et al, 2015). A multitude of variables in the body are susceptible to continual and significant fluctuation, and most of the major organ systems of the body are dedicated to keeping these variables within their normal physiological ranges.

The internal biochemical processes necessary for life are primarily driven by biological catalysts known as enzymes, which generally fall into two categories:

  • Anabolic enzymes – these are responsible for building molecules in the body. For example, DNA polymerase builds new molecules of DNA necessary for cell division and growth, while glycogen synthase takes single molecules of glucose and polymerises them (links them together) to form long, branching chains of glycogen (animal starch), which is stored in large amounts in liver and muscle
  • Catabolic enzymes – these break down molecules and include the enzymes of the digestive tract, which digest the macromolecules (large, complex molecules) of food into simple components that can be absorbed and used by the body. Other key catabolic enzymes are those involved in cellular respiration, in which sugars are metabolised (usually in the presence of oxygen) to release the energy necessary for life.

Anabolic and catabolic enzymes can only function efficiently in narrow ranges of temperature and pH they also require a steady supply of the substrate molecules on which they act (Puri, 2018). As an example, for aerobic cellular metabolism to occur, the respiratory enzymes in cells require a steady stream of glucose and oxygen.

The homoeostatic mechanisms that ensure a stable environment in the body rely on a process called negative feedback, which is discussed below.

Set points, negative feedback and the role of hormones

For each variable in the human body, there is a hypothetical ideal value – the set point. As an example, the set point for glucose is around 5mmol/L (Fig 4) at 5mmol/L, human cells are supplied with a steady supply of glucose, which can be used to release energy during cellular respiration.

The body strives to maintain variables as close to their set points as possible using negative-feedback mechanisms. During negative feedback, any deviations from the set point are resisted and minimised, allowing a variable to be constrained within a narrow, normal physiological range. If blood–glucose concentration is measured throughout the day, it would be expected to fluctuate around its set point. As an example, after exercise, blood–glucose concentration typically falls as glucose is used to provide energy for muscle contraction conversely, after a carbohydrate-rich meal or snack (such as a chocolate bar), the blood–glucose level rises.

Hormones frequently play major roles in negative feedback and often work together in antagonistic pairs. Fig 4 shows that when blood–glucose concentration rises, the hormone insulin is released this promotes glucose uptake by the cells of the body and the blood–glucose level drops. Conversely, if blood–glucose concentration falls, the hormone glucagon is released this stimulates the release of stored glucose from the liver, which causes blood glucose to rise again. The two pancreatic hormones, insulin and glucagon, work antagonistically to each other to effectively constrain the blood–glucose concentration in its normal physiological range of 4-6mmol/L (Knight et al, 2020).

Effects of variables outside of their normal range

One in 14 people in the UK has the chronic metabolic disease, diabetes mellitus, which means they no longer produce insulin (type 1) or become resistant to its effects (type 2). Without an effective insulin response, blood–glucose concentration will rise markedly above its normal physiological range. Some undiagnosed patients with diabetes can have seriously high blood–glucose concentrations of >33mmol/L requiring immediate treatment. Elevated blood glucose is called hyperglycaemia and is the key clinical feature of diabetes.

Many patients with diabetes inject insulin to manage and normalise their blood–glucose levels. On occasion, some may inject too much insulin or eat insufficient carbohydrate so their blood–glucose concentration falls far below its normal physiological range this is called hypoglycaemia and can be extremely dangerous. When pronounced, hypoglycaemia can lead to mental impairment, behavioural changes, unconsciousness, coma and potentially death (Mukherjee et al, 2011).

The example of hyperglycaemia and hypoglycaemia shows how, when a variable is taken outside of its normal range for any protracted length of time, it is detrimental to health and leads to pathology (disease states) both hyperglycaemia and hypoglycaemia are frequently encountered in poorly managed diabetes.

Conclusion

This article has provided a general overview of the nature of hormones, along with the major endocrine glands and their importance in regulating and coordinating vital bodily functions. Each of the major endocrine glands and their hormonal secretions will be be examined in greater detail later in the series part 2 focuses on the hypothalamus and pituitary gland.

Key points

  • The endocrine system comprises glands and tissues that secrete hormones to regulate and coordinate vital functions in the body
  • Endocrine glands differ from exocrine glands by releasing their secretions directly into the bloodstream, rather than a central duct
  • Endocrine glands’ highly vascular nature allows variables in the blood to be monitored continuously and appropriate hormones to be rapidly released into the circulation
  • Hormones exert their physiological effects by binding to specific receptors associated with their target cells
  • Hormones regulate physiological processes and are key to maintaining homoeostatic balance in the body
  • Test your knowledge with Nursing Times Self-assessment after reading this article. If you score 80% or more, you will receive a personalised certificate that you can download and store in your NT Portfolio as CPD or revalidation evidence.

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General Features of Plant Hormones, Their Analysis, and Quantitation

8. REGULATION OF HORMONE LEVELS (HORMONAL HOMEOSTASIS)

Hormones are required for specific actions at specific times in growth and development, and it is important for the plant, not only to be able to synthesize the hormone, but also to inactivate it when not needed. Furthermore, hormones are required in small amounts, picomolar to micromolar quantities, and plants often produce far more bioactive hormone than is actually required. Evidence comes from synthesis mutants that are leaky, i.e., the mutated allele is not a null allele, but is still able to produce a partly functional enzyme. Such leaky mutants often produce enough hormone to carry out many responses, although perhaps not all. Thus, the regulation of endogenous levels of bioactive hormones, or hormone homeostasis, is of prime importance to normal growth and development of plants.

Plants use three mechanisms to regulate endogenous levels of hormone: (i) regulation of the rate of hormone synthesis, (ii) inactivation of the hormone by conjugation with carbohydrates, amino acids, or peptides, and (iii) an irreversible breakdown of the hormone. Other means of regulating the levels of free hormone include transport to other parts of the plant and/or inactivation and storage in some compartment ( Fig. 5-7 ).

FIGURE 5-7 . Summary diagram showing regulation of endogenous levels of a hormone.

Inactivation or breakdown of hormones and compartmentation in an inactive form are strategies that are regularly utilized. Similar inactivation or breakdown is also seen if plant tissues are presented with exogenous hormone in unnaturally large quantities or if the plant produces an excessive amount of the hormone as a result of a mutation or genetic transformation.

Before leaving this section, it is important to emphasize that mutants deficient in a particular hormone, or mutants or plants that have been transformed to overproduce a hormone, are invaluable tools in deciphering the physiological and/or biochemical roles of that hormone in plant growth and development. They point out with great specificity the particular roles a hormone plays and far surpass in accuracy the conclusions drawn from supplying the hormone to a whole plant or plant tissues and noting the effect(s).


See where doses have gone, and who is eligible for a shot in each state.

But why do these sex differences happen? Part of the answer could be behavioral. It’s possible that women are more likely than men to report side effects even when their symptoms are the same, said Rosemary Morgan, an international health researcher at the Johns Hopkins Bloomberg School of Public Health. There’s no vaccine-specific research to support this claim, but men are less likely than women to see doctors when they are sick, so they may also be less likely to report side effects, she said.

Still, there’s no question that biology plays an important role. “The female immune response is distinct, in many ways, from the male immune response,” said Eleanor Fish, an immunologist at the University of Toronto.

Research has shown that, compared with their male counterparts, women and girls produce more — sometimes twice as many — infection-fighting antibodies in response to the vaccines for influenza, M.M.R., yellow fever, rabies, and hepatitis A and B. They often mount stronger responses from immune fighters called T cells, too, Ms. Gee noted. These differences are often most robust among younger adults, which “suggests a biological effect, possibly associated with reproductive hormones,” she said.

Sex hormones including estrogen, progesterone and testosterone can bind to the surface of immune cells and influence how they work. Exposure to estrogen causes immune cells to produce more antibodies in response to the flu vaccine, for example.

And testosterone, Dr. Klein said, “is kind of beautifully immunosuppressive.” The flu vaccine tends to be less protective in men with lots of testosterone compared with men with less of the sex hormone. Among other things, testosterone suppresses the body’s production of immune chemicals known as cytokines.

Genetic differences between men and women may also influence immunity. Many immune-related genes are on the X chromosome, of which women have two copies and men have only one. Historically, immunologists believed that only one X chromosome in women was turned on, and that the other was inactivated. But research now shows that 15 percent of genes escape this inactivation and are more highly expressed in women.

These robust immune responses help to explain why 80 percent of autoimmune diseases afflict women. “Women have greater immunity, whether it’s to ourselves, whether it’s to a vaccine antigen, whether it’s to a virus,” Dr. Klein said.

The size of a vaccine dose may also be important. Studies have shown that women absorb and metabolize drugs differently than men do, often needing lower doses for the same effect. But until the 1990s, drug and vaccine clinical trials largely excluded women. “The drug dosages that are recommended are historically based on clinical trials that involve male participants,” Dr. Morgan said.

Clinical trials today do include women. But in the trials for the new Covid vaccines, side effects were not sufficiently separated and analyzed by sex, Dr. Klein said. And they did not test whether lower doses might be just as effective for women but cause fewer side effects.

Until they do, Dr. Klein said, health care providers should talk to women about vaccine side effects so they are not scared by them. “I think that there is value to preparing women that they may experience more adverse reactions,” she said. “That is normal, and likely reflective of their immune system working.”


Soceity’s responsibility

There are those who decry the small differences that have been recorded, or even consider that they do not exist. But why should we want to abolish them? It seems to me that these both reflect identity and contribute to it.

It’s no secret that sex differences have been used as an excuse for gender inequality. But that just means we need to redress that inequality, not deny that gender differences exist. It’s opportunity that is crucial.

A man’s job? Alfred T. Palmer

If this were equal, would we see an even distribution of males and females across all occupations and activities? Not in my opinion. If a job requires physical strength, then it is likely that men will predominate. Also, in the branch of medicine dealing with brain disorders, about 50% of psychiatrists are female, but only about 15-20% are neurologists, and a mere 5% neurosurgeons. Is this gender-related prejudice, or individual preference? Should we insist on an equal gender distribution? Of course not, provided the choice was unfettered. It may be that males are attracted by more technical aspects of medicine, and females by the more person-orientated specialities for reasons that are not just due to upbringing or expectations, but genuine differences in the brain.

But, of course, social norms also contribute to which professions we choose. So we have to make an effort to ensure that women are not hindered from a free choice of profession by social expectations, burdens of child-rearing or selective education. But ultimately, an unequal gender distribution is no longer controversial if opportunities are the same for all. If gender differences then remain, we should accept them.

Thankfully we now see an increasing number of women as distinguished scientists, CEOs of major companies and world leaders. We don’t even bat an eyelid when a woman plays King Lear, that most masculine of roles. Gender identities are changing but let us not muddle the essential distinction between similarity and equality.


Watch the video: Οικογένεια ρομά: Ένα αυτοκινητάκι έκλεψε - Στον εισαγγελέα οι επτά αστυνομικοί (January 2023).