What Organs Respond To Insulin In Animals Bodies

Learning Objectives

1. Identify the major glands and body structures involved in hormone synthesis in vertebrates
2. Remember the functions of selected hormones produced by select major glands
3. Describe the hormone pathway in given examples, including blood glucose, hunger, metamorphosis, stress, and/or sexual practice, and make predictions on how an fauna would respond to given stimuli for each case
4. Recognize instances of negative feedback loops, positive feedback loops, and crosstalk in the example hormone pathways

Vertebrate Endocrine Glands and Hormones

The data below was adapted from OpenStax Biology 37.5

Unlike plant hormones, fauna hormones are often (though not always) produced in specialized hormone-synthesizing glands (shown below). The hormones are so secreted from the glands into the blood stream, where they are transported throughout the trunk. At that place are many glands and hormones in different animal species, and nosotros will focus on only a modest drove of them.

Locations of endocrine glands in the human trunk. Image credit: OpenStax Anatomy and Physiology.

In vertebrates, glands and hormones they produce include (notation that the following listing is non consummate):

• hypothalamus: integrates the endocrine and nervous systems; receives input from the body and other brain areas and initiates endocrine responses to environmental changes; synthesizes hormones which are stored in the posterior pituitary gland; also synthesizes and secretes regulatory hormones that control the endocrine cells in the inductive pituitary gland. Hormones produced include
  • growth-hormone releasing hormone: stimulates release of growth hormone (GH) from the anterior pituitary
  • corticotropin-releasing hormone: stimulates release of adrenocorticotropic hormone (ACTH) from the anterior pituitary
  • thyrotropin-releasing hormone: stimulates release of thyroid-stimulating hormone (TSH) from the anterior pituitary
  • gonadotropin-releasing hormone: stimulates release offollicle -stimulating hormone and luteinizing hormone from the anterior pituitary
  • antidiuretic hormone (vasopressin): promotes reabsorption of water by kidneys; stored in posterior pituitary
  • oxytocin: induces uterine contractions labor and milk release from mammary glands; stored in posterior pituitary
• pituitary gland: the body's master gland; located at the base of the brain and attached to the hypothalamus via a stalk called the pituitary stem; has two distinct regions: the anterior portion of the pituitary gland is regulated by releasing or release-inhibiting hormones produced by the hypothalamus, and the posterior pituitary receives signals via neurosecretory cells to release hormones produced by the hypothalamus. Hormones produced (or secreted) past the gland include:
  • anterior pituitary: the following hormones areproduced by the anterior pituitary and released in response to hormone signals from the hypothalamus
    • growth hormone: stimulates growth factors
    • adrenocorticotropic hormone (ACTH): simulates adrenal glands to secrete glucocorticoids such as cortisol
    • thyroid-stimulating hormone: stimulates thyroid gland to secrete thyroid hormones
    • follicle-stimulating hormone (FSH)andluteinizing hormone (LH): stimulates production of gametes and sex steroid hormones
    • prolactin: stimulates mammary gland growth and milk product
  • posterior pituitary: the following hormones areproducedby the hypothalamus andstored in the posterior pituitary
    • antidiuretic hormone: promotes reabsorption of water by kidneys; stored in posterior pituitary
    • oxytocin: induces uterine contractions during labor and milk release from mammary glands during suckling; stored in posterior pituitary
• thyroid gland: butterfly-shaped gland located in the neck; regulated by the hypothalamus-pituitary axis; produces hormones involved in regulating metabolism and growth:
  • thyroxine (T₄) andtriiodothyronine (T3): increase the basal metabolic rate, affect protein synthesis and other metabolic processes, assistance regulate long bone growth (synergy with growth hormone)
• adrenal glands: two glands, each located on ane kidney; consist of adrenal cortex (outer layer) and adrenal medulla (inner layer), which each produce different sets of hormones:
  • adrenal cortex:
    • mineralocorticoids, such as aldosterone:increases reabsorption of sodium past kidneys to regulate water rest
    • glucocorticoids, such as cortisol and related hormones: long-term stress response hormones that increase blood glucose levels by stimulating synthesis of glucose and gluconeogenesis (converting a non-carbohydrate to glucose) by liver cells; promote the release of fatty acids from adipose tissue
  • adrenal medulla:
    • epinephrine (adrenaline)andnorepinephrine (noradrenaline): brusque-term stress response ("fight-or-flying") hormones that increase heart charge per unit, animate rate, cardiac musculus contractions, blood pressure, and blood glucose levels; accelerate the breakup of glucose in skeletal muscles and stored fats in adipose tissue; release of epinephrine and norepinephrine is stimulated direct by neural impulses from the sympathetic nervous arrangement
• pancreas: located between the breadbasket and the proximal portion of the pocket-sized intestine; regulates claret glucose levels via the hormones:
  • insulin: decreases blood glucose levels by promoting uptake of glucose by liver and muscle cells and conversion to glycogen (a sugar storage molecule)
  • glucagon: increases claret glucose levels by promoting breakdown of glycogen and release of glucose from the liver and musculus
• gonads: produce sex steroid hormones that promote development of secondary sex characteristics and regulation of gonad function:
  • ovaries(in females):
    • estradiol: regulates development and maintenance of ovarian and menstrual cycles
    • progesterone: prepares uterus for pregnancy
  • testes (in males): regulates development and maintenance of sperm production

The hormones produced and/or stored past the pituitary gland are summarized here:

Modification of work by OpenStax Higher – Beefcake & Physiology, Connexions Web site. http://cnx.org/content/col11496/one.six/, Jun 19, 2013., CC BY 3.0, https://eatables.wikimedia.org/w/index.php?curid=30148147

This video provides a nice overview of the glands and hormones of the vertebrate endocrine organization:

Hormonal Regulation of Body Processes in Animals

The data beneath was adapted from OpenStax Biology 37.3

Hormones have a wide range of effects and modulate many different body processes. The key regulatory processes that will exist examined here are those affecting blood glucose, hunger, metamorphosis, stress, and sex. Nosotros will primarily focus on these processes in vertebrates, merely volition besides consider invertebrates in some cases.

Blood Glucose

Glucose is the primary energy source for virtually animal cells, and it is distributed throughout the body via the blood stream. The ideal, or target, claret glucose concentration is about 90 mg/100 mL of blood, which equates to near 1 tsp of glucose per half dozen quarts of blood. Afterward a repast, carbohydrates are cleaved down during digestion and absorbed into the blood stream. The amount present following a repast is typically more than what the body needs at that moment, and then the extra glucose must be removed and stored for later use. The opposite phenomenon occurs following a menstruation of fasting.Insulin and glucagon are the 2 hormones primarily responsible for maintaining advisable blood glucose levels.

Insulin is produced by the beta cells of the pancreas, which are stimulated to release insulin as claret glucose levels rise (for example, subsequently a meal is consumed). Insulin lowers blood glucose levels through several processes:

• enhances the rate of glucose uptake and utilization by target cells, which use glucose for ATP product
• stimulates the liver to convert glucose to glycogen, which is then stored by cells for after utilize
• increases glucose transport into sure cells, such equally muscle cells and the liver
• stimulates the conversion of glucose to fatty in adipocytes and the synthesis of proteins.

These deportment together cause cause blood glucose concentrations to fall, called a hypoglycemic 'depression sugar' effect, which inhibits further insulin release from beta cells through a negative feedback loop.

When claret glucose levels pass up beneath normal levels, for example between meals or when glucose is utilized speedily during practise, the hormone glucagon is released from the alpha cells of the pancreas. Glucagon raises blood glucose levels, eliciting what is called a hyperglycemic upshot through several mechanisms:

• stimulates the breakdown and release of glucose from glycogen in skeletal muscle cells and liver cells
• stimulates absorption of amino acids from the blood by the liver, which so converts them to glucose
• stimulates adipose cells to release fatty acids into the claret

Glucose can then be utilized as energy by muscle cells and released into apportionment by the liver cells. These actions mediated by glucagon effect in an increase in blood glucose levels to normal homeostatic levels. Rising blood glucose levels inhibit further glucagon release by the pancreas via a negative feedback machinery. In this way, insulin and glucagon work together to maintain homeostatic glucose levels, as shown in beneath.

Insulin and glucagon regulate blood glucose levels. When blood glucose levels autumn, the pancreas secretes the hormone glucagon. Glucagon causes the liver to pause down glycogen, releasing glucose into the claret. Every bit a effect, blood glucose levels ascension. In response to loftier glucose levels, the pancreas releases insulin. In response to insulin, target cells have upward glucose, and the liver converts glucose to glycogen. Equally a outcome, blood glucose levels fall. Image credit: OpenStax Biology

Uncontrolled blood glucose levels can lead to different types of serious medical conditions:

• Impaired insulin function can lead to a status called diabetes mellitus. Diabetes mellitus can be caused past depression levels of insulin production by the beta cells of the pancreas, or by reduced sensitivity of tissue cells to insulin. Either of these situations prevents glucose from beingness captivated by cells, causing high levels of blood glucose, or hyperglycemia (high saccharide). Loftier claret glucose levels get in difficult for the kidneys to recover all the glucose from nascent urine, resulting in glucose beingness lost in urine. High glucose levels too result in less water being reabsorbed by the kidneys, causing loftier amounts of urine to be produced; this may result in dehydration. Over time, loftier claret glucose levels can cause nerve damage to the optics and peripheral trunk tissues, as well as impairment to the kidneys and cardiovascular system.
• Oversecretion of insulin can crusade hypoglycemia, low blood glucose levels, which causes insufficient glucose availability to cells, often leading to musculus weakness, and can sometimes crusade unconsciousness or expiry if left untreated.

This animation describes diabetes and the roles of insulin and the pancreas in blood glucose regulation:

Hunger Management

The immediate class of energy for almost brute cells is glucose, and actress glucose is stored as glycogen which is readily cleaved downwards into glucose when needed. Longer term reserves of free energy are stored as fats, in cells called adipocytes.  Likewise trivial fat means at that place may no be enough energy reserves in times when food is less bachelor, and will crusade an animal to experience hungry; still, besides much fat is more often than not unhealthy and is likely to cause an animate being to feel satisfied. The hormone leptin helps maintain an appropriate amount of fat reserves in the body.

Rather than being secreted from a specialized gland, leptin is produced by adipocytes in proportion to their number and size. More and larger adiopcytes means more leptin; fewer and smaller adipocytes means less leptin. Leptin levels are detected by sensors in the hypothalamus. High lepin levels suppress appetite and speed up metabolism, while low levels of leptin stimulate hunger and wearisome downwards metabolism, resulting in a negative feedback loop. These activities are mediated through signaling from the hypothalamus-pituitary axis to the thyroid, which plays a major role in regulating metabolic function.

In response to high levels of leptin, the hypothalamus releases thyrotropin-releasing hormone, signals to the anterior pituitary to release thyroid-stimulating hormone. The thyroid the releasesthyroxine, also known as tetraiodothyronine or T_iv , and triiodothyronine, also known as T₃ . These hormones affect nearly every cell in the trunk except for the adult brain, uterus, testes, blood cells, and spleen. T₃ and T₄ actuate genes involved in energy production and glucose oxidation, resulting in increased rates of metabolism and trunk heat production which together cause an increased rate of caloric usage. Low levels of leptin cause the opposite response, leading to a decreased metabolic charge per unit to conserve free energy.

This video describes how the thyroid manages metabolic processes:

Growth and Metamorphosis

In vertebrate species that undergo metamorphosis, such as amphibians, surges of T_three are responsible for initiating development of new structures, reorganization of  internal organ systems, and other processes that occur during metamorphosis. In insects, metamorphosis is controlled past a set of hormones that determine whether the fauna grows into the side by side larval stage or changes into an adult as it gets larger. The corpus allatum, an endocrine gland in the encephalon, secretes a hormone calledjuvenile hormone during all larval stages, which maintains the larval status of the animal. As the larvae grows, another endocrine gland in the brain releases prothoracicotropic hormone, which signals to the prothoracic gland to release the hormoneecdysone. Ecdysone promotes either molting (shedding the exoskeleton) or metamorphosis, depending on the level of juvenile hormone. Ecdysone in combination with loftier juvenile hormone results in molting into the next larval phase; ecdysone in combination with low juvenile hormone results in metamorphosis into an developed.

Stress: Brusk vs Long Term Responses

I of the main functions of endocrine hormones is to ensure the torso's internal environment remains stable (homeostasis). Stressors are stimuli that disrupt homeostasis. Some stressors crave immediate attention and activate the brusk term, "fight-or-flight" stress response, which stimulates an increase in energy levels through increased blood glucose levels. This prepares the body for physical activity that may be required to answer to stress: to either fight for survival or to flee from danger. The fight-or-flying response exists in some form in all vertebrates.

In contrast, some stresses, such as illness or injury, can terminal for a long fourth dimension. Glycogen reserves, which provide energy in the short-term response to stress, are exhausted afterwards several hours and cannot come across long-term energy needs. If glycogen reserves were the just energy source available, neural functioning could non be maintained once the reserves became depleted due to the nervous organization's loftier requirement for glucose. In this situation, the body has evolved a response to counter long-term stress through the actions of the glucocorticoids, which ensure that long-term energy requirements tin be met. The glucocorticoids mobilize lipid and protein reserves, stimulate gluconeogenesis, conserve glucose for use by neural tissue, and stimulate the conservation of salts and water.

The sympathetic nervous organization regulates the stress response via the hypothalamus. Stressful stimuli cause the hypothalamus to point the adrenal medulla (which mediates short-term stress responses) via nerve impulses, and the adrenal cortex, which mediates long-term stress responses, via the hormone adrenocorticotropic hormone (ACTH), which is produced by the inductive pituitary.

Short-term Stress Response

When presented with a stressful state of affairs, the body responds by calling for the release of hormones that provide a burst of energy. The hormones epinephrine (too known equally adrenaline) and norepinephrine (too known as noradrenaline) are released by the adrenal medulla. These two hormones fix the body for a outburst of free energy in the following ways:

• cause glycogen to exist cleaved down into glucose and released from liver and muscle cells
• increase blood pressure
• increase animate rate
• increase metabolic charge per unit
• change blood flow patterns, leading to increased blood flow to skeletal muscles, center, and brain; and decreased blood menses to digestive system, skin, and kidneys

Long-term Stress Response

Long-term stress response differs substantially from short-term stress response. The torso cannot sustain the bursts of energy mediated by epinephrine and norepinephrine for long times. Instead, other hormones come up into play. In a long-term stress response, the hypothalamus triggers the release of ACTH from the inductive pituitary gland. The adrenal cortex is stimulated by ACTH to release steroid hormones called corticosteroids. The 2 main corticosteroids are glucocorticoids such every bit cortisol, and mineralocorticoids such as aldosterone. These hormones mediate the long-term stress response in the following ways:

• glucocorticoids:
  • promote breakdown of fat into fat acids in the adipose tissue and release into bloodstream for ATP product
  • stimulate glucose synthesis from fats and proteins to increment blood glucose levels
  • inhibit immune role to conserve energy
• mineralcorticoids:
  • promote retentiveness of sodium ions and water by kidneys
  • increase claret pressure and volume (via sodium/h2o retention)

Coticosteriods are under control of a negative feedback loop (illustrated below), which tin become mis-regulated in cases of chronic long-term stress.

Diagram of physiologic negative feedback loop for glucocorticoids. Paradigm credit: DRosenbach [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

In contrast to chronic long-term stress, the video below discusses some of the circumstances where stress can exist practiced for y'all:

Source: https://organismalbio.biosci.gatech.edu/chemical-and-electrical-signals/animal-hormones/

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