Hormonal Communication Flashcards
what are hormones?
Hormones are signalling molecules that are released into the blood.
what are target cells?
Cells in the body that have a specific receptor for a given hormone
where are hormones released from?
Hormones are released by endocrine glands which are found in the endocrine system
what is the endocrine system?
A communication system that uses hormones as signalling molecules
what are endocrine glands?
Endocrine glands are ductless glands and include the pancreas, pituitary gland, testes and ovaries.
They are made up of groups of cells, which secrete the hormone into capillaries associated with the gland.
whats the difference between endocrine glands and exocrine glands?
endocrine glands secrete hormones directly into the blood, while exocrine glands secrete substances such as enzymes into ducts
what are adrenal glands?
he adrenal glands are endocrine glands which sit just above the kidney. They are composed of an adrenal cortex and an adrenal medulla
what is the role of the adrenal medulla?
• The adrenal medulla is responsible for the secretion of adrenaline,which carries out part of the body’s response to stress (including raising heart rate)
what is the adrenal cortex made up of?
• The adrenal cortex is made up of three distinct layers — the zona glomerulosa, the zona fasciculata and the zona reticularis, which are surrounded by an outer capsule
why are there different layers of the cortex?
Each of the layers of the cortex secretes different hormones
where is the zona glomerulosa and what does it do?
• The zona glomerulosa is the outermost layer and secretes mineralocorticoids
what are mineralocorticoids?
• Mineralocorticoids are hormones involved in controlling the levels of sodium and potassium in the blood
what is aldosterone?
• Aldosterone is a mineralocorticoid which acts on cells in the distal tubules and collecting ducts of the kidneys
what is the role of aldosterone?
• Aldosterone increases sodium absorption, decreases potassium absorption, and reduces the amount of water leaving in the urine, thus increasing blood pressure
where is the zona fasciculata and what does it do?
• The zona fasciculata is the middle layer of the adrenal cortex, and it secretes glucocorticoids
what are glucocorticoids?
• Glucocorticoids are hormones which control the metabolism of different respiratory substrates in the body
what is the role of the glucocorticoids cortisol?
• The glucocorticoid cortisol increases blood glucose concentration by stimulating glucose production from larger stored compounds such as glycogen, as well as fats and proteins
where is the zona reticularis?
• The zona reticularis is the inner-most layer of the adrenal cortex
what is the role of the zona reticularis?
- Like the zona fasciculata, it can secrete cortisol
- It is also thought to secrete precursor androgens which are taken up by the ovaries or testes and converted to sex hormones
what is the role of sex hormones?
• Sex hormones, like testosterone or oestrogen, bring about the development of secondary sexual characteristics
how is the fight or flight response carried out?
- The first stage of the response is to detect a threat — this is carried out by the cerebrum
- The cerebrum then passes this information down to association centres
- When a threat is recognised the hypothalamus is stimulated which has two responses:
• It activates the sympathetic nervous system
• It stimulates the anterior pituitary gland to secrete hormones
what is the role of the sympathetic nervous system in threat aversion?
- When the hypothalamus activates the sympathetic nervous system, impulses are sent down sympathetic neurones
- This stimulates sympathetic responses such as increased heart rate and pupil dilation
what happens when the sympathetic neurones that target the adrenal medulla stimulate the release of adrenaline?
○Increases stroke volume, heart rate and mental awareness
○Relaxes smooth muscle in the bronchioles
○Initiates general vasoconstriction to increase blood pressure
how do determine whether we need a sympathetic nervous system or endocrine system?
Sympathetic nervous communication is used for rapid responses. If the threat is prolonged the action of the endocrine system is needed.
what is the role of the anterior pituitary gland in threat aversion?
- During the fight or flight response the hypothalamus secretes releasing hormones (also known as releasing factors) into the bloodstream
- The releasing factors travel to the anterior pituitary (down a portal vessel)where they stimulate the release of tropic hormones (hormones that stimulate the activity of other endocrine glands)
- The hypothalamus produces two releasing factors — corticotropin-releasing hormone (CRH) and thyrotropin-releasing hormone (TRH) — which cause the release of two different tropic hormones from the pituitary
what is the role of the corticotropin- releasing hormone?
• CRH is a releasing factor secreted by the hypothalamus which stimulates the release of adrenocorticotropic hormone (ACTH) in the anterior pituitary
what is the role of the ACTH?
- ACTH targets the adrenal cortex, where it stimulates the release of glucocorticoids like cortisol, which regulate carbohydrate metabolism
- This helps to raise the blood glucose levels to prepare the body for activity
what process does the release of thyrotropin- releasing hormone initiate?
- TRH is another releasing factor secreted by the hypothalamus
- It stimulates the release of thyroid-stimulating hormone (TSH) in the anterior pituitary
- TSH stimulates the thyroid gland to release thyroxine
- Thyroxine has a widespread impact as most cells in the body have receptors specific for it
- Thyroxine stimulates these cells by making them more sensitive to adrenaline and increasing the rate of metabolism
what are the 2 different types of hormones?
- peptide
- steroid
what are steroid hormones made up of?
steroid hormones are formed from lipids
describe the properties of steroid hormones
• They are soluble in the cell surface membrane, and therefore can enter cells directly through the membrane
what happens after steroids go into the cell and bind to specific receptors in the cytoplasm
- The receptor-steroid complex enters the nucleus, where it binds to another specific receptor on chromatin
- The production of mRNA is stimulated as a result of this binding
what are peptide hormone made up of?
• Peptide (or protein) hormones are made of amino acids
describe the properties of peptide hormones
• They are not soluble in the cell surface membrane, and therefore cannot enter cells
how do peptide hormones influence target cells?
- This means they can only influence target cells by binding to receptors on the cell surface
- Hormone-binding causes the release of molecules inside the cell called second messengers
- The second messengers then carry out the effect by switching the transcription of genes on or off
whats a secondary molecule?
A signalling molecule inside a cell that stimulates a change in the activity of the cell.
give some examples of some first messengers and how they often carry out their effects
Non-steroid (or peptide) hormones such as adrenaline are first messengers, and they often carry out their effects by binding to and activating G-proteins embedded in the membrane.
what is the process that initiates a secondary molecule (include steps)?
- A hormone binds to its corresponding hormone receptor, activating the coupled G-protein
- The active G-protein activates an effector molecule. The effector molecule is usually an enzyme that changes an inactive second messenger into an active second messenger
- The activated second messenger can then either act directly on another protein or initiate a cascade of enzyme-controlled reactions which alter the activity of the cell
what is adenyl cyclase?
Adenyl cyclase is a common effector molecule and it acts by converting ATP to cyclic AMP (cAMP).
what is the pancreas and what does it do?
The pancreas is a small organ involved in digestive and endocrine (hormonal) functions.It forms,then secretes digestive juices into the duodenum of the small intestine.
how does the pancreas act as both a exocrine and endocrine gland?
Hormones from the islets of Langerhans in the pancreas are secreted into the blood.
Therefore, the pancreas acts as both an exocrine (secretes substances into a duct) and an endocrine gland (substances secreted into the blood).
describe the structure of the pancreas
- The pancreas contains small groups of exocrine cells called acini (singular acinus). These cells synthesise digestive enzymes and secrete them, within pancreatic juices, into a tubule
- The acini are grouped together into lobules surrounding a tubule
- These tubules join together to form intralobular ducts,which then combine to form the pancreatic duct
what path do the pancreatic cells take?
• Pancreatic juices travel into the duodenum through the pancreatic duct
describe the structure and function of the islets of langerhans
• Islets of Langerhans are groups of cells which containα- and β-cells.
These endocrine cells synthesise and secrete hormones into the blood vessels
how does the pancreas act as an exocrine?
Exocrine cells of the acini secrete pancreatic juices that travel through a series of ducts and eventually into the small intestine.
what does the fluid secreted by the exocrine cells of the pancreas contain?
• Enzymes involved in digestion
○Pancreatic amylase (a carbohydrase) digests amylose to maltose
○Trypsinogen (an inactive protease), is converted into its active form (trypsin) upon entry to the duodenum
○Lipase which digests lipids
• Sodium hydrogen carbonate, which neutralises acid coming from the low pH environment of the stomach
what is the endocrine function of the pancreas?
Amongst the lobules of acini cells are islets of Langerhans, groups of cells containing two endocrine cell types that secrete hormones directly into blood vessels:
• α-cells, which secrete glucagon
• β-cells, which insulin
what is the role of the hormone insulin?
Insulin is a hormone synthesised in and released from the β-cells in the pancreas when blood glucose concentration rises too high.
It acts on hepatocytes, causing the removal of glucose from the blood. Glucose is then converted to and stored as glycogenin these cells.
where are the b-cells located?
within the islets of langerhans
what is the role of the b-cells?
β-cells, within the islets of Langerhans, detect the increase in blood glucose concentration and respond by secreting insulin into the blood.
When blood glucose levels drop below a certain level, insulin secretion is halted.
describe the steps involved in the mechanism of insulin release?
- When there is no glucose in the blood, the β-cell has a negative resting potential. This is because positive potassium ions leak out of the open potassium channels, making the inside of the cell more negative
- When blood glucose concentrations are high, glucose diffuses into β-cells
- Inside the cell, glucokinase attaches a phosphate group to glucose,preventing its exit from the cell
- Respiration rapidly converts the glucose into molecules of ATP
- The newly formed ATP causes potassium channels to close
- Without potassium leaving, the membrane potential of the cell becomes less negative as the positive potassium ions accumulate inside the cell
- This change in membrane potential causes calcium channels to open
- Calcium enters the cell and binds to vesicles full of insulin
- The binding of calcium causes the vesicles to fuse with the membrane, and insulin is released into the blood by exocytosis
how is the blood glucose concentration regulated?
Cells within the islets of Langerhans monitor blood glucose concentration
what happens if the blood glucose concentration strays away form the optimum?
if the level strays from the optimum range the α and β-cells respond by releasing glucagon or insulin respectively.
These hormones act on the hepatocyte cells in the liver triggering either the release or storage (as glycogen)of glucose.
what is the difference between hypoglycaemic and hyperglycaemic?
When blood glucose concentration is below 4 mmoldm-3a person is said to be hypoglycaemic.
When blood glucose concentration is above 6mmoldm-3, this is referred to as hyperglycaemia.
what happens to a person who is hypoglycaemic?
When blood glucose concentration is below 4 mmoldm-3a person is said to be
hypoglycaemic.
The main worry of hypoglycaemia is poor delivery of glucose to the brain.
- Mild hypoglycaemia causes tiredness and irritability
- Severe hypoglycaemia can cause impaired brain function, confusion, seizures and may even lead to unconsciousness, coma and death
what is the risk of hyperglycamia?
When blood glucose concentration is above 6mmoldm-3, this is referred to as hyperglycaemia. The risk associated with hyperglycaemia is that long-term raised blood glucose levels can cause organ damage.
why is insulin unbale to pass through the cell-surface membrane and what does it do instead?
Insulin is unable to pass through the cell-surface membrane as it is a small protein, therefore it binds to specific membrane bound receptors on its target cells’ surfaces to exert its effects.
describe the negative feedback mechanism of insulin
- When blood glucose concentration rises above 6 mmoldm-3, the β-cells in the pancreas detect this change and release insulin into the blood stream
- Insulin travels in the blood and attaches to receptors on the surfaces of its target cells, which include liver hepatocytes, muscle cells and some types of brain cell
- The enzyme tyrosine kinase is associated with insulin receptors on the inside of the membrane. Upon the binding of insulin, tyrosine kinase phosphorylates (adds a phosphate group to) inactive enzymes inside the cell
- Phosphorylation activates these previously inactive enzymes and triggers a cascade of enzyme-controlled, intracellular reactions
- Insulin brings about changes inside the cell that lower the blood glucose levels
- After blood glucose concentration has been lowered back to its optimum level, insulin stops being secreted.This is an example of negative feedback
how do we make sure more glucose is used in respiration rather than fats and proteins?
- At low insulin concentrations vesicles of glucose transporter lie in the cytoplasm of cells
- When insulin binds to its receptors, these vesicles fuse with the cell-surface membrane and insert glucose transporters into it. Glucose transporters allow more glucose to enter the cell from the bloodstream
- Insulin also causes glucose transporters to change shape, opening them and allowing more glucose into the cell via facilitated diffusion
- Both of the above lead to more glucose being absorbed from the blood into cells
- Insulin causes more glucose (rather than fats or proteins) to be used in respiration
how do we reduce the concentration of glucose in the blood?
- Insulin causes more glucose (rather than fats or proteins) to be used in respiration
- Insulin also activates enzymes which convert glucose into glycogen(glycogenesis) and fats
Working together, these processes reduce the concentration of glucose in the blood
where is glucagon released from?
Glucagon is a hormone released fromα-cells, within islets of Langerhans, in response to low blood glucose levels.
how does glucagon increase blood glucose conc when it’s too low?
When blood glucose concentration is low, α-cells in the pancreas detect this change and release glucagon.
- Glucagon travels in the blood to liver hepatocyte cells which possess specific receptors for glucagon on the cell surface membranes
- Glucagon binds to these receptors and stimulates a G-protein inside the membrane to activate adenyl cyclase inside the cell
- The adenyl cyclase converts ATP to cAMP. cAMP goes on to activate a series of enzyme-controlled reactions in the cell which then act to increase the concentration of glucose in the blood
- After blood glucose concentration has returned to its optimum, glucagon stops being released
how does glucagon increase blood glucose concentration?
- Glucagon increases blood glucose concentration by producing glucose from other molecules
- One way of doing this is by activating enzymes which break down glycogen into glucose (glycogenolysis) via the phosphorylase A enzyme
- Glucagon stimulates more fatty acids to be used in respiration, therefore sparing glucose
- Another method is to activate enzymes that convert glycerol (from lipids) and amino acids into glucose. This is called gluconeogenesis
what is gluconneogenesis?
converting glycerol (from lipids) and amino acids into glucose
describe the process of glycogenesis
- When blood glucose concentration is too high, the cells of the liver can take in glucose from the blood
- They then join the glucose molecules together to make glycogen. This is called glycogenesis
- The liver stores this glycogen, allowing glucose to be removed from the blood, reducing blood glucose concentration
- This is a result of the actions of insulin
describe the process of glycogenolysis
- The process of glycogenesis means that the liver has lots of glycogen stores
- This glycogen can be utilised when the blood glucose concentration is low
- Glycogen is broken up into glucose molecules. This is called glycogenolysis
- This is a result of the actions of glucagon
describe the process of gluconeogenesis
- When the liver’s supply of glycogen has runout, the liver can use other molecules, like glycerol and amino acids, to make glucose. This is called gluconeogenesis
- This is a result of the actions of glucagon
define diabetes
A condition where the concentration of glucose in the blood cannot be controlled effectively.
what can diabetes lead to after eating and after exercising?
- Diabetes can lead to high blood glucose concentrations(hyperglycaemia) after eating a meal
- It can also lead to low blood glucose concentrations(hypoglycaemia) after exercising
what is the difference in the body’s response to glucose with healthy people and diabetics?
- When healthy people are given glucose solution, their body produces insulin in response to the increase in blood glucose concentration. This causes blood glucose to drop back to normal levels
- When diabetics are given glucose solution, a reduced insulin response (or no response at all) occurs
- This means that the blood glucose concentration peaks higher and is raised for longer as excess glucose is not removed quickly
what age group does type 1 diabetes usually present in?
• Type 1 diabetes usually presents itself in young people, thus described as early-onset
describe type 1 diabetes
- In type 1 (insulin-dependent) diabetes the body cannot produce insulin
- Type1diabetes is thought to be caused by an autoimmune attack on the β-cells of the pancreas, preventing them responding to increases in blood glucose concentration
- Diabetics can’t produce any insulin, therefore when glucose is ingested it cannot be converted to other molecules such as glycogen
what are the 2 effects of type 1 diabetes?
1) Excess glucose remains in the blood for longer, leading to hyperglycaemia
2) There are no glycogen stores, so when blood glucose drops, there is no stored glycogen to be broken down into glucose. This can lead to hypoglycaemia
what age group is type 2 diabetes usually present in?
• Type 2 diabetes usually presents itself in people over the age of 40, thus is described as mature-onset
describe type 2 diabetes
• In type 2 (insulin-independent) diabetes, individuals can produce insulin, but not enough. Additionally, the cells do not respond to insulin as effectively. This is because the insulin receptors on the surface of muscle and liver cells have become less sensitive to insulin
what is the effect of type 2 diabetes?
• People with type2 diabetes have almost permanently raised levels of blood glucose (hyperglycaemia) which can damage the major organs and circulation
what are the risk factors of type 2 diabetes?
There are environmental and genetic causes of type 2 diabetes. Environmental factors that increase the risk of getting type 2 diabetes include:
- Obesity
- High sugar diet
- Lack of regular exercise
Genetic factors that increase the risk of getting type 2 diabetes include:
- Being from an Asian or African-Caribbean background
- A family history of type 2 diabetes
what are some treatments for type 1 diabetes?
Type1diabetes is caused by an inability to produce insulin. The main method of treatment through insulin injections. In order to know when to inject insulin and the correct dose of injection, blood glucose concentration must be carefully monitored.Alternative treatment options instead of regular insulin injections include:
- A device which pumps insulin at a controlled level into the body through a small needle into the bloodstream. This is called insulin pump therapy
- Islet cell transplantation of healthy beta cells from a donor into a type 1 diabetic patient
- Complete pancreas transplant from a donor
- Stem cell research has shown the potential of growing new islets of Langerhans in the pancreas. These stem cells may be taken from the bone marrow or placenta
what are some sources of insulin?
In the past, insulin was extracted from the pancreases of pigs.
Nowadays insulin is made using Escherichia coli bacteria that have been genetically modified to produce human insulin
why insulin made using Escherichia coli bacteria preferable to insulin extracted from pigs?
- The insulin produced is an exact copy of human insulin, meaning it is specific to the human insulin receptor
- This allows it to be more effective in smaller doses, reducing the risk of insulin tolerance
- It also means that the risk of infection and rejection by the immune system is less likely
- Not having to use pigs reduces ethical problems, is more adaptable to demand, and cheaper
what are some treatments for type 2 diabetes?
Type2diabetes is a less severe disease and is mostly treated with lifestyle changes, including:
- Losing weight
- Exercising more
- Making sure energy intake matches the amount of energy burnt, especially monitoring carbohydrate intake
Drugs can be used to help slow down the absorption of glucose in the digestive system or reduce the release of glucose from the liver into the bloodstream. They can also stimulate insulin production in the pancreas. In more severe cases insulin injections are used.
