5.1.4 Hormonal Communication Flashcards
what is another word for the hormonal system
endocrine system
what is the hormonal system made up of
glands (called endocrine glands) and hormones
what are endocrine glands
group of cells that are specialised to secrete hormones
- e.g. the pancrease secretes hormones
what are hormones
“chemical messengers”
- most are proteins and peptides, e.g. insulin
- can be steroids, e.g. progesterone
when are hormones secreted by glands
when the endocrine gland is stimulated
when can an endocrine gland be secreted
- by a change in concentration of a specific substance, e.g. another hormone
- or can also be stimulated by electrical impulses
how do hormones travel around the body
- diffuse directly into the blood
- then are taken around by the circulatory system
when do hormones leave the blood
- diffuse out of the blood all over the body
- but each hormone will only bind to specific receptors for that hormone, found on the membranes of some cells
- = target cells
what is target tissue
- tissue that contains target cells
- contains the specific receptors for the hormone to bind to
what happens when hormones attach to a receptor on a target cell
they trigger a response in these cells (the effectors)
what is the chain of events that occurs in the hormonal system, and give example of low blood concentration
STIMULUS [low blood conc.]
RECEPTORS [on the pancreas cells detect this low conc.]
HORMONES [pancreas releases hormone glucagon into the blood]
EFFECTORS [target cells in the liver detect glucagon and convert glycogen into glucose]
RESPONSE [glucose is released into the blood, and so the glucose conc. increases]
why are hormones referred to as first messengers
because they carry the chemical message the first part of the way
- endocrine gland → the receptors on the target cell
what do hormones do when they bind to a receptor, as a first messenger
- it activates an enzyme in the cell membrane
- this enzyme catalyses the production of a molecule inside the cell called a signalling molecule
- this molecule signals to other parts of the cell to change how the cell works
why are signalling molecules called second messengers
they carry the chemical message the second part of the way
- receptor → other parts of the cell
what do second messengers activate
a cascade (chain of events) inside the cell
what is an example of a second messenger
cAMP - cyclic AMP
how does cAMP work as a second messenger
- the hormone adrenaline is the first messenger
- it binds to specific receptors in the cell membranes of many cells, e.g. liver cells
- when adrenaline binds, it activates an enzyme in the membrane called adenylyl cyclase
- activated adenylyl cyclase catalyses the production of second messenger cyclic AMP from ATP
- the cAMP then activates a cascade (e.g. the cascade of enzyme reactions that make more glucose available to the cell by catalysing the breakdown of glycogen into glucose
how could you show in a diagram how cAMP is made
- on the cell membrane, you have the receptor
- outside the cell, adrenaline binds to the receptor
- this activates adenylyl cyclase
- this transfers ATP to cAMP
- which leads to a cascade of reactions inside the cell
where are the adrenal glands found
just above your kidneys
what are the two parts of your adrenal glands
- outer part called cortex
- inner part called the medulla
- both have different functions, and produce different responses
what does the adrenal cortex secrete
- steroid hormones
- such as cortisol (a glucocorticoid) and aldosterone (mineralocorticoids) when your stressed
- have both a short-term and long term response to stress, but also vital to life
- also small amount of androgens, male and female sex hormones
what are the effects of hormones released by the cortex in short and long term responses to stress
- stimulating the breakdown of proteins and fats into glucose, increasing the amount of energy available so the brain and muscles can respond to the situation (cortisol)
- increasing blood volume and pressure by increasing the uptake of sodium ions and water by the kidneys (aldosterone)
- suppressing the immune system
what type of hormones does your medulla secrete
- catecholamine hormones (modified amino acids)
- e.g. adrenaline and noradrenaline when you’re stressed
- make more energy available short-term
what are the effects of hormones released by your medulla as short-term responses to stress
- increasing heart rate and breathing rate
- causing cells to break down glycogen into glucose
- constricting some blood vessels so that blood is diverted to the brain and muscles
what response are hormones released by the adrenal glands involved in
fight or flight
where is the pancreas found
below the stomach
- attached to the duodenum of the stomach via the pancreatic duct
- surrounded by blood vessels
what are the islets of Langerhans
the areas of the pancreas that contain endocrine tissue
where are the islets of Langerhans found
found in clusters around blood capillaries
what do the islets of Langerhans secrete
hormones directly into the blood
what are the two types of cells that make up the islets of Langerhans
- alpha cells α : secrete glucagon
- beta cells β : secrete insulin
- both hormones help to control blood glucose concentration
what is a beta cell made up of
- β cell membrane
- nucleus
- mitochondria
- secretory vesicle containing insulin
- rough endoplasmic reticulum
how would you be able to view pancreatic tissue under a light microscope
- the islets of Langerhans (the endocrine tissue) would appear as paler patches amongst all the other cells
- the stained cells in them would be alpha and beta cells
how would you be able to differentiate between alpha and beta cells in the islets of Langerhans
- via using differential staining, otherwise very difficult to tell
- e.g. use chrome haematoxylin and phloxine
- the beta cells would be stained purple
- the alpha cells would be stained pink
why does blood glucose need to be so carefully controlled
all cells need a constant energy supply to work
what is the normal concentration of glucose in the blood
90 mg per 100 cm3
what monitors blood glucose concentration
cells in the pancreas
why may blood glucose levels rise and fall
- rise when eating foods containing carbohydrates
- fall after exercise, as more glucose is used in respiration to release energy
what are the two hormones that control blood glucose concentration, and how are they secreted
- beta cells secrete insulin into the blood
- alpha cells secrete glucagon into the blood
- these two hormones act on effectors, which respond to restore the blood glucose concentration to a normal level
what is the role of insulin:
- what secretes it
- where does it bind to
- secreted by beta cells when blood glucose concentration is too high
- LOWERS BLOOD GLUCOSE CONCENTRATION
- binds to specific receptors on the cell membranes of LIVER(hepatocytes) and MUSCLE cells
- increases the permeability of cell membranes to glucose, so cells take up more glucose
- also activates enzymes that convert glucose into glycogen
- cells are then able to store glycogen in their cytoplasm, as an energy source
- also increases the rate of respiration of glucose, especially in muscle cells
what is glycogenesis
- the process of forming glycogen from glucose
- glyco = glycogen
- genesis = making
what does glucagon do:
- what secretes it
- what does it bind to
- RAISES BLOOD GLUCOSE CONCENTRATION when too low
- secreted by alpha cells
- binds to specific receptors on the cell membranes of liver cells
- activates enzymes that break down glycogen into glucose
- also promotes the formation of glucose from glycerol and amino acids
what is glycogenolysis
the breakdown of glycogen into glucose
- glycogen
- lysis = splitting
what is gluconeogenesis
the process of forming glucose from non-carbohydrates, e.g. glycerol and amino acids
- gluco = glucose
- neo = new molecules
- genesis = making
what is the negative feedback mechanisms for controlling blood glucose when it is too high
- there is a rise in blood glucose concentration
- the pancreas detects this
- beta-cells secrete insulin
- alpha-cells stop secreting glucagon
- insulin binds to receptors on liver and muscle cells
- cells take up more glucose, glycogenesis is activated and cells respire more glucose
- there is less glucose in the blood
- and levels return back to normal
what is the negative feedback mechanism for blood glucose when levels are too low
- there is a fall in blood glucose
- the pancreas detects that these levels are too low
- alpha cells secrete glucagon
- beta cells stop secreting insulin
- glucagon binds to receptors on liver cells
- glycogenolysis is activated, gluconeogenesis is activated and cells respire less glucose
- cells release glucose into the blood
- levels return back to normal
how do beta-cells contain insulin, and when is this secreted
- contain insulin stored in vesicles
- secrete the insulin when they detect high blood glucose concentration
at what state do beta cells secrete insulin
when they are depolarised
explain how beta cells secrete insulin
1) when blood glucose concentration is high, more glucose enters beta-cells via facilitated diffusion
2) more glucose in beta cells causes the rate of respiration to increase, making more ATP
3) this rise in ATP triggers the potassium ion channels in the beta-cell plasma membrane to close
4) this means potassium ions cannot get through the membrane, so they build up inside the cell
5) this makes the inside of the beta cell less negative, as there is a build up of more positively charged potassium ions inside the cell, so the plasma membrane of the cell becomes depolarised
6) depolarisation triggers the calcium ion channels in the membrane to open, so calcium ions diffuse into the beta cell
7) this causes vesicles to fuse with the beta cell plasma membrane, releasing insulin - VIA EXOCYTOSIS
what is diabetes mellitus
a condition where blood glucose concentration can’t be controlled properly
what type of disease is type 1 diabetes
- an auto-immune disease
- where the body attacks and destroys beta-cells in the islets of Langerhans
- meaning that people with type 1 diabetes don’t produce any insulin
what happens to a person with type 1 diabetes after eating
- their blood glucose concentration rises and stays high
- can result in death if left untreated
- the kidneys are unable to absorb all this glucose
- so some of it is excreted in the urine
whos most likely to get type 1 diabetes
- usually develops in children and young adults
- the risk is slightly increased if they have a close family member with the disease
how can type 1 diabetes be treated
- with insulin therapy
- most people need regular insulin injections throughout the day
- some people can also use an insulin pump, which is a machine that constantly delivers insulin into the body via a tube under the skin
what is an alternative treatment to type 1 diabetes rather than insulin therapy
- having an islet cell transplantation
- they are able to receive healthy islet cells from a donor
- this means that their pancreas can produce some insulin
- still usually do require additional insulin therapy
how do people with type 1 diabetes monitor their blood glucose, and what do they need to carefully think about
- DIET: need to eat a healthy, balanced diet to reduce the amount of insulin that needs to be injected, often having a carefully planned diet so that they can manage the amount of glucose they are taking in
- ACTIVITY: regularly exercising reduces the amount of insulin that needs to be injected by using up the blood glucose
what causes type 2 diabetes
- when the beta cells aren’t producing enough insulin, or when the body’s cells dont respond properly to the insulin
why may body cells not respond properly to insulin in someone with type 2 diabetes
- because the insulin receptors on their membranes aren’t working properly
- so the cells don’t take up enough glucose
- means blood glucose levels are higher than normal
who is most likely to get type 2 diabetes
- usually occurs later in life
- often linked to obesity
- risk is increased in certain ethnic groups, e.g. african and asian
- risk is increased for those with a close family history of the disease
what is the initial way you can go about managing type 2 diabetes
- through lifestyle changes
- e.g. eating a healthy, balanced diet
- e.g. getting regular exercise and losing weight if needed
- can all help prevent the onset of type 2 diabetes and control the effects
what medication can be prescribed to those who are unable to control their type 2 diabetes with lifestyle changes alone
- METFORMIN: acts on liver cells to reduce the amount of glucose that they release into the blood
- also acts to increase the sensitivity of cells to insulin, so that more glucose can be taken up with the same amount of insulin
- SULFONYLUREAS (e.g. gliclazide): these stimulate the pancreas to produce more insulin
- THIAZOLIDINEDIONES (e.g. pioglitazone): these also make your body more sensitive to insulin
what can be done to patients with type 2 diabetes, where medications are not enough
insulin therapy can be used in addition, or instead of
how did we used to get insulin to treat people with type 1 diabetes
used to be extracted from animal pancreases, e.g. pigs and cattle
how do we now get insulin for people with type 1 diabetes
we can make human insulin using genetically modified GM bacteria
why is using insulin made from GM bacteria better than from animal pancreases
- producing it from GM bacteria is cheaper than extracting it from animal pancreases
- larger quantities of insulin can be produced using GM bacteria
- GM bacteria make HUMAN insulin, which is more effective than pig and cattle (which is slightly different) SO:
- less likely to trigger an allergic reaction
- less likely to be rejected by the immune response
- also ethical and religious reasons, e.g. vegetarians object to the use of animals, and some religious object the use of insulin from pigs
what is thought to have the potential of curing diabetes
stem cells
- unspecialised cells with the ability to develop into any type of cell
how can stem cells potentially cure diabetes
- stem cells can be grown to beta cells
- these beta cells can then be implanted into the pancreas of someone with type 1 diabetes
- this means the person would be able to make insulin as normal
- the treatment is still being developed, but if effective, it will cure people with type diabetes
