5.1.4 Hormonal communication Flashcards
basics of endocrine communicatiohn
- Cells in an endocrine gland produce hormones and secrete them directly into the blood
- The hormones dissolve in the blood plasma and thus are carried around the body;
- The hormones bind to complementary glycoprotein receptors, usually located in the plasma membrane of specific ‘target’ cells;
- The consequence is a response in the target cells, e.g. a change in metabolism.
what is an endocrine gland?
an organ containing cells specialised to produce hormones and secrete these directly into the blood, usually via exocytosis.
what do endocrine glands not use?
DUCTS!
examples of endocrine glands
pituitary gland
thyroid glands
endocrine pancrease
adrenal gland
ovaries
testes
what is the pituitary gland?
Brain
Master gland - it controls secretions of hormones from some other glands
Secretes:
Human growth hormone (HGH) - promotes muscle/bone growth in children
Anti‐diuretic hormone (ADH) - control of water potential
What is the thyroid gland?
neck
secretes thyroid hormones:
Thyroxine - controls overall metabolic rate, including rate of respiration
what is the endocrine pancreas?
clusters of cells called islets of Langerhans
what is the adrenal gland?
one on top of each kidney
hormones that coordinate responses to short‐ and long‐term stress
Cortisol - (adrenal cortex) - coordinates responses to ongoing stress
Adrenaline - (adrenal medulla) - coordinates the ‘fight‐or‐flight’ response to perceived threat
what are the ovaries?
produces female sex hormones
Oestrogen - controls development of secondary sexual characteristics
during puberty and prepares the uterus lining to receive a fertilised egg;
what are the testis?
produces male sex hormones
Testosterone - controls development of secondary sexual characteristics
during puberty and sperm production.
what is a exocrine gland?
an organ containing cells specialised to produce hormones and secrete the chemicals they produce via a duct
sweat glands
salivary glands
exocrine pancreas
What is this diagram showing? label it.
the endocrine and exocrine glands in the body and their locations
what is a hormone?
chemical messengers which target specific target cells and are soluble in blood plasma, and trael round the body in the blood stream. They are slow acting but have a long effect
how do hormones work?
To produce an effect in a specific target cell, the hormone must bind to a receptor which has a binding site of complementary shape. This receptor may be in the plasma membrane of the target cell or in the cytoplasm (depending on whether the hormone cannot or can cross the plasma membrane).
the binding of a hormone to a complementary receptor will trigger a change in the metabolism of a target cell.
what are the two main types of hormones?
Steroid hormones
Non-steroid hormones
describe a steroid hormone
lipid-soluble - hydrophobic + non‐polar molecular structure
Able to pass through the phospholipid bilayer of a plasma membrane by simple diffusion
their receptors are located within the cell cytoplasm.
what is the the sequence of events which leads to an effect in the target cell for STEROID hormones?
- Steroid hormone diffuses through the phospholipid bilayer into the target cell.
- When the steroid hormone binds to its complementary receptor in the cytoplasm of a target cell, a hormone‐receptor complex is formed.
- This complex may then enter the nucleus (via a nuclear pore) and bind directly to DNA: the hormone‐receptor complex is now an active transcription factor (whereas the receptor alone was an inactive transcription factor which didn’t have the appropriate shape to bind to the DNA).
- The active transcription factor (i.e. the hormone‐receptor complex) may bind directly to the promoter of a gene and help (or hinder) the binding of RNA polymerase to the promotor; or, it may bind to a control sequence some distance in front of the promoter and indirectly influence the binding of RNA polymerase.
- The effect of the hormone is therefore to trigger a change in the gene expression of the target cell, e.g. a gene that was previously switched off may now be switched on, i.e. transcribed to mRNA which is then translated. For example, the cell may now start producing a new enzyme, altering its metabolism.
what is a promoter?
region of DNA in front of a gene which acts as binding site for RNA polymerase
describe a non-steroid hormone
Protein or amino acid-derivatives
water-soluble - hydrophilic polar structure
they cannot freely pass through the phospholipid bilayer of a plasma membrane
receptors embedded in the plasma membrane of target cells - hormone can bind to the receptor without entering the cell
receptors made of glycoprotein and have a specific binding site that is complementary in shape to a specific hormone
what is the the sequence of events which leads to an effect in the target cell for NON-STEROID hormones?
- When the hormone binds to the complementary binding site of its specific receptor (located in the plasma membrane of the target cells), there is a change in the 3D shape of the receptor;
- This causes activation of an enzyme called adenyl cyclase, which is located on the cytoplasmic (inner) surface of the plasma membrane;
- Adenylyl cyclase catalyses the synthesis of cAMP (cyclic adenosine monophosphate) from ATP;
- As cAMP concentration rises in the cytoplasm, it starts binding to proteins that have an allosteric site of the appropriate complementary shape;
- This activates the proteins (by causing a change in their 3D shape), including some that act as protein kinase enzymes;
- The activated protein kinase enzymes catalyse the phosphorylation (attachment of a phosphate group) of other proteins, activating these proteins (including other enzymes);
- In this way, there is a change in the metabolism of the target cell, as enzymes that were previous inactive have been activated by the binding of cAMP or by phosphorylation. In this mechanism, the hormone – which doesn’t actually enter the target cell
what is the first messenger?
the hormone
what is the secondary messenger?
cAMP
why is cAMP the secondary messenger?
it causes the activation of enzymes, which causes the target cells to undergo a change in metabolism.
why is non-steroid hormone events concidered a cascade?
there are several amplification effects.
describe the cacading effect of non-steroid hormones
the binding of one hormone molecule to one receptor may only activate one adenylyl cyclase enzyme – but this enzyme will synthesise thousands of cAMP molecules from ATP in a short time, which are collectively able to activate thousands of enzymes; if protein kinase enzymes are activated by cAMP, each one of these can catalyse the attachment of a phosphate group to thousands of other enzymes in a short time.
Therefore the effect of just a few hormones binding to receptors in the plasma membrane is significantly amplified by the cascade of reactions that results, and can bring about dramatic changes to the metabolism of the target cell.
why may different tissues have a differnt response to the same hormone?
have different types of receptor;
have different types of enzyme ready to be activated by the binding of cAMP;
use different second messenger systems
other than cAMP, what is another example of a secondary messenger?
some cells use Ca2+ ions
(released from stores in the SER)
compare the endocrine system to the nervous sytem with these points
where is the adrenal glawnd located?
one above each kidney
what surrounds each adrenal gland? what is its purpose
A protective capsule of collagen‐rich connective tissue
what type of gland is the adrenal gland
Endocrine glands, producing hormones and secreting them directly into the blood
what are the layers of the adrenal gland? what does each produce/do?
innermost - Medulla - Adrenaline and Noradrenaline
middle layer - Cortex - Cortisol
Outer layer - collagen rich connective tissue - protective capsule
Draw the adrenal gland
what controlls what hormones are released by the adrenal cortex?
trophic hormones released by the pituitary gland
what controlls what hormones are released by the adrenal medulla?
Sympathetic nervous system
what are the main 3 hormones produced by the adrenal cortex?
glucocorticoids
mineralocorticoids
androgens
what are the main 2 hormones produced by the adrenal medulla?
Adrenaline
Noradrenaline
what is the functiuon of glucocorticoids
cortisol
coordinates the body’s response to long‐term stress, affecting various aspects of metabolism and physiology including control of the metabolic rate (increased respiration), use of different respiratory substrates (increasing blood sugar levels), blood pressure (increases), inflammation (increases)
and specific immune responses (decreases);
what is the functiuon of mineralocorticoids
aldosterone
has a role in controlling the balance between water and salt ions in body fluids (by influencing Na+ and K+ ion and water reabsorption in the kidneys) and hence blood pressure;
what is the functiuon of androgens
Act like sex hormones
what is the functiuon of adrenaline
causes effects on multiple body systems, preparing the body for action, e.g. increased heart and breathing rate (so more oxygen is delivered to muscles) and increased breakdown of glycogen (i.e. glycogenolysis) in the liver (so that blood sugar level increases)
ANIMAL RESPONSES
what is the functiuon of noradrenaline
has synergistic effects to adrenaline, e.g. causes dilation of the bronchi (decreasing resistance to air flow) and constriction of arterioles to the digestive system (so a greater proportion of blood flow goes to muscles)
what is the function of the pancreas?
functions both as an exocrine gland and as an endocrine gland, with each role carried out by distinct tissues within the organ
how to remember endocrine gland
enDo = blooD
what makes up the exocrine portion of the pancreas?
tiny berry‐like cell clusters called pancreatic acini;
what do the acini look like when stained?
they stain heavily and look like small dark blobs
what do the acinar cells do?
produce hydrolytic enzymes for digenstion whhich are secreted by exocytosis into their cenral duct
what does the central ducts from all the acini merge into?
The pancreatic duct
exocrine pancreas enzymes
amylase (starch to maltose)
trypsin (proetin to aminoacid)
lipase (triglycerides to fatty acids and glycerol)
what makes up the endocrine pancrease?
large spherical cell clusters called islets of Langerhans;
what do the islets of langerhans look like when stained?
large pale round circles
Function of the islets of langerhans and where are they secreted?
the islets of Langerhans produce the hormones involved in control of blood glucose concentration, secreting them directly into the blood
what are the two cell types in the islets of langerhans?
alpha and beta cells
what to alpha cells do?
Thye produce glucagon in response to low blood sugar
what do beta cells do?
they produced insulin in response to high blood sugar levels
What is this? what is each structure?
Pancreatic tissue
why do we need to regulate blood glucose?
The concentration of glucose dissolved in the blood plasma needs to be high enough that all body cells are provided (passively) with glucose in sufficient amounts for use as a respiratory substrate; however, if the blood glucose levels becomes too high, this creates low water potential in the blood plasma (since glucose is highly soluble in water) – this could lead to body cells losing water by osmosis and suffering irreversible damage.
what are the three processes that increases blood glucose concentration?
Digestion of food containing carbohydrartes
Glycogenolysis
Gluconeogenesis
what is Glycogenolysis?
the hydrolysis (by glycogen phosphorylase) of glycogen stored in the liver and muscles; the glucose produced is released into the blood (if not used by the cell itself);
what is gluconeogenesis
the synthesis of new glucose molecules from non-carbohydrates, including glycerol (from fatty acid hydrolysis) and amino acids (from protein hydrolysis);
occurs mainly in the liver, which releases the glucose it produces into the blood.
what two processes decrease the blood glucoses concentration?
rrespiration
glycogenesis
how does increasing respiratrion decrease blood glucose levels?
body cells absorb glucose from the blood/tissue fluid and use it as a respiratory substrate
the rate can be increased further during exercise
what is glycogenesis
the synthesis of glycogen from glucose – this mainly occurs in the liver and muscles, whenever there is an excess of glucose available in the blood (e.g. following digestion of a recent meal)
what is the mechanism in response to high blood glucose?
- beta cells in islets of langerhans of the pancrease pancreas detect that the blood glucose concentration is higher than is optimal
- The β‐cells secrete more insulin, directly into the blood + α‐cells secrete less glucagon
- insulin dissolves in the blood plasma and is carried around the body
- liver and muscle cells are main target cells and therfore have more insulin receptros on their plasma membrane and respond most strongly (other body cells also have some insulin receptiors)
- insulin binds to comlplementary recptor on plasma membrane of target cell
- binding of the hormone to the receptor causes a small change in the 3D shape of the receptor; this will have the some consequences that lower blood glucose concentration (see other flashcard)
- insulin is broken down continuously by liver enzymes, the β‐cells in the islets of Langerhans as long as the blood glucose level is about the optimum
- As the blood sugar level falls, there may now be an undershoot, triggering the mechanisms that will increase blood sugar level
what responses do cells have after insulin binding?
Opening of glucose channel proteins in the plasma membrane, so more uptake of glucose into the cells takes place by facilitated diffusion
Increased respiration rate, using up some of the glucose absorbed;
Activation of intracellular enzymes which convert glucose to glycogen for storage (i.e. more glycogenesis);
Activation of intracellular enzymes which convert glucose to lipids for longerterm storage;
Inhibition of glucagon secretion from α‐cells, to avoid stimulating processes which would increase blood glucose levels.
what is the regulation of blood glucose an example of?
negative feedback
what is negative feedback?
the deviation in blood sugar level form the optimum was detected and triggered a mechanism that corrected the change
why do beta cells detect the incrtease of blood glucose?
the plasma membrane of a β‐cell has a potential difference (voltage) across it, i.e. an imbalance of charge; the membrane is said to be polarised.
More specifically, when glucose concentration is optimal, the membrane will have a resting potential of ‐70mV, with an excess of negative charge inside the cell relative to the outside.
In this state, ATP‐sensitive potassium (K+) ion channels in the membrane are open and allow movement of K+ ions out of the cell by facilitated diffusion.
This significant efflux of cations from the cell is primarily responsible for the resting potential being such a negative value.
what is the mechanism for insulin secretion from β‐cells in response to high blood glucose levels?
- blood glucose rise and more glucose enter the beta cells by facilitated diffusion, using a glucose carrier protein
- The glucose is used as a respiratory substrate (glucoses enters glycolysis…) resulting in more ATP prodcued ijn mitochondria of beta cells
- ATP binds to the ATP‐sensitive K+ channels in the plasma membrane, causing them to close
- K+ ions can no longer diffuse out of the β‐cell, resulting in the potential difference across the membrane becoming less negative, from ‐70mV to around ‐30mV. THE MEMBRANE DEPOLARISES
- Depolarisation of membrane causes voltage‐gated calcium (Ca2+) ion channels now open in the plasma membrane
- Ca2+ ions move into the β‐cell by facilitated diffusion, down their concentration
gradient, and bind to secretory vesicles in the cytoplasm containing insulin - This triggers the secretory vesicles to move towards the plasma membrane using
microtubules (cytoskeleton) as tracks using mortor proteins (Requres energy from ATP hydrolysis) - secretory vesicles merge with the plasma membrane, releasing the insulin by exocytosis into an adjoining blood capillary
what is this diagram showing?
how higher blood glucose levels lead to increased insulin secretion from β‐cells
what is the mechanism in response to low blood glucose?
- The α‐cells in the islets of Langerhans in the pancreas detect that the blood glucose concentration is lower than is optimal;
- The α‐cells secrete more glucagon, directly into the blood; meanwhile, the β‐cells secrete less insulin;
- The glucagon dissolves in the blood plasma and is carried around the body;
- Only liver and fat cells have any glucagon receptors in their plasma membranes; other cell types are not able to respond to glucagon;
- Glucagon binds to its specific receptor (made of glycoprotein), which has the correct complementary shape for the hormone to fit;
- The binding of the hormone to the receptor causes a small change in the 3D shape of the receptor casusing a response in the cell (see next flashcard)
- Since glucagon is broken down continuously by liver enzymes, the α‐cells in the islets of Langerhans must continue secreting glucagon as long as blood sugar level is below the optimum, so that the above responses do continue;
- As the blood sugar level increases, there may now be an overshoot beyond the optimum, triggering the mechanisms that will decrease blood sugar level
what responses do cells have after glucagon binding?
Decreased uptake of glucose into body cells;
Activation of intracellular glycogen phosphorylase enzymes (by binding of cAMP to allosteric site) which hydrolyse glycogen to glucose; this increased glycogenolysis is followed by release of the glucose into the blood;
Activation of intracellular enzymes which convert amino acids or glycerol into new glucose molecules, i.e. more gluconeogenesis, followed by release of this glucose into the blood;
Inhibition of insulin secretion from β‐cells, to avoid stimulating processes which would decrease blood glucose levels.
what other hormone mimics the effects of glucagon?
Adrenaline
What is type 1 diabetes?
beta cells dont produce insulin
autoimmune diseases where wbc target beta cells
pancreases is damaged by infection or trauama
What is type 2 diabetes?
β‐cells in the pancreas may still be producing insulin normally, but liver and muscle cells show insulin resistance: these cells are no longer responding appropriately to this insulin, meaning that glucose is not absorbed by cells but instead remains in the blood;
The cause may be a problem with the insulin receptors (e.g. not enough of them or faulty shapes) or with the cellular response to the binding of insulin to these receptors (e.g. the second messenger system failing to activate);
how do we treat type 2 diabetes?
low carbohydrate diet
exercise
weight loss
some medication
what are the three types of treatment of type 1 diabetes?
insulin injections
pancreas transplant
stemcell injections
explain pancreas transplant
human pancreas from a deceased donor does in theory provide a cure for type 1 diabetes: the pancreas will contain healthy β‐cells that produce insulin in response to high glucose concentration; the patient’s blood sugar levels should now be well controlled
what is liver tissue known as?
hepatocytes
what is this image showing?
downside of pancreas transplant
risky surgery
immunosuppressants
explain insulin injections
insulin produced by biuotechnology
injected directly into blood steam and does its job
explain stem cell treatment
The aim would be to grow β‐cells in the lab and transplant them into the patient, or transplant stem cells into the patient that are then triggered to differentiate into β‐cells within the body
totipotent or pluripotent stem cells from donated embryos
