hormonal comunication Flashcards
define target cells
for non steroid hormones , cells that possess a specific receptors on their plasma membrane. the shape of the receptor is complementary to the shape of the hormone molecule, many similar cells together from a target tissue
define hormone
molecules ( protein or steroid ) that are released by endocrine glands directly into the blood. they act as messengers, carrying a signal from the endocrine gland to a specific target or organ tissue
what are the two types of hormones
protein and steroids
examples of proteins
adrenaline , insulin, glucagon
examples of steroids
oestrogen, testosterone
describe how proteins work
are not soluble in the phospholipid membrane and do not enter the cell. protein hormones need to bind to the cell surface membrane and release a second messenger inside the cell
bind to receptor
describe how steroids work
can pass through the membrane and enters the cell and the nucleus , to have a direct effect on the DNA in the nucleus
soluble - diffuse
define endocrine glands
hormones are released directly into the blood from endocrine glands , directly into the blood
define exocrine glands
along a duct not directly into blood stream, no hormones
describe first and second messengers process
non steroid hormones are known as first messengers . they are signalling molecules outside the cell that bind to the cell surface membrane and initiate an effect inside the cell. they usually cause the release of another signalling molecule in the cell, which is called the second messenger . the second messenger stimulates a change in the activity of the cell
many non steroid hormones act via a g protein in the membrane . the g protein is activated when the hormone binds to the receptor . the g protein in turn activates an effector molecule , usually an enzyme that converts an inactive molecule into the active second messenger . in many cells the effector molecule is the enzyme adenyl cyclase , which converts ATP to cyclic AMP ( cAMP) . cAMP is the second messenger, this second messenger may act directly on another protein or it may initiate a cascade of enzyme controlled reactions
define the adrenal cortex
the outermost layer of the adrenal glands
define adrenal gland
one of a pair of glands lying above the kidneys , which release adrenaline and a number of other hormones known as corticoids such as aldosterone
define adrenal medulla
the innermost layer of the adrenal glands
define adrenaline
a hormone released from the adrenal glands into the blood , which stimulates the body to prepare for flight or fight
what are the three parts of the adrenal cortex
zona glomerulosa
zona fasciculata
zona reticularis
describe the zona glomerulosa
the outermost layer , which secretes mineralocorticoids such as aldosterone
mineralocorticoids , role in the body
helps to control the concentrations of sodium and potassium in the blood. as a result they contribute to maintaining blood pressure. aldosterone acts on the cells of the distal tubules and collecting ducts in the kidney . it increases absorption of sodium ions, decreases absorption of potassium ions, and increases water retention so increasing blood pressure
describe the zona fasciculata
the middle layer , which secretes glucocorticoids such as cortisol
glucocorticoids role in the body
helps to control the metabolism of carbohydrates , fats and proteins in the liver . cortisol is released in response to stress or as a result of low blood glucose concentration . it stimulates the production of glucose from stored compounds in the liver
describe the zona reticularis
the innermost layer, which is thought to secrete precursor molecules that are used to make sex hormones
describe cortisol and the roles in the body released by the zona reticularis
cortisol may also be released, however if the correct enzymes are not present for the release of cortisol , then it will release precursor androgens into the blood. these are taken up by the ovaries or testes and converted to sex hormones . the sex hormone development of the secondary sexual characteristics and regulate the production of gametes
describe the action of steroid hormones
- the steroid hormone passes through the cell membrane of the target cell
- the steroid hormone binds with a specific receptor (with a complementary shape) in the cytoplasm
- the receptor steroid hormone complex enters the nucleus of the target cell and binds to another specific receptor on the chromosomal material
- binding stimulates the production of messenger RNA molecules , which code for the production of proteins
effects of adrenaline
- relaxing smooth muscle in the bronchioles
- increasing stroke volume of the heart
- increasing heart rate
- increasing heart rate
- causing general vasoconstriction to raise blood pressure
- stimulating conversion of glycogen to glucose
- dilating pupils
- increasing mental awareness
- inhibition of the gut
- causing body hair to stand erect
describe the pancreas
is a small organ lying below the stomach . it is unusual in that both exocrine and endocrine functions
the two main secretions of the pancreas are
- pancreatic juices containing enzymes which are secreted into the small intestines
- hormones which are secreted from the islet of Langerhans into the blood
describe the exocrine function in the pancreas
exocrine glands secrete substances into a duct . most cells in the pancreas synthesis and release digestive enzymes . this is the exocrine function of the pancreas . the exocrine cells are in small groups surrounding tiny tubules . each group of the cells is called acini . the acini are grouped together in small lobules separated by connective tissues . the cells of the acini secrete the enzymes they synthesise into the tubule at the centre of the group . the tubules from the acini join to form intralobular ducts that eventually combine to make up the pancreatic duct the pancreatic duct carries the fluid containing the enzymes into the first part of the small intestines
the fluid from the pancreatic duct contains the following enzymes
name the enzymes and describe them
pancreatic amylase- a carbohydrase which digests amylose to maltose
trypsinogen- an inactive protease which will be converted to the active form trypsin when it enters the duodenum
lipase - which digests lipid molecules
describe endocrine function in the pancreas
dispersed in small patches among the lobules of acini are the islets of langerhan
the islets of langerhan contain the alpha and beta cells that make up the endocrine tissues in the pancreas
alpha cells secrete ..
glucagon
beta cells secrete ….
insulin
describe the process of releasing insulin
1- the cell membranes of the beta cells contain both calcium ion channels and potassium ion channels
2-the potassium ion channels are normally open and the calcium ion channels are normally closed . potassium ions diffuse out of the cell making the inside of the cell more negative, at rest the potential difference across the cell membrane is about -70 mv
3- when glucose concentrations outside the cell are high, glucose molecules move into the cell
4-the glucose is quickly used in metabolism to produce ATP , this involves the enzyme glucokinase
5- the extra ATP causes the potassium channels to close
6-the potassium can no longer diffuse out and this alters the potential difference across the cell membrane , it becomes less negative inside
7-this change in potential difference opens the calcium ion channels
8-calcium ions enter the cell and cause the secretion of insulin by making the vesicles containing insulin move to the cell surface membrane and fuse with it, releasing by exocytosis
what are the liver cells called
hepatocytes
what is it called if you have low blood glucose concentrations
hypoglycaemia , an inadequate delivery of glucose to the body tissue
hypoglycaemia causes….
tiredness , irritability , impairment of brain functions , confusion which can lead to seizures and unconsciousness and even death
what is it called if you have high blood glucose concentrations
hyperglycaemia
hyperglycaemia causes ….
significant organ damage , diagnosis for diabetes mellitus
if blood glucose rises too high ….
a high blood glucose concentration is detected by the beta cells in the islets of langerhan . the beta cells respond by secreting insulin into the blood. insulin travels throughout the body in the circulatory system . the target cells are the liver cells , muscle cells and some other body cells including those in the brain
human insulin is a small protein of 51 amino acids therefore it is unable to pass through the cell surface membrane , the target cells possess the specific membrane bound receptors for insulin . when insulin binds to the insulin receptor, this activates the enzyme tyrosine kinase which is associated with the receptors on the inside of the membrane . tyrosine kinase causes phosphorylation of inactive enzymes in the cell, this activates the enzymes leading to a cascade of enzyme controlled reactions
what are the target cells if blood glucose rises too high
liver cells , muscles and some other brain cells including the brain
if blood glucose rises too high
insulin has several effects on the body , which are …
- more transporter proteins specific to glucose are placed into the cell surface membrane . this is achieved by causing vesicles containing these transporter proteins to fuse with the membrane
- more glucose enters the cell
- glucose in the cell is converted to glycogen for storage ( glycogenesis)
- more glucose is converted to fats
- more glucose is used in respiration
the increased uptake of glucose , through the specific transporter proteins , reduces the blood glucose concentration
if blood glucose drops to low ….
a low blood glucose concentration is detected by the alpha cells in the islets of langerhan, the alpha cells then secrete the hormone glucogan into the blood
glucgon Is a small protein containing 29 amino acids . its target cells are the hepatocytes , which possess the specific receptor for glucagon, when the blood passes these cells the glucagon binds to the receptors , this stimulates a G protein inside the membrane , which activates adenyl cyclase inside each cell . the adenyl cyclase converts ATP to Camp , which activates a series of enzyme controlled reactions in the cell
what are the target cells if blood glucose drops too low
hepatocytes (liver cells)
when blood glucose drops too low
the effects of glucagon include the following
- glycogen is converted to glucose (glycogenolysis) by phosphorylase A, which is one of the enzymes activated in the cascade
- more fatty acids are used in respiration
- amino acids and fats are converted into additional glucose by gluconeogenesis
the overall effect of these changes is to increase the blood glucose concentration
define glycogenesis
the conversion of glucose to glycogen for storage
define glycogenolysis
glycogen is converted to glucose
define gluconeogenesis
amino acids and fats are converted into additional glucose
what is negative feedback
when you reverse a change
why is the concentration of blood glucose considered to be negative feedback
it reverses a change
when the glucose concentration rises too high the release of insulin will act to bring the concentration down, but if the concentration falls too low the release of glucagon will act to raise the concentration again
define diabetes mellitus
a condition in which blood glucose concentrations cannot be controlled effectively
describe type 1 diabetes
is also known as insulin dependent diabetes. it usually starts during childhood. it is thought to be the result of autoimmune response in which the bodys immune system attacks and destroys the beta cells, type 1 diabetes may also result from a viral attack
in a healthy person , glucose is absorbed into the blood and…
any excess is converted to glucagon in the liver and muscle. the glycogen can then be used to release glucose when the blood glucose concentrations fall
a person with type 1 diabetes is no longer able to ….
synthesis sufficient insulin and cannot store excess glucose as glycogen , excess glucose in the blood is not removed quickly , leaving a prolonged period of high concentrations . however when the blood glucose falls there is no store of glycogen that can be used to release glucose , therefore the blood glucose concentration falls too low, this is when a diabetic can suffer a hypo - a period of hypoglycaemia
describe type 2 diabetes
is also known as non insulin dependent diabetes , a person with type 2 diabetes can produce insulin , but not enough , also as people age their responsiveness to insulin declines . this Is probably because the specific receptors on the surface of the liver and muscle cells become less responsive and the cells lose their ability to respond to the insulin in the blood
in type 2 diabetics the blood glucose concentration Is almost always raised , which can damage major organs and circulation
certain factors seem to bring on earlier onset of type 2 diabetes include
- obesity
- lack of regular exercise
- a diet high on sugars, especially refined sugars
- being of Asian or afro-Caribbean origin
- family history
treating type 1 diabetes
-with insulin injections
alternatives
- insulin pump therapy, a small device constantly pumps insulin into the bloodstream through a needle that is permanently inserted under the skin
- islet cell transplantation , healthy beta cells from the pancreas of a deceased donor are implanted into the pancreas of someone with type 1 diabetes
- a complete pancreas transplant
- stem cells to grown new islets of langerhan
how to treat type 2 diabetes
usually treated by changes in lifestyle , will be advised to lose weight , exercise regularly and monitor their diet , taking care to match carbohydrate intake and use , this may be supplemented by medication that reduces the amount of glucose the liver releases to the blood stream or that boost the amount of insulin released from the pancreas
what’s the source of insulin for treating diabetes
from the pancreas of animals , usually from pigs as this matches human insulin most closely , however more recently insulin has been produced by Escherichia coli bacteria that have undergone genetic modification to manufacture human insulin
advantages of using insulin from genetically modified bacteria include the following
- it is an exact copy of human insulin, therefore it is faster acting and more effective
- there is less chance of developing tolerance to the insulin
- there is a less chance of rejection due to an immune response
- there is a lower risk of infection
- it is cheaper to manufacture the insulin than to extract it from animals
- the manufacturing process is more adaptable to demand
