Hormone communication Flashcards
What is a hormone
molecules such as proteins or steroids that are released by endocrine glands directly into the blood, they act as messengers carrying a signal from the endocrine glands to a specific target organ or tissue
What is a target cell
for non-steroid hormones, cells that possess a specific receptor on their plasma membrane, shape of the receptor is complementary to the shape of the hormone molecule and many similar cells together form a target tissue
what is the endocrine system
this is a communication system using hormones as signalling molecules
What are the two types of hormone
- Protein and peptide hormones and derivatives of amino acids for example adrenaline, insulin and glucagon
- Steroid hormones for example oestrogen and testosterone
Describe protein hormones
Proteins are not soluble in the phospholipid membrane so do not enter the cell therefore they need to bind to the cell surface membrane and release a secondary messenger inside the cell
Describe steroid hormones
Steroid hormones can pass through the membrane and enter the cell and the nucleus this has a direct effect of the DNA in the nucleus
Describe endocrine glands
- Hormones are released directly into the blood from the endocrine glands
- Endocrine glands are ductless glands and consist of groups of cells that release the hormone directly into the blood in capillaries running through the gland
How do hormones cause responses
- Hormones have a specific function and are transported all over the body but they only effect on kind of tissue
- Cells receiving an endocrine signal are called target cells
- May be grouped into a target tissue
- Or they may be widely dispersed in multiple tissues such as the receptors for adrenaline found in the central nervous system and cardiac muscle, smooth muscle and skeletal muscle
- For non-steroid hormones the target cell must have a specific receptor on plasma membrane that is complementary to the shape of the molecule
- This overall means that hormones can be carried in the blood without affecting cells that do not possess the correct specific receptor, only those that are specific possess the correct receptor and will respond to the hormone
Describe First and secondary messengers
- Non steroid hormones are known as first messengers; they are signalling molecules outside the cell bind to the plasma membrane and causes a change
1. Cause the release of another signalling molecule called the secondary messenger which stimulate the change in activity
2. G protein is activated when the hormone binds to the receptor
3. G protein in turn activates an effector molecule usually an enzyme that converts the inactive molecule into the active second messenger
4. Effector molecule is adenyl cyclase this converts ATP to cyclic AMP (CAMP)
5. CAMP is a second messenger and this acts directly on another protein or initiates a cascade of enzyme controlled reactions that alter the activity of the cell
Describe the structure of the adrenal glands
- Found just above the kidneys
- Divided into the outer adrenal cortex and the inner adrenal medulla
- Well supplied with blood and produce hormones which are directly secreted into the blood vessels
Describe the parts of the adrenal cortex
- Zona Glomerulosa – outermost layer, this secretes mineralocorticoids such as aldosterone
- Zona fasciculata – the middle layer which secretes glucocorticoids such as cortisol
- Zona reticularis – the innermost layer which is thought to secrete precursor molecules that are used to make sex hormones
What does the adrenal medulla do
Secretes adrenaline and noradrenaline
Describe adrenaline
- Polar molecule derived from the amino acid tyrosine
- Cannot enter cells through the plasma membrane therefore it must be detected by specialised receptors on the plasma membrane of the target cells
What is the function of the hormones from the adrenal glands
- Relaxes smooth muscle in bronchioles
- Increase stroke volume
- Increase heart rate
- Causes vasocontriction to raise blood pressure
- Dilates pupils
- Increases conversion of glycogen to glucose
- Increase mental awareness
- Inhibit the action of the gut
- Causing body hair to stand erect
what does the adrenal cortex use to produce a range of hormones
- cholesterol, therefore the hormones are steroid base and are able to enter cells directly by dissolving into the cell surface membrane
- steroid hormones have an direct effect on the DNA to cause protein synthesis
What is 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 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 which codes for production of proteins
What does the zona glomerulosa produce
Mineralcorticoids from the zona glomerulosa control the concentrations of sodium and potassium in the blood and therefore they contribute to maintaining blood pressure, it acts of the cells of the distal tubules and collecting ducts in the kidney increasing the absorption of sodium ions and decreasing the absorption of potassium ions increases water retention so increases the blood pressure
What does the zona fasciculata produce
Glucocorticodis from the zona fasciculata help 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 concentrations. It stimulates the production of glucose from stored compounds
What does the zona reticularis produce
Cortisol may be released by zona reticularis, but if the correct enzymes are not present then the zona reticularis releases precursor androgens into the blood which are taken up by the ovaries and testes and converted to sex hormones which help the development of secondary sexual characteristics and production of gametes
Describe the structure of the pancreas
- Below the stomach
- Has both endocrine and exocrine functions
- Pancreatic juices contain enzymes which are secreted into the small intestine (exocrine)
- Hormones which are secreted from the islets of Langerhans into the blood
Describe the pancreases exocrine function and structure
Exocrine function
- Secrete substances into a duct
- Most cells in the pancreas synthesise and release digestive enzymes
- Small groups surrounding tiny tubules, each group is called an acinus
- Ancini are grouped together into small lobules separated by connective tissue, the ancini secrete the enzymes that they synthesise into the tubule at the centre of the group
- Tubules from the ancini join to form intralobular ducts that combine to make up the pancreatic duct, this carries the fluid containing the enzymes into the duodenum (first part of small intestine)
what enzymes are in the pancreatic fluid
- Pancreatic amylase
- Trypsinogen
- Lipase
What does pancreatic amylase do
carbohydrase that digests amylase to maltose
What does trypsinogen do
an inactive protease which is converted to the active form of trypsin when it enters the duodenum
What does lipase do
digests lipid molecules
describe endocrine function
- Alpha cells – secrete glucagon
- Beta cells – secrete insulin
Describe the releasing of insulin
- Cell membrane of beta cells contains both calcium ions and potassium ion channels
- Potassium ions channels are normally open so potassium ions flow out
- When blood glucose concentration is high the glucose moves into the cell
- Glucose is converted to glucose phosphate by glucokinase this is metbaolised to produce ATP
- ATP causes potassium ions to close
- The accumulation of potassium ions alters the potential difference across the cell membrane and the inside becomes less negative
- Charge in potential difference causes calcium ion channels to open
- Calcium ions move down concentration gradient into the beta cell
- Calcium ions cause movement of vesicles containing insulin to fuse with the cell membrane
- Insulin released by exocytosis
What is hypoglycaemia
this is when a persons blood glucose concentration is allowed to drop below 4mmoldm-3 and remain low for long periods of time
what is hyperglycaemia
If blood glucose is rise too high for long periods this is known as hyperglycaemia, and can lead to organ damage, if its consistently higher than 7 mmoldm-3 then this can be diagnosed as diabetes melitus
what is glycogenesis
this is when glucose is converted to glycogen for storage in the cell
What is glycogenolysis
glycogen is converted to glucose by phosphorylase A which is one of the enzymes activated in the cascade
what is gluconeogensis
- amino acids and fats are converted into additional glucose
what monitors blood glucose
- Islets of Langerhands monitor the concentration of glucose in the blood and it releases the hormones to respond to it
- Hormones act on cells in the liver which can store glucose in the form of glycogen and convert it back
If the blood glucose rises too high
- Beta cells in islet of Langerhand secrete insulin into the blood
- Insulin travles throughout the body
- Target cells are in the liver, muscle cells and some other cells such as those in the brain
- Insulin is a small protein of 51 amino acids therefore is unable to pass through the cell surface membrane, target cells possess specific membrane bound receptors for insulin
- When insulin binds it activates tyrosine kinase which is associated with the receptor on the inside of the membrane causing phosphorylation of inactive enzymes in the cell which activates the enzymes leading to a cascade of enzyme controlled reaction inside the cell
- this is negative feedback
THIS HAS SEVERAL EFFECTS:
1. More transporter proteins specific to glucose are placed into the cell surface membrane caused by vesicles containing these transport proteins to fuse with the membrane
2. More glucose enters the cell
3. Glucose in the cell is converted to glycogen for storage
4. More glucose converted to fats
5. More glucose is used in respiration
if the blood glucose concentration drops too low
- Alpaha cells secrete glucagon into the blood
- Small protein containing 29 amino acids and its target cells are liver cells which posses the specific receptor for glucagon
- When blood passes these cells the glucagon binds to the receptor
- Stimulates a G protein activates the adenyl cyclase inside the cell and this converts ATP to CAMP this activates a series of enzyme controlled reactions in the cell
THE EFFECTS OF GLUCAGON INCLUDE THE FOLLOWING
1. Glycogen is converted to glucose this is called glycogenolysis by phosphorylase A
2. More fatty acids are used in respiration
3. Amino acids and fats are converted into additional glucose by gluconeogenesis - this is negative feedback
What is diabetes meullitus
- Condition in which the body is no longer able to produce sufficient insulin to control blood glucose concentration
- Leads to prolonged very high concentrations of glucose
Describe Type 1 diabetes
- Starts in childhood
- Result of an autoimmune response which the bodies immune system destroys the beta cells
- No longer able to synthesis sufficient insulin and cannot store excess glucose as glycogen
- Glucose is not removed quick enough causes high concentration
- Or glycagon cannot be converted into glucose quick enough leading to it being too low
Describe how to treat Type 1 diabetes
- Insulin pump therpay
- Islet cell transplantation
- Complete pancreas transplant
- Stem cells to grow new islet of Langerhands in the pancreas – bone marrow or placenta
Describe type 2 diabetes
- Can produce insulin but not enough as specific receptors on the surface of the liver and muscle cells become less responsive
- May be due too…
1. Obesity
2. Lack of exercise
3. Diet in high sugars
4. Being Asian or Afro-caribbean
5. Family history
Describe treating type 2 diabetes
- Changes in lifestyle
- Lose weight
- Exercise regularly
- Monitor diet
- May use medication that reduces the amount of glucose released into the bloodstream
- Insulin pump in extreme cases
where do we get insulin from
- used to be extracted from the pancreas of animals as this matched human insulin more closely
- more recently it is used and produced by the bacteria that have undergone genetic modification to manufacture human insulin
Why is it better to use insulin from bacteria
- Exact copy of human insulin so faster and more effective
- Less chance of developing tolerance
- Less chance of rejection
- Lower risk of infection
- Cheaper
- Adaptable to demand
- Less likely to have moral objections
