Hormonal communication Flashcards
Endocrine system
A communication system using hormones as signalling molecules
where the hormones are released directly into the blood
What are the major endocrine organs in the body
Pituitary gland
Thyroid gland
Thymus
Adrenal gland
Pancreas
Ovaries / Testes
Exocrine system
Involved in non-hormonal communication
Exocrine glands consist of a group of cells surrounding a small duct
The products are secreted into the duct which lead to the site where the secretion is required
Hormones
Molecules (proteins/steroids) are released by endocrine glands directly into the blood. They act as messengers, carrying a signal from the endocrine gland to a specific organ/tissue
Target cells
For non-steroid hormones
cells possess a specific receptor on their plasma membrane. The shape of the receptor is complimentary to the shape of the hormone molecule. Many similar cells together form a target tissue.
What are the two different types of hormones with eg.
Protein and peptide hormones, and derivatives of amino acids (i.e. adrenaline, insulin, glucagon)
Steroid hormones (oestrogen, testosterone)
How do protein hormones work (briefly)
Are not soluble in phospholipid membrane and do not enter the cell
Need to bind to the plasma membrane and release a second messenger inside the cell
How do steroid hormones work (briefly)
Pass through the plasma membrane through simple diffusion and diffuse into the nucleus
Have a direct effect on the DNA in the nucleus
First messengers
Hormones that act as signaling molecules outside the cell that bind to the plasma membrane and initiate an effect inside the cell
Second messengers
A signalling molecule inside the cell that stimulates a change in the activity of the cell
First and second messengers - how a protein hormone initiate an effect inside a cell
- all except insulin
Act via a G protein in the membrane
1) G protein becomes activated when the hormone binds to the receptor
2) G protein activates an effector molecule which is the enzyme adenyl cyclase
3) This converts ATP to cyclic AMP (cAMP)
4) cAMP is the secondary messenger and may act on another protein (i.e. an ion channel) or initiate a cascade of enzyme - controlled reactions that alter the activity of a cell
The action of steroid hormones
1) The steroid hormone passes through the plasma membrane of the target cell
2) The steroid hormone binds with the specific receptor (which has a complimentary shape) in the cytoplasm
3) The receptor-steroid hormone complex enters the nucleus of the target cell and binds to another specific receptor on the chromosomal material
4) Binding stimulates the production of mRNA molecules which code for the production of proteins
Adrenal glands
Pair of glands lying above the kidneys which releases adrenaline and a number of other hormones known as corticoids such as aldosterone
The adrenal medulla
Found at the centre of the adrenal gland and secretes adrenaline and noradrenaline
-Hormones released work as protein hormones
Adrenaline:
- Polar molecule derived from the amino acid tyrosine
Adrenaline effects
Released from the adrenal medulla
Prepares the body for fight/ flight
Many cells have adrenal receptors so its effects are widespread
Tries to get more O2 in the body
- Relaxing smooth muscle in the bronchioles
- Increasing stroke volume of the heart
- Increasing heart rate
- Causing general vasoconstriction to increase heart pressure
- Stimulating conversion of glycogen to glucose (respiration)
- dilating the pupils
- Increasing mental awareness
- Inhibiting the action of the gut
- Causing body hair to stand erect
The adrenal cortex
The outer layer of the adrenal gland which releases steroid hormones
- uses cholesterol to produce a range of hormones
Has three distinct layers of cells
What are the layers of the adrenal cortex
1) Zona glomerulosa - the outermost layer, which secretes mineralocorticoids such as aldosterone
2) Zona fasciculata - the middle layer, which releases glucocorticoids such as cortisol
3) Zona reticularis - the innermost layer, which is thought to secrete precursor molecules that are used to make sex hormones
Role of mineralocorticoids (Zona glomerulosa)
Help to control the concentrations of sodium and potassium in the blood as a result they also contribute to maintaining blood pressure
- Aldosterone acts on the cells of distal tubules and collecting ducts in the kidney
- It increases absorption of sodium ions and decreases absorption of potassium ions and increases water retention
- This increases blood pressure
Role of glucocorticoids (Zona fasciculata)
Help to control the metabolism of fats, carbohydrates, 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 (especially glycogen fats and proteins) in the liver
Role of Zona reticularis
May also release Cortisol but if the correct enzymes are not present releases precursor androgens into the blood
- These are taken up by the ovaries / testes and converted to sex hormones (oestrogen/ testosterone)
- The sex hormone helps the development of the secondary sexual characteristics and regulate the production of gametes
What is unusual about the pancreas
It does both endocrine and exocrine
What are the two main functions of the pancreas
- Pancreatic juices containing enzymes are secreted into the small intestine
- Hormones are secreted from the islets of Langerhans, which monitor the blood glucose concentration and release the hormones directly into the blood
Exocrine function in the pancreas
Cells synthesise and release digestive enzymes into a duct
- Cells are in small groups surrounding the tubules, each group acinus (plural acini)
-Acini are grouped in small lobules separated by connective tissue
- The cells of the acini secrete enzymes into a tubule at the centre of the group
- The tubules from the acini join to form intralobular ducts that eventually make up the pancreatic duct
-Release triggered by hormonal/nervous communication
-Pancreatic secretions into duodenum
Where does the pancreatic duct take the fluid containing the enzymes
Into the first part of the intestine called the duodenum
How are the cells of the acini specialised
Used to synthesise and secrete proteins
-Need ribosomes; RER; Golgi
-Mitochondria for ATP to carry out active porcesses
The fluid from the pancreatic duct contains
1) Pancreatic amylase - a carbohydrate that digests amylose to maltose
2) Trysinogen - inactive protease which will be converted to form trypsin when it enters the duodenum
3) Lipase - digests lipids molecules
4) Sodium hydrogen carbonate - makes fluid alkaline, neutralises the contents of the digestive system that has left the acidic environment of the stomach
Why must be trypsin be in its inactive form
As it is a digestive enzyme and will digest any proteins within the cell and the pancreatic duct
Endocrine function in the pancreas
Dispersed in small patches among the lobules of acini are the islets of Langerhans
It consists of:
- Alpha cells - secrete glycogen
- Beta cells - secrete insulin
Process of releasing insulin - first three steps
1) Plasma membrane has both potassium and calcium in Beta cells
2) Potassium ion channels are open, Calcium closed - potassium ions diffuse out making more negative , resting potential of -70mV
3) When glucose conc outside cell is high, glucose molecules move into the cell
Process of releasing insulin - steps 4-8
4) Glucose used in metabolism to produce ATP involves enzyme glucokinase
5) Extra ATP closes potassium ion channels
6) Potassium ions no longer diffuse out, which alters pd and cell becomes less negative
7) Change in pd opens calcium ion channels
8) Calcium ions diffuse in and casue secretion of insulin by makeing the vesicles containing insulin move to the plasma membrane and fuse with it
9) Insulin is released by exocytosis
What is the normal blood concentration glucose
Between 4-6 mmol/dm3
What is the condition of a person with low blood sugars called and what are the symptoms
Hypoglycaemia - inadequate supply of glucose to tissues especially the brain
Mild: Tiredness and irritability
Severe: impairment of brain function and confusion which may lead to seizures; unconsciousness; death
What is the condition of a person with high blood sugar called and what are the symptoms
Hyperglycaemia - can lead to organ damage
Blood glucose that is constantly higher is used to diagnose for diabetes mellitus
If blood glucose is too high - till target cells
1)A high blood concentration detected by Beta Cells in the islets of Langerhans
2) Beta cells respond by secreting insulin into the blood and Alpha cells stop secreting glucagon
3)Insulin travels in blood to target cells
Examples of target cells for insulin
Liver cells/ Muscle Cells/ Brain
If blood glucose is too high - Once insulin arrives at the plasma membrane
Insulin unable to mass through plasma membrane
1)Target cells have the specific complimentary receptor for insulin on plasma membrane
2) When insulin binds to receptor it activates the enzyme tyrosine kinase which is associated with the receptor on the inside of the plasma membrane
3) Tyrosine Kinase causes phosphorylation of inactive enzymes in the cell
4) This activates the enzymes leading to a cascade of enzyme controlled reactions in the cell
What affects does insulin have on the cell
-More transporter proteins specific to glucose are placed inside the plasma membrane - caused by vesicles containing transporter proteins fuse with the plasma membrane
-More glucose enters the effector cell
-Glucose is converted to glycogen for storage (glycogenesis)
-More glucose is converted to fats
-More glucose is used in respiration
Increases uptake of glucose, through specific transporter proteins, reduced blood glucose concentration
Glycogenesis
Glucose is converted to glycogen for storage - as glycogen is insoluble and will not affect the wp of the cell
If blood glucose drops too low
Low blood glucose concentration detected by the alpha cells
1)Alpha cells secrete glucagon into blood and Beta cells stop secreting insulin
2) When blood passes liver cells glucagon binds to specific membrane-bound receptor which is complimentary
3)Stimulates G protein which activates adenyl cyclase which converts ATP to cAMP
4) This activates a series of enzyme controlled reactions inside the cell
Target cells for glucagon
Hepatocytes - liver cells
Effects of glucagon on the cell
-Glycogen is converted to glucose (glycogenolysis) by phosphorylase A - an enzyme 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 increases blood glucose concentrations
Glycogenolysis
Glycogen is converted to glucose
Gluconeogenesis
Amino acids and fats are converted to additional glucose
Negative Feedback
When Blood concentration is taken away from its optimum a mechanism is in place to take it back to the optimum
-Antagonistic - one of their effects is to inhibit the effects of the opposing hormone
-Blood glucose concentration will fluctuate and not remain constant
Diabetes mellitus
A condition in which blood glucose concentrations cannot be controlled effectively as can no longer produce sufficient insulin
- Can lead to hyperglycaemia / hypoglycaemia
Type 1 diabetes
Insulin-dependant diabetes / juvenile-onset diabetes (starts early in childhood)
-the result of an autoimmune response in which the body’s immune system attacks and destroys Beta cells/result of viral attack
Effects of type 1 Diabetes
Cannot synthesise sufficient insulin and cannot store excess glucose as glycogen
- Leaves prolonged period of high blood glucose concentration
- When blood glucose falls no store of glycogen to produce glucose - hypoglycaemia
How to treat type 1 diabetes
Treated using insulin injections - blood glucose levels must be monitored and correct doses of insulin
Alternatives:
1) Insulin pump therapy - small device pumps insulin (at a controlled rate) into the bloodstream through a needle permanently inserted in the skin
2) Islet cell transplantation - healthy Beta cells of deceased donor implanted into pancreas of someone with type one diabetes
3) A complete pancreas transplant
How are stem cells used to treat type one diabetes
Unspecialised cells that have the potential to develop into any type of cell - grow new islets of Langerhans in the pancreas
Bone marrow and Placenta / precursor cells in pancreas of adult mice, can develop
Common sources of stem cells for treating type one diabetes
Bone marrow and Placenta
precursor cells in pancreas of adult mice, can develop into a variety of cell types and may be stem cells if similar in human then can produce beta cells in pancreas
-Freedom from daily injections
Type 2 diabetes
Non-insulin-dependant diabetes
-Can produce insulin but not enough
-As age responsiveness to insulin declines - specific receptors on the surface of the liver and muscle cells become less responsive and cells lose the ability to respond to insulin in the blood
-Blood sugars almost permanetly raised which can damage both organs and circulation
What factors cause type two diabetes
-Obesity
-Lack of regular exercise
-A diet in high sugars, particularly refined
- Being of Asian or Afro-Caribbean origin
-Family history
Treating type two diabetes
Treated by changes lifestyle changes: Lose weight, exercise regularly, carefully monitor their diet
-May also be given medication that reduces amount of glucose in the liver releases into the bloodstream / boosts the amount of insulin released from the pancreas
Treating type two diabetes in extreme cases
This may include insulin injections/use of other drugs that slow down the absorption of glucose from the digestive system
The source of insulin for treating diabetes
Insulin used to be extracted from the pancreas of animals usually pigs
-Recently extracted from genetically modified bacteria Escherichia coli to manufacture human insulin
Advantages of using insulin from genetically modified bacteria
-It is an exact copy of human insulin - faster and more effective
-Less chance of developing a tolerance to insulin
-Less chance of rejection due to auto-immune response
-Lower risk of infection
-Cheaper to manufacture insulin than extract from animals
-Manufacturing process more adaptable to demand
- More ethical
Why are transplants ideal
Has the potential to cure the condition and long-term effect
Example of what cAMP does
glycogen to glucose - glycogenolysis
Suggest how the adrenaline molecule can cause different effects in different target tissues
-different tissues have different types of adrenaline receptors
-Causing cAMP concentration to increase/decrease
-Second messenger may be different
-cAMP activates other enzymes within the cell
How does cAMP activate enzymes
Phosphorylation
Secretion/ Excretion
-Diff
-Product
-Sim
-Useful product/ metabolic waste
-Enzymes/ urea
-Products are formed by other cells
