Hormonal Communication Flashcards
What is a hormone?
Molecules that are released by endocrine glands directly into the blood, acting as messengers, carrying a signal from the endocrine gland to a specific target organ or tissues.
What are the two types of hormone?
- Protein and peptide hormones
- Steroid hormones
Name 3 examples of Protein hormones
- Adrenaline
- Insulin
- Glucagon
Name 2 examples of Steroid hormones
- Oestrogen
- Testosterone
How do Protein hormones act?
They’re not soluble in the phospholipid membrane so don’t enter the cell. They need to bind to the cell surface membrane and release a second messenger inside the cell.
How to Steroid hormones act?
They can pass through the membrane and enter the cell and the nucleus, to have a direct effect on the DNA in the nucleus.
Why are endocrine glands described as ductless?
They consist of groups of cells that manufacture and release the hormone directly into the blood in capillaries running through the gland.
Cells that receive an endocrine signal are called what?
Target Cells
Name a place that target cells are grouped together in a target tissue
Eg. Epithelium of the collecting ducts
What must the target cells of non-steroid hormones posses?
A specific receptor on their plasma membrane that is complementary to the shape of the signalling molecule (hormone).
What does the necessity of a complementary surface receptor enable hormones to do?
Hormones can be carried in the blood without affecting cells that do not posses the correct specific receptor.
Which hormones are known as first messengers?
Non-steroid hormones
What does a first messenger usually stimulate?
Stimulate the release of another signalling molecule inside the cell, a secondary messenger.
What does a second messenger stimulate?
Stimulates a change in the activity of the cell?
Give an example of a common effector molecule in a cell
Adenyl Cyclase
Outline the process of activation of a secondary messenger
- G-protein activated when the hormone binds to the receptor
- G-protein activates an effector molecule (usually an enzyme that converts an inactive molecule in to the active secondary messenger)
- 2nd messenger could cat directly another protein/initiate cascade of enzyme-controlled reactions that alter activity of the cell.
What are two difference between Endocrine and Exocrine glands?
Endocrine glands release hormones, exocrine do not.
Exocrine glands have ducts, Endocrine are ductless
Name two differences between the first and second messengers.
- First messengers are signalling molecules outside the cell where as secondary are INSIDE the cell
- First’s stimulate release of ANOTHER signalling molecule whereas seconds stimulate a change in activity of the cell
Why can Steroid hormones enter the cell?
Because they are soluble in the phospholipid membrane unlike Protein hormones.
What are the Adrenal glands?
A pair of endocrine glands that lye above the kidneys, which release adrenaline and other hormones called corticoids.
What is the name of the inner layer of the Medulla?
The Adrenal Medulla
What are the three layers of the Adrenal Cortex?
- Zona Glomerulosa (outermost layer)
- Zona fasciculata (middle layer)
- Zona reticularis (innermost layer)
What is the function of the outer layer of the adrenal cortex? (the zona glomerulosa)
It secretes mineralocorticoids
What is the function of the middle layer of the adrenal cortex? (the zona fasciculata)
It secretes glucocorticoids
What is the function of the innermost layer of the adrenal cortex? (the zona reticularis)
Secretes precursor molecules that are used to make sex hormones
Where is the adrenal medulla found?
At the centre of the adrenal glands
What does the adrenal medulla secrete?
Adrenaline and Nonadrenaline
What molecule is used by the adrenal cortex to produce a range of hormones?
Cholesterol
What can hormones from the adrenal glands do?
They’re steroid based so can enter cell by dissolving into the cell surface membrane. They enter the nucleus and have a direct impact on the DNA to cause PROTEIN SYNTHESIS
What happens with the adrenal gland hormones once inside the cell?
- The receptor-steroid hormone complex enters nucleus of target cell and binds to another specific receptor on the chromosomal material.
- Binding stimulates production of messenger RNA molecules which code for the structure of proteins
Name the 3 hormones secreted from the adrenal cortex
- Mineralocorticoids
- Glucocorticoids
- Cortisol
Give 2 functions of Mineralocorticoids
- Help control Na and K concentrations in the blood,
- As a result they help maintain blood pressure by increasing absorption of Na, decreasing K, increasing water retention so increasing blood pressure
What is the function of Glucocorticoids?
They help control the metabolism of carbohydrates, fats, and proteins in the liver.
What is the function of Cortisol?
- Secretes precursor molecules that are used to make sex hormones
- (they help regulate the production of gametes.)
What type of molecule is adrenaline and from what is it derived?
- A polar molecule
- From the AA Tyrosine
Why can’t adrenaline enter cells through the plasma membrane like a steroid hormone?
It derives from an amino acid meaning it is a non-steroid hormone.
Why are the effects of adrenaline widespread?
Many cells and tissues have adrenaline receptors?
Name 4 effects of adrenaline on the body
- Relaxing smooth muscles in the bronchioles
- Increasing heart rate
- Pupils dilate
- Stimulating conversion of glycogen to glucose
Describe the process of the action of a steroid hormone
- Steroid hormone passes through cell membrane
- Steroid hormone binds with a specific receptor in the cytoplasm
- Receptor-steroid hormone complex enters nucleus of target cell and binds to another specific receptor on the chromosomal material
- Binding stimulates production of mRNA molecules
What’s the difference between the hormones released by the adrenal cortex and the hormones released by the medulla?
Adrenal cortex hormones = Steroid based
Medulla hormones = Protein based/ non steroid
Why does adrenaline cause an increase in blood glucose levels?
It has the effect of stimulating the conversion of glycogen into glucose so glucose levels will quickly increase
What are the two main secretions of the pancreas?
- Pancreatic juices, containing enzymes which are secreted into the small intestine
- Hormones, that are secreted from the islets of Langerhaans into the blood.
What do most cells in the pancreas synthesise and release?
Digestive enzymes
The exocrine cells are in small groups surrounding tiny tubules, what is the name of each group of cells?
Acinus
What substance do 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 what?
Intralobular ducts that eventually combine to make up the pancreatic duct.
What does the pancreatic duct do?
It carries the fluid containing the enzymes into the first part of the small intestine.
What 3 enzymes does the fluid from the pancreatic duct contain?
- Amylase (pancreatic) = a carbohydrate which digests amylase to maltose
- Trypsinogen
- Lipase = Digests lipid molecules
What two types of cells do the islets of Langerhaans contain?
The Alpha and Beta cells that make up the endocrine tissues in the pancreas
What substances do Alpha and Beta cells secrete?
Alpha = Glucagon Beta = Insulin
What effect does the release of insulin from the islets of langerhaans produce?
Blood glucose concentration reduces
Outline how Insulin is released from the Beta cells
- Cell membrane has Na+ and K+ channels
- The K+ channels are usually open, so K+ ions flow out
- When blood glucose conc. high, glucose moves into cell
- The glucose is metabolised to produce ATP
- The extra ATP closes the K+ ion channels
- Accumulation of K+ ions alters P.D across membrane (Inside becomes less negative)
- Change in P.D opens up the Sodium channels
- Calcium ions cause vesicles of insulin to fuse with cell membrane, releasing insulin by EXOCYTOSIS
If a persons blood glucose concentration remains too low for long periods of time, the person is considered to be what?
Hypoglycaemic
What is the main problem caused by Hypoglycaemia?
Inadequate delivery of glucose to the body tissues and in particular the brain
Which cells constantly monitor the concentration of glucose?
The cells in the Islets of Langerhaans
How do the Islets of Langerhans respond to a change in the blood glucose concentration?
By releasing the relevant hormone
- Insulin if the blood glucose is high
- Glucagon if blood glucose is too low
What happens if blood glucose drops too low?
Beta cells respond by secreting insulin into the blood
Outline the process of human insulin’s effect on a cell
- Human Insulin is a small protein so can’t pass through the cell surface membrane
- Insulin binds to the insulin receptor, activating the enzyme Tyrosine Kinase
- TK causes phosphorylation of inactive enzymes in the cell
Name 4 effects that Insulin has on the cell
- More transporter proteins specific to glucose are placed near the cell membrane
- More glucose enters the cell
- Glucose in cell converted to glycogen for storage (Glycogenesis)
- More glucose is converted to fats
What cells detect if blood glucose drops too low, and what do they do?
Alpha cells in the Islets of Langerhans, which then secrete the hormone Glucagon
What are the target cells of glucagon?
Hepatocytes (liver cells)
What happens when blood passes the liver cells?
- Glucagon binds to the receptors
- This stimulates a G protein
- The G protein activates the adenyl cyclase inside each cell
- Adenyl Cyclase converts ATP into cAMP
- This activates a series of enzyme-controlled reactions in the cell
Name 3 effects of glucagon in the cell
- Glycogen converted to glucose (glycogenolysis)
- More fatty acids used in respiration
- AAs and fats converted into additional glucose
The concentration of blood glucose is controlled by a negative feedback mechanism involving what two hormones?
Insulin and Glucagon
What is the term for the blood glucose concentration dropping too low?
Hypoglycaemic
What is the term for the blood glucose concentration rising high?
Hyperglycaemic
Diabetes is thought to be the result of what?
The result of an autoimmune response in which the body’s immune system attacks and destroys the beta cells
What happens to excess glucose in a healthy person?
It’s converted into glycogen in the liver and muscles
What can a person with diabetes not do?
They’re no longer able to synthesise sufficient insulin and cannot store excess glucose as glycogen.
Name 2 factors that bring on an earlier onset of type 2 diabetes
- Obesity/Lack of regular exercise
- Being Afro-caribbean or Asian origin
Name 3 alternatives to insulin injections to treat type 1 diabetes
- Insulin pump therapy
- Islet cell transplantation
- Complete pancreas transplant
Insulin is now produced from genetically modified bacteria rather than pig insulin. Name two advantages of this
- Less chance of rejection due to an immune response
- lower risk of infection
