Module 5.1.4 Hormonal Communication Flashcards
How can cell-signalling occur?
Between cells that are near (nerves) and far away (hormones)
What are some differences between the nervous & the endocrine system?
Nervous system -> rapid & precise, communicates through electrical impulse, carried in nerves to a specific location
Endocrine system -> slower but longer-lasting, communicates through chemical messengers (hormones), carried in the bloodstream but only affects target organs
What is a hormone?
Chemical messengers that can either be a protein or steroid molecule & cause a specific response in a target cell
Transported via blood plasma
What is a target cell?
A cell that has a specific receptor on the cell surface membrane or in the cytoplasm, complementary to a hormone
What is an endocrine gland?
A gland which produces hormones & releases them directly into the blood or lymph
What is an exocrine gland?
A gland which produces substances & releases them via a duct
What is an example of an organ that is both an endocrine & exocrine gland?
The pancreas
What are some of the features of the pancreas?
The bile duct
The duodenum
Blood vessels
The pancreatic duct
Islets of Langerham cells
Acinar cells
How can the pancreas be considered an endocrine gland?
The islets of langerham cells secrete hormones into the blood via the blood vessels
How can the pancreas be considered an exocrine gland?
The acinar cells secrete digestive hormones into the pancreatic duct
What are steroid hormones?
A lipid soluble hormone made from cholesterol that can pass through the phospholipid-bilayer of the cell surface membrane and binds to receptors within the cell to form a hormone-receptor (HR) complex
What is an example of a steroid hormone?
Sex hormones e.g. oestrogen
What is the action for steroid hormones?
The lipid-soluble steroid hormone passes through the cell surface membrane and binds to the receptor protein. The hormone-receptor attaches to the DNA in the nucleus and the mRNA is transcribed and exits the nucleus through the nuclear pores. The polypeptides are then synthesised by ribosomes
Using oestrogen as an example, how is a hormone turned into a gene?
Oestrogen stimulates the transcriptional factor. Because oestrogen is a lipid soluble hormone, it easily enters the cytoplasm. It then binds to a receptor molecule which causes it to release the inhibitor molecule from the DNA binding site, activating the transcription factor. The hormone-receptor complex goes in the nucleus and gets attached to the gene and is then transcribed into the DNA
What are non-steroid hormones?
Hydrophilic hormones that cannot pass directly through the phospholipid bilayer and binds to receptors on the cell surface membrane which triggers a second messenger
What is an example of a non-steroid hormone?
Adrenaline
What is the action for non-steroid hormones?
The non-steroid hormone (1st messenger) binds to the receptor protein on the cell surface membrane. In the cytoplasm, G protein activates adenylate cyclase enzyme to make cAMP (cyclic-adenosine monophosphate) from ATP. cAMP then has an effect on cellular function
What are the effects that cAMP has on cellular function?
Activates enzymes
Stimulate cellular secretions
Opens ion channels
What is ADH?
Anti diuretic hormone
What are the target cells for ADH and aquaporins?
Cells in the DCT and collecting duct in the nephrons in the kidneys
What is the role of ADH & aquaporins?
To maintain the water potential of the blood
What is the action of ADH & aquaporins?
ADH attaches to the cell surface membrane of the cells lining the collecting duct which triggers cAMP (the 2nd messenger). Vesicles containing aquaporins move to the plasma membrane, forming channels that allow water molecules to pass into the medulla of the kidneys. Water is then reabsorbed by the kidneys
Why must target cells have specific receptors on the cell surface membrane?
So hormones can be carried in the blood without affecting every organ in the body and rather just the target organs
What is the biochemical identity of insulin and does it code for a protein?
Insulin is made of protein and binds with a protein but doesn’t code for proteins
What is the biochemical identity of cAMP and does it code for a protein?
cAMP isn’t made of protein but binds with a protein & doesnt code for a protein
What is the biochemical identity of the lac inhibitor gene and does it code for a protein?
The lac i gene isnt made of protein but binds & codes for a protein
What is the biochemical identity of the lac operator gene and does it code for a protein?
The lac o gene isnt made of protein and doesn’t code for a protein but binds with a protein
What is the biochemical identity of the homeotic gene product and does it code for a protein?
It is made of protein but doesn’t bind or code for a protein
What is one difference between excretion and secretion?
Excretion -> the substance is a waste/not useful/harmful
Secretion -> the substance is beneficial for the organism
What is an example of an excreted product?
Urea
What is an example of a secreted product?
Sweat
What is one similarity between excretion and secretion?
Both require ATP
What is the structure of the adrenal glands?
They sit above the kidneys and are divided into the outer adrenal cortex & the inner adrenal medulla
Both areas produce endocrine hormones (directly secreted into blood)
What hormones does the adrenal cortex secrete?
Vital hormones -> glucocorticoids, mineralocorticoids & androgens
What hormones does the adrenal medulla secrete?
Non-essential hormones -> adrenaline & noradrenaline
What is the adrenal gland capsule made of?
Connective tissue
What is the adrenal cortex do and how?
It is controlled by the pituitary gland and uses cholesterol to produce steroid hormones
What are glucocorticoids?
There release is controlled by the hypothalamus
Releases cortisol which regulates the metabolism, blood pressure & cardiovascular function in response to stress & corticosterone which works with cortisol to regulate the immune response & suppresses inflammation
What do mineralocorticoids secrete & what does it do?
Aldosterone -> controls blood pressure
It acts on the PCT (nephrons) to increase the uptake of sodium ions -> increases water potential which increases blood pressure due to osmosis of water into capillaries
What is the action of mineralocorticoids in the adrenal medulla?
The sodium/potassium pump is activated by aldosterone. There is a net gain of sodium ions outside the nephron tubule, chloride ions diffuse between cells down the electrochemical gradient. Water then leaves the tubule
What are androgens & what is their effect in the body?
They’re small amounts of male & sex hormones & have less of an impact than those released by the testes/ovaries but important in woman after menopause
What hormones does the adrenal medulla secrete?
non-steroid hormones -> adrenaline & noradrenaline in response to stress (fight or flight)
What effects does adrenaline have on the body?
Glycogen is converted to glucose in the liver
Increases heart rate
More oxygen & oxygen delivered to muscle
What effects does noradrenaline have on the body?
Increases heart rate
Widens pupils
Widens airways in the lungs
Narrow blood vessels in non-essential -> increases blood pressure
What are the roles of the pancreas?
To secrete hormones (endocrine) & secrete digestive enzymes & pancreatic juice to aid in digestion (exocrine)
What are islets of langerhams made up of?
Alpha, beta & delta cells
What percentage do alpha cells make up of the islets of langerhams?
20%
What do the alpha cells in the islets of langerhams do?
Secrete glucagon -> converts glycogen to glucose to increase blood sugar levels
What do the beta cells in the islets of langerhams do?
Secrete insulin -> stimulates glucose to convert to glycogen
What do delta cells in the islets of langerhams do?
Secrete somatostatins -> inhibits hormone secretion
What are the 3 important digestive enzymes that the pancreas secretes & what is their effect?
Amylases -> break down starch into simple sugar
Proteases -> break down proteins into amino acids
Lipases -> break down lipids into fatty acids & glycerol
On a microscope, what is the appearance of the islets of langerhams?
Lightly stained
On a microscope, what is the shape of the islets of langerhams?
Large, spherical clusters
What type of tissue is the islets of langerhams?
Endocrine pancreatic tissue
RECAP: What is the function of the islets of langerhams?
Produce & secrete hormones e.g. insulin
On a microscope, what is the appearance of the acinar cells?
Darker stained
On a microscope, what is the shape of the acinar cells?
Small, berry-like clusters
What type of tissue is acinar cells?
Exocrine pancreatic tissue
RECAP: What is the function of acinar cells?
Produce & secrete digestive enzymes
On a microscope, how can you differentiate alpha & beta cells from the islets of langerhams?
Alpha cells larger & more of them the beta cells
What is the normal level of blood glucose?
4-6 mmol dm-3
How is the concentration of blood glucose monitored?
The alpha & beta islets of langerhans cells by releasing the required hormone-> insulin/glucagon
How is the concentration of blood glucose monitored?
The alpha & beta islets of langerhans cells by releasing the required hormone-> insulin/glucagon
What is the term for when blood glucose drops under 4 mmol dm-3?
Hypoglycaemia
What are the mild and severe symptoms of hypoglycaemia?
Mild -> tiredness, irritable
Severe -> impairement of brain function & confusion, seizures, unconsciousness or death
What is the term for when blood glucose is over 6 mmol dm-3?
Hyperglycaemia
What are the implications of hyperglycaemia & what is it used for?
Can lead to organ damage
It is the diagnosis for diabetes mellitus (type 1)
How are insulin & glucagon released?
In a negative feedback loop -> blood glucose high = insulin, blood glucose low = glucagon
What happens when the body goes into hyperglycaemia?
It is detected by the alpha & beta cells in the pancreas -> the alpha cells stop glucagon production & the beta cells will secrete more insulin into the blood
What cell controls insulin secretion?
The beta cells in the islets of langerhans
Describe the mechanism of insulin secretion
Glucose enters the cell through facilitated diffusion in a glucose transporter (GLuT) protein and causes the mitochondria to increase the rate of respiration. This generates more ATP in the cell. The increase in ATP production causes potassium ion channels to close and build up inside the cell, so it becomes more positive. This causes depolarisation which leads the calcium ion channels to open (they are voltage-gated) and calcium ions diffuse into the cell. This leads vesicles containing insulin to migrate to the plasma membrane & release the insulin by exocytosis
What cells does insulin target?
Hepatocytes, muscle cells & others cells e.g. brain cells
What changes does insulin cause in cells?
Increases respiration rate
Activates enzymes that convert glucose-> glycogen (glycogenesis)
Increases the cell’s permeability to glucose
How does insulin cause the cell to be more permeable to glucose?
The insulin molecule binds to a specific reception on the cell surface membrane. Chemical signals then cause vesicles with GLuT proteins to fuse with the membrane, increasing the availability of the membrane to take up glucose
What cells detect hypoglycaemia & secrete glucagon into the blood
Alpha cells in the islets of langerhans
What cells does glucagon target?
Specific receptors on hepatocytes
What effects does glucagon have on the body?
Decreases respiration rate, stimulates glycogenelysis & gluconeogenesis
What is the action of glucagon?
Glycogenolysis -> activates enzymes to break down glycogen -> glucose
Gluconeogenesis -> promotes formation of glucose from non-carb sources (fatty acids & amino acids -> glucose)
