5.1.4: Hormonal communication Flashcards
Exocrine glands
Secrete molecules into a duct which transports them to their site of action
• Don’t secrete hormones
• e.g. salivary glands
Endocrine glands
Secrete hormones directly into the bloodstream, have no ducts.
How does a hormone know where to act?
- Target cells have specific receptors that are complementary to the shape of the hormone.
- Cells only respond to the hormones for which they have receptors.
- Target cells are usually grouped together to form target tissues.
Types of hormones
• Protein, peptide, amino acid derivatives
⟶ e.g. adrenaline, insulin
⟶ Act on cell surface receptors triggering a cascade reaction mediated by second messengers
• Steroid hormones = lipid based
Adrenal glands are exocrine/endocrine glands?
Endocrine glands
Adrenal cortex
Outer region of adrenal gland
The adrenal cortex secretes
Hormones vital to life
• Glucocorticoids
• Mineralocorticoids
• Androgens
Adrenal medulla
Inner region of adrenal gland
The adrenal medulla secretes
Non-essential (for the day-to-day) hormones that help the body respond to stress
• Adrenaline
• Noradrenaline
Mineralocorticoids
- controls blood pressure by maintaining salt and water concentrations of blood and bodily fluids
- mediated by signals from kidney
- e.g. aldosterone
Glucocorticoids
- regulate metabolism by controlling how body converts fats, proteins, etc. to energy
- regulate immune response
- associated with responses to stress
Androgens
- small amounts of male and female hormones
* effect is minor by important
Adrenaline
- increases heart rate
* stimulates glycogenolysis in the liver
Noradrenaline
- dilates bronchi
* stimulates narrowing of blood vessels to non-essential organs which raises blood pressure
Pancreas contains
both exocrine and endocrine tissues
• Exocrine tissue secretes digestive enzymes (pancreatic amylase) into pancreatic duct to duodenum
• Endocrine tissue secretes insulin, glucagon into blood
Islets of Langerhans
- Endocrine tissue: produce and secrete hormones
- Large spherical clusters made up of 𝜶 and 𝛽 cells
- Lightly staining
Pancreatic acini
• Exocrine tissue: produce and secrete digestive enzymes
• Small, berry-like clusters
• Darkly staining
• 1 acinar cell –cluster of–> an acinus
many clusters = acini
Normal blood glucose level
90mg per 100cm³ of blood
Hyperglycaemia
Abnormally high blood glucose
⟶ Can impact osmotic balance leading to water being excreted
Hypoglycaemia
Abnormally low blood glucose
⟶ Can mean insufficient glucose for respiration, leading to coma and death
Insulin is produced by
𝛽 cells in the Islets of Langerhans in the pancreas
Glucagon is produced by
𝜶 cells in the Islets of Langerhans in the pancreas
Insulin (effect on body)
- Inhibit the release of glucagon from 𝜶 cells
- Increase respiratory rate of body
- Stimulates glycogenesis in liver and muscle cells
- Activates enzymes which convert glucose into fat
Glucagon (effect on body)
- Stimulates glycogenolysis in liver cells
- Liver cells absorb less glucose from blood
- Liver cells convert amino acids and glycerol into glucose (gluconeogenesis)
- Fatty acids are used in respiration rather than glucose
Which hormone responds to low blood glucose?
Glucagon
Which hormone responds to high blood glucose?
Insulin
Control of blood sugar (and homeostatic control generally) is an example of
negative feedback
Negative feedback
feedback causes the corrective measures to be switched off when the system returns to ‘set point’
Control of insulin secretion (resting state)
- K+ channels in the plasma membrane of 𝛽 cells are open
- K+ ions diffuse out of the cell
- The potential difference across the membrane is -70mV
Control of insulin secretion (increase in blood glucose)
• Glucose enters cell via glucose transporter
• Glucose is used in respiration –> mitochondria synthesise ATP
• ATP binds to ATP-sensitive K+ channels, causing them to close
• K+ ions can no longer diffuse out of the cell
The potential difference across the membrane reduces to -30mV as the membrane becomes depolarised
• Voltage gated Ca2+ ion channels open
• Ca2+ ions diffuse into the cell
• This causes secretory vesicles containing insulin to fuse with the plasma membrane and release insulin by exocytosis
Cause of Type 1 diabetes
𝛽 cells in the Islets of Langerhans do not produce insulin
Cause of Type 2 diabetes
𝛽 cells do not produce enough insulin
or
person’s body cells do not respond to insulin
Original cause of Type 1 diabetes
Not known; maybe an autoimmune attack on 𝛽 cells
Original cause of Type 2 diabetes
- (generally) excess body weight, physical inactivity, overeating of refined carbohydrates
- genetic components in some cases
Typically age of onset Type 1 diabetes
Childhood (usually)
Typically age of onset Type 2 diabetes
Traditionally 40+
Treatment for Type 1 diabetes
Regular insulin injections
Treatment for Type 2 diabetes
- Regulation of carbohydrate intake
- Increased exercise
- Drugs to stimulate insulin production
Current treatments for diabetes
Pancreas transplant
Insulin produced by genetically engineered bacteria
Future treatments for diabetes
Potential use of stem cells to create person’s 𝛽 cells
