T16 Flashcards
What is the cell signalling pathway for adrenaline?
Adrenaline binds to complementary receptor on the cell-surface membrane of a liver cell.
The binding of adrenaline causes the protein to change shape, activating a G protein.
This activates the enzyme adenylyl cyclase.
The activated adenyl cyclase converts ATP into cAMP.
cAMP acts as a second messenger, binding to and activating many protein kinases via phosphorylation, amplifying the signal from adrenaline.
Protein kinases activate enzymes that catalyse the breakdown of glycogen into glucose.
Glucose moves out of liver cells by facilitated diffusion and into the blood through channel proteins.
This increases the blood glucose concentration so that more glucose can be delivered to body cells for respiration.
The cascade effect in this process means that one hormone molecule can generate multiple cAMP molecules. This effect amplifies at each stage, increasing the number of molecules involved.
What hormone do Beta cells secrete?
Insuline
What hormone do alpha cells secrete?
Glucagon
What is the negative feedback mechanism when glucose levels increase?
When glucose levels increase, insulin acts to reduce blood glucose through several mechanisms:
Inhibition of α cells - Reduces glucagon secretion.
Increased glucose uptake - Insulin increases the permeability of muscle and fat cells to glucose.
Increased respiration - Increased glucose breakdown for energy production.
Glycogenesis - Glucose is converted into glycogen for storage, primarily in the liver.
What is the negative feedback mechanism when glucose levels decrease?
When glucose levels decrease, glucagon acts to increase blood glucose through several mechanisms:
Inhibition of β cells - Lowers insulin secretion.
Reduced respiration - Decreases glucose breakdown.
Glycogenolysis - Glycogen is converted back into glucose in liver and muscle cells.
Gluconeogenesis - Glucose is produced from amino acids and fats in the liver.
Adrenaline also works with glucagon to increase blood glucose levels when they are too low by promoting glycogenolysis and gluconeogenesis in liver and muscle cells.
Features of type 1 diabetes
Often results from an autoimmune disease destroying insulin-producing beta cells in the pancreas.
Leads to no insulin production and high blood glucose levels.
Typically develops in childhood or early adulthood.
Features of type 2 diabetes
Occurs when beta cells don’t produce enough insulin or the body’s cells resist insulin.
Results in higher than normal blood glucose levels.
Commonly develops later in life and is associated with obesity.
Treatments for type 1 diabetes
Regular insulin injections for most individuals.
Use of an insulin pump providing continuous insulin administration.
Pancreas transplants of healthy islet cells to enable some insulin production.
Careful blood glucose monitoring and a diet balanced with insulin dosage.
Exercise to help regulate blood glucose and insulin requirements.
Treatments for type 2 diabetes
Diet control to reduce sugar intake.
Regular physical activity.
Medications to increase cells’ sensitivity to insulin.
Medications to stimulate more insulin production in cells.
In some cases, insulin therapy is necessary to manage blood glucose levels.
What order does filtrate move through the structures in a nephron
1 Bowmans capsule (renal capsule) - surrounds the glomerulus (where filtrate is formed), contains podocytes in its inner layer
2 Proximal convoluted tubule (PCT) - Reabsorption of water, glucose and salts into surrounding capillaries - contain microvilli
3 Loop of Henle - high solute gradient in the medulla - helping with reabsorption
4 Distal convoluted tubule (DCT) - Reabsorbs water into surround capillaries - influenced by antidiuretic hormone
5 Collecting duct - Collects filtrate and fine-tunes the water balance, before the urine formed is passed to the bladder
Define glycogenesis
Glucose converted into glycogen for storage, primarily in the liver
Define Glycogenolysis
Glycogen is converted back into glucose in liver and muscle cells
Define gluconeogenesis
Glucose is produced from amino acids and fats in the liver
What does the afferent arteriole do?
Supplies the glomerulus with blood
What does the glomerulus do?
Fluid is forced out of the blood within this mass of capillaries into the Bowmans capsule through ultrafiltration
What does the efferent arteriole do?
Carries blood away from the glomerulus
What are the role of the capillaries surrounding structures in the nephron?
Aborb salts,glucose and water
Describe the process of ultrafiltration
Blood enters the glomerulus through the afferent arteriole.
Blood leaves the glomerulus via the smaller efferent arteriole, maintaining a high hydrostatic pressure.
This high pressure forces molecules, like water and small solutes, out of the blood through pores in the capillary endothelium.
The molecules move through the basement membrane, which has collagen fibres that act as a selective filter preventing large molecules and blood cells from passing into the Bowman’s capsule.
The molecules move through the Bowman’s capsule epithelium, which has specialised cells called podocytes with extensions known as pedicels that wrap around capillaries and help to filter the blood.
Filtered fluid collects in Bowman’s capsule.
What substances are flitered into glomerular filtrate and what substances remain in the blood?
Filtered into:
Water, salts, glucose, urea
Remain in blood:
Blood cells, platelets, proteins
Adaptations of the PCT
Microvilli - These are small, finger-like projections that greatly increase the surface area for reabsorption.
Basal infoldings - These structures further increase the surface area for moving substances into surrounding blood capillaries.
Numerous mitochondria - These organelles provide ATP for the active transport processes involved in reabsorption.
Co-transporter proteins in the plasma membrane - These allow co-transport of substances from filtrate into epithelial cells.
Describe the reabsorption process in the PCT
Sodium ions (Na+) are actively transported into blood capillaries, reducing the Na+ concentration in epithelial cells lining the PCT.
Na+ moves from the PCT lumen into the epithelial cells, down its concentration gradient.
Na+ is co-transported with substances like glucose and amino acids into the epithelial cells.
These reabsorbed molecules can then diffuse into blood capillaries.
85% of water is reabsorbed, along with, most glucose, amino acids and ions
Describe the reabsorption process in the DCT
The reabsorption of any remaining useful substances, primarily through active transport.
The alteration of DCT membrane permeability to regulate further reabsorption of water and solutes.
The regulation of blood pH by selectively reabsorbing certain ions.
Like the PCT, the DCT has microvilli and mitochondria to help with these processes. Hormones can also influence the adjustments made in the DCT, further fine-tuning the composition of the urine.
Describe the process of water reabsorption in the loop of Henle
The descending limb’s walls are permeable to water, so water leaves the filtrate via osmosis into the interstitial space.
Filtrate loses water as it moves down the descending limb, reaching its lowest water potential at the tip in the medulla.
Water that is lost is reabsorbed into blood in the surrounding capillaries by osmosis and is carried away.
The ascending limb is impermeable to water, but is permeable to sodium (Na+) and chloride (Cl-) ions.
Na+ and Cl- diffuse out of the filtrate into the interstitial space at the bottom of the ascending limb, due to the low water potential of the filtrate.
This concentrates ions in the interstitial space in the medulla, making its water potential very low.
Na+ and Cl- need to be actively transported out of the top of the ascending limb, because their concentration in filtrate decreases as it ascends (the water potential increases).
Overall, this creates a water potential gradient in the interstitial space, with the highest water potential in the cortex
Describe what happens in the collecting duct
Water moves from the filtrate in the collecting duct into the interstitial space, and then into surrounding capillaries, by osmosis to be carried away.
Water continues to exit the filtrate as it moves through the collecting duct, even deep in the medulla when most water has already been lost, because of the low water potential established by the loop of Henle in the surrounding interstitial space.
Urine leaving the collecting duct has a very low water potential, as most water has been reabsorbed into the blood.
How is the countercurrent multiplier set up and its importance in the loop of Henle
It intensifies the salt gradient in the kidney medulla
As filtrate moves down the collecting duct, it loses water, decreasing its water potential.
However, due to the pumping of ions out of the ascending limb of the loop of Henle, especially deeper in the medulla, the water potential of the surrounding tissues in the medulla is even lower than in the collecting duct.
This allows water to continue to move out of filtrate down the whole length of the collecting duct.
So, the countercurrent system concentrates urine, and ensures that there is always a water potential gradient drawing water out of the collecting duct. If the flows were parallel, less water reabsorption would occur.
Features of antidiuretic hormone (ADH)
It is produced in the hypothalamus.
It is stored in the posterior pituitary gland after production.
Its target cells are those lining the distal convoluted tubules (DCTs) and collecting ducts in the kidneys.
Describe the mechanism of ADH action
ADH attaches to receptors on the surface of cells in the DCT and collecting duct.
This triggers the activation of the enzyme phosphorylase.
This results in water channel proteins called aquaporins being integrated into the cell-surface membrane.
Water then moves through aquaporins by osmosis from the DCT and collecting duct into the surrounding interstitial space.
Water is then reabsorbed into the surrounding blood vessels.
This process effectively returns water to the bloodstream while facilitating the removal of concentrated urine.
