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Define Homeostasis:
the regulation of internal conditions to maintain optimal conditions for enzyme action and cell function
State things that need to be regulated in our bodies:
blood glucose concentration
water potential of the blood
blood pH
body temperature
What is a negative feedback loop?
counteract changes and bring the body back to its set point
What is a positive feedback loop?
they amplify changes and move the body further away from the set point
What would happen if blood glucose concentration was too high or too low?
lower/higher water potential than cells
water moves out/in by osmosis
causes cells to shrivel/lyse
What is the outcome of negative feedback?
the stimulus is constantly monitored
system is restored to its original level
reduce initial effect of stimulus
Positive feedback in bone repair (do not need to memorise but good out of spec knowledge)
osteocalcin is a protein secreted by osteoblasts, they are inactive when secreted
The osteoclasts secrete acid
lowers the pH
cause the osteocalcin to become activated
The low pH alters the hydrogen and ionic bonds in the protein which changes the tertiary structure
osteocalcin binds to a receptor on beta (β) cells in the pancreas
stimulates them to release insulin
Osteoblast cells possess insulin receptors which when stimulated causes them to release more inactive osteocalcin
The osteoblast cells enhance the effect of the original stimulus (insulin)
Where are insulin and glucagon secreted from?
pancreas
endocrine tissue
tissue is made up of cells called islets of Langerhans
a cells secrete glucagon
B cells secrete insulin
a cells and B cells act as receptors
Which cells act as the effectors in blood glucose conc regulation?
liver cells
muscle cells
fat cells
have glucose transporter proteins on cell surface (limits rate of glucose uptake by cells)
What is gluconeogenesis?
produces glucose from amino acids, pyruvate, lactate
triggered by glucagon by activating enzymes within the liver
These enzymes convert other molecules, such as fatty acids and amino acids, into glucose molecules
What is glycogenesis?
glycogen is synthesised from glucose
glucose molecules added to glycogen chains
triggered by insulin
What is glycogenolysis?
breakdown of glycogen (n) to glucose-1-phosphate and glycogen (n-1)
triggered by glucagon
How does insulin increase uptake of glucose by liver cells?
stimulates glycogenesis
attach to receptors on liver/muscle cells
changes structure of channel proteins, more glucose absorbed by facilitated diffusion
more protein carriers incorportated into cell membranes, more glucose absorbed from body cells
activates enzymes involved in conversion of glucose to glycogen
How are more protein carriers incorporated into cell membranes?
insulin bound to insulin receptor
intracellular chemical released
causes vesicles containing glucose channel proteins to fuse with cell surface membrane
Describe what occurs when there is a decrease in blood glucose concentration:
SECOND MESSENGER MODEL
GLYCOGENOLYSIS
detected by a cells and b cells in pancreas
a cells secrete glucagon
b cells stop secreting insulin
decrease in insulin = decrease in use of glucose by liver and muscle cells
glucagon binds to receptors on liver cells
causes conformational change in receptor protein
activates G protein
activated G protein activates enzyme Adenylyl Cyclase
activated Adenylyl Cyclase catalyses conversion of ADP to cyclic AMP
cAMP binds to protein kinase enzymes, activating them
Active protein kinase A enzymes activate phosphorylase kinase enzymes by adding phosphate groups to them
Active phosphorylase kinase enzymes activate glycogen phosphorylase enzymes
Active glycogen phosphorylase enzymes catalyse the breakdown of glycogen to glucose
What is the result of the second messenger model process?
breakdown of glycogen into glucose
releasing of extra glucose by the liver to increase the blood glucose concentration back to a normal level
enzyme cascade amplifies the original signal from glucagon
ONLY OCCURS IN LIVER CELLS
Outline how regulation of blood glucose is a negative feedback loop process:
When blood glucose concentration is low, more glucagon is secreted and less insulin is secreted
When blood glucose concentration is high, more insulin is secreted and less glucagon is secreted
State the different cells, proteins and enzymes involved in the second messenger model:
a cells and B cells
liver cell receptor
G protein
Adenylyl Cyclase enzyme
ADP to cAMP (second messenger)
protein kinase enzymes
glycogen phosphorylase enzymes
Describe the role of adrenaline in blood glucose regulation:
when secreted, increases concentration of blood glucose
binds to same receptors on liver cell as glucagon to stimulate enzyme cascade
also stimulates the breakdown of glycogen stores in muscle during exercise
glucose in the muscle cells in then used for respiration
What are the three ways glucose can enter the bloodstream?
Absorption in the gut following carbohydrate digestion
Hydrolysis of glycogen stores
Non-carbohydrates such as lipids, lactate and amino acids that have been converted to glucose
What causes type 1 diabetes?
What are the treatments?
pancreas cannot secrete sufficient insulin to control blood glucose levels
immune system (T cells) attack B cells
lack of insulin affects glycogen stores- individual feels fatigued
control diet, insulin injections- can be fast or slow acting
What causes Type 2 diabetes?
What are the treatments?
pancreas still produces insulin but the receptors have reduced in number or no longer respond to it
occurs in liver and fat storage tissues
reduced glucose uptake = higher concentration = β cells to produce larger amounts of insulin which ultimately damages them
exercise, sugar and fat reduced diet
Why do diabetic people often have high blood pressure?
high concentration of glucose in blood
water moves out of cell
increases volume of blood
Why do diabetic patients often suffer from dehydration?
high concentration of glucose in blood
kidneys cannot filter out excess glucose
kidneys produce large quantities of urine
What is the method and process to calculate concentration of glucose in urine?
Producing a dilution series and a calibration curve
set up standard solutions with known concentration of glucose
do benedicts test on all, control variables
carry out on urine sample(s)
use colorimeter
find unknown value
How do we set up the colorimeter?
set colorimeter wavelength to red (complementary to blue, blue solution will absorb red wavelength the best)
calibrate colorimeter using cuvette with only distilled water (blank: 100% transmission of light)