Section 6- Homeostasis Flashcards
What is homeostasis?
The regulation and maintenance of the internal environment, within restrictive limits, controlled by physiological control systems
(e.g. temperature, blood pH, blood sugar levels, water potential of blood)
Why is temperature controlled internally?
Prevents proteins denaturing and to keep enzymes at their optimum
True for endotherms (warm blooded, mammals and birds)
What is negative feedback?
A negative feedback mechanism is one where a stimulus causes a response that reverses the effect of that stimulus
What happens when we are too cold?
Goosebumps, hairs become erect: erector pili muscles cause hairs to become erect to trap a layer of insulating hair
Shivering: by repeatedly contracting muscles we increase respiration rate, which produces heat as a waste product
Vasoconstriction: More blood is diverted away from the skin surface to prevent heat loss by radiation
Will gluconeogenesis require energy, or release energy?
Require energy
Reversing glycolysis
Why are diabetics encouraged to eat starchy foods rather than sugary foods?
Fatty foods contain sucrose which hydrolyse quick
What is gluconeogenesis?
Making new glucose from pyruvate, amino acids or glycerol
What is glycogenolysis?
Hydrolysis of glycogen
What 3 hormones does the control of blood glucose depend upon?
Insulin
Glucagon
Adrenaline
What 3 factors are blood glucose levels increased by?
Diet
Gluconeogenesis
Glycogenolysis
What happens if blood glucose goes too high?
Cells in the pancreas celled Beta-cells, islets of Langerhans, detects the rise in blood glucose and secret insulin
Insulin binds to complementary receptors on the surface membranes of target cells
Binding stimulates the cells to take up more glucose by facilitated diffusion
Also stimulates the process of glycogenesis
What detects rise in blood glucose?
Beta-cells found in islets of Langerhans
What happens if blood glucose goes too low?
Alpha cells in the islets of Langerhans detect the drop and secrete glucagon
Binds to complementary receptors on the surface of liver cells, stimulating process of glycogenolysis
If glycogen stores are depleted then gluconeogenesis is stimulated
How does adrenaline stimulate glycogenolysis?
Adrenalin is secreted from the adrenal glands on top of the kidneys
Binds to complementary receptors on liver cells where it stimulates glycogenolysis
What does the second messenger model describe?
How adrenaline and glucagon can stimulate glycogenolysis without entering the cell
What is the second messenger model?
- Hormone (first messenger) binds to the complementary receptor on the surface membrane of the target cell
- This binding activates adenylate cyclase - enzymes catalyses ATP into cyclic AMP (cAMP)
- cAMP is second messenger which activates an enzymes called proteinkinase A
- Proteinkinase A starts a cascade of reactions resulting in glycogenolysis
What are 2 reasons why it was better to start with mRNA from pancreas cell rather than with the DNA from these cells?
Contains no introns
Specific mRNA is found in pancreas cells
How can the kidney be adapted to reduce the volume of urine produced in an organism that does not need to drink water?
Long loop of Henle
Very low water potential in medulla
Large number of aquaporins in the collecting duct
How does insulin increase permeability of cells to glucose?
Increases the number of carrier proteins
Triggers conformational change which opens glucose carrier proteins
How does insulin lead to a decrease in blood glucose concentration?
Increases permeability of cells to glucose
Increases glucose concentration gradient
Triggers inhibition of enzymes of glycogenolysis
How does insulin increase permeability of cells to glucose?
Increases number of glucose carrier proteins
Triggers conformational change which opens glucose carrier proteins
How does insulin increase the glucose concentration gradient?
Activates enzymes for glycogenesis in liver and muscles
Stimulates fat synthesis in adipose tissue
What is the cause of Type 1 diabetes and how can it be controlled?
Body cannot produce insulin due to autoimmune response which attacks B-cells of Islets of Langerhans
Treated by injecting insulin
What is the cause of Type 2 diabetes and how is it controlled?
Glycoprotein receptors are damaged or become less responsive to insulin
Poor diet / obesity
Treat by controlling diet and exercise regime
What are the common signs of diabetes?
Glucose in urine
Blurred vision
Sudden weight loss
High blood glucose concentration
How could colorimetry be used to identify the glucose concentration in a sample
- Benedict’s test on solutions of known glucose concentration - use colorimeter to record absorbance
- Plot calibration curve: absorbance (y-axis), glucose concentration (x-axis)
- Benedict’s test on unknown sample - use calibration curve to read glucose concentration at its absorbance value
What is osmoregulation?
Control of blood water potential via homeostatic mechanisms
What is the structure of the nephron?
Bowman’s capsule: surrounds glomerulus, inner layer of podocytes
Proximal convoluted tubule: loops surrounded by capillaries, villi and microvilli
Loop of Henle: hairpin loop extends from cortex into medulla
Distal convoluted tubule
Collecting duct: leads into pelvis of kidney
What happens in the Bowman’s capsule?
As the Efferent arteriole is narrower than the Afferent arteriole, the hydrostatic pressure of the blood inside the capillary bed is increased
This leads to ultrafiltration: urea, water, amino acids, glucose, ions
What is in the filtrate out of the podocytes in the Bowman’s capsule?
Water, glucose, urea, amino acids and ions
What happens in the proximal convoluted tubule?
Selective reabsorption
Cells will actively transport all of the glucose and amino acids back into the blood
Done with co-transport mechanism
Most of water is reabsorbed through osmosis
What is the proximal convoluted tubule like in texture?
Tube has high surface area due to its convoluted nature
Cells are covered in microvilli, forming villi.
How are cells in the proximal convoluted tubule adapted for selective reabsorption?
Microvilli: large surface area for co-transporter proteins
Many mitochondria: ATP for active transport of glucose into intercellular spaces
Folded basal membrane: large surface area
What happens in the loop of Henle?
Water moves out of the filtrate by osmosis to be reabsorbed into the blood - descending limb due to decreasing water potential in the medulla
Ascending limb is impermeable to water
Carrier proteins will actively transport ions out into the medulla depending on both the concentration of ions required in the medulla and in the body
What is the structure of the Loop of Henle?
Descending limb: decreasing water potential
Ascending limb: impermeable to water
What is the salt concentration in the medulla?
Gradient of salt concentration
Lower concentration at the top, more concentrated at the bottom of the loop of Henle
What happens in the collecting duct?
More water can be reabsorbed by osmosis back into the blood
Via osmosis through the aquaporins
Why is it important to maintain an Na+ gradient in the nephron?
Counter-current multiplier: filtrate in collecting ducts is always beside an area of interstitial fluid that has a lower water potential
Maintains water potential gradient for maximum
What is the role of the hypothalamus in osmoregulation?
Osmosis of water out of osmoreceptors in hypothalamus causes them to shrink
Triggers hypothalamus to produce more antidiuretic hormone
Why happens if the body is dehydrated?
Osmoreceptors in the hypothalamus detect this as they monitor the water potential of blood
What happens if the water potential decreases?
The pituitary gland releases anti-diuretic hormone (ADH)
Travels in the blood to receptors on the cells lining the collecting duct
Response involves a second messenger and results in aquaporins
Allow even more water to be reabsorbed from the filtrate - resulting urine produced will be more concentrated with urea and lower in volume
What are aquaporins?
Channel proteins specific to water being added to their membranes
What are factors that increase a persons risk of developing type 2 diabetes?
Obesity
Age
Family history
Males
What is the tissue that lines the proximal convoluted tubule?
Epithelial
After a prolonged period of fasting, glycogen levels in the liver are depleted. However, the liver can still produce glucose by the process of gluconeogenesis?
Breakdown of lipid
Glycerol and triose phosphate
Condensation
What is the action of antidiuretic hormone?
Increases the permeability of epithelial cells of the distal convoluted tubule and the collecting ducts to water
Why must a patient not eat anything before doing a glucose test?
Eating before test causes glucose to be present in blood
May affect changes caused by consumption of glucose drink
How does glucagon increase blood glucose concentration?
Glucagon binds to complementary receptor
Causes G-protein attached to receptor to bind and activate adenylate cyclase
Converts ATP to cAMP which activates protein Kinase A causing glycogen into glucose
Some cancer cells express glucagon receptors
How does this encourages the growth of cancer cells?
Rapidly dividing cancer cells require lots of energy
Express glucagon receptors to increase amount of glucose available in cell for respiration
Why is tiredness a symptom of diabetes?
Lack of glucose of respiration causing tiredness
What is the basement membrane?
Fine filter in the Renal capsule
What are 2 reasons why the concentration of glucose decreased after 1 hour in a diabetic even though no insulin was being produced?
Glucose used in glycolysis for respiration
Glucose enters cells
Excreted in urine
People with type 1 diabetes are described as being insulin-dependent. Suggest why they are being described as insulin-dependent?
Treatment requires person receiving insulin
