6C Homeostasis Flashcards
What is homeostasis?
Changes in your external environment can affect your internal environment so homeostasis is the maintenance of a stable internal environment
What is the importance of homeostasis?
- Maintain core body
temperature - Blood Ph
- Blood glucose concentration
Why does temperature need to be maintained?
- The rate of metabolic reactions increase so more substrate molecules collide with the enzymes active sites resulting in a reaction
- But if the temperature gets too high the reaction will stop because the vibration of enzymes break the hydrogen bonds that hold enzyme in 3D shape
- This denatures enzyme so it no longer functions
Why does pH need to be maintained?
- Too alkaline or acidic enzymes become denatured
- Ionic and hydrogen bonds break so shape of enzymes active site change
- Optimum ph is when metabolic reactions are fastest
How is Ph calculated
Based on the concentration of hydrogen ions (H+), the greater the conc of H+ the lower the ph so more acidic
What equation is needed to work out the Ph of a solution
pH = -log10 [h+]
What is a logarithmic scale?
A scale that used the logarithm of a number instead of a number itself eg Log10 means each value is 10x larger than the value before
A blood sample has a hydrogen ion concentration of 3.9 x 10^-8 [h+] moldm-3. What is the ph of the blood?
ph = -log10 [h+]
= log10 ( 3.9 x 10^-8 )
= 7.4
Why does blood glucose need to be maintained?
- If blood glucose is too high the water potential of blood is reduced to the point where water molecules diffuse out of cells into blood by osmosis where there is a lower concentration
- This can cause cells to shrivel up and die
- If blood glucose is too low cells are unable to carry out normal activities because glucose is a respiratory substrate so a lack means they cant provide energy
What is the negative feedback mechanism?
When receptors detect a level is too low or high the information is communicated via the nervous/hormonal to effectors. The effectors will counteract the change by bringing the level back to normal
What is the benefit to the body of having multiple negative feedback mechanisms?
- More control over changes in your internal environment so you can actively increase and decrease a level so it returns to normal eg one to increase and one to decrease body temperature
What is a positive negative feedback system?
The mechanism that amplifies a change away from normal level to rapidly activate processes in the body
What is an example of a positive negative system?
Hypothermia is a low body temperature so the reaction is to stop shivering making the body temp fall even further
Positive feedback takes body temperature further away from normal level and decreases unless action is taken
What monitors blood glucose concentration?
Cells in the pancreas
In what situation does blood glucose rise and fall?
It rises after eating carbohydrates and falls after exercise as more glucose is used in respiration
What hormones control blood glucose concentration
Insulin and Glucagon
What secretes insulin and glucagon
Cluster of cells in pancreas called Islets of Langerhan
What do islets of langerhan contain
beta cells
alpha cells
what do beta and alpha cells do
beta cells secrete insulin and alpha cells secrete glucagon
What is glycogenesis and what activates it
The formation of glycogen from glucose activated by insulin
How does insulin lower blood glucose concentration?
- It binds to specific receptors on muscle and liver cells
- This increases the permeability of muscle cells to glucose so they take up more glucose
- Increasing the number of channel proteins
- Activates the process of glycogenesis so glycogen can be stored in muscle and liver cells cytoplasm
How does glucagon raise blood glucose concentration?
- Binds to specific receptors on liver cells
- Activates enzymes to break glycogen into glucose
What is the process of breaking down glycogen called
Glycogenolysis
What is gluconeogenesis?
This is the process of forming glucose from non carbs
What is the negative feedback mechanism when there is a rise in blood glucose concentration? hint : beta cells/alpha
- Pancreas detects high concentration
- Beta cells secrete insulin and alpha cells stop secreting glucagon
- Insulin binds to receptors on liver and muscle cells
- Decrease by glycogenesis
What is the negative feedback mechanism when there is a fall in blood glucose concentration? hint : beta cells/alpha
- When pancreas detects fall in blood glucose concentration
- Alpha cells secrete glucagon and beta cells stop insulin secretion
- Liver cells activate glycogenolysis
What are glucose transporters?
Channel Proteins that allow glucose to be transported across a cell membrane
What glucose transporter does skeletal and muscle cells contain
GLUT4
How does the availability of GLUT4 effect insulin?
- When insulin levels are low GLUT4 is stored in vesicles of cytoplasm
- When insulin binds to receptors on cell surface membrane it triggers movement of GLUT4
- Glucose is then transported into the cell through the GLUT4 protein by facilitated diffusion
What is adrenaline and where it is secreted from?
A hormone thats secreted from your adrenal glands
When is adrenaline secreted
Low concentration of glucose, when stressed and when exercising
What is the effect of adrenaline on glycogenesis and glycogenolysis
- It activates glycogenesis and glycogenolysis
- Activates glucagon secretion and inhibits insulin secretion which increases glucose concentration
What is a second messenger model?
The binding of the hormone to cell receptors activating an enzyme on the inside of the cell membrane then producing a chemical known as second messenger which activates other enyzmes to bring about a response
What is the second messenger model for adrenaline and glucagon - GLYCOGENOLYSIS?
- The receptors for adrenaline and glucagon have specific tertiary structures that make them complementary to hormones
- To activate glycogenolysis, adrenaline and glucagon bind to receptors and activate an enzyme called ADENYLATE CYCLASE
- This converts ATP into CYCLIC AMP (cAMP) - Second messenger
- Activating an enzyme called PROTEIN KINASE A
- Activating a cascade of glycogenolysis
what is the name of the second messenger
Cyclic amp
What is diabetes
Where blood glucose cant be controlled properly
What happens in type I diabetes?
- Immune system attacks B cells in islets of langerhan
- Cant produce any insulin so levels stay high - Hyperglycaemia
- Kidneys cant reabsorb so excreted in urine
How do you treat type I diabetes?
- Regular insulin injections
- Insulin pump
- Food habits
What happens in type 2 diabetes?
- B cells dont produce or body doesnt respond
- Insulin receptors on cell membranes dont work
How is type II treated
- Balanced diet
- Exercise
- Weight loss
What are the risk factors for type II
Exercise
Age
Poor diet
What are the functions of the kidneys?
Osmoregulatory Organ - regulate water content of the blood
Excretory organ - excrete toxic waste products of metabolism
What carries oxygenated blood to kidneys?
Renal Artery
What does the renal vein do?
Carries deoxygenated blood away from kidneys
What carries urine to bladder?
Ureter
What is the function of the bladder?
Temporarily store urine
What is the function of the urethra?
Releases urine outside of body
What surrounds the kidney?
Fibrous Capsule
What are the 3 main areas in the kidney?
Cortex
Medulla
Renal Pelvis
What is the function of the renal pelvis?
Ureter joins kidney
What is a nephron?
Functional Tubes that are responsible for formation of urine
What structures are within a nephron?
Glomerulus
Bowmans Capsule
Proximal convoluted tubule
Distal convoluted tubule
Loop of henle
Collecting duct
Renal Pelvis
What structures and networks are within the bowmans capsule?
Glomerulus
Supplied with blood by an afferent arteriole
The capillaries of the glomerulus rejoin to form an efferent arteriole
Blood then flows from the efferent arteriole into a network of capillaries that run closely alongside the rest of the nephron
Blood from these capillaries eventually flows into the renal vein
What is an afferent arteriole?
Takes blood into each glomerulus
What is an efferent arteriole?
Takes filtered blood away from glomerulus
What are the 2 stages in urine formation
Ultra Filtration
Selective reabsorption
Where does ultra filtration occur
bowmans capsule
proximal convoluted tube
Why is the blood in the glomurelus under high pressure? - ultra filtration
Efferent arteriole is smaller in diameter so blood in gloemeruls is under high pressure
What does the high pressure force? - - ultra filtration
Liquid and small molecules in the blood out of capillary and into bowmans capsule
What are the 3 layers separating the globalmerular capillary and bowmans capsule?
Capillary Endothelium
Basement membrane
Epithelium of bowmans capsule which contain Podocytes
What is the glomerular filtrate?
The substances that pass through and enter Bowmans capsule by passing through the gaps in the between the podocytes
Where does the filtrate pass through and collect?
The collecting duct and passes out of kidney through ureter
What does selective reabsorption take place?
As the glomulerar filtrate flows along proximal convoluted tube, through loop of henle and along distal convoluted tube
Where do the useful substances leave from and where do they go? - selective reabsorption
Leave nephron tubules and enter capillary network
Why is there microvilli on the PCT- selective reabsorption
Provide a large surface area for reabsorption of useful materials from glomerular filtrate into blood
What process reabsorb useful solutes?
Active Transport
Facilitated Diffusion
Why does water enter and how? -selective reabsorption
through osmosis because water potential
of blood is lower than filtrate
What structures reabsorb water ? - selective reabsorption
Pct, Loop of henle , DCT and collecting duct
What is the filtrate the remains? -selective reabsorption
urine
What is urine made up of?
Water, dissolved salts, urea, hormones, ecxess vitamins
what happens if the water potential of blood is too low?
more water is reabsorbed by osmosis into blood through tubules of nephrons
so water is more concentrated and less is lost
what happens if the water potential of blood is too high?
less water reabsorbed by osmosis into blood into tubules of nephrons so water is more concentrated and more is lost
what is the loop of henles structure and function?
ascending limb and descending limb which control movement of sodium ions so water can be reabsorbed by the blood
where is the loop of henle located ?
medulla of kidneys
how does the loop of Henle work?
- at the ascending limb NA+ are pumped out into medulla and since it is impermeable the water stays inside tubule creating a low water potential in medulla as there’s a high conc of ions
- lower water potential in medulla than in descending water moves out so glomerular is more concentrated
- water is reabsorbed into blood through capillary network
- bottom of ascending limb na+ diffuse out into medulla lowering water potential of medulla
- water moves out of dct by osmosis and reabsorbed into blood
- since w.p is lowered water moves out of collecting duct by osmosis and reabsorbed into capillary network
where is water potential monitored?
osmoreceptors in hypothalamus
what is the role of the posterior pituitary gland?
release ADH
what does adh do ?
- bind to receptors on plasma membrane of cells in dct and collecting duct
- aquaporins inserted into plasma membrane
- allow water to pass through making walls of dct and collecting duct more permeable
- more water absorbed by tubules of medulla and into blood by osmosis
- concentrated urine produced
What happens when you are dehydrated?
water content of blood drops so w.p drops
osmoreceptors detect
pituitary gland releases adh
this increases permeability of collecting duct and dct so more water reabsorbed
concentrated urine produced as less water lost
what happens when you are hydrated?
water content of blood is high so w.p is high
osmoreceptors detect
less adh released
less permable
less water absorbed
large amount of dilute urine produced
Describe how urea is removed from the blood.
Hydrostatic pressure
Causes ultrafiltration at Bowman’s capsule /
glomeruli / renal capsule
Through basement membrane
Enabled by small size urea molecule
Explain how urea is concentrated in the filtrate.
Reabsorption of water / by osmosis;
At the PCT / descending LoH;
At the DCT / CD;
Active transport of ions / glucose creates gradient (in context);
Some desert mammals have long loops of Henle and secrete large amounts of ADH.
Explain how these two features are adaptations to living in desert
conditions.
- More water (from filtrate) reabsorbed / returned to blood / less lost in urine;
- By osmosis;
- From collecting duct / from end of second convoluted tubule;
- Due to longer loop of Henle;
- Sodium / chloride ions absorbed from filtrate in ascending limb;
- Gradient established in medulla / concentration of ions increases down medulla;
For ADH, maximum 2 marks: - Acts on collecting duct / distal convoluted tubule / second convoluted tubule;
- Makes cells more permeable / inserts aquaporins in plasma membranes;
