Homeostasis Flashcards
Define homeostasis
Homeostasis involves physiological control systems that maintain the internal environment within restricted limits
Name 2 things homeostasis is important in maintaining
A stable core temp
Stable blood pH in relation to enzyme activity
What type of feedback is involved in homeostasis?
Negative
How is negative feedback involved in homeostasis?
Neg feedback is involved and this is when any deviation from the normal values are restored to their original level
This involved the nervous system often hormones too
When will blood glucose concentrations increase?
Ingestion of food or drink containing carbs
When will blood glucose concentration decrease?
Following exercise or if you have not eaten
What does the pancreas do in terms of blood glucose concentration?
Detects changes in the blood glucose level, islets of Langerhans cells release insulin and glucagon to bring glucose levels to normal
What does insulin do in terms of blood glucose concentration?
Released when blood glucose levels are too high it causes a decrease in blood glucose levels
What does glucagon do in terms of blood glucose concentration?
Released when blood glucose levels are too low, causing an increase in blood glucose levels
What does adrenaline do in terms of blood glucose concentration?
Released by adrenal glands when your body anticipates danger and this results in more glucose being released from hydrolysis of glycogen in the liver
Explain the process of blood glucose levels increasing- what happens after?
1) Detected by beta cells in the islets of Langethans (pancreas)
2) Beta cells release insulin
3) Liver cells become more permeable to glucose and enzymes are activated to convert glucose to glycogen
4) Glucose is removed from the blood and stores as glycogen in the cells
5)Levels return to normal
Explain the process of blood glucose levels decreasing- what happens after?
1) Detected by the alpha cells in the islets of Langerhans (pancreas)
2)Alpha cells release glucagon, adrenal gland release adrenaline
3) Second messenger model occurs to activate enzymes to hydrolyse glycogen
4) Glycogen is hydrolysed to glucose and more glucose is released back into blood
5) Levels return to normal
What are the 3 actions of insulin?
Attaching to receptors on the surfaces of target cells, changing the tertiary structure of the channel proteins resulting in ,for glucose being absorbed by facilitated diffusion
More protein carriers are incorporated into cell membranes so that more glucose is absorbed from the blood into cells
Activating enzymes involved in conversation of glucose to glycogen this results in glycogenesis in the liver
How does having more protein carriers happen and increase glucose absorbed?
Insulin binds to insulin receptors
Intracellular chemicals released
Vesicles containing glucose change, proteins fuse with cell membrane
So more protein channels embedded in membrane so more glucose can be absorbed
What are the 3 actions of glucagon?
Attaching to receptors on the surface of target cells (liver cells)
When glucagon binds it causes a protein to be activated into adenylate Cyclades and to convert ATP in a molecule called cyclic AMP (cAMP) high activates an enzyme protein kinase that can hydrolyse glycogen into glucose
Activating enzymes involved in the conversion of glycerol and AA into glucose
Explain the second messenger model?
Glucagon binding to glucagon receptors on the target cells
Once bound it causes a change in shape to the enzyme adenyl cyclase which activates it
Activates adenyl cyclase enzyme converts ATP into cyclic AMP (cAMP)
cAMP is the second messenger
cAMP coverts inactive protein kinase into active kinase which an hydrolyse glycogen to glucose
What is the role of adrenaline in terms of controlling blood glucose concentration?
If the blood glucose is too low the adrenal glands will secrete adrenaline and will increase the blood glucose conc
In what 3 ways does adrenaline increase blood glucose concentration?
Adrenaline attaches to receptors on the surfaces of target cells, this causes a protein (G protein) to be activated and to convert ATP into cAMP
cAMP activates an enzyme that can hydrolyse glycogen into glucose
This is known as the second messenger model of adrenaline and glucagon action, because the process results in the formation of cAMP, which acts as a 2nd messenger
What is meant by glucogenesis?
Converting glucose into glycogen, this occurs in the liver and is catalysed by enzymes there
What is meant by glucogenolysis?
Hydrolysis of glycogen to glucose, this occurs in the liver due to second messenger model
What is meant by gluconeogenesis?
Creating of glucose from other molecules, such as amino acids and glycerol in the liver
What is type one diabetes?
When people are unable to produce insulin
What’s the treatment for type one diabetes?
Insulin injections
What is type two diabetes?
Receptors on the tater cells lose their responsiveness to insulin
When and how do people get type one diabetes?
Usually starts in childhood and could be results of an autoimmune disease where beta cells are attacked
When and how do people hey type two diabetes?
Usually develops in adults due to obesity and poor diet
How do we help to treat type 2 diabetes?
Controlled by regulating intake of carbs, increasing expressed
Also insulin injections
What is osmoregulaction?
Controlling water potential of the blood
What is it called when blood has too low of a water potential?
Hypertonic
What is it called when blood has a too high of of water potential?
Hypotonic
What’s the problem with hypertonic blood?
When too much water will leave the cells and move into the blood by osmosis, cells will shrivel (crenation)
What is the problem with hypotonic blood?
Too much water will move from the blood into the cells by osmosis
Cells will burst (lysis)
What can cause hypertonic blood?
Excess sweating
Not drinking enough water
A diet with too many Ions (salty diet)
What causes blood to be hypotonic?
Drinking too much water
Not enough salt in their diet
What’s the correcting mechanism for hypertonic blood?
More water is reabsorbed by osmosis into the blood from the tubules of the nephrons
This means that urine is more concentrated as less water is last in the urine
What’s the correcting mechanism for hypotonic blood?
Less water is re absorbed by osmosis into the blood from the tubules of the nephrons.
This means that urine is more dilute and more water is lost ion the urine
Where does osomoregulation occur?
Within the nephrons in the kidneys
What are nephrons?
Long tubules surrounded by capillaries and there are around 1million per kidney
What happens at the nephron?
The blood is filtered here to remove waste and selectively reabsorb useful substances back into the blood
How do the nephrons selectively reabsorb useful substances back into the blood
Ultrafiltration occurs due to high hydrostatic pressure, water and small molecules are forced out
Explain process of ultrafiltration?
1) blood from the renal artery enters smaller arterioles in the cortex of the kidney
2) The arteriole that takes blood into each glomerulus is called the afferent arteiole, and the arteiole that takes the filtered blood away from the glomerulus is called efferent arteriole
3) Efferent arteriole is smaller in diameter than afferent so the blood in glomerulus is under high pressure
4) The high pressure forces liquid and small molecules in the blood out of the cap and into the Bowman’s capsule
5) Large molecules like proteins and blood cells can’t pass through so stay in the blood
6) Glomerular filtrate passes along the rest of the nephron and useful substances are reabsorbed along the way
7) Filtrate flows through the collecting duct and passes out of the kidney along ureter
What does each arteriole split into?
Glomerulus
What is the Glomerulus?
A bundle of capillaries lopped inside a hollow ball called Bowman’s capsule
Where does ultrafiltration occur?
Bowman’s capsule
What is the substance that moves into the Bowman’s capsule called?
Glomerular filtrate
What are the 3 layers tat liquid and small molecules move through to get to the Bowman’s capsule?
Capillary endothelium
Membrane
Epithelium of bowman’s capsule
Where does selective reabsorption occur?
Reabsorption of useful substances takes place as the glomerular filtrate flows along the PCT through the loop of hence and along the DCT, useful substances leave the tubules of nephrons and enter the capillary network that’s wrapped around them
What is the PCT?
Proximal convoluted tubule
What is the DCT?
Distal convoluted tubule
What happens at selective reabsorption?
1) Epithelium of the wall of PCT microvilli provide a large surface area for the reabsorption of useful materials from the glomerular filtrate into the blood
2) Useful solutes like glucose, are reabsorbed along PCT by active transport and facilitated diffusion
3) Water enters the blood by osmosis as the water potential of the blood is lower than that of the filtrate
4) Water is reabsorbed from PCT, loop of henle, DCT and collecting duct
5) Filtrate that remains is urine which passes along the uteter to the bladder
What is Urine made up of?
Water, dissolved salts p, urea and other substances such as hormones and excess vitamins
What isn’t found in urine?
Contain proteins or blood cells as they are too big to be filtered out of the blood, glucose is actively reabsorbed back into the blood so isn’t in the urine either
Name 2 ways water is lost from the body?
Urea and sweat
What regulates water potential of the blood?
Kidney, by osmoregulation
What happens if the water potential is too low?
More water is reabsorbed by osmosis into the blood from tubules of the nephrons, meaning the urine is more concentrated so less water is lost during excretion
What happens when the water potential of the blood is too high?
Less water is reabsorbed by osmosis into the blood from the tubules of the nephrons meaning urine is more dilute so ware is lost during excretion
Where is the loop of henle found?
Medulla of the kidneys
What is the loop of henle made up of?
Ascending and descending limb
On the loop of henle what do the limbs control?
movement of sodium ions so water can be reabsorbed into the blood
How does the loop of henle system work?
1) Near top the AL, Na+ are actively pumped out into the medulla. AL is impermeable to water so water stays into the tubule, this creates a low water potential in the medulla as there’s a high concentration of ions
2) Lower WP in medulla than DL so water moves out of the descending limb into medulla by osmosis making glomerular filtrate more conc and water reabsorbed through cap network
3) Near bottom of AL Na+ ions diffuse out into medulla, lowering WP in medulla
4) Water moves out DCT by osmosis and reabsorbed into the blood
5) stages 1-3 massive,g increase ion conc in medulla, lowering WP cashing water to move out of collecting duct by osmosis and water from medulla reabsorbed into blood by cap network
What controls the volume of water reabsorbed into the capillaries?
DCT and collecting duct
What is the WP of the blood monitored by and where are they?
Osmoreceptors, in the hypothalamus
When WP of the blood decreases how do the osmoreceptors act?
Water moves out of the osmoreceptors cells by osmosis causing a decrease in volume sending signals to other cells in the hypothalamus sending a signal to posterior pituitary gland which release ADH
What does ADH stand for?
Antidiuretic hormone
How does ADH work when we are dehydrated?
Water content of the blood drops, so WP drops
Detected by osmoreceptors in the hypothalamus
The posterior pituitary grand is stimulated to release more ADH into the blood
More ADH means DCT and CD are more permeable so more water is reabsorbed into the blood by osmosis
Small amount of high conc urine is produced so less water lost
How does ADH work when we are hydrated?
