Homeostasis- responding to changes in the environment Flashcards
Define Homeostasis
The maintenance of an organisms internal environment within set limits
Explain enzyme activity
-Operate best over a specific range of conditions
-By maintaining pH and body temp, all enzyme-linked reactions are efficient
Explain cell size
-Will change if water potential in blood, effects the amount of water in tissue fluid and cells
-Could cause swelling and bursting
What is negative feedback?
Initiates corrective mechanisms whenever the internal environment deviates from its normal levels.
What is an example of negative feedback and explain?
Thermoregulation:
Normal body temp -> Body temp increase -> corrective mechanism (e.g. sweating) -> normal body temp
What is positive feedback?
Deviation from normal conditions is amplified, so further deviation.
e.g. normal -> level increase -> positive feedback -> further increase
e.g. oxytocin
What is Osmoregulation?
Controls water potential of blood
What is the outer and inner area of the kidney called?
Outer-cortex
Inner- Medulla
What do we need kidneys for?
-filter blood
-re-absorb glucose
-re-absorb dissolves ions
-re-absorb water
-releases urea, excess salts, excess water as urine
How does waste get extracted from blood?
- Blood enters kidney through renal artery which branches into tiny vessels called the afferent arterioles, and enters the Bowman’s Capsule
- The capillaries leaving the Bowman’s capsule merge to form the efferent arteriole. These have a smaller diameter than the afferent, resulting in a build up of hydrostatic pressure.
- Build up of pressure causes water, glucose, and mineral ions to be squeezed out of the capillary to form the globmerular filtrate.
- Blood cells and large proteins are too large to pass into the nephron and will stay in the blood.
Explain using a negative feedback loop how normal water potential of blood is maintained
Conserve water:
Normal. -> decrease in WP -> change detected by osmoreceptors in hypothalmus -> Hypothalamus signals pitiutary gland to release more ADH -> ADH increases permeability of collecting ducts. -> urine. -> normal
Expel water:
same as above but releases less ADH
What is osmoregulation?
Controlling the water potential of the blood
What is the Bowman’s capsule, and function?
(nephron)
-Closed end at start of nephron, cup shaped and surrounds a mass of blood capillaries called the glomerulus.
-Made up of specialised cells called podocytes.
-Glomerulus filters small solutes from blood.
What is the proximal convoluted tubule, and function?
(nephron)
-Series of loops surrounded by blood capillaries
-Walls are made up of epithelial cells that have microvilli
-It reabsorbs ions, water, nutrients, removes toxins, and adjusts filtrate pH
What is the Loop of Henle, and function?
(nephron)
-Long hairpin loop that extends from the cortex to the medulla of the kidney, surrounded by capillaries
-Ascending loop: reabsorbs sodium ions and chlorine ions from the filtrate
-Descending loop: aquaporins allow water to pass from the filtrate into the interstitial fluid
What is the distal convoluted tubule, and function?
(nephron)
-Series of loops surrounded by blood capillaries
-selectively secretes and absorbs different ions to maintain blood pH and electrolyte balance.
What is the collecting duct, and function?
(nephron)
-A tube into which a number of distal convoluted tubules from a number of nephrons empty
-Reabsorbs solutes and water from filtrate.
Explain the filtration and reabsorption process within the kidney
- Ultrafiltration:
a high hydrostatic pressure forces water and small molecules out of capillaries to form glomerular filtrate. This is because blood goes from the afferent arteriole with a large lumen, to the efferent arteriole, with a small lumen. - Selective reabsorption:
85% of filtrate is reabsorbed back into the blood in the proximal convoluted tubule via co-transport. - Maintenance of sodium ion gradient:
by the Loop of Henle, acts as a counter current multiplier as Na+ is actively transported out of ascending limb, creating a lower WP inbertween the two limbs, filtrate passes out of descending limb, H2O enters capillaries, filtrate in collecting duct. - Active transport:
water moves out of distal convoluted tubule and collecting duct into blood.
Rapidly absorb materials from filtrate by active tansport.
Collecting duct carries remaining liquid (urine) to ureter.
What is ADH?
Antidiuretic hormone
-causes an increase in permeability of the walls of the collecting duct and distal convoluted tubule to water
-this causes more water to leave the nephron and be reabsorbed into the blood, so urine is more conc
Where is ADH produced and released from?
Hypothalamus
Briefly describe ADH regulate water levels?
-Dehydration
-Decreased water potential of blood
-Osmoreceptors cells in hypothalamus lose water
-Stimulates nerve cells in the hypothalamus
-Increased ADH production by posterior pituitary gland
-ADH carried in blood
-ADH arrives at collecting duct
What is the hypothalamus?
Changes in water potential of blood are detected by osmoreceptors here.
In depth, explain how ADH works?
- Osmoreceptors detect low water content of body fluids
- ADH produced, secreted into capillaries of posterior pituitary gland.
- Presence of ADH detected by receptors in membrane of collecting duct
- Enzyme active phophorylase produced
- Vesicles containing water permeable channels move to and fuse with membrane of the cell.
- Water diffuses down water potential gradient out of capillary duct.
What organ is blood glucose concs monitored by?
Pancreas
What causes blood glucose concs to increase?
eating carbohydrates
What does the pancreas do?
Detects changes in blood glucose levels. Islets of Langerhans cells release insulin and glucagon to bring levels back to normal.
What is insulin?
Released when blood glucose levels are too high, so causes a decrease.
What is glucagon?
Released when blood glucose levels are too low, causes an increase
What is adrenaline?
Released by adrenal glands when your body anticipates danger and results in more glucose being release from hydrolysis of glycogen in the liver.
Explain how a normal blood glucose level is maintained when blood glucose levels increase
-Blood glucose increases
-Detected by beta cells in Islets of Langerhans
-Beta cells release insulin
-Liver cells become more permeable to glucose and enzymes are activated to go from glucose to glycogen.
-Glucose removed from blood and stored as glycogen in cells
Explain how a normal blood glucose level is maintained when blood glucose levels decrease
-Blood glucose levels decrease
-Detected by alpha cells in Islets of Langerhans
-Alpha cells release glucagon, adrenal glands release adrenaline
-2nd messenger model occurs and activates enzymes to hydrolyse glycogen
-Glucose released back into blood
Describe the action of insulin
Beta cells in the islets of langerhans detect when blood glucose levels are too high and secrete insulin in response, this decreses it in the following ways:
- Attaching to receptors on the surfaces of target cells. Changes the tertiary structure of the channel proteins resulting in more glucose being absorbed by facilitated diffusion.
- More protein channels are incorporated into cell membranes so that more glucose is absorbed from the blood into the cells.
- Activating enzymes involved in the conversion of glucose to glycogen. This results in glycogenesis in the liver
Describe the action of Glucagon
Alpha cells in the Islets of Langerhans detect when blood glucose is too low and secrete glucagon. Glucagon increases blood glucose in the following ways:
- Attaching to receptors on the surface of target cells (liver cells)
- When glucagon binds, it causes a protein to be activated into adenylate cyclase and converts ATP into a molecule called cyclic AMP (cAMP) which activates the enzyme protein kinase, that can hydrolyse glycogen into glucose.
- Activating enzymes involved in the conversion of glycerol and amino acids into glucose.
Explain the second messenger model
- Glucagon binding to glucagon receptors
- Once bound, causes a change in shape to the enzyme adenyl cyclase, which activates it.
- Activated adenyl cyclase enzymes converts ATP into cyclic AMP which is the ‘second messenger’
- cAMP converts the inactive protein kinase to activate protein kinase which hydrolyses glycogen to glucose.
Explain the role of adrenaline
(increases blood glucose)
- Attaches to receptors on the surface of target cells. Causes the G protein to be activated and convert ATP into cAMP.
- cAMP activates enzyme to hydrolyse glycogen into glucose.
(second messenger model)
Explain what happens when blood glucose levels are too high
-Insulin binds to receptor molecules on the surface of body cells
-This increases the rate of absorption of glucose into body cells
-The hormone stimulates an increase in the conversion of glucose to glycogen (glycogenesis) and glucose to fat.
Explain what happens when blood glucose levels are too low
- Glucagon binds to receptors on liver cells, which stimulates an increase in the conversion of glycogen to glucose and amino acids, and glycerol into glucose (glucogenesis) .
What is insulin, glucagon, and adrenaline examples of?
Hormones
messenger molecules
What are insulins target tissues?
Liver and muscle
What are glucagons target tissues?
Liver
What are adrenalines target tissues?
Muscles
Describe Glycogenesis
Converting glucose into glycogen. this occurs in the liver and is catalysed by enzymes
Describe Glycogenolysis
Hydrolysis of glycogen to glucose
Describe Gluconeogenesis
Creating glucose from other molecules such as amino acids and glycerol in the liver
What is Hyperglycaemia?
Occurs when blood glucose conc becomes too high
What does hyperglycaemia do and what are the symptoms?
-Can lower water potential, create osmotic problems that can cause dehydration
-Thirst, frequent unrination, glucose in urine
What is Hypoglycaemia?
Occurs when blood glucose conc becomes too low
What does hypoglycaemia do and what are the symptoms?
-Can result in cells being deprived of energy
-Nausea, loss of concentration, coma
What is diabetes Mellitus?
(just diabetes)
A disorder that effects the bodys ability to regulate blood glucose levels
What is Type 1 diabetes?
Insulin dependent, usually occurs in childhood.
-Body is not able to produce their own insulin
-Thought to be caused by the immune system attacking the insulin producing beta cells or gene encoding for insulin is faulty
-Controlled with regular insulin injections and careful diet
-Immunotherapy: particular t cell that prevents body destroying islets of langerhans
What is Type 2 diabetes?
Insulin dependent diabetes, normally over 40
-produces insulin yet bodys glycoprotein receptors lose responsiveness to it
-eventually an inadequate amount of insulin is produced
-regulation of diet and exercise
