16: Homeostasis Flashcards
What is homeostasis?
Maintenance of a constant internal environment in restricted limits in organisms
What is tissue fluid?
Liquid which bathes each cell
Supplies nutrients and removing wastes
What does homeostasis do?
Maintains optimum point
Does not prevent changes from occurring
What things are homeostasis important for?
Enzymes
Water potential
Geographical range
Why is homeostasis important for enzyme function?
Sensitive to changes in pH and temperatures
Any changes can cause them to denature and not be effective
Allows reactions to occur at the same rate
Why is homeostasis important for water potential?
Could cause cells to shrink and expand due to osmosis
Affected by glucose concentration
This could kill the cells
Why is homeostasis important for geographical range?
Constant internal environment means animal is more independent of external changes in environment
Gives wider geographical range
What are the stages of self-regulating systems?
Optimum point Receptor Coordinator Effector Feedback mechanism
What is the optimum point stage in a self-regulating system?
Point at which the system operates best
Monitored a receptor
What is the receptor stage in a self-regulating system?
Monitoring system which detects any deviation from optimum point
Informs the coordinator
What is the coordinator stage in a self-regulating system?
Coordinates information from receptors
Sends instruction to an appropriate effector
What is the effector stage in a self-regulating system?
Thing which causes a change returning system to optimum point
Often muscle or gland
What occurs in feedback control?
Process by which a response to a stimulus is created in the form of a change to the system
This is brought about by the effector and caused by a receptor
What are the two types of feedback mechanisms?
Negative feedback
Positive feedback
When does negative feedback occur?
When the change produced by control mechanism which turns the system off
When does positive feedback occur?
When the change produced involves an even greater deviation from normal
Are there many or one receptors and effectors in a control system?
Many receptors and effectors per control system
Why do control systems have multiple receptors and effectors?
Separate mechanisms
Allows greater degree of control of particular factor being regulated
When does negative feedback occur?
Stimulus causes corrective measures to be turned off
Returns system to optimum level
Where are hormones produced?
Glands
Secrete hormone directly into blood
What are hormones carried in?
Blood plasma
How are only certain cells affected by hormones?
Hormones act only on target cells with specific receptors on cell-surface membrane
Receptor is complementary to a specific hormone
How long do hormones affect systems?
Effective in very low concentrations
Often widespread and long-lasting effects
What is a second messenger model?
Extracellular hormone binds to receptor
Causes an intracellular process to start by producing a secondary messenger
How does adrenaline affect liver cells?
Adrenalin binds to receptor on liver cell
Makes receptor protein to change shape on inside membrane
Activates adenyl cyclase enzyme in cytoplasm which converts ATP to cAMP
cAMP binds to protein kinase, changing its shape and activating it
This catalyses conversion of glycogen to glucose which moves out of liver cells
What is cAMP?
Cyclic AMP
Acts as a secondary messenger in liver cells
How does glucose leave liver cells?
Facilitated diffusion into the blood through channel proteins
Where is the pancreas located?
Upper abdomen
Behind the stomach
What is the pancreas?
Large, pale-coloured gland
Produces enzymes for digestion
Produces hormones for regulating blood glucose conc
What enzymes are produced by the pancreas?
Protease
Amylase
Lipase
What hormones are produced by the pancreas?
Insulin
Glucagon
What are islets of Langerhans?
Groups of hormone-producing cells in pancreas
What cells are found in the islets of Langerhans?
α cells
β cells
What do α cells produce?
Larger cells
Produces glucagon hormone
What do β cells produce?
Smaller cells
Produces insulin hormone
What are the name of cells found in the liver?
Hepatocyte
What are the three processes regulating blood sugar in the liver?
Glycogenesis
Glycogenolysis
Gluconeogenesis
What is Glycogenesis?
Conversion of glucose to glycogen
Removes glucose from blood
When does Glycogenesis occur?
Occurs when blood glucose conc is higher than normal
How much glycogen can the liver store?
75-100 grams of glycogen
What is Glycogenolysis?
Breakdown of glycogen to glucose
Diffuses into blood
Increases glucose conc in blood
When does Glycogenolysis occur?
When the blood glucose conc is lower than normal
What is the process of Gluconeogenesis ?
Production of glucose from sources other than carbohydrate
Glycerol and amino acids
When does Gluconeogenesis occur?
When supply of glycogen is exhausted
What occurs if glucose conc of the blood falls too much?
Substrate for respiration
Lack means not enough energy produced and animal dies
What occurs if the glucose conc of the blood increases too much?
Lowers Ψ of blood
Creates osmotic problems
What is the normal concentration of blood glucose?
5 mmol/dm3
What sources does blood glucose come from?
Directly from the diet
Hydrolysis of glycogen in small intestine and glycogenolysis to store it
Gluconeogenesis
Which hormones are responsible for blood glucose regulation?
Insulin
Glucagon
Adrenaline
Why are blood glucose hormones needed?
Fluctuates due to varying amounts of respiration at different times
Where is insulin produced?
β cells in the islets of Langerhans
Found in the pancreas
How do β cells know to release insulin?
Receptors that detect stimulus of rise in blood glucose conc
Responds to secrete insulin into blood plasma
What is insulin?
Globular protein made of 51 amino acids
Hormone
Which body cells have receptors which bind to insulin?
Nearly all cells
Except some such as red blood cells
What receptors are found on cells for detecting insulin?
Glycoprotein
What does increasing insulin cause in cells after binding to receptors?
Change in 3° structure of glucose transport carrier proteins, causing them to open
More carrier proteins put into membrane as vesicles with them fuse with membrane
Activation of enzymes to convert glucose to glycogen and fat
How is the blood glucose conc decreased due to insulin?
Increased rate of glucose absorption into cells
Increase rate of respiration
Increase glycogenesis (glucose to glycogen)
Increase glucose to fat
Why does an increased rate of respiration lower blood glucose conc ?
Cells use more glucose
Increases uptake of glucose from the blood
What type of feedback is the use of insulin?
Negative feedback
Lowers conc to normal
In which cell is glucose absorbed into most when insulin is present?
Muscle cells
Which cells store glycogen?
Liver and muscle cells
What occurs to the β cells when the blood glucose conc decreases?
Reduces secretion of insulin
Which hormone do α cells produce?
Glucagon
When do α cells produce glucagon?
After detecting a fall in blood glucose conc
What is glucagon secreted into?
Blood plasma
What are the actions of glucagon?
Attaches to specific protein receptor on cell-surface membrane of hepatocytes
Activates membrane for glycogen to glucose
Activates enzymes for gluconeogenesis (alternative sources for glucose production)
What is the overall effect of glucagon?
Increases conc of glucose in the blood to optimum
What type of feedback is the use of glucagon?
Negative feedback
Raises conc back to normal
What occurs to α cells when [glucose] increases in the blood?
Reduce the secretion of glucagon
Which hormone other than glucagon raises blood glucose conc?
Adrenaline
How does adrenaline raise blood glucose conc?
Attaches to protein receptors on cell-surface membrane of target cells
Activates enzymes causing glycogenolysis in liver (glycogen to glucose)
How do glucagon and insulin act with respect to eachother?
Antagonistically
Insulin decreases [glucose]
Glucagon increases [glucose]
Why does the blood glucose conc fluctuate?
Negative feedback
Insulin and glucagon production determined by conc present
Only more produced if reaches threshold value
What is diabetes?
Metabolic disorder
Unable to control blood glucose conc
Either lack of insulin or lack of response to it
What are the two types of diabetes?
Type I (insulin dependent) Type II (insulin independent)
How is type I diabetes formed?
Autoimmune response
Body attacks β cells
What is type I diabetes?
Body is unable to produce insulin
Symptoms develop quickly
What are the signs of diabetes?
High blood [glucose]
Glucose present in urine
Weight loss
Tiredness
How does type II diabetes form?
Glycoprotein receptors on body cells being lost/losing responsiveness to insulin
or
Inadequate supply of insulin
Who usually develops type II diabetes?
People over 40
Increasingly in younger due to obesity
How is type I diabetes controlled?
Injections of insulin
2 to 4 times a day
Dose matched to glucose intake
Why is insulin injected?
Protein
Would be digested into amino acids
Why are insulin injections matched to glucose intake?
Too much leads to low blood glucose conc
Results in unconsciousness
How are insulin injections matched to blood glucose levels?
Biosensors monitor blood glucose conc
How is type II diabetes controlled?
Regulating intake of carbohydrate depending on exercise
Could use injections of insulin if not enough produced
What is osmoregulation?
Homeostatic control of water potential in the blood
Where are kidneys found?
Two kidneys
Back of abdominal cavity
Each side of spinal cord
What is the kidney made of?
Fibrous capsule Cortex Medulla Renal pelvis Ureter Renal artery Renal vein
What does the fibrous capsule do in a kidney?
Outer membrane which protects the kidney
What does the cortex contain in the kidney?
Lighter coloured outer region
Contains Bowman’s capsule, convoluted tubules and blood vessels
What does the medulla contain in the kidney?
Darker coloured inner region
Loops of Henle, collecting ducts and blood vessels
What is the renal pelvis in the kidney?
A funnel-shaped cavity that collects urine into teh ureter
What does the ureter in the kidney?
A tube that carries urine to the bladder
What does the renal artery do in the kidney?
Supplies kidney with blood from heart via aorta
What does the renal vein do in the kidney?
Returns blood to the heart via the vena cava
Where are nephrons found?
One million tiny tubular structures in each kidney
Found in cortex and medulla
What is the nephron structure?
Functional unit of the kidney
Up to 14mm long, closed at one end, with two twisted regions separated by a long hairpin loop
What is the nephron made of?
Renal (Bowman's) capsule Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct
What is the Bowman’s capsule?
Closed end at start of nephron
Cup-shaped and surrounds a mass of blood capillaries called a glomerulus
What is the inner layer of the renal capsule?
Podocytes
What is the structure of the proximal convoluted tubule?
Series of loops surrounded by blood capillaries
Made of epithelial cells which have microvilli
What is the structure of the Loop of Henle?
Long, hairpin loop that extends from the cortex into the medulla of kidney
Surrounded by blood capillaries
What is the structure of the distal convoluted tubule?
Series of loops surrounded by blood capillaries
Wall of epithelial cells, less capillaries than proximal
What is the collecting duct?
Tube which many distal convoluted tubules from many nephrons empty
What is the structure of the collecting duct?
Lined by epithelial cells
Increasingly wide as it empties into pelvis of the kidney
Which blood vessels are found in the nephron?
Afferent arteriole
Glomerulus
Efferent arteriole
Blood capillaries
What is the afferent arteriole?
Tiny vessel which comes from renal artery
Supplies nephron with blood
Where does the afferent arteriole enter the nephron?
Enters renal capsule of the nephron
What is the glomerulus?
Many-branched knot of capillaries from which fluid is forced out of the blood
What does the glomerulus capillaries recombine to form?
Efferent arteriole
What is the efferent arteriole?
Tiny vessel that leaves renal capsule
Carries blood away from the renal capsule to form blood capillaries
What is the size of the efferent and afferent arteriole?
Efferent arteriole has a smaller diameter than the afferent arteriole
Why is the efferent diameter smaller than afferent?
Increases blood pressure within the glomerulus
Where are blood capillaries used in the kidney?
Conc network surrounding proximal and distal convoluted tubule, as well as loop of Henle
Merge together to form venules which merge to form a renal vein
What are blood capillaries used for in the kidney?
Reabsorb mineral salts, glucose and water
What are the four stages of osmoregulation in the kidney?
Ultrafiltration
Selective re-absorption
Concentrating Na+ in medulla
Water re-absorption
Where does ultrafiltration occur in the kidney?
Glomerulus
Where does selective reabsorption occur in the kidney?
Proximal convoluted tubule
Where does the concentrating of Na+ in the medulla occur?
Loop of Henle
Where does water reabsorption occur in the kidney?
Distal convoluted tubule
Collecting duct
Where does the nephron start in the kidney?
Cortex
What surrounds the glomerulus?
Bowman’s capsule
What is ultrafiltration?
Fluid is pushed from capillaries into Bowman’s capsule under high pressure
What is filtered out of the blood in ultrafiltration?
Water Amino acids Glucose Urea Inorganic ions (Na+,Cl-,K+)
What is not filtered out of the blood in ultrafiltration?
Blood cells
Proteins
What occurs to the blood itself in ultrafiltration?
Water potential is lowered
Allows water to reabsorb at a later stage
What causes the glomerulus to have a high pressure?
Efferent arteriole has a smaller diameter than the afferent, creates high hydrostatic pressure
Twisting capillaries into a knot increases pressure
What is and isn’t reabsorbed from the proximal distal tubules?
85% of water
All glucose
All amino acids
No urea
Where are molecules reabsorbed to in selective reabsorption?
Surrounding capillaries
How are the cells in the proximal convoluted tubule adapted to selective reabsorption?
Microvilli provide large SA
Opposite membrane next to capillaries folded to increase SA
Cell cytoplasm has many mitochondria producing ATP for active transport
What prevents the removal of filtrate from the glomerulus?
Capillary and renal capsule epithelial cells
Connective tissue and epithelial cells of blood capillary
Hydrostatic pressure of fluid in renal capsule space
Low water potential of blood in glomerulus
How is it ensured that fluid leaves the glomerulus using permeability?
Podocytes line inner layer of renal capsule
Endothelium of glomerular capillaries have spaces
How do podocytes increase permeability?
Cells have spaces between them
Allows only filtrate to pass through gaps
How are things selectively reabsorbed into the proximal tubule?
Na+ actively transported out into blood capillaries
Na+ diffuse down conc gradient from lumen of PCT into epithelial cells through special carrier proteins by facilitated diffusion
Carrier proteins specifically transport another molecule with Na+ (co-transport)
Molecules co-transported into cells then diffuse into the blood
Which molecules are co-transported with sodium into the epithelium of the proximal tubule?
Glucose
Amino acids
Inorganic ions etc.
What does the Loop of Henle consist of?
Descending limb - into medulla
Ascending limb - back out to cortex
What is the ultimate function of the loop of Henle?
Produce concentrated urine
What is a feature of the descending limb?
Narrow and thin walls
Highly permeable to water
What is a feature of the ascending limb?
Wider and thicker walls
Impermeable to water
How does the Loop of Henle produce conc urine?
Salt leaves ascending limb - actively transported into medulla
Lowers water potential of medulla between two limbs
Water leaves descending limb by osmosis which then enters capillaries
Fluid in descending limb becomes more conc as it descends into medulla
Water leaves collecting duct due to low water potential of the medulla
What are aquaporins?
Channel proteins which are specific to water
What is the acronym for anti-diuretic hormone?
ADH
What does the distal convoluted tubule do?
Actively transports water and salts into capillaries
Used to alter pH of the blood
How does the distal convoluted tubule change to absorb more?
Permeability increases to cause more to diffuse into
Caused by various hormones
What is the counter-current multiplier in the kidney?
Filtrate in collecting duct meets interstitial fluid that has a lower water potential
Why is the counter-current multiplier important in the kidney?
Water potential gradient between collecting duct stays constant for the length of the duct
What do hormones affect in the kidney to affect water concentration?
Distal convoluted tubule
Collecting duct
What does the water potential of the blood depend on?
Conc of: Glucose Proteins Sodium chloride Other minerals
What causes the rise in solute conc and lowering in water potential?
Too little water consumption
A lot of sweating
Large amounts of ions (salt) intake
What detects water potential?
Osmoreceptor cells
Where are osmoreceptors located?
Hypothalamus of the brain
How do osmoreceptors work?
Water is lost from osmoreceptors by osmosis
Cells shrink and causes hypothalamus to produce ADH
Moved to pituitary gland
Where is ADH secreted from and to?
Pituitary gland to capillaries
How does ADH work?
ADH binds to protein receptors on cells on wall of the DCT and collecting duct
Activates phosphorylase in the cell causing vesicles to move to and fuse with cell membrane
Vesicles contain aquaporins and increase water channels increasing permeability in DCT
ADH increases permeability to urea in CD which passes out, lowering water potential around it
More water leaves CD and into blood
How does the ADH affect the water potential of the blood?
Does not increase water potential as reabsorbed from blood
Prevents it from lowering
What is the use of ADH an example of feedback?
Negative feedback
Rise in water potential means osmoreceptors detect it and produce less ADH
What causes the water potential of the blood to increase?
Large volume of water consumed
Salts used in metabolism or excreted
How does the body respond to a rise in water potential?
Osmoreceptors detect it and decreases frequency of nerve impulse
Reduces amount of ADH released by pituitary
Less ADH means decreased permeability of collecting ducts to water and urea
Less water reabsorbed so more urine produced, lowers water potential
How long does ADH last for?
Slowly broken down
Half life of around 20 minutes
