16.Homeostasis Flashcards
What is homeostasis
The maintenance of a constant internal environment
Ability to return to optimum point and maintain organisms around balanced equilibrium
Why is homeostasis important
Enzymes-control biochemical reactions in cells, reduce rate of enzyme reactions, impair enzymes
Water potential-can change w.p of cells and tissue fluid, causing them to shrink or burst
Glucose conc-affect w.p of blood plasma, and food source for respiring cells
What are the stages of control mechanism involved in self regulating
Input-deviation from optimum
Receptor-detects change and informs
Coordinator-sends info to appropriate
Effector-muscle or gland brings changes needed to return to opt
Feedback mechanism-receptor responses to stimulus creates by change to system brought about by effector
What’s negative feedback
- When change produced by control system leads to change in the stimulus detected by the receptor turns the system off
- series of changes that result in substance being restored to normal level
What’s positive feedback
When deviation from optimum causes changes that result in even greater deviation from norm. Eg neurones, stimulus leads to small influx of Na ions, leads to more Na ions entering etc.
What do ectotherms do to maintain body temperature
Expose themselves to sun-gain heat, expose as much of themselves as possible
Taking shelter - prevent over heating and burrow to reduce heat loss at night
Gain warmth from ground-press bodies against hot ground to warm themselves, when reach required temp raise themselves off ground
What are some ways of gaining heat in cold environment (endotherms)
Vasoconstriction-reduce volume blood reaching surface less heat loss by radiation
Shivering-muscle contraction produce metabolic heat
Contraction of hair erector muscles-thick layer still air trapped next skin creates insulation
Increased metabolic rate-metabolic heat
Decrease sweating-reduces heat loss by evaporation
Behavioural mechanism-to maintain core body temp
What are ways of losing heat in response to warm environment
Vasodilation-in erase heat loss by radiation
Increased sweating-heat loss by evaporation
Relaxation of hair erector muscles-reduce layer of air trapped
Behavioural-shade, prevent core body temp rising
Example of negative feedback of drop in blood glucose conc
Input-drop of blood glucose conc
Receptor-hypothalamus
Coordinator-alpha cells of pancreas
Effector-pancreas secretes glucagon to convert glycogen to glucose
Output-blood glucose conc raises
Negative feedback-increase in conc, reduces stimulation of alpha cells, less secretion of glycogen
What receptors detect temperature changes
Thermoreceptors in hypothalamus
What’s the negative feedback control of increase in temperature
Input-rise in blood temperature
Receptor-thermoreceptors in hypothalamus
Coordinator-heat loss in centre of hypothalamus
Effector-skin vasodilation, sweating
Output-cooler blood temperature
Negative feedback-cooler temperature turns off corrective measures
What characteristics do all hormones have in common
Produced in glands Secreted directly into the blood Carried in blood plasma Act on target cels which have specific receptors Effective in low concs Widespread and long lasting effects
What is the second messenger model use adrenaline
- adrenaline bind to transmembrane protein receptor embedded in the cell surface membrane of liver cell
- binding of adrenaline cause protein to change shape on side of membrane
- change in shape=activation of enzyme called adenyl cyclase, activated adenyl cyclase converts atp to cyclic AMP
- cAMP acts as second messenger and bids to protein kinase enzyme, changing its shape, activating it
- Active protein kinase catalyses conversion of glycogen to glucose which moves out liver by facilitated diffusion into blood through channel proteins
What’s the role of pancreas in regulating blood glucose
Situated upper abdomen behind stomach
Prices enzymes for digestion and hormones for regulating blood glucose conc
Hormone producing cells called Islets of Langerhans
Two types; alpha cells and beta cells
What do alpha cells of pancreas do
What do beta cells of pancreas do
Alpha are larger and produce hormone glucagon
Beta are smallee and produce hormone insulin
What are the three important processes of regulating blood sugar
Glycogenesis
Glycogenolysis
Gluconeogenesis
Whats glycogenesis
Conversion of glucose into glycogen,
When blood glucose level higher than normal, liver removes glucose from blood and converts to glycogen, which is stored
What’s glycogenolysis
Breakdown of glycogen to glucose, when blood glucose concentration lower than normal, liver converts stored glycogen back into glucose which diffuses into blood to restore normal conc
What is gluconeogeneos
Production ofglucsoe from sources other than carbohydrates, when supply of glycogen is exhausted the liver can produce glucose form non-carbs sources such as glycerol and amino acids
What factors influence blood glucose concentration
Glucose comes from 3 sources
Directly from diet
From hydrolysis in small intestine of glycogen
From gluconeogenesis
What does insulin do when it binds to the receptors
- change in the tertiary structure of glucose transport carriers, change shape, more glucose into cells by facilitated diffusion
- rise in insulin conc means vesicles containing the glucose transport carriers fuse with membrane increasing number of channels
- activation of enzymes that convert glucose to glycogen and fat
- glucose removed from blood into cells, respiration rate of cells increased to use up glucose, rate of conversion to glycogen or fat removes glucose from blood
How is blood glucose concentration lowered by insulin
- increasing rate of absorption into cells
- increase rate of respiration of cells which uses up more glucose further increasing uptake
- increasing rate or conversion of glucose into glycogen in cells of liver and muscle
- increase rate of conversion of glucose to fat
What does glucagon do
- Attach to specific protein receptors on cell curvaceous membrane of alpha liver cells
- activating enzymes that convert glycogen to glucose
- activating enzymes in loved in conversion of amino acids and glycerol to glucose (gluconeogenesis
What’s the role of adrenaline in regulating blood glucose levels
Raises blood glucose levels by
- Attaching to protein receptors on cell surface membrane of target cells
- activating enzymes that causes break down if glycogen to glucose in liver
What is type 1 diabetes
- Insulin dependent
- Body unable to produce insulin
- Begin at childhood normally
- May be result of auto immune response where body’s immune system attacks beta cells of islets of langerhan
- develops quickly
- symptoms obvious
What’s type 2 diabetes
- Insulin independent
- due to glycoproteins receptors being lost or losing responsiveness or inadequate supply of insulin
- develops later in life
- poor diet and little exercise
- develops slowly
- symptoms less severe and less noticeable
- overweight more likely to have type 2
How can you control type 1 diabetes
- Controlled by injections of insulin
- Must be injected as if orally taken it’ll be broken down as its protein
- dose of insulin is matched to exactly to glucose intake
- blood glucose conc monitored by biosensors
How to control type 2 diabetes
Regulating intake of carbohydrates in diet and matching it to the exercise
Some may get supplements of insulin to stimulate insulin
What is osmoregulation
The homeostatic control of the water potential of the blood
What organ carries out osmoregulation
The kidney, nephron
What area kidneys made of
- Fibrous capsule-outer membrane that protects kidney
- Cortex-lighter coloured outer region made up of renal Bowman capsules, convoluted tubules and blood vessels
- Medulla-dark coloured inner region made up of loops of Henley collecting ducts and blood vessels
- Renal pelvis-funnel shaped cavity that collects urine into ureter
- ureter-tube carry urine to bladder
- renal artery-supplies kidney with blood from heart via aorta
- renal vein-returns blood to heart via vena cave
What makes up a nephron
Renal Bowmans capsule Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct
What is loop of Henle
Long hairpin loop that extends from the cortex and into medulla of kidney and back again surrounded by capillaries
What is the distal convoluted tubule
Series of loops surrounded by blood capillaries, it’s walls are ade of epithelial cells, but it is surrounded by fewer capillaries than the proximal tubule
What’s the collecting duct
Tube into which many distal convoluted tubules from many nephrons empty into, lined with epithelial cells and becomes increasingly wider as it empties into pelvis of kidney
What is the bowmans capulse
Closed end at start of nephron it’s cup shaped surrounds a mass of capillaries called glomerulus, inner layer of capsule is made up of specialised cells called podocytes
What’s the proximal convoluted tubule
Series of loops surrounded by blood capillaries it’s walls are made of epithelial cells which have micro villi
What’s the afferent arteriole
Tiny vessel that ultimately arises from renal artery and supplies the nephron with blood, afferent arteriole enters renal capsule
What’s the glomerulus
Many branched knot of capillaries from which fluid is forced out of the blood.
What is efferent arteriole
Glomerulus capillaries that combines to form tiny vesssel that leaves renal capsule, smaller diameter er than afferent arteriole so increases blood pressure within glomerulus. Carries blood away from renal capsule
What are blood capillaries involved with nephron
Concentrated network of capillaries that surrounds proximal convoluted tubule and distal convoluted tubule from where they reabsorb mineral salts glucose and water.. the capillaries merge together into venules which in turn merge to for renal vein
What are the stages the nephron uses in osmoregulation
1-formation of glomerular filtrate by ultrafiltration
2-reabsorptionnof glucose and water by proximal convoluted tubule
3-maintenance of gradient of sodium ions in medulla by loop of Henle
4-reabsorption of water by distal convoluted tubule and collecting ducts
How is glomerular filtrate formed
Ultrafiltration
- blood enter kidney through renal artery
- afferent arteriole enter renal capsule, efferent leaves capsule
- efferent is narrower than afferent, build up of hydrostatic pressure I’m glomerulus
- water, glucose, mineral ions squeezed out of pores between epithelial cells
- forms glomerular filtrate
What resists the movement of filtrate out of glomerulus
Capillary epithelial cells
Connective tissue and epithelial cells of blood capillary
Epithelial cells of renal capsule
Hydrostatic pressure of fluid in renal capsule space
Low water potential of blood in glomerulus
Why does hydrostatic pressure of glomerulus over come the resistance
Inner layer of renal capsule is made up of podocytes, these have cells have spaces between, allowing filtrate to pass beneath them and through gaps between their branches
Endothelium of glomerular capillaries has spaces between its cells, fluid pass between rather than through the cells
How does reabsorption of glucose and water happen
Proximal convoluted tubule
- sodium ions are actively transported out of cells sliming proximal tubule into blood capillaries, sodium ion conc of cells reduced
- sodium ions now diffuse down conc grad from lumen of PCT into epithelial lining cells by facilitated diffusion
- through co transport glucose or amino acids are transported into lining cells
- the molecules then diffuse into blood once co transported into cells of PCT
How are PCT cells adapted for reabsorption
Microvilli-larger SA to reabsorb substances
High density of mitochondria-provide ATP for active transport
How does loop of Henle act as a counter current multiplier
- ascending limb sodium ions actively transported out using ATP
- create lower water potential in region between two limbs, thick walls mean water doesn’t diffus out
- descending limb is permeable, water diffuses into interstitial space and into capillaries by osmosis
- lowering w.p of filtrate
- at base of ascending limb sodium ions diffuse out, raising w.p
- between ascending limb and collecting duct sodium conc increases furhter into medulla, lower w.p
- collecting duct permeable water moves out by osmosis and passes into capillaries
- loop henle ensures theres always w.p drawing water out of tubule
How does distal convoluted tubule reabsorb material
Has many micro villi and mitochondria to allow rapid diffusion by active transport from filtrate
Mainjob is to control ph of blood by selecting which ions to reabsorb, permeability changes due to hormones
How does the body respond to a fall in water potential
- osmoreceptors in hypothalamus detect fall, they shrink due to water loss by osmosis
- change in size causes hypothalamus to produce ADH
- ADH passes into bloodstream from the posterior pituitary gland
- ADH passes into kidneys, increasing permeability to water of distal convoluted tubule and collecting ducts cell surface membrane cells
- ADH binds to specific protein receptors on cells, leads to activation of phosphorylase
- activation causes vesicles containing plasma membrane with water channel proteins in to fuse with c.s membrane
- increasing no. Of channels
- ADH increases permeability of collecting ductto urea lowering w.p
- water diffuses by osmosis out of collecting duct into capillaries
- osmoreceptors detect rise in w.p send fewer impulses to pituitary gland
- ADH levels secreted reduce, permeability reverts back to normal state
How does body respond to rise in water potential
- Osmoreceptors in hypothalamus detect rise, increase frequency of nerve impulses to pituitary gland
- pituitary gland reduces ADH released
- Less ADH, decreased permeability of collecting ducts to water and urea
- more dilute urine produced, w.p of blood reduces
- osmoreceptors detect normal levels of w.p, decrease frequency of impulses to pituitary
