6 Homeostasis Flashcards
Homeostasis
The maintenance of an internal environment within certain limits of an organism
Importance of Homeostasis
- changes to pH and temperature affects the rate of reaction of enzymes
- maintaining blood glucose concentrations ensures a constant water potential
- some organisms that maintain a constant internal environment have wider geographical ranges and so are more adapted to surviving
Control mechanisms
- optimum point
- receptor
- coordinator
- effector
- feedback mechanism
Negative feedback
The change produced by the control system leads to a change in the stimulus detected by the receptor, turning the system off
E.g regulation of blood glucose
Positive feedback
When a deviation from the optimum point causes changes leading to more deviation from the normal
E.g a stimulus leads to influx of sodium ions in neurones
Hormones
- produced in glands
- carried in blood plasma to target cells that have specific receptors complementary to a specific hormone
- effective in low conc, widespread and has long-lasting effects
Second Messenger Model
- adrenaline binds to a protein receptor in a liver cells membrane
- changes shape of protein
- this leads to activation of enzyme adenyl cyclase- converts ATP to cAMP
- cAMP is a second messenger, binds to protein kinase enzyme- changing its shape and activating it
- enzyme catalyses conversion of glycogen to glucose
- glucose moves out of liver cell via facilitated diffusion into bloody through channel proteins
Role of Pancreas in Regulating Blood Glucose
- produces insulin and glucagon
* has groups of hormone-producing cells called “islets of Langerhans”
Islets of Langerhans
Includes:
•a-cells that produce glucagon
•B-cells that produce insulin
Glycogenesis
- conversion of glucose into glycogen
* when blood glucose is higher than normal, liver removes glucose from blood to convert into glycogen
Glycogenolysis
- the breakdown of glycogen to glucose
- when blood glucose concentration is lower than normal, liver converts stored glycogen into glucose
- glucose diffuses into blood to raise conc back to normal
Gluconeogenesis
- production of glucose from sources that aren’t carbohydrates
- when there is less glycogen stores, liver can produce glucose from glycerol and amino acids
Regulation of Blood Glucose Conc
- if conc is too low, cells won’t have enough energy and will die
- if conc is too high, water potential of blood decreases creating osmotic problems that can lead to dehydration
Factors for Blood Glucose Conc
- diet from absorbing glucose or hydrolysis of carbohydrates
- hydrolysis in small intestine of glycogen (glycogenolysis)
- producing glucose from other sources of carbohydrate (gluconeogenesis)
- changes in rate of respiration
B-cells in the Pancreas
- have receptors that detect the rise in blood glucose conc
- responds by secreting insulin into blood plasma
- most body cells have receptors specific to insulin molecules, so combine to change the tertiary structure of the glucose transport carrier proteins, causing them to open and more glucose to enter cells
- rise in insulin leads to an increase in glucose transport carrier proteins
- insulin activates enzymes to convert glucose to glycogen
How Insulin Lowers Blood Glucose Conc
- increases absorption rate of glucose into cells
- increases respiratory rate of cells, so use up more glucose
- increases rate of conversion of glucose into glycogen and fat
- lowering of blood glucose conc causes B-cells to reduce secretion of insulin
a-cells in the Pancreas
They detect the fall in blood glucose concentration and respond by secreting glucagon into the blood plasma
Glucagon’s Role
- attaches to specific protein receptors on cell surface membranes of liver cells
- activates enzymes to convert glycogen to glucose
- activates enzymes to convert amino acids and glycerol into glucose
Adrenaline in Regulating Blood Glucose
- attaches to protein receptors on cell surface membrane of target cells
- activates enzymes to break down glycogen into glucose
Type I Diabetes
- insulin dependant
- body is unable to produce insulin
- may be due to body’s immune system attacking it’s B-cells
Type II Diabetes
- insulin independent
- normally due to losing glycoprotein receptors on body cells or their response to insulin
- can be due to inadequate supply of insulin from pancreas
Controlling Type I Diabetes
- by insulin injections which dosage needs to be matched to the glucose intake
- too much insulin could cause too low blood glucose concentrations leading to unconsciousness
- blood glucose measured by biosensors
Controlling Type II Diabetes
- regulating intake of carbohydrate in diet, matching to exercise done
- can be done by insulin injections or drug use to stimulate insulin production
Osmoregulation
The homeostatic control of the water potential of the blood
Structure of the Kidney
- fibrous capsule - outer membrane
- cortex - outside region made of renal capsules
- medulla - inner region made of loops of Henle
- renal pelvis - funnel shaped cavity that collects urine
- ureter - tube that carries urine to bladder
- renal artery - supplies kidney with blood
- renal vein - returns blood to heart
Renal (Bowman’s) Capsule
- closed end of the start of nephron
- cup-shaped
- surrounds glomerulus
- inner layer made of cells called podocytes
Proximal Convoluted Tubule
- series of loops surrounded by capillaries
* walls made of epithelial cells that have microvilli
Loop of Henle
- long loop from the cortex into the medulla of the kidney and back
- surrounded by blood capillaries
Distal Convoluted Tubule
- series of loops surrounded by blood capillaries
* walls made of epithelial cells
Collecting Duct
- tube that many distal convoluted tubules from the nephrons empty into
- lined by epithelial cells
- becomes wide as it empties into pelvis
Afferent Arteriole
- tiny vessel coming from the renal artery
- supplies nephron with blood
- it forms the glomerulus
Glomerulus
- many branched capillaries where fluid is forced out of blood
- capillaries recombine to form the efferent arteriole
Efferent Arteriole
- tiny vessel leaving renal capsule
- small diameter so increases blood pressure in glomerulus
- carries blood away from renal capsule and branches to form blood capillaries
Blood Capillaries
- concentrated network of capillaries surrounding proximal and distal convoluted tubule and loop of Henle
- reabsorb mineral salts, glucose and water
- capillaries form veins that form the renal vein
