Glucoregulation and osmoregulation Flashcards
What is homeostasis?
the maintenance of a constant internal environment in a living organism
What things do homeostasis control?
body temp, blood glucose concentration, water potential of blood
What two systems are involved in homeostasis?
nervous and endocrine system
Why is homeostasis important?
for enzyme activity - pH/temp, for cell size - osmosis due to water potential changes, independence from external conditions - can maintain internal conditions regardless of the external environment
What are alpha receptor cells?
an islet of langerhans cell which produces glucagon
what is the autonomic nervous system?
part of the nervous system that is not under voluntary control
What are beta receptor cells?
an islet of langerhans cell which produces insulin
What is glucagon?
a hormone that increases blood glucose levels
What are effectors?
brings about a change to the system, either a muscle or a gland
What is gluconeogenesis?
the conversion of non-carbohydrate molecules to glucose
What is glucoregulation?
regulation of glucose
What is glycogenesis?
the conversion of glucose to glycogen
What is glycogenolysis?
the conversion of glycogen to glucose
What is the hypothalamus?
the region of the brain involved in homeostasis
What is insulin?
a hormone which decreases blood glucose levels
What is negative feedback?
a series of changes that results in a substance being restored to it’s normal/optimum level
What is osmoregulation?
regulation of water
What is the pancreas?
organ, location of islet of langerhans
What is positive feedback?
a process where the level of a substance becomes further away from the normal/optimum level
What are receptors?
a cell adapted to detect changes in the environment
What is the difference between type 1 and type 2 diabetes?
type 1 - sufferers do not produce any/enough insulin
type 2 - have lost receptiveness to insulin
What are hormones?
proteins that are produced in endocrine glands and secreted into the blood plasma to target cells that have complimentary receptors specific to the hormone
Which hormones CAN diffuse through the phospholipid membrane?
steroid hormones
Which hormones follow the second messenger model of action?
adrenaline and glucagon (do the same job)
How does glucagon cause the conversion of glycogen to glucose?
-Water soluble glucagon binds to its receptor in cell surface membrane of target cells
-this changes the shape of the protein that spans the membrane
-an enzyme called adenylate cyclase inside the cell surface membrane is activated
-the enzyme converts ATP to cAMP (cyclic adenosine monophosphate- a second messenger)
-cAMP activates enzymes in a cascade of reactions. Protein kinases activate the enzymes that catalyse the breakdown of glycogen to glucose
Why is it bad for blood glucose to get too high?
dysregulated water potential in cells- water will be lost by osmosis
Why is it bad for blood glucose to get too low?
can cause the body to start breaking down proteins
less respiration
Why is osmoregulation important?
water is vital to the function of the body, water potential of blood is carefully controlled
What monitors the water potential of blood?
osmoreceptors in the hypothalamus
What happens to excess amino acids?
broken down in the liver to produce the waste product urea (a salt) which is safe to transport to the kidneys, then the kidneys filter the blood removing ALL urea, and excess water/salt, forming urine
What is the ureter?
tube through which urine passes from the kidney to the bladder
What is the urethra?
tube from bladder to outside of body
What is the cortex and the medulla?
cortex is closer to outside, has a high blood supply, medulla is closer to the inside and contains the loops of henlé from the nephrons
What is a pyramid?
a collection of tubules, collecting ducts, and blood vessels
Name the parts of the nephron in order?
bowmans capsule, proximal convoluted tubule, loop of henlé, distal convoluted tubule, collecting duct
What is the role of the bowmans capsule?
formation of glomerular filtrate/ultrafiltration
What is the role of the PCT?
selective reabsorption of water and glucose
What is the role of the loop of henlé?
maintenance of a gradient of sodium ions in the medulla
What does the DCT do?
reabsorption of water (permeability controlled by ADH)
How is glomerular filtrate formed?
there is a high hydrostatic pressure in the glomerulus due to the efferent arteriole having a smaller/thinner lumen than the afferent arteriole, so small molecules like glucose/urea/ions/water are forced out of the blood to form glomerular filtrate. this is filtered by fenestrations/pores in the capillary endothelium, the basement membrane, and podocytes. large molecules such as proteins remain in the blood
How is glucose and water reabsorbed in the PCT?
-Na+ actively transported out of the epithelial cells and into the capillary lumen
-This creates a concentration gradient in the epithelial cells, so Na+ moves in by facilitated diffusion, bringing glucose against its concentration gradient
-glucose concentration inside the epithelial cell increases, so it moves out into the lumen by facilitated diffusion down it’s concentration gradient
-glucose lowers water potential so water moves by osmosis down a water potential gradient
What does/doesn’t get absorbed in selective reabsorption?
ALL glucose/amino acids
MOST water
NO urea
Why would all glucose not be absorbed?
-if you have uncontrolled diabetes you will have a high concentration of glucose in your blood
-so the carrier proteins could be working at their maximum rate
What actually happens in the loop of Henlé?
-acts as a countercurrent multiplier
-in ascending limb- (away from bowmans capsule)- Na+ is actively transported out so the filtrate concentration decreases, but water remains as it is impermeable to water, increases the conc of Na+ in the medulla which lowers the water potential
-in descending limb- (closest to bowmans capsule)- permeable to water so the water moves out by osmosis, then reabsorbed by capillaries, Na+ moves in
Why might animals needing to conserve water have longer loops of Henlé/thick medulla?
-more Na+ is moved out so Na+ gradient is maintained for longer in medulla
-so water potential gradient is maintained for longer and more water can be reabsorbed from collecting duct by osmosis
What is the role of the hypothalamus in osmoregulation?
-contains osmoreceptors that detect blood water potential, and produce ADH when it is low
What is the role of the posterior pituitary gland in osmoregulation?
secretes ADH into the blood when signalled by hypothalamus
What is the role of ADH in osmoregulation?
-more secreted when blood water potential is too low, as it increases water permeability of DCT and collecting duct
How does the body respond to decreased water potential?
-change detected by osmoreceptors in hypothalamus
-posterior pituitary gland secretes ADH
-ADH increases permeability of DCT and collecting duct to water by increasing the number of aquaporins
-more water reabsorbed
-so urine is more concentrated
