Topic 6 - Homeostasis Flashcards
What is homeostasis
control systems that keep your internal environment roughly constant to stop cell damage
what happens to cells if blood glucose concentration is too low or too high
- too high - the water potential of blood is reduced to a point where water molecules diffuse out of cells into the blood by osmosis, the cells can shrivel up and die
- too low - cells are unable to carry out normal activities because there isn’t enough glucose for respiration to provide energy
what is a negative feedback response
- change is counteracted to bring the level back to normal
what is a positive feedback mechanism
- the change is amplified
- further increase the level away from the normal level
When does bood glucose concentration level fall and rise
- rise - after eating food containing carbohdrates
- fall - after exercise
what are the 2 hormones involved in blood glucose control
insulin
glucagon
where is insulin and glucagon secreted from
- insulin - beta cells in the islets of langerhans in the pancreas
- glucagon - alpha cells in the islets of langerhans in the pancreas
How does insulin work
- it lowers levels of blood glucose concentration when its too high
- Insulin binds to specific receptors on the cell membranes of liver cells and muscle cells
- it increases the permeability of muscle cell membranes to glucose, so the cell take up more glucose. this involves increasing the number of channel proteins in the cell membranes
- insulin also activates enzymes in liver and muscle cells that convert glucose into glycogen (glycogenesis)
- the cells are able to store glycoen in their cytoplasm, as an energy source
what is glycogenesis
forming glycogen from glucose
what is the name for forming glycogen from glucose
what is glycogenesis
what does glucagon do
- rises blood glucose concentration levels
- glucagon binds to specific receptors on the cell membranes of liver cells
- glucagon activates enzymes in liver cells that break down glycogen into glucose (glycogenolysis)
- glucagon also activates enzymes that are involved in the formation of glucose from glycerol and amino acids (gluconeogenesis)
- glucagon decreases the rate of respiration of glucose in cells
how does adrenaline increase blood glucose concentration
- adrenaline is secreted from the adrenal glands when there is a low concentration of glucose in the blood, when youre stressed and exercising
- adrenaline binds to receptors in the cell membrane of liver cells
- it activates glycogenolysis
- it inhibits glycogenesis
- it also activates glucagon secretion and inhibits insulin secretion which increased glucose
- adrenaline gets the body ready for action by making more glucose available for muscles to respire
what is the second messenger model for adrenaline and glucagon
- adrenaline and glucagon bind to their receptors and activate an enzyme called adenylate cyclase.
- activated adenlyate cyclase converts ATP into a chemical signal called cAMP
- cAMP activates an enzyme called protein kinase A.
- it activates a chain of reactions that cause glycogenolysis
- to produce glucose
what is type 1 diabetes caused by
- The immune system attacks b cells in the islets of langerhans so they cannot produce insulin.
How is type 1 diabetes treated
insulin injections
controlling sugar intake
what causes type II diabetes
- usually acquired later in life and linked with obesity
- b cells dont produce enough insulin the body cells dont respond properly to insulin because insulin receptors dont respond properly.
how can type II diabetes be treated
- eating healthy balanced diet
- loosing weight
- regular exercise
how would you determine the concentration of a glucose solution
- make serial dilutions
- do a quantitative benedicts test on each solution
- use a colorimeter to measure the absorbance of the benedicts solution remaining in each solution
- use the results to make a calibration curve
what is the function of the kidneys
- excrete waste products like urea
- regulate the water potential of the blood
- ultrafiltration
- selective reabsorption
where, in the kidney, does ultrafiltration and selective reabsorption occur
nephrons
what happens during ultrafiltration
- blood from the renal artery enters afferent arterioles in the cortex of the kidney
- each arteriole splits into a glomerulus - a bundle of capillaries looped inside the bowman’s capsule
- the efferent arteriole is smaller in diameter than the afferent arteriole, so blood in the glomerulus is at high pressure.
- the high hydrostatic pressure forces small moleucles like water and glucose out of the capillarie and into the bowman’s capsule
- the liquid and small molecules pass through 3 layers to get into the bowman’s capsule and enter the nephron tubules ( a capillary wall, a basement membrane and the epithelium with gaps called podocytes)
- larger molecules like proteins and blood cells stay in the blood
what is the glomerulus
a bundle of capillaries inside the bowman’s capsule
where is a nephron
in the cortex and medulla of the kidney
list the structure of a nephron
- afferent/efferent arteriole
- glomerulus
- bowman’s capsule
- proximal convoluted tube (PCT)
- loop of henle
- distal convoluted tube (DCT)
- collecting duct
what happens during selective reabsorption of glucose
- sodium ions are actively transported from the epithelial cells into the blood by tha sodium potassium ion pump
- this creates a lower concentration of sodium ions in the epithelial cells compared to the lumen, so sodium inos diffuse down their gradient using a co transporter protein
- this also binds to glucose, transporting glucose and sodium into the epithelial cells
- the concentration of glucose is then higher in the epithilial cells compared to the blood so it moves down this concentration gradient via facilitated diffusion through a channel protein.
how is the proximal convoluted tubule adapted for selective reabsorption
- microvilli
- co transporter proteins
- high number of mitochondria
what is the function of the liver
makes urea
what are water potential receptors called and where are they found
- osmoreceptors
- hypothalamus of brain
where is the cortex found on the kidney
outer layer of kidney
what happens when you are dehydrated
- osmoreceptors in the hypothalamus detect a low water potential
- the posterior pituitary glandis stimulated and releases more ADH into the blood
- more ADH means that the distal convoluted tubule and collecting duct become more permeable so more water is reabsorbed into the blood by osmosis
- a small amount of highly concentrated urine is produced and less water is lost
where are osmoreceptors found
hypothalamus
what happens when you are hydrated
- osmoreceptors in the hypothalamus detect high water potential
- posterior pituitary gland releases less ADH into the blood
- less ADH meas that the distal convolute tubule and the collecting duct become less permeable so less water is reabsorbed into the blood
- a large amount of dilute urine is produced and more water is lost
what happens to concentration of urine as the medulla is thicker
- longer loop of henle
- sodium ion gradient is maintained for longer
- more water reabsorbed from loop of henle by osmosis
how is water selectively reabsorbed
- Happens in the loop of Henle and collecting duct
- in the ascending limb, sodium ions are actively transported out at the top, and diffuse out at the bottom
- water cannot move as the limb is impermeable to water
- water potential of the filtrate increases
- the descending limb is hihgly permeable to water
- water leaves by osmosis down the water potential gradient formed by the loss of sodium ions.
- water is reabsorbed into the blood stream in the loop of henle and collecting duct
where is ADH secreted from
posterior pituitary gland
explain how the concentration of filtrate changes through the loop of henle
- Concentration rises in descending limb because sodium ions enter
and water lost; - Concentration falls in ascending limb because sodium ions (and
chloride) ions actively removed; - But water remains (in ascending limb) because its walls are impermeable to water
