6c (homeostasis)

Question 1

what is homeostasis?

Answer 1

the maintenance of a stable internal environment

• involves control systems that keep internal environment roughly constant so kept in state of dynamic eqm
• ensures cells are in an environment that meets requirements

Question 2

what is the importance of homeostasis?

Answer 2

helps us to maintain core body temp and blood pH as these effect enzyme activity, therefore rate of metabolic reactions

also maintains blood glucose conc which is important as this affects water potential

Question 3

temperature and homestasis

Answer 3

temp increase= rate of metabolic reactions increases as particles have more kinetic energy so more likely to collide w enzymes active site. also, energy of collisions increases so more likely to result in a reaction

temp too high, hydrogen bonds in enzyme break as vibrations too strong. enzymes-substrate complex no longer able to form so reaction essentially stops

body temp too low, rate of metabolic reactions decreases

37C is optimum

Question 4

pH and homeostasis

Answer 4

pH too high/ low, enzymes denature as ionic and hydrogen bonds break so active site changes shape and no longer works as a catalyst

pH7 is typically optimum

Question 5

how do you work out pH?

Answer 5

pH= -log[H+]

Question 6

blood glucose conc and homeostasis

Answer 6

too high, water pot is reduced so water molecules diffuse out of cells into blood by osmosis, causing them to shrivel up and die

too low, unable to carry out normal activities as there isnt enough glucose for resp to provide energy

Question 7

what is negative feedback?
what happens in negative feedback?

Answer 7

the mechanism that restores levels back to normal and keeps things around the normal level

receptors detect when a level is too high/low and informations communicated via nervous system or hormonal system to effectors.
effectors respond to counteract change- bringing levels back to normal

Question 8

can negative feedback work with all changes in levels?

Answer 8

if too big, may not be able to counteract it eg huge drop in body temp due to prolonged exposure to cold weather

Question 9

why do we have multiple negative feedback mechanisms?
what is the benefit?

Answer 9

means theyre all rapid so we can eg very quickly increase temp or decrease temp rather than being able to do one then just waiting for the other

Question 10

what is positive feedback?

Answer 10

encourages further diversion from the norm

Question 11

breakdown of homeostatic systems

Question 12

what is the normal blood glucose conc?
what happens after eating carbs?
what happens after exercise?

Answer 12

90 mg per 100cm^3 of blood
increases
decreases- more glucose used in resp

Question 13

what are islets of Langerhans?

Answer 13

clusters of cells in the pancreas that secrete insulin and glucagon

Question 14

what are alpha cells?

Answer 14

larger cells in islets of Langerhans that secrete glucagon

Question 15

what are beta cells?

Answer 15

smaller cells in islets of Langerhans that secrete insulin

Question 16

insulin

Answer 16

lowers blood glucose conc when its too high

binds to specific receptors on cell membranes of muscle cells and liver cells (hepatocytes)

increases permeability of muscle-cell membranes to glucose so cells take up more glucose

involves increasing number of channel proteins in cell membranes

also activates enzymes in muscle and liver cells that convert glucose into glycogen (glycogenesis) which can be stored in cytoplasm

also increases rate of resp especially in muscle cells

Question 17

what is glycogenesis?

Answer 17

converting glucose to glycogen (activated by insulin)

Question 18

glucagon

Answer 18

raises blood glucose when its too low

binds to specific receptors on cell membranes of liver cells and activates enzymes that break down glycogen into glucose (glycogenolysis)

also activates enzymes involved in formation of glucose from glycerol and amino acids (gluconeogenesis)

decreases rate of resp in cells

Question 19

what is glycogenolysis?

Answer 19

breaking down glycogen into glucose
(activated by glucagon)

Question 20

what is gluconeogenesis?

Answer 20

forming glucose from non-carbohydrates (glycerol and amino acids)
(activated by glucagon)

Question 21

responses produced by hormones compared to nervous impulses

Answer 21

slower as they travel in the blood

response can be all over body if target cells are widespread (nervous impulses are localised)

not broken down as quickly as neurotransmitters so longer lasting effects

Question 22

negative feedback mechanism when blood glucose conc rises

Answer 22

pancreas detects blood glucose conc too high so b cells secrete insulin and a cells stop secreting glucagon

insulin binds to receptors on liver and muscle cells (effectors)

liver and muscle cells respond to decrease the blood glucose conc eg glycogenesis is activated, cells take up more glucose, cells respire more

Question 23

negative feedback mechanism when blood glucose conc falls

Answer 23

pancreas detects blood glucose conc too low so a cells secrete glucagon and b cells stop secreting insulin

glucagon binds to receptors on liver cells (effectors)

liver cells respond to increase the blood glucose conc eg glycogenolysis and gluconeogenesis are activated, cells respire less glucose

Question 24

what are glucose transporters?

Answer 24

channel proteins that which allow glucose to be transported across cell membrane

Question 25

glucose transporter in skeletal and cardiac muscle cells

Answer 25

GLUT4 insulin low- GLUT4 stored in vesicles but when insulin binds to receptors on cell surface membrane, triggers movement of GLUT4 out of cell glucose can then be transported into cell through GLUT4 by facilitated diffusion

Question 26

what is adrenaline/ role?

Answer 26

hormone secreted by adrenal glands when low conc of glucose in blood/ stressed/ exercising binds to receptors in cell membrane of liver cells and increases blood glucose conc by: - activating glycogenolysis - inhibits glycogenesis - activates glucagon secretion - inhibits insulin secretion

Question 27

what is the second messenger model?

Answer 27

the binding of the hormone to cell receptors activates an enzyme inside the the cell membrane which then produces a chemical known as the second messenger second messenger activates other enzymes in cell to bring about response FINISH

Question 28

what is type 1 diabetes?

Answer 28

immune system attacks b cells so cant produce insulin after eating, blood glucose stays high (hyperglycaemia) kidneys cant reabsorb all the glucose so some excreted in urine treated w insulin therapy but very controlled to prevent hypoglycaemia may be genetic, may be triggered by viral infection

Question 29

what is type 2 diabetes?

Answer 29

b cells dont produce enough insulin/ body's cells dont respond properly (because insulin receptors dont work so dont take up enough glucose) acquired later in life often linked w obesity and family history. lack of exercise, age, poor diet treated w healthy balanced diet, losing weight, regular exercise. can have medication/ insulin injections if required

Question 30

responses to type 2

Answer 30

health advisors - recommend low fat, sugar, salt diet w lots of whole grains, f&v, reg exercise - campaigns eg change4life help to educate - challenged food industry to reduce advertising junk food, improve nutritional value, use clearer labelling food companies - use sugar alternatives, reduce sugar, fat and salt content - however, pressure to increase profit so reluctant to spend money on alternatives if other still popular and generating profit - will only respond fully in long term when public perception changes

Question 31

required practical

Question 32

excretion of waste products

Answer 32

blood enters kidney through renal artery and passes through capillaries in cortex of kidneys where substances are filtered out into tubules surrounding capillaries (ultrafiltration) useful substances are reabsorbed (selective reabsorption) and the remaining unwanted substances pass along bladder and are excreted as urine

Question 33

what are nephrons? how many are there?

Answer 33

long tubules along with bundles of capillaries where blood is filtered around 1 million per kidney

Question 34

what is the structure of the kidneys?

Question 35

what is ultrafiltration?

Answer 35

blood from renal artery enters arterioles in cortex of kidney each arteriole splits into a glomerulus (bundle of capillaries looped inside hollow ball (Bowman's capsule) this is where ultrafiltration takes place afferent arteriole- takes blood into glomeruli efferent arteriole- takes filtered blood away from the glomeruli efferent has smaller diameter so blood in glomerulus is under high pressure which forces liquid and small molecules out of cap into Bowman's capsule (through cap endothelium, basement membrane and epithelium of Bowman's capsule) larger molecules (proteins, blood cells) cant pass through so stay in blood substances that enter Bowman's capsule are called glomerular filtrate. this passes along rest of nephron and useful substances are reabsorbed along the way. finally, filtrate flows through collecting duct and passes out of kidney along ureter

Question 36

what is selective reabsorption?

Question 37

urine

Answer 37

usually made of water, dissolved salts, urea, hormones, excess vitamins doesnt usually contain proteins/ blood cells as theyre too big to be filtered out glucose actively reabsorbed back into blood so also not found in urine

Question 38

how is water content regulated?

Answer 38

osmoregulation - if water pot of blood is too low, more water reabsorbed by osmosis into blood from tubules of nephrons. so, urine more concentrated, so less water lost in excretion - if water pot of blood is too high, less water reabsorbed by osmosis into blood from tubules of nephrons. so, urine more dilute so water lost in excretion water reabsorbed along nephron but reg of water pot mainly occurs in loop of henle, DCT, and collecting duct. vol of h2o reabsorbed is controlled by hormones

Question 39

what is the loop of Henle?

Question 40

describe the process that occurs in the loop of Henle

Question 41

what is ADH?

Question 42

dehydration

Question 43

hydration