Chapter 16 - Homeostasis

Question 1

What is homeostasis

Answer 1

The maintenance of a constant internal environment within an organism

Question 2

Why is homeostasis important

Answer 2

• Enzymes - It keeps the internal environment constant for metabolic reactions (which is controlled by enzymes)
• Water potential - maintenance of blood glucose level is essential for the maintenance of water potential which ensures cells function properly and avoid damage as they don’t shrink or burst
• Independence - if you can control your internal environment you are more independent of the changes in your external environment so organisms can have a wider geographical range
• It helps organisms respond and adapt to external changes.

Question 3

how does negative feedback work

Answer 3

1) Receptors detect a change in one direction, like rising blood glucose.
2) Signals trigger effectors to produce responses that reverse the initial change, like releasing insulin to lower blood glucose.
3) Conditions return to their set range.

Question 4

examples of negative feedback

Answer 4

Maintaining blood glucose concentration
Maintaining blood pH
Maintaining temperature
Water regulation

Question 5

why is it important to maintain temperature and how is it achieved

Answer 5

Why it is important - Changes in temperature can impair enzyme action.
How it is achieved - Adjustments are made, for instance by sweating or shivering, to maintain the optimum temperature.

Question 6

why is water potential important and how is it achieved

Answer 6

Why it is important - Too much or too little water in the blood and cells can cause cells to burst or shrink due to osmosis.
How it is achieved - Water is removed or reabsorbed from blood or tissue fluid to maintain the optimum water potential.

Question 7

why is water regulation important and how is it achieved

Answer 7

Why it is important - Changes in pH can impair enzyme action.
How it is achieved - Adjustments are made to the acid-base balance in the blood to maintain the optimum pH.

Question 8

why is Maintaining blood glucose concentration important

Answer 8

Glucose is needed for respiration, but too much glucose can affect water potential in blood and cells.

Question 9

how does positive feedback occur

Answer 9

1) An initial change occurs, like the release of clotting factors after a blood vessel injury.
2) Effectors are stimulated and enhance the change, like more clotting factors being released.
3) The change continues until an endpoint is met, like a clot being fully formed.

Question 10

what is positive feedback

Answer 10

positive feedback amplifies changes rather than reversing them

Question 11

what does the endocrine system do

Answer 11

uses hormones to send information about changes in the environment around the body to bring about a designated response

Question 12

what does the endocrine system consist of

Answer 12

the pancreas, adrenal glands, and the pituitary gland

Question 13

how does hormones act as a chemical messenger

Answer 13

1) Hormones are produced by endocrine gland cells.
2) When stimulated, glands release hormones into the bloodstream.
3) The blood carries hormones to their target cells.
4) They attach to receptors on or inside the target cells.
The cells then respond to the hormones.

Question 14

properties of non steroid hormones

Answer 14

• Water soluble (hydrophilic)
• Cannot diffuse across the phospholipid bilayer
• Bind to receptors on the cell-surface membrane of their target cells to activate second messengers
  e.g adrenaline

Question 15

properties of steroid hormones

Answer 15

• Lipid soluble (hydrophobic)
• Can diffuse across the phospholipid bilayer
• Bind to receptor molecules in the cytoplasm or the nucleus, forming a hormone-receptor complex that acts as a transcription factor
  e.g oestrogen

Question 16

difference between endocrine and nervous system

Answer 16

Signals
Endocrine sytem: Hormones
Nervous system: Nerve

Transmission
Endocrine system: By blood Nervous system: By neurones

Speed
Endocrine system: Slow Nervous system: Very rapid

Spread
Endocrine system: Widespread
Nervous system: Localised

Duration of effect
Endocrine system: Long Nervous system: Short

Question 17

what does the second messenger model of hormone action do and what is the second messenger

Answer 17

The second messenger model of hormone action involves a hormone triggering the formation of a second messenger (cAMP) inside the cell, which activates enzymes to carry out a function.

second messenger = the next molecule which causes activation

Question 18

how does adrenaline increase blood glucose (second messenger model of adrenaline)

Answer 18

1)Adrenaline binds to complementary receptor on the cell-surface membrane of a liver cell.
2) The binding of adrenaline causes the protein to change shape, activating a G protein.
3) This activates the enzyme adenylate cyclase.
4) The activated adenylate cyclase converts ATP into cAMP.
5) cAMP acts as a second messenger, activating protein kinase via phosphorylation, amplifying the signal from adrenaline.
6) Protein kinases activate enzymes that catalyse the breakdown of glycogen into glucose (glycogenolysis)
7) Glucose moves out of liver cells by facilitated diffusion and into the blood through channel proteins.
8) This increases the blood glucose concentration so that more glucose can be delivered to body cells for respiration.

Question 19

what are islets of langerhans

Answer 19

special cell clusters that produce hormones found in the pancreas

Question 20

which cells do the islets of langerhans contains

Answer 20

• Beta (β) cells - They secrete the hormone insulin.
• Alpha (α) cells - They secrete the hormone glucagon.

Question 21

what is negative feed back

Answer 21

when any deviation from the normal values are restored to their original level

Question 22

where is the adrenaline hormone released from

Answer 22

the adrenal glands

Question 23

What effect does adrenaline have on glucose levels?

Answer 23

It causes more glucose to be released from glycogen stores in the liver.

Question 24

what is Glycogenolysis

Answer 24

Glycogen is converted back into glucose in liver and muscle cells

Question 25

what is Gluconeogenesis

Answer 25

Glucose is produced from amino acids and fats in the liver

Question 26

what happens when there is an increase in blood glucose levels

Answer 26

1) this rise is detected by beta cells in the islets of Langerhans 2) Beta cells then release insulin 3) causing cells become more permeable to glucose and enzymes are activated to undergo Glycogenesis 4) Glucose is then removed from the blood and stored as glycogen in cells 5) this results the blood glucose levels to return as normal

Question 27

what is Glycogenesis

Answer 27

Glucose is converted into glycogen for storage, primarily in the liver

Question 28

what happens if the blood glucose levels decrease

Answer 28

1) this decrease is detected by the alpha cells in the islets of Langerhans 2) Alpha cells will release glucagon and adrenal gland will release adrenaline 3) second messenger model occurs to activate enzymes to hydrolyse glycogen 4) Glycogenolysis occurs and the glucose is released back into the blood 5) Glucose levels return back to normal

Question 29

how does insulin decrease blood glucose

Answer 29

1) insulin binds to receptors on the surface of target cells (liver cells), this changes the tertiary structure of the channel proteins, resulting in more glucose being absorbed by faciliated diffusion 2) the binding of insulin to the receptor causes intracellular chemicals to be released 3) this results in vesicles containing glucose protein channels to move towards the cell surface membrane **AND** fuse with the cell surface membrane 4) this allows more channel proteins to be incorporated into cell membrane so that more glucose is absorbed from the blood into cells 5) this activates enzymes which stimulates glycogenesis to occur in the liver

Question 30

why does glycogenesis occur in the action of insulin when blood glucose levels are too high

Answer 30

this is because glucose is soluble so will dissolve into the cytoplasm of the cell causing water to move in by osmosis whilst glycogen is an insoluble store of glucose so doesn't alter the osmotic pressure of the cell

Question 31

how does glucagon increase blood glucose concentration (second messenger model of glucagon)

Answer 31

1) glucagon attached to glucagon receptors on the surface of target cells (liver cells) 2) when glucagon binds it causes an enzyme to be activated into adenylate cyclase and that enzyme catalyses the reaction to convert ATP into cyclic AMP (cAMP) (which is the second messenger) 3) cAMP activates an enzyme called protein kinase that can catalyse glycogenolysis (hydrolyse glycogen into glucose) 4) This activates enzymes to convert glycerol and amino acids into glucose (gluconeogenesis)

Question 32

what is type 1 diabetes caused by

Answer 32

when the body is unable to produce insulin which could be a result of an autoimmune disease where beta cells were attacked leading to no insulin production and high blood glucose levels

Question 33

what is type 2 diabetes caused by

Answer 33

when the receptors on the target cells lose their responsiveness to insulin or beta cells dont produce enough insulin due to obesity and poor diet results in

Question 34

treatments for type 1 diabetes

Answer 34

- Regular insulin injections - Use of an insulin pump providing continuous insulin administration. - Pancreas transplants of healthy islet cells to enable some insulin production. - Careful blood glucose monitoring and a diet balanced with insulin dosage. - Exercise to help regulate blood glucose and insulin requirements.

Question 35

treatments for type 2 diabetes

Answer 35

- Diet control to reduce sugar intake. - Regular physical activity. - Medications to increase cells' sensitivity to insulin. - Medications to stimulate more insulin production in cells. - insulin therapy to manage blood glucose levels.

Question 36

symptoms of diabetes and why they are caused

Answer 36

- excess urination = due to more water leaving the cell by osmosis so more urine is produced - weight loss = less glucose is absorbed into cells so therefore more gluconeogenesis from lipids - tiredness - less respiration due to less glucose in cell - blurred vision - less blood flow to the retina so retina functions less well due to excess glucose

Question 37

draw and label the structure of a kidney

Answer 37

labelled structures should include: - Fibrous capsule - An outer membrane that surrounds and protects the kidney. - The renal cortex - The outer region that contains Bowman's capsules, convoluted tubules, and blood vessels. - The renal medulla - The inner region with structures called pyramids that contain loops of Henle, collecting ducts, and blood vessels. - The renal pelvis - The funnel-shaped cavity that collects urine into the ureters. - ureter - renal vein and artery - renal pelvis

Question 38

draw and label the nephron structure

Answer 38

This should include labels: - renal capsule/bowmans capsule with glomerulus - proximal tube - loop of henle - distal convulated tube - collecting ducts - efferent and afferent arteriole - ascending and descending tube

Question 39

where is the nephron found

Answer 39

medulla

Question 40

function of the nephron

Answer 40

- filters the blood to remove waste and selectively reabsorb useful substances back into the blood

Question 41

what does urine contain

Answer 41

- water - dissolved salts - urea - small substances e.g hormones and excess vitamins

Question 42

why does the urine not contain proteins, blood cells and glucose

Answer 42

proteins and blood cells - too large to be filtered out of the blood glucose - all glucose is absorbed at the selective reabsorption stage in the PCT (proximal convoluted tubule)

Question 43

how does filtering and reabsorption occur (steps of making urine)

Answer 43

Stage 1) Ultrafiltration - due to high hydrostatic pressure water and small molecules are forced out of the glamorous into the renal capsule Stage 2) Selective reabsorption - occurs in the proximal convoluted tubule Stage 3 + 4) The loop of henle -maintains a sodium gradient so water can be reabsorbed by the blood Stage 5 + 6) Distal convoluted tubule (DCT) and collecting duct - water moves out DCT and collecting duct to return back to blood, collecting duct then carries the remaining liquid to ureter

Question 44

Steps of ultrafiltration

Answer 44

1) blood enters through afferent arteriole and this splits into smaller capillaries which make up the glomerulus, causing high hydrostatic pressure of blood 2) Water and small molecules e.g glucose and mineral ions are forced out the capillaries through gaps in the capillary endothelium and through basement membrane and forms the glomerulus filtrate 3) Large proteins and blood cells are too big to fit through the gaps in the capillary endothelium so remain in the blood 4) The blood leaves via the efferent arteriole

Question 45

adaptions of the proximal convoluted tubule

Answer 45

- microvilli - provide a large surface area for reabsorption - lots of mitochondria - provides energy for active transport

Question 46

process of selective reabsorption

Answer 46

1) Sodium ions (Na+) are actively transported into blood capillaries, reducing the Na+ concentration in epithelial cells lining the PCT. 2) Na+ moves from the PCT lumen into the epithelial cells, down its concentration gradient. 3) Na+ is co-transported with substances like glucose and amino acids into the epithelial cells. 4) These reabsorbed molecules can then diffuse into blood capillaries. 5) All the glucose is REABSORBED

Question 47

properties of ascending and descending limb

Answer 47

ascending - walls are impermeable to water and has thicker walls descending - walls are permeable to water and the walls are thinner

Question 48

how is the sodium ion gradient maintained by the loop of Henle

Answer 48

1) Mitochondria in the walls of the cells provide energy to actively transport sodium ions out of the ascending limb of the loop of Henle into the interstitial space 2) The accumulation of sodium ions outside the nephron in the medulla lowers the water potential 3) In the descending limb water diffuse out by osmosis into the interstitial space and the water is then reabsorbed into the blood 4) At the base of the ascending limb some sodium ions are transported out by diffusion since the solution is dilute due to all the water that has moved out

Question 49

Process of reabsorption of water at the DCT and collecting duct DCT = distal convoluted tubule

Answer 49

1) Due to all the sodium ions being actively transported out of the loop of Henle when the filtrate reaches the DCT it is very dilute 2) The filtrate moves into the DCT and collecting duct 3) This causes more water to diffuse out of the DCT and collecting duct 4) Whatever filtrate remains in collecting duct forms urine

Question 50

suggest how the length of the loop of henle will differ for as desert animal compared to a human and explain why?

Answer 50

- Desert animals will have a longer loop of henle - the longer the loop of henle the surface area increases causing more sodium ions to be actively transported out, so a more negative water potential is created, resulting in more water being reabsorbed into the blood and very concentrated urine

Question 51

why is homeostasis of water potential (osmoregulation) important

Answer 51

- if blood has too low water potential (hypertonic) - too much water will leave the cell and move into the blood by osmosis, causing cells to shrivel (crenation) - if blood has too high a water potential (hypotonic) - too much water will move from the blood into the cells by osmosis, causing the cells to burst (lysis)

Question 52

what causes hypertonic and hypotonic blood

Answer 52

hypertonic - too much sweating, not drinking enough water, lots of iron in diet hypotonic - drinking too much water, not enough salt in diet

Question 53

what is the role of the hypothalamus

Answer 53

- changes in the water potential of the blood are detected by osmoreceptors found in the hypothalamus

Question 54

what happens when the water potential of the blood is too low

Answer 54

1) water leaves the osmosreceptors by osmosis, causing them to shrivel 2) This stimulates the hypothalamus to produce more ADH 3) ADH then moves to the posterior pituitary gland and from there it is released into the blood where it travels to the kidneys 4) DCT and collecting duct become more permeable to water 5) so more water is reabsorbed into the blood and less water is lost in the urine 6) water potential of the blood returns to normal

Question 55

what happens when the water potential of the blood is too high

Answer 55

1) water enters the osmosreceptors by osmosis 2) this stimulated the hypothalamus to produce less ADH 3) ADH then moves to the posterior pituitary gland and from there it is released into the blood where it travels to the kidneys 4) DCT and collecting duct become less permeable to water 5) so less water is reabsorbed into the blood and more water is lost in the urine 6) water potential of the blood returns to normal

Question 56

what happens when ADH reaches the kidneys

Answer 56

1) when ADH reaches the kidney it causes an increase in the permeability of the walls of the collecting duct and distal convoluted tube to water 2) this means that more water leaves the nephron and is reabsorbed into the blood so urine is more concentrated

Question 57

How does ADH increase the permeability of the DCT and collecting duct to water

Answer 57

1) ADH binds to the receptors on the cell membrane of the collecting duct and DCT 2) when bound, it activates a phosphorylase enzyme in the cells 3) Phosphorylase causes the vesicles containing aquaporins (channel proteins) to fuse with the cell membrane and the aquaporins embed into the membrane 4) this causes more water to leave the DCT and collecting duct via the aquaporins and be reabsorbed into the blood

Question 58

what are aquaporins

Answer 58

protein channels for water to pass through