Homeostasis

Question 1

Describe the nature of homeostasis

Answer 1

The maintenance of a more or less stable internal environment in organisms

Question 2

The importance of homeostasis

Answer 2

1. Enzymes are sensitive to changes in temp and pH and are essential for all chemical reactions in cells 2. Blood glucose needs to be high to supply cells with respiratory substrate if conc falls, cells are deprived of energy and won’t function, if too much, water potential is lowered= cells dehydrated 3. Changes in water potential can cause cells to shrink, swell or burst which impair functioning so solute concs must be maintained 4. Ability to maintain stable internal environment means organisms can live in wider range of external environments

Question 3

What are the features of a control mechanism and the order they go in

Answer 3

1. Input- a change occurs in the system 2. Receptor- detects change in the system 3. Coordinator- storage of operational information used for onward communication 4. Effector- produces a change in the system 5. Output- change is made to the system 6. Feedback loop back to beginning- corrective mechanism to maintain system ad a set or optimum point

Question 4

Definition of negative feedback

Answer 4

When the change produced by control system/ the output leads to a change in stimulus detected/ input by receptor and turns the system off NO: deviation of a value from norm initiates corrective mechanisms

Question 5

Definition of positive feedback

Answer 5

When deviation from optimum causes change that results in even greater deviation from the normal (amplification mechanism to reinforce the disturbance of a system) e.g opening of Na+ channels in synapse

Question 6

How do hormones generally work

Answer 6

Endocrine glands have secretory vesicles which release hormones into the blood. Hormones have specific tertiary structure to receptors on target cells

Question 7

Difference in responses between nerve impulses and hormones

Answer 7

Nerves: rapid, short lived and localised hormones: slow, long lasting and wide spread

Question 8

What is the structure of the pancreas

Answer 8

Within the pancreas are cells called islets of langerhands which contain a cells (larger and produce the hormone glucagon) and b cells (smaller and produce the hormone insulin)

Question 9

Describe the action of insulin on the concentration of blood glucose

Answer 9

1. B cells have receptors that detect the stimulus of a rise in blood glucose concentration and secrete insulin into the blood 2. Insulin binds to insulin receptors on target cells (in liver, muscle and fat) which activates enzymes that convert glucose to glycogen (glycogenisis) and lipid. 3. Binding also causes glucose transport proteins to move to the cell membrane and more glucose diffuses in this collectively lowers the blood glucose concentration

Question 10

Describe the action of glucagon on blood glucose concentration (made when all the GLUcose is GONe)

Answer 10

1. A cells detect a fall in blood glucose conc and secrete glucagon into the blood 2. Glucagon binds to cell surface protein receptors on liver cells, which triggers the release of glucose into the blood via activating enzymes that convert glycogen to glucose (glycogenolysis) and enzymes that convert AAs and glycerol into glucose (gluconeogenisis) 3. Overall this increases blood glucose conc as there is facilitated diffusion of glucose out of liver

Question 11

Describe the action of adrenaline on blood glucose concentration

Answer 11

At times of excitement or stress, adrenaline is released from adrenal glands above the kidneys. Adrenaline binds to protein receptors on the cell surface membrane of target cells. This activates enzymes that cause the breakdown of glycogen into glucose in the liver (glycogenolysis) which raises blood glucose concentration

Question 12

What are the affecting factors of blood glucose concentration

Answer 12

Affected by diet e.g absorbing more glucose and exercise ( as G used in respiration) also by glycogenolysis and gluconeogenisis

Question 13

How do second messengers work

Answer 13

The hormone (glucagon, adrenaline, insulin) binds to protein receptors on the target cell surface membrane 2. This activated the enzyme adenyl/adenylate cyclase inside the membrane 3. ATP binds to the active site of AC and activated AC converts ATP to cyclic AMP( adenine mono phosphate), which acts as a second messenger 4. cAMP activates the enzyme protein kinase into active protein kinase which activates enzymes/catalyses the conversion of glycogen to glucose

Question 14

What are the features of type one diabetes and how is it controlled

Answer 14

It is when no insulin is released in response to an increase in blood glucose concentration (due to autoimmune response where body attacks B cells) so b.g.c remains high and glucose remains in urine. It has a genetic predisposition, insulin dependent, autoimmune response, early onset. It is treated as b.g.c is monitored using biosensors and with injections of insulin (as if taken orally, it would be digested)

Question 15

What are the features to type 2 diabetes and how is it controlled

Answer 15

It is a problem with the target organs so insulin levels/ protein receptors on cells lose their responsiveness to insulin so insulin levels are higher than normal to compensate. It is lifestyle induced, insulin resistant and layer onset. It is controlled with diet and exercise which can change insulin sensitivity, oral drugs can improve target cells sensitivity or slow the rate the body absorbs glucose. Pancreatic failure can occur from over secretion, then insulin injections are needed

Question 16

Describe the structure of a kidney and draw it out!

Answer 16

1. Fibrous capsule that protects the kidney 2. Cortex (a lighter outer region made up of bowmans capsules, convoluted tubules and blood vessels) 3. Medulla (darker coloured inner region made up of loops of henle, collecting ducts and vessels) 4. Renal pelvis (cavity that collects urine into ureter) 5. Ureter (tube that carries urine to bladder) 6. Renal artery (supplies kidney with blood from aorta) 7. Renal vein (returns blood to heart via vena cava)

Question 17

What are the functions of the kidney and explain excretion of urea

Answer 17

Excretion and osmoregulation. The kidney excretes urea made by the liver as it deaminates amino acids and ammonia into urea.

Question 18

Describe the main pathway through the kidney

Answer 18

Blood enters the kidneys via the renal artery and exits via the renal vein, blood is filtered by specialised structures called nephrons which produce urine. The urine is transported from the kidneys via the ureter, where it is stored by the bladder prior to excretion

Question 19

Describe the structure of a nephron

Answer 19

1. Bowmans capsule which surrounds the glomerulus (mass of blood capillaries with blood that is supplied by the Afferent arteriole ). The inner layer of the renal capsule is made up of podocyte cells. 2. The proximal convoluted tubule (first, closest to capsule), series of loops surrounded by blood capillaries. Walls are made of epithelial cells with microvilli. 3. Loop of henle (hairpin loop that extend from cortex into ,medulla and back, surrounded by blood capillaries) 4. Distal convoluted tubule (further) same as proximal but less capillaries 5. Collecting duct (distal tubules empty into, lined with epithelial and becomes wider). 5. Efferent arteriole (a is before e) vessel that carries blood away from capsule and forms capillaries, it has smaller diameter than afferent so causes increase in blood pressure in glomerulus

Question 20

Describe the process of ultrafiltration

Answer 20

As the diameter of the afferent arteriole is greater than the efferent arteriole, there is a buildup of hydrostatic pressure in the glomerulus. As a result, water, urea, mineral ions, glucose and amino acids are squeezed out to form the glomerular filtrate (blood clerks and large proteins cannot pass as they are too large). Glomerular blood vessels are fenestrated (have pores) so blood can freely exit the glomerulus. Blood is filtered by the basement membrane (between glomerulus and capsule) it is size selective and restricts the passage of blood cells and large proteins. The inner layer of the capsule has podocyte cells with gaps between their pedicels, which allow filtrate to pass through and move into the nephron.

Question 21

Describe the process of reabsorption of glucose/ AA AND WATER in the proximal c.t from glomerular filtrate and why diabetics have glucose in urine

Answer 21

1. Sodium ions are actively transported out of cells lining the proximal c.t via a sodium potassium ion ATPase pump (using ATP) into blood capillaries. 2. This means that Na+ inside the cells are at a lower conc than in the lumen so Na+ diffuses into cells down this conc gradients via carrier proteins 3. Glucose moves in with it against its conc gradient (which creates a higher conc inside the cells) and G moves into blood via facilitated diffusion down this conc gradient where it is removed by flow which maintains it. Water follows the movement of G and AA passively by osmosis . In diabetes: too much glucose as carriers working at max capacity

Question 22

Explain the role of the loop of henle in the absorption of water from filtrate (osmoregulation)

Answer 22

1. The loop of henle operates a countercurrent multiplier system. 2. In the ascending limb, Na+ are actively transported/removed (using ATP from mito) from the tubule to the interstitial fluid in the medulla 3. This creates a lower W.p in the fluid but the ascending limb is impermeable to water so no water leaves via osmosis 4. At the base of ascending limb, Na+ diffuse in 5. As a result, a salt gradient is formed in the fluid of medulla where the deeper into medulla, the lower the water potential of the tissue fluid. 6. The walls of descending limb are permeable so water moves out by osmosis. Water also leaves the collecting duct by osmosis, down a water potential gradient

Question 23

Explain the role of ADH in the production of concentrated urine

Answer 23

1. Osmoreceptors in the hypothalamus detects low water potential of blood (as water leaves them by osmosis down W.p gradient and cells shrink), this stimulates the posterior pituitary gland to secrete more ADH. ADH increases the permeability/ stimulates aquaporins to move to DCT/CD. Means more water is reabsorbed as more leaves the nephron by osmosis down the W.p gradient. Means a smaller volume of urine is produced and it is more concentrated/hypertonic