Chapter 16 - Homeostasis

Question 1

What is homeostasis?

Answer 1

The control of the internal environment of an organism within normal limits, based upon several different systems working together

Question 2

Why is it important for the body to maintain constant Ph levels and temperature?

Answer 2

So that the enzymes essential for biological processes are able to continue to function as close to their optimum as possible, and so that they do not denature

Question 3

Why is it important to keep glucose levels as stable as possible in the blood?

Answer 3

So that cells always have available respiratory substrates in the event of an increase of metabolic output, but also to keep water potential levels stable so cells neither rupture nor crenalate

Question 4

What is negative feedback?

Answer 4

Negative feedback is a biological response to when things begin to increase, to oppose the change and make them decrease instead

Question 5

Why is negative feedback useful and why is it used?

Answer 5

Negative feedback allows biological systems to constantly oppose natural changes in both directions and counteract the changes which it is causing with antagonistic hormones for example, to keep different levels within stable parameters

Question 6

What factors affect blood glucose levels?

Answer 6

Eating food will tend to increase glucose levels in the blood, whilst they will naturally decrease through normal metabolic processes, but especially during periods of exercise when glucose is used as a respiratory substrate

Question 7

What is a hormone?

Answer 7

A hormone is a chemical messenger secreted by glands which travel through the blood to “target cells”, or cells which have receptors specific and complementary to that hormone

Question 8

Which gland cells are responsible for the production of glucagon and insulin?

Answer 8

The Islets of Langerhans cells are responsible for their production and are found in the pancreas. The alpha cells produce glucagon whilst the beta cells produce insulin

Question 9

Which three blood glucose level regulatory processes happen in the liver?

Answer 9

Glycogenesis - the formation of glucose into glycogen (stored in the liver)
Glycogenolysis - the breakdown of glycogen into glucose
Gluconeogenesis - When glycogen stores are exhausted the liver will begin to make glucose from other sources, such as amino acids and glycerol

Question 10

How does insulin affect cells across the body?

Answer 10

Almost all cells in the body have receptors to insulin. When beta cells in the Islets of Langerhans detect lowered blood glucose levels, insulin is released. This insulin spreads across the body and binds to cell receptors. This opens glucose channel proteins already present on the membrane, however it also causes vesicles in the cell which have more channel proteins to fuse with the membrane, resulting in an increase of glucose channels so more glucose enters the cells in the body and its rate of absorbtion increases, lowering its levels in the blood

Question 11

How does insulin affect cells

Answer 11

Insulin is able to activate enzymes in muscle and liver cells which convert glucose to glycogen, and in regular cells it either increases respiratory rate or activate enzymes which make fat. Once the beta cells in the Islets detect decreasing blood sugar levels, they decrease the release of insulin, resulting in a negative feedback effect

Question 12

How does glucagon increase levels of glucose in the blood?

Answer 12

Glucagon is released by alpha Islet cells when a decrease in blood sugar levels is detected. Glucagon binds to receptors in the liver and activates enzymes which either leads to glycogenolysis or gluconeogenesis. This increases glucose levels and leads to reduced amounts of glucagon being released by the pancreas (negative feedback)

Question 13

How does adrenaline increase blood sugar concentration? (SMM)

Answer 13

When stressed or excited the adrenal glands (above kidneys) release adrenaline which goes to the liver and binds to an intrinsic protein there. This intrinsic protein being bound to changes its shape on the membrane side, activating adenylate cyclase, which converts AMP to cyclic AMP (cAMP). This is able to active protein kinase enzyme, which converts glycogen to glucose, and this is released from the hepatocytes by facilitated diffusion

Question 14

What causes diabetes type 1?

Answer 14

It is a genetic condition where the body cannot make an active form of insulin, however it is relatively easily treatable nowadays by monitoring glucose levels and insulin shots

Question 15

What is type 2 diabetes?

Answer 15

It is an acquired disease where your body stops responding to insulin for a variety of reasons, and therefore its only treatment tends to be careful monitoring of food intake and blood glucose levels

Question 16

What is osmoregulation?

Answer 16

Control of water potential in the blood

Question 17

What is the structure of the kidney?

Answer 17

There are two kidneys, each is roughly ovular shaped with three main tubes coming out of the back: the renal artery which supplies the kidney with blood, the renal venal which takes blood back to the heart and the ureter which goes to the urethra. Furthermore there are two distinct areas in each kidney, the cortex which contains the bowmans capsule and the proximal convoluted tubule, and then the medulla with the loop of Henle and the collecting duct (as well the distal convoluted tubule)

Question 18

What is the structure of the nephron?

Answer 18

The nephron contains the Bowman’s capsule, a ball like structure which houses the glomerulus and leads to the proximal convoluted tubule and leads to the loop of henle, a sharp downwards tube (descending limb) which bends at the bottom (hairpin bend) and goes back up (ascending limb) to the distal convoluted tubule, finally leading to the collecting duct

Question 19

What is the glomerular filtrate?

Answer 19

The glomerular filtrate is the mineral ions, urea, glucose and other solutes which fall out of the blood when the afferent arteriole enters the Bowmans capsule. They are forced out due the hydrostatic pressure of the glomerulus, but also assisted by small holes in the golomerular capillaries and also the podocytes which provide small pores for the arteries. The red blood cells and blood proteins however are unable to exit the capillary

Question 20

How are the majority of the useful molecules in the glomerular filtrate reabsorbed?

Answer 20

They are reabsorbed in the proximal convoluted tubule by cotransport, almost identically to the way it is carried out in the digestive tract

Question 21

What is the Loop of Henle used for and how does it work?

Answer 21

The easiest way to explain the Loop of Henle is to start with the ascending limb. The membrane on this limb is almost completely impermeable to water, and actively transports lots of sodium ions into the interstitial space, reducing its water potential. This results in water diffusing out of the descending limb into the interstital space, where it further diffuses into the capillaries and it taken away.

Question 22

What is the counter current multiplier effect in the Loop of Henle?

Answer 22

Because no sodium ions are lost before the hairpin bend, there are lots of sodium ions which can be actively transported out, and some even move by diffusion meaning the bend has the lowest water potential, whereas by the time the distal convoluted tubule has been reached not many sodium ions can be transported out of the limb, meaning the top of the interstital space has the relative highest water potential, which works because the top of the descending limb also has large amounts of water therefore a high water potential, so water can still diffuse out into a lower water potential environment, reducing water potential in the descending limb. This means as the water potential of the limb decreases, so does the intertitial space by approximately the same amount, therefore there is always a gradient for the water to diffuse into the space for

Question 23

What controls the absorbtion of water in the collecting duct?

Answer 23

Horomones released by the hypothallmus and pituitary gland

Question 24

How do hormones help with the control of water absorbtion in the collecting duct?

Answer 24

The hypothallmus has osmoregulators which are able to detect levels of water in the body, and when they drop it send ADH to the pituitary gland which releases it to the kidney. The ADH binds to surface receptors in the distal convoluted tubule and collecting duct which causes two things:
An increase in permeability of the membrane to urea, meaning it leaves the ducts
The activation of phosphorylase, which binds more aquaporins to the duct membranes, increased water permeability
This leads to more water leaving the duct cells and re entering the blood