B16 - Homeostasis

Question 1

What is homeostasis?

Answer 1

Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes

Question 2

What does a negative feedback loop do?

Answer 2

It counteracts a change, bringing the value of a parameter—such as temperature or blood sugar—back towards it set point

Question 3

What does a positive feedback loop do?

Answer 3

The feedback causes the corrective measures to remain turned on. The system deviates even more from the optimum level. Stops when there is no more stimulus

Question 4

What occurs in the second messenger model using adrenaline as the hormone?

Answer 4

Adrenaline binds to its receptor on the target liver cell
Receptor changes shape activating adenyl cyclase
Activated adenyl cyclase converts ATP to cAMP
cAMP binds to protein kinase, changes its shape, and therefore activates PK, which will convert glycogen into glucose. Glucose leave cells by facilitated diffusion

Question 5

What is the role of the pancreas?

Answer 5

Produces digestive enzymes (protease, amylase and lipase) as well as hormones (insulin and glucagon)

Question 6

Where in the pancreas are hormones produced?

Answer 6

The islets of Langerhans, containing α and β cells

Question 7

What does the liver do?

Answer 7

Stores glycogen and produces bile and urea

Question 8

What does glycogenolysis do?

Answer 8

Turns glycogen into glucose

Question 9

What does glycogenesis do?

Answer 9

Turns glucose into glycogen

Question 10

What does gluconeogenesis do?

Answer 10

Glucose is formed from sources other than carbohydrates, e.g. amino acids and glycerol

Question 11

What is the role of insulin?

Answer 11

Increases uptake of glucose into cell so lowers blood glucose concentration

Question 12

What cells detect a rise in blood glucose concentration so secrete insulin into blood plasma?

Answer 12

β cells

Question 13

What is the mechanism of insulin?

Answer 13

Insulin binds to receptors on the C.S.M, which makes the glucose transporter carrier protein (stored in vesicles) move up to the cell membrane where they fuse, so glucose enters the cells via facilitated diffusion

Question 14

What is the role of glucagon?

Answer 14

Convert glycogen into glucose

Question 15

What cells detect a fall in blood glucose concentration and secrete glucagon into blood plasma?

Answer 15

α cells

Question 16

What is the mechanism of glucagon

Answer 16

Glucagon binds to receptors on liver cells and activate enzymes which convert glycogen into glucose (second messenger model)
Binds to its receptor on the target liver cell
Receptor changes shape activating adenyl cyclase
Activated adenyl cyclase converts ATP to cAMP
cAMP binds to protein kinase, changes its shape, and therefore activates PK, which will convert glycogen into glucose. Glucose leave cells by facilitated diffusion

Question 17

What is diabetes?

Answer 17

Diabetes is a metabolic disorder caused by the inability to control blood glucose concentration. It is either due to lack of insulin or loss of responsiveness to insulin

Question 18

What is the glucose tolerance test?

Answer 18

After 8-12 hours of fasting prior to test, the patient is given a drink with 75g glucose in it. Blood glucose levels are then monitored at regular intervals or in a single test after 2 hours. It should then come down over time to a normal level showing insulin works

Question 19

How can diabetes be diagnosed?

Answer 19

Test strips allow rapid clinical diagnosis or home monitor of blood glucose levels
Urine dipsticks detect glucose in urine sample
“Pinprick” test fingertip is pricked with needle, the test strip monitor blood glucose levels

Question 20

What is type 1 diabetes?

Answer 20

Insulin dependent diabetes, the body is unable to produce insulin. Lack of insulin results in less glycogen stored in the liver and dangerously high blood glucose level that can lead to serious organ damage

Question 21

How does type 1 diabetes occur?

Answer 21

Genetic causes, could be result of an autoimmune response: the patient’s own immune system destroys the 𝜷 cells in the islets of Langerhans
Develops in childhood usually in a few weeks, with the sign and symptoms being obvious

Question 22

How is type 1 diabetes treated?

Answer 22

It is controlled by having a good diet and exercising, insulin injections
Injection not pill as insulin is a protein and would be broken down in the stomach
The dose of insulin matches the amount of glucose consumed so biosensors and insulin pumps monitor blood glucose levels and adjust dosage of insulin

Question 23

What is type 2 diabetes?

Answer 23

Insulin independent diabetes and it is much more common than type 1
The glycoprotein receptors on the cell surface lost their responsiveness to insulin. It can also be a result of inadequate insulin supply from pancreas

Question 24

How does type 2 diabetes occur?

Answer 24

Starts at older age, develops much slower. Symptoms are less severe so it can remain unnoticed
Over-eating, obesity and lack of exercise are causing increasing numbers of cases in younger people

Question 25

How is type 2 diabetes treated?

Answer 25

Controlled diet and exercise can sometimes reverse type 2 diabetes
Insulin injection sometimes used, other drugs can reduce the amount of glucose released to bloodstream, can also slow down rate of glucose absorption

Question 26

What is the name of the functional units that make up the kidney and span the cortex and the medulla?

Answer 26

A nephron

Question 27

What is the renal capsule?

Answer 27

Renal capsule is a cup shaped structure which surrounds the glomerulus (mass of capillaries). Inner layer is made up of podocytes

Question 28

What are the afferent and efferent arterioles in the renal capsule?

Answer 28

Afferent arteriole is where blood enters, efferent is where blood leaves
Diameter of afferent arteriole is greater than of efferent → hydrostatic pressure builds up in the glomerulus

Question 29

What happens when the blood flows through the renal capsule?

Answer 29

There is a high blood/hydrostatic pressure meaning that small substances pass out e.g. water, glucose, ions, urea in small gaps/pores in capillary endothelium and through basement membrane

Question 30

What is the proximal convoluted tubule and what is its role?

Answer 30

They are a series of loops surrounded by capillaries, its walls are made of epithelial cells which have microvilli. It is like a tiny small intestine
Ultrafiltration is based on the size of the molecule. The filtrate contains urea, and a lot of extremely useful substances that must be reabsorbed

Question 31

What is the loop of Henle?

Answer 31

A hairpin loop spanning from cortex to medulla and back, surrounded by capillaries

Question 32

What happens in the ascending limb of the loop of Henle?

Answer 32

Na+ ions are diffused and actively transported out, so the water potential of the filtrate increases

Question 33

What happens in the descending limb of the loop of Henle?

Answer 33

H2O leaves via osmosis meaning the water potential is at the lowest at the hairpin. A few sodium ions diffuse in

Question 34

What is the distal convoluted tubule and what is its role?

Answer 34

Cells in walls have microvilli and mitochondria → rapid reabsorption
Final adjustments to water and salts in filtrate, control of pH by selective reabsorption

Question 35

What effect does ADH have on the distal convoluted tubule and collecting duct?

Answer 35

ADH affects the water permeability of the cell surface membrane of the epithelial cells in the distal convoluted tubule and collecting duct. More ADH means more water reabsorbed
ADH also makes membrane more permeable for urea, lowering the Ψ further. Even more water passes out from the filtrate and re-enters the blood