Homepstatis- Paper 2

Question 1

Define homeostasis

Answer 1

The maintenance of a stable/constant internal environment
The ability to respond to changes and maintain organisms’s cells, tissues and organ systems in a balanced equilibrium around an optimum point of

Question 2

What is the benefit of maintaining a constant internal environment and why is this important

Answer 2

Enzyme controlled biological reactions can take place at a constant optimum rate
Organism that control this are more independent as they have a greater geographical range so can colonise more habitats and ecosystems
Also have a greater chance of finding food, shelter and mates

Question 3

Control mechanisms pathway

Answer 3

Receptors—> sensory neurones—> CNS—> motor neurones—> effectors

Question 4

Negative feedback definition

Answer 4

Negative feedback means that there is an increase/ decrease from the set point, the opposite effect is instigated- produces a response that returns the value to the norm

Question 5

Positive feedback definition

Answer 5

Occurs when a deviation from an optimum causes even greater deviation from the normal

Question 6

What are endotherms

Answer 6

Maintain body temperature by both physiological and behavioural means

Question 7

What are ectotherms

Answer 7

Maintain body temperatures by behavioural means only- exposing themselves to the sun, taking shelter and gaining warmth from the ground.

Question 8

The temperature control system in endotherms - hot and cold

Answer 8

Monitored by receptor in the hypothalamus

Hot:
- a rise in blood temperature is detected by thermo receptors in the heat loss centre
- the heat loss centre sends nerve impulses to the sphincter muscles in the skin arterioles and to the sweat glands. Vasodilation and increased sweating result. The blood is cooled and the core temperature falls.

Cold:
- a fall in blood temperature is detected by thermoreceptors in the heat gain centre
- the heat gain centre stimulates vasoconstriction and shivering. The hairs on the skin are pulled upright.
- thermoreceptors are also found in the skin which will detect a change in skin temperature and send nerve impulses via the autonomic nervous system to the hypothalamus.

Question 9

Describe how a hormone works

Answer 9

• produced by pancreas glands, which secrete directly into the blood
• carried in the blood plasma to target cells
• receptors are complementary shape to the hormone
• hormones bind to specific receptors only on the target cells which have the complementary receptor
  -they are effective in small quantities but often widespread and have long lasting effects

Question 10

Describe the pathway of blood glucose regulation

Answer 10

Islets of langerhans- beta cells- capillaries into which hormones are secreted- pancreas has glucose receptor cells which control glucose concentration

Question 11

What is the range for blood glucose concentration

Answer 11

80-100mg 100cm-3

Question 12

Name the classifications of high and low blood glucose concentration

Answer 12

Hypoglycaemia- very low levels
Hyperglycaemia- very high levels of

Question 13

What are the endocrine cells of the pancreas called and what do they secrete specifically - what is their relationship

Answer 13

Islets of langerhans
Alpha cells secrete glucagon
Beta cells secrete insulin
They are antagonistic

Question 14

Describe the process behind insulin secretin

Answer 14

Insulin is a peptide hormone and is synthesised and secreted by beta cells in the pancreas
Insulin reduces blood glucose levels to a normal range

1. Insulin binds to complementary receptors on the cell surface membrane of target cells
2. This controls the uptake of glucose by regulating the inclusion of glucose carrier proteins in the surface membranes of target cells (striated muscle cells and adipose tissue)
3. Insulin also activates enzymes hat stimulate the conversion of glucose to glycogen (glycogenesis). this therefore decreases blood glucose

Off spec: GLUT1 channel proteins are found on all cell membranes

Question 15

Describe the process behind glucagon secretion

Answer 15

Synthesised and secreted by alpha cells in the pancreas- aim is to increase blood glucose levels to a normal range

1. Glucagon binds to receptors on the cell surface membrane of target cells
2. Activate enzymes involved in the hydrolysis of glycogen to glucose (Glucogenolysis)
3. Activates enzymes involved in the conversion of glycerol and amino acids into glucose (gluconeogenesis)

Question 16

Explain the action of glucagon

Answer 16

• works by activating enzymes
• hydrolysis of glycogen to glucose (Glycogenolysis)
• gluconeogenesis

Question 17

Describe the role of glycogen formation and its role in lowering blood glucose levels

Answer 17

• glucose concentration in the cell/liver falls
  -below that in blood
• creates glucose concentration diffusion gradient
• glucose enters cell by facilitated diffusion via carrier proteins

Question 18

Describe how blood glucose levels can be increased using hormones

Answer 18

• release of glucagon from alpha cells
• leads to the formation of glucose in liver cells
• from non-carbohydrates

Question 19

Describe what happens after a meal

Answer 19

• glucose is absorbed from the ilium into the hepatic portal vein
• blood glucose concentration increases, which is detected by the pancreas
• pancreas secretes insulin from its beta cells
• insulin causes glucose to be taken up by the liver and converted into glycogen
• this reduces blood glucose, which is detected by the pancreas which stops secreting insulin
• if the glucose level falls too far this is detected by the pancreas
• pancreas now secretes glucagon from its alpha cells
• glucagon causes the liver to hydrolyse some of its glycogen store to glucose, which diffuses into the blood via facilitated diffusion
• this increases blood blood glucose and pancreas stops secreting glucagon

Question 20

Describe the second messenger model of hormone action

Answer 20

Adrenaline is a hormone released by adrenal glands which also increases blood glucose levels

1. Adrenaline and glucagon both bind to specific transmembrane protein receptor on the surface of the target cell membrane- they are called the first messenger
2. A hormone- receptor complex is formed (causing the receptors protein to change tertiary structure)
3. The hormone receptor complex activates adenylate cyclase (an enzyme inside the cell that results in the conversion of ATP into cyclic AMP that acts as second messenger)
4. The second messenger causes a series of chemical changes that produce the required rapid response
5. The CAMP is the second messenger and activates protein kinase enzymes which produce a cascade of chain reactions that catalyse the conversion of glycogen to glucose

Question 21

Glucagon definition

Answer 21

Hormone that causes hydrolysis of glycogen to glucose

Question 22

Glycogen definition

Answer 22

Energy storage carbohydrate found in liver and muscles

Question 23

Glycogenolysis definition

Answer 23

Glycogen hydrolysed to glucose

Question 24

Glycogenesis definition

Answer 24

Glucose to glycogen

Question 25

Gluconeogenesis definition

Answer 25

Glucose from amino acids and glycerol

Question 26

What is diabetes caused by

Answer 26

Failure of glucose homeostatis

In both types there is a very high blood glucose concentration after a meal so active transport pumps in the proximal convoluted tubule of the kidney can’t reabsorb it all from the kidney filtrate- much of the glucose is excreted in urine

Question 27

Type 1 diabetes

Answer 27

Insulin- dependant diabetes

A severe insulin deficiency due to autoimmune killing of beta cells either caused by a virus or faulty gene

Question 28

Type 2 diabetes

Answer 28

Non-insulin dependant diabetes

Insulin is produced but the insulin receptors in the target cells are unresponsive, so insulin has no effect

This is sometimes described as having a lack of sensitivity to insulin

Question 29

Type 3 diabetes off spec

Answer 29

Gestational diabetes

Question 30

Symptoms of diabetes

Answer 30

High thirst due to osmosis of water from cells to the blood, which has a low water potential
Large volumes of urine production due to excess water in the blood
Poor vision due to osmotic loss of water from the eye lens
Tiredness due to loss of glucose in urine and poor uptake of glucose by liver and muscle cells
Muscle wasting dye to gluconeogenesis caused by increased glucagon

Question 31

What are the three basic functions of the kidney

Answer 31

1. Forms glomerular filtrate through ultrafiltration
2. Reabsorption of glucose and water through proximal convoluted tubule
3. Osmoregulation- maintaining concentration gradient in the medulla by the loop of Henle

Question 32

What is a fibrous capsule

Answer 32

An outer membrane that protects the kidneys

Question 33

What is a cortex

Answer 33

A lighter coloured outer region made up of renal capsules, convoluted tubules and blood vessels

Question 34

What is a medulla

Answer 34

A darker coloured inner region made up of loops of henle, collecting ducts and blood vessels

Question 35

What is a renal pelvis

Answer 35

A funnel shaped cavity that collects urine into the ureter

Question 36

What is a ureter

Answer 36

A tube that carries urine to the bladder

Question 37

What is a renal artery

Answer 37

Supplies the kidney with blood from the heart via the aorta

Question 38

What is the renal vein

Answer 38

Returns blood to the heart via the vena cava

Question 39

Describe Osmoregulation

Answer 39

Osmoreceptors in the hypothalamus of the brain detect the fall in water potential
ADH is secreted into the capillaries by the posterior pituitary gland
ADH travels to kidneys in blood and increases the permeability of the cells of the distal convoluted tubule and collecting duct to water
ADH works by causing vesicles found with aquaporin proteins,to fuse with the cell surface membranes of cells of the distal convoluted tubule and collecting duct

Question 40

The formation of glomerular filtrate

Answer 40

Blood enters the kidney through the renal artery, which branches into one million tiny arterioles, each of which enters a renal capsule

Affront arteriole is wider, efferent arteriole is narrower- creating a high hydrostatic pressure
Ultrafiltration of small molecules, urea, water, mineral ions pass through basement membranes, acting as a filter
Blood cells and proteins are too large so stay behind
Fluid travels through fenestrations in capillary walls then through podocytes into bowman’s capsule

Question 41

What can’t be passed through fenestrations, provide small facts about the filtrate

Answer 41

Blood cells and large plasma cannot pass through
Filtrate can pass out of the glomerulus due to the holes of the capillaries, through the connective tissue and through the spaces between the branches of the podocytes- nearly 85% of filtrate is reabsorbed back into the blood

Question 42

Maintaining a gradient of sodium ions in the medulla by the loop of Henle

Answer 42

Descending limb is narrow and highly permeable to water
Ascending limb is wider and impermeable to water

Na+ actively transported out for ascending arm, impermeable to water, using ATP and into interstitial fluid, which lowers the water potential
Water moves out of descending limb, permeable to water and into blood capillaries by osmosis. Water potential decreases further down the medulla, urea is concentrated in the filtrate

Question 43

The reabsorption of glucose and water by the proximal convoluted tubule

Answer 43

• Na+ actively transported out of the cell lining the PCT and into the blood
• creates a concentration gradient of Na+ between the lumen of the PCTand the cell lining the PCT
• Na+ diffuses into cell from the lumen of the PCT through the same protein by facilitated diffusion (Co-transport)
• glucose moves into cell from the lumen of the PCT against its concentration gradient
• glucose diffuses into blood, glucose removed from filtrate

Question 44

Reabsorption of water by the distal convoluted tubule and the collecting ducts

Answer 44

Distal convoluted tubule:
Makes final adjustments
Reabsorbed water and salts
Changes permeability pf wall
Collecting duct:
Lower water potential down the medulla
Water moves out collecting duct via osmosis
Water then reabsorbed into the blood, everything left in the collecting duct becomes urine
Permeability can change