Homeostasis

Question 1

Can you describe the nature of homeostasis

Answer 1

Need to clarify but:

Maintenance of an internal environment within the restricted limits of an organism.

Question 2

Why is homeostasis important? (4)

Answer 2

Ensures an organism is more independent of changes in external environment

Enzymes are sensitive to changes in ph and temperature - reduces rate/ denatures

Changes to WP of blood and tissue fluid may cause cells to shrink and expand.

Constant blood glucose concentration needed as a glucose source for respiration and ensuring a constant WP of blood.

Question 3

Can you explain how control mechanisms work? (6)

Answer 3

An optimum point
Is monitored by a receptor
A co ordination transfers information to an effector
Effector brings changes to return to optimum point
Feedback mechanism occurs
Receptor responds to stimulus from effector

Question 4

Explain negative feedback loops and an example (3)

Answer 4

Change produced by control system is detected by receptor and turns the system off
INHIBITS FURTHER CHANGE
Regulation of blood glucose

Question 5

Can you explain what positive feedback loops are and give an example (3)

Answer 5

Deviation from optimum results in an even greater deviation from optimum
AMPLIFIES EFFECT
Labour contractions
Influx of Na+ into axon

Question 6

Can you explain how hormones work? (4)

Answer 6

Hormones are secreted from endocrine glands directly into the bloodstream.
Some are steroid but most are proteins.
Are effective in low concentration but have long lasting effects
Specific target cells with specific and complementary cell - surface receptors

Question 7

Why can steroid hormones enter the cell?

Answer 7

Lipid soluble, hence simple diffusion

Question 8

Exocrine glands

Answer 8

Secrete substances (not hormones) into tubes or ducts

Question 9

Endocrine glands

Answer 9

Secreted hormones directly into blood capillaries

Question 10

Is the pancreas exocrine or endocrine? (3)

Answer 10

Both
Protease, lipase
Glucagon and insulin

Question 11

Where are receptors found for water soluble hormones and steroid hormones

Answer 11

Water soluble can not pass by simple diffusion hence OUTSIDE cell
Steroid = lipid soluble = simple diffusion = INSIDE CELL

Question 12

Islets of Langerhams contain

Answer 12

Alpha and Beta cells

Question 13

Hyperglycemic

Answer 13

Too high blood glucose concentration

Question 14

Hypoglycaemic

Answer 14

Too low blood glucose concentration

Question 15

Is regulation of blood glucose concentration a positive or negative feedback loop?

Answer 15

Negative

Question 16

4 ways blood glucose is lowered

Answer 16

Increase uptake of glucose increase in respiratory rate ( glucose is respiratory substrate)
Increased rate of glycogenesis - conversion from glucose to glycogen
Increased rate of conversion of glucose into adipose/fat.

Question 17

Describe insulin action (6 includes 4 ways)

Answer 17

Insulin attaches to specific and complementary glycoprotein receptors on body cells.
Causes glucose transport channel proteins to change shape and open
Also rise in insulin results in fusion of vesicles with cell surface membrane. Vesicles contain many channel proteins, hence once fused more channel proteins available for glucose entry into cells
Glucose enters cells by facilitated diffusion p, which increases rate of absorption
Increases glycogenesis
Increases glucose conversion to fats in fat cells

Question 18

What is glycogenesis

Answer 18

Conversion of glucose to glycogen

Question 19

What is glycogenolysis

Answer 19

Conversion of glycogen to glucose

Question 20

What is gluconeogensis?

Answer 20

Conversion of amino acids and glycerolinto glucose

Question 21

Describe and explain regulation of an increase in blood glucose concentration (hyperglycaemia)

Answer 21

Receptor: Beta cells in Islets of Langerhams (pancreas) are stimulated to release
Regulator: insulin INTO BLOODSTREAM
Insulin attaches to specific and complementary glycoproteins receptors on body cells, which cause glucose transport channel proteins to change shape and open - also fusion of vesicles which contain many channel proteins so more entry points to cell for glucose.
Effector: body cells. Increased uptake of glucose. Increased rate of respiration because glucose is respiratory substrate. Increased rate of glycogenesis (glucose to glycogen). Increased rate of conversion of glucose into adipose/fats in fat cells.
Hence blood glucose concentration decreases.

Question 22

4 ways an increase in blood glucose is regulated (hypoglycaemia)

Answer 22

Glucagon attaching to specific and complementary protein receptors on cell surface membrane of liver cells.
Activating enzymes for glycogenolysis ( glycogen to glucose)
Activating enzymes involved in gluconeogensis (converting amino acids and glycerol to glucose)
Fatty acids used in respiration instead of glucose, hence lowers uptake of glucose for aerobic respiration so higher glucose concentration in blood.

Question 23

State the name of the model by which Glucagon and Adrenaline action occurs

Answer 23

Second Messenger model

Question 24

Second messenger model with glucagon

Answer 24

Glucagon binds to specific and complementary glucagon receptor on cell surface membrane of liver and muscle cells
Causes an enzyme cascade reaction in cells
Adenylate cylase is activated
Active adenylate cylase causes ATP to become cyclic AMP, which acts as a second messenger
Causes protein kinase to become active
Active protein kinase causes glycogen conversion to glucose
Gluconeogenesis also occurs

Question 25

Second messenger model with adrenaline

Answer 25

Adrenaline binds to specific and complementary adrenaline receptor on cell surface membrane of liver and muscle cells Causes an enzyme cascade reaction in cells Adenylate cylase is activated Active adenylate cylase causes ATP to become cyclic AMP, which acts as a second messenger Causes protein kinase to become active Active protein kinase causes glycogen conversion to glucose Gluconeogenesis also occurs

Question 26

Describe and explain including glucagon action how low blood glucose concentration is regulated

Answer 26

Receptor: Alpha cells in islets of Langerhams in pancreas detect low blood glucose concentration, and stimulate the release of glucagon INTO BLOOD. Regulator: glucagon binds to specific and complementary receptors on cell surface membrane of liver and muscle cells. Causes and enzyme cascade reaction. Causes adenylate cylase it become activated. Active adenylate cylase cause ATP to become cyclic AMP, which acts as a second messenger. Causes activation of protein kinase. Active protein kinase converts glycogen to glucose (glycogenolysis) Gluconeogenesis also occurs Effector: body cells and liver cells - glycogenolysis, gluconeogensis, fatty acids used in respiration instead of glucose hence lowers glucose uptake for respiration so HIGHER GLUCOSE CONC IN BLOOD

Question 27

Can you explain roles of pancreas and liver in regulation of blood glucose concentration?

Answer 27

Pancreas -> islets of Langerhams cells are receptors | Liver -> effectors

Question 28

Can you outline factors which influence blood glucose concentration? (3)

Answer 28

``` Diet = glucose absorbed following hydrolysis of other carbohydrates, directly consumed in diet Glycogenolysis = hydrolysis of glycogen (stored in liver and muscle cells) into glucose in SMALL INTESTINE Gluconeogenesis = conversion of amino acids and glycerol into glucose ```

Question 29

How can efficiency of homeostatic models be judged?

Answer 29

How little change there is from the reference point and the speed with which they are restored after disturbance

Question 30

Type 1 diabetes is insulin — and three background points

Answer 30

Dependent Body’s inability to produce insulin Generally from childhood Autoimmune response where body attacks it’s own cells

Question 31

Test for diabetes

Answer 31

High blood glucose concentration | Presence of blood glucose in urine

Question 32

Signs of diabetes

Answer 32

Excessive need to urinate Weight loss Blurred vision

Question 33

Symptoms of diabetes

Answer 33

Tiredness | Increased thirst and hunger

Question 34

Type 2 diabetes is insulin — and six background points

Answer 34

Independent Due to glycoproteins on body cells damaged or lose their responsiveness Or inadequate supply of insulin from pancreas Generally +40 years Due to obesity and poor diet is now seen in adolescents

Question 35

Control of type 1 diabetes (3 points)

Answer 35

Injections of insulin matched to glucose intake Too much insulin injected causes too low blood glucose concentration and then lose consciousness so biosensors used to control

Question 36

Control of type 2 diabetes

Answer 36

Regulation of carbohydrate intake and more exercise | Some drugs slow absorption of glucose

Question 37

Describe the structure of the mammalian kidney (6)

Answer 37

Fibrous capsule - outer membrane that protects the kidney Cortex - lighter coloured outer region made up of Bowman/ Renal capsules Medulla - made up of loops of Henle and collecting ducts Renal Pelvis - funnel shaped cavity that collects urine into ureter Renal artery - supplies blood to kidney Renal Vein - returns blood to heart via vena cava

Question 38

Describe the structure of a nephron (7)

Answer 38

Bowman’s/Renal capsule - contains GLOMERULUS (mass of blood capillaries). Inner layer made up of PODOCYTES Proximal Convoluted tubule - epithelial cells in its walls which contain microvilli and surrounded by many blood capillaries Loop of Henle Distal Convoluted tubule - epithelial cell walls but no microvilli and less capillaries Collecting duct Afferent artieriole is THICKER to each nephron Efferent arterioles

Question 39

Which is on outside in cross section of kidney medulla or cortex? And what does it contain

Answer 39

Cortex (bowmans capsule on outside)

Question 40

Draw and label diagram of nephron

Answer 40

Yes

Question 41

Where, why and how is urea formed

Answer 41

In the liver Ammonia is very soluble and toxic - urea is less soluble and less toxic Deamination due to excess protein consumption releases NH2 (amine) which is converted into ammonia NH3. Ammonia is then converted into urea and CO2 in the liver.

Question 42

Excretion is

Answer 42

Removal of toxic substances processed by cells eg: urea and CO2

Question 43

Ejestion is

Answer 43

Removal of undigested matter

Question 44

How is the liver involved with urea

Answer 44

Production

Question 45

How are the kidneys involved with urea?

Answer 45

Removal

Question 46

State term that describes the formation of glomerular filtrate

Answer 46

Ultrafiltration

Question 47

What is the glomerular capillaries separated from lumen of bowmans capsule by?

Answer 47

``` Endothelium of capillary has fensters! Basement membrane (not an actual membrane) mesh of collagen and glycoproteins Epithelium of Bowmans capsule with specialised cells called podocytes ```

Question 48

Podocytes structure and function

Answer 48

Many finger like projection Extensions wrap aroudn glomukar capillaries and interlink with other podocyte extensions Leave filtration slits for filtered fluid to pass through

Question 49

Basement membrane structure and function

Answer 49

Mesh of fibres contains glycoproteins and collagen | Negative charges on fibres repel plasma proteins that pass through endothelium of capillary.

Question 50

Endothelium of capillary structure and purpose for ultrafiltration in kidney

Answer 50

Festers that allow small molecules to pass (plasma proteins too!) but not RBC

Question 51

Describe and explain ultrafiltration to produce glomerular filtrate

Answer 51

Diameter of afferent ARTERIOLE is greater than diameter of the efferent arteriole resulting in build up of hydrostatic pressure, which forces small molecules out through 3 layers: endothelium of capillary, basement membrane and then epithelium of capillary. Endothelium of capillary has fensters that prevent RBC not plasma proteins Basement membrane has negative charges that repel plasma proteins. Epithelium of bowmans capsule contains podocytes with finger like extensions that interlink with each other leaving filtration slits allowing filtered fluid to enter renal capsule. As water AND water soluble substances leave blood, water potential decreases hence osmosis back into capillary HOWEVER hydrostatic pressure is greater than osmotic pressure so net movement of fluid from glomerulus into renal capsule

Question 52

Damage to filtration process due to high BP. Causes and how damage affects filtration process.

Answer 52

High BP damages capillaries, widens podocyte slits and damages the basement membrane hence allows plasma proteins and RBC to enter bowmans capsule ``` Diabetes Stress Obesity CHD Cholesterol -> narrows artery ```

Question 53

Glomerular filtration rate is affected by two things

Answer 53

Damage to filtration process | Osmosis the wrong way but hydrostatic pressure is greater than osmotic.

Question 54

Glomerular filtrate contains? What is left behind in capillary?

Answer 54

``` Water Amino acids Glucose Urea Mineral ions ``` Left = RBC, plasma proteins, some H2O

Question 55

When looking at microscopic image/diagram of cortex of kidney what to look out for?

Answer 55

Glomerulus cluster of many tiny cells surrounded by capsule Outside is bowmans capsule Proximal convoluted tubules cells have microvilli Distal convoluted tubules don’t have microvilli Small round circles = may be capillaries

Question 56

Five adaptations of proximal convoluted tubules and explain

Answer 56

Microvilli provide a large surface area for efficient absorption (by Fick’s law) of WANTED MOLECULES Numerous mitochondria - AEROIBIC RESPIRATION producing ATP needed for Na+/K+ pump. Closeness of blood capillaries - short diffusion PATHWAY; increases efficiency by Fick’s law Contains co - transport carrier proteins - carries TWO molecules via FCAILLITATED DIFFUSION; one Na+ and one glucose/ amino acid Cells tightly packed together means that no fluid can pass between cells and all substances reabsorbed must pass through PCT epithelial cells

Question 57

How does solute concentration affect water potential in glomerulus and Bowmans capsule? Resulting movement of water is?

Answer 57

Plasma proteins are repelled by negative charges of basement membrane and hence stay in capillaries. Solute concentration in blood plasma is higher than that of filtrate in Bowmans capsule Water potential of blood plasma is lower than that of filtrate Hence water into capillaries BUT HYDROSTATIC PRESSURE GREATER THAN OSMOTIC PRESSURE SO NET MOVEMENT OF FLUID INTO BOWMANS CAPSULE

Question 58

Where is most water re- absorbed in the nephron?

Answer 58

Proximal convoluted tubule

Question 59

What is selectively re-absorbed in the proximal convoluted tubule?

Answer 59

``` Water Na+ K+ Cl- 50% urea ```

Question 60

Why is urea selectively re-absorbed in the proximal convoluted tubule

Answer 60

Small molecule hence passes through plasma membrane even though urea is polar. Concentration of urea in filtrate is higher than capillaries causing diffusion back into blood from Bowmans capsule

Question 61

Purpose of tight junctions in epithelial cell of proximal convoluted tubule

Answer 61

Prevents water and mineral ions from escaping to adjacent cells

Question 62

Describe and explain re-absorption in cells of the proximal convoluted tubule

Answer 62

Sodium ions actively transported out of cells into tissue fluid via Na+/K+ pump in BASAL membrane, which creates a deficit of Na+ ions in PCT cell allowing for Co - transport of sodium and glucose or amino acids. Sodium ions diffuse down concentration gradient via facilitated diffusion. Creates an electroptoential gradient which pulls in glucose or amino acid molecule at the same time against its concentration gradient. One Na+ and one glucose/amino acid enter epithelial cell of PCT from PCT lumen. Increase in glucose and amino acid inside cell increases solute concentration and hence lowers water potential compared to lumen of PCT so water enters cell via osmosis. Glucose and amino acid then leave epithelial cell by facilitated diffusion through a channel protein into capillaries.

Question 63

What is the function of the loop of Henle?

Answer 63

To maintain a gradient of sodium ions in the medulla using a counter current multiplier- increases solute concentration in the interstitial region

Question 64

Adaptations of loop of Henle (x2)

Answer 64

Cells contains lots of mitochondria for aerobic respiration to produce ATP used for Na+/K+ pump. Many capillaries wind around loop of Henle for a shorter diffusion pathway, which by Fick’s law increases efficiency

Question 65

Loop of Henle uses a — — — and why is it useful?

Answer 65

A counter current multiplier Two limbs of loop run side by side with fluid moving in opposite directions enables maximum concentration gradients to be built up both inside and outside tube, hence a greater exchange if substances than if limbs contained fluid that flowed in the same direction

Question 66

Which limb of the loop of Henle is permeable to salts and not water?

Answer 66

Ascending

Question 67

Which limb of the loop of Henle is permeable to water but not to salts?

Answer 67

Descending

Question 68

How is a concentration gradient of sodium ions maintained by the loop of Henle? (5)

Answer 68

Na+ and Cl- are actively transported out of ascending limb using ATP from mitochondria in cells of Henles wall. This raises the concentration of solute in the interstitial region, and creates a lower water potential in this region. Due to thick water impermeable walls of ascending limb, very little if any water escapes from ascending limb. Causes loss of water via OSMOSIS from descending limb (higher water potential to lower water potential in the interstitial region). Some Na+ and Cl-enters descending limb via diffusion. Water potential down descending limb decreases. Hence Na+ and Cl- concentration increases at the bottom of descending limb. Na+ and Cl- diffuse out of via facilitated diffusion at bottom of ascending limb as glomerulus filtrate is now concentrated. Due to diffusion of ions out of filtrate water potential of filtrate increases up the ascending limb.

Question 69

Summary of water potential changes of filtrate up and down loop of Henle

Answer 69

Down descending limb water potential decreases Up ascending limb water potential increases

Question 70

What happens to concentration of filtrate and volume down descending limb of loop of Henle?

Answer 70

``` Concentration of glomerular filtrate increases (less water!) Volume decreases (less water!) ```

Question 71

What happens to concentration of filtrate and volume up ascending limb of loop of Henle?

Answer 71

Concentration of glomerular filtrate decreases (ions move out!) Volume is constant (no loss of water!)

Question 72

Length of desert animals loop of Henle compared to humans and why?

Answer 72

Longer Longer cross current multiplier More concentrated glomerular filtrate formed More water reabsorbed via osmosis into the bloodstream from loop of Henle

Question 73

Briefly explain role of distal convoluted tubule and collecting duct in the reabsorption of water.

Answer 73

Very little but if necessary and regulated by ADH

Question 74

State components and roles (brief) of osmoregulatory system?

Answer 74

Receptor - hypothalamus and posterior pituitary gland releases ADH into blood Coordinator - ADH levels in blood Effector - collecting ducts of kidney Distal convoluted tubule

Question 75

What to talk about when “how does ADH level affect urine”?

Answer 75

volume and concentration of urine

Question 76

How does high ADH levels in blood affect urine?

Answer 76

Small volumes of concentrated urine produced

Question 77

How does low ADH levels in blood affect urine?

Answer 77

Large volumes of dilute urine produced

Question 78

High ADH levels in blood mean body wants to lose or retain water?

Answer 78

Retain

Question 79

Low ADH levels in the blood mean body wants to lose or retain water?

Answer 79

Lose

Question 80

Osmoregulation definition

Answer 80

Control of water potential of the blood

Question 81

Process that occurs when low water potential of blood is detected. Include how it is detected and hormone actions and volumes and concentration of urine.

Answer 81

Receptor : Osmoreceptors in hypothalamus shrink and released ADH to posterior pituitary gland from which ADH is released into the blood. Coordinator: ADH levels in blood increase Mechanism: more ADH binds to specific and complementary receptors on plasma membrane of cells lining DCT and collecting tube. Causes activation of phosphorylase enzyme Phosphorylase causes vesicles containing aquaporins ( water permeable protein channels) to fuse with plasma membrane. Hence plasma cells are more permeable to water as more aquaporins on plasma membrane. Water can now move freely from collecting duct via osmosis through aquaporins into plasma membrane, down its water potential gradient and re-enter blood. Effector: cells of DCT or collecting tube become more permeable, hence water enters blood stream via osmosis and small volume of concentrated urine formed. Therefore INCREASE in water potential of blood

Question 82

Why do osmorecpetors shrink when low water potential of blood is detected?

Answer 82

Osmorecpetor has a higher water potential, hence water leaves via osmosis into blood.

Question 83

Water potential in blood may change due to

Answer 83

Little/more consumption of water Sweating Uptake of a large amount of ions

Question 84

Process that occurs when high water potential of blood is detected. Include detection but not hormone mechanism. Include volume and concentration of urine.

Answer 84

Receptor: osmoreceptors in hypothalamus increase in volume and decrease release of ADH, which is released into bloodstream from the posterior pituitary. Coordinator: ADH level in blood decreases, hence less binding to specific and complementary receptors on plasma membrane of cells lining DCT and collecting duct. Effector: cells of DCT and collecting duct less permeable to water and hence a large volume of dilute urine is produced. Therefore DECREASE in water potential of blood.