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Biology Y2 > 6.4: Homeostasis > Flashcards

6.4: Homeostasis Flashcards

1
Q

Define what homeostasis is in mammals and what is involved

A

the maintenance of a constant internal environment. Maintaining optimum conditions within cells - temperature, pH, water potential, concentration of solutes (specifically glucose)

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2
Q

How are conditions like temperature, pH, water potential, concentration of solutes within cells maintained

A

Within the blood plasma which then in turn controls these factors in the tissue fluid and the cytoplasm within cells

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3
Q

Simply describe the process that happens when a stimulus causes a factor (temperature, pH, water potential, concentration of solutes) to increase/decrease

A

Stimulus causes an increase/decrease of a factor from the norm, this stimulus reaches the receptors, then the co-ordinator and then the effector (these two are the correction mechanisms), which results in a response to decrease/increase to get back to the norm

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4
Q

How is homeostasis achieved in a sentence

A

through negative feedback where a change from the norm sets up a corrective mechanism to restore the norm

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5
Q

Explain why it is important that our body temperature and blood pH is maintained

A

Enzymes within our body have an optimum temperature and pH

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6
Q

Explain why is is important that our blood glucose concentration is maintained

A

to maintain water potential of blood and supply glucose to cells as a respiratory substrate

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7
Q

Explain why is is important that our blood water potential is maintained

A

In order to prevent cells losing or gaining water by osmosis

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8
Q

Explain the role of the pancreas in regulating blood glucose concentrations

A

In the pancreas there are a group of cells called Islets of Langerhans, within these are alpha and beta cells which secrete hormones. Beta cells secrete insulin in response to increased glucose concentrations, alpha cells secrete glucagon in response to lowered glucose concentrations

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9
Q

What increases/decreases blood glucose concentration (stimulus) from the norm

A

intake of carbohydrates increases
higher rate of respiration decreases

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10
Q

Describe 3 ways insulin restores normal blood glucose concentration through negative feedback

A

increase rate of glucose uptake into liver cells
glucose -> glycogen (glycogenesis)
glucose -> lipids

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11
Q

Describe 3 ways glucagon restores normal blood glucose concentration through negative feedback

A

glycogen -> glucose (glycogenolysis)
lipids -> glucose
amino acids -> glucose (gluconeogenesis)

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12
Q

Explain the role of insulin and how it decreases blood glucose concentration

A

Insulin binds to specific insulin receptors on the surface of the cells of the liver, muscle, adipose. This causes vesicles containing glucose channel proteins to fuse with the cell surface membrane and so increasing the rate of glucose uptake. Insulin also activates enzymes that convert glucose to glycogen (Glycogenesis)

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13
Q

Explain the role of glucagon/adrenalin and how it increases blood glucose concentration via the second messenger system

A

Glucagon/adrenalin binds to specific glucagon/adrenalin receptors on the surface of liver cells. This causes the receptor protein to change shape (induced fit theory) which activates the enzyme adenylate cyclase (changes shape and now has complementary active site to ATP). Activated adenylate cyclase converts ATP to cyclic AMP. This acts as a secondary messenger, the cAMP activates another enzyme - protein kinase. Activated protein kinase catalyses the conversion of glycogen to glucose (glycogenolysis)

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14
Q

In the second messenger system of glucagon/adrenalin converting glycogen to glucose, what is the first messenger and the second messenger?

A

Glucagon/adrenalin is the first messenger
Cyclic AMP is the second messenger

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15
Q

Explain what triggers the release of glucagon

A

Decreased glucose levels are detected by the alpha cells in the Islets of Langerhans. Vesicles containing glucagon move to the cell surface membrane and release glucagon into the surrounding capillaries

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16
Q

Explain what triggers the release of insulin

A

Increased glucose levels are detected by the beta cells in the Islets of Langerhans. Vesicles containing insulin move to the cell surface membrane and release insulin into the surrounding capillaries

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17
Q

Explain what triggers the release of adrenalin

A

In stress or excitement, adrenalin is produced by the adrenal glands

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18
Q

Describe the role of adenylate cyclase

A

Activated adenylate cyclase converts ATP to cyclic AMP

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19
Q

Describe the role of cyclic AMP

A

cyclic AMP activates the enzyme protein kinase

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20
Q

Describe the role of the enzyme protein kinase

A

Activated protein kinase catalyses the conversion of glycogen to glucose

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21
Q

Explain the cause of type 1 diabetes

A

Due to the body being unable to produce insulin - may be due to an auto immune response whereby the body’s own immune system destroys its own beta cells of the Islets of Langerhans

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22
Q

Explain the cause of type 2 diabetes

A

Due to the insulin receptors on liver/muscle/adipose cells becoming less sensitive to insulin - often linked to obesity and unbalanced diet

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23
Q

Explain how type 1 diabetes can be controlled

A

Insulin injections to match glucose intake

24
Q

Explain how type 2 diabetes can be controlled

A

Regulating intake of carbohydrates
Improving exercise levels

25
What are the 2 functions of the kidney
1- removal of urea (Excretion of nitrogenous waste) 2- osmoregulation (maintenance of blood water potential
26
What is the nephron
The nephron is the functional microscopic structure found in our kidneys that is positioned within the cortex and medulla
27
What is the nephron made up of
Renal capsule Glomerulus, afferent and efferent arteriole Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct
28
Describe the renal capsule in the structure of the nephron
A cup shaped capsule at the start of the nephron that surrounds the glomerulus
29
Describe the glomerulus, afferent and efferent arterioles in the structure of the nephron
A mass of capillaries receiving blood from the afferent arteriole, and blood leaving the glomerulus via the efferent arteriole
30
Describe the proximal convoluted tubule in the structure of the nephron
a section of winding tubule that exits the renal capsule carrying the glomerular filtrate away, surrounded by capillaries
31
Describe the Loop of Henle in the structure of the nephron
a long hairpin loop that descends from the cortex into the medulla, surrounded by capillaries
32
Describe the distal convoluted tubule in the structure of the nephron
a section of winding tubule leading from the Loop of Henle
33
Describe the collecting duct in the structure of the nephron
a tube into which a number of distal convoluted tubules from a number of nephrons empty, it then empties into the pelvis of the kidney
34
What 3 steps are involved in the production of urine and where do each occur
1- Ultrafiltration - occurs between the glomerulus and the renal capsule 2- Selective reabsorption - occurs in the proximal convoluted tubule 3- Conservation of water/concentration of urine - occurs in the loop of Henle and the collecting duct
35
Explain the process of ultrafiltration in the production of urine
High hydrostatic pressure is created in the glomerulus as the efferent arteriole is narrower than the afferent arteriole creating a bottle-neck effect, and also due to ventricular systole. Fenestrations in the endothelium of the capillary allows small substances through. The basement membrane allows only small molecules through acting as a molecular filter. These small solutes pass out of the capillary and into the renal capsule to form the glomerular filtrate - water, glucose, amino acids, inorganic ions and urea. The basement membrane prevents larger solutes like plasma proteins from leaving the capillary
36
Where in the kidney does ultrafiltration occur
Between the glomerulus and the renal capsule
37
Where in the kidney does selective reabsorption occur
Proximal convoluted tubule
38
Explain why selective reabsorption in the kidney is named selective reabsorption
Selection - specific channel / carrier proteins, active transport and/or facilitated diffusion Reabsorption - water and solutes were first absorbed from the lumen of the gut in the ileum, and so are REabsorbed by the PCT
39
Explain how the epithelial cells of the proximal convoluted tubule are adapted for reabsorption (of water and solutes)
1- microvilli (folds in the cell surface membrane) provide a large surface area therefore a greater number of channel/carrier proteins and so increased rate of uptake 2- many mitochondria - provides ATP for active transport 3- single layer of cells - short diffusion pathway
40
By what mechanism are glucose and amino acids reabsorbed in the proximal convoluted tubule
Co-transport with sodium ions
41
Explain the process of selective reabsorption in the proximal convoluted tubule
Sodium ions are actively transported out of the epithelial cells lining the PCT by a Na+/K+ pump into the blood Na+ concentration in these cells is lowered Na+ ions diffuse down a concentration gradient from lumen of PCT into the epithelial cells by facilitated diffusion, glucose/amino acids are cotransported into the cell with the Na+ ions Glucose/amino acids move into blood by facilitated diffusion Water potential increases in lumen, and so water moves into the cell then into the blood capillaries by osmosis down a water potential gradient
42
By the time the glomerular filtrate reaches the end of the proximal convoluted tubule, how much of each molecule in the filtrate is reabsorbed, and what happens to the concentration of urea
80% of the water 100% of glucose/amino acids 66% of Na+/Cl- ions concentration of urea has increased due to reabsorption of water
43
Where in the kidney does conservation of water occur
in the loop of Henle and the collecting duct
44
Describe the permeability of the descending and ascending limb of the loop of Henle and of the collecting duct
Descending limb is permeable to water Ascending limb is permeable to ions but impermeable to water Collecting duct's permeability varies due to the concentration of ADH in the blood
45
By what system does the conservation of water in the loop of Henle occur
Counter-current multiplier system
46
Fully explain how the the conservation of water in the kidney occurs (by the counter-current multiplier system in the loop of Henle)
1- Na+ and Cl- are actively transported out of the filtrate from the ascending limb of the loop 2- Lowering the 🔱 of the tissue fluid of the medulla, causing water to leave the filtrate from the descending limb, by osmosis 3- This process is repeated down the loop, generating a solute gradient through the medulla - highest solute concentration found at the apex of the loop 4- as the filtrate flows down the collecting duct, it constantly meets tissues with a lower 🔱 and so water leaves filtrate down the entire length of the duct, resulting in the production of a small volume of concentrated urine
47
Describe and compare the volume, solute concentration and water potential between the PCT with the apex of the loop of Henle
As the filtrate flows down the descending limb volume decreases solute concentration increases water potential decreases
48
Describe and compare the volume, solute concentration and water potential between the DCT with the apex of the loop of Henle
As the filtrate flows up the ascending limb volume stays the same solute concentration decreases water potential increases
49
What is the importance of the loop of Henle in the kidney
generates a solute gradient in the tissue fluid of the medulla
50
What is the importance of the distal convoluted tubule and the collecting duct
reabsorption of water during osmoregulation
51
What is osmoregulation
control of blood water potential
52
Why does blood water potential increase
intake of water
53
Why does blood water potential decrease
expiration sweating high solute intake
54
What receptors, co-ordinator and effector are involved in osmoregulation
receptors - osmoreceptors located in the hypothalamus co-ordinator - posterior pituitary gland - secretes ADH effector - cells of the DCT and collecting duct
55
Fully explain the process of what happens when the blood water potential increases above the norm and what causes this
high water intake - increases blood water potential osmoreceptors in the hypothalamus swell and release less nerve impulses to the posterior pituitary gland, posterior pituitary gland secretes less ADH resulting in the cells of the DCT and collecting duct to be less permeable to water and so less water is reabsorbed (large volume of dilute urine), thus, blood water potential returns to normal
56
Fully explain the process of what happens when the blood water potential decreases below the norm and what causes this
expiration, sweating, high solute intake - decreases blood water potential osmoreceptors in the hypothalamus shrink and release more nerve impulses to the posterior pituitary gland, posterior pituitary gland secretes more ADH resulting in the cells of the DCT and collecting duct to be more permeable to water and so more water is reabsorbed (small volume of concentrated urine), thus, blood water potential returns to normal

Biology Y2 (16 decks)

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