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Biology Year 13 > Homeostasis > Flashcards

Homeostasis Flashcards

1
Q

define homeostasis

A

the maintenance of stable conditions (within narrow limits) inside the body

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2
Q

define negative feedback

A

the mechanism controlling homeostasis; a change in a parameter leads to the reversal of the change

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3
Q

what must a control system contain

A

a set point: represents desired value around which negative feedback mechanism operates, physiological factors tend to vary over small range either side of set point, this represents normal range

receptors: detect stimuli and deviations from set point

controller (communication pathway): coordinates information from receptors and sends instructions to effectors. Nervous system and hormonal system tend to act as controllers

effectors: produce the changes required to return system to set point

feedback loop: return to set point creates a feedback loop

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4
Q

whats the difference between positive and negative feedback, give eg for positive

A

Positive: enhances original stimulus (attraction of platelets to a site for blood clotting, generation of action potentials, childbirth-oxytocin stimulates uterine contraction)

Negative: inhibits original stimulus

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5
Q

in the context of the control system, state what is meant by the terms A:set point, B: normal range (2 marks)

A

A: the desired value around which negative feedback operates
B: range of values across which a physiological factor caries and negative feedback operates

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6
Q

describe the positive feedback mechanism that controls uterine contractions during labour, and suggest how positive feedback is beneficial during this process (4 marks)

A

oxytocin increases the strength and frequency of contractions,
this increase in contraction causes more oxytocin to be released,
contractions are therefore intensified further and gradually increased,
gradual increase in contractions enables a baby to be born using minimum intensity of contraction

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7
Q

explain why homeostasis relies on negative feedback and not positive feedback (3 marks)

A

homeostasis maintains conditions within a narrow range around an optimal value (set point),
negative feedback reverses any deviation away from set point,
positive feedback increases any change made to a physiological factor

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8
Q

what are ectotherms

A

an animal that depends on external sources of heat to determine body temperature

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9
Q

what is a endotherm

A

an animal that can use internal sources of heat to control body temperatures

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10
Q

how do ectotherms behave when it is too cold

A

basking (expose body to sun)

change body shape (increase SA to gain heat in hot weather)

pressing body against warm ground (to gain heat through conduction)

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11
Q

how do ectotherms behave when it is too hot

A

finding shade or burrowing

change body shape

pressing body against cool stones (to lose heat through conduction)

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12
Q

what does homeostasis in endotherms relies on

A

receptors: peripheral temperature receptors (in skin), temperature-sensitive neurones in the hypothalamus (to monitor core temperature)

Controller: hypothalamus

Effectors: eg sweat glands, erector muscles controlling hair follicles, skeletal muscle, sphincter muscles controlling vasodilation and vasoconstriction in arterioles

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13
Q

how do endotherms respond to warm up

A

less sweat: less heat lost through evaporation of sweat

Hairs raised: a layer of insulating air is trapped

vasoconstriction: less blood flow through capillaries hear skin surface; less heat radiated from the body

high metabolic rate in liver cells: respiration generates more heat

Skeletal muscles contract spontaneously (shivering): heat generated from respiration

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14
Q

how do endotherms respond to cool down

A

more sweat: sweat evaporation requires heat from blood, producing cooling effect

Hairs lie flat on skin: more heat can be lost through radiation

vasodilation: more blood flows through capillaries closer to the skin surface; more heat is radiated from the body

low metabolic rate in liver cells: respiration generates less heat

no spontaneous contractions: no additional heat generated from respiration in muscles

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15
Q

name 4 structures located in the skin that are used by endotherms in thermoregulation (4 marks)

A

arterioles (and shunt vessels),
sweat glands,
hair erector muscles,
fat tissue,

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16
Q

discuss the advantages and disadvantages of ectothermy (4 marks)

A

ADV: lower food requirements (than endo),
greater proportion of energy intake can be used for growth,

DIS: lower activity levels in cold temp (compared to endo),
(therefore) greater risk of predation,
may need to survive winter without food intake (due to lack of activity)

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17
Q

suggest why the food intake of an endothermic species is likely to increase during winter compared to summer months (3 marks)

A

more heat is lost to the environment,
more food provides additional substrates for respiration,
more respiration increases metabolic rate,
more heat is generated (in response to colder winter temps),
some species, especially hibernating species, increase their fat reserves

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18
Q

what is excretion

A

removal of metabolic waste products from the body

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19
Q

give examples that need to be excreted

A

like CO2, urea, bile pigments (formed from haemoglobin broken down by kupffer cells)

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20
Q

describe the structure of a lobule

A

contains hepatocytes, which border sinusoids (vessels in which blood from hepatic artery and hepatic portal vein mix), and bile canaliculi (which drain bile into the gall bladder)

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21
Q

what do the hepatic artery and portal vein transport

A

artery: oxygenated blood from the heart

portal vein: supplies blood glucose, amino acids and fats from small intestine and deoxygenated blood

22
Q

describe deamination in the liver

A

an amino acid can be converted to ammonia (NH3) and a keto acid.
ammonia then converted to urea in the ornithine cycle
(2NH3+CO2–>CO(NH2)2+H20)

23
Q

describe transamination in the liver

A

the conversion of one amino acid to another

24
Q

describe glycogen storage in the liver

A

glucose is converted to glycogen in hepatocytes; a glycogen stores are hydrolysed to glucose when required

25
describe detoxification in the liver
eg hydrogen peroxide (a metabolic waste product) is converted to H20 and O2 by catalase. eg ethanol converted to ethanal by alcohol dehydrogenase
26
list the functions of the liver
deamination, transamination, glycogen storage, detoxification
27
state 2 examples of substances that the liver removes in its role as an organ of detoxification (2 marks)
hydrogen peroxide. ethanol, a (named) drug
28
explain the importance of transamination (2 marks)
(transamination) is the conversion of one amino acid into another, some amino acids are not supplied in an organisms diet,
29
describe the role of enzymes in aspects of liver function (5 marks)
in hepatocytes/intracellular enzymes, enzymes control deamination and the reactions in the ornithine cycle, (glycogen synthase), catalyses glucose to glycogen conversion, (glycogen phosphorylase) catalyses glycogen to glucose conversion, catalase, breaks down hydrogen peroxide, alcohol dehydrogenase, removes ethanol
30
what 2 homeostatic functions does the kidney perform
excretion and osmoregulation (control of water and ion concentration in an organism)
31
what is the kidney structure
blood supplied by renal artery and a renal vein drains each organ. Urine produced passes through ureter to bladder. cortex: the outer region Medulla: inner region renal pelvis: most central region which leads to ureter
32
what 3 different filters prevent cells and large molecules from leaving the blood during ultrafiltration
narrow gaps (fenestrations) between endothelium cells in capillaries podocytes (epithelial cells of capsule that have finger-like projections, which form filtration slits) basement membrane (a mesh of collagen and glycoprotein around the glomerulus)
33
what is the function and how does it work for the bowman's capsule
function: ultrafiltration Water and other small molecules are forced from blood (network of capillaries called glomerulus) into bowman's capsule. Large molecules and blood cells remain in glomerulus. High hydrostatic pressure is created in glomerular capillaries by afferent (incoming) arteriole being wider than efferent (outgoing) arteriole fluid that is filtered into capsule is called glomerular filtrate
34
what is the function and how does it work for the proximal convoluted tubule (PCT)
Function: selective reabsorption All glucose, amino acids, vitamins, hormones are reabsorbed into blood. 85% of water and NaCl is reabsorbed. cells of PCT wall are specialised for reabsorption by: microvilli to increase SA for reabsorption, plasma membrane have many pumps and transport proteins for active transport and facilitated diffusion, many mitochondria to produce ATP for active transport. toxic compounds (eg urea), excess water and some ions remain in the filtrate
35
what is the function and how does it work for the loop of henle
function: establishing a water potential gradient filtrate and blood are isotonic at beginning of loop of henle, by end water potential in filtrate is higher than the medulla, this enables additional water to be reabsorbed from collecting duct down water potential gradient, descending limb is permeable to water, however ascending limb is impermeable to water but Na+ and Cl- ions are actively transported from filtrate to medulla, which raises water potential of filtrate
36
what is the function and how does it work for the distal convoluted tubule
function: additional ion reabsorption additional active transport and reabsorption of ions can occur here
37
what is the function and how does it work for the collecting duct
function: determination of urine concentration and volume water can be reabsorbed, depending on body's needs. permeability of collecting duct (and therefore volume of water that is reabsorbed) is controlled by ADH
38
what happens if water potential gets below the set point
osmoreceptors in hypothalamus detect low water potential, neurosecretory cells (specialised nerve cells) in hypothalamus are stimulated to release ADH from posterior pituitary gland, ADH travels through blood to kidneys ADH binds to receptors on cell surface membrane of cells in collecting duct wall concentration of cycle AMP in these cells is increased cAMP acts as a second messenger and causes aquaporins to be inserted into membrane of cells in collecting duct wall aquaporins are membrane spanning channel proteins that increase permeability of collecting duct wall, they allow water to diffuse through but prevent passage of ions more water is reabsorbed from collecting duct by osmosis urine with high solute concentration is produced water potential of blood is increased
39
what happens if blood water potential rises above set point
same system responds, less ADH produced, less water reabsorbed into blood from collecting duct, large volume of dilute urine is produced
40
if glucose is an excretory product, what is diagnosed and give details
diagnosis: diabetes details: glucose should be reabsorbed in the PCT of nephrons. presence of glucose may indicate diabetes
41
if human chorionic gonadotrophin (hCG) is an excretory product, what is diagnosed and give details
Diagnosis: pregnancy Monoclonal antibodies detect presence of hCG (produced during pregnancy) in urine
42
if anabolic steroids (and other drugs) is an excretory product, what is diagnosed and give details
Diagnosed: use of banned drugs in sports Urine samples are tested using gas chromatography and mass spectrometry
43
Give reasons why kidneys fail
Bacterial infection, kidney stones, uncontrolled diabetes, hypertension, certain inherited diseases
44
Describe and give advantages and disadvantages of kidney transplant
Surgery to replace failed kidney with a donors kidney Adv: if successful, removed need for dialysis treatment Dis: possible transport rejection (patient required immunosuppressants)
45
Describe and give advantages and disadvantages for haemodialysis
A patients blood filtered through a dialysis machine Adv: daily dialysis not required Dis: patients must spend hours in hospitals each week
46
Describe and give advantages and disadvantages for peritoneal dialysis
A patients abdominal membrane (peritoneum) is use as a dialysis membrane Adv: it can be done at home, patients are able to walk and work during dialysis Dis: must be performed daily and required an initial implantation of a tube
47
Outline the likely differences in composition between blood in the renal artery and blood in the renal vein (2 marks)
Renal vein will have lower concentration of urea (and other toxins) Water potential may be different in the 2 blood vessels
48
Cells in lining the proximal convoluted tubule use endocytosis and exocytosis, in addition to active transport and facilitated diffusion, to move molecules across their membranes. Suggest why endocytosis and exocytosis are used (3 marks)
To transport (the few) proteins that have been filtered into the nephron Endocytosis transports proteins from the PCT lumpen into cells in its wall
49
Evaluate the costs and benefits of dialysis and transplant surgery as treatments for kidney failure (6 marks)
Dialysis does not provide a cure, only an improvement in condition for the patient, Successful kidney transplantation provides a cure, However transplant surgery Carrie’s a high risk of organ rejection, Future transplant surgery may use therapeutic cloning to reduce possibility of rejection, Haemodialysis usually requires regular trips to health clinic and is time consuming , Peritoneal dialysis can be carried out by patient while they work, but must be done every day
50
Identify liver lobule under a microscope
Hepatic arteriole has slightly thicker walls then portal venule Hepatocytes surrounds blood, kupffer cells slightly in the blood Bile duct surrounded by hepatocytes and above where blood mixes
51
Give the structure of a nephron
Glomerulus: filters small solutes from blood (round ball at start of nephron) Proximal convoluted tubule: from glomerulus to descending loop Descending loop of Henle: where it descends and goes to ascending Ascending loop of henle: ascends into distal tubule Distal tubule: from ascending to collecting duct Collecting duct: from distal tubule carry’s blood away

Biology Year 13 (12 decks)

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