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Biology > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

what does negative feedback regulate

A

the magnitude of correction required to bring a factor back within its normal range - as factor gets close to normal value , level of correction reduces

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2
Q

negative feedback process

A
  • receptor detects stimulus eg. body temp too low
  • coordination system - transfers info between different parts of body
  • effector - carries out response to reverse the initial stimulus
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3
Q

positive feedback process

A
  • the original stimulus produces a response that causes the factor to deviate from the normal range even more
  • enhances the effect of the original stimulus
  • eg. platelets in blood clotting, oxytocin release during childbirth
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4
Q

cell signalling

A
  • coordinates activities of cells, either ones close together or far apart
  • stimulus detected by receptor and converted into message by transduction, message is transmitted to effector to produce a response
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5
Q

paracrine signalling

A

signalling between cells that are close together

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6
Q

endocrine signalling

A

signalling between cells that are far apart - signalling molecule is transported in circulatory system

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7
Q

ectotherm

A
  • organisms that rely on external sources of heat and behavioural activities to regulate their body temperature
  • they have no internal mechanisms to regulate their temperature
  • eg. reptiles, amphibians, fish
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8
Q

advantages of ectotherms

A
  • require less energy intake to regulate temp
  • they can use energy for growth rather than thermoregulation
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9
Q

disadvantages of ectotherms

A
  • very dependent on their environment so can’t live in as many places
  • basking and hibernation makes them vulnerable to predation
  • have to rely on ambush predation rather than sustained
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10
Q

how do ectotherms regulate body temp?

A
  • expose body to sun
  • orientate body to/away from sun
  • hide in burrow
  • alter body shape
  • increase breathing movements
  • hibernation
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11
Q

endotherm

A
  • organisms that control production and loss of heat to maintain their body temp
  • many chemical reactions in the body are exergonic - release energy in the form of heat
  • eg. increasing rate of respiration in the liver to release heat - uses energy intake
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12
Q

endotherms advantages

A
  • don’t rely on environment to regulate temp - can live in more places in the world
  • can be active all year round - no hibernation
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13
Q

endotherms disadvantages

A
  • lots of energy intake used on temperature regulation
  • less energy can be used for growth
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14
Q

what detects changes in body temp in endotherms?

A
  • thermoregulatory centre in hypothalamus monitors blood temp and core temp
    peripheral temp receptors:
  • skin receptors - monitor skin temp
  • ‘early warning system’ - skin is first to change
  • detects changes in temp of extremeties
  • signals sent to brain to initiate behavioural mechanisms to maintain core temp
  • helps hypothalamus react quicker
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15
Q

physiological adaptations of endotherms to regulate temp

A
  • sweat glands in skin: secrete/ don’t secrete sweat
  • lungs, mouth and nose: pant/don’t pant
  • hairs on skin: lie flat/stand on end
  • blood vessels: vasodilation/vasoconstriction
  • liver cells: lower respiration/ increase respiration
  • skeletal muscles: don’t/do shiver
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16
Q

behavioural adaptations of endotherms to regulate temp

A
  • move to shade/sunlight
  • decrease/increase exposed SA
  • remain inactive/move to generate heat in muscles
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17
Q

excretion

A

removal of metabolic waste from the body - by-products or unwanted substances from normal cellular process

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18
Q

what substances need to be excreted?

A

urea - from excess amino acids
carbon dioxide - from cellular respiration
bile pigments - from breakdown of haemoglobin

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19
Q

why do we need to remove carbon dioxide?

A
  • high levels can lead to decrease of pH of blood leading to respiratory acidosis
  • below pH 7.35 (optimum) - difficulty breathing, headache, drowsiness, restlessness, tremors, confusion
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20
Q

why do we need to excrete urea?

A
  • urea is the breakdown of excess amino acids
  • amino acids contain as much energy as carbohydrates but the body cannot store excess amino acids
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21
Q

how is urea formed?

A

Deamination:
- in liver, ammonia - toxic amino group is removed
- amino acid + oxygen = keto acid + ammonia
Formation of urea:
- ammonia reacts with carbon dioxide and urea is formed
- ammonia + carbon dioxide = urea + water
- 2NH3 + CO2 —> CO(NH2)2 + H2O
Urea is excreted from body in urine

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22
Q

where does blood flow through the liver?

A

hepatic portal vein — hepatic artery — central vein in lobule — hepatic vein

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23
Q

hepatic artery

A
  • carries oxygenated blood from heart via aorta to the liver
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24
Q

hepatic portal vein

A

takes blood rich in products from digestion from intestines to liver

25
Q

hepatic vein

A

rejoins to vena cava, takes products of liver metabolism away

26
Q

bile duct

A

carries non-blood products out of the liver into the associated place eg. gallbladder, small intestine

27
Q

hepatocytes

A

cells that make up the liver
carry out hundreds of functions due t their position in the structure of the liver

28
Q

lobule

A
  • repeating unit of the liver
  • 6 sides - made up of tightly packed rows of hepatocytes radiating out from a central vein and surrounded by sinusoids
  • branches of hepatic artery and hepatic portal vein allow blood supply through the central vein for lobules
  • sinusoids - similar to capillaries but more porous endothelium so small/medium proteins can travel through walls
  • arranged in irregular, branching plates surrounding central vein
  • blood passes through sinusoids inwards
29
Q

canaliculi

A
  • channels in lobules carrying bile made by hepatocytes
  • carry bile to bile ductules then to bile duct
  • bile flows from centre of lobule outwards
30
Q

kupffer cells

A
  1. specialised macrophages:
    - destroy worn out red and white blood cells, bacteria and foreign matter arriving from digestive tract
  2. Break down haemoglobin into bilirubin which is excreted in faeces - brown pigment
31
Q

vessel supplying blood to kideny

A

renal artery (branches off aorta)

32
Q

vessel taking blood away from kidney

A

renal vein (connects to vena cava)

33
Q

capsule - kidney

A

dark red outer layer made from collagen and elastin

34
Q

cortex - kidney

A

next layer in from capsule - dark

35
Q

medulla - kidney

A

next layer in from cortex - paler

36
Q

pelvis - kidney

A

next layer in from medulla - whitish

37
Q

nephron

A

tiny functional subunits in kidney
begins in cortex and extends to medulla

38
Q

podocyte cells

A
  • have projecting fingers that wrap closely around capillaries of glomerous
  • as a result tiny slits are left between interlocking podocyte fingers
39
Q

how is blood in the glomerulus separated from the glomerular filtrate?

A
  1. endothelium of blood capillary - small pores
  2. basement membrane - mesh of collagen fibres and glycoproteins - act as filter to prevent molecules with molecular mass over 69000 getting through
  3. podocytes - epithelial cells making up lining of renal capsule
40
Q

ultrafiltration

A
  • occurs in Bowman’s capsule
  • glomerulus supplied with blood through afferent arteriole from renal artery and blood leaves through narrower efferent arteriole - higher pressure in capillaries of glomerulus
  • this forces blood out glomerulus through slits in podocytes which passes through basement membrane to the bowman’s capsule
  • most plasma contents pass through basement membrane but blood cells and many proteins retained in capillary bc too big
  • the filtrate left behind in the glomerulus contains amino acids, water, glucose, urea and inorganic ions
41
Q

how does differences in water pot cause ultrafiltration?

A
  • pressure rises in glomeruler capillaries, increasing water pot of blood plasma compared to the filtrate in Bowman’s capsule
  • water moves down water pot gradient from glomeruler capillaries into Bowman’s capsule
  • due to high conc of proteins left in blood - low water pot which ensures some water stays in blood and water is reabsorbed later
  • total volume of fluid filtered by both kidneys per day in 180dm3
42
Q

adaptations of cells lining proximal convoluted tubule

A
  • 85% re-absorption
  • made up of tightly packed cuboidal cells with microvilli on the inside (increase SA)
  • co-transporter proteins
  • large no of mitochondria for active transport of Na+
43
Q

selective re-absorption in kidney

A
  • most substances in glomeruler filtrate are required by the body so must be re-absorbed
  • capillaries close to outer surface of tubule
  • outer membranes of cells actively transport Na+ ions out cytoplasm to tissue fluid
  • glucose or amino acids enter cells with Na+ by facilitated diffusion
  • glucose and amino acids diffuse into blood capillary
  • re-absorption of salts, glucose and amino acids reduces water pot of cells, increases water pot in tubule
44
Q

The loop of Henle funtion and advantage

A
  • creates high conc of Na+ and Cl- in tissue fluid of medulla
  • this allows water to be reabsorbed from contents of nephron as they pass through collecting duct
  • advantage - concentrated urine produced, conserves water preventing dehydration
45
Q

the loop of henle descending limb

A
  • water permeable
  • water moves out loop of henle to tissue fluid by osmosis, then down conc grad to surrounding capillaries
  • no active transport
46
Q

loop of henle ascending limb

A

lower part:
- fluid very concentrated
- Na+ and Cl- ions diffuse out into surrounding tissue
upper part:
- active transport of Na+ and Cl- ions out nephron into surrounding tissue
- increases water pot of fluid in nephron, decreases water pot outside
- water continues moving out by osmosis

47
Q

distal convoluted tubule

A
  • permeability of walls dependent on levels of ADH
  • cells lining walls have many mitochondria for active transport
48
Q

action of ADH when released

A
  • released from pituitary gland and carried in blood to collecting duct cells
  • binds to receptors on cell membrane to trigger formation of cAMP - second messenger relaying signals received at cell surface receptors to molecules in cells
  • vesicles in cells lining collecting duct fuse with cell membrane in contact with tissue fluid of medulla
  • membranes of vesicles contain aquaporins - when inserted to membrane, makes it permeable to water
  • this makes it easy for water to leave tubules, creating small amount of concentrated urine and maintaining water pot of blood
48
Q

what happens in distal convoluted tubule when body lacks salt?

A
  • Na+ actively pumped out
  • Cl- follow down electrochemical gradient
48
Q

what happens in collecting duct?

A
  • water moves out by osmosis down conc grad
  • urine becomes more concentrated
  • level of Na+ in surrounding fluid increases through medulla and cortex so water can be removed all the way along when body needs to conserve urine
49
Q

negative feedback control when water in short supply

A
  • conc of inorganic ions in blood rises
  • water pot of blood and tissue fluid decreases
  • this is detected by osmoreceptors in hypothalamus
  • they send nerve impulses to posterior pituitary, releases ADH to blood
  • ADH picked up by receptors lining collecting duct, making the walls more permeable to water
50
Q

negative feedback control in excess water

A
  • blood becomes more dilute, water pot higher
  • change detected by osmoreceptors in hypothaluamus
  • nerve impulses sent to posterior pituitary are reduced or stopped
  • release of ADH inhibited
  • little reabsorption of water can take place as walls of collecting duct remain impermeable
51
Q

causes of kidney failure

A
  • type 2 diabetes
  • high blood pressure (hypertension)
  • infection
  • injury
  • drug use
52
Q

what does hypertension leading to kidney failure cause?

A
  • protein or blood in urine - if podocytes or basement membrane in Bowman’s capsule damaged - large plasma proteins and blood cells can pass into filtrate and urine
53
Q

what does kidney failure and urea and mineral ions building up in blood cause?

A
  • loss of electrolyte balance
  • build up of toxic urea in blood
  • high blood pressure
  • weak bones - calcium/phosphorus balance in blood lost
    -pain in joints - abnormal protein build up in blood
  • anaemia - kidney produce hormone that stimulates production of RBC - can cause tiredness and lethargy
54
Q

haemodialysis

A
  • involves dialysis machine - home or hospital
  • blood leaves body and flows through machine - through partially permeable dialysis membranes (mimic basement membrane of bowman’s capsule)
  • dialysis fluid on other side of membrane
  • urea and excess mineral ions leave blood by diffusion
  • blood and dialysis fluid move in countercurrent system to maximise exchange taking place
55
Q

peritoneal dialysis

A
  • takes place inside body
  • dialysis fluid moves into abdomen by catheter
  • urea and excess mineral ions move out blood capillaries to tissue fluid across peritoneal membrane (lining of abdomen), into dialysis fluid
56
Q

dialysis fluid

A
  • plasma levels of glucose so no net movement
  • plasma levels of mineral ions so excess in blood can move down conc grad
  • no urea so much can move out blood down steep conc grad
57
Q

disadvantages of kidney transplant

A
  • risk of body rejecting donor organ
  • antigens on donor differ from those on recipient
  • immune system may recognise this and destroy the new kidney
  • immunosuppressant drugs can be taken for the rest of their lives to counter this but the patient will not respond effectively to other infectious diseases

Biology (16 decks)

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