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A-Level EDUQUAS Biology > Component 3: Homeostasis and Hormones > Flashcards

Component 3: Homeostasis and Hormones Flashcards

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1
Q

What is meant by negative feedback?

A

A change in a system produces a second change which reverses the first

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2
Q

What is meant by excretion?

A

The removal of metabolic waste made by the body. The mammalian body excretes compounds using 4 excretory organs: kidneys, lungs, skin and liver

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3
Q

What is meant by osmoregulation?

A

The control of the water potential of the body’s fluids (plasma, tissue fluid and lymph) by regulating the water content and there the solute concentration

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4
Q

What is meant by deamination?

A

The removal of an amine group from a molecule. Excess amino acids are deaminated in the liver and the amine group is converted to urea.

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5
Q

What is ultrafiltration?

A

The filtration of small molecules from the blood plasma to the lumen of the nephron under high pressure, occuring at the Bowman’s capsule (filtration under high pressure)

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6
Q

What is selective reabsorption?

A

The uptake of specific molecules and ions from the glomerular filtrate in the nephron back into the bloodstream.

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7
Q

What is secondary active transport?

A

The coupling of diffusion, e.g. of sodium ions, down an electrochemical gradient providing energy for the transport, e.g. of glucose up its concentration gradient

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8
Q

What is the antidiuretic hormone?

A

Hormone produced in the hypothalamus and secreted by the posterior pituitary gland. It increases permeability of the cells of the distal convoluted tubule and collecting duct walls to water, increasing water reabsorption.

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9
Q

What is meant by transamination?

A

An enzyme-catalysed reaction that transfers an amino group to an alpha-keto acid, making an amino acid

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10
Q

What is meant by metabolic water?

A

Water produced from the oxidation of food reserves

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11
Q

What are the 2 definitions of homeostasis?

A
  1. Homeostasis is the maintenance of a constant internal environment by an organism at a set point (environment = tissue fluid that bathes cells which supplies nutrients and removes waste)
  2. Homeostasis is the ability to return to the set point for the factor being controlled
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12
Q

What does the ‘maintenance’ of homeostasis entail?

A
  • maintenance ensures that reactions continue at a constant/appropriate rate, allowing cells to function normally despite external changes
  • factors controlled: temperature, pH, blood glucose and water potential
  • the body is kept in a dynamic equilibrium - changes take place, fluctuating around a set point or norm
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13
Q

What is the response flow chart for homeostasis?

A

INPUT -> change to the system (factor moves away from the set point)
RECEPTOR -> receptors detect the change from the norm (measuring its deviation) and send instructions to a co-ordinator
CO-ORDINATOR -> co-ordinator communicates with one or more effectors which carry out corrective procedures to bring the factor back to normal
EFFECTOR -> muscles and glands that carry out corrective procedures (changes to the system) in order to return it to the set point
RESPONSE -> factor returns to normal

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14
Q

What happens after the response in a negative feedback loop?

A
  • information is fed back to the detectors (receptors in input) and “switched off”
  • this feedback causes the co-ordinator to no longer be altered to the deviation from normal, therefore effectors will stop making the correction
  • this is called negative feedback
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15
Q

What is an example of a negative feedback loop?

A

Control of blood glucose:

  • cells in the pancreas that produce insulin (hormone that lowers blood glucose) and glucagon (hormone that raises blood glucose) are the receptors and the co-ordinator
  • hormones produced control blood glucose level within a narrow range around a set point and directly travel to the liver (effector), bringing changes to restore glucose levels to the norm (response) - insulin converts glucose into glycogen or glucagon converts glycogen into glucose
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16
Q

What is positive feedback?

A

an effector increases the change (movement away from the norm causes a furter movement away from the norm)

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17
Q

What are the 2 example of positive feedback?

A
  1. Labour - oxytocin stimulates contraction of the uterus at the end of pregnancy, contractions stimulate production of more oxytocin, which increases the stimulus
  2. Blood Clotting - when the skin is cut platelets adhere to the cut surface, they secrete signalling molecules which attract more platelets
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18
Q

What are target cells (or organs)?

A
  • target cells are cells that have receptors embedded in the plasma membrane that are complementary in shape to specific hormone molecules
  • only these cells will respond to that hormone
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19
Q

What is meant by egestion?

A

The removal of undigested food material as faeces

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20
Q

What is meant by secretion?

A

The release of useful substances from cells

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21
Q

What are the 2 main functions of the kidneys?

A
  1. Excretion - filtering the blood to remove nitrogenous waste from the body (e.g. urea)
  2. Osmoregulation - the mechanism by which the kidneys regulate the water and solute composition of the blood
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22
Q

Describe the production of urea?

A
  • excess amino acids have to be broken down as they’re toxic, so can’t be stored
  • therefore excess amino acids are deaminated (removal of an amine group from a molecule) in the liver to produce ammonia and pyruvic acid
  • ammonia is then converted into urea and transported in the blood plasma
  • pyruvic acid can be used in respiration as a source of energy or is converted into fat and stored
  • urea is released into the blood and stays there until it’s removed by kidneys and excreted in urine
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23
Q

What happens to the products of deamination?

A

Ammonia is converted into urea, transported in the blood plasma
Pyruvic acid can be used in respiration as a source of energy or converted into fat and stored

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24
Q

What does the type of organic nitrogenous waste depend on?

A

The inhabited environment of the organism - availability of water in the habitat

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25
Q

Describe ammonia (NH3) as nitrogenous waste

A
  • excreted by most aquatic animals (e.g. freshwater fish and Amoeba)
  • gills have a large surface area allowing for ammonium ions (NH4+) to diffuse out rapidly (instantly diluted by water)
  • in soft-bodied invertebrates, ammonia can diffuse out the body surface into the water
  • ammonia molecules are highly toxic, small and extremely soluble in water (diluted easily)
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26
Q

Describe uric acid as nitrogenous waste

A
  • excreted by birds, reptiles and insects
  • non-toxic and almost insoluble in water - excreted as a precipitate with faeces
  • allows them to conserve water or allows birds to be light enough for flight
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27
Q

Describe urea as nitrogenous waste

A
  • excreted by most terrestrial animals
  • less toxic than ammonia (allows it to be transported in a less concentrated form - less urination to remove it)
  • urea excretion enables the animal to lose less water when excreting nitrogenous waste, important for living on land
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28
Q

What does urea and uric acid have in common?

A

Urea and uric acid are adaptations that enable terrestrial animals to excrete nitrogenous waste with minimal water loss

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29
Q

What are the parts to the internal structure of the kidney?

A
  • Renal Artery & Renal Vein
  • Renal Capsule
  • Cortex
  • Medulla
  • Pelvis
  • Ureter
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30
Q

What are the parts of the kidney nephron?

A 
Branch of renal artery
Afferent Arteriole
Glomerulus
Bowman's Capsule
Efferent Arteriole -> capillaries
Branch of renal vein
Proximal convoluted tubule (PCT)
Loop of Henle (ascending and descending limb)
Distal convoluted tubule (PCT)
Collecting duct
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31
Q

Describe the blood vessels in the kidneys?

A
  • each kidney receives blood from the aorta via the renal artery and returns blood to the vena cava via the renal vein
  • the nephron is supplied blood from the afferent arteriole which splits into the glomerulus
  • blood is carried away from the nephron by the efferent arteriole to the peritubular capillaries, consisting of…
    · a peritubular capillary network serving the PCT and DCT
    · a peritubular capillary network running alongside the loop of Henle called the vasa recta
32
Q

Why is there high pressure in the glomerulus when blood arrives from the afferent arteriole?

A
  • contraction of the heart (left ventricle) increases pressure in the renal artery
  • the afferent arteriole has a wider diameter than the efferent arteriole (difference in diameter)
33
Q

What are the 3 layers of the Bowman’s capsule?

A
  1. A single layer of endothelium cells of the capillary walls (contain pores called fenestrae)
  2. The capillary basement membrane (an extra-cellular layer of proteins which is the selective barrier, acting like a sieve between blood and nephron)
  3. Podocytes (squamous epithelial cells that make up the wall of the Bowman’s capsule)
    - processes from each podocytes (pedicels) wrap around a capillary and the gaps between pedicels are called filtrations slits
34
Q

What is the passage of molecules across the Bowman’s capsule from the glomerulus?

A
  • The basement membrane of the capillary network acts as a molecular sieve
    · large molecules (e.g. plasma proteins) and cells (e.g. RBC) can’t cross this barrier
    · any small molecules in the blood can cross the barrier to make up the glomerular filtrate, these include: water, urea, glucose, amino acids, vitamins, sodium ions and salts
  • Ions have a slow passage into the Bowman’s capsule as the basement membrane and podocytes have a negative charge
  • Blood in the efferent arteriole has a low water potential flowing out of the glomerulus as lots of water is lost, leaving a high concentration of proteins and red blood cells
35
Q

Describe selective reabsorption?

A

The reabsorption of glucose, amino acids, ions (Na+ and Cl-), water and vitamins from the filtrate in the PCT/nephron into the blood plasma
- this process is active for Na+ ions and indirectly active for glucose and amino acids

36
Q

Characteristics of the proximal convoluted tubule?

A
  • a large surface area from microvilli
  • numerous carrier proteins embedded in these membranes
  • invaginations called basal channels in the surface facing the basement membrane and capillary
  • cells in the PCT contain numerous mitochondria to provide ATP for active transport
  • capillaries lie close by PCT cells so there is a short diffusion distance between cell and blood
  • tight junctions between cells which attach it tightly to its neighbours
37
Q

How does the PCT regulate pH of the filtrate?

A

Regulates pH of the filtrate by exchanging hydrogen carbonate ions, which increase the pH, with H+ ions that are decreasing the pH

38
Q

What is the process of glucose reabsorption?

A
  1. Na+ ions are pumped out and K+ ions pumped into the PCT cell, both via active transport
  2. There is now a higher concentration of Na+ in the filtrate than inside the cell, therefore Na+ ions move into the cell via facilitated diffusion. The protein only allows Na+ to diffuse if it is with a glucose molecule bringing glucose from the filtrate back into the tissues
  3. A channel protein allows glucose to pass into the blood down its concentration gradient via facilitated diffusion - this is secondary active transport
39
Q

What happens to glucose reabsorption when it doesn’t happen under normal circumstances?

A
  • normal circumstances = the PCT reabsorbs all the glucose from the glomerular filtrate
  • If the concentration of glucose in the filtrate is too high there may not be enough transport molecules to absorb it all, therefore glucose passes through the loop of Henle and is lost in the urine
40
Q

Why may there be a high concentration of glucose in the glomerular filtrate?

A
  1. The pancreas secreted too little insulin (type I diabetes)
  2. The response of liver cells to insulin is reduced because insulin receptors in surface membranes are damaged (type II diabetes or gestational diabetes)
41
Q

What is secondary active transport?

A

The coupling of diffusion (e.g. of Na+ ions) down am electrochemical gradient providing energy for the transport (e.g. of glucose up its concentration gradient)

42
Q

Describe what is being reabsorbed in selective reabsorption in the PCT

A
  • All of the glucose, some of the urea and most of the water and salts are reabsorbed from the glomerular filtrate back into the blood leaving what makes up urine
  • 70% of ions in filtrate are reabsorbed in the PCT (mainly by active transport)
  • 90% of water is reabsorbed into the blood passively by osmosis (at this point) as the reabsorbed ions lower the water potential of the blood
  • 50% of the urea and small proteins are reabsorbed by diffusion as lots of water is lost from the filtrate their concentration becomes much higher, steep conc gradient
  • At the base of the proximal convoluted tubule the filtrate is isotonic with the blood plasma
43
Q

Why can’t the PCT absorb all the water from the filtrate?

A
  • Can’t absorb all the water because excretory products have to be in solution to move through the nephron and out of the body
  • Some is reabsorbed by the distal convoluted tubule, the loop of Henle and 5% is reabsorbed in the collecting duct
  • DCT and collecting duct reabsorb varying volumes of water in response to the body’s needs (control body’s water content to prevent dehydration)
44
Q

Describe the loop of Henle?

A
  • a hairpin, counter-current multiplier (flow in the 2 limbs is in opposite directions and the concentration of solutes is increased)
  • function is to conserve water
  • concentrates salts (NaCl) in the medulla by active transport
  • causes water to be reabsorbed into the blood (vasa recta) from the loop of Henle
  • the ascending limb is impermeable to water, the descending limb is permeable to water
45
Q

What is the role of the loop of Henle in the counter-current mechanism in osmoregulation?

A
  1. Na+ and Cl- are actively pumped out the ascending limb, causing the solute potential in the medulla tissue to increase, water potential decreases
  2. Water moves out of descending limb by osmosis, doesn’t increase water potential of medulla as the water moves directly into the blood of vasa recta (reabsorbed into blood)
  3. Fluid in descending limb becomes more concentrated as is moves down due to loss of water
  4. The filtrate in the descending limb and the tissue fluid of the medulla are most concentrated at the tip of the loop of Henle
46
Q

What does the length of the loop of Henle mean?

A

The relative length of the loop of Henle is adapted to the typical availability of water in the environment of species of a mammal

47
Q

Describe osmoregulation

A

The homeostatic control of water and solute composition of the blood, another example of negative feedback

  • this maintains the concentrations of enzymes and metabolites, so reactions within cells occur at an appropriate rate - as water balance/loss maintains osmotic properties of tissues and fluids
  • occurs in the collecting duct and DCT
  • permeability of the tubes is regulated by ADH
  • negative feedback mechanism
48
Q

What is an endocrine gland?

A

Endocrine glands secrete hormones into the blood (e.g. pituitary and thyroid)

49
Q

What is an exocrine gland?

A

Exocrine glands secrete substances (often enzymes) into a duct
- pancreases is both an endocrine and an exocrine gland

50
Q

What causes a fall in water potential in the blood?

A
  • reduced water intake
  • sweating
  • intake of large amounts of salt
  • tears
  • keeping exchange surfaces moist (e.g. alveoli)
51
Q

Describe the feedback loop of a decrease in blood water potential

A
  • Stimulus: decrease in water potential of blood plasma
  • Detector/Receptor: osmoreceptors in hypothalamus detect the decrease in water potential of blood flowing through it
  • Co-ordinator: posterior lobe of pituitary gland releases ADH
  • Effector: cells of the collecting duct and DCt of the kidney nephron (target cells) become more permeable to water (due to aquaporins fusing with the cell membranes)
  • Response: more water is reabsorbed from the collecting duct into the blood, small volume of concentrated urine is produced
52
Q

Describe the feedback loop of an increase in blood water potential?

A
  • Stimulus: increase in water potential of blood plasma
  • Detector/Receptor: osmoreceptors in hypothalamus detect the increase in water potential of blood flowing through it
  • Co-ordinator: posterior lobe of pituitary gland stops the release of ADH
  • Effector: cells of the collecting duct and DCT of kidney nephron become less permeable to water (due to aquaporins moving out of the membrane)
  • Response: less water is reabsorbed from the collecting duct into the blood, a large volume of dilute urine is produced
53
Q

What is the ADH mechanism?

A
  1. ADH diffuses out of the blood capillaries and binds to the receptor site on membranes of cells of DCT and collecting duct
  2. This causes secondary messengers to travel through the cytoplasm to cause the vesicles containing aquaporins to fuse with the membrane and aquaporins are incorporated into the membrane of the cell increasing permeability to water
  3. Water molecules move into the cell cytoplasm from the lumen of collecting duct/DCT by osmosis down the water potential gradient via aquaporins, and then diffuse into blood capillaries
54
Q

What happens if no ADH is released?

A
  • the reabsorption of water is crucial for maintaining the correct osmotic balance in the body, so if no ADH was released the body would dehydrate in 3 minutes
  • Diabetes Insipidus is when the body doesn’t produce enough ADH
  • the lack of production of ADH means the kidney can’t make enough concentrated urine and too much water is passed from the body
55
Q

What happens if the kidneys fail?

A

The major roles of the kidneys are excretion and osmoregulation, so if the kidneys fail urea builds up to toxic levels and excess water in the body fluids cause reactants for chemical reactions to become diluted, compromising metabolic reactions

56
Q

What are the main causes of kidney failure?

A
  • Diabetes -> high glucose concentrations in the plasma results in glomeruli losing protein into the filtrate, some may link together, triggering scarring, resulting in a condition called glomerulosclerosis
  • High Blood Pressure -> causes damage to glomeruli capillaries preventing ultrafiltration
  • Low Blood Pressure (loss of) -> due to dehydration of blood loss, ultrafiltration can’t happen
  • Infection (e.g. E.coli infection)
  • Auto-immune disease -> the body makes antibodies against its own tissues
  • Crushing Injuries (e.g. road traffic accidents)
57
Q

How can kidney disease be treated?

A

If both kidneys fail, treatments are put in place to reduce conc of toxic waste products and regulate body fluid volumes, these include:

  • low protein diet to reduce urea formation
  • drugs
  • dialysis
  • kidney transplant
58
Q

Drugs to reduce blood pressure: calcium channel blockers

A

Calcium channel blockers dilate blood vessels so reducing the pressure of blood flowing through them

59
Q

Drugs to reduce blood pressure: beta blockers

A

Beta blockers reduce the effects of adrenalin which increases heart rate and thus blood pressure

60
Q

Drugs to reduce blood pressure: ACE and ARBs

A

Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) reduce the effect of the hormone angiotensin which causes blood vessel constriction and thus increased blood pressure inside the blood vessels

61
Q

How are K+ and Ca2+ ion concentrations usually regulated in the body?

A

Concentrations of these ions in the body fluids are usually regulated by absorption in the small intestine and selective reabsorption in the PCTs

62
Q

What drugs regulate K+ concentrations?

A
  • With reduced kidney function, high blood potassium concentration lead to heart arrhythmias (irregular heart rhythm)
  • Glucose and insulin are used to treat high potassium concentration together with intravenous calcium to stabilise the heart muscle membrane
63
Q

What drugs regulate Ca2+ concentrations?

A
  • With reduced kidney function, high blood calcium concentration is linked to an increased risk in heart disease, kidney stones and osteoporosis (a condition that weakens bones, more likely to break)
  • The activity of cells (osteoclasts) that break down bone (causing the calcium to be released into the blood) is decreased using bisphosphonates
  • These drugs cause calcium to accumulate in the bone, reducing calcium concentration in the blood
64
Q

What is dialysis?

A
  • The process of removing nitrogenous waste and excess water from the blood and is used as an artificial replacement for lost kidney function
    There are two main types:
    1. Haemodialysis
    2. Continuous ambulatory peritoneal dialysis (CAPD)
65
Q

What is haemodialysis?

A

Using a dialysis machine which removes the blood to be ‘cleaned’ by using dialysis fluid with a selectively permeable membrane

66
Q

How does haemodialysis work?

A
  • blood is taken from an artery in the arm and passed though thousands of narrow fibres made from selectively permeable dialysis tubing which are surrounded by dialysis fluid
  • pores of tubing allows small molecules only to move into dialysis fluid
  • blood and dialysis fluid run through the machine in opposite directions
  • blood is then returned to a vein in the arm
  • heparin is added to the blood to thin it and prevent it from clotting
67
Q

Why does the blood and dialysis fluid run it different directions?

A

Encourages diffusion out of the blood due to the counter-current mechanism

68
Q

How often haemodialysis have to take place?

A

Carried out for several hours, several days a week

69
Q

Describe the diffusion gradients in haemodialysis?

A
  • dialysis fluid and blood have the same water potential (isotonic)
  • dialysis fluid has a low ion concentration and no urea to create a diffusion gradient
  • ions and urea then diffuse down their concentration gradients out of the blood through the pores of fibres and into dialysis fluid which continues until equilibrium is reaches
  • dialysis fluid has a normal blood glucose concentration, therefore no glucose will diffuse out the blood
  • fresh dialysis fluid constantly passes through the machine in order to maintain the concentration gradients and the used fluid is discarded
70
Q

How does CAPD work?

A
  • uses the peritoneum, a layer of tissue that lines the abdomen which has a rich supply of capillaries and acts as a dialysis membrane
  • a catheter is inserted into the abdominal cavity and dialysis fluid is passed into the abdominal cavity
  • ions and urea pass from the blood in the capillaries into fluid
  • after 40 mins the fluid is drained from the abdomen using gravity into an empty bag
  • the fluid will be changed about 4 times each day
  • liquid retention does occur so potassium ions accumulate in the blood so the patient must drink very little and avoid food high in potassium
71
Q

What are the pros and cons to haemodialysis?

A
  • takes several hours
  • while connected to the machine the patient is unable to carry out other activities
  • regular visits to the hospital for treatment
  • machinery is expensive and in short supply
  • reduced risk of fluctuations in blood volume and content
  • more efficient at removing salts, urea and excess water
  • less risk of infection
72
Q

What are the pros and cons of CAPD?

A
  • less time consuming
  • patient can carry on with normal activities while dialysis takes place
  • can be completed at home, less visits to the hospital needed
  • less expensive machinery needed
  • patient may experience fluctuations in blood volume and content
  • less efficient at removing salts, urea and excess water
  • greater risk of infection of peritoneum as a result of the catheter
73
Q

Kidney transplants

A
  • Donors are either living or have suffered a brain or circulatory death
  • kidney from lives donors generally work quickly and last longer (dialysis is used in the meantime for kidneys from deceased donors as it can take weeks to work)
  • donor and recipient must be ABO blood group compatible as well as a close tissue match
  • high risk donors include those over 50, high blood pressure or diabetes
74
Q

Kidney transplants and immunosuppressants

A
  • patient has to take immunosuppressants after transplant for the rest of their life however rejection make still occur
  • as their immune system is suppressed, they are more susceptible to infection, especially of the urinary tract which can damage the kidney
  • long term, low-dose antivirals may also be used to prevent infection by cytomegalovirus
75
Q

Explain why the blood pressure in the glomerular capillaries is considerable higher than other capillaries?

A
  • high blood pressure in the renal artery due to contractions of the left ventricle
  • difference in diameter of arterioles, efferent is narrow and afferent is wide
76
Q

Explain why it is unusual for protein molecules to appear in the urine?

A

They are too large to pass through the basement membrane, have to be forced through

A-Level EDUQUAS Biology (24 decks)

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