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Homeostasis Flashcards

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1
Q

What are some physiological factors controlled by homeostasis?

A
  1. Core body temperature
  2. Metabolic wastes, particularly carbon dioxide and urea
  3. Blood pH
  4. Blood glucose concentration
  5. Water potential of the blood
  6. The concentrations in the blood of respiratory gases, oxygen and carbon dioxide
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2
Q

What are three features of tissue fluid that will influence the cell activities?

A
  1. Temperature: low temperatures slow down metabolic reactions; at high temperatures proteins, including enzymes and denatured and cannot function
  2. Water potential: if the water potential decrease, water may move out of cells by osmosis, causing metabolic reactions in the cell to slow or stop; if the water poetical increases, water may enter the cell causing it to swell and maybe burst
  3. Concentration of glucose: glucose is the feel for respiration so lack of it causes respiration to slow or stop, depriving the cell of an energy source; too much glucose may cause water to move out of the cell by homeosis, again disturbing the metabolism of the cell
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3
Q

What is homeostasis?

A

Maintaining a relatively constant internal environment for the cells within the body

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4
Q

What is negative feedback?

A
  • A process in which a change in some parameter such as blood glucose level brings about processes which move its level beak towards normal again
  • An increase in the factor result in something happening that makes the factor decreases and if there is a decrease in the factor then something happens to increase this factor
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5
Q

What does negative feedback involve?

A
  1. A receptor (or sensor) and an effector
  2. Effectors include muscles and glands
  3. The receptor detects the stimuli that are involved with the condition (or physiological factor) being regulated
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6
Q

What is a receptor?

A

-

  • The body has receptors than detect external stimuli and other receptors that detect internal stimuli
  • These receptors send change they detect through the nervous system to a central control in the brain or spinal cord
  • This sensory information is known as the input
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7
Q

What is a receptor?

A
  • The body has receptors than detect external stimuli and other receptors that detect internal stimuli
  • These receptors send change they detect through the nervous system to a central control in the brain or spinal cord
  • This sensory information is known as the input
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8
Q

What is an effector?

A

An organ or tissue that carries out an action in response to a stimulus; muscles and glads are effectors

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9
Q

What is stimuli?

A
  • A change in the environment that is detected by a receptor and which may cause a response
  • Any change in a factor such as change in blood temperature or change in water content of the blood
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10
Q

What is a set point?

A

The real value of a physiological factor that the body controls in homeostasis

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11
Q

What is a hormone?

A

A substance secreted by an endocrine gland, that is carried in the blood plasma to another part of the body where it has an effect

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12
Q

What is thermoregulation?

A
  • The control of body temperature and involves the endocrine and nervous systems
  • The control of core body temperature
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13
Q

How is the heat that mammals generated released?

A
  • By respiration
  • Much of the heat produced by liver cells that have a huge energy requirement for energy
  • The heat they produced is absorbed by the blood flowing through the liver and distributed around the rest of the body
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14
Q

What does the hypothalamus do?

A
  • Control blood temperature
  • Thermorecpetor cells that monitor the temperature of blood flowing through it and also receives information about temperature of surroundings
  • The skin contains receptors and if the core temp decreases, or if the temp receptors in the skin detect a decrease in the temp of the surrounding the hypothalamus sends impulses to activate physiological response
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15
Q

What is the temperature that the hypothalamus records?

A
  • The temperature that the hypothalamus monitors is the core temperature
  • The temperature inside the body that remind very close to the set point of 37 degrees in humans and this temperature fluctuates a little, but is kept within very narrow limits by the hypothalamus
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16
Q

What are the physiological responses to cold weather?

A
  1. Vasoconstriction:
    - Muscles in the walls of the arterioles that supply blood to capillaries never the skin surface contract
    - This narrows the lumens of the arterioles and reduces eh supply of blood to the capillaries so that less heat is lost from the blood
  2. Shivering:
    - The involuntary contraction of skeletal muscles generates heat which is absorbed by the blood and carried around the rest of the body
  3. Raising body hairs:
    - Muscles at the base of hairs in the skin contract to increase the depth of fur so trapping air close to the skin
    - Air is a poor conductor of heat and therefore a good insulator
    - This is not much use in humans but highly effective for most mammals
  4. Decreasing the production of sweat
    - This reduces the loss of heat by evaporation from the skin surface
  5. Increasing the secretion of adrenaline:
    - This hormone from the adrenal gland increases the rate of heat production in the liver
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17
Q

What are some behavioural responses brought about by the hypothalamus in cold environment?

A
  1. Animals respond by curling up to reduce the surface area exposed to the air and by huddling together
  2. We respond by finding a source of warmth and putting on warm clothing
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18
Q

What happens when an increase in environmental temperature is detected by skin receptors or the central thermoreceptors?

A
  • The hypothalamus increases the loss of heat from the body and reduces heat production
    1. Vasodilation:
  • The muscles in the arterioles in the skin relax, a flowing more blood to flow through the capillaries so that heat is lost to the surroundings
    2. Lowering body hairs: muscles attached to the hairs real so they lie flat, reducing the depth of fur and the layer of insulation
    3. Increasing sweat production: sweat glands increase the production of sweat which evaporated on the surface of the skin so removing heat from the body
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19
Q

What are some behavioural responses brought about by the hypothalamus in hot environment?

A
  1. Resting or lying down with the limbs spread out to increase the body surface exposed to the air
  2. We respond by wearing loose fitting clothing, turning on fans or air conditioning and taking cold drinks
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20
Q

What happens when the environmental temperature decreases gradually?

A
  1. The hypothalamus relates a hormone which activates the anterior pituitary gland to release thyroid stimulating hormone (TSH)
  2. TSH stimulates the thyroid gland to secrete the hormone thyroxine into the blood
  3. Thyroxine increases metabolic rate which increases heat production especially in the liver
    - When temperatures start to increase again, the hypothalamus responds by reducing the relates of TSH by the anterior pituitary gland so less thyroxine is released from the thyroid gland
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21
Q

What are two other examples of negative feedback?

A

Osmoregulation and blood glucose control

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22
Q

What is an example of positive feedback?

A
  1. If a person breathes air that has a very high carbon dioxide content, this produces a high concentration of carbon dioxide in the blood
  2. This is seed by carbon dioxide receptors which cause the breathing rate to increase
  3. So the person breathes faster taking in more carbon dioxide, which simulates the receptors even more so the person breathes faster and faster
    - Positive Feedback is also involved in transmission of nerve impulses
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23
Q

What is positive feedback?

A

A process in which a change in some parameter brings about processes that move its level further in the direction of the initial change

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24
Q

What is excretion?

A

The removal of toxic or waste products of metabolism from the body

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25
Q

What happens if more protein is eaten than needed?

A

The excess cannot be stored in the body and so to make use of the energy from the amino acid, the liver removes the amino groups by deamination

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26
Q

Describe deamination

A
  1. In the liver cells the amino group (-NH2) of an amino cid is removed with an extra hydrogen atom
  2. These combine to produce ammonia (NH3)
  3. The keto acid that remains may enter the Krebs cycle and be repaired, or it may be converted to glucose or converted to glycogen or fat for storage
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27
Q

What is deamination?

A

The breakdown of excess amino acids in the liver, by the removal of the amine groups; ammonia and eventually urea are formed from the amine group

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28
Q

Describe ammonia and how is it stopped from causing damage

A
  1. Ammonia is a very soluble and highly toxic compound
  2. In many aquatic animals, such as fish that live in fresh water, ammonia diffuses from the blood and dissolves in the water around the animal
  3. In terrestrial animals, ammonia would rapidly build up in the blood and cause damage and so ammonia is converted immediately to use which is less soluble and less toxic
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29
Q

What are some waste products

A
  1. Urea is the main nitrogenous excretory product of humans
  2. Also produce small quantities of other nitrogenous excretory products, meaning creatine and uric acid
  3. Creatine is made in the liver from certain amino acid and much of this is used in the muscles in the form of creatine phosphate where it acts as an energy store
  4. However some is converted to creaitnine and excreted
  5. Uric acid is made from the breakdown of purines from nucleotides, not from amino acids
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30
Q

What happens to urea?

A
  • Urea diffuses from liver cells into the blood plasma
  • All of the urea made each day must be excreted and an adult produces around 25-30g of urea per day, or its concentration in the blood would build up and become dangerous
  • As the blood passes through the kidneys, the urea is filtered out and excreted
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31
Q

What is a nitrogenous excretory product?

A

An unwanted products of metabolism that contains nitrogen e.g. ammonia urea or uric acid

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32
Q

What is creatinine?

A

A nitrogenous excretory substances produced from he breakdown of creatine

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33
Q

What is uric acid ?

A

A nitrogenous excretory product and by the breakdown of purines

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34
Q

Where does each kidney receive blood from and return blood?

A

The renal artery and reruns blood via a renal vine

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35
Q

What does the ureter do?

A

Carries urine from the kidney to the bladder and then the urethra carries urine to outside the body

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36
Q

What is the whole kidney covered by? What is beneath it?

A

A tough capsule, and beneath is the context and the centra area is made up of a medulla and where the ureter joins is called the pelvis. Mad cup of tiny nephrons and blood vessels

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37
Q

What is the ureter?

A

A tube that carrier urine from a kidney to the bladder

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38
Q

What is the urethra?

A

A tube that carries urine from the bladder to the outside

39
Q

What are nephrons?

A

A kidney tubule

40
Q

What is ultrafiltration? ADD

A

-Involves filtering small molecules, including urea, out of the blood and into the Bowman’s capsule

41
Q

What is the glomerulus?

A

A group of capillaries within the ‘cup’ of a Bowman’s capsule in the cortex of the kidney

42
Q

What is the loop of Henle?

A

The part of the nephron between the proximal and distal convoluted tubules; in humans, some of the loops of Henle are long and reach down into the medulla of the kidney

43
Q

What is the collecting duct?

A

The last section of a nephron from which water can be absorbed back into the blood stream before the flows into the ureter

44
Q

What is the glomerular filtration rate?

A

-

-In humans about 125cm^3min01

45
Q

What is afferent arteriole?

A

Leading towards e.g. the afferent blood vessel leads towards a glomerulus

46
Q

What is efferent arteriole?

A

Leading away from

47
Q

What is ultrafiltration?

A
  • Involves filtering small molecules, including urea, out of the blood and into the Bowman’s capsule
  • filtration on a molecular scale
48
Q

What is selective reabsorption?

A
  • Involves taking back any useful molecules from the fluid in the nephron as it flows along
  • Movement of certain substances from the filtrate back into the blood of the kidney nephron
49
Q

What is the endothelium?

A

A tissue that lines the inside of a structure, such as the inner surface of a blood vessel

50
Q

What are podocytes?

A

One of the cells that makes up the lining of Bowman’s capsule surrounding the glomerular capillaries (tiny finger like projections with gaps in between them)

51
Q

What is the glomerular filtration rate?

A
  • The rate at which fluid passes from the glomerular capillaries into the Bowman’s capsule in the kidneys
  • In humans about 125cm^3min01
52
Q

What affects glomerular filtration rate?

A
  1. Differences in water potential between plasma in glomerular capillaries and filtrate in Bowman’s capsule
  2. Water potential is lowered by the presence of solutes and raised by high pressures
53
Q

What is the water potential in capillaries?

A
  1. Inside the capillaries in the glomerulus, the blood pressure is relatively high, because the diameter of the afferent arteriole is wider than the ferret arteriole, causing a head of pressure in the glomerulus
  2. This raises the water potential of the blood plasma above that of the contents of the Bowman’s capsule
54
Q

What is the concentration of solutes in the blood plasma in the capillaries?

A
  1. The concentration of solutes in the blood plasma of the capillaries is higher than the concentration of solutes in the filtrate in the Bowman’s capsule
  2. This is because whilst most of the contents of the blood plasma filter through the basement membrane and into the capsule, the plasma poetics are too big to get through so stay in the blood
  3. This difference in solute concentration tends to make the water potential in the blood capillaries lower than that of the filtrate in the Bowman’s capsule
55
Q

Which part has higher water potential?

A
  1. Effect of difference in pressure outweighs effect of difference in solute concentration
  2. The water potentials of the blood plasma in the glomerulus is higher than the water potential of the filtrate in the capsule
  3. So water continues to move down the water poet nail gradient from the blood into the capsule
56
Q

Where does most of selective reabsorption occur?

A
  • Proximal convoluted tubule
  • The lining of this part of the nephron is made up of single layer of cuboidal epithelial cells
  • To keep some of substances in glomerular filtrate in body
57
Q

How are the cells in the proximal convoluted tubules adapted for their function of reabsorption?

A
  1. Microvilli to increase the surface area of the inner surface facing the lumen
  2. Tight junctions that hold adjcent cells together so that fluid cannot pass between the cells (all substances that are reabsorbed must go through the cells)
  3. Many mitochondria to provide energy for sodium-potassium pump proteins in the outer membranes of the cells
  4. Co-transporter proteins in the membrane facing the lumen
58
Q

How are blood capillaries organised near the proximal convoluted tubule?

A
  • Blood capillaries are very close to the outer surface of the tubule
  • The blood in these capillaries has come directly from the glomerulus, so it has much less plasma in it than usual and has lost much of its water and many of the ions and other small solutes
59
Q

Describe the movement of sodium ions in the lining of the proximal convoluted tubule

A
  1. The basal membranes of the cells lining the proximal convoluted tubule are those nearest the blood capillaries
  2. Sodium-potassium pumps in these membranes move sodium ions out of the cells and so the sodium ions are carried away in the blood
  3. Lowering the concentration of sodium ions inside the cell so that they passively diffuse into it, down their concentration gradient from the fluid in the lumen of the tubule
  4. However, sodium ions do not diffuse freely through the membrane and can only enter through special co-transporter proteins in the membrane and several types of which transport something else e.g. amino acid or glucose molecule with Na+
60
Q

What is an example of secondary/indirect active transport?

A
  1. The passive movement of sodium ions into the cell down their concentration gradient provides the energy to move glucose molecules, even against a concentration gradient
  2. This movement of glucose, and of other solutes is an example of indirect or secondary active transport, since the energy (as ATP) is used in the pumping of sodium ions, not in moving these solutes
  3. Once inside the cell, glucose diffuses down its concentration gradient, through. transport protein in the basal membrane into the blood
61
Q

What is reabsorbed in the proximal convoluted tubule?

A
  • All of the glucose
  • Amino acids, vitamins and many sodium and chloride ions
  • Urea is reabsorbed (small molecule passes easily through cell membrane and diffuses passively through the cells of pct and into blood due to concentration difference)
  • uric acid NOT reabsorbed and creatinine is actively secreted into the lumen
62
Q

What happens as a result of the removal of these solutes from the filtrate?

A
  1. Removal of these solutes from the filtrate increases its water potential
  2. Movement of solutes into then cell and then into blood decreases the water potential there so a water potential gradient between the filtrate and the blood
  3. Water moves down this gradient through the cells and Ito the blood
  4. The water and reabsorbed solutes are carried away, back into the circulation
63
Q

What is the result of the reabsorption of so much water and solutes from the filtrate?

A

Reduces volume of liquid remaining and only 64% of 125cm^3 entering each minute passes to loop of Henle

64
Q

What happens in the ascending limb?

A
  1. Cells actively transport sodium and chloride ions out of the fluid in the loop, into the tissue fluid
  2. This decreases the water potential in the tissue fluid and increases the water potential of the fluid inside the ascending limb
  3. At the bottom of the hairpin, sodium and chloride ions diffuse out if this concentrated solution in the lower part of the ascending loop
    - All the way up conc of sodium and chloride ions not very different from conc in tissue fluid
65
Q

What happens in the descending limb?

A
  1. Cells permeable to water and to sodium and and chloride ions
  2. As fluid moves down, water from filtrate moves down a water potential gradient into the tissue fluid by osmosis
  3. At the same time sodium and chloride ions diffuse into the loop, down their concentration gradient
  4. So by time fluid reaches both of hairpin contains much less water and more sodium and chloride ions then when it entered from pct
66
Q

What happens the longer the loop of Henle?

A

The more concentrated the fluid can become

67
Q

What is a counter current multiplier?

A
  • An arrangement in which fluid in a adjacent tubes flows in opposite directions, allowing relatively large difference in concentration to be built up
    1. Having the two limbs of the loop running side by side like this with the fluid flowing down in one and up in the other, enables maximum conc of solutes to be built up both inside and outside the tube at the bottom of the loop
68
Q

What happens to the blood as it leaves the Loop of Henle?

A
  1. As fluid flows up the ascending limb it loses sodium and chloride ions so becomes more dilute and increases water potential
  2. Cells of ascending limb and cell lining the collecting ducts are permeable to urea which diffuses into the tissue fluid
  3. Urea is concentrated int the tissue fluid in the medulla
69
Q

What happens in the collecting duct?

A
  • Fluid continue around through the distal convoluted tubule into the collecting duct which runs down into he medulla again
    1. Fluid passes through regions where solute concentration of the tissue fluid is very high and the water potential is very low
    2. Water therefore can move out of the collecting duct by osmosis until the water potential of the urine is the same as the water potential of the tissue fluid in the medulla, which may be much greater than the water potential of the blood
    3. The degree to which this happens is controlled by ADH
70
Q

What is anti-diuretic hormone (ADH)?

A

A hormone secreted form the pituitary gland that increase water reabsorption in the kidneys and therefore reduces water loss in urine

71
Q

How have some animals adapted their kidneys?

A
  1. Small mammals can produce very contrasted urine related to relative thickness of the medulla in their kidneys
    - The max conc of urine we can produce is 4 times the one of our blood plasma and desert rodents can produce 20 times their blood plasma
  2. This is possible because medulla is relatively large and the cells that line the ascending limb of their loops have deep unfolds with many Na+-k+ pumps and cytoplasm filed with many mitochondria, each with many rustle than allow the production of much ATP to provide energy for the pumping of sodium ions into the tissue fluid
72
Q

What is the benefit of the loop of Henle?

A
  • Dip down into medulla
  • Create a very high concentration of sodium and chloride ions in the tissue fluid in the medulla
  • This enable a lot of water to be reabsorbed from the fluid in the collecting duct as it flows through the medulla
  • This allows the production of very concreted urine, which means that water is conserved in the body, rather than lost in urine, helping to prevent dehydration
73
Q

Which limb is permeable to water?

A

Descending limb is permeable to water whereas ascending limb is not

74
Q

Summarise reabsorption in the proximal convoluted tubule

A
  1. Na+-K+ pumps in the basal membrane of proximal convoluted tubule cells use ATP made by the mitochondria. These pumps decrease the concentration of sodium ions in the cytoplasm. The basal membrane is folded to give a large SA for many of these carrier proteins
  2. Very close nearby, the blood plasma, rapidly removes absorbed Na+ and Cl- glucose and amino acids. This helps further uptake from the lumen of the tubule
  3. Microvilli increase SA, helping uptake of solute. Na+ move passively into the cell down its concentration. Ot moves in using protein co-transporter molecules in the membrane which bring in glucose and amino acids at the same time
75
Q

Summarise how the counter current mechanism in the loop of help builds up high contractions of sodium ions and chloride ions in the tissue fluid of the medulla

A
  1. Na+ and Cl- are actively transport out of the ascending limb
  2. This raises the concentration fo Na+ and Cl- in the tissue fluid
  3. This in turns causes the loss of water from the descending limb
  4. The loss of water concentrates Na+ and Cl- in the descending limb
  5. Na+ and Cl- ions diffuse out of this concentrated solution in the lower part of the ascending limb
    (AT or diffusion check?)
76
Q

Describe how water can pass out of the fluid in the collecting duct by osmosis, as the surrounding tissue fluid has a lower water potential

A
  1. The tissue in the deeper layers of the medulla contains a very concentrated solution of Na+ and Cl- and urea
  2. As urine passes down the collecting duct, water can pass out of it by osmosis. The reabsorbed water is carried away by the blood in the capillaries
77
Q

How does the distal convoluted tube and collecting duct behave?

A
  • DCT first half is like ascending limb of LoH and second half like collecting duct
    1. In DCT and CD, sodium ions are actively pumped form the fluid in the tubule into the tissue fluid, from where they pass into the blood
    2. Potassium ions are actively transported into the tubule
    3. The rate at which these two ions are moved into and out of the fluid in the nephron can be varied, and helps to regulate the concentration of these ions in the blood
78
Q

What is osmoregulation?

A
  • The control of water potential of body fluid

- Involves the hypothalamus, posterior pituitary gland and the kidneys

79
Q

How is the water potential of the blood monitored?

A

Specialised sensory neurones in the hypothalamus, osmoreceptors

80
Q

What happens when osmoreceptors detect a decrease in the water potential of the blood below the set point?

A
  1. Nerve impulses are sent from where they terminate in the posterior pituitary gland
  2. These impulses stimulate the release of ADH which is a peptide hormone made up of nine amino acids
  3. Molecules of ADH enter the blood in capillaries and are carried all over the body
  4. The effect of ADH is to reduce the loss of water in the urine by making the kidney reabsorb as much water as possible
81
Q

What are the target cells for ADH?

A

Cells of the collecting duct

82
Q

Where does ADH act?

A

On the cell surface membrane of the collecting duct cells making them more permeable to water than usual

83
Q

How is this change in permeability achieved?

A

By increasing the number of water-permeable channels known as aquaporins in the cell surface membrane of the collecting duct cells

  1. ADH molecules bind to receptor proteins on the cell surface membrane which in turn activate enzymes inside the cells
  2. The cells contain ready-made vesicles that have many aquaporins in their membranes
  3. Once the enzymes in each cell are activated by the arrival of ADH, these vesicles move towards the cell surface membrane and fuse with it, so increasing the permeability of the membrane to water
84
Q

What happens as fluid flows down through the collecting duct?

A
  1. Water molecules move through the aquaporins out of the tubule and into the tissue fluid
  2. This happens because the tissue fluid in the medulla has a very low water potential and the fluid in the collecting ducts loses water and becomes more concentrated
  3. The secretion of ADH has caused the increased reabsorption of water into the blood
  4. The volume of urine which flows from the kidneys into the bladder will be smaller and the urine will be more concentrated
85
Q

What happens when there is an increase in the water potential of the blood?

A
  1. The osmoreceptors in the hypothalamus are no longer stimulated and the neurons in the posterior pituitary gland stop secreting ADH
  2. This affects the cells that line the collecting ducts
  3. The aqauporins are moved out of the cell surface membrane of the collecting duct cells, back into the cytoplasm as part of the vesicles
  4. This makes the cells impermeable to water
  5. The fluid flows down the collecting duct without losing any water so a dilute urine collects in the pelvis and flows down the ureter to the bladder
    - Under these conditions we tend to produce large volumes of dilute urine, losing much of the water we drank in order to keep the water potential of the blood constant
86
Q

How long does in take for ADH to act?

A
  1. The collecting duct cells do not respond immediately to the reduction in ADH secretion by the posterior pituitary gland
  2. This is because it takes some time for the ADH already in the blood to be broken down (half destroyed every 15-20 mins)
  3. Once ADH stops arriving at the collecting duct cells, it takes only 10-15mins for aquaporins to be removed from the CSM and taken back into the cytoplasm until they are needed again
87
Q

Summarise how ADH increases water rebasorption in the collecting duct

A
  1. ADH binds to receptors in the cell surface membrane of the cells lining the collecting duct
  2. This activates a series of enzyme-controlled reactions, ending with the production of an active phosphorylase enzyme
  3. The phosphorylase causes vesicles surrounded by membrane containing water-permeable channels (aqauporins) to move to the cell surface membrane
  4. The vesicles fuse with the cell surface membrane
  5. Water can now move freely through the membrane, down its water potential gradient, into the concentrated tissue fluid and blood plasma in the medulla of the kidney
88
Q

What is the effect of ADH?

A
  1. ADH binds to receptors in the plasma membranes of the cells in the collecting ducts and distal convoluted tubules
  2. Activates a series of reactions ending with eh synthesis of phosphorylase enzyme
  3. Phosphorylase causes vesicles surrounded by membrane continuing water permeable channels to move to plasma membrane
  4. Vesicles fuse with the plasma membrane
  5. Water can now move freely through the membrane, down its water potential gradient into the concentrated tissue fluid and the blood plasma in the medulla of the kidney
89
Q

Describe the structure of the kidney including its associated blood vessels

A
  1. Outer cortex
  2. Medulla
  3. Pelvis
  4. Nephron
  5. Proximal Convoluted tubule
  6. Renal Artery
  7. Renal Vein
  8. Glomerulus
  9. Loop of Henlé
  10. Afferent and efferent arterioles
  11. Capillary network surrounds tubule
90
Q

Describe the mechanisms involved in reabsorption in the proximal convoluted tubule and describer how the epithelial cells of the pct are adapted to carry out this process

A
  1. Active transport out of pct cells/ into blood
  2. Sets up Na+ gradient
  3. Facilitated diffusion
  4. Using protein carrier
  5. Co-transporter from lumen to pct cell
  6. Of glucose/amino acids/ ions
  7. Osmosis
  8. Down water potential gradient
  9. Diffusion
  10. Down a concentration gradient
    Adaptations:
  11. Microvilli
  12. Many mitochondria
  13. Tight junctions
  14. Folded basal membrane
91
Q

Outline with reference to blood glucose concentration the principles of homeostasis in mammals

A
  1. Homeostasis is maintenance of constant internal environment
  2. Irrespective of external environment
  3. Negative feedback
  4. Receptor detects change in blood glucose concentration
  5. Receptors are the alpha and beta cells in the islets of Langerhans
  6. Insulin/glucagon is secreted in response
  7. Action is taken by effector
  8. Restoration of normal/set point
  9. Fluctuation around normal
92
Q

Describe the roles of the endocrine and nervous systems in control and coordination in mammals

A 
Endocrine:
1. Hormones 
2. Chemical messengers 
3. Ductless glands (released into blood)
4. To target organs 
5. Receptors on cell membrane 
6. E.G of hormone and effect 
Nervous:
7. Impulses/action potentials 
8. Neurones 
9. Synapses 
10. Receptor/effector or sensory/motor neurone 
Difference:
1. Endocrine, slow effect, long lasting, widespread effect
93
Q

Describe the part plated by the proximal convoluted tubules in the functioning of the kidneys

A
  1. Selective reabsorption
  2. PCT cell have LSA/microvilli
  3. PCT cells have many mitochondria
  4. Na+ leaves pct cells
  5. By active transport
  6. Na+ concentration in pct cells fall
  7. Na+ diffuse from lumen into pct cell
  8. Through transport proteins
  9. Co-transporter
  10. Of glucose/amino acids/ chloride ions
  11. From pct cells into intracellular fluid
  12. Then diffusion into blood
  13. All glucose reabsorbed
  14. Some water reabsorbed
  15. Some urea reabsorbed
94
Q

Explain how the collecting ducts in the kidneys may reduce the loss of water from the body

A
  1. ADH affects collecting duct
  2. Binds to receptor on membrane
  3. Increase membrane permeability to water
  4. Enzyme controlled reactions
  5. Produces active phosphorylase
  6. Which causes vesicles with water channels
  7. To fuse with plasma membrane
  8. MORE water flows out of collecting duct
  9. Down/along water potential gradient
  10. Then into blood
  11. Urine more concentrated
  12. Negative feedback

Z A Level Biology 2 (18 decks)

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