Kidney and Homeostasis C3

Question 1

define homeostasis

Answer 1

maintenance of a constant internal environment within a living organism, irrespective of external conditions

Question 2

why is homeostasis important?

Answer 2

so that cells can function efficiently and independently of fluctuations in the conditions of the external environment

therefore cells are provided with constant conditions, even during different levels of activity of the organism

Question 3

give three examples of homeostatic control

Answer 3

regulation of blood glucose levels

regulation of solute potential eg water is lost via excretion, sweating and expiration

regulation of core body temperature and pH

Question 4

what effect might a change in temperature and pH have on enzyme-catalysed reactions? why is this important for life?

Answer 4

changing temp. and pH can affect the rate of reactions

if these factors were affected by the environment, we would be restricted to very specific environments

this would increase competition for food and shelter

Question 5

describe homeostatic control in 5 points

Answer 5

there is a set point which is desired level/norm at which system operates

nevertheless, changes in pH, temperature and solute potential take place and fluctuate around set point

(homeostasis uses negative feedback to return body to set point)

set point is determined by a control centre

deviations from set point are corrected by negative feedback so that set point is restored

Question 6

give the role of negative feedback

Answer 6

uses detector/receptor -> monitors condition -> provides input to control centre/coordinator -> evaluates the information -> provides output to effector -> makes a response designed to take away deviation i.e. restore the set point/norm

Question 7

define negative feedback

Answer 7

a reaction to a change in a system that negates (reverses) the first change

Question 8

what does positive feedback do?

Answer 8

an effector increases a change

Question 9

give two examples of positive feedback

Answer 9

oxytocin stimulates the contraction of the uterus at the end of the pregnancy and the contractions stimulate the production of more oxytocin, which increases the stimulus

when the skin is cut, the first stage of clot formation is that platelets adhere to the cut surface and also they secrete signalling molecules which attract more platelets to the site

Question 10

what is thermoregulation?

Answer 10

restoration of core body temp. back to norm

Question 11

where is the control centre of thermoregulation?

Answer 11

the hypothalamus in the brain

Question 12

explain why a tall, thin swimmer is more likely to suffer from hyperthermia than a short, stout swimmer of the same body mass?

Answer 12

larger SA:V ratio

less insulation so loses more heat by conduction

Question 13

give two functions of the kidney

Answer 13

nitrogenous excretion

osmoregulation

Question 14

what is the difference between excretion and egestion?

Answer 14

excretion - removal from body of indigestible waste products

egestion - defaecation which is removal of unwanted material from digestive system

Question 15

what is nitrogenous excretion?

Answer 15

amino acids can’t be stored and surplus amino acids which are not used for the synthesis of proteins and other nitrogenous compounds are deaminated in the mammalian liver

Question 16

give 4 steps simply describing how nitrogenous excretion works

Answer 16

1- amine group is removed from amino acid

2- the removed amine group is converted to ammonia which is highly toxic

3- with the addition of CO2, urea which is less toxic is formed and transported in the blood plasma to kidneys

4- urea is removed by the kidneys and excreted in the urine

Question 17

what is osmoregulation?

Answer 17

the control of water content and solute composition of body fluids eg blood, tissue fluid and lymph

Question 18

give two ways humans gain water and three ways they lose water

Answer 18

gain:
food and drinks
respiration (metabolic water)

lose:
urination and egestion of faeces
sweating
exhalation - to keep exchange surfaces moisture

Question 19

give the different labels of the human urinary system

Answer 19

kidneys
ureters
bladder
sphincter
urethra

Question 20

what is the function of the kidneys?

Answer 20

filter waste products from the blood

Question 21

what is the function of the ureters?

Answer 21

carries urine to the bladder

Question 22

what is the function of the bladders?

Answer 22

stores urine prior to elimination

Question 23

what is the function of the sphincters?

Answer 23

it is a muscle that allows conscious control of urine release

Question 24

what is the urethra?

Answer 24

it transports urine outside of the body for elimination

Question 25

what are vasa recta?

Answer 25

blood cells that run parallel to the loop of Henle

Question 26

give the labels of the kidney

Answer 26

cortex medulla pelvis tough fibrous capsule ureter renal vein renal artery

Question 27

give labels for the structure of the nephron inside the kidney

Answer 27

glomerulus bowman's capsule - glomerular capsular space, glomerular capillary afferent arteriole efferent arteriole proximal convoluted tubule distal convoluted tubule loop of Henle collecting duct

Question 28

what is ultrafiltration?

Answer 28

filtration under pressure that separates small soluble molecules from the blood plasma the small molecules like water, glucose, urea and salts are filtered from the knot of capillaries (glomerulus) to form a filtrate in the Bowman's capsule high hydrostatic pressure is generated in the glomerulus because the afferent arteriole diameter is wider than the efferent arteriole

Question 29

what does the proximal convoluted tubule contain in the Bowman's capsule?

Answer 29

villi

Question 30

what type of cells are surrounding the Bowman's capsule?

Answer 30

squamous epithelial cells

Question 31

what direction does the glomerular filtrate move in?

Answer 31

from glomerular capillary to lumen of Bowman's capsule and into proximal convoluted tubule

Question 32

what are podocyte cells?

Answer 32

inner layer of Bowman's capsule which wrap around the capillaries of glomerulus

Question 33

how is the blood in the glomerulus separated?

Answer 33

blood entering the glomerulus is separated from the space inside the Bowman's capsule by two cell layers and a basement membrane

Question 34

describe the movement of glomerular filtrate from top to bottom

Answer 34

the squamous endothelium has many gaps the basement membrane acts as a molecular sieve during ultrafiltration then we have podocyte cells then the glomerular filtrate in the lumen of the Bowman's capsule there are squamous epithelial cells on the outer wall of Bowman's capsule

Question 35

what three ways are water and small soluble molecules filtrated by?

Answer 35

pores in the glomerular capillary wall the basement membrane acting as a molecular sieve filtered between the feet of the podocytes aka the epithelial cells of the Bowman's capsule

Question 36

what passes into the glomerular filtrate (has been mentioned before)?

Answer 36

amino acids glucose urea water salts aka Na+ Cl-

Question 37

what remains in the blood plasma after ultrafiltration?

Answer 37

red blood cells platelets white blood cells plasma proteins

Question 38

summarise ultrafiltration in 4 points

Answer 38

1- there is a high hydrostatic pressure in the glomerulus due to the efferent arteriole having a narrower lumen than the afferent arteriole 2- due to this, high-pressure fluid containing water and small soluble molecules is forced out of the blood capillaries through the pores in the capillary walls, and then through the pores in the basement membrane 3- the basement membrane acts as a molecular sieve, allowing small molecules through like glucose, amino acids, urea, water and salts but preventing large molecules and cells through like red blood cells, platelets, white blood cells and plasma proteins 4- the small soluble molecules are then filtered through the feet of the podocyte cells and glomerular filtrate is formed in the Bowman's capsule

Question 39

what is selective reabsorption?

Answer 39

the process by which useful products, such as glucose and salts, are reabsorbed back into the blood as the filtrate flows along the nephron the filtrate at the end of the proximal convoluted tubule is isotonic to blood plasma

Question 40

give 4 products selectively reabsorbed

Answer 40

all of glucose most of the mineral ions most of water urea

Question 41

how are the different products selectively reabsorbed?

Answer 41

glucose - secondary active transport using a co-transport mechanism with Na+ mineral ions - active transport/co-transport water - osmosis down a water potential gradient urea - diffusion

Question 42

give four adaptations in the proximal convoluted tubule for selective reabsorption

Answer 42

large surface area due to length and large number per kidney cuboidal epithelial cells with microvilli to provide large surface area and basal channels numerous mitochondria to provide ATP for active transport tight junctions to prevent seepage of reabsorbed materials back into the filtrate and close association with peritubular capillaries

Question 43

give the labels of a proximal convoluted tubule

Answer 43

apical microvilli intrinsic proteins in the cell membrane tight junctions basal channels - allow build-up of substances so they can travel into the blood by diffusion mitochondria folded basal membrane - increases the surface area capillary

Question 44

what does the loop of Henle do?

Answer 44

concentrates Na+ in the tissue fluid of the medulla, decreasing the water potential gradient, causing an osmotic flow of water out of the collecting ducts and distal convoluted tubules this water can then be reabsorbed into the bloodstream via the capillaries of the vasa recta. this concentrates the urine and makes it hypertonic to the blood lowering water potential the loop of Henle prevents dehydration

Question 45

describe the ascending limb

Answer 45

it is impermeable to water since water can't enter the a.l it goes into the blood the thin part of the a.l is highly permeable to Na+ and Cl- which diffuse into the tissue fluid from the filtrate the thick part of the a.l pumps Na+ by active transport into the tissue fluid since Cl- is attracted to the Na+ (ionic), it follows the Na+

Question 46

describe the descending limb

Answer 46

highly permeable to water longer the loop of Henle, the lower the volume of water in urine

Question 47

summarise the mechanism in the loop of Henle in 7 points

Answer 47

1- first part of loop is descending limb, second part is ascending limb 2- Na+ and Cl- are actively transported out of the filtrate in the ascending limb into the tissue fluid creating a lower water potential 3- the lower water potential of the medulla tissue fluid means that water leaves the descending limb by osmosis down a water potential gradient and can then move by osmosis into the capillaries of the vasa recta 4- the filtrate in the descending limb becomes more concentrated as it reaches the bottom of the loop of Henle due to the loss of water Na+ and Cl- can also diffuse back into the filtrate near the bottom of the descending limb 5- as the filtrate passes up the ascending limb it becomes more diluted due to the loss of ions 6- an osmotic gradient is maintained down to the bottom of the loop of Henle 7- this is known as a hair-pin counter current multiplier effect

Question 48

describe the osmolarity across the loop of Henle

Answer 48

as you go down water potential more positive towards the bottom of the descending limb, water potential very negative the loop of Henle very concentrated so water potential very negative as you go up ascending limb, water potential becomes more positive

Question 49

describe what happens in the collecting duct

Answer 49

as the loop of Henle creates a high Na+ concentration in the tissue fluid of the medulla, water will also leave the permeable collecting ducts by osmosis to be reabsorbed into the capillaries

Question 50

what hormone affects the permeability of the collecting duct walls?

Answer 50

antidiuretic hormone (ADH)

Question 51

Describe the mechanism of how ADH hormone works in 4 points

Answer 51

ADH enables more concentrated urine to be formed: 1- ADH makes the plasma membranes of the distal convoluted tubule cells and collecting duct cells more permeable to water 2- ADH causes aquaporins (which are channel proteins for water) to become incorporated in the plasma membranes, from within the cytosol (which is the liquid phase of the cytoplasm) 3- water is reabsorbed by osmosis from the filtrate into the surrounding hypertonic tissue fluid and hence blood capillaries around the distal convoluted tubules and collecting ducts 4- the urine reaching the bottom of the collecting ducts has a concentration close to the concentration of the tissue fluid near the bottom of the loop, that is, hypertonic to the general body fluids The volume of urine produced is small and concentrated ADH presence makes collecting duct walls highly permeable to water and is the opposite to when no ADH presence ADH is secreted when a person is dehydrated

Question 52

Describe ADH’s role in negative feedback

Answer 52

Osmoreceptors in the hypothalamus detect changes in water potential of the blood A nerve impulse in initiated and cells in the posterior lobe of the pituitary gland secrete more or less ADH ADH travels in the bloodstream and cells of the distal convoluted tubules and collecting ducts become more or less permeable to water

Question 53

Describe the role of ADH when a person is dehydrated

Answer 53

Osmoreceptors in the hypothalamus detect a decrease in the water potential of the blood Nerve impulses are sent to the posterior pituitary gland that releases more ADH ADH travels in the bloodstream to the nephrons where it affects the cells of the collecting duct walls The collecting duct walls become more permeable to water Water therefore leaves the filtrate in the collecting duct by osmosis into the tissue fluid of the medulla Water is then reabsorbed back into the bloodstream This results in a small volume of concentrated urine being produced

Question 54

what do different animals have in terms of the kidney?

Answer 54

they produce different forms of nitrogenous waste and have different lengths of the loop of Henle due to the environment in which they live

Question 55

how are the kidneys of aquatic animals adapted?

Answer 55

they excrete ammonia which is highly toxic and is very soluble in water. it can diffuse quickly across the gills of fish into the water where it is diluted to a non-toxic level

Question 56

how are the kidneys of birds, reptiles and insects adapted?

Answer 56

they excrete uric acid which is a bit toxic and is almost insoluble in water they use a lot of energy to excrete this waste but very little water is needed so their waste is light therefore, these animals can survive in dry environments

Question 57

how are the kidneys of mammals adapted?

Answer 57

we excrete urea requires a lot of water but is less toxic than ammonia so body tissues can tolerate it in higher concentrations for short periods of time

Question 58

how are the kidneys of desert animals adapted?

Answer 58

they survive with very little water water is produced from the breakdown of food during respiration in the cells (metabolic water) they may live in underground burrows which are cooler to reduce water loss by evaporation

Question 59

why does the kangaroo rat have a longer loop of Henle than average? (it lives in desert regions)

Answer 59

longer loop of Henle means more ions can be pumped from the ascending limb into the medulla tissue fluid this increases the concentration of ions in the tissue fluid, lowering the water potential more water can be reabsorbed from the descending limb, distal convoluted tubules and collecting duct, resulting in a more concentrated, small volume of urine

Question 60

what does the length of the loop of Henle relate to?

Answer 60

the typical availability of water in the environment the longer the loop of Henle, the greater the water potential gradient in the medulla

Question 61

what is the length of the loop of Henle, the position in the kidney and the reabsorption level for species that live in water like beavers?

Answer 61

short loH doesn't extend into medulla minimal reabsorption

Question 62

what are the symptoms of kidney failure?

Answer 62

unable to remove urea and the concentration can rise to toxic levels bodily fluids can become very dilute you can remain healthy with one kidney fatigue, shortness of breath, nausea, confusion and coma

Question 63

give 6 causes of kidney failure

Answer 63

auto-immune disease - where your immune system attacks itself diabetes kidney infections road traffic accidents (physical trauma) genetic conditions raised blood pressure

Question 64

what doe kidney problems almost always affect?

Answer 64

the rate at which blood is filtered in the Bowman's capsule

Question 65

what can treatments be used for?

Answer 65

to balance fluids in the blood and reduce the concentration of waste products

Question 66

give 5 treatments for kidney failure

Answer 66

medication to control blood potassium and calcium levels - high blood K conc. could lead to heart arrhythmia, high Ca in the blood is linked to increased risk of heart disease and kidney stones transplant dialysis reduce the intake of protein in diet to reduce urea formation use of drugs to reduce blood pressure - inhibit/block angiotensin hormone which constricts blood vessels, cause dilation of blood vessels, reduce adrenaline to prevent it from increasing heart rate

Question 67

describe the process of dialysis

Answer 67

it's the process of removing excess water, inorganic ions and urea from the blood in people whose kidneys can no longer perform these functions naturally the dialysate runs in counter-current flow next to the blood to be cleaned maintaining a concentration gradient blood and dialysate are separated by a selectively permeable membrane to prevent loss of plasma proteins replacement with fresh dialysate further maintains a concentration gradient

Question 68

compare the concentrations of solutes and water potential between the blood and the dialysis fluid

Answer 68

glucose: same in both sodium ions: high in blood, lower in D amino acids: same in both water: higher in blood, lower in D urea: high in blood, non in D

Question 69

what substances will diffuse out of the blood across the membrane to the dialysate and why?

Answer 69

inorganic ions, water and urea down their concentration gradient

Question 70

why should the concentration of glucose be the same in dialysis fluid as that of the blood?

Answer 70

so that none diffuses out of the blood

Question 71

why should the temperature of the dialysate be maintained at 37 degrees?

Answer 71

to increase the rate of diffusion maintains the patient temperature prevents temperature shock

Question 72

describe a kidney transplant

Answer 72

the functions of the failing kidneys can be taken over by a single healthy kidney from a donor the transplanted kidney should function normally in its new body, cleaning and balancing the blood, however it may only last 9 years the kidney from the donor can be rejected since antigens on the donor organ differ from antigens on the cells of the recipient and the immune system is likely to recognise this immunosuppressant medicines must be taken for the rest of their life

Question 73

evaluate this statement: having a kidney transplant is not a good solution for those who have kidney failure as it may have complications.

Answer 73

true: transplant lists are long close matches could potentially be rejected requires taking immunosuppressants life-span of a transplanted kidney is limited - 1, 2 decades the live donor is down one kidney - which increases stress on the remaining kidney, increasing the risk of further transplants in the future false: dialysis, on the other hand, is only a stepping-stone treatment and restricts an individual's life

Question 74

Aldosterone is released when blood pressure decreases. This results in a greater reuptake of sodium in the blood. What effect would this have on the blood pressure? Why?

Answer 74

The blood pressure would start to increase Sodium ions reduce the water potential of blood So more water enters the blood (from surrounding cells) by osmosis.

Question 75

Describe in detail the effects of ingesting a large quantity of salt. State which hormones would be involved and whether their output would be increased or decreased.

Answer 75

The salt is absorbed into the blood. This makes the blood water potential very negative. This is sensed by the cells within the hypothalamus. Water begins to leave cells by osmosis. This increases the blood volume and raises blood pressure. The person is also likely to become thirsty, and consume more liquid which will also add to the blood volume. The more water in the blood, the more dilute the salt, increasing the blood water potential. The release of aldosterone will stop but there will be an increase in ADH.

Question 76

Suggest what precautions a person who suffers from diabetes insipidus should take.

Answer 76

they should drink lots of water to replace the water lost in urine; try to conserve water by not getting too hot and so reduce sweating; avoid eating large amounts of salt.

Question 77

Explain the symptoms of diabetes insipidus.

Answer 77

Large quantity of dilute urine à only a small quantity of the water is reabsorbed back into the blood. Most leave the kidney in the urine as it passes through the collecting duct without being reabsorbed. As the person is constantly losing water, they will feel thirsty, as the blood water potential will be very negative.