Homeostasis And The Kidney

Question 1

What is homeostasis ?

Answer 1

The maintenance of a state of dynamic equilibrium in the body despite fluctuations in the internal and external conditions

Question 2

Why is homeostasis important ?

Answer 2

Ensuring optimum conditions for enzymes and cellular processes in the body

Question 3

Define negative feedback

Answer 3

Self regulatory mechanisms return the internal environment to the optimum when there is a fluctuation

Question 4

Define positive feedback

Answer 4

A fluctuation which triggers changes that result in an even greater deviation from the normal level

Question 5

What is a set point ?

Answer 5

A desired value or range of values determined by a coordinator

Question 6

What are the components of a negative feedback system ?

Answer 6

Set point
Receptors
Coordinators
Effectors

Question 7

What is osmoregulation?

Answer 7

Control of body fluid water potential via negative feedback

Question 8

Why is osmoregulation so important ?

Answer 8

• Prevents the cells from bursting / shrinking when water enter of leaves via osmosis
• Cellular reactions occur in aqueous solution therefor water levels affect concentration and the rate of reaction in cells

Question 9

Define excretion

Answer 9

The process of removing metabolic waste from an organism
(From lungs, kidneys, skin and liver)

Question 10

How are excess amino acids secreted ?

Answer 10

Amino acids delaminated in the liver to form ammonia
Ammonia is converted into urea
Urea is transported into the blood plasma ( by facilitated diffusion )and eliminated by the kidneys

Question 11

What is the function of the renal artery?

Answer 11

Supplies blood to the kidneys

Question 12

What is the function of the renal vein?

Answer 12

Drain blood from the kidneys

Question 13

What is the function of the ureter and urethra?

Answer 13

Ureter = Takes urine to the bladder from the kidneys
Urethra = Releases urine from the bladder, out of the body

Question 14

Describe and explain the functions of the structures within a mammalian kidney

Answer 14

Cortex= outer region consists of the Bowman’s Capsule, convoluted tubules and blood vessels (ultrafiltration and selective reabsorption)
Medulla = inner region consists of collecting duct, loop of Henle and blood vessels (reabsorption of water )
Renal Pelvis = funnel shaped dilated section of ureter allows urine to be emptied to ureter
Fibrous Capsule = protects the kidney

Question 15

What is a nephron ?

Answer 15

The functions unit of a kidney.

Question 16

What part of the kidney is the nephron located in?

Answer 16

Bowman’s Capsule and Proximal & Distal convoluted tubule = Cortex
Loop of Henle = Medulla

Question 17

Describe Ultrafiltration

Answer 17

Occurring in the Bowman’s Capsule
1) Blood enter the glomerulus via the afferent arteriole (wider) and leaves via the efferent arteriole (narrower). This generated high hydrostatic pressure.
2) Small molecules pass through 3 layers and enters the Bowman’s Capsule and tubule as filtrate.

Question 18

What does Glomerular Filtrate contain?

Answer 18

Water
Glucose
Salts
Urea
Amino Acids

Question 19

What 3 layers separate the blood entering the glomerulus from the Bowman’s space?

Answer 19

1) Capillary Walls - one cell thick, tiny pores between cells called fenestrations allow solute to pass to the basement membrane
2) Basement Membrane - A selective molecular filter. Only allows small molecules to pass through, blood cells and platelets are too large.
3) Squamous Epithelial Layer - Podocytes have extensions called pedicels these wrap around capillary’s pulling it closer to the basement membrane. Gaps between pedicels are called filtration slits

Question 20

Define selective reabsorption

Answer 20

Process by which useful substances such as glucose, amino acids and salts are reabsorbed back into the blood plasma, taking place in the proximal convoluted tubule

Question 21

Describe how cells in the proximal convoluted tubule are adapted for selective reabsorption

Answer 21

MICROVILLI - provide large surface area for cotransporter proteins
MITOCHONDRIA - Lots to produce ATP for active transport of glucose into the intercellular space
FOLDED BASEMENT MEMBRANE - large surface area and also basement channels help
TIGHT JUNCTIONS - between cells to stop reabsorbed materials leaking back into the filtrate

Question 22

How are amino acids and glucose selectively reabsorbed back into the blood?

Answer 22

Glucose and amino acids enter the PCT by cotransport with sodium ions.
Once inside the cell they diffuse to the opposite cell membrane
Glucose leaves via facilitated diffusion and secondary active transport
Amino acids leave by facilitated diffusion

Question 23

How are chloride ions selectively reabsorbed ?

Answer 23

Chloride ions enter by facilitated diffusion
They then leave via facilitated diffusion

Question 24

What mechanism allows mineral ions to be selectively reabsorbed back into the blood ?

Answer 24

Active Transport

Question 25

By what mechanism is water selective,g reabsorbed into the blood?

Answer 25

Osmosis

Question 26

Describe the different parts of the loop of Henle

Answer 26

Descending Limb (dips into the medulla ) Ascending Limb ( rises into the cortex )

Question 27

What is the overall function of the loop of Henle ?

Answer 27

Creates a low water potential in the medulla, allowing reabsorption of water to occur

Question 28

Describe the process that occurs in the loop of Henle

Answer 28

- Water moves out of the descending limb ( permeable to water ) and into the blood via osmosis - Na and Cl ions diffuse into the descending limb at the same time from the medulla - Filtrate becomes more concentrated as it gets towards the apex - The ascending limb expels the Na and Cl ions by facilitated diffusion and then active transport. ( AT takes over when concentration of solutes decreases too much) into the tissue fluid of the medulla

Question 29

What hormone controls the concentration and volume of urine?

Answer 29

Anti-diuretic hormone (ADH)

Question 30

Explain the roles of the hypothalamus in osmoregulation

Answer 30

Osmoreceptors in the hypothalamus detect the concentration in blood plasma ADH is secreted from the hypothalamus

Question 31

Explain the role of the posterior lobe of the pituitary gland in osmoregulation

Answer 31

Signals are sent here Stores and secreted the ADH produced by the hypothalamus

Question 32

How does ADH affect the reabsorption of water from the kidney tubules?

Answer 32

Release of ADH causes insertions of Aquaporins into the cell membranes of the DCT and collecting duct This increases the permeability of the DCT and collecting duct More water is reabsorbed and therefore a more concentrated urine is produced

Question 33

How do the length of the loop of Henle differ between different animals ?

Answer 33

Long loop = Desert Animals - more ions can be pumped into the medulla, lowering the water potential and as a result more water to be reabsorbed into the blood stream Shorter loop = fresh water e.g otters

Question 34

Describe the effects of kidney failure

Answer 34

- build up of toxic waste products - fluid accumulation

Question 35

Outline the potential treatments for kidney failure

Answer 35

- Low protein diet - control blood calcium and potassium levels using medication - kidney transplant - dialysis

Question 36

How is dialysis carried out?

Answer 36

- Blood taken out of artery in patients arm entering dialysis machine. - blood is passed through thousands of long narrow strands of selectively permeable dialysis tubing. - waste passes through the pores into the dialysis fluid - fluid and blood flow in opposite directions, maintaining a strong concentration gradient - clean blood is returned via veins

Question 37

What are the 2 types of dialysis ?

Answer 37

- haemodialysis - peritoneal dialysis

Question 38

What is a kidney transplant ?

Answer 38

- organ from living or dead donor is given to the patient - needs to be correct tissue types and blood - patient will be on immunosuppressants for rest of life to decrease chance of rejection

Question 39

How do animals excrete nitrogenous waste?

Answer 39

Fish = excrete ammonia into surrounding water via diffusion across gills. Ammonia is toxic but highly soluble in water Birds & Insects = uric acid, little water needed to excrete so save water loss Mammals = Urea, requires ATP less toxic then ammonia