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A2 BIO UNIT3 > 3.7 Homeostasis & the Kidney > Flashcards

3.7 Homeostasis & the Kidney Flashcards

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1
Q

What is meant by homeostasis?

A
  • maintenance of a constant internal environment
  • body kept in dynamic equilibrium
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2
Q

What is homeostasis controlled by?

A
  • endocrine system
  • hormones that operate by negative feedback
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3
Q

Define negative feedback

A
  • where a change in a system produced a second change which reverses the initial change
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4
Q

Explain negative feedback mechanism

A
  • set point for a factor is the norm at which a system operates
  • a receptor detects the level of the factor and its deviation from the set point
  • the receptor sends instructions to a coordinator or controller
  • the coordinator communicates with one or more effectors which make responses that are corrective
  • the factor returns to normal, monitored by the receptor and the information is fed back to effectors which stop making the correction
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5
Q

Briefly explain how glucose concentration in blood plasma is maintained

A
  • if too high, insulin is secreted to encourage conversion of glucose to glycogen for storage
  • if too low, glucagon is secreted to break down glycogen to glucose
    —> all detected by pancreas and go to liver
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6
Q

Briefly explain how body temp is maintained

A
  • if get too cold, increased respiration generates heat and the constriction of blood vessels enables the body to retain heat
  • if get too warm, blood vessels dilate and heat radiates from body
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7
Q

Explain 2 examples of positive feedback

A

Oxytocin stimulates the contract of the uterus at the end of a pregnancy. The contractions stimulate more oxytocin which increases the stimulus

When the skin is cut, the first stage of a clot is that platelets adhere to the cut surface. They secrete signalling molecules which attract more platelets

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8
Q

Define excretion

A
  • the removal of nitrogenous metabolic waste from the body
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9
Q

Define osmoregulation

A
  • the control of the water potential of body fluids (plasma, tissue fluid and lymph) by regulating the water content and therefore solute concentration
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10
Q

Equation for production of urea

A

amino acid —> alpha keto acid + ammonia —> urea

CHR.NH2.COOH —> R.CO.COOH + NH3 —> O=C(NH2)2

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11
Q

Draw and label a kidney

A
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12
Q

What is found in the cortex?

A

Nephrons

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13
Q

What is found in the pyramids of medulla?

A

The loop of henle

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14
Q

Role of renal vein and artery

A

Artery: blood to kidney
Vein: blood from kidney

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15
Q

Draw and label a nephron

A
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16
Q

Describe a nephron

A
  • blood filtering unit
  • afferent arteriole brings blood to nephron
  • blood carried by efferent arteriole to a capillary network and the vasa recta (capillary network around loop of henle)
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17
Q

What arteriole brings blood to the glomerus?

A

Afferent

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18
Q

Why is blood in the afferent arteriole under high pressure?

A
  • afferent arteriole has wider diameter than the efferent arteriole
  • the hearts contraction increases the pressure of arterial blood
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19
Q

What 3 layers separate the blood entering the glomerus and the Bowman’s capsule?

A
  • the wall of the capillary which is a single layer of endothelial cells
  • basement membrane is an extra cellular layer of proteins, mainly collagen and glycoproteins. It has a molecular filter and selective barrier that act like a sieve between the capillary and nephron
  • the wall of the capsule is made of squamous epithelial cells called podocytes which has pedicels that wrap around the capillaries. The gaps between pedicels are filtration slits
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20
Q

Components of the glomerular filtrate

A

Water, glucose, salts, urea, amino acids

21
Q

Water potential of blood flowing into efferent arteriole

A

Low

22
Q

What is meant by selective reabsorption?

A

The uptake of specific molecules and ions from the glomerular filtrate in the nephron back into the blood stream

23
Q

Describe role of PCT

A
  • longest and widest part of nephron
  • carries filtrate away from bowman’s capsule
  • blood around PCT reabsorbs all the glucose and amino acids, some urea and most of the water and sodium and chloride ions from the filtrate
24
Q

Features of the PCT

A
  • large SA as longest part of the nephron and there are millions of nephrons
  • cuboidal epithelial cells increase the SA with microvilli and invaginations called basal channels - short diffusion distance
  • many mitochondria to provide ATP for active transport
  • a close association with capillaries - short diffusion distance
  • tight junctions between the cells of the PCT epithelium - multi protein complexes encircle the cell and attach to it tightly to prevent molecules from diffusing to adjacent cells
25
Q

Briefly explain selective reabsorption from the PCT

A
  • 70% of salts in filtrate are reabsorbed into blood by active transport using membrane pumps
  • all glucose and amino acids are reabsorbed into blood by co-transport with Na+ ions
  • 90% of water in the glomerular filtrate is reabsorbed passively by osmosis as the reabsorbed ions lower the water potential
  • 50% of urea and small proteins is reabsorbed into blood by diffusion and a steep conc gradient
26
Q

Explain the co-transport of glucose and amino acids

A
  • glucose or amino acids and 2x Na+ ions binds to a transporter protein in the cuboidal epithelial cell membrane and enter by facilitated diffusion
  • Na+ ions pumped into capillary, reducing their conc and more Na+ enters cell
27
Q

Define and explain secondary active transport

A
  • the coupling of movement, eg of Na+ ions, down their electrochemical gradient with the movement of another molecule, eg glucose
    —> not using energy from ATP directly but from electrochemical gradient of Na+ ions from lumen into cell, which was generated by active transport of Na+ into capillary
28
Q

What happens to the filtrate at the base of the PCT?

A

It is isotonic with the blood plasma

29
Q

What happens if the glucose concentration in the filtrate is too high?

A
  • cannot absorb all the glucose
  • too few transport molecules in the membrane to absorb it
  • glucose pass through loop of henle and is lost in urine
30
Q

What might cause the glucose conc of urine to be too high?

A
  • the pancreas secreting too little insulin (type I diabetes)
  • the response of liver cells to insulin is reduced because insulin receptors in surface membranes are damaged (type II diabetes and gestational diabetes)
31
Q

% of water reabsorbed by PCT and collecting duct

A
  • 90% of water filtered at Bowman’s capsule is reabsorbed into PCT
  • 5% reabsorbed from collecting duct
32
Q

Describe the role of the ascending limb in water reabsorption

A
  • walls are impermeable to water
  • actively transport sodium and chloride ions out of the filtrate in the tubule into the tissue fluid in the medulla
  • loops of henle collectively concentrate salts in the tissue fluid which has a low water potential
33
Q

Describe the role of the descending limb in water reabsorption

A
  • walls are permeable to water and slightly permeable to sodium and chloride ions
  • as filtrate flows down the limb, water diffuses out by osmosis into tissue fluid of medulla which has low water potential
  • water moves into the vasa recta (capillaries surrounding nephron)
  • some Na+ and Cl- also diffuses in
34
Q

Describe the counter current mechanism

A
  • 2 limbs work side by side with filtrate flowing in opposite directions which enables the maximum concentration and the apex of the loop
35
Q

Briefly explain role of ascending and descending limbs of the loop of henle in water reabsorption

A

Top of ascending: active transport of Na+/Cl- lowering water potential
Bottom of ascending: water out by osmosis into tissue fluid of medulla

Bottom of ascending: water out by osmosis leaving conc solute at apex
Bottom of descending: facilitated diffusion of Na+ and Cl- lowering water potential

36
Q

How do birds and reptiles remove their nitrogenous waste?

A
  • Uric acid
  • expensive process but lightweight needed to fly
37
Q

How do fish remove their nitrogenous waste?

A
  • Ammonia diffuse through gills into freshwater
  • freshwater dilutes it
38
Q

Define antidiuretic hormone

A
  • hormone produced in the hypothalamus and secreted by posterior pituitary gland
  • increases the permeability of the cells of the distal convulatesd tubule and collecting duct to water, increasing water absorption
39
Q

Define diuresis and anti-diuretic

A
  • production of large volumes of dilute urine
  • production of a small volume of concentrated urine
40
Q

What can cause the water potential of the blood to fall?

A
  • ingestion of large quantities of salts
  • reduced water intake
  • sweating
41
Q

Describe how ADH gets produced and what it does

A
  • reduced water potential detected by osmoreceptors in the hypothalamus
  • secretory granules carry ADH along axons from the hypothalamus to posterior pituitary gland
  • increases permeability of cell walls so me water absorbed into medulla
  • water water to blood in capillaries
  • water potential restored to normal
42
Q

Describe the ADH mechanism of action

A
  • ADH binds to membrane receptors on cells of CD and DCT
  • adenyl cyclase catalyses the production of cyclic AMP, the second messenger
  • vesicles containing aqua porins move and use with the cell membrane
  • aquaporins now in the membrane allow the water molecules to move in single file into the cell down a water potential gradient

—> when Intracellular cyclic AMP levels fall, the aquaporins are removed from the cell membrane and they accumulate again in vesicles

43
Q

What happens if the kidneys fail?

A
  • urea builds up to toxic concentrations and body fluids increase in volume and are diluted, compromising metabolic reactions
44
Q

What are the causes of kidney failure?

A
  • diabetes: high glucose concentration in plasma results in the glomeruli losing protein into the filtrate, triggering scarring in a condition called glomerulosclerosis
  • high blood pressure: damage to capillaries of glomerulus prevents ultrafiltration
  • autoimmune disease
  • infection
  • crushing injuries
45
Q

Describe treatments when both kidneys are compromised

A
  • reduce intake of certain nutrients (mainly protein) to reduce urea production
  • drugs to regulate BP
    —> angiotensin converting enzyme (ACE) inhibits and angiotensin receptor blockers (ARB) reduce impact of angiotensin, a hormone which constricts blood vessels thus increasing BP
    —> calcium channel blockers dilate blood vessels
    —> beta blockers reduce effect of Adrenalin
  • control of conc of potassium and calcium ions
    —> high potassium treated with glucose and insulin - can lead to arrhythmias so intravenous calcium added too
    —> high calcium in blood is correlated with risk of heart disease, kidney stones, and osteoporosis - treated with biophosphonates which decrease activity of osteoclasts so calcium accumulates in bone instead
  • dialysis to artificially filter blood
    —> fluid has same water potential as blood but low ion conc and no urea
    —> inorganic ions, water, and urea diffuse out of blood
    —> no glucose leaves
  • kidney transplant
46
Q

Describe haemodialysis

A
  • use of dialysis machine to artificially filter blood
  • blood taken from artery in arm and ran through selectively permeable tubing
  • counter current to maintain diffusion gradients
  • anticoagulant added to thin blood and stop clotting
47
Q

Describe continuous ambulatory peritoneal dialysis

A
  • allows patient to walk and live normal life whilst dialysis operates
  • drains fluid through catheter in abdomen
  • uses peritoneum lining body cavity as has rich supply of capillaries
  • happens 4x a day
  • retention of liquid is common and K+ ions accumulate in blood so must drink v little and avoid foods rich in potassium
48
Q

Describe kidney transplants and the challenges

A
  • donors may be living or suffered a brain stem or circulatory death
  • ABO blood groups and HLA must be compatible
  • dialysis still required initially if kidney came from dead donor
  • placed in lower abdomen
  • renal artery and vein attached to iliac artery and vein
  • circulation restored when gos pink, and when urine is seen emerging the ureter is attached to the bladder
  • must take immunosuppressants for rest of life - increased risk of cancer
  • patients vulnerable to infection
  • could result in long term antibiotic use - antibiotic resistance
49
Q

What is transamination?

A

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

A2 BIO UNIT3 (8 decks)

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