5.2 Excretion Flashcards
Define excretion
removal of metabolic waste from the body
What are the 4 main excretory organs?
- lungs: CO2 diffuses into and out of alveoli to be excreted as you breathe out
- liver: some substances produced passed into bile for excretion with faeces. also involved in converting amino acids to urea.
- kidneys: urea removed to form part of urine
- skin: loss of water and salts as sweat
How is the pH of blood kept fairly constant?
- proteins in blood act as buffers
- if theres a small change. the extra H+ is detected by medulla oblongata and breathing rate will increase to remove CO2 formed.
- if it drops too much = acidosis. Rapid heart rate.
CO2 + H2O <-> H2CO3 <-> H+ + HCO3-
Why do amino acids have to be removed? How?
body cannot store excess
deamination -> keto acid formed and used in respiration. ammonia formed also.
Then ornithine cycle
What is a key adaptation for all liver cells?
good blood supply to ensure as much blood as possible flows past as many cells as possible
What is the role of the hepatic artery, hepatic portal vein, and hepatic vein?
artery: supplies oxygen needed for aerobic respiration
portal vein: deoxygenated blood straight from digestive system, carrying digestion products. concs must be adjusted
vein: blood leaving liver, rejoins vena cava
What is the role of the bile duct and bile canaliculus?
canaliculus: join together to form bile duct
bile duct carries bile from liver to gallbladder
How are liver cells organised?
Into cylindrical lobules in lobes
What are the inter-lobular and intra-lobular vessels?
inter run between and parallel to lobules - branches from hepatic portal vein and hepatic artery at intervals.
intra = central hepatic vein
What is the sinusoid?
- lined with hepatocytes
- where blood from vessels are mixed
- hepatocytes able to remove substances from the blood
- empty into intra-lobular vessel
What is the role of Kupffer cells?
- special macrophages break down and recycle old RBC - bilirubin
- also engulf pathogens
Adaptations of hepatocytes?
- many mitochondria
- dense cytoplasm
- thin cells for short diffusion distance
- fennestrations for increased permeability
What are the functions of the liver?
- storage of glycogen and vitamins, iron
- detoxification of alcohol
- control of amino acid, glucose and lipid levels
- synthesis of bile, plasma proteins and cholesterol
- breakdown of RBC and hormones
What does detoxification involve? What enzymes help?
- methylation, combination with another molecule, oxidation, reduction
- catalase which catalyses formation of water and oxygen from hydrogen peroxide
- cytochrome p450 catalyses breakdown of drugs. can interfere with other metabolic roles and cause unwanted side effects
What is the process of alcohol detoxification?
- ethanol -> ethanal (dehydrogenation, ethanol dehydrogenase)
- ethanal -> ethanoic acid (dehydrogenation, ethanal dehydrogenase)
- ethanoic acid/acetate joins with coenzyme A to form acetyl coenzyme A which enters Krebs cycle.
Whats the problem if too much alcohol has been consumed?
- too much detoxified
- it uses up NAD and has insufficient for fatty acid breakdown
- lipids in hepatocytes -> liver enlargement -> fatty liver -> cirrhosis/hepatitis
Describe deamination
- amino acid + oxygen -> keto acid + ammonia (highly soluble and highly toxic)
Describe the ornithine cycle
ammonia and carbon dioxide in
water out
CITRULINE
ammonia in and water out
ARGININE
water in and urea out (less soluble and less toxic)
ORNITHINE
Starting from inside to outside, what is the structure of a kidney?
ureter, pelvis, medulla, cortex, capsule
How to tell between PCT and DCT?
PCT has microvilli/brush border
What are the 3 layers of the barrier between the glomerulus and bowmans lumen? What are the specialised epithelium cells called?
1) endothelium: fenestrations allow blood plasma and dissolved substances to leave capillary
2) basement membrane: mesh of collagen fibres and glycoproteins act as a filter -> prevents most proteins (and all RBC) from leaving
3) epithelial: special shaped podocytes -> major processes and minor/foot processes that hold cells away from endothelium.
What is the journey of fluid through the nephron?
glomerular filtrate
PCT
loop of Henle DC
loop of Henle AC
DCT
collecting ducts to pelvis
What is ultrafiltration?
filtering of blood at the molecular level
What about the arterioles make it easier?
- afferent WIDER than efferent -> ensures higher hydrostatic pressure in glomerulus than bowman’s -> push fluid out
What does the blood plasma contain?
water, amino acids, glucose, urea, inorganic ions
What are the functions of PCT and DCT?
- PCT: reabsorption of sugars, most mineral ions and some water
- DCT: movement of mineral ions occurs to maintain balance of mineral ions in the blood
What are the functions of DL and AL?
- DL: decreases WP due to addition of mineral ions and removal of water
- AL: increases WP due to removal of ions by active transport
What is the function of the collecting duct?
- decreases WP by removal of water, to form urine with a high solute concentration
How are cells lining PCT specialised to carry out selective reabsorption?
- microvilli to increase SA ( both sides)
- special cotransport proteins next to lumen
- membrane next to capillaries contains sodium/potassium pumps
- cell cytoplasm contains many mitochondria
What is the process of selective reabsorption? How are larger molecules be reabsorbed?
1) Sodium actively pumped out of cells lining the tubule, into the blood
2) Sodium conc decreases in the cytoplasm, forming a conc gradient
3) These ions diffuse from the lumen into PCT lining cell through cotransport protein, carrying glucose or amino acid also—facilitated diffusion.
4) Water moves in by osmosis
5) Glucose/amino acids diffuse into the blood, and water continues to follow
- endocytosis
Describe reabsorption of water
1) Ions actively pumped out + accumulate in interstitial fluid. Water cannot follow due to impermeability.
2) Water drawn out of DL by osmosis into fluid and blood.
3) Bottom of limb has very concentrated fluid. Bottom of medulla also very conc.
4) Sodium ions and chloride ions diffuse out of lower AL,n and pumped out of upper AL
5) Dilute fluid at top of AL
6) Empties into collecting ducts which pass through conc medulla
7) Water osmotically drawn out and into blood capillaries = conc urine
What is the loop of henle called?
Hairpin countercurrent multiplier system. Increases efficiency of transfer of mineral ions from AL to create water potential gradient and allow effective reabsorption
What is osmoregulation?
- control of water potential
How do kidneys alter the volume of urine produced?
- altering permeability of collecting ducts
- conserve less water = less permeable = less water reabsorbed and greater urine volume
- conserve more water = more permeable = more water reabsorbed = smaller urine volume.
What is the process that occurs when the level of antidiuretic hormone increases?
1) detected by cell-surface receptors
2) enzyme-controlled reactions
3) vesicles containing aquaporins fuse to membrane
4) more water can be reabsorbed
What is the process that occurs when the level of antidiuretic hormone decreases?
1)cell surface membrane invaginates to create new vesicles to remove aquaporins 2)decreases permeability so less water is reabsorbed = more dilute urine
What is an osmoreceptor?
Monitors water potential of blood and responds to effect of osmosis -> low water potential = shrink = stimulate neurosecretory cells in hypothalamus
Where is ADH manufactured? Where does it move to? What causes its release in the hypothalamus?
- Cell body of the neurosecretory cell in hypothalamus, and moves down to terminal bulb in posterior pituitary, stored in vesicles
- Neurosecretory cells stimulated = carry action potentials down their axons and causes release by exocytosis
- Enters blood capillaries
What are the causes of kidney failure?
- diabetes mellitus, heart disease, hypertension, infection, age
How do you assess kidney failure?
- estimation of glomerular filtration rate + urine analysis for e.g. proteins.
What is renal dialysis?
- where waste products and excess fluids and ions are removed from the blood through passing it over a partially permeable dialysis membrane into dialysis fluid. (contains correct conc of everything)
- excess in blood diffuses INTO fluid and substances too low diffuse OUT of fluid
Describe haemodialysis
- blood removed for cleansing
- blood pump
- heparin to prevent clotting
- passes through a dialyser through artificial capillaries, in the opposite direction to the fluid. (fluid continuously refreshed)
- air detector clamp removes air bubbles
- clean blood returns to patient
Describe peritoneal dialysis
- membrane is the bodys own abdominal membrane (peritoneum)
- dialysate introduced via catheter tube to fill space between abdominal wall and organs
- dialysate containing excess substances + urea is removed
What are the advantages and disadvantages of a kidney transplant?
ADV:
- feel physically fitter
- dont need frequent hospital visits for dialysis = freedom
- cost removed of dialysers
- long term solution
DISADV:
- need to take immunosuppressant drugs
- need for major surgery under general anaesthetic
- regular checks for signs of rejection
What can urine analysis be used for?
- glucose (diabetes), alcohol (drink-driving), recreational drugs, anabolic steroids.
How does pregnancy testing work?
- urine poured onto stick
- hCG binds to mobile antibodies attached to blue bead
- move down test stick
- the hCG with these antibodies attached also binds to fixed antibodies holding beads in place = blue line
- CONTROL ( negative = 1 line) has mobile antibodies with no hCG attached binded to another fixed site
What do anabolic steroids do and how do we analyse the urine sample for them?
- increase protein synthesis = build up of tissue esp in muscle
- gas chromatography
Which of the following statements describes a feature of peritoneal dialysis?
- Urea and mineral ions pass into tissue fluid
- Blood is passed over an artificial membrane to remove toxins
- The patient receives immunosuppressant drugs
A) 1,2,3
B) 1,2
C) 2,3
D) 1
D
The process of ultrafiltration in the kidney shares similarities with the formation of tissue fluid.
(a)* Describe the similarities and differences between ultrafiltration and the formation of tissue
fluid.
Similarities:
Small molecules are filtered from/diffuse out
of the blood.
Both processes occur in capillaries.
Large molecules/proteins/ cells, remain in the
blood.
High (hydrostatic) pressure in both
processes.
Many molecules (e.g. water, sugars, ions) are
reabsorbed back into capillaries.
Blood vessels become narrower to maintain
(hydrostatic) pressure
Hydrostatic pressure greater than oncotic
pressure in both
Neutrophils / lymphocytes, can pass through
in both
Both involve basement membranes
Differences:
Filtrate enters the Bowman’s capsule and
then the PCT in the kidney, but tissue fluid
bathes cells/enters intercellular space.
Molecules that are not reabsorbed by
capillaries form urine in the kidney, but
molecules that are not reabsorbed from
tissue fluid will, enter cells / form lymph.
Blood filtered through 3(named) layers in
ultrafiltration, but only 1 (named) layer in
formation of tissue fluid
knot of capillaries in ultrafiltration but a
network of capillaries in formation of tissue
fluid
