Module 5.2 - Excretion as an Example of Homeostatic Control Flashcards
(MA) What structures are present in the lobule of the liver?
- hepatic artery
- hepatic portal vein
- bile duct
- sinusoid
- hepatocytes
- Kupffer cells
(MA) How do the structures of the liver relate to their function?
- hepatic artery: brings oxygenated blood from heat, supplies hepatocytes w O2 etc for aerobic respiration
- hepatic portal vein: brings deoxygenated blood from digestive system. May contai toxic compounds which need detoxification or products of digestion for storage etc
- bile duct: bile made in hepatocytes (exocrine) + secreted into bile canaliculi which drains into bile duct. Bile stored in gall bladder until release into small intestine. Bile neutralises stomach acid + emulsifies lipids in s intestine-blood from hepatic artery+heptatic portal vein mix + go into a sinusoid surrounded closely by liver cells (hepatocytes)
- blood from sinusoid drains to intra-cellular hepatic vein which return blood to heart
- hepatocytes: remove molecules eg glucose from blood + release others back in eg fibrinogen. Covered in microvilli, large SA for diffusion. Make bile, plasma protein, store vitamins, carry out detoxification. Contain many mitochondria as v metabolically active. High density of organelles eg ribosomes for protein synthesis
- Kupffer cells: macrophages found in sinusoids which break down RBCs. Products of this are released into bile to be sent into digestive system for excretion eg bilirubin from Hb is brown colour in faeces
(MA) How is urea made in the liver?
- deamination: amine group removed from amino acids + forms a keto acid (which can be respired) + NH3
- ammonia is highly soluble + highly toxic so must be converted to urea (less toxic/soluble)
- ornithine cycle: ammonia react w CO2 to form urea + H2O. Other products eg ornithing (+ other amino acids) also made
- urea transported in blood for removal by nephrons in kidney into urine
(MA) How does detoxification in the liver occur?
-converting toxic molecules to less/non-toxic ones
-needed to remove toxic molecules from diet or from metabolic processes from blood. If weren’t removed could kill us
-detoxification of alcohol
>ethanol dehydrogenase converts ethanol to ethanol
>ethanol converted to ethanoic acid
>both stages: NAD combines w/ H to form reduced NAD which can take them to the inner mitochondrial membrane to make ATP in oxidative phosphorylation
>ethanoic acid converted to acetyl CoA + carries it to the Krebs cycle
-detoxification ot hydrogen peroxide: catalase enzyme in hepatocytes hydrolyses H2O2 (made by WBCs) into H2O + O2
(MA) What are the biological problems associated with having too much alcohol?
- NAD needed to break down alcohol
- NAD also needed to break down fatty acids for respiration
- too much alcohol means not enough NAD is present to break down fatty acids
- means fatty acids converted back into lipids + get stored in hepatocytes
- fatty liver can cause cirrhosis of liver
(MA) How is the structure of the glomerulus related to its function?
- afferent arteriole wider than efferent arterioles
- causes high HS pressure
- endothelium of capillaries has many small gaps
- allow smaller molecules through for ultrafiltration (by basement membrane)
(MA) What are the structures of the nephron?
- Bowman’s capsule
- PCT
- loop of Henle
- DCT
- collecting duct
(MA) How is the structure of the Bowman’s capsule related to its function?
- ultrafiltration
- basement membrane stops removal of large molecules e.g. RBCs
- basement membrane mesh like made of glycoproteins
- epithelial cells of Bowman’s capsule are podocytes which have finger like projections
- ensure gaps to allow passage of substances underneath into lumen
(MA) How is the structure of the proximal convoluted tubule related to its function?
- epithelial cells covered in microvilli increase SA
- for selective reabsorption
- many co transporter proteins in cell surface membrane of epithelial cells
- to reabsorb all of the glucose + amino acids into blood
(MA) How is the structure of the Loop of Henle related to its function?
- hairpin counter current multiplier
- purpose is to cause a decrease in water potential in tissue fluid of medulla
- many carrier proteins to transport ions (out of ascending limb)
- so water can be reabsorbed from the collecting duct
(MA) How is the structure of the collecting duct related to its function?
-epithelial cells contain many aquaporins in the cell surface membranes
(MA) What happens during ultrafiltration?
- afferent arteriole wider than efferent arteriole
- causes high HS pressure
- endothelium of capillaries has many small gaps to allow smaller molecules through
- basement membrane stops removal of large molecules e.g. RBCs
- epithelial cells of Bowman’s capsule are podocytes (have finger like projections)
- ensure gaps to allow passage of substances underneath into lumen
(MA) What happens during selective reabsorption?
- occurs in PCT
- Na pumped into blood + K pumped into epithelial cells from blood
- reabsorption of all glucose + amino acids into blood
- through co transporter proteins by facilitated diff (carry glucose/aa and Na+)
- water follows by osmosis
(MA) What happens in the Loop of Henle?
- purpose: decrease water potential of tissue fluid of medulla
- ions actively transported out of ascending limb into tissue fluid of medulla
- water potential of tissue fluid surrounding LoH + collecting duct is lower than inside them
- descending limb + collecting duct are permeable to water
- water is absorbed from descending limb + collecting duct of nephron into tissue fluid + then into blood
(MA) Describe the release of ADH.
- osmoreceptors in hypothalamus monitor water potential of blood
- neurosecretory cell bodies in hypothalamus produce ADH
- ADH travels down axon of neurosecretory cells to terminal bulb in posterior pituitary gland to be stored
- if osmoreceptors sense water potential of blood is too low, they lose water by osmosis
- triggers an action potential down axon of neurosecretory cell
- stimulates the release of ADH from the terminal bulb in posterior pituitary gland
(MA) Describe the role of ADH in osmoregulation on hot days.
- posterior pituitary gland secretes lots of ADH
- ADH travels in blood
- target cells for ADH are cells lining collecting duct in nephrons of kidneys
- ADH binds to receptors of the cell surface membranes of target cells, triggers a series of enzyme controlled reactions
- causes vesicles containing aquaporins to be made + fuse w the membranes, increasing membrane’s permeability to H2O
- more ADH = more aquaporins in cell surface membrane = collecting duct more permeable to water = more reabsorption of water from collecting duct via osmosis
- produces a smaller volume of more conc urine
(MA) Describe the role of ADH in osmoregulation on cold days.
- posterior pituitary gland secretes less ADH
- less ADH travels in blood
- target cells for ADH are cells lining collecting duct in nephrons of kidneys
- less ADH binds to receptors on cell surface membranes of target cells
- fewer vesicles containing aquaporins made + fuse w membranes decreasing membrane’s permeability to water
- less ADH = less aquaporins in cell surface membrane = collecting duct less permeable to water = less reabsorption of water from collecting duct via osmosis
- produce a larger volume of less conc urine
(MA) How does haemodialysis work?
- blood from artery removed
- blood pumps keep blood moving
- heparin added to prevent clotting (anticoagulant) during dialysis
- blood passes into a machine w partially permeable artificial dialysis membrane
- on other side of membrane is dialysis fluid which has correct conc of glucose, ions, urea
- blood + dialysis fluid flow in opposite directions to one another to maintain conc grad for diff
- urea diffuses from blood to dialysis fluid, excess water moves into it by osmosis
- air trap + air detector needed to remove bubbles before blood returned to a vein
- 3-4 hours, 2-4 times per week
(MA) What is a kidney transplant?
A new kidney is given to a patient surgically under general anaesthetic
(MA) What are the advantages of getting a kidney transplant?
- no need for time consuming dialysis
- diet less limited
- better qol than on dialysis ie can travel
(MA) What are the disadvantages of getting a kidney transplant?
- have to take immunosuppressants for lifetime of organ to avoid rejection; more likely to get infections
- risk of major surgery ie infections
- risk of rejecting organ
(MA) Why do kidney transplants need to be a match?
- donated kidneys will be recognised as foreign
- as antigens on kidney will be different to own ones
- causes rejection by immune system
- use immunosuppressant drugs to decrease chance of rejection
- also needs to be a match in size ie wouldn’t use child’s organ in an adult
(MA) Ethically, should kidney transplant be used?
- people should have a right to choose what to do with their kidneys
- donor could be paid + benefit from money by selling kidney
- people can donate a kidney to a family member
- people can donate w/out payment
- poorer people could be exploited into donating by offering them a lot of money
- whether you get a kidney or not shouldn’t depend on if you can pay for it
(MA) How do pregnancy tests work?
- embryos secrete human chorionic gonadotrophin, released into urine during pregnancy
- hCG acts as antigen
- has complementary shape to free monoclonal antibodies (anti-hCG)
- binds to free antibodies (w coloured beads on them)
- hCG-antibody complex moves along the test strip w urine
- hCG-antibody complex binds w immobilised antibodies specific to the complex
- binding of antibodies produces coloured line (due to coloured beads) = pregnant
- control antibodies bind w any urine + bind to immobilised antibodies on control line to form a coloured strip to indicate if test is working
- 2 lines = pregnant
(MA) How does anabolic steroid testing work?
- gas chromatography used to test urine for presence of anabolic steroids
- sample is vaporised in gaseous solvent
- moves down tubes lined w absorption agent
- different substances will be at different but unique times (retention value)
- this is analysed on a chromatogram
(MA) What are the side effects of anabolic steroids?
- increased risks of heart attacks
- liver damage
- infertility
- facial hair growth, breasts get smaller in women
- testes + breasts develop in men
(MA) Why are anabolic steroids banned in sport?
- gives people who take them an unfair advantage
- many side effects so it’s dangerous e.g. liver damage
- doesn’t reflect athlete’s natural ability
What are the main excretory products from the body?
- CO2 from respiration
- nitrogen containing compounds eg urea (nitrogenous waste)
- other compounds eg bile pigments found in faeces
How are the lungs used as an excretory organ?
CO2 passed from cells of respiring tissues to bloodstream where transported to lungs. Here, CO2 diffuses into alveoli to be excreted as breathed out
How is the liver used as an excretory organ?
Not directly involved in excretion. Has many metabolic processes + some substances produced passes to bile for excretion eg pigment bilirubin. Involved in converting excess amino acids to urea. Amino acids broken down by deamination. Nitrogen containing part of molecules combined w CO2 to make urea
How are the kidneys used as an excretory organ?
- urea passes to bloodstream to be transported in solution - dissolved in the plasma
- in kidneys: urea removed from blood to become part of urine
- urine stored in bladder before excreted from body via urethra
How is the skin used as an excretory organ?
- sweat contains salts, urea, water, uric acid + ammonia
- urea, uric acid + NH3 all excretory products
- loss of water/salts may be important part of homeostasis (maintaining body temp + water potential of blood)
Why is excretion important?
Build up of metabolic waste could be fatal esp if toxic ie NH3, CO2 as interfere w cell processes by altering pH
What causes build up of H+ ions in blood plasma and how is this prevented?
- dissociation of carbonic acid for transportation of CO2 around body
- change in pH detected by respiratory centre in medulla oblongata of brain causing increased breathing rate to help remove excess CO2
What happens if blood pH gets too low from too many H+ ions?
- below pH 7.35
- may cause headaches, drowsiness, restlessness, tremor, confusion
- may be a rapid heart rate + changes in blood pressure (respiratory acidosis). Can be caused by diseases or conditions that affect lungs (eg emphysema, chronic bronchitis, asthma, severe pneumonia).
- Blockage of airway due to swelling, foreign object or vomit can also induce acute respiratory acidosis
Why does deamination occur?
- Body can’t store excess amino acids but they contain almost as much energy as carbs so would be wasteful to excrete
- potentially toxic amino group removed (deamination)
- initially forms NH3 (v soluble/toxic) so converted to less soluble/toxic urea which can be transported to kidneys for excretion
- remaining keto acid used directly in respiration to release its energy or converted to a carb/fat for storage
What is the word equation for deamination?
amino acid + oxygen –> keto acid + ammonia
What is the word equation for the formation of urea?
ammonia + carbon dioxide –> urea + water
What is the formula for urea?
(NH2)2CO
What are liver cells called?
hepatocytes
What is the name of the blood vessel that supplies the liver with oxygen and what is the blood used for?
- hepatic artery
- oxygenated blood from heart travels from aorta via hepatic artery to liver
- supplies O2 for aerobic respiration
- liver cells v metabolically active, many of these processes require ATP, so important liver has a good supply of O2 for aerobic respiration
What is the name of the blood vessel that supplies the liver with the products of digestion and why does it do this?
- hepatic portal vein
- deoxygenated blood from digestive system enter liver
- rich in products of digestion. Concs of various substances is uncontrolled as just entered body from products of digestion in intestines
- blood may also contain toxic compounds absorbed from intestine
- important such substances don’t continue to circulate body before concs have been adjusted
How does blood enter/leave the liver?
hepatic vein - rejoins vena cava + blood returns to body’s normal circulation
What is bile?
-secretion from liver which has functions in digestion/excretion
What does the bile duct do?
Carries bile from liver to gall bladder where it’s stored until required to aid digestion of fats in small intestine. Also contains some excretory products eg bile pigments eg bilirubin, which will leave body in faeces
What are inter-lobular vessels?
Run between+parallel to lobules. The splitting of hepatic artery and portal vein
What happens in the sinusoid?
(Is lined with liver cells) Blood from hepatic artery and hepatic portal vein mix. As blood flows it’s in close contact w liver cells. Able to remove substances from blood + return other substances
What is the function of Kupffer cells?
- move within sinusoid
- breakdown + recycle old RBCs
- one product of Hb breakdown is bilirubin, which is one of the bile pigments excreted as part of bile
How does bile travel from where it’s produced to where it’s stored?
- made in liver cells
- released into bile canaliculi
- they join to form a bile duct which transports bile to gall bladder
What is at the centre of each lobule?
branch of the hepatic vein known as the intra-lobular vessel
- sinusoids empty into this vessel
- branches of hepatic vein from different lobules join to form hepatic vein, which drains blood from liver
What is the structure of liver cells?
- relatively unspecialised
- simple cuboidal shape w many microvilli on surface
What are the metabolic functions of hepatocytes?
- protein synthesis
- transformation and storage of carbs
- synthesis of cholesterol + bile salts
- detoxification
- means their cytoplasm must be v dense + is specialised in numbers of certain organelles it contains
What are the metabolic functions of the liver?
- control blood glucose/amino acid/lipid levels
- synthesis of bile/plasma proteins/cholesterol
- synthesis of RBCs in fetus
- store vitamins A, D, B12, iron, glycogen
- detoxification of alcohol, drugs
- breakdown of hormones
- destruction of RBCs
How is glycogen stored in the liver?
- store 100-120g of glycogen (8% of fresh weight of liver)
- glycogen forms granules in cytoplasm of hepatocytes
- glycogen can be broken down to release glucose into blood as required
How is hydrogen peroxide detoxified in the liver?
- catalase
- converts H2O2 to O2 + H2O
- particularly high turnover no. (no of molecules one molecule of catalase can render harmless/sec) of 5 million
How are drugs such as cocaine detoxified in the liver?
- cytochrome P450 (group of enzymes)
- these enzyme’s role in metabolising drugs can interfere w their other metabolic processes eg electron transport in respiration + can cause unwanted side effects in some medicinal drugs
What is formed throughout the breakdown of ethanol?
ethanol –> ethanol –> ethanoic acid –> acetyl coenzyme A
What happens if the liver has to detoxify too much alcohol?
Stores of NAD used up + insufficient left to deal w fatty acids so fatty acids converted back to lipis + stored as fat in hepatocytes so liver becomes enlarged (fatty liver, which can lead to alcohol related hepatitis or cirrhosis)
What is the ornithine cycle?
A series of biochemical reactions that convert ammonia to urea
What is the formula of keto acid?
RC=OCOOH
Why must ammonia quickly be converted to urea?
Highly soluble + toxic
In the ornithine cycle, what is formed when ammonia and carbon dioxide combine?
citrulline
How is citrulline converted to arginine?
Further addition of ammonia
How is arginine re converted to ornithine?
Removal of urea
What equation can be used to summarise the ornithine cycle?
2NH3 + CO2 –> CO(NH2)2 + H2O
ammonia + carbon dioxide –> urea + water
