Biology Unit 4.2.1- Excretion

Excretion
1. excretion- removal of metabolic waste from the body
2. metabolic waste- consists of toxins, excess substances produced by reactions in the cell
3. what needs to be excreted and where are they produced
  1. CO2, from respiring cells - every living cell in the body
  2. Urea/nitrogen containing components- liver from excess amino acids
4. where are they excreted:
  1. CO2: Cells->Blood Stream -> Lungs -> alveoli -> Breathe out
  2. Urea: Liver -> Bloodstream -> Kidneys -> Urine -> bladder -> Urethra
  3. deamination- removal of amine group from amino acid to produce ammonia
5. Why are they removed-
  1. CO2- if there is excess...
    1. creating hydrocarbons H+ also formed, H+ competes with O2 in haemoglobin. can reduce O2 transport
    2. carbaminohaemoglobin- lower affinity fro O2
    3. causes respiratory acidosis (CO2+H2O-->H2CO3
      1. Disassociation of carbonic acid- H2CO3 -->H+ + HCO3-
    4. Blood becomes too acidic, therefore, increased breathing. If alkaline- difficulty breathing, headaches, drowsy
  2. Nitrogenous compounds
    1. Deamination: amino acids + O2 ---> Keto Acid + 2NH3
      1. Formation of Urea: 2NH3 + CO2 ----> CO(NH2)2 +H2O
The Liver
1. Structure
  1. hepatocytes (liver cells)- carry out metabolic processes
  2. internal structure is in such a way that as much blood flows
2. Blood flow to and from the liver- blood supply from 2 sources:
  1. 1. Oxygenated from heart: blood travels from aorta via hepatic artery into the liver. the liver cells require ATP therefore, important to have enough oxygen
  2. 2. Deoxygenated from digestive system: blood enters liver via hepatic portal vein (capillaries are both ends)- rich with products from digestion. blood leaves hepatic portal vein, rejoins vena cava and blood returns to normal circulation
  3. bile duct- carries secretion from liver to gall bladder where its stored until requiredt o aid digestion of fats in small intestine
3. Arrangement of cells inside liver
  1. arranged to ensure best possible contact between blood and liver
  2. divided into lobes which are further divided into cylindrical lobules
  3. hepatic artery and hepatic portal vein enter liver and split into smaller vessels. they run inbetween and parallel to lobules (inter-lobular vessels)- at intervals, branches off the artery and vein lobules. blood mixed and along the sinusoid (lined by liver cells). empties into lobular vessels (branch off hepatic vein)
  4. Branches of hepatic vein from different lobules join to form hepatic vein--> drains blood from liver
  5. blood flows along sinusoid, close to liver cells, able to remove molecules from blood and pass molecules into blood
  6. liver cells- manufacture bile. released into the bile canaliculi join therefore, forms bile duct
4. liver cells- hepatocytes: simple cuboidal shappe with microvilli. cytoplasm=dense and specialised in amount of different organelles it contains
  1. protein synthesis
  2. storage of carbohydrates
  3. cholesterol
  4. bile
5. kupffer cells
  1. specialised macrophages- move about within sinusoid and involved with breaking down and recycling red blood cells.
  2. bilirubin is a product of the breakdown of haemoglobin. excreted as part of bile and faeces
6. functions of the liver
  1. include...
    1. blood glucose control , amino and lipid levels
    2. synthesis of rbc, plasma, protein, cholesterol
    3. storage of Vitamin DA, D, B12, iron, glycogen
    4. detoxification
    5. breakdown of hormones
    6. destruction of rbc
  2. Formation of urea
    1. urea: excretatory product formed from breakdown of amino acids
    2. 2 steps:
      1. 1.deamination- produces ammonia, organic compound Keto Acid, which can enter respiration and release energy . Amine acod + oxygen = keto acid + ammonia
      2. 2. ornithine cycle- ammonia is soluble but toxic, converted to less toxic. ammonia combined with carbon dioxide to produce urea. urea is less soluble and toxic so can be passed back into blood and transported to kidney. kidneys: Urea --> ura. Ammonia + Carbon Dioxide ---> Urea + Water
  3. Detoxification
    1. liver able to detoxify many compounds- hydrogen peroxide, alcohol, drugs
    2. toxins rendered harmless by oxidation reduction, methylination
    3. liver cells contain enzymes that render toxic --> less toxic. catalase (hydrogen peroxide--> O2 + H2O
    4. of alcohol
      1. 1. ethanol dehydrogenase breaks down ethanol- creates ethanal
      2. 2. ethanal dehydrogenated futher by ethanal dehydrogenase --> ethanoate
      3. 3. ethanoate + Coenzyme A ---> acetyl Coenzyme A which enters respiration
      4. 4. H2 atoms released combined with coenzyme NAD
      5. NAD requuired to oxidse/breakdown fatty acids needed for respiration
      6. fatty liver- fatty acids stored as lipids in liver- leads to alcohol releated illnesses- hepatitis and cirrhosis
The Kidney
1. Structure of the kidney
  1. supplied with blood from Renal Artery and drained via renal vein
  2. role- remove waste from blood and produce urine
  3. cortex- outer region
  4. medulla- inner regions
  5. pelvis- leads to ureter
2. nephron
  1. Tiny tubules- 1 million in each kidney
  2. 1. start in cortex- from glomerulus
  3. 2. fluid pushed down bowmans capsule by ultrafilteration
  4. capsule leads to nephron, divided into 4
    1. proximal convoluted tubule
    2. loop henle
    3. distal convoluted tubule
    4. collecting duct
  5. 3. fluid moves along nephron, composition alters (selective reabsorption)
  6. selective reabsorption- useful substances are reabsorbed from nephron to blood stream, while excratory products stay in nephron
  7. reabsorbed into tissue fluid
  8. final product in collecting duct = urine. passes into pelvis and down ureter into bladder
3. How does the composition of fluid change
  1. proximal convoluted tubule- fluid altered by reabsorption of sugars, salts and water (85% reabsorbed)
  2. descending limb of loop of henle- low WP by additon of salts and removal of water
  3. ascending limb- high WP, salts removed via active transport
  4. collecting duct- low WP- removal of water. ensures urine has low WP and urine has high concentration of solutes found in blood
Formation of urine
1. what is filtered out the blood:
  1. water
  2. amino acids
  3. glucose
  4. urea
  5. inorganic ions
2. what is left in the capillary
  1. rbc
  2. proteins
  3. presence of proteins = blood has low WP
  4. low WP ensures fluid retained in blood and contains water and dissolved substances
  5. low WP important to help reabsorb water later
  6. 125cm3min-1 total vol filtered out, 180dm3 a day
3. selective reabsorption
  1. occurs at proximal convoluted tubule- 85% of filtrate reabsorbed
  2. glucose, amino acids, salts and water reabsorbed
  3. cells lining proximal convoluted tubule specialised to achieve reabsorption
  4. microvilli- increase reabsorption SA
  5. co transporter proteins- transport glucose and amino acids in association with NA+ from tubule to cell (facilitated diffusion)
  6. opposite membrane (Close to TF) is folded, increasing SA. contains sodium potassium pumps- Na+ out, K+ in.
4. how reabsorption occurs
  1. sodium potassium pumps- remove Na+ from cells lining proximal- lowers conc of Na+ in cytoplasm
  2. Na+ transported into cell with glucose and amino acids.
  3. glucose/amino acid concentrations increase, able to diffuse out of opposite sides of cell TF
    1. enhanced by active removal of glucose and amino acids from cells
  4. substances in TF diffuse diffuse into rbc and carried away
  5. reabsorption of salts/glucose/amino decrease WP in cells, increased WP in tubule fluid
    1. H20--->cell then reabsorbed into rbc via osmosis
  6. larger molecules that have entered tubule, reabsorbed by endocytosis
5. Ultrafilteration
  1. Afferent arteriole- where blood flows into the glomerulus (wider then efferent)
  2. Efferent arteriole- carries blood away from arterioles- Narrow
  3. difference in diameters ensures blood in capillaries of glomerulus is under pressure. pressure in glomerulus high in bowmans capsule. pressure difference pushes flow from bowmans capsule to glomerulus
  4. barriers between blood capillary and lumen of bowmans consist of 3 layers:
    1. 1. endothelium (capillary)- narrow gaps betweens cells where blood/substances can diffuse in and out
    2. 2. basement membrane- collagen + glycoproteins. filter to prevent passage of molecules with rmm above 69000
    3. 3. epithelial cells (bowmans capsule)- podocytes have specialised cells- finger like shaped. ensures gap between cells. fluid from blood in glomerulus pass between these cells into lumen of bowmans
water reabsorption
1. reabsorption of water
  1. each minute: 125 cm3 filtered from blood entering nephron
  2. after selective reabsorption, 45cm3 left in proximal
  3. loop of henle: creats low or high WP in medulla. ensures more water can be rabsorbed from collecting duct.
    1. descending limb- descends into medulla
      1. achieved: fluid descends deeper into medulla, low WP- water lost osmotically, ions diffuse in
    2. ascending limb- ascends out of cortex
      1. achieved: ascending up cortex, high WP- ions actively transported out, fluid loses salts, not water
    3. arrangement allows salts to be transferred from ascending to descending.
    4. overall effect: increase salt conc in TF therefore they diffuse out thin wall of ascending (surroinding TF = low WP
2. hairpin arrangement multiplier- name given to arrangement. effect of this arrangement increases efficiency of salt transfer from ascedning to descending. causes build up of salts in TF
  1. movemnt of salts from ascending to medulla increses salt conc in TF of medulla therefore, low WP
  2. removal of ions from ascnding means at top, urine is dilute. water reabsorbed from urine in distal tubule and collelcting duct
3. collecting duct
  1. top of ascending , fluid goes to distal convoluted tubule (active transport adjusts salts). Distal to collecting duct (water removved, fluid is high wp) to medulla then pelvis
  2. 1.5 - 2 dm3 reaches pelvis daily. -ve WP, conc of salts and urea is high
Osmoregulation
1. control and regulation of WP in blood and body fluid. Kidney controls WP in blood
2. water gained:
  1. food
  2. drink
  3. metabolism
3. water lost:
  1. urine
  2. sweat
  3. exhale
  4. faeces
4. cool day: a lot of fluid, large and dilute volumes of urine
  1. less water conserved, walls decrease permeability , less water reabsorbed
5. hot day, little water, small and concentrated urine
  1. more water conserved
6. walls of collecting duct vary in permeability according to water needs of the body
7. altering permeability of collecting duct
  1. responds to ADH (antidiuretic hormone). cells have ADH receptors. ADH binds to receptors, cause enzyme controlled reactions in cell. therefore, vesicle containing water permeable channels are inserted. Allows more water to be transported in as permeability increases
    1. more ADH, more permeability, more water reabsorbed, less urine, low WP
8. Adjusting conc of ADH in blood
  1. osmoreceptors- within hypothalamus, monitor WP of blood. respond to effects of osmosis. if WP is low, osmorecptor cells lose water, shrink and stimulate neurosecetory cells in hypothalamus
  2. neurosecetory cells- specialised neurones, produce and release ADH. manufactured in cell body which lie in hypothalamus. ADH flows down axon to terminal build in posterior pituitary gland
  3. ADH-> blood capilliaries (posterior pituitary gland) -> around body and acts on cells of collecting duct.
  4. WP of blood increase, WP decrease.
  5. H breaks down (half life of 20mins)
Kidney Failure
1. can occur for a number of reaons:
  1. Diabetes
  2. hypertension
  3. infection
2. Kidney fails completely?- body cannot remove excess water and waste from blood. unable to regulate levels of water and salts in body and could lead to death
3. Treatments:
  1. 1. Diyalysis- use of partially permeable membrane to filter blood. most common treatment, removes waste and excess fluid and salts by passing over a diyalisis membrane. Permeable membrane allows exchange of substances between blood and dialysis fluid. Excess substances diffuse into dialysis membrane, too low, substances diffuse from dialysis membrane to blood
    1. Diyalysis membrane- partially permeable that separates the dialysis fluid from patients blood in the machine
    2. Dialysis fluid- complex solution that matches the composition of body fluid
    3. Haemodialysis- blood from vein to machine containing artificial dialysis membrane . Hepanin added to avoid clotting and removes bubbles before returning to the body. performed at clinic, three times a week
    4. peritoneal dialysis
      1. filter = bodies own abdominal membrane
      2. 1. implant permanent tube into abdomen
      3. 2. dialysis solution poured through tubes and fills space between abdominal wall and organ.
      4. 3. several hours later: used solution drained from abdomen. patient can walk around as its happening
4. Kidney Transplant
  1. old kidney is left in place unless if infected or cancerous. usually a living rlative or someone who has dies. Major surgery, patient kept under anaesthesia. surgeon implants lower abdomen and blood supply and bladder. many feel better. Immunosuppresents- provideto help prevent bodys own immune system from rejecting foreign object.
    1. Advantages: diet less limited, better, quality of life,
    2. Disadvantages: immunosuppressents for life, major surgery, infections, bleeding, increased BP
5. Pregnancy testing

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Biology Unit 4.2.1- Excretion

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	Created by Sarah Pirbhai almost 11 years ago