excretion Flashcards
IMPORTANCE OF EXCRETION-
what is excretion?
what is the importance of excretion?
what metabolic wastes do mammals excrete?
why?
-the process by which toxic waste products of metabolism and substances in excess of requirement are removed from the body
-a key process in homeostasis and is important in maintaining metabolism
•as metabolic waste can have serious negative consequences on the body if they accumulate
•carbon dioxide
•nitrogenous waste (ammonia, urea, uric acid)
•bile pigment (produced during breakdown of haemoglobin)
-because they have a high metabolic rate so large amounts of metabolic waste
draw the metabolic waste table-
waste source effects if accumulate
what happens if carbon dioxide and ammonia are not excreted properly?
-they can accumulate and change the cytoplasm and body fluid pH = enzymes work less effectively
LIVER STRUCTURE- external
what does the liver require?
where from?
what is the liver directly connected to?
draw-
-a good blood supply to carry out production of excretory waste
•oxygenated blood from the heart = carried to liver by the hepatic artery
•blood from digestive system = carried to liver by hepatic portal vein (absorb and metabolise nutrients that are absorbed into the blood in the small intestine)
•deoxygenated blood exits the liver = by hepatic vein and flows back to the heart
-the gall bladder, functions:
~to store bile, a liquid that contains:
•bile salts for lipid digestion
•bile pigments from the breakdown of haemoglobin
~to release bile into the duodenum via the bile duct
STRUCTURE- internal
what is the liver made up of?
what are the liver cells arranged into?
and?
what then happens to the blood?
what are the capillaries called?
and?
what is each lobule also connected to?
what are kupffer cells?
draw lobule-
draw histology of liver-
-cells called hepatocytes
-arranged into structures called lubules
•each lobule is supplied with blood by branches of the hepatic artery and the hepatic portal vein
-the blood from the hepatic artery and the hepatic portal vein then mixes within each lobule inside wide capillaries
-sinusoids
•blood within the sinusoid exchanges substances with nearby hepatocytes = allowing hepatocytes to perform functions of the liver
-a branch of the hepatic vein that drains blood away from the lobule and into the main hepatic vein
-they move around in the sinusoids, and they are specialised resistant macrophages, involved in the breakdown and recycling of old red blood cells
•products of haemoglobin is bilirubin (makes poo brown)
LIVER FUNCTION-
what are the 3 liver functions?
•storage of glycogen
•formation of urea
•detoxification
describe the storage of glycogen-
-liver converts glucose into glycogen = process called glycogenesis
-insulin triggers this process after the pancreas detects an increase in blood glucose concentration
-the synthesis of glycogen removes glucose molecules from the bloodstream and decreases the blood glucose concentration to within normal range
-the glycogen produced during glycogenesis is stored inside hepatocytes
-glycogen is a compact molecule that is easily hydrolysed to form glucose
describe the formation of urea-
-proteins in our diet are broken down into amino acids
-these are absorbed into the bloodstream and transported to the liver by the hepatic portal vein
-excess amino acids are processed inside hepatocytes during a two step process:
•deamination
•the ornithine cycle
describe deamination-
what happens after deamination?
draw-
-the amino group (NH2) is removed from each amino acid, together with an extra hydrogen atom (H+)
-so NH2 and H+ combine to form ammonia (NH3)
-the part of the amino acid that remains after deamination is a keto acid which can:
•enter the krebs cycle to be respired
•be converted to glucose
•be converted to glycogen or fat for storage
describe the ornithine cycle-
draw-
-ammonia is a very soluble and highly toxic compound that can damage us if it builds up in the blood
-to avoid this, ammonia is converted to urea (less toxic) by the ornithine cycle
-ammonia is combined with carbon dioxide to form urea
•one molecule of urea is produced from one molecule of carbon dioxide and two amino groups
-the urea diffuses through the phospholipid bilayer of the hepatocytes and is transported to the kidneys dissolved in the blood plasma
-urea is then excreted by the kidneys
what is detoxification?
what substances undergo detoxification?
describe the detoxification of alcohol-
continuous alcohol detoxification can cause liver problems such as:
-the breakdown of substances that are not needed or are toxic
•alcohol
•hydrogen peroxide
•lactate
•medicinal drugs
-once consumed alcohol, or ethanol, is absorbed by the stomach and transported in the blood until it reaches the hepatocytes
-inside the hepatocytes, the enzyme alcohol dehydrogenase converts ethanol into a molecule called ethanal, ethanal is then converted into other molecules that enter respiration
•the metabolism of ethanol generates ATP, so hepatocytes do not metabolise as much fat as usual and instead store the fat = causes a condition called fatty liver
•stored fat reduces the ability of hepatocytes to carry out other functions and can lead to cirrhosis = scarring of the liver caused by excessive alcohol consumption
THE MAMMALIAN KIDNEY-
what are the kidneys two functions?
draw the kidney and it’s attached blood vessels-
draw out the table of each structure-
•its an osmoregulatory organ = regulate water content of the blood (maintain blood pressure)
•its an excretory organ = they excrete the toxic waste products of metabolism (such as urea) and substances in excess of requirements (such as salts)
what are the three main areas below the kidney? and what do they contain?
what are nephrons?
-the cortex = contains the glomerulus, bowman’s capsule, proximal convoluted tubule and distal convoluted tubule
-the medulla = contains the loop of Henle and the collecting duct
-the renal pelvis = where the urethane joins the kidney
-functional units of the kidney, responsible for the formation of urine
within the bowman’s capsule, there is a glomerulus, how is the glomerulus supplied with blood?
what do the capillaries of the glomerulus rejoin to form?
what does blood then do?
what does blood from these capillaries then flow into?
look at pic
-by the afferent arteriole (carries blood from renal artery)
-an efferent arteriole
-blood then flows from the efferent arteriole into a network of capillaries that run closely alongside the rest of the nephron
-the renal vein
KIDNEY FUNCTION-
the nephron is the functional unit of the kidneys and is responsible for the formation of urine, what two stages occur in the process of urine formation?
-ultrafiltration
•small molecules are filtered out of the blood and into the bowman’s capsule, forming glomerular filtrate
-selective reabsorption
•useful molecules are absorbed from the filtrate and returned to the blood
•the remaining filtrate forms the urine
ultrafiltration-
what afferent arteriole is wider in diameter than the efferent arteriole, meaning?
what’s is then formed?
what are the main substances that pass out of the capillaries and form glomerular filtrate?
what remains in the blood?
-results in high blood pressure within the glomerulus
•causes smaller molecules to be forced out of the capillaries of the glomerulus and into the bowman’s capsule
•this then forms the glomerular filtrate
•amino acids
•water
•glucose
•urea
•inorganic ions e.g Na+ , k+ and Cl-
-blood cells and large proteins as they are too large to pass though the holes in the capillary endothelial cells
how is blood in the capillaries, and the lumen of the bowman’s capsule separated?
what are they?
draw bowman’s capsule and glomerulus-
-by two cell layers with a basement membrane in between them:
•first layer = endothelium of the capillary, gaps in the endothelial cells allow small molecules to pass through this layer
•between the first cell layer and second cell layer = the basement membrane, made up of a mesh of collagen and glycoproteins, small molecules can pass through the holes in the mesh
•second cell layer = the epithelium of the bowman’s capsule, the epithelial cells have finger-like projections called podocytes with small gaps between them for small molecules to pass through
selective reabsorption-
what substances are reabsorbed?
why?
how is the proximal convoluted tubule epithelial cell adapted for reabsorption?
-?
-?
-?
-?
draw the table of where and why molecules are reabsorbed-
•water
•salts
•glucose
•amino acids
-because they need to be kept in the body
-microvilli on the cell surface membrane that faces the lumen (luminal membrane)
•increases surface area for reabsorption
-co-transporter proteins in the luminal membrane
•each transporting a specific solute across the luminal membrane
-many mitochondria
•provide energy for sodium-potassium pump proteins in the basal membranes of the cells
-cells tightly packed together
•means no fluid can pass between cells and all the substance that is reabsorbed must pass THROUGH the cells
explain how substances are reabsorbed?
-sodium-potassium pumps in the cells that line the proximal convoluted tubule actively transport sodium ions out of the epithelial cells and into the blood, they are then carried away
-this lowers the concentration gradient of sodium ions inside the epithelial cells, causing sodium ions in the filtrate to diffuse down their concentration gradient from the filtrate into the epithelial cells
-the sodium ions move my co-transporter proteins in the membrane, and as they move, co-transporters transport glucose and amino acids or other solutes, at the same time
-once inside the epithelial cells, these solutes diffuse down their concentration gradients into the blood.
osmoregulation-
what monitors water potential of the blood and where are they found?
what happens when the osmoreceptors detect a decrease in water potential of the blood?
and?
what does ADH do?
-sensory neurons called osmoreceptors, these are found in the hypothalamus
-nerve impulses are sent along these sensory neurones to the posterior pituitary gland
•stimulation it to release ADH
-ADH molecules enter the blood and travel throughout the body
•causes the kidneys to reabsorb more water
•reducing the loss of water in urine
explain how ADH has this effect?
-water is absorbed by osmosis from the filtrate in the nephron
-this reabsorption occurs as the filtrate passes through the collecting ducts
-ADH causes the luminal membranes of the collecting duct cells to become more permeable to water
-ADH does this by causing an increase in the number of aquaporins (water-permeable channels) in the luminal membranes of the collecting ducts, this is how:
•collecting ducts contain vesicles with aquaporins in their membranes
•ADH molecules bind to receptor proteins, this activates adenyl cyclase to make cAMP (phosphorylation of the aquaporin molecules)
•this activates aquaporins, causing vesicles to fuse with the luminal membranes of the collecting ducts
•increasing the permeability of the membrane to water
-as the filtrate in the nephron travels along the collecting duct, water molecules move from the collecting duct (high water potential), through aquaporins, and into the tissue fluid and blood plasma in the medulla (low water potential)
-as the filtrate in the collecting duct loses water it becomes more concentrated
-so a small volume of urine is produced
-it flows from the kidneys the the ureters and into the bladder
this flashcard should be after 19
explain the reabsorption of water and salts-
draw-
-sodium chloride ions are actively transported out of the filtrate in the ascending limb of the loop of Henle and into the surrounding medullary tissues = lowering its water potential
-the ascending limb of the loop of Henle is impermeable to water, so water is unable to leave the loop here by osmosis
-the water potential of the ascending limb increases as it rises back to the cortex due to the removal of solutes and the retention of water
-the descending limb is permeable to water, so water moves out of the descending limb by osmosis due to the low water potential of the medulla created by the ascending limb
-the descending limb has few transport proteins in the membranes of its cells, so has low permeability to ions
-water potential of the filtrate decreases as the descending limb moves down into the medulla due to the loss of water and retention of ions
-the low water potential in the medulla created by the ascending limb also enables the reabsorption of water from the collecting duct by osmosis
-the water and ions leave the loop of Henle and make their way into nearby capillaries
KIDNEY FAILURE-
what problems arise from kidney failure?
•urea, water, salts and various toxins are retained and not excreted
•less blood is filtered by the glomerulus, causing the glomerular filtration rate (GFR) to decrease = leading to a buildup of toxins in the blood
•also, the electrolyte balance in the blood is disrupted (the concs of ions and charged compounds are not maintained)
the importance of electrolyte balance-
what harmful consequences?
-excess potassium ions in the blood can lead to abdominal cramps, tiredness, muscle weakness and even paralysis
•if potassium ions concentrations continue to increase, the frequency of impulses from the sinoatrial node in the heart may decrease = can lead to arrhythmia and cardiac arrest
-depending on bodily needs, the kidneys can either conserve or secrete sodium = important in neuromuscular function, fluid balance and acid/base balance
•a build up of sodium can cause disorientation, muscle spasms, higher blood pressure and general weakness
what are the two potential treatments for kidney failure?
•renal dialysis = toxins, metabolic waste products and excess substances are removed from the blood by diffusion via a dialysis membrane
•kidney transplant = the non-functioning kidney or kidneys is replaced with a functioning kidney
