excretion Flashcards
why is excretion important?
if the toxic materials remain in the body, the internal environment fluctuate and continuation of metabolic processes is hindered
define excretion
it is the removal of waste products that were formed during metabolic reactions in the body cells
products of excretion
co2, excess water and salt, products from deamination in the liver (eg urea), products from detoxification of substances such as alcohol
what are nitrogenous excretory products?
deanimated excess amino acids
includes: uric acid, creatinine, ammonia
how are bile pigments excreted?
bile pigment is formed from break down of haemoglobin of rbcs and it is excreted through urine, sweat and expired/exhaled air
formation of urea
enzymes in the liver deaminate the excess amino acids by removing amino groups. the leftover amino acids cannot be used and are converted to ammonia. ammonia is quite toxic to all cells so it is combined with carbon dioxide to form urea. its removal from the body requires a lot of water
formation of uric acid
uric acid is formed from the breakdown of nucleic acids (DNA, RNA) from the cell of the food consumed and from metabolic reactions of nucleic acids and ATP. it is almost insoluble in water and cannot diffuse into the body cells so it is harmless to cells. it requires a lot of energy but little water to remove
formation of creatinine
it is mainly derived froma nitrogen-containing molecule called creatine found in muscle cells
what does urine consists of?
it consists of urea, water and smaller amounts of creatinine and uric acid
what does the urinary system consists of?
kidneys and the nephrons within it, the ureters, urinary bladder and urethra
what is the kidney made up of?
- fibrous capsule
- renal cortex
- renal medulla
- renal pelvis
- renal vein
- renal artery
- ureter
what is the fibrous capsule?
it is the outer membrane that surrounds the kidney and serves as a protection layer
what is the renal cortex?
it is the lighter-coloured outer region which consists of the Bowman’s capsule, convoluted tubules and blood vessels
what is the renal medulla?
it is the darker-coloured inner region made up of the loop of Henle, collecting duct and blood vessels
what is the renal pelvis?
it is a funnel-shaped cavity that drains urine into the ureter
what does the nephron consist of?
- Bowman’s capsule
- Proximal convoluted tubule
- Loop if Henle
- Distal convoluted tubule
- Collecting duct
what is the Bowman’s capsule?
it is the closed end at the start of the nephron. it is cup-shaped and it contains a mass of blood capillaries aka the glomerulus. Its inner layer is made up of a thin layer of specialised cells known as podocytes
what is the proximal convoluted tubule?
it is a series of loops surrounded by a dense network of peritubular capillaries. Its walls are made up of epithelial cells with microvilli
what is the Loop of Henle?
it is the long loop that extends from the cortex region to the medulla region and back up again. It is surrounded by peritubular capillaries.
what is the distal convoluted tubule?
it is the series of loops that is surrounded by a less dense network of peritubular cells than proximal convoluted tubule. Its walls are also made up of epithelial cells with microvilli
what is the collecting duct?
it is a tube in which multiple distal convoluted tubules empty. it is lined by specialised cells and becomes increasingly wide as it drains into the renal pelvis
what are the blood vessels associated with each nephron?
- Afferent arteriole
- Glomerulus
- Efferent arteriole
- Peritubular capillaries
what is the afferent arteriole?
it is the tiny vessel arising from the renal artery that enters the Bowman’s capsule in the nephron
it supplies the nephron with bloodn
what is the glomerulus?
network of capillaries from which fluids are forced out of the blood due to the high hydrostatic blood pressure
what is the efferent arteriole?
it is the tiny vessel leaving the Bowman’s capsule and its lumen diameter is narrower than that of afferent arteriole. this causes the increase in the hydrostatic blood pressure in the glomerulus
what are the peritubular capillaries?
they are a dense network of blood capillaries which surrounds the convoluted tubules and loop of Henle. they reabsorb mineral salts, glucose and water from them and merge to form venules which are further merged to form the renal vein.
what are the stages of urine formation?
Ultrafiltration, selective re-absorption and secretion
what happens during ultrafiltration?
Due to the high hydrostatic pressure created as a result of the difference in lumen diameter between the afferent and efferent arteriole, most of the components of blood apart from plasma proteins and blood cells are forced out of the glomerulus and into the Bowman’s capsule to form the glomerulus filtrate. Since this process relies on the steepness of the hydrostatic pressure gradient, it can be affected by changes in blood pressure.
How is the glomerulus filtrate determined?
Ultrafiltration does not select for which substance can enetr the nephron tubule. Molecular size determines which substances can enter. The capillary walls of the glomerulus is made up of one layer of endothelial cellswith pores between them which are large enough for blood cells and protein molecules to pass through. However, the basement membrane of the Bowman’s capsule only allows small molecules like urea, glucose and water to enter it, thereby preventing plasma protein and red blood cells from entering the nephron tubule
What happens during selective-reabsorption?
Useful substances such as glucose and amino acids are actively transported out of the nephron tubules and into the interstitial fluid and back into the peritubular blood capillaries. hence only the excretory waste materials remain the glomerular filtrate
what happens at the loop of henle?
Selective-reabsorption of amino acids and glucose lowers the water potential of the intertitial fluid and water potential in the glomerular filtrate is higher. This results in a large amount of water being reabsorbed along the loop of Henle. At the ascending limb of the loop of henle, active transport of salt from the glomerular filtrate occurs which increases the rate of osmosis by increasing the water potential in the glomerular filtrate.
what happens at the distal convoluted tubule and collecting duct?
The walls of the ascending limb of the loop of Henle is impermeable to water but the walls of the end of the distal convoluted tubule and collecting duct are not. Hence the rate of osmosis is high due to the high water potential of the glomerular filtrate as a result of active transport of salt out of it. forms concentrated urine
what are some the structural features of the nephron for selective re-absorption?
- parts of nephron are very coiled, this increases surface area to volume ratio and increases time taken for glomerular filtrate to travl through the nephron thus giving more time for selective reabsorption to occur
- epithelial cells of coiled tubules contains many mitochondria. more energy released for reabsorption of substances via active transport
what happens during secretion?
Certain substances like creatinine, hydrogen ions and drugs are removed from the peritubular capillaries and into the distal convoluted tubule and collecting duct
what is kidney failure?
it is when the kidneys are unable to function properly, resulting in the accumulation of waste products in the blood
what causes kidney failure?
obstruction of blood supply to the kidneys, diabetes and high blood pressure
how to treat kidney failure?
patients have to undergo dialysis where waste products such as urea are removed from the blood before it is returned to the vein
how does dialysis work?
- Blood is drawn from a vein in the patient’s arm
- Blood is pumped into the dialysis machine through a tubing
- the semi-permeable tubing is bathed in dialysis fluid
- small molecules (eg urea) and metabolic waste products diffuse from the tubing and into the fluid
- larger molecules like red blood cells remain in the tubing
- filtered blood is returned to the a vein in the patient’s arm
features of dialysis machine
- fluid contains same concentration of amino acids, glucose and mineral salts as the blood to esnure no net movement of these essential substances from blood to the fluid. if the blood lacks any of these substances, they will diffuse from the fluid and into the blood
- metabolic waste is absent in the fluid to create a steep gradient for the diffusion of excretory products into the fluid
- dialysis tubing is long and coiled to increase surface area to volume ratio for increase rate of diffusion of substances
it is semi-permeable so that large molecules like protein and red blood cells are retained in the blood while small molecules like urea is removed - dialysis fluid flows from opposite direction to maintain steep concentration gradient for removal of waste products
