EXCRETION Flashcards
Liver functions
Breaks down excess amino acids
DEAMINATION- nitrogen containing amino groups are removed from any excess amino acids, forming ammonia and organic acids
Organic acids can be respired to give ATP and converted to carbohydrate and stored as glycogen
Ammonia is too toxic for mammals to excrete directly so it’s combined with CO2 in the ornithine cycle to create urea
DETOXIFICATION- removes harmful substances like alcohol, drugs and unwanted hormones, they are broken down into less harmful compounds that can be excreted from the body
What are the functions of the kidney
Blood filtration
Selective reabsorption of useful substances
Regulates water potential
Water reabsorption
Blood filtration
Blood from the renal artery enters small arterioles in the cortex
Each arteriole splits into a structure called a glomerulus (a bundle of capillaries looped inside a hollow ball called the Bowman’s capsule) this is where ultrafiltration takes place
Afferent arteriole- takes blood into each glomerulus, efferent arteriole- takes the filtered blood away from the glomerulus, this arteriole is smaller in diameter so the blood in the glomerulus is under high pressure, this high pressure forces liquids and small molecules in the blood out the capillary into the Bowman’s capsule
The liquid and small molecules pass through 3 layers to get into the Bowman’s capsule and enter the nephron tubule (the capillary wall, the basement membrane and the epithelium of the Bowman’s capsule)
Larger molecules like proteins and blood cells can’t pass through and stay in the blood
The liquid and small molecules now called filtrate pass along the rest of the nephron and useful substances are reabsorbed on the way
Selective reabsorbtion
Useful substances leave the tubules of the nephrons and enter the capillary network that’s wrapped around them
The epithelium of the PCT wall has microvilli to provide a large surface area for reabsorption of useful materials from the filtrate into the blood
Useful solutes like glucose, amino acids, vitamins and some salts are reabsorbed along the PCT by active transport and facilitated diffusion
Some urea is also reabsorbed by diffusion
Water enters the blood by osmosis because the water potential of the blood is lower than that of the filtrate
Water is reabsorbed from the loop of Henle, collecting duct and DCT
The remaining filtrate is urine which passes from the ureter to the bladder
Water reabsorbtion
Countercurrent multiplier mechanism
At the top of the ascending limb, Na+ and Cl- ions are actively pumped into the medulla, the ascending limb is impermeable to water so water stays inside the tubule which creates a low water potential in the medulla due to a high concentration of ions
Water moves out the descending limb into the medulla by osmosis, the filtrate becomes more concentrated and water in the medulla is reabsorbed into the blood through the capillary network
Near the bottom of the ascending limb, Na+ and Cl- ions diffuse out into the medulla
The ion concentration in the medulla is increased- lowering the water potential so water moves out the collecting duct by osmosis, the water is then reabsorbed into the blood through the capillary network
The volume of water is reabsorbed from the collecting duct into the capillaries is controlled by changing the permeability of the collecting duct
Osmoregulation
Osmoreceptors in the hypothalamus detect changes in water potential
Neurosecretory cells in the hypothalamus release ADH
ADH travels to the kidneys
ADH is detected by cells in walls of the collecting duct
Activates phosphorylase
Causes the vesicles containing aquaporins to fuse with the plasma membrane
Water moves by osmosis into the blood
Blood water potential rises which is detected by osmoreceptors and fewer impulses are sent to the pituitary gland so less ADH is released and aquaporins stop inserting into the membrane (negative feedback)
Kidney failure
Detected using the GFR rate
Causes kidney infections and high blood pressure
Problems- waste products build up in the blood, fluid accumulates in tissues, unbalanced electrolytes, anaemia and death
Treatments of kidney failure
Renal dialysis or kidney transplant
RENAL DIALYSIS- patients blood passes through dialysis machine (blood flows on one side of the partially permeable membrane and dialysis fluid on the other)
Waste products and excess water/ions diffuse across the membrane into the dialysis fluid- removing them from the blood
Blood cells and larger molecules are prevented from leaving the blood
