Excretion Flashcards
What is the purpose of excretion?
- wastes are produced by chemical reactions and must be removed from cells from your body
- the wastes must be excreted by your body
What is excretion?
- the removal from the body of the waste products of metabolic pathways
- performed by kidneys(excrete nitrogenous wastes), liver(excrete bile pigments), lungs(excrete CO2), and skin(excretes salts and water)
- excretion is the same as defecation, which is the process which rids the body of undigested food remains, plus bacteria, not metabolic end products
What are nitrogenous wastes?
- ammonia(NH3)comes from deamination of amino groups; it’s very toxic to tissues so it’s converted to urea in liver which is water soluble so it is excreted in urine
- creatinine is another nitrogenous waste; it comes from creatinine phosphate muscle metabolism(a phosphate storage molecule used for energy)
What are some other wastes besides nitrogenous wastes?
- bile pigments from the breakdown of red blood cells
- CO2
- HCO3
- ions such as salts, K+, Na+, Ca2+, Mg++, Fe+
- water which helps to maintain blood pressure
- urine is composed of urea(3%), salts(2%), water(95%)
What are the excretory organs and what are their functions?
- kidneys excrete urine, regulate blood volume, pH, filter the blood
- skin excretes perspiration which consists of water, salt, and small amounts urea; excretion from the skin is primarily for cooling
- liver excretes bile, which contains pigments that are breakdown products of RBC metabolism
- lungs excrete CO2 and some water
- intestines excrete some iron and calcium salts into feces
What are the parts of the urinary system?
- renal vein carries blood from kidneys back to the heart
- renal artery carries blood to kidneys from heart
- ureters are muscular tubes that move urine from kidneys to bladder via peristalsis
- the bladder holds urine, and it can expand/contract; it has stretch receptors that indicate when it is full and notifies the brain
- urethra is a tube connecting bladder to outside; the urethra of a man is about 6 inch long and it also transports semen; for women the urethra is only 1 inch long
What are the parts of the kidney?
- cortex(outer layer)
- medulla(middle, striated)
- pelvis(inner cavity)
- nephrons are the functional units of the kidney; they filter wastes from the blood while retaining water and other needed materials, there are about 1 million nephrons per kidney; urine formation occurs in the nephron
Describe the nephron
- the blood enters the capillary tuft called the glomerulus
- the afferent arteriole carries blood to the glomerulus while the efferent arteriole carries blood from the glomerulus
- the bowman’s capsule is the cup-like end of nephron where wasters are forced out of the blood and into the nephron
- from the capsule the nephron narrows into the proximal convoluted tubule; this makes a turn to form the the loop of henle
- the loop of henle is surrounded by a dense network of capillaries called the peritubular network
- the loop leads to the distal convoluted tubule which finally enters the collecting duct
What are the steps of urine formation?
- this occurs in the nephron as molecules are exchanged between blood vessels(i.e. the glomerulus and peritubular capillary network) and nephrons
1. pressure filtration occurs inside bowman’s capsule as molecules are forced through the glomerulus
2. selective reabsorption occurs in the proximal convoluted tubule(Na+, Cl-, water)
3. tubular excretion occurs in the distal convoluted tissue
What is ultrafiltration?
- the process where molecules are filtered through the glomerulus due to high blood pressure
- this “ultrafiltered” fluid is called filtrate, passes through the capsule’s porous basement membrane(which further prevents large molecule from entering the filtrate)
- the filtrate then carries through the proximal convoluted tubule down the loop of Henle and across the distal convoluted tubule and it enters the collecting duct and drains from the pelvis of the kidney
What is pressure filtration?
-high blood pressure in the glomerulus forces small molecules such as water, nitrogenous wastes, nutrients, and ions(salts) into the bowman’s capsule
^the glomerulus is similar to capillaries except it has small slits called fenestrations that open with an increase of blood pressure
-the large molecules(blood cells, platelets, proteins); these remain in the blood and leave the glomerulus via the efferent arteriole; the efferent arteriole is smaller in diameter to the afferent arteriole which also helps to increase blood pressure
-the small, filterable molecules are forced into bowman’s capsule from the filtrate
-high blood pressure is necessary for filtration; this is accomplished through the functioning of the juxtaglomerular apparatus(a special region of afferent arteriole)that will, if necessary, release renin to increase blood pressure
What is selective reabsorption?
- after the filtration occurs, molecules are reabsorbed in filtrate that are needed by the body
- the molecules that are reabsorbed move from the proximal convoluted tubule to the peritubular capillary network(back into the bloodstream)
- most water, nutrients, some salts move back to the blood while some water wastes, excess slats continue through the loop of Henle
- reabsorption requires active(requiring ATP and as seen with glucose & Na+) and passive (as seen with Cl- & water)
- the proximal tubule is only one cell thick and is lined with microvilli; the cells are packed with mitochondria and proton pumps
What happens in the loop of Henle?
- still part of selective reabsorption
- after the essential nutrients are reabsorbed, tubular fluid now enters the loop of Henle
- the primary role of loop of Henle is reabsorption of water
- over 99% of the water in original filtrate is reabsorbed by the nephron during urine formation
- salt is also passively and actively reabsorbed; this concentrates the urine allowing it to be hypertonic to the plasma
- in the descending limb, this section is permeable to water but to sodium ions; this makes this region high in solute concentration; as loops overlap, this makes the water be drawn out by the pressure of the descending limb
- in the ascending limb, this section is permeable to sodium ions but not to water; as the concentration filtrate flows up the Na+ is actively pumped out; this makes the medulla tissue of the kidney high in solutes
What is tubular excretion?
- an active process by which other non-filterable wastes can be added to the tubular fluid so that these wastes will also be excreted in the urine
- it occurs in the distal convoluted tubule and the secreted substances include some chemicals (H+ ions and NH3)
- the fluid now enters the collecting duct in the cortex; the fluid in the collecting duct is isotonic to the surrounding cells(therefore there is no net movement of water)
- as the fluid moves this changes; in the medulla, fluid is hypotonic to cells of medulla; therefore water passively diffuses out of the collecting duct
- the tubular fluid we now call urine passes from the duct into the pelvis of the kidney and enters the ureter for transport to bladder
What is ADH?
-antidiuretic hormone
-made by the hypothalamus and and sent to pituitary gland which releases ADH and promotes reabsorption of water from collecting duct and distal convoluted tubule; in other words ADH is a hormone that makes us produce less urine
-when released, it travels in the blood to the kidney, where it acts on the distal convoluted tubule and collecting duct
-makes collecting duct and distal convoluted tubule permeable to water so water moves from nephron(filtrate) & capillaries (blood)
^this water is reabsorbed into the peritubular capillary network so more water goes back into the blood; this will increase the amount of water(solvent) in the blood and therefore increase blood volume
-as the the blood becomes dilute, the hypothalamus detects this and ADH secretion stops(negative feedback loop)
