Hi there! Shreyas here. Today, I will be talking about excretion in
humans. The main organs of excretion in humans are
kidneys, lungs, liver and the skin. The kidneys are a pair of bean shaped organs
located on either side of the backbone and at the back of the abdomen. The kidneys are about 4 to 5 inches, about the size of a fist. The kidney is made up of two zones. The outer cortex and the inner medulla. At the concave region towards the centre on
the inner surface, you find a structure called Hilum. At this point, ureter, nerves and the blood
vessels enter. Each kidney is made up of a million unit of
nephron. The nephron is called as the functional unit
of kidney through which blood filters. The nephron is made up of many structures. First is the bowman’s capsule. The bowman’s capsule is a cup like structure
and the glomerulus is enclosed inside the bowman’s capsule. The glomerulus consists of afferent arteriole
or the incoming arteriole and the efferent arteriole or the outgoing arteriole. After the bowman’s capsule, is the proximal
convoluted tubule. Proximal, because it is near to the bowman’s
capsule. After the proximal convoluted tubule or the
PCT, is the descending limb of loop of henle. The loop of henle is a hairpin like structure. After the descending limb, is the ascending
limb followed by the distal convoluted tubule or the DCT. The DCT opens out into the collecting duct. These collecting duct, many of which passes
through the medullary pyramid and opens out into the renal pelvis which is connected to
the ureter. So, the urine trickles down from the collecting
duct, passes through the medullary pyramid, reaches the renal pelvis and the urine is
excreted out through the ureter. From the ureter, the urine passes into the
urinary bladder wherein the urine is stored temporarily before being excreted out through
the urethra. This forms the basic structure of kidney and
the nephron. The main function of kidney is to filter the
blood, remove the wastes, maintain body fluid balance and also the electrolyte balance. Process of urine formation. Urine formation happens mainly in three processes. Glomerular filtration, tubular re-absorption
and tubular secretion. Glomerular filtration. Blood from the afferent arteriole, enters
towards the bowman’s capsule and the blood is filtered out from the capillary, into the
bowman’s capsule. The afferent arteriole has a diameter which
is much greater than the diameter of the efferent or the outgoing arteriole. This difference in the diameter causes blood
pressure. This blood pressure is responsible for excretion
of substances out of the capillaries into the bowman’s capsule. Some of the substances that are excreted out
of the capillaries into the bowman’s capsule include most of salts, most of glucose, urea
and variable concentration of few ions. From the bowman’s capsule, the filtrate which
is now called as the glomerular filtrate, is passed on to the proximal convoluted tubule. From here, tubular re-absorption takes place. Out of the filtrate, only 1 percent of the
filtrate is excreted out of the body. The rest, all substances, are reabsorbed back
into the body. This is vital, because the body requires vital
nutrients. Hence, tubular re-absorption is very important. So, some of the substances that are excreted
out into the blood are water, sodium ions inside the water and glucose. From the proximal convoluted tubule, the filtrate
then passes onto the descending limb of loop of henle. The tubes are highly permeable to water but
less permeable to electrolytes. Hence, water moves away from the tubes into
the interstitium surrounding the tubule, making the filtrate concentrated. From here, the filtrate then passes onto the
ascending limb of loop of henle, wherein the tubes are less permeable to water and highly
permeable to electrolytes. The filtrate then passes onto the distal convoluted
tubule. From here, tubular secretion takes place. The anti-diuretic hormone or the ADH plays
a very important role at this point or location. If the ADH concentration is more in the blood,
water passes out from the tubes into the blood, making the filtrate or the urine more concentrated
and if ADH is less in the blood, the opposite happens. At the tubular secretion region, most of the
substances that are in the blood are absorbed back into the tubules. Some of the substances that are secreted into
the tubules include potassium, hydrogen ions, sodium ions, some hormones, urea, creatinine
and some drugs. So, these are the three processes wherein
urine formation happens. The urine formed over here, is passed on to
the collecting duct through the medullary pyramid to the renal pelvis and to the ureter. The urine consists of just 1 percent of the
filtrate and contains urea, creatinine and variable concentration of ions. The urea and creatinine are highly concentrated. This forms the excretion in humans through
kidneys. On an average, an adult human produces 1.5
to 2 decimeter cube of urine per day. Other organs of excretion are lungs and skin. The lungs help in exhalation or expelling
the carbon-di-oxide out of the body and sweat is produced from the sweat glands which are
located in the skin. From the sweat glands, the sweat comes out
through the tiny pores on the skin or the surface of the skin. The sweat evaporates causing a cooling sensation
to the body. The sweat consists of sodium chloride, urea
and lactic acid. So, these are other forms of excretion, through
lungs and skin. The main disorder of excretory system is nephritis,
which is an inflammation of the kidney. Another disorder is formation of kidney stones,
which is the deposition of calcium compounds obstructing the passage of urine. Patients with kidney failure undergo a process
called dialysis. This is excretion in humans. Thank you for watching the video. If you have any questions, please feel free
to comment. Have a great day!