excretory system Archives

In this 3D animation we go over the anatomy and physiology of the human excretory system, the kidneys, nephrons, and glomeruli. This 3D animation of the human excretory system describes in detailed yet easy to understand language the anatomy and physiology of the kidneys, nephrons, glomerulus, and the processes of excretion, filtration, reabsorption and secretion, showing the location and anatomy of all the important structures involved, including the Bowman’s capsule, loop of Henle, pyramids and collecting ducts. USMLE test content. Review: The kidneys are the primary organs involved in the process of excretion. The kidneys are part of the urinary system. The two kidneys on either side of the backbone are connected to two ureters that empty into the urinary bladder down below. The urethra is the tube at the bottom of the urinary bladder. Kidneys are bean shaped, dark red, somewhat flattened and located under the diaphragm near the back wall of the abdominal cavity. Each kidney weighs about 150 grams and is 10 cm long. The left kidney is slightly higher than the right kidney. Kidneys filter metabolic waste out of blood and remove water. This allows the urinary system to regulate composition of fluids including salts, water, waste. The kidneys also regulate blood pressure, maintain pH. Kidneys process more than 200 liters of blood a day. A kidney consists of: renal sinus- cavity where you can find fat, nerves, blood vessels and renal pelvis renal pelvis- funnel shape part of ureter that funnels urine flowing into kidney Ureter- long tubes that move urine to urinary bladder from kidneys outer renal Cortex- outer portion of kidney between medulla and renal capsule inner Medulla- innermost part of kidney, divided into renal pyramids, renal pyramids- cone shaped structures of kidney that have a striped appearance due to being made up of the nephrons Loops of Henle A Nephron is the functional unit of kidney. Name comes from greek Nephros which stands for kidney. Nephrons are very small filters (millions tightly packed). A part of the nephron is in the cortex of kidney and part is in medulla. Nephrons are about 4cm long. The renal corpuscle is made up of cluster of a capillaries named the glomerulus and a sac like structure called the Bowmans capsule around the glomerulus. The renal tubule, the other part of the nephron that starts at the Bowmans capsule and ends at ducts of kidney is made up of 3 parts: proximal convoluted tubule- part by bowmans capsule thats why called proximal (in cortex of kidney) loop of henle- in renal medulla, and descending and then ascending limb distal convoluted tubule- named because far from bowmans capsule, that one empties into the collecting duct (located in cortex of kidney) The collecting duct is where many nephrons drain into (it is in medulla of kidney). Many collecting ducts drain into the renal pelvis which drains into the ureter. Thin walled capillaries run the entire length of the nephron. They bring in blood with metabolic waste. Renal artery and vein: The renal artery (branch of aorta) brings in unfiltered blood into kidney; filtered blood leaves via the renal vein. An afferent vessel brings blood into the glomerulus. An efferent vessel takes blood out of glomerulus. Glomerulus comes from latin Glomeris meaning ball of yarn. The glomerulus is a ball of capillaries between afferent and efferent vessel. The ball increases surface area for filtration into the bowmans capsule. Waste in the form of urine passes from the kidneys down the ureters into the urinary bladder where it is stored until it can be released. Pressure in the bladder from stored urine causes an urgency to release. Urine is formed through filtration, reabsorption, secretion, excretion. Items not filtered include proteins and RBCs. Waste (uric acid, urea-nitrogenous waste) is removed from blood in the glomerulus. Urine is formed in the nephron from the glomerular filtrate. Reabsorption occurs of some substances such as salts, excess water, amino acids, glucose that are filtered together with nitrogenous waste that are needed by body. Reabsorption occurs along proximal convoluted tubule of nephron into peritubular capillaries and back into circulation. More reabsorption happens in the loop of henle for things such as magnesium, calcium, potassium, sodium. This is made possible by aquaporins Secretion occurs when reabsorbed waste is secreted into blood from urine flowing through the tubes of the nephron. Secretion occurs when waste that did not get filtered goes from capillaries into proximal and distal convoluted tubule and becomes urine. Substances secreted include urea, creatine, uric acid, hydrogen, ammonium, potassium ions Click here for an animation on human brain anatomy and physiology.