The Complex Structure of Our Urinary System The Human Excretory System Excretion is the removal of toxic waste product of metabolism from our bodies. Metabolic waste include carbon dioxide, water, bile pigments, and waste products that contain nitrogen. This include urea, ammonia, and uric acids. Accumulation of wastes in the body interferes with the proper functioning of the cells. Excretory organs in humans are the skin, lungs, liver, and kidney. The lungs, in the form of exhaled air, excrete carbon dioxide.
Our skin, in the form of sweat, eliminates heat, mineral salts, urea and excess water. The liver, together with our kidney, also excrete urea in the form of urine. The urine also contains excess water, mineral salts, and nitrogen as wastes. The Urinary System The human urinary system consists of the kidney, ureter, urinary bladder, sphincter muscle, and the urethra. The kidney filters blood and excretes the waste as urine. Ureter is a tube that transports urine from the kidney to the urinary bladder. It moves the urine through peristalsis
and by gravity. Inside the urinary bladder, which is the muscular bag that acts as a temporary storage, the urine is held for later discharge.
The sphincter muscle controls the flow of urine and relaxes to release urine in the bladder. The urethra carries urine out of the body. Kidney There are two kidneys, both are reddish-brown and bean-shaped. Kidneys are located toward the back of the abdominal cavity. Attached to the kidney are ureter, renal artery, and renal vein. The artery supplies the kidney with blood and the vein carries it out. The structures of a kidney include a capsule, outer cortex, inner medulla, renal pyramids, renal pelvis, and the ureter. At the top of the ureter, we will find a cavity called the pelvis. The pelvis collects urine and opens to an area called pyramids. The pyramids are not those we see in Egypt, but these are cone-shaped areas in the medulla region of our kidney.
The inner medulla is lighter in color and contains Loops of Henle and the collecting ducts. The outer cortex contains Bowman’s capsule
and glomeruli. It is dark brown due to the large network of blood capillaries from the glomeruli. All of those are covered by the capsule; a thin, transparent membrane that surrounds the kidney. Nephron and Urine Formation Nephron is the basic construct of the kidney. Glomerulus, the Bowman’s capsule, Loop of Henle, and collecting ducts is what nephron consists of. It separates water, ions and small molecules from the blood, filters out wastes and toxins, and returns the needed molecules to the blood. It functions through ultrafiltration. The glomerulus is a cluster of capillaries that forces the blood to pass through it in high pressure so that the blood filters out. Only blood cells and proteins remain
in the capillary while the filtered substances go to
the Bowman’s capsule. The Bowman’s capsule collects filtrate
from the glomerulus, which contains glucose, amino acids, salts, and nitrogenous waste products. The filtrate is sent off along a tube that forms the Loop of Henle. As it moves along this tube, all useful substances are reabsorbed into the surrounding blood capillaries.
This absorption is against the
concentration gradient and helped by active transport. After passing through the Loop of Henle, the remaining fluid is passed through
the collecting duct as urine..