Excretory System - 1

Diffusion is the tendency of molecules  to spread into an available space. This tendency is a result of the intrinsic thermal energy (heat) found in all molecules, at temperatures above absolute zero. Without other outside forces at work, substances will move/diffuse from a more concentrated environment to a less concentrated environment. The chloride ions from the glomerular filtrate are reabsorbed through diffusion.

One quarter of the total blood output from the heart comes to the kidneys along the renal artery. Two renal arteries arise from the abdominal section of the aorta, each artery supplies a lobe of the kidney. The incoming artery divides into four or five branches, eventually forming arterioles, each of which leads to the compact ball of capillaries, called the glomerulus.

The renal pyramids are conical segments within the internal medulla of the kidney. The pyramids contain the secreting apparatus and tubules, and are also known as the malphighian pyramids.

The hilus is the slit-like opening in the middle of the concave medial border of the kidney. Nerves and blood vessels pass through the hilus into the renal sinus within.

Henle's loop or loop of Henle is asociated with excretory system. It is a component of nephron in humans, which progresses from proximal straight tubule to distal convoluted tubule (DCT).

Blood plasma is the yellow liquid component of blood, in which the blood cells in whole blood, are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid (all body fluid outside of cells). It is mostly water (93% by volume) and contains dissolved proteins, glucose, clotting factors, mineral ions, hormones and carbon dioxide. It transports urea.

The process by which the water content and the ion concentration is regulated and kept constant in the cells, is known as, osmoregulation.

The contractile vacuole is known as the kidney of the protozoans. Its function is to pump out excess water from the cytoplasm of amoeba. They are most prominent and active in freshwater amoebae as marine amoebae are closer to isotonicity with seawater than freshwater.

It is a V shaped segment of the nephron located in the renal medulla. It consists of two straight parallel limbs: a descending limb which is a continuation of the PCT and enters into the renal medulla and an ascending limb which reenters the renal cortex and joins the DCT.

A supply of amino acids in the blood is kept at a normal level. Any spare which has not been absorbed cannot be stored,  but is converted into the waste products, called urea,  when at the liver, and is then sent to the kidneys to be removed from the body as urine. The remainder of the amino acid molecule is not wasted;   it is changed into a carbohydrate,  that can be used.

It starts from the neck of the Bowman's capsule and it is highly convoluted. It lies in the renal cortex. The wall consists of a single layer of columnar cells bearing a lot of microvilli on the surface. It mainly reabsorbs glucose in the kidney.

It is a V-shaped segment of the nephron, located in the renal medulla. It consists of two straight parallel limbs, a descending limb, which is a continuation of the PCT and enters into the renal medulla and an ascending limb, which re-enters the renal cortex and joins the DCT.

The glomerulus lining is such that it only allows small molecules, to filter through, like glucose, plasma, ions like sodium and potassium, urea, etc. The larger molecules, like blood cells and protein, cannot pass through the glomerulus. So, proteins are not present in glomerular filtrate. The glomerular filtrate consists,  primarily of water, excess salts (primarily Na+ and K+), glucose and urea.

Jaundice occurs, when there is too much bilirubin being produced for the liver, to remove from the blood, due to a defect in the liver that prevents bilirubin from being removed from the blood, or from getting converted to bilirubin/glucuronic acid (conjugated), or from being secreted in bile.

The renal sinus is the cavity within the kidney, which houses the renal pyramid. Nerves and blood vessels pass into the renal sinus,  through the hilus.

The cortex of the kidney is the outer section,  which covers the internal medulla. The cortex is visible near the outer edge of the cross-sectioned kidney. It is composedof blood vessels and urine tubes and is supported by a fibrous matrix.

A hepatic vein carries oxygen depleted blood out of the liver, with highest concentration of urea, into the inferior vena cava. The term vein refers to a blood vessel,  that transports blood back to the heart. The term hepatic, relates to the liver.

The cortex of the kidney is the outer section,  which covers the internal medulla. The cortex is visible near the outer edge of the cross-sectioned kidney. It is composedof blood vessels and urine tubes, and is supported by a fibrous matrix.

Cirrhosis is a condition in which the liver slowly deteriorates and malfunctions due to chronic injury. Scar tissue replaces healthy liver tissue, partially blocking the flow of blood, through the liver.

It contains least amount of urea.Cell waste is discharged in the veins for excretion through the kidneys. The body circulates about 425 gallons of blood through the kidneys on a daily basis, but only about a thousandth of this is converted in urine. The remainder goes back into circulation,  through the renal arteries. From the Bowman's capsule, the blood is carried through the compact network of capillaries,  that forms the glomerulus within the capsule. The capillaries eventually reconverge into small venules,  which lead to the larger renal veins. There are two renal veins, one extending from each lobe of the kidney, and opening into the vena cava.

Glucagon is a hormone, secreted by the pancreas, that raises blood glucose levels. It's effect is opposite that of insulin, which lowers blood glucose levels. The pancreas releases glucagon when blood glucose levels fall too low. Glucagon causes the liver to convert stored glycogen into glucose, which is released, into the bloodstream.

Ultrafiltration occurs at the barrier between the blood and the filtrate, in the renal corpuscle or Bowman's capsule in the kidneys. The Bowman's capsule contains a dense capillary network called the glomerulus. Blood flows into these capillaries through a wide afferent arteriole and leaves through a narrower efferent arteriole. The high pressure forces small molecules, such as,  water, glucose, amino acids, sodium chloride and urea,  through the filter, from the blood in the glomerular capsule across the basement membrane of the Bowman's capsule,  and into the nephron. This type of high pressure filtration is ultrafiltration. The fluid formed in this way is called glomerular filtrate.

The renal capsule is the membranous covering of the kidney. It directly covers the renal cortex, which forms the outer stratum

The bowman's capsule and the glomerulus together constitutes the renal corpuscle or malpighian body. Glomerulous is a large double walled cup. It contains a tuft of capillaries called glomerulus and the outer wall is continuous with the rest of the nephron. The space between the two walls of the Bowman's capsule is continuous with the lumen of the next part of the nephron.

The regulation of body water and sodium ion (Na⁺) concentration in the blood is controlled through the release of anti-diuretic hormone (ADH). This system operates using a negative feedback loop. The release of ADH is regulated by the hypothalamus.