Excretory Products and their Elimination

Ornithine cycle takes place in liver. The amino acid arginine and citrulline are formed during this cycle. Therefore it is referred as ornithine, arginine cycle and also Kreb-Henseleit cycle. The products of this cycle are urea and ornithine. The substances excreted through this cycle are CO₂ and NH₂

Haemodialysis helps the patient suffering from uremia. In this condition, the excretory products (i.e., urea) go on accumulating in blood. This happens due to kidney, failure. In haemodialysis, the patients blood is passed through disposable dialyser and is then returned to body by the intravenous route.

The vasopressin hormone, secreted by neurohypophysis of pituitary gland promotes the reabsorption of water from the distal convoluted tubules of nephrons, reducing excretion of water in urine (diuresis). Hence, it is called Antidiuretic Hormone (ADH). Its release in blood is controlled by an 'osmoregulatory centre' located in hypothalamus. Hyposecretion of ADH causes diabetes incipidus.

During ornithine cycle in liver cell, ammonia and CO₂ are combined to form urea which is released into the blood.

Uricotelic animals are those animals which excrete uric acid as their excretory product, for e.g. lizard and crow. They conserve water in their bodies and synthesize crystals of uric acids from ammonia. These crystals can be retained in the body (in solid form) for a longer time before being discharged from the body.

Vasopressin or ADH secreted from posterior pituitary stimulates reabsorption of water by the distal convoluted tubule and the collecting renal tubules and thus regulates urine volume. It has no such important effect on glucose metabolism. Therefore, a person whose blood glucose level is normal, but passes much urine and drinks much water has a reduction in vasopressin secretion which ultimately leads to diabetes insipidus.

Phenlyketonuria is a genetic disorder in which there is disordered metabolism of the amino acid phenylalanine, leading to severe mental retardation of affected children. The disease is caused by the  absence or deficiency of the enzyme phenylalanine hydroxylase, which results in the accumulation of phenylalanine in all body fluids. There are also high levels of the ketone phenylpyruvate in the urine.

The glomerular filtrate contains a large amount of water and other dissolved substances such as urea, uric acid, creatinine, amino acids, glucose, sodium, potassium, vitamins etc. Both glomerular filterate and blood plasma are similar except former does not consists of proteins.

Ornithine combines with one molecule of NH₃ and CO₂ to produce citrulline. Citrulline combines with another molecule of NH₃ to form arginine. Arginine is broken down into urea and ornithine which repeats the cycle.

X-rays are used in CT-scan (computed tomographic scanning). It uses X-rays but employs a computer for reconstructing the image instead of directly recording it on a photographic film. This technique is used in the diagnosis of diseases of brain, spinal cord, chest, etc. It is also useful in detecting tumors.

ECG or Electrocardiogram is a medical test that detects cardiac (heart) abnormalities by measuring the electrical activity generated by the heart as it contracts.

EEg or Electroencephalogram is a non- invasive test that records electrical patterns in your brain. It is used to help diagnose conditions such as seizures, epilepsy, head injuries, dizziness etc.

Endoscopy helps in identifying inflammation, ulcers and tumors. It is more accurate than X- rays for detecting abnormal growths such as cancer and for examining the inside of the upper digestive system.