`star` Micturition
`star` Role of Other organs in Excretion
`star` Disorders of the Excretory System


● `color{violet}("Urine formed")` by the `color{violet}("nephrons")` is ultimately carried to the `color{violet}("urinary bladder")` where it is stored till a voluntary signal is given by the `color{brown}("central nervous system (CNS).")`

● This signal is initiated by the stretching of the `color{violet}("urinary bladder")` as it gets filled with urine.

● In response, the `color{brown}("stretch receptors")` on the walls of the `color{violet}("bladder")` send `color{violet}("signals")` to the `color{violet}("CNS.")`

● The `color{violet}("CNS")` passes on motor messages to initiate the `color{brown}("contraction of smooth muscles")` of the `color{violet}("bladder")` and simultaneous relaxation of the urethral sphincter causing the release of `color{violet}("urine.")`

● The process of release of `color{violet}("urine")` is called `color{brown}("micturition")` and the `color{violet}("neural mechanisms causing")` it is called the `color{brown}("micturition reflex.")`

● An adult human excretes, on an average, `color{brown}("1 to 1.5 litres")` of `color{violet}("urine")` per day.

● The `color{violet}("urine")` formed is a light yellow coloured watery fluid which is slightly `color{violet}("acidic (pH-6.0)")` and has a characterestic odour.

● On an average, `color{brown}("25-30 gm")` of `color{violet}("urea")` is excreted out per day.

● Various conditions can affect the characteristics of `color{violet}("urine.")`

● Analysis of `color{violet}("urine")` helps in `color{violet}("clinical diagnosis")` of many `color{violet}("metabolic discorders")` as well as malfunctioning of the `color{violet}("kidney.")`

● For example, presence of glucose ( `color{brown}("Glycosuria")`) and ketone bodies ( `color{brown}("Ketonuria")`) in urine are indicative of `color{brown}("diabetes mellitus.")`


● Other than the `color{violet}("kidneys, lungs, liver and skin")` also help in the `color{violet}("elimination of excretory wastes.")`

● Our lungs remove large amounts of `color{violet}(CO_2)` (18 litres/day) and also `color{violet}("significant quantities of water")` every day.

● `color{brown}("Liver,")` the largest gland in our body, secretes bile-containing substances like `color{violet}("bilirubin, biliverdin, cholesterol, degraded steroid hormones, vitamins and drugs.")`

● Most of these substances ultimately pass out alongwith `color{violet}("digestive wastes.")`

● The `color{brown}("sweat and sebaceous glands")` in the skin can eliminate certain substances through their secretions.

● `color{brown}("Sweat")` produced by the sweat glands is a `color{violet}("watery fluid")` containing `color{violet}(NaCl)`, small amounts of `color{violet}("urea, lactic acid, etc.")`

● Though the `color{violet}("primary function")` of sweat is to facilitate a cooling effect on the `color{violet}("body surface,")` it also helps in the removal of some of the wastes mentioned above.

● `color{brown}("Sebaceous glands")` eliminate certain substances like `color{violet}("sterols, hydrocarbons")` and `color{violet}("waxes")` through `color{brown}("sebum.")`

● This secretion provides a protective `color{violet}("oily covering for the skin.")`

● Small amounts of `color{violet}("nitrogenous wastes")` could be eliminated through `color{brown}("saliva")` too.


`star` `color{green}("Hemodialysis:")`

● `color{violet}("Malfunctioning of kidneys")` can lead to `color{violet}("accumulation of urea")` in blood, a condition called `color{brown}("uremia")`, which is highly harmful and may lead to `color{violet}("kidney failure.")`

● In such patients, `color{violet}("urea")` can be removed by a process called `color{brown}("hemodialysis.")`

● `color{violet}("Blood drained")` from a convenient artery is `color{violet}("pumped")` into a dialysing unit after adding an anticoagulant like `color{brown}("heparin.")`

● The unit contains a `color{brown}("coiled cellophane tube")` surrounded by a fluid ( `color{brown}("dialysing fluid")`) having the same composition as that of `color{violet}("plasma except")` the `color{violet}("nitrogenous wastes")`.

● The `color{violet}("porous cellophane membrance")` of the tube allows the passage of `color{violet}("molecules")` based on concentration gradient.

● As `color{violet}("nitrogenous wastes")` are absent in the `color{violet}("dialysing fluid,")` these substances freely move out, thereby `color{violet}("clearing the blood.")`

● The `color{violet}("cleared blood")` is pumped back to the body through a vein after adding `color{brown}("anti-heparin")` to it.

● This method is a boon for thousands of `color{violet}("uremic patients")` all over the world.

`star` `color{green}("Renal Failure:")`

● `color{violet}("Kidney transplantation")` is the ultimate method in the correction of acute `color{brown}("renal failures")` (kidney failure).

● A `color{violet}("functioning kidney")` is used in transplantation from a donor, preferably a close relative, to minimise its
chances of rejection by the `color{violet}("immune system ")`of the host.

● `color{violet}("Modern clinical procedures")` have increased the success rate of such a complicated technique.

`star` `color{green}("Renal calculi:")`

`color{violet}("Stone or insoluble mass")` of `color{violet}("crystallised salts (oxalates, etc.)")` formed within the kidney.

`star` `color{green}("Glomerulonephritis")`

Inflammation of `color{violet}("glomeruli of kidney.")`