chapter 1 excretion system (kidney and skin )

3. The kidney

Kidney is main excretory organ in human. Human kidney is one pair, shaped like kidney bean and has red color or purplish. The length of kidney is about 10 cm, and lies inside abdominal cavity to the right-left of vertebral column. Left kidney is higher than right kidney. The weight of kidney of adult people is about 200 grams.

The kidney has function as follows :

a. Filtering blood from the renal artery that comes from aorta that is waste matters that are not required but found in the blood and collected in the form of urine.

In normal condition urine contains :

1) Water of 95%

2) Urea , acid , and ammonia that is waste of restore of protein.

3) The gill pigments (bilirubin and biliverdin) that give yellow colour in urine.

4) Excessive in blood such as vitamin B and C , drugs , poison , and hormone.

5) Various kinds of salt , particularly common salt (NaCl)

b. Keep water equilibrium inside the body, by the following method.

1) If water excessive (water supply too much) then water will be removed.

2) If the supply of water is small in amount , the excretion of water is decreased.

Kidney consist of three parts, those are cortex , medulla , and pelvis.

a) The cortex

In this part there are hundreds thousands of malphigian bodies. The malphigian body consist of glomerulus and bowman’s capsule. Glomerulus is collection of smooth blood vessels that are branches of renal artery , while bowman’s capsule is a part that has a shape of a bowl or cup that is in pair with glomerulus.

In bowman’s capsule, the blood from glomerulus is filtered. Substances that still use are absorbed again by the blood while the waste matters are nor required anymore will be discharged. From the bowman’s capsule the waste matters go to minor calyx and major calyx, finally it arrives to pelvis and is discharged in the form of urine.

b) The medulla

Medulla is bodies of conical shape that are called pyramids. In this part of pyramid there are smooth vessels that are repercussion of bowman’s capsule. Smooth vessels flow urine into the larger duct and ended in pelvis. Then, the urine is conducted through ureter and received in urethra. If the ureter contains the urine, then ureter wall will be pushed so circular muscle in the end stretches. This cause the impulse if feeling to urinate. Then the urine is released through urethra.

c) The pelvis

Pelvis is the place to receive urine before it is conducted to urethra.


The order of urine discharged is as follows. 
Glomerulus – Bowman’s capsule – small collecting duct (proximal tubulous and distal tubulous) – big collecting duct – pelvis – ureter – urinary bladder – urine discharging duct (urethra) 


4.    Skin  
Skin is thin layer that covers the entire of body surface. The skin is included in the one excretory organs because it discharged sweat. Sweat consist of minerals salts, mainly common salt. The quantity of sweat produced corresponds to the regulation of body temperature. Of the air is hot then sweat discharged is large in quantity , but if the air is cold, the sweat discharged is small.

a)  The structure of skin

(1)  Epidermis

The epidermis consist of two layers, those are epithelium layer and malpighian layer.

(2)  The dermis

Dermis contains blood vessel , the sweat gland , the hair follicle , the subaceous gland , and the end of sensoric nerve.

(3)  The connective tissue under the skin

b)   The function of skin

(1)  As excretory organ

(2)   As protector

(3)  As place of feeler sense and touching sense

(4)  As place to store surplus of fat

(5)  As place to form vitamin D

(6)  As regulator of body temperature