Process of excretion - Biological processes in human body - science lessons for life


Wednesday, December 21, 2016

Process of excretion - Biological processes in human body

Process of excretion

Summation of bio chemical reactions that take place in the living body is known as metabolism

Examples for several metabolic activities are given below

  • Production of carbondioxide, water and energy during cellular respiration
  • Production of urea, uric acid in protein catabolism in liver

When metabolic processes occur in the cells, necessary as well as unnecessary materials are produced. These unnecessary materials should be removed from the body.

The waste products that are produced during metabolic process are called excretory materials. Removal of excretory products produced during metabolism from the body is called excretion.

Different excretory materials, organs through which the excretory materials are excreted and the form of excretion is shown in the table below.
Different excretory materials
Why faecal matter is not an excretory substance?
Faeces is the undigested materials of the digestion process. Digestion takes place within the digestive system. Digestion of food is not a bio chemical reaction that takes place in the cells. So faeces is not considered as an excretory material. The bile pigments that is released with faeces is an excretory substances.

Urinary System
Human urinary system
The main organ that carries out nitrogenous excretion is the kidney. A pair of kidneys and other organs are organized to form urinary system. The main parts of the urinary system are as follows

  • Pair of kidneys
  • Pair of ureters
  • Urinary bladder
  • Urethra

The waste materials in blood enter through renal arteries are filltered inside the kidney. This filterate is known as urine and it is transported through ureters and released out of the body through urethra.

Activity 01
Observation of internal structure of a kidney
Required materials :- A specimen or a model of a kidney of a goat or a cow
Method :- 
  1. Observe the above specimem carefully (get the assistance from your science techaer)
  2. Use the diagram below to identify the parts of kidny
Longitudinal view of kidney
Location of nephrons in kidnay
The structural and functional unit of kindney is nephron. Nephron is microscopic and there are about
one million of them in a kidney. The parts of a nephron can be identified as in the diagram given

Structure of a nephron
Process of urine formation
Urine formation in kidney follows three main processes,
  1. Ultra filtration
  2. Selective reabsorption
  3. Secretion

Glomerular filterate collected
into the cavity of bowman’s capsule

Each afferent arteriole enters into each Bowman's capsule, where they further divide forming a dense
network of capillaries. It is known as glomerulus.The blood flow through the glomerulus is having a
high blood pressure because the diameter of efferent arteriole is smaller than diameter of afferent
arteriols. So blood gets filtered through the wall of glomerulus and the inner wall of the bowman’s capsule and collected into the cavity of Bowman’s capsule. This process is known as ultrafiltration. This filtered fluid is referred to as glomerular filterate. Large molecules like plasma proteins and blood cells are not filtered into the glomerular filterate. Glomerular filterate is as same as blood plasma. The constituents of glomerulur filterate are water, glucose, amino acids, vitamins, medicine, various ions, hormones and urea.

Selective reabsorption
When glomerular filterate moves along the nephron most of the constituents absorb again into the blood capillaries associated with nephron. This is called Selective reabsorption. 90% of the water, all glucose, part of amino acids, vitamins, salts, urea and uric acid and medicine reabsorb into blood. The composition of glomerular filtrate change with selecteve reabsorption and then the glomerular filterate is referred to as urine.

Materials reaborsobed during urine formation
Urine is released into collecting ducts and then to the pelvis. The volume of glomerular filterate formed during one minute in a healthy adult is about 120 cm3. But 95% of the glomerular filterate reabsorb when it moves along the nephrone. 100% of glucose is reabsorbed in a healthy adult. But in diabetes patients glucose is not totally reabsorbed. The remaining glucose is released with urine.
Secretion Some of the materials in the blood capillaries associated with nephrone, are secreted into the tubules of nephron.

E.g (¡ Hydrogen ions (H+), Potasium ions (K+), Ammonium ions (NH+4), Creatinine, Medicine, Vitamin B

Removal of urine from the body
Urine released into the pelvis is transported along ureters into bladder and is temporally stored in bladder. Release of urine takes place according to the need of urination.

The composition of urine in a healthy person is given below in the table
Composition of urine in a healthy person
Diseases associated with urinary system
Let us discuss some of the diseases associated with urinary system.
Renal failure
The weakening of urine filteration process in nephrons is renal failure. Infections by micro oganisums, heavy metals (mercury, arseric) various medicine and carbon tetrachloride (CCl4) may cause renal failure. The basic symptom is oedema and increase of blood pressure due to accumulation of water and salts. pH of blood decreases due to accumulation of urea and other excretory materials. By taking immediate treatments and healthy life style one can maintain a healthy kidney. If treatments are not taken immediately after the symptoms, acute renal failure may occur within 8-14 days. Then blood is filtered by a machine in a process called dialysis. When both kidneys are failed, a healthy kidney from a donor should be transplanted.

Nephritis or swelling of kidney occurs due to infections and toxins. Infections in ureters and other changes that occur in the body are reasons for nephritis. During nephritis, it affects glomerulus and also uriniferous tubules. Due to damages occur in glomerulus the volume of blood flow through it reduces. So the amount of urine formed also reduces. Therefore the waste materials remaining within the body become high. Sometimes due to damages that occur in glomerules, filtering process is affected and as a result red blood cells can be passed into the glomerular filtrate. Similarly proteins also can be filtered and due to loss of these essential proteins, strokes may occur. Medical advice should be taken immediately for this condition.

Calculi in kidney and bladder
Crystalization of calcium oxalate in kidney and bladder is the reason for this condition. When these stones block ureters, a terrible pain would occur. The removal of these stones can be done by drugs or a surgery. These stones can be crushed by applying laser rays, and this technique is called Lithotrypsy technology. The feeding habit of a person is also a reason for these stones. Postponing of urination is also a reason for the above disorder.

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