Classwork Series and Exercises {Biology – SS3}: Regulation of Internal Environment

 Biology, SS 3 Week: 1

Topic: Regulation of Internal Environment (Homeostasis)

Homeostasis is defined as the maintenance of a steady internal environment. In order words, homeostasis is the regulation of the internal environment of the body so as to maintain a steady state by self regulation adjustments in order to provide optimum conditions for normal and efficient functioning of the body cells.

 An organism regulates its internal environment and keeps it in a steady state by constantly adjusting any changes in the physical and chemical conditions of its body fluids. These conditions include temperature, pH, osmotic pressure and concentrations of dissolved substances in the body fluids like carbon dioxide, oxygen, urea, food substances (glucose, amino-acids, etc.) and ions (sodium, potassium, chlorides).

Parts Involved in Homeostasis

The main organs and substances involved in homeostasis are:

• Kidneys
• Liver
• Skin
• Hormones (substances secreted by endocrine glands).

But the brain has overall control over the homeostatic processes in the body.

The Kidneys

The paired kidneys are the excretory organs of humans which help to regulate the internal environment.

Functions of the Kidneys

• The kidneys remove nitrogenous waste like urea and other ammonium compounds from the blood – the excretory function
• The kidneys control the amount of water, salt (Sodium, Potassium and Chloride ions) and acids (Potassium and Hydrogencarbonate ions) – the Osmoregulatory function.

Water Balance

On cold day or when much water is drunk, we excrete a large amount of dilute urine when sweat is less. On hot days, we lose water from the body through sweating and we excrete small amount of concentrated urine. This is because the kidneys regulate the amount of water excreted in the urine in order to keep the osmotic pressure of blood constant. Increase in the osmotic pressure of blood is detected by osmoreceptors in the hypothalamus in the brain.

When there is an increase in the osmotic pressure of the blood, the osmoreceptors in the hypothalamus send nerve impulses to stimulate the release of anti-diuretic hormone (ADH) from the posterior pituitary gland. The ADH is carried by the blood to the kidneys where it causes an increase in the reabsorption of water by the tubules into the bloodstream. The urine becomes concentrated as its volume decreases, while the blood becomes diluted, and its osmotic pressure decreases. When the osmoregulators detect a normal osmotic pressure, they stop stimulating the release of ADH and less water is reabsorbed by the kidneys and the urine produced is dilute.

Urine Formation

 

• Ultra filtration: It is the process of filtering materials from the glomerulus into the Bowman’s capsule. As blood circulates through the glomerulus, ultrafiltration occurs. The blood is filtered blocking the passing of larger molecules like plasma proteins and the blood cells and allowing the small molecules  such as water, urea, mineral salts, sugar to pass through the wall of capillaries and the Bowman`s capsule into the capsular space.
  
• Selective reabsorption: It is the process of reabsorbing useful materials back into the blood.The filtered fluid known as glomerular filtrate passes through the Proximal convoluted tubule and the Henle`s loop and this process allows  selective reabsorption to take place. Water and useful substances like sugar, amino acids and salts are reabsorbed into the surrounding blood capillaries.
  
• Tubular secretion: The filtrate then moves into the distal convoluted tubule and tubular secretion occurs. Large waste molecules like creatinine and ions (hydrogen, potassium and hydrogencarbonate) if necessary are secreted into the tubules to keep the osmotic concentration of the blood constant.The fluid that eventually remains in the tubule is concentrated and is known as urine; this moves down through the ureter and collects it in the bladder. An average of 1.5 litres of urine is produced daily.

Diseases of the Kidney

1. Diuresis: It is a condition in which the cells of the kidney tubules are not reabsorbing water from the glomerular filtrate and as a result, a large amount of water is passed out in urine

Effects of Diuresis

1. It leads to loss of weight
2. It leads to excretion of large amount of urine

Remedy

1. Drugs such as diuretics should be administered to get rid of excess water in the body.
2. Surgical operation should be performed on the patient.

Nephritis: It is the condition in which the blood vessel in Bowman’s capsule becomes inflamed and porous as a result of which they cannot carry out the function of ultra filtration completely.

Effects of Nephritis

1. Presence of amino acid in urine
2. Weakness of the body

Remedy

1.   Use of dialysis
2.   Kidney transplant
3. Use of antibiotics

  Kidney stones: It is caused by some diseased growth within the tubules.

Effects of Kidney Stones

1. It obstructs the passage of urine.
2. Pain is experienced on passing out urine.

Remedy

1. Patient should avoid excessive intake of calcium.
   
2. Surgery called nephrectomy can be performed i.e. involves the opening up of the kidney over more stones.