REGULATION OF INTERNAL ENVIRONMENTS;
Topic: Regulation of Internal Environment (Homeostasis)
Introduction;
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 and provision of optimum conditions for normal and efficient functioning of the body cells.
homeostasis
/ˌhɒmɪə(ʊ)ˈsteɪsɪs,ˌhəʊmɪə(ʊ)ˈsteɪsɪs/
noun
- the tendency towards a relatively stable equilibrium between interdependent elements, especially as maintained by physiological processes.
Homeostasis, any self-regulating process by which biological systems tend to maintain stability while adjusting to conditions that are optimal for survival. If homeostasis is successful, life continues; if unsuccessful, disaster or death ensues. The stability attained is actually a dynamic equilibrium, in which continuous change occurs yet relatively uniform conditions prevail.- Britannica
Examples of homeostasis in humans include the regulation of blood sugar via insulin,
the regulation of body temperature by the hypothalamus,
the constant surveillance and functioning of the immune system,
regulation of blood pressure via sensors in the walls of arteries,
the pH balance maintained by the lungs
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.
3. 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
3. 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.
The Liver
The liver is a large dark reddish-brown organ that weighs about 3 pounds, located in the upper right-hand portion of the abdominal cavity, beneath the diaphragm, and on top of the stomach, right kidney, and intestines.
There are two distinct sources that supply blood to the liver,
• Oxygenated blood flows in from the hepatic artery
• Nutrient-rich blood flows in from the hepatic portal vein
The liver holds about one pint (13 percent) of the body’s blood supply at any given moment. The liver consists of two main lobes, both of which are made up of thousands of lobules.
These lobules are connected to small ducts that connect with larger ducts to ultimately form the hepatic duct.
The hepatic duct transports the bile produced by the liver cells to the gallbladder and duodenum (the first part of the small intestine). The liver can lose three-quarters of its cells before it stops functioning. In addition, the liver is the only organ in the body that can regenerate itself.
The peritoneum connects the liver in 4 locations: the coronary ligament, the left and right triangular ligaments, and the falciform ligament. These connections are not true ligaments in the anatomical sense; rather, they are condensed regions of peritoneal membrane that support the liver.
• The wide coronary ligament connects the central superior portion of the liver to the diaphragm.
• Located on the lateral borders of the left and right lobes, respectively, the left and right triangular ligaments connect the superior ends of the liver to the diaphragm.
• The falciform ligament runs inferiorly from the diaphragm across the anterior edge of the liver to its inferior border. At the inferior end of the liver, the falciform ligament forms the round ligament (ligamentum teres) of the liver and connects the liver to the umbilicus. The round ligament is a remnant of the umbilical vein that carries blood into the body during fetal development.
The liver consists of 4 distinct lobes – the left, right, caudate, and quadrate lobes.
• The left and right lobes are the largest lobes and are separated by the falciform ligament. The right lobe is about 5 to 6 times larger than the tapered left lobe.
• The small caudate lobe extends from the posterior side of the right lobe and wraps around the inferior vena cava.
• The small quadrate lobe is inferior to the caudate lobe and extends from the posterior side of the right lobe and wraps around the gallbladder.
Functions of the Liver
The liver regulates most chemical levels in the blood and excretes a product called bile, which helps carry away waste products from the liver. All the blood leaving the stomach and intestines passes through the liver. The liver processes this blood and breaks down the nutrients and drugs into forms that are easier to use for the rest of the body.
Some of the more well-known functions include the following:
• Production of bile, which helps carry away waste and break down fats in the small intestine during digestion
• Production of certain proteins for blood plasma
• Production of cholesterol and special proteins to help carry fats through the body
• Conversion of excess glucose into glycogen for storage (glycogen can later be converted back to glucose for energy)
• Regulation of blood levels of amino acids, which form the building blocks of proteins
• Processing of hemoglobin for use of its iron content (the liver stores iron)
• Conversion of poisonous ammonia to urea (urea is an end product of protein metabolism and is excreted in the urine)
• Clearing the blood of drugs and other poisonous substances
• Regulating blood clotting
• Resisting infections by producing
immune factors and removing bacteria from the bloodstream
When the liver has broken down harmful substances, its by-products are excreted into the bile or blood. Bile by-products enter the intestine and ultimately leave the body in the form of feces. Blood by-products are filtered out by the kidneys, and leave the body in the form of urine.
The Diseases of the Liver
Important diseases of the liver include the following;
(1) Gall Stone: These are stony masses that form in the gall bladder or bile duct as a result of the production of abnormal bile by the liver. Gall stone obstruct the flow of bile and causes inflammation of the gall bladder.
(2) Viral Hepatitis: There are two types of viral hepatitis. Hepatitis A and Hepatitis B. In both cases, the virus causes inflammation and destruction of the liver cells.
(3) Cirrhosis: This is a serious liver disease in which the damaged liver cells become replaced by useless fibrous tissue. Cirrhosis may be caused by excessive drinking of alcohol over a period.
(4) Amoebic Liver Abscess: The parasitic amoeba, Entamoeba histolytica, gets into the liver from the large intestine via the hepatic-portal vein, produces an enzyme that destroys liver tissues and causes an abscess to form.
Effects of Diseases of the Liver
The effects of liver diseases are due to failure of the liver cells to function properly. The most common signs and symptoms are:
• Weakness and tiredness
• Jaundices
• Slight fever
• Tendency to bleed and bruise easily
• High blood pressure in the hepatic-portal vein in cirrhosis.
• Oedema
• Mental changes such as apathy in most liver disease.
Remedy/Treatment
The liver has a high capacity to replace damaged cells and function normally. In most cases of liver diseases, the basic treatment procedures include:
• Rest, preferably in bed
• A nutritious but controlled low fat diet
• No taking of alcoholic drinks (for the rest of the patient’s life in the of cirrhosis)
• Removal of liver disorder where possible, in the case of bile duct obstruction
• Liver transplanting
Reference;
Passnownow.com
Britannica
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