Module on Excretory and Nervous
Immaculate Heart of Mary College
SY 2012-2013
BIOLOGY
EXCRETORY SYSTEM MODULE
Urea is the main nitrogenous waste excreted by most mammals and is formed in the liver. It circulates the body and most of the urea produced by the body is transported to the kidneys.
ORGANS OF EXCRETION
ORGAN | WASTE EXCRETED | Skin | Sweat | Lungs | Carbon dioxide | Liver | Water, salts | Large intestine | Feces | Kidneys | Urine |
THE KIDNEYS
The kidneys are the main organs of excretion. Their main function is to separate urine from the blood which flows through it. Each kidney receives blood through the renal artery and are drained by the renal veins. The excretory units of the kidneys are called nephrons. The nephrons filter out water, wastes and other substances such as urea and salts from the blood. This is followed by the reabsorption of water and other essential substances such as amino acids and glucose by the kidneys. The waste (or filtrate) are actively removed from the blood, not reabsorbed from the urine.
1. Filtration * The blood plasma is filtered through the walls of the glomerulus and collects in the Bowman’s capsule * This process forms a fluid, the nephric filtrate, which contains all the ions and small molecules present in the blood plasma.
2. Tubular reabsorption * The nephric filtrate passes through the tubular parts of the nephron where very large quantities of water and smaller quantities of glucose and other useful compounds are saved and reabsorbed. * This process of selective reabsorption demands the transfer the reabsorbed compounds back into the blood through the capillaries surrounding the tubule.
3. Tubular secretion * The nephric tubules secrete additional quantities of metabolic wastes into the nephric filtrate * Waste are extracted from the capillaries around the tubule and passed into the nephron. * Reabsorption and secretion greatly change the composition of the nephric
SY 2012-2013
BIOLOGY
EXCRETORY SYSTEM MODULE
Urea is the main nitrogenous waste excreted by most mammals and is formed in the liver. It circulates the body and most of the urea produced by the body is transported to the kidneys.
ORGANS OF EXCRETION
ORGAN | WASTE EXCRETED | Skin | Sweat | Lungs | Carbon dioxide | Liver | Water, salts | Large intestine | Feces | Kidneys | Urine |
THE KIDNEYS
The kidneys are the main organs of excretion. Their main function is to separate urine from the blood which flows through it. Each kidney receives blood through the renal artery and are drained by the renal veins. The excretory units of the kidneys are called nephrons. The nephrons filter out water, wastes and other substances such as urea and salts from the blood. This is followed by the reabsorption of water and other essential substances such as amino acids and glucose by the kidneys. The waste (or filtrate) are actively removed from the blood, not reabsorbed from the urine.
1. Filtration * The blood plasma is filtered through the walls of the glomerulus and collects in the Bowman’s capsule * This process forms a fluid, the nephric filtrate, which contains all the ions and small molecules present in the blood plasma.
2. Tubular reabsorption * The nephric filtrate passes through the tubular parts of the nephron where very large quantities of water and smaller quantities of glucose and other useful compounds are saved and reabsorbed. * This process of selective reabsorption demands the transfer the reabsorbed compounds back into the blood through the capillaries surrounding the tubule.
3. Tubular secretion * The nephric tubules secrete additional quantities of metabolic wastes into the nephric filtrate * Waste are extracted from the capillaries around the tubule and passed into the nephron. * Reabsorption and secretion greatly change the composition of the nephric