Module on Excretory and Nervous

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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 filtrate as this fluid drains through the nephron toward the collecting tubules.

The urine formed in the kidneys passes out into long, narrow tubes called ureters. The ureter from each kidney connects to the urinary bladder, a sac of smooth muscle that can hold 400-500 ml of urine. When the bladder is full, it contracts and forces the urine out through the urethra. The process of expelling out urine is called urination.

Immaculate Heart of Mary College
SY 2012-2013

BIOLOGY
NERVOUS SYSTEM MODULE

The nervous system controls and coordinates essential body functions. It sends special signals to and receives responses from every organ and tissue of the body. This system makes it possible for you to process information. It is composed of a system of nerve cells or neurons, which are bundled together to form structures such as nerves.

THE NEURON

Neurons are specialized cells for the transmission of messages from an organ or tissue to another. Each neuron is made up of a cell body or soma, which contains the axon and dendrites. Dendrites are branching treelike extensions that carry impulses toward the cell body. On the other hand, the axon carries impulses away from the cell body. Impulses can travel from one neuron to another i.e. a neuron that transmits an impulse will send the impulse through its axon to the dendrites of another neuron.

Aside from the neuron, the nervous system contains neuroglia or glial cells, which support, protect and convey food and other molecules to neurons. Neuroglia surround the neurons and hold them in place. Some glial cells wrap around the axons of some neruons and form a fatty insulating layer called the myelin sheath. There are two kinds of myelin-forming cells: the oligodendroglia and the Schwann cells. The oligodendroglia are found in the myelin sheath of the central nervous system. The Schwann cells make up the myelin sheath of the peripheral nervous system. The gaps between the Schwann cells are called...
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