biologia
THE LYMPHATIC SYSTEM
Is involved in the function of exchanging substances between the circulatory system and the cells.
The lymphatic system collects the excess of interstitial fluid that remains between the cells and returning it to the blood. It also transports fats that are absorbed in the intestine, and takes part in the body’s defence system.
Functions
Return excess interstitial fluid to the blood
Transport absorbed fat from the small intestine to the blood
Take park in the body’s defence system
Components of the lymphatic system
Lymph. Is the fluid that circulates inside the lymphatic vessels; it comes from the intercellular plasma and also contains lymphocytes.
Lymphatic capillaries. They are small vessels found in all tissues. Their function is to reabsorb the intercellular plasma.
Lymphatic vessels.Larger vessels with valvesthat prevent the lymph from flowing backwards. The most important are the great lymphatic veinand the thoracic duct.
Lymph nodes.They are very small organs, linked by the lymphatic vessels. They are located along major arteries and veins, but are most abundant around the ears and in the neck and armpits. They contain lymphocytes. During an infection, the nodes become larger.
THE EXCRETORY SYSTEM
Cells produce waste as a result of cellular metabolism. If this waste accumulates, it can be harmful. Waste is released into the blood and the blood carry it to the responsible organs for elimination.
Excretionis the process by which the waste products from cell metabolism are eliminated from the blood. The main substances that are excreted are:
Urea.A substance synthesised by liver cells from ammonia produce during the metabolism of proteins.
Uric acid. A substance produced from the breakdown of purines, which are molecules that make up nucleic acids. Also produced by the liver.
Dissolved mineral salts.They are only excreted when there is an excess in the blood; the main salt is sodium chloride.
Substances foreign to the body.They have been broken down by the cells and have accumulated in the blood, for example some drugs and food additives.
Organs involved in excretion
Kidneys. They eliminate toxic substances resulting from cell metabolism through the urine.
The liver. Eliminates substances resulting from the decomposition of red blood cells,which are stored in the bile and are expelled through the faeces.
The lungs. They expel the carbon dioxide from cellular respiration.
The sweat glands The sweat glands are distributed all over the skin.They form sweat with the waste they take from the blood. Sweat is excreted through the pores in our skin.
Anatomy of the excretory system
The kidneys: are two organs located in the lumbar region. In the kidney we can see:
An outer region, the cortex.
A medulla,divided into sections.
The renal pelvis,which is a cavity that collects the urine (urea, uric acid and mineral salts)
Each kidney is made up of nephrons. Each nephron is composed of the glomerulus, which it is surrounded by the Browman’s capsule, and a renal tubule.Several nephrons form a collecting duct.
The urinary tract: the urinary tract carries the urine from the kidneys to outside the body. It is composed of:
Ureters: They carry urine to the bladder.
Urinary bladder: it is a muscular elastic bag where urine is collected before being expelled.
The sphincter, regulates its opening. It is connected to the outside through the urethra.
Urethra:it carries urine from the bladder to outside of the body during urination. In men, the urethra carries urine and semen. In women, the urethra is only used for urination.
The functions of the excretory system
Purifies the blood by the urine and also regulates the water in the body. The formation of urine has 2 stages: filtration and reabsorption:
Filtration.: Due to the pressure of the blood and the permeability of the glomerulus capillaries, a first filtration takes place. Water, nutrients and waste substances are filter. The filtered fluid then enters Bowman’s capsuleand primary urineis formed.
Reabsorption.: The primary urine moves through the renal tubule, so most water, nutrients and mineral salts are reabsorbed to the blood. The finally fluid is the definitely urine.
NERVOUS COORDINATION
Made up of nerve tissue. The nervous system unit is theneuronand the transmission of information between neurons through electric signals is called nerve impulses.
NEURONS
They are the most specialised cells inthebody. They don’t reproduce. They are made up of dendrites and axons. Parts:
Cell bodycontains the nucleus and other organelles, and is filled with cytoplasm.
Dendritesare short projection of the cell body that receive nerve impulses from other neurons.
The axonis a longer projection made up of cytoplasm and carries nerve impulses from the cell body to another neuron. The axon ends in a series of branches calledaxon terminals.
Axons can be protected by a white substance called myelin. The axons of various neurons sometimes group together to form nerve fibres, an these can group again to form nerves.
Depending on their function, neurons are classifiedin:
Sensory neurons. Transmit information from the receptors to the most important nerve centres.
Motor neurons.Transmit the signals from the nerve centres to the effector organs.
Interneurons.Connect the sensory neurons and the motor neurons. They are located in the brain.
TRANSMITTING A NERVE IMPULSE
Neurons only generate and transmit nerve impulse. When a neuron is stimulated some electrical changes occurs and they transmit the electrical signals from the dendrites towards the axon.
A nerve impulse is like and electrical signal which is transmitted from the cell’s membrane toother neurons.
Neurons work together to establish connections called synapses, which allows the nerve impulse to cross from one neuron to another. It is found between the end of one axon and a dendrite of another neuron.
Neurons are transmitter and receptor neurons.
The transmitter and the receptor neurons are not together but the message is transmitted by chemical substances called neurotransmitters which are in the terminal axon.
FUNCTIONS OF THE NERVOUS SYSTEM:
Receives the information transmitted by the sensory organs.
Interprets that information and create responses.
Transfers the signals to the effector organs.
Coordinates the organs so that they function properly.
Carries out intellectual and mental functions.
Is responsible for our emotions and feelings.
THE CENTRAL NERVOUS SYSTEM
The CNS is made up of nerve centres, that receive the information, coordinate it and prepare a response. It is formed by the encephalonand the spinal cord.
The CNS is made up of two types of tissue: grey matterwhich are neuron cell bodies and dendrites, which are control centres that carry out certain functions; and white matter, which has neuron extensions, generally axons, covered in myelin.
֎ The encephalon
The encephalon is protected by the cranium and 3 membranes called meninges. A liquid called cerebrospinal fluid also protects it.
The brain. divided in 2 hemispheres, and its surface is called cerebral cortex, is full of folds and furrows, known as circumvolutions. Brain functions:
It receives information from sensory organs and produces sensations. It transmits the response to the effector organs; it coordinates the function of the nervous system; it controls functions like memory, reasoning or intelligence.
The cerebellumcontrols balance and voluntary movements, such as walking
The diencephalonthat includes the thalamus and the hypothalamus.
The thalamus relay sensory signals to the cerebral cortex and controls the consciousness actions(sleep).
The hypothalamus connects and controls a gland that secretes regulatory hormones to the rest of the organs.
The brainstemlinks the encephalon and the spinal cord and controls the involuntary actions (breathing) (heart beat) The left side of the brain controls the right side of the body and the right side of the brain the left side of the body (medulla oblongata)
֎ The spinal cord
The grey matter is found in the centre of the spinal cord while the white matter is in the outer part. There is a channel in the grey matter (ependyma) which runs to the top to the bottom and contains cerebrospinal fluid. The spinal cord reaches all parts of the body except the head.
The spinal cord has 2 functions: Produces reflex actions without the participation of the brain and carries the sensory nerve impulse thought the brain to the effector organs.
THE PERIPHERIAL NERVOUS SYSTEM
The PNS connects all the effector and receptors of the body to the CNS. It is made up of nerves. (31 nerves originate in the spinal cord) (12 originate in the encephalon). Nerves can be classified in sensory, motor and mixed nerves. PNS is divided into 2 parts: the somatic system and the autonomic system.
SOMATIC SYSTEM
It connects the sensory receptors from the sensory organs to the nervous system and this to the skeletal muscles.
It receives information of the external stimuli about body position.
Transmit signals for muscle voluntary contractions.
AUTONOMIC NERVOUS SYSTEM
It regulates the involuntary actions and is located in the grey matter of the spinal cord.
Sympathetic nervous system: stimulates the body to react to fear, stress…
Parasympathetic nervous system: causes the body to relax.
They are antagonistic, they act in opposite ways.
HOW DOES THE NERVOUS SYSTEM WORK?
The stimuli perceived by internal or external receptors reach the central nervous system where a response is created.
REFLEX ACTIONS
These actions are fast and involuntary ones that are controlled by the spinal cord and are done in emergency situations.
The elements involved are:
Receptors. Perceives stimulus
Sensory nerve. Transmit the impulse to the spinal cord
Interneurons. Generates an immediate response order
Motor nerves. The order travels to the effector organ
Effector organs. Executes the response.
VOLUNTARY ACTIONS
These actions are conscious ones deliberated by the encephalon.
The elements involved are:
Receptors. Perceives stimulus
Sensory nerves. Transmit the impulse to the cerebral cortex
Cerebral cortex. Turns the inf. Into a conscious sensation.
Motor nerves. The order travels to the effector organ
Effector organs. Executes the response.