Respiratory system includes all the organs and tissues associated with the exchange of gases between an animal and its environment, leading to the release of energy.
The purpose of respiration is to supply oxygen to the cells which oxidise or burn down the food to release energy.
This process is also referred to as fermentation.
The most important organ of respiration in all land animals is the lung, while aquatic animals like fish use the gills to respire. Other organs associated with respiration are the nostrils and diaphragm.
The lung is located in the thoracic cavity of farm animals. The atmospheric oxygen passes through the nostrils, the pharynx, larynx or voice box, bronchi and to the lungs. The movement of oxygen through these organs finally terminates in the alveoli where exchange of gases (oxygen and carbon dioxide) takes place.
Processes of Breathing
Breathing involves two processes:
(1) Inspiration (Inhalation): This involes the breathing in of air into the lungs. During the process, the following take place within and around the lungs.
(i) The diaphragm contracts and flattens out.
(ii) Intercostal muscles contract and ribs are thus raised.
(iii) Sternum moves forward.
(iv) The volume of thoracic cavity therefore increases and the pressure in the lungs is lowered.
(v) This therefore creates a high pressure in the lungs and oxygen is taken into the lungs.
2) Expiration (Exhalation): This involves he breathing out of air from the lungs. During he process, the following take place within and round the lungs.
(i) The diaphragm relaxes and returns to its dome shape
(ii) Intercostal muscles relax and the ribs are lowered.
(iii) The sternum moves backwards.
(iv) The volume of thoracic cavity therefore decreases; pressure in the lungs is increased and carbon dioxide is expelled from the lungs.
The oxygen which diffuse into the blood through the lungs is now transported by the haemoglobin of the blood cells to various cells in the body. This oxygen is used to oxidise food substances in the mitochondria of the cells during tissue respiration to release energy used by farm animals for movement, growth, reproduction and other body metabolic activities.
Importance of the Respiratory System
(i) It supplies oxygen to the body cells.
(ii) It helps to reduce heat load in the body, especially in poultry.
(iii) It removes carbon dioxide from the body.
(iv) It promotes gaseous exchange.
The nervous system includes all the organs and tissues which enable animals to respond to changes in their environment. A change in the environment is called a response.
The nervous system of mammals is composed of two parts: the central nervous system and the peripheral nervous system.
Central Nervous System
This is made up of the brain and the spinal cord. Both are made up of thousands of nerve cells or neurones. The functions of the central nervous system are the correlation of impulses from various sense organs and storage of impulses as information or impressions in the brain for reaction to future similar stimuli.
(a) The Brain: The brain is enclosed in a bony case called the cranium. It is divided into fore, mid and hind brain.
(b) The fore brain consists of olfactory lobes which receive sensory impulses for smell and the cerebrum which is the seat of consciousness, intelligence, memory and all voluntary actions. The mid brain consists mainly of optic lobes which control sight. The hind brain consists of the cerebellum which is concerned with balance and body posture, receives impulses and coordinates action, respiration, heartbeat, digestive movements and blood supply.
(b) The Spinal Cord: The spinal cord stems from the medulla oblongata and runs through the neural canal of the vertebral column or backbone. It communicates between the brain and other parts of the body. It controls all the reflex (involuntary) actions of the body.
The Peripheral Nervous System:
The peripheral nervous system consists of the cranial and spinal nerves and the autonomic nervous system. The cranial and spinal nerves of the peripheral nervous system together with the central nervous system mediate relations between the animal and its external environment. On the other hand, the autonomic nervous system, consisting of the sympathetic and parasympathetic nervous system regulates events within the animal.
A neurone (nerve cell) (Fig. 2.17) is the structural and functional unit of the nervous system. It helps in receiving and relaying or transmission of impulses. A neurone has three main parts: the dendrite, cell body and axon (nerve fibre or axis cylinder).
The cell body has dendrites extending from it, and a central nucleus. The axon is surrounded by myelin sheath which is interrupted at intervals, forming nodes of ranvier. The axon terminates in dendrites.
Types of Neurones
Sensory or Afferent Neurones: These neurones carry impulses from receptors such as the eyes, skin, ears, etc. to the central nervous system.
Motor or Efferent Neurones: These neurones carry impulses from the central nervous system to effectors such as muscles and glands in the body.
Intermediate or Relay Neurones: These neurones receive, transmit and interpret messages in the spinal cord and brain.
Transmission of Nerve Impulse: The drites usually receive messages and pass m to the cell body which then passes them ssages) out through the long axon to the drites of another nerve cell. However, there O direct connection between the fibres of cent neurones. The junction between one of a dendrite of one neurone and that of an axon of the next neurone is known as a synapse. The message passes from cell to cell across these synapses.
Reflex Actions: These are actions carried out by animals in response to certain stimuli without first thinking or planning for them. They are not under the control of the brain. They are quick, automatic responses and entirely stereotype in nature. Examples of simple reflex or invoulntary actions include: (i) the blinking of the eyes (ii) the beating of the heart (iii) sneezing (iv) sudden removal of hands, legs or skin from hot objects. (v) the jerking of the legs on tapping the knee cap.

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