Zoology

• Ascaris Lumbricoides is the largest intestinal nematode parasitizing man.
• When fresh, Ascaris Lumbricoides is a light pink in colour but it changes to white.
• Ascaris Lumbricoides is rounded and tapers at both ends.
• The interior part of Ascaris Lumbricoides is thinner than the posterior end.
• The mouth of Ascaris Lumbricoides opens at the posterior end and possesses three finely toothed lips, one dorsal and two ventral.
• The digestive and reproductive organs of Ascaris Lumbricoides float inside the body containing an irritating fluid.
• The irritant action of Ascaris Lumbricoides is due to the presence of toxin, ascaron.
• The life span of the adult worm of Ascaris Lumbricoides in the human host is less than one year.
• male of Ascaris Lumbricoides measures about 15 to 25 cm in length with a maximum diameter of 3 to 4 mm. The tail end is curved ventrally having a conical tip. The genital pore opens into the cloaca from two curved copulatory spicules protrude. The anus opens with the ejaculatory duct into the cloaca .
• Ascaris Lumbricoides

  Female

  It is longer and stouter than the male and measures 25to 40cm in length with a maximum diameter of 5 mm. The posterior end is neither curved not pointed but it is conical and straight The anus us sub-terminal and opens directly on the ventral aspect in the form of a transverse slit. The vulva opens at the junction of the anterior and the middle thirds of the body on the mid-ventral aspect. this section of the worm is narrower and is called the vulvar waist.
• Eggs of Ascaris Lumbricoides are passed out with the faeces of the host. The eggs may be either fertilizes or unfertilized.
• The characteristics of fertilized eggs are

  (1) round of oval shape.

  (2)70micron*45microns

  (3)surrounded by a think smooth translucent shell with an outer mammillated albuminous coat. This coat is sometimes lost.

  (4)always bile stained and brownish in colour

  (5)Contains a very large conspicuous unsegmented ovum there is a clear crescentic area at each pole

  (6)floats in saturated salt solution
• The characteristics of unfertilized eggs are

  (1)narrower, longer, and more elliptical in shape

  (2)80micron*55micron

  (3)has a thinner shell with an irregular coating of albumin.

  (4)brownish colour

  (5)contains a small atrophied ovum with a mass of disorganized highly refractive granule of various sizes.

  (6)does not float in saturated salt solution.
• The human exchange gas system links the circulatory system with the atmosphere.
• The gas exchange system in humans is adapted to clean and warm the air that enters during breathing, maximise the surface area for diffusion of oxygen and carbon dioxide between the blood and atmosphere, minimise the distance for this diffusion, and maintain adequate gradients for this diffusion.
• Most organisms need a supply of oxygen for respiration.
• In a single-celled organism, the oxygen simply diffuses from the fluid outside the cell, through the cell surface membrane and into the cytoplasm.
• In a multicellular organism such as human, however, most of the cells are a considerable distance away from the external environment from which the oxygen is obtained.
• Multicellular organisms usually have a specialized gas exchange surface where oxygen from the external environment can diffuse into the body, and carbon dioxide can diffuse out.
• In humans, the gas exchange surface is alveoli(singular alveolus) in the lungs.
• Alveoli collectively have a huge surface area, probably totaling around 70m² in an adult, allowing a large number of oxygen and carbon dioxide molecules to diffuse through the surface at any one movement to give us a high rate of gas exchange.
• The lungs are in the thoracic (chest) cavity surrounded by the pleural membranes, which enclose the trachea, bronchi and bronchioles.
• The lungs are ventilated with air that passes through a branching system of airways Leading from the throat to the lungs is the trachea.
• At the base of the trachea are two bronchi (singular bronchus), which subdivide and branch extensively forming a 'bronchial tree' in each lung.
• Each bronchus divided many times to form smaller bronchioles.
• Terminal bronchioles divide to form even narrower respiratory bronchioles that supply the alveoli with air.
• Cartilage in the trachea and bronchi keeps these airway open and air resistance low, and prevent them from collapsing or bursting as the air pressure changes during breathing.
• In the trachea, there is a regular arrangement of C-shaped rings of cartilage, in the bronchi, there are irregular blocks of cartilage instead.
• Bronchioles are surrounded by smooth muscle, which can contract or relax to adjust the diameter of these tiny airway.
• During exercise, the muscles in the bronchioles open a greater flow of air to the alveoli.
• The absence of cartilage in the bronchioles makes these adjustments possible.
• As air flows through the nose and the trachea, it is warmed to body temperature and moistened by evaporation from the lining, so protecting the delicate surface in the lungs from desiccation (drying out).
• Protection is also needed against the suspended matter carried in the air, which may include dust, sand, pollen, fungal spores, bacteria and viruses.
• All are potential threats to the proper functioning of the lungs.
• Alveolar walls contain clastic fibres which stretch during inspiration and recoil during expiration to help force out air.
• The continual beating of their cilia carries the carpet of mucus upwards towards the larynx at a speed of about 1 cm min.
• When mucus reaches the top of the trachea it is usually swallowed so that panthogens are destroyed by the acid in the stomach.
• At the end of the pathway between the atmosphere and the bloodstreams are the alveoli.
• Some chemical pollutants, such as sulfur dioxide and nitrogen dioxide, can dissolve in mucus to form an acidic solution that irritates the lining of the airways.
• Breathing brings supplies of fresh air into the lungs, with a relatively high oxygen concentration and a relatively low carbon dioxide concentration.