7.2 THE RESPIRATORY STRUCTURES & BREATHING MECHANISMS IN HUMANS & ANIMALS

LEARNING OUTCOMESState the respiratory structures in humans & some animals;Make an inference on the various adaptations of the respiratory structures;Describe the characteristics of respiratory surfaces in humans & other organisms;Describe the breathing mechanisms in humans & other organisms.Compare & contrast the human respiratory system with that of other organisms.

BREATHING - Involvement of inhalation of O2 & exhalation of CO2Each organisms have their special structure with the adaptation for gaseous exchange:-Large surface area to volume ratio increase the rate of exchangeVery thin walls one cell thickA rich supply of blood covered with blood capillariesA moist surface easier for the gases to diffuse

PROTOZOAUnicellular organisms Amoeba & ParameciumHave a large surface area to volume ratio, the external area is fully permeable to the gasesNo need specific respiratory stuructureGases diffuse in & out of the organisms over the whole cell membrane.Depends on the concentration of respiratory gases in & out of the cell

FISHA bony fish has four pairs of gills, support by a bony arch

The gills consist of two rows of gill filament numerous gill lamela

Each gill lamela is folded into gill plate, have thin walls & well supplied with blood capillaries to increase the surface area of the gillsCharacteristics :-bony/gill arches to support the filamentsFilaments numerous (increase the surface area for gaseous exchange)Thin membrane (to ease the gases absorption)Many blood capillaries (efficients transportation)

Breathing Mechanism of FishOpen its mouth lower the floor of the mouth- volume of the mouth is increased the pressure inside the mouth falls below that of the external pressure- water with high conc. of O2 enter-operculum close.

Floor of the mouth is raise up - Gaseous exchange occurs as water flows past the gills the pressure in the mouth is increased. water then passes out though the operculum operculum then opens

BREATHING MECHANISM

INSECTSThe body is protected by the exoskeleton, which is impervious to the gases.

Air reaches the body cells via an elaborated system of branching tubes called tracheae (singular : trachea)

Air enters the tracheae through a series of openings along the sides of the body spiracles

Reinforced with the chitin, the trachea are subdivided in numerous tiny tracheoles (singular : tracheole) thin, permeable walls & intimate contact with the body cells

Tracheal system provides a large surface area for gaseous exchange

O2 dissolves in the fluid found in the tracheoles & passes directly to the body cells through diffusion

BREATHING MECHANISM OF INSECTSThe rhythmic expansion & contraction of the abdominal wall help to drive the air in & out of the body

Contraction flattens the body, decreases the volume of the trachea, force the air out

Abdomen expands, air is drawn into the trachea through the spiracles

Each spiracle is controlled by a system of valves operated by tiny muscles

The level of CO2 in the body determines the size of the spiracles aperture

Some insect (such as grasshopper) have air sacs connected to the trachea that can pump the air throughout the tracheal system

AMPHIBIANSRespire through 4 different organs the gills, lungs, skin & mucous lining of the mouth have moist surfaces & have a good supplies of the blood capillariesThe tadpoles breathe through the skin & gills.The adult frog lungs, skin & mucous lining of the mouth many blood capillariesMany folds inside the lung sacs increase the respiratory surfaceIn water, O2 enters through its skin

AMPHIBIANInspiration nostrils open, the mouth closes, the glottis closses & the floor of the mouth cavity is loweredAir pressure inside the mouth reduced. Air is drawn through the nostrils into the mouth cavityThe noistrils close & the floor of the mouth cavity is raised to force the air through the glottis into the lungs.The lungs expand & gaseous exchange takes place.Expiration nostrils open, the muscles of the body wall contract to force the air from the lungs to the mouth cavity & nostrils

HUMANSConsist of a series of tube-like structures connecting a pair of lungs

Nasal passage, pharynx, larynx, trachea, bronchi (singular : bronchus), bronchioles & alveoli (singular : alveolus)

Lungs large sac-like organs, made up of mainly the bronchioles, alveoli & a network of blood capillaries

Left lung 2 lobes, right lungs 3 lobes

A double membrane called the pleura surrounds each lungs.

Outer pleural membrane attached to the chest wall, inner pleural membrane attached to the lungs.

Each lungs is packed with 1.5 2.5 million of alveoli.

Adaptation of the alveoli for gaseous exchange :A large surface areaVery thin wallsA moist surfaceA rich supply of blood

BREATHING MECHANISM OF HUMANSThe diaphragm is a dome-shaped sheet of muscles that separates the thorax from the abdomen

2 sets of intercostal muscles are located between the ribs external & internal intercostal muscles

INSPIRATION/INHALATIONThe external intercostal contract while the internal relax. the ribs & sternum move upwards & outwards

The diaphragm muscles contract & flatterns

The movement of the ribs & the diaphragm increase the volume of the thoracic cavity

Increasing the volume of the thoracic cavity until it is less than the atmospheric pressure air drawn into the lungs

BREATHING MECHANISM OF HUMANS

EXPIRATION/EXHALATIONThe internal intercostal muscles contract while the external relax ribs & sternum move downwards & inwards back to its resting position

The diaphragm muscles relax & arches upwards.

The movement of the rib cage & the diaphragm decrease the volume of the thoracic cavity increases the pressure inside until it is greater than the atmospheric pressure.

Air is forced out of the lungs.

COMPARISON BETWEEN THE HUMAN RESPIRATORY SYSTEM WITH THAT OF OTHER ORGANISMS

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