Human Respiratory and Cardiac Systems

HUMAN RESPIRATORY AND CARDIAC SYSTEMS
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6th April, 2019
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Task 1
1. Nasal Cavity
2. Bronchus
3. Bronchiole
4. Alveolar duct
5. Pharynx
6. Trachea
7. Bronchus
8. Diaphragm
B ) Inspiration
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Rijnberk and Stokhof (2009, p 63-74) explain the process of inspiration. Respiration
occurs due to the movements of the respiratory muscles, the internal and external
intercostal muscles along with the diaphragm. During inspiration, the diaphragm
contracts, the internal intercostal muscles relax while the external intercostal muscles
contract thereby causing the rib cage to expand and move outward leading to an
increase in the volume of the thoracic cavity. This increase in the volume of the lungs
leads to a decrease in intra-alveolar pressure making it lower than atmospheric
pressure. The pressure accumulated then drives air into the lungs.
Expiration
During expiration, the diaphragm relaxes, the external intercostal muscles relax
whereas the internal intercostal muscles contract. This causes the ribcage to move
inwards and exerting pressure on the lungs. The effect is that the interpulmonary
pressure in the chest cavity rises above the atmospheric pressure, causing air to be
pushed out of the lungs.
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Figure 1: Inspiration and Expiration, Rijnberk, Stokhof(2009)
C
The trachea is a wide hollow tube that connects the larynx and the bronchi of
the lungs. It also allows the passage of air in and out of the lungs during the breathing
process. To perform its functions effectively, the trachea’s structure has certain
adaptations.
The trachea has a thin membranous wall which is made up of C-shaped rings of
cartilage. The rings of cartilage may be between 16 and 20 in number along the whole
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length of the trachea. These rings of cartilage provide support to the trachea and keep
it open at all times for efficient airflow.
The walls of the trachea are made up of four walls of specialized tissues:
1. The Mucosa: it is the innermost layer and is made up of ciliated pseudostratified
columnar epithelium with numerous goblet cells. Goblet cells produce mucus, a sticky
substance that covers the inner lining of the trachea, used to trap any debris and
particles that may be in inhaled air before the particles reach the lungs. On the surface
of the columnar cells are cilia that work together in a rhythmic movement hence
pushing the mucous along with the trapped debris away from the lungs to the larynx
where it is either swallowed or expelled through coughing.
2. The Submucosa layer: this is a layer just below the mucosa. This layer of tissue
consists of areolar connective tissue containing blood vessels and the nervous tissue.
The collagen, elastic and reticular protein fibers provide support and elasticity to the
tracheal walls (Barclay, 2018). The blood vessels and nerves, on the other hand,
support the other layers of the tracheal wall. For the trachea to be able to adjust its
diameter appropriately, there are longitudinal smooth muscle fibers on the outside
trachea between the rings of cartilage.
3. Hyaline Cartilage: this is a layer surrounding the submucosa, and it forms the
supportive rings of the trachea. It also forms a strong and flexible structure that helps
in maintaining an open airway in the trachea while being resistant to external forces.
4. The Adventitia: this is the outermost layer of the tracheal wall made up of areolar
connective tissue. It anchors the trachea loosely to other surrounding soft tissues
structures.
D)
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Structure and functions of the alveolus
The alveoli are only one cell thick in order to make the path of diffusion of oxygen
between alveoli and blood capillaries shorter.
An alveolar duct is a tube that is made up of connective tissue and smooth muscle and
opens up to a cluster of alveoli. A collection of many individual alveoli is known as
an alveolar sac (Biga et al. 2019).
Alveoli epithelium is composed of two types of cells, type 1 and type 2. Type 1 cells
make up about 95 percent of the surface and constitute mainly the air-blood barrier.
The type 1 cells form an epithelium that is attached to a thin elastic basement
membrane. The membrane is extremely thin and borders the capillary endothelial
membrane. These two epithelial membranes taken together form what is known as a
respiratory membrane, which is about 0.5mm, thick.it is across this membrane that
gaseous exchange occurs (Knudsen and Ochs, 2018).
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