LARYNX AND ESOPHAGUS: SWALLOWING
/MOTILITY, SOUND, PROTECTION
Pharynx is a fibro muscular tube that is semicircular
in cross section and is situated directly anterior to the vertebral column. Six
muscles are predominately responsible for its voluntary action. Three are
pharyngeal constrictor muscles and three are vertically oriented muscles. These
muscles aid in the act of swallowing. It is divided into three sections, that is,
nasopharynx, oropharynx, and larypharynx. It receives blood supply from
pharyngeal branch of the ascending pharyngeal artery.
The larynx is located within the anterior aspect of
the neck, anterior of the inferior portion of the pharynx and superior to the
trachea. Its primary function is to protect the lower airway by closing
abruptly upon mechanical stimulation, therefore halting respiration and
preventing entry of foreign matter into the airway. Other functions include
production of sound, coughing sensation and acting as a sensory organ. The
larynx is composed of three large unpaired cartilages, three paired of smaller
cartilages and a number of intrinsic muscles.
The esophagus is a 25 cm long muscular tube that
connects the pharynx to the stomach. The esophagus extends from the lower
boarder of the cricoid cartilage to the cardiac orifice of the stomach. In its
vertical course, the esophagus has two gentle curves in the coronal plane. It
also has three constrictions on its vertical course. It is divided into three portions.
The cervical portion, thoracic portion and the abdominal portion. Blood supply
is by inferior thyroid artery, phrenic and gastric artery. Nerve supply is by
laryngeal branches of the vagus nerve.
Pharyngeal phase descriptively is that period from
when the swallowed bolus first enters the pharyngeal cavity until it exists.
During this phase, the tongue seals the oropharynx. The soft plate and proximal
pharyngeal wall seal off the nasopharynx. The vocal cords and arytenoids close
off the laryngeal opening and the epiglottis swings down to cover the laryngeal
vestibule. The pharynx also widens and shortens, which is accompanied by the
elevation of the upper esophageal sphincter. These activities move food bolus
through into the esophagus. As it enters the esophagus, the lower esophageal
sphincter relaxes to receive the bolus. The liquid bolus moves by gravity
alone. The residual bolus is cleared by the peristaltic contraction wave.
During phonation, the vocal cords and arytenoid
cartilages are abducted. When air is forced through the closed rima glottidis,
the vocal cords vibrate against one another to produce sound.
INTESTINES, RECTUM AND ANUS: ABSORPTION, MOTILITY, DEFECATION AND REFLEXES
The large intestines the final section of the
gastrointestinal tract that performs the vital task of absorbing water and
vitamins while converting food into feces. It is thicker in diameter compared
to the small intestines. It is about 1.5m in length.it is made up of four tissue
layer namely mucosa, sub mucosa, muscularis and finally serosa forms the
The large intestine performs the vital function of
converting food into feces by absorbing essential vitamins produced by gut
bacteria and reclaiming water from feces. Chime, slurry of digested food,
passes through where it is mixed with beneficial bacteria that have colonized
the large intestines throughout a person’s lifetime. Most of the movement of
chime is achieved by slow waves of peristalsis over a period of several hours.
The bacterial fermentation of indigestible food converts the chime into feces
The rectum is a hollow muscular tube of 20cm in
length. It extends from inferior end of the sigmoid colon along the anterior
surface of the sacrum and coccyx in the posterior of the pelvic cavity. At its
inferior end, the rectum opens slightly before ending at the anus. Feces enter
the rectum from the colon where they are stored until they can be eliminated
through defecation. While being stored the walls of the rectum absorb some after
and return it o the blood supply. Bacteria continue to liberate some of the remaining
nutrients which are absorbed by the rectal walls. As feces accumulate and fill
the rectum, they exert pressure on the walls. This stimulates stretch receptors
to send impulses to the brain resulting in feelings of discomfort and mounting
pressure to empty the rectum. It also causes relaxation of the smooth muscle of
the internal anal sphincter to allow defecation.
The anus is a short tube at the end of the rectum
that ends at the body’s exterior. It is around 2-3 cm long and varies widely in
its diameter. It is line with columnar epithelial tissue. The tissue forms
folds known as anal column with anal valleys between the folds. The anus plays
a major role in controlling elimination of solid waste through defecation. When
filled the internal anal sphincter opens due to stimulation of the rectal walls
but the external and sphincter continues to old feces until voluntary signal
from the cerebral cortex cause it to relax during reflex.