Digestive System

Six Processes in Gastrointestinal Activity
Gastrointestinal activity begins with ingestion, which involves the
voluntary placement of food into the mouth. This is followed propulsion,
which involves the movement of food from mouth to anus along the
alimentary canal. Other activities associated with propulsion include
swallowing, segmentation, peristalsis, and mass movement. The ingested
food undergoes the process of mechanical digestion, which is the
breakdown of food into small particles. The process of chemical
digestion, on the other hand, involves the further breakdown of food by
enzymes in a sequence of reactions. The absorption process involves the
uptake of the digested food products from the gastrointestinal tract
into the blood system or lymphatic system. Defecation is the final
process, which is the removal of indigested material through the anus in
the form of feces (Berman, 2013).
Role of hormones in hunger and satiety
Hunger and satiety are controlled by leptin and ghrelin hormones. Leptin
functions by making someone feel full. Once the hormone is secreted, it
signals thyroid t inform about the presence of fats that needs to be
burnt. Leptin resistance results in storage of excess fats, which may
lead to obesity. In addition, leptin resistance results in less calories
being burnt, thus increasing appetite that leads to overeating. The
hormone ghrelin, on the other hand, is made in the stomach and increases
appetite when the stomach is empty. It functions by regulating the genes
that so that fat is held instead of burning it off. The release of the
two hormones is affected by different factors such as lifestyle,
environment, and diet (Berman, 2013).
Digestion of triglycerides
Fats are broken down into small droplets (micelles) bile that is
produced by the liver. Micelles are then hydrolyzed by pancreatic lipase
to release glycerol, fatty acids, and monoglycerides. Glycerol diffuses
into epithelial cells where they are converted to fatty acids. The fat
molecules are passed from Golgi into lamina propria where they enter
lacteal. The molecules are then transported to venous circulation
located at thoracic duct (McNamara, 2013).
Cholecystokinin and secretin
The release of the two hormones (Cholecystokinin and secretin) is
stimulated by chyme in the small intestine. The hormones are then
transported through the blood stream to target organ, which include
liver, pancreas, and gallbladder. Cholecystokinin stimulates pancreas to
release pancreatic juice, which is rich in digestive enzymes. Secretin
stimulates release of pancreatic juice that is rich in bicarbonates.
Secretin stimulates the liver to release bile and cholecystokinin
stimulates gallbladder to release bile (National Geographic Society,
Importance of acidic stomach content
The acidic condition (produced by HCl) produces an optimal environment
for pepsin to function. The acid also kills bacteria that may have been
ingested together with food. The stomach wall is lined with mucous cells
that secret alkaline mucus to protect the stomach from acidic corrosion.
The cells of mucosa are tightly joined to prevent penetration of gastric
juice into tissues. The degraded epithelial cells are replaced regularly
and rapidly to ensure that the stomach wall is well protected from
acidic corrosion (NGS, 2013).
Modification of small intestine to increase surface area
The small intestine has several types of small projections such as
villi, plicae circulars, and microvilli. Villi projections take the
shape of fingers and increase the surface area for absorption. Plicae
circulars and located in the submucosa and mucosa and function by
forcing chyme through lumen. Microvilli are located in the plasma
membrane of mucosa and functions by increasing surface area for
absorption (NGS, 2013).
Berman, R. (2013). The role of hunger hormones in your metabolism.
Hoboken: John Wiley & Sons Incorporation.
McNamara, M. (2013). Triglycerides and digestion. Santa Monoca: Demand
Media Incorporation.
National Geographic Society (2013). Digestive system. Des Moines: NGS.

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