Download Digestion

The Digestive System
MEDICAL TERMINOLOGY
M S . PA S T O R
Nutrition and Digestion
Objectives
- Identify and describe the structures of the digestive
using proper medical terminology
- Explore careers relating to this system
There are six types of nutrients:
• Water
• Carbohydrates
• Proteins
• Fats
• Minerals
• Vitamins
Carbohydrates
• Carbohydrates are the main source of energy for the body.
• simple and complex carbohydrates supply glucose
• fiber from plant foods helps elimination
• Proteins are necessary for growth and repair of the body’s
cells.
– body makes 12 out of 20 amino acids
– other eight essential amino acids come from food
• Fats provide energy and key building components.
– fats are saturated and unsaturated
– butter, lard and oils
– essential fatty acids come from food
• Minerals are inorganic materials needed in small amounts
– help to build or repair tissues
– replenished by eating variety of foods
• Vitamins are organic molecules that work with enzymes.
– vitamins are fat-soluble and water-soluble
– Fat soluble: A, D, E, K
– Water-soluble: B, C (ascorbic acid) , folic acid
– regulate cell functions, growth, development
• Unbalanced diets can lead to malnutrition or undernutrition
– Malnutrition occurs in when you don’t get the right
nutrients for your body, or you over consume some
nutrients.
– Undernutrition is when you lack the essential nutrients
your body needs in order to function properly.
Key Concept #2
The main stages of food processing are ingestion,
digestion, absorption, and elimination
• Ingestion is the act of eating
• Digestion is the process of breaking food down into
molecules small enough to absorb
• Absorption is uptake of nutrients by body cells
• Elimination is the passage of undigested material out of the
digestive compartment
LE 41-12
Small
molecules
Pieces
of food
Mechanical
digestion
Chemical digestion
Nutrient
(enzymatic hydrolysis) molecules
enter body
cells
Undigested
material
Food
INGESTION
DIGESTION
ABSORPTION
ELIMINATION
• More complex animals have a digestive tube with two
openings, a mouth and an anus
– This digestive tube is called a complete digestive
tract or an alimentary canal
– It can have specialized regions that carry out digestion and
absorption in a stepwise fashion
Key Concept #3
Each organ of the mammalian digestive system has
specialized food-processing functions
• The human digestive system consists of an alimentary
canal and accessory glands that secrete digestive juices through
ducts
• Accessory glands are the
– salivary glands
– pancreas
– liver
– gallbladder
• Food is pushed along by peristalsis, rhythmic contractions of
muscles in the wall of the canal
LE 41-15a
Cardiac
orifice
Tongue
Salivary
glands
Oral cavity
Parotid gland
Sublingual gland
Pharynx
Esophagus
Submandibular gland
Pyloric
sphincter
Liver
Stomach
Ascending
portion of
large intestine
Gallbladder
Pancreas
Ileum
of small
intestine
Small
intestine
Large
intestine
Rectum
Anus
Appendix
Cecum
Duodenum of
small intestine
The Oral Cavity, Pharynx, and Esophagus
• In the oral cavity, food is
lubricated and digestion
begins
• Teeth chew food into
smaller particles that are
exposed to salivary
amylase, initiating
breakdown of carbohydrates
• The region we call our throat is the pharynx, a junction that
opens to both the esophagus and the windpipe (trachea)
• The esophagus pushes food from the pharynx down to the
stomach by peristalsis
Bolus of food
Tongue
Epiglottis
up
Epiglottis
up
Pharynx
Glottis
Larynx
Trachea
Glottis
down
and open
Esophageal
sphincter
contracted
Epiglottis
down
Esophagus
Glottis up
and closed
Esophageal
sphincter
relaxed
Esophageal
sphincter
contracted
Relaxed
muscles
To lungs To stomach
Contracted
muscles
Relaxed
muscles
Stomach
The Stomach
• The stomach stores food and secretes gastric juice, which
converts a meal to acid chyme
• Gastric juice is made up of hydrochloric acid and the
enzyme pepsin
• Pepsin is secreted as inactive pepsinogen by chief cells;
pepsin is activated when mixed with hydrochloric acid in the
stomach
– It’s purpose is to break down protein
• Mucus protects the stomach lining from gastric juice
Esophagus
Cardiac orifice
Stomach
5 µm
Pyloric sphincter
Interior surface of
stomach
Small
intestine
Folds of
epithelial
tissue
Epithelium
Pepsinogen
Pepsin
(active enzyme)
HCl
Gastric gland
HCl converts
pepsinogen to pepsin.
Pepsin then activates
more pepsinogen,
starting a chain
reaction. Pepsin
begins the chemical
digestion of proteins.
Mucus cells
Chief cells
Parietal cells
Pepsinogen and HCl
are secreted into the
lumsden of the stomach.
Chief cell
Parietal cell
• Gastric ulcers, lesions in the lining, are caused mainly by
the bacterium Helicobacter pylori
Bacteria
1 µm
Mucus
layer of
stomach
The Small Intestine
• The small intestine is the longest section of the alimentary
canal
• It is the major organ of digestion and absorption
• The first portion of the small intestine is the duodenum
– Where acid chyme from the stomach mixes with digestive
juices from the pancreas, liver, gallbladder, and the small
intestine itself
Accessory Glands
Liver
Bile
Gallbladder
Stomach
Acid chyme
Intestinal
juice
Pancreas
Duodenum of
small intestine
The Pancreas
• The pancreas has both digestive and endocrine
(hormone) functions.
• Digestive Function
– Releases bicarbonate to neutralize the acid
chyme that enters the small intestine
– Releases proteases to help with further digestion
of proteins
• Endocrine Function
– Releases insulin & glucagon to control bloodsugar levels
The Liver
• The liver produces bile, which aids in digestion and
absorption of fats
The Small Intestine: Absorption of Nutrients
• The small intestine has a large surface area, due to villi and
microvilli that are exposed to the intestinal lumen
• The enormous microvillar surface greatly increases the rate of
nutrient absorption
Key
Vein carrying blood
to hepatic portal
vessel
Nutrient
absorption
Microvilli
(brush border)
Blood
capillaries
Epithelial
cells
Muscle layers
Epithelial cells
Large
circular
folds
Villi
Lacteal
Villi
Intestinal wall
Lymph
vessel
The Large Intestine
• The large intestine, or colon, is connected to the small
intestine
• Its major function is to recover water that has entered the
alimentary canal
• Wastes of the digestive tract, the feces, become more solid as
they move through the colon
• Feces is stored in the rectum until it exits via the anus
Glucose Regulation as an Example of Homeostasis
• Animals store excess calories as glycogen in the liver and fats
in the muscles.
• Hormones like insulin & glucagon regulate glucose
metabolism
• When fewer calories are taken in than are expended, fuel is
taken from storage and broken down to be used by cells.
LE 41-3
STIMULUS:
Blood glucose
level rises
after eating.
Homeostasis:
90 mg glucose/
100 mL blood
STIMULUS:
Blood glucose
level drops
below set point.