Cell Constituents
• Cell membrane-separates cell from external environment; a lipid bilayer
• Cytoplasm-the semifluid contents of the cell; aqueous
• Nucleus-location of the DNA
• Mitochondria-the cell’s “power plants”
• Endoplasmic reticulum-site of protein synthesis
HIERARCHY OF THE BODY
• Cell
• Tissue
• Organ
• Organ system
• Individual Organism
Examples of Enzyme-Dependent Reactions in the Body
• DNA replication
• Digestion of nutrients
• Energy production from nutrients
• Energy storage (as fat or glycogen)
Hormones
• Chemicals that travel through the blood and turn on/off various functions in
target cells
• For example, insulin allows glucose (sugar) to enter muscle cells
• Glucagon stimulates liver to make glucose during fasting situations
Neurotransmitters
• Chemicals released at nerve endings that stimulate or inhibit “firing” of an
adjacent nerve--or muscle
• Examples--Acetylcholine, epinephrine (alias adrenaline), serotonin
The Nervous System and Nutrition
• Hypothalamus monitors fluid and nutrient status in the blood and sends
messages to cortex (thinking part) of brain for a response
– Thirst
– Fullness
drink water
stop eating
The Fight or Flight Response
• During times of stress (injury, imminent danger), body releases chemicals such
as epinephrine and norepinephrine to increase metabolism of nutrients
• This can be beneficial or detrimental
Gut Feelings
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Although people can be fed intravenously long term, eating is preferred
– Psychologically beneficial
– Intravenous (IV) feeding formulas lack most phytochemicals and some
trace micronutrients
– IV feeding long term can lead to liver or bone disease
Cell Types in the Gastrointestinal Tract
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Epithelial--on surfaces
Muscle
Nerve
Connective tissue
Secretory--secrete acid, mucus, & enzymes
White blood cells
The Mouth
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Tongue
Teeth & Gums
Salivary glands
Digestion begins in the mouth
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Amylase (an enzyme that can break down starch) in saliva is mixed with food
during chewing
• Saliva also serves to moisten food and form it into a ball (bolus)
• Tongue pushes bolus of food to rear of mouth, setting up swallowing reflex
Swallowing is Complex
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Must be coordinated with breathing
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If not--choking, possibly infection
Epiglottis must close over trachea during swallowing process to prevent food
from entering respiratory tract
Infants and elderly may have problems with swallowing (dysphagia)
The Esophagus
• Muscular tube connecting throat (pharynx) to stomach
• Muscle contractions propel food towards stomach
• At top of stomach-the lower esophageal sphincter keeps food and stomach
acid from coming back up
• When it’s less efficient---“heartburn”, or gastro-esophageal reflux
The Stomach
• Parietal cells of stomach secrete acid pH of ~2
• Protein digestion begins in stomach with pepsin (secreted by chief cells)
• Muscular actions of stomach continue to break up food into smaller pieces,
increasing surface area to facilitate digestion
• Stomach emptying is dependent on nutrient comp of meal-water empties
quickest, high fat meal slowest
A few nutrients are absorbed in the stomach
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Fluoride
Alcohol
Maybe copper