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 drink water

– Fullness 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

• 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

• Epithelial--on surfaces

• Muscle

• Nerve

• Connective tissue

• Secretory--secrete acid, mucus, & enzymes

• White blood cells

The Mouth

• Tongue

• Teeth & Gums

• Salivary glands

Digestion begins in the mouth

• 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

• Must be coordinated with breathing

• Epiglottis must close over trachea during swallowing process to prevent food from entering respiratory tract

• If not--choking, possibly infection

• 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

• Fluoride

• Alcohol

• Maybe copper