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BPK 110 Lecture Notes - Gastric Acid, Gastric Glands, Pylorus

Biomedical Physio & Kines
Course Code
BPK 110
Gina Whitaker

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Kin110 Chapter 3 Digestion: From Meals to Molecules
Atoms (the smallest unit of elements) form molecules (groups of two or more atoms of the
same or different element bonded together), which form cells (the smallest unit of life), which
form tissues (collection of similar cells that together carry out a specific function), which form
organs (discrete structures composed of more than one tissue that performs a specialized
function), which form organ systems (group of cooperative organs), which form the entire
The Digestive System-the organ system that is primarily responsible for the digestion and for
the absorption of nutrients into the body
Made up of the gastrointestinal (GI) tract (mouth to anus) and accessory organs (salivary
glands, pancreas, liver, gallbladder)
The inside tube of the GI tract is the lumen. There are four tissue layers that make up the wall
of the GI tract
External layer-provides support and protection
Contraction layers of smooth muscles (which we do not have voluntary control)-helps mix food,
break it into small particles, and propel it through the digestive tract
Connective tissue-contains nerves and blood vessels that provides support, nourishes the
mucosa, and sends nerve signals that control secretions and muscle contractions
The mucosa which lines the GI tract is a type of epithelial tissue. Nutrients must pass through
before they can reach the blood or lymph
Digestion Functions
Ingestion-take in food
Transport-moving food down the esophagus and into the stomach
Secretion-lining food with various enzymes that help in the process of breaking down food
Digestion-breaking down food into components small enough to be absorbed into the body
Absorption-the process of taking substances from the GI tract into the interior of the body
Elimination-getting rid of any excess body waste
Transit time through the GI Tract is typically 24-72 hours.
-varies with diet, physical activity, emotional state, health status and medication use
Overview of Digestion
Physical movement
Peristalsis-coordinated muscular components that move material through the GI tract
Segmentation-rhythmic local contractions of the intestine that mix food with digestive juices
and speed absorption by repeatedly moving the food mass over the intestinal wall
Chemical breakdown
Enzymes-a protein molecule that accelerates the rate of specific chemical reactions without
itself being changed
Other secretions
Mucus-a viscous fluid secreted by glands in the digestive tract and other parts of the body
-lubricates, moistens, and protects cells from harsh environments
Ions-an atom or a group of atoms that carries an electrical charge (e.g. bicarbonate)

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Hormones-a chemical messenger that is produced in one location in the body, released into the
blood, and travels to other locations where it elicits responses
Digestive Enzymes-proteins that catalyze reactions that are responsible for breaking down food
into smaller units that can be absorbed
The Mouth
Mechanical and chemical digestion begins
Saliva is secreted from salivary glands after the sight, smell, or presence of food. It contains
lubricants, enzymes, and other substances (It also helps protect against tooth decay because it
washes away food particles and contains substances that inhabit the growth of bacteria that
cause tooth decay)
Enzyme salivary amylase digests starch into maltose (sweet tasting)
Teeth break down food particles. This makes food easier to swallow and increase the surface
area in contact with digestive juices. Chewing also breaks up fiber, which traps nutrients. If fiber
is not broken up, some of the nutrients in the food cannot be absorbed
Tongue helps mix food and aids chewing by constantly repositioning food between the teeth
Taste buds detect food chemicals
The Pharynx-the part of the GI tract that is responsible for swallowing. (also part of the
respiratory tract
The bolus (a ball of chewed food mixed with saliva) forces the epiglottis to cover the
passageway to the lungs
Epiglottis-a piece of elastic connective that covers the opening to the lungs during swallowing
Sometimes eating too quickly or talking while eating interferes with the movement of the
epiglottis and food passes into an upper air passageway. This food can usually be dislodged
with a cough, but if it becomes stuck and causes choking, it may need to be forced out by the
means of the Heimlich maneuver
The epiglottis returns to its original position once bolus has passed; airway to the lungs reopen
The Esophagus-connects the pharynx with the stomach
Sphincter-a muscular valve that helps control the follow of materials in the GI tract
-prevents food from the stomach back into the esophagus
-circular muscles contract, pushing the bolus down
-longitudinal muscles contract, shortening the passageway ahead of the bolus
-the rhythmic contraction of peristalsis propels food down the esophagus
-when a wave of peristaltic contraction reaches the stomach, it causes the sphincter to relax,
allowing the bolus to enter the stomach
Food that enters the stomach
Protein-large folded polypeptides
Fat-triglycerides, cholesterol, phospholipids, long chain fatty acids
-90% of fat calories are from triglycerides
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