Unit 1 a&p digestive system cti

ANATOMY AND PHYSIOLOGY OF THE DIGESTIVE SYSTEM © COLON THERAPY INSTITUTE

ANATOMY AND PHYSIOLOGY OF THE DIGESTIVE SYSTEMCOLON THERAPY INSTITUTE


Agenda

A. Basic digestive processes

B. Regulation of the digestive tract

C. Components of the digestive system


There are four basic digestive processes…

1. Digestion: mechanical and chemical breakdown of food

2. Motility: movement of material along the digestive tract

3. Secretion: release of enzymes into the digestive tract

4. Absorption: active or passive transfer of substances from the lumen of the digestive tract to ECF


• What’s digestion? • Digestion refers to the breakdown of food structure by enzymes

produced within the digestive system so that the nutrients locked in the complex foods become available for absorption and use

• How does it work?• Say a carbohydrate molecule is too large to be able to be absorbed

into the circulation…• Enzymes will first break down this large molecule into smaller

molecules called monosaccharides• The monosaccharides are then able to be absorbed across the cells

and into circulation• Similarly, proteins are degraded into amino acids and small

polypeptides, and fats are degraded into monoglycerides and free fatty acids

1 Digestion is the breakdown of food


• What’s motility? • Motility is a term used to describe

the contraction of the muscles that mix and propel contents in the digestive tract

• How does it work?• Muscle contraction causes motility

in two ways:

1. Peristalsis: progressive waves of contraction that move from one section to the next

2. Segmentation: short segments of the small and large intestines alternately contracting and relaxing which mixes contents and keeps them in contact with absorptive epithelium

2 Motility is muscle contraction


• What’s secretion? • Secretion involves the release of

digestive juices (e.g., hydrochloric acid, enzymes) into the the digestive tract

• These juices aid in digestion and absorption of food

• How does it work?• This process is under neural and/or

hormonal regulation

• How much secretion occurs daily?• About 9 liters of fluid pass through

the digestive system each day, and only about 2 liters are ingested, the rest represent secretions from the system itself

3 Secretion involves the release of fluids


• What’s absorption? • Absorption refers to the

process whereby the products that result from digestion are transferred from the digestive track into the blood or lymph

• How does it work?• Digested molecules of food,

as well as water and minerals from the diet, are absorbed from the cavity of the upper small intestine

• The absorbed materials cross the mucosa into the blood, mainly, and are carried off in the bloodstream to other parts of the body for storage or further chemical change

4 Absorption occurs when materials enter the blood or lymph


Agenda





The digestive system is controlled by both nerves and hormones


The nerves that control digestion are in the submucosa layer of the tissue


These nerves are part of the Autonomic Nervous System (ANS)• What’s the Autonomic Nervous System (ANS)?

• The ANS sends messages from the central nervous system to the internal organs and triggers automatic bodily functions without conscious effort

• It helps control the heart rate, blood pressure, digestion, respiration, blood pH and other bodily functions


The ANS consists of two branches: the parasympathetic nervous system and the sympathetic nervous system

Note: The activity of the digestive system increases if the parasympathetic nervous system is aroused and decreases if the sympathetic nervous system is aroused


Too much arousal of either branch can lead to problems• If the sympathetic nervous system is too

aroused:• Food will not move through the digestive

tract and mucus will not be released

• If the parasympathetic nervous system is too aroused:• Food will move through the digestive tract

too fast• Not enough nutrients may be absorbed into

the body

• Thus, both branches work together to attain the correct balance so that food moves through the tract at a suitable pace


The hormones that control digestion are produced and secreted by various organs along the digestive tractThese hormones cause the various chemicals that aid in digestion to be released or prevented from being released


Nerves and hormones work together to ensure that food moves at an appropriate pace and is digested


Agenda





The digestive tract is a series of hollow organs joined in a long tube running from the mouth to the anus

Components of the digestive tract: 1. Mouth2. Pharynx3. Esophagus4. Stomach5. Small intestine6. Accessory organs7. Large intestine (colon)


1 Food is ingested by the mouth

• What does it do?• Ingests food• Chews and mixes

food• Begins chemical

breakdown of carbohydrates

• Moves food into the pharynx

• Begins breakdown of lipids via lingual lipase

• Moistens and dissolves food, allowing you to taste it

• Cleans and lubricates the teeth and oral cavity

• Has some antimicrobial activity


2 The pharynx moves food from the oral cavity to the esophagus

• What does it do?• Propels food from the oral cavity to the esophagus• Lubricates food and passageways


3 The esophagus sends food to the stomach

• What does it do?• Propels food to the stomach• Lubricates food and passageways


4 The stomach mixes and churns food to form chyme

• What does it do?• Mixes and churns food

with gastric juices to form chyme

• Begins chemical breakdown of proteins

• Releases food into the duodenum as chyme

• Absorbs some fat-soluble substances (for example, alcohol, aspirin)

• Possesses antimicrobial functions

• Stimulates protein-digesting enzymes

• Secretes intrinsic factor required for vitamin B12 absorption in small intestine


5 The small intestine absorbs and digests

• What does it do?• Mixes chyme with

digestive juices• Propels food at a rate

slow enough for digestion and absorption

• Absorbs breakdown products of carbohydrates, proteins, lipids, and nucleic acids, along with vitamins, minerals, and water

• Performs physical digestion via segmentation

• Provides optimal medium for enzymatic activity


6 Accessory organs secrete digestive fluids

• Liver: produces bile salts, which emulsify lipids, aiding their digestion and absorption

• Gallbladder: stores, concentrates, and releases bile

• Pancreas: produces digestive enzymes and bicarbonate


7 The large intestine (colon) absorbs water; stores and eliminates stool

• What does it do?• Further breaks down

food residues• Absorbs most

residual water, electrolytes, and vitamins produced by enteric bacteria

• Temporarily stores stool

• Propels stool toward rectum

• Eliminates stool• Mucus eases

passage of stool through colon

Health & Medicine

Unit 1 a&p digestive system cti