[Anaphy Lab] Digestive System Part 1

digestive system

a complex set of organs, glands, and ducts that work together to transform food into nutrients for cells.

Enzymes

break the particles down into small molecules, which are absorbed into the blood and transported all over the body

1. Ingestion and mastication

2. Propulsion and mixing

3. Digestion and secretion

4. Absorption

5. Elimination

Functions of Digestive System

ingestion

consumption of solid or liquid food

Mastication

the process of chewing

Propulsion

the movement of food from one end of the digestive tract to the other.

Mixing

the movement of food back and forth in the digestive tract to mix it with enzymes and facilitate absorption

Digestion

is the mechanical and chemical breakdown of large molecules into smaller molecules that can be absorbed

Secretion

the addition of liquids, enzymes, and mucus to the ingested food

Absorption

the movement of molecules out of the digestive tract and into the blood or lymphatic system.

Elimination

the removal of undigested material, such as fiber from food, plus other waste products from the body as feces

digestive tract

- also referred to as the GIT (gastrointestinal tract)

- one long tube from the mouth to the anus

oral cavity (mouth)

pharynx

esophagus

stomach

small intestines

large intestines

anus

Organs included in the Digestive Tract

salivary glands

liver

gallbladder

pancreas

Associated Organs in the Digestive Tract

1. Mucosa

2. Submucosa

3. Muscularis

4. Serosa/Adventitia

Layers of Digestive Tract Wall

Mucosa

- innermost layer

- secretes mucus

Submucosa

- above mucosa

- contains blood vessels, nerves, small glands

Muscularis

- above submucosa

- longitudinal, circular, and oblique muscles

Serosa/Adventitia

outermost layer of the digestive tract

Serosa

If peritoneum is present

Adventitia

if there is no peritoneum present

Visceral peritoneum

- also called serosa

- the serous membrane that covers the organs

Parietal peritoneum

the serous membrane that lines the wall of the abdominal cavity

Mesenteries

connective tissue sheets that hold organs in place in the abdominal cavity

Lesser omentum

mesentery connecting lesser curvature of stomach to liver and diaphragm

Greater omentum

mesentery connecting greater curvature of stomach to transverse colon and posterior body wall

Lips

muscular structures, formed by the orbicularis oris muscle and covered by skin.

Cheeks

lateral walls of the oral cavity

buccinator muscles

muscle within the cheeks which flatten the cheeks against the teeth

Tongue

- large, muscular organ that occupies most of the oral cavity.

- moves food in the mouth and, in cooperation with the lips and cheeks, holds the food in place during mastication.

32

number of teeth in normal adult

Incisors

canine

premolars

molars

wisdom

5 components/elements of teeth

20

number of primary (deciduous) teeth

dentin

cellular tissue that forms the bulk of the tooth

enamel

an extremely hard, acellular that covers the dentin in the crown of the tooth

pulp cavity

the center of tooth filled with pulp

pulp

a material in the pulp cavity which consists of blood vessels, nerves, and connective tissue

alveoli

a bone where teeth are held in place within its pockets

Dental caries

- or cavities

- breakdown of enamel by acids from bacteria

Palate

roof of oral cavity

Hard palate

anterior part of the oral cavity made of bone

Soft palate

posterior part of the oral cavity that consists of skeletal muscle and connective tissue

Salivary glands

Produce saliva

saliva

a mixture of serous (watery) and mucous fluids

Keeps the oral cavity moist

Needed for normal speech

Dissolves food particles so they can be tasted

Protects against bacteria and neutralizes pH

Begins the process of digestion

Functions of Saliva

Parotid, Submandibular, Sublingual

Three Subparts of Salivary Glands

Parotid

serous glands anterior to each ear.

Submandibular

produce more serous than mucous secretions, found along the inferior border of the mandible

Sublingual

produce primarily mucous and lie below the mucous membrane in the floor of the oral cavity.

Amylase and Lysozyme

Enzymes found in Serous portion of Saliva

Amylase

Digestive enzyme that breaks down carbohydrates

Lysozyme

Enzymes that are active against bacteria

Mucin

- enzyme found in mucous portion of saliva

- for lubrication

Pharynx

- also known as the throat

- connects the mouth to the esophagus

nasopharynx

oropharynx

laryngopharynx

Three parts of Pharynx

Esophagus

- Tube that connects the pharynx to the stomach

- Transports food to the stomach

- joins stomach at cardiac opening

Heartburn

- occurs when gastric juices regurgitate into esophagus

caffeine

smoking

eating or drinking in excess

Habits that can cause heartburn

Voluntary phase

- swallowing phase where bolus (mass of food) formed in mouth and pushed into oropharynx

- the food is still in the oral cavity

- you still have complete control

Pharyngeal phase

swallowing reflex initiated when bolus stimulates receptors in oropharynx

Esophageal phase

moves food from pharynx to stomach

Peristalsis

wave-like contractions moves food through digestive tract

Stomach

- Located in abdomen

- Storage tank for food

- Produces mucus, hydrochloric acid, protein digesting enzymes

- Contains a thick mucus layer that lubricates and protects epithelial cells on stomach wall from acidic pH (3)

pH 3

pH value of the acidity within the stomach wall

2 liters

amount of food that the stomach can hold up

Fundus

is to the left of, and superior to, the cardiac part of the stomach

body

largest part of the stomach

greater curvature and lesser curvature

created when the body of the stomach turns to the right

funnel-shaped pyloric part of the stomach

formed when the body narrows inferiorly

1. Outer longitudinal

2. Middle circular

3. Inner oblique

3 layers of Muscularis

3 layers of Muscularis

are used to produce the churning action in the stomach

Rugae

large folds that allow stomach to stretch

Chyme

- paste-like substance that forms when food begins to be broken down

Pyloric opening

opening between stomach and small intestine

Pyloric sphincter

thick, ring of smooth muscle around pyloric opening which regulates movement of food into the small intestine

gastric pits

- formed by the mucosa

- openings for the gastric glands

1. surface mucous cells

2. mucous neck cells

3. parietal cells

4. endocrine cells

5. chief cells

5 Groups of epithelial cells of the stomach

Surface mucous cells

- produce mucus that coats and protects the stomach

- protects the lining of the stomach from too much acid of the Hydrochloric acid

mucous neck cells

- also produce mucus that protects he lining of the stomach from too much acid

parietal cells

- produce hydrochloric acid and intrinsic factor

endocrine cells

- produce hormones and paracrine molecules

chief cells

produce pepsinogen

pepsinogen

a precursor of the protein-digesting enzyme pepsin

Hydrochloric acid

- Produces a pH of about 2.0 in the stomach.

- Kills microorganisms, activates pepsin.

Pepsin

breaks covalent bonds of proteins to form smaller peptide chains

Mucus

- A thick layer, which lubricates the mucosa of the stomach

- Protects mucosa from acidic chyme and pepsi

Intrinsic factor

- Binds with vitamin B12 making it more readily absorbed by small intestine

Vitamin B12

is important in DNA synthesis and red blood cell production

Parasympathetic stimulation, gastrin, and histamine

increase stomach secretions

Cephalic phase

- Stomach secretions are initiated by sight, smell, taste, or food thought

- Hydrochloric acid, pepsin, mucus, and intrinsic factor, gastrin and histamine are released in the stomach

- The time when the volume of stomach secretions is at its lowest

- the time when stomach secretions are just starting as it was stimulated by sense since the food in not yet in the stomach

Gastric phase

- Food in stomach, partially digested proteins and distention of stomach promote increase of secretion

- Peptides, produced by the action of pepsin on proteins, stimulate the secretion of gastrin.

- Gastrin is carried through the blood back to the stomach stimulating more secretion.

- The time when stomach secretions is at its highest

- The food is already in the stomach

- The stomach expands

Intestinal phase

- Inhibits secretion and movement in stomach

- Entrance of chyme into duodenum stimulates neuronal reflexes and secretions of hormones

- The hormones secretin and cholecystokinin are released into the blood by the duodenum and they inhibit secretion and movement in the stomach

- Time when stomach secretions start to decline to stop

- This is because during this phase the food is already in the intestine, so stomach secretions is no longer needed

- The hormones secretin and cholecystokinin are released into the blood by the duodenum and they inhibit secretion and movement in the stomach

secretin and cholecystokinin

hormones released into the blood by the duodenum and they inhibit secretion and movement in the stomach during intestinal phase

1. Mixing waves

2. Peristaltic waves

Two types of movement in the Stomach

Mixing waves

- weak contraction

- thoroughly mix food to form chyme

Peristaltic waves

- stronger contraction

- force chyme toward and through pyloric sphincter

Hormonal and neural mechanisms

regulate stomach secretions and movement

4 hours

number of hours when stomach empties after regular meal

6 to 8 hours

number of hours when stomach empties after high fatty meal

Small Intestine

- Major absorptive organ of the gastrointestinal tract

- Contains enzymes to further breakdown food

- Contains secretions for protection against the acidity of chyme