notes: the digestive system (ch 14, part 1)...*the alimentary canal is a muscular tube that passes...
TRANSCRIPT
NOTES: The Digestive
System (Ch 14, part 1)
DIGESTION…
Digestion is the process of mechanically and chemically breaking down foods and absorbing the breakdown products. The digestive system consists of an alimentary canal and several accessory organs.
Alimentary canal includes:
● mouth● pharynx● esophagus ● stomach ● small intestine● large intestine● rectum ● anus
Accessory organs are:
● salivary glands● liver● gallbladder ● pancreas
GENERAL CHARACTERISTICS OF THE ALIMENTARY CANAL
*The alimentary canal is a muscular tube that passes through the body’s ventral cavity. Different regions carry out different functions, but certain structural characteristics are similar throughout its length.
Structure of the alimentary wall:4 DISTINCT LAYERS:• MUCOSA (or mucous membrane)-surface epithelium, underlying connective
tissue, and a small amount of smooth muscle
-in some regions, folds and tiny projections increase the surface area (for absorption)
• SUBMUCOSA-loose connective tissue, glands, blood
vessels, lymphatic vessels, and nerves
4 layers of alimentary wall…● MUSCULAR LAYER-consists of two coats of smooth muscle tissue
and some nerves; produces movement of the tube
● SEROSA (or serous layer)-outer covering of the tube (also the visceral
peritoneum)-protects underlying tissue-cells here secrete serous fluid, which moistens
and lubricates tube’s outer surface
Movements of the tube:*motor functions include:
MIXING MOVEMENTSand PROPELLING MOVMENTS(include a wavelike motion called PERISTALSIS)
MOUTH (Oral Cavity)*receives food and begins digestion Tongue:-rough projections (PAPILLAE)
on surface of tongue provide friction to handle food
-papillae also contain TASTE BUDS-covering the root of the tongue are masses
of lymphatic tissue: LINGUAL TONSILS
MOUTH (Oral Cavity)
Palate:-forms the roof of the oral cavity-hard palate (anterior) and soft palate
(posterior)-soft palate extends posteriorly and downward as a projection called the UVULA
MOUTH (Oral Cavity) Teeth:-primary teeth (“baby teeth”) are replaced by the
secondary teeth (permanent teeth)-teeth are used to mechanically break food into smaller pieces (this increases the surface area of food allowing digestive enzymes to react more effectively with the food molecules)
SALIVARY GLANDS
*salivary glands secrete saliva, which moistens food, helps bind food particles, begins chemical digestion ofcarbohydrates, makes taste possible, and helps cleanse the mouth.
SALIVARY GLANDS
Serous cells: secrete a watery fluid that contains the digestive enzyme AMYLASE(starts to break down starch and glycogen into smaller disaccharides)
Mucous cells: secrete a thick fluid called mucus, which binds food particles and lubricates during swallowing
SALIVARY GLANDS
There are 3 pairs of salivary glands:
1) Parotid glands (largest)•releases salivary amylase: breaks down starch•makes up about 25% of
saliva
SALIVARY GLANDS
2) Submandibular glands•on the floor of the mouth•produces mucin
(glycoprotein) •makes up 70% of the saliva
and responsible lubrication of food
SALIVARY GLANDS
3) Sublingual glands (underneath the tongue)•produces secretions that act as a buffer and lubricant• secretions are mostly mucus…thick and stringy•makes up only 5% of saliva
PHARYNX and ESOPHAGUS (important passageways!)
PHARYNX: connects the nasal and oral cavities with the larynx and esophagus
ESOPHAGUSESOPHAGUS: a food passageway
from the pharynx to the stomach; passes through the diaphragm
-at distal end, circular smooth muscle fibers thicken and close the entrance to the stomach (prevents regurgitation);
-if some of the acidic stomach contents are regurgitated (reflux) into the esophagus, may cause HEARTBURN
STOMACH*the stomach receives food, mixes it with
gastric juice, initiates protein digestion, carries on a limited amount of absorption, and moves food into the small intestine.
STOMACH Structure / Parts:-J-shaped, pouch-like organ that
sits inferior to diaphragm in upper left of abdominal cavity
-has a capacity of about 1 L-thick folds (rugae) in the inner lining
disappear when the stomach wall stretches-separated from the small intestine by a
powerful circular muscle: PYLORIC SPHINCTER
Rugae
STOMACH Gastric Secretions - produced by
GASTRIC GLANDS, which have 3 types of cells:● mucous cells: secrete mucus● chief cells: secrete digestive enzymes● parietal cells: secrete hydrochloric acid
(HCl)*together, these secretions form
GASTRIC JUICE
Next slide, some folks might find gross
STOMACH PEPSIN: most important digestive
enzyme in gastric juice-secreted by chief cells in an inactive
form: PEPSINOGEN-when it comes into
contact with hydrochloric acid, it becomes the active PEPSIN
STOMACH
*a layer of thick mucus is produced by cells in the stomach’s inner lining…this protective coating prevents the stomach from digesting itself.
STOMACH Mixing and emptying actions:- CHYME = a mixture
of food particles and gastric juice produced by mixing
-chyme is emptied into the small intestine where chemical digestion continues
-the rate of emptying depends on the fluidity of chyme and the type of food