Digestive
SystemDigestive
SystemFunction: the mechanical and chemical
breakdown of foods and the absorption of nutrients by cells
Consists of: alimentary canal ( 9 m from mouth to anus) and accessory organs
Structure of the Wall of the Alimentary
Canal
1. Mucosa (mucous membrane) - protects tissues, carries out absorption
2. Submucosa - contains glands, blood vessels, lymphatic vessels, nerves
3. Muscular layer - smooth muscle tissue, circular and longitudinal fibers,
pushes food
4. Serosa (serous layer) - visceral peritoneum, outer covering of the tube,
moistens and lubricates structures
Movements of the Tube
Mixing Movements - rhythmic contractions that mix food with digestive juices
Propelling Movements - rings of muscles contract and relax to push food down
the canal (PERISTALSIS)
Mouth
- begins digestion by reducing size of particles (chewing) and mixing with saliva
Tongue - moves food during chewing, connects to the floor of the mouth via the
frenulum, contains papillae (taste buds)
Palate - forms roof of oral cavity (hard and soft), uvula at back of the mouth
Palatine tonsils - back of the mouth/throat, lymph organs that protect against
infection
Teeth - primary vs. secondary teeth; incisors, cuspids, bicuspids (premolars), molars
Anatomy of a Tooth
Crown - projects above the gums
Root - anchored to the alveolar process of the jaw
Enamel - made of calcium salts, hardest substance in body (outer surface)
Dentin - similar to bone, surrounds tooth's central cavity
Blood vessels and nerves extend through the tooth via the root canal
Serous cells produce amylase - splits
starch and glycogen into disaccharides
Mucous cells produce mucus - lubrication during swallowing
1. Parotid Glands
2. Submandibular Glands
3. Sublingual Glands
Pharynx - nasal and oral cavitys
- nasopharynx, oropharynx, laryngopharynx
Esophagus - moves to the stomach, penetrates the diaphragm at the esophageal
hiatus
lower esophageal sphincter (cardiac sphincter) - prevent food and chemicals
from moving up out of stomach
*J-shaped, puchlike organs that hangs
inferior to the diaphragm, 1 liter capacity
Four main parts of the stomach
1. Cardiac (esophageal opening)
2. Fundic (temporary storage area, lies slightly above the cardiac region)
3. Body (central area of the stomach)
4. Pyloric (pyloric sphincter, controls emptying of the stomach into the sm.
Intestine)
Lining of the stomach is a mucous
membrane - with small openings called gastric pits, containing gastric glands
Gastric Juice - pepsin / intrinsic factor
Chyme - paste of food molecules after its been broken down by the movement of
stomach and gastric juices, it is released from the pyloric sphincter valve
into the first portion of the small intestine - duodenum
Rugae - folds within the stomach, increase surface area
Muscles: Longitudinal / Circular / Oblique
has
endocrine and exocrine functions - secretes pancreatic juice
Pancreatic juice - digests fats, breaks down nucleic acids into nucleotides
- has a large right lobe and a smaller
left lobe
Hepatic lobules - liver's functional
units, contain bile canals ' hepatic ducts ' common hepatic duct
Hepatic portal vein - delivers blood to the liver
Functions: maintains normal concentration of blood glucose, breakdown of lipids and fats, protein metabolism (forming urea, synthesizing plasma proteins such as clotting factors, converting amino acids); stores iron and vitamins, destroys damaged red blood cells, removes toxic substances from the blood, secretes bile
Bile - yellowish-green liquid secreted from hepatic cells (when bile pigments build up in blood, skin turns green, a condition called jaundice). The cystic duct delivers bile to the gall bladder.
Bile is stored in the gall bladder
and then secreted into the duodenum via the common bile duct
Cholesterol in bile may form crystals called gallstones
Bile aids in digestion, bile salts break down fat globules into smaller droplets - emulsification
*tubular
organ that extends from the pyloric sphincter, many loops and coils, fills much
of the abdominal cavity
*receives secretions from the pancreas and liver, completes digestion of nutrients
and chime, absorbs
1. Duodenum - first part of the small
intestine
2. Jejunum - second part, ~2.2 m
3. Ilium - third part, longest ~3.3 m *jejunum and ilium are continuous
Mesentery - supports the coils of
the small intestine, contains blood vessels to carry nutrients away
Greater Omentum - peritoneum membrane that drapes like an apron over parts of
the system
Intestinal Villi - increase surface area for absorption
*the main function of the small intestine is to secrete chemicals to break down
food and carry away these nutrients in the blood (absorption)
1. Cecum - beginning of the large
intestine, pouchlike, closed end called the vermiform appendix (ileocecal valve)
2. Colon - ascending / transverse / descending / sigmoid
3. Rectum
4. Anal canal - ends in the anus
Functions - secretes mucus to protect the wall against abrasion; re-absorbs
water and passes along material that was not digested; contains intestinal flora
(bacteria to break down cellulose, also produce intestinal gas)
Mass movements - large portions of the colon contract to move material through
it, 2-3 times a day usually after eating
Carbohydrates, lipids, proteins, vitamins, minerals / Food Pyramid
1. GERD (gastroesophageal reflux
disease) / Heartburn
2. Diarrhea or Dysentery
3. Hepatitis (A, B, C)
4. Crohn's Disease
5. Irritable Bowel Syndrome
6. Stomach Ulcers
7. Lactose Intolerance
8. Appendicitis
9. Hernia