digestive system

Question 1

stages of digestion

Answer 1

• Ingestion: selective intake of food.
• Digestion: mechanical and chemical breakdown of food.
• Absorption: uptake of nutrient molecules into epithelial cells of digestive tract and then to blood and lymph.
• Compaction: absorption of water and consolidation of the indigestible residue.
• Defecation: elimination of waste.

Question 2

Digestive tract

Answer 2

muscular tube extending from the mouth to the anus.

• Mucosa: simple columnar epithelium except for mouth and anus (stratified squamous epithelium).

Question 3

Mechanical digestion

Answer 3

Physical breakdown of food into smaller parts (produces greater surface area for enzymes to act on).
⟶ Cutting and grinding with teeth.
⟶ Churning and mixing action in the stomach and small intestine.

Question 4

chemical digestion

Answer 4

Chemical digestion:

• Enzymes (produced by glands associated with the digestive tract).

Question 5

THE DIGESTIVE WALL

Answer 5

• Lumen: central space containing food being digested.
• Mucosa: inner mucous membrane layer modified according to the digestive organ consisting of an inner
  epithelium, lamina propria and muscularis mucosa.
• Submucosa: a layer of loose connective tissue containing nerves, blood and lymphatic vessels.
• Muscularis externa: usually 2 layers of smooth muscle (inner circular and outer longitudinal layer).
• Serosa/adventitia: serous, thin, moist layer of connective tissue and mesothelium or alternatively a fibrous
  connective tissue (usually around the mouth and anus).

Question 6

what are mechanisms to move food along and within the gut

Answer 6

• perstalisis

- segmentation

Question 7

different layers of peritoneum

Answer 7

Parietal peritoneum (outer layer): lines the abdominal cavity wall.
• Visceral peritoneum (inner layer): turns inward from the body wall and wraps around the abdominal viscera forming the serosa.
• Peritoneal cavity: space between parietal and visceral layers lubricated by peritoneal fluid.

Question 8

Enteric nervous system:

Answer 8

regulates the digestive tract’s motility, secretion and blood flow.

Question 9

Autonomic Nervous System

Answer 9

• Parasympathetic (rest phase): messages sent via vagus nerve and sacral spinal cord = ↑ secretion, ↑ motility.
  • Sympathetic (active phase): messages sent via thoracic and lumbar spinal cord = ↓ secretion, ↓ motility

Question 10

Arterial circulation

Answer 10

aorta supplies oxygenated blood to the gut branching into the celiac trunk (blood to the liver, stomach, oesophagus, spleen, pancreas and superior half of the duodenum) and mesenteric arteries.

Question 11

Hepatic portal vein:

Answer 11

delivers venous blood from organs of the gastrointestinal tract (and spleen) to liver.

Question 12

oral cavity

Answer 12

food ingestion, chewing, swallowing, speech, respiration, and chemical digestion.
- Lined with stratified squamous epithelium.

Question 13

pharynx

Answer 13

3 regions: nasopharynx, oropharynx, and laryngopharynx.

• Pharyngeal constrictor muscles: force food downward during swallowing.
• startified squamous epilthelium

Question 14

oesophagus

Answer 14

• Transfers food from the pharynx to the stomach. Passes through the diaphragm.
• Longitudinal folds of mucosa and submucosa.

Question 15

stomach

Answer 15

food storage, mechanically breaks up food particles (muscular churning), liquefies food (chyme), and begins chemical digestion of protein and fat.

Question 16

liver and gall bladder

Answer 16

• secretes bile (aids in fat digestion and absorption by emulsifying fats).
• Gall bladder: stores and concentrates bile

Question 17

pancreas

Answer 17

Secretes pancreatic enzymes into the SI.
• Pancreatic amylase: digests carbohydrates.
• Pancreatic lipase: digests fat.
• Ribonuclease: digests RNA.
• Deoxyribonuclease: digests DNA

Question 18

large intestine

Answer 18

The SI empties into the LI at the Ileocecal valve

- Simple columnar epithelium (no plicae or villi.