Digestive system lecture 16

Question 1

2 parts digestive system is divided into

Answer 1

alimentary canal

associated organs

Question 2

alimentary canal

Answer 2

– mouth
– pharynx
– oesophagous
– stomach
– small intestine
– large intestine

Question 3

associated organs- digestive system

Answer 3

– teeth
– tongue
– gallbladder
– salivary glands
– liver
– pancreas

Question 4

digestive processes

Answer 4

1. Ingestion
2. Propulsion
3. Mechanical digestion
4. Chemical digestion
5. Absorption
6. Defecation

Question 5

ingestion

Answer 5

– taking food into the digestive tract via the mouth

Question 6

propulsion

Answer 6

– movement along digestive tract (swallowing, peristalsis)

Question 7

mechanical digestion

Answer 7

– chewing, mixing with saliva, churning food in stomach, segmentation

Question 8

chemical digestion

Answer 8

– Enzymatic, beginning in mouth and essentially complete in small intestine

Question 9

absorption

Answer 9

mainly in the small intestine

Question 10

defecation

Answer 10

– elimination of indigestible substances

Question 11

The mouth: muscles of mastication

Answer 11

Temporalis
Masseter
Lateral pterygoid
Medial pterygoid

Question 12

saliva

Answer 12

• Cleanses the mouth
• Dissolves food so that it can be tasted
• Moistens food and aids compaction
• Contains enzymes that begin breakdown of starch
• Human saliva contains histatins, that speed
would healing independent of antimicrobial
action

Question 13

salivary glands

Answer 13

• Extrinsic salivary glands
– parotid gland
– submandibular gland
– sublingual gland
• Intrinsic salivary glands (buccal glands)
– scattered throughout oral cavity mucosa

Question 14

Sjogren’s syndrome

Answer 14

• Chronic autoimmune disease
• Overproduction of B lymphocytes damages moisture -producing glands all over the body
• Effects o n kidneys, lungs, liver and pancreas and CNS
• Teeth often s o soft that patients cannot eat properly
• Characteristic tongue with damaged papillae

Question 15

bolus

Answer 15

Food compacted by tongue to form bolus

Question 16

buccal phase

Answer 16

Voluntary; tongue passes bolus into pharynx

Question 17

Pharyngeal-oesophageal phase

Answer 17

• Involuntary
• Tongue blocks mouth
• Uvula blocks nasopharynx
• Larynx rises; epiglottis prevents food entering trachea

Question 18

larynx

Answer 18

• Because the respiratory and digestive pathways share a common pathway, it is vital to have a mechanism to prevent
food entering the respiratory pathway
• The epiglottis achieves this
• Normally, the epiglottis is fully open, with its free end projecting upwards
• During swallowing, the larynx is pulled superiorly, tipping the free edge of the epiglottis inferiorly to cover the laryngeal
outlet
• The cough reflex is triggered when anything other than air enters the larynx, but this doesn’t work when we are unconscious

Question 19

oesophagus

Answer 19

• Muscular tube, 25cm long, collapsed when not involved in food propulsion
• Pierces diaphragm at oesophageal hiatus to enter abdomen
• Joins stomach at cardiac orifice

Question 20

stomach

Answer 20

• Upper left quadrant of abdominopelvic cavity
• Below the oesophagous, the GI tract expands to form stomach
• Temporary ‘storage tank’ where chemical breakdown of proteins begins
• Food converted to chyme (‘juice’)
• Pyloric sphincter (pylorus = ‘gatekeeper’) controls stomach emptying into duodenum
• Solid food reaches the stomach approx. 8s after swallowing
• Fluids reach the stomach approx. 1s after swallowing
• Food usually spends 4-6 hours in the stomach

Question 21

liver

Answer 21

• Right and left upper quadrants of abdominopelvic cavity (mainly right)
• Lies almost entirely within rib cage
• Largest gland in body (about 1.5 kg)
• Accessory organ associated with small intestine
• Liver functions include metabolism of carbohydrate, fat and protein, plus mineral/vitamin storage and others
• In digestion, liver excretes bile for export to duodenum

Question 22

gross anatomy of liver

Answer 22

• the hepatic artery and hepatic portal vein both enter the liver at the porta hepatis
• Hepatic veins exit to inferior vena cava
• Four primary lobes
– large right lobe
– smaller left lobe
– posterior caudate lobe
– posterior quadrate lobe
• Some anatomists consider quadrate and caudate lobes part of the left lobe, since they are – like the left lobe – served by the left hepatic duct

Question 23

small intestine

Answer 23

• Extends from pyloric sphincter to ileocecal valve
• Digestion is completed
• Almost all absorption occurs

Question 24

organs associated with small intestine

Answer 24

gall bladder

appendix

Question 25

small intestine anatomy

Answer 25

Duodenum (‘12 fingers long’)
• Short segment distal to stomach that receives digestive enzymes from pancreas, liver, and gall bladder
• 5 % of total length
Jejunum (‘empty’)
• Not very distinct from ileum, but somewhat less vascularised and active.
• 40% of total length
Ileum (‘twisted’)
• Longest, most distal section.
• 60% of total length
• Ends at ileocecal valve

Question 26

gallbladder

Answer 26

• Stores bile produced by liver until needed for digestion
• Concentrates bile (up to 10x), removing water and ions
• Expels bile into cystic duct, and from there to bile duct and duodenum, where it is used to digest fats

Question 27

pancreas

Answer 27

• Produces enzymes that break down a variety of foods

* Pancreatic juice drains via main pancreatic duct, which fuses with bile duct as it enters the duodenum

Question 28

The large intestine, or colon

Answer 28

• Frames small intestine on three sides
• Extends from ileocecal valve to anus
• Greater diameter than small intestine
Comprises
• Cecum
• Appendix
• Colon
• Rectum
• Anal canal

• Material arriving in the large intestine contains few nutrients
• Very little digestion, apart from some by enteric bacteria
• Harvests vitamins produced by these bacteria, plus water and electrolytes (Na, Cl)
• Not essential for life; a surgical technique called ileoanal juncture links the ileum directly to the anal canal
• Primary function is elimination of faecal matter