5: Digestive System

Question 1

4 basic processes of DIGESTION

Answer 1

1. motility
2. secretion
3. digestion
4. absorption

Question 2

motility

Answer 2

muscular contraction that MIX and MOVE FORWARD the contents of the tract

Question 3

secretion

Answer 3

secretion of digestive juices by DIGESTIVE EXOCRINE GLAND CELLS

Question 4

location of digestive endocrine gland cells

Answer 4

lining the digestive tract AND in acessory digestive organs

Question 5

type of cell

Answer 5

specialised epithelial cells

Question 6

mechanism of action

Answer 6

secrete also a range of signal proteins classified either as GI HORMONE or GI PEPTIDES –> enter blood –> carried to target organs, regulating digestive function

Question 7

digestion

Answer 7

the breakdown of starch, glycogen and disaccharides into their constituent monosaccharides

Question 8

absorption

Answer 8

transfer of vitamin, electrolytes, nutrients and some water from digestive tract lumen into the blood OR lymph

Question 9

what makes up the digestive system

Answer 9

1. digestive tract

2. accessory digestive organs

Question 10

accessory digestive organs

Answer 10

1.the biliary system [liver and gallbladder]
2.exocrine pancreas
3.salivary glands
they lie outside the digestive tract but empty their contents into the digestive tract

Question 11

length of digestive tract

Answer 11

4.5 m in its NORMAL CONTRACTILE STATE

Question 12

organs comprising the digestive TRACT

Answer 12

1. mouth
2. pharynx (throat)
3. oesophagus
4. stomach
5. small intestine (DJI - duodenum, jejunum, ileum)
6. large intestine [CACR - cecum, appendix, colon, rectum]
7. anus

Question 13

why these considered separate entities despite being continous w one another

Answer 13

because of their regional modifications allowing them to carry out their special function

Question 14

when is a substance considered INSIDE the body

Answer 14

only after it moves from the lumen of digestive tract into absorptive epithelial cells (everything IN the DT is considered outside the body as the DT is continous w the external environment)

Question 15

4 layers of digestive tract from innermost layer outward

Answer 15

1. mucosa
2. submucosa
3. muscularis externa
4. SEROSA

Question 16

1.mucosa’s innermost layer (1st)

Answer 16

mucous membrane

• serves as protective surface
• epithelial layer
• modified in some areas for absorption/secretion
• contains exocrine gland cells for secretion of DIGESTIVE JUICES
• contains endocrine gland cells for secretion of blood-borne GI hormones
• contains epithelial cells specialised in ABSORBING nutrients

Question 17

1.mucosa’s middle layer

Answer 17

lamina propria

• thin middle layer of connective tissue
• contains GALT which is important in defence against disease.
• GALT = gut-associated lymphoid tissue

Question 18

1.mucosa’s 3rd layer

Answer 18

muscularis mucosa

• outermost layer of smooth muscle
• highly folded in some parts of the GIT (eg. small intestine) for greater surface area for absorption
• pattern of surface folding can be modified by contraction

Question 19

2.Submucosa

Answer 19

• thick layer
• connective tissue
• contains submucosal nerve plexus
• contains large blood and lymph vessels
• provides distensibility and elasticity

Question 20

3. Muscularis Externa

Answer 20

MAJOR smooth muscle coat of the GIT
two layers
1.Inner Circular Layer
2.Outer Longitudinal Layer

Question 21

Inner circular layer

Answer 21

muscle fibres running circularly around the tube

contraction = decrease in diameter of tube at poin of constriction

Question 22

Outer longitudinal layer

Answer 22

muscle fibres running longitudinally along the length of the tube
contraction = shortening of GIT

Question 23

combined effects of contraction of these two

Answer 23

creates propulsive and mixing movements of GIT

Question 24

Myenteric Nerve Plexus

Answer 24

Between the inner circular & outer longitudinal layer.

-help regulate local gut activity

Question 25

4. Serosa

Answer 25

- outer connective tissue layer (covering) - secretes SEROUS fluid -lubricates &prevents friction of GIT w neighbouring organs - throughout much of the tract, SEROSA is continuous w Mesentry (suspends digestive organs from inner wall of abdominal cavity like a sling)

Question 26

4 factors involved in REGULATION of Digestive System Function

Answer 26

1. Autonomous SMOOTH MUSCLE function 2. intrinsic nerve plexuses 3. extrinsic nerves 4. GI hormones

Question 27

1.Autonomous Smooth Muscle Function

Answer 27

- SLOW-WAVE POTENTIALS: self-induced electrical activity in digestive smooth muscle - by pacemaker cells "Interstitial Cells of Cajal" - located in the layers of MUSCULARIS EXTERNA - slow waves are NOT action potentials, only induce rhythmic cycles of depolarisation and repolarisation close to the threshold potential. - if waves REACH threshold potential at peak of depolarization--> rhythmic cycles of MUSCLE CONTRACTION

Question 28

another name for Slow-wave Potentials

Answer 28

BER (Basic Electrical Rhythm) of the digestive tract

Question 29

2.Intrinsic Nerve Plexuses

Answer 29

consists of: 1. The Submucosal Plexus 2. The Myenteric Plexus collectively, referred to as ENTERIC NERVOUS SYSTEM. Has a considerable degree of self-regulation. -the only body system to have its own INTRAMURAL NERVOUS SYSTEM

Question 30

Intrinsic Nerve Plexus subdivision

Answer 30

Intrinsic Afferent Neurons (respond to local stimuli in digestive tract) Intrinsic Efferent Neurons: control smooth muscle. -endocrine and exocrine cells of digestive tract

Question 31

Intrinsic EFFERENT Neurons affect...

Answer 31

- digestive tract motility - secretion digestive juices - secretion GI hormones - LOCALLY eg. if large piece food stuck in oesophagus, local response to push the food forward

Question 32

3. Extrinsic Nerves

Answer 32

- formed from both branches of the autonomic NS (Sympathetic Division and Parasympathetic Division) - originate outside the digestive tract

Question 33

Extrinsic Nerves affect...

Answer 33

- activity of intrinsic nerve plexuses - level of GI hormone secretion - act directly on Smooth Muscle AND glands

Question 34

Sympathetic division effect...

Answer 34

- dominates in "fight or flight" situations-inhibit /slow down digestive tract CONTRACTION and SECRETION - digestive processes not of highest priority when faced w emergency situation

Question 35

Parasympathetic division effect...

Answer 35

- dominates in quiet "rest and digest" situations - promotes smooth muscle motility - promotes secretion of digestive enzymes & hormones

Question 36

role of vagus nerve reflexes before food gets in the stomach (extrinsic nerve)

Answer 36

increases salivary secretion, stomach, pancreatic and liver secretion in anticipation of arrival of food

Question 37

4.GI Hormones

Answer 37

inhibitory or excitatory influences on digestive smooth muscle AND exocrine glands -GI hormones produced by SPECIALISED ENDOCRINE cells in certain regions of the mucosa

Question 38

3 types of SENSORY RECEPTORS to LOCAL changes in GIT

Answer 38

1. Chemoreceptors - sensitive to chemical components within the lumen 2. Mechanoreceptors - stretch or tension within the wall 3. Osmoreceptors - sensitive to osmolarity of luminal contents

Question 39

what does stimulation of either of these elicit

Answer 39

a. neural reflexes | b. secretion of hormones