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PHYSIOLOGY III > LECTURE 4 (Large Intestine) > Flashcards

LECTURE 4 (Large Intestine) Flashcards

1
Q

What does the large intestine consist of?

A
  • Colon
  • Cecum
  • Appendix
  • Rectum
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2
Q

Describe the colon

A
  • The CECUM forms a blind-ended pouch below the JUNCTION of the small and large intestines at the ILEOCECAL VALVE
  • The small, fingerlike projection at the bottom of the CECUM is called the APPENDIX
  • Not coiled
  • Consists of ASCENDING COLON, TRANSVERSE COLON and DESCENDING COLON
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3
Q

What is the function of the colon?

A

Extracts H2O and salt, drying and compacting the contents to form a firm mass known as faeces for elimination from the body

Explanation: contents delivered to colon consist of indigestible food residues, unabsorbed biliary components and the remaining fluid

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4
Q

_________ contractions slowly shuffle the colonic contents back and forth

A

Haustral

[30 mins may elapse between austral contractions, whereas segmentation contractions in the small intestine occur between 9-12 per minute]

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5
Q

What happens after meals?

A

A marked increase in motility takes place during which large segments of the ASCENDING and TRANSVERSE COLON contract SIMULTANEOUSLY -> driving faeces one-third to three-fourths of the length of the colon in a few seconds (MASS MOVEMENT) -> drive colonic contents into the distal part of the large intestine, where material is stored until defecation occurs

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6
Q

Which reflex causes mass movements in the colon when food enters the stomach?

A

Gastrocolic reflex

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7
Q

What is the Gastrocolic reflex mediated by?

A

Gastrin by Parasympathetic innervation

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8
Q

What happens in Defecation?

A

1) Mass movements move feces into the RECTUM -> Resultant distention of the rectum stimulates STRETCH RECEPTORS in the rectal wall, initiating the DEFECATION REFLEX
2) Reflex causes the INTERNAL ANAL SPHINCTER (a smooth muscle) to relax and the RECTUM and SIGMOID COLON to contract more vigorously
3) If the EXTERNAL ANAL SPHINCTER (a skeletal muscle) is also relaxed, defecation occurs

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9
Q

The external anal sphincter is under what control?

A

Voluntary control

[Because it is a skeletal muscle]

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10
Q

What happens if defecation is delayed too long?

A

Constipation

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11
Q

What happens in Constipation?

A

Colonic contents are retained for longer periods than normal -> More than the usual amount of H2O is absorbed from the faces -> Becomes hard and dry -> Causes symptoms due to the prolonged distention of the large intestine

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12
Q

What are symptoms of constipation?

A
  • Abdominal discomfort
  • Dull headache
  • Loss of appetite
  • Nausea
  • Mental depression
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13
Q

What are some possible causes for delayed defecation?

A
  • Ignoring the urge to defecate
  • Decreased colon motility accompanying ageing, emotion or a low-bulk diet
  • Obstruction in large bowel caused by a local tumour or colonic spasm
  • Impairment of the defecation reflex
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14
Q

What does Colonic secretion consist of?

A

An alkaline (NaHCO3) mucus solution which functions to protect the large intestine mucosa from mechanical and chemical injury

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15
Q

Does the large intestine secrete any digestive enzymes?

A

NO

Explanation: Large-intestine secretion is entirely protective

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16
Q

What is the function of the alkaline mucus solution?

A

The mucus = provides lubrication to facilitate passage of faeces

NaHCO3 = neutralises irritating acids produces by local bacterial fermentation

17
Q

The outer longitudinal smooth muscle layer does not completely surround the large intestine, what does it consist of instead?

A

TAENIAE COLI

18
Q

What are the properties of Taeniae Coli?

A
  • Run the length of the large intestine
  • Shorter than underlying circular smooth muscle and mucosal layers -> cause underlying layers to gather into sacs/pouches called HAUSTRA
19
Q

What are Haustral contractions initiated by?

A

Basal electrical rhythm of colonic smooth muscle cells

20
Q

What are the properties of Haustral contractions?

A
  • Oscillating ringlike contractions
  • Location of HAUSTRAL SACS gradually changes as a relaxed segment that has formed a new sac slowly contracts while a previously contracted area simultaneously relaxes to form a new sac
  • NON-PROPULSIVE -> contents slowly shuffled back and forth to expose colonic contents to absorptive mucosa
21
Q

What are Haustral contractions largely controlled by?

A

Locally mediated reflexes involving the intrinsic plexuses

22
Q

What is the difference between the Gastroileal reflex and the Gastrocolic reflex?

A

GASTROILEAL REFLEX = moves the remaining small-intestine contents into the large intestine

GASTROCOLIC REFLEX = pushes the colonic contents into the rectum, triggering the defecation reflex

23
Q

What is the state of the anal sphincter during periods of inactivity?

A

Both anal sphincters remain contracted to ensure faecal continence

24
Q

What helps expel faeces?

A

Assisted by voluntary contraction of the abdominal muscles and a forcible expiration against a closed glottis -> greatly increases intra-abdominal pressure -> helps to expel faeces

25
Q

What happens if hardened faecal material becomes lodges in the appendix?

A

It may obstruct normal circulation and mucus secretion leading to APPENDICITIS

26
Q

What happens in Appendicitis?

A

Inflamed appendicitis becomes swollen and filled with pus -> Tissue may die as a result of local circulatory interference -> If not surgically removed, diseases appendix may rupture -> Spewing its infectious contents into the abdominal cavity

27
Q

What are intestinal gas/flatus derived from?

A
  • Swallowed air
  • Gas produced by bacterial fermentation in the colon
28
Q

Why’s is very little gas present in the small intestine?

A
  • Gas is quickly absorbed
  • Passes on into the colon
29
Q

What happens during Gas release?

A

The person voluntarily contracts the abdominal muscles and external anal sphincter at the same time -> Abdominal contraction raises the pressure against the contracted anal sphincter sufficiently -> Pressure gradient forces air out at a high velocity

30
Q

What is Microbiota?

A

Community of microbes that coexist peacefully and usefully with their human host

31
Q

How do microbes help us?

A
  • Promote colonic motility
  • Help maintain colonic mucosal integrity
  • Aid immune function
  • Compete with potentially pathogenic microbes for nutrients and space
  • Help digest food and make nutritional contributions
  • Influence brain and behaviour
32
Q

How can the composition of gut microbiota be altered?

A

Consumption of PROBIOTICS (food or dietary supplements that contain live bacteria) or PREBIOTICS (nondigestible dietary supplements that stimulate growth and activity of beneficial resident colonic bacteria)

33
Q

How does the colon absorb salt and water?

A

Na+ is actively absorbed, Cl- follows passively down the electrical gradient and H2O follows osmotically

34
Q
A

PHYSIOLOGY III (7 decks)

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