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Chapter 16: Digestive system > 16.1 General Aspects of digestion > Flashcards

16.1 General Aspects of digestion Flashcards

1
Q

How does the digestive system contribute to homeostasis (the primary function of it)?

A

By transferring nutrients, water, and electrolytes from the external environment to the internal environment, not regulating their concentrations but rather optimizing conditions for digestion and absorption.

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2
Q

How long is the GIT?

A

4,5 m long

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3
Q

What is the other name of the digestive system

A

Gastrointestinal tract (GIT)

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4
Q

The GIT starts from the mouth and ends with?

A

the anal sphincter

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5
Q

What are the four basic processes that the digestive system performs?

A

MSDA
1. Motility
2.Secretion
3.Digestion
4.Absorption

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6
Q

What is motility?

A

The muscular contraction that mix and move forward the contents within the GIT

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7
Q

The smooth muscle in the walls of the GIT is?

A

Phasic meaning it displays action potential-induced bursts of contraction and it also maintains tone

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8
Q

what is tone?

A

Maintenance of a constant low level of contraction. In order to maintain a steady pressure of the contents of GIT and preventing permanent stretching following distension.

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9
Q

What are the two basic types of phasic digestive motility ?

A

Propulsive movements and Mixing movements

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10
Q

What do propulsive movements do?

A

Propel or push the contents forward through the GIT

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11
Q

what are the two functions of mixing movements?

A
  1. Mixing food ingested with the digestivie juices, thus promoting digestion
  2. Facilitate absorption by exposing all the parts of the intestinal contents to the absorbing surfaces of the GIT
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12
Q

Why is it that for the ends of the GIT (Mouth and External anal sphincter) smooth muscle contraction doesn’t occur?

A

This is because the ends are controlled by skeletal muscle which is primarily voluntary, think about chewing, swallowing and defecation. Motility by smooth muscle is accomplisehd by involuntary mechanisms think about peristalsis.

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13
Q

What are digestive exocrine gland cells?

A

They are specialised epithelial cells found in the lining of the digestive organs as well as that of accessory digestive organs. They secrete digestive juices into the digestive tract in response to neural and hormonal cues.

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14
Q

What are the two types of secretions of the digestive system?

A

Exocrine and endocrine

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15
Q

give me the 4 steps of the digestive secretion process

A
  1. Secretory cells extract water and raw materials from plasma
  2. Energy is required for: Active transport for some materials to enter the cells, and synthesis of secretory products
  3. Digestive juices are normally reabsorbed into the blood after digestion
  4. Failure to reabsorb (due to diarrhea, vomitting) results in fluid loss.
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16
Q

The endocrine tissue of the GIT is organised as?

A

single, individual cells scattered throughout the entire GIT

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17
Q

What are the two types of signal proteins that the endocrine tissue produce?

A

GI hormones
GI peptides

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18
Q

What are the three primary categories of energy-rich foodstuffs consumed by humans?

A

Carbohydrates
proteins
fats

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19
Q

Macronutrients vs Micronutrients in terms of energy

A

Macronutrients provide energy for the body while micronutrients assist as co-factors for providing energy (but they cannot provide energy themselves).

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20
Q

What is the purpose of digestion in terms of foodstuffs

A

To chemically break down the structurally complex foodstuffs of the diet into smaller, absorbable units.

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21
Q

What are the carbohydrate monosaccharides(simple sugars)? AKA soluble units of carbohydrates

A

Glucose, fructose and galactose (very rare in diet)

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22
Q

Carbohydrate Polysaccharides consist of……..

A

interconnected glucose chains

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23
Q

What are the 3 main types of carbohydrate polysaccharides, name their components and explain them briefly

A
  1. Starch from plants:
    Amylose- Unbranched glucose chain
    Amylopectin- Branched glucose chain
  2. Glycogen (from meat): Highly branched glucose storage form in muscle
  3. Indigestible fiber(from plant walls):
    Insoluble fiber like cellulose
    Soluble fiber like pectin
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24
Q

What are the carbohydrate disaccharides?

A

galactose + glucose = lactose
fructose + glucose = Sucrose
glucose + glucose = maltose
(less common in diet)

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25
Q

Dietary proteins consist of various combinations of……

A

Amino acids held together by peptide bonds

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26
Q

Through the process of digestion, Proteins are broken down into their absorbable units being?

A

amino acids and small peptides

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27
Q

Most dietary fats are in the form of?

A

Triglycerides (neutral fats)

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28
Q

What is a triglyceride made up of?

A

A glycerol and 3 fatty acids attached

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29
Q

What are the absorbable units of fats after digestion has broken down triglycerides?

A

monoglycerides and free fatty acids ( 2 from each triglyceride molecule)

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30
Q

What process ensures that digestion of all foodstuffs is accomplished

A

Enzymatic hydrolysis

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31
Q

Where does most digestion occur

A

Stomach

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32
Q

Where does most absorption occur

A

Small intestine

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33
Q

What is the purpose of absorption in terms of the foodstuffs

A

To ensure that the absorbable units of the foodstuff after digestion along with vitamins, water and electrolytes are absorbed from the digestive tract lumen and into the blood or lymph

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34
Q

What are the three exocrine digestive accessory organs?

A
  1. salivary glands
  2. biliary system (liver and gallballder)
  3. Exocrine Pancreas
35
Q

the digestive tract includes?

A

Mouth
Pharynx
Esophagus
Stomach
small intestine (duodenum, jejunum, ileum)
Large intestine (cecum, appendix, colon, rectum)
anus

36
Q

Only after ____________ are substances viewed as part of the body. Before then they are foreign.

A

Absorption

37
Q

What are some of the characteristics of the GIT that are beneficial for digestion but would be harmful in any other part of the body? (4)

A
  1. The stomach’s pH being 2 due to HCl
  2. Enzymes that hydrolyse proteins remain inactive until needed for digestion
  3. The millions of microorganisms
  4. foodstuffs are complex foreign particles that would be attacked by the immune system elsewhere.
38
Q

What are the four layers of the digestive tract wall (inner to outer)

A
  1. Mucosa
  2. Submucosa
  3. Muscularis Externa
  4. Serosa
39
Q

What is the mucosa?

A

It is the layer that lines the luminal surface of the digestive tract.

40
Q

what are the three layers of the mucosa? (inner to outer)

A
  1. Mucous membrane (primary component)
  2. Lamina propria
  3. Muscularis mucosa
41
Q

What is the mucous membrane and what does it do?

A

It is the inner epithelial layer of the mucosa that serves as a protection surface. In some regions of the GIT, it is modified for secretion and absorption (meaning it has exocrine gland cells for the secretion of digestive juices, endocrine gland cells for secreting GI hormones, and specialised epithelial cells for absorbing digested nutrients)

42
Q

What is the lamina propria

A

It is the thin middle layer of the mucosa made up of connective tissue on which the epithelium rests. It houses the gut-associated lymphoid tissue (GALT)

43
Q

What is the function of GALT?

A

Gut-associated lymphoid tissue defends the GIT against disease-causing intestinal bacteria.

44
Q

What is the muscularis mucosa?

A

It is the sparse outermost layer of the mucosa made of smooth muscle

45
Q

The small intestine has a highly folded………….to maximise…….

A

Mucosa, Absorption

46
Q

What is the submucosa

A

It is a thick layer of connective tissue that provides the digestive tract with its distensibility.

47
Q

What is the submucosal plexus

A

a nerve network that lies within the submucosa

48
Q

What is the muscularis externa?

A

The major smooth muscle coat of the GIT surrounding the submucosa.

49
Q

What two layers does the muscularis externa have in certain regions of the GIT?

A
  1. Inner circular layer- Adjacent to the submucosa
  2. Outer longitudinal layer
50
Q

What do the contractions of the inner circular layer fibers of the muscularis externa do?

A

they decrease the diameter of the lumen, constricting it

51
Q

What do the contractions of the outer longitudinal layer fibers of the muscularis externa do?

A

Shorten the tube

52
Q

The contractile activity of the two smooth muscle layers of the muscularis externa……..

A

bring about propulsive and mixing movements

53
Q

What nerve network is situated in between the two smooth muscle layers of the muscularis externa

A

myenteric plexus

54
Q

What is the collective function of the submucosal plexus, myenteric plexus, GI hormones and local chemical mediators

A

They help regulate local gut activity

55
Q

What is the serosa?

A

It is the outer connective tissue covering the digestive tract and secretes serous fluid

56
Q

What does the serous fluid (watery slippery fluid) do?

A

it lubricates and prevents friction between the digestive organs and surrounding viscera.

57
Q

What suspends the digestive organs from the inner wall of the abdominal cavity like a sling to keep them in the right fixed position?

A

the mesentery

58
Q

What are the 4 factors that regulate the digestive system function? (motility and secretion are carefully regulated in order to maximise digestion and absorption)

A
  1. Autonomous smooth muscle function
  2. Intrinsic nerve plexuses
  3. Extrinsic nerves
  4. GI hormones
59
Q

What is the main electrical activity of the GIT smooth muscle

A

Basic electrical rhythm (BER) / slow-wave potentials

60
Q

What determines the frequency of the BER

A

Pacemaker cells (interstitial cells of Cajal)

61
Q

What are interstitial cells of Cajal

A

They act as pacemaker cells located in the muscularis externa. They generate slow-wave potentials that propagate to adjust smooth muacle cells via gap junctions

62
Q

true or false: slow-wave potentials are action potentials and directly cause muscle contraction

A

false

63
Q

What are slow-wave potentials

A

They are rhythmic fluctuations in membrane potential that bring it closer or farther from threshold.
If threshold is reached, it triggers action potentials that cause for muscle contraction.

64
Q

Factors that influence contractile activity

A
  • hormonal, neural, mchanical factors affecting starting point of slow-wave oscillations
    -absence/presence of food
65
Q

Contractile activity rate and intensity depends on:

A
  1. rate (frequency) depends on pacemaker cells
  2. intensity (strength) depends on the number of action potentials when slow-wave potential reaches threshold
66
Q

What is the role of calcium when slow-wave potentials reach threshold

A

the Ca2+ voltage gate channels open causing for an influx of calcium. The influx is responsible for action potential rising phase and triggers contractile response

67
Q

high cystosolic Ca2+ concentration=

A

sttronger more intense contractions

68
Q

What is the name of the unique nervous system of the digestive system ?

A

Enteric nervous system(ENS)

69
Q

What are the two nerve networks that make up the ENS

A

submucosal plexus and myenteric plexus

70
Q

What are thr three types of neurons of the enteric nervous system

A
  1. Intrinsic primary afferent neurons (sensory neurons)
  2. Intrinsic efferent neurons
  3. Interneurons
71
Q

What is the function of the sensory neurons

A

reaspond to specific local stimuli in the GIT

72
Q

what is the function of the intrinsic efferent neurons

A

control smooth muscle and exocrine and endocrine cells

73
Q

What is the function of interneurons

A

they modulate the communication between sensory neurons and efferent neurons

74
Q

The intrinsic nerve plexuses influence all aspects of ………….

A

GIT activity

75
Q

What are the extrinsic nerves

A

They are the nerve fibers from both branches of the autonomic nervous system that originate outside the GIT and regulate GIT function

76
Q

What is the function of the extrinsic (autonomic) nerves ?

A

They influence GIT motility and secretion, altering GI hormones secretion, or acting directly on the smooth muscle and glands

77
Q

Distinguish between the antagonistic roles of sympathetic and parasympathetic nerves in digestion

A

1.The sympathetic nerves are dominant during “fight or flight” situations. They supress or slow down GIT secretion and motility because these activities are not the highest priority when the body faces an emergency.
2. The parasympathetic nerves are dominant during “rest and digest” when the general maintenance type of activities such as digedtion function optimally. Supplied to the GIT via the vagus nerve, they increase motility and secretion of digestive elements.

77
Q

Where are GI hormones produced and what is their function

A

They are produced by specilaised endocrine cells within the mucosa of certain regions of the GIT. They exert either excitatory or inhibitory influences on digestive smooth muscle and exocrine gland cells

78
Q

Receptor activation alters digestive activity through ____________

A

Neural and hormonal pathways thus modifying motility, secretion of digestive juices and GI hormone

79
Q

What are the three types of sensory receptors of the digestive tract wall that respond to local changes in the GIT

A
  1. Mechanoreceptors (stretch receptors)- sensitive ot stretch or tension within the wall
  2. Chemoreceptors- sensitive to chemical components within the lumen
  3. Osmoreceptors- sensitive to the osmolarity of the luminal contents
80
Q

What are the two types of neural reflexes that receptor activation may bring out

A

short reflexes and long reflexes

81
Q

Explain what short reflexes

A

They take place when all elements of the of the reflex are located within the wall of the GIT itself (when the intrinsic nerve networks influence local motility or secretion in response to specific local stimulation)

82
Q

Explain long reflexes

A

The autonomic reflexes involve long pathways between the CNS and the digestive system.

Chapter 16: Digestive system (6 decks)

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