Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Alimentary system > 3. Small intestine > Flashcards

3. Small intestine Flashcards

1
Q

What is the function of the small intestine?

A

To absorb nutrients, salt and water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the lengths of the duodenum, jejunum and ileum?

A

Duodenum: 25cm
Jejunum: 2.5m
Ileum: 3.75m

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Small intestine approximate length and diameter

A

Length: 6m
Diameter: 3.5cm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the shape and function of the mesentery in the small intestine?

A

Fan shaped
Throws small intestine into folds
Acts as substrate for blood and nerve supply to small intestine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Histological organisation in the small intestine

A

Duodenum, jejenum and ileum have same basic histological organisation
No sudden transition between

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe the layers in the small intestinal wall

A 
Serosa
Longitudinal muscle
Circular muscle
Submucosa
Mucosa
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How is the internal mucosa arranged in the small intestine and what is it covered in?

A

Internal mucosa arranged in circular folds.

Mucosa covered in villi

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How tall are villi?

A

1mm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is found between villi?

A

Crypts of Lieberkuhn

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How do the villi enhance the functioning of the small intestine?

A

Increase SA for absorption

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

List 4 facts about villi

A

Only occur in small intestine
Motile
Have a rich blood supply and lymph drainage for absorption of digested nutrients
Have good innervation from the submucosal plexus.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Epithelium of villi

A

Simple epithelium
1 cell thick
Dominated by enterocytes (columnar absorptive cells)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What 3 cells comprise the simple columnar epithelium of the small intestine mucosa?

A

Enterocytes (absorptive cells)
Scattered goblet cells
Enteroendocrine cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What cells are found in the Crypts of Lieberkuhn?

A

Paneth cells

Stem cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q 
Describe enterocytes 
(prevalence, structure, function, lifespan)
A

Most abundant cells in small intestine
Tall columnar cells with apical microvilli and a basal nucleus.
Specialised for absorption and transport of substances.
Short lifespan of 1-6 days.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

In which direction does absorption occur in enterocytes?

A

From the apical surface where there are microvilli to the basal surface where the nucleus is located and the cell is attached to the basement membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the length of a microvillus?

A

0.5-1.5 micrometers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the layer that covers the microvilli?

A

Glycocalyx

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the properties of the glycocalyx?

A

Rich in carbohydrates and protects the epithelia from the digestional lumen but is still allows absorption.
It traps a layer of water and mucus called the ‘unstirred layer’, which regulates the rate of absorption from the intestinal lumen.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What makes up the brush border?

A

Microvilli

There are several thousand microvilli per cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

The folds, villi and microvilli increase the surface area of the small intestine by what factor?

A

500 fold

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What increases the surface area in the small intestine? What is the consequence of this?

A 
Folds in wall
Villi in folds
Microvilli on villi
Makes gut more effective at absorption
Can absorb more than needed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the 2nd most abundant epithelial cell in the small intestine?

A

Goblet cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What causes the goblet shape in goblet cells?

A

Mucous containing granules accumulate at the apical end of the cel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is mucous?

A

Large glycoprotein that facilitates passage of material through the bowel.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

How does goblet cell distribution change across the intestines?

A

Goblet cells increase in number as you go down the small intestine
This is because the intestinal contents become more and more solid meaning that you require more lubrication to facilitate movement.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is the role of enteroendocrine cells?

A

Hormone secreting cells:

Produce hormones that influence gut motility

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What type of cells are enteroendocrine cells, where are they most often found and what are they also known as?

A

Columnar epithelial cells
Most often found in the lower parts of the crypts
Chromaffin cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Where are paneth cells located?

A

They are ONLY found in the bases of crypts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What do paneth cells contain and what is their role?

A

Contain large acidophilic granules containing antibacterial enzyme (LYSOZYME), glycoproteins and zinc.
Protective function against bacteria
Engulf some bacteria and protozoa
Regulate intestinal flora and protect stem cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Why are paneth cells located at the bottom of crypts?

A

To protect stem cells from damage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Epithelial lifespan

A

Cell proliferation, differentiation, and death are continuous processes in gut epithelium.
Enterocytes and goblet cells of the small intestine have a short life span (~36 hrs).
Continually replaced by dividing stem cells in the crypts.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Why is there such a rapid turnover of enterocytes?

A

Enterocytes are the 1st line of defence against GI pathogens and they may be directly affected by toxic substances in the diet.
Rapid turnover means that any lesions are short lived and that any interference with host cell function will be diminished.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Stem cells

A

Undifferentiated cells which remain capable of cell division to replace cells which die

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Life of stem cells in the small intestine

A

Continually divide by mitosis
Migrate up to tip of villus, replacing older cells that die by apoptosis
Differentiate into various cell types (pluripotent)
Have memory (as different epithelial cells in different parts of gut)

36
Q

Movement of stem cells in the small intestine

A

“Escalator” of epithelial migration
Dividing stem cells in the crypts migrate to the surface and tips of villi
At villus tips, cells become senescent and are sloughed into the lumen of the intestine to be digested and reabsorbed.

37
Q

What happens if the escalator-like transit of enterocytes is interrupted through impaired production of new cells (e.g. by radiation?

A

Severe intestinal dysfunction will occur

38
Q

How does the cholera endotoxin affect the gut?

A

Results in prolonged opening of the chloride channels in the small intestine allowing uncontrolled secretion of water.
Leads to rapid, massive dehydration and death

39
Q

Treatment for cholera

A

Rehydration
Cholera bacteria will clear
Epithelium will be replaced

40
Q

Describe a characteristic feature of the duodenum.

A

Brunner’s Glands: submucosal coiled tubular mucus glands secreting alkaline fluid.

41
Q

Where do Brunner’s gland open and what is the effect of their alkaline secretions?

A

Open into base of crypts
Alkaline fluid neutralises acidic chyme from the stomach, protecting the proximal small intestine
Helps optimise the pH for pancreatic enzymes

42
Q

Describe a characteristic feature of the jejunum.

A 
Plicae circulares (valves of Kerckring): numerous large folds in the submucosa 
Also present in the duodenum and ileum but in the jejunum they are taller, thinner and more frequent.
43
Q

Describe the appearance of jejunum interior

A

Jejunum has a frilly interior formed of circular folds in the mucosa

44
Q

Describe a characteristic feature of the ileum.

A

Peyer’s patches: large clusters of lymph nodules in the submucosa

45
Q

What is the function of Peyer’s patches?

A

Prime immune system against intestinal bacteria
Well positioned to prevent bacteria from the colon
migrating into the small intestine

46
Q

3 functions of small intestine motility

A

Mix ingested food with digestive secretions and enzymes
Facilitate contact between contents of intestine and the intestinal mucosa
Propel intestinal contents along alimentary tract

47
Q

Describe segmentation and the point of it.

A

Occurs by the stationary contraction of circular muscles at intervals.
More frequent contractions in duodenum compared to ileum
It mixes the contents of the lumen (pancreatic enzymes and bile mix with the chyme)
Net movement towards colon

48
Q

Describe peristalsis.

A

Involves sequential contraction of adjacent circular rings of smooth muscle.
It propels chyme towards the colon.
Most waves ~10cm

49
Q

What do segmentation and peristalsis result in?

A

Chyme being segmented, mixed and propelled towards the colon

50
Q

Migrating motor complex

A

Cycles of smooth muscle contraction (contraction of adjacent segments of small intestine)
Begins in the stomach, through the small intestine and stops at the start of the colon.

51
Q

What is the purpose of the migrating motor complex?

A

Prevents migration of colonic bacteria into the ileum

Cleans the intestine of residual food

52
Q

When is the migrating motor complex more frequent and more organised?

A

In fasting

occurs in fed state, but less ordered and frequent

53
Q

Digestion in the duodenum

A

Food moves into small intestine (alkaline environment)
Digestive enzymes from pancreas and bile from gall bladder squirted into duodenum and mixed with food
On glycocalyx of microvilli there are digestive enzymes
As food is mixed with enzymes in lumen= digestion: breaks very large molecules
Further breakdown occurs at brush border (glycocalyx and microvilli layer)

54
Q

Passive diffusion

A

Drifts across cell membranes, down gradient, no energy required, no carrier proteins
(but it is difficult to cross cell walls, so most things don’t cross cell walls like this)

55
Q

Facilitated diffusion

A

Move down concentration gradient but need carrier protein, no energy required

56
Q

Primary active transport

A 
Needs energy (usually ATP) 
Working against concentration gradient
Transport mechanism directly coupled to the substance that is giving it energy, usually a capacity for hydrolysing ATP, and using that energy to pump something against its concentration gradient e.g. Na+/K+ pump
57
Q

Secondary active transport

A

Working against concentration gradient
Uses energy second hand
e.g. by electrochemical gradient that’s been set up previously e.g. Na+ gradient that is being set up continuously by the Na+/K+ pump

58
Q

Digestion of carbohydrate

A

Begins in mouth with the action of salivary alpha-amylase
Most digestion takes place in the duodenum by the action of pancreatic alpha-amylase
Digestion of amylase products and simple carbohydrates occurs at the membrane

59
Q

Simple carbohydrates

A

Monosaccharides: Glucose, Fructose
Disaccharides: Sucrose, Maltose

60
Q

Complex carbohydrates

A

Sugars bonded together to form a chain

e.g. Starch, Cellulose

61
Q

What conditions does pancreatic alpha-amylase need to function properly?

A

Needs CHLORIDE for optimum activity

Also needs SLIGHTLY ALKALINE pH

62
Q

Where does pancreatic alpha-amylase mainly act?

A

In the lumen

some also adsorbs to the brush border

63
Q

Once the pancreatic enzymes have acted on the carbohydrates, where does the rest of the digestion take place?

A

Digestion of amylase products and simple carbohydrates takes place at the membrane

64
Q

Describe the absorption of carbohydrates.

A

Absorption of glucose and galactose is by secondary active transport via SGLT-1.
Glucose and galactose then move into the plasma by facilitated diffusion through GLUT-2.

65
Q

How does fructose absorption differ from glucose and galactose absorption?

A

Fructose has a lower concentration inside cells so it can move in by facilitated diffusion via GLUT-5

66
Q

Mechanism of action of SGLT-1

A

Highjacks energy from sodium gradient
Low sodium in cells as lots of energy used to pump sodium out
If let sodium enter cell down its concentration gradient, energy released from that can be used to pump a monosaccaride (glucose/ galactose) into the cell against its concentration gradient

67
Q

What is the main pancreatic protease that is required to activate other proteases and how is it activated?

A

TRYPSIN: secreted by the pancreas as an inactive precursor.
Activated by ENTEROKINASE (an enzyme found in the duodenal brush border).
Trypsin can then activate other enzymes.

68
Q

Digestion of proteins

A

Starts in the stomach by pepsin (acid environment), but pepsin is inactivated in the alkaline duodenum.
In duodenum need activated trypsin

69
Q

How are amino acids absorbed by the cells?

A

Large molecules of protein broken down by pepsin then pancreatic proteases to form individual AAs and peptides
Brush border peptidases break down the larger peptides before absorption.
AAs are then absorbed by facilitated diffusion or secondary active transport.
Cytoplasmic peptidases break down the di and tripeptides before they cross the basolateral membrane

70
Q

State the 4 step procedure by which lipids are digested.

A

Secretion of bile (for emulsification) and lipases (for breakdown)
Emulsification
Enzymatic hydrolysis of ester linkages
Solubilisation of lipid products in bile salt micelles

71
Q

What makes lipids more complicated to digest?

A

Lipids are poorly soluble in water

72
Q

What is the function of emulsification by bile salts?

A

Increases the surface area for digestion

73
Q

What is the point of bile salt micelles?

A

Allows pancreatic lipase to break down the triglycerides

74
Q

How does lipase break down triglycerides?

A

Triglycerides are broken down to 2 free fatty acids and a monoglyceride

75
Q

How are trypsin and lipase different in the way that they are activated?

A

Trypsin is secreted by the pancreas as an inactive precursor that is converted to its active form by enterokinase.
Pancreatic lipase is secreted in its active form but it must bind to a cofactor (Colipase: which is secreted in an inactive form) to become active.

76
Q

What does colipase do?

A

In an emulsion: droplet of fat surrounded by bile salt molecules (very effective at surrounding fat molecule) so Lipase cant get in to attack it unless it is joined with colipase
Colipase helps move bile salts out of the way so lipase can act on the emulsion and break down TAGs

77
Q

State 2 important enzymes involved in lipid hydrolysis.

A

Phospholipase A2: hydrolyses fatty acids in the 2 position in many phospholipids, resulting in lyso-phospholipids and free fatty acids
Pancreatic Cholesterol Esterase: hydrolyses cholesterol ester to free cholesterol and fatty acid

78
Q

What is the role of micelles?

A

Transport lipids to the surface of the epithelium (across the unstirred layer) and present the fatty acids and monoglycerides to the brush border.

79
Q

Describe a bile salt molecule

A

Amphipathic:
Hydrophobic (nucleus and methyl) face dissolves in fat
Hydrophilic (hydroxyl and carboxyl) face dissolves in water

80
Q

Structure of mixed micelle in small intestine

A

Water insoluble monoglycerides from lipolysis are solubilised by forming a hydrophobic core, stabilised by the hydrophilic heads of bile salts

81
Q

Why are micelles important for absorption

A

They are absorbed much quicker than emulsion.

82
Q

Mixed micelles are not absorbed whole…

A

Lipid absorption is usually complete by the middle of the jejunum
Bile salts are absorbed in the ileum and are transported back to the liver for recycling (enterohepatic circulation)

83
Q

What are the two pathways of resynthesis of triglycerides? Describe them.

A 
Monoglyeride Acylation (MAIN one): acylates the monoglyceride to produce a triglyceride
Phosphatidic Acid Pathway: triglycerides are synthesised from CoA fatty acid and alpha-glycerophosphate
84
Q

Describe Monoglyeride Acylation

A

Fatty acids bind to the apical membrane.
Fatty acid binding proteins (FABP) facilitate transfer of fatty acids from apical membrane to the smooth ER.
In the smooth ER: fatty acids esterified into diglycerides and triglycerides.

85
Q

How are TAGs packaged and released from the basolateral membrane?

A 
TAGs are packaged into chylomicrons 
Protein and carbohydrate in it allow it to travel in aqueous environment
Secreted across basement membrane 
Too big to enter capillaries
Enter the lacteals (lymph channels)
86
Q

What separate the ileum and colon?

A

Ileocaecal sphincter

87
Q

What is the function of the Ileocaecal sphincter?

A

Relaxation and contraction controls the passage of material into the colon.
Also prevents the back flow of bacteria into the ileum.

Alimentary system (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions