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IBDP Biology SL > Topic 6.1 - Human Physiology > Flashcards

Topic 6.1 - Human Physiology Flashcards

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1
Q

What are two major groups of organs which comprise the human digestive system?

A

Alimentary canal

Accessory organs

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2
Q

What is the alimentary canal?

A

The alimentary canal consists of organs that that passes food through them. Eg, esophagus, stomach, small & large intestine.

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3
Q

What are accessory organs and what does it do?

A

The accessory organs aid in digestion but do not actually transfer food (salivary glands, pancreas, liver, gall bladder)

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4
Q

What’s the Oesophagus and its function?

A

A hollow tube connecting the oral cavity to the stomach (separated from the trachea by the epiglottis)

• Food is mixed with saliva and then is moved in a bolus via the action of peristalsis

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5
Q

What’s the Stomach and its function?

A
  • A temporary storage tank where food is mixed by churning and protein digestion begins
  • It is lined by gastric pits that release digestive juices, which create an acidic environment (pH ~2)
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6
Q

What’s the small intestine and its function?

A
  • A long, highly folded tube where usable food substances (nutrients) are absorbed
  • Consists of three sections – the duodenum, jejunum, and ileum
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7
Q

What’s the large intestine and its function?

A
  • The final section of the alimentary canal, where water and dissolved minerals (i.e. ions) are absorbed
  • Consists of the ascending/transverse/descending/sigmoidal colon, as well as the rectum
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8
Q

What’s the Salivary Gland and its function?

A
  • Release saliva to moisten food and contains enzymes (e.g. amylase) to initiate starch breakdown
  • Salivary glands include the parotid gland, submandibular gland, and sublingual gland
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9
Q

What’s the pancreas and its function?

A
  • Produces a broad spectrum of enzymes that are released into the small intestine via the duodenum
  • Also secretes certain hormones (insulin, glucagon), which regulate blood sugar concentrations
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10
Q

What’s the liver and its function?

A
  • Takes the raw materials absorbed by the small intestine and uses them to make key chemicals
  • Its role includes detoxification, storage, metabolism, bile production, and hemoglobin breakdown
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11
Q

What’s the gall bladder and its function?

A
  • The gall bladder stores the bile produced by the liver (bile salts are used to emulsify fats)
  • Bile stored in the gall bladder is released into the small intestine via the common bile duct
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12
Q

Food can be digested by a combination of two methods, what are they?

A

Mechanical digestion and chemical digestion?

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13
Q

How does mechanical digestion work?

A

Food is physically broken down into smaller fragments via the acts of chewing (mouth), churning (stomach) and segmentation (small intestine)

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14
Q

2 examples of mechanical digestion:

A

Chewing (mouth)

Churning (stomach)

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15
Q

2 examples of how food is transported:

A

Peristalsis

Segmentation

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16
Q

What is peristalsis?

A
  • Peristalsis is the principal mechanism of movement in the esophagus, although it also occurs in both the stomach and gut
  • Continuous segments of longitudinal smooth-muscle rhythmically contract and relax
  • Food is moved unidirectionally along the alimentary canal in a caudal direction (mouth to anus)
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17
Q

What is segmentation?

A
  • Segmentation involves the contraction and relaxation of non-adjacent segments of circular smooth muscle in the intestines
  • Segmentation contractions move chyme in both directions, allowing for a greater mixing of food with digestive juices
  • While segmentation helps to physically digest food particles, its bidirectional propulsion of chyme can slow overall movement
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18
Q

How does chemical digestion work?

A

In chemical digestion, food is broken down by the action of chemical agents (such as enzymes, acids, and bile)

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19
Q

What are carbohydrates?

A
  • Carbohydrate digestion begins in the mouth with the release of amylase from the salivary glands (amylase = starch digestion)
  • Amylase is also secreted by the pancreas in order to continue carbohydrate digestion within the small intestine
  • Enzymes for disaccharide hydrolysis are often immobilized on the epithelial lining of the small intestine, near channel proteins
  • Humans do not possess an enzyme capable of digesting cellulose (cellulose) and hence it passes through the body undigested
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20
Q

What are proteins?

A
  • Protein digestion begins in the stomach with the release of proteases that function optimally in an acidic pH (e.g. pepsin = pH 2)
  • Smaller polypeptide chains enter the small intestine where they are broken down by endopeptidases released by the pancreas
  • These endopeptidases work optimally in neutral environments (pH ~ 7) as the pancreas neutralizes the acids in the intestine
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21
Q

What are lipids?

A
  • Lipid breakdown occurs in the intestines, beginning with emulsification of fat globules by bile released from the gall bladder
  • The smaller fat droplets are then digested by lipases released from the pancreas
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22
Q

What are the nucleic acids?

A
  • The pancreas also releases nucleases which digest nucleic acids (DNA, RNA) into smaller nucleosides
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23
Q

Why does the human intestine?

A

The human intestines function to absorb the products of digestion and have specialized structures to fulfill this function

The small intestine absorbs usable food substances (i.e. nutrients – monosaccharides, amino acids, fatty acids, vitamins, etc.)

The large intestine absorbs water and dissolved minerals (i.e. ions) from the indigestible food residues

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24
Q

What are the 4 main tissue layers of the small intestine?

A
  • Serosa – a protective outer covering composed of a layer of cells reinforced by fibrous connective tissue
  • Muscle layer – an outer layer of longitudinal muscle (peristalsis) and an inner layer of circular muscle (segmentation)
  • Submucosa – composed of connective tissue separating the muscle layer from the innermost mucosa
  • Mucosa – a highly folded inner layer which absorbs material through its surface epithelium from the intestinal lumen
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25
Q

What does the small intestine absorb?

A

The small intestine absorbs usable food substances (i.e. nutrients – monosaccharides, amino acids, fatty acids, vitamins, etc.)

26
Q

What does the large intestine absorb?

A

The large intestine absorbs water and dissolved minerals (i.e. ions) from the indigestible food residues

27
Q

What does the inner epithelial lining of the intestine consist of?

A

Villi

28
Q

What are the 6 key features of villi? (MRSLIM)

A 
Microvilli 
Rich blood supply
Single-layer epithelium
Lacteals
Intestinal glands
Membrane proteins
29
Q

Structure of Villus Epithelium?

A

Pinocytotic Vesicles
Mitochondria
Microvilli
Tight Junctions

30
Q

What mus happen during absorption?

A

Digested food monomers must pass from the lumen into the epithelial lining of the small intestine

31
Q

What are the four Membrane Transport Mechanisms?

A

Secondary Active Transport
Facilitated Diffusion
Osmosis
Simple Diffusion

32
Q

What is Secondary Active Transport?

A

A transport protein couples the active translocation of one molecule to the passive movement of another (co-transport)
Glucose and amino acids are co-transported across the epithelial membrane by the active translocation of sodium ions (Na+)

33
Q

What is Facilitated Diffusion?

A 
Channel proteins help hydrophilic food molecules pass through the hydrophobic portion of the plasma membrane
Channel proteins are often situated near specific membrane-bound enzymes (creates a localized concentration gradient)
Certain monosaccharides (e.g. fructose), vitamins and some minerals are transported by facilitated diffusion
34
Q

What is Osmosis?

A

Water molecules will diffuse across the membrane in response to the movement of ions and hydrophilic monomers (solutes)
The absorption of water and dissolved ions occurs in both the small and large intestine

35
Q

What is Simple Diffusion?

A 
Hydrophobic materials (e.g. lipids) may freely pass through the hydrophobic portion of the plasma membrane
Once absorbed, lipids will often pass first into the lacteals rather than being transported via the blood
36
Q

What is bulk transport?

A

Endocytosis

37
Q

What is endocytosis?

A

Endocytosis involves the invagination of the plasma membrane to create an internal vesicle containing extracellular material
Vesicle formation requires the breaking and reforming of the phospholipid bilayer and hence is an energy-dependent process
In the intestines, vesicles commonly form around fluid containing dissolved materials (pinocytosis – cell ‘drinking’)
Pinocytosis allows materials to be ingested en masse and hence takes less time than shuttling via membrane proteinsa

38
Q

What is starch?

A

Starch is a polysaccharide composed of glucose monomers and accounts for ~ 60% of the carbohydrates consumed by humans

39
Q

What are the two possible forms that starch can exist as?

A

Linear chains (amylose) or branched chains (amylopectin)

40
Q

Where does the digestion of starch initiate?

A

The digestion of starch is initiated by salivary amylase in the mouth and continued by pancreatic amylase in the intestines

41
Q

Why can’t starch digest in the stomach?

A

Amylase does not occur in the stomach as the pH is unsuitable for amylase activity (optimal pH ~ 7)

42
Q

What does amylase digest amylose into?

A

Into maltose subunits (disaccharide) and digests amylopectin into branched chains called dextrins

43
Q

Glucose can be hydrolyzed to…

A

Glucose can be hydrolyzed to produce ATP (cell respiration) or stored in animals as the polysaccharide glycogen

44
Q

What is the role of the pancreas?

A
  • It produces the enzyme amylase which is released from exocrine glands (acinar cells) into the intestinal tract
  • It produces the hormones insulin and glucagon which are released from endocrine glands (islets of Langerhans) into the blood
45
Q

What do the hormones insulin and glucagon regulate?

A

The concentration of glucose in the bloodstream (controls availability to cells)

46
Q

How does insulin decrease blood glucose levels?

A

By increasing glycogen synthesis and storage in the liver and adipose tissues

47
Q

How does Glucagon increase blood glucose levels?

A

By limiting the synthesis and storage of glycogen by the liver and adipose tissues

48
Q

The process of digestion performs two key functions:

A
  • It breaks down insoluble molecules into smaller subunits which can be readily absorbed into body tissues
  • It breaks down inert molecules into usable subunits which can be assimilated by cells and reassembled into new products
49
Q

Use of dialysis tubing is to…

A

Model absorption of digested foods in the intestine

50
Q

What is dialysis tubing and the process?

A
  • Dialysis tubing contains pores typically ranging from 1 - 10 nm in diameter and is semi-permeable according to molecular size
  • Large molecules such as starch cannot pass through the tubing, however smaller molecules (such as maltose) can cross
  • Unlike the membranes of living cells, dialysis tubing is not selectively permeable based on charge (ions can freely cross)
51
Q

What are the two digestion experiments?

A

Experiment 1: Measuring Meniscus Levels

Experiment 2: Measuring Maltose Diffusion

52
Q

How to do experiment 1: Measuring Meniscus Levels

A
  • A length of dialysis tubing is attached to a thistle funnel and filled with a starch solution (control condition)
  • A second length of tubing is attached to a thistle funnel and filled with starch and amylase solution (experimental condition)
  • Both apparatuses are placed in a beaker filled with water
  • Over time, water will move into the tubing via osmosis (towards the solute) causing the meniscus level to rise
  • The tube with amylase will have less solute (as starch is digested) and hence the meniscus level should not rise as much
53
Q

How to do experiment 2: Measuring Maltose Diffusion

A
  • A length of dialysis tubing is filled with starch solution and suspended in a beaker of water (control condition)
  • A second length of tubing is filled with starch and amylase solution and suspended in a beaker of water (experimental condition)
  • The amylase will digest the starch into maltose, which is small enough to diffuse out of the tubing and into the beaker
  • The presence of maltose can be detected using Benedict’s reagent or glucose indicator strips
54
Q

What are the 5 processes of digestion that occur?

A 
Ingestion
Digestion 
Absorption
Assimilation
Elimination
55
Q

What is bile?

A

Is a watery fluid that contains bile salts and pigments (bilirubin) – it is made by the liver and released from the gall bladder

56
Q

Bile salt molecules:

A
  • Bile salt molecules have both a hydrophobic surface and a hydrophilic surface
  • The hydrophobic end interacts with the lipid while the hydrophilic end faces out and prevents lipids from coalescing
  • This divides the fat globule into smaller droplets (emulsification), increasing the total surface area available for enzyme activity
57
Q

The small intestine is comprised of three distinct regions:

A

duodenum, jejunum, and ileum

58
Q

duodenum

A

First segment of the small intestine which is fed by digestive fluids from the pancreas and gall bladder
Bile emulsifies fat globules into smaller droplets and pancreatic juice contains digestive enzymes
Sodium bicarbonate is released from the pancreas to neutralise stomach acids such that intestinal pH is ~ 7

59
Q

Jejunum

A

Second segment of the small intestine where the digestive process is largely completed
Pancreatic enzymes and enzymes released from intestinal glands complete the break down of sugars, proteins and lipids

60
Q

Ileum

A

The final segment of the small intestine with the principal function of nutrient absorption
The intestinal tract is highly folded (villi and microvilli) to increase surface area and optimize material absorption
Bile is also absorbed here and returned to the liver via blood vessels

61
Q

The principal function of the large intestine is to…

A

Absorb any remaining water and mineral ions

62
Q

The large intestine is divided into …

A

the ascending colon, transverse colon, descending colon, sigmoidal colon and rectum

IBDP Biology SL (5 decks)

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