Digestive system (7) Flashcards

1
Q

How is homeostasis involved in the digestive system?

A

> Digestive system is vital for homeostasis because it helps to ensure that cells are provided with nutritional requirements needed to maintain cellular functions
Balanced diet includes all of these: carbohydrates, lipids and proteins
DS reduces complexity of food molecules so we can absorb them into the bloodstream
Then transported to their site of action and used by cells to produce energy- this energy used for growth, repair, etc.

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2
Q

What is the role of the gastrointestinal tract?

A

> Digests and absorbs food

> Nutrients become more available in each step

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3
Q

What is the alimentary canal?

A
> Mouth
> Pharynx
> Oesophagus 
> Stomach 
> Small intestine 
> Large intestine
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4
Q

What are the accessory digestive organs?

A
> Teeth
> Tongue 
> Gallbladder
> Salivary glands
> Liver
> Pancreas
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5
Q

What are the 6 essential activities in the digestive process?

A

1) Ingestion (taking food into digestive tract)
2) Propulsion (swallowing and peristalsis- waves of contraction and relaxation of muscles in the organ walls)
3) Mechanical digestion (chewing)
4) Chemical digestion (catabolic breakdown of food e.g. by enzymes)
5) Absorption (movement of nutrients from GI tract to blood or lymph)
6) Defaecation (elimination of indigestible solid waste)

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6
Q

What is the peritoneum?

A

> The serous membrane of the abdominal cavity (largest in the body)
Has 2 parts which are in close contact- visceral and parietal

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7
Q

What is the visceral peritoneum?

A

> Covers the external surface of most digestive organs

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8
Q

What is the parietal peritoneum?

A

Lines the abdominal wall

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9
Q

What is the peritoneal cavity?

A

> Allows the digestive organs to glide across each other and along the body wall
Lubricates digestive organs

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10
Q

What is the oral/buccal cavity?

A

> The mouth
Bounded by lips, cheeks, palate and tongue
The oral orifice is its anterior opening
Continuous with the oropharynx posteriorly

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11
Q

How is the oral/buccal cavity made to withstand abrasions?

A

> Lined with thick stratified squamous epithelium which can withstand considerable friction
Gums, hard palate and dorsum of the tongue are slightly keratinised for extra protection against abrasion when eating

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12
Q

What is the tongue?

A

> Occupies the floor of the mouth

> Fills the oral cavity when mouth is closed

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13
Q

What are the functions of the tongue?

A

1) Gripping and repositioning food during chewing
2) Mixing food with saliva and forming the bolus (bolus is food mixed with saliva)
3) Begins process of deglutition (swallowing)
4) Initiation of speech

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14
Q

What are the salivary glands?

A

> Extrinsic glands are parotid, submandibular and sublingual
Intrinsic glands are scattered throughout the oral mucosa (the moist membrane covering in the mouth)
They produce and secrete saliva

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15
Q

What are the functions of saliva?

A

1) Cleanses the mouth
2) Moistens and dissolves food chemicals so they can be tasted
3) Aids in bolus formation
4) Contains amylase (an enzyme) which breaks down starch

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16
Q

What are the steps of the digestive process?

A

1) Food is ingested
2) Mechanical digestion begins
3) Propulsion initiated by swallowing
4) Salivary amylase begins chemical breakdown of starch
5) Pharynx and oesophagus allow food to pass from mouth to stomach

17
Q

What occurs in the stomach?

A

Chemical breakdown of proteins begins and food is converted to chyme (an acidic fluid)

18
Q

What are the 4 parts of the stomach?

A

1) Cardiac region- Surrounds the cardiac sphincter
2) Fundus- dome shaped region beneath the diaphragm
3) Body- Midportion of the stomach
4) Pyloric region- Made up of antrum and canal which terminated at the pylorus (pylorus is continuous with duodenum through the pyloric sphincter).

19
Q

What is the stomach lining?

A

> Stomach is exposed to harshest conditions in the digestive tract so to keep it from digesting itself, it has a mucosal barrier with…
Thick coat of bicarbonate-rich mucus on the stomach wall
Epithelial cells that are joined by tight junctions
Gastric glands which have cells that are impermeable to HCL
Damaged epithelial cells replaced quickly

20
Q

How does digestion occur in the stomach?

A

> Holds ingested food
Degrades the food physically and chemically
Delivers chyme to the small intestine
Enzymatically digests protein with pepsin
Secretes intrinsic factor required for absorption of vitamin B12

21
Q

How does digestion occur in the small intestine?

A

> Has 3 parts- duodenum (25cm long), jejunum (2m long) and ilium (3m long)
Chemical digestion of food is completed here and virtuall all nutrient absorption absorption takes place here.
Chyme which passes from stomach to small intestine is released into duodenum where carbohydrates and proteins are partially digested and no fat digestion has taken place yet.
Chyme is hypertonic and has a low pH so mixing is required for proper digestion (required substances are supplied by the liver)

22
Q

What is the role of the villi in the small intestine?

A

> Intestinal wall contains series of folds (plicae circulares) which are lined with fingerlike projections called villi
Their covering consists of columnar epithelium
They increase the surface area for absorption
Each villus has a network of capillaries which carry absorbed nutrients to the hepatic portal circulation to be delivered to the liver

23
Q

What are intestinal hormones?

A

> Dueodenal endocrine cells produce hormones to coordinate the secretory activities of the stomach, duodenum, pancreas and liver

24
Q

What is gastrin?

A

> Intestinal hormone
Secreted by cells of duodenal walls in response to large amounts of incompletely digested proteins
Promotes gastric motility (process where food passes through GI tract)
Stimulates production of acids and enzymes

25
Q

What is secretin?

A

> Intestinal hormone
Released when pH in the duodenum falls when the acidic chyme arrives from the stomach
Main role is to increase secretion of bile and buffers by the liver and pancreas (to neutralise pH)

26
Q

What is cholecystokinin (CCK)?

A

> Intestinal hormone
Secreted when chyme arrives in duodenum
In pancreas, increases production of large numbers of digestive enzymes
In gallbladder, causes ejection of bile into duodenum

27
Q

What is gastric inhibatory peptide (GIP)?

A

> Released when fats and carbohydrates (especially glucose) enter the small intestine
Inhibits gastric activity and causes release of insulin from Islets of Langerhans

28
Q

What is the large intestine?

A

> Begins at end of ilium and finishes at anus

> 1.5m long

29
Q

What are the parts of the large intestine?

A
  • Need diagram of large intestine
    1) Caecum- Expanded pouch where compaction begins
    2) Ileocaecal valve guards entrance between ilium and caecum
    3) Vermiform appendix- About 8-9cm long, is a fine tube which attaches to the caecum
    4) Colon- 4 parts
    1) Ascending colon- Begins at illeocaecal valve and ascends right side of the abdomen
30
Q

What are the parts of the large intestine?

A

*Need diagram of large intestine
1) Caecum- Expanded pouch where compaction begins
2) Ileocaecal valve guards entrance between ilium and caecum
3) Vermiform appendix- About 8-9cm long, is a fine tube which attaches to the caecum
4) Colon- 4 parts
1) Ascending colon- Begins at illeocaecal valve and ascends right side of the
abdomen to the liver where it becomes the transverse colon
2) Transverse colon- Extends across abdominal cavity towards the left side, below
the stomach. At spleen it becomes the descending colon
3) Descending colon- Travels down left side of abdomen until it becomes the
sigmoid colon which empties into the rectum
5) Rectum- End of digestive tract. Expandable organ for temporary storage of faeces
6) Two sphincters- Internal anal sphincter has smooth muscle cells not under voluntary control and the external anal sphincter which has skeletal muscle fibres and is under voluntary control

31
Q

What are the haustra of the colon?

A

The small pouches which give the colon its segmented appearance

32
Q

What are the functions of the large intestine?

A

> Main function is propulsion of faecal material towards anus
Digest enteric bacteria
Reclaims vitamins, water and electrolytes
Colon is not essential for life

33
Q

What is defaecation?

A

> Rectum is usually empty until a powerful peristaltic contraction forces faeces out of the sigmoid colon
The distention of the rectal walls triggers the defacation reflex which involves 2 positive feedback mechanisms

34
Q

What are the 2 positive feedback mechanisms involved in defacation?

A

1) Stretch receptors in the rectum stimulate series of peristaltic contractions in the sigmoid colon and the rectum which moves faeces towards the anus and increases distension of the anus
2) The stretch receptors also stimulate parasympathetic neurones in the sacral spinal cord and these neurones stimulate increased peristalsis in the descending colon and the sigmoid colon which pushes more faeces towards the rectum, further increasing distension.

35
Q

How does defaecation require conscious effort?

A

> Passage of faeces through anus requires relaxation of interal anal sphincter but as it relaxes, the external sphincter automatically closes.
Passage of faeces requires conscious effort- if command doesnt come then peristalsis stops until more rectal expansion triggers the defecation reflex again
Opening external sphincter also requires conscious effort such as tensing abdominal muscles or exhaling whilst closing the glottis- this raises intra-abdominal pressure which helps to force the faeces out of the rectum
This increase in pressure also forces extra blood into the network of veins in the rectal wall, causing them to stretch
Repeated stretching of these veins (straining at stool) can cause veins to be permanently distended leading to haemorrhoids.