S8) The Digestive System Flashcards Preview

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Flashcards in S8) The Digestive System Deck (43)
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1
Q

Label the following components of the alimentary canal:

A
2
Q

What are the four layers of the gut wall?

A
  • Mucosa (innermost)
  • Submucosa
  • Muscularis externae
  • Serosa (outermost)
3
Q

Identify the 8 functions of the gut

A
  • Provides a port of entry for food
  • Mechanically disrupts food
  • Temporarily stores food
  • Chemically digests food
  • Kills pathogens in food
  • Moves food along the tract
  • Absorb nutrients from the resultant solution
  • Eliminate residual waste material
4
Q

What is digestion?

A

Digestion is the conversion of what we eat by physical and chemical disruption into a solution that is relatively sterile, neutral in pH and isotonic; from which we can absorb our nutrients

5
Q

Identify 4 roles of saliva in the GI tract

A
  • Starts digestion (amylase & lipase)
  • Assists swallowing
  • Protects mouth & teeth (high calcium)
  • Bacteriostatic (IgA antibody)
6
Q

Compare physical and chemical disruption in the mouth and stomach respectively

A

- Begins in the mouth:

I. Physical - by teeth, tongue, muscles of mastication

II. Chemical - by salivary amylase and lipase

  • Continues in the stomach:

I. Physical - by churning

II. Chemical - by HCl and enzymes

7
Q

Describe the transport of food in the GI tract

A
  • Mouth forms a bolus which enters the oesophagus
  • Rapid peristaltic transport (even when upside down) moves bolus to stomach (8-9 seconds)
8
Q

Describe the neural control of the oesophagus

A
  • Upper end oesophagus – voluntary control (striated skeletal muscle)
  • Lower end oesophagus – involuntary control (solely smooth muscle)
9
Q

Identify and describe the different components of oesophageal mucosa

A

- Epithelium – stratified squamous non-keratinized

- Lamina propria – loose connective tissue bearing blood & lymph vessels, smooth muscle and immune cells

- Muscularis mucosae – thin layer of smooth muscle cells

10
Q

Identify and describe the structure of the layer of the oesophageal wall, apart from the mucosa

A

- Submucosa – connective tissue containing mucus-secreting glands

- Muscularis externa – smooth muscle layers which move food by peristalsis

- Adventitia – thin outermost layer of connective tissue

11
Q

Identify the different smooth muscle layers in the muscularis externa of the oesophageal wall

A
  • Inner layer is circular muscle
  • Outer layer is longitudinal muscle
12
Q

State 4 roles of the stomach

A
  • Temporarily stores food
  • Receptive relaxation to maintain pressure
  • Proteolytic enzyme and acid secretion
  • Produces hypertonic incompletely digested chyme
13
Q

What are the three layers of smooth muscle in the stomach?

A
  • Oblique
  • Circular
  • Longitudinal
14
Q

How does the stomach protect its epithelium

A

The stomach protects its epithelium by secreting bicarbonate-rich mucus

15
Q

What is rugae?

A

Rugae are folds of gastric mucosa, forming longitudinal ridges in the empty stomach

16
Q

What is the gastric pit of the gastric gland ?

A

The gastric pit is the region of the gastric gland lined by mucus secreting cells, similar to goblet cells

17
Q

What is the isthmus (of the gastric gland)?

A

The isthmus is the region in which stem cells divide to populate the gland by upward or downward migration

18
Q

What do parietal cells do?

A

Parietal cells secrete H+ ions into the lumen and HCO3+ ions into nearby capillaries, which move it to the surface mucous cells

19
Q

What do chief cells do?

A

Chief cells secrete pepsinogens which are converted into pepsins which partly hydrolyse proteins

20
Q

What are enteroendrocrine cells?

A

Gastric enteroendrocrine cells (G cells) are cells found at the base of the gastric gland which secrete gastrin

21
Q

What are surface mucous cells and what do they do?

A

Surface mucous cells are cells which are abundant in gastric pits and release mucus in response to distension, stomach contents and acid secretion from gastric glands

22
Q

Discuss the resistance/vulnerability of surface mucous cells

A
  • Their secreted mucus is resistant to pepsin degradation
  • They can be damaged by aspirin/alcohol
23
Q

Describe the structure, location and function of the duodenum

A
  • Structure: proximal portion of the small intestine
  • Location: curves around the head of the pancreas
  • Function: walls contain Brunner’s glands which secrete bicarbonate-rich mucus to neutralise acidic chyme
24
Q

Describe the dilution and neutralisation of chyme

A
  • Water drawn in from ECF to dilute hypertonic chyme
  • Pancreas & liver secrete alkali and bile to neutralise acidic chyme
25
Q

Digestion is completed by enzymes from the pancreas and intestine.

What does this entail?

A
  • Cleaves peptides to amino acids
  • Cleaves polysaccharides to monosaccharides
  • Breaks down and re-form lipids
  • Breaks down nucleic acids
26
Q

What are the 3 main requirements of absorption?

A
  • Large amounts of energy (active process)
  • High surface area (slow process)
  • Good blood supply/drainage
27
Q

Identify the components of the small intestine and their individual roles

A
  • Duodenum absorbs iron
  • Jejunum absorbs most sugars, amino acids and fatty acids
  • Ileum absorbs Vitamin B12, bile acids and remaining nutrients
28
Q

Plicae circulares are found in the jejunum. What are they?

A

Plicae circulares are circular folds of mucosa and submucosa that project into the gut lumen

29
Q

What is a lacteal?

A

A lacteal is a dilated lymphatic capillary vessel

30
Q

What are the components of the large intestine?

A
31
Q

What are the roles of the bacteria of the large intestine?

A
  • Synthesis of vitamins K, B12, thiamine and riboflavin
  • Breakdown of bile acids
  • Conversion of bilirubin to non-pigmented metabolites
32
Q

Identify 2 consequences of disrupted fluid balance in the gut

A
  • Life threatening dehydration (depletion of body fluids)
  • Life threatening electrolyte imbalance
33
Q

Describe the neural control of the gut

A
  • Somatic:

I. Ingestion - mouth & upper oesophagus

II. Excretion - last spinchter of anus

  • Autonomic:

I. Range of neurotransmitters

II. Post ganglionic neurones form plexuses

34
Q

In the paracrine control of the gut, substances act locally.

Describe this

A
  • Histamine controls production of acid in stomach
  • Vasoactive substances affect blood flow in gut
35
Q

Which 3 actions are controlled by endocrine hormones of the gut?

A
  • Stomach acid secretion
  • Alkali secretion from liver and pancreas
  • Enzyme secretion
36
Q

What does gastrin do?

A

Gastrin promotes production of HCl by stomach parietal cells

37
Q

Which three structures produce gastrin?

A
  • G cells of pyloric antrum of stomach
  • Pancreas
  • Duodenum
38
Q

Where does CCK come from?

A

CCK is synthesised and secreted by enteroendocrine cells of the duodenum

39
Q

Which 3 things does CCK do?

A
  • Promotes release of digestive enzymes from the pancreas
  • Promotes release of bile from gall bladder
  • Suppresses hunger
40
Q

Which 3 things does secretin do?

A
  • Promotes HCO3 secretion from duct cells of pancreas
  • Promotes bile production by the liver
  • Inhibits acid secretion by parietal cells of stomach
41
Q

Why don’t we inhale what we are trying to swallow?

A

The epiglottis is a flap of elastic cartilage that projects behind the tongue and closes during swallowing, preventing aspiration forcing liquids/food down the oesophagus

42
Q

What is bile?

A

Bile is a digestive juice that is secreted by the liver and stored in the gallbladder

43
Q

Identify 3 roles of bile

A
  • Emulsify fat to increase surface area for enzymes
  • Assists in absorption of fat soluble substances e.g. Vitamin A D E K
  • Neutralise acidic pH of the stomach contents as they enter the duodenum