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Kofi: Pure Clinical Sem 3 > GI: Physiology > Flashcards

GI: Physiology Flashcards

1
Q

What is secreted in the GI tract?

A
  • Water
  • Acid
  • Alkali
  • Enzymes
  • Mucus
  • Waste products
  • Emulsifiers
  • Intrinsic factor
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2
Q

Where do secretion come from in the GI tract?

A
  • Saliva (acini of salivary glands)
  • Gastric (gastric glands)
  • Intestinal (Brunner’s glands, intestinal glands, Goblet cells)
  • Liver (hepatocytes)
  • Pancreas (exocrine pancreas)
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3
Q

What are the purposes of stomach acid?

A
  • Innate barrier to infection
  • Prepares proteins for digestion
  • Activate enzymes
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4
Q

What are the emulsifiers in the GI tract and their purpose ?

A
  • Bile salts
  • Increase surface area of lipids
  • Aids digestion by lipases
  • Allows lipid breakdown products to be transported in the gut
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5
Q

What is the purpose of mucus in the GI tract?

A
  • Protects against chemical damage due to acidic environment in stomach
  • Protects against bacteria in small intestine
  • Habours bacteria in large intestine
  • Lubricates to reduce friction
  • Forms physical barrier against bacterial inflammation
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6
Q

What are the principles of absorption in the GI tract?

A
  • Movement across enterocyte

- Movement paracellularly

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7
Q

How is the large surface in the Gi tract created?

A
  • Plica circulares (Permanent folds in small intestine)
  • Villi
  • Microvill
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8
Q

What are the effects of disrupting surface area in the gut?

A
  • Diarrhoea
  • Malnutrition
  • Anaemia (Crohn’s, Coeliac)
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9
Q

What is absorbed in the GI tract?

A
  • Nutrients (carbohydrates, proteins, lipids, fat soluble vitamins, Vitamin B12, Bile salts, Ca2+, Fe2+)
  • Electrolytes
  • Water
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10
Q

How is water reabsorbed in the GI tract?

A

Passive
-After a meal, water uptake is driven by nutrients coupled with Na+ (sodium co-transporters)

In between meals
-Na+ and Cl- absorbed (sodium/hydrogen and chloride/bicarbonate exchangers)

In colon
-Additional mechanism so that stool can be desiccated (ENaC)

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11
Q

What are the layers of the gut tube?

A
  • Mucosa
  • Submucosa
  • External muscle layers
  • Serosa
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12
Q

What are the regions of the mucosa?

A
  • Epithelial layer
  • Lamina propria
  • Muscularis mucosa
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13
Q

What is the purpose of the epithelial layer?

A
  • Selectively permeable barrier
  • Facilitate transport and digestion of food
  • Promote absorption
  • Produce hormones
  • Produce mucus
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14
Q

What is the purpose of the lamina propria?

A
  • Lots of lymphoid nodules and macropahes

- Produces antibodies to protect against bacteria/viral invasion

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15
Q

What is the purpose of the Muscularis Mucosae?

A

-Layer of smooth muscle in different direction to help keep crypt contents dynamic and epithelium in contact with gut contents

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16
Q

What are the contents of the submucosa?

A
  • Contains dense connective tissue, blood vessels, glands, lymphoid tissue
  • Contain submucosal plexus (Meissner’s)
17
Q

What are the contents inner circular muscle?

A

-Myenteric plexus

18
Q

What are the contents of the serosa?

A
  • Blood and lymph vessels and adipose tissue

- Continuous with mesenteries

19
Q

What are the epithelial regions of the gut?

A
  • Stratified squamous in oesaphagus and distal anus

- Everything in between is simple columnar

20
Q

What is an enterocyte?

A
  • Simple columnar epithelial cell that absorbs
  • Predominant cell of small intestine and colon
  • One cell thick
  • Has microvilli
  • Blood vessels/lymphatics lie immediately below the basolateral membrane of the enterocyte
21
Q

What is the purpose of the enterocyte?

A
  • Apical membrane (faces the lumen)

- Basolateral membrane (faces blood vessels)

22
Q

What is the structure of the goblet cells?

A
  • Has a wide top and pushed down base nucleus
  • Has a terminal bar, mucus droplet and basal nucleus
  • Produces mucus to protect the epithelia against pathogens and keeps some bacteria alive
  • Scattered in between enterocytes in intestinal epithelia
23
Q

What the defences of the stomach ageing acid?

A
  • Surface mucus cells line gastric mucosa/gastric pits in stomach and secrete mucus/HCO3 that forms thick alkaline viscous layer that adheres to stomach epithelium acid to protect the stomach and keep the epithelial surface at a higher pH
  • High turnover of epithelial cells to help keep epithelia intact
  • Prostagladins to maintain mucosal blood flow to supply epithelium with nutrients
24
Q

What are crypts of lieberkuhn (intestinal gland) and what do they contain?

A

Intestinal glands

  • Stem cells
  • Paneth cells
  • Enteroendocrine cells
25
Q

What is the purpose of the cells in the crypts of lieberkuhn?

A

Stem cells

  • Constantly divide to replace epithelia (2-4 days)
  • Mature as they migrate to surface

Paneth cells

  • Located at base of crypts
  • Secrete antibacterial proteins to protect stem cells

Enteroendocrine cells

  • Secrete hormones to control functions of the gut
  • Hormones such as gastrin, CCK and secretin
26
Q

What do the acini glands tend to secrete?

A
  • Serous (+enzymes) secretions
  • Tubules tend to secrete mucous (Brunner’s glands)

*salivary glands can be mixed

27
Q

What is ulceration in the GI tract?

A
  • Erosion through muscularis mucosae

- Failure of protective merchiasnm such as mucus production

28
Q

What is the oral preparatory phase?

A
  • Voluntary
  • Pushes the bolus towards the pharynx
  • Once bolus touches the pharyngeal wall, pharyngeal phase begins
29
Q

Describe the structure of the oesophagus and outline its functions

A
  • Muscular layers

- Transport of bolus from oral cavity to the stomach by peristalsis

30
Q

Outline the pharyngeal phase of swallowing?

A
  • Involuntary
  • Soft palate seals of the nasopharynx
  • Pharyngeal constrictors push bolus downwards
  • Larynx elevates closing epiglottis
  • Vocal cords duct to protect the airway and breathing temporarily ceases
  • The upper oesophageal sphincter opens
31
Q

Describe the anatomical mechanisms that prevent gastro-oesophageal reflux.

A
  • Lower oesophageal sphincter (diaphragm)
  • Intra-abdominal oesophagus which gets compressed when intra-abdominal pressure rises
  • Mucosal rosette at cardia to prevent back flow
  • Acute angle of entry of oesophagus
32
Q

Give an overview of the control of saliva production

A

-Autonomic control
-Mainly parasympathetically controlled to stimulate salivary secretion
-Sympathetic also causes small amounts of saliva
secretion and can also vasoconstrict blood vessels

33
Q

What is the structure of a salivary cell?

A
  • Acinus line with acinus cells
  • Ductal portion with ductal cells
  • Myoepithelial cells
34
Q

Outline the production of saliva.

A
  • Acinus produces initial saliva which is isotonic and releases it into the ductal portion
  • Ductal cells modify the initial solution to produce hypotonic saliva.
  • Myoepithelial cells which help move saliva from the structure into the mouth
35
Q

What is the purpose of kallikrein released in the saliva?

A

-Helps to produces bradykinin to vasodilate in the mouth in periods of maximum activity to allow blood flow to get to salivary glands

36
Q

How does saliva flow rate affect its modification by duct cells?

A
  • Increased flow rate of saliva results in less modification
  • Decreased flow rate of saliva results in more modification by duct cells

*Bicarbonate gets excreted more at higher flow rates as an exception

37
Q

How do duct cells form hypotonic saliva?

A
  • Exchanging increased amounts of sodium, chloride from the saliva in the lumen into the cell compared to excreting bicarbonate and potassium back into the lumen.
  • This results in a hypotonic solution
38
Q

Outline the oesohaphgeal phase of swallowing?

A
  • Involuntary
  • Closure of the upper oesophageal sphincter
  • Peristaltic wave carries bolus downwards into oesophagus
39
Q

Outline the neural control of swallowing and the gag reflex?

A
  • Mechanoreceptors in wall of pharynx detect the bolus
  • Glossopharyngeal nerve carries sensory impulses to medulla
  • Vagus nerve carries impulses to the Pharyngeal constrictors which contract to cause an effect
  • Pushes the bolus inferiorly

*Gag reflex works the same. Psychological possibly

Kofi: Pure Clinical Sem 3 (44 decks)

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