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Flashcards in Salivary and gastric secretion Deck (45):
1

Three functions of saliva

Lubrication

Protection

Digestion

2

Lubrication

Moistening the mouth to aid swallowing

Facilitates movement of the mouth and tongue for speech

Helps to dissolve chemicals within food for its presentation to the taste receptors

3

Protection

Reduces the adverse effects of oral bacteria

Alkalinity of fresh saliva neutralises acid produced by oral bacteria

Flow of saliva across teeth helps wash away bacteria

4

Digestion

Begin breakdown of carbs and fats via alpha amylase and lingual lipase

5

Sjogren's syndrome

Autoimmune disease

Destroys exocrine glands, mostly tear and salvia

Dry eyes and mouth

6

Xerostomia

Lack adequate saliva

Dental caries and haltosis due to bacterial overgrowth

Difficulty speaking or swallowing food

7

Volume of saliva produced

1.5L per day

8

Two types of secretions

Serous secretions:
- the main type of protein secreted is ptyalin

Mucous secretions:
- main protein is mucin acting as a lubricant

9

Three major salivary glands

Submandibular glands secrete approximately 70% of saliva

Parotid glands secrete 25%

Sublingual glands secrete 5%

10

Structure of salivary glands

Contain blind-ended acini connecting with ducts draining major ducts

Acinar cells histologically distinct from duct cells

Serous acini distint to mucous secreting acinus

11

Composition of saliva

Functional unit consists of acinar cells, secrete primary saliva into a duct system

Primary saliva secreted by acinus is isotonic solution resembling interstitial fluid

Duct reabsorbs NaCl, causing saliva to become hypotonic

12

Secretion and modification of saliva by salivary acinar

Cl- uptake by a basolaterally located Na+, K+, 2Cl- cotransporter and release through the calcium activated apical chloride channel

Sustained by Na+/K+/ATPase

Na+ enters acinar lumen paracellularly through leaky tight junctions

H2O follows via aquaporin 5 or paracellularly

13

Secretion and modification of saliva by ductal cells

Removal of Na+ from saliva via apical sodium channel and basolateral Na+/ K+ ATPase

Cl- removal from saliva via different chloride channels in the apical and basolateral membranes of ductal cells

Removal of salt not accompanied by water since ductal tight junctions are not leaky and aquaporins are not expressed in apical membranes

Secrete bicarbonate and potassium via unidentified apical bicarbonate chloride and potassium proton exchangers

14

Composition of saliva changes with flow rate

Electrolytes
- Na+ and Cl- < plasma
- HCO3- and K+ > plasma

High flow rate less time for ducts to absorb NaCl so resembles isotonic solution produced by acini

15

Central control of salivary secretions

Stimulated through thought, smell or taste of food by reflexes and nausea

Sleep, dehydration, fatigue and fear inhibit salivation

Integrated by salivary nuclei in the pons

Efferent nerves reach salivary glands via glossopharyngeal and facial nerves

Acinar secretion stimulated by acetylcholine via muscarinic receptors

16

Parasympathetic stimulation

Promotes watery secretion myoepithelial cells surrounding acini

Ducts contract and eject preformed saliva

Leads to increased blood flow

17

Superior cervical ganglion

The only hormonal effect on saliva secretion is from aldosterone which increases ductal Na+ absorption and K+ secretion

18

Composition of gastric juice

1-2L from several cell types produced per day

- water, electrolytes
- HCl
- pepsins
- mucus
- intrinsic factor

19

Water, electrolytes

Dissolve and dilute digested food

20

HCl

Hydrolyses fat and starch

Antiseptic

Converts pepsinogen to pepsin and provides optimum pH

21

Pepsins

Secreted as inactive pepsinogens away from stomach lining activated to form pepsins at low pH

22

Mucus

Bicarbonate barrier

Protect surface epithelial cells from acid/ pepsin erosion

23

Intrinsic factor

Glycoprotein binds vitamin B12 needed for absorption in the ileum

The indispensable substance in gastric juice

24

Origins of secretion

Stomach has two major regions:
- an exocrine or glandular portion consists of the fundus and body or acid secreting area
- an endocrine or hormone secreting area that is located in the antrum or gastrin secreting area

25

Structure of gastric gland

Mucous cell

Endocrine cells- D cells

Chief cells

Parietal cells

Histamine cells

Endocrine cells- G cells

26

Mucous cells

Secrete protective barrier

27

Endocrine cells- D cells

Secrete somatostatin
- regulateor of gastrin release and gastric acid secretion

28

Chief cells

Secrete pepsinogen

Converted by gastric acid to active form of pepsin

29

Pariteal cells

Acid secreting, IF

30

Endocrine cells- G cells

Produce gastrin

31

Protection against self digestion and mechanical damage

Lumen

32

Gartitis

Many causes

Most commonly caused by an infection by the bacteria helicobacter pylori

Other common causes include smoking, use of alcohol and nonsteroidal anti- inflammatory drugs and chronic stress

Surface of epithelium acutely damages

33

Acid secretion- oxyntic cell

Tubolovesicular membrane contains H+-K+ pumps responsible for acid secretion

Upon stimulation tubulovesicular membrane fuses into canalicular membrane

Fusion accompanied by insertion of H+/K+ ATPase and K+ and Cl- ion channels into canalicular membrane

Dense mitochondria to support high metabolic activity of cell

34

Acid secretion at the luminal membrane of a stimulated parietal cell

Major component if H+/K+ ATPase which actively exchanges H+ for K+

Enormous active secretory capacity, capable of secreting protons against large electrochemical gradients

Luminal pH can approach 1-2

No other part of the body can approach this level of acidification

35

Mechanism of gastric acid secretion by oxyntic cells

H+ and HCO3- made inside the cell by carbonic anhydrase

H+ pumped out of the luminal membrane by H+/K+ ATPase

Cl- leaves by diffusion

Cl-HCO3- exchanger in basolateral membrane provides Cl- for HCl and HCO3- exits in large quantities so gastric venous blood becomes alkaline

36

Omeprazole

Proton pump inhibitor

Binds irreversibly to the H+/K+ ATPase inhibiting H+ secretion until new H+/K+ ATPase protein is synthesised

37

Three major stimulators of acid secretion

1. Gastrin- predominantly secreted by antral G cells
2. Histamine- in humans probably arising from mast cells
3. Acetylcholine- secreted by postsynaptic vagal fibres innervating the gastric mucosa

38

Two major paracrine inhibitors of gastric acid secretion

1. Somatostatin- secreted from antral and oxyntic gland D cells as well as pancreatic islet cells
2. Prostaglandins- from mucosal cells

39

Atrophic gastritis

Autoimmune

Antibody mediated destruction of gastric parietal cells

Causes hypochlorydria and a deficiency of IF

Loss off IF results in vitamin B12 malabsorption and pernicious anaemia

40

Three phases of gastric acid secretion

Cephalic: sight, cell, taste, though

Gastric: antral distension, protein content, increase pH

Intestinal: intestinal gastrin, absorption amino acids

41

Gatrin

G cells of pylorus and duodenum

Endocrine effect

Release triggered by aa and peptides in stomach

Low pH inhibits release

42

Histamine

ECL cells close to parietal cells

Paracrine effect by local diffusion

ECL cells stimulated by gastrin and acetylcholine

ACh/ gastrin has direct and indirect route of stimulation which amplify signal

Leads to vasodilation of arterioles

43

Acetylcholine

Acts on parietal and ECL cells to promote acid and histamine secretion

Acts on D cells to inhibit somostatin release

44

Vagal stimulation- corpus

Via ACh

Increases acid secretion directly via parietal cells and indirectly via ECL and D cells

45

Vagal stimulation- antrum

Via GRP

Stimulates both G and D cells

Gastrin from antrum promotes acid secretion by two endocrine mechanisms
- directly via parietal cells
- indirectly via ECL cells