Lecture 38 Flashcards
Digestive system
Structure Irregular tube Open at both ends – ‘outside’ the body! Alimentary canal or gastrointestinal (GI) tract Organs (see Box in Textbook)
Functions
Digestion
Absorption
Metabolism
Walls of the GI tract
Four layers of tissue
Structure varies among organs
From inside to outside, they are:
Mucosa
Submucosa
Muscularis
Serosa
Mucosa layer
Production of mucus to coat lining of ‘tube’.
Secretion of digestive enzymes and hormones
Absorption of the end products of digestion
Protection against pathogens
Submucosa layer
Connective tissue layer
Contains glands, blood vessels, lymphatic vessels, & parasympathetic nerves
Contains lots of elastic fibres, allowing the tube to stretch and recoil (especially the stomach)
Muscularis layer
Mixes & churns food Peristalsis Consists of 2 or 3 layers (depending on location in GI tract): 1Inner circular (lots at sphincters) 2Outer longitudinal 3Oblique
Serosa layer
Protective outermost layer
Composed of visceral and parietal peritoneum in abdominal cavity
Mouth (oral/buccal cavity)
Where process of digestion begins!
Hollow ‘chamber’ Lined with mucosa 3 ‘parts’: Roof Floor Walls
Mouth roof
Hard palate (2 maxillary & 2 palatine bones)
Soft palate (arch-shaped muscle; separates mouth from nasopharynx)
Uvula – projection of soft palate
Uvula & soft palate prevent food & liquid from entering nasal cavities
Floor of mouth
Tongue and its muscles
Tongue is skeletal muscle, and is anchored to floor of mouth by the frenulum
Consist of a tip, a body and a root
Small nipple-like projections on tongue, called papillae
Taste buds found in many papillae
Ankyloglossia
Tongue tied
Frenulum is unusually short and thick
Can be mild (bands) to complete (entire tongue is attached to the floor of the mouth)
Affects feeding/eating, swallowing, oral hygiene/structure, speech
May recede on its own; surgery is an option
Mouth walls
Lateral walls formed by the cheeks (buccinator muscle); contain mucous-secreting glands
Anterior wall formed by the lips
Skin on outside, mucous membrane on inside; junction highly sensitive
Line of contact between closed lips = oral fissure
Salivary glands
Function:
Secrete approximately 1 litre of saliva (salivary amylase + mucus) each day!
Parotid glands (largest) Submandibular glands (‘below mandible’) Sublingual glands (‘below tongue
Parotid glands
Largest
Bottom of ear at jaw angle
Ducts secrete into mouth cavity
Function:
Produce watery saliva containing enzymes
Submandibular glands
Middle of mandible
Ducts secrete on either side of lingual frenulum
Function:
Contain enzyme- and mucous-producing substances
Sublingual glands
Anterior to submandibular glands
Ducts secrete into floor of mouth
Function:
Produce a mucus type of saliva
Sections of a typical tooth
Crown
Neck
Root
Crown
Covered by enamel
Enamel = hardest tissue in body, perfect for withstanding the abrasion of chewing food
Pulp cavity in centre of tooth contains connective tissue, blood & lymphatic vessels & sensory nerves
Neck of tooth
Joins crown to root
Surrounded by pink tissue = gingival tissue = ‘gums
Roots
Fits in socket/jaw bone
Socket lined with periodontal membrane – anchors tooth to bone
Deciduous teeth
Baby teeth 20 teeth 6 months: average age for first eruption 8 incisors are cut first Complete set at about 2 years of age No premolars; 2 pairs of molars per jaw Lost between 6 – 13 years of age
Permanent teeth
Adult teeth
32 teeth
6 years: average age for first eruption
Complete set of 32 teeth between 17-24 years of age
Pharynx
Tube-like structure made of muscle and lined with mucous membrane
Dual function: digestion & respiration - RECALL:
Air must pass through pharynx on its way to the lungs
Food must pass through pharynx on its way to the stomach
Three divisions - RECALL
Esophagus
Muscular, mucus-lined tube (25cm long)
Connects the pharynx with the stomach; sphincters at both ends
Peristaltic action conducts food to the stomach
Mucous secretion facilitates passage of food
Collapses when not moving food
Stomach
In upper abdominal cavity (under diaphragm & liver)
Temporary ‘storage’ sac for chewed food
Where chemical digestion of protein begins
About the size of a large sausage when empty - expands after large meal (1.0 to 1.5 litre capacity)
Divisions of stomach
Cardia: collar-like region at junction with esophagus
Fundus: enlarged portion to the left and above the opening of the esophagus into the stomach
Body: central portion of the stomach
Pylorus: lower part of the stomach
Cardiac sphincter
Lower esophageal sphincter (LES)
Ring of muscle at end of esophagus
Prevents stomach contents from refluxing back into esophagus
Hiatal hernia
Due to weakening of ‘hiatus’ (opening in diaphragm for esophagus)
End of esophagus may bulge
Part/all of stomach can bulge upwards
Can lead to GERD
Pyloric sphincter
Controls emptying of stomach into the duodenum (first part of small intestine)
Stomach wall layers
Gastric mucosa*
Gastric submucosa
Gastric muscularis*
Gastric serosa
Gastric mucosa
Epithelial lining has rugae marked by gastric pits. Gastric glands below the gastric pits secrete the majority of gastric juice:
Chief cells secrete the enzymes of gastric juice
Parietal cells secrete HCl instrinsic factor B12
Endocrine cells – secrete hormones (gastrin & ghrelin)
Gastric muscularis
3 different directions/arrangements (oblique, ciruclar, and longitudinal) that allow the stomach to ‘churn’ (contract) in many directions
Stomach functions
‘Holding tank’ for food until it is partially digested and moved further along the GI tract
Secretes gastric juice to aid in digestion of food
Breaks food into small particles and mixes them with gastric juice
Secretes intrinsic factor
Performs limited absorption
Produces gastrin and ghrelin
Helps protect the body from pathogenic bacteria swallowed with food
