Digestive system

digestive system functions

• ingestion & mastication

• secretion

• mixing & propulsion

• mechanical digestion

• chemical digestion

• absorption

• defecation

peristalsis

movement of food (bolus) and waste in GI, in one direction

segmentation

movement of food in a non-propulsive way, both directions

digestive system organs

pharynx, esophagus, stomach, small and large intestines, oral cavity, rectum, anus

DS associated structures

salivary glands, liver, pancreas, gallbladder

mucosal layer

• gives off mucous

• consists of an epithelium, lamina propria, and muscularis mucosa

submucosa layer

• consists of areolar connective tissue

• regulates movements of the mucosa, vasoconstriction of blood vessels, and innervates secretory cells of mucosal glands

muscularis layer - skeletal muscle

• voluntary control

• in mouth, pharynx, upper esophagus, anus

• control over swallowing and defecation

muscularis layer - smooth muscle

• involuntary control

• inner circular fibers & outer longitudinal fibers

• mixes, crushes & propels food along by peristalsis

serosa layer

• Covers all organs and walls of cavities not open to the outside of the body

• secretes sliipery fluid

• Consists of connective tissue covered with simple squamous epithelium

enteric nervous system

• consists of neurons that extend from the esophagus to the gut

• can function independently of the CNS

peritoneum

• visceral layer covers organs

• parietal layer located on the peripheries & lines the walls of body cavity for protection

peritoneal cavity

potential space containing a bit of serous fluid

mesentery

membrane allowing intestines to attach to the abdominal wall, store fat, allows blood/lymph vessels/nerves to supply nourishment to the intestines.

vestibule

• space between lips/cheeks and the teeth

• Lips: formed by the orbicularis Oris muscle

• Cheek: later walls of the mouth, stratified squamous, buccinator muscle

• teeth, gums

oral cavity proper

• hard palate: made up of bone, contains palatine glands(produces salvia)

• soft palate: formed by tendons, during swallowing

• Tongue: helps move food around your mouth

• Pharynx: part of respiratory and digestive, carries airs, food and fluid

tongue

• together with its associated muscle, forms the floor of the oral cavity

• composed of skeletal muscle covered with mucous membrane

• Function: mastication, deglutition(swallowing) and speech

teeth

• Responsible for mastication

• made up of the crown, neck, root

enamel

• hardest substance in body; calcium phosphate

• covers the crown of the tooth

• can’t repair itself from damage or decay

dentin

• calcified connective tissue

• Living tissue, elastic; Protected by the enamel

cementum

• Hard tissue cover the root of the tooth

• periodontal ligament penetrates it bindings the root of the tooth to the gums/jaw (alveolar bone)

deciduous teeth

• primary teeth

• 20 teeth that start erupting at 6 months, Replaced by 6-12 years of age

permanent teeth

• 32 teeth that erupt between 6 and 12 years of age

• incisors for biting (8)

• canines/cuspids for tearing (4)

• Premolars (8), molars, (8), wisdom (4) for crushing and grinding food

parotid salivary glands

• largest gland, below ear and over the masseter

• Produces watery saliva, contains serous fluid

submandibular salivary glands

• under lower edge of mandible, opens into the oral cavity

• contains seromucous

sublingual salivary glands

• smallest gland

• deep to the tongue in floor of mouth

• seromucous and mucous

pharynx

• Funnel-shaped tube, passage between nose, mouth and larynx

• Conducts air to the larynx, while food is conducted into the esophagus

• made up of: nasopharynx, oropharynx, laryngopharynx

nasopharynx

connects nasal to the respiratory pathway

oropharynx

allows air and food to pass through into the esophagus

laryngopharynx

allows air and food into the esophagus

esophagus

• muscular tube that lies behind the trachea and connected to stomach

• secretes mucus and transports, by peristalsis, food to the stomach

• skeletal and smooth muscle

Upper Esophageal sphincter

• made up of skeletal muscle

• prevents back flow of contents; under our control (swallowing)

Lower esophageal sphincter

no control; protects esophagus from reflux of gastric content

sphincter

valves/gates that open and closes

stomach

• begins at the bottom of esophagus at the cardiac sphincter and ends at the pyloric sphincter of the duodenum of small intestine

• serves as a mixing and holding area for food; begins digestion of proteins and continues digestion of triglycerides

• converts bolus to chyme

chyme

gastric juices and broken-down food

stomach anatomy

• Fundus: stores digestive gas, does not store food but can if stomach needs to

• Body: where food is stored until it moves to the small intestines

• Cardiac Sphincter: valve opening btwn esophagus and stomach

Pyloric sphincter

valve which opens and closes and connects the stomach to the small intestines

cardia

entrance to the stomach allowing food/liquid to enter

rugae

folds which increases surface area

greater curvature

longer border of the stomach, allows for the omentum to attach

lesser curvature

smaller curvature and facilitates the passage of saliva and fluid during swallowing

mucosa - stomach layer

Epithelial tissues, made up of gastric glands

submucosa - stomach layer

• Dense connective tissue, contains blood and lymphatic vessels

• Have folds called rugae

serosa - stomach layer

• outermost layer

• made of simple squamous

muscularis - stomach layer

• Outer longitudinal layer: aids in food movement towards the pyloric sphincter

• Middle circular layer : aids in moving the food into the duodenum (first part of the SI)

• Inner oblique layer: Enables the stomach to contract and break down food into smaller pieces

Surface mucous cells

protects stomach from acid and enzymes, cells are connected by tight junction

Mucous neck cells

produce mucous

Parietal cells

produces hydrochloric acid

chief cells

produces pepsinogen, lipase which digest fats in the stomach

endocrine cells

• produces Gastrin hormone; release more gastric juice

• increase gastric motility; relax pyloric sphincter

• constrict esophageal sphincter preventing entry

small intestine

• Large surface area 16 to 20 feet long responsible for majority of the absorption

• 3 parts: duodenum, jejunum, ileum

duodenum

• 10-12 inches; Shortest part of small intestine, branches from the stomach

• absorb carbohydrates

jejunum

• 8 feet; absorbs most fats

ileum

• 6-13 feet; absorbs vitamin B12, bile, salts, and anything left

• ends at ileocecal valve

absorptive cell - SI

Digestion & absorption

goblet cell - SI

secretes mucus

endocrine cell - SI

releases hormones, ex. secretin, cholecystokinin

granular cells - SI

secretes lysozymes for phagocytosis

large intestine

• extends from the ileocecal valve to the anus

• cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anus

cecum

between the SI and beginning of LI; contains ileocecal valve, mixes food content with mucus

ascending colon

absorbs water/salts, and forming it into stool

transverse colon

longest colon, absorbs water and salt

descending colon

storage of stool before moving into sigmoid colon

sigmoid colon

last part of the colon, solidify/stores stool before entering the rectum and anal canal for excretions

anus

• last part of the DS, surrounded by sphincter muscles, allowing for contraction of stool

• Internal sphincter: prevents from popping involuntary (asleep or unaware)

• External sphincter: holds stool until ready to expel

rectum

receives stool from sigmoid colon, receives signal from brain to release stool

pancreas

Located behind the stomach (endocrine and exocrine gland)

exocrine

salts and enzymes released into the duodenum

endocrine

insulin secreted into the blood (lowers blood sugar)

bicarbonate

neutralize the gastric acid (HCL)

amylase

breaks down starch

lipase

breaks down lipids (fats)

proteolytic enzymes

break down protein

duct of wirsung

• collects pancreatic juice and empties it into the duodenum

• digestive enzymes which breaks down sugar, fats and starches

duct of santorini

• empties into the duodenum

• Digestive enzymes which breaks down carbohydrates, fat and protein

acinar gland

Produces, stores and secretes digestive enzymes

liver

• heaviest gland in the body; second largest organ in the body after the skin

• 4 lobes: left and right lobe, caudate and quadrate lobe

liver functions

• Stores carbs, fats, protein

• detoxification, bile production, Stores fat soluble vitamins (A, B12, D, E, K, activated vitamin D)

• Phagocytizes worn out blood cells & bacteria

common bile duct

carries bile from the liver and gallbladder through the pancreas and into the small intestines (duodenum)

bile

made in the liver and stored in the gallbladder which helps digest fats

hepatocytes

• functional cells of the liver

• control nutrient and secrete bile

Stellate macrophages

engulf pathogen, damaged rbc, store ingested iron, lipids and heavy metals

reticuloendothelial (Kupffer’s) cells

phagocytotic cells clearing blood of bacteria and foreign materials

gallbladder

• Saclike structure which stores bile produced from the liver; Bile breaks down fat

inner mucosa - GB

contains rugae; allows for expansion

muscularis layer - GB

smooth muscles allowing for contraction

outer serosa - GB

made up of loose CT, BV, LV and nerves