Chapter 24: The Digestive System Flashcards
What are the functions of the digestive system?
- ingestion
- mechanical processing
- digestion
- secretion
- absorption
- excretion
Digestive System Function: Ingestion
- materials enter the digestive tract via the mouth (oral cavity
- the process of swallowing is called delutition
Digestive System Function: Mechanical Processing
- crushing and shearing the ingested material to make it easier to propel along the digestive tract
- processes of chewing is called mastication
- increases the surface area allowing for enzymatic attack and subsequent breakdown of the material
Digestive System Function: Digestion
- refers to the chemical breakdown of food into small organic fragments allowing for absorption by the digestive epithelium
- proteins, carbohydrates, lipids, nucleic acids must all be broken down to their monomers (building blocks) before it can be absorbed (done by digestive enzymes)
Digestive System Function: Secretion
- release of water, acids, enzymes, buffers, salts by the epithelium of the digestive tract and by glandular organs
Digestive System Function: Absorption
- movement of organic monomers, electrolytes, vitamins and water across the epithelium and into the interstitial fluid of the digestive tract
Digestive System Function: Excretion
- removal of waste products from body fluids
- ejection of material as feces from the digestive tract is called defection or egestion
The Digestive System is divided into 2 main groups:
- Digestive Tract Organs
2. Accessory Digestive Organs
Digestive Tract Organs
- make up the Alimentary Canal (Gastrointestinal (GI) Tract)
- digestion and absorption
Accessory Digestive Organs
assist in the process of digestion and absorption
List the Digest Tract Organs
- Mouth (Oral Cavity)
- Pharynx
- Esophagus
- Stomach
- Small intestine
- Large intestine
- Rectum
- Anus
List the Accessory Digestive Organs
- Salivary Glands
- Liver
- Gallbladder
- Pancreas
Salivary Glands
secrete salivary amylase that begins carbohydrate digestion/breakdown
Liver
a large metabolic organ that lies under the diaphragm and is made of 100,000 lobules
Gallbladder
stores bile from liver and sends it to small intestine
Functions of the Pancreas
- Exocrine produces pancreatic juice:
- Endocrine gland produces hormones that are released into the bloodstream after eating:
- insulin and glucagon
Mouth (oral cavity)
- has 3 pairs of salivary glands
- stratified squamous epithelial tissue
- has tonsils at the back of the mouth and other lymphatic tissues important in fighting disease
- has teeth that begin mechanical breakdown of food (mastication)
- has tongue that tastes and pushes food for chewing and swallowing
Pharynx
common passageway for solid foods, liquid and air
-material that is swallowed and enters the pharynx is now referred to as a bolus (mass of masticated material)
Esophagus
- hollow muscular tube where peristalsis pushes food to stomach
- length is approximately 1 foot
- first third is skeletal muscle
Stomach: Function
- stores food, starts digestion of proteins
- produces gastric juice that contains pepsin (an enzyme that breaks down protein)
- mechanical breakdown of the bolus liquefying it into a semi-liquid/solid paste called Chyme
Small Intestine: Main functions
- mixes chyme with digestive enzymes for final breakdown
- absorbs nutrient molecules into body
- secretes digestive hormones into blood
Large Intestine
also known as the large bowl ~5 feet
larger in diameter but shorter than the small intestines
Rectum
Stores and regulates elimination of feces
Pathway of Food
Mouth -> Pharynx -> Esophagus -> Stomach -> Small Intestines -> Large Intestines -> Rectum -> Anus
4 Major Layers that Makeup the Wall of the Alimentary (GI) Tract
- Mucosa (innermost layer)
- Submucosa (second layer)
- Muscularis Externa (third layer)
- Serosa (outermost layer)
Mucosa layer
- produces mucus (line with mucous membranes) that protect lining
- simple columnar epithelial tissue
- involved in absorption (in certain regions of GI tract)
- also produces digestive enzymes and hormones (in certain regions of GI tract)
Submucosa layer
layer of loose areolar connective tissue that contain blood vessels, lymphatic vessels and nerves
Muscularis Externa layer
made of 2 layers of smooth muscle that move food along the GI tract (in the stomach, there are 3 layers)
Serosa layer
part of the peritoneum
Enteric Nervous System
- “brains of the gut”
- accounts for intrinsic control of digestion which consists of 2 major intrinsic nerve plexuses.
.. (add more later)
What are the two major intrinsic nerve plexuses?
- Submucosal Nerve Plexus
2. Myenteric Nerve Plexus (lies between circular and longitudinal muscles of the muscularis externa)
Tongue
covered in taste buds called Gustatory cells and assist in the mechanical breakdown and swallowing of food (deglutition) and moves it toward the pharynx
What are the three pairs of salivary glands?
- parotid (cheek area)
- sublingual (under the tongue)
- submandibular (jaw area)
Saliva contains
- water, mucins (lubricant
- mucous
- lysozyme
- salivary amylase
- lingual lipase
- electrolytes
- IgA
2 Types of Teeth
- Primary Dentition (aka deciduous teeth or baby teeth) - 20 deciduous teeth
- Secondary Dentition (aka permanent teeth or adult teeth) - 32 permanent teeth
The Process of Swallowing
- Voluntary Phase
2. Involuntary Phase
Voluntary Phase of Swallowing
the beginning of food being swallowed from the mouth into the pharynx
Involuntary Phase of Swallowing
- once the food is in the pharynx swallowing becomes a reflex.
- the epiglottis covers the glottis to make sure food is routed into the esophagus
- food moves down the esophagus through peristalsis
Peristalsis
rhythmic contractions
Stomach: Structure
- thick-walled J-shaped organ that lies on the left side of the body beneath the diaphragm
- mucosa layer has deep folds called rugae and gastric pits that lead into gastric glands that secrete gastric juice
What are the three smooth muscle layers in the muscularis layer of the stomach?
- Oblique (inner)
- Circular (middle)
- Longitudinal (outer)
What are the 4 types of secreting cells?
- Chief Cells
- Parietal Cells
- Enteroendocrine Cells (G cells)
- Mucus Neck Cells
Chief Cells
produce Pepsinogen (inactive enzyme that breaks down protein)
Parietal Cells
- produces intrinsic factor (helps the absorption of Vitamin B12 in the small intestines)
- produces Hydrochloric Acid (HCl) which makes the stomach extremely acidic (pH of 2)
- This acidic condition activates Pepsinogen -> Pepsin (an active enzyme)
Enteroendocrine Cells (G Cells)
- produces Gastrin
- other secretions: Histamine, Serotonin & Somatostatin
Mucus Neck Cells
produce mucus (thin, soluble)
Small Intestines: Structure
- main site of absorption for the entire GI tract (90%) of absorption
- consists of cells called Brush Border cells (Absorptive Cells)
- smaller in diameter than the large intestines, but longer than the large intestines (~18-20 feet long)
Brush Border cells (Absorptive cells)
absorb the organic building blocks and also has attached enzymes called brush border enzymes
lactose
galactose + glucose