Lab 14: Digestive System Flashcards
The digestive system can be separated into two main components:
- digestive tract - a continuous tube that begins at the mouth and ends at the anus.
- accessory organs - teeth, tongue, salivary glands, liver, gall bladder, and pancreas
gingiva
gums, a delicate mucosa,
Cranial nerves for taste
facial nerve VII, the glossopharyngeal nerve IX, vagus nerve X
Mastication
• accomplished via teeth
Teeth Used:
- Incisors: cutting and shearing food
- Canines (cuspids): tearing food
- Premolars (bicuspids): crushing and cracking food
- Molars (tricuspids): grinding food into fine pieces
Teeth Evolution
- deciduous (primary or baby) teeth
* permanent (secondary) teeth
Teeth From birth to 6
- Teeth erupt at six months
* By six years old, full set of deciduous teeth (consisting of 20 teeth)
dental formula
• Each half of each jaw contains two incisors, one canine and two molars
Infant Dental Formula: I 2/2 , C 1/1 , P 0/0 , M 2/2
Adult Dental Formula: I 2/2 , C 1/1 , P 2/2 , M 3/3
How do permenat teeth grow in?
- permanent teeth grow in the jaws beneath the deciduous teeth.
- When enlarged sufficiently, they exert pressure on the roots of the deciduous teeth above.
- Roots are resorbed and the deciduous teeth are shed (exfoliated).
- Process begins at 6 years old, completed by 11 - 12.
- At the same time, the permanent teeth start erupting. All of the permanent teeth do not appear until a person is 18 to 20 years of age.
- In the adult, there are 16 teeth in each jaw, 32 teeth altogether. It is not unusual for the third molar (the “wisdom” tooth) never to develop or erupt.
- Extra teeth (supernumerary teeth) occur frequently as well.
primary salivary glands
• Accessory organs • secrete saliva 3 Types: • parotid glands • submandibular glands • sublingual glands
Saliva Functions
- lubricating the mouth
- moistening the food
- dissolving chemicals in food so that they can be tasted. • contains the enzyme – salivary amylase that begins the digestion of carbohydrates.
oropharynx and the laryngopharynx
- common passageways for food, liquids and air.
* nasopharynx is not part of the digestive tract.
esophagus
- muscular tube that functions in the transport of food to the stomach
- enters the abdominal cavity through an opening in the diaphragm
- opening to the larynx is closed off by the epiglottis
stomach
- chemical digestion of proteins begins
* functions as a temporary storage area for food.
small intestine
• primary digestive organ • chemical digestion of food is completed • absorption of nutrients occurs. • 3 Regions: -duodenum -jejunum -ileum
large intestine
- absorption of water from the undigested food material
* cecum–> ascending colon –>transverse colon.–>descending colon –> sigmoid colon –> rectum–> anus
Pathway of food
mouth–>oropharynx –> laryngopharynx–>esophagus–>stomach–>duodenum–>jejunum–>ileum–>cecum –>ascending colon –>transverse colon.–>descending colon –> sigmoid colon (s-shaped) –> rectum–> anus
liver
• function: production + secretion of bile (main function),
- removing nutrients from blood
- storing glucose, liver glycogen, and vitamins
- detoxification of metabolic waste
- synthesis of blood-clotting factors
• divided into two main lobes
• lobes made up of functional units = lobules
gall bladder
- green-coloured muscular sac attached to the ventral surface of the liver
- bile stored and concentrated until needed
- Bile release into duodenum (under nervous and hormonal control)
pancreas
Exocrine glands:
- comprise 98% of the organ.
- produce pancreatic juice
Endocrine tissue
- comprises 2% of the organ
- “ductless glands”
- Islets of Langerhans (release hormones into blood)
lobules
• consisting of plates of liver cells or hepatocytes
- manufacture bile (fat emulsifier)
• portal triad: hepatic artery + hepatic portal vein + bile duct
function of the fluid produced by the peritoneum?
Lubricates parietanel surfaces to reduce fricton, allow organs to slide easily over each other
mesenteries
• membranes, made up of folds of the peritoneum, which hold the digestive organs in place and contain blood vessels, lymphatic vessels and nerves
Omentum – bind organs to each other
Mesentareies – bind organs to abdominal wall
- greater omentum: greater curvature over S.I/L.I
- lesser omentum: lesser curvature to liver
- falciform ligament: suspends liver from diaphragm / abdominal wall
- mesentery proper: connects parts of small intestine to itself
Function. keeps organs from tangling, gives roots for blood vessels and nerves and a way to store fat.
spleen
removal of aged and defective blood cells, but is not involved in digestion
Four layers compose the wall of the digestive tract
- mucosa - inner lining, stratified squamous epithelium
- submucosa - layer of connective tissue, infiltrated with blood vessels and nerves,
- muscularis (externa)- 2 layers of smooth muscle
- serosa - outermost layer (visceral peritoneum)
Function of stratified squamous epithelium in muscosa
many layers to protect from abrasion of rough food and protection from wear and tear as you swallow food
What is the purpose of this additional layer of smooth muscle in the stomach?
Extra layer of smooth muscle (oblique layer) stregthens stomach walls and assists in mixing churning activity’s to produce chime
Why would mucous production be important in this region of the digestive tract?
because mucus in alkaline (basic) so helps neutralize the stomach acid, forms a protective layer over epithelium of acid doesn’t damange stomach lining.
What is a gastric ulcer?
develop when stomach protective layer breaks down and digestive juces start to damage stomach tissue
Histology: esophagus
- Non-keratanized stratified squamous epithelium
* No serosa - Adventitia
Histology: Stomach
- simple columnar epithelium
- gastric pits
- additional oblique layer of smooth muscle
Histology Small I.
- simple columnar cells
- goblet cells
- Increase absorption: microvilli (increase surface area) + villi + plicae circulares ( force chyme to spiral through the intestine, mixing it and slowing its progress)
Hisotlogy: Large I.
- no villi, many goblet cells
- simple columnar epithelium
- Crypts: intestinal glands of the mucosa are deep and straight
What is the major type of movement in the digestive tract?
peristalsis
What is the purpose of villi in the small intestine?
increase surface area for absortion
In what part of the digestive tract does most digestion of nutrients occur?
small intestine
Why are mucus producing goblet cells so abundant in the large intestine?
Site of formation of feces and absorption of water so we need mucus to prevent abrasion of cells and protect wall from acids and bacteria
digestion
chemical breakdown of large food molecules into smaller molecules that are easily absorbed into the body (Enzymes speed up these reactions)
digestive enzymes
- secreted by accessory glands
- catalyze chemical reactions.
- binds with food molecules, enzymes speed up the digestive reactions, allowing them to occur at normal body temperature and pH.
- If enzymes not present, these hydrolysis reactions would occur only at very high temperatures (such as 100°C) or in very acidic conditions.
Carbohydrate Digestion
NEEDS:
• Salivary Amylase: enzyme in mouth present in saliva (hydrolysis of starches into sugars)
• starch (a polysaccharide) is broken down into sugars
• Benedict’s searches for simple sugars (digested starch)
• Iodine searches for complex sugars (polysaccharides pre-digestion)
Protein Digestion
NEEDS:
• Pepsin: enzyme (secreted by chief cells of stomach)
• Acidic pH: pepsin functions most effectively in an acidic pH of 1.5 to 2.0)
• stomach parietal cells secrete HCL for optimum pH
Lipid Digestion
NEEDS:
• Bile Salts: emulsify lipids (Produced by liver)
• Pancreatic Lipase: enzyme turns lipids –> fatty acids + glycerol. (Produced by pancreas)
• Litmus cream: colour indicator (turns pink in acids)
Visceral smooth muscle
- propulsive force for moving foods along the digestive tract
- Exhibits Automaticity + Rhythmicity (responsible for peristalsis)
role of the autonomic nervous system in visceral smooth muscle
- regulate the rate and the relative strength of contraction
* regulate the smooth muscke activity of the gut, the effects are oppostie to cardiac muscle
Experiment: Effects of autonomic nervous system on smooth muscle activity
- epinephrine: decrease smooth muscle activity of small intestine.
- acetylcholine: increase smooth muscle activity of small intestine
Automaticity
ability to contract without nervous stimulation
Rhythmicity
regular pattern of repeated contractions, results from the presence of specialized fibers
