Digestive System

Human Anatomy and Physiology Lecture

mechanical digestion

• breakdown of solid components using the teeth

• breakdown by muscle action

• breakdown of food from large to small

chemical digestion

• digestion that starts the breakdown of carbohydrates

• breakdown by enzyme

• the breakdown of food from small to simplest (building blocks)

alimentary canal organs

• mouth

• pharynx

• esophagus

• stomach

• small & large intestine

• anal canal

accessory organs

• salivary glands

• liver

• gallbladder

• pancreas

• food does not necessarily pass through but they are the juice producers and secreters

digestive system

• absorbs nutrients, mostly occurs in the small intestine

• defecation/elimination in the large intestine

alimentary canal

muscular tube or tract that food passes through mouth to anal canal

4 layers of the Alimentary Canal

• Mucosa

• Submucosa

• Muscularis mucosa

• Serosa

Mucosa

• innermost layer that lines the tube

• vary depending on organ

• secretion and absorption

Submucosa

• Mucus glands, blood vessels, mainly made of connective tissue

• nerve innervation

Muscularis Mucosa

• 2 layers in most organs

• 3 layers in stomach

• longitudinal that runs along the alimentary canal

• circular muscle that surrounds the canal that helps wave like contractions to move food

Serosa

• visceral peritoneum

Peristalsis

• wavelike contractions which push food from esophagus to anus

• muscular contraction begins when you swallow

Mixing

• stomach has 3 muscle layers for this

Peristalsis and Mixing

• the two main actions of food movement through the alimentary canal

effects of Parasympathetic impulses on alimentary canal

• increases activity and movement

• housekeeping

effects of Sympathetic impulses on alimentary canal

• decreases activity and movement

Stratified Squamous

• type of epithelium on mouth

Tounge

• muscle, mechanical digestion

Frenulum and Hyoid Bone

• anchor

Hard and Soft Palate

• divider between nasal cavity and oral cavity

Uvula

• part of soft palate

• doesnt do much other than block throat opening kinda

Lingual Tonsils

• posterior to tongue

Palatine Tonsils

• on either side of uvula

Pharyngeal Tonsils

• above soft palatine in nasopharynx

Lingual, palatine, Pharyngeal Tonsils

• lymphatic tissue that play important roles in immunity

Incisors

• biting large pieces of food

Cuspids (Canines)

• tearing or grasping

Premolars and Molars

• grinding

Permanent/Secondary Teeth

• 32 (2 incisors, 1 canine, 2 premolars, 3 molars)

Odontoclasts

• located into root of baby teeth that dissolve and wear away baby teeth

Crown

• above gum line

root

• below gum line

enamel

• covers crown

• Ca salts

• very hard

• not replaceable

Dentin

• bone like

• living cellular tissue

Pulp Cavity

• blood vessels

• nerves

• Connective Tissue

• surrounded by dentin

Root Canal

• blood vessels

• nerves enter here

Cementum

• encloses root

• thin

Periodontal ligament

• surrounds cementum

• collagenous

• anchors tooth to bone

Parotid, Submandibular, Sublingual Glands

• scattered throughout the mucosa of the tongue palate, and cheeks

Parotid Glands

• Secrete clear watery, serous fluid

• Rich in salivary amylase

Submandibular Glands

• Secrete primarily serous fluid and some mucus

Sublingual Glands

• Secret primarily mucus

Saliva

• lubricate food (mucus from mucous cells)

• dissolve food for taste

• begins digestion of carbohydrates

• Enzyme- Amylase

helps maintain oral health

bicarbonate ions role in saliva

3 major regions of the pharynx

• Nasopharynx

• Oropharynx

• laryngopharynx

Nasopharynx

• air

Oropharynx

• food

Laryngopharynx

• stomach

Bolus

• lubricated ball of food

Esophageal Hiatus

• gives passage to the oesophagus as well as the anterior and posterior vagal trunk

Lower Esophageal Sphincter

• Regulates food passage into stomach

• smooth muscle ring at opening that contracts or relaxes for food movement

Cardiac Region

• stomach

• near esophageal opening

• cardiac sphincter muscle controls entry of food

Funic Region

• stomach

• hump above cardiac

• temporary storage area

Body

• stomach

• main

Pyloric Region

• stomach

• lower

• narrows as it become pyloric canal that leads to pyloric sphincter

Pyloric Sphincter

• controls movement into small intestine (gastric emptying)

rugae

• folding inside the stomach

Gastric Glands

• microscopic glands in the stomachs mucosa which secrete gastric juice

Mucus Cells

• near neck

• secrete mucus that protects the stomach from pepsin

Chief Cells

• secrete enzymes

Parietal Cells

• secrete HCl (needed to convert pepsinogen to pepsin)

• secrete intrinsic factor required for B12 absorption in small intestine

Pepsinogen

• converts to pepsin

Pepsin

• most important enzyme that breaks down proteins

Gastrin

• hormone

• sight, taste, smell of food triggers parasympathetic reflexes

• gastric juice secreted

• released by stomach cells when food enters stomach

• functions to increase gastric juice secretion

Cholecystokinin

• hormone

• released by small intestine when fat enters it

• functions to slow gastric juice secretion

Somatostatin

• hormone

• released by small intestine in response to presence of lots of food there

• functions to inhibit acid secretion by stomach

Enterogastric Reflex

• relaxes the stomach in preparation for food

Enzymes of Pancreatic Juice

• Amylase

• Lipase

• Trypsin

• Chymotrypsin

• Carboxypeptidase

• Nucleases

Pancreatic Amylase

• digestion of carbohydrates

• starch to disaccharides

Pancreatic Lipase

• digestion of lipids (fats)

• fats to fatty acids and monoglycerides

Trypsin

• digestion of proteins

• always has to be activated

• activated by enterokinase from small intestine

Chymotrypsin

• digestion of proteins

• activated by trypsin

Carboxypeptides

• digestion of proteins

• activated by trypsin

Nucleases

• digestion of nucleic acids

• nucleic acids to nucleotides

Secretin

• peptide hormone released when acidic chyme enters small intestine

• triggers pancreatic juice high in bicarbonate ion that neutralize chyme

Cholecystokinin

• released when fats enter small intestine

• triggers secretion of pancreatic juice high in digestive enzymes (activates serous cells)

Functions of Liver

• carbohydrate, lipid, and protein metabolism

• storage

• blood filtering

• detoxification

• secretion of bile

blood flow through liver

• deoxygenated, nutrient-rich blood from digestive tract enters the liver via the hepatic portal vein. It branches to each lobule, and the blood flows into the hepatic sinusoids emptying into the central vein in the center of each lobule. The blood is then carried to the inferior vena cava.

Bile

• yellowish green liquid

pathway of bile from bile canal to small intestine

• produced in hepatic cells, the travels through bile canaliculi which unite to flow into bile duct.

• Bile ducts join together to form the hepatic duct which leaves liver

Gallbladder

• function to store, concentrate, and release bile

Cystic Duct

• joins the hepatic duct from liver to form the common bile duct that leads to the sphincter of the Oddi

Gallstones formation

• when cholesterol comes out of solution in gallbladder

Cholecystokinin affect

• makes gallbladder release when stimulated to be secreted when proteins/fats enter small intestine

Duodenum

• 1st section of small intestine

• chemical digestion begins

Jejenum

• 2nd section of small intestine

• longest

Ileum

• connects small intestine to large intestine

• absorption should be finished

Plicae Circulares

• mucosa with finger like projections (villi)

• small intestine

Lacteal

• fat absorption

• small intestine

Intestinal glands/crypt of Lieberkun

• digestive enzymes

• small intestine

significance of villi

• absorption

Enzymes of intestinal juice

• protease

• lipase

• carb digestion

• enterokinase

protease

• enzyme of intestinal juice

• breakdown proteins

Lipase

• enzyme of intestinal juice

• breakdown fats

Carb digestion

• enzyme of intestinal juice

• breakdown sugars

Enterokinase

• enzyme of intestinal juice

• Activate protease enzyme from pancreas

Mesentary

• big flap of fat that covers and protects the small and large intestine (gut)

Large Intestine

• covered by a large extension of peritoneum that drapes downward and covers abdominal organ insulating them and protecting them

• also contains collections of lymphatic tissue for protection

Large intestine functions

• water reabsorption

• electrolyte absorption

• vitamin synthesis

• bacterial action

• storage

• peristalsis- movement

small intestine

• nothing is absorbed until it gets here