Human anat unit 2

Digestive system

The organ system that breaks food into molecules the body can use and removes solid waste

Digestion

Breaking food down

2 types of digestion

Mechanical- chewing and chemical(hydrolysis)-enzymes and secretions break macromolecules into smaller monomers

Absorption

Transporting nutrients - moving digested molecules from the GI tract into blood or lymph for transport to cells

Alimentary canal (GI tract)

Where food tevels through and makes contact with one long tube

Components of the alimentary tract

Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus

Accessory organs

Organs that help digestion by adding secretion, but food does not pass through them.

Components of accessory organs

Salivary glands, pancreas, liver, gallbladder

Layers of the alimentary canal wall

1. mucosa

2. submucosa

3. muscularis

4. serosa

Mucosa

Innermost layer responsible for

protection, secretion, and absorption and is a mucus membrane

Protection

Provides a barrier from enzymes acids and microbes

secretion

a mucus and enzymes

absorption

of nutrients and water

type of epithelium tissue in the mucosa

Simple columnar epithilium- a common lining tissue for absorption and secretion

Goblet cells

Secrete mucus for protection of the epithelium and lubrication

Lamina propria

Underlying connective and smooth muscle tissue

3 structures allow for increased surface area

Circular fold aka plicae circulares, mucosal and submucosal transverse folds.

Villi

Finger like projections of mucosa

Microvilli

AKA brush border- microscopic on epithelial cells

Submucosa

a “supply and control” layer supports the mucosa by nourishing surrounding tissues and transporting absorbed materials. Has loose connective tissue and submucosal glands

Blood vessels

Carry away absorbed lipids

Nerves

help regulate secretion and movement

Lymphatic vessels

carry away absorbed lipids

Nerves

Helps regulate secretion and movement

Enteric nervous system

Innervation of the submucosa GI activity is strongly influenced by the automatic nervous system

Parasympathetic nervous system

Promotes digestive activity, increased mobility and secretion

Sympathetic nervous system

Inhibits digestive activity, decreased motility and secretion

Muscularis

Is the muscular layer which allows for mixing and propulsive wave like movements, histology-2 layers of smooth muscle(circular inner, longitudinal outer)

Peristalsis

Wave like propulsion that moves contents forward(caudally) through the tube, primarily in esophagus

Segmentation

Back and forth contractions that mix and segment contents, increasing contact with mucosa and optimizing absorption, primarily in the intestine

Serosa

Is the protective outer covering that secretes serous fluid for lubrication. Histology-serous membrane= simple squamous epithelium and loose connective tissue.

Oral cavity

Mechanical digestion begins here with chewing food called mastication

bolus

a small rounded mass of chewed food mixed with saliva that is ready to be swallowed

oral vestibule

space between yout teeth, gums, lips, and cheeks.

labia (oris)

regulate speech and food containment, moved by orbicularis oris

teeth

designed to tear and grind food ingula(tongue), masseter, and buccinator muscles move food around oral cavity and put it to esophagus.

Hard palate, maxilla and palatine

Hard ridge, separates oral/ navel cavities, helps form bolus, sound production.

soft palate and uvula muscle portion

control air flow to nasal cavity, produce certain speech sounds, block food from entering nasopharynx

Premolar (bicuspids) and molars

Flatter crown for grinding and crushing food

Incisors and cannies

pointed/sharp crowns for tearing

Crown

Portion of tooth above gingiva (gums)

Root

Portion of tooth embedded in gums

dentin

Bone like tissue surrounding the pulp cavity

enamel

Crystalline form of calcium phosphate(hard), protects the crown

Pulp cavity

Connective tissue and blood vessels

Cementum

Modified bone that covers the root and hold teeth in place (forms synarthrotic joints)

Saliva

A complex fluid, drains via ducts to opening in the mouth. Includes water, enzymes, mucus, minerals, and antibodies

Enzymes

Begin digestion of macromolecules

Mucus

Lubricates food, assists in swallowing

Buffering agents

maintain PH by neutralizing acids

Serous fluid

Thin and watery, enzyme rich parotid and submandibular glands- secrete amylase (begins hydrolysis of carbs like starch into glucose)

VonEber’s gland

Secrete lingual lipase (begins some fat digestion)

Mucous fluid

Thicker protein rich

Sublingual glands

Secrete mucin

Parasympathetic

Maintains resting saliva flow, increase serous saliva production

sympathetic

Reduces serous saliva flow during stress, increases mucin production, reflective stimuli: sight, smell ,taste.

Nasopharynx

Superior region for breathing and speech

Oropharynx

Inferior region connecting to esophagus and larynx

Upper esophageal sphincter

Controls food entry from pharynx into the esophgus

esophagus hiatus

Opening in the diaphragm where the esophagus enters abdomen

Lower esophagus sphincter

Relaxes to let food enter the stomach and prevents acid reflux

Phase 1: oral phase

From mouth to pharynx tongue presses the bolus against the hard palate then pushes it to the oropharynx - volunatary

Phase 2: pharyngeal phase

through the pharynx into the esophagus, soft palate and hyoid elevate to close the nasopharynx and raise larynx, epiglottis fold over the larynx and the vocal cords to the airway as bolus is pushed downward - involuntary

Phase 3: esophageal phase

from pharynx to stomach, relaxes as the bolus enters esophagus, peristalsis moves bolus downward, LES relaxes, bolus enters stomach and the LES closes

Mumps

Viral causing inflammation of the parotid glands

GERD (gastroesophageal reflux disorder)

Reflux caused by incomplete closure of LES

Lips/cheeks

Confine food for even chewing

Tongue

Manipulates food ans shapes the bolus

Salivary glands

Lubricates food and initiate chemical digestion

Esophagus

Propels bolus via peristalsis

Chyme

thick, acidic, semi fluid mixture of partially digested food and gastric secretions *pyloric sphincter regulates when chyme leaves the stomach. Bolus to churning to gastric juice to chyme.

Mechanical digestion

3 layers of smooth muscle help to shorten, constrict, and twist the stomach wall in order to churn the food. Longitudinal, circular, and oblique fibers.

Rugae

Folds in the stomach that allow the stomach to expand as it fills

HCI

Made by parietal cells, creates acidic environment, helps activate pepsinogen

Pepsin

Made by chief cells, pepsinogen activated into pepsin (active form of enzyme) by HCI

Begins protein digestion by breaking proteins into smaller peptides

Mucus

Made by mucous cells in glandular epithelium protects stomach epithelial lining from acidic environment

Accessory structures

Secretions into the small intestines

Liver

Produces bile (emulsifies fats) , processes absorbed nutrients

Gallbladder

Stores and concentrates bile, bile ducts drain

Pancreas

Produces digestive enzymes and bicarbonate

Enzymes

Amylase to carbohydrates

lipase to fats

proteases to proteins

The small intestine

Final chemical digestion-duodenum completes most enzymatic digestion of carbohydrates, proteins, and lipids. Nutrient absorbed:jejunum. Moves and mixes- segmentation and peristalsis

cecum

Receives material from ileum

Appendix

Lymphoid tissue, immune function

Large intestine

Water absorption and electrolyte balance, mucus secretion, form and compacts feces, intestinal flora synthesize vitamins.

Major regions

Cecum to appendix to colon to rectum *no digestive enzymes produced here

Internal sphincter

Smooth muscle, involuntary

External sphincter

Skeletal muscle, vouluntary