Digestive System

The teeth lie in sockets called __________ in the gum-covered margins of the mandible and maxilla.

(alveolar processes) , they house the teeth

Six major processes of digestion

1) Ingestion- taking food into the digestive tract (eating) 2) Secretion- release of secretions (fluids) into the digestive tract 3) Mixing and Propulsion- Mixing is achieved via muscular contractions (smooth muscle) muscle contraction is important for blending or changing composition/texture. Mixing is important to blend food with digestive fluids which contain enzymes important for breakdown. Propulsion is achieved via muscular contractions. Propulsion moves food through GI tract. 4) Digestion- mechanical digestion (muscle contraction and physical force, I.E. teeth) vs chemical digestion(chemicals and enzymes) 5) Absorption- passage of digested end products, vitamins, minerals, and water from lumen of GI to the blood or lymph. Small intestine allows our body to bring nutrients that are ingested into the blood. 6) Defecation- eliminates indigestible substances from the body via the anus in form of feces

Phases of swallowing/deglutition

1) voluntary stage; bolus passed into oropharynx 2)involuntary; pharyngeal stage, bolus passed from pharynx into esophagus 3)involuntary; esophageal stage

lesser omentum

Anterior fold in serosa of stomach/duodenum Suspends stomach and duodenum from the liver Pathway for blood vessels entering the liver

Mesencolon

Binds transverse and sigmoid colon to posterior abdominal wall Holds intestines loosely in place

The tongue also mixes food with saliva, forming it into a compact mass called a _______. The tongue initiates swallowing by pushing the bolus posteriorly into the pharynx.

Bolus

Phases of Digestion; voluntary vs involuntary

Buccal Phase - occurs in the mouth and is voluntary. It ends when the food bolus leaves the mouth and enters the oropharynx. Pharyngeal Phase - involuntary; begins when the bolus passes into the oropharynx Esophageal Phase - involuntary; begins when the bolus passes into the esophgus

ANS; autonomic nervous system

Can sometimes override ENS. Sympathetic- decrease GI secretion/mobility Parasympathetic- increase digestive activities. GI secretion/motility

Important Anatomical Structures of the Stomach

Cardia - portion of stomach that connects to the esophagus; location of the cardiac or lower esophageal sphincter, made of smooth muscle Fundus - dome-shaped portion of stomach that bulges superolaterally to the cardia Body - midportion of stomach, pouch Pylorus - inferior portion of stomach that narrows; connects to the duodenum; contains the pyloric sphincter, made of smooth muscle Greater Curvature - convex lateral surface Lesser Curvature - concave medial surface Rugae - folds of the mucosa; expand to help accomodate volume in the stomach

GERD occurs when

Cardiac sphincter (lower esophageal sphincter) fails to close adequately after food has entered stomach.

The mouth is made up of what structures?

Cheeks (NKSS epithelium), hard and soft palate, tongue

Mechanical Digestion:

Churning, which is achieved through contraction and relaxation of the smooth muscle in the wall of the stomach mechanically digests food in the stomach, converting it into chyme.

Anatomical features in the tooth

Crown - covered in enamel, visible portion, when people brush teeth they are brushing the crown. Root - portion of tooth embedded in process. Neck - connects crown to root, constricted junction of crown and root near the gum tissue. Cementum - calcified connective tissue that covers the outer surface of the root and attaches the tooth to periodontal ligament Periodontal Ligament - anchors tooth in alveolar process Dentin - protein-rich material that forms bulk of tooth; bone-like, consists of calcified connective tissue gives tooth basic shape and rigidity. 70% calcium salt. Enamel- covers the dentin of the crown. Consists primarily of calcium phosphate (CaPO4) and calcium carbonate (CaCO3). 95% calcium salt. Hardest substance in body. Protects tooth from wear and tear of chewing, protects against acids that can dissolve dentin. Pulp - blood vessels and nerve fibers inside tooth cavity Pulp Cavity - hollow region of tooth that contains pulp, lies within crown. Root Canal - extension of pulp cavity into root Apical Forament - opening in root canal that allows blood vessels and nerves to enter pulp cavity

Human Dentition consists of two sets of teeth

Deciduous Teeth (primary teeth) (20) (baby teeth) Permanent Teeth (32) *KNOW DIFFERENCE BWTEEN PERMANENT AND BABY TEETH*

Then chyme will be introduced into the _______.

Duodenum (1st part of small intestine).

Tooth structure

Each tooth has three major regions: crown, neck and root.

The__________ is the in-house nerve supply of the GI tract.

Enteric Nervous System (ENS)

T or F; are liver, gallbladder, and pancreas apart of GI tract?

False; they just send secretions to GI tract. They never come in contact with food

Mesentery

Fan shaped double layer Binds jejunem/ileum to posterior abdominal wall

This otherwise smooth lining is dotted with millions of deep _________, which lead into tubular ________ that produce the stomach secretion called ____________.

Gastric pits Gastric glands gastric juice.

Alveolar processes are covered by ____________?

Gingivae(gums/gum tissue)

Often the peritoneum is such a large serous membrane that it is referred to in folds;

Greater Omentum, Lesser Omentum, Falciform Ligament, Mesentery and Mesocolon

Teeth are classified according to their shape and function.

Incisors - adapted for cutting or nipping off pieces off food Canines - tear and pierce Premolars - grinding and crushing Molars - grinding and crushing

The MUCOSA of GI (deepest layer)

Innermost layer Moist, epithelial tissue Lamina propria, muscularis mucosae . (Most of the GI is simple columnar epithelia. The exceptions are mouth, esophagus, and anus. Major functions: SECRETE mucus, digestive enzymes, and hormones; ABSORB end products of digestion into blood; PROTECT against infections disease. (The mucosa in a particular region of the GI may perform one or all three of these functions.

Muscles of the tongue

Intrinsic - are confined in the tongue and are not attached to bone. Their muscle fibers allow tongue to change shape (but not position). Intrinsic muscles are important for speech. Extrinsic - extend to tongue from their points of origin on bones of the skull or soft palate. They alter position of the tongue. (protrude, retract, side to side), to maneuver food for chewing, shape food into rounded mass, and force food to back of mouth for swallowing. Hyoglossus Styloglossus Genioglossus

Explain chemical digestion

Involves enzymes and other fluids such as HCl in the stomach and Bile, which is MADE in the liver and STORED in the gallbladder and FUNCTIONAL in the small intestine!

Even though lingual lipase is released in oral cavity, it will NOT begin to digest _____ or _____ until it gets to stomach.

Lipid or fat

GI tract (alimentary canal) passageway:

Mouth, oral cavity, oropharyx, laryngopharynx, esophagus, stomach, small intestine, large intestine, to rectum and anus

Histology of the Esophagus

Mucosa - Nonkeratinized stratified squamous epithelium Submucosa - Areolar connective tissue Muscularis - Skeletal muscle, blend of skeletal and smooth, smooth muscle Adventitia - Areolar connective tissue and fibrous connective tissue, connects esophaguses to surrounding structures

Histology of the Stomach

Mucosa - simple columnar epithelium, gastric glands line gastric pits, mucus neck cells, chief cells, parietal cells, G cells Submucosa - areolar connective tissue Muscularis - oblique, circular, and longitudinal layers (different from other parts of the GI tract); this added oblique layer allows stomach to mix, churn, and move food as well as pummel the food physically breaking it down into smaller fragments and pushing it into the small intestine. Serosa - visceral peritoneum.

Histology of the Pharyngeal Wall

Mucosa of the oropharynx and laryngopharynx: stratified squamous epithelium The external muscle layer consists of two skeletal muscle layers. The cells of the inner layer run longitudinally. Those of the outer layer, the pharyngeal constrictor muscles, encircle the wall like three stacked fists. Contraction of these muscles propel food into the esophagus below.

Types of Gland Cells in the Stomach

Mucous Neck Cells - scattered in neck and more basal regions of gland; produce mucus Parietal Cells - release hydrochloric acid (HCl) and intrinsic factor. Exchange hydrogen and chloride ions to collect and make HCl. HCl makes the stomach contents extremely acidic, a condition necessary for activation of pepsin (protein-digesting enzyme) and lipase (triglyceride-digesting enzyme). Intrinsic factor is required for absorption of vitamin B12 *lack of leads to pernicious anemia.* Chief Cells - release the enzyme pepsinogen and gastric lipase. Pepsinogen is inactive; HCl converts pepsinogen into pepsin, the active form of the enzyme. G cells - release the hormone gastrin

We begin to digest starch in the ______ cavity.

Oral

Chemical digestion in the small intestine depends on activities of the ______, ________, and ________.

Pancreas, liver, gallbladder.

Most saliva is produced by the major salivary glands that lie outside the oral cavity and empty their secretions into it.

Parotid - large, roughly triangular gland that lies anterior to ear between masseter muscle and skin (watery fluid with salivary amylase) Sublingual - small almond shaped gland under the tongue (mucus, small amount of amylase) Submandibular - located at the base of the mandible, medial and partly inferior to mandible ( amylase with mucus)

Sockets are lined with __________

Periodontal Ligament, consist of dense fibrous connective tissue that anchors the teeth to docket walls and acts as shock absorber when chewing.

Most digestive organs reside in the abdominopelvic cavity. The __________ of the abdominopelvic cavity is the most extensive of these membranes

Peritoneum

The esophagus lays:

Posterior to trachea and anterior to vertebral column, it is a collapsible tube.*

Chemical Digestion:

Protein digestion begins with the release of pepsinogen from chief cells. Pepsin, the active form of the enzyme will begin to digest protein Lipid digestion begins with the release of gastric lipase from chief cells. Gastric lipase will begin to digest triglycerides in the stomach.

_______ or _______ will not begin digesting until we reach the stomach.

Protein or lipid

As chyme passes through stomach to small intestine, it moves through __________ sphincter.

Pyloric

The pancreas lies __________.

Retroperitoneal. Consist of a head, body, and tail.

The ENS is staffed by enteric neurons that communicate widely with one another to regulate digestive system activity. These semiautonomous enteric neurons constitute the bulk of two major nerve plexuses found in the walls of the GI tract; *brain in the gut

SUBMUCOSAL PLEXUS - found within the submucosa (important for sending impulses to glandular bodies embedded in the submucosa; stimulates secretion MYENTERIC PLEXUS - found between the two layers of the muscularis; important for GI motility

Composition of Saliva

Saliva is mostly water. It contains electrolytes (Na, K, Cl), digestive enzymes (lingual lipase, salivary amylase), proteins, dissolved gases, and metabolic wastes.

Control of Salivation

Salivation is controlled primarily by the parasympathetic division of the Autonomic Nervous System (ANS). When we ingest food, chemoreceptors and mechanoreceptors in mouth send signals to the salivatory nuclei in the brain stem (pons and medulla). As a result, parasympathetic nervous system activity increases. Impulses sent via motor fibers in facial and glossopharyngeal nerves dramatically increase the output of watery, enzyme-rich saliva. Sometimes just the sight or smell of food is enough to get saliva flowing. In contrast, sympathetic division causes release of thick, mucus rich saliva. Strong activation of the sympathetic division constricts blood vessels serving the salivary glands and almost completely inhibits saliva release, causing a dry mouth (xerostomia). Dehydraion also inhibits salivation because low blood volume reduces filtration pressure at capillary beds.

Function of the esphagus

Secrete mucus, transports food into stomach. No chemical or mechanical digestion here.

Gasterointernal Reflex Pathway

Sensory receptor-> sensory neurons -> synapse with neurons in ENS, ANS, and/or CNS. -activation or inhibition of GI glands/smooth muscle

falciform ligament

Sickle shaped, attaches liver to anterior abdominal wall and diaphragm Only fold that we see have an association with anterior abdominal wall!

The tongue is composed of what kind of muscle fibers?

Skeletal muscle fibers

We will NOT have chemical digestion of starch in the _______.

Stomach, once pH drops.

Anatomical Structures to Note: Lips (labia) - superior lip (labial fold) and inferior lip (labial fold); muscle found in fleshy lips - orbicularis oris Cheek - contains buccinator muscles which help to compress cheek and trap food between teeth Oral Vestibule - area bounded externally by cheeks/lips and internally by gums/teeth, space between lip and gum Labial Frenulum - median fold that joins lips to gum (superior labial frenulum, inferior labial frenulum) Hard Palate - formed by maxillae and palatine bones; rigid surface against which tongue forces food during chewing, made of bone tissue (maxillae and palatine) Soft Palate - made up of fibromuscular tissue; mobile; rises reflexively during swallowing to close off the nasopharynx (uvula associated, during swallowing soft palate and uvula draw superiorly and close of nasopharynx so food/liquid does not enter this cavity Palatoglossal arches - anchors soft palate to tongue Palatopharyngealarches - anchors the soft palate to the wall of the oropharynx, extends to side of pharynx Fauces - arched area of oropharynx; passageway or opening between oral cavity and orophrarynx Uvula - finger-like projection extending from free edge of soft palate

The mouth is also called the oral cavity (or buccal cavity). The walls of the mouth are lined with a thick stratified nonkeratinized squamous epithelium which withstands considerable friction. (The epithelium on the gums, hard palate and dorsum of the tongue is slightly keratinized for extra protection against abrasion during eating.)

tongue papillae

The superior tongue surface has papillae. Filiform Papillae - roughen tongue surface and provide friction for manipulating foods; smallest of the papillae; most numerous Fungiform Papillae - scattered over tongue surface Vallate Papillae - located in a V-shaped row at back of tongue Foliate Papillae - lateral aspect of tongue The fungiform, vallate, and foliate contain taste buds - important for sense of taste (gustation).

The esophagus has two sphincters that help with regulating the passage of food (bolus).

Upper esophageal sphincter - band of skeletal muscle that is normally contracted; it relaxes during swallowing Lower esophageal sphincter (cardiac sphincter) - band of smooth muscle that is normally contracted; involuntary action - relaxes during swallowing

Which nerve supplies most of GI?

Vagus, cranial nerve number 10

The organs of the digestive system fall into two main groups:

alimentary canal (GI tract), and accessory digestive organs

They produce a cloudy, protective two-layer coat of __________________ in which the surface layer consists of viscous, insoluble mucus that traps a layer of bicarbonate-rich fluid beneath it.

alkaline mucus

Explain mechanical digestion

application of physical force to break down food particles into smaller molecules. Involves chewing, mixing food with saliva by the tongue, churning food in the stomach, and segmentation in the small intestine.

To send food on its way from the mouth, it is first compacted by the tongue into a ________.

bolus (A bolus is a rounded mass of chewed up food and saliva.)

After a meal, peristalsis begins near the ________, where it produces gentle rippling movements of thin stomach wall

cardiac sphincter

The esophagus is a muscular tube and is ______________ when not involved in food propulsion. As food moves through the laryngopharynx, it is routed in to the esophagus posteriorly because the epiglottis closes off the larynx to incoming food.

collapsed

The tongue has a median septum of ____________ and each half contains identical muscle groups.

connective tissue

Visceral peritoneum

covers the external surfaces of most digestive organs and is continuous with the parietal peritoneum.

Swallowing is also called ___________.

deglutition

alimentary canal (GI tract)

digests food and absorbs digested fragments through its lining in the blood. Organs include: Mouth, Pharynx, Esophagus, Stomach, Small Intestine, and Large Intestine (LI leads to terminus; the anus) Food material in this tube is technically outside the body because the canal is open to the external environment at both ends

retroperitoneal organs include;

duodenum (1st part of small intestine), pancreas, kidneys, ascending colon, and descending colon, cecum, appendix and rectum.

As chyme enters the duodenum, receptors in its wall respond to chemical signals and stretch, initiating the ____________.

enterogastric reflex

The esophagus pierces the diaphragm at the ______________ to enter the abdomen (stomach).

esophageal hiatus

Since the diaphragm no longer reinforces the sphincter, gastric juice may enter the esophagus, particularly when lying down. If the episodes are frequent and prolonged, ______________ ulcers may result.

esophagitis, and esophageal ulcers

Heartburn, the first symptom of GERD, is the burning, radiating substernal pain that occurs when stomach acid regurgitates into the ___________.

esophagus

The pancreas contains endocrine and exocrine parts. The __________ part of the pancreas produces pancreatic juice.

exocrine

The SUBMUCOSA of GI

external to mucosa made up of areolar connective tissue (rich with blood vessels, lymphatic vessels and nerve fibers) -submucosal plexus, glands, lymphatic tissue

The MUSCULARIS of GI

external to the submucosa Smooth muscle (circular and longitudinal) Skeletal muscle responsible for muscle contractions along the length of the GI (muscle contractions include: peristalsis, churning in the stomach, segmentations in the small intestine, haustral churning in the large intestine) typically made up of two layers: inner circular layer and outer longitudinal layer (exception is the stomach - which as an added oblique layer) in several locations along the tract, the circular layer thickens, forming sphincters (sphincters act as valves to control passage of material from one region to the next and prevent backflow

Heartburn is also common in those with a ___________, a structure abnormality in which the superior part of the stomach protrudes slightly above the diaphragm

hiatal hernia

greater omentum

largest peritoneal fold, "fatty apron", double sheet that folds back over itself, many lymph nodes located here which contain or combat infections in GI TRACT.

Parietal peritoneum -

lines the body wall

A fold of mucosa called the _________ secures the tongue to the floor of the mouth and limits its posterior movements.

lingual frenulum

Children born with an extremely short_________ are often referred to as "tongue tied". This congenital condition is called ______________. It can be corrected surgically by snipping the frenulum.

lingual frenulum, ankyloglossia

The cells forming the walls of the gastric pits are primarily ______________, but those composing the gastric glands vary in different stomach regions.

mucous cells

intraperitoneal

organs that lie within the peritoneum are characterized as intraperitoneal or peritoneal organs

The SEROSA of GI

outermost layer in most GI tract organs, it is formed of areolarconnective tissue (in the esophagus it is replaced by adventitia) retroperitonal organs have both an adventitia (on the side facing the dorsal wall) and serosa (side facing the peritoneal cavity)

The __________ is important to the digestive process because it produces enzymes that break down all categories of foodstuffs. The pancreas is soft, tadpole-shaped gland that extends across the abdomen from its tail to its head, which is encircled by the C-shaped duodenum.

pancreas

Endocrine cells in pancreas

pancreatic islets (islets of Langerhans) which regulate blood sugar

As contractions approach the ______, where the stomach musculature is thicker, they become much more powerful.

pylorus

The lining epithelium of the stomach mucosa is a ________________, composed entirely of mucous cells

simple columnar epithelium

peritoneal cavity

slit-like space containing fluid secreted by the serous membranes. Where fluid collects. ( between visceral/parietal) *when irritation to peritoneum and excess fluid that collects in pericardial space, sometimes has to be drained, it's called ascites*

Below the esophagus, the GI tract expands to form the __________, where food is converted to a fluid-like substance known as ________.

stomach, chyme

Propulsion includes

swallowing (voluntarily) and peristalsis (involuntary) Peristalsis is the major means of propulsion and involves alternating waves of contraction and relaxation of muscles in the organ walls

accessory digestive organs include

teeth, tongue, salivary glands, liver, gallbladder, and pancreas The accessory digestive glands produce a variety of secretions that help to digest food

retroperitoneal

term applied to those organs that lie behind the peritoneum

The stomach lies in the ________________________, nearly hidden by liver and diaphragm.

upper left quadrant of the peritoneal cavity

acinar cells of pancreas

what cells produce enzyme rich juice used for digestion (exocrine product), epithelial cells , send their secretions into pancreatic duct.