Digestive+System+Anatomy

__THE DIGESTIVE SYSTEM __ __ PROCESSES OF THE BODY RELATED TO THE DIGESTIVE SYSTEM __


 * Digestion = Breakdown of ingested food


 * Absorption of nutrients into the blood


 * Assimilation of nutrients into cells


 * Cellular Respiration : A.Liberation of energy (ATP) from nutrients

CELLULAR ACTIVITIES
 * Constructive (Anabolic) and (Catabolic) degradative cellular activities


 * Defaecation

__FUNCTIONS OF THE DIGESTIVE SYSTEM__ ** Ingestion **—placing food into the mouth
 * Propulsion **—moving foods from one region of the digestive system to another
 * Peristalsis—alternating waves of contraction and relaxation that squeezes food along the GI tract


 * Segmentation—moving materials back and forth to aid with mixing in the small intestine

Food breakdown as mechanical digestion


 * Examples:**


 * 1.Mixing food in the mouth by the tongue


 * 2.Churning food in the stomach


 * 3.Segmentation in the small intestine

Mechanical digestion prepares food for further degradation by enzymes

Food breakdown as **chemical digestion**

Enzymes break down food molecules into their building blocks

Each major food group uses different enzymes


 * 1.Carbohydrates are broken to simple sugars


 * 2.Proteins are broken to amino acids


 * 3.Fats are broken to fatty acids and alcohols

Absorption

A.End products of digestion are absorbed in the blood or lymph

B.Food must enter mucosal cells and then into blood or lymph capillaries


 * Defecation **

Elimination of indigestible substances from the GI tract in the form of feces

__ORGANS OF THE DIGESTIVE SYSTEM __ __IN PROGRESSSS__ __ Two main groups __


 * A.Alimentary canal ̵ continuous coiled hollow tube
 * B.Accessory digestive organs



__ Digestive Tract/Alimentary Canal __
 * A.Mouth
 * B.Pharynx
 * C.Esophagus
 * D.Stomach
 * E.Small intestine
 * F.Large intestine
 * G.Anus

__ THE ORAL CAVITY/BUCCAL CAVITY __
 * Lips ̵ protect the anterior opening
 * [[image:craniumcommander/tonsils.jpg width="382" height="294" align="right"]]

> Hard palate ̵ forms the anterior roof
 * Cheeks ̵ form the lateral walls
 * Cheeks ̵ form the lateral walls
 * Soft palate ̵ forms the posterior roof
 * Uvula ̵ fleshy projection of the soft palate
 * Vestibule ̵ space between lips and teeth and gums internally
 * Oral cavity ̵ area contained by the teeth
 * Tongue ̵ attached at hyoid and styloid processes of the skull, and by the lingual frenulum
 * Vestibule ̵ space between lips and teeth and gums internally
 * Oral cavity ̵ area contained by the teeth
 * Tongue ̵ attached at hyoid and styloid processes of the skull, and by the lingual frenulum
 * Tongue ̵ attached at hyoid and styloid processes of the skull, and by the lingual frenulum

__ Processes of the Mouth __

Teeth cut food - bite size to fit in mouth

Mastication (chewing) of food

Mixing masticated food with saliva

Allowing for the sense of taste

Initiation of swallowing by the tongue

Formation of bolus

__ THE TEETH __



__ Pharynx Anatomy and Functions __

Nasopharynx ̵ not part of the digestive system

Oropharynx ̵ posterior to oral cavity

Laryngopharynx ̵ below the oropharynx and connected to the esophagus

Functions : Serves as a passageway for air and food

Food is propelled to the esophagus by two muscle layers
 * A.Longitudinal inner layer
 * B.Circular outer layer

Food movement is by alternating contractions of the muscle layers (peristalsis)

__ OESOPHAGUS __ Food Runs from pharynx to stomach in the esophagus throught diaphragmatic hiatus

Esophagus Conducts food by peristalsis (slow rhythmic squeezing)

Esophagus is the Passageway for food only (respiratory system branches off after the pharynx)

__ Layers of Walls of AC Organs __ **Mucosa** =Innermost layer= Moist membrane
 * 1.Surface epithelium
 * 2.Small amount of connective tissue (lamina propria)
 * 3.Small smooth muscle layer
 * 3.Small smooth muscle layer
 * 3.Small smooth muscle layer


 * Submucosa**
 * 1.Just beneath the mucosa
 * 2.Soft connective tissue with blood vessels, nerve endings, and lymphatic
 * 2.Soft connective tissue with blood vessels, nerve endings, and lymphatic


 * Muscularis externa ̵ smooth muscle**


 * Inner circular layer
 * Outer longitudinal layer


 * Serosa**
 * Outermost layer ̵ visceral peritoneum
 * Layer of serous fluid-producing cells

Nervous Networks in A.C. All are part of the autonomic nervous system

Three separate networks of nerve fibers __ THE STOMACH __ Regions of the stomach
 * A.Submucosal nerve plexus
 * B.Myenteric nerve plexus
 * C.Subserous plexus
 * A.Cardiac region ̵ near the heart
 * B.Fundus
 * C.Body
 * D.Pylorus ̵ funnel-shaped terminal end

Food empties into the small intestine from the pyloric sphincter Layers of peritoneum attached to the stomach


 * A.Lesser omentum ̵ attaches the liver to the lesser curvature
 * B.Greater omentum ̵ attaches the greater curvature to the posterior body wall
 * C.Contains fat to insulate, cushion, and protect abdominal organs
 * C.Contains fat to insulate, cushion, and protect abdominal organs
 * C.Contains fat to insulate, cushion, and protect abdominal organs

FUNCTIONS OF THE STOMACH Site of food breakdown Chemical breakdown of protein begins Delivers chyme (processed food) to the small intestine The body’s major digestive organ Site of nutrient absorption into the blood

Specialized mucosa of the stomach
 * Simple columnar epithelium**

Gastric pits formed by folded mucosa Glands and specialized cells are in the gastric gland region
 * A.Mucous neck cells ̵ produce a sticky alkaline mucus
 * B.Gastric glands ̵ secrete gastric juice
 * C.Chief cells ̵ produce protein-digesting enzymes (pepsinogens)
 * D.Parietal cells ̵ produce hydrochloric acid
 * E.Endocrine cells ̵ produce gastrin

__ THE SMALL INTESTINE __ Muscular tube extending form the pyloric sphincter to the ileocecal valve

Suspended from the posterior abdominal wall by the mesentery

__ Regions of the small intestine __ Duodenum Jejunum : Attaches anteriorly to the duodenum
 * Attached to the stomach
 * Curves around the head of the pancreas

Ileum : Extends from jejunum to large intestine

__ Properties of the small intestine __ Source of enzymes that are mixed with chyme: A.Intestinal cells B.Pancreas

Bile enters from the gall bladder - does not contain any enzymes

Fingerlike structures formed by the mucosa give the small intestine more surface area

Contains Absorptive cells .Blood capillaries Lacteals (specialized lymphatic capillaries)

__ Folds of the Small Intestine __ Called circular folds or plicae circulares

Deep folds of the mucosa and submucosa

Do not disappear when filled with food

The submucosa has Peyer’s patches (collections of lymphatic tissue)

__ THE LARGE INTESTINE [COLON] __

Larger in diameter, but shorter than the small intestine Frames the internal abdomen __ FUNCTIONS OF LARGE INTESTINE __ Absorption of water Eliminates indigestible food from the body as feces Does not participate in digestion of food Goblet cells produce mucus to act as a lubricant Bacteria produce vitamins

__ STRUCTURES OF THE LARGE INTESTINE __ Caecum ̵ saclike first part of the large intestine
 * Appendix Hangs from the caecum.
 * Contains an accumulation of lymphatic tissue that sometimes becomes inflamed (appendicitis)

Colon : Ascending, Transverse , Descending , S-shaped sigmoidal Rectum Anus ̵ external body opening Smooth muscle is reduced to three bands (teniae coli) V.Muscle bands have some degree of tone Walls are formed into pocketlike sacs called haustra

__ACCESSORY GLANDS OF THE DIGESTIVE SYSTEM __

Salivary glands, Teeth , Pancreas , Liver , Gall bladder __ THE SALIVARY GLANDS __

Three pairs of salivary glands empty secretions into the mouth

A.Parotid glands .Found anterior to the ears

B.Submandibular glands

C.Sublingual glands

Both submandibular and sublingual glands empty saliva into the floor of the mouth through small ducts


 * __COMPOSITION OF SALIVA__**

Approx 98% water

Contains solutes: Na+, K + , Cl - , PO4=- ,HCO3-

Has pH of 6.7 - 7.00

Contains lysozyme, IgA, defensin, cyanidic compound

Some metabolic waste

Mixture of mucus and serous fluids


 * __FUNCTIONS OF SALIVA__**

Helps to form a food bolus

Contains salivary amylase to begin starch digestion

Dissolves chemicals so they can be tasted

Intrinsic salivary glands - continuous secretions - keep mouth moist Small amounts from intrinsic glands

__**REGULATION OF SALIVATION**__

Stimulation by food - chemoreceptors in mouth send signal to Salivatory nuclei in Pons and MO

Parasympathetic stimulation via Facial & Glossopharyngeal to salivary glands

Extrinsic glands secrete large qty of saliva I.Approx 1 - 1,5 litre saliva per day

Smell or sight of food enough to set off salivatory nuclei

Sympathetic stimulation - thick saliva - dry mouth syndrome

__** THE TEETH **__ THE DENTAL FORMULA ** Primary Dentition / Milk Teeth ** 2 I 1 C 2 M (5 teeth left / also 5 right) --- 2 I 1 C 2 M “ ” “ ”

Thus a total of 20 deciduous teeth

** Permanent Dentition ** 2 I 1 C 2 PM 3 M 2 I 1 C 2 PM 3 M

A total of 32 permanent teeth

STRUCTURE OF A TYPICAL TOOTH
 * Crown**—exposed part


 * A.Enamel—hardest substance in the body
 * B.Dentin (Dentyne) —found deep to the enamel and forms the bulk of the tooth
 * C.Pulp cavity—contains connective tissue, blood vessels, and nerve fibers
 * D.Root canal—where the pulp cavity extends into the root
 * C.Pulp cavity—contains connective tissue, blood vessels, and nerve fibers
 * D.Root canal—where the pulp cavity extends into the root
 * D.Root canal—where the pulp cavity extends into the root


 * Neck**


 * A.Region in contact with the gum
 * B.Connects crown to root
 * B.Connects crown to root


 * Root**

Cementum—covers outer surface and attaches the tooth to the periodontal membrane

__** THE LIVER **__ Largest gland in the body

Located on the right side of the body under the diaphragm

Consists of four lobes suspended from the diaphragm and abdominal wall by the falciform ligament

Connected to the gallbladder via the common hepatic duct Mass about 1,2 - 1,5 kg

Functional units = lobules = hexagonal Hepatocytes radiate outward from central vein Each corner of hexagonal lobule has triad: = branch of :hepatic artery, hepatic portal vein and bile duct

Between hepatocytes = large sinusoidal capillaries--- form liver sinusoids Sinusoids contain blood from HA and HPV Blood collects in central vein Contains bile canaliculi through which bile flows to larger ducts


 * The liver has several roles in digestion**
 * Manufactures bile
 * Detoxifies drugs and alcohol
 * Degrades hormones
 * Produces cholesterol, blood proteins (albumin and clotting proteins)
 * Contains star-shaped macrophages (Kupffer cells) that remove debris -bacteria, worn out rbc.
 * Can regenerate if part of it is damaged or removed
 * Produces cholesterol, blood proteins (albumin and clotting proteins)
 * Contains star-shaped macrophages (Kupffer cells) that remove debris -bacteria, worn out rbc.
 * Can regenerate if part of it is damaged or removed
 * Can regenerate if part of it is damaged or removed
 * Can regenerate if part of it is damaged or removed

__ THE GALL BLADDER __

Sac found in hollow fossa of liver

When no digestion is occurring, bile backs up the cystic duct for storage in the gallbladder

When digestion of fatty food is occurring, bile is introduced into the duodenum from the gallbladder

Gallstones are crystallized cholesterol which can cause blockages

** BILE ** Produced by cells in the liver

Bile leaves the liver through the common hepatic duct


 * Composition is:**
 * Bile salts
 * Bile pigments (mostly bilirubin from the breakdown of hemoglobin)
 * Cholesterol, Phospholipids , Electrolytes
 * Cholesterol, Phospholipids , Electrolytes
 * Cholesterol, Phospholipids , Electrolytes

Function—emulsify fats by physically breaking large fat globules into smaller ones

__** THE PANCREAS **__ Large part located posterior to the parietal peritoneum

Its location is partially retroperitoneal

Extends across the abdomen from spleen to duodenum

“Behind” greater curvature of the stomach __**STRUCTURE OF THE PANCREAS**__

Pancreatic acini = clusters of secretory cells

Extensive RER - Zymogen granules with digestive enzymes

Pancreatic Islets (Langerhans) - Alpha cells,,, Beta cells

__**FUNCTIONS**__

Produces a wide spectrum of digestive enzymes that break down all categories of food

Enzymes are secreted into the duodenum

Alkaline fluid introduced with enzymes neutralizes acidic chyme coming from stomach

Hormones produced by the pancreas : Insulin, Glucagon

Approx 1,2- 1,5 litre produced daily

Clear watery fluid

Has pH of about 8

Contains enzymes and electrolytes