CH. 25 DIGESTIVE Exam 3 Rebecca Effler SUMMERTIME

Digestive system has two subdivisions:

digestive tract and accessory organs

Digestive tract

-30 ft long muscular tube extending from mouth to anus

-Mouth, pharynx, esophagus, stomach, small intestine, and large intestine

-Gastrointestinal (GI) tract is the stomach and intestines

Accessory organs

Teeth, tongue, salivary glands, liver, gallbladder, and pancreas

Digestive system

-Organ system that processes food, extracts nutrients, and eliminates residue

-Five stages of digestion: ingestion, digestion, absorption, compaction, defecation

Mechanical digestion

-The physical breakdown of food into smaller particles

-Cutting and grinding action of the teeth

-Churning action of stomach and small intestines

-Exposes more food surface to digestive enzymes

Chemical digestion

-A series of hydrolysis reactions that breaks dietary macromolecules into their monomers

-Carried out by digestive enzymes produced by salivary glands, stomach, pancreas, and small intestine

4 Layers of the Digestive Tract

1. Mucosa- epithelium, lamina propria, muscularis mucosae

2. Submucosa

3. Muscularis externa- inner circular layer, outer longitudinal layer

4. Serosa- areolar tissue ,mesothelium

Mucosa

lines the lumen!!!! (mucous membrane)

Epithelium

-Stratified squamous from mouth through esophagus, and in lower anal canal

-Simple columnar in most of digestive tract

Lamina propria

loose connective tissue layer

Muscularis mucosae

-Thin layer of smooth muscle

-Tenses mucosa creating grooves and ridges that enhance surface area and contact with food

-Improves efficiency of digestion and nutrient absorption

Submucosa

-Thicker layer of loose connective tissue

Composed of:

-Blood vessels, lymphatic vessels

-Nerve plexus

-Glands that dump lubricating mucus into the lumen

Muscularis externa

-Two layers of smooth muscle

-Inner layer—cells encircle tract

-Outer layer—cells run longitudinally; propels food and residue through the digestive tract

Serosa

outermost layer with two layers (areolar tissue, simple squamous mesothelium)

Areolar tissue

-Loose connective tissue, consists of collagen and elastic fibers

-Almost all cells obtain nutrients from and release their waste into this tissue

-Found beneath all epithelial tissue

Simple squamous mesothelium

-Lining of cavity

-Begins in lower esophagus, ends just before the rectum -Pharynx, upper esophagus, and the rectum have no serosa but are surrounded by a layer called adventitia

The mouth and its functions

-The oral cavity, or buccal cavity

-Functions: ingestion (food intake); chewing and chemical digestion; swallowing, speech, and respiration

Tongue

contains lingual papillae that contain taste buds

Intrinsic muscles

-Contained entirely within the tongue

-Produce subtle tongue movements of speech

Extrinsic muscles

-Attachments outside in the tongue

-Produce stronger movements of food manipulation

Palate

-Separates oral cavity from nasal cavity

-Makes it possible to breathe while chewing food

Uvula

hangs down from the soft palate at the back of theoral cavity

Teeth

-Dentition

-32 adult teeth

-16 in mandible (lower jaw), 16 in maxilla (upper jaw)•

-2 incisors—chisel-like cutting teeth used to bite off a piece of food

-1 canine—pointed and act to puncture and shred food

-2 premolars- have two rounded bumps = bicuspid

-3 molars—4-5 cusps

-Premolars and molars-crushing, shredding, and grinding -Wisdom Teeth are the 3rd molar

Mastication

-Chewing—breaks food into smaller pieces to be swallowed and exposes more surface to digestive enzymes

-1st step in mechanical digestion

-Food stimulates oral receptors that trigger an involuntary chewing reflex

Functions of saliva:

-Moistens mouth

-Begins starch and fat digestion

-Saliva production begins when you see, smell, or think about food

-Vitamins, free amino acids, minerals, cholesterol, and water do not need to be digested (already in usable form)

There are two kinds of salivary glands:

intrinsic and extrinsic

Intrinsic (minor) salivary glands

-Small glands among oral tissues; secrete saliva at constant rate (whether we are eating or not)

-Lingual glands: in the tongue; produce

-Labial glands: inside of the lips

-Palatine glands: of the palate

-Buccal glands: inside of the cheek

-Secrete lingual lipase and lysozyme

Extrinsic (major) salivary glands

-Connected by ducts

-Parotid glands—front of earlobe

-Submandibular gland—beneath mandible, 70% of saliva

-Sublingual gland—located in the floor of the mouth

Saliva is a hypotonic solution of

97.0% to 99.5% water, a pH of 6.8 to 7.0, and the following solutes: mucus, electrolytes, lysozyme, immunoglobulin A (IgA), salivary amylase, lingual lipase

Mucus

binds and lubricates a mass of food and aids in swallowing

Electrolytes

salts of Na+, K+, Cl-, phosphate, and bicarbonate

Lysozyme

enzyme that kills bacteria

Immunoglobulin A (IgA)

antimicrobial antibody

Salivary amylase

enzyme that begins starch digestion inthe mouth, deactivated by stomach acid

Lingual lipase

enzyme that begins fat digestion(activated in stomach by HCl)

Pharynx

-Circular skeletal muscles that form pharyngeal constrictors (superior, middle, and inferior)

-Force food downward during swallowing

-When not swallowing, the inferior constrictor remains contracted to exclude air from the esophagus (upper esophageal sphincter)

Esophagus

straight muscular tube 25 to 30 cm long between pharynx and stomach

Lower esophageal sphincter (LES)

-At inferior end of esophagus

-Prevents stomach contents from regurgitating into the esophagus

-Protects esophageal mucosa from erosive stomach acid -Heartburn—burning sensation produced by acid reflux into the esophagus

Swallowing

-Deglutition—a complex action involving over 22 muscles in the mouth, pharynx, and esophagus

-Coordinated by swallowing center—a pair of nuclei inmedulla oblongata

3 phases of swallowing

1. Oral- the tongue forms a food bolus and pushes it into the laryngopharynx

2. Pharyngeal- the palate, tongue, vocal cords, and epiglottis block the oral and nasal cavities and airway while pharyngeal constrictors push the bolus into the esophagus

3. Esophageal- peristalsis drives the bolus downward, and relaxation of the lower esophageal sphincter admits it into the stomach

Stomach

Primarily functions as a food storage organ, mechanical digestion, chemical digestion of proteins and some fat

Results in chyme

acidic, soupy mixture of semi digested food that passes on to the small intestine

Mucosa and submucosa

are flat when the stomach is full. wrinkled when the stomach is empty

Rugae

increases surface area

4 regions of the stomach

cardiac, fundic, body, pyloric

Regenerative (stem) cells

produce new cells to replacecells that die

Parietal cells

-Secrete hydrochloric acid (HCl), intrinsic factor

-HCl - activates Pepsin and lingual lipase and helps to liquidize food

-Intrinsic factor needed for B12 absorption

Chief cells

-Secrete gastric lipase and pepsinogen

-Gastric lipase - fat in milk

-Pepsinogen is converted toPepsin by HCL

Enteroendocrine cells

Secrete hormones and paracrine messengers that regulate digestion

Gastrin

stimulates gastric juice production

Gastric juice

secretion of gastric glands- mostly water, HCL, and pepsin

The small intestine

-Duodenum• Jejunum• Ileum•

-The site of nearly all chemical digestion and nutrient absorption

-Receives secretions from the pancreas liver and gallbladder

Large intestine size and regions:

-Measures 5 ft long and 2.5 in

-Functions to absorb water and salts from indigested food before it is eliminated

-Begins with cecum - Appendix attached to cecum

-Appendix is densely populated with lymphocytes and is a significant source of immune cells

Colon

portion of large intestine between ileocecal junction and rectum

The motility and secretion of the digestive tract are controlled by

hormonal, paracrine mechanisms, and neural

Hormonal Controls

-Gastrin- stimulates the release of gastric juice

-Secretin- stimulates the pancreas to produce digestive enzymes

Paracrine Controls

-Cell to cell signaling; autocrine-same cell, paracrine-next cell or into tissue fluids

-Histamine-increases HCl

-Prostaglandins-inhibits gastric secretion

Neural Controls

long and short autonomic reflexes

Short-reflexes

-myentericnerve plexus - stretching or chemical stimulation of the digestive tract•

-Causes contractions in nearby regions of the muscularis externa (peristaltic contractions)

Long-reflexes

-(vagovagal) involve the CNS

-Regulates motility and secretion

-Sight, smell, and taste trigger long reflexes

Enteric Nervous System

regulates the digestive tract motility, secretion, and blood flow

Submucosa plexus (Meissner)

-In submucosa (CNS viavagus nerve)

-Controls movements in the muscularis mucosae and the glandular secretions of the mucosa

Myenteric plexus (Auerbach)

-In between the layers of the muscularis externa.

-Controls movements (peristalsis) and contractions of muscularis externa

Regulation of Gastric Function

-Gastric secretion and motility regulated by nervous and endocrine systems•

-Increase gastric secretion and motility when food is eaten; suppress them when the stomach empties

Gastric activity is divided into three phases:

-Cephalic phase: stomach being controlled by brain

-Gastric phase: stomach controlling itself

-Intestinal phase: stomach being controlled by small intestine Phases overlap and can occur simultaneously

chyme also stimulates duodenal enteroendocrine cells to release?

-Secretin and cholecystokinin (CCK)

-These stimulate the pancreas and gallbladder, but suppress gastric secretion

Liver

-Reddish brown gland

-The body's largest gland, weighs about1.4 kg (3 lbs)

-Huge variety of functions, but only one contributes to digestion: the secretion of bile

-Gallbladder adheres to a depression on the inferior surface of the liver

Hepatocytes functions between meals and after meals:

-After a meal, hepatocytes absorb from the blood: glucose, amino acids, iron, vitamins, and other nutrients for metabolism or storage•

-Remove and degrade: hormones, toxins, bile pigments, and drugs

-Between meals, hepatocytes break down stored glycogen and release glucose into the blood

-Secrete into the blood: albumin, lipoproteins, clotting factors ,angiotensinogen, and other products

Bile

-Is an emulsifier

-Assists in lipid digestion

-Hydrophilic and hydrophobic components (like soap)

-The liver produces bile acids from cholesterol

-Bile acids break down and suspend fat molecules into smaller droplets

-Pancreatic lipases have maximum surface area for digestion -Only way to get rid of excess cholesterol

Gallbladder

-Concentrates and stores bile

-Bile acids are reabsorbed (80%) by the ileum and then sent back to the liver to be reused

Gallstones

(biliary calculi)

-Hard masses in either the gallbladder or bile ducts -Composed of cholesterol, calcium carbonate, and bilirubin

-Most common in obese women over 40, but also men and even children

-Can occur when cholesterol becomes too concentrated, precipitates as crystals that grow in size

-Painful obstruction of ducts

-Result in jaundice (yellowing of skin), poor fat digestion, and impaired absorption of fat-soluble vitamins

-Gallstones usually removed by laparoscopic surgery

The Pancreas endocrine and exocrine portion

-Endocrine portion: pancreatic islets that secrete insulin and glucagon

-Exocrine portion: secretes pancreatic juice - alkaline mixture of water, bicarbonate, and enzymes

Duodenum

-Receives stomach contents, pancreatic juice, and bile

-Neutralizes stomach acid

-Emulsifies fats

-Inactivates pepsin (due to the elevated pH)

-Reactivates amylase

-Pancreatic enzymes take over chemical digestion

Jejunum

-Most digestion and nutrient absorption

-Has large circular folds for increased absorption

Ileum

-Contains Peyer's Patches -lymphoid nodules•

-Contents move by segmentation- circular constrictions along the intestine (time to churn and mix material)

-Pacemaker cells in the muscle of the intestines set the rhythm for segmentation

-When the majority of the nutrients have been absorbed, segmentation ends

Migrating motor complex

-Activates successive waves of peristalsis

-Moves chyme to colon (2 hours)

-Refilling the stomach at the next meal suppresses peristalsis and reactivates segmentation

Fecal Content

-Water make up the majority

-Bacteria make up the majority of the solid material

-Followed by fiber, fat, and proteins

Bacterial Flora

-Digest cellulose (absorb sugar)

-Produce B vitamins and Vitamin K (blood clotting)

Water involvement in digestion

-Digestive system is involved in water balance

-Digestive tract receives about 9 L of water/day

-Water is absorbed by osmosis following the absorption of salts and organic nutrients

-Diarrhea—occurs when large intestine absorbs too little water

-Feces pass through too quickly if intestine is irritated

-Feces contain high concentrations of a solute (such as lactose)

-Constipation—occurs when fecal movement is slow, toomuch water gets reabsorbed, and feces become hardened55

Haustra

pouches in the walls of the colon

Haustral contractions

-Occur every 30 minutes

-Distension of a haustrum stimulates it to contract

-Promoting water and salt absorption

Mass movements

-Stronger contractions that occur one to three times a day

-Moves further distance than haustral

-Filling of the stomach and duodenum stimulates motility of the colon

Stretching of rectum yields two defecation reflexes:

-Contraction of the rectum (myenteric plexus)

-Relaxation of the internalanal sphincter(parasympathetic)

External anal sphincter

remains contracted (voluntary control)

What is number 1?

oral cavity

What is number 2?

tongue

What is number 3?

teeth

What is number 4?

sublingual gland

What is number 5?

submandibular gland

What is number 6?

diaphragm

What is number 7?

liver

What is number 8?

gallbladder

What is number 9?

bile duct

What is number 10?

ascending colon

What is number 11?

small intestine

What is number 12?

cecum

What is number 13?

appendix

What is number 14?

parotid gland

What is number 15?

pharynx

What is number 16?

esophagus