Ch2: Digestive System

digestion characteristics

-uses mechanical and chemical mechanisms

-mechanical: choosing to put food in your mouth, choosing to chew

-chemical: breakdown in body, we can’t use foods just as they are our body has to break them down

alimentary canal

-GI tract

-food passageway & muscular tube 8m long

-tube that runs from mouth to anus

accessory organs

-consists of organs that empty secretions into alimentary canal

-food does not pass through them

-salivary glands, liver, gallbladder, pancreas

4 layers of the alimentary canal

1. mucosa

2. submucosa

3. muscularis

4. serosa

mucosa

-innermost layer of alimentary canal

-mucous membrane, directly surrounds the passageway (lumen)

-folded in some areas to increase surface area

-absorbs dietary nutrients, secretes mucus and enzymes

submucosa

-second layer from innermost of alimentary canal

-nourishes cells, transports absorbed food molecules

-major blood supply, blood vessels, nerves, connective tissue

muscularis

-third layer from innermost of alimentary canal

-muscle layer that squeezes food down into stomach

-has circular and longitudinal layers

serosa

-outermost layer of alimentary canal

-serous fluid eliminates friction

-visceral peritoneum of organs within abdominal cavity aka slippery outer covering that helps organs move against each other

-protection and lubrication

2 types of movements in alimentary canal

mixing movements & propelling movements

mixing movements

-muscle in small sections contracts rhythmically

-does not move materials in one direction, food moves back and forth

-ex: segmentation in small intestine, churning in stomach

propelling movements

-moves materials in one direction, forward through the digestive tract

-peristalsis: ring of contraction progresses down tube; propels food particles down the tract in wavelike motion

submucosal plexus

controls secretions and absorptions

myenteric plexus

-controls gastrointestinal motility

-between circular and longitudinal muscle layers

increases

parasympathetic impulses _______ digestive activity

inhibits

sympathetic impulses ________ digestive actions

enteroendocrine cells

-found in stomach and small intestine

-secrete chemical messengers to regulate GI organs and processes

mouth characteristics

-first organ of alimentary canal, ingests food

-mastication: mechanical breakdown of solid particles, mixes them with saliva

-functions as an organ of speech & sensory reception

papillae

-projections that move food

-contains taste buds

-part of the tongue

lingual frenulum

-line under tongue

-connects the tongue to the bottom of the mouth

lingual tonsils

tonsils found at the base of the tongue

front; back

the mouth’s hard palate is found at the ____ of the mouth, and the soft palate is found at the ____

palatine tonsils

masses/tonsils found on the sides of tongue

pharyngeal tonsils (adenoids)

-tonsils on the posterior wall of pharynx

-this is what kids normally have removed

32 secondary (adult) teeth

how many teeth do adults have?

20 primary (deciduous or baby) teeth

how many teeth do babies have?

cheeks

-form lateral walls of mouth

-hold food in mouth; muscles chew food

lips

-surround mouth opening

-contain sensory receptors used to judge characteristics of foods

tongue

-floor of mouth

-mixes food with saliva; moves food toward pharynx, and contains taste receptors

palate

-forms roof of mouth

-holds food in mouth; directs food to pharynx

teeth

-in sockets of mandible & maxillae

-break food particles into smaller pieces; helps mix food with saliva during chewing

secrete saliva

major role of salivary glands is to ________

3 major salivary glands:

1. Parotid glands (largest, secretes serous saliva with amylase)

2. Submandibular glands (floor of mouth, serous & mucous)

3. Sublingual glands (under tongue, mainly mucous)

serous cells & mucous cells

salivary glands have two types of secretory cells, ______ and _______

serous cells

-found in salivary glands

-produce a watery fluid, containing digestive enzyme called salivary amylase

-amylase splits starch and glycogen into disaccharides

mucous cells

-found in salivary glands

-secrete mucus that binds food particles and lubricates food while swallowing

salivary amylase

enzyme that breaks down carbohydrates (-lase = enzyme)

pharynx (throat)

-extends from nasal cavity to esophagus, and has 3 different parts

-Nasopharynx: posterior to nasal cavity, air passage, contain openings to auditory tubes

-Oropharynx: posterior to oral cavity, air and food passage

-Laryngopharynx: posterior to larynx, passageway to esophagus

esophagus

-tubular organ that extends from pharynx to the stomach

-has a sphincter, ring of muscle (or door), at the end of esophagus and is a passage into the stomach

-another name is lower esophageal sphincter

-damaged ones cause vomitting

swallowing mechanism: first stage

-voluntary stage

-saliva is mixed with chewed food forming bolus

swallowing mechanism: second stage

-starts as food reaches oropharynx, stimulates sensory receptors and triggers swallowing reflex

swallowing reflex steps

1. soft palate and uvula rise to protect nasal cavity from food

2. hyoid bone and larynx rise

3. epiglottis closes off at the top of larynx to protect trachea

4. longitudinal muscles of pharynx contract

5. inferior constrictor muscles relax and esophagus opens

6. peristaltic waves forced food into esophagus

swallowing mechanism: third stage

peristalsis transports food in the esophagus to the stomach

stomach characteristics

-J-shaped, pouch like organ under left breast

-rugae are folds found here (folds of mucosa and submucosa that allow for stretching)

-most of digestion does not take place here

-functions: receives food from esophagus, mixes food with gastric juice, initiates protein digestion

portions of the stomach

1. Cardia: region near opening to esophagus; contains lower esophageal sphincter

2. Fundus: rounded area that rises above cardia; temporary food storage which sometimes contains swallowed air

3. Body: main portion; lies between fundus and pylorus

4. Pylorus: distal portion that’s clostest to small intestine; funnel shapped that narrows; contains Pyloric sphincter (circular smooth muscle that controls gastric emptying)

mucus

-gastric secretion that provides lubrication and protects stomach lining

-secreted by mucous neck cells

pepsinogen

-inactive form of pepsin

-gastric secretion that is constantly secreted by chief cells

pepsin

-formed from hydrochloric acid and pepsinogen

-active enzyme that breaks down proteins into polypeptides

gastric lipase

-fat splitting enzyme that breaks down triglycerides

-found in small quantities; action inhibited by low pH

hydrochloric acid

-converts pepsinogen into pepsin

-produced by parietal cells

intrinsic factor

-required for absorption of vitamin B12

-produced by parietal cells

chemical messengers

-substances (hormones & local messengers) that regulate digestive processes

-secreted by enteroendocrine cells

neural regulation & hormonal regulation

how are gastric secretions regulated?

neural regulation of gastric juices

-sympathetic impulses: decrease gastric activity

-parasympathetic impulses: increase gastric activity, promote release of histamine which regulates gastric secretion

hormonal regulation of gastric juices

-somatostatin: inhibits hydrochloric acid secretion, “slow”

-gastrin: increases gastric juice secretion, “go”

-cholecystokinin (CCK): released by small intestine cells when proteins and fat enter the small intestine, decreases gastric motility, “handle the fat”

cephalic phase

-phase of gastric secretion

-sight, taste, smell, or thought of food triggers parasympathetic reflexes

-gastric juice is secreted as response

gastric phase

-phase of gastric secretion

-food in stomach chemically & mechanically stimulates gastrin release, which then stimulates gastric juice secretion

intestinal phase

-phase of gastric secretion

-food enters the small intestine, which stimulates intestinal cells to release gastrin, which promotes gastric juices in stomach

-primarily inhibits gastric juice secretion by sympathetic reflex and the hormone cholecystokinin responses

gastric absorption

-pepsin begins breaking down proteins

-most nutrients are absorbed in the small intestine

-stomach absorbs: some H2O, certain salts, certain lipid soluble drugs, some alcohol

mixing & emptying actions of stomach

-chyme: mixing of food in stomach with gastric juice, semifluid paste

-peristaltic waves: push chyme towards pylorus of stomach so it can move into the small intestine

-enterogastric reflex: happens when chyme starts to fill the duodenum, this slows stomach emptying and intestinal filling

medulla oblongata

where is the vomiting center located?

pancreas

functions as an endocrine & exocrine gland

endocrine: secretes insulin and glucagon to regulate blood glucose

exocrine: secretes digestive fluid called pancreatic juice

structure of exocrine pancreas

-Pancreatic acinar cells: make up most of pancreas, release juices into tiny ducts which lead to pancreatic duct

-Pancreatic duct: empties into the duodenum of the small intestine

-Hepatopancreatic sphincter: controls movement of bile and pancreatic juice into duodenum

Pancreatic amylase

-pancreatic juice

-splits starch & glycogen into disaccharides

Pancreatic lipase

-pancreatic juice

-breaks down triglycerides, acts as a 2nd wave

Trypsin

-pancreatic juice

-digests proteins

-released as inactive trypsinogen

Chymotrypsin & Carboxypeptidase

-pancreatic juice

-digests proteins

-released as inactive, activated by trypsin

Nucleases

-pancreatic juice

-digest nucleic acids

Bicarbonate ions

-pancreatic juice

-makes pancreatic juice alkaline, buffer stomach acid

-small intestine wants to increase pH

regulation of pancreatic secretion:

1. Hormones: Secretin (stimulates pancreas to release juices) & CCK (stimulates pancreas to release pancreatic juice high in enzymes)

2. Nervous system: during cephalic & gastric phases, parasympathetic impulses stimulate pancreas to secrete digestive enzymes

liver

-largest organ, reddish-brown color, well supplied with blood vessels, helps break down blood, has 4 lobes

liver structure

-Hepatic sinusoids: channels for blood, found between plates of cells

-Hepatic portal vein: brings absorbed nutrients to sinusoids

-Hepatic artery: brings oxygen rich blood, which mixes with oxygen-poor blood from portal vein

detoxification

-major function of liver

-removes toxins from the blood

Carbohydrate metabolism

-major function of liver

-polymerizes glucose to glycogen; breaks down glycogen to glucose; converts noncarbohydrates to glucose

Lipid metabolism

-major function of liver

-oxidizes fatty acids; synthesizes lipoproteins, phospholipids, and cholesterol; converts excess portions of carbohydrate molecules into fat molecules

Protein metabolism

-major function of liver

-deaminates amino acids; forms urea; synthesizes plasma proteins; converts certain amino acids into other amino acids

Storage

-major function of liver

-stores glycogen, vitamins A, D, and B12, iron, and blood

Blood filtering

-major function of liver

-removes damaged red blood cells and foreign substances by phagocytosis; degrades certain hormones

Secretion

-major function of liver

-produces and secretes bile

bile characteristics

-yellowish green liquid secreted from liver, produced by gallbladder

-emulsifies fats (breaks fat down)

-bile salts: produced from cholesterol, emulsify fats, are recycled

-bile pigments: derived from hemoglobin breakdown

-jaundice: bile ducts are blocked, yellowing of skin

gallbladder

-pear shaped sac

-Cystic duct: only entry/exit duct, merges with common hepatic duct to form common bile duct

-stores and concentrates bile

small intestine

-fills most of abdominal cavity, receives chyme, bile & pancreatic juices, absorbs nutrients

-mesentery: tissue with blood vessels that keeps small intestine connected

-has 3 parts: Duodenum, Jejunum, Ileum

mucus (w/ small intestine)

-secreted by goblet cells

-secrete a thick, alkaline mucus in response to certain stimuli

watery fluid

-secreted by intestinal glands

-picks up digestion products, and transports them into villi

-does not contain digestive enzymes

enzymes (w/ small intestine)

-Peptidases: break down peptides into amino acids

-Sucrase, maltase, lactase: break down disaccharides into monosaccharides

-Lipase: Breaks down fats into fatty acids and glycerol

chemical messengers (w/ small intestine)

-Secretin & CCK: secreted by enteroendocrine cells scattered throughout mucosa of duodenum

antimicrobial substances

-defend against certain bacteria

-secreted by special cells in intestinal glands

movements of small intestine:

-peristalsis: wave-like pushing movements that propel chyme

in proper direction down the small intestine

-segmentation: ring-like contractions that move chyme back

and forth (mixing movement); places chyme in contact with

digestive enzymes in brush border and aids in absorption

-parasympathetic impulses: makes sure peristalsis happens when content needs to be moved

peristaltic rush

irritation in small intestine, causes diarrhea, contents are rushed quickly from small intestine to large intestine

ileocecal sphincter

-joins ileum of small intestine to cecum of large intestine

-helps regulate the flow of chyme

large intestine

-absorbs excess water & electrolytes

-compacts waste and leaves no nutrients left to get once here

-4 different parts: Cecum, Colon, Rectum, Anal canal

4 parts of large intestine

1. Cecum: pouch, forms beginning of large intestine, appendix is attached to this

2. Colon: has ascending, transverse, and descending portions, this is most of the large intestine

3. Rectum: extends from end of colon to anal canal

4. Anal canal: last cm of large intestine, opens to outside of anus, has internal & external anal sphincters

internal anal; external anal

stretch receptors from rectum send signals to __________ sphincter (we don’t control this!) we do however control the _________ sphincter

nutrients

no villi in large intestine = no _______ absorbed

haustra

muscle bands that help form feces

intestinal flora

it’s okay as long as it’s in the large intestine; gives feces it’s smell

movements of large intestine

-defecation reflex: allows us to move fecal matter through body, involves holding deep breath and contracting abdominal muscles, relaxes internal anal sphincter and then external anal sphincter

-peristaltic waste: mass movements, 2 to 3 times/day which usually follows meals