Digestive system ap150

Mechanical digestion

breaking large foods into small without chemical change

Chemical digestion

breaking chemical bonds with enzymes

• Large molecules -> smaller absorbable molecules

Digestion compared to absorbtion

breaking down food

Absorption compared to digestion

movement of substances out of the digestive tract into circulation (blood or lymph)

Mechanical digestion chords

• Mastication

• Mixing (churning, segmentation, etc.)

Propulsion

movement of food through the alimentary canal

• Peristalsis

• Smooth muscle v. skeletal muscle

Peristalsis

• How material is moved/propelled through the digestive tract

• Involves a circularly and a longitudinally arranged layer of muscle

Secretion

release of substances into the alimentary canal that aid digestive system function

• Enzymes for chemical digestion

• Mucus and other substances neutralize acidity

• Mucus for lubrication

Elimination

digestive wastes exiting the body as feces

• defecation

Accessory organs

Salivary glands (+intrinsic glands):

• Parotid gland, Sublingual gland, Submandibular gland

• Release secretions in oral cavity/mouth

Liver, Gallbladder, Pancreas:

• Release secretions in duodenum

Oral cavity to lower esophageal sphincter (cardiac), and anal canal epithelium

Stratified squamous for protection

Stomach to rectum epithelium

Simple columnar for absorption and secretion

Oral cavity

• Lined with stratified squamous

• Main area of mechanical digestion by teeth

• Chemical digestion

  • Salivary and intrinsic enzymes

  • Salivary amylase and lipase

• pH approximately 7, relatively neutral

• Sensation: taste and texture

  • Trigeminal, glossopharyngeal and facial nerve

• Propulsion (with tongue)

  • Voluntary swallowing

  • Bolus

What ANS branch innervates salivary glands

Dual innervation by ANS, but PD signals stimulate and increases gland activity

Mucus cells in saliva

• mucin -> mucus

  • Lubricates and binds material

Serous cells in saliva

• Salivary amylase and lipase

• Chemical digestion

• Antimicrobial components

  • Lysozyme: antibacterial

Water in saliva

95%, dissolves chemical to enhance taste sensations

What cranial nerve innervates tongue

Hypoglossal nerve XII

Hard palate function

Serves as a wall between nasal and oral cavity

Soft palate function

Allows you to manipulate it to sing, yawn, swallow, etc.

Processes/functions in the pharynx

• Propulsion

  •  With skeletal muscle mostly innervated by cranial nerves

• Involuntary swallowing

  • Medulla oblongata

What cranial nerve innervates pharynx

• Glossopharyngeal and vagus nerve

4 layers of digestive system innermost to outermost

1. Mucosa

2. Submucosa

3. Muscularis

4. Serosa or adventitia

Mucosa of small intestine

• Inner most layer -> in contact with ingested material

• Lined with epithelial tissue (stratified squamous or columnar)

• Laminal propria containing loose CT, capillaries, nerves, lymph capillaries

Submucosa of small intestine

• Dense CT, larger vessels

• nerves/submucosal plexus that innervates/regulates mucosa and submucosa

Muscularis (externa) of small intestine

• Muscle (mostly smooth) that propels

  • Produces peristalsis

• Circular and longitudinal layers

  • Produces peristalsis

• Myenteric plexus (innervates/controls muscularis)

Serosa OR adventitia

Outermost later

Serosa tissue

visceral peritoneum

Adventitia tissue

dense CT (fibrous)

Esophagus function

Soft muscular tube, propels bolus to stomach

What happens to the muscularis of the esophagus as you move from the superior end to the inferior end of the organ?

• Transitions from skeleton to smooth

• Inner circular layer

Cardiac sphincter function (lower esophogeal sphincter

• Poorly defined muscular thickening at end of esophagus

• Reinforced by diaphragm

• Prevents movement of stomach contents back into esophagus

Esophageal hiatus

Where esophagus goes through the hole diaphragm

Pyloric sphincter function

• Well defined sphincter at junction with duodenum

• Controls emptying of stomach

Stomach functions

• Mechanical digestion

  • Churning

  • Involves inner oblique layer

• Denaturing proteins by acids

• Kills pathogens with acidity (2.5-4.5 pH)

• Chemical digestion

  • Proteins by enzymes

• Soupy mixture/contents of stomach = chyme

• Vagus nerve

Absorption in stomach?

• Minimal absorption

  • Alcohol and lipid soluble substances

Parietal cells of gastric glands

• Produce HCL (hydrochloric acids)

• Intrinsic factor

  • Absorption of B12

Chief cells of gastric glands

• Produce Pepsinogen

  • Inactive enzyme

  • HCL = pepsinogen = pepsin

Enteroendocrine cells of gastric glands

• Produce Gastrin (released due to increased pH)

Pepsin function

• Protease

• Chemically digests proteins

HCL function

• Activates pepsinogen

• Kills pathogens

• denatures/breaks some bonds

• Increase stomach acidity

What stimulates the production and release of gastric secretions?

Stretch and increase pH of stomach main stimulators

Gastrin function

• Chemical regulation of digestive function

• E.g increased parietal and chief cell secretion or increased gastric motility

Mucous cells function?

Secrete protective alkaline mucous

Rugae (gastric folds) function

Allow expansion of stomach

Small intestine functions

• Primary site of chemical digestion

• Primary site of absorption

• Propulsion 

• Mechanical digestion (segmentation)

• pH around 8

4 features of small intestine that enhance absorption

• Length

• Plicea circulares/circular folds

• Vili

• microvili

Vili difference from microvili

Contains lacteal and capillaries to receive absorbed nutrients

Intestinal crypt function

• Source of new columnar cells

• Produce alkaline mucus

  • Neutralizes acidic chyme of stomach

Submucosal glands in duodenum function

• Regulation of gallbladder and pancreas

• Releases secretin from acidic chyme

  • Secretin stimulates production of bicarbonate (alkaline) by pancreas

• Releases cholecystokinin (CKK)

  • Stimulates production of lipases by pancreas

  • Stimulates release of bile by gallbladder

  • Releases hepotopancreatic sphincter

Goblet cells function in small intestine

Lubricating mucus that protects against acidic chyme

Absorptive cells in small intestine function

• Intrinsic enzymes for chemical digestion

• absorption

Functions of blood/lymph capillaries in mucosa of intestines

• Accept absorbed nutrients

• Lymphatic tissue to protect against harmful microorganisms

What nutrients absorbed into blood

Carbohydrates and protein (amino acids)

What nutrients absorbed into lymph

Triglycerides (lipids)

What patterns exist in the wall of the small intestine as you move from duodenum toward the large intestine?

• duodenum has poorly developed plicae and villi

• jejunum has well developed plicae and villi

• absorptive features decline and disappear

• lymphatic tissue increase moving down

• mucus production increases

Large intestine functions

• Reabsorbs water to consolidate into feces

• Stores feces until defecation

  • But not main site of water absorption

• Houses normal flora/bacteria

• Propulsion/defecation

Mucosa of large intestine

• Simple columnar

• Absorptive cells

• Mucus cells, predominate

  • To lubricate the solidifying mass of material

• Invaginated glands; crypts 

  • With many mucus cells

Muscularis of long intestine

• Circular layer present throughout

• Longitudinal layer concentrated into the 3 teniae coli

• Muscle tone (partial contraction) causes L.I to gather and produce haustra

• Ascending and descending colon are retroperitoneal

Colon and long intestine difference

Colon does not include the cecum, rectum, and anal canal

Ileocecal valve function

Allows food to enter the cecum

Normal flora/bacteria

• Produce vitamin K and some B vitamins

• Influence regularity, immune function, fat deposition

• Evidence of influence on CNS and neurological function

• Produce flatus (farts)

Rectum/rectal valves function

• Last 6’ of digestive tract

• Retroperitoneal

• Mucose -> simple columnar -> stratified squamous by anal canal

• Submucosa and lamina propria rich in blood vessels

  • Hemorrhoids

• Thick muscular layer

  • For defecation

  • Circular layer forms internal anal sphincter

• Externa; anal sphincter is skeletal muscle

  • Part of pelvic floor

  • Pudendal nerve

Anal canal

• Few centimeters long

• Passageway out of rectum

• Anal sinuses and columns

Hemorrhoids

Swollen veins in the anus and lower rectum, causing discomfort, itching, and bright red bleeding during bowel movements

Relationship between the anal canal, the internal anal sphincter and the external anal sphincter and defecation?

Anal canal has external (voluntary) and internal (involuntary) anal sphincters that both usually remain closed

Parietal peritoneum

• Fused to inner surface of body wall

• Simple squamous and areolar

• Secretes serous fluid

  • Lubricates

Visceral peritoneum

• Simple squamous and areolar

• Fused to outer surface of an organ

• Serosa

Mesentery

• Double layer of peritoneum, not surrounding major openings

• Connects to both parietal and visceral peritoneum

Mesentery function

• Contains blood vessels

• Site for adipose deposition

• Holds/supports abdominal organs

Retroperitoneal meaning

Organ will have peritoneum on one or more body surface, not surrounded

• Duodenum, pancreas, ascending colon, descending colon, rectum, kidneys/adrenal gland and urinary bladder

Liver functions

• Stores and releases glucose (primary organ that releases glucose)

  • To stabilize blood glucose

• Synthesizes and stores lipids (cholesterole…) also regulates circulating lipids

• Produces plasma proteins

• Amino acid interconversion and breakdown (gluconeogenesis)

• Detoxify absorbed toxins

• Removes old RCS’s and cellular debri

• PRODUCES BILE

Falciform ligament

separates left and right lobe of liver

Hepatocytes

• Liver’s main cell type

• Secretory, metabolic, and endocrine function

Portal triad

• Contain hepatic duct, hepatic portal vein, and hepatic artery

Sinusoids

• Porous blood space formed by fenestrated capillaries

• From portal veins that are nutrient rich and oxygen rich hepatic arteries

• Send blood to central vein

Bile canaliculi

• Grooves in the cell membrane

• Accumulate bile from hepatocytes

• Bile flows out into hepatic duct branches and ducts

Blood/bile flow through lobule

1. Hepatocytes

2. Bile canaliculi

3. Hepatic ducts

4. L&R hepatic ducts

5. Common hepatic and bile duct 

6. Cystic duct

7. duodenum

Hepatic portal system

• A collection of blood vessels carrying venous blood from spleen and digestive organs to liver

• O2 poor, nutrient rich

• Portal vein (vein between 2 capillary beds)

• Inferior mesenteric vein + splenic vein + superior mesenteric vein = (75% blood into liver)

2 vessels that supply liver?

1. Hepatic artery

2. Hepatic portal vein

Hepatic artery

O2 rich blood sent to liver

Hepatic portal vein

O2 poor, nutrient rich blood to liver

Mesenteric artery

O2 rich blood into intestines

Hepatic vein

O2 poor and nutrient diminished

Gallbladder

• Right upper quadrant

• Stores bile

• Releases bile in response to CCK

• Lined by smooth muscle

• Absorbs water/concentrates bile

Bile

• Emulsifies fat, breaks large droplets into smaller droplets that remain mixed with water

  • Bile salts

• Bile is also used to excrete cholesterol and bilirubin (from hemoglobin breakdown-bile pigments) from body

Biliary apparatus

• Comes from liver in L/R hepatic ducts which join in common hepatic duct

• Goes up cystic duct to gallbladder where it is stored

• Bile is released out of cystic duct 

• Goes down common bile duct

• Enters duodenum via duodenal papilla

  • Common bile -> hepatopancreatic ampullar sphincter/duodenal papilla

Exocrine function of pancreas

• Digestive function

• Pancreatic juice

  • Contains enzymes that break down:

    • Carbohydrates, pancreatic amylase

    • Proteins, proteases

    • Lipids, lipases

    • Nucleases, nucleic acids

Endocrine function of pancreas

• Release insulin (beta cells)

  • Reduces blood sugar and encourages cells to store away nutrients

• Releases glucagon (alpha cells)

  • Increases blood sugar and encourages cells to release stored energy

Acini/acinar cells?

Creates and secretes enzyme rich pancreatic juice

What part of ANS stimulates digestive system to increase activity

Parasympathetic division

RUQ organs

• Duodenum

• Gallbladder

• Liver 

• Pancreas

• Kidney

• Intestines

• Small portion of stomach

RLQ organs

• Appendix

• Ureter

• Intestines

• ovaries/uterine tubes

• Spermatic cord?

LUQ organs

• Stomach

• Pancreas

• Spleen

• Kidney

• Liver

• Intestines

LLQ organs

• Ureter

• Intestines

• ovaries/uterine tubes

• Spermatic cord?