Digestive system lecture

Oral cavity functions

Oral cavity functions

• mastication

• deglutination

Pharynx/esophagus functions

• swallowing

• transport

stomach functions

• mechanical digestion

• intital digestion of proteins and lipids

small intestine functions

chemical and mechanical digestion

absorption

large intestine functions

• compaction of feces

• absorption

• defecation

What is ingestion?

taking food and drinks into oral cavity

what is digestion?

• breaking down foods into usable forms

What is the difference between chemical and mechanical digestion?

• chemical: use of enzymes to break down polymers into monomers for absorption

• mechanical: alters consistency of food to ease transport

What is the movement of materials into digestive tract epithelium → interstitial fluid→ blood/lymph?

absorption

What is compaction?

absorbing all usable material and consolidating the ingestible and nonabsorbable materials as feces

What is the function of protection of the digestive system( (epithelium and lymphoid tissue)

• epithelia protect against abrasion, chemical damage, pathogens

• lymphoid tissue protects against pathogens that enter interstitial fluid

• stomach acid

What structures are included in the digestive tract (alimentary canal)?

mouth, esophagus, stomach, small intestine, large intestine

What are the accessory organs?

teeth, tongue, salivary glands, liver, gallbladder, pancreas

What are the functions of the accessory organs?

many produce secretions that are released into the lumen of digestive tract through ducts

What are the 4 digestive tract layers? list from innermost to outermost.

• mucosa

• submucosa

• muscularis externa

• serosa

What is the function of mucosa?

• absorb monosaccharides, amino acids, lipids

• protect from abrasion

What are the functions of submucosa?

• contains blood vessels and lymphatic vessels

• exocrine glands

• MALT

What are the functions of muscularis externa?

• inner circular/outer longitudinal smooth muscle

• stomach contains a third oblique layer

• churns and propels waste

What are the functions of serosa?

• secrete serous fluid

Which membrane maintains spatial relationships between organs?

• mesentery

What is the function of mesentery?

• supply blood vessels, nerves, lymphatic vessels, lymph nodes

What are the two posterior mesenteries?

mesocolon and mesentery proper

What are the two anterior mesenteries?

lesser omentum and greater omentum

What is peritonitis?

acute inflammation of the peritoneum caused my infection microbes, GI tract rupture, perforated ulcer, trauma, appendicitis

which cranial nerve controls the tongue?

CN XII (hypoglossal)

What is the function of the tongue?

• mechanically break up food

• manipulate food into a bolus

• glands secrete saliva and ligual lipase

• ducts of salivary glands open near lingual frenulum

What are the functions of saliva?

• mucus for lubrication

• enzymes that initiate the digestion of carbs and lipids

• IgA antibodies and lysozyme

• solvent for dissolving food molecules

• bicarbonate that neutralizes bacterial acids

What is the function of the upper esophageal sphincter?

prevents air from entering esophagus when contracted

How many layers of muscularis externa is in the stomach? what is the function of the extra layer?

• 3

• prevents over-stretching and helps churn food

What is the function of the mucus neck cell?

• secrete acidic fluid containing mucin

What do parietal cells secrete?

• Hydrochloric acid (HCl)

• intrinsic factor (IF)

• Ghrelin

What is ghrelin?

appetite stimulating hormone

What is the importance of IF and B12?

• essential for Hb synthesis

• both get taken up via receptor mediated endocytosis

What do the chief cells secrete?

• pepsinogen

• gastric lipase

What activates pepsinogen to pepsin?

HCl

Pepsin

initiates chemical digestion of protein

what do enteroendocrine cells secrete

• localized paracrines

• gastrin from G cells

What is the function of gastrin?

• stimulates parietal and chief cell secretion

• increases stomach motility, relaxes pyloric sphincter, constricts cardiac sphincter

Regenerative cells

• stem cells that replace lost pit and gland cells

G cells

secrete gastrin

Parietal cells generate __ from __ , then pump into lumen while exchanging __.

• H+

• carbonic acid

• K+

what is bicarbonate exchanged for in gastric hydrochoric acid?

• plasma chloride ions

CO2 is converted to carbonic acid, carbonic acid dissociates into _____ ,__ , , then , _ moves in and __moves out.

• K+, H+, HCO3-

• chloride moves in

• bicarbonate moves out

What pump facilitates the gastric hydrochloric acid formula

protein H+ K+ ATPase pump

What is the function of gastric hydrochloric acid

• kills microbes, denatures food enzymes, breaks down plant cell walls, meat CTs

• activates pepsinogen and lingual lipase

Where does the initial digestion of lipids take place, and by what?

in the mouth/stomach by lingual lipase and gastric lipase

How is pepsin autocatalytic?

catalyzes own reaction by splitting amino acids to activate pepsinogen, that activates more pepsin

why is there little absorption in the stomach?

• thick mucus

• lack of transport proteins

• tight junctions

Mucus cells contain ___________ which converts ethanol to acetaldehyde

alcohol dehydrogenase

Function of duodenum

• recieves chyme from stomach and secretions from accessory organs

• neutralizes stomach acid

• inactivates pepsin

• emulsifies lipids

• site of pancreatic enzyme function

Jejunum function

• majority of chemical digestion and absorption occur here

Ileum function

• lymphoid nodules protect against bacteria

Small intestine villi

• absorb nutrients and deliver to liver

• each contains a lacteal

What is a lacteal?

• lymphatic capillary that absorbs lipids

small intestine microvilli

• form brush border enzymes (BBEs)

• increase surface area for absorption

BBE functions

• carry out final stage of digestion

• peptidases and enteropeptidase

Small intestine - intestinal crypts

• what does upper portion contain?

• what does lower portion contain?

• what cell secretes lysozyme?

• upper: enterocytes, goblet cells

• lower: stem cells

• paneth cells

What is the function of the duodenal glands?

• produce mucus to protect epithelium

• contains bicarbonate ions

• increases pH

__ of foodstuffs are used to make __ for biosynthesis

• monomers

• ATP

What is a hydrolysis reaction?

use water to break polymers into monomers

What initiates digestion of carbohydrates?

• salivary amylase

What initiates digestion of lipids?

• lingual and gastric lipase

what initiates digestion of proteins?

• pepsin

Maltase, sucrase, lactase:

• source?

• target?

• products?

• brush border of small intestine

• maltose, sucrose, lactose

• monosaccharides

pancreatic amylase:

• source

• target

• products

• pancreas

• starch

• oligosacchardies, trisaccharides, maltose

salivary amylase

• source

• target

• products

• salivary glands

• starch

• oligosaccharides, trisaccharides, maltose

What bond does pepsin break?

tyrosine and phenylalanine bond

Pepsinogen (pepsin) --- stomach

• source

• target

• products

• chief cells of gastric glands

• proteins and polypeptides

• smaller polypeptides

pepsinogen (pepsin) remarks (3)?

• activated by HCl

• autocatalytic

• breaks bonds between tyrosine and phenylalanine

enteropeptidase --- sm intestine

• source

• target

• products

• brush border and lumen of sm intestine

• trypsinogen

• trypsin

trypsinogen --- sm intestine

• source

• target

• products

• pancreatic juice

• proteins and polypeptides

• smaller polypeptides

chymotrypsinogen (chymotrypsin)

procarboxypeptidase (carboxypeptidase) --- sm intestine

• source

• target

• products

• activated by?

• pancreatic juice

• proteins and polypeptides

• smaller polypeptides

• activated by trypsin

proelastase (elastase) --- sm intestine

• source

• target

• products

• activated by

• pancreatic juice

• elastin

• smaller polypeptides

• trypsin

dipeptidases and peptidases --- sm intestine

• source

• target

• products

• brush border of small intestine

• dipeptides and tripeptides

• amino acids

Which two factors break lipid globules into smaller globules?

• stomach churning and segmentation

• called emulsification

and ___ from bile coat surface of small globules

• lecithin

• bile acids

what is the purpose of coating the small globules?

• prevent them from coming back together

• increase SA for lipase enzymes

Lipase breaks ____ into ____ and a ____

• triglycerides

• 2 FFAs

• monoglyceride

lingual lipase

• source

• target

• products

• glands of tongue

• triglycerides

• FFAs and monoglycerides

gastric lipase

• source

• target

• products

• chief cells of gastric glands

• triglycerides

• FFAs and monoglycerides

pancreatic lipase

• source

• target

• products

• pancreatic juice

• triglycerides

• FFAs and monoglycerides

What 2 nucleases are contained in pancreatic juice?

• deoxyribonuclease

• ribonuclease

what is the function of deoxyribonuclease and ribonuclease?

• break polymers into nucleotides

Brush border contains nucleosidases and phosphatases that result in which 3 things?

• sugar (deoxyribose or ribose)

• phosphate ions

• nitrogenous base