Digestive System Pennix (copy)

Digestive Processes

ingestion, movement, digestion (breakdown of food via mechanical/chemical processes), absorption (into cardiovascular/lymphatic systems), defecation

Chemical digestion

catabolic reactions that break down carbs, lipids, and proteins into smaller molecules

Mechanical Digestion

Purpose: Increase the surface area of ingested foods to be physically prepared for digestion by enzymes

• Includes:

• chewing,

• mixing food with saliva by the tongue

• churning food in the stomach,

• segmentation within the small intestine

  • Segmentation = mixing food with digestive juices, making absorption faster by repeatedly moving different parts of food mass over intestinal wall

GI Tract Organs

mouth, pharynx, esophagus, stomach, S/L intestine, liver, pancreas, gallbladder, rectum, anus

GI tract structure

tube running down the ventral cavity from the mouth to the anus

GI Tract accessory structure/function

teeth, tongue, salivary glands, liver, gallbladder, and pancreas that produce/store secretions that aid in chemical breakdown of food

Mucosa

inner lining of GI tract

Mucosa Epithelium (Part of Mucosa)

stratified in mouth/esophagus and simple throughout the rest of the GI tract

Mucosa lamina propria

loose CT that connects the epithelial layer to the muscularis mucosae and provides space for blood and lymphatic vessels

Muscularis mucosa

smooth muscle that puts folds into the intestine to increase the surface area of the intestine

-contains longitudinal layer and circular layer

Submucosa(middle)

dense CT that binds the mucosa(inner) to the muscularis(layer before serosa).

Highly vascular and contains an autonomic nerve supply to the muscularis mucosa

Muscularis

-in the mouth, pharynx, and upper esophagus,

-some skeletal muscle -voluntary swallowing,

-helps to fix food and move it through the GI tract

Serosa (visceral peritoneum)

outermost layer of GI tract, the part you see

Parietal peritoneum

lines the wall of the abdominal cavity

Visceral peritoneum

covers organs

peritoneal cavity

open space between visceral peritoneum and parietal peritoneum

uvula

tissue protrudes past end of soft palate (hang down in back)

Medial Septum

divides tongue symmetrically lateral halves and tongue attached to hyoid bone inferiorly

tongue

composed of skeletal muscle covered by mucous membranes

lingual frenulum

attaches tongue to the floor of the mouth

Papillae

bumps on tongue

filiform papillae- roughen tongue surface to help manipulate food

fungiform papillae- scattered and vascular TASTE BUD

vallate papillae - V shape row back of tongue TASTE BUD

foliate papillae- lateral aspects TASTE BUD

Salivary glands

lubricates and produces salivary amylase

Salivary amylase

enzyme, hydrolyse dietary starch into disaccharides and trisaccharides that are converted into glucose by other enzymes to supply the body with energy

Teeth order

Deciduous - 6 mo

Permanent= 32 total

6- 1 set molars

12- 2 set molars

18- 3 set molars or wisdom teeth

mastification

chewing

bolus

food reduced to a soft flexible mass

Voluntary process of deglutition

bolus forced to back of mouth cavity by the tongue

Pharyngeal process of deglutition involuntary

bolus stimulates nerves in orpharynx

impulses cause the soft palate to move up and seal off the nasopharynx

Esophageal process of deglutition

bolus pushed down esophagus by peristalsis

Peristalsis

-function of the muscularis (part of the mucosa layers) that is controlled by the medulla

- circular and longitudinal layers of the muscularis contract, forcing food down

-involuntary muscle movements

esophagus

collapsed tube behind trachea

stomach

j-shaped and inferior to diaphragm

Cardiac Sphincter

sphincter between esophagus and start of stomach

cardia (part of stomach)

closet to esophagus

Fundus part of stomach

rounded portion above cardiac and space for extra food

body of stomach

central portion and most of stomach

pylorus

narrow, inferior region prior to sm int

pyloric sphincter

Connection spot between duodenum (small intestine) and stomach

Function: controls stomach emptying

rugae

large folds of an empty stomach

chief cells

secrete pepsin, enzyme to chemically digest proteins

parietal cells

Secretes hydrochloric acid and intrinsic factor helps absorption of B12

Hydrochloric acid = super acidic stomach necessary for activation of protein-digesting enzyme, pepsin

enteroendocrine cells (gastric juice)

produce gastrin that regulates stomach secretion and motiliy, stims hcl and pepsin production

closes cardiac sphincter(opening) and relaxes pyloric sphincter (last)

Digestion in stomach

• peristalsis movement begin and passes over stomach every 15-25 seconds

• Gastric juices reduce bolus to a thin liquid=chyme

• excess food stored in the fundus

• mixing waves force chyme toward the pyloric sphincter

• sphincter only allows a portion of chyme to pass

Chemical Digestion in Stomach (amino acids)

• Pepsin breaks peptide bonds that hold amino acids together

• only works in an acidic environment (ph of 2)

Alkaline mucous

lines stomach and prevents breakdown of stomach walls

Cephalic phase

before food enters the stomach,

sight, smell, taste, or thought of food = stimulation of the production of gastric juices

gastric phase

• Food enters the stomach

• Distention of the stomach that activates stretch receptors and initiates short/long reflexes travels to the medulla

• Partially digested proteins and caffeine stimulate the secretion of stomach gastrin

  • Stomach gastrin increases the production of gastric juice, increases the coordinated contractions of the GI tract, and relaxes pyloric (bet. duodenum/stomach) and ileocecal spincters

intestinal phase

Overall effect=inhibition of gastric secretions

Stimulation caused by digested food entering duodenum of small intestine causing mucosal cells to release enteric gastric hormone that encourages gastric glands to continue to secrete UNTIL OVERRIDDEN BY INHIBITORS

Inhibition begins when distension of the duodenum or the presence of acidic, fatty, or hypertonic chyme

secretin (hormonal inhibitor)

stims pancreatic secretion

gastric juice inhibitors

secretin, cholecystokinin, GIP

cholecystokinin (hormonal inhibitor)

induces contraction of gallbladder that releases bile

GIP (Gastric inhibiting peptide)

stims release of insulin

pancreas structure

oblong gland connected by two ducts to the duodenum

posterior (under) greater curvature of stomach

pancreatic duct

above ampulla

function: carrying pancreatic juice from the pancreas

unites with the bile duct from the gallbladder at the wall of the duodenum to fuse and form the hepatopancreatic ampulla

hepatopancreatic ampulla

empties pancreatic juice and bile into the small intestine below pylorus

pancreatic histology

Glandular epithelial cells include:

Islets of Langerhans = endocrine portion that secretes hormones like insulin (only 1%)

remaining 99% acini = exocrine glands that secrete digestive enzymes called pancreatic juice

pancreatic juice

slightly basic, enzymes for all foods, especially for lipids, secretion triggered by chyme entering duodenum

liver

4 lobes (largest=right lobe, left lobe(smaller seperated by fissure, caudate, and quadrate lobe) 1.4 kg in average adult

Function: producing bile for export to duodenum

lobules

• functional unit of liver that are made of hepatocytes(liver cells) each surrounding a vein

• At the corner of each bile is a portal triad that has:

  • hepatic artery for blood to the liver

  • hepatic portal vein carrying nutrient blood to digestive system

  • a bile duct

• Lobules cells secrete:

  • bile

  • Kupffer’s cells

bile

yellow, brown, olive-green liquid with a pH of 7.6

mostly water with bile salts = emulsifiers that break down large fat

Kupffer’s cells-

destroy old RBC and WBC, bacteria, and toxins

Carbohydrate metabolism (Liver Physiology)

maintains normal blood glucose levels

Fat metabolism (Liver Physiology)

synthesises and digests cholesterol and stores fats

Protein Metabolism (Liver Physiology)

removal of nitrates

conversion of NH3 to urea

synthesizes plasma proteins

synthesis of anticoagulants and fibrenogen (blood coagulent)

conversion of amino acids

loss of this functiion = death

Liver Physiology steps 5 and 6

excretion and synthesis of bile salts

Removal of drugs and hormones (Liver Physiology)

detoxify penicillin, ampicillin, and excrete or alter into bile, estrogen, or aldosterene

Storage (Liver Physiology)

stores glycogen and vitamins A, B , D, E, K, iron, copper

Steps 8 and 9 (Liver Physiology)

Phagocytosis (kupffer’s cells) and activation of vitamin d

gallbladder structure

pear shaped sac, located in the fossa of the liver attach to right lobe

gallbladder physiology

Hormonal stimulation causes the smooth muscle to contract and squeeze contents into the cystic duct and common bile duct

stores and concentrates bile until small intestine needs

small intestine empty=closed hepatopancreatic ampulla = bile flows back to gallbladder

small intestine

6-7 m long, absorption and most digestion occurs here

mesentery (outer covering)

extends to the digestive organs from the body wall (tip is attached to the posterior abdominal wall)

supplies small intestine with blood supply and nerves

hold organs in place (binds small intestine to wall)

store fat

duodenum

1st 12 fingers width from pyloric sphincter

jejunum (squiggly part)

portion is empty at death

ileum

longest part, joints the large intestine at ileocecal sphincter

Histology of Small intestine

large surface area= better absorption

intestinal glands = secrete juices

duodenal gland

secrete alkaline mucous (that neutralizes acidic chyme)

length of small intestine allows?

times for chyme to pass through

villi

increase surface area for absorption

in core of each villi is a capillary bed and a lymphatic capillary called a lacteal

Digested food is absorbed into capillary blood and lacteal

contain: arteriole and venule also

circular folds

permanent ridges, causes chyme to spiral which enhances absorption by increasing the contact with vili

Microvilli

absorptive cells that form brush border that complete digestion of carbohydrates and proteins in small intestine

segmentation

localized contractions and doesn’t move chyme

Chemical

pancreatic juice, bile, intestinal juice complete breakdown of carbohydrates, proteins, and lipids

Absorption in small intestine

• diffusion(high to low without energy/carrier)

  • lipid soluble molecules

  • short fatty chains

• facilitated diffusion(high to low w carrier)

  • monosaccharides(carbohydrate)

• Osmosis (low to high water)

• Active transport (low to high w ATP)

  • amino acids

  • most carbohydrates

  • irons/electrolytes

Fats/lipid absorption

bile salts dissolve and form bubbles called micelles

micelles= come in contact with epithelial cells they allow contents to diffuse out into small intestine

lipoproteins

when lipids hitch rides with protein transporters

HDL (high density lipids)

removes cholesterol from arteriole walls to take to the liver

LDL (low density lipoproteins)

transport cholesterol to tissues for hormone production and causes buildup in arteries

water

absorbed by osmosis except for 1 liter

large intestine

completes absorption mostly water and forms/expels feces

cecum structure

portion below ileocecal valve

Where is the appendix located at?

attached to the pouch of cecum

colon

absorbs water, electrolytes, vitamins and solidifying waste into stool

ascending colon

up

descending colon

down

transverse

across

sigmoid colon

angles toward the midline of the body (s-shaped)

pepsin

breaks down dietary proteins into smaller peptides and amino acids in the stomach

rectum

last 20cm of the GI tract

anal canal

last 204cm of rectum