The Digestive System

Anatomy of the Pancreas

- located posterior to the stomach - pancreatic duct enters duodenum at the duodenal papilla (along with the common bile duct) - hepatopancreatic sphincter controls release of pancreatic exocrine secretions.

functions of saliva

- lubricates food to form a bolus - digestion of carbohydrates by salivary amylase and digestion of lipids by lingual lipase - suppresses bacteria growth

Mechenical Processing using teeth, tounge and hard palate

- muscles of masitcation: temporalis and masster; controlled by trigeminal nerve (CN V) - Tounge muscle: controlled by hypoglossal nerve (CN XII)

steps of swallowing

-elevation of soft palate -elevation of larynx and folding of the epiglottis to cover the glottis

3 regions of large intestine

1. Cecum- Pouchlike that material first enter when leaving the ileum or small intestine. Compaction begins here. ileocecal valve guards the connection between ileum and cecum. (appendix attaches here) 2. Colon- lack villi. has an abundace of mucus cells. Haustra permit the colon to expand and elongate. created by bands of taeniae coli. Divided into ascending, transverse, descending and sigmoid colon. 3. Rectum- expandable organ for the temporary storage of feces. epithelium of mucosa is stratified squamous for protection from mechanical stress. terminates in the anal canal: ~internal anal sphincter: smooth muscle under involuntary control ~external anal sphincter: skeletal mucle under voluntary control.

regions of small intestine

1. Duodenum: closest to stomach. "mixing bowl". Recieves chyme from stomach and digestive secretions from pancreas and liver. curves to form a c shape that encloses the pancreas. ~ Pyloric sphincter: controls the passage of material from stomach to small intestines 2. Jejunum: bulk of chemical digestion and nutrient absorption. 3. Ileum: final and longest segment. ~ends at Ileocecal valve: sphincter that controls the passage of material from the small intestine (ileum) to the large intestine (cecum)

Defensive Role: Lining of digestive tract

1. corrosive effects of digestive acids and enzymes 2. physical stresses, such as abraison 3. bacteria swallowed or reside in digestive tract enter underlying tissues where microphages and other cells of immune system attack

Functions of the liver

1. metabolic regulation: store glucose (insulin) and release glucose (glucagon) as needed 2. production of bile: required for efficient lipid digestion (bile is an emulsifier, not an enzyme). Bile breaks a droplet of lipid into smaller droplets; increasing the surface area of the lipid exposed to lipase.

Digestive tract: 4 major layers

1. mucosa: inner lining of digestive tract (mucous membrane). consists of epithelium moistened by glandular secretions. permanent transvers circular folds that increase surface area. in small intestines villi~ increase area of absobtion. - lamina propria (connective tissue) -muscularis mucosae (smooth muscle) 2. submucosa: Dense irregular connective tissue. binds mucosa to muscular layer. neural network involved in controlling contractions of smooth muscle. regulating secretion of digestive glands 3. muscular layer: band of smooth muscle cells arranged in an inner circular layer and inner longitudinal layer. contractions propel material 4. serosa: serous membrane that covers the muscular layer along most portions of the digestive tract enclosed by peritoneal cavity.

Functions of the oral cavity

1. sensory analysis 2. mechanical processing 3. lubrication 4. limited digestion

Digestion and absorption of carbohydrates

1. starch is digested into disaccharides and trisaccharides by amylases: ~ salivary amylase: released from salivary glands in the oral cavity ~ pancreatic amylase: released from the pancreas; enters into the duodenum through the pancreatic duct 2. brush border enzymes on one of the SI epithelium split disaccharides and trisaccharides into monosaccharides (glucose) 3. monosaccharides are absorbed by the intestinal epithelium by facilitated diffusion 4. monosacchariedes are secreted by the SI epithelium into the interstitial fluid by facilited diffusion 5. monosaccharides diffuse into capillaries of the cardiovascular system which brings nutrients to the liver via the hepatic portal vein

Anatomy of the stomach

> Cardia: where esophagus enters into the stomach > Fundus: "hump" on top > Body: main portion of stomach > pylorus: pyloric sphincter guards the exit to the duodenum > Greater and Lesser Curvature > Rugae: accordion-like folds of the inner wall of the stomach that allow the stomach to expand > Greater Omentum: large fold of visceral peritoneum that extends from the liver to the lesser curvature of the stomach; contains the common bile duct

Molecular structure of carbohydrates

> Complex carbohydrates: starch is a molecule composed of 1000s of glucose molecules bonded together > Simple carbohydrates: ~ trisaccharides: 3 glucose molecules bonded together ~ disaccharides: 2 glucose molecules bonded together ~ monosaccharides: 1 glucose molecule (this is the nutrient that is absorbed across the epithelial layer of the intestinal mucosa)

Functions of Digestive System

> Ingestion: food enters mouth > Mechanical Processing: physical manipulation of food (chewing) > Digestion: chemical breakdown of carbohydrates, triglycerides and proteins into smaller molecules for absorbtion across intestinal epithelium. Digestive enzymes break down bonds that hold molecules together (breaking protiens into individual amino acids) > Secretion: release of water, hydrochloric acid (HCI), buffers and digestive enzymes into the lumen of the gastrointestinal tract. > Absorbtion: movement of small organic molecules from lumen to gastrointestinal tract across epithelial cell layer of the digestive tract. > Excretion: waste products are compacted into feces which leaves the body through the process of defecation.

Digestive Tract Anatomy

> Lumen: the cavity or channel within a tublualr structure > Proximal vs. distal: in a tubular structure with a one-direction flow of material the term proximal can be used for a region closer to the "start" (mouth) and distal can be used for a region closer to the "end" anus. > Peritoneum: visceral peritoneum is directly attached to the surface of the abdominopelbic organs; the parietal peritoneum lines the wall of the abdominopelvic cavity. The peritoneal cavity is located between the visceral peritoneum and the parietal peritonneum. > Mesentery Proper: folds of visceral peritoneum that suspends the small intestine from the posterior abdominal wall.

Molecular structure of proteins

> Protien: is a molecule made up of 1000s of individual amino acids bonded together in a long string, then the string is folded and twisted into a 3D shape. > Denatured Protien: same as above except the 3D structure has been uncoiled > Polypeptide: shorter string of amino acids; contains several 100 > Peptide: even shorter amino acid chain; 25-50 > Amino Acid: individual molecule that is the building blocks of the above structures (this is the nutrient that is absorbed across the epithelial layer of the intestinal mucosa)

Digestion and absorption of proteins

> Stomach: hydrochloric acid denatures protiens (alters their 3D shape) and pepsin digest protiens into polypeptides. > Small Intestine: Pancreatic proteases (trypsin, chymotrypsin, carboxypeptidase) digest polypeptiede into small peptides. --> brush boarder enzymes on the SI epithelium into the interstitial fluid by facilitated diffusion. --> amino acids diffuse into capillaries of the cardiovascular system which brings nutrients to the liver via the hepatic portal vein.

Molecular structure of lipids

> triglycerides are composed of 3 fatty acids attached to 3 carbon molecule called glycerol > triglycerides can be digested into free fatty acids and monoglycerides (glycerol with only 1 fatty acid attached). Free fatty acids and monoglycerides are the nutrients that are absorbed across epithelial layer of the intestinal mucosa.

Gallbladder

A muscular sac attached to the liver that secretes bile and stores it until needed for digestion, it is then released into the duodenum > bile ducts: the common bile duct is formed from the union of the common hepatic duct and the cystic duct > Duodenal papilla: entry of the common bile duct and the pancreatic duct into the lumen of the duodenum > hepatopancreatic sphincter: relaxation of this sphincter permits bile and pancreatic exocrine secretions to enter duodenum.

Esophagus

A muscular tube that connects the mouth to the stomach. - stratified squamous epithelium - muscular tube for the passage of the bolus from the pharynx to the stomach - posterior to trachea - penetrates diaphragm at esphageal hiatus; allows the esophagus to pass from the throacic cavity to the abdominal cavity

Bolus

A soft mass of chewed food.

The Small Intestine & Function

Absorbs 90% 0f nutrients; Main absorption organ of the digestive tract. 20ft long > Most enzymatic digestion and absorption occurs in the small intestine > Digestive enxymes, bile and buffers are released into the lumen of the small intestines by the pancreas, liver and gall bladder.

The digestive system

Breaks down food into absorbable units that enter the blood for distribution to body cells. > consists of the muscular digestive tract assisted by various accessory organs > oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus > accessory organs: teeth, tounge, glandular organs and salivary glands, liver, pancreas, gallbladder

How is the small intestine adapted for absorption?

Circular folds (plicae circulares), Villi and microvilli provide a very large surface area.

Secretions of the pancreas

Endocrine secretion hormone: insulin and glucagon Exocrine secretion (digestive enzymes): ~ buffers to neutralize chyme ~ Digestive enzymes: 1. pancreatic amylase to digest carbohydrates 2. pancreatic lipase to digest lipids 3. proteases to digest proteins: trypsin, chymotrypsin, carboxypeptidase.

Wall of small intestine

Highly convoluted (folded) mucosa for better absorption through increased surface area > Circular folds: mucosa has 800 transverse folds called plicae circulares > plicae circulares have small projections called villi. > Microvilli: because it gives the surface of the cells the appearance of bristles of a brush- so this region is termed "brush border" > Plicae, villi and micro villi all serve to increase surface area for more efficient absorption of nutrients > each villus has a capillary bed and a lacteal (lymphatic capillary), that carry nutrients to hepatic portal circulation to liver.

large intestine (colon)

Horseshoe shaped. Begins at end of ileum and ends at anus. 5 ft long. Absorbs water, vitamins and minerals from gut content > simple columnar epithelium (cecum & colon) or stratified squamous epithelium (rectum) > absorbs water: about 9 liters/day enter the digestive tract (2 L of ingested water + 7 L of secretion) ~ all but about 150 ml is absorbed by osmosis 3 main functions 1. Reabsorption of water 2. absorbs vitamins made by bacteria 3. compacts and stores feces before defecation

Movement of Digestive Materials

Involuntary control of smooth muscle of muscularis externa > Peristalisis: "wave-like" contractions & movement of material > segmentation: non-directional contractions; churns material in the stomach and small intestine for the mechanical processing and mixing with sectretions.

anatomy of liver

Largest internal organ of the body, weighing about 1.36 kg located in the right-upper quadrant of the abdomen, tucked against the inferior surface of the diaphragm consists of two major lobes: right and left; two minor lobes: caudate and quadrate

Exocytosis

Movement of material out of the cell, by packaging the material in vesicles

Name the layers of the digestice tract superficial to deep

Mucosa, submucosa, muscular layer, serosa

intestinal juice

Secreted by the walls of the small intestine, works with the pancreatic juice to chemically break down food and complete the digestive process.

Tissue type: oral cavity, pharynx, esophagus, anus

Stratified squamous epithelium~ areas of stress

Catabolism

The sum total of all processes in an organism which break down chemicals to produce energy and simple chemical building blocks.

facilitated diffusion

a type of carrier mediated transport that is passive and therefore dependent on concentration gradients. The solute moves from an area of high concentraition to an area of low concentration. The solute (ligand) must mind to a specific receptor site on the carrier protein and the carrier protein actually changes shape allowing the molecule to be moved across the cell membrane.

Digestion

chemical breakdown of carbohydrates, triglycerides and proteins into smaller molecules which are small enough for absorption across the intestinal epithelium. Digestive enzymes break the bonds that hold the molecule together (altering the molecular structure; i.e. breaking a protein into individual amino acids

bile salts

compounds in bile that aid in emulsification. most of the bile salts entering the large intestine are rapidly absorbed in the cecum. They are then transported to the liver for secretion in bile.

Name 3 segments of the small intestine from proximal to distal.

duodenum, jejunum, ileum

a narrowing of the ileocecal valve would hamper movement of chyme between what two organs?

from small intestine to large

sensory analysis of potential foods

gustation is the sense of taste: facial nerve (CN VIII) and glossopharyngeal nerve (CN IX); processed by frontal lobe of brain

Gastric Pits & Glands

invaginations of the stomach mucosa containing cells that produce the gastric juices > epithelium of the stomach: simple columnar epithelial cells > gastric pit: - mucus cells: produce mucus that coats the peithelial cells to protect them from the very acidic conditions in the stomach > Gastric Gland: -Parietal Cells: sectrete hydrochloric acid (HCI is a strong acid) ~ Kills pathogens (bacteria and viruses) ~ HCI denatures proteins (to denature is to uncoil the 3D structure of the protein) ~ HCI activates pepsinogen to pepsin -Cheif Cells: produce pepsinogen, an inactive form of the enzyme pepsin (digests protiens) ~ HCI activates pepsinogen to pepsin

stomach function

large muscular sac that continues the mechanical and chemical digestion of food > temporary storage of ingested material > Mechanical processing of materials - forms chyme: a liquid suspension of ingested material mixed with salivia and stomach secretions > digestion of carbohydrates (salivary amylase) triglycerides (lingual lipase) and proteins (pepsin)

Absorption

movement of small organic molecules (monosaccharides, amino acids, fatty acids, monoglycerides) from the lumen of the gastrointestinal tract (outside the body) across the epithelial cell of the intestinal mucosa (to inside the body)

Digestion and absorption of lipids

no digestion or absorption occurs in the mouth or stomach 1. lingual lipase is released in the oral cavity and begins to digest triglycerides into monoglycerides and free fatty acids. 2. in small intestine (duodenum) bile emulsifies triglycerides into fatty acids and monoglycerides 3. lipid products for micelles (small droplets of fatty acids and monoglycerides coated in bile salts) 4. micelles diffuse into epithelial cells (can directly cross the phospholipids bilayer) 5. epithelial cells reform triglycerides 6. triglycerides are coated with proteins to form chylomicrons (small triglycerides droplets coated in proteins) 7. chylomicrons are secreted from the intestinal epithelium by exocytosis 8. chylomicrons diffuse into lacreals (lymphatic system capillaries) where they are transported in lymph vessels to the toracic duct, which empties into the left subclavian vein

Three phases of swallowing

oral (buccal), pharyngeal, esophageal

salivary glands

parotid, sublingual, and submandibular glands produce 1-1.5 liters of saliva each day.

Which ring of muscle regulates the flow of chyme from the stomach to the small intestine?

pyloric sphincter

Tissue type: digestive tract

simple columnar epithelium~ sectretion/absorbtion

deglutition

the act of swallowing

Pharynx

throat; passageway for food to the esophagus and air to the larynx - stratified squamous epithelium - oropharynx and larynogopharynx (food, drink, air) - paryngeal muscles propel food into the esophagus during swallowing (glossopharyngeal nerve (CN IX) and accessory nerve (CN XI) - during swallowing muscles elevate the larynx, causeing the epiglottis (elastic cartilage) to cover the glottis, so food and liquid don't move into respiratory passages.

Defecation

~distension of stomach and duodenum triggers peristalisis of feces from colon into rectum ~stretching of rectum triggers defecation reflex, which relaxes the internal anal sphincter *release of feces requires conscous relaxation of external anal sphincter