ANATOMY & PHYSIOLOGY_DIGESTIVE SYSTEM | Study notes Anatomy

ANATOMY & PHYSIOLOGY (Lecture): Digestive System

JAILOUI SE A. PE REZ

BACHEL OR OF SCI ENCE IN NURSING

DIGESTIVE SYSTEM

Digestive System

The digestive system consists of a group of organs that

break down the food we eat into smaller molecules that

can be used by body cells.

Two groups of organs compose the digestive system:

gastrointestinal tract and accessory organs

As fetuses, we received nutrients through the umbilical

cord which connects to our mothers. After being born

all important meals are taken orally and ex pelled

through the anus.

Digestive Processes

1. Ingestion - Partaking foods and liquids into the mouth

(eating).

a. Transport and Metabolism of Food – food

moves through your GI tract by a process

called peristalsis. The large, hollow organs of

your GI tract contain a layer of muscle that

enables their walls to move. The movement

pushes food and liquid through your GI tract

and mixes the contents within each organ.

b. Metabolism – refers to all of the chemical

reactions that occur in the body that change

food into energy.

2. Digestion – breakdown of large insoluble food

molecules into small water-soluble food molecules so

that they can be absorbed into the watery blood

plasma.

3. Mechanical Mastication – food is physically broken into

smaller parts. For instance, by chewing.

4. Chemical Digestion through Enzymes – food is broken

down by the action off chemical agents (such as

enzymes, acids, and bile)

a. Enzymes are biological catalysts which speed

up the rate off a chemical reaction (i.e.

digestion) by lowering activation energy.

i. Example of digestive enzymes are:

1. Amylase

2. Pepsin

3. Trypsin

4. Pancreatic lipase

5. Deoxyribonuclease and

ribonuclease

5. Absorption – is the movement off the products of

digestion from the lumen of the GI tract into blood or

lymph.

a. A few substances in food can be absorbed

without undergoing digestion. These include

vitamins, ions, cholesterol, and water.

b. Occurs in the intestines

6. Provide Nutrients – the walls of the small intestine

absorb the digested nutrients into the bloodstream.

7. Elimination - The removal of undigested food content

and waste

a. Vomiting – elimination of food by forceful

expulsion of digested materials through the

mouth

b. Defecation - Wastes, indigestible substances,

bacteria, cells sloughed from the lining of the

GI tract, and digested materials that were not

absorbed in their journey through the

digestive tract leave the body through the

anus eliminated material is termed feces or

stool.

Organization of the Digestive System

Gastrointestinal tract

Also called the alimentary tract

Continuous tube that extends from the mouth to the

anus through the thoracic and abdominopelvic cavities

Organs include the mouth, most of the pharynx,

esophagus, stomach, small intestine, and large

intestine.

5–7 meters (16.5–23 ft) in a living person when the

muscles along the wall of the GI tract organs are in a

state of tonus (sustained contraction), longer in a

cadaver (about 7–9 meters or 23–29.5 f) because of

the loss of muscle tone after death.

GI tract contains food from the time it is eaten until it is

digested and absorbed or eliminated

Physically breaks down the food by churning it and

propel the food along the tract

Histology of the GI Tract

1. Mucosa - inner lining of the GI tract, is a mucous

membrane. Composed of:

a. Epithelium - In the mouth, esophagus, and

anal canal is mainly nonkeratinized stratified

squamous epithelium that serves a protective

function. Simple columnar epithelium, which

functions in secretion and absorption, lines

the stomach and intestines forms continuous

sheets of cells that line internal surfaces and

cover the external surface of the body

b. Lamina Propria - Lamina means thin and

propria means one’s own. It constitutes the

layer of loose connective tissue and interstitial

matrix located just below the epithelium,

which includes:

i. Collagen and elastin

ii. Blood and lymphatic vessels

iii. Myofibroblast

c. Muscularis Mucosae - Thin layer of smooth

muscle found in the stomach, located outside

the lamina propria mucosa, and separating it

from the submucosa and composed of

several thin layers of smooth muscle fibers

2. Submucosa – consists of areolar connective tissue that

binds the mucosa to the muscularis. Absorbed

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JAILOUISE A. PEREZ

BACHELOR OF SCIENCE IN NURSING

DIGESTIVE SYSTEM

Digestive System  The digestive system consists of a group of organs that break down the food we eat into smaller molecules that can be used by body cells.  Two groups of organs compose the digestive system: gastrointestinal tract and accessory organs  As fetuses, we received nutrients through the umbilical cord which connects to our mothers. After being born all important meals are taken orally and ex pelled through the anus. Digestive Processes

Ingestion - Partaking foods and liquids into the mouth (eating). a. Transport and Metabolism of Food – food moves through your GI tract by a process called peristalsis. The large, hollow organs of your GI tract contain a layer of muscle that enables their walls to move. The movement pushes food and liquid through your GI tract and mixes the contents within each organ. b. Metabolism – refers to all of the chemical reactions that occur in the body that change food into energy.
Digestion – breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma.
Mechanical Mastication – food is physically broken into smaller parts. For instance, by chewing.
Chemical Digestion through Enzymes – food is broken down by the action off chemical agents (such as enzymes, acids, and bile) a. Enzymes are biological catalysts which speed up the rate off a chemical reaction (i.e. digestion) by lowering activation energy. i. Example of digestive enzymes are: 1. Amylase 2. Pepsin 3. Trypsin 4. Pancreatic lipase 5. Deoxyribonuclease and ribonuclease
Absorption – is the movement off the products of digestion from the lumen of the GI tract into blood or lymph. a. A few substances in food can be absorbed without undergoing digestion. These include vitamins, ions, cholesterol, and water. b. Occurs in the intestines
Provide Nutrients – the walls of the small intestine absorb the digested nutrients into the bloodstream.
Elimination - The removal of undigested food content and waste a. Vomiting – elimination of food by forceful expulsion of digested materials through the mouth b. Defecation - Wastes, indigestible substances, bacteria, cells sloughed from the lining of the GI tract, and digested materials that were not absorbed in their journey through the digestive tract leave the body through the anus eliminated material is termed feces or stool. Organization of the Digestive System Gastrointestinal tract  Also called the alimentary tract  Continuous tube that extends from the mouth to the anus through the thoracic and abdominopelvic cavities  Organs include the mouth, most of the pharynx, esophagus, stomach, small intestine, and large intestine.  5–7 meters (16.5–23 ft) in a living person when the muscles along the wall of the GI tract organs are in a state of tonus (sustained contraction), longer in a cadaver (about 7–9 meters or 23–29.5 f) because of the loss of muscle tone after death.  GI tract contains food from the time it is eaten until it is digested and absorbed or eliminated  Physically breaks down the food by churning it and propel the food along the tract Histology of the GI Tract
Mucosa - inner lining of the GI tract, is a mucous membrane. Composed of: a. Epithelium - In the mouth, esophagus, and anal canal is mainly nonkeratinized stratified squamous epithelium that serves a protective function. Simple columnar epithelium, which functions in secretion and absorption, lines the stomach and intestines forms continuous sheets of cells that line internal surfaces and cover the external surface of the body b. Lamina Propria - Lamina means thin and propria means one’s own. It constitutes the layer of loose connective tissue and interstitial matrix located just below the epithelium, which includes: i. Collagen and elastin ii. Blood and lymphatic vessels iii. Myofibroblast c. Muscularis Mucosae - Thin layer of smooth muscle found in the stomach, located outside the lamina propria mucosa, and separating it from the submucosa and composed of several thin layers of smooth muscle fibers
Submucosa – consists of areolar connective tissue that binds the mucosa to the muscularis. Absorbed

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BACHELOR OF SCIENCE IN NURSING

elements that pass through the mucosa are picked up from the blood vessels of the submucosa. It contains many blood and lymphatic vessels that receive absorbed food molecules.

Muscularis - responsible for segmental contractions and peristaltic movement in the GI tract. Throughout the rest of the tract, the muscularis consists of smooth muscle that is generally found in two sheets: a. inner sheet of circular fibers b. outer sheet of longitudinal fibers.
Serosa - smooth membrane that consists of a thin connective tissue layer and a thin layer of cells that secrete serous fluid. It is composed of areolar connective tissue and simple squamous epithelium. NOTE: In some organs of the GI tract, the serosa forms part of the peritoneum which covers it. As for the esophagus, as it lacks a serosa, a single layer of areolar connective tissue called adventitia lines it. Nervous Regulation of the Digestive System  Peripheral Nervous System – a network of nerves that connects the brain and the spinal cord to the other parts of the body  Central Nervous System (CNS) – the origin of control over body movement. It controls voluntary and involuntary movements.  Autonomic Nervous System – it regulates the involuntary physiological processes to maintain homeostasis. 3 Anatomically Distinct Parts of ANS o Sympathetic Nervous System - Is viewed as a quickly responding system that mobilizes the body for action also known as “flight-or-fight” response. o Parasympathetic Nervous System - Acts slowly to dampen responses or the one that inhibits the response. o Enteric Nervous System - It is the nervous system of the GI tract. It can be found in the linings of the GI tract system and communicates with the CNS through sympathetic and parasympathetic system. The ENS has more neurons than spinal cord. Due to this, it is also known as “second brain” because of its extent and degree of autonomy. Examples of the Connection between GI Tract and Nervous System  Fear of public speaking cause digestive system to either slow down or speed up depending on the GI tract disorder that can disorder and can cause abdominal pain, diarrhea, and other symptoms  Emotions, feelings of excitement, or nervousness can cause the familiar churning in the stomach or the so- called “butterflies in your stomach” feeling. Two Types of Ganglia  Myenteric Plexus - is located between the inner and outer layer of the muscularis externa, it is mainly organized as a longitudinal chain of neurons and is concerned with motility throughout the whole gut  Submucosal Plexus - located in the submucosa and is involved with local conditions and controls local secretion and absorption, as well as local muscle movements. Major Types of Enteric Neuron 1. Enteric Sensory neurons - it is the one that detects changes in the chemical composition of digestive tract contents or detects mechanical changes 2. Enteric motor neurons - stimulates or inhibit smooth muscle contraction and glandular secretion in the digestive system 3. Enteric interneurons - connects enteric sensory and motor neurons Chemical Regulation of the Digestive System There are 30 neurotransmitters are associated with the enteric nervous system. Some examples of neurotransmitters in digestive tract are:
Acetylcholine - Stimulates smooth muscle contraction, increases intestinal secretions, release of enteric hormones, and dilation of blood vessels.
Norepinephrine - inhibits the digestive tract motility and secretions
Serotonin - stimulates digestive tract motility
Catecholamine - help the body respond to stress or fright and prepare the body for "fight-or-flight" reactions Two Types of Nerves  Extrinsic nerves or outside nerves that connect the digestive organs to brain and spinal cord. These nerves release chemicals that cause the muscle layer ofthe GI tract to either contract or relax, depending on whether food needs digesting  Intrinsic nerves are nerves within the GI tract are triggered when food stretches the walls of the hollow organs. The nerves release many different substances that speed up or delay the movement of food and the production of digestive juices. Accessory Digestive Organs  Include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas.  Produce or store secretions that flow into the GI tract through ducts, the secretions aid in the chemical breakdown of food. Mouth  It is also known as the oral or buccal cavity. The opening of the digestive system where solids and fluids enter. Solids are masticated by the teeth and pushed down to the pharynx with the tongue. o The oral cavity contains the teeth, the tongue, the gums of the teeth, and the salivary glands. o Two Regions of the mouth:

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BACHELOR OF SCIENCE IN NURSING

o Oral phase – the Bolus moves from the oral cavity into the oropharynx. o Pharyngeal phase – moves from the oropharynx into the esophagus o Esophageal phase – moves through the esophagus and into the stomach. Pharynx  An opening comprising of three parts: the nasopharynx, oropharynx, and laryngopharynx.  The laryngopharynx contains the epiglottis which keeps the opening to the esophagus closed until there is a need for swallowing, from which the opening to the trachea would be closed. This is to prevent foods and liquids from going to the lungs. Esophagus  A 25-centimeter tract found resting within the mediastinum. It has two sphincters: the upper esophageal sphincter regulates food coming from the mouth to the esophagus, while the lower esophageal sphincter regulates food coming from the esophagus to the stomach. Stomach  J-shaped enlargement of the GI tract directly inferior to the diaphragm in the abdomen. Regions of the Stomach  The lower esophageal sphincter, also known as the cardiac sphincter, opens food and liquids from the esophagus to the stomach. The lower esophagus and the sphincter make up the cardiac region.  The fundus is the extended area that is superior to the cardiac sphincter.  The body, also called the intermediate region, is the largest area of the stomach.  The pyloric region makes up the bottom region of the stomach and transports the digested food from the stomach to the duodenum of the small intestine. The pyloric sphincter keeps the materials within the stomach until it is digested enough to go to the duodenum of the small intestine. Secretions of the Stomach  Cephalic – controlled by the CNS that triggers smell, taste, sight, or thoughts.  Gastric – secretion lasts 3 to 4 hours and is set in motion by local neural and hormonal mechanisms triggered by the entry of food into the stomach  The stomach secretes water, electrolytes, hydrochloric acid, and glycoproteins, including mucin, pepsinogen, histamine, intrinsic factor, and enzymes. Once food enters the stomach, it is mixed with stomach secretions to form a semifluid material called chime.  Pepsinogen is the inactive form of the protein-digesting enzyme pepsin. Intrinsic factor is a glycoprotein that binds with vitamin b12, making the vitamin more readily absorbed in the ileum. Hydrochloric acid produces the low pH of the stomach’s contents that ranges between 1 to 3.  Intestinal - secretions are inhibited when the pH of the chime entering the duodenum drops to 2 or below Movements of the Stomach  Stomach Filling - enlargement of rugae to allow the stomach to accommodate a large amount of food  Mixing of the Stomach - Mixing waves is gentle. Peristaltic waves process is about the movement of chime inside the stomach.  Stomach Emptying - The amount of time food remains in the stomach depends on a number of factors, including the type and volume of food. Small Intestine  The small intestine is the longest part of the digestive system that spans six meters long. The three regions of the small intestine are the duodenum, jejunum, and the ileum near the long intestine.  The intestinal walls are lined with finger-like projections called villi which absorb the nutrients remaining in the materials digested by the stomach. Regions of the Small Intestine

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BACHELOR OF SCIENCE IN NURSING

 Duodenum - The duodenum is 12 inches long and curves around the head of the pancreas within the cavity and has two small mounds two-thirds of the way down the descending portion: the major and minor duodenal papilla. These papillae allow ducts from the liver and pancreas secrete bile and pancreatic juice that will aid in further digestion. o Cell Types within the Duodenum  Absorptive cells that are microvilli that produce digestive enzymes and absorb digested food  Goblet cells produce a protective mucus to protect the duodenum  Granular cells (Paneth cells) protect the intestinal epithelium from bacteria  Endocrine cells produce regulatory hormones within the intestine  Jejunum - The jejunum is 3.5 inches long and absorbs nutrients present in the digested materials.  Ileum - The last 2.5 inches of the intestine and has Peyer patches that can be found in its mucosa and submucosa that initiate immune responses against any microorganisms that withstood the digestive juice of the stomach. The ileocecal valve at the end of the small intestine is a one-way valve to keep digested materials from going back to the small intestine. Secretions of the Small Intestine  The mucosa of the small intestine produces secretions that contain primarily mucus, electrolytes, and water. Exocrine of the pancreas in the mucosa of the small intestine secrete mucus peptidase, sucrose, maltase, lactase, lipase, and enterokinase Regulation of the Small Intestine  Acidic chyme stimulates the secretion of 3 hormones: Secretin stimulates the pancreas juice, Cholecystokinin is the one that stimulates gallbladder to contract and release bile into the small intestine, and Gastric Inhibitory Peptide function is to slows down entrance of food into the small intestine by inhibiting peristalsis and slows down the digestive process to allow reactions to reach completion Movement of the Small Intestine  After you eat a meal, your small intestine contracts in a random, unsynchronized matter, this movements are known as peristalsis. After food leaves your small intestine, contractions push any food that remains in your digestive tract into your large intestine. Water, minerals, and any nutrients are then absorbed from your food. The leftover waste is formed into a bowel movement. Large Intestine  The large intestine is the last organ in the digestive tract before it is expelled as fecal matter through the anus. It is comprised of the cecum, colon, rectum, and the anal canal.  The large intestine absorbs water and electrolytes left from the small intestine. It does so as the organ is lined with crypts that have goblet, absorptive, and granular cells. Parts of the Large Intestine  Cecum is a pouch that receives the chyme from the ileum. Attached to the cecum is the vermiform appendix which is a lymphatic tissue that has immune functions.  Colon of the intestine comprises the four regions: ascending, transverse, descending, and sigmoid. The right and left colic flexures section the three regions.  Taenia coli are the three bands that run along the longitudinal muscle layer of the large intestine. When contractions occur in the large intestine, folds called haustra appear along the intestine, giving it a puckered appearance.  Omental appendages, also known as the epiploic appendix, are pouches that attach to the intestine. They have no known function  rectum is a tube where the feces remain after all water and electrolytes have been absorbed from the material until it is time for defecation.  anal canal is the last part of the digestive tract and is the opening comprised of the internal anal sphincter and external anal sphincter. Pancreas  Composed of both endocrine and exocrine glands. The exocrine part produces mainly digestive enzymes and helps in digestion, while the endocrine part is responsible for the regulation of carbohydrate and metabolism.  Endocrine Glands - consists of pancreatic islets that produce insulin and glucagon, which is important in controlling blood level nutrients such as glucose and amino acids.  Exocrine Glands - Exocrine secretion is called pancreatic juice. Pancreatic Juice major part is the bicarbonate (HCO3-) that neutralizes the acidic chyme that enters the small intestine from the stomach. Biliary Tract (Liver and Gallbladder)  The biliary tract refers to the organ (liver) and ducts (bile ducts and gallbladder) and involved in the secretion, storing, and production of bile. Bile consists of water, electrolytes, bile acids, cholesterol, phospholipids, and conjugated bilirubin.  Bile Production - The liver produces and secretes bile. It doesn’t have digestive enzymes. It neutralizes

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down into tripeptides, dipeptides, and amino acids by peptidases bound to the microvilli of the small intestine. Lipids  The liver and pancreas are important sites for lipid metabolism.  Bile emulsifies fats into small particles. The small intestine and lipase from the pancreas hydrolyze fatty acids into free fatty acids and monoglycerides. These small molecules (glycerol, short-chain, medium-chain fatty acids) are absorbed into the body by the small intestine and are re-synthesized in small intestine. Then it will be re-synthesized in small intestinal cells and along with phospholipids, cholesterol, and proteins to form chylomicron, which will enter the blood circulation from lymphatic cells Water and Minerals  About 9L of water can enter our digestive tract and 92% is absorbed in the small intestine, and about 6-7% is absorbed in the large intestine. Osmotic gradient determines the direction of this diffusion. When chime is dilute, it will go to the intestinal wall into the blood, and when the chime is concentrated, the water moves by osmosis into the lumen of the small intestine. Active transport in the small intestine drives the absorption of sodium, potassium, calcium, magnesium, and phosphate.

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Download ANATOMY & PHYSIOLOGY_DIGESTIVE SYSTEM and more Study notes Anatomy in PDF only on Docsity!

JAILOUISE A. PEREZ

BACHELOR OF SCIENCE IN NURSING

DIGESTIVE SYSTEM

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