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314151 Lecture Notes - Lecture 3: Serous Gland, Enteric Nervous System, Semipermeable Membrane

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rubyduck59
24 May 2018
School
Curtin University
Department
Rehabilitation Therapies
Course
314151
Professor
Carly Brade

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Lecture 3 – 15/3/16
The Digestive System
The digestive tract is a tube that runs from the mouth to the anus. It has accessory organs (glands that secrete
fluids into the canal) that help break down foods.
Food goes in the oral cavity (mouth), down the pharynx and esophagus, into the stomach where it goes to the
small intestine (where the accessory organs are), the large intestine and then through to the anus.
Functions of the digestive system
1. Ingestion – the introduction of food to the oral cavity.
2. Mastication – food is mechanically broken down to increase surface area so enzymes can start
chemical digestion.
3. Propulsion – the movement of food through the digestive system.
➢ Swallowing – moves the bolus from oral cavity to the esophagus.
➢ Peristalsis – wave of smooth muscle contracting behind the bolus to propel forward and then
the relaxation of smooth muscle in front of the bolus.
➢ Mass movements – contractions that move material in the large intestine.
4. Mixing – food is mixed with digestion secretions to help with the break down of the food into smaller
parts.
5. Secretion – purpose is to break down the food. Mucus covers the entire digestive tract to help
lubricate. It also coats the stomach, esophagus and intestine to protect the epithelial cells from the
stomach acid. Enzymes secreted from the pancreas, small intestine and stomach break down the
food.
6. Digestion – Mechanical (mastication) and chemical (enzymes) digestion.
7. Absorption – Molecules move out of the digestive tract into the circulatory or lymphatic system.
Movement is achieved through diffusion (movement of air from high-low pressure), osmosis
(movement of water across a semi-permeable membrane), facilitated diffusion (molecules combine
with a carrier protein and cross the membrane), active transport pumped across ,
endocytosis (plasma membrane wraps around the molecule and carries it away) or
(waste products are eliminated from the body via. Defecation.
The main aim of the digestive system is to break down foods to smaller molecules that can be absorbed into
the circulatory system.
Histology of the digestive tract
There are 4 layers:
1. Mucosa – inner most layer that secretes mucous.
2. Submucosa – nerves, lymphatic, blood vessels and small glands.
3. Musculairs – smooth muscle – two circular layers and a longitudinal layer.
4. Serosa – smooth layer that covers the digestive tract.
Regulation of the digestive system
Nervous Regulation
- Enteric nervous system (ENS) is within the wall of the digestive tract. It controls blood flow and
propulsions
Chemical Regulation
- Neurotransmitters - Acetylcholine stimulates and norepinephrine inhibits digestive secretion and
movement.
- Hormones – Endocrine secretions – serotonin, gastrin, secretin.
- Paracrine secretions – histamine.
Levels of the Digestive System
1. Oral Cavity
- Assists with mastication of food.
- Incisors and canines tear and cut food.
- Molars and Premolars grind and crush food.
2. Salivary Glands
- Acinar glands made up of acini. Saliva is made up of serous and mucus secretion.
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- Three large salivary glands .
o Parotid – Largest, serous gland and secretes watery saliva.
o Submandibular – mostly serous and some mucus glands.
o Sublingual – some serous, mostly mucous glands.
- Function of saliva
o Keeps the oral cavity moist
o Acts as lubricant for the esophagus
o Begins digestion – amylase breaks down 3-5% of carbohydrates.
o Protective functions – washes foods, contains bicarbonate ions.
3. Pharynx
- Three parts
o Nasopharynx – not associated with digestion
o Oropharynx
o Laryngopharynx
- Epiglottis covers the larynx to prevent food going down air passages.
- Uvula and soft palate prevent food going into the nasal cavity.
4. Esophagus
- Extends from the pharynx to the stomach and is posterior to the trachea. It travels through the
opening of the diaphragm ()
- Swallowing phases
o Voluntary phase – bolus is moved by the tongue posteriorly.
o Pharyngeal phase – soft palate elevates pushing the bolus into the pharynx and the epiglottis
closes the larynx.
o Esophageal phase – peristaltic waves move the food towards the stomach.
- Peritoneum is the serous membrane that lines the abdominal walls (parietal) and lines the organs
(visceral)
- Organs inside the peritoneal cavity is called INTRAperitoneal
- Organs outside the peritoneal cavity are called RETROperitoneal
5. Stomach
- Pyloric sphincter regulates the release of food from the stomach into the small intestine
- Food exits 3-4 hours after digestion.
- Liquids exits hour after digestion
- Submucosa and mucosa are rugae (folded) which increases the surface area and expands when the
stomach is full. The inner most layer forms gastric pits which are openings of the gastric glands. 5
types of epithelial cell make up a gastric gland.
i. Surface mucous cells
ii. Mucous neck cells – produces an alkaline mucous which protects the stomach lining from
digestive acids.
iii. Parietal cells – secretes hydrochloric acid, kills bacteria,
iv. Chief cells – secretes pepsinogen (converts to pepsin when in the stomach) which breaks
down proteins and gastric lipase which breaks down fats.
v. Endocrine cells – produces regulatory hormones such as histamine that stimulates secretion
of acid from parietal cells.
Regulation of the stomach secretions
i. Cephali Phase or   phase. “tiulus is aused y the sell, taste or thoughts of food.
Secretion of stomach mucosa. Release of neurotransmitter acetylcholine that increases chief and
parietal cell secretions. Stimulates secretions of Gastrin and Histamine. Gastrin and Histamine
stimulates parietal cell secretion also.
ii. Gastri Phase = go for it phase. “timulus causes enlargement of the stomach (smoothing out of
the rugae) as food enters. Activation of mechanoreceptors (stretch receptors). Presence of
protein leads to an increase in secretions in a similar fashion to the cephalic phase.
iii. Intestinal Phase = slow dow phase. Low pH hye siulates heoreeptors i the
duodenum. Chyme containing lipids makes the hormone secretin be secreted. It inhibits gastric
secretions.
Regulation of the stomach emptying
If chyme exits too fast, acidic chyme enters the duodenum and damages the lining. It also reduces the
digestion and absorption efficiency. Too slow and gastric secretions can damage the stomach wall and the rate
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Document Summary

The digestive tract is a tube that runs from the mouth to the anus. It has accessory organs (glands that secrete fluids into the canal) that help break down foods. Food goes in the oral cavity (mouth), down the pharynx and esophagus, into the stomach where it goes to the small intestine (where the accessory organs are), the large intestine and then through to the anus. Ingestion the introduction of food to the oral cavity: mastication food is mechanically broken down to increase surface area so enzymes can start chemical digestion, propulsion the movement of food through the digestive system. Swallowing moves the bolus from oral cavity to the esophagus. Peristalsis wave of smooth muscle contracting behind the bolus to propel forward and then the relaxation of smooth muscle in front of the bolus. Mucus covers the entire digestive tract to help lubricate. It also coats the stomach, esophagus and intestine to protect the epithelial cells from the stomach acid.

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Related Questions

2. General questions about the digestive tract A. Mechanical digestion of all foods begins in the oral cavity. Describe how food is digested mechanically in the oral cavity. B. What is the scientific name for swallowing? Which portions of the pharynx does food pass through when swallowing? What is the function of the esophagus? C. Cells lining the stomach release hydrochloric acid (HCl). How does HCl assist in food digestion? How are the cells lining the stomach protected from being auto-digested by HCl? D. Carbohydrates, fats, and proteins must be broken down into their smallest subunits (AKA building blocks) in order to be absorbed through the epithelial lining of the small intestine. Name the building blocks of each of the major classes of nutrients: complex carbohydrates (AKA polysaccharides), fats, and proteins. E. About 99% of all nutrients are absorbed in the small intestine. Name the 3 portions of the small intestine. In which of these 3 portions does the greatest amount of nutrient absorption occur (think about the location and length of each segment)? Which type(s) of nutrient(s) is/are absorbed into blood capillaries? Which type(s) of nutrient(s) is/are absorbed into lymphatic capillaries? F. The last portions of the digestive tract are the rectum, anal canal and anus. Name the 2 muscular sphincters located at the anus. When the rectum fills, the defecation reflex is initiated. Describe the events that occur during the defecation reflex. Name the 2 sphincters located at the anus. Which sphincter undergoes involuntary relaxation during the defecation reflex? Which division of the autonomic nervous system causes this sphincter to relax and open? Name the sphincter that you control consciously to stop or initiate defecation.

Food that we consume is composed of very complex molecules. During the digestive process these compounds are broken down into smaller and smaller subunits in preparation for use by the body as building blocks needed for the many components of the human body.

The digestion process begins at the mouth. Food enters and then accessory digestive organs like the tongue, teeth, and salivary glands break down the substance. It then travels through the pharynx and esophagus into the stomach, where the stomach acid further breaks down the food (UXL Complete Health Resource). After that, the food travels through the small and large intestines where a majority of its nutrients are absorbed. The waste then exits through the end of the large intestine which is made up of the rectum and anus. After the teeth assist in chewing, food rolls over the tongue and reaches stomach through the esophagus within 8 seconds. General Tso’s Chicken and Rice consist of carbohydrates, fats and proteins. However, carbohydrates are digested easily than the fats and proteins. After broken down in the stomach, most of the nutrients are absorbed from the small intestine, and it takes 6 to 8 hours to pass through small intestine. The remaining unabsorbed material, “moves very slowly through the large intestine where the final absorption of water and other nutrients take place” (UXL Complete Health Resource). The parasympathetic nervous system encourages the food to move through the digestive tract and motivates digestion process. The sympathetic nervous system works against the parasympathetic nervous system by decreasing the contraction and relaxation of the digestive tract (Taylor). Mouth produces saliva, which contains amylase. Amylase is key in digesting carbohydrates. The stomach produces hydrochloric acid, pepsinogen, intrinsic factor, and mucus (Taylor). Hydrochloric acid kills the bacteria and other organisms that enter the stomach, and then continues to activate pepsinogen. Pepsinogen then changes into pepsin, which digests protein peptides. The pancreas produces trypsin, chymotrypsin, carboxypeptidases, lipases, and phospholipases. Trypsin, chymotrypsin, and carboxypeptidases digest proteins, whereas lipases, phospholipases digest lipid molecules. Small intestine produces lactase, sucrase, maltase, lipases, and peptidases. Lactase, sucrase, and maltase digest carbohydrates (UXL Complete Health Resource). Saliva glands, pancreas, liver, and gallbladder are the accessory organs of the digestive process. Saliva glands produce mucus and amylase which digests starch into simple sugars and binds food particles together, while lubricating the palette when one swallows. The pancreas produces amylase, lipases, and proteinases etc. These digestive juices are responsible for breaking down carbohydrates, proteins, and fats. The liver is the largest gland in the body, “It produces bile salts to emulsify lipids. It detoxifies metabolic end products to protect the body” (UXL Complete Health Resource). Gallbladder stores bile juice. The chicken in the General Tso’s contains proteins. Proteins cannot be digested in mouth. However, the mouth can physically digest chicken into smaller pieces. These partially digested chicken pieces travel to stomach, where it is digested by pepsin. The pancreas produces trypsin, chymotrypsin, carboxypeptidases, lipases, and phospholipases (UXL Complete Health Resource). The chicken is then digested by trypsin, chymotrypsin, and carboxypeptidases in the duodenum of the small intestine. After the complete digestion, the chicken’s proteins change into amino acids, which are then absorbed into blood. The rice of the General Tso’s is a carbohydrate. Carbohydrates are partially digested inside the mouth by amylase. The rest of the rice travels to the stomach where it is digested by pancreatic juices and enzymes that are produced by small intestine. The digestion of the rice produces monosaccharides that absorb into the blood stream. The left over, and undigested parts of the chicken and rice that are useless to the body are excreted by large intestine through rectum.

1) Based on your finding in the Module 3 Report, begin the Module 4 Report by identifying which metabolites are being absorbed and specifically which vessels of the cardiovascular or lymphatic system are the initial vessel of transport from the digestive system. 2) From the point that the specific metabolites are absorbed from the GI tract, trace the path of the resulting metabolites to the following locations in the body for incorporation into the body structure: Metabolites of protein for use in the Gastrocnemius muscle for muscle maintenance. Metabolites of the carbohydrates for energy to contract the cardiac muscle cells. Metabolites of fat to incorporate into the myelin sheaths of the Schwann cells of the Trigeminal nerve that innervates the Masseter muscle. Water for incorporation into the synovial fluid of the hip joint. Iron for incorporation into red blood cells in the bone marrow of the sternum.

Food that we consume is composed of very complex molecules. During the digestive process these compounds are broken down into smaller and smaller subunits in preparation for use by the body as building blocks needed for the many components of the human body. The digestion process begins at the mouth. Food enters and then accessory digestive organs like the tongue, teeth, and salivary glands break down the substance. It then travels through the pharynx and esophagus into the stomach, where the stomach acid further breaks down the food (UXL Complete Health Resource). After that, the food travels through the small and large intestines where a majority of its nutrients are absorbed. The waste then exits through the end of the large intestine which is made up of the rectum and anus. After the teeth assist in chewing, food rolls over the tongue and reaches stomach through the esophagus within 8 seconds. General Tso’s Chicken and Rice consist of carbohydrates, fats and proteins. However, carbohydrates are digested easily than the fats and proteins. After broken down in the stomach, most of the nutrients are absorbed from the small intestine, and it takes 6 to 8 hours to pass through small intestine. The remaining unabsorbed material, “moves very slowly through the large intestine where the final absorption of water and other nutrients take place” (UXL Complete Health Resource). The parasympathetic nervous system encourages the food to move through the digestive tract and motivates digestion process. The sympathetic nervous system works against the parasympathetic nervous system by decreasing the contraction and relaxation of the digestive tract (Taylor). Mouth produces saliva, which contains amylase. Amylase is key in digesting carbohydrates. The stomach produces hydrochloric acid, pepsinogen, intrinsic factor, and mucus (Taylor). Hydrochloric acid kills the bacteria and other organisms that enter the stomach, and then continues to activate pepsinogen. Pepsinogen then changes into pepsin, which digests protein peptides. The pancreas produces trypsin, chymotrypsin, carboxypeptidases, lipases, and phospholipases. Trypsin, chymotrypsin, and carboxypeptidases digest proteins, whereas lipases, phospholipases digest lipid molecules. Small intestine produces lactase, sucrase, maltase, lipases, and peptidases. Lactase, sucrase, and maltase digest carbohydrates (UXL Complete Health Resource). Saliva glands, pancreas, liver, and gallbladder are the accessory organs of the digestive process. Saliva glands produce mucus and amylase which digests starch into simple sugars and binds food particles together, while lubricating the palette when one swallows. The pancreas produces amylase, lipases, and proteinases etc. These digestive juices are responsible for breaking down carbohydrates, proteins, and fats. The liver is the largest gland in the body, “It produces bile salts to emulsify lipids. It detoxifies metabolic end products to protect the body” (UXL Complete Health Resource). Gallbladder stores bile juice. The chicken in the General Tso’s contains proteins. Proteins cannot be digested in mouth. However, the mouth can physically digest chicken into smaller pieces. These partially digested chicken pieces travel to stomach, where it is digested by pepsin. The pancreas produces trypsin, chymotrypsin, carboxypeptidases, lipases, and phospholipases (UXL Complete Health Resource). The chicken is then digested by trypsin, chymotrypsin, and carboxypeptidases in the duodenum of the small intestine. After the complete digestion, the chicken’s proteins change into amino acids, which are then absorbed into blood. The rice of the General Tso’s is a carbohydrate. Carbohydrates are partially digested inside the mouth by amylase. The rest of the rice travels to the stomach where it is digested by pancreatic juices and enzymes that are produced by small intestine. The digestion of the rice produces monosaccharides that absorb into the blood stream. The left over, and undigested parts of the chicken and rice that are useless to the body are excreted by large intestine through rectum. 1) Based on your finding in the Module 3 Report, begin the Module 4 Report by identifying which metabolites are being absorbed and specifically which vessels of the cardiovascular or lymphatic system are the initial vessel of transport from the digestive system. 2) From the point that the specific metabolites are absorbed from the GI tract, trace the path of the resulting metabolites to the following locations in the body for incorporation into the body structure: Metabolites of protein for use in the Gastrocnemius muscle for muscle maintenance. Metabolites of the carbohydrates for energy to contract the cardiac muscle cells. Metabolites of fat to incorporate into the myelin sheaths of the Schwann cells of the Trigeminal nerve that innervates the Masseter muscle. Water for incorporation into the synovial fluid of the hip joint. Iron for incorporation into red blood cells in the bone marrow of the sternum.