The Digestive System Flashcards
The human digestive system consists of
The alimentary canal and accessory organs
The alimentary canal
Long, tubular structure that extends throughout the body
The alimentary canal consists of
Mouth and mouth cavity
Pharynx
Oesophagus
Stomach
Small intestine
Large intestine and anus
The accessory organs include the following
Tongue
Salivary glands
Pancreas
Liver
Fall bladder
Five main processes in nutrition
Ingestion, digestion, absorption, assimilation and egestion
Ingestion
The food is taken in and enters the alimentary canal
Digestion
Food is exposed to mechanical and chemical processes that change solid, insoluble food to simpler, soluble substances.
Absorption
The end products of digestion are absorbed into the blood stream
Assimilation
The cells absorb the nutrients from the blood and use It to build new cell structures and compounds
Egestion
The process through which undigested remains are removed from the body in the form of faeces.
Necessity of food
It provides energy through the egestion of carbohydrates and fats.
It provides growth and repair of damaged tissues through the egestion of proteins.
It regulates body processes such as cellular respiration and excretion which requires ingestion of vitamins vitamins, water and mineral salts
Herbivores-animals that feed on plant material
Consume large amounts of cellulose (found in cell walls). Some herbivores have microorganisms in their small intestine that digest cellulose which is hard to digest. Large amount of plant material is consumed as it has a very low energy value with the incisors of herbivores and large premolar and molars to grind the food.
Herbivores produce large amounts of faeces
Because they eat so much indigestible plant material
Herbivores have very long, specialized alimentary canals while carnivores
Have a shorter alimentary canal because the protein is easier to digest along with the stomach which has acidic medium that easily digests protein.
Carnivores have sharp pointed incisors to
Bite food, long string canines to pierce the prey and to kill and tear it apart.
Carnivores eat less than herbivores
Because fats and proteins have a much higher energy value than plant material therefore less faeces are produced.
Mouth and mouth cavity
The mouth is the upper opening of the alimentary canal.
The opening of the mouth is surrounded by 2 fleshy lips.
The cavity on the inside is known as the mouth cavity which is lined with a mucous membrane.
The roof of the mouth cavity consists of a hard, ridged palate at the front and a soft palate at the back which ends in the uvula, which closes the opening to the nasal cavity when swallowing.
The mouth cavity also contain the tongue and the teeth toward the front as well as the openings of the 3 pairs of Salivary glands (tongue, teeth and Salivary glands)
Functions of the mouth and mouth cavity
The mouth cavity receives the food and begins the process of mechanical digestion by breaking down larger particles of food into smaller particles and mixing it with saliva
Pharynx
The back of the moth cavity opens to the Pharynx which leads to 2 openings : the Oesophagus and trachea(windpipe)
During swallowing, the opening of the trachea
Is closed by a leaf-shaped cartilage structure called the epiglottis which prevents food from entering the trachea and choking a person.
Function of the Pharynx
The Pharynx is the common passage for food and air from the mouth to the Oesophagus and the trachea.
Passageway that connects nasal and oral cavity to Oesophagus.
Respiratory and digestive function occur and food triggers involuntary reflexes
Oesophagus
A hollow, muscular tube that connects the Pharynx to the stomach which is located behind the trachea.
Function of the Oesophagus
The muscles in the wall of the Oesophagus are responsible for peristaltic movements which push the food bolus forward.
Food bolus
A round ball of chewed food that is mixed with saliva in the mouth cavity and pushed in the direction of the Oesophagus during swallowing
Stomach
A sickle shaped, sac like organ located below the diaphragm. The wall is thick and muscular. At the top, the opening of Oesophagus is closed by the cardiac sphincter.
At the lower end the opening to the small intestine is closed by the pylori sphincter which keeps food from being forced into the intestine too early.
When food enters the stomach the stomach mucosa begins to produce the hormone gastrin which is transported by the blood to the gastric glands to stimulate them to secrete juice.
What happens in the stomach under stressful conditions
The gastric glands secrete excessive amounts of gastric juice which destroys the mucous lining of the stomach which leads to stomach ulcers.
What leads to heartburn
The acidic fluid mass in the stomach pushes into the Oesophagus which results in heartburn especially as a result of fatty food, excessive alcohol use, caffeine or obesity
Functions of the stomach
The walls causes churning movements that assist with physical digestion and ensure that the food is mixed with the gastric juices.
The glands in the stomach wall secrete the gastric juices for digestion.
Chyme
Food that leaves the stomach in a semi solid state
Small intestine
Long muscular tube which approximately 5 to 6 m in length
It consists of 3 parts : duodenum
Jejunum
Ileum
The walls of the small intestine consist of the serous membrane, muscle layer, submucosa and mucosa
Tongue
The tongue attaches to the hyoid bone and to the styloid process of the skull. The inguinal frenelum holds to the tongue to the floor of the mouth and keeps it from sliding posteriorly
Frenulum medical problem
When a child has a short frenulum or an attachment that is farther forward, surgery is required to improve speech
Tonsils
Part of the body’s defense system
Palatine tonsils and the lingual tonsils are at the base of the tongue.
Salivary glands
Food enters the mouth and the teeth breaks down the food mechanically.
Ptyalin and amylase work on chemically digesting starches.
Salivary enzymes attack bacteria in the food.
Gastric pits
Cover the lining of the stomach.
Secretes gastric juice.
Intrinsic factor - absorption of B12
Parietal cells produce hydrochloric acid (HCI) which provides the protein digesting enzyme, pepsin
Duodenum
First and shortest part of the small intestine
The common bile duct from the gall bladder and the pancreatic duct from the pancreas open as a joint tube in the duodenum.
Jejunum
Middle part of the small intestine
Ileum
Last and longest part of the small intestine.
It joins the first part of the large intestine like the caecum.
The opening between the iluem and caecum is closed by a ring muscle called the ileo-caecal sphincter.
Serous membrane
Outer connective tissue layer
Muscle layer consists of
An outer layer of longitudinal muscles and inner layer of circular muscles
Submucosa
A layer of connective tissue with blood vessels, lymph vessels, nerves and glands
Mucosa
The innermost layer which has transverse folds and there are million of finger like projections called villi on these folds.
Peristaltic movements
Peristalsis is the wave-like movement of the smooth muscles that line your digestive system. It is an involuntary process that moves food and waste through your gastrointestinal tract
The stomach empties into the small intestine which looks like
Coised hose
What juices mix in the small intestine
Juices from the pancreas and gall bladder
Explain the absorption process that occurs in the small intestine
Vitamins, minerals, carbons, protein, fat and bile salts go through the bloodstream and are absorped by the cells. This occurs at a site where the large surface area is covered with projections(villi)
The mucosa in the small intestine will have finger like projections called
Villi (villus for one)
Structure of villus 1
A villus is surrounded by a single layer of columnar epithelial cells.
2) in the columnar epithelium there are
Goblet cells secrete mucous to protect and lubricate the body’s surfaces, trap pathogens and allergens, and support immune function.
Microvilli
Cells on the surface of the columnar epithelial cells that are microscopic projection.
Lacteal
The centre where there is a capillary lymph vessel.
An arteriole
Brings blood to the villus and form a capillary network that surrounds the lacteal.
Venule
Cappilaries join together and leave the villus as a venule
Crypts of lieberkuhn
Small cavities Located at the base of the villi
Brunner glands
Occur in the submucosa of the duodenum
Functions of the small intestine
The layer of muscles in the wall of the small intestine causes peristaltic movements moving the chyme forward and ensures that it becomes throughly mixed with the digestive juices.
Glands in the duodenum (brunner glands and crypts of lieberkuhn) secrete digestive juices (intestinal juice) which plays a role in digestion.
The small intestine has millions of villi to increase surface area for the absorption of digested nutrients
3 colons of the large intestine
Caecum, colon, sigmoid and rectum
Caecum
Sac like structure where it joins the small intestine and a small small appendage is attached to caecum, the appendix
Colon
Largest part of the large intestine. It’s consists of ascending, transverse and descending colon
Rectum
Last muscular point of the colon it ends with an opening on the outside, an anus
Functions of the large intestine
Secrets large amounts of mucus to aid egestion.
Water and useful substances (certain vitamins and bile salts) are absorbed from the semi-solid waste in the colon.
Undigested waste(faeces) is stored temporarily in the colon before it is egested via the anus.
A tongue is a muscular accessory organ with small projections on the tongue called
Papillae where the taste buds occur
Function of the tongue
Has taste buds and serves as a taste organ.
Helps with the chewing process by pression food against the hard palate and between the teeth.
This ensures that chewed food mixes with saliva..
It rolls the food into a bolus (ball)
Helps with swallowing process as it pushes down the food bolus towards the opening of the throat.
Teeth has 4 types of teeth
Incisors, canines, premolar, molars
Incisors
Bite and cut off food
Canines
Hold food in place and tear it off
Premolar and molars
Chew and grind the food
Tooth decay is caused by
Plaque
Plaque
Thin transparent layer deposited on teeth consisting of bacteria, food particles, mucus and saliva. The bacteria feeds on sugar and releases acids that dissolve the tooth enamel which causes holes. The bacteria can then penetrate the tooth leading to tooth decay.
What prevents tooth decay
Toothpaste containing fluoride or fluoride supplements
Salivary glands are what type of glands
Exocrine glands that release secretion in ducts that open into the moth cavity
Pancreas
Tongue-shaped gland located below the stomach.
It’s composed of the normal pancreatic cells and the islets of langerhans cells.
It produces digestive enzymes.
It’s part of the endocrine system producing the hormones :insulin and glucagon
Normal pancreatic cells
Secrete the digestive juice, pancreatic juice
The islets of langerhans
Secretes two hormones : insulin and glucagon - part of the endocrine system
Pancreatic juice is transported via
The pancreatic duct which joins the common bile duct.
The common bile and pancreatic duct
Opens in the duodenum
Endocrine
(ductless) glands that release their secretions directly into the blood stream
The mucosa of the small intestine Secretes
The hormone secretin when the acidic chyme reaches the duodenum. Secretin is the transported into the blood stream and it stimulates the pancreatic cells to secrete pancreatic juice
Normal pancreatic cells secrete pancreatic juice
Into the pancreatic duct which opens into the duodenum(exocrine function)
Islets of langerhans secret the hormones
Insulin and glucagon directly into the bloodstream (endocrine function)
Function of the pancreas
Secrete pancreatic juices with enzymes which play a role in digestion
Secretes insulin and glucagon which controls the blood glucose levels in the body
Liver
Largest gland in the body located under the diaphragm. It has 4 lobes each made it tiny lobules that consist of liver cells
Metabolic and regulatory
theliver regulateslipid metabolism to meet systemic energy needs in the fed and fasted states. The processes of fatty acid uptake, fatty acid synthesis and the intracellular partitioning of fatty acids into storage, oxidation and secretion pathways are tightly regulated.
Functions of the liver
Produces bile stored in the gall bladder
Glucose is converted into glycogen for storage in the liver.
Excess glucose is converted into fat and stored.
The liver is a detoxifying organ that absorbs and neutralizes certain toxins such as alcohol.
Deamination in the liver
Excess amino acids are broken down to form urea and glucose in the process called deamination.
What vitamins are stored in the liver
A
D
E
K
B12
What prevents blood clotting
Liver synthesis heparin
Gall bladder
Muscular sac located between liver lobes that contracts to release bile when it is stimulated. The bile moves along the cystic duct, common bile duct and common bile and pancreatic duct into the duodenum.
Function of the gall bladder
Stores and releases bile which is produced by the liver.
Digestion
Nutrients must be in a simple, soluble form to be absorbed by the blood and transported to the body cells.
Complex insoluble food particles are broken down by digestion into simpler soluble nutrients.
There Is mechanical/physical digestion and chemical digestion
Mechanical/physical digestion
Food is broken down into smaller particles.
The smaller food particles have a large surface area for digestive enzyme action to break them down further into simpler molecules.
Mechanical digestion includes chewing process /mastication ; bolus formation, churning movement and peristaltic movements
Mastication /chewing process
Food is broken down into smaller particles by the teeth and tongue.
Bolus formation
The chewed food is mixed with saliva and rolled into a ball of food(bolus) using the tongue. The swallowing process starts with the tongue pushing the bolus through the Pharynx, from where it enters the Oesophagus
Churning movements
These e takes place by the contraction and relaxation of the muscles of the stomach wall. Food particles are broken down for effective enzyme action and thoroughly mixed with gastric juice.
Peristaltic movements
Rhythmic contraction and relaxation of the muscles in the wall of the alimentary canal. Which helps move the food particles forward through the entire length of the alimentary canal
Peristalsis also helps
Mix food particles with other digestive juices like the pancreatic juice and bile.
Chemical digestion
Breaking down of large, insoluble molecules in food into smaller, soluble molecules by the addition of water through the catabolic reaction known as hydrolysis
Hydrolytic reactions cannot occur
Without the help of enzymes
Catabolic reaction : large insoluble food molecules plus
Addition of H20 broken down by digestive enzymes into small, soluble food molecules
Catabolic reaction
Breaking down of the large insoluble molecules of a compound with the addition of of water to be broken down by an enzyme into small soluble type of molecules.
Role of water during chemical digestion
Acts as a solvent for digested food
Transports digested food
Medium for which digestive reactions occur and acts like a lubricant and facilitates chewing and swallowing.
Reagent for hydrolysis
Water
Hydrolysis
Water molecules are added to split larger molecules. Water is a softening agent
Absorption
Nutrients move from the lumen of the gastrointestinal tract of the blood or lymph.
Most absorption of digested food occurs in the small intestine since it adapted for maximum absorption due to length of the intestine and the transverse folds/villus that increase the absorption surface area.
Columnar epithelial surrounding the villus
Is only one cell layer thick for fast and easy diffusion
Villus are richly supplied with
Capillaries for the absorption of glucose, amino acids, vitamins, mineral salts and water. And haaa a central lacteal for the absorption of fats.
Goblet cells in the columnar epithelium
Secrete mucus which is the medium in which nutrients can dissolve.
The columnar epithelium has many mitochondria
To provide energy for active transport.
The micro villi on the columnar epithelium
Increase the absorption surface
Absorption process
The end products of digestion like glucose, amino acids, fatty acids and glycerol as well as vitamins, mineral salts and water are absorbed by the villi in the small interest.
Glucose and amino acids in the absorption process
Glucose and amino acids are actively absorbed against the concentration gradient, into the blood capillaries of the villi
Glycerol and fatty acids in the absorption process
Glycerol and fatty acids are absorbed by diffusion into the lacteals aided by bile salts.
Vitamins in the absorption process
Fat soluble Vitamins(A, D, E AND K) are absorbed by blood capillaries while water soluble like B and C are absorbed by carrier molecules
Mineral salts in the absorption process
Actively and passively absorbed by capillaries
Water in the absorption process
Absorbed into the cappilaries by osmosis
Glucose is the end product for
Carbohydrate digestion
Amino acids are the end products of
Protein digestion
Glycerol and fatty acids are the end products of
Lipid digestion
Active transport requires
Energy and help of a carrier molecules as it goes against the concentration of gradient
Passive transport occurs
Spontaneously and doesn’t require energy as it goes down the concentration gradient
Propulsion before digestion
Deglutination by swallowing
Propelled to next digestive organ by peristalsis
Contraction and relaxation of muscles is involuntary
Osmosis is
Osmosis is the movement of water molecules from an area of high concentration to an area of low concentration through a semipermeable membrane.
Transport of absorbed nutrients
Glucose, amino acids, vitamins, mineral salts and water are absorbed through the blood capillaries in the villi.
Larger veins are formed in order to open into the hepatic portal vein when capillaries join.
Hepatic portal veins transport absorbed nutrients to the liver
Where glucose is converted and stored as glycogen and excess amino acids undergo deamination to form urea and glucose.
Remaining glucose and amino acids leave the liver via hepatic veins and are transported to the inferior vena cava of the heart and to the rest of the body.
Glucose is transported to tissues like muscle tissues broken down by cellular respiration to form co2 plus water and release of energy
Fatty acids and glycerol absorbed by the lacteal of the villi
Fork lymphatic vessels that open up the thoracic duct.
Egestion process
Large amounts of water are absorbed from the semi solid waste in the colon to reduce liquidity.
Undigested or indigestible waste is stored in the rectum as faeces.
Muscles contractions of the rectum and relaxation of the circular muscles of the anus causes expulsion of faeces.
Egestion is known as
Defecation
Microorganisms in the gastrointestinal tract
In Healthy individuals, the stomach and proximal small intestine contain few microorganisms resulted in bacteriodical activity of gastric acid.
Msot microorganisms are located in
The Ileum and colon
Bacterial populations in large intestine digest
Carbohydrates, proteins and lipids that escape digestion and absorption in the small intestine, this fermentation of cellulose is important in herbivores
Assists in the absorption of vitamin K
Homeostasis
Maintenance of a constant internal environment in the body
Homeostasis includes the maintenance of
Glucose concentration
Water concentration
Carbon dioxide and oxygen concentration
Ph
Temperature
Hormonal control of glucose concentration in the blood
Two hormones, insulin and glycogen are secreted by the islets of langerhans in the pancreas to control the glucose concentration in the blood.
If the glucose concentration in the blood rises above normal
The beta cells of the islets of langerhans detect this increase and respond by secreting insulin into the blood.
Insulin stimulates the absorption of glucose from the blood into the body cells and conversion of glucose to glycogen in the liver and muscles.
Glucose is removed from the blood which causes glucose concentration to decrease which is detected by beta cells which inhibit the secretion of insulin
If the glucose concentration in the blood falls below normal
The alpha cells of the islets of langerhans detect the decrease and respond by secreting glucagon into the blood which stimulates the conversion of glycogen to glucose in the liver and muscles.
Glucose is released into the blood which causes the glucose concentration to increase. The increase in the blood glucose concentration is detected by the alpha cells which then inhibit the secretjon of glucagon.
Insulin and glucagon are
Antagonistic hormones as they have opposite effects in the body s
Glucose
Building block of carbohydrates and the body’s main energy source
Glycogen
A carbohydrate. The storage form of glucose in animals
Glucagon
Hormone which increases the blood glucose concentration
Silvary amylase
Also called pytalin
Breaks down starch (polysaccharide) down to maltose
Bicarbonate ions in saliva as buffers
Mucins(mucous) lubricate and help hold chewed food together in a bolus
