Digestive system Flashcards
2 main parts of the digestive system
Alimentary canal
Associated glands
Constituents of saliva
water
salt
cells
mucins (slippery glycoprotein)
buffers
anti-microbial components- immunoglobulines and lysozymes.
Functions of Saliva
• Salivary amylase: Chemical digestion of polysaccharides (e.g. starch and glacogen) into smaller polysaccharides and disaccharide maltose.
• Water: Liquefy food and provide watery medium for chemical digestion. Aids in taste reception.
• Mucus: Lubrication of food which makes it easier for swallowing. Clean the mouth and protects the lining of the mouth from abrasion.
• Antimicrobial substances such as immunoglobulin and lysozymes: Protect against bacteria that enter the mouth.
• Buffers prevent tooth decay by neutralizing acid
Oral cavity is lined by?
Non-keratinized squamous epithelium
Types of cells present in gastric gland?
Mucus cells - secrete mucus
Chief cells - secrete pepsinogen
Parietal cells - Release hydogen ions and chloride ions separately into the stomach where HCl is formed.
Gastric juice mainly consist of?
Mucus, pepsinogen, HCl and intrinsic factor( glycol-protein secreted by chief cells)
Chemical digestion in the stomach
Pepsinogen is initially converted to pepsin by HCl
This activated pepsin intiates the protein digestion (churning action of the stomach facilitates it.)
Proteins are hydrolyzed to small polypeptides by pepsin.
Stomach
The stomach is a J- shaped dilated sac in the abdominal cavity. The inner surface of the stomach is highly folded and contains large number of pits that leads to gastric glands. Sphincters are found at the junctions between esophagus and stomach (cardiac sphincter) and stomach and the small intestine(pyloric sphincter). They are made up of circular smooth muscles. These sphincters help to regulate the passage of materials between these organs.
What is chyme?
Partially digested semisolid, acidic, food mass
Small intestine
Longest organ in the alimentary canal.
3 regions: duodenum, jejunum and ileum.
Surface area is greatly increased by permenant circular folds and villi.
Most of the digestion is completed in the duodenum while major sites of nutrition absorption are jejunum and ileum.
Highest absorption of water is found in the small intestine.
Intestinal glands
Crypts of Liberkuhn
How nutrients are absorbed in the small intestine
Products of fat digestion are absorbed into the lacteal of the villus while products of digestion of other nutrients are absorbed into blood capillaries. Blood capillaries are converged in to the hepatic portal veins and are transported to the liver and then to the tissues.
What are ulses in stomach
Wounds in stomach
Chyme is mixed with
Secretions from intestinal wall, pancrease and liver.
Glands of intestinal wall secretes
Disaccharidases
Dipeptidases
Carboxypeptidases
Aminopeptidases
Neucleotidases
Nucleosidaaes
Phosphotases
What are the hormones secreted by the duodenum which stimulates the release of pancreatic juice and bile
Secreton and cholecystokonin
Pancreatic juice contains
Pancreatic amylase
Pancreatic trypsin
Pancreatic chymoptripsin
Pancreatic carboxypeptidase
Panceatic lipase
Pancreatic nuclease
Bicarbonates
Bile
Bile is secreted by the liver and stored in the gall bladder untill relasing to the duodenum
It contains bile salts which act as emulsifiers involving in fat digestion and absorption.
Digestion of nucleic acid starts in the
Small intestine
3 types of associated glands present in human digestive system
Pancreas
Liver
Salivary gland (parotid, sub mandibular, sub lingual
Cecum of the large intestine is important
Because it involves in fermentation of undigested materials by microbes.
Functions of large intestine
Completes water reabsorption, synthesis of vitamin B,K.Folic acid complexes and moves feces along the cecum through peristalsis.
Rectum stores faces until elimination.
Exocrine and endocrine
Exocrine glands have ducts to transport their secretions while endocrine glands lack a duct and hence their secretions are transported through blood.
Examples for exocrine glands are pancreas and salivary gland while examples for endocrine glands are pancreas and thyroid gland.
Exocrine and endocrine glands of pancreas
Exocrine part consists of a large number of lobules made up of small acini, they secrete pancreatic juice.
Endocrine part consists of islets of Langerhan which secretes hormones insulin and glucagon involved in glucose homeostatis.
Glands exhibiting both exocrine and endocrine functions
Pancreas, stomach and duodenum
Cecum of the large intestine is important
Because it involves in fermentation of undigested materials by microbes.
Histological structure of the pancreas
Pale grey gland which consist of broad head and narrow tail.
Pancreas is both an exocrine and an endocrine gland
Exocrine part of the pancreas secretes pancreatic juice
while the endocrine part is islets of Langerhans secreting hormones like glucagon and insulin which involves in glucose homeostatis.
Largest gland in the human body?
Liver
Functional unit of the liver, structure and functions
Functional unit of the liver is the liver lobule consisting of cuboidal cells called hepatocytes arranged in pairs forming columns. Between this columns contains sinusoids (blood vessels with incomplete walls)
Hepatic macrophages (kupffer cells) are found in the lining of sinusoids. Bile canaliculi run between columns of liver. In the corner of hexagonal structure contains a branch of hepatic artery, hepatic portal vein and bile duct.
Functions include metabolism of carbohydrates, fats and proteins, detoxification, defense against microbes,hormone inactivation and heat production.
Functions of liver related to digestion
Produce bile which contains bile salts involving in emulsification fats.
Most of the absorbed nutrients reach the liver which regulated the distribution of nutrients to rest of the body.
Excess glucose is stored as glycogen in the liver.
Fat soluble vitamins (K,A,D,E) and water soluble vitamins (B12) , iron and copper are also stored in liver.
Regulation of digestion in man
2 types namely nervous and endocrine
When food enters the stomach, the stomach wall is stretched triggering the release of gastrin hormone which stimulates secretion of gastric juice
Fatty acids and amino acids in the chyme trigger the release of Cholecystokinin and Secretin from the duodenum. Cholecystokinin triggers release of bile from the gall bladder and digestive enzymes from the pancreas. Secretin stimulates the release of bicarbonate from the pancreas. Bicarbonate neutralize the chyme received from the stomach
Drugs causing Gastritis
Aspirin
Gastritis
Occurs due to the inflammation of the stomach. Caused due to the stimulation of gastric glands releasing excess HCl which damages mucosa.
Prolonged gastritis occurs due to the infection of acid tolerance bacterium Helicobacter pylori
Causes are mental stress and prolonged starvation
Constipation
Occurs due to the slow movement of feces that promotes the water reabsorption and as a result feces become more solid. Inhibition of the reflex action in defecation may also leads to constipation.
Intake of adequate fiber in the diet can help prevent constipation.
Vitamins acting as anti-oxidants
Vitamin C and E
Functions of dietary fibres
Provides bulk to the diet and satisfy the appetite
Prevents constipation (stimulates peristalsis)
Protects against some gastro-intestinal disorders such as cancers in the colon and rectum
Malnutrition arises if BMI is less than
18.5
Obesity arises if BMI is on or more than
30
Functions of the stomach
Mechanical digestion of food by the churning action of the stomach
Acts as a temporary reservoir for food due to high convolution and elasticity
Produces gastric juice which initiates chemical digestion of proteins into small polypeptides by pepsin
Absorption of some materials like water, alcohol and some drugs
Non-specific defense - HCl kills microbes
Small jets of gastric content pushed from the pyloric spinchter as chyme
Secretion of gastrin hormone which regulates digestion in the stomach
Role of intrinsic factor
A glycoprotein produced by the parietal cells (humans) or chief cells. It is necessary for the absorption ofvitamin B12later on in the distalileum
