Digestion and Absorption Flashcards
Thecodont
Teeth are embedded in the jaw
Heterodont
Different teeth for different functions Incisors- cutting food Canines- cutting and tearing food Premolars- crushing food Molars- grinding food
Diphydont
Two sets of teeth in a lifetime-
milk teeth
permanent teeth
Dental formula in an adult human
2123/2123
Rugae
The mucous membrane of the stomach is thrown into numerous longitudinal folds called rugae when the stomach is empty.
Composition of saliva
It contains 99.5% water
It contains two enzymes:
> Salivary amylase
> Lysozyme
First step in the digestion of food
Salivary amylase action
Function of salivary amylase
Breaks down starch in food into simple sugars
Function of lysozyme
Lysozyme destroys the bacteria that enter along with the food
OR
causes lysis of several common bacteria that may be present in the mouth
Function of mucin
Helps in the lubrication of food for swallowing
Gastric glands + their functions
- Fundic glands (Oxyntic glands)- secrete HCl, pepsinogen, soluble mucin (ACIDIC)
- Pyloric glands- secrete mucin but no HCl (ALKALINE). Also secretes the hormone gastrin
- Cardiac glands- secrete mucin, pepsinogen (ALKALINE)
Why is gastric chyme acidic in nature?
Gastric chyme is acidic in nature because of the presence of HCl
Functions of HCl (Functions of gastric juice)
+ Converts pepsinogen —> pepsin
+ Kills the bacteria in food
Functions of pepsin (Functions of gastric juices)
Breaks down the proteins in food into peptones and polypeptides.
This stimulates the secretion of gastro-intestinal hormones in the small intestine
Functions of mucus (Functions of gastric juices)
Protects the gastric mucosa from the acidic pepsin.
Lubrication of food in the stomach
Retains water as the aqueous environment facilitates digestion in stomach.
Functions of liver
- Acts as an exocrine gland with the secretion of bile.
- Metabolism of carbohydrates, proteins and fats.
- Regulation of blood glucose and lipids.
- Storehouse of vitamins, glycogen and iron.
- Detoxification of drugs and alcohol.
- Removal of unwanted particulate matter from blood through the mediation of macrophages.
Functions of bile
- Emulsification of fats.
- Helps to keep the cholesterol in solution.
- Mild purgative action.
Functions of pancreas
• Pancreas has both exocrine and endocrine part.
• Exocrine part secretes enzymes that play an important role in digestion of proteins, carbohydrates and fats.
• Endocrine part (Islets of Langerhans) consists of three types of cells.
→ Alpha cells- secretes the hormone glucagon.
→ Beta cells- secretes the hormone insulin.
→ Delta cells- produces the hormones gastrin and somatostatin.
Process of ingestion
• It is a process that takes place in the mouth (buccal cavity).
• Food is taken in the buccal cavity, cut and chewed by the teeth.
• The saliva mixes with the food, lubricating it.
• The salivary amylase breaks the starch into maltose.
• The masticated food is now called a BOLUS
• From the pharynx, the bolus is swallowed and the process is called DEGLUTITION.
• The food that travels along the oesophagus, reaches the stomach by muscular
contractions of the food pipe (oesophagus) called PERISTALSIS.
Digestion of carbohydrates
- BUCCAL CAVITY
Salivary Amylase (pH 6.8)
Starch –> Maltose
(3-5%) Parotid glands
2. STOMACH
There is no carbohydrate digesting enzyme in the stomach
HCl
Starch -----> Maltose
(30-40%)
3. INTESTINE (Duodenum)
Acidic chyme mixes with bile (not enzyme), pancreatic juices, intestinal juices
Pancreatic amylase (pH 8.8)
Starch ----------------------------------------> Maltose
(50%) Duodenum
4. INTESTINE (Small Intestine)
Maltase
Maltose -------------> 2 Glucose
Sucrase
Sucrose -----------------> 1 Glucose
Dextrinase
Dextrin -------------------> 1 Glucose
Lactase
Lactose ----------> 1 Glucose + 1 Galactose
Digestion of proteins
- STOMACH
HCI (pH 1-2)
Pepsinogen ————-> Pepsin
Pepsin
Protein ————> Proteoses / Peptones
Pepsin
Casein —————> Paracasein (milk coagulation)
Rennin (Seen in infants and absent in adults; rennin is more effective than
casein because infants only drink milk) - SMALL INTESTINE (Upper small intestine)- Pancreatic peptidases
Enterokinase Inactive trypsinogen --------------------> Trypsin Trypsin Proteins ---------------> polypeptides Carboxypeptidase Polypeptides ------------------------------> Simple peptides Chymotrypsin Casein ----------------------> Paracasein - SMALL INTESTINE (Intestinal juices)
aminopeptidases
Peptides ————————> Aminoacids
Digestion of fats
All fat digestion takes place in the small intestine.
Bile
Fat —————> Emulsified fat
pancreatic lipase Emulsified fat -----------------------------> Fatty acids, Glycerol, 2 monoglycerides
Why doesn’t protein digestion take place in the buccal cavity?
Saliva has no proteolytic enzyme, so no protein digestion takes place in the buccal cavity.
Absorption
> Carbohydrates —> Monosaccharides (Glucose) —> absorbed by the blood stream
blood > Monosaccharides ------------> Glycogen (Liver) > Proteins ---> amino acids ---> absorbed by blood stream Amino acids ---> Energy (tissues) for metabolic activities > Fats ---> Fatty acids, glycerol ---> duodenum and jejunum Fats are incorporated into water soluble droplets called Micelles and then absorbed
Egestion
Unwanted food is eliminated from the body by a process called DEFAECATION
Mechanism of absorption
> Passive transport-
Diffusion and osmosis
> Active transport
Calorific values of
i) proteins
ii) fats
iii) carbohydrates
i) proteins- 5.65 kcal
ii) fats- 9.45 kcal
iii) carbohydrates- 4.1 kcal
Constipation: definition + causes + symptoms + treatment
Defintion:
Infrequent or difficult defaecation which causes discomfort is known as constipation.
Causes: > improper bowel habits > colon spasms > insufficient fibre intake > inadequate fluid intake
Symptoms:
> difficult or infrequent passing of motions
Treatment:
> Use of mild laxative that induce defaecation
> Eating fibrous foods like apples, bananas, drumstick, snake gourd
Emesis/vomiting: definition + process
Definition: Emesis is a condition when contents of the stomach come out through the oesophagus into the mouth and out of it.
It could be cause by nausea, constipation or changes in the body’s equilibrium due to motion. Irritation in the stomach causes the abdominal muscles to contract leading to emesis/vomiting.
Diarrhoea: definition + causes + symptoms
Definition: Frequent and profuse defaecation of liquid faeces is called diarrhoea.
Causes:
Increased motility and decreased absorption by the intestines.
Lactose intolerance, stress, microbes irritating gastrointestinal mucosa.
Symptoms:
Liquid faeces
Continuous abdominal pain, bleeding from the rectum
Jaundice + characteristics + 3 types
It is a symptom that always indicates serious disease.
Characterised by:
i) yellow pigmentation of the skin and sclera of the eye due to bilirubin
ii) excess bilirubin concentration in the blood
3 types:
- prehepatic jaundice
- hepatic jaundice
- extrehepatic jaundice
Prehepatic jaundice: cause + characteristics
Medically known as haemolysis
> Caused due to excess production of bilirubin.
> It is a neonatal disease i.e. seen in small babies, usually 3 to 5 days after their birth
> If it doesn’t go away, the baby is kept in an incubator that provides light in the NICU
> In abnormal conditions, can also be caused by sickle cell anaemia, rhesus
incompatibility, thalassaemia major
Hepatic jaundice: causes
Due to congenital liver diseases, liver cirrhosis (in an alcoholic), or hepatitis
Infections are usually responsible for this kind of jaundice
Extrahepatic jaundice
> occurs outside the liver, not inside
when the cystic duct or the bile duct gets blocked
blockage of bile drainage by gallstones
bowel cancer, pancreatic cancer or liver cancer
PEM- full form + two main disorders
Protein energy malnutrition
two main disorders:
- Kwashiorkor
- Marasmus
Kwashiorkor
> wet protein energy malnutrition > protein deficiency > age - from 6 months > fluid retention (edema) > dry, peeling skin > extremely thin extremities/legs and arms
Dysentery
A different form of diarrhoea as it is caused by a protozoan or bacterial infection and streaks of blood, mucus are seen in the faeces
Indigestion
Any minor discomfort coming on after meals is called indigestion
It causes a feeling of fullness, heart burn, regurgitation of water (water brash), bloated stomach
