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Digestion and Absorption
Introduction
 Aim: the aim of digestive system is to make available the food substances to the cells of body,
after being digested and absorbed in alimentary canal.
 Food is one of the basic requirement of all living organisms
 The major component of our are carbohydrates, proteins and fats
 Food provides energy and organic materials for the growth and repair of tissues.
 The water we take in plays an important role in metabolic processes and also prevents
dehydration of the body
 Biomacromolecules in food cannot be utilized b our body in their original form. They have to be
broken down and converted into simple substances in the digestive system
Definition of digestion
 The process of conversion of complex food substances to simple absorbable forms is called
digestion and is carried out by our digestive system by mechanical an biochemical methods
Additional to Remember
 Digestion id the process by which complex organic food substances [proteins, fats.
Polysaccharide and disaccharide] re broken down in different parts of alimentary canal, in stepby-step manner, with the help of enzymes, by the process of hydrolysis, into simpler absorbable
substances [amino acids, fatty acids and glycerol, and monosacchrides respectively]
 Digestion is universally observed in the whole animal kingdom except Tapeworms, where
digestive system is absent, and they absorb digested food of host through their general body
surface
 Since trypsin and amylase enzymes are found in the whole animal kingdom, so they are
regarded as universal enzymes [Amalyase is, however absent in Coelenterata]
 Enzymes pepsin is found in vertebrate only
 Development of digestive system
 The lining of whole alimentary canal is developed from endoderm, except the lining of
buccal cavity and canal, which is ectodermal
 The wall of alimentary canal [from oesophagus to rectum] s the developed from
endodermal lining and messodermal rest of the structures
 Liver and pancreas are developed from the lining of duodenum, so are endodermal
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 The human digestive system consists of Alimentary canal and associated glands
Alimentary Canal
 The alimentary canal begins with an anterior opening – the mouth, the it opens out posteriorly
through the anus Length: 8-10 meter
 The wall of alimentary canal from oesophagus to rectum possesses four layers namely Serosa,
Muscularis, Sub-mucosa and Mucosa
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 Serosa
 Serosa is the outermost layer
 It is made up of a thin mesothium (epithelium of visceral organs) with some connective
tissues. It is simple squamous epithelium
 Muscularis
 Muscularis is formed by smooth muscles usually arrange into an inner circular and an outer
longitudinal layers
 An oblique muscle layer may be present in some region specifically stomach
 Sub-mucosa
 The submucosal layer is formed of loose connective tissues containing nedrves, blood and
lymph vessels
 In duodenum, glands are also present in sub- mucosa Brunner’ glands – Mucous secreting
multicellular glands
 Sub mucosa is thickest in oesophagus
 Mucosa
 The innermost layers lining the lumen of the alimentary canal are the mucosa.
 This layers forms irregular folds (rugae) in the stomach small finger-like folding called vili in
the small intestine
 The cells lining the villi produce numerous microscopic projections called microvilli giving a
brush border appearance
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

Villi and microvilli icrease the surface area enormously
Villi are supplied with a network of capillaries and a large lymph vessel called the lacteal
Parts of Alimentary Canal
 The mouth leads to the buccal cavity or oral cavity. Posterior opening of buccal cavity into
pharynx is known as Fauces
 The lining of bucal cavity is made up of striatified non- keratinized squamous epithelium
 The oral cavity has a number of teeth and a muscular tongue
 Teeth
 Man has the codont, heterodont, brachydont, bunodont, hypsodont [upper incisors, which
are also known as “similing”], diphyodont [20] and monophyodont [12] teeth
 Each tooth is embedded in a socket of jaw bone. This type of attachment is called codont
joint between root of tooth and socket / alveolous of jaw bone is an immovable joint,
known as Gomphosis
 Majority of mammals including human being forms two sets of teeth during their life
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
A set of temporary milk or deciduous teeth replaced by set permanent or adult teeth. This
type of dentition is called diphyodont
Additional to Remember
 Temporary set / Milk set
 1st tooth of milk set erupts by the age of 6 month in the form of 1st incisor
 The last tooth of milk set erupts by the age of 24 months in the form 2nd molar, so the whole
milk set is acquired by the age of 2 years
 Dental formula [the representation of the type and number of teeth, present in half of the
upper and lower jaw, in the form of a formula with the sequence of incisors, canine,
2102
premolar and molar] of child 2102 × 2 = 20 Premolars are absent in the milk set, but there
is no toothless space between canine and molar because molars have been ereupted at the
site of premolars
 Permanent set / Adult set / Non-deciduous set [32 in number]
 1st tooth of permanent set is acquired by the age of 6 years in the form of 1st molar.
However, the 1st milk tooth, which is broken, 1st incisor
 The last tooth of permanent set erupts by the age of 24 year in the form of 3rd molar, which
is a vestigial tooth, and is also known a wisdom tooth
Dental formula of adult
Sequence of eruption of permanent teeth
1st Molar
Mummy
1st Incisors
Is
2nd Incisors
In
1st Premolar
Power
2nd Premolar
Papa
Canine
Cannot
2nd Molar
Make
3rd Molar
Mistake
Dental formula of rabbit:
2033
×
1023
2 = 28
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Since canines are absent in rabbit, so there is toothless space / diastema, present in between
incisor and premolars

An adult human has 32 permanent teeth which are of four different types (heterodont
dentition), namely Incisors (I), Canine(C), Premolars (PM) and Molars (M)
Arrangement of teeth in each half of the upper and lower jaw in the order C, PM, M is
represented by a dental formula, which in human is

2123
2123
The hard chewing surfaces of the teeth, made up of enamel, helps in the mastication of
food
Additional to Remembers
 Tooth is octomesodermally developed structure [like adrenal gland, eye and skin], where
enamel is ectodermal and dentine is mesodermal.
 It is developed as >Mesenchyme>Scleroblast>Ameloblast>Enamel
 Enamel is present only around crown part, and is developed [from outside to inside]
even before the eruption of tooth.
 Since after the eruption of tooth, the ameoblast cells become inactive so enamel cannot
be repaired, if gets damaged
 Enamel is non living, translucent, whitish, hardest [highest concentration of minerals in
the whole body] substance of the body that carries almost 97% of Ca3PO4 and 3% CaF2
and proteins, but fibers are absent in enamel. Due to its mineral content, the enamel is
so hard that sparks will be produced if a steel rod is rubbed against itself
 Dentine
 It is developed as >Mesenchyme>Scleroblast>Odontoblast>Dentine
 It is living, whitish major part of tooth, which is developed from inside to outside, and is
composed of 70% of Ca3PO4 [remaining is organic matter]
 Dentine is present not only in crown part but also in the neck [behind gums / gingiva]
and root [part embedded into alveolus of jaw bone]
 The root of the tooth is firmly held in position because of cementum, which is secreted
by periodontal membrane [type of periosteum that forms the lining of alveolus of jaw
bone]
 The position of roots is further strengthened by collagenous sharper’s fibers, which run
across periodontal membrane to detine of roots through cementum. Thus the root of
the tooth and alveolus of jaw bone, together form immovable joint, known as
Gomphosis
 The tip of the root carries an aperture as apical pore that leads to narrow root canal,
which becomes wider as pulp cavity in upper part of tooth
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
The apical pore allows the entry and exit of blood vessels and nerves into pulp cavity,
the pore remains wider during childhood, and gets constricted after acquiring full
growth
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

Teeth give shape to the face
They bring about mastication of food
They help in speech
Tongue
 The tongue is a freely movable muscular organ
 It attached to the floor of the oral cavity by the frenulum mucous fold posteriorly, it is attached
to hyoid bone, and its anterior end remains free of three types.
 Some papillae bear taste buds
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Additional to Remember
 It is made up of striated voluntary muscles, which are immune to be fatigued. They are of 2
types on the basis of their attachment
 Extrinsic muscles
 These muscles have their “origin” attached to hyoid and or mandible. The “belly” and
“insertion” parts lie freely into fatigue
 These muscles help to move the tongue
 Intrinsic muscle
 These muscles have their “origin”, “belly” and “insertion” parts, all together in tongue
 These muscles help to change the shape of tongue
 The upper surface of tongue carries stratified non-keratinised squamous epithelium, and
several small projections as papillae of following three types
 Circumvallate / Vallate papillae
 These papillae are the largest in size and minimum in number
 These papillae carry the taste buds concerned with bitter taste
 Fungiform papillae
 These are the moderate in size and number
 These also carry taste buds, which are concerned with sweet and salty [at the tip], and sour
[at antero-lateral margin]
 Filiform papillae
 These are the smallest and most abundant papillae
 These are conical-shaped, and are found on the anterior part tongue
 They have keratinized tip, so are also known as keratinized / cornified papillae
 Filiform papillae do not have taste buds. Taste buds : these are the group of
gustatoreceptors, receptor, located not on the the tongue but also in the hard palate, upper
surface of epiglottis and oropharynx
 The taste sensation from anterior 2/3 part of tongue is carried by VII- cranial nerve / facial
nerve, and from posterior 1/3 part of tongue by IX-cranial nerve / Glosopharyngeal nerve
 Function of tongue
 It help to mix the food and make the same bolus [ball of food]
 It helps in taste sensation
 It helps in speech
 It helps to cleanse the teeth
 It help to protect the body by preventing the entry of contaminated decomposed food
with the help of taste buds
 It helps in deglutition / swallowing
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Salivary Glands
 Saliva is mainly produced by three pairs of salivary glands, as parotid gland, sub-maxillary / submandibullary gland, and sub-lingual gland
 Parotids (cheek)
 Sub-maxillary sub-mandibular (lower jaw)
 Sub-linguals (below the tongue)
 These glands situated just outside the buccal cavity and so are extrinsic in position other
extrinsic glands of digestive system are liver and pancreas. The glands, which are located within
the wall of alimentary canal, are known as intrinsic glands, like gastric glands
 These salivary glands secrete salivary juice into the buccal cavity through ducts
Additional to Remember
 True salivary glands are present only in mammals
 The salivary glands of man are merocrine in nature

Parotid gland
 These are largest in size, but contribute only 25% of total saliva
 Located in cheek
 They have pair of ducts, known as Stensen’s ducts [parosen = paro (parotid) +sen (stensen)]
 They secrete serous type [watery but rich in enzymes] of saliva
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
Sub-maxillary / Sub-mandibullary gland
 These are moderate in size, but contribute only 70% of total saliva
 Located on the posterior angle of lower jaw
 They have a pair of ducts, known as Wharton’s ducts [Sum what = Sum(Sub maxillary) =
What (Wharton)]
 They secrete serous type as well as mucoustype [ thick, viscous, white, saliva, which is poor
in enzymes] of alive
 Sub-lingual gland
 These are smallest in size and contribute only 5% of total alive
 Located below tongue
 They have several ducts, known as ducts of Rivinus / Bartholine’s ducts
 They secrete mucous type of saliva
 Control of secretion of saliva : It is neutrally controlled by Parasympathetic nerve
 Composition of saliva :
 Quantity :500-1000 ml/day
 pH : 6.8 [slightly acidic]
 Inorganic content : HCO3 –CO3 –Cl-K+,Na+
 Organic content : Mucin [glycoprotein] / Amylase / Ptyalin / Amylopsin
 Function of saliva
 It helps to keep the lining of buccal cavity moist and smooth by mucin
 It help to mix the food and make the same bolus
 It help in taste sensation by dissolving the chemicals present in food
 It is antiseptic / antibacterial because of the presence of lysozyme, and acidic nature of saliva
 It is excretory as well, because of the presence of urea
 It helps in speech by keeping the tongue mobile
Role of Buccal Cavity in Digestion
 The process of digestion is accomplished by mechanical and chemical process
 mechanical process: the buccal cavity performs two major function mastication of food and
facilitation of swallowing
 Mucus in saliva helps in lubricating and adhering the masticated food particles into a bolus. Thu
bolus is then conveyed into the pharynx and then into the oesophagus by swallowing or deglutition
 The bolus further passes down through the oesophagus by successive waves of muscular
contraction called peristalsis
 The gastro-oesophageal sphincter controls the passage of food into the stomach.
 The saliva secreted into the oral cavity contains
 Electrolytes (Na+,K+,Cl-,HCO- ) and
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 Enzymes salivary amylase and lysozyme
 Chemical process :the chemical process of digestion is initiated I the oral cavity by the hydrolytic
action of the carbohydrate splitting enzyme, the salivary amylase
 About 30 per cent of starch I hydrolyzed here by this enzyme (optimum pH 6.8) into a disacchride –
maltoe
𝑆𝑡𝑎𝑟𝑐ℎ
𝑆𝑎𝑙𝑖𝑣𝑎𝑟𝑦 𝐴𝑚𝑦𝑙𝑎𝑠𝑒
𝑀𝑎𝑙𝑡𝑜𝑠𝑒.
𝑝𝐻6.8
 Lysozyme present in saliva acts as an antibacterial agent that prevents infection
Deglutition / Swallowing


1.
2.
3.
4.
5.
6.
It is the act of pushing the bolus from buccal cavity to stomach
It is basically a voluntary action but during eating process, it become involuntary [ and also,
when bolus has crossed the fauces], nd is carried out as reflex action through following steps
Tongue is raised above, and presses against had palate to push the bolus through fauces
Trachea is raised above and its opening [glottis] come below epiglottis to be closed, so as to
prevent the entry of any solid or liquid
Uvul is raised above, ad separates the oro-pharynx from nso-pharynx
Breathing is momentarily stopped
The bolus goes down into oesophagus its opening [gullet]
The bolus passes through oesophagus by peristalsis, then finally enters into cardiac part [the
gastro-oesophageal sphincter controls the passage of food into the stomach]
Pharynx,Oesophagous and Stomach
Pharynx









The oral cavity leads into a short pharynx
Pharynx serves as a common passage for food and air
The Oesophagous and the trachea (wind pipe) open into the pharynx
The cartilaginous flap called epiglottis prevents the entry of food into the glottis – opening of
the wind pipe, during swallowing
Additional to Remember
It is passage of seven openings
Lining: Endodermal
Muscles : Circular muscle fibres / CMF
Glands : Mucous glands only “No enzyme, no digestion” because food does not stay here
It is divided into three parts
 Naso-pharynx
 Oro-pharynx
 Laryngo-pharynx
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 Oesophagous
 The oesophagous is thin, long tube, which extends posteriorly passing through the neck, thorax
and diaphragm and leads to a ’J’ shaped bag like structure called stomach
 A muscular sphincter (gastro-oesophagous) regulates the opening of oesophagous into the
stomach
 Stomach
 The stomach, located in the upper left portion of the abdominal cavity
 It has three major parts
 Cardiac portion into which the oesophagous opens
 Fundic region main part of stomach
 Phloric portion which opens into the first part of small intestine Duodenum
Role of Stomach in Digestion


The stomach stores the food for 4-5 hours
The food mixes thoroughly with the acidic gastric juice (HCl) of the stomach by the churning
movements of its muscular all and is called the chime
 The mucosa of stomach has gastric glands
 Gastric glands have three major types of cells in fundic part specifically namely
 Mucus neck cells Globet cells which secrete mucus
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 Peptic or chief cells most abundant cells of gastric glands which secrete the proenzyme
pepsinogen and proprenin in infant. Since these are enzymes secreting cells, so are also known
as Zymogen cells
 Parietal or oxyntic cells which secrete HCl and intrinsic factor of castle 9factor essential for
absorption of vitamin B12)
 HCl provides the acidic ph (ph 1.8) optimal for pepsins
 The proenzyme pepsinogen, on exposure to hydrochloric acid gets converted into the active
enzyme pepsin Proenzyme pepsinogen
HCl
Active enzyme pepsin.
 Pepsin is the proteolytic enzyme of the stomach. It converts proteins into proteoses and
peptones (peptidas).
Proteins
pepsin
Prteoses and peptones.
 The mucus and bicarbonates, present in the gastric juice play an important role in lubrication
and protection of the mucosal epithelium from excoriation by the highly concentrated
hydrochloric acid
 Small amounts of ipases are also secreted by gastric glands
 Rennin is a proteiolytic enzyme found in gastric juice of infants. It helps in the digestion of milk
proteins
Stomach / Gaster
 It is the thickest walled reservoir of alimentary canal
 Shape : J-shaped
 Apertures : It has two openings as cardiac orifice [opening for oesopahagus] and pyloric orifice
[opening into duodenum]. The openings carry gastro-oesophageal sphincters and pyloric sphincter
respectively, so as to prevent the backflow of gut contents
 Histrologically ,the wall of stomach carries following modifications
 Oblique Muscle Fibre B [present only in the all of stomach, and is also the thickest of the three
muscular layers] along with normal laongitudinal Muscles Fibre and Circular Muscle Fibre
 Mucosa : It carries lining of simple column epithelium with supportive connective tissue
 The lining of stomach is thrown into several gastric folds and gastric pits [function as glands]
 The lining shows the presence of thick layers of mucous with several smaller apertures as
faveola to allow the release of gastric juice in the lumen of stomach
 The lining of stomach shows the presence of some other irregular folds in empty state [which
disappear when stomach is full of meal],known as Rugae
 Gastric glands
 These are intrinsic [present in the mucosa of wall ] glands, which are merocrine in nature
 Number: 35 million / 3.5 crore
 These glands secrete gastric juice from different types of cells, in the following part of stomach
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




1.
2.
Cardiac part
It is part of stomach, which lies close to heart with only diaphragm in between
The gastric glands of his part carry only goblets cells for the secretion of mucous
Fundic part
The gastric glands of fundic part secrete maximum gastric juice through following types of cells
Peptic cells :these are located deep into gastric glands
Parietal cells / oxygentic cels : The cells are located in the neck part of the glands and they
secrete cone. HCl and Intrinsic factor of castle
 Pyloric part
 It is the distal par of stomach that opens into duodenum
 The gastric glands of pyloric part carry following cells
1. G-cells : These cells secrete hormone gastrin into blood, which stimulates the gastric glands for
the secretion of gastric juice
2. Goblet cells are present only present only in neck part of the gastric glands of whole stomach,
and they secrete only mucous
 Control of the Secretion of Gastric Juice
 It is neurally controlled by parasympathetic nerve running with Vagus cranial nerve, and
chemically by gastrin
 Composition of Gastric Juice
 Quantity : 50 ml to 1000 ml/day
 pH : 1.8,strongly acidic
 inorganic contents : con. HCl and bicarbonates
 Organic content : Mucin, glycoprotein, pepsinogen, Pro-rennin, Lipase
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Functions of Gastric Juice
 It changes the medium of food from slightly acidic to strongly acidic for the action of pepsin
 It protects the wall of stomach from excoriation by the highly concentrated HCl and gastric enxymes
with the help of mucous and bicarbonate ions
 It secrets intrinsic factor of castle, which is the main function of stomach, which helps to absorb
vitamin B12 at the level of distal part of ileum
 It help to free the iron fee the iron of diet from its conjugated state to be absorbed at the level of
duodenum
 It is antiseptic / antibacterial
 It brings about the digestion of proteins [all types, except keratin] mainly, and fats to soe extent, in
the following manner
Small Intestine
 It is the longest part of alimentary canal
 Length : 6-7 meter
 Proximally, itbegins from pyloric orifice, and distally opens into caecum through ileocaecal orifice,
which carries the sphincter, to prevent the back flow
 The lining of small intestine is simple columnar epithelium with microvilli / brush border epithelium,
and is thrown into several folds and pits , known as villi and crutes of leiberkuhn respectively
 Each villus accommodates a capillary network and a lymphatic vessel [which is known as lacteal
when it has absorbed fat]
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 Small intestine is distinguishable into three regions
 U-shaped duodenum
 Long coiled middle portion jejunum
 Highly coiled ileum
 The opening of the stomach into the duodenum is guarded by the pyloric sphincter
 Ileum opens into the large intestine
 Duodenum
 It is the U-shaped proximal part of small intestine with a length of 25 cm ony
 It receives the bile duct of Wirsung [pancreatic duct] as common hepato-pancreatic duct
through an ampulla-like opening, known flow of bile juice as well as pancreatic juice
 The sub-mucosa od duodenum accommodates mucous- secreting Burnner’s gland, which are
intrinsic in position
 The lining of duodenum secretes following four hormones
 Enterogastrone / Gastric inhibitory peptide
 Secretin
 Panceozymin / Pz
 Cholecystokinin / CCK
 Duodenum provides the site for the maximum digestion of food
 Jejunum
 It is the middle part of small intestine
 Length: 2.5 meter
 The crypts the of leiberkuhn in jejunum functions as intestinal gland, [intrinsic gands], which
secrete intestinal juice / succus entericus and the zymogen cell of these glands, are known as
Paneth cells
 The lining of jejunum secretes the hormone, Enterocrinin
 The main function of jejunum is digestion
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 It is the terminal, highly coiled and the longest part of small intestine.
 Length: 3.5 meter
 The main function of ileum is absorption, and for that purpose, it carries longest and most abundant
villi of the small intestine.
 The mucosa of ileum [and also of vermiform appendix] carries lymphoid tissue, known as peyer’s
patches
Role of Small Intestine
 Small intestine brings about digestion of food in duodenum and jejunum, and then absorption in
jejunum and ileum
 Various types of movements are enerated by the muscularis layers of the of the small intestine.
These movements help in a trough mixing up of the food with various secretions in the intestine
and thereby facilitate digestion
 Secretion released into small intestine: Bile juice and Pancreatic juice
 Bile juice
 In the absence of bile, fats are not digested properly which results in fatty diarrhoea. Thus
bile is essential for digestion though it does not contain any digestive enzymes. The bile is
taken by the hepatic duct and is stored in the gall bladder which is situated on the lower
surface of the liver. The bile is concentrated and sent to the duodenum through the cystic
duct when chyme from the stomach enters the duodenum. Bile contains bile salt, bile
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pigment, mucin and water. The two pigments present in the bile are called Bilirubin and
Biliverdin. These pigments give colour to the faeces and urine. Due to liver damage or
obstruction of the bile duct, bilirubin collects in excess quantities in blood and change the
colour of the skin and the eyes. There may be changes in the colour of the urine also. This is
called Jaundice.
 Functions of Bile Juice
 It stimulates the functions of the proteolytic enzymes and Amylase.
 It dissolves fatty acid, and glycerol.
 It coordinates with lipase to convert the fat into fatty acids.
 It helps in the absorption of the fatty acids and glycerol.
 With the help of other digestive juices it neutralises the acidic nature of food
 Pancreatic Juice
 It is regarded as “complete digestive juice”
 It contains inactive enzymes like: Trysinogen, Chymotrypsinogen, Procarboxypeptidases,
Amylases, Lipases, and Nucleases.
 It also conatins bicarbonates to raise the pH of chime.
 Activation of inactive trypisnogen. Trypsinogen is activated by an enzyme,
Enterokinase,which is secreted by the intestinal mucosa.
Enterokinase change Trypsinogen into active Trypsin
Trypsinogen(inactive enzyme)
Enterkinase
Trypsin (active enzyme)
 Function of enzymes, present in pancreatic juice
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 Intestinal juice or succus entericus
 The intestinal mucoal epithelium has goblet cells, which secrete mucus
 Intestinal Juice =Secretions of the brush border cells of mucosa + secretions juice of the
goblet cells
 Intestinal juice contains a variety of enzymes like Disaccharidases (e.g. Maltase),
Dipeptidases, Lipases, nucleosidades,etc.
 Function of enzymes of intestinal juice
 The mucus , along with bicarbonates from the pancreas protects the intestinal mucosa
fromacid as well as provide an alkaline medium (pH 7.8) for enzyme activities
 Sub-mucosal glands (Burnner’s glands0 also help in this
 The enzymes in the succus entericus act on the end products of chime to form the
respective simple absorbable forms
 These final steps in digestion occurs very close to the mucosal epithelial cells of the
intestine
 Control and Coordination of Digestive System
 The activities of the gastro-intestinal tract are under neural and hormonal cotro for proper
coordination of different parts
 The sight, smell and or to presence of food in the oral cavity can stimulate the secretion of saliva
 Gastric and intestinal secretions are also, similarly stimulated b neural signals
 The muscular activities of different of different parts of the alimentary canal also be moderated
by neural mechanisms, both local and through CNs
 Hormonal control of the secretion of digestive juices is carried out by the local hormones
produced by the gastric and intestinal mucosa
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 Absorption of food
Absorption is the process by which the products of digestion are absorbed by the blood to be
supplied to the rest of the body.
During absorption, the digested products are transported into the blood or lymph through the
mucous membrane. Absorption is achieved by the following mechanisms.
1.
2.
3.
4.
Simple diffusion.
Active transport
Facilitated transport.
Passive transport.
 Simple diffusion
Simple diffusion is defined as the movement of solute from the higher concentration to the lower
concentration through the membrane.
After digestion, a few monosaccharides diffuse into the blood based on the concentration gradient.
Example: Glucose, amino acids and ions like chloride.
 Active transport
Active transport may be defined as the process of solute movement from the lower concentration to
the higher concentration by the expense of energy.Electrolytes like Na ions are absorbed by active
transport into the blood.
 Facilitated transport
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Facilitated transport is defined as the process of movement of solutes across the biological
membrane with the help of specific carrier proteins. Some digested amino acids and glucose are
absorbed into the blood by this method.
 Passive transport
Passive transport is defined as the process of solute movement across a cell membrane without a
requirement of energy. After digestion, simpler food substances are absorbed into the blood by
passive transport.
 Assimilation
Some digested products from fats cannot be absorbed into the blood. Example: Fatty acids and
glycerol. These components attach to micelles which are small droplets and form micellecomponent complex. This micelle – component complexes are re-formed into chylomicrons.
Chylomicrons are a small protein coated fat globules. Then, chylomicrons move into the lymph
vessels and release the digested products into the blood. Finally, the digested and absorbed
products reach the tissue to be utilized for their activities. This process is called as assimilation.
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Role of large intestine
Large intestine consists of caecum, colon and rectum
Caecum
Caecum is a small blind sac
It hosts some symbiotic micro-organisms
The vermiform appendix which is narrow finger-like tubular projections. It is a vestigial organ,
arises the caecum
The caecum opens into the colon
Colon
The colon is divided into three parts
 An ascending
 A transverse only part of colon, which is attached to body wall
 A descending part
 Colon exhibits the fastest peristalsis, slowest in rectum
Rectum
The descending part opens into the rectuim which opens out through the anus. The undigested
and unabsorbed substances are passed on to the large intestine
Function of large intestine
 Absorption of some water, mineral and certain drugs
 Secretion of mucus, which helps in adhering the waste [undisgested] particles together and
together and lubricating it for an easy passage
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 The undigested, unabsorbed substance called faeces, enters into the caecum of large intestine
through ileo-ceacal vcalve. The valve prevents the back flow of the faecel matter
 The digestive wastes, solidified into coherent faeces in the rectum, where it is temporarily
stored till defaecation egestion
 Rectum initiates a neural reflex causing an urge or desire for its removal
 The egestion of faeces to the outside through the anal opening (defeacation) is a voluntary
process
 It carried out by a mas peristaltic movement
Liver / Hepar
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Liver is the largest gl and also largest visceral organ of the body
Liver weighs about 1.2 to 1.5 kg in adult human
In infants, liver constitutes about 5% of body weight due to his higher BMR
It is endodermally developed gland from the lining of duodenum
It is situated in the abdominal cavity, just below the diaphragm and has two lobe right lobe is
almost six times biger than the left lovbe.
All lobules are separated from one another by means of a sheath of coolagen fibres known
asGlisson’s capsule [mammalian character]
The hepatic lobules polygonal / hexagonal chambers are the structural and functional Units of
liver
These lobules conatin hepatic cells binucleated busiest cels of body arranged in the form of
cords.
Each lobule is covered b thin connective tissue sheath called the Glisson’s capsule
Secretion of bile : The bile secreted by the hepatic cells passes through the hepatic ducts
Gall bladder: bile is stored and concentrated by about 10 times as compared to liver bile thin
muscular sac called the gall bladder, located on their inferior border of right lobe
The lining of gall bladder is simple cubiodal epithelium with microvilli, and it also carries rugae
Formation of bile ducts – the duct of gall bladder (crystic duct) along with the hrpatic duct from
the liver forms the common bile duct
The bile ducts and the pancreatic duct also known as duct of wirsung open together into
ampulla of vater of the duodenum as the common hepato-pancreatic duct
Hepato-pancreatic ducts is guarded by a sphincter called the sphincter of Oddi
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Additional to Remember
 Liver has dual blood supply lpure as well as imp hepatic portal wein Hepatic artery brings pure
blood and provides nutrition a status of the whole body, where as hepatic portal vein brings
absorbed food substances from alimentary canal though it has impure blood
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 FUNCTIONS OF LIVER
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It is the busiest organt, and it performs as many as 100 duties
it is haemopoietic during embryonic period, producing blood corpuscles
It is the largest producer of lymph
It produces au plasma proteins except igG [produced by plasma cells]
The urea cycle / ormithine cycle runs only in liver because of the presence of enzyme Arginase
[present only in liver].
it produces at blood clotting factors except factor IV [calcium ions]
 lt stores fat solubie vitamins [A, D, E and K] and also vitamin B12
 It stores iron
 It detoxify the toxins and alcohol but in doing so, the liver cells also get damaged, however, they
are regenerated soon because liver has got the maximum power of regeneration
 Glycogenesis [formation of glycogen from glucose) is carried out in live under the influence of
hormone Insulin, which stimulates the 1st enzyme of the reaction i.e. Hexokinase, and then the
whole process is completed through Cascade effect
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 Glycogenolysis (breakdown of glycogenl is also carried out in liver under the influence of
hormone Glucagon (only in liverl and Adrenaline [in liver and muscles], which stimulates the
enzyme of the reaction i.e. Phosphorylase and then the whole process is completed through
Cascade effec
 since phosphatase is found only in liver, so complete glycogenolysis takes place on in liver and in
muscles, the glycogenolysis takes place up to the level of Glucose 6 PO4 from where Glucose 6PO4 enters directly into glycolysis
 Gluconeogenesis [formation of glucose from non-carbohydrate source like glycerol and amino
acids] also takes place in lver, under the influence of hormone Cortisol [released from adrenal
cortex] and glucagon, so as to maintain the normal blood glucose level
 Glyconeogenesis [formation of glycogen from lactic acid] takes place in liver through Glucose
Cori cycle
 Liver secretes hormone Insulin-like growth factor-1 [GF-1]. And angiotensinogen,
 Growth hormone of anterior pituitary binds to the receptors on the of liver cells, which
stimulate the synthesis and release of IGF-1 from them. Many cells have receptors for IGF-1
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especially cells in the bone marrow and in the cartilaginous growing regions of tho long bones,
where
 it stimulates the mitosis.
 Angiotensinogen: It is released into blood as plasma protein and helps in operating RAAS
PANCREAS
 Pancreas is endodermal gland developed from the lining of duodenum
 The pancreas is a compound (both exocrine and endocrine) elongated organ situated between
the limbs of the U shaped duodenum
 The exaorine portion secretes an alkaline pancreatic juice containing enzymes,and the enzyme
secreting zymogen cells of pancreas are known as Pyriform cells
 The endocrine pancreas consists of 1slets of Langerhans'
 There is about 1 to 2 million lslets of Langerhans in a normal human pancreas representing only
1 to 2 per cent of the pancreatic tissue
 The two main types ot kelis im the inlato Lange hans are Alpha cells and Beta cels
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∝ cells
 The ∝ colle secrete a hormone called glucagon
 Glucagon is a peptide hormone and plays an important role in maintaining the normal blood
glucose levels
 Glucagon acts mainly on the liver cells (hepatoeytee) and stimulates glycogenolysis,
resulting in increased blood ougar (hyperglycomi
 In addition, this hormone stimulales the process of gluconeouemesin which also contributes
to hyperglycemia
 Glucagon reduces the cellular glucose uptake and utilisation
 Thus, glucagon is a hyperglycemic hormone
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𝛽-cells
 The 𝛽-cells secrete a peptide hormone, which plays a major role in the regulation of glucose
homeostasis
 Insulin acts mainly on hepatocytes and adipocytes (cells of adipose tissue), and enhances
cellular glucose uptake and utilisation
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 As a result, there is a rapid movement of glucose from blood to hepatocytes and adipocytes
resulting in decreated blood glucose levels (hypoglycemia)
 Insuln also stimulates conversion of glucose to glycogen (glycogenesis) in the target cells
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Diabetes mellitus
 Prolonged hyperglycemia leads to a complex diaorder called diabetes mellitus, which
associated with loan of glucose through urine Glycosuria and formation of harmful
compounds, known as ketone bodies
 Diabetic patients are successfully treated with insulin therapy
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In addition to a cells and B-cells, the island of Langerhans also accommodate two other
endocrine cells as D-cells and F-cells
 D-cells: These cells secrete hormone Somatostatin, which is STH of Pituitary. Somatostatin
hormone also released from hypothalamus the form of somatotropic hormone inhibiting
hormone STHIH
 F-cells: These cells secrete Pancreatic polypeptide /PP hormone which regulates the
secretion of other three hormones
DISORDER OF DIGESTIVE SYSTEM
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The inflammation of the intestinal tract is the most common ailment due to bacteri or viral
infections. The infections are also caused by the parasites of the intestine like tape worm, round
worm, thread worm, hook worm pin worm, etc
1. Vomiting l Emesis: It is the ejection of stomach contents through the mouth. This reflex action
controlled by the vomit centie in the medulla. A feeling of nausea uneasiness before vomiting/
ch fraeTHT precedes vomiting
2. Diarrhoea: The abnormal frequency of bowel movement and increased liquidity of the faecal
discharge is known as diarrhoea It reduces the absorption of food
3. Constipation:In constipation, the facces are retained within the rectum as the bowel movements
occur irregularly
4. Indigestion: ln this condition, the food is not properly digested leading to a feeling of fullness.
The causes of indigation are inadequate enzyme anxiety, food poisoning, over eating, and spicy
food
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