Download - Heterotrophic nutrition
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A) HETEROTROPHSB) DENTITIONC) THE ALIMENTARY CANAL IN HUMANSD) THE CONTROL OF DIGESTIVE SECRETIONSE) CELLULOSE DIGESTION IN RUMINANTS
Topic Overview
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Heterotrophs are:organisms that feed on complex, ready-
made organic food all animals fungi majority of bacteria
on the synthetic activities of autotrophs
survival of heterotrophs depends:
either directly or indirectly
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Forms of heterotrophic nutrition :
1. holozoic
2. saprophytic
3. symbiotic mutualism commensalism parasitism
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1. Holozoic nutritionfood taken in, is digested into smaller
soluble molecules which can be absorbed and assimilated
BloodFood in intestine
enzyme
digestion
absorption
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Processes involved in holozoic nutrition:-
1. Ingestion
2. Digestion
3. Absorption into the bloodstream
5. Egestion
4. Assimilation
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2. Saprophytic nutrition
organisms feeding on dead or decaying organic matter: saprophytes or saprotrophs secrete enzymes on food digested food is digested externally
Very soft!!
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3. Nutrients are
absorbed from all
over the hyphae.
1. Extracellular
enzymes from
growing tips.
2. Digestion takes place outside the body.
The saprophytic nutrition of Mucor and Rhizopus
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Many of the simple substances formed are
not used by the saprotrophs themselves:
Are absorbed by plants
but
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protease
the thin, much-branched mycelium ensures a large surface area for absorption
starch is broken down to glucose by:carbohydrase
protein is broken down into amino acids by:
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Surplus food is stored in the hyphal cytoplasm
Glucose is converted to:
glycogen & fat
Amino acids are stored as:
protein granules
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3. Symbiosis:
is the living together in close association of two (or more) organisms of different species
includes:
1. Mutualism
2. Commensalism
3. Parasitism
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Mutualism
is a relationship between two organisms which is beneficial to both
the association may be between two organisms of the:
same or different kingdoms
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Example of mutualism the sea anemone Calliactis parasitica
attaches itself to a shell used by the hermit crab Eupagurus
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ANEMONE: obtains food from scraps left by
the crab is transported around by the
crab cannot survive if removed from
the shell of the crab
HERMIT CRAB: is camouflaged by the anemone may be protected by nematocysts seeks another anemone (if it is
removed) and actually places it on its shell
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Commensalism: is a close association between two living
organisms of different species which is: beneficial to one (the commensal) and does not affect the other (the host)
Hermit crab:is unaffected
Colonial Hydrozoan Hydractinia echinata :
attaches itself to whelk shells inhabited by hermit crabs & gets scraps of food left by crab
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Parasitism is a close association between two living organisms
of different species which is beneficial to one (the
parasite) and harmful to the other (the host)
the parasite obtains:
1. food &
2. generally shelter
a successful parasite is able to live with the host
without causing it any great harm
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Parasites may be:
live on the outer
surface of a host e.g.
leech ectoparasites cling to
host by:
ECTOPARASITES
Suckers e.g.
leech
Claws e.g.
lice
ENDOPARASITES
live within a host
FasciolaTapeworm
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Ectoparasites in plants have haustoria for attachment:
Haustorium in the parasitic plant Cuscuta [dodder]
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obligate parasites: live parasitically at all times
Parasites may be:
facultative parasites: e.g. fungi : feed parasitically at first but having eventually killed their host:continue to feed saprotrophically on the dead body
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A) HETEROTROPHS
B) DENTITIONC) THE ALIMENTARY CANAL IN HUMANSD) THE CONTROL OF DIGESTIVE SECRETIONSE) CELLULOSE DIGESTION IN RUMINANTS
Topic Overview
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Incisors:situated at the front of the buccal cavityhave flat, sharp edgesused for cutting and biting food
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Canines:are pointed teeth
poorly developed in humans
highly developed in carnivores
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Canines are designed for: piercing killing prey hold prey tearing flesh
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Premolars:posses: two cusps (projections on
the surface of a tooth)
used for: crushing & grinding food,
in humans they may also be used to tear food
root
cusp
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Molars:each tooth has 4 or 5 cusps
used to crush & grind food
premolarsare not present in the milk teeth
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Humans have two sets of teeth:
Deciduous
or milk teeth
[20 teeth]
Permanent
teeth [32 teeth]
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2 1 2 322 1 2 3
i c pm m
Total: 32
Upper jaw: 16Lower jaw: 16
Dental Formula shows the arrangement of teeth:
Dental Formula for human permanent dentition
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Dental Formula for a cat (permanent teeth):
Dental formula Upper jaw: 16Lower jaw: 14Canine [C]
Incisor [I]
Molar [M]Premolars [P]
3 1 3 12 303 1 2 1
i c pm m
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Dentition in a carnivore (cat)teeth are adapted to:
catch & break down animal food
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Dentition in a carnivore (cat)
temporalis muscle[provides a powerful bite]
masseter muscle [needed to masticate]
1st molar (carnassial)
molar
canine
incisor
premolars
incisor
canine
3rd premolar (carnassial)
premolars
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Incisors:are closely fitting, small and chisel-
shaped
Canines:enlarged, curved and fang-like
used to tear away flesh near the bone surface
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Cheek teeth:are the molars and premolarstwo on each side of the jaw are called:
carnassial teeth
Carnassials are: enlarged with prominent ridges running
parallel with the line of the jaw shear (act like scissors) flesh from prey
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Carnassial teeth:
p4 and m1
the other cheek teeth: are flattened possess sharp edges used for cutting
flesh and cracking bones
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Jaw point:operates as a closely fitting
hinge
permits only up- and-down movement
cheek teeth are placed nearest the point as they require the greater force for their operation
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Temporal / Temporalis muscle:
on contracting closes the lower jaw [mandible]
provides a powerful bite
Function:
1. Food is crushed between molars
2. In carnivores, canines are clenched into the prey
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Temporal muscle: is attached to a prominent
bone extension from the
lower jaw which projects upwards towards the ears
this arrangement provides efficient leverage on the food:
1. as it is sheared by the teeth
2. when the mouth is snapped shut while killing the prey
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Masseter muscle: needed to masticate (chew)
pulls the base of the lower jaw upwards and reduces the strain on the jaw joint
masseter
masseter
temporalis
temporalis
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Temporalis & masseter muscles in carnivores & herbivores compared
temporalis
masseter
Carnivores HerbivoresTemporalis Large SmallMasseter Small Very largeJaw movements Up & down jaw Sideways &
back and forth
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Jaw joint in herbivores: very loose and allows:
forward, backward and sideways movements possible because: masseter is large in
herbivores to masticate the tough grass
during chewing the lower joint moves from
side to side
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Dentition in a herbivore (sheep)
Sheep crop grass
[bite off the ends]
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Fig. 4 Jaws, dentition and musculature of the sheep.
Masseter muscle
[Large – needed for grinding]
Temporalis muscle
[Small – no powerful biting is needed]
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In a sheep:upper incisors & canines are absenta horny pad takes their place
chisel-shaped lower incisors & canines bite against the pad when the sheep is cropping grass
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Herbivores can be divided into:
horse
Ruminants [horny pad of
gum]
Non-ruminants – hindgut fermenters[have teeth at the
front]
sheep
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Dental Formula for a sheep
0 0 3 323 1 3 3
i c pm m
Total number of teeth on:
Lower jaw:Incisors: 6Canines: 2Premolars: 6Molars: 6
Upper jaw:Incisors: 0Canines: 0Premolars: 6Molars: 6
32
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Function of:
Cheek teeth:grinding
Front teeth:cropping
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Diastema:is a gap between
the: front & cheek
teeth
grass being chewed is kept apart from that freshly gathered
provides space for the tongue to manipulate cropped grass
Diastema:
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Open roots in herbivores:
teeth grow throughout life
Closed roots & Open roots
Closed roots in carnivores:
teeth stop growing
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The area of the cheek teeth is increased by the surfaces of the:
upper teeth being folded into a W-shape
those of the lower teeth being folded into an M-shape
W-shaped ridges fit closely into the grooves of the M-shaped lower teeth during girding
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Ridges:
are composed of hard enamel
Troughs:
composed of dentine
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Question: MAY, 2012This question is about herbivores.The diagram below represents the lower jaw of a herbivorous mammal.
Feature Function1. Diastema A space that holds grass while
animal crops2. Flat premolars and molars
Offer a large surface area for grinding grass
a) With reference to the diagram above, list TWO features which indicate that the jaw is that of a herbivore. Include the function of such features. (4)
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b) Name ONE structural difference that would be present in the jaw of a typical carnivore but is not observed in that of a herbivore. Give ONE reason for this difference. (2)
Long and pointed canines.
Canines are needed by carnivores to kill the prey, hold it in position and tear flesh. Herbivores feed on grass and such canines are useless.
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A) HETEROTROPHSB) DENTITIONC) THE ALIMENTARY CANAL IN HUMANSD) THE CONTROL OF DIGESTIVE SECRETIONS
E) CELLULOSE DIGESTION IN RUMINANTS
Topic Overview
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Herbivores have a problem:
They eat grass:
principal component is cellulose
BUT cannot produce cellulases
Mutualistic bacteria in gut produce cellulase.
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ruminants
Herbivores may be:non-ruminants/
hind-gut fermenters e.g. cattle, sheep,
goatse.g. rabbit, horse
Monogastric herbivores: one-stomach chamberFour stomach chambers
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A ruminant is:any hooved animal that digests its
food in two steps:
1. by eating the raw material
2. regurgitating a semi-digested form known as cud, then eating the cud
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Ruminants have a specialised digestive system capable of digesting cellulose:
stomach with 4 distinct compartments
3. Omasum
4. Abomasum1. Rumen 2. Reticulum
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Functions of stomach chambers:
2. Reticulum
3. Omasum
4. Abomasum
breakdown of cellulose
true stomach: secretes HCl & proteases
1. Rumen
absorbs water & salts from food
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Rumen & Reticulum:
are packed with anaerobic microbes
A cow's rumen has a capacity of up to 95 litres.
Mutualistic microbes
act as fermentation vats for cellulose
digestion
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Fermentation is the enzymatic transformation of organic substances
[acids]
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End-products of fermentation in rumen are:
ethanoic acidpropanoic acidbutyric acidCO2
methane CH4
Are absorbed by ruminant & used as a
source of energy
Waste gases
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Why are microbes important to ruminants?
1. produce cellulase which digest cellulose
2. microbes are themselves digested – supply proteins to host
3. release organic acids by fermentation – a source of energy to host
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RUMEN has a very thick, muscular wall food is mixed with saliva
SALIVA: acts as a buffer to acids produced by
microbes
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The rumen provides an excellent environment for microbial growth:
1. Is anaerobic
2. Provides a stable temperature and osmotic conditions
3. Food & water are present
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Reticulum full
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Reticulum cleaned
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ABOMASUM very similar to the stomach of non-ruminants where the majority of chemical breakdown of
food material occurs mixes in digestive enzymes (pepsin)
killed by the acid & digested by proteases
passed into intestines for further digestion & absorption
What happens to the microbes in the abomasum?
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RUMINANTS: cud-chewers
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Ruminant animals:grasp mouthfuls of food and swallow it before it is chewed. wrap their tongue around a mouthful of
grass, clamp down their teeth, and pull to break the grass at its weakest point, and swallow.
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Ruminants “chew their cud” (regurgitate) their food material and then grind it with their molars at a time when the animal is resting.
– This is done until the food particles are small enough to pass through the reticulum into the rumen.
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Rumination – chewing the cudDepending on the amount of fibre in their food, cattle
may spend between 3 – 6 hours per day chewing their cud
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Where are microbes located in mammalian herbivores other than
ruminants?
caecum
Hindgut fermenter
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Compare gut of:
Ruminant HerbivoreFour-chambered stomach with
large rumen, long small & large
intestine
Hindgut fermenter
Simple stomach,
Large caecum
caecum
caecum
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CarnivoreShort intestine & colon,
small caecum
Compare gut of:
Ruminant HerbivoreFour-chambered stomach
with large rumen,
long small & large intestine
caecum caecum
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REASON:
To get nutrients that otherwise would be
lost
Coprophagy:
a behaviour of certain mammalian herbivores
where they ingest faeces
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Rabbits produce two types of faeces:
soft, edible, mucous covered packets of protein and vitamins
true faeces are drier and contain undigested fibre
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Question: MAY, 2012Apart from their dentition, some herbivores have
additional adaptations that make them particularly
suited for a herbivorous mode of life. Give ONE
example of a hind-gut fermenter and briefly explain how
hind-gut fermenters have unique mechanisms to
maximise nutrient absorption from their food. (4)
Rabbit
A large caecum for absorption.
Animal practices coprophagy – pellets egested from the
caecum are eaten. As these pass through the digestive
system a second time, more nutrient absorption occurs.
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MAY 2009Use your knowledge of biology to describe the selective advantage of each of the following adaptations:
Gut fermentation in ruminants. (5) Ruminants fed on grass containing a high content of cellulose but
cannot produce an enzyme to digest it. Rumen contains mutualistic bacteria that can digest cellulose. Microbes break the cellulose into sugars which they use for
anaerobic fermentation. Producing fatty acids and methane. Methane is eliminated by belching and the fatty acids are absorbed
by the rumen – serve as a source of energy for the ruminant. Ruminants regurgitate the partially digested food and re-chew it
(chewing the cud) to increase the surface area where enzymes can act.
Bacteria themselves are digested: serve as a source of protein
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A) HETEROTROPHSB) DENTITION
C) THE ALIMENTARY CANAL IN HUMANSD) THE CONTROL OF DIGESTIVE SECRETIONSE) CELLULOSE DIGESTION IN RUMINANTS
Topic Overview
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The basic structure of the digestive tract consists of 4 layers:-
[liver, pancreas]
1. Mucosa[innermost layer of gut]
2. Submucosa[contains connective tissue]
3. Muscularis externa[muscle layer]
4. Serosa[outermost layer; composed of loose connective tissue]
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Variations in the gut wall
Oesophagus Stomach Large intestineSmall
intestine
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The mucosa is composed of:
1. glandular epithelium:
Secretes mucus + digestive enzymes
2. Lamina propria: contains connective tissue blood vessels lymph vessels
3. Muscularis mucosa: smooth muscle to move the mucosa
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connective tissue blood vessels lymph vessels
sub-mucosa
contains blood vessels & nerves
epithelial cells rest on a basement membrane
lamina propria lies beneath the epithelial cells & contains:
epithelium
muscle or bone LS through oesophagus
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Three functions of mucus:
i) lubricates food
ii) facilitates passage along digestive tract
iii) prevents digestion of the gut wall by its own enzymes
Goblet cell in human small
intestine
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Submucosa: a layer of connective tissue containing:
nerves blood vessels lymph vessels collagen elastic fibres
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The submucosa may contain some mucus-secreting glands
that deposit their contents via ducts e.g. Brunner’s glands in the duodenum
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Two plexuses [nerve nets] in gut
Mucosa Epithelium
Lamina propria
Muscularis mucosa
Submucosa Meissner’s plexus
Circular muscle
Longitudinal muscle
Auerbach’s plexus
Serosa
Muscularis
externa
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Both plexuses consist of nerves from the autonomic NS
Auerbach’s
plexus
Meissner’s
plexus
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Location & Role of plexuses
Epithelium
Lamina propria
Muscularis mucosa
Submucosa Meissner’s plexus
Auerbach’s plexus
Serosa
Between the circular
muscle & submucosa Controls secretion of
glands in the
mucosal epithelium
Mucosa
Muscularis
externaLongitudinal muscle
Circular muscle
Submucosa
circular muscle
longitudinal muscle Between: circular &
longitudinal muscle
layers Controls peristalsis
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Auerbach’s plexus: impulses in:
Sympathetic nerves cause:
gut muscles to relax
sphincters to close
Parasympathetic nerves stimulate :gut wall to
contract sphincters to
open
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Muscularis externa: composed of an:
inner circular muscle outer longitudinal muscle
(smooth type)
action of these muscles propel food along the gut
at a number of points along the gut the circular muscle thickens into structures called sphincters
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Sphincters contract or relax:
to move the food from one part of the alimentary canal to another
1 Pyloric sphincter contracted
Pyloric sphincter relaxed
2
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Sphincters are found at the junctions of:-
oesophagus & stomach (cardiac sphincter)
stomach & duodenum (pyloric sphincter)
ileum & caecum
the anus
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Serosa: outermost coat of gut
composed of loose connective tissue
serosa
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Peritoneum: covers the whole of the
outer surface of the gut forms the mesenteries
mesenteryperitoneum
mesentery
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Peritoneum cells are moist & help to reduce friction :
when the gut wall slides over other portions of itself or other organs
Hernia: peritoneum is torn
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Mesenteries:
stomach & intestines from the dorsal body wall
consist of double layers of peritoneum containing:
nerves blood vessels lymph vessels that pass
to and from the gutmesentery
suspend &
support
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Peyer’s patches in ileum
Peyer’s patch [function?]
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Peyer’s patches: have a role in the immune response
aggregations of lymphoid tissue that are usually found in the ileum in humans
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SEP 2006 Paper 3Draw an annotated map of the structure shown in Figure 1. (10 marks)
Scale: x 1
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Buccal cavity
region enclosing the jaws and tongue
lined with stratified squamous epithelium
Basal layer undergoes mitosis
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The tongue: mixes & moistens food possesses taste buds sensitive to: sweet salty sour bitter
Taste bud
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Saliva is produced by: three pairs of salivary glands
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Saliva contains:1. salivary amylase :
begins digestion of starch to dextrins (shorter polysaccharides) and then to maltose
Salivary amylase
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Saliva contains:
2. lysozyme: kills bacteria by catalysing the
breakdown of their cell walls
3. various mineral salts, including chloride ions: Cl- speed up activity of enzymes
4. mucus: moistens and lubricates the food
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The semi-solid, partially digested food particles are:
stuck by mucin [a glycoprotein that is the chief component of mucus]
moulded into a bolus
food is swallowed by a reflex action
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Oesophagus
a narrow muscular tube lined by stratified squamous epithelium containing mucus glands
about 25 cm long in humans
quickly conveys food and fluids by peristalsis from:pharynx to the stomach
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Pharynx is where the: mouth cavity &
the nasal passages join
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Muscle contractions in the gut occur for two reasons:
1. move food forward [peristaltic contractions]
2. stir & mix food
[segmental movements]
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Peristaltic contractions:are progressive waves of contraction
that move progressively down the gut
1
2
BolusDigestive tract
Wave ofcontraction
Wave ofrelaxation
Bolusmoves
2
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Peristaltic contractions:
Step 1Contraction of circular muscles behind mass
Step 2Contraction of longitudinal
muscles ahead of food mass
Step 3Contraction in circular muscle layer forces food mass forward
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What initiates peristaltic contractions?
Stretching of the smooth muscle of the gut
swallowing a bolus of food stretches the upper end of the oesophagus, and this stretching initiates a wave of contraction that slowly pushes the contents of the gut toward the anus
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STOMACH
in humans: is situated below the diaphragm and on the left side of the abdominal cavity
is a muscular bag which can stretch to hold nearly 5 dm3 of food
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2 smooth muscle layers in gut BUT 3 in stomach:-
Circular muscle (middle)
Longitudinal muscle (outer)
Oblique muscle (inner)
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The thick mucosa has:
1. numerous gastric pits
2. mucus-secreting
epithelial cells
mucosa of the cardiac region of the stomach contains only mucus glands
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Six functions of the stomach1. Stores food temporarily after meals, releasing
food slowly into the rest of the gut
food can be retained in the stomach up to 4-5 hours
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Six functions of the stomach
2. The stomach continues mechanical digestion by the churning action.
Food digested by churning
Food digested by enzymes
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3. The mucus made by the stomach:provides a barrier between the
stomach mucosa & gastric juice
An ulcer results if the stomach wall is exposed to:
HCl pepsin
prevents the stomach self-digesting
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lesions started by the bacterial infection are made worse by HCl and pepsin
Helicobacter pylori is an infectious bacterium considered the basis for most
ulcers
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4. The main part of the stomach, is dotted with numerous gastric pits.
There are two specialised types of cell:
Six functions of the stomach
Gastric pits lead into long tubular gastric glands.
Gastric glands are lined with cells which secrete the gastric juice (collective name for stomach
secretions)
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zymogen or chief cells - secrete pepsinogen &
prorennin
oxyntic or parietal cells - secrete HCl
pH = 1 - 2.5
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7 Functions of hydrochloric acid:
1. creates optimum pH for enzyme activity
2. kills many bacteria, thus acts as a defence mechanism
3. loosens fibrous and cellular components of tissue
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Low pH
Active site
Masking sequence
A masking sequence is cleaved from the
pepsinogen molecule……
….…. transforming pepsinogen into the
active enzyme pepsin.
4. promotes conversion of pepsinogen to pepsin
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5. converts prorennin to rennin
6. renders Ca and Fe salts suitable for absorption in the intestine
7. begins hydrolysis of sucrose to glucose and fructose
7 Functions of hydrochloric acid:
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5. Produces pepsin and rennin:-Pepsin:
Six functions of the stomach
2. converts more molecules of pepsinogen to pepsin: process is autocatalysis
1. hydrolyses protein into smaller polypeptides
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Rennin:coagulates caseinogen (soluble protein
in milk) into the insoluble calcium salt of casein in the presence of calcium ions
Casein is then digested by pepsin
Changes into insoluble calcium salt: casein
rennin
Soluble protein in milk caseinogen
calcium
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6. Stomach contains endocrine cells which secrete the hormone gastrin.
Gastrin stimulates
gastric glands to
secrete gastric juice
rich in HCl.
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Chyme is a semi-liquid mass consisting of food and gastric juice :
gradually the stomach squirts the chyme into the duodenum through the relaxed, ring-shaped pyloric sphincter
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A few substances can be absorbed from the chyme across the stomach wall:
E.g. alcohol aspirin caffeine
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The intestines are named for their diameter, not length :
Small intestine:Length: up to 7 m Diameter: 2.5 cm
Large intestine:Length: 1.5 m Diameter: 7.6 cm
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SMALL INTESTINE4.5 m long in an adult - consists of the:
1. Duodenum (25 cm long) the site of most digestion pancreatic & bile ducts open into it
2. jejunum
3. ileum
(2-4 m long)
Pyloric sphincter
90% of the nutrient absorption
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The submucosa & mucosa together are folded
Numerous villi:
finger-like projections.
Microvilli
(brush border)
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Structural features which
increase the surface area of
the small intestine
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How is the structure of the small intestine
related to its function?
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TS ileum showing
villus
villi on mucosa
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Walls of villi are richly supplied with:
blood capillaries lymph vessels smooth muscle
Villi contract and relax to come in
close contact with the food
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Goblet cells
are special epithelial cells : secrete mucus throughout the small intestine
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Location: base of the villi
where the epithelium
folds inwards
Function: make new epithelial
cells
secrete intestinal juice
(succus entericus)
Crypts of Lieberkühn are narrow tubes:
Paneth cells at the base of the crypts secrete lysozyme (antibacterial enzyme)
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Submucosal Brunner’s glands secrete:
1. mucus 2. alkaline fluid in first part of the duodenum
(pH = 7 - 8)
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Digestion by enzymes in the small intestine
in the small intestine:
1. the digestion of:
2. the absorption of nutrients begins
carbohydrates & proteins continues fats begins
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Intestinal juice (succus entericus):
contains a number of enzymes secreted by the
epithelial lining of the small intestine
1) amylase - converts the amylose of starch to
maltose
2) lactase - converts lactose to glucose and galactose
3) sucrase converts sucrose to glucose and fructose
4) aminopeptidases and dipeptidases that convert
peptides and dipeptides to amino acids
5) enterokinase - converts trypsinogen to trypsin
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Location of enzymes in small intestine
All other digestive enzymes are:
1. bound to the cell surface membranes of the microvilli
2. or located within the epithelial cells
Pancreatic enzymes: NOT membrane-bound
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Digestion of proteinswhole
proteins
endopeptidases exopeptidases
dipeptidases
dipeptidesshorter
polypeptides
amino acids
Carboxypeptidase cuts at C terminus
Aminopeptidase: cuts at N terminus
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Digestion of proteins involves endopeptidases & exopeptidases.
EN D O PEPTID A SES:
catalyze the hydrolysis of
peptide bonds in the
interior of a polypeptide
chain
ENDOPEPTIDASES:
catalyze the hydrolysis of
peptide bonds in the
interior of a polypeptide
chainEXOPEPTIDASES:
catalyze the hydrolysis of single amino acids
from the end of a polypeptide chain
EXOPEPTIDASES:catalyze the hydrolysis of single amino acids
from the end of a polypeptide chain
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Explain how the action of endopeptidases increases the rate of
action of exopeptidases. (1)
Creates more ends / increases surface area where exopeptidases work.
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In addition to its own secretions, the small intestine receives:
2. alkaline pancreatic juice
1. bile
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Pancreas & Liver:
provide important secretions
are two accessory organs that are not part of the digestive system
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The pancreas :
Exocrine tissue composed of acini (groups of cells
which produce enzymes)
is a large gland just beneath the stomach
Topancreaticduct
Hormones tobloodstream
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The pancreas releases enzymes as zymogens:
[inactive enzyme precursors]
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The pancreas :
pours enzymes via
the pancreatic duct
Pancreatic amylase
TrypsinogenLipase Pancreatic
enzymes includeChymotrypsinogen
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Pancreatic enzymes include-
1. amylase - converts amylose to maltose
2. lipase - converts fats to fatty acids and glycerol
3. trypsinogen is activated by enterokinase is converted to trypsin which changes:
i) proteins to smaller polypeptides
ii) more trypsinogen into trypsin (an example of autocatalysis)
4. chymotrypsinogen - when converted to chymotrypsin by trypsin, digests proteins to amino acids
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Enterokinase is produced by: wall of duodenum
Enterokinase
[membrane-bound enzyme]
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The liver synthesises bile
Bile is a dark green to
yellowish brown fluid
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Flow of bile:
To gallbladder through a side branch of the hepatic duct
From liver to hepatic duct
Bile is stored in the gallbladder until needed to
assist in fat digestion
Bile from gallbladder flows down the common bile duct to
the duodenum
What causes the gallbladder to contract
to release bile?
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The hormone cholecystokinin (CCK) causes the gallbladder to contract
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Gallstones may block bile duct
Contraction of the gallbladder will cause pain
Gallstones are formed from a hardened precipitate
of cholesterol
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Bile contains:
water bile salts bile pigments
[bilirubin, biliverdin]
pH paper turns green in bile
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Bile pigments:
do not participate in digestion
are waste products from the destruction of old red blood cells
are finally eliminated with the faeces
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i.e. work like detergents, dispersing large fat droplets into smaller ones
Bile salts emulsify fats:
Bile salts are made from cholesterol. cholesterol is:
1. synthesised in the liver
2. taken in with the diet
Micelles are small fat particles that result from the action of
bile salts.
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The importance of emulsification:
Large fat globules form smaller droplets, so increasing their total surface area, thus lipase
acts quicker
LIPASE
Fatty acids & monoglycerides enter epithelial cells by simple diffusion.
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What happens to fatty acids & monoglycerides ?
In the epithelial cells they are: resynthesised into
triglycerides combined with cholesterol
& phospholipids coated with protein to form
water-soluble chylomicrons
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Chylomicron composition:
90% triglyceride5% cholesterol
4% phospholipid
1% protein
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Fatty acid absorptionFatty acids & monoglycerides associated with micelles in lumen of intestine.
Fatty acids & monoglycerides resulting from fat digestion leave micelles & enter cell by diffusion.
Fatty acids are used to synthesise triglycerides in the smooth endoplasmic reticulum.
Fatty globules are combined with proteins to form chylomicrons (within Golgi apparatus).
Lymph in the lacteal transports chylomicrons away from intestine.
Vesicles containing chylomicrons migrate to the basal membrane where by exocytosis they move out of the epithelial cell & enter a lacteal.
1
2
3
4
5
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Note milky colour of plasma:
due to a genetic disorder leading
to excessive triglycerides in
blood
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What happens to the bile salts in the small intestine?
Bile salts are actively
reabsorbed and returned to
the liver via the blood
stream
Bile salts returned to liver
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Absorption of food in the small intestine
monosaccharides dipeptides amino acids
Microvilli of epithelial cells on villi absorb:
absorbed by:
active transport & diffusion
Where does the absorbed food travel to
once absorbed into the blood stream?
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To liver via the hepatic portal vein
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Monosaccharide (glucose) transportGlucose is absorbed by symport with Na+ into intestinal epithelial cells.
Symport is driven by a sodium gradientestablished by a Na+–K+ pump.
Glucose moves out of the intestinal epithelial cells by facilitated diffusion.
Glucose enters the capillaries of theintestinal villi and is carried through thehepatic portal vein to the liver.
Villus
Glucose1
1
2
3
4
4
ADPATPNa+ Na+
Na+K+
Intestinalepithelial cell
To liver
CapillaryLacteal
1
2
3
1
2
3
4
Villus
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Amino acid transport
3
Amino acids are absorbed by symport into intestinal epithelial cells.
Symport is driven by a sodium gradient establishedby a Na+–K+ pump.
Amino acids move out of intestinal epithelialcells.
Amino acids enter the capillaries of the intestinal villi and are carried through the hepatic portal vein to the liver.
Capillary Lacteal
Amino acid
Na+
1
2
Villus
Intestinalepithelial cell
K+
To liver
Na+Na+ ADPATP
4
2
1
1 34
2
Villus
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THE LARGE INTESTINE
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THE LARGE INTESTINE
1.Caecum
Anus
2. Appendix
3. Colon
4. Rectum
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The large intestine absorbs:
2. any remaining inorganic nutrients
8900 ml1. bulk
of water
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Epithelial cells secrete mucus to lubricate the solidifying food - faeces
Faeces consist of:- dead bacteria cellulose & other plant
fibres dead mucosal cells mucus cholesterol bile pigment derivatives water
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Two anal sphincters: An internal one of smooth
muscle, controlled by the
autonomic nervous system
An outer one of striated
muscle, controlled by the
voluntary nervous system
1
2
12
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Many mutualistic bacteria in the large intestine synthesise:-
1. some vitamins especially vitamin K
2. amino acids which are absorbed into the bloodstream
mutualism
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Essay Title: [SEP, 2011]
Describe the structure of the alimentary canal of the human body in relation to its function.
SEP, 2013
This question is about digestion.
Relate the following to their biological function:
non-pathogenic bacteria in the large intestine of humans; (2) Produce vitamins B and K. Produce some amino acids.
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A) HETEROTROPHSB) DENTITIONC) THE ALIMENTARY CANAL IN HUMANS
D) THE CONTROL OF DIGESTIVE SECRETIONS
E) CELLULOSE DIGESTION IN RUMINANTS
Topic Overview
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Production of digestive enzymes & HCl occurs only when food is
present - ADVANTAGE:
To save energy & materials in the body
The overall control of digestive activity is coordinated and regulated by the:
1. Nervous system
2. Endocrine system
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The control of the secretion of:
1. Saliva
2. Gastric juice
3. Pancreatic juice & bile
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The control of the secretion of:
1.Saliva 2. Gastric juice
3. Pancreatic juice & bile
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Salivary secretion is controlled by two reflex actions:-
1. an unconditioned cranial reflex occurs when food is present in the buccal cavity
Food contacts taste buds: impulses fired
Impulses travel to brain
Salivary glands secrete saliva
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2. conditioned reflexes of seeing, smelling or thinking of food
Sight
Smell Thinking
of food
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The control of the secretion of:
1. Saliva
2.Gastric juice3. Pancreatic juice & bile
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Three phases occur in the secretion of gastric juice:-
1. nervous / cephalic phase lasts 1h occurs before food reaches stomach
2. gastric phase takes place in the stomach involves both nervous & hormonal control
3. intestinal phase takes place in the small intestine secretion of gastric juice is inhibited and the release of
chyme from the stomach is slowed
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1. nervous phase
The presence of food in mouth + its
swallowing trigger reflex nerve impulses
which pass along the vagus nerve from the
brain to the stomach.
SightSmellTaste
Thought of foodGastrin
can trigger the same reflex
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2. gastric phase
Stretch receptors send nerve impulses to Meissner’s plexus
in the submucosa, which in turn sends impulses to the
gastric glands, stimulating the flow of gastric juice.
Food in stomach stimulates stretch
receptors in the wall of the stomach.
Stretching of the stomach + presence of food also stimulate special endocrine
cells in the mucosa to secrete the hormone gastrin.
Gastrin stimulates
gastric glands to
secrete gastric juice
rich in HCl for 4 h.
1
2
3
4
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3. intestinal phase:
Acidified chyme in contact with the
walls of duodenum, triggers both
nervous & hormonal responses
duodenal mucosa secretes secretin & cholecystokinin (CCK)
Receptors in the small intestine are stimulated by the presence
of food, but the reflexes, which pass through the brain:
1. inhibit secretion of gastric juice
2. slow the release of chyme from the stomach
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The control of the secretion of:
1. Saliva
2. Gastric juice
3.Pancreatic juice & bile
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The secretion of bile & pancreatic juice is stimulated by:
produced in: duodenum
stimulus: acidified chyme from stomach
during the nervous & gastric phases of gastric
digestion, the vagus nerve also stimulates the : liver to secrete bile pancreas to secrete enzymes
1. HORMONES: secretin & CCK:
2. NERVOUS REFLEXES
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Effects of CCK & secretin Hormone Target organ ResponseCCK pancreas Increased secretion of
pancreatic juice rich in enzymes
gall bladder Contraction of gall bladder to release bile
Secretin pancreas Increased flow of HCO3-
in pancreatic juiceliver Synthesis of bile rich in HCO3
-
stomach Inhibits secretion of gastric juice
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Question: MAY, 2011
Hormone that stimulates the production of gastric acid by the stomach.
gastrin
Hormone that stimulates delivery into the small intestine of digestive enzymes from the pancreas and bile from the gallbladder.
cholecystokinin
Hormone that controls secretions into the duodenum.
secretin
Site of initial carbohydrate digestion. mouth
Complete the table by entering the most appropriate terms in the spaces below: (4)
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REVISE:
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Question: MAY, 2004
The broad dietary preferences of vertebrates may be inferred by observing their dentition.a. Why should different dietary preferences
necessitate specialist dentition? (2)Teeth must be adapted to the type of food eaten. E.g. carnivores need sharp teeth for cutting while herbivores need flat surfaces for grinding.
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Question: MAY, 2004
a. List two differences between the dentition of a generalised herbivore and that of a generalised carnivore. (2)
Herbivore : Small or no canines; diastema present; blunt incisors; flat premolars and molars.
Carnivore : Long, pointed canines; diastema absent; sharp incisors; premolars and molars with ridges.
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Question: MAY, 2004
c. Name ONE adaptation, characteristic of some herbivores, that is not concerned with specialist dentition. (1)
Four chambered stomach; well-developed masseter muscle to allow grinding actions.
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Question: MAY, 2011
Name, and briefly describe, THREE adaptations of ruminant mammals to their mode of nutrition. (6)
1) Rumen is full of bacteria that produce cellulase to digest cellulose.
2) Food is regurgitated and animal chews the cud to increase surface area for enzyme action.
3) The upper jaw is a hard tough pad and the grass is cut between the teeth and the pad.
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Essay titles
1. Compare and contrast the mode of nutrition of humans with that of ruminant mammals. [SEP, 2005]
2. Give an overview of the adaptations of ruminant and carnivorous mammals to their respective modes of nutrition. [SEP, 2008]
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THE END