Heterotrophic Nutrition

A) HETEROTROPHSB) DENTITIONC) THE ALIMENTARY CANAL IN HUMANSD) THE CONTROL OF DIGESTIVE SECRETIONSE) CELLULOSE DIGESTION IN RUMINANTS

Topic Overview

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

Forms of heterotrophic nutrition :

1. holozoic

2. saprophytic

3. symbiotic mutualism commensalism parasitism

1. Holozoic nutritionfood taken in, is digested into smaller

soluble molecules which can be absorbed and assimilated

BloodFood in intestine

enzyme

digestion

absorption

Processes involved in holozoic nutrition:-

1. Ingestion

2. Digestion

3. Absorption into the bloodstream

5. Egestion

4. Assimilation

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!!

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

Many of the simple substances formed are

not used by the saprotrophs themselves:

Are absorbed by plants

but

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:

Surplus food is stored in the hyphal cytoplasm

Glucose is converted to:

glycogen & fat

Amino acids are stored as:

protein granules

3. Symbiosis:

is the living together in close association of two (or more) organisms of different species

includes:

1. Mutualism

2. Commensalism

3. Parasitism

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

Example of mutualism the sea anemone Calliactis parasitica

attaches itself to a shell used by the hermit crab Eupagurus

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

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

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

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

Ectoparasites in plants have haustoria for attachment:

Haustorium in the parasitic plant Cuscuta [dodder]

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

A) HETEROTROPHS

B) DENTITIONC) THE ALIMENTARY CANAL IN HUMANSD) THE CONTROL OF DIGESTIVE SECRETIONSE) CELLULOSE DIGESTION IN RUMINANTS

Topic Overview

Incisors:situated at the front of the buccal cavityhave flat, sharp edgesused for cutting and biting food

Canines:are pointed teeth

poorly developed in humans

highly developed in carnivores

Canines are designed for: piercing killing prey hold prey tearing flesh

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

Molars:each tooth has 4 or 5 cusps

used to crush & grind food

premolarsare not present in the milk teeth

Humans have two sets of teeth:

Deciduous

or milk teeth

[20 teeth]

Permanent

teeth [32 teeth]

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

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

Dentition in a carnivore (cat)teeth are adapted to:

catch & break down animal food

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

Incisors:are closely fitting, small and chisel-

shaped

Canines:enlarged, curved and fang-like

used to tear away flesh near the bone surface

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

Carnassial teeth:

p4 and m1

the other cheek teeth: are flattened possess sharp edges used for cutting

flesh and cracking bones

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

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

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

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

Temporalis & masseter muscles in carnivores & herbivores compared

temporalis

masseter

Carnivores HerbivoresTemporalis Large SmallMasseter Small Very largeJaw movements Up & down jaw Sideways &

back and forth

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

Dentition in a herbivore (sheep)

Sheep crop grass

[bite off the ends]

Fig. 4 Jaws, dentition and musculature of the sheep.

Masseter muscle

[Large – needed for grinding]

Temporalis muscle

[Small – no powerful biting is needed]

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

Herbivores can be divided into:

horse

Ruminants [horny pad of

gum]

Non-ruminants – hindgut fermenters[have teeth at the

front]

sheep

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

Function of:

Cheek teeth:grinding

Front teeth:cropping

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:

Cheek teethpossess broad grinding surfaces

Open roots in herbivores:

teeth grow throughout life

Closed roots & Open roots

Closed roots in carnivores:

teeth stop growing

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

Ridges:

are composed of hard enamel

Troughs:

composed of dentine

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)

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.

A) HETEROTROPHSB) DENTITIONC) THE ALIMENTARY CANAL IN HUMANSD) THE CONTROL OF DIGESTIVE SECRETIONS

E) CELLULOSE DIGESTION IN RUMINANTS

Topic Overview

Herbivores have a problem:

They eat grass:

principal component is cellulose

BUT cannot produce cellulases

Mutualistic bacteria in gut produce cellulase.

ruminants

Herbivores may be:non-ruminants/

hind-gut fermenters e.g. cattle, sheep,

goatse.g. rabbit, horse

Monogastric herbivores: one-stomach chamberFour stomach chambers

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

Ruminants have a specialised digestive system capable of digesting cellulose:

stomach with 4 distinct compartments

3. Omasum

4. Abomasum1. Rumen 2. Reticulum

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

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

Fermentation is the enzymatic transformation of organic substances

[acids]

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

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

RUMEN has a very thick, muscular wall food is mixed with saliva

SALIVA: acts as a buffer to acids produced by

microbes

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

Reticulum full

Reticulum cleaned

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?

RUMINANTS: cud-chewers

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.

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.

Rumination – chewing the cudDepending on the amount of fibre in their food, cattle

may spend between 3 – 6 hours per day chewing their cud

Where are microbes located in mammalian herbivores other than

ruminants?

caecum

Hindgut fermenter

Compare gut of:

Ruminant HerbivoreFour-chambered stomach with

large rumen, long small & large

intestine

Hindgut fermenter

Simple stomach,

Large caecum

caecum

caecum

CarnivoreShort intestine & colon,

small caecum

Compare gut of:

Ruminant HerbivoreFour-chambered stomach

with large rumen,

long small & large intestine

caecum caecum

REASON:

To get nutrients that otherwise would be

lost

Coprophagy:

a behaviour of certain mammalian herbivores

where they ingest faeces

Rabbits produce two types of faeces:

soft, edible, mucous covered packets of protein and vitamins

true faeces are drier and contain undigested fibre

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.

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

A) HETEROTROPHSB) DENTITION

C) THE ALIMENTARY CANAL IN HUMANSD) THE CONTROL OF DIGESTIVE SECRETIONSE) CELLULOSE DIGESTION IN RUMINANTS

Topic Overview

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]

Variations in the gut wall

Oesophagus Stomach Large intestineSmall

intestine

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

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

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

Submucosa: a layer of connective tissue containing:

nerves blood vessels lymph vessels collagen elastic fibres

The submucosa may contain some mucus-secreting glands

that deposit their contents via ducts e.g. Brunner’s glands in the duodenum

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

Both plexuses consist of nerves from the autonomic NS

Auerbach’s

plexus

Meissner’s

plexus

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

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

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

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

Sphincters are found at the junctions of:-

oesophagus & stomach (cardiac sphincter)

stomach & duodenum (pyloric sphincter)

ileum & caecum

the anus

Serosa: outermost coat of gut

composed of loose connective tissue

serosa

Peritoneum: covers the whole of the

outer surface of the gut forms the mesenteries

mesenteryperitoneum

mesentery

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

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

Peyer’s patches in ileum

Peyer’s patch [function?]

Peyer’s patches: have a role in the immune response

aggregations of lymphoid tissue that are usually found in the ileum in humans

SEP 2006 Paper 3Draw an annotated map of the structure shown in Figure 1. (10 marks)

Scale: x 1

Buccal cavity

region enclosing the jaws and tongue

lined with stratified squamous epithelium

 

Basal layer undergoes mitosis

The tongue: mixes & moistens food possesses taste buds sensitive to: sweet salty sour bitter

Taste bud

Saliva is produced by: three pairs of salivary glands

Saliva contains:1. salivary amylase :

begins digestion of starch to dextrins (shorter polysaccharides) and then to maltose

Salivary amylase

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

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

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

Pharynx is where the: mouth cavity &

the nasal passages join

Muscle contractions in the gut occur for two reasons:

1. move food forward [peristaltic contractions]

2. stir & mix food

[segmental movements]

Peristaltic contractions:are progressive waves of contraction

that move progressively down the gut

1

2

BolusDigestive tract

Wave ofcontraction

Wave ofrelaxation

Bolusmoves

2

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

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

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 

2 smooth muscle layers in gut BUT 3 in stomach:-

Circular muscle (middle)

Longitudinal muscle (outer)

Oblique muscle (inner)

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

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

Six functions of the stomach

2. The stomach continues mechanical digestion by the churning action.

Food digested by churning

Food digested by enzymes

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

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

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)

zymogen or chief cells - secrete pepsinogen &

prorennin

oxyntic or parietal cells - secrete HCl

pH = 1 - 2.5

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

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

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:

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

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

6. Stomach contains endocrine cells which secrete the hormone gastrin.

Gastrin stimulates

gastric glands to

secrete gastric juice

rich in HCl.

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

A few substances can be absorbed from the chyme across the stomach wall:

E.g. alcohol aspirin caffeine

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

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

The submucosa & mucosa together are folded

Numerous villi:

finger-like projections.

Microvilli

(brush border)

Structural features which

increase the surface area of

the small intestine

How is the structure of the small intestine

related to its function?

TS ileum showing

villus

villi on mucosa

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

Goblet cells

are special epithelial cells : secrete mucus throughout the small intestine

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) 

Submucosal Brunner’s glands secrete:

1. mucus 2. alkaline fluid in first part of the duodenum

(pH = 7 - 8)

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

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

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

Digestion of proteinswhole

proteins

endopeptidases exopeptidases

dipeptidases

dipeptidesshorter

polypeptides

amino acids

Carboxypeptidase cuts at C terminus

Aminopeptidase: cuts at N terminus

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

Explain how the action of endopeptidases increases the rate of

action of exopeptidases. (1)

Creates more ends / increases surface area where exopeptidases work.

In addition to its own secretions, the small intestine receives:

2. alkaline pancreatic juice

1. bile

Pancreas & Liver:

provide important secretions

are two accessory organs that are not part of the digestive system

The pancreas :

Exocrine tissue composed of acini (groups of cells

which produce enzymes)

is a large gland just beneath the stomach

Topancreaticduct

Hormones tobloodstream

The pancreas releases enzymes as zymogens:

[inactive enzyme precursors]

The pancreas :

pours enzymes via

the pancreatic duct

Pancreatic amylase

TrypsinogenLipase Pancreatic

enzymes includeChymotrypsinogen

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

Enterokinase is produced by: wall of duodenum

Enterokinase

[membrane-bound enzyme]

The liver synthesises bile

Bile is a dark green to

yellowish brown fluid

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?

The hormone cholecystokinin (CCK) causes the gallbladder to contract

Gallstones may block bile duct

Contraction of the gallbladder will cause pain

Gallstones are formed from a hardened precipitate

of cholesterol

Bile contains:

water bile salts bile pigments

[bilirubin, biliverdin]

pH paper turns green in bile

Bile pigments:

do not participate in digestion

are waste products from the destruction of old red blood cells

are finally eliminated with the faeces

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.

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.

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

Chylomicron composition:

90% triglyceride5% cholesterol

4% phospholipid

1% protein

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

Note milky colour of plasma:

due to a genetic disorder leading

to excessive triglycerides in

blood

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

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?

To liver via the hepatic portal vein

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

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

THE LARGE INTESTINE

THE LARGE INTESTINE

1.Caecum

Anus

2. Appendix

3. Colon

4. Rectum

The large intestine absorbs:

2. any remaining inorganic nutrients

8900 ml1. bulk

of water

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

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

Many mutualistic bacteria in the large intestine synthesise:-

1. some vitamins especially vitamin K

2. amino acids which are absorbed into the bloodstream

mutualism

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.

A) HETEROTROPHSB) DENTITIONC) THE ALIMENTARY CANAL IN HUMANS

D) THE CONTROL OF DIGESTIVE SECRETIONS

E) CELLULOSE DIGESTION IN RUMINANTS

Topic Overview

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

The control of the secretion of:

1. Saliva

2. Gastric juice

3. Pancreatic juice & bile

The control of the secretion of:

1.Saliva 2. Gastric juice

3. Pancreatic juice & bile

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

2. conditioned reflexes of seeing, smelling or thinking of food

Sight

Smell Thinking

of food

The control of the secretion of:

1. Saliva

2.Gastric juice3. Pancreatic juice & bile

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

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

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

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

The control of the secretion of:

1. Saliva

2. Gastric juice

3.Pancreatic juice & bile

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

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

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)

REVISE:

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.

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.

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.

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.

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]

THE END