The document discusses mammalian nutrition and digestion. It begins by defining heterotrophic and mammalian nutrition. It then describes the multi-step digestion process, including ingestion, physical and chemical digestion in the mouth, stomach, small intestine, liver and pancreas. Key enzymes and sites of action are identified. Absorption of digested end products like glucose, amino acids and fatty acids occurs in the small intestine. These are then distributed and utilized by cells for energy production or protein/fat synthesis.

1. 5.2
Heterotrophic
Nutrition
Ong Yee Sing
2017

2. Quiz
• Which of the following defines a heterotroph?
A. An organism that must obtain its carbon in an organic form.
B. An organism that does not require essential nutrients for growth.
C. n organism that uses CO3
-2 as its carbon source.
D. An organism that produces all the trace elements it requires for
growth.
E. An organism that uses CO2 as its carbon source.

3. Quiz
• Molecules that satisfy heterotrophic nutritional requirements include
all but which of the following?
A) Water
B) Nucleic acids
C) Lipids
D) Carbohydrates
E) Proteins

4. Quiz
• Nitrogen is required for the production of what category of
molecules?
A) Fatty acids
B) Phospholipids
C) Nucleotides
D) Carbohydrates
E) Cellulose

5. Quiz
• The more successful of the parasitic microorganisms have what type
of effect on their host?
A. They have a mutualistic relationship with a host cell.
B. They have no fatal effects on the host and eventually evolve to a
less harmful relationship with the host.
C. They eventually kill the host cell.
D. They have no effect whatsoever on the host cell.
E. They cause an infection when the host is compromised.

6. 5.2.2
Mammalian
Nutrition

8. Mammalian mode of nutrition
• The mammalian mode of nutrition is the holozoic nutrition.
• a type of heterotrophic nutrition that is characterized by the internalization
(ingestion) and internal processing of liquids or solid food particles
• The whole process of nutrition includes ingestion, digestion,
absorption, assimilation and egestion.
全动物式营养

9. Ingestion
• the process of taking food, drink,
or another substance into the body
by swallowing or absorbing it.
• In mammals (and birds and reptiles
etc.) the act is carried out by the
mouth.
摄取
Adélie penguin
rabbithippopotamus

10. 5.2.2.1 Digestion

11. Digestion
• Digestion of food includes physical
digestion and chemical digestion.
• Physical digestion is where food is
broken up into smaller pieces by
physical action.
• Chemical digestion breaks up large
molecular substances such as proteins,
lipids and carbohydrates into small
molecules such as short peptide chains,
glucose etc using chemical reactions.

12. Physical digestion
• After food has been ingested through the mouth,
physical digestion occurs in the alimentary canal.
• from Latin alimentarius, from alimentum ‘nourishment’
• Alimentary canal is the whole passage along which food
passes through the body from mouth to anus.
• Physical digestion breaks up the food into smaller
pieces with mechanical actions to increase the
surface area of the food and thus speed up the
process of chemical digestion.
• Examples of physical digestion:
• Chewing by teeth in mouth cavity and swallowing
• Stirring and mixing by stomach (by peristalsis and
contraction)
• Peristalsis of small intestine
物理性消化/机械性消化
蠕动
消化道

13. 咽
口腔
小舌
唾液腺
食管/食道
肝
胆囊
总胆管
胃
舌
结肠（大肠）
横结肠
升结肠
降结肠
盲肠
阑尾
十二指肠
小肠
回肠
空肠
直肠
肛门
胰脏

15. Chemical digestion
• Chemical digestion is the process of breaking down food into simple,
soluble molecules with chemical reactions with the help of acids and
enzymes.
• Chemical digestion starts in the mouth and ends in the small intestine.
Digestive enzymes are enzymes that
break down large molecules into
their smaller building blocks, in order
to facilitate their absorption by the
body.

16. Site of
digestion
Digestive
juice
Site of
secretion
Digestive
enzyme
Opt
pH
Action of enzymes
Substrates  Products
Mouth
cavity
Saliva
Salivary
gland
Salivary
amylase
6.8 Starches  maltose
Stomach
Gastric
juice
Gastric
gland
Pepsin 1.5 Protein  Peptides
Rennin 1.5 Caseinogen  Casein
Gastric acid, HCI
Kills germs; provides and acidic medium for the action of pepsin and
rennin
Small
intestine
Bile Liver cell Bile salt Emulsify fats
Pancreatic
juice
Gland
cells of
pancreas
Pancreatic
amylase
7.8 Starches/ glycogen  maltose
Trypsin 7.8 Protein or Peptides  Peptides + Amino acids
Nuclease 7.8 Nucleic acids  Nucleotides
Lipase 7.8 Fats  Fatty acids + Glycerol
Intestinal
juice
Cells of
intestinal
gland
Maltase 7.6 Maltose  Glucose
Sucrase 7.6 Sucrose  Glucose + Fructose
Lactase 7.6 Lactose  Glucose + Galactose
Peptidase 7.6 Peptides  Amino acids
Lipase 7.6 Fats  Fatty acids + Glycerol
Nucleotidase 7.6 Nucleotides  Nitrogenous base + pentose sugar + phosphates

17. Chemical digestion: Mouth
• The salivary glands in the mouth secrets
saliva, which contains salivary amylase.
• The optimum pH of salivary amylase is
6.8.
• Salivary amylase break down starch into
maltose (and dextrin – small glucose
chain).

18. Chemical digestion: Stomach
• In the stomach, the gastric gland secretes the
gastric juice, pepsins (in the form of pepsinogen)
and rennin (in the form of prorennin).
• The gastric juice is highly acidic (pH 1.5) because
it contains hydrochloric acid (HCl) that can kill
pathogens and maintain an acidic environment
for the other digestive enzymes.
• Pepsins breaks down protein into polypeptide
chains.
• Rennin breaks down caseinogen into casein.
• Latin caseus, "cheese“
• Caseinogen for the uncoagulated milk protein and
casein for the coagulated milk protein
• To increase the time of milk proteins stay in stomach
液态蛋白 固态蛋白凝乳酶
胃蛋白酶
胃腺
胃液
胃酸

19. Chemical digestion: Small intestine - liver
• The liver cell secrets the bile.
• Bile is an alkaline substance produced by the
liver and stored in the gall bladder.
• The bile neutralize the stomach acid.
• The bile contain the non-enzymatic bile salt.
• The bile salt emulsifies fats to provide a larger
surface area in which the lipases can work.
乳化
肝 胆汁
胆盐

20. • The pancreatic cells secretes the pancreatic juice that contain various
enzymes.
• The optimal pH of these enzymes is at 7.8.
Chemical digestion: Small intestine - pancreas
starch/ glycogen  maltose
Protein or Peptides  Peptides + Amino acids
Nucleic acids  Nucleotides
Lipids/fats  Fatty acids + Glycerol
lipase
脂肪
胰脂肪酶
脂肪酸 甘油
nuclease 胰核酸酶
核酸 核苷酸
pancreatic amylase 胰淀粉酶
淀粉/糖元 麦芽糖
胰蛋白酶trypsin
多肽 多肽蛋白质 氨基酸

21. Chemical digestion: Small intestine
• Small intestine itself secretes intestinal juice with the help of various
intestinal glands that helps to complete the digestion process.
• The optimal pH of these enzymes found in the intestinal juice is 7.6.
Maltose  Glucose
maltase
麦芽糖 葡萄糖
麦芽糖酶
Sucrose  Glucose + Fructose
sucrase 蔗糖酶
蔗糖 葡萄糖 果糖
Lactose  Glucose + Galactose
lactase 乳糖酶
乳糖 半乳糖葡萄糖
Peptides  Amino acids
peptidase 肠肽酶
多肽 氨基酸
Lipids/fats  Fatty acids + Glycerol
lipase
脂肪
肠脂肪酶
脂肪酸 甘油
Nucleotides  base + 5C sugar + phosphate
nucleotidase 肠核苷酸酶
核苷酸 碱基 五碳糖 磷酸根

22. Digestion of polysaccharides
Saliva + pancreatic
Small intestine

23. Digestion of protein
Peptidase

25. Quiz
• Where does protein digestion begin?
• Mouth
• Small intestines
• Stomach
• Liver

26. 5.2.2.2 The role
of liver in the
digestion
process

28. The liver
• Liver is the largest digestive gland消化腺 in
mammals.
• It is located immediately below the right side of
diaphragm横膈.
• It is brownish-red in colour and is divided into
the left lobe and the right lobe.
• The right lobe of the liver is larger than the left
lobe.
• The hepatic artery肝动脉 serves to provide
nutrients to the liver.
• The hepatic portal vein肝门静脉 connects the
liber with the small intestine.
• The bile juice胆汁, manufactured by the liver
cells, is drained into the hepatic duct肝管 and is
stored in the gall bladder胆囊.
• The bile duct (cystic duct)胆管 is connected to
the pancreatic duct胰管 to form the common
bile duct总胆管 which, in turn, is connected to
the duodenum十二指肠. `
肝

29. Secretions of the liver: Bile
• Bile is a greenish secretion contains bilirubin,
bile salt, sodium hydrogen carbonate (NaHCO3)
and organic salt but no digestive enzyme.
• Bilirubin is the brownish yellow pigment
produced from haemoglobin broken down by
the liver cell.
• Bile is basic (alkaline solution) as it contains
sodium hydrogen carbonate and organic salt
• Neutralize the acidic chyme
• Provide a basic environment for the pancreatic
enzymes to function effectively.
• Bile salt can lead to emulsification乳化 of fat
• increases the surface area of fats for lipase-catalysed
the hydrolysis of fats.
食糜
胆色素
碳酸氢钠
胆盐

31. Functions of the liver
• Secretion
• Bile juice - bilirubin, bile salt, NaHCO3
• Metabolic
• Deamination脱氨 - breaks down excess amino acids into urea
• Produce glycogen from glucose for storage
• Break down red blood cells.
• Detoxication
• Removes the toxins e.g. steroids, thyroid hormone
• Synthesis
• Blood proteins or plasma proteins such as fibrinogen纤维蛋白原
and prothrombin凝血酶原 (both responsible for blood clotting
process)
• Storage
• iron from old RBCs to use in the production of new RBCs.
• Vitamins such as vitamins A, D and B12.
• Blood storage
• Maintain homeostasis体内动态平衡
• Blood volume regulation
• Heat production

32. 5.2.2.3 The role of pancreas in
the digestion process

34. The pancreas胰脏
• A large gland that consists of exocrine gland
and endocrine gland.
• Exocrine glands 外分泌腺 produce and secrete
substances onto an epithelial surface by way of a
duct. E.g. pancreatic juice secretes into the
pancreatic duct
• Endocrine glands 内分泌腺 secrete their products,
hormones, directly into the blood rather than
through a duct. E.g. insulin and glucagon into the
blood
• In general, the pancreas of mammals is a group
of scattered or separated gland but the human
pancreas is “long and narrow” in shape.
• It is pink in colour and is located in the loop of
the duodenum.
• The acinous cells 腺细胞 secrete pancreatic juice
which contains trypsin, pancreatic amylase and
pancreatic lipase.
• Pancreatic juice also contains basic sodium
hydrogen carbonate碳酸氢钠 which can
neutralizes chime and provide alkaline
environment.

35. 5.2.2.4 The absorption,
distribution and
utilization of the
digested food

36. Ileum
• Glucose, amino acids, fatty acids
and glycerol are the main final
products of digestion.
• These substances are absorbed
in the small intestine, especially
ileum.
• Ileum is the third portion of the
small intestine, between the
jejunum空肠 and the cecum盲肠.
回肠

37. Characteristics of ileum
• The ileum increases the total surface are for absorption.
• Its epithelium is folded to form villi (sig. villus)绒毛.
• from Latin, literally ‘shaggy hair.’
• The epithelial cells on the villus bear microvilli微绒毛.
• The villi and microvilli further increase the total surface area for absorption.

38. Characteristics of ileum
• The epithelium of the villus is
only one-cell thick since it
consists of a single layer of
cells.
• It is a simple columnar
epithelium柱状上皮.
• The modes or mechanisms of
absorption be carried out
through diffusion, osmosis or
active transport.

39. Characteristics of ileum
• The villus绒毛 contains numerous
blood capillaries and a lacteal.
• The blood capillaries绒毛微血管
absorb glucose and amino acids.
• A lacteal绒毛乳糜管 is a lymphatic
capillary that absorbs dietary fats
in the villi of the small intestine.
The villus contains numerous blood capillaries compared to the
jejunum.

40. Histology of ileum

41. (ileum)

42. Absorption, distribution and utilization of the
end-products of digestion
End-product
Site of
absorption
Distribution Utilisation
1. Glucose Blood
capillaries of
the villus
Glucose enters the liver through the hepatic portal
vein. Most of it is converted into glycogen for
storage in the liver. Some directly enters the
circulatory system.
Glucose reaches the tissue cells via the blood. It is utilized by
the cells to release energy. Excess glucose is converted into fats
for storage in the adipose tissue located below the skin or
around certain organs such as the heart and kidney.
2. Amino
acids
Blood
capillaries of
the villus
Amino acids enter the liver through the hepatic
portal vein. Most of the amino acids enter the
hepatic vein and the general circulation. Some
remains in the liver produces urea through the
process deamination. Urea is removed from the
body through the kidneys.
Amino acids enter the tissue cells via the blood. It is utilized as
the material for the synthesis of proteins of the cells. The
remains of amino acids (amino acid residue) after deamination
are converted into glucose in the liver and the glucose can
produce energy during cellular respiration of be converted into
glycogen for storage in the liver.
3. Fatty
Acids
and
glycerol
Lacteal of the
villus
Fatty acids and glycerol enter lymph vessel through
the lacteal of the villus, each lymph vessel comes
together to form the thoracic duct, then lymph flows
back to the blood system through the left subclavian
vein.
Fatty acids and glycerol reach the tissue cells via the blood.
They are oxidized to provide energy to the cells. The amount
left over is stored around the kidneys, heart and liver, near
mesentery or in the adipose tissue located below the skin.
When the blood is deficient in glucose, the stored fats can be
converted into glucose which can be utilized by the cells.
4. Water, vitamins
and inorganic salts
blood
capillaries (fat-
soluble vitamins
– lacteal)

43. Glucose葡萄糖
• Glucose is absorbed by the blood capillaries in the
villi though active transport and facilitated
diffusion.
• active transport into intestinal epithelial cells
• facilitated diffusion across the membrane of red blood
cells.
• Glucose enters the liver through the hepatic portal
vein肝门静脉.
• Most of it is converted into glycogen糖元 for storage in
the liver.
• Some directly enters the circulatory system.
• Glucose reaches the tissue cells via the blood.
• It is utilized by the cells to release energy.
• Excess glucose is converted into fats for storage in the
adipose tissue that located below the skin or around
certain organs such as the heart and kidney.
villi
liver
tissues
glucose
Blood capillaries
Hepatic portal vein
Blood
circulatory
system

44. Quiz
• Glycogen is stored for later use in:
A. kidney cells
B. blood cells
C. liver cells (and muscle cells)
D. brain cells

45. Amino acids氨基酸
• Amino acids are absorbed by the blood capillaries in the
villi though active transport and facilitated diffusion.
• active transport into intestinal epithelial cells
• facilitated diffusion across the membrane of red blood cells.
• Amino acids enter the liver through the hepatic portal
vein.
• Most of the amino acids enter the hepatic vein and the general
circulation.
• Some remains in the liver to become urea尿素 through
deamination去氨作用. Urea is removed from the body through
the kidneys肾脏.
• Amino acids enter the tissue cells via the blood.
• It is utilized as the material for the protein synthesis.
• The amino acid residue after deamination are converted into
glucose in the liver.
villa
liver
tissues
Amino acids
Blood capillaries
Hepatic portal
vein
Hepatic vein
kidney
Deaminated
urea
egestion
liver
Deaminated
glucose
Left: Urea
Right: Deamination is the
removal of an amino
group from a molecule.

46. Fatty acids脂肪酸 and glycerol甘油
• Fatty acids and glycerol enter the lymph vessel
through the lacteal乳糜管 of the villus through
free diffusion.
• Each lymph vessel comes together to form the
thoracic duct胸管.
• The lymph flows back to the blood system
through the left subclavian vein左锁骨下静脉.
• Fatty acids and glycerol reach the tissue cells via
the blood.
• They are oxidized to provide energy to the cells.
• The amount left over is stored around the kidneys,
heart and liver, near mesentery肠膜 or in the adipose
tissue located below the skin.
• When the blood is deficient in glucose, the stored fats
can be converted into glucose.
villi
thoracic duct
blood circulatory system
Fatty acids + glycerol
lacteal
lymph vessels
left subclavian
vein
storage energy
kidney, heart,
liver, adipose
glucose

49. Water and inorganic salt
• They are not digested.
• Absorbed into the capillaries by osmosis (water) or passive diffusion
(inorganic salt)
• Also absorbed by the large intestines
Vitamins
• Not digested.
• Water-soluble vitamins (vitamins B and C) are absorbed into the
capillaries by diffusion or active transport.
• Fat-soluble vitamins (vitamins A, D, E and K) absorbed into the lacteal
by diffusion.

50. Summary: Absorption
Fat (glycerol + fatty acids),
Fat-soluble vitamins (A, D, E, K)
lacteal
Lymph vessel
Thoracic duct
Left subclavian
vein
Superior vena
cava
Heart

51. Summary: Absorption
Glucose, water, minerals, ions
Water-soluble vitamins (B, C)
Blood
capillaries
Hepatic
portal vein
Liver
Hepatic
vein
Inferior
vena cava
Heart

52. Summary: Assimilation
• Glucose
• Excessive glucose is
stored as glycogen in
the liver and the muscle
• Transform glycogen into
glucose by the liver
• Excessive glucose is
stored as fat in the
adipose layer
• Oxidises glucose to
release energy through
respiration
• Amino acids
• Synthesis proteins
(hormones, enzymes,
structural proteins) to
form structure such as
muscle, hair, blood
• Excessive amino acid is
transform into urea and
glucose through
deamination
• Fatty acid and glycerol
• Oxidises fat to release
energy through
respiration
• Stored as fat in the
adipose layer under the
skin and surrounding
important internal
organs
• Protects the organ
• Store energy
• Transform into glucose

53. 5.2.4.5 Egestion

54. Egestion排遗
• Egestion is the discharge or expulsion of
undigested material (food) from a cell in case of
unicellular organisms, and from the digestive
tract via the anus in case of multicellular
organisms.
• When the food reaches the rectum直肠, most of
the water and useful substances have been
absorbed.
• Half-solid indigestible substances such as
cellulose, secretion of the alimentary canal, the
cells worn off from the wall of the intestine,
bacteria and a small quantify of water is known
as faeces粪便.
• It appears brownish as it contains bilirubin胆色素.
• The foul smell is caused by the methane甲烷 gas.

55. 5.2.3 Alimentary
canal of herbivores

56. Herbivore
• A herbivore is an animal that feed on plants.
• from Latin herba ‘herb’ + -vore ‘feeding on a specific food’
• In herbivores have specialized their alimentary canal to digest cellulose of plants.
• Herbivores can be divided into ruminants反刍动物 and non-ruminants非反刍动物.
• Ruminants are mammals that are able to acquire nutrients from plant-based food
by fermenting it in a specialized stomach prior to digestion, principally through
microbial actions. The process typically requires the fermented ingesta (known
as cud) to be regurgitated and chewed again. The process of rechewing the cud
to further break down plant matter and stimulate digestion is called rumination.
• Latin ruminare "to chew over again“
• Non-ruminants do not have divided stomach.

58. 5.2.3.1 Ruminant
herbivore

59. Example of ruminant herbivore

60. Characteristics of the alimentary canal of the
ruminants
• The alimentary canal
is longer than that of
omnivores, especially
the caecum.
• Compound stomach
or four-chambered
stomach.

61. Compound stomach of the ruminants
• The four chambers
of the ruminants
consists of rumen,
reticulum,
omasum and
abomasums.
rumination

63. The Rumen

64. Rumen瘤胃
• Rumen is the largest chamber of stomachs.
• The internal surface of its walls is covered with tumour-like
projections.
• This chamber contains mutualistic共生 microorganisms (or
symbiotic organisms) which ferments food that was mixed with
saliva.
• Cellulose and other indigestible plant materials are broken
down by the microbe enzymes, such as cellulases纤维素酶.
• The end-products of fermentation include glucose, acetic acid
(ethanoic acid)醋酸, propanoic acid丙酸, butanoic acid丁酸,
carbon dioxide二氧化碳, methane甲烷, etc.
• The herbivores absorb the organic acids (with the rumen) as
the major source of energy.
• In return the microorganisms obtain their energy requirements
through the chemical reactions of fermentation.
TEMs of O. guilliermondii obtained from rumen content of
Norwegian reindeer

65. Reticulum网胃
• After fermentation, the food enters
the chamber reticulum (also known as
honeycomb stomach).
• Latin, diminutive of rete ‘net.’
• The internal surface of its walls
possesses numerous reticulated folds
网状褶襞 and fine keratinised papillae角
质乳突 (sg. papilla) which are able to
grind food into small pieces.
• from Latin papilla ‘nipple,’
• Then food flows back to the rumen
and to the mouth for chewing and re-
digestion.
• This process is known as rumination.
• Rumination occurs in both the rumen and
the reticulum.
reticulum in a water buffalo (Bubalus bubalis)

66. Omasum重瓣胃
• After one more time of fermentation in
the rumen, food passes from the
reticulum into the chamber omasum.
• from Latin, literally ‘bullock's tripe.’
• Water, magnesium and acids are
absorbed in the omasum.
• The omasum which possesses leaf-like
longitudinal valves叶状纵瓣 and
numerous keratinised papillae角质乳突
can further grind the food.
Sheep Omasum

67. Abomasum皱胃
• modern Latin, from ab- ‘away, from’
+ omasum
• Then food passes into the chamber
abomasum which also possesses
longitudinal folds纵皱.
• Abomasum is the true stomach
(corresponds to the stomach in humans)
which possess digestive glands胃腺 to
secrete digestive juice胃液, the food
undergoes complete digestion here.
• The first three chambers are the
modified esophagus食道, whose main
function is to store up the food and carry
out preliminary digestion

69. 5.1.3.2 Non-
ruminant herbivore

70. Example of non-ruminants

71. Non-ruminants
• The non-ruminants such as rabbit and horse carry out fermentation of food
in the caecum盲肠.
• The caecum of rabbit is large and long.
• It contains numerous symbiotic microorganisms which are able to secrete
cellulase纤维素酶 to break down cellulose into glucose.
• Besides that, faeces of rabbits are in the form of pellets (“pill”) or is known
as faecal pellets粪丸.
• The faecal pellets contain cellulose which has not been completely
digested. Its texture is soft and sticky.
• The faecal pellet can be once again swallowed and digested in order to
absorb more nutrients.

72. Comparison between human and herbivores
Human Ruminant
herbivore
Non-ruminant
herbivore
Number of stomach 1 4 1
Size of cecum Small Not large Long and large
Cellulase production None Bacteria resident
in the rumen and
the reticulum
Bacteria resident
in cecum
Cellulose digestion None Yes Yes
Rumination None Yes None
Gastric acid production Stomach Abomasum Stomach
Number of time food pass
through digestive tract
One One Two (rabbit)

73. Quiz
• Where does microbial fermentation occur in the horse?
A. Colon
B. Stomach
C. Small intestine
D. Cecum