Complex Lipids: Glycerophospholipids and Sphingolipids

Lipids

Bioc. 201

بسم الله الرحمن الرحيم

1

Complex Lipids:

Glycerophospholipids

2

Glycerophospholipids



Glycerophospholipids are similar

in structure to triglycerides

except that they only have 

two

esterified fatty acids. The third

position on the glycerol

backbone instead contains a

phospholipid head group

.



The two fatty acids in

phospholipids are normally 14

to 24 carbon atoms long, with

one fatty acid commonly

saturated and the other

unsaturated.

3

Glycerophospholipids

•

There are several types of phospholipid head groups, such as:

choline, inositol, serine, and ethanolamine, which are all

hydrophilic in nature.

•

The various types of glycerophospholipids are named based on

the type of phospholipid head group present, e.g.

phosphatidylcholine.

4

Glycerophospholipids

•

Because glycerophospholipids contain both hydrophobic fatty acid

C―H chains and a hydrophilic head group, they are by definition

amphipathic lipid molecules 

and, as such, are found on the surface

of lipid layers.

•

The polar hydrophilic head group faces outward the aqueous

environment, whereas the fatty acid chains face inward away from

the water in a perpendicular orientation with respect to the lipid

surface.

5

Complex Lipids:

Sphingolipids

(Sphingomyelin, Cerebrosides and Gangliosides)

6

Sphingolipids

•

Shingolipids

 are typically found in brain

tissues.

•

Sphingolipids are derivatives of the C18

amino alcohols  

sphingosine

,

dihydrosphingosine

, and their C16, C17,

C19, and C20 homologs.

•

Sphingosine is rare in plants and animals

while  sphingolipids are common.

7

Sphingolipids

8

Sphingolipids

•

Simplest sphingolipids are 

ceramides.

Sphingosine + N-linked fatty acid = ceramide

•

Ceramides occur only in small amounts in

plant and animal tissues but form the parent

compounds of more abundant sphingolipids:

1.

Sphingomyelins.

2.

Cerebrosides.

3.

Gangliosides.

9

Sphingolipids: 1. Sphingomyelin

•

Sphingomyelin

 the only

significant sphingophospholipid in

humans.

•

The backbone of sphingomyelin is

the amino alcohol sphingosine,

rather than glycerol.

•

A long-chain fatty acid is attached

to the amino group of

sphingosine through an 

amide

linkage

, producing a 

ceramide

,

which can also serve as a

precursor of glycolipids.

10

Sphingolipids: 1. Sphingomyelin

•

The alcohol group at 

carbon

1

 of sphingosine is

esterified to

phosphorylcholine,

producing sphingomyelin.

•

They can also be classified

as 

sphingophposholipids

.

•

Sphingomyelin is an

important constituent of

the myelin of nerve fibers.

11

Sphingolipids: 2. Cerebrosides

•

Cerebrosides,

 the simplest sphingoglycolipids (alternatively

glycosphingolipids), are ceramides with head groups that

consist of a single sugar residue.

•

The carbohydrates are most often 

glucose

 or 

galactose

.

•

Cerebrosides, in contrast to phospholipids, 

lack phosphate

groups

 and hence are most frequently 

nonionic 

compounds.

12

Sphingolipids: 2. Cerebrosides



Galactocerebrosides:

•

Most prevalent in the

neuronal cell membranes

of the brain.

•

have a 

β

-D-galactose 

head

group.

13

Sphingolipids: 2. Cerebrosides



Glucocerebrosides:

•

They occur mostly in non-neuronal tissues.

•

have a 

β

-D-glucose 

head group.

14

Sphingolipids: 3. Gangliosides

•

Gangliosides form the most complex group of

sphingolipids.

•

They are ceramide oligosaccharides that include

among their sugar groups 

at least one sialic acid

residue.

•

Gangliosides are primarily components of cell

surface membranes and constitute a significant

fraction of brain lipids. Other tissues also contain

gangliosides but in lesser amount.

15

Sphingolipids: 3. Gangliosides

16

Sphingolipids: 3. Gangliosides

•

Glycosphingolipids are the determinants of

blood types.

17

* The symbol Fuc represents the sugar fucose.

Waxes

18

Waxes

•

Waxes are typically

esters of fatty acids and

fatty alcohols.

•

They protect the skin of

plants and fur of

animal.

•

Natural protective layer

in fruits and vegetables.

19

Waxes

20

•

Weakly polar head

group with saturated

fatty acid and

unsaturated fatty

alcohol (typically).

Steroids:

Cholesterol and Bile Acids

21

Steroids

•

Another major class of lipids is steroids, which have

structures totally different from the other classes of lipids.

•

The main feature of steroids

is the 

ring system 

of 

three

cyclohexanes

 and 

one

cyclopentane 

in a fused ring

system.

•

 There are a variety of

functional groups that may

be attached. The main

feature, as in all lipids, is the

large number of carbon-

hydrogens which make

steroids non-polar.

22

Steroids



Steroids include such well known compounds

as:

•

Cholesterol

•

Male & female sex hormones

•

Bile acids

•

Vitamin D

•

Adrenal corticosteroids

23

Cholesterol

•

Cholesterol is an unsaturated steroid

alcohol.

•

It consists of 

four fused hydrocarbon

rings

 (A, B, C, and D) called the “steroid

nucleus”), and it has an 

eight-carbon,

branched hydrocarbon chain

 attached to

carbon 17 of the D ring. Ring A has a

hydroxyl group at carbon 3, and ring B

has a double bond between carbon 5 and

carbon 6

•

Cholesterol is a very hydrophobic

compound. The only hydrophilic part of

cholesterol is the hydroxyl group in the A-

ring. It is, therefore, also an amphipathic

lipid and is found on the surface of lipid

layer along with phospholipids.

24

Cholesterol

•

Cholesterol can also exist in an

esterified form called 

cholesterol ester

,

with the hydroxyl group conjugated by

an ester bond to a fatty acid, in the

same way as in triglycerides.

•

In contrast to free cholesterol, there

are 

no polar 

groups on cholesterol

esters, making them very 

hydrophobic

.

•

Because it is not charged, cholesterol

ester are classified as a neutral lipid

and are not found on the surface of

lipids layers but instead are located in

the center of lipid drops and

lipoproteins, along with triglycerides.

25

Cholesterol



Cholesterol is almost exclusively synthesized by animals, but plants

do contain other sterols similar in structure to cholesterol.

Cholesterol is also unique in that, unlike other lipids, it is not readily

catabolized by most cells and, therefore, does not serve as a source

of fuel.



Cholesterol performs a number of essential functions in the body.

For example:

•

Cholesterol is a structural component of all cell membranes,

modulating their fluidity.

•

In specialized tissues, cholesterol is a precursor of bile acids, steroid

hormones, and vitamin D. It is therefore of critical importance that

the cells of the body be assured an appropriate supply of

cholesterol.

26

Synthesis of Cholesterol

•

Occurs in cytosol.

•

Requires NADPH, ATP, and O

2

.

•

Highly regulated.

•

80 % in liver, ~10% intestine, ~5% skin.

•

The overall equation:

27

Synthesis of Cholesterol

•

Cholesterol is synthesized

by virtually all tissues in

humans, although liver,

intestine, adrenal cortex,

and reproductive tissues,

including ovaries, testes,

and placenta, make the

largest contributions to the

body’s cholesterol pool.

28

Cholesterol

•

The liver plays a central role

in the regulation of the

body’s cholesterol

homeostasis. For example,

cholesterol enters the liver’s

cholesterol pool from a

number of sources including

dietary cholesterol

, as well

as cholesterol synthesized

de novo by extrahepatic

tissues 

and 

by the liver

itself.

29

Synthesis of Cholesterol

30

•

The key step in the biosynthesis of cholesterol is the conversion of

3-hydroxy-3-methyl-glutaryl-Coenzyme A

 to 

mevalonate

 by 

HMG

CoA reductase

. This is the 

rate limiting step 

in cholesterol

biosynthesis.

Synthesis of Cholesterol

31

Degradation of Cholesterol

•

The ring structure of

cholesterol cannot be

metabolized to CO2 and

H2O in humans.

•

Rather, the intact sterol

nucleus is eliminated from

the body by conversion to

bile acids 

and 

bile salts

,

which are excreted in the

feces, and by secretion of

cholesterol into the bile,

which transports it to the

intestine for elimination.

32

Degradation of Cholesterol

•

Some of the cholesterol in

the intestine is modified by

bacteria before excretion.

The primary compounds

made are the isomers

coprostanol

 and

cholestanol

, which are

reduced derivatives of

cholesterol. Together with

cholesterol, these

compounds make up the

bulk of neutral fecal sterols.

33

Bile Acids and Bile Salts

•

Bile consists of a watery mixture of organic and

inorganic compounds.

•

Phosphatidylcholine and bile salts (conjugated

bile acids) are quantitatively the most important

organic components of bile.

•

Bile can either pass directly from the liver where

it is synthesized into the duodenum through the

common bile duct, or be stored in the gallbladder

when not immediately needed for digestion.

34

Structure of Bile Acids

•

The bile acids contain 24 carbons, with

two or three hydroxyl groups and a side

chain that terminates in a carboxyl group.

•

The bile acids are 

amphipathic

 in that the

hydroxyl groups are α in orientation (they

lie “below” the plane of the rings) and the

methyl groups are β (they lie “above” the

plane of the rings). Therefore, the

molecules have both a polar and a

nonpolar face, and can act as 

emulsifying

agents

 in the intestine, helping prepare

dietary triacylglycerol and other complex

lipids for degradation by pancreatic

digestive enzymes.

35

Synthesis of Bile Acids

•

Bile acids are synthesized

in the liver by a multistep,

multiorganelle pathway

•

The most common

resulting compounds,

cholic acid (a triol) and

chenodeoxycholic acid (a

diol), are called “primary”

bile acids.

36

Synthesis of Bile Salts

•

Before the bile acids leave the

liver, they are conjugated to a

molecule of either 

glycine

 or

taurine

 by an 

amide bond

between the carboxyl group of

the bile acid and the amino

group of the added compound.

•

These new structures include

glycocholic and glycocheno-

deoxycholic acids, and

taurocholic and taurocheno-

deoxycholic acids

37

Lipoproteins

38

Plasma Lipoproteins



The plasma lipoproteins are

spherical

 macromolecular

complexes of 

lipids

 and specific

proteins 

(apolipoproteins or

apoproteins).



Lipoproteins function:

•

The main role is the delivery of fuel

to peripheral cells.

•

to provide an efficient mechanism

for transporting their lipid contents

to (and from) the tissues.

•

to keep their component lipids

soluble as they transport them in

the plasma.

39

Plasma Lipoproteins



The lipoprotein particles include:

•

chylomicrons (CM),

•

very-low-density lipoproteins (VLDL),

•

low-density lipoproteins (LDL),

•

high-density lipoproteins (HDL).



They differ in lipid and protein

composition, size (range from 10 to

1200 nm), density, and site of origin.



[Note: Although cholesterol and its

esters are shown as one component in

the center of each particle, physically

cholesterol is a surface component

whereas cholesteryl esters are located

in the interior of the lipoproteins.]

40

Apolipoproteins



Apolipoprotein are primarily located on the 

surface

 of

lipoprotein particles.

•

Apolipoproteins are divided by 

structure

 and 

function 

into

five major classes

, A, B, C, D, and E, with most classes

having 

subclasses

. For example, apolipoprotein (or apo) A-I

and apo C-II.



Functions:

•

providing recognition sites for cell-surface receptors

•

they help maintain the structural integrity of lipoproteins

•

serving as activators or coenzymes for enzymes involved in

lipoprotein metabolism.

•

[Note: Functions of all of the apolipoproteins are not yet

known.]

41

Composition of plasma lipoproteins

•

Lipoproteins are composed of 

a

neutral lipid core 

(containing

triacylglycerol and cholesteryl esters)

surrounded by a 

shell of amphipathic

apolipoproteins, phospholipid, and

non-esterified (free) cholesterol.

•

These amphipathic compounds are

oriented so that their polar portions

are exposed on the surface of the

lipoprotein, thus making the particle

soluble in aqueous solution.

•

The triacylglycerol and cholesterol

carried by the lipoproteins are

obtained either from the diet

(exogenous source) or from de novo

synthesis (endogenous source).

42

Size and density of lipoprotein

particles

•

Chylomicrons are the lipoprotein

particles lowest in density and

largest in size, and contain the

highest percentage of lipid and the

lowest percentage of protein.

•

VLDLs and LDLs are successively

denser, having higher ratios of

protein to lipid.

•

HDL particles are the densest.

43

Chylomicrons

•

Chylomicrons are the largest and

least dense of the lipoproteins.

•

These 1000-nanometer particles

originate in the intestinal mucosa.

•

 Their function is to transport

dietary triglycerides and

cholesterol absorbed by the

intestinal epithelial cells.

•

Chylomicrons contain about 1-2%

protein, 85-88% triglycerides,

~8% phospholipids, ~3%

cholesteryl esters and ~1%

cholesterol.

44

very-low-density lipoproteins (VLDL)

•

Very low density lipoproteins are

approximately 25-90

nanometers in size.

•

produced primarily by the liver

with lesser amounts contributed

by the intestine

•

VLDL contains 5-12% protein,

50-55% triglycerides, 18-20%

phospholipids, 12-15%

cholesteryl esters and 8-10%

cholesterol.

•

leaves a residue of cholesterol in

the tissues during the process of

conversion to LDL.

45

low-density lipoproteins (LDL)

•

Low density lipoproteins (bad

cholesterol) are smaller than VLDL,

approximately 26 nanometers.

•

LDL contains 20-22% protein, 10-15%

triglycerides, 20-28% phospholipids,

37-48% cholesteryl esters, and 8-10%

cholesterol.

•

LDL is produced by the liver.

•

LDL and HDL transport both dietary

and endogenous cholesterol in the

plasma, but LDL is the main

transporter of cholesterol and

cholesteryl esters and makes up more

than half of the total lipoprotein in

plasma.

46

high-density lipoproteins (HDL)

•

High density lipoproteins (good cholesterol)

are the smallest of the lipoproteins. HDL

particles have a size of 6-12.5 nanometers.

•

HDL contains approximately 55% protein, 3-

15% triglycerides, 26-46% phospholipids, 15-

30% cholesteryl esters, and 2-10%

cholesterol.

•

HDL is produced in the liver and intestine .

•

HDL contains a large number of different

proteins including apolipoproteins such as

apo-AI (apolipoprotein A1), apo-CI, apo-CII,

apo-D, and apo-E.

•

The HDL proteins serve in lipid metabolism,

complement regulation, and participate as

proteinase inhibitors and acute phase

response to support the immune system

against inflammation and parasitic diseases.

47

LDL 

vs

 HDL

48

Plasma Lipoproteins

•

In humans, the transport

system is less perfect than

in other animals and, as a

result, humans experience a

gradual deposition of lipid—

especially cholesterol—in

tissues. This is a potentially

life-threatening occurrence

when the lipid deposition

contributes to plaque

formation, causing the

narrowing of blood vessels

(atherosclerosis).

49

Biological Membranes

50

Biological Membranes

•

Biological membranes are

thin, fluid structures that

form the boundary

between the exterior and

interior of the cell, as well

as between different

cellular compartments.

•

Biological membranes are

made of three major

components: 

lipids

,

proteins

, and 

sugars

.

51

Fluid Mosaic Membrane Model

•

Membrane structure according to

the famous “

fluid mosaic

membrane model

” of Singer and

Nicolson is described as a sea of

lipids with protein icebergs.

•

Nowadays, it has been believed

that biological membranes are

crowded and much more complex

dynamic systems, consisting of

lipids assembled into patches that

have different protein

composition than the surrounding

membrane. These patches can

vary in thickness and fluidity.

52

History of Fluid Mosaic Model

53

Functions of Biological Membranes

•

Form cell’s boundary.

•

Control the selective transport of substances in and out of

cells (transport of nutrients and keep out unwanted molecules

and toxic material).

•

Allow passage of water

•

Maintain intracellular pH, ionic concentration

•

Hold the cells together by cell: cell interactions.

•

Role in cell recognition and adhesion.

•

Control the signaling and the communication between cells.

•

provide a unique environment for protein-protein and

protein-lipid interactions.

54

Structure of Biological Membranes

•

All biomembranes of eukaryotes and eubacteria have a

common general structure, in which two-layered sheets of

lipid molecules have protein embedded in them

(Archebacteria have membranes that are monolayers but look

and behave like bilayers).

•

Non-covalent interactions are between lipids: lipids, lipids:

proteins and proteins: proteins

•

Sugars are attached by covalent bonds to some of the lipid

and protein molecules. They are found on one side of the

membrane only (carbohydrate moieties are always outside

the cell).

•

Specific function of each membrane depends on the

membrane proteins that are present in that membrane.

55

Lipid Bilayer

•

Membrane lipids are 

amphipathic

molecules consisting of a hydrophilic

section (the polar head) and a

hydrophobic section (the

hydrocarbon tail).

•

They 

self-assemble 

into a bilayer

structure in an aqueous environment

where the hydrophobic tails point

towards the interior facing each

other, while the hydrophilic head

groups face the aqueous exterior on

each side of the bilayer. 

By this way,

the contact between the tails and

water is minimized.

•

The thickness of lipid bilayers is

typically about 5-10 nm.

56

Lipid Bilayer

57

•

The major classes of lipids present in biological membrane

are:

1.

Fatty Acids.

2.

Glycerophospholipids (the most abundant class of lipid

molecules found in cell membranes).

3.

Sphingolipids (the second major class of lipid found in cell

membranes).

4.

Sterols (cholesterol).

•

The other lipids are:

5. Galactolipids and Sulpholipids present specifically in thylakoid

membranes in chloroplasts.

6. Glycerol Dialkyl Tetra Ether lipids present only in

Archaebacteria.

Lipid Bilayer

58

Membrane Proteins

59

•

Although the basic structure of biological membranes

is provided by the lipid bilayer, membrane proteins

perform most of their specific functions.

•

Proteins give each type of membrane in the cell its

characteristic functional properties.

•

Because lipid molecules are small compared with

protein molecules, there are always many more lipid

molecules than protein molecules in membranes.

•

The outer membrane of a cell, the plasma membrane,

typically consists of about 50 lipid molecules for each

protein molecule in a membrane that is 50% protein by

mass (w/w; molar ratio of ~50:1).

Protein:Lipid Ratio



Protein:lipid ratio in the membrane depends

on the function.

•

Pure lipid: insulation (neuronal cells).

•

Myelin (Schwann cell) membrane has 18%

protein (phospholipids are great insulators).

•

Mitochondrial membrane is 76% protein (has

many transporters and enzymes)

60

Membrane Proteins



Membrane proteins can be divided into two types:

•

Integral membrane proteins.

•

Peripheral membrane proteins.

61

Integral Membrane Proteins



Integral membrane proteins:

•

insoluble in water.

•

permanently 

embedded in lipid

bilayers.

•

portions

 of these proteins are in

van der Waals

 contact with the

hydrophobic region

 of the

membrane.

•

Integral membrane proteins may

be 

exposed

 either to the 

exterior

surface of the membrane or to

the 

interior 

compartment, or they

may 

span 

(cross)

the bilayer

completely.

62

Peripheral Membrane Proteins



Peripheral membrane

proteins:

•

usually water soluble.

•

adhere temporarily to the

lipid bilayer or to integral

membrane proteins by

various interactions (weakly

bound) such as

hydrophobic, electrostatic

and other types of non-

covalent interactions.

•

may be attached to either

the interior or exterior

surface of the bilayer.

63

Pore- and Channel- Forming Proteins

and Peptides

•

Most integral proteins are

transmembrane proteins which go from

one side of a membrane through to the

other side of the membrane, function

as gateways to deny or permit the

transport of specific substances across

the hydrophobic barrier of cellular

membrane to get into the cell or out of

the cell as in the case of waste

byproducts.

•

Pore-forming molecules are ranging

from small 

peptides

 that can self-

assemble to pores with weak selectivity

for specific ions to large

transmembrane 

proteins

 that regulate

the passage of small charged molecules.

64

Micelles, Bilayers and Liposomes

•

An inherent property of the

lipid molecules is to expel

water and close upon itself.

•

When salts of fatty acids or

soap molecules or

phospholipids are added

drop wise to aqueous

medium (water), they form

monolayers initially, as the

hydrophilic head interacts

with water at the air -water

interface and the

hydrophobic tail faces

outwards to the air.

65

Micelles

•

In aqueous solution (water),

amphiphilic molecules, such as

soaps and detergents, 

can

form 

monolayers

 on the air-

water interface and can also

form 

micelles

.

•

Fatty acids (one tail).

•

max 20 nm.

•

the hydrophilic heads interact

with the aqueous medium and

the tails with each other with

some aqueous solution

trapped inside the micelles

which are thermodynamically

stable.

66

Bilayers

•

Soap bubbles are the

bilayers of soap molecules.

•

The hydrophobic tails 

of

the soap molecules are

packed beside one another

and point into the

hydrophobic air. 

The

hydrophilic heads

 of the

soap molecules surround a

thin shell of water that

packed in the center of the

bilayer.

67

Bilayers

•

Unlike soap bilayers,

l

ipid bilayers are

oriented with their

hydrophobic tails inside

the bilayers

 w

hile the

hydrophilic heads are in

contact with  the

aqueous solution on

each side.

•

Charged polar head

group of two layers

p

rovides both  surfaces

with an 

ionic coat

.

68

Liposomes

•

A

 suspension of

phospholipid in water

forms multilamellar

vesicles that have an

onion-like arrangement

of lipid bilayer.

•

Phospholipids bilayers

that

 e

nclose an

aqueous compartment

69

Hormones

70

Hormones



Hormones

 are 

chemical signals 

that are secreted into

the circulatory system and communicate regulatory

messages within the body.



secrete by 

endocrine glands.



reach all parts of the body, but only 

target cells 

are

equipped to respond.



recognized by the presence of 

hormone receptors 

on:

•

The outside of the plasma membrane or

•

In the cytoplasm.

71

Endocrine System

72



Endocrine glands

is a structure whose

primary function is to secrete hormones.



Endocrine Organs:

1.

Purely endocrine organs:

•

Pituitary gland

•

Pineal gland

•

Thyroid gland

•

Parathyroid glands

•

Adrenal glands

 (

Cortex and Medulla ).

2.

Endocrine cells in other organs

•

Pancreas

•

Thymus

•

Gonads

•

Hypothalamus

Hormones



There are two main types of hormones:

1.

Circulating hormones

2.

Local hormones

73

Circulating Hormones (Endocrines)

1. Circulating hormones (Endocrines):



Are hormones that diffuse into the blood and act

on distant target cells.



Most circulating hormones are synthesized and

secreted by specialized epithelial cells (endocrine)

located in structures called endocrine glands.



Some endocrine cells are not found in structures

limited to the production of hormones, For

example:

•

Enteroendocrine cells: 

are scattered among other

epithelial cells that line the digestive tract. They

secrete hormones involved in the digestive

process.

•

Neurohormones: 

secreted by neurons are called

neurohormones that are secreted by cells in the

hypothalamus.

74

Local Hormones

2. Local hormones:



Paracrines Hormones:

•

are chemical messengers that act on

nearby cells.

•

An example is 

histamine

 which is

released by Mast cells and damaged

tissue cells. It acts on nearby blood

vessels, causing them to dilate.



Autocrines Hormones:

•

are chemical messengers act on the

same cells that secreted them.

•

An example is interleukin-2 (IL-2).

75

How Hormones work?

•

The endocrine system secretes hormones that

coordinate 

slower

 but 

longer-acting

responses including reproduction,

development, energy metabolism, growth,

and behavior.

•

Hormones only influence cells that have

specific target receptors for that particular

hormone.

76

How Hormones work?



Mechanisms of hormone

release:

•

Humoral

:

 in response to

changing levels of ions or

nutrients in the blood.

•

Neural

:

 stimulation by

nerves.

•

Hormonal

: 

stimulation

received from other

hormones.

77

Chemistry of Hormones

•

There are four principal classes of hormones:

1.

Steroids.

2.

Biogenic amines.

3.

Eicosanoids.

4.

Peptides and proteins.

78

1. Steroid Hormones



They are all derived from 

cholesterol

.



synthesized by the adrenal cortex, the gonads, and the

placenta.



exert their effects in two ways:

•

They bind directly to membrane receptors.

•

As they are fat-soluble, they pass through cell membranes (by

diffusion) where they attach to receptors in the cytoplasm.



Being water-insoluble, they circulate in the blood bound to

plasma proteins.



There are several types of steroid hormones:

•

Corticoids.

•

Sex Steroids.

79

1. Steroid Hormones

80

1. Steroid Hormones: Corticoids



Glucocorticoids

 (

mainly

Cortisol

, and also 

cortisone

and 

corticosterone

) 

are

released by the adrenal

cortex in response to stress.

•

They increase the

breakdown of fats and

proteins into glucose to

stop inflammation (immune

defence).



Mineralocorticoids 

(e.g.

aldosterone) are also

produced by the adrenal

glands and reduce salt

secretion in the kidneys.

81

1. Steroid Hormones: 

Sex Steroids



These are released mainly by the ovaries

and testes but also by the adrenal

glands.



The ovaries secrete:

•

Estrogens: 

Estradiol is produced in large

amounts in females and has feminising

effects, promoting female secondary

sexual characteristics, water retention,

calcium metabolism, sexual behaviour

and maternal behaviours.

•

Progesterone

 prepares the uterus for

the implantation of a fertilised ovum and

regulates the stages of pregnancy.

82

1. Steroid Hormones: 

Sex Steroids



The testes secrete:

•

Androgens:

 Testosterone is

produced in large amounts in

males and has masculinising

and defeminising effects;

maintaining male secondary

sexual characteristics and

promoting aggressive and

sexual behaviours.

83

2. Biogenic Amines

•

Biogenic amines are 

small, water-soluble

compounds.

•

synthesized from 

amino acids 

and act as

neurotransmitters and hormones in animals.

•

Hormones of this chemical type include the:

1. Thyroid Hormones.

2. Catecholamines.

3. Histamine.

84

2. Biogenic Amines Functions

•

sources of nitrogen and precursors for the

synthesis of hormones, alkaloides, nucleic

acids, and proteins.

•

influence the processes in the organism such

as the regulation of body temperature,

increase or decrease of blood pressure.

•

Some biogenic amines contribute to the flavor

and taste of food.

85

2. Biogenic Amines: Thyroid Hormones

•

The thyroid hormones,

thyroxine (T4) 

and

triiodothyronine (T3),

are 

tyrosine-based

hormones

 produced by

the thyroid gland.

•

Thyroid hormones are

unique biological

molecules in that they

incorporate iodine in

their structure.

86

2. Biogenic Amines: Thyroid

Hormones Functions

•

Control proteins, fats,

and carbohydrates

metabolism (

metabolic

rate

).

•

Regulate heart rate,

energy level, body

temperature, 

fetal and

childhood growth, and

central nervous system

(CNS) 

development

.

•

Stimulate Na

+

-K

+

 pumps.

87

2. Biogenic Amines: Catecholamines



Catecholamines are synthesized in the brain, in

the adrenal medulla, and by some nerve fibres.



Catecholamines are released into the blood when

a person is under physical or emotional stress.



The main catecholamines are:

•

Dopamine.

•

Norepinephrine (Noradrenalin).

•

Epinephrine (Adrenalin).

88

2. Biogenic Amines: Catecholamines

89

2. Biogenic Amines: Catecholamines

Functions



Mediates a variety of the central nervous system

functions such as cognition, emotion, and memory

processing.

•

Dopamine

 helps control include behavior, mental

health, and voluntary movement.

•

Norepinephrine

 controls alertness, emotions, sleeping,

dreaming and learning. It is also responsible for

increasing the heart rate and blood flow to some parts

of the body such as the heart.

•

Adrenaline,

 the flight or fight response hormone, is

largely responsible for the immediate reactions in

response to stress.

90

2. Biogenic Amines: Histamine



Histamine is derived from the amino acid histidine.



Histamine produced by:

•

Mast cells (typically found in areas such as the nasal passages,

mouth, and blood vessels).

•

Basophil (a type of white blood cells).



Its biological effects are usually seen only when it is released in large

amounts in the course of allergic and other reactions.

91

2. Biogenic Amines: Histamine

Functions



The histamine reaction in relation to the immune

response (in both allergic reactions and immune

reactions) serves two main functions:

•

It causes vasodilation.

•

It induces fluid secretion at the site of infection.



Histamine plays a role in gastric secretion by

helping to induce the production of acid in the

stomach.



helps to regulate sleep.

92

3. Eicosanoids



Eicosanoids are derived

from the 20-carbon

fatty acid.



They are synthesized by

all cells of the body



The three major types

of eicosanoids are:

•

Prostaglandins.

•

Leukotrienes

•

Thromboxanes

93

3. Eicosanoids Functions

•

Thromboxane 

constricts blood vessels, supresses

cyclic AMP, and promotes platelet aggregation.

•

Leukotrienes

 are involved in several immune-

mediated inflammatory reactions.

•

Prostaglandins

 are known to dilate arterioles and

capillaries (control blood pressure), relax vascular

smooth muscle, open the bronchi of the lungs,

enhance blood flow through the kidneys, increase

urinary volume as well as the excretion of sodium

ions, and cause contraction of gut muscle in

humans.

94

References

•

Biochemistry

(Lippincott´s Illustrated Reviews series) 

by Champe P, Harvey

R, and Ferrier D.

•

Clinical Chemistry by Bishop M, Fody E and Schoeff L.

•

Biochemistry, by Voet D and Voet J.

95