The document is an introductory lecture on medical physiology, focusing on the characteristics of living matter, cell structure, and the functions of various cellular organelles in eukaryotes, particularly human cells. It outlines the fundamental role of medical physiology in understanding normal bodily functions and homeostasis, emphasizing the dynamic processes of cells and organ systems. Additionally, it details the organization of cells, the cytoskeleton, and the importance of cellular components such as the plasma membrane, organelles, and their mechanisms in physiological activities.

1. Medical Physiology I
(HLS 122)
Prepared By;
Nathan G. Kiboi
Dept. of Medical Laboratory Sciences
S.E.KU
Lecture 1: Intro. to
Medical Physiology

2. Learning outcomes…,
• Brief Intro. and Dfn of Medical Physiology
• Familiarize with characteristics of living matter
• Understand the cell and cellular organelles in
eukaryotes:-
–The Human Cell (Dfn, Different shapes,
Locations and functions)
–Identify Cellular organization and structure
–Prominent cellular organelles and functions
–Identify the plasma membrane & properties

3. Introduction to Medical Physiology..,
The discipline: What is Medical Physiology?
• Dynamic study of normal life processes that deals
with the study of normal human body organ
functions
• Branch of Medical science that describes vital
functions of different organs, cells and
biomolecules, and changes the body undergoes
in the course of its activities
• Medical physiology provides knowledge on
mechanisms of life at organ, tissue, cellular and
molecular levels

4. Introduction to Medical Physiology Cont..,
The discipline cont: What is Medical
Physiology?
• Medical physiology attempts to explain the
specific characteristics and mechanisms of
the human body that make it a living being
• Also describes the contribution of specific
organ -systems to homeostasis
• The teaching of Medical Physiology forms a
basic part of the Medical students initial
educational training

5. THE CELL AND CELLULAR
ORGANELLES
(EUKARYOTES)

6. The Cell…,
• The basic living unit of the body is the cell
(fundamental working unit of all organisms)
• Represents the functional unit of Physiological
Processes
• Each organ is an aggregate of many different cells
held together by intercellular supporting
structures
• Each type of cell is specially adapted to perform
one or a few particular functions
• NB: The Type, Size and Shape of each specific cell
varies with function and location

7. Characteristics of Living matter…,
• Living matter is unique and associated or
characterized with specific functions:-
–Nutrition
–Growth and Development
–Respiration
–Locomotion
–Reproduction
–Excretion
–Irritability/Responsiveness to
stimuli/communication

8. 8
SINGLE CELL ORGANISMS
Examples:-
(i) Paramecium (ii) Protozoa (Amoeba)
(iii) Green Algae (iv) Bacteria (E. Coli)

9. Co-ordination Of Physiological Activity..,
• CELLS
• CELLS TISSUE
• CELLS ORGAN
• CELLS TISSUE SYSTEM
• CELLS ORGAN
• CELLS

10. The Human Cell..,
•A number of structures ie. organelles are common to
most cells

11. 11
Fig: DIFFERENT SHAPES OF CELLS…,
MUSCLE NERVE
NERVE
GLIAL

12. Bone Marrow cells (Blast cell; immature)
BLAST CELL

13. Megakaryocytes (Platelet precursors)..,

14. Red (RBC’s) and White (WBC’s)…,
RBC
Neutrophil
Large lymphocyte

15. Cell Organization & Structures..,

16. Arrangement of organelles in
mammmalian cell…,

17. 17
Functions Of The Various Organelles..,
• Storage of genetic blue print
• Transcription of messages
• Storage of coded messages for physiological
processes
• Directs synthesis and cell reproduction
• Synthesis of DNA
• Protein Synthesis
• Translation
• Protein Modification
• Post-translational modification
• Phospholipid synthesis
• Energy provision (ATP)
Nucleus
Ribosomes, ER,
and Mitochondria

18. 18
Functions Of The Various Organelles Cont..,
• Packaging of proteins, lipids and
amines into secretory granules
or vesicles
• Phospholipid synthesis
• Initial Glycosylation of proteins
• Carboxylation
• Folding & assembly of multi-
chain proteins
• Post-translation modification of
polypeptides
Golgi Apparatus,
Secretory Vesicles,
&
Rough E. Reticulum

19. 19
Functions of the various organelles cont..,
• Transport of proteins, organelles and other cell
parts/molecules within the cell: Performed by:-
• Cytoskeketon
- Microtubules
- Microfilaments
- Intermediate Filaments
- Molecular Motors; are contractile proteins that
comprise of kinesin, dynein, and myosin
Cytoskeleton
filaments

20. Functions of the various organelles cont..,
• Cytoskeleton:- All cells possess a
cytoskeleton; a system of fibers that
maintains cell structure but also permit
change of shape & movement
• Cytoskeleton composition: primarily made of
microtubules, intermediate filaments, and
microfilaments
• In addition, proteins and organelles move
along microtubules and microfilaments from
one part of the cell to another, propelled by
molecular motors

21. Functions of the various organelles cont..,
Microfilaments :-
• Are long solid fibers with a 4-6 nm diameter
that are made of actin
• Although actin is most often associated with
muscle contraction, its present in all types of
cells and most abundant protein in
mammalian cells
• Actin filaments interact with integrin
receptors and form focal adhesion complexes
that serve as traction points over which the
cell pulls itself

22. Microtubules :-
• Are long hollow structures with 5nm walls
surrounding a cavity 15 nm in diameter
• Microfilaments are made of two globular protein
sub-units: alpha (α) and beta (β)-tubulin
• Gamma (γ)-tubulin is associated with production of
microtubules by the centrosomes
• Microtubules interact with GTP (guanosine
triphosphate) to facilitate their formation
• Microtubules provide the tracks along which several
different molecular motors move transport vesicles,
organelles eg. secretory granules and mitochondria
from one part of the cell to another

23. Intermediate filaments:-
• Are 8-14 nm in diameter and made of various sub-
units
• Some intermediate filaments connect the nuclear
membrane to the cell membrane
• They also form a flexible scaffolding for the cell and
help it resist external pressure
• In absence of intermediate filaments, cells rapture
more easily and blistering of skin is common
• Proteins making up intermediate filaments are cell-
type specific & hence frequently used as cellular
markers eg. cytokeratin is expressed in epithelial cells
and vimentin is an intermediate filament in fibroblasts

24. Molecular motors :-
• There are three super-families of molecular motors:
kinesin, dynein, and myosin
• There is extensive variation among super family
members allowing for specialization of function eg.
cytoskeleton filament type, choice of cargo and/or
direction of movement
• Molecular motors move proteins, organelles, and other
cell parts collectively termed “cell cargo” to all parts of
the cell. They attach cargo at one end of the molecule
and to microtubules or actin polymers to the other end
• Through enzymatic action of ATPases, molecular motors
convert energy of ATP into movement along the
cytoskeleton, thus carrying their cargo along

25. 25
• Lysis or digestion of debris and toxic substances:-
- Lysosomes
- Phagosomes
- Peroxisomes
a) Lysosome; Interior is maintained acidic by action of
proton pump (ie. H+
Atpase enzyme); near pH 5
•Lysosomes contain > 40 types of hydrolytic enzymes eg.
phosphatase [substrate; phosphate], collagenase
[collagen], ribonuclease [RNA], deoxyriboneclease [DNA,
arylsufatase [sulfates]
•The enzymes are all acid hydrolases functioning best at
acidic pH of the lysosome

26. 26
b) Peroxisomes; are surrounded by a membrane and
contain enzymes that either produce H202 (oxidases)
or break it down (catalases)
•Proteins are directed to the peroxisome by a unique
signal sequence with the help of peroxins
•These are peroxisome specific proteins concerned
with transport of substances into and out of the
peroxisome matrix
•Peroxisomes can form by budding of endoplasmic
reticulum, or by division
Functions of the various organelles cont..,

27. 27
Centrosomes:-they are microtubule-organizing
centres (MTOC’s) that contain γ-tubulin
•Are located near the nucleus in the cytoplasm of
eukaryotic cells
• The centrosome is made of 2 (two) centrioles and
surrounding amorphous pericentriolar material
•Centrioles are short cylinders arranged at right
angles to each other
•Microtubules in groups of three run longitudinally
in the walls of each centriole
• Regulation of Mechanism for Direction of Motion

28. 28
Functions of the various organelles cont..,
• Cysternae: are projections from
the cell
• Cysternae function in:-
-Movement of Particles
-Intracellular Connections and
Communication

29. 29
Functions of the various organelles cont..,
• Proteins functioning in Intercellular
Communication:
- Enzymes in Second Messengers systems
(adenylyl cyclase, guanylyl cyclase)
- Calcium Transport Channels
- Receptors e.g. G. Proteins coupled
receptors, Tyrosine kinase receptors
- Binding Proteins
- ADP, ATP, GDP, GTP (Adenosine
triphosphate, guanosine triphosphate)

30. 30
Functions of the various organelles cont..,
• Inclusion Bodies & Artifacts. Are commonly
observed in Micrographs and include:-
- Organic and inorganic particles
- Lipids Droplets
- Debris from worn out organelles
- Intracellular Bacteria e.g. Gonococcus
- Parasites e.g. Plasmodium, Leishmania
Donovani Bodies etc.

31. Fig: Nucleus…,

32. Fig: Ribosomes..,

33. Ribosomes Cont..,

34. Fig: Endoplasmic Reticulum…,

35. Fig: Golgi apparatus..,

36. Microtubules…,

37. Kinesins

38. Dyneins

39. Fig: The mitochondrion…,

40. The mitochondrion cont..,

41. Mitochondrial compartments…,

42. Mitochondrial compartments cont..,
• The mitochondrial matrix contains Pyruvate
Dehydrogenase and enzymes of Krebs Cycle, plus
other pathways such as fatty acid oxidation
• The mitochondrial outer membrane contains large
channels, similar to bacterial porin channels,
making the outer membrane leaky to ions and
small molecules
• Enzymes are localised on the inner membrane but
project into the matrix where they carry out
cellular respiration or aerobic respiration
(OXIDATIVE PHOSPHORYLATION)

43. 43
For example:- Acetyl Co-
enzyme A functions as:-
input to the Krebs Cycle,
where the acetate moiety is
further degraded to CO2.
donor of acetate for synthesis
of fatty acids, ketone bodies,
and cholesterol.
Acetyl CoA:- a product of the
Pyruvate Dehydrogenase
reaction, is a central compound
in metabolism. The "high
energy" thioester linkage makes
it an excellent donor of the
acetate moiety
XXXI

44. Mitochondrial membranes…,
OUTER MEMBRANE
•Much like plasma membrane but has
porins
•Protein: Phospholids = 1:1 by weight
Ratio
•Leaky internal Channels that allow
permeability of molecules
•Active transport for larger molecules
•Lesser surface area compared to inner
membrane
INNER MEMBRANE
-No porins
-Protein : phospholipid = 3:1 by weight ratio
Phospholipid bilayer and proteins
100 different polypeptides
-Highly impermeable
-Special membrane transporters
Rich in Cardiolipin
-Surface area is 5X more than outer
membrane

45. Mitochondria Cont..,
• Other Metabolic functions of mitochondria in
addition to converting organic materials into
cellular energy (ATP)
–Apoptosis – programmed cell death
–Cellular proliferation
–Regulation of cellular redox state
–Heme synthesis
–Plays role in Steroid synthesis
–Detoxifying ammonia in liver cells only

46. Fig: Lysosome..,

47. Fig: Centriole…,

48. Plasma/cell membrane…,
• Its composed of phospholipids and proteins. It
acts as a selective barrier to maintain
composition of the intracellular environment
• Proteins and lipids can move freely in the plane
of the membrane, thus producing the fluid
nature of the membrane
• Membrane lipids can be classified into three (3)
major classes:-
–Phospholipids
–Cholesterol
–Sphingolipids

49. Plasma/cell membrane cont…,
a)Phospholipids
• Are the most abundant membrane lipids
• They have a bipolar (amphipathic) nature,
containing polar/hydrophilic charged heads
and hydrophobic/water insoluble non-
charged tails
• The hydrophobic tails face each other,
forming a bilayer and exposing the polar
head group to the aqueous environment
on either side of the membrane

50. Plasma/cell membrane cont…,
b)Cholesterol
• Is the predominant sterol
(unsaturated alcohol found in
animal and plant tissues) in humans
cells; it increases the fluidity of the
membrane by inserting itself
between phospholipids, improving
membrane stability

51. Plasma/cell membrane cont…,
c) Sphingolipids
• Have an amphipathic structure
similar to phospholipids that allows
them to insert into membranes
• Sphingolipids can be modified by
the addition of carbohydrate units
at their polar end, creating
glycosphingolipids in brain cells

52. Plasma/cell membrane cont…,
• Membrane proteins:- those that
span the lipid bilayer are referred to
as integral membrane proteins,
whereas those associated with
either the inner or outer surface of
the plasma membrane are known
as peripheral or lipid-anchored
membrane proteins

53. Plasma/cell membrane cont…,
• Majority of integral membrane
proteins span the bilayer through
formation of α-helices, a group of
20-25 amino acids twisted to
expose the hydrophobic portion of
the amino acids to the lipid
environment in the membrane

54. Plasma/cell membrane cont…,
• On the other hand, protein content of
membranes varies from <20% for
myelin (helps in propagation of action
potential or nerve impulses), to >60% in
liver cells (responsible for metabolic
activities)
• Notably, cellular proteins act as
receptor sites for:- antibodies, hormone
neurotransmitters, & drug binding sites

55. • Membrane proteins cont:- Enzymes bound to cell
membranes are often involved in
phosphorylation reactions of various metabolic
intermediates
• Carrier proteins located in the membrane
transport materials across the cell membrane
• Membrane channels allow polar charged ions
(Na+, K+, CL-, and Ca2+) to flow across the
plasma membrane. Ion channel gates regulate
passage of ions and are controlled by voltage
(voltage gated), ligands (ligand gated), or
mechanical means (mechanically gated)

56. Properties of the plasma/cell membrane.,
(i) Composition:
• Molecular composition- Lipid: Protein Ratio (70:
30) respectively
• Hydrophobic (lipophylic) fatty acid chains
• Hydrophylic (water soluble/polar) phosphate
heads
(ii)Major phospholipid compounds:
– Phosphatidyl choline
– Phosphatidyl ethanolamine
– Others Sphingomyelins : Lecithin
glycosphingolipids

57. (iii)Protein component:
STRUCTURAL CLASSIFICATION
• Primary, secondary, tertiary & quartenary structures
FUNCTIONAL CLASSIFICATION
1. Structural Proteins
Carrier Proteins
2. Pumps – involved in Active Transport
3. Ionic channels – involved in Facilitated Diffusion
4. Receptors eg. G-proteins
5. Enzymes – Catalyzing Reactions

58. iv) Properties: nature
• Presence of functional or biological boundary
limiting membrane (plasma membrane)
• Semi-permeable selectivity to various
substances
• Has electrical polarity difference across its
thickness; propagates electrical activity (inside -
70 mV charge compared to outside)
• Unstable, undergoing depolarization and
depolarization (k+, Na+, Ca2+ etc.)
• Has a mean resting membrane Potential
• Excitable – Action Potential

59. v) Properties; communication
• Presence of receptors at different
locations
• Cell adhesion molecules to neighboring
cells
• Intercellular connections for distant
communication
• Presence of GAP JUNCTIONS
Properties of plasma/cell membrane cont.,

60. PROPERTIES OF THE CELL MEMBRANE
(i) Contains the cell contents within the cell
(ii) Protects the contents within a defined
environment
(iii) Ensures ;Turgidity, Rigidity & Shape of cell
(iv) Selective Permeability – Transport
• FUNCTIONS OF THE CELL MEMBRANE..,

61. v. Biological Activity – enzymes (functional)
and receptors (structural)
v. Generation and propagation of electrical
potentials
vi. Both cellular and intercellular
communication
vii. Special transport e.g. exocytosis /
endocytosis
Functions Of The Cell Membrane Cont..,

62. •Next Lecture Class:-
–Transport mechanisms Across
Cell Membranes
–NB:- Cell Membrane Resting
Potentials (Read and make short
notes; for collection during 4th
week) Max 2 foolscaps…..

63. •
End …
Thank
you…