Transcript Human cell physiology

Human Cell Biology and
Physiology
Timothy Billington PhD
CLOUD OF KNOWLEDGE
4th Formative test
1. In bone, there are which 4 types of cells? What are each of their functions?
2. Where would you find the linear proteins Myosin and Actin?
3. We know that muscle cells produce large amounts of ATP, even at rest. The energy in ATP is then
stored in the phosphate bond of another compound. What is this compound? Explain energy transfer
using simple equations
4. What name is given to the voltage across a muscle cell sarcolemma?
5. Inside a muscle cell there are long structures running the length of the cell. Name them.
6. Which filamentous structures do you find in a sarcomere? Explain what happens in a sarcomere when
a muscle contracts
7. What event initiates a contraction in a leg muscle?
8. What is the neuromuscular junction? What sequence of events happens in an NMJ?
9. What is a cholinergic synapse? Name the 4 events which occur at such a synapse.
4th Formative test continues
10. What is an Axon? What is the Myelin sheath and what does it do?
11. What is a Synapse?
12. Describe the distinctive structural features of a Neuron
13. What is an Action Potential?
14. Which ionic movements are occurring during a Depolarisation?
15. What happens when the peak transmembrane voltage is reached?
16. Which ionic events are occurring during Repolarisation?
17. Bone structure is continuously broken down and then replaced as growth occurs. This process is a
balance of the activities of 2 types of bone cells. Which are they?
18. The matrix of bone consists of a metal salt. Name the salt.
QUICK REMINDER OF WHAT WE WERE LOOKING AT LAST WEEK
Cells in the Immune System
LYMPHOCYTES
CLASSES of LYMPHOCYTE CELLS in the IMMUNE SYSTEM
T - CELLS
CYTOTOXIC T-CELLS
B - CELLS
NK CELLS
Differentiate into
‘PLASMA’ CELLS
NATURAL
KILLER CELLS
Attack foreign cells
infected by viruses
MEMORY T-CELLS
Respond to
previously
encountered
Antigens
Make & secrete
Antibodies in
response to
antigenic
compounds
Perform
immune
surveillance
Attack cancer
cells in normal
tissues
Week 6 (Nov 10) begins here
ACTION OF NK CELLS IN THE IMMUNE SYSTEM
Target
NK
NK cell detects a foreign cell and adheres to it. NK cell has detected that the foreign cell (Target) has
unusual components in its cell membrane
Golgi Apparatus [ )))) ] in NK is re-aligned to face the target cell. GA produces a flood of enzymes
(perforins, ) which move toward the target cell’s membrane.
))))
((((
Week 6 begins here
ACTION OF NK CELLS IN THE IMMUNE SYSTEM
Perforins are (exocytosed) released by the NK, and perforate the Target cell membrane. The
enzymes then destroy Target cell membrane proteins and kill the Target cell
Debris from Target
cell.
EXOCYTOSIS: process by which materials are actively moved out of a cell
vesicle
cytoplasm
Material to be moved out of cell, is packaged in a membrane-bound vesicle in the cytoplasm
Vesicle moves to the cell membrane, combines with it and then releases its contents
In the NK story above, the vesicle contained enzymes called perforins
ENDOCYTOSIS: process by which materials are moved into a cell
1
2
3
1. Cell detects a substance in the extracellular fluid
2. Cell membrane envelops the substance, forming a membrane bound vesicle
3. Vesicle buds off and enters the cytoplasm
WHAT IS AN ANTIGEN?
An antigen is a substance ( protein, carbohydrate, nucleic acid or lipid) that is produced by a
foreign body.
Pollen grains are examples of antigens.
Our immune system cells ( B-CELLS ) detect that the substance is foreign
B-cells make an Antibody specific to the Antigen
WHAT is the STRUCTURE of an ANTIBODY MOLECULE?
Antigen
binding sites
Pale shading indicates
the structures common
to all antibody
molecules. They are
invariant.
Heavy shading indicates Antigen
binding sites have variable protein
structure. In this way they can be made
specific for a given antigen.
Light protein chain
Heavy protein chain
TWO most important & frequent processes in the immune system
manufacture of Antibody molecules
Ab
formation of Antigen-Antibody complexes
AgAb
B-CELLS
RESPOND to ANTIGENS by MANUFACTURING SPECIFIC ANTIBODY PROTEINS
Antigen – Antibody complex
Antigenic
Determinants
‘Key and lock’ analogy
Antigen-Antibody complex is then destroyed by proteinases ( hydrolytic enzymes )
ANTIGEN-ANTIBODY BINDING
Antigen shapes are called EPITOPES
Corresponding binding site shapes on Antibodies are called PARATOPES
3 Antigens
3 different antibodies
MEMORY B- CELL
Retains information about the shape and type of antigens it comes into contact with
Memory cells:
remain in the tissue
recognize an antigen that they have ‘seen’ previously [ “IMMUNE MEMORY”]
produce the required antibody which is specific for that antigen
antigen-antibody complex is formed
the complex is then destroyed by proteinase enzymes
Nett result
ANTIGEN IS DESTROYED
Let’s return to GASEOUS EXCHANGE
We have seen that Oxygen diffuses from the blood stream to the cells
AND THAT
Carbon Dioxide diffuses from cells to the blood stream
Capillary
CELL
DIFFUSION of GASES
ALWAYS
DOWN THEIR CONCENTRATION GRADIENT
IN LUNGS
Oxygen diffuses from AIR to BLOOD
Carbon Dioxide diffuses from BLOOD to AIR
IN TISSUES
Oxygen diffuses from BLOOD to CELL
Carbon Dioxide diffuses from CELL to BLOOD
Concentration gradients for gaseous diffusion
For any gas, the concentration is measured as Partial
ppO2 in Air in the lung alveoli is
>
Pressure (pp) in mm Hg
ppO2 in blood in the lung capillaries
oxygen will diffuse from Air to Blood
AIR IN / OUT
Blood In
Respiratory membrane
De-oxygenated blood
Oxygenated blood
ALVEOLUS
Blood Out
Concentration gradients for gaseous diffusion
ppCO2 in the Cell
Question:
> ppCO2
in Blood
In which direction will Carbon Dioxide diffuse??
Now let’s look at some actual partial pressure examples
For all gases, the greater the difference in pp between two environments, the faster will be the diffusion.
The ALVEOLI are the smallest air spaces in the lung. Exchange of gases with Air only takes place there.
In the lung
ALVEOLUS
Alveolar Air
ppO2 = 100
ppCO2 = 40
ppO2 =
40
ppCO2
= 45
Lung capillary blood
Respiratory membrane
[ 1 cell thick ]
Question: Which arrow represents Carbon Dioxide
diffusion?
Now let’s move to a tissue in the body, perfused by capillaries, and look at a typical cell:
Body tissue capillary
pp O2 = 95
pp CO2 =
40
Respiratory membrane
Question: Which arrow indicates
diffusion of Oxygen?
CELL
pp O2 = 40
pp CO2 = 45
HOW is CARBON DIOXIDE TRANSPORTED in the BLOODSTREAM?
CO2 diffuses into the capillary blood stream from aerobically metabolising cells in peripheral tissues
For every 100 molecules of diffused CO2
7 diffuse into the plasma and dissolve
93 diffuse into red blood cells
23 bind to Hb and form carbamino-haemoglobin Hb.CO2
70 react chemically with water to form carbonic acid (hydrogen carbonate)
H2 O + CO2
Hydrogen carbonate
carbonic anhydrase
Question: What do we mean by aerobic?
Question:
What do we mean by anaerobic?
Example: interior of muscles. [Lactic acid is an end product]
Let’s review briefly the material on CHEMORECEPTORS
CHEMORECEPTORS
= Neurons which are sensitive to minute CHANGES in the concentration of specific
chemicals in body fluids
eg carbon dioxide levels in blood, acidity (hydrogen ion levels) in blood
Neurons are in the walls of the Carotid arteries and monitor blood going to the brain
Also in the wall of the Aorta, where they monitor blood going to the periphery
We are not consciously aware of the action of chemoreceptors because they do not
send action potentials to the sensory cortex of the brain
CHEMORECEPTORS continue
when the chemoreceptors for Carbon Dioxide register a CHANGE to an abnormally
high pp of this gas in blood
cells in the respiratory control centres in the base of the brain send an
action potential to the diaphragm and thoracic cavity muscles which leads
to deeper inhalation and fuller exhalation
by exhaling more fully, CO2 is blown off in the alveoli and so the normal CO2 pp in the
blood is re-established .
Question:
As the depth of inhalation is increased, which dissolved gas would you expect to increase its pp
in capillary blood?
HOMEOSTASIS: A VERY IMPORTANT CONCEPT
Maintenance of a constant
internal environment in the body
The pp Carbon Dioxide control mechanism is a good example of a homeostatic regulation
Think of homeostasis in terms of a familiar analogy
Maintenance of a constant
room temperature
ROOM TEMPERATURE
CONTROL
RECEPTOR =
GETTING
TOO HOT
INFORMATION IS
SENT
THERMOMETER
CONTROL
CENTRE =
THERMOSTAT
HOMEOSTASIS
NORMAL ROOM
TEMPERATURE
SET POINT 20C
EFFECTOR =
TEMP
FALLS
AIR CONDITIONER
TURNS ON
COMMAND IS
SENT
HOW IS BODY TEMPERATURE REGULATED?
RECEPTORS =
GETTING
TOO HOT
TEMPERATURE
SENSOR NEURONS IN
SKIN and BRAIN
HOMEOSTASIS
INFORMATION IS SENT
via action potentials
CONTROL CENTRE
= BRAIN
Thermoregulation
in hypothalamus
(set point 37 C)
NORMAL
BODY
TEMPERATURE
EFFECTORS =
SWEAT GLANDS IN SKIN
INCREASED SECRETION
TEMP
FALLS
BLOOD VESSELS IN SKIN
DILATE
COMMAND IS
SENT via action
potentials
Question:
To alter the set point on a room thermostat you simply choose a point on the dial
How would you alter the set point of the sensitive cells in the hypothalamus?
BLOOD: FUNCTIONS and PHYSICAL PROPERTIES
FUNCTIONS include:
Transport
nutrients, dissolved gases, hormones, wastes
Regulation
acidity and ionic composition
Fluid Loss restriction
clotting @ sites of injury
Defence against toxins, antigens & pathogens white cells & antibodies
Body temperature regulation
Question:
absorbs & redistributes heat generated by active skeletal
muscles
Which 2 dissolved gases are of particular clinical interest?
Which 4 ions?
BLOOD continues
PROPERTIES
Physical
Composed of Plasma and Formed Elements (Cells)
Temperature
@ ~ 38 C
< 0 .1%
Centrifuged
whole blood
Viscosity
About 5x water, [ 5x as sticky, 5x as cohesive and 5x as resistant to flow ]
Chemical
Slightly alkaline, p H range: 7.35 - 7.45
ANTIGENS on the OUTER SURFACE of ERYTHROCYTES DETERMINE BLOOD GROUPS
ABO blood types are genetically-determined
Cells:
A antigen
Type A
Plasma: B antibody
B antigen
Type B
A antibody
Both antigens
Type AB
No antibodies
No antigen
Type O
B and A antibodies
TRANSFUSIONS of BLOOD:
GIVEN FACT:
Antigen F
AS YOU ALREADY KNOW:
+ Antibody to F
Ag
+
Antigen F-Antibody F complex (ppt)
Ab
Observation: Type A person is transfused with Type B blood
AgAb complex (precipitate)
pptn of whole blood system
and patient is then deceased
Exercise:
Explain what events happened in the above
Question:
Type B person is transfused with Type B blood. What happens?
Type AB person is transfused with Type O blood. What do you predict?
(NEW) TERMINOLOGY and DEFINITIONS
Mitochondrion: often called the powerhouse of the cell. Energy is made here. Pl. Mitochondria. Cells usually
have thousands of these, depending on their energy needs.
Nucleus: houses the Deoxyribo Nucleic Acid (DNA)
Nuclear membrane: encloses the nucleus and has pores for ingress and egress
Nucleolus: Pl nucleoli. Nucleoli are transient organelles within the nucleus, which synthesise ribosomal RNA.
Nucleoli are most prominent in cells which need to synthesise large amounts of protein.
Rough Endoplasmic Reticulum: stacked membrane complex, studded with ribosomes, site of protein synthesis
Smooth Endoplasmic Reticulum: stacked membrane complex, lacks ribosomes, site of lipid/fat synthesis
Centrioles: cylindrical structures, composed of short microtubules. During cell division, the centrioles form the
spindle apparatus which is used in the movement of DNA strands. Cells without centrioles cannot divide.
(NEW) TERMINOLOGY and DEFINITIONS
Plasma Membrane: semi-permeable, bi-layered phospholipid structure, enclosing the contents of each cell
Cytoplasm: fluid interior of each cell. Composed of salts and water.
Cytoskeleton: Literally the cell’s skeleton, an internal protein framework, gives the cytoplasm its strength and
flexibility. Other details of this network are poorly understood.
Organelle: any macromolecular structure suspended in the cytoplasm
Ribosome: site of protein synthesis. Where m RNA is deciphered and amino acids are joined together to form
proteins
Protein: chain of amino acids in a particular sequence
Golgi Apparatus: series of stacked membranes where newly-made proteins can be modified
(NEW) TERMINOLOGY and DEFINITIONS
Lysosome: vesicle containing digestive enzymes
Secretory vesicle: contains products for export from the cell
Cilium: finger-like structure extending from the cell and continuous with the plasma membrane. Pl. Cilia
Microvilli: secondary folds in the cilia.
Messenger RNA (m RNA) (mRiboNucleic Acid): linear chain structure, composed of nucleotides, which carries
information from DNA to ribosomes for protein synthesis
DNA: double-helical structure, composed of nucleotides, the basis of genes. Specifies inherited characteristics
Chromosome: macro structure composed of very long DNA segments complexed with specific proteins