This document provides an overview of the circulatory system, including its major components such as the heart, blood vessels, and their functions in nutrient and waste transport. It discusses the differences between arteries and veins, the anatomy of the heart, and the specific roles of various types of blood vessels in circulation. Additionally, it covers the structure and function of cardiac muscle and the conduction system that regulates heartbeats.

1. Lecture 37:Introduction to Circulation
Dr Shamshad

2. 1. Identify the two divisions of circulation and track the pathway of
the blood through both circulations.
2. Outline the various parts of circulation and identify the differences
in structure, function, pressure and velocity of blood in different
vessels.
3. Describe the physiological anatomy of the heart and identify its
various specialized functional parts.
OBJECTIVES
Guyton & Hall Textbook of Physiology - 12th ed. P. 157-159 & 101-102

3. Veins- Deoxygenated blood towards heart
Except pulmonary veins.
Arteries- Oxygenated blood away from heart
Except pulmonary arteries.
Pumps blood through vessels
Capillaries- location of internal respiration
in all body tissues.
Blood- Viscous transport medium.
Heart
Vascular
system
Overview of the Cardiovascular System

4.  Supplies the tissues nutrients like:
O2,carbohydrates,aminoacids, fats, hormones, and
immunological agents.
 Removes wastes products of tissue metabolism:
CO2, lactic acids.
 Control blood flow to the skin & limbs:
Heat loss to the environment :regulate body temperature.
 Body defense mechanisms :
Transportation of antibodies/platelets/WBCs..
Functions of Circulatory System

5. Functions of Heart
 Generating blood pressure.
 Ensuring one-way blood flow: with help of valves
 Routing blood: separates pulmonary and systemic
circulations.
 Regulating blood supply according to the need of the
body [increase in exercise & pregnancy..].

6. Pulmonary Circuit
Lesser circulation
Systemic Circuit
Greater/Peripheral circulation.
DOUBLE PUMP

8. Function of blood vessels layers
1.Tunica intima Tunica media Tunica externa
Reduces friction b/w
vessel walls & blood.
Controls
vasoconstriction &
vasodilation of the
vessel.
Protects, reinforces,
& anchors the vessel
to surrounding
structures.

9. Types of blood vessels based on functions
1. Windkessel /Distensible vessels
3. Exchange vessels
4. Capacitance vessels
2. Resistance vessels
5. Shunts vessels

10. 1. Windkessel /Distensible vessels
Highly elastic vessels
Ex :Aorta, pulmonary artery & other larger arteries.
Function: Pressure & blood flow is pulsatile in nature due to
effect of heart contraction and relaxation.
Applied Aspects: Degeneration of the T.media lead to loss of
Windkessel effect.

11. 2. Resistance vessels
Vessels offer resistance to blood flow towards the capillaries
Ex: Arterioles, metarterioles, and pre capillary sphincters
Arterioles/peripheral resistance vessels.
Function:
Decrease the hydrostatic pressure within capillaries
Resistance to blood flow is inversely proportional to the 4th
power of radius of arterioles
Show efficient myogenic control of their own radius.

12. 3. Exchange vessels
 Allow the exchange of gases and nutritive substances
and others
 Single layer of endothelial cells
 Large surface area
 Millions of capillaries
 At rest only 25% active
 Vital organs posses dense capillary network
 Not controlled by nervous or metabolic factors
 Determined by pre-capillary sphincters

13. Structure of capillaries network
Types Site Functions
Continuous Common Allow passage of fluids & small solutes
Fenestrated Kidneys More permeable to fluids & solutes
Sinusoidal Liver Leaky capillaries that allow large molecules
to pass b/w the blood & surrounding
tissues

14. 4. Capacitance vessels
Vessels which accommodated large vol of blood by change
in their luminal shape without change in trans mural
pressure
Ex: Venules, venous compartments
Function: Myogenic tone under control of sympathetic
constrictor nerves
Collapsible in nature.

15. 5. Shunts vessels
Vessels bypass the capillaries network/ Aterio-venous shunts
Ex: Skin ear lobes, palms, fingers, legs, toes lips…
Walls are strong muscular coated
Supplied by sympathetic nerves
Function:
Help rapid blood flow
Exposure to heat dilates these vessels increase blood flow to
veins and promote heat loss and body temp regulation.

16. Pressure and Volume of blood
in different blood vessels
A
B

17. Velocity and
cross sectional areas of
different blood vessels

19. Heart has 4 chambers
Two thin atria separated by interatrial septum
Two thick ventricles separated by interventrucular septum
Atria: Functions:
 Produces low pressure when they contract.
 Acts as Blood reservoirs.
 Pumping 30% of venous return into the ventricles by
contraction of the atrial muscle.
 locates SAN and AVN.
 Right atrium contains receptors of many cardiac reflexes
 Secretes Atrial Natriuretic Peptide (ANP) ,regulates ABP.

20. Ventricles: left : right ventricle ::3:1 thickness
Structure: Has 4 groups of spirally arranged fibers
 That run from base to apex in three layers: inner, outer &
intermediate layers.
 The middle is thick and transverse.
 A valve is attached to each ring to direct the flow of blood.
 Functions: Receive blood from atria and eject into great
vessels.

21. Cardiac Muscle
5. Short branched cells
4. T-tubules larger &
over z-discs
2. Uninucleate
3. Intercalated discs
1. Striated

22. Intercalated disc: The cell membranes fuse with one another to
form permeable “communicating” junctions (gap junctions).
Function: Allow rapid diffusion of ions.
Cardiac muscle: Syncytium of many heart muscle cells
Function: when one cell gets excited, the action potential rapidly
spreads to all of cardiac cells.
Two syncytiums: Atrial syncytium [the walls of the two atria]
Ventricular syncytium [ two ventricles].
Purpose of syncytiums: Allows the atria to contract a short time
ahead of ventricular contraction, which is important for
effectiveness of heart pumping.

23. Cardiac Valves
Atrioventricular Valves Semilunar Valves
Mitral/Bicuspid: Left atrium & left
ventricle.
Lt Ventricles & aorta
Tricuspid: Rt atrium & Rt ventricle Rt Ventricles & pulmonary trunk
Prevent backflow to the atria from
ventricles during ventricular systole
Prevent backflow into ventricles from
gr vessels.
Adapted to withstand extra stress.
• Prolapse is prevented by the
chordae tendinae
• Tensioned by the papillary
muscles
• Applied: weakness of
papillary muscle lead to
regurgitation.

24. The Conduction System of the Heart

25. SA N AVN Bundle of
His/AV
Bundle
Purkinje
fibers
Site Superior
Posterolateral wall
of rt atrium.
At junction of SVC
with Rt atrium
posterior wall of
the right atrium
immediately
behind the
tricuspid valve
From AVN
Continue in IV
septum
From
terminal
divisions of
right and left
brance of
bundle of
His
Size 15*3*1mm 1*3*5mm 20*4mm 10-46*70-
80Um
Structu
re
Primitive, highly
vascular-cells
abundant glycogen
less mitochondria
Contain P cells
Same as SAN Divide into rt
& lt branches
Primitive,
granular
cytoplasm,
multinucleat
ed
Rich in
glycogen

26. SA N AVN Bundle of
His/AV
Bundle
Purkinje
fibers
Inner
vation
Rt Vagus
Sympathetic
nerve fibers
from rt side
Left vagus N
Sympathetic
supply from
left
Funct
ion
Cardiac
pacemaker
Determine HR
Pacemaker
secondary to
SAN
connection
between the
atria and
ventricles.
Transmit
fast
impulse
throughout
ventricles
Rate 60/min 40/min 25-40/min 25-40/min