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Negative inotropic agents include hypoxia, acidosis, hyperkalemia, and a variety of synthetic drugs. These include numerous beta blockers and calcium channel blockers. Early beta blocker drugs include propranolol and pronethalol, and are credited with revolutionizing treatment of cardiac patients experiencing angina pectoris. There is also a large class of dihydropyridine, phenylalkylamine, and benzothiazepine calcium channel blockers that may be administered decreasing the strength of contraction and SV.

Afterload

Afterload refers to the tension that the ventricles must develop to pump blood effectively against the resistance in the vascular system. Any condition that increases resistance requires a greater afterload to force open the semilunar valves and pump the blood. Damage to the valves, such as stenosis, which makes them harder to open will also increase afterload. Any decrease in resistance decreases the afterload. [link] summarizes the major factors influencing SV, [link] summarizes the major factors influencing CO, and [link] and [link] summarize cardiac responses to increased and decreased blood flow and pressure in order to restore homeostasis.

Major factors influencing stroke volume

This table describes major factors influencing stroke volume. Preload may be raised due to fast filling time or increased venous return. These factors increase end diastolic volume and increase stroke volume. Preload may be lowered due to decreased thyroid hormones, decreased calcium ions, high or low potassium ions, high or low sodium, low body temperature, hypoxia, abnormal pH balance, or drugs (for example, calcium channel blockers). These factors decrease end diastolic volume and decrease stroke volume. Contractility may be raised due to sympathetic stimulation, epinephrine and norepinephrine, high intracellular calcium ions, high blood calcium level, thyroid hormones, or glucagon. These factors decrease end systolic volume and increase stroke volume. Contractility may be lowered due to parasympathetic stimulation, acetylcholine, hypoxia, or hyperkalemia. These factors increase end systolic volume and decrease stroke volume. Afterload may be raised due to increased vascular resistance or semilunar valve damage. These factors increase end systolic volume and decrease stroke volume. Afterload may be lowered due to decreased vascular resistance. This factor decreases end systolic volume and increases stroke volume.
Multiple factors impact preload, afterload, and contractility, and are the major considerations influencing SV.

Summary of major factors influencing cardiac output

This flowchart lists all the important factors that affect cardiac output.
The primary factors influencing HR include autonomic innervation plus endocrine control. Not shown are environmental factors, such as electrolytes, metabolic products, and temperature. The primary factors controlling SV include preload, contractility, and afterload. Other factors such as electrolytes may be classified as either positive or negative inotropic agents.
Cardiac Response to Decreasing Blood Flow and Pressure Due to Decreasing Cardiac Output
Baroreceptors (aorta, carotid arteries, venae cavae, and atria) Chemoreceptors (both central nervous system and in proximity to baroreceptors)
Sensitive to Decreasing stretch Decreasing O 2 and increasing CO 2 , H + , and lactic acid
Target Parasympathetic stimulation suppressed Sympathetic stimulation increased
Response of heart Increasing heart rate and increasing stroke volume Increasing heart rate and increasing stroke volume
Overall effect Increasing blood flow and pressure due to increasing cardiac output; hemostasis restored Increasing blood flow and pressure due to increasing cardiac output; hemostasis restored
Cardiac Response to Increasing Blood Flow and Pressure Due to Increasing Cardiac Output
Baroreceptors (aorta, carotid arteries, venae cavae, and atria) Chemoreceptors (both central nervous system and in proximity to baroreceptors)
Sensitive to Increasing stretch Increasing O 2 and decreasing CO 2 , H + , and lactic acid
Target Parasympathetic stimulation increased Sympathetic stimulation suppressed
Response of heart Decreasing heart rate and decreasing stroke volume Decreasing heart rate and decreasing stroke volume
Overall effect Decreasing blood flow and pressure due to decreasing cardiac output; hemostasis restored Decreasing blood flow and pressure due to decreasing cardiac output; hemostasis restored

Chapter review

Many factors affect HR and SV, and together, they contribute to cardiac function. HR is largely determined and regulated by autonomic stimulation and hormones. There are several feedback loops that contribute to maintaining homeostasis dependent upon activity levels, such as the atrial reflex, which is determined by venous return.

SV is regulated by autonomic innervation and hormones, but also by filling time and venous return. Venous return is determined by activity of the skeletal muscles, blood volume, and changes in peripheral circulation. Venous return determines preload and the atrial reflex. Filling time directly related to HR also determines preload. Preload then impacts both EDV and ESV. Autonomic innervation and hormones largely regulate contractility. Contractility impacts EDV as does afterload. CO is the product of HR multiplied by SV. SV is the difference between EDV and ESV.

Questions & Answers

5. Discuss thoroughly the renal regulation of acid-base balance in the body with the illustration of conservation of bicarbonate ion in the kidney
Jonathan Reply
What is anatomy
Tiamiyu Reply
anatomy is the study of the different organs of the body being internal and external organ
Cyrille
is't possible for non-identical twins to have different father ? ?
Cyrille
ANATOMY is the scientific study of the structure of human or animal bodies.
jagriti
Anatomy is the branch of science concerned with the bodily structure of humans, animals, and other living organisms, especially as revealed by dissection and the separation of parts.
Brightone
anatomy is the branch of science that duty with the study structure of the human and living organisms.
Masiame
examples of lymph nodes
Arimpa Reply
Clusters of lymph nodes are found in the neck, axilla (underarm), chest, abdomen, and groin. For example, there are about 20-40 lymph nodes in the axilla. Also called lymph gland. Anatomy of the lymph system, showing the lymph vessels and lymph organs including lymph nodes, tonsils, thymus, spleen,
Adnan
Excellent 😊
Sharon
in part of body where did we get medulla
Olawale Reply
Are you referring to the medulla oblongata? In which case, this is a part of the brain, located at the brain stem. It controls a lot of our unconscious behaviors such as motor coordination, breathing, etc.. But medulla generally refers to an innermost structure, so it can be found in hair or kidneys
Elliot
How does blood circulate in the upper limbs
Mary Reply
From the aortic arch, blood is supplied to the brain via the R and L carotid arteries. To supply the upper limbs, blood goes to the R and L subclavian arteries, axillary, radial/ulnar, palmar and carpal arteries.
Elliot
describe the muscles found in the heart
Atotwe Reply
myocardial
Kenndy
thank you very much
Atotwe
asalamu aleikum
Cabdala
waalekum salam
Tifu
types of connective tissues?
Tifu
the muscle found in the body is myocardial muscles
Freeman
what is a muscular system and details about it
Jackson Reply
what is the type of homones responseble for blenking of eyes
Moses Reply
what are the functions of cell?
Keyirangzile Reply
how does the femur act as a lever?
Mutoni Reply
what is stumac
Abdussalam Reply
What is phagocytosis
Mohamed Reply
Phagocytosis, process by which certain living cells called phagocyte
Sadashiv
It is the process that is carried out by the immune system of the body, that certain specialized immune cells (macrophages, Nks, dendritic cells, etc) that engulf and neutralize the foreign substances that invades the body.
Wesley
So that they can be predicate out of the body.
Wesley
phagocytosis is the process by which living cell or yh plasma membrane engulf large molecules into it internal environment ... it also known as food feeding
Boateng
all that you are say what does it mean?
Dzah
simply is the way the immune system fights foreign bodies by engulfing them..
Dzah
by the help of the immune cells...
Dzah
The process by which a cell engulfs particles such as bacteria, other microorganisms, debris of dead cell.e.g: neutrophils and monocytes (types of white blood cells)
Tifu
what are the six types of connective tissues
Athieno Reply
loose and dense , cartilage and bone , blood and lymph
Queen
describe the structure of the liver
Atwebembeire Reply
what is specific name for spinal cord
Stanley Reply
what is the best description for skeletal muscular
Stanley
what is the best description for skeletal muscular
Stanley
costs of bones of skeleton, their joint s and voluntary
grace
what are examples of long bones
grace
example of long bones will be the femur tibia and humerus and even radius
Nina
so basically long bones are mostly in you hands and feets
Nina
skeletal muscular are voluntary and are attached to the bone by tendon which help maintain the posture and position of the body and it also protects internal organs in the abdominal region
Nina
The specific name for spinal cord is coccygeal segment
Sandra
what are the hormones responseble for blenking of eyes.
Moses
vertebral column
SRIPRIYADHARSHINI

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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