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Otto Frank (1865–1944) was a German physiologist; among his many published works are detailed studies of this important heart relationship. Ernest Starling (1866–1927) was an important English physiologist who also studied the heart. Although they worked largely independently, their combined efforts and similar conclusions have been recognized in the name “Frank-Starling mechanism.”

Any sympathetic stimulation to the venous system will increase venous return to the heart, which contributes to ventricular filling, and EDV and preload. While much of the ventricular filling occurs while both atria and ventricles are in diastole, the contraction of the atria, the atrial kick, plays a crucial role by providing the last 20–30 percent of ventricular filling.

Contractility

It is virtually impossible to consider preload or ESV without including an early mention of the concept of contractility. Indeed, the two parameters are intimately linked. Contractility refers to the force of the contraction of the heart muscle, which controls SV, and is the primary parameter for impacting ESV. The more forceful the contraction is, the greater the SV and smaller the ESV are. Less forceful contractions result in smaller SVs and larger ESVs. Factors that increase contractility are described as positive inotropic factors    , and those that decrease contractility are described as negative inotropic factors    (ino- = “fiber;” -tropic = “turning toward”).

Not surprisingly, sympathetic stimulation is a positive inotrope, whereas parasympathetic stimulation is a negative inotrope. Sympathetic stimulation triggers the release of NE at the neuromuscular junction from the cardiac nerves and also stimulates the adrenal cortex to secrete epinephrine and NE. In addition to their stimulatory effects on HR, they also bind to both alpha and beta receptors on the cardiac muscle cell membrane to increase metabolic rate and the force of contraction. This combination of actions has the net effect of increasing SV and leaving a smaller residual ESV in the ventricles. In comparison, parasympathetic stimulation releases ACh at the neuromuscular junction from the vagus nerve. The membrane hyperpolarizes and inhibits contraction to decrease the strength of contraction and SV, and to raise ESV. Since parasympathetic fibers are more widespread in the atria than in the ventricles, the primary site of action is in the upper chambers. Parasympathetic stimulation in the atria decreases the atrial kick and reduces EDV, which decreases ventricular stretch and preload, thereby further limiting the force of ventricular contraction. Stronger parasympathetic stimulation also directly decreases the force of contraction of the ventricles.

Several synthetic drugs, including dopamine and isoproterenol, have been developed that mimic the effects of epinephrine and NE by stimulating the influx of calcium ions from the extracellular fluid. Higher concentrations of intracellular calcium ions increase the strength of contraction. Excess calcium (hypercalcemia) also acts as a positive inotropic agent. The drug digitalis lowers HR and increases the strength of the contraction, acting as a positive inotropic agent by blocking the sequestering of calcium ions into the sarcoplasmic reticulum. This leads to higher intracellular calcium levels and greater strength of contraction. In addition to the catecholamines from the adrenal medulla, other hormones also demonstrate positive inotropic effects. These include thyroid hormones and glucagon from the pancreas.

Questions & Answers

what are the body plains
Sanjana Reply
median plane,transverse or horizontal plane and coronal or frontal plane
ASIMENU
How do I summarize the whole of muscular system
Mary Reply
briefly explain the similarities between transcription and DNA replication
Emmanuel Reply
transcription copies DNA into RNA while replication makes another copy of DNA
Goode
A general explanation: Replication occurs when a copy of DNA is made. Transcription is the first step in the process of protein synthesis. Messenger RNA is made using a portion of the DNA molecule as a template.
Lessa
please what group is this?
Winifred
hello guys
PRINCE
Relationship between essential amino acids and immune response
Eunice
transcription from DNA to rna involves the matching of the nucleotides represented by c,g, t and A, but where there is a t, it is replaced by a u- uracil
Patrick
what is the main function of the pcn?
DAVID Reply
career in the health professions, respond appropriately to signs of illness, help you in your roles as a parent, spouse
Coach Reply
student would have an appreciation of the heart anatomy to give understanding of anatomy while opening ideas of function and physiology
Coach
study of the parts of the body
Coach
macro anatomy, study of big structures of the body that can be viewed with the naked eye
Coach
that is called gross anatomy
Patrick
what is integumentry
Amiebo Reply
chemical level cell level tissue level organs level organ system organism
sam Reply
when you sitting close to a campfire your sense smell adapts the smell but when the trace of smoke is introduced into your environments it becomes unsual for you
sam
I need to know mechanism of body fluid
johnson
OK but I need to know where are you coming from
johnson
ask how
Amiebo
oh ft, help out with integumentary system now
Amiebo
Pls give me a brief description of vetebra
Deborah Reply
7 cervical (c1 atlas and c2 axis help the neck rotate) 12 thoracic 5 lumbar 1 sacral and 2 coccyx
Anna
breakfast at 7, lunch at 12, and dinner at 5. sacrum holds 5, coccyx holds 4
Patrick
really there's just one coccyx and sacrum
Patrick
atlas like the Greek God holds the weight of the world on top of him
Patrick
elasticity of the vagina
Mariam Reply
The vagina is an elastic muscular wall
antouman
*organ
antouman
It has I think squamous cuboidal or maybe columnar epithelium designed for secretion, expansion and friction.
Patrick
how can you remember the integumentary system
Naomi Reply
integumentary system is the skin the skin is protection all the body and contain deid cells
Drs
how can you remember the formation of bone?
Maame
the largest organ of the body
Toni
skin is largest organ
Zara
what is the best way to remember the cranial bones or any other bones ?
Savannah
skeletal system?
Savannah
look at the diagram structure and then remember it considering it your own body i memorise like that
Zara
hi guys! do you have to remember ALL the structures of the bones- I mean every single hole, depression or tuberosity?
Kristina
tuborisity
Zara
hey guz i hv to remember Immune antibodies and antigens how? i found it difficult
Zara
well, they are all grouped, aren't they? I mean they all come in series like H1, H2A, H2B and so on. In this case I learn the common part first and then that what's different
Kristina
nd what about IgG , IgE etc.
Zara
the majors
Toni
the thin skin does not have stratum lucidium I believe
Patrick
acronyms
Patrick
if u know the bones, the muscle has part of the name of the bone in it
Patrick
epidermis, I believe epi means on top. dermis in the middle and hypodermis, hypo meaning below. the hypodermis is actually considered not part of the skin or int system
Patrick
big sweet guys love candy = basale, spinosum, granulosum, lucidum ( only in thick skin), corneum
Anna
I love it ☝🏾
Savannah
thank you Zara !
Savannah
can anyone send diet plan for asthma patients
waseem
is
Drs
hey
Daud
jam how are you
Daud
Hey guys l am Matrin
Matrin
blood is a connective tissue which transport oxygen and other nutrients to body
Zara Reply
which type of protein is blood?
Zara
what is blood?
Masthan Reply
blood is a connective tissue which transport oxygen and nutrients to body
Zara
which type of protein is blood?
Zara
haemoglobin
Rashid
and what about its structure i think its Quartenary structure 🤔💭
Zara
yes it is
Rashid
it is globular
Rashid
a vascular structure compose of vessels.
Toni
what is the functions of lymph
moula Reply
what is plasma
Chukwu Reply
A plasma is a hot ionized gas consisting of approximately af a equal number of positive ly charged ionized and negative ly charged electron is called plasma.
Muhammad
what is an atomical position?
Madinatu
military position, body erect where by the body will be up straight..the cephalic and thoracic are straight
Mwita
functions of plasma membrane
Dinyando Reply

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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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